@article{mehta_chien_lei_gundogdu_chang_so_2024, title={Hybrid Laser Cavity Design for Improved Photon Lifetime and Performance}, volume={36}, ISSN={["1941-0174"]}, DOI={10.1109/LPT.2024.3374261}, abstractNote={We report an optical cavity design that combines a distributed feedback (DFB) cavity as the primary feedback element for lasing with a silver mirror acting as a Fabry-Pérot cavity for broadband reflection and mode confinement. To evaluate the design, we studied the effects of the silver mirror by excluding the DFB cavity and compared its amplified spontaneous emission (ASE) properties with the sample without the mirror. In the structure with the mirror, the gain medium undergoes ASE at an excitation fluence of <inline-formula> <tex-math notation="LaTeX">$17.5\,\,\mathrm { {\mu J c}}\mathrm {m}^{\mathrm {-2}}$ </tex-math></inline-formula> compared to <inline-formula> <tex-math notation="LaTeX">$37\,\,\mathrm { {\mu J c}}\mathrm {m}^{\mathrm {-2}}$ </tex-math></inline-formula> for the sample without the mirror. This lower ASE threshold is attributed to enhanced mode confinement and photon density of states (PDOS) from the silver mirror increasing the cavity photon lifetime (<inline-formula> <tex-math notation="LaTeX">$ {\tau }_{\mathrm {c}}\mathrm {)}$ </tex-math></inline-formula>. Using this hybrid cavity, a multimode optically pumped laser with a threshold of <inline-formula> <tex-math notation="LaTeX">$42\,\,\mathrm { {\mu J c}}\mathrm {m}^{\mathrm {-2}}$ </tex-math></inline-formula> is demonstrated. This hybrid cavity design offers an effective solution that can be readily applied to other thin film-based laser devices.}, number={7}, journal={IEEE PHOTONICS TECHNOLOGY LETTERS}, author={Mehta, Yash and Chien, Kun-Chieh and Lei, Lei and Gundogdu, Kenan and Chang, Chih-Hao and So, Franky}, year={2024}, month={Apr}, pages={516–519} }
 @article{mohanty_chen_chen_so_chang_2024, title={Modeling the co-assembly of binary nanoparticles}, volume={35}, ISSN={["1361-6528"]}, DOI={10.1088/1361-6528/ad0248}, abstractNote={In this work, we present a binary assembly model that can predict the co-assembly structure and spatial frequency spectra of monodispersed nanoparticles with two different particle sizes. The approach relies on an iterative algorithm based on geometric constraints, which can simulate the assembly patterns of particles with two distinct diameters, size distributions, and at various mixture ratios on a planar surface. The two-dimensional spatial-frequency spectra of the modeled assembles can be analyzed using fast Fourier transform analysis to examine their frequency content. The simulated co-assembly structures and spectra are compared with assembled nanoparticles fabricated using transfer coating method are in qualitative agreement with the experimental results. The co-assembly model can also be used to predict the peak spatial frequency and the full-width at half-maximum bandwidth, which can lead to the design of the structure spectra by selection of different monodispersed particles. This work can find applications in fabrication of non-periodic nanostructures for functional surfaces, light extraction structures, and broadband nanophotonics.}, number={3}, journal={NANOTECHNOLOGY}, author={Mohanty, Saurav and Chen, Timothy and Chen, I-Te and So, Franky and Chang, Chih-Hao}, year={2024}, month={Jan} }
 @article{dong_zhu_yin_lei_gundogdu_so_2023, title={High-Efficiency Linearly Polarized Organic Light-Emitting Diodes}, volume={10}, ISSN={["2330-4022"]}, DOI={10.1021/acsphotonics.3c00812}, abstractNote={Thin-film light-emitting diodes (LEDs) with linearly polarized emission enable advanced photonic applications. Here, we demonstrate a linearly polarized light emission organic LED by utilizing the intrinsic polarization nature of the transverse electric (TE) waveguide mode present in the device and extracting it using a linear grating. With a device having 67.6% of the light trapped in the TE waveguide mode, we demonstrated a linearly polarized organic LED with a high current efficiency (CE) of 136 cd/A and a large polarization ratio above 30. Our analysis indicates that the CE can further be increased at least by 2-fold to 280 cd/A. Our device architecture can easily be adopted for other thin-film LED platforms for photonic applications.}, number={9}, journal={ACS PHOTONICS}, author={Dong, Qi and Zhu, Liping and Yin, Shichen and Lei, Lei and Gundogdu, Kenan and So, Franky}, year={2023}, month={Sep}, pages={3342–3349} }
 @article{moon_mehta_gundogdu_so_gu_2023, title={Metal-Halide Perovskite Lasers: Cavity Formation and Emission Characteristics}, volume={7}, ISSN={["1521-4095"]}, DOI={10.1002/adma.202211284}, abstractNote={Hybrid metal halide perovskites (MHPs) have shown remarkable optoelectronic properties as well as facile and cost-effective processability. With the success of MHP solar cells and light-emitting diodes (LEDs), MHPs have also exhibited great potential as gain media for on-chip lasers. However, to date, stable operation of optically pumped MHP lasers and electrically driven MHP lasers - an essential requirement for MHP laser's insertion into chip-scale photonic integrated circuits - have not yet been demonstrated. The main obstacles include the instability of MHPs in the atmosphere, rudimentary MHP laser cavity patterning methods, and insufficient understanding of emission mechanisms in MHP materials and cavities. This review aims to provide a detailed overview of different strategies to improve the intrinsic properties of MHPs in the atmosphere and to establish an optimal MHP cavity patterning method. In addition, this review discusses different emission mechanisms in MHP materials and cavities and how to distinguish them. This article is protected by copyright. All rights reserved.}, journal={ADVANCED MATERIALS}, author={Moon, Jiyoung and Mehta, Yash and Gundogdu, Kenan and So, Franky and Gu, Qing}, year={2023}, month={Jul} }
 @article{dong_fu_seyitliyev_darabi_mendes_lei_chen_chang_amassian_gundogdu_et al._2022, title={Cavity Engineering of Perovskite Distributed Feedback Lasers}, volume={9}, ISSN={2330-4022 2330-4022}, url={http://dx.doi.org/10.1021/acsphotonics.2c00917}, DOI={10.1021/acsphotonics.2c00917}, number={9}, journal={ACS Photonics}, publisher={American Chemical Society (ACS)}, author={Dong, Qi and Fu, Xiangyu and Seyitliyev, Dovletgeldi and Darabi, Kasra and Mendes, Juliana and Lei, Lei and Chen, Yi-An and Chang, Chih-Hao and Amassian, Aram and Gundogdu, Kenan and et al.}, year={2022}, month={Aug}, pages={3124–3133} }
 @article{yang_atwater_baldo_baran_barile_barr_bates_bawendi_bergren_borhan_et al._2022, title={Consensus statement: Standardized reporting of power-producing luminescent solar concentrator performance}, volume={6}, ISSN={["2542-4351"]}, DOI={10.1016/j.joule.2021.12.004}, abstractNote={Fair and meaningful device performance comparison among luminescent solar concentrator-photovoltaic (LSC-PV) reports cannot be realized without a general consensus on reporting standards in LSC-PV research. Therefore, it is imperative to adopt standardized characterization protocols for these emerging types of PV devices that are consistent with other PV devices. This commentary highlights several common limitations in LSC literature and summarizes the best practices moving forward to harmonize with standard PV reporting, considering the greater nuances present with LSC-PV. Based on these practices, a checklist of actionable items is provided to help standardize the characterization/reporting protocols and offer a set of baseline expectations for authors, reviewers, and editors. The general consensus combined with the checklist will ultimately guide LSC-PV research towards reliable and meaningful advances.}, number={1}, journal={JOULE}, author={Yang, Chenchen and Atwater, Harry A. and Baldo, Marc A. and Baran, Derya and Barile, Christopher J. and Barr, Miles C. and Bates, Matthew and Bawendi, Moungi G. and Bergren, Matthew R. and Borhan, Babak and et al.}, year={2022}, month={Jan}, pages={8–15} }
 @article{amoah_fu_yin_dong_dong_so_2022, title={Curved Mirror Arrays for Light Extraction in Top-Emitting Organic Light-Emitting Diodes}, volume={2}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.1c21128}, abstractNote={The light outcoupling efficiency of a top-emitting organic light-emitting diode (OLED) is only about 20%, and the majority of the light is trapped in the waveguide modes and surface plasmon polariton (SPP) modes. Extracting the trapped modes can reduce the device power consumption and improve the operating lifetime. In this study, we demonstrate a top-emitting OLED structure with a dielectric spacer to suppress the SPP mode and with a patterned back mirror to extract the waveguide modes. We examine and compare several curved mirror arrays and conclude that a micromirror array (μMA) can efficiently extract the waveguide modes while minimizing the absorption loss. The optimized μMA device with a semi-transparent top electrode shows a 36% external quantum efficiency, 2 times higher than the referenced device. This optical design can be easily incorporated into a top-emitting device and has a great potential for displays and lighting applications.}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Amoah, Stephen and Fu, Xiangyu and Yin, Shichen and Dong, Qi and Dong, Chen and So, Franky}, year={2022}, month={Feb}, pages={9377–9385} }
 @article{yin_ho_ding_fu_zhu_gullett_dong_so_2022, title={Enhanced Surface Passivation of Lead Sulfide Quantum Dots for Short-Wavelength Photodetectors}, volume={34}, ISSN={["1520-5002"]}, DOI={10.1021/acs.chemmater.2c00293}, abstractNote={Lead sulfide (PbS) quantum dots are promising solution-processed materials for short-wave infrared (SWIR) photodetectors due to their tunable band gap and solution processability. Phase-transfer ligand exchange is a common method to prepare quantum dot (QD) inks used in device fabrication. For large-sized PbS QDs used for SWIR detection, the conventional phase-transfer ligand exchange has been problematic due to the densely packed organic ligands and charge-neutral (100) facets. Here, we report a new strategy to carry out the efficient phase-transfer ligand exchange in large-sized QDs. Specifically, using lead acetate trihydrate (PbAc2·3H2O) as a precursor and methylammonium acetate (MAAc) as an additive in the ligand solution, we can facilitate the efficient phase-transfer ligand exchange and epitaxial growth of perovskite intermediate (MAPbI3–xAcx) on the (100) facets, resulting in a significant improvement in film quality suitable for device fabrication. The resulting photodiodes show a 2.5× enhancement in external quantum efficiency (EQE) compared to devices using QD inks obtained using the conventional method. Considering the low transmittance of the ITO electrode in the SWIR regime, our devices exhibit an internal quantum efficiency of over 90%.}, number={12}, journal={CHEMISTRY OF MATERIALS}, author={Yin, Shichen and Ho, Carr Hoi Yi and Ding, Shuo and Fu, Xiangyu and Zhu, Liping and Gullett, Julian and Dong, Chen and So, Franky}, year={2022}, month={Jun}, pages={5433–5442} }
 @article{ho_pei_qin_zhang_peng_angunawela_jones_yin_iqbal_reynolds_et al._2022, title={Importance of Electric-Field-Independent Mobilities in Thick-Film Organic Solar Cells}, volume={10}, ISSN={["1944-8252"]}, url={http://dx.doi.org/10.1021/acsami.2c11265}, DOI={10.1021/acsami.2c11265}, abstractNote={In organic solar cells (OSCs), a thick active layer usually yields a higher photocurrent with broader optical absorption than a thin active layer. In fact, a ∼300 nm thick active layer is more compatible with large-area processing methods and theoretically should be a better spot for efficiency optimization. However, the bottleneck of developing high-efficiency thick-film OSCs is the loss in fill factor (FF). The origin of the FF loss is not clearly understood, and there a direct method to identify photoactive materials for high-efficiency thick-film OSCs is lacking. Here, we demonstrate that the mobility field-dependent coefficient is an important parameter directly determining the FF loss in thick-film OSCs. Simulation results based on the drift-diffusion model reveal that a mobility field-dependent coefficient smaller than 10-3 (V/cm)-1/2 is required to maintain a good FF in thick-film devices. To confirm our simulation results, we studied the performance of two ternary bulk heterojunction (BHJ) blends, PTQ10:N3:PC71BM and PM6:N3:PC71BM. We found that the PTQ10 blend film has weaker field-dependent mobilities, giving rise to a more balanced electron-hole transport at low fields. While both the PM6 blend and PTQ10 blend yield good performance in thin-film devices (∼100 nm), only the PTQ10 blend can retain a FF = 74% with an active layer thickness of up to 300 nm. Combining the benefits of a higher JSC in thick-film devices, we achieved a PCE of 16.8% in a 300 nm thick PTQ10:N3:PC71BM OSC. Such a high FF in the thick-film PTQ10 blend is also consistent with the observation of lower charge recombination from light-intensity-dependent measurements and lower energetic disorder observed in photothermal deflection spectroscopy.}, journal={ACS APPLIED MATERIALS & INTERFACES}, publisher={American Chemical Society (ACS)}, author={Ho, Carr Hoi Yi and Pei, Yusen and Qin, Yunpeng and Zhang, Chujun and Peng, Zhengxing and Angunawela, Indunil and Jones, Austin L. and Yin, Hang and Iqbal, Hamna F. and Reynolds, John R. and et al.}, year={2022}, month={Oct} }
 @article{jones_ho_schneider_zhang_pei_wang_zhan_marder_toney_so_et al._2022, title={Insights into the Local Bulk-Heterojunction Packing Interactions and Donor-Acceptor Energy Level Offsets in Scalable Photovoltaic Polymers}, volume={7}, ISSN={["1520-5002"]}, url={http://dx.doi.org/10.1021/acs.chemmater.2c01121}, DOI={10.1021/acs.chemmater.2c01121}, abstractNote={An energy level offset in organic solar cells (OSCs) is necessary for efficient charge generation and separation. To date, there are several polymer donor–non-fullerene acceptor (NFA) bulk-heterojunction (BHJ) systems with a negligible ionization energy (IE) level offset achieving high power conversion efficiencies (PCEs) over 15%. Although these donor–acceptor pairs perform well in solar cells, there is little understanding on why some systems can achieve this phenomenon, and therefore, many of these BHJs are discovered through a trial-and-error process. Here, we investigate how OSC efficiencies can be modulated by adjusting the IE level offset in a series of PTQ10 n:m random terpolymer donors by means of solar cell performance (open circuit voltage (VOC) and short-circuit current (JSC)) when paired with Y6 and IDIC acceptors. PTQ10’s IE level was adjusted through a copolymerization of thiophene (n), bithiophene (m), and quinoxaline monomer units in different ratios, whereby 10% bithiophene leads to a 0.05 eV decrease in the polymer’s IE. The incorporation of 10% bithiophene (PTQ10 90:10) led to a 1.3 ± 0.5 mA/cm2 increase in JSC when paired with Y6 (PCE = 13.8 ± 0.4%) in conjunction with an incremental decrease in VOC and fill factor (FF) when compared to PTQ10 (PCE = 14.7 ± 0.1%). Increasing the bithiophene content to 20% (PTQ10 80:20) exacerbated the decrease in VOC and FF further without the benefit of increased JSC. The drop in FF with increasing bithiophene incorporation correlated with increasing edge-on orientation in the neat polymer and polymer:Y6 BHJ blend films, shown by grazing-incidence wide-angle X-ray scattering measurements. High-field solid-state (ss)NMR spectroscopy analysis of single component PTQ10, Y6, and PTQ10:Y6 BHJ blends provides a complementary insight into how a low IE level offset system (PTQ10:Y6) imparts high performance. By resolving inter- and intramolecular packing interactions at sub-nanometer distances, ssNMR results offer key insights into the changes in local structures and conformations in the vicinity of the alkoxy PTQ10 side chains and in the Y6 end group in BHJ blends when compared to the neat compounds. Despite the changes in local structures, the BHJ morphology maintains pure D-A domains and preserves the microstructure, which correlates with the high-performing solar cells. A synergic combination of chemical design, multiscale morphology characterization, and device physics shown in this study provides an excellent strategy to investigate the BHJ and its role in organic solar cell performance.}, journal={CHEMISTRY OF MATERIALS}, author={Jones, Austin L. and Ho, Carr Hoi Yi and Schneider, Sebastian A. and Zhang, Junxiang and Pei, Yusen and Wang, Jiayu and Zhan, Xiaowei and Marder, Seth R. and Toney, Michael F. and So, Franky and et al.}, year={2022}, month={Jul} }
 @article{biliroglu_findik_mendes_seyitliyev_lei_dong_mehta_temnov_so_gundogdu_2022, title={Room-temperature superfluorescence in hybrid perovskites and its origins}, volume={16}, ISSN={["1749-4893"]}, url={https://doi.org/10.1038/s41566-022-00974-4}, DOI={10.1038/s41566-022-00974-4}, number={4}, journal={NATURE PHOTONICS}, publisher={Springer Science and Business Media LLC}, author={Biliroglu, Melike and Findik, Gamze and Mendes, Juliana and Seyitliyev, Dovletgeldi and Lei, Lei and Dong, Qi and Mehta, Yash and Temnov, Vasily V. and So, Franky and Gundogdu, Kenan}, year={2022}, month={Apr}, pages={324-+} }
 @article{ravishankar_charles_xiong_henry_swift_rech_calero_cho_booth_kim_et al._2021, title={Balancing crop production and energy harvesting in organic solar-powered greenhouses}, volume={2}, ISSN={["2666-3864"]}, DOI={10.1016/j.xcrp.2021.100381}, abstractNote={Adding semitransparent organic solar cells (ST-OSCs) to a greenhouse structure enables simultaneous plant cultivation and electricity generation, thereby reducing the greenhouse energy demand. However, there is a need to establish the impact of such systems on plant growth and indoor climate and to optimize system tradeoffs. In this work, we consider plant growth under OSCs and system-relevant design. We evaluate the growth of red leaf lettuce under ST-OSC filters and compare the impact of three different OSC active layers that have unique transmittance. We find no significant differences in the fresh weight and chlorophyll content of the lettuce grown under these OSC filters. In addition, OSCs provide an opportunity for further light and thermal management of the greenhouse through device design and optical coatings. The OSCs can thus affect plant growth, power generation, and thermal load of the greenhouse, and this design trade space is reviewed and exemplified.}, number={3}, journal={CELL REPORTS PHYSICAL SCIENCE}, publisher={Elsevier BV}, author={Ravishankar, Eshwar and Charles, Melodi and Xiong, Yuan and Henry, Reece and Swift, Jennifer and Rech, Jeromy and Calero, John and Cho, Sam and Booth, Ronald E. and Kim, Taesoo and et al.}, year={2021}, month={Mar} }
 @article{worku_ben-akacha_sridhar_frick_yin_he_robb_chaaban_liu_winfred_et al._2021, title={Band Edge Control of Quasi-2D Metal Halide Perovskites for Blue Light-Emitting Diodes with Enhanced Performance}, volume={8}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.202103299}, abstractNote={Perovskite light‐emitting diodes (PeLEDs) have received great attention for their potential as next‐generation display technology. While remarkable progress has been achieved in green, red, and near‐infrared PeLEDs with external quantum efficiencies (EQEs) exceeding 20%, obtaining high performance blue PeLEDs remains a challenge. Poor charge balance due to large charge injection barriers in blue PeLEDs has been identified as one of the major roadblocks to achieve high efficiency. Here band edge control of perovskite emitting layers for blue PeLEDs with enhanced charge balance and device performance is reported. By using organic spacer cations with different dipole moments, that is, phenethyl ammonium (PEA), methoxy phenethyl ammonium (MePEA), and 4‐fluoro phenethyl ammonium (4FPEA), the band edges of quasi‐2D perovskites are tuned without affecting their band gaps. Detailed characterization and computational studies have confirmed the effect of dipole moment modification to be mostly electrostatic, resulting in changes in the ionization energies of ≈0.45 eV for MePEA and ≈ −0.65 eV for 4FPEA based thin films relative to PEA‐based thin films. With improved charge balance, blue PeLEDs based on MePEA quasi‐2D perovskites show twofold increase of the EQE as compared to the control PEA based devices.}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Worku, Michael and Ben-Akacha, Azza and Sridhar, Samanvitha and Frick, Jordan R. and Yin, Shichen and He, Qingquan and Robb, Alex J. and Chaaban, Maya and Liu, He and Winfred, J. S. Raaj Vellore and et al.}, year={2021}, month={Aug} }
 @article{fu_mehta_chen_lei_zhu_barange_dong_yin_mendes_he_et al._2021, title={Directional Polarized Light Emission from Thin‐Film Light‐Emitting Diodes}, volume={33}, ISSN={0935-9648 1521-4095}, url={http://dx.doi.org/10.1002/adma.202006801}, DOI={10.1002/adma.202006801}, abstractNote={Abstract}, number={9}, journal={Advanced Materials}, publisher={Wiley}, author={Fu, Xiangyu and Mehta, Yash and Chen, Yi‐An and Lei, Lei and Zhu, Liping and Barange, Nilesh and Dong, Qi and Yin, Shichen and Mendes, Juliana and He, Siliang and et al.}, year={2021}, month={Jan}, pages={2006801} }
 @article{pile_so_2021, title={Emitting organically}, volume={15}, ISSN={["1749-4893"]}, DOI={10.1038/s41566-021-00869-w}, number={9}, journal={NATURE PHOTONICS}, author={Pile, David F. P. and So, Franky}, year={2021}, month={Sep}, pages={635–636} }
 @article{findik_biliroglu_seyitliyev_mendes_barrette_ardekani_lei_dong_so_gundogdu_2021, title={High-temperature superfluorescence in methyl ammonium lead iodide}, volume={15}, ISSN={1749-4885 1749-4893}, url={http://dx.doi.org/10.1038/s41566-021-00830-x}, DOI={10.1038/s41566-021-00830-x}, abstractNote={Light–matter interactions can create and manipulate collective many-body phases in solids1–3, which are promising for the realization of emerging quantum applications. However, in most cases, these collective quantum states are fragile, with a short decoherence and dephasing time, limiting their existence to precision tailored structures under delicate conditions such as cryogenic temperatures and/or high magnetic fields. In this work, we discovered that the archetypal hybrid perovskite, MAPbI3 thin film, exhibits such a collective coherent quantum many-body phase, namely superfluorescence, at 78 K and above. Pulsed laser excitation first creates a population of high-energy electron–hole pairs, which quickly relax to lower energy domains and then develop a macroscopic quantum coherence through spontaneous synchronization. The excitation fluence dependence of the spectroscopic features and the population kinetics in such films unambiguously confirm all the well-known characteristics of superfluorescence. These results show that the creation and manipulation of collective coherent states in hybrid perovskites can be used as the basic building blocks for quantum applications4,5. A collective coherent quantum many-body phase, namely superfluorescence, is observed in CH3NH3PbI3 at 78 K. The excitation fluence dependence of the spectroscopic features and the population kinetics confirm all its well-known characteristics.}, number={9}, journal={Nature Photonics}, publisher={Springer Science and Business Media LLC}, author={Findik, Gamze and Biliroglu, Melike and Seyitliyev, Dovletgeldi and Mendes, Juliana and Barrette, Andrew and Ardekani, Hossein and Lei, Lei and Dong, Qi and So, Franky and Gundogdu, Kenan}, year={2021}, month={Jun}, pages={676–680} }
 @article{ho_kothari_fu_so_2021, title={Interconnecting layers for tandem organic solar cells}, volume={21}, ISSN={["2468-6069"]}, DOI={10.1016/j.mtener.Y021.100707}, journal={MATERIALS TODAY ENERGY}, author={Ho, C. H. Y. and Kothari, J. and Fu, X. and So, F.}, year={2021}, month={Sep} }
 @article{fu_yin_chen_zhu_dong_chang_so_2021, title={Light extraction in tandem organic light emitting diodes}, volume={119}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/5.0057325}, DOI={10.1063/5.0057325}, abstractNote={Since the invention of organic light emitting diodes (OLEDs), great research efforts have been dedicated to improving their efficiency and lifetime. For high-brightness applications, tandem OLED structures have advantages because of the lower current densities required to achieve high brightness. With the successful development of highly efficient charge generation layers, high brightness tandem OLEDs are used in displays and lighting. However, the major challenge for tandem OLEDs is the low light extraction efficiency, because about 50% of the light is trapped inside the device as waveguide modes. In this Perspective, we first review the recent works done on light extraction, analyze different waveguide mode extraction structures, and then identify the key factors determining the extraction efficiencies in tandem OLEDs.}, number={6}, journal={APPLIED PHYSICS LETTERS}, author={Fu, Xiangyu and Yin, Shichen and Chen, Yi-An and Zhu, Liping and Dong, Qi and Chang, Chih-Hao and So, Franky}, year={2021}, month={Aug} }
 @misc{lei_dong_gundogdu_so_2021, title={Metal Halide Perovskites for Laser Applications}, volume={31}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.202010144}, abstractNote={Abstract}, number={16}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Lei, Lei and Dong, Qi and Gundogdu, Kenan and So, Franky}, year={2021}, month={Apr} }
 @article{yi_peng_xu_seyitliyev_ho_danilov_kim_reynolds_amassian_gundogdu_et al._2020, title={Critical Role of Polymer Aggregation and Miscibility in Nonfullerene-Based Organic Photovoltaics}, volume={10}, ISSN={["1614-6840"]}, url={http://dx.doi.org/10.1002/aenm.201902430}, DOI={10.1002/aenm.201902430}, abstractNote={Abstract}, number={8}, journal={ADVANCED ENERGY MATERIALS}, author={Yi, Xueping and Peng, Zhengxing and Xu, Bing and Seyitliyev, Dovletgeldi and Ho, Carr Hoi Yi and Danilov, Evgeny O. and Kim, Taesoo and Reynolds, John R. and Amassian, Aram and Gundogdu, Kenan and et al.}, year={2020}, month={Feb} }
 @article{yu_kim_kim_barange_jiang_so_2020, title={Direct Acoustic Imaging Using a Piezoelectric Organic Light-Emitting Diode}, volume={12}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.0c05615}, abstractNote={Conventional ultrasonic imaging requires acoustic scanning over a target object using a piezoelectric transducer array, followed by signal processing to reconstruct the image. Here, we report a novel ultrasonic imaging device that can optically display an acoustic signal on the surface of a piezoelectric transducer. By fabricating an organic light-emitting diode (OLED) on top of a piezoelectric crystal (lead zirconate titanate, PZT), an acousto-optical piezoelectric OLED (p-OLED) transducer is realized, converting an acoustic wave profile directly to an optical image. Due to the integrated device architecture, the resulting p-OLED features a high acousto-optic conversion efficiency at the resonant ultrasound frequency, providing a piezoelectric field to drive the OLED. By incorporating an electrode array in the p-OLED, we demonstrate a novel tomographic ultrasound imaging device that is operated without a need for conventional signal processing.}, number={32}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Yu, Hyeonggeun and Kim, Jinwook and Kim, Howuk and Barange, Nilesh and Jiang, Xiaoning and So, Franky}, year={2020}, month={Aug}, pages={36409–36416} }
 @article{yi_ho_gautam_lei_chowdhury_bahrami_qiao_so_2020, title={Effects of polymer crystallinity on non-fullerene acceptor based organic solar cell photostability}, volume={8}, ISSN={["2050-7534"]}, DOI={10.1039/d0tc03969a}, abstractNote={Organic solar cell shows significantly different degradation rate with different donor polymer crystallinity, even the donors and acceptors are all photostable.}, number={45}, journal={JOURNAL OF MATERIALS CHEMISTRY C}, author={Yi, Xueping and Ho, Carr Hoi Yi and Gautam, Bhoj and Lei, Lei and Chowdhury, Ashraful Haider and Bahrami, Behzad and Qiao, Qiquan and So, Franky}, year={2020}, month={Dec}, pages={16092–16099} }
 @article{firdaus_ho_lin_yengel_le corre_nugraha_yarali_so_anthopoulos_2020, title={Efficient Double- and Triple-Junction Nonfullerene Organic Photovoltaics and Design Guidelines for Optimal Cell Performance}, volume={5}, ISSN={["2380-8195"]}, DOI={10.1021/acsenergylett.0c02077}, abstractNote={The performance of multijunction devices lags behind single-junction organic photovoltaics (OPVs) mainly because of the lack of suitable subcells. Here, we attempt to address this bottleneck and demonstrate efficient nonfullerene-based multijunction OPVs while at the same time highlighting the remaining challenges. We first demonstrate double-junction OPVs with power conversion efficiency (PCE) of 16.5%. Going a step further, we developed triple-junction OPVs with a PCE of 14.9%, the highest value reported to date for this triple-junction cells. Device simulations suggest that improving the front-cell’s carrier mobility to >5 × 10–4 cm2 V–1 s–1 is needed to boost the efficiency of double- and triple-junction OPVs. Analysis of the efficiency limit of triple-junction devices predicts that PCE values of close to 26% are possible. To achieve this, however, the optical absorption and charge transport within the subcells would need to be optimized. The work is an important step toward next-generation multijunction OPVs.}, number={12}, journal={ACS ENERGY LETTERS}, author={Firdaus, Yuliar and Ho, Carr Hoi Yi and Lin, Yuanbao and Yengel, Emre and Le Corre, Vincent M. and Nugraha, Mohamad I and Yarali, Emre and So, Franky and Anthopoulos, Thomas D.}, year={2020}, month={Dec}, pages={3692–3701} }
 @article{lei_seyitliyev_stuard_mendes_dong_fu_chen_he_yi_zhu_et al._2020, title={Efficient Energy Funneling in Quasi-2D Perovskites: From Light Emission to Lasing}, volume={32}, ISSN={["1521-4095"]}, DOI={10.1002/adma.201906571}, abstractNote={Abstract}, number={16}, journal={ADVANCED MATERIALS}, author={Lei, Lei and Seyitliyev, Dovletgeldi and Stuard, Samuel and Mendes, Juliana and Dong, Qi and Fu, Xiangyu and Chen, Yi-An and He, Siliang and Yi, Xueping and Zhu, Liping and et al.}, year={2020}, month={Apr} }
 @article{ho_kim_xiong_firdaus_yi_dong_rech_gadisa_booth_brendan t. o'connor_et al._2020, title={High-Performance Tandem Organic Solar Cells Using HSolar as the Interconnecting Layer}, volume={10}, ISSN={["1614-6840"]}, url={https://doi.org/10.1002/aenm.202000823}, DOI={10.1002/aenm.202000823}, abstractNote={Abstract}, number={25}, journal={ADVANCED ENERGY MATERIALS}, publisher={Wiley}, author={Ho, Carr Hoi Yi and Kim, Taesoo and Xiong, Yuan and Firdaus, Yuliar and Yi, Xueping and Dong, Qi and Rech, Jeromy J. and Gadisa, Abay and Booth, Ronald and Brendan T. O'Connor and et al.}, year={2020}, month={Jul} }
 @article{fu_peng_samal_barange_chen_shin_mehta_rozelle_chang_so_2020, title={Mode Dispersion in Photonic Crystal Organic Light-Emitting Diodes}, volume={2}, ISSN={["2637-6113"]}, DOI={10.1021/acsaelm.0c00326}, abstractNote={Similar to an electronic lattice determining the motion of electrons in solids, photonic crystals (PhCs) are periodic photonic nanostructures which determine the propagation of photons. By incorpor...}, number={6}, journal={ACS APPLIED ELECTRONIC MATERIALS}, author={Fu, Xiangyu and Peng, Cheng and Samal, Monica and Barange, Nilesh and Chen, Yi-An and Shin, Dong-Hun and Mehta, Yash and Rozelle, Adam and Chang, Chih-Hao and So, Franky}, year={2020}, month={Jun}, pages={1759–1767} }
 @article{dong_fu_cao_amoah_gundogdu_li_so_2020, title={Multi-mode Organic Light-Emitting Diode to Suppress the Viewing Angle Dependence}, volume={12}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.0c05825}, abstractNote={A typical top emitting OLED has a strong microcavity effect because of the two reflective electrodes. The cavity effect causes a serious color shift with the viewing angles and restricts the organic layer thickness. To overcome these drawbacks, we designed a multi-mode OLED structure having dual-dielectric spacer layers, which extend the cavity length by more than 10 times. This design completely eliminates the intrinsic cavity effect caused by the top and bottom boundaries respectively and provides freedom for the organic layer thickness. We demonstrate these effects in a white multi-mode OLED using a white emitter, which shows a negligible angular chromaticity shift of 0.006 from 0° to 70° and a Lambertian emission profile. The simple design and the perfect angular color profiles make the multi-mode OLED structure promising in large-area displays and solid-state lighting applications.}, number={28}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Dong, Chen and Fu, Xiangyu and Cao, Linyu and Amoah, Stephen and Gundogdu, Kenan and Li, Jian and So, Franky}, year={2020}, month={Jul}, pages={31667–31676} }
 @misc{dong_lei_mendes_so_2020, title={Operational stability of perovskite light emitting diodes}, volume={3}, ISSN={["2515-7639"]}, DOI={10.1088/2515-7639/ab60c4}, abstractNote={Abstract}, number={1}, journal={JOURNAL OF PHYSICS-MATERIALS}, author={Dong, Qi and Lei, Lei and Mendes, Juliana and So, Franky}, year={2020}, month={Jan} }
 @article{fu_chen_shin_mehta_chen_barange_zhu_amoah_chang_so_2020, title={Recovering cavity effects in corrugated organic light emitting diodes}, volume={28}, ISSN={["1094-4087"]}, DOI={10.1364/OE.404412}, abstractNote={Cavity effects play an important role in determining the out-coupling efficiency of an OLED. By fabricating OLEDs on corrugated substrates, the waveguide and SPP modes can be extracted by diffraction. However, corrugation does not always lead to an enhancement in out-coupling efficiency due to the reduction of the electrode reflectance and hence the cavity effects. Based on the results of our rigorous couple-wave analysis (RCWA) simulation, we found that the cavity effects can be partially recovered using a low index Teflon layer inserted between the ITO anode and the substrate due to the enhancement of the reflectance of the corrugated electrodes. To verify the simulation results, we fabricated corrugated OLEDs having a low-index Teflon interlayer with an EQE of 36%, which is 29% higher than an optimized planar OLED. By experimentally measuring the OLED air mode dispersion, we confirm the cavity emission of a corrugated OLED is enhanced by the low index layer.}, number={21}, journal={OPTICS EXPRESS}, author={Fu, Xiangyu and Chen, Yi-An and Shin, Dong-Hun and Mehta, Yash and Chen, I-Te and Barange, Nilesh and Zhu, Liping and Amoah, Stephen and Chang, Chih-Hao and So, Franky}, year={2020}, month={Oct}, pages={32214–32225} }
 @article{dong_mendes_lei_seyitliyev_zhu_he_gundogdu_so_2020, title={Understanding the Role of Ion Migration in the Operation of Perovskite Light-Emitting Diodes by Transient Measurements}, volume={12}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.0c14269}, abstractNote={Perovskite light-emitting diodes have been gaining attention in recent years due to their high efficiencies. Despite of the recent progress made in device efficiency, the operation mechanisms of these devices are still not well understood, especially the effects of ion migration. In this work, the role of ion migration is investigated by measuring the transient electroluminescence and current responses, with both the current and efficiency showing a slow response in a time scale of tens of milliseconds. The results of the charge injection dynamics show that the slow response of the current is attributed to the migration and accumulation of halide ions at the anode interface, facilitating hole injection and leading to a strong charge imbalance. Further, the results of the charge recombination dynamics show that the slow response of the efficiency is attributed to enhanced charge injection facilitated by ion migration, which leads to an increased carrier density favoring bimolecular radiative recombination. Through a combined analysis of both charge injection and recombination dynamics, we finally present a comprehensive picture of the role of ion migration in device operation.}, number={43}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Dong, Qi and Mendes, Juliana and Lei, Lei and Seyitliyev, Dovletgeldi and Zhu, Liping and He, Siliang and Gundogdu, Kenan and So, Franky}, year={2020}, month={Oct}, pages={48845–48853} }
 @article{jones_zheng_riley_pelse_zhang_abdelsamie_toney_marder_so_bredas_et al._2019, title={Acceptor Gradient Polymer Donors for Non-Fullerene Organic Solar Cells}, volume={31}, ISSN={["1520-5002"]}, DOI={10.1021/acs.chemmater.9b03327}, abstractNote={In organic solar cells, maximizing the open-circuit voltage (VOC) via minimization of the ionization energy or electron affinity offsets of the blended donor and acceptor often comes at the expense...}, number={23}, journal={CHEMISTRY OF MATERIALS}, author={Jones, Austin L. and Zheng, Zilong and Riley, Parand and Pelse, Ian and Zhang, Junxiang and Abdelsamie, Maged and Toney, Michael F. and Marder, Seth R. and So, Franky and Bredas, Jean-Luc and et al.}, year={2019}, month={Dec}, pages={9729–9741} }
 @article{dong_ho_yu_salehi_so_2019, title={Defect Passivation by Fullerene Derivative in Perovskite Solar Cells with Aluminum-Doped Zinc Oxide as Electron Transporting Layer}, volume={31}, ISSN={["1520-5002"]}, DOI={10.1021/acs.chemmater.9b01292}, abstractNote={ZnO is a potential replacement for TiO2 as an electron transport layer (ETL) used in low-temperature processed hybrid perovskite solar cells. However, poor thermal stability of perovskites on ZnO and interfacial traps introduced during processing are obstacles to achieve a good device performance. Here, we demonstrate perovskite solar cells using aluminum doped zinc oxide (AZO) nanoparticles for the ETL having a better thermal stability compared with ZnO. However, the device shows a lower short circuit current density and a large photocurrent hysteresis, which are attributed to the poor interfacial properties between the ETL and the perovskite layer. To address this issue, a thin interfacial modification layer of phenyl-C61-butyric acid methyl ester (PCBM) was employed. The resulting device shows the efficiency is improved from 13 to 17% along with a significant reduction in hysteresis. Results from our thermal admittance spectroscopy show that the interface defect states are significantly reduced with th...}, number={17}, journal={CHEMISTRY OF MATERIALS}, author={Dong, Qi and Ho, Carr Hoi Yi and Yu, Hyeonggeun and Salehi, Amin and So, Franky}, year={2019}, month={Sep}, pages={6833–6840} }
 @article{dong_fu_amoah_rozelle_shin_salehi_mendes_so_2019, title={Eliminate angular color shift in top-emitting OLEDs through cavity design}, volume={27}, ISSN={["1938-3657"]}, DOI={10.1002/jsid.792}, abstractNote={Abstract}, number={8}, journal={JOURNAL OF THE SOCIETY FOR INFORMATION DISPLAY}, author={Dong, Chen and Fu, Xiangyu and Amoah, Stephen and Rozelle, Adam and Shin, Dong-Hun and Salehi, Amin and Mendes, Juliana and So, Franky}, year={2019}, month={Aug}, pages={469–479} }
 @article{dong_liu_barange_lee_pardue_yi_yin_so_2019, title={Long-Wavelength Lead Sulfide Quantum Dots Sensing up to 2600 nm for Short-Wavelength Infrared Photodetectors}, volume={11}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.9b16539}, abstractNote={Lead sulfide nanoparticles (PbS NPs) are used in the short wavelength infrared (SWIR) photodetectors because of their excellent photosensitivity, bandgap tunability, and solution processability. It has been a challenge to synthesize high quality PbS NPs with an absorption peak beyond 2000 nm. In this work, using PbS seed crystals with an absorption peak at 1960 nm, we report a successful synthesis of very large mono-dispersed PbS NPs having a diameter up to 16 nm by multiple injections. The resulting NPs have an absorption peak over 2500 nm with a small full-width-at-half-maximum (FWHM) of 24 meV. To demonstrate the applications of such large QDs, broadband heterojunction photodetectors are fabricated with the large PbS QDs of an absorption peak at 2100 nm. The resulting devices have an EQE of 25% (over 50% IQE) at 2100 nm corresponding to a responsivity of 0.385 A/W, and an EQE ~60% in the visible range.}, number={47}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Dong, Chen and Liu, Shuyi and Barange, Nilesh and Lee, Jaewoong and Pardue, Tyler and Yi, Xueping and Yin, Shichen and So, Franky}, year={2019}, month={Nov}, pages={44451–44457} }
 @article{sen_yang_rech_feng_ho_huang_so_kline_you_kudenov_et al._2019, title={Panchromatic All-Polymer Photodetector with Tunable Polarization Sensitivity}, volume={7}, ISSN={["2195-1071"]}, DOI={10.1002/adom.201801346}, abstractNote={Abstract}, number={4}, journal={ADVANCED OPTICAL MATERIALS}, author={Sen, Pratik and Yang, Ruonan and Rech, Jeromy J. and Feng, Yuanxiang and Ho, Carr Hoi Yi and Huang, Jinsong and So, Franky and Kline, R. Joseph and You, Wei and Kudenov, Michael W. and et al.}, year={2019}, month={Feb} }
 @misc{cheng_so_tsang_2019, title={Progress in air-processed perovskite solar cells: from crystallization to photovoltaic performance}, volume={6}, ISSN={["2051-6355"]}, DOI={10.1039/c9mh00325h}, abstractNote={This review focuses on oxygen and moisture effects on perovskite crystallization, state-of-the-art engineering for highly efficient air-processed perovskite solar cells.}, number={8}, journal={MATERIALS HORIZONS}, author={Cheng, Yuanhang and So, Franky and Tsang, Sai-Wing}, year={2019}, month={Oct}, pages={1611–1624} }
 @article{salehi_dong_shin_zhu_papa_thy bui_castellano_so_2019, title={Realization of high-efficiency fluorescent organic light-emitting diodes with low driving voltage}, volume={10}, ISSN={2041-1723}, url={http://dx.doi.org/10.1038/s41467-019-10260-7}, DOI={10.1038/s41467-019-10260-7}, abstractNote={Abstract}, number={1}, journal={Nature Communications}, publisher={Springer Science and Business Media LLC}, author={Salehi, Amin and Dong, Chen and Shin, Dong-Hun and Zhu, Liping and Papa, Christopher and Thy Bui, Anh and Castellano, Felix N. and So, Franky}, year={2019}, month={May} }
 @misc{salehi_fu_shin_so_2019, title={Recent Advances in OLED Optical Design}, volume={29}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.201808803}, abstractNote={Abstract}, number={15}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Salehi, Amin and Fu, Xiangyu and Shin, Dong-Hun and So, Franky}, year={2019}, month={Apr} }
 @article{kim_schaefer_ma_zhao_turner_ghasemi_constantinou_so_yan_gadisa_et al._2019, title={The Critical Impact of Material and Process Compatibility on the Active Layer Morphology and Performance of Organic Ternary Solar Cells}, volume={9}, ISSN={["1614-6840"]}, url={https://doi.org/10.1002/aenm.201802293}, DOI={10.1002/aenm.201802293}, abstractNote={Abstract}, number={2}, journal={ADVANCED ENERGY MATERIALS}, author={Kim, Joo-Hyun and Schaefer, Charley and Ma, Tingxuan and Zhao, Jingbo and Turner, Johnathan and Ghasemi, Masoud and Constantinou, Iordania and So, Franky and Yan, He and Gadisa, Abay and et al.}, year={2019}, month={Jan} }
 @article{xu_yi_huang_zheng_zhang_salehi_coropceanu_ho_marder_toney_et al._2018, title={Donor Conjugated Polymers with Polar Side Chain Groups: The Role of Dielectric Constant and Energetic Disorder on Photovoltaic Performance}, volume={28}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.201803418}, abstractNote={Abstract}, number={46}, journal={Advanced Functional Materials}, author={Xu, B. and Yi, X. and Huang, T. and Zheng, Z. and Zhang, J. and Salehi, A. and Coropceanu, V. and Ho, C.H.Y. and Marder, S.R. and Toney, M.F. and et al.}, year={2018}, pages={1803418} }
 @article{hsain_sharma_yu_jones_so_seidel_2018, title={Enhanced piezoelectricity of thin film hafnia-zirconia (HZO) by inorganic flexible substrates}, volume={113}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.5031134}, DOI={10.1063/1.5031134}, abstractNote={Hf0.5Zr0.5O2 (HZO) films are grown on rigid glass and flexible polyimide substrates using non-rapid thermal annealing. Films are comparatively investigated using macroscopic and local probe-based approaches to characterize their ferroelectric and piezoelectric properties. The polarization-electric field (P-E) measurements reveal that the ferroelectric characteristics of these thin films agree with the observed switchable piezoresponse hysteresis loops as well as electrically written, oppositely oriented domains. Moreover, the HZO thin films grown on flexible polyimide substrates display significantly enhanced piezoelectric response in comparison to the films grown on rigid substrates. This effect is likely due to improved domain wall motion caused by the mechanical release of the film-substrate couple. These findings suggest that inherently lead-free HZO thin films on flexible substrates are potential candidate materials for improved piezoelectric applications in wearable devices.}, number={2}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Hsain, H. Alex and Sharma, Pankaj and Yu, Hyeonggeun and Jones, Jacob L. and So, Franky and Seidel, Jan}, year={2018}, month={Jul}, pages={022905} }
 @article{lo_gautam_selter_zheng_oosterhout_constantinou_knitsch_wolfe_yi_bredas_et al._2018, title={Every Atom Counts: Elucidating the Fundamental Impact of Structural Change in Conjugated Polymers for Organic Photovoltaics}, volume={30}, ISSN={["1520-5002"]}, DOI={10.1021/acs.chemmater.8b00590}, abstractNote={As many conjugated polymer-based organic photovoltaic (OPV) materials provide substantial solar power conversion efficiencies (as high as 13%), it is important to develop a deeper understanding of how the primary repeat unit structures impact device performance. In this work, we have varied the group 14 atom (C, Si, Ge) at the center of a bithiophene fused ring to elucidate the impact of a minimal repeat unit structure change on the optical, transport, and morphological properties, which ultimately control device performance. Careful polymerization and polymer purification produced three “one-atom change” donor–acceptor conjugated alternating copolymers with similar molecular weights and dispersities. DFT calculation, absorption spectroscopy, and high-temperature solution 1H nuclear magnetic resonance (NMR) results indicate that poly(dithienosilole-alt-thienopyrrolodione), P(DTS-TPD), and poly(dithienogermole-alt-thienopyrrolodione), P(DTG-TPD) exhibit different rotational conformations when compared to p...}, number={9}, journal={CHEMISTRY OF MATERIALS}, author={Lo, Chi Kin and Gautam, Bhoj R. and Selter, Philipp and Zheng, Zilong and Oosterhout, Stefan D. and Constantinou, Iordania and Knitsch, Robert and Wolfe, Rylan M. W. and Yi, Xueping and Bredas, Jean-Luc and et al.}, year={2018}, month={May}, pages={2995–3009} }
 @article{huang_yau_yu_qi_so_dai_jiang_2018, title={Flexoelectricity in a metal/ferroelectric/semiconductor heterostructure}, volume={8}, ISSN={["2158-3226"]}, DOI={10.1063/1.5031162}, abstractNote={The flexoelectricity in a 100 nm-thick BaTiO3 (BTO) thin film based metal/ferroelectric insulator/semiconductor (MFS) heterostructure was reported in this letter. The transverse flexoelectric coefficient of the BTO thin film in the heterojunction structure was measured to be 287-418 μC/m at room temperature, and its temperature dependence shows that the flexoelectric effect in the BTO thin film was dominated in the paraelectric phase. We showed that the BTO thin film capacitance could be controlled at multi-levels by introducing ferroelectric and flexoelectric polarization in the film. These results are promising for understanding of the flexoelectricity in epitaxial ferroelectric thin films and practical applications of the enhanced flexoelectricity in nanoscale devices.}, number={6}, journal={AIP ADVANCES}, author={Huang, Shujin and Yau, Hei-Man and Yu, Hyeonggeun and Qi, Lu and So, Franky and Dai, Ji-Yan and Jiang, Xiaoning}, year={2018}, month={Jun} }
 @article{yi_gautam_constantinou_cheng_peng_klump_ba_ho_dong_marder_et al._2018, title={Impact of Nonfullerene Molecular Architecture on Charge Generation, Transport, and Morphology in PTB7-Th-Based Organic Solar Cells}, volume={28}, ISSN={1616-301X}, url={http://dx.doi.org/10.1002/adfm.201802702}, DOI={10.1002/adfm.201802702}, abstractNote={Abstract}, number={32}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Yi, Xueping and Gautam, Bhoj and Constantinou, Iordania and Cheng, Yuanhang and Peng, Zhengxing and Klump, Erik and Ba, Xiaochu and Ho, Carr Hoi Yi and Dong, Chen and Marder, Seth R. and et al.}, year={2018}, month={Jun}, pages={1802702} }
 @article{gautam_klump_yi_constantinou_shewmon_salehi_lo_zheng_brédas_gundogdu_et al._2018, title={Increased Exciton Delocalization of Polymer upon Blending with Fullerene}, volume={30}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/adma.201801392}, DOI={10.1002/adma.201801392}, abstractNote={Abstract}, number={30}, journal={Advanced Materials}, publisher={Wiley}, author={Gautam, Bhoj and Klump, Erik and Yi, Xueping and Constantinou, Iordania and Shewmon, Nathan and Salehi, Amin and Lo, Chi Kin and Zheng, Zilong and Brédas, Jean-Luc and Gundogdu, Kenan and et al.}, year={2018}, month={Jun}, pages={1801392} }
 @article{lo_wang_oosterhout_zheng_yi_fuentes-hernandez_so_coropceanu_bredas_toney_et al._2018, title={Langmuir-Blodgett Thin Films of Diketopyrrolopyrrole-Based Amphiphiles}, volume={10}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.7b18239}, abstractNote={We report on two π-conjugated donor-acceptor-donor (D-A-D) molecules of amphiphilic nature, aiming to promote intermolecular ordering and carrier mobility in organic electronic devices. Diketopyrrolopyrrole was selected as the acceptor moiety that was disubstituted with nonpolar and polar functional groups, thereby providing the amphiphilic structures. This structural design resulted in materials with a strong intermolecular order in the solid state, which was confirmed by differential scanning calorimetry and polarized optical microscopy. Langmuir-Blodgett (LB) films of ordered mono- and multilayers were transferred onto glass and silicon substrates, with layer quality, coverage, and intermolecular order controlled by layer compression pressure on the LB trough. Organic field-effect transistors and organic photovoltaics devices with active layers consisting of the amphiphilic conjugated D-A-D-type molecules were constructed to demonstrate that the LB technique is an effective layer-by-layer deposition approach to fabricate self-assembled, ordered thin films.}, number={14}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Lo, Chi Kin and Wang, Cheng-Yin and Oosterhout, Stefan D. and Zheng, Zilong and Yi, Xueping and Fuentes-Hernandez, Canek and So, Franky and Coropceanu, Veaceslav and Bredas, Jean-Luc and Toney, Michael F. and et al.}, year={2018}, month={Apr}, pages={11995–12004} }
 @article{salehi_chen_fu_peng_so_2018, title={Manipulating Refractive Index in Organic Light-Emitting Diodes}, volume={10}, ISSN={["1944-8244"]}, DOI={10.1021/acsami.7b18514}, abstractNote={In a conventional organic light-emitting diode (OLED), only a fraction of light can escape to the glass substrate and air. Most radiation is lost to two major channels: waveguide modes and surface plasmon polaritons. It is known that reducing the refractive indices of the constituent layers in an OLED can enhance light extraction. Among all of the layers, the refractive index of the electron transport layer (ETL) has the largest impact on light extraction because it is the layer adjacent to the metallic cathode. Oblique angle deposition (OAD) provides a way to manipulate the refractive index of a thin film by creating an ordered columnar void structure. In this work, using OAD, the refractive index of tris(8-hydroxyquinoline)aluminum (Alq3) can be tuned from 1.75 to 1.45. With this low-index ETL deposited by OAD, the resulting phosphorescent OLED shows nearly 30% increase in light extraction efficiency.}, number={11}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Salehi, Amin and Chen, Ying and Fu, Xiangyu and Peng, Cheng and So, Franky}, year={2018}, month={Mar}, pages={9595–9601} }
 @article{xu_pelse_agarkar_ito_zhang_yi_chujo_marder_so_reynolds_et al._2018, title={Randomly Distributed Conjugated Polymer Repeat Units for High-Efficiency Photovoltaic Materials with Enhanced Solubility and Processability}, volume={10}, ISSN={["1944-8244"]}, DOI={10.1021/acsami.8b15522}, abstractNote={Three structurally disordered terpolymer derivatives of PffBT4T-2OD (PCE11), prepared by replacing a varied amount of bithiophene linkers with single thiophenes, were found to exhibit reduced aggregation in solution with increasing thiophene content, while important redox and optoelectronic properties remained similar to those of PffBT4T-2OD. Solar cells based on random terpolymer-PC71BM blends exhibited average power conversion efficiencies of over 9.5% when processed with preheated substrates, with fill factors above 70%, exceeding those from PffBT4T-2OD. Thanks to increased solubility, random terpolymer devices were able to be fabricated on room-temperature substrates, reaching virtually identical performance among all three polymers despite remarkable thicknesses of ∼400 nm. Thus, we show that the random terpolymer approach is successful in improving processability while maintaining device performance.}, number={51}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Xu, Bing and Pelse, Ian and Agarkar, Shruti and Ito, Shunichiro and Zhang, Junxiang and Yi, Xueping and Chujo, Yoshiki and Marder, Seth and So, Franky and Reynolds, John R. and et al.}, year={2018}, month={Dec}, pages={44583–44588} }
 @article{yu_ho_barange_larrabee_so_2018, title={Semi-transparent vertical organic light-emitting transistors}, volume={55}, ISSN={1566-1199}, url={http://dx.doi.org/10.1016/J.ORGEL.2018.01.030}, DOI={10.1016/J.ORGEL.2018.01.030}, abstractNote={Vertical organic light-emitting transistor (VOLET) having an organic light-emitting diode integrated with a vertical thin-film transistor is promising for transparent electronics because the vertical device structure potentially offers a display with a large aperture ratio and a low power consumption. However, making a transparent VOLET has been challenging due to the requirements for all transparent electrodes including fabrication of a porous source electrode for current modulation in the device. Here, we report a semi-transparent VOLET with a large modulation of light emitted through the top and bottom electrodes using a nano-porous indium-tin oxide (ITO) source electrode, a Mg:Ag drain electrode, and an ITO gate electrode. The porous ITO source electrode is not only important for luminance modulation, but the nano-textured film morphology also enhances light extraction from the device. Finally, we show that the off current of the VOLET can be suppressed with an electron transporting layer (C60), leading to a large luminance on/off ratio of 104.}, journal={Organic Electronics}, publisher={Elsevier BV}, author={Yu, Hyeonggeun and Ho, Szuheng and Barange, Nilesh and Larrabee, Ryan and So, Franky}, year={2018}, month={Apr}, pages={126–132} }
 @article{luo_tran_kadlubowski_ho_riley_so_mei_2018, title={Side-Chain Sequence Enabled Regioisomeric Acceptors for Conjugated Polymers}, volume={51}, ISSN={["1520-5835"]}, url={https://doi.org/10.1021/acs.macromol.8b01946}, DOI={10.1021/acs.macromol.8b01946}, abstractNote={Side-chain sequence enabled regioisomeric acceptors, bearing different side-chain sequences on the same conjugated backbone, are herein reported. Two regioregular polymers PTBI-1 and PTBI-2 and one regiorandom polymer PTBI-3 were synthesized from these two regioisomeric acceptors for a comparative study. UV–vis–NIR absorption spectroscopy and electrochemical study confirmed similar frontier molecular orbital levels of the three polymers in their solid state. More intriguingly, absorption profiles suggest that the sequence of side chains greatly governs the aggregation behaviors. Furthermore, the PTBI-2 film shows larger ordered domains than PTBI-1 and PTBI-3 films, as supported by AFM and GIWAXS measurements. As a result, PTBI-2-based FET devices achieved an average hole mobility of 1.37 cm2 V–1 s–1, much higher than the two polymers with other side-chain sequences. The regiorandom PTBI-3 exhibited the lowest average hole mobility of 0.27 cm2 V–1 s–1. This study highlights the significant impact of side-c...}, number={21}, journal={MACROMOLECULES}, publisher={American Chemical Society (ACS)}, author={Luo, Xuyi and Tran, Dung T. and Kadlubowski, Natalie M. and Ho, Carr Hoi Yi and Riley, Parand and So, Franky and Mei, Jianguo}, year={2018}, month={Nov}, pages={8486–8492} }
 @article{yu_cheng_li_tsang_so_2018, title={Sub-Band Gap Turn-On Near-Infrared-to-Visible Up-Conversion Device Enabled by an Organic?Inorganic Hybrid Perovskite Photovoltaic Absorber}, volume={10}, ISSN={["1944-8244"]}, DOI={10.1021/acsami.8b00592}, abstractNote={Direct integration of an infrared (IR) photodetector with an organic light-emitting diode (OLED) enables low-cost, pixel-free IR imaging. However, the operation voltage of the resulting IR-to-visible up-conversion is large because of the series device architecture. Here, we report a low-voltage near-IR (NIR)-to-visible up-conversion device using formamidinium lead iodide as a NIR absorber integrated with a phosphorescent OLED. Because of the efficient photocarrier injection from the hybrid perovskite layer to the OLED, we observed a sub-band gap turn-on of the OLED under NIR illumination. The device showed a NIR-to-visible up-conversion efficiency of 3% and a luminance on/off ratio of 103 at only 5 V. Finally, we demonstrate pixel-free NIR imaging using the up-conversion device.}, number={18}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Yu, Hyeonggeun and Cheng, Yuanhang and Li, Menglin and Tsang, Sai-Wing and So, Franky}, year={2018}, month={May}, pages={15920–15925} }
 @article{yu_cheng_shin_tsang_so_2018, title={Vertical Organic-Inorganic Hybrid Perovskite Schottky Junction Transistors}, volume={4}, ISSN={2199-160X}, url={http://dx.doi.org/10.1002/AELM.201800039}, DOI={10.1002/AELM.201800039}, abstractNote={Abstract}, number={5}, journal={Advanced Electronic Materials}, publisher={Wiley}, author={Yu, Hyeonggeun and Cheng, Yuanhang and Shin, Donghun and Tsang, Sai-Wing and So, Franky}, year={2018}, month={Mar}, pages={1800039} }
 @book{so_huang_yongbo_thompson_2018, place={Singapore ; Hackensack, NJ}, title={World Scientific handbook of organic optoelectronic devices}, publisher={World Scientific Publishing Company}, year={2018} }
 @article{cheng_xu_xie_li_qing_ma_lee_so_tsang_2017, title={18% High-Efficiency Air-Processed Perovskite Solar Cells Made in a Humid Atmosphere of 70% RH}, volume={1}, ISSN={2367-198X}, url={http://dx.doi.org/10.1002/SOLR.201700097}, DOI={10.1002/SOLR.201700097}, abstractNote={Despite the advanced progress in power conversion efficiency (PCE), developing air-processed high-efficiency perovskite solar cells (PVSCs) for future commercialization is still challenging. Here, we report that besides the general wisdom of the effect of moisture, oxygen in air has a severe impact on the quality of the solution-deposited perovskite films. Interestingly, as opposed to moisture that induces fast crystallization of PbI2 upon deposition, oxygen exacerbates the wettability of the PbI2 solution on the substrates. We find that simply preheating the substrate and PbI2 solution a fully covered and uniform PbI2 film deposited in air can be obtained. This is possibly due to the increased vapor pressure of the solvent at higher temperatures to reduce the ingress of oxygen and moisture during the PbI2 deposition. Using this simple method, an air-processed PVSC made under a humid atmosphere of 70% RH has a record PCE of 18.11%. Our work not only reveals the origin of the detrimental effects on perovskite film formation in ambient air, but also provides a simple practical strategy to develop air-processed high-efficiency PVSCs for future commercialization.}, number={9}, journal={Solar RRL}, publisher={Wiley}, author={Cheng, Yuanhang and Xu, Xiuwen and Xie, Yuemin and Li, Ho-Wa and Qing, Jian and Ma, Chunqing and Lee, Chun-Sing and So, Franky and Tsang, Sai-Wing}, year={2017}, month={Jul}, pages={1700097} }
 @article{cheng_xu_xie_li_qing_ma_lee_so_tsang_2017, title={18% high-efficiency air-processed perovskite solar cells made in a humid atmosphere of 70% RH}, volume={1}, DOI={10.1002/solr.201770131}, abstractNote={Solar RRLVolume 1, Issue 9 1770131 Cover PictureFree Access 18% High-Efficiency Air-Processed Perovskite Solar Cells Made in a Humid Atmosphere of 70% RH (Solar RRL 9∕2017) Yuanhang Cheng, Yuanhang Cheng Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong SAR, P. R. China City University of Hong Kong Shenzhen Research Institute, Shenzhen, P. R. ChinaSearch for more papers by this authorXiuwen Xu, Xiuwen Xu Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong SAR, P. R. China City University of Hong Kong Shenzhen Research Institute, Shenzhen, P. R. ChinaSearch for more papers by this authorYuemin Xie, Yuemin Xie Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong SAR, P. R. China City University of Hong Kong Shenzhen Research Institute, Shenzhen, P. R. ChinaSearch for more papers by this authorHo-Wa Li, Ho-Wa Li Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong SAR, P. R. China City University of Hong Kong Shenzhen Research Institute, Shenzhen, P. R. ChinaSearch for more papers by this authorJian Qing, Jian Qing Center of Super-Diamond and Advanced Films (COSDAF) & Department of Chemistry, City University of Hong Kong, Hong Kong SAR, P. R. ChinaSearch for more papers by this authorChunqing Ma, Chunqing Ma Center of Super-Diamond and Advanced Films (COSDAF) & Department of Chemistry, City University of Hong Kong, Hong Kong SAR, P. R. ChinaSearch for more papers by this authorChun-Sing Lee, Chun-Sing Lee Center of Super-Diamond and Advanced Films (COSDAF) & Department of Chemistry, City University of Hong Kong, Hong Kong SAR, P. R. ChinaSearch for more papers by this authorFranky So, Franky So Department of Materials Science and Engineering, North Carolina State University, Raleigh NC, 27695 United StatesSearch for more papers by this authorSai-Wing Tsang, Corresponding Author Sai-Wing Tsang saitsang@cityu.edu.hk orcid.org/0000-0003-0788-4905 Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong SAR, P. R. China City University of Hong Kong Shenzhen Research Institute, Shenzhen, P. R. ChinaSearch for more papers by this author Yuanhang Cheng, Yuanhang Cheng Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong SAR, P. R. China City University of Hong Kong Shenzhen Research Institute, Shenzhen, P. R. ChinaSearch for more papers by this authorXiuwen Xu, Xiuwen Xu Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong SAR, P. R. China City University of Hong Kong Shenzhen Research Institute, Shenzhen, P. R. ChinaSearch for more papers by this authorYuemin Xie, Yuemin Xie Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong SAR, P. R. China City University of Hong Kong Shenzhen Research Institute, Shenzhen, P. R. ChinaSearch for more papers by this authorHo-Wa Li, Ho-Wa Li Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong SAR, P. R. China City University of Hong Kong Shenzhen Research Institute, Shenzhen, P. R. ChinaSearch for more papers by this authorJian Qing, Jian Qing Center of Super-Diamond and Advanced Films (COSDAF) & Department of Chemistry, City University of Hong Kong, Hong Kong SAR, P. R. ChinaSearch for more papers by this authorChunqing Ma, Chunqing Ma Center of Super-Diamond and Advanced Films (COSDAF) & Department of Chemistry, City University of Hong Kong, Hong Kong SAR, P. R. ChinaSearch for more papers by this authorChun-Sing Lee, Chun-Sing Lee Center of Super-Diamond and Advanced Films (COSDAF) & Department of Chemistry, City University of Hong Kong, Hong Kong SAR, P. R. ChinaSearch for more papers by this authorFranky So, Franky So Department of Materials Science and Engineering, North Carolina State University, Raleigh NC, 27695 United StatesSearch for more papers by this authorSai-Wing Tsang, Corresponding Author Sai-Wing Tsang saitsang@cityu.edu.hk orcid.org/0000-0003-0788-4905 Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong SAR, P. R. China City University of Hong Kong Shenzhen Research Institute, Shenzhen, P. R. ChinaSearch for more papers by this author First published: 06 September 2017 https://doi.org/10.1002/solr.201770131Citations: 7AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract To realize high-efficiency air-processable perovskite solar cells (PVSCs), understanding the impact of ambient conditions on the formation of the light absorber perovskite materials is of the utmost importance. Herein, Cheng et al. (article No. 201700097) have found that the moisture in air rapidly accelerates the crystallization of the precursor materials and leads to an uncontrollable film morphology. More importantly, for the first time, it is found that the oxygen in air significantly reduces the wettability of the precursor solution on substrate and results in a non-continuous thin film. The two limiting factors can be eliminated by simply escalating the deposition temperture, through which a fully covered and uniform precursor thin films in air was achieved, even at humidity as high as 70%. It is proposed that such improvement is due to the increased vapor pressure of the solvent at higher temperature to reduce the ingress of oxygen and moisture into the precursor materials during the solution deposition process. By further optimizing the deposition temperature, air-processed PVSCs with a champion efficiency of 18.1% under a high humidity environment of 70% RH was achieved. Citing Literature Volume1, Issue9September 20171770131 RelatedInformation}, number={9}, journal={Solar RRL}, author={Cheng, Y. H. and Xu, X. W. and Xie, Y. M. and Li, H. W. and Qing, J. and Ma, C. Q. and Lee, C. S. and So, Franky and Tsang, S. W.}, year={2017} }
 @article{bauer_zhang_zhao_ye_kim_constantinou_yan_so_ade_yan_et al._2017, title={Comparing non-fullerene acceptors with fullerene in polymer solar cells: a case study with FTAZ and PyCNTAZ}, volume={5}, ISSN={["2050-7496"]}, url={https://doi.org/10.1039/C6TA10450A}, DOI={10.1039/c6ta10450a}, abstractNote={Non-fullerene acceptors (NFAs) are becoming a serious contender to fullerene-based electron acceptors in organic photovoltaics, due to their structural versatility and easily tunable optical and electronic properties.}, number={10}, journal={JOURNAL OF MATERIALS CHEMISTRY A}, publisher={Royal Society of Chemistry (RSC)}, author={Bauer, Nicole and Zhang, Qianqian and Zhao, Jingbo and Ye, Long and Kim, Joo-Hyun and Constantinou, Iordania and Yan, Liang and So, Franky and Ade, Harald and Yan, He and et al.}, year={2017}, month={Mar}, pages={4886–4893} }
 @article{constantinou_yi_shewmon_klump_peng_garakyaraghi_lo_reynolds_castellano_so_2017, title={Effect of Polymer-Fullerene Interaction on the Dielectric Properties of the Blend}, volume={7}, ISSN={1614-6832}, url={http://dx.doi.org/10.1002/AENM.201601947}, DOI={10.1002/AENM.201601947}, abstractNote={It is commonly believed that large dielectric constants are required for efficient charge separation in polymer photovoltaic devices. However, many polymers used in high‐performance solar cells do not possess high dielectric constants. In this work, the effect of polymer–fullerene interactions on the dielectric environment of the active layer blend and the device performance for several donor–acceptor conjugated polymer systems is investigated. It is found that, while none of the high‐performing polymers studied has a dielectric constant value larger than 3, all polymer–fullerene blends have a significantly larger dielectric constant compared to their pristine constituents. Additionally, it is found that the blend dielectric constant reaches a maximum value in fully optimized devices. Using PTB7:PC71BM blends as an example, it is showed that, in addition to a small increase in the dielectric constant, devices fabricated using the optimum processing additive concentration exhibit almost 3X larger excited state polarizability. This large increase in excited state polarizability results in a substantial difference in short‐circuit current and ultimately device performance. The results show that the excited state polarizability critically depends on polymer–fullerene interactions, and can be a leading indicator of device performance for a given material system.}, number={13}, journal={Advanced Energy Materials}, publisher={Wiley}, author={Constantinou, Iordania and Yi, Xueping and Shewmon, Nathan T. and Klump, Erik D. and Peng, Cheng and Garakyaraghi, Sofia and Lo, Chi Kin and Reynolds, John R. and Castellano, Felix N. and So, Franky}, year={2017}, month={Feb}, pages={1601947} }
 @article{yu_chung_shewmon_ho_carpenter_larrabee_sun_jones_ade_o'connor_et al._2017, title={Flexible Inorganic Ferroelectric Thin Films for Nonvolatile Memory Devices}, volume={27}, ISSN={1616-301X}, url={http://dx.doi.org/10.1002/ADFM.201700461}, DOI={10.1002/ADFM.201700461}, abstractNote={Next‐generation wearable electronics call for flexible nonvolatile devices for ubiquitous data storage. Thus far, only organic ferroelectric materials have shown intrinsic flexibility and processability on plastic substrates. Here, it is shown that by controlling the heating rate, ferroelectric hafnia films can be grown on plastic substrates. The resulting highly flexible capacitor with a film thickness of 30 nm yields a remnant polarization of 10 µC cm−2. Bending tests show that the film ferroelectricity can be retained under a bending radius below 8 mm with up to 1000 bending cycles. The excellent flexibility is due to the extremely thin hafnia film thickness. Using the ferroelectric film as a gate insulator, a low voltage nonvolatile vertical organic transistor is demonstrated on a plastic substrate with an extrapolated date retention time of up to 10 years.}, number={21}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Yu, Hyeonggeun and Chung, Ching-Chang and Shewmon, Nate and Ho, Szuheng and Carpenter, Joshua H. and Larrabee, Ryan and Sun, Tianlei and Jones, Jacob L. and Ade, Harald and O'Connor, Brendan T. and et al.}, year={2017}, month={Apr}, pages={1700461} }
 @article{zhang_yan_jiao_peng_liu_rech_klump_ade_so_you_2017, title={Fluorinated Thiophene Units Improve Photovoltaic Device Performance of Donor–Acceptor Copolymers}, volume={29}, ISSN={0897-4756 1520-5002}, url={http://dx.doi.org/10.1021/ACS.CHEMMATER.7B01683}, DOI={10.1021/ACS.CHEMMATER.7B01683}, abstractNote={Fluorinated conjugated polymers leading to enhanced photovoltaic device performance has been widely observed in a variety of donor–acceptor copolymers; however, almost all these polymers have fluorine substituents on the acceptor unit. Building upon our previously reported PBnDT-FTAZ, a fluorinated donor–acceptor conjugated polymer with impressive device performance, we set this study to explore the effect of adding the fluorine substituents onto the flanking thiophene units between the donor unit (BnDT) and the acceptor unit (TAZ). We developed new synthetic approaches to control the position of the fluorination (3′ or 4′) on the thiophene unit, and synthesized four additional PBnDT-TAZ polymers incorporating the fluorine-substituted-thiophene (FT) units, 3′-FT-HTAZ, 4′-FT-HTAZ, 3′-FT-FTAZ, and 4′-FT-FTAZ. We discover that relocating the fluorine substituents from the acceptor to the flanking thiophene units have a negligible impact on the device characteristics (short circuit current, open circuit volta...}, number={14}, journal={Chemistry of Materials}, publisher={American Chemical Society (ACS)}, author={Zhang, Qianqian and Yan, Liang and Jiao, Xuechen and Peng, Zhengxing and Liu, Shubin and Rech, Jeromy James and Klump, Erik and Ade, Harald and So, Franky and You, Wei}, year={2017}, month={Jul}, pages={5990–6002} }
 @article{salehi_ho_chen_peng_yersin_so_2017, title={Highly Efficient Organic Light-Emitting Diode Using A Low Refractive Index Electron Transport Layer}, volume={5}, ISSN={["2195-1071"]}, DOI={10.1002/adom.201700197}, abstractNote={A low refractive index electron transport layer (ETL) can be very effective in enhancing the out‐coupling efficiency of an organic light‐emitting diode (OLED). However, most organic films show a refractive index close to 1.8. In this work, it has been discovered that tris‐[3‐(3‐pyridyl)mesityl]borane (3TPYMB) has a low refractive index of 1.65 (at 550 nm), which is the lowest refractive index ETL among the commonly used ETLs up to date. Using 3TPYMB as an ETL, a solution processed OLED is demonstrated with nearly a 76% enhancement in external quantum efficiency (EQE). Optical simulation results of this study show that 59% of the enhancement comes from the low refractive index 3TPYMB, and the remaining 17% from the change in charge balance due to the 3TPYMB ETL in the OLED devices.}, number={11}, journal={ADVANCED OPTICAL MATERIALS}, author={Salehi, Amin and Ho, Szuheng and Chen, Ying and Peng, Cheng and Yersin, Hartmut and So, Franky}, year={2017}, month={Jun} }
 @article{bullock_salehi_zeman_abboud_so_schanze_2017, title={In Search of Deeper Blues: Trans-N-Heterocyclic Carbene Platinum Phenylacetylide as a Dopant for Phosphorescent OLEDs}, volume={9}, ISSN={["1944-8244"]}, DOI={10.1021/acsami.7b12107}, abstractNote={A trans-N-heterocyclic carbene (NHC) platinum(II) acetylide complex bearing phenyl acetylene ligands (NPtPE1) has been synthesized via the Hagihara reaction in 64% yield. The complex features spectrally narrow deep blue emission with a phosphorescence quantum yield (0.30) and lifetime (∼10 μs) in the solid state. The modest quantum yield and lifetime make NPtPE1 a candidate for incorporation into an organic light emitting diode (OLED). Prototype devices exhibited a maximum EQE of 8% with CIE (0.20,0.20). To the best of our knowledge, this is the first example of a platinum(II) acetylide bearing NHC ligands to be incorporated into an OLED.}, number={47}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Bullock, James D. and Salehi, Amin and Zeman, Charles J. and Abboud, Khalil A. and So, Franky and Schanze, Kirk S.}, year={2017}, month={Nov}, pages={41111–41114} }
 @article{so_shi_2017, title={Organic molecular light-emitting materials and devices}, journal={Introduction to Organic Electronic and Optoelectronic Materials and Devices, 2nd edition}, author={So, F. and Shi, J. M.}, year={2017}, pages={363–385} }
 @article{peng_salehi_chen_danz_liaptsis_so_2017, title={Probing the Emission Zone Length in Organic Light Emitting Diodes via Photoluminescence and Electroluminescence Degradation Analysis}, volume={9}, ISSN={["1944-8244"]}, DOI={10.1021/acsami.7b13537}, abstractNote={The understanding and control of the emission zone in organic light emitting diodes (OLEDs) is crucial to the device operational stability. Using the photoluminescence and electroluminescence degradation data, we have developed a modeling methodology to quantitatively determine the length of the emission zone and correlate that with the degradation mechanism. We first validate the modeling results by studying the emitter concentration effect on operational stability of devices using the well-studied thermal activated delayed fluorescent (TADF) emitter (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN), and our results are consistent with previous published data. We further applied this methodology to study the emitter concentration effect using another TADF emitter, 4-carbazolyl-2-methylisoindole-1,3-dione (dopant 1). The results show that the emission zone of the dopant 1 devices is narrower than the 4CzIPN device, leading to faster degradation. While a higher emitter concentration does not result in widening of the emission zone, we were able to widen the emission zone and hence extend the device lifetime using a mixed host.}, number={47}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Peng, Cheng and Salehi, Amin and Chen, Ying and Danz, Michael and Liaptsis, Georgios and So, Franky}, year={2017}, month={Nov}, pages={41421–41427} }
 @article{kim_gadisa_schaefer_yao_gautam_balar_ghasemi_constantinou_so_o'connor_et al._2017, title={Strong polymer molecular weight-dependent material interactions: impact on the formation of the polymer/fullerene bulk heterojunction morphology}, volume={5}, ISSN={2050-7488 2050-7496}, url={http://dx.doi.org/10.1039/C7TA03052E}, DOI={10.1039/c7ta03052e}, abstractNote={The morphological evolution is initiated by L–L or L–S phase separation (left) and further developed by molecular mobility, governed by polymer–solvent interactions which determine the final domain size of the BHJ layer (right).}, number={25}, journal={Journal of Materials Chemistry A}, publisher={Royal Society of Chemistry (RSC)}, author={Kim, Joo-Hyun and Gadisa, Abay and Schaefer, Charley and Yao, Huifeng and Gautam, Bhoj R. and Balar, Nrup and Ghasemi, Masoud and Constantinou, Iordania and So, Franky and O'Connor, Brendan T. and et al.}, year={2017}, pages={13176–13188} }
 @article{ho_yu_so_2017, title={Transparent indium-tin oxide/indium-gallium-zinc oxide Schottky diodes formed by gradient oxygen doping}, volume={111}, ISSN={["1077-3118"]}, DOI={10.1063/1.4993430}, abstractNote={Amorphous InGaZnO (a-IGZO) is promising for transparent electronics due to its high carrier mobility and optical transparency. However, most metal/a-IGZO junctions are ohmic due to the Fermi-level pinning at the interface, restricting their device applications. Here, we report that indium-tin oxide/a-IGZO Schottky diodes can be formed by gradient oxygen doping in the a-IGZO layer that would otherwise form an ohmic contact. Making use of back-to-back a-IGZO Schottky junctions, a transparent IGZO permeable metal-base transistor is also demonstrated with a high common-base gain.}, number={21}, journal={APPLIED PHYSICS LETTERS}, author={Ho, Szuheng and Yu, Hyeonggeun and So, Franky}, year={2017}, month={Nov} }
 @article{xu_ma_cheng_xie_yi_gautam_chen_li_lee_so_et al._2017, title={Ultraviolet-ozone surface modification for non-wetting hole transport materials based inverted planar perovskite solar cells with efficiency exceeding 18%}, volume={360}, ISSN={["1873-2755"]}, DOI={10.1016/j.jpowsour.2017.06.013}, abstractNote={Non-wetting hole transport materials (HTMs) have great potential in facilitating large-sized perovskite crystal growth and enhancing device stability by opposing moisture ingress, However, the severe non-wetting issue limits the wide application of these materials in low-temperature solution-processed inverted planar perovskite solar cells (PVSCs), and corresponding devices are rarely reported. Here, a facile ultraviolet-ozone (UVO) modification method is demonstrated to overcome this issue. By carefully controlling the UVO modification time, the surface wettability of poly-TPD can be tuned without affecting the bulk properties of the film, hence perovskite films with desired grain size and excellent coverage can be deposited via a one-step spin-coating method. Benefiting from the high-quality perovskite, well-matched energy level alignment and hydrophobic property of poly-TPD, the resulting PVSCs show a champion power conversion efficiency of 18.19% with significantly enhanced stability as compared to the PEDOT:PSS counterparts. Moreover, the UVO modification approach also demonstrates its validity when being extended to other hydrophobic HTMs. This work not only provides a general strategy to broaden the selection pool of HTMs for solution-processed inverted planar PVSCs, but also may triggers the exploration of more advanced strategies to make non-wetting HTMs applicable in solution-processed inverted planar PVSCs.}, journal={JOURNAL OF POWER SOURCES}, author={Xu, Xiuwen and Ma, Chunqing and Cheng, Yuanhang and Xie, Yue-Min and Yi, Xueping and Gautam, Bhoj and Chen, Shengmei and Li, Ho-Wa and Lee, Chun-Sing and So, Franky and et al.}, year={2017}, month={Aug}, pages={157–165} }
 @article{ho_cheung_li_chiu_cheng_yin_chan_so_tsang_so_et al._2017, title={Using Ultralow Dosages of Electron Acceptor to Reveal the Early Stage Donor-Acceptor Electronic Interactions in Bulk Heterojunction Blends}, volume={7}, ISSN={["1614-6840"]}, url={http://onlinelibrary.wiley.com/doi/10.1002/aenm.201602360/full}, DOI={10.1002/aenm.201602360}, abstractNote={Tuning the donor–acceptor (D–A) weight ratio is an essential step to optimize the performance of a bulk heterojunction (BHJ) solar cell. The unoptimized regime with a low acceptor concentration is generally unexplored despite it may reveal the early stage electronic D–A interactions. In this study, PTB7:PC71BM is used to examine factors that limit the device performance in unoptimized regime. The key limiting factor is the creation of traps and localized states originated from fullerene molecules. Photothermal deflection spectroscopy is used to quantify the trap density. Starting with pristine PTB7, addition of small concentration of fullerene increases the electron trap density and lowers the electron mobility. When the D–A weight ratio reaches 1:0.1, fullerene percolation occurs. There is an abrupt drop in trap density and simultaneously a six orders of magnitude increase in the electron mobility. Furthermore, the fill factors of the corresponding photovoltaic devices are found to anticorrelate with the trap density. This study reveals that electron trapping is the key limiting factor for unoptimized BHJ solar cells in low fullerene regime.}, number={12}, journal={ADVANCED ENERGY MATERIALS}, publisher={Wiley-Blackwell}, author={Ho, C. H. Y. and Cheung, S. H. and Li, H. W. and Chiu, K. L. and Cheng, Y. H. and Yin, H. and Chan, M. H. and So, Franky and Tsang, S. W. and So, S. K. and et al.}, year={2017}, month={Jun} }
 @article{klump_constantinou_lai_so_2017, title={Utilizing Forster resonance energy transfer to extend spectral response of PCDTBT:PCBM solar cells}, volume={42}, ISSN={["1878-5530"]}, DOI={10.1016/j.orgel.2016.12.010}, abstractNote={Light harvesting in the near-infrared part of the solar spectrum is important to achieve high efficiency polymer solar cells (PSCs). In this work, we demonstrate that we take an existing polymer:fullerene blend and extend its spectral response into the near-IR region by adding a small amount near-IR absorbing dye in the blend. The polymer studied in this work is Poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT). By adding only 2.5% squaraine dye to the blend, we were able to extend the spectral response of the resulting devices 100 nm into the near-IR spectral region. We show that the enhanced light harvesting is due to efficient Forster resonance energy transfer (FRET) between PCDTBT and the squaraine dye, resulting in an increase in power conversion efficiency. This type of ternary polymer solar cells is unique in that it allows the use of a small amount of selected dyes to extend light harvesting in infrared region.}, journal={ORGANIC ELECTRONICS}, author={Klump, Erik and Constantinou, Iordania and Lai, Tzung-Han and So, Franky}, year={2017}, month={Mar}, pages={87–92} }
 @article{gautam_younts_li_yan_danilov_klump_constantinou_so_you_ade_et al._2016, title={Charge photogeneration in organic photovoltaics: Role of hot versus cold charge-transfer excitons}, volume={6}, DOI={10.1002/aenm.201670002}, abstractNote={In article number 1501032, Kenan Gundogdu and co-workers present hot and cold exciton charge separation at the polymer/fullerene interface. On the left of the image high energy photons create excitons with excess energy. On the right of the image low energy photons create solely low energy charge transfer excitons. Both types separate into free charges effectively.}, number={1}, journal={Advanced Energy Materials}, author={Gautam, B. R. and Younts, R. and Li, W. T. and Yan, L. and Danilov, E. and Klump, E. and Constantinou, I. and So, Franky and You, W. and Ade, H. and et al.}, year={2016} }
 @article{peng_liu_fu_pan_chen_so_schanze_2016, title={Corrugated Organic Light Emitting Diodes Using Low T-g Electron Transporting Materials}, volume={8}, ISSN={["1944-8244"]}, DOI={10.1021/acsami.6b02669}, abstractNote={A corrugated organic light emitting diode (OLED) with enhanced light extraction is realized by incorporating a corrugated composite electron transport layer (ETL) consisting of two ETLs with different glass transition temperatures. The morphology of the corrugated structure is characterized with atomic force microscopy. The results show that the corrugation can be controlled by the layer thicknesses and annealing temperature. Compared with the control planar device, the corrugated OLED shows a more than 35% enhancement in current efficiency from 31 cd/A to 43 cd/A and a 20% enhancement in external quantum efficiency from 10% to 12% at 100 cd/m(2). In addition, the corrugated OLED also has a greatly improved operational stability. The LT90 lifetime of a device operated at 1000 cd/m(2) is improved greater than 100-fold in the corrugated OLED.}, number={25}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Peng, Cheng and Liu, Shuyi and Fu, Xiangyu and Pan, Zhenxing and Chen, Ying and So, Franky and Schanze, Kirk S.}, year={2016}, month={Jun}, pages={16192–16199} }
 @article{liu_peng_cruz_chen_so_2016, title={Degradation study of organic light-emitting diodes with solution-processed small molecule phosphorescent emitting layers}, volume={4}, ISSN={["2050-7534"]}, DOI={10.1039/c6tc02962k}, abstractNote={Charge injection and solvent impurities effects on degradation of solution-processed small molecule phosphorescent organic light-emitting diodes.}, number={37}, journal={JOURNAL OF MATERIALS CHEMISTRY C}, author={Liu, Shuyi and Peng, Cheng and Cruz, Alexandria and Chen, Ying and So, Franky}, year={2016}, month={Oct}, pages={8696–8703} }
 @article{xiang_fu_wei_liu_zhang_balema_nelson_so_2016, title={Efficiency Roll-Off in Blue Emitting Phosphorescent Organic Light Emitting Diodes with Carbazole Host Materials}, volume={26}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.201504357}, abstractNote={The efficiency roll‐off in blue phosphorescent organic light emitting diodes (OLEDs) using different carbazole compounds as the host is systematically studied. While there is no significant difference in device efficiency, OLEDs using ter‐carbazole as the host show a reduction in efficiency roll‐off at high luminance. Data from transient photoluminescence and electroluminescence measurements show that the lower triplet–triplet annihilation (TTA) and triplet–polaron quenching (TPQ) rates in devices with the ter‐carbazole host compared with other carbazole hosts are the reasons for this reduced efficiency roll‐off. It is also found that the host materials with low glass transition temperatures are more susceptible to the efficiency roll‐off problem.}, number={9}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Xiang, Chaoyu and Fu, Xiangyu and Wei, Wei and Liu, Rui and Zhang, Yong and Balema, Viktor and Nelson, Bryce and So, Franky}, year={2016}, month={Mar}, pages={1463–1469} }
 @article{lai_constantinou_grand_klump_baek_hsu_tsang_schanze_reynolds_so_et al._2016, title={Evidence of Molecular Structure Dependent Charge Transfer between Isoindigo-Based Polymers and Fullerene}, volume={28}, ISSN={["1520-5002"]}, DOI={10.1021/acs.chemmater.6b00824}, abstractNote={The effects of the oligothiophene length of two thiophene-isoindigo copolymers on film morphology, charge transfer, and photovoltaic device performance are reported. Despite the similarities in their repeat unit structures, the two polymers show distinctly different film morphologies and photovoltaic performance upon blending with PC71BM. We found that there is a significant increase in the dielectric constant of the photoactive film upon blending fullerene with the polymer that exhibits a higher power conversion efficiency. Blend photoluminescence transients revealed a fast dissociation route in the better performing polymer followed by a slower decay. The fast decay in transient PL is attributed to a higher charge transfer efficiency when blending with the fullerene. We suggest that the charge transfer efficiency is determined not only by the microscopic morphology but also whether the polymer can accommodate the fullerene molecules in close proximity to the acceptor moiety to facilitate electronic coup...}, number={7}, journal={CHEMISTRY OF MATERIALS}, author={Lai, T. H. and Constantinou, I. and Grand, C. M. and Klump, E. D. and Baek, S. and Hsu, H. Y. and Tsang, S. W. and Schanze, K. S. and Reynolds, J. R. and So, Franky and et al.}, year={2016}, month={Apr}, pages={2433–2440} }
 @article{shewmon_yu_constantinou_klump_so_2016, title={Formation of Perovskite Heterostructures by Ion Exchange}, volume={8}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.6b10034}, abstractNote={Thin-film optoelectronic devices based on polycrystalline organolead-halide perovskites have recently become a topic of intense research. Single crystals of these materials have been grown from solution with electrical properties superior to those of polycrystalline films. In order to enable the development of more complex device architectures based on organolead-halide perovskite single crystals, we developed a process to form epitaxial layers of methylammonium lead iodide (MAPbI3) on methylammonium lead bromide (MAPbBr3) single crystals. The formation of the MAPbI3 layer is found to be dominated by the diffusion of halide ions, leading to a shift in the photoluminescence and absorption spectra. X-ray diffraction measurements confirm the single-crystal nature of the MAPbI3 layer, while carrier transport measurements show that the converted layer retains the high carrier mobility typical of single-crystal perovskite materials. Such heterostructures on perovskite single crystals open possibilities for new types of devices.}, number={48}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Shewmon, Nathan T. and Yu, Hyeonggeun and Constantinou, Iordania and Klump, Erik and So, Franky}, year={2016}, month={Dec}, pages={33273–33279} }
 @article{yu_kim_lee_baek_lee_singh_so_2016, title={High-gain infrared-to-visible upconversion light-emitting phototransistors}, volume={10}, ISSN={["1749-4893"]}, DOI={10.1038/nphoton.2015.270}, number={2}, journal={NATURE PHOTONICS}, author={Yu, Hyeonggeun and Kim, Doyoung and Lee, Jinhyung and Baek, Sujin and Lee, Jaewoong and Singh, Rajiv and So, Franky}, year={2016}, month={Feb}, pages={129-+} }
 @article{lee_kim_baek_yu_so_2016, title={Inorganic UV-Visible-SWIR Broadband Photodetector Based on Monodisperse PbS Nanocrystals}, volume={12}, ISSN={["1613-6829"]}, DOI={10.1002/smll.201503244}, abstractNote={Solution-processed inorganic UV-visible short-wave-infrared photodetectors with light sensitivity from 350 nm to 2000 nm are fabricated using highly monodispersed large PbS NCs. These devices showed detectivity values over 1 × 10(11) Jones from 350 nm to 2000 nm, and a maximum detectivity value of 1.2 × 10(12) Jones at 1800 nm.}, number={10}, journal={SMALL}, author={Lee, Jae Woong and Kim, Do Young and Baek, Sujin and Yu, Hyeonggeun and So, Franky}, year={2016}, month={Mar}, pages={1328–1333} }
 @article{ho_chen_liu_peng_zhao_so_2016, title={Interface Effect on Efficiency Loss in Organic Light Emitting Diodes with Solution Processed Emitting Layers}, volume={3}, ISSN={["2196-7350"]}, DOI={10.1002/admi.201600320}, abstractNote={The performance of multilayered OLEDs with a solution processed emitting layer (EML) is compared to that of counterparts with an evaporated EML and it is found that the interfacial energy changes at the EML and electron transport layer (ETL) interface is a key factor determining the device efficiency. From the results of exciplex photoluminescence emission at the EML/ETL interface and energetic disorder measurements, it is revealed that there is an energy shift in the solution processed EML along with a band tail broadening compared with the device with an evaporated EML, resulting in inefficient hole blocking at the EML/ETL interface and a decrease in device efficiency. Using an ETL with a deep highest occupied molecular orbital (HOMO) level can ameliorate this problem, resulting in a solution processed OLED with a high external quantum efficiency of 29%.}, number={19}, journal={ADVANCED MATERIALS INTERFACES}, author={Ho, Szuheng and Chen, Ying and Liu, Shuyi and Peng, Cheng and Zhao, Dewei and So, Franky}, year={2016}, month={Oct} }
 @article{liu_ho_so_2016, title={Novel Patterning Method for Silver Nanowire Electrodes for Thermal-Evaporated Organic Light Emitting Diodes}, volume={8}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/ACSAMI.6B00719}, DOI={10.1021/ACSAMI.6B00719}, abstractNote={UNLABELLED
Silver nanowires (AgNWs) mesh has been used as transparent electrodes in optoelectronic devices. However, the lack of practical patterning techniques for the random percolating nanowire network has limited its applications in devices where a well-defined pixel is required. Here, by controlling the surface wetting properties of a polydimethylsiloxane (PDMS) release template, we are able to pattern the random AgNWs network with uniform conducting property; and due to the hydrophobic recovery nature of PDMS, a multilayer patterning and transferring process can be realized, resulting in a fine-patterned, smooth, and uniform AgNWs mesh/poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (


PEDOT
PSS) composite electrode. A thermal-evaporated organic light-emitting diode (OLED) is directly fabricated onto the patterned AgNWs/


PEDOT
PSS composite electrode. The device shows well-defined pixel edges and a uniformly lighted pixel area. A uniform OLED with very low leakage current is realized. The enhanced efficiency compared to the controlled device with prepatterned indium tin oxide (ITO) electrode is attributed to the scattering effects of the AgNWs electrode.}, number={14}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Liu, Shuyi and Ho, Szuheng and So, Franky}, year={2016}, month={Mar}, pages={9268–9274} }
 @article{luo_liu_barange_wang_so_2016, title={Perovskite Solar Cells on Corrugated Substrates with Enhanced Efficiency}, volume={12}, ISSN={1613-6810}, url={http://dx.doi.org/10.1002/SMLL.201601974}, DOI={10.1002/SMLL.201601974}, abstractNote={Organometallic halide perovskites solar cells are fabricated on nano‐scaled corrugated substrates using a sequential deposition method. The corrugated substrates are fabricated using colloidal lithography followed by reactive ion etching. The corrugated structure is found to accelerate the chemical reaction between the sequentially deposited lead iodide (PbI2) and methyl ammonium iodide layers to form stoichiometric perovskite films, and the corrugated morphology is preserved at the interface of the hole transport layer (HTL) and the perovskite layer. The shunt resistance of the corrugated devices is found to be higher than that of the planar devices, leading to a higher open circuit voltage (VOC) and fill factor (FF) in the corrugated devices. Finite‐difference time‐domain simulation is carried out on both planar and corrugated devices. The results revealed that light absorption is enhanced in the corrugated devices due to the corrugated HTL/perovskite interface, resulting in a significantly higher short circuit current (JSC) observed in the corrugated devices. As a result, the average power conversion efficiency increases from 8.7% for the planar devices to 13% for the corrugated devices.}, number={46}, journal={Small}, publisher={Wiley}, author={Luo, Yu and Liu, Shuyi and Barange, Nilesh and Wang, Li and So, Franky}, year={2016}, month={Sep}, pages={6346–6352} }
 @article{luo_liu_barange_wang_so_2016, title={Perovskite solar cells on corrugated substrates with enhanced efficiency}, volume={12}, DOI={10.1002/smll.201670241}, abstractNote={On page 6346, F. So and co-workers fabricate organometallic halide perovskite solar cells on nanoscaled corrugated substrates using colloidal lithography followed by reactive ion etching. The results reveal that light absorption is enhanced, demonstrated by an increase in average power conversion efficiency from 8.7% for the planar devices to 13% for the corrugated devices.}, number={46}, journal={Small (Weinheim An Der Bergstrasse, Germany)}, author={Luo, Y. and Liu, S. Y. and Barange, N. and Wang, L. and So, Franky}, year={2016}, pages={6346–6352} }
 @article{constantinou_shewmon_lo_deininger_reynolds_so_2016, title={Photodegradation of Metal Oxide Interlayers in Polymer Solar Cells}, volume={3}, ISSN={["2196-7350"]}, DOI={10.1002/admi.201600741}, abstractNote={The effect of 1 sun illumination for 24 h on encapsulated inverted organic photovoltaic devices is studied through a series of electrical and optical characterizations for donor/acceptor polymer solar cells based on poly(dithienogermole‐alt‐thienopyrrolodione)/[6,6]‐phenyl C71 butyric acid methyl ester blends. Power conversion efficiency is significantly reduced after light exposure due to a 45% drop in the device fill factor and a 40% drop in both the open circuit voltage and short circuit current. The decrease in open circuit voltage is attributed to a reduction in the built‐in field in the device due to photodegradation of the ZnO interlayer. The reduction in fill factor and short circuit current is shown to be due to the formation of an extraction barrier for hole collection as a result of photodegradation of the MoOx interlayer. Using a 400 nm long pass filter to block the UV light, device stability is significantly enhanced, resulting in a decrease in power conversion efficiency of less than 5% under the same operation conditions.}, number={23}, journal={ADVANCED MATERIALS INTERFACES}, author={Constantinou, Iordania and Shewmon, Nathan T. and Lo, Chi Kin and Deininger, James J. and Reynolds, John R. and So, Franky}, year={2016}, month={Dec} }
 @article{lee_kim_baek_yu_so_2016, title={Photodetectors: Inorganic UV-Visible-SWIR Broadband Photodetector Based on Monodisperse PbS Nanocrystals (Small 10/2016)}, volume={12}, ISSN={1613-6810}, url={http://dx.doi.org/10.1002/SMLL.201670050}, DOI={10.1002/SMLL.201670050}, abstractNote={Synthesis of highly mono-dispersed large PbS nanocrystals (NCs) with low particle size dispersion is demonstrated by F. So and co-workers on page 1328, by controlling the sulfur concentration below the nucleation threshold during multiple injections of the sulfur precursor. These NCs are used to fabricate multi-spectral photodetectors and high detectivity values in the UV-Visible-SWIR (short-wave-IR) wavelength range from 350 nm to 2000 nm are demonstrated.}, number={10}, journal={Small}, publisher={Wiley}, author={Lee, Jae Woong and Kim, Do Young and Baek, Sujin and Yu, Hyeonggeun and So, Franky}, year={2016}, month={Mar}, pages={1246–1246} }
 @article{yu_liu_baek_kim_dong_so_2016, title={Solution-processed copper oxide interlayers for broadband PbS quantum-dot photodiodes}, volume={4}, ISSN={["2050-7534"]}, DOI={10.1039/c6tc03531k}, abstractNote={Metal oxide interlayers are promising for optoelectronic applications due to solution processability, optical transparency, and excellent charge blocking properties.}, number={47}, journal={JOURNAL OF MATERIALS CHEMISTRY C}, author={Yu, Hyeonggeun and Liu, Shyui and Baek, Sujin and Kim, Do Young and Dong, Chen and So, Franky}, year={2016}, month={Dec}, pages={11205–11211} }
 @article{grand_baek_lai_deb_zajaczkowski_stalder_muellen_pisula_bucknal_so_et al._2016, title={Structure-Property Relationships Directing Transport and Charge Separation in Isoindigo Polymers}, volume={49}, ISSN={["1520-5835"]}, DOI={10.1021/acs.macromol.6b00540}, abstractNote={Since being introduced to the open literature in 2010, the isoindigo heterocycle has been extensively studied as a novel electron-deficient building block for organic electronic materials in conjugated polymers, discrete length oligomers, and molecular systems, particularly targeting high charge mobility values and ambipolar transport in organic field effect transistors, along with high power conversion efficiencies in organic photovoltaic devices. This article introduces results obtained on copolymers of isoindigo with thiophene and alkylated terthiophenes to highlight fundamental characteristics in isoindigo-based polymers and the resulting organic field-effect transistors and photovoltaic devices. By comparing and contrasting the optoelectronic properties, thin film morphology, organic field-effect transistor (OFET) mobilities, and organic photovoltaic (OPV) performance to previously reported polymers, structure–processing–property relationships were uncovered. In particular, isoindigo-containing polym...}, number={11}, journal={MACROMOLECULES}, author={Grand, Caroline and Baek, Sujin and Lai, Tzung-Han and Deb, Nabankur and Zajaczkowski, Wojciech and Stalder, Romain and Muellen, Klaus and Pisula, Wojciech and Bucknal, David G. and So, Franky and et al.}, year={2016}, month={Jun}, pages={4008–4022} }
 @article{yu_dong_guo_kim_so_2016, title={Vertical Organic Field-Effect Transistors for Integrated Optoelectronic Applications}, volume={8}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.6b00182}, abstractNote={Direct integration of a vertical organic field-effect transistor (VOFET) and an optoelectronic device offers a single stacked, low power optoelectronic VOFET with high aperture ratios. However, a functional optoelectronic VOFET could not be realized because of the difficulty in fabricating transparent source and gate electrodes. Here, we report a VOFET with an on/off ratio up to 10(5) as well as output current saturation by fabricating a transparent gate capacitor consisting of a perforated indium tin oxide (ITO) source electrode, HfO2 gate dielectric, and ITO gate electrode. Effects of the pore size and the pore depth within the porous ITO electrodes on the on/off characteristic of a VOFET are systematically explained in this work. By combining a phosphorescent organic light-emitting diode with an optimized VOFET structure, a vertical organic light-emitting transistor with a luminance on/off ratio of 10(4) can be fabricated.}, number={16}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Yu, Hyeonggeun and Dong, Zhipeng and Guo, Jing and Kim, Doyoung and So, Franky}, year={2016}, month={Apr}, pages={10430–10435} }
 @article{volz_chen_wallesch_liu_fléchon_zink_friedrichs_flügge_steininger_göttlicher_et al._2015, title={Bridging the Efficiency Gap: Fully Bridged Dinuclear Cu(I)-Complexes for Singlet Harvesting in High-Efficiency OLEDs}, volume={27}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/ADMA.201405897}, DOI={10.1002/ADMA.201405897}, abstractNote={The substitution of rare metals such as iridium and platinum in light-emitting materials is a key step to enable low-cost mass-production of organic light-emitting diodes (OLEDs). Here, it is demonstrated that using a solution-processed, fully bridged dinuclear Cu(I)-complex can yield very high efficiencies. An optimized device gives a maximum external quantum efficiency of 23 ± 1% (73 ± 2 cd A(-1) ).}, number={15}, journal={Advanced Materials}, publisher={Wiley}, author={Volz, Daniel and Chen, Ying and Wallesch, Manuela and Liu, Rui and Fléchon, Charlotte and Zink, Daniel M. and Friedrichs, Jana and Flügge, Harald and Steininger, Ralph and Göttlicher, Jörg and et al.}, year={2015}, month={Mar}, pages={2538–2543} }
 @article{gautam_younts_li_yan_danilov_klump_constantinou_so_you_ade_et al._2015, title={Charge Photogeneration in Organic Photovoltaics: Role of Hot versus Cold Charge-Transfer Excitons}, volume={6}, ISSN={1614-6832}, url={http://dx.doi.org/10.1002/AENM.201501032}, DOI={10.1002/AENM.201501032}, abstractNote={The role of excess excitation energy on long‐range charge separation in organic donor/acceptor bulk heterojunctions (BHJs) continues to be unclear. While ultrafast spectroscopy results argue for efficient charge separation through high‐energy charge‐transfer (CT) states within the first picosecond (ps) of excitation, charge collection measurements suggest excess photon energy does not increase the current density in BHJ devices. Here, the population dynamics of charge‐separated polarons upon excitation of high‐energy polymer states and low‐energy interfacial CT states in two polymer/fullerene blends from ps to nanosecond time scales are studied. It is observed that the charge‐separation dynamics do not show significant dependence on excitation energy. These results confirm that excess exciton energy is not necessary for the effective generation of charges.}, number={1}, journal={Advanced Energy Materials}, publisher={Wiley}, author={Gautam, Bhoj R. and Younts, Robert and Li, Wentao and Yan, Liang and Danilov, Evgeny and Klump, Erik and Constantinou, Iordania and So, Franky and You, Wei and Ade, Harald and et al.}, year={2015}, month={Oct}, pages={1301032} }
 @article{youn_lee_xu_singh_so_2015, title={Corrugated Sapphire Substrates for Organic Light-Emitting Diode Light Extraction}, volume={7}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/ACSAMI.5B01533}, DOI={10.1021/ACSAMI.5B01533}, abstractNote={In an organic light-emitting diode (OLED), only about 20-30% of the generated light can be extracted because of the light lost to the thin film guided modes and surface plasmon. Using corrugated high-index-refractive substrates, the thin film guided modes can be effectively out-coupled from the device because of the high index substrate and the loss to the surface plamon is suppressed due to the corrugated structure. With an additional macro lens attached to the substrate to extract the substrate mode, we finally demonstrated a green phosphorescent OLED with an extremely high external quantum efficiency of 63%.}, number={17}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Youn, Wooram and Lee, Jinhyung and Xu, Minfei and Singh, Rajiv and So, Franky}, year={2015}, month={Apr}, pages={8974–8978} }
 @article{constantinou_lai_klump_goswami_schanze_so_2015, title={Effect of Polymer Side Chains on Charge Generation and Disorder in PBDTTPD Solar Cells}, volume={7}, ISSN={["1944-8244"]}, DOI={10.1021/acsami.5b09497}, abstractNote={The effect of polymer side chains on device performance was investigated for PBDT(EtHex)-TPD(Oct):PC70BM and PBDT(EtHex)-TPD(EtHex):PC70BM BHJ solar cells. Going from a linear side chain on the polymer's acceptor moiety to a branched side chain was determined to have a negative impact on the overall device efficiency, because of significantly reduced short-circuit current (J(sc)) and fill factor (FF) values. Sub-bandgap external quantum efficiency (EQE) and transient photoluminescence (PL) measurements showed more-efficient carrier generation for the polymer with linear side chains, because of a higher degree of charge-transfer (CT) state delocalization, leading to more-efficient exciton dissociation. Furthermore, the increase in π-π stacking distance and disorder for the bulkier ethylhexyl side chain were shown to result in a lower hole mobility, a higher bimolecular recombination, and a higher energetic disorder. The use of linear side chains on the polymer's acceptor moiety was shown to promote photogeneration, because of more-effective CT states and favorable carrier transport resulting in improved solar cell performance.}, number={48}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Constantinou, Iordania and Lai, Tzung-Han and Klump, Erik D. and Goswami, Subhadip and Schanze, Kirk S. and So, Franky}, year={2015}, month={Dec}, pages={26999–27005} }
 @article{constantinou_lai_hsu_cheung_klump_schanze_so_so_2015, title={Effect of Thermal Annealing on Charge Transfer States and Charge Trapping in PCDTBT:PC70BM Solar Cells}, volume={1}, ISSN={2199-160X}, url={http://dx.doi.org/10.1002/AELM.201500167}, DOI={10.1002/AELM.201500167}, abstractNote={I. Constantinou, Dr. T.-H. Lai, E. D. Klump, Prof. F. So Department of Materials Science and Engineering University of Florida Gainesville , FL 32611 , USA E-mail: fso@mse.ufl .edu Dr. H.-Y. Hsu, Prof. K. S. Schanze Department of Chemistry University of Florida Gainesville , FL 32611 , USA S.-H. Cheung, Prof. S. K. So Department of Physics and Institute of Advanced Materials Hong Kong Baptist University Kowloon Tong, Hong Kong , P. R. China}, number={9}, journal={Advanced Electronic Materials}, publisher={Wiley}, author={Constantinou, Iordania and Lai, Tzung-Han and Hsu, Hsien-Yi and Cheung, Sin-Hang and Klump, Erik D. and Schanze, Kirk S. and So, Shu-Kong and So, Franky}, year={2015}, month={Jul}, pages={1500167} }
 @article{constantinou_lai_zhao_klump_deininger_lo_reynolds_so_2015, title={High Efficiency Air-Processed Dithienogermole-Based Polymer Solar Cells}, volume={7}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/AM5087566}, DOI={10.1021/AM5087566}, abstractNote={The effect of air processing, with air exposure varying from minutes to hours prior to encapsulation, on photovoltaic device performance has been studied through a series of electrical characterizations and optical simulations for a donor/acceptor polymer-based organic solar cell based on poly(dithienogermole-alt-thienopyrrolodione) p(DTG-TPD)/PC71BM blends. A ∼10% degradation in power conversion efficiency was observed due to air processing with 10 min exposure time, with AM1.5 power conversion efficiencies (PCEs) decreasing from 8.5 ± 0.25% for devices processed in inert nitrogen atmosphere to 7.7 ± 0.18% for devices processed in ambient air. After 3 h air exposure, the PCE leveled off at 7.04 ± 0.1%. This decrease is attributed partially to interface issues caused by exposure of the electrode materials to oxygen and water and partially to a degradation of the hole transport in the active layer.}, number={8}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Constantinou, Iordania and Lai, Tzung-Han and Zhao, Dewei and Klump, Erik D. and Deininger, James J. and Lo, Chi Kin and Reynolds, John R. and So, Franky}, year={2015}, month={Feb}, pages={4826–4832} }
 @article{xiang_peng_chen_so_2015, title={Origin of Sub-Bandgap Electroluminescence in Organic Light-Emitting Diodes}, volume={11}, ISSN={["1613-6829"]}, DOI={10.1002/smll.201501355}, abstractNote={Sub‐bandgap electroluminescence in organic light emitting diodes is a phenomenon in which the electroluminescence turn‐on voltage is lower than the bandgap voltage of the emitter. Based on the results of transient electroluminescence (EL) and photoluminescence and electroabsorption spectroscopy measurements, it is concluded that in rubrene/C60 devices, charge transfer excitons are generated at the rubrene/C60 interface under sub‐bandgap driving conditions, leading to the formation of triplet excitons, and sub‐bandgap EL is the result of the subsequent triplet–triplet annihilation process.}, number={40}, journal={SMALL}, author={Xiang, Chaoyu and Peng, Cheng and Chen, Ying and So, Franky}, year={2015}, month={Oct}, pages={5439–5443} }
 @article{liu_ho_chen_so_2015, title={Passivation of Metal Oxide Surfaces for High-Performance Organic and Hybrid Optoelectronic Devices}, volume={27}, ISSN={0897-4756 1520-5002}, url={http://dx.doi.org/10.1021/ACS.CHEMMATER.5B00129}, DOI={10.1021/ACS.CHEMMATER.5B00129}, abstractNote={The exciton quenching properties of solution-processed nickel oxide (NiOx) and vanadium oxide (VOx) are studied by measuring the photoluminescence (PL) of a thin emitting layer (EML) deposited on top of the metal oxides. Strong exciton quenching is evidenced at the metal oxide/EML interface, which is proved to be detrimental to the performance of optoelectronic devices. With a thin polyvinylpyrrolidone (PVP) passivation polymer adsorbed on top of metal oxides, the PL quenching is found to be effectively suppressed. A short UV–O3 treatment on top of the PVP-passivated metal oxides turns out to be a key procedure to trigger the chemical binding between the PVP passivation polymer and the metal oxide surface species, which turns out to be necessary for efficient hole injection and extraction for organic light emitting diodes (OLEDs) and solar cell devices, respectively. With the PVP passivation layer followed by UV–O3 treatment, the OLEDs incorporating NiOx as a hole transport layer (HTL) shows a record curr...}, number={7}, journal={Chemistry of Materials}, publisher={American Chemical Society (ACS)}, author={Liu, Shuyi and Ho, Szuheng and Chen, Ying and So, Franky}, year={2015}, month={Mar}, pages={2532–2539} }
 @article{tansu_so_2015, title={Solid-state lighting: photonics and technologies}, volume={5}, journal={Journal of Photonics for Energy}, author={Tansu, N. and So, F.}, year={2015} }
 @misc{kafafi_martin-palma_nogueira_deirdre m. o'carroll_pietron_samuel_so_tansu_tsakalakos_2015, title={The role of photonics in energy}, volume={5}, ISSN={["1947-7988"]}, DOI={10.1117/1.jpe.5.050997}, abstractNote={Abstract. In celebration of the 2015 International Year of Light, we highlight major breakthroughs in photonics for energy conversion and conservation. The section on energy conversion discusses the role of light in solar light harvesting for electrical and thermal power generation; chemical energy conversion and fuel generation; as well as photonic sensors for energy applications. The section on energy conservation focuses on solid-state lighting, flat-panel displays, and optical communications and interconnects.}, journal={JOURNAL OF PHOTONICS FOR ENERGY}, author={Kafafi, Zakya H. and Martin-Palma, Raul J. and Nogueira, Ana F. and Deirdre M. O'Carroll and Pietron, Jeremy J. and Samuel, Ifor D. W. and So, Franky and Tansu, Nelson and Tsakalakos, Loucas}, year={2015}, month={Oct} }
 @article{lee_kim_so_2015, title={Unraveling the Gain Mechanism in High Performance Solution-Processed PbS Infrared PIN Photodiodes}, volume={25}, ISSN={1616-301X}, url={http://dx.doi.org/10.1002/ADFM.201403673}, DOI={10.1002/ADFM.201403673}, abstractNote={High gain and low dark current solution‐processed colloidal PbS quantum dots infrared (IR) PIN photodetectors with IR sensitivity up to 1500 nm are demonstrated. The low dark current is due to the P‐I‐N structure with both electron and hole blockers. The high gain in our IR photodiodes is due to the enhancement of electron tunneling injection through the 1,1‐bis[(di‐4‐tolylamino) phenyl]cyclohexane (TAPC) electron blocker under IR illumination resulting from a distorted electron blocking barrier in the presence of photo‐generated holes trapped in the TAPC electron blocker. It is further found that the trap states in the TAPC layer are generated by the Ag atoms penetrated in the TAPC layer during the thermal evaporation process. The resulting photodetectors have a high detectivity value of 7 × 1013 Jones, which is even higher than that of a commercial InGaAs photodiode.}, number={8}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Lee, Jae Woong and Kim, Do Young and So, Franky}, year={2015}, month={Jan}, pages={1233–1238} }
 @article{youn_lee_xu_xiang_singh_so_2014, title={5.3: Highly Efficient Phosphorescent OLEDs Fabricated on Corrugated High-Index-Refractive Substrates}, volume={45}, ISSN={0097-966X}, url={http://dx.doi.org/10.1002/J.2168-0159.2014.TB00011.X}, DOI={10.1002/J.2168-0159.2014.TB00011.X}, abstractNote={Abstract}, number={1}, journal={SID Symposium Digest of Technical Papers}, publisher={Wiley}, author={Youn, Wooram and Lee, Jinhyung and Xu, Minfei and Xiang, Chaoyu and Singh, Rajiv and So, Franky}, year={2014}, month={Jun}, pages={40–41} }
 @article{kim_ryu_manders_lee_so_2014, title={Air-Stable, Solution-Processed Oxide p–n Heterojunction Ultraviolet Photodetector}, volume={6}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/AM4050019}, DOI={10.1021/AM4050019}, abstractNote={Air-stable solution processed all-inorganic p-n heterojunction ultraviolet photodetector is fabricated with a high gain (EQE, 25 300%). Solution-processed NiO and ZnO films are used as p-type and n-type ultraviolet sensitizing materials, respectively. The high gain in the detector is due to the interfacial trap-induced charge injection that occurs at the ITO/NiO interface by photogenerated holes trapped in the NiO film. The gain of the detector is controlled by the post-annealing temperature of the solution-processed NiO films, which are studied by X-ray photoelectron spectroscopy (XPS).}, number={3}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Kim, Do Young and Ryu, Jiho and Manders, Jesse and Lee, Jaewoong and So, Franky}, year={2014}, month={Jan}, pages={1370–1374} }
 @article{kim_yu_liu_kim_so_2014, title={All Solution-Processed Inorganic/Organic Hybrid Permeable Metal-Base Transistor}, volume={10}, ISSN={1613-6810}, url={http://dx.doi.org/10.1002/SMLL.201303959}, DOI={10.1002/SMLL.201303959}, abstractNote={All solution-processed inorganic/organic hybrid permeable-base transistor (PMBT) based on nickel oxide emitter and P3HT collector is developed. Due to the high charge injection properties of nickel oxide and spontaneously formed nano-pinholes in the base electrode, the devices exhibit high common-base and common-emitter current gains up to 0.98 and 304, respectively with saturated output current.}, number={18}, journal={Small}, publisher={Wiley}, author={Kim, Jong H. and Yu, Hyeonggeun and Liu, Rui and Kim, Do Young and So, Franky}, year={2014}, month={May}, pages={3650–3654} }
 @article{lee_li_constantinou_so_tsang_so_2014, title={Batch-to-Batch Variation of Polymeric Photovoltaic Materials: its Origin and Impacts on Charge Carrier Transport and Device Performances}, volume={4}, ISSN={1614-6832}, url={http://dx.doi.org/10.1002/AENM.201400768}, DOI={10.1002/AENM.201400768}, abstractNote={A detailed investigation of the impact of molecular weight distribution of a photoactive polymer, poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT), on photovoltaic device performance and carrier transport properties is reported. It is found that different batches of as‐received polymers have substantial differences in their molecular weight distribution. As revealed by gel permeation chromatography (GPC), two peaks can generally be observed. One of the peaks corresponds to a high molecular weight component and the other peak corresponds to a low molecular weight component. Photovoltaic devices fabricated with a higher proportion of low molecular weight component have power conversion efficiencies (PCEs) reduced from 5.7% to 2.5%. The corresponding charge carrier mobility at the short‐circuit region is also significantly reduced from 2.7 × 10−5 to 1.6 × 10−8 cm2 V−1 s−1. The carrier transport properties of the polymers at various temperatures are further analyzed by the Gaussian disorder model (GDM). All polymers have similar energetic disorders. However, they appear to have significant differences in carrier hopping distances. This result provides insight into the origin of the molecular weight effect on carrier transport in polymeric semiconducting materials.}, number={16}, journal={Advanced Energy Materials}, publisher={Wiley}, author={Lee, Harrison Ka Hin and Li, Zhao and Constantinou, Iordania and So, Franky and Tsang, Sai Wing and So, Shu Kong}, year={2014}, month={Jul}, pages={1400768} }
 @article{chen_tsang_lai_reynolds_so_2014, title={Dielectric Effect on the Photovoltage Loss in Organic Photovoltaic Cells}, volume={26}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/ADMA.201401987}, DOI={10.1002/ADMA.201401987}, abstractNote={The VOC loss in several polymer-fullerene solar cells is determined. Based on these data, a major source of photovoltage loss is attributed to the low dielectric constants of the polymers. Such loss is close to zero if the dielectric constant of the polymer-fullerene blend is close to 5.}, number={35}, journal={Advanced Materials}, publisher={Wiley}, author={Chen, Song and Tsang, Sai-Wing and Lai, Tzung-Han and Reynolds, John R. and So, Franky}, year={2014}, month={Jul}, pages={6125–6131} }
 @article{yu_kim_chen_kim_guo_so_2014, title={Effect of Nano-Porosity on High Gain Permeable Metal-Base Transistors}, volume={24}, ISSN={1616-301X}, url={http://dx.doi.org/10.1002/ADFM.201400634}, DOI={10.1002/ADFM.201400634}, abstractNote={As one type of vertical thin‐film transistors, permeable metal‐base transistors (PMBTs) with a permeable metal film embedded between two semiconductor layers have been proposed for high gain current amplifier. In principle, compared with conventional bipolar transistors, PMBTs should have a higher speed and are easier to fabricate compatible with flexible and printed electronics. However, functional PMBTs are not realized due to low current gains (<50) and lack of output current saturation. In this paper, making use of the nano‐textured surface of an organic semiconductor, we are able to fabricate devices with permeable metal base films having a pore size of about 20 nm and achieve current gains up to 476 with output current saturation. Correlations between the nano‐scale porosity and the charge transmission/amplification behaviors in the device are explained with characterization of the metal base porosity. From our device simulation results, the small pore size is essential to achieve current saturation in the device due to the potential‐pinning effect in the small pore regions. Finally, using a similar strategy, we also demonstrate a high gain (=260) solution‐processed metal oxide‐based PMBTs with output current saturation.}, number={38}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Yu, Hyeonggeun and Kim, Jong H. and Chen, Wenchao and Kim, Doyoung and Guo, Jing and So, Franky}, year={2014}, month={Jul}, pages={6056–6065} }
 @article{zhao_sexton_park_baure_nino_so_2014, title={High-Efficiency Solution-Processed Planar Perovskite Solar Cells with a Polymer Hole Transport Layer}, volume={5}, ISSN={1614-6832}, url={http://dx.doi.org/10.1002/AENM.201401855}, DOI={10.1002/AENM.201401855}, abstractNote={DOI: 10.1002/aenm.201401855 In this work we demonstrate a high-effi ciency solutionprocessed inverted CH 3 NH 3 PbI 3 perovskite solar cell, which is free of PEDOT:PSS and high-temperature processed metal oxides ( Figure 1 a). We use poly[ N , N ′-bis(4-butylphenyl)N , N ′bis(phenyl)benzidine] (poly-TPD) as the HTL and electron blocking layer for the perovskite cells. In previous reports, polyTPD was used as an HTL in vacuum deposited perovskite solar cells. [ 14 ] Here, the perovskite fi lm was formed by sequential deposition of lead iodide (PbI 2 ) and methyl ammonium iodide (CH 3 NH 3 I). We found that the resulting fi lm consisted of large crystallites with a complete coverage on the poly-TPD surface, and the average effi ciency of the fi nal devices reach a value of 13.8% and a maximum value as high as 15.3%. To deposit the perovskite fi lm on the poly-TPD surface, a concentrated solution of PbI 2 was fi rst spin-coated and then heated to partially evaporate the solvent and crystallize PbI 2 . Subsequently, a dilute solution of CH 3 NH 3 I is spin-coated on top of the PbI 2 layer and CH 3 NH 3 PbI 3 is formed by interdiffusion of the precursors. As shown in Figure 1 b, a composite layer of spin-coated [6,6]-phenyl-C 61 -butyric acid methyl ester (PC 60 BM), and thermally evaporated C 60 and 2,9-dimethyl4,7-diphenyl-1,10-phenanthroline (BCP) is deposited on top of the CH 3 NH 3 PbI 3 layer to planarize the surface of the perovskite layer, and to facilitate electron extraction and hole blocking. [ 17 ]}, number={6}, journal={Advanced Energy Materials}, publisher={Wiley}, author={Zhao, Dewei and Sexton, Michael and Park, Hye-Yun and Baure, George and Nino, Juan C. and So, Franky}, year={2014}, month={Dec}, pages={1401855} }
 @article{zhao_sexton_park_baure_nino_so_2014, title={High-Efficiency Solution-Processed Planar Perovskite Solar Cells with a Polymer Hole Transport Layer}, volume={5}, ISSN={1614-6832}, url={http://dx.doi.org/10.1002/aenm.201401855}, DOI={10.1002/AENM.201500436}, abstractNote={Adv. Energy Mater. 2015, 5, 1401855 Shuyi Liu was inadvertently omitted as an author of this article. The byline should read: Dewei Zhao, Michael Sexton, Hye-Yun Park, Shuyi Liu, George Baure, Juan C. Nino, and Franky So* The affiliation for Shuyi Liu is Department of Materials Science and Engineering, University of Florida, 100 Rhines Hall, Gainesville, FL 32611, USA.}, number={6}, journal={Advanced Energy Materials}, publisher={Wiley}, author={Zhao, Dewei and Sexton, Michael and Park, Hye-Yun and Baure, George and Nino, Juan C. and So, Franky}, year={2014}, month={Dec}, pages={1401855} }
 @article{chen_so_guo_2014, title={Intrinsic delay of permeable base transistor}, volume={116}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4891231}, DOI={10.1063/1.4891231}, abstractNote={Permeable base transistors (PBTs) fabricated by vacuum deposition or solution process have the advantages of easy fabrication and low power operation and are a promising device structure for flexible electronics. Intrinsic delay of PBT, which characterizes the speed of the transistor, is investigated by solving the three-dimensional Poisson equation and drift-diffusion equation self-consistently using finite element method. Decreasing the emitter thickness lowers the intrinsic delay by improving on-current, and a thinner base is also preferred for low intrinsic delay because of fewer carriers in the base region at off-state. The intrinsic delay exponentially decreases as the emitter contact Schottky barrier height decreases, and it linearly depends on the carrier mobility. With an optimized emitter contact barrier height and device geometry, a sub-nano-second intrinsic delay can be achieved with a carrier mobility of ∼10 cm2/V/s obtainable in solution processed indium gallium zinc oxide, which indicates the potential of solution processed PBTs for GHz operations.}, number={4}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Chen, Wenchao and So, Franky and Guo, Jing}, year={2014}, month={Jul}, pages={044505} }
 @article{manders_lai_an_xu_lee_kim_bosman_so_2014, title={Low-Noise Multispectral Photodetectors Made from All Solution-Processed Inorganic Semiconductors}, volume={9}, ISSN={1616-301X}, url={http://dx.doi.org/10.1002/ADFM.201402094}, DOI={10.1002/ADFM.201402094}, abstractNote={Infrared, visible, and multispectral photodetectors are important components for sensing, security and electronics applications. Current fabrication of these devices is based on inorganic materials grown by epitaxial techniques which are not compatible with low‐cost large‐scale processing. Here, air‐stable multispectral solution‐processed inorganic double heterostructure photodetectors, using PbS quantum dots (QDs) as the photoactive layer, colloidal ZnO nanoparticles as the electron transport/hole blocking layer (ETL/HBL), and solution‐derived NiO as the hole transport/electron blocking layer (HTL/EBL) are reported. The resulting device has low dark current density of 20 nA cm‐2 with a noise equivalent power (NEP) on the order of tens of picowatts across the detection spectra and a specific detectivity (D*) value of 1.2 × 1012 cm Hz1/2 W‐1. These parameters are comparable to commercially available Si, Ge, and InGaAs photodetectors. The devices have a linear dynamic range (LDR) over 65 dB and a bandwidth over 35 kHz, which are sufficient for imaging applications. Finally, these solution‐processed inorganic devices have a long storage lifetime in air, even without encapsulation.}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Manders, Jesse R. and Lai, Tzung-Han and An, Yanbin and Xu, Weikai and Lee, Jaewoong and Kim, Do Young and Bosman, Gijs and So, Franky}, year={2014}, month={Sep}, pages={n/a-n/a} }
 @article{kim_lai_lee_manders_so_2014, title={Multi-spectral imaging with infrared sensitive organic light emitting diode}, volume={4}, ISSN={2045-2322}, url={http://dx.doi.org/10.1038/SREP05946}, DOI={10.1038/SREP05946}, abstractNote={Commercially available near-infrared (IR) imagers are fabricated by integrating expensive epitaxial grown III-V compound semiconductor sensors with Si-based readout integrated circuits (ROIC) by indium bump bonding which significantly increases the fabrication costs of these image sensors. Furthermore, these typical III-V compound semiconductors are not sensitive to the visible region and thus cannot be used for multi-spectral (visible to near-IR) sensing. Here, a low cost infrared (IR) imaging camera is demonstrated with a commercially available digital single-lens reflex (DSLR) camera and an IR sensitive organic light emitting diode (IR-OLED). With an IR-OLED, IR images at a wavelength of 1.2 µm are directly converted to visible images which are then recorded in a Si-CMOS DSLR camera. This multi-spectral imaging system is capable of capturing images at wavelengths in the near-infrared as well as visible regions.}, number={1}, journal={Scientific Reports}, publisher={Springer Science and Business Media LLC}, author={Kim, Do Young and Lai, Tzung-Han and Lee, Jae Woong and Manders, Jesse R. and So, Franky}, year={2014}, month={Aug} }
 @article{liu_liu_chen_ho_kim_so_2014, title={Nickel Oxide Hole Injection/Transport Layers for Efficient Solution-Processed Organic Light-Emitting Diodes}, volume={26}, ISSN={0897-4756 1520-5002}, url={http://dx.doi.org/10.1021/CM501898Y}, DOI={10.1021/CM501898Y}, abstractNote={Solution-processed nickel oxides (s-NiOx) are used as hole injection and transport layers in solution-processed organic light-emitting diodes (OLEDs). By increasing the annealing temperature, the nickel acetate precursor fully decomposes and the s-NiOx film shows larger crystalline grain sizes, which lead to better hole injection and transport properties. UV–ozone treatment on the s-NiOx surface is carried out to further modify its surface chemistry, improving the hole injection efficiency. The introduction of more dipolar species of nickel oxy-hydroxide (NiO(OH)) is evidenced after the treatment. Dark injection–space charge limited (DI–SCL) transient measurement was carried out to compare the hole injection efficiency of s-NiOx and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole injection layers (HIL). The UV–ozone treated s-NiOx shows significantly better hole injection, with a high injection efficiency of 0.8. With a p-type thin film transistor (TFT) configuration, the high-tem...}, number={15}, journal={Chemistry of Materials}, publisher={American Chemical Society (ACS)}, author={Liu, Shuyi and Liu, Rui and Chen, Ying and Ho, Szuheng and Kim, Jong H. and So, Franky}, year={2014}, month={Jul}, pages={4528–4534} }
 @article{chen_tsang_lai_reynolds_so_2014, title={Organic Photovoltaic Cells: Dielectric Effect on the Photovoltage Loss in Organic Photovoltaic Cells (Adv. Mater. 35/2014)}, volume={26}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/ADMA.201470237}, DOI={10.1002/ADMA.201470237}, abstractNote={S.-W. Tsang, F. So, and co-workers use charge modulation electroabsorption spectroscopy (CMEAS) to determine the VOC loss in several polymer-fullerene solar cells. Based on their data, they conclude on page 6125 that the VOC loss is due to the low dielectric constants of the polymers. The photovoltage loss is found to be close to zero if the dielectric constant of the polymer-fullerene blend is close to a value of five.}, number={35}, journal={Advanced Materials}, publisher={Wiley}, author={Chen, Song and Tsang, Sai-Wing and Lai, Tzung-Han and Reynolds, John R. and So, Franky}, year={2014}, month={Sep}, pages={6045–6045} }
 @article{kim_chen_liu_so_2014, title={Phosphorescent dye-doped hole transporting layer for organic light-emitting diodes}, volume={15}, ISSN={1566-1199}, url={http://dx.doi.org/10.1016/J.ORGEL.2014.07.012}, DOI={10.1016/J.ORGEL.2014.07.012}, abstractNote={Hole transport materials are critical to the performance of organic light-emitting diodes (OLEDs). While 1,1-bis(di-4-tolylaminophenyl)cyclohexane (TAPC) with a high triplet energy is widely used for high efficiency phosphorescent OLEDs, devices using TAPC as a hole transport layer (HTL) have a short operating lifetime due to the build-up of trapped charges at the TAPC/emitting layer (EML) interface during device operation. In this work, to solve the operating stability problem, instead of using conventional HTLs, we use a(fac-tris(2-phenylpyridine)iridium (III))(Ir(ppy)3) doped layer as an HTL to replace the conventional HTLs. Because of the hole injecting and transporting abilities of the phosphorescent dye, holes can be directly injected into the emitting layer without an injection barrier. OLEDs based on a phosphorescent dye-doped HTL show significant improvement in operational stability without loss of efficiency.}, number={10}, journal={Organic Electronics}, publisher={Elsevier BV}, author={Kim, Jong H. and Chen, Ying and Liu, Rui and So, Franky}, year={2014}, month={Oct}, pages={2381–2386} }
 @article{xiang_chopra_wang_brown_ho_mathai_so_2014, title={Phosphorescent organic light emitting diodes with a cross-linkable hole transporting material}, volume={15}, ISSN={1566-1199}, url={http://dx.doi.org/10.1016/J.ORGEL.2014.03.009}, DOI={10.1016/J.ORGEL.2014.03.009}, abstractNote={A cross-linkable hole transporting material PLEXCORE® HTL was incorporated in phosphorescent organic light emitting diodes. This hole transporting material is based on an arylamine derivate. The device performance in terms of efficiency and lifetime was compared to the same devices with a thermally evaporated 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB)-based hole transporting layer. The resulting devices with the cross-linkable HTL gave higher efficiency, smaller roll-off and longer lifetime compared with devices with the NPB-based devices. This new hole transporting material paves the road toward solution processed multilayer light emitting devices.}, number={7}, journal={Organic Electronics}, publisher={Elsevier BV}, author={Xiang, Chaoyu and Chopra, Neetu and Wang, Jing and Brown, Christopher and Ho, Szuheng and Mathai, Mathew and So, Franky}, year={2014}, month={Jul}, pages={1702–1706} }
 @article{ho_xiang_liu_chopra_mathai_so_2014, title={Stable solution processed hole injection material for organic light-emitting diodes}, volume={15}, ISSN={1566-1199}, url={http://dx.doi.org/10.1016/J.ORGEL.2014.07.022}, DOI={10.1016/J.ORGEL.2014.07.022}, abstractNote={A new aqueous based polymer, Plexcore® OC AQ1200 (AQ1200) was used as a hole injection layer (HIL) in organic light emitting diodes (OLEDs) and the device results are compared with polyethylene dioxythiophene:polystyrene sulfonate (PEDOT:PSS) in terms of injection efficiency and stability. Dark injection transient measurements show a higher injection efficiency in hole-only devices using AQ1200 HIL compared with PEDOT:PSS. Using AQ1200 as an HIL, high efficiency phosphorescent OLEDs are demonstrated to have a long lifetime, with an estimated operational half lifetime (LT 50) of more than 8000 h from an initial luminance of 1000 cd/m2.}, number={10}, journal={Organic Electronics}, publisher={Elsevier BV}, author={Ho, Szuheng and Xiang, Chaoyu and Liu, Rui and Chopra, Neetu and Mathai, Mathew and So, Franky}, year={2014}, month={Oct}, pages={2513–2517} }
 @article{xiang_koo_so_sasabe_kido_2013, title={A systematic study on efficiency enhancements in phosphorescent green, red and blue microcavity organic light emitting devices}, volume={2}, ISSN={2047-7538}, url={http://dx.doi.org/10.1038/LSA.2013.30}, DOI={10.1038/LSA.2013.30}, abstractNote={A systematic study has been conducted on microcavity organic light emitting diodes (OLEDs) based on green, red and blue phosphorescent emitters to elucidate the microcavity effects for different color emitters. We found that the luminance output is determined by the reflectivity of the semitransparent electrode and the photopic response of the green, red and blue emitters. While the luminance enhancements of blue and red phosphorescent microcavity devices are small, a current efficiency as high as 224 cd A−1 is obtained in the green phosphorescent microcavity OLEDs. The role that microcavities play in the output of an organic light-emitting device (OLED) has now been studied in detail. Chaoyu Xiang and co-workers from the University of Florida in the USA and Yamagata University in Japan investigated the efficiency and spectral characteristics of phosphorescent green, red and blue microcavity OLEDs. They concluded that the luminance output of a device is strongly affected by the reflectivity of its semitransparent electrode and its spectral match to the organic material’s electroluminescence. They fabricated device electrodes from indium-tin-oxide-coated distributed Bragg reflectors comprising two separated stacks of alternating layers of titanium oxide and silicon dioxide. They recorded a luminous efficiency of up 224 cd A–1 for an optimized green microcavity device, with smaller values achieved for blue and red devices.}, number={6}, journal={Light: Science & Applications}, publisher={Springer Science and Business Media LLC}, author={Xiang, Chaoyu and Koo, Wonhoe and So, Franky and Sasabe, Hisahiro and Kido, Junji}, year={2013}, month={Jun}, pages={e74–e74} }
 @article{chan_tsang_lee_so_so_2013, title={Charge transport study of semiconducting polymers and their bulk heterojunction blends by capacitance measurements}, volume={51}, ISSN={0887-6266}, url={http://dx.doi.org/10.1002/polb.23236}, DOI={10.1002/polb.23236}, abstractNote={Abstract}, number={8}, journal={Journal of Polymer Science Part B: Polymer Physics}, publisher={Wiley}, author={Chan, Kevin K. H. and Tsang, S. W. and Lee, Harrison K. H. and So, F. and So, S. K.}, year={2013}, month={Jan}, pages={649–658} }
 @article{hartel_chen_swerdlow_hsu_manders_schanze_so_2013, title={Defect-Induced Loss Mechanisms in Polymer–Inorganic Planar Heterojunction Solar Cells}, volume={5}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/AM4015605}, DOI={10.1021/AM4015605}, abstractNote={The effect of ZnO defects on photoexcited charge carrier recombination and forward induced charge transfer was studied in organic-inorganic bilayer organic heterojunction solar cells. Decreased bimolecular recombination via passivation of ZnO nanopariticle defects resulted in longer carrier lifetime as determined by transient photovoltage (TPV) measurements. It was also found by time-resolved photoluminescence (TRPL) measurements that defect passivation decreased the fluorescence lifetime which indicated higher exciton dissociation efficiency. Through passivation of the ZnO nanoparticles defects, the two loss mechanisms were reduced and the power conversion efficiency (PCE) is significantly enhanced.}, number={15}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Hartel, Michael and Chen, Song and Swerdlow, Benjamin and Hsu, Hsien-Yi and Manders, Jesse and Schanze, Kirk and So, Franky}, year={2013}, month={Jul}, pages={7215–7218} }
 @article{koo_zhe_so_2013, title={Direct Fabrication of Organic Light-Emitting Diodes on Buckled Substrates for Light Extraction}, volume={1}, ISSN={2195-1071}, url={http://dx.doi.org/10.1002/ADOM.201300030}, DOI={10.1002/ADOM.201300030}, abstractNote={The organic light-emitting diode (OLED) has become a mainstream display technology due to recent advances made in materials development and manufacturing. OLEDs have also become an attractive technology for solid-state lighting because of their high effi ciency and high color-rendering index. However, despite their high internal quantum effi ciency, [ 1 ] their external quantum effi ciency is typically less than ∼ 20% due to poor outcoupling effi ciency, with ∼ 80% of emitted light trapped in the indium tin oxide (ITO)/organic layers (ITO/organic mode) and the glass substrate (substrate mode). While the easiest way to improve the outcoupling effi ciency is to introduce microlens arrays on the back of the substrate to extract the substrate mode, [ 2–5 ] a more effective but challenging way is to incorporate gratings or photonic crystals into the device structure to extract the ITO/organic mode. [ 6–11 ] However, most of the reported light-extraction techniques to outcouple the ITO/organic mode require ebeam or interference lithography to fabricate periodic microstructures as a template and imprinting process to transfer the pattern to the substrate, which are not compatible with low-cost, largearea manufacturing. [ 6–11 ] Moreover, periodic microstructures created by these lithography processes result in out-coupled light with a strong wavelength dependence and directionality, and the resulting devices are not suitable for general lighting applications. [ 6–10 ] Koo et al. developed a technique to fabricate quasi-periodic buckled structures for light extraction over a broad range of emission wavelengths with a Lambertian-like emission pattern. [ 12,13 ] The buckling template was fabricated by thermal evaporation of aluminium on a polydimethylsiloxane (PDMS) layer. However, the buckled structure formed by this technique does not have the mechanical stability for device fabrication, and an imprinting process is required to transfer the buckled pattern to the device substrate. Therefore, further development is needed to eliminate the imprinting and transfer processes. To overcome this limitation, here, for the fi rst time, we demonstrate a lithographyand imprinting-free light-extraction scheme which is compatible with low-cost, large-area manufacturing by fabricating OLEDs directly on a hardened, buckled PDMS surface.}, number={5}, journal={Advanced Optical Materials}, publisher={Wiley}, author={Koo, Won Hoe and Zhe, Yin and So, Franky}, year={2013}, month={Apr}, pages={404–408} }
 @article{tsang_chen_so_2013, title={Energy Level Alignment and Sub-Bandgap Charge Generation in Polymer:Fullerene Bulk Heterojunction Solar Cells}, volume={25}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/ADMA.201204495}, DOI={10.1002/ADMA.201204495}, abstractNote={Using charge modulated electroabsorption spectroscopy (CMEAS), for the first time, the energy level alignment of a polymer:fullerene bulk heterojunction photovoltaic cell is directly measured. The charge-transfer excitons generated by the sub-bandgap optical pumping are coupled with the modulating electric field and introduce subtle changes in optical absorption in the sub-bandgap region. This minimum required energy for sub-bandgap charge genreation is defined as the effective bandgap.}, number={17}, journal={Advanced Materials}, publisher={Wiley}, author={Tsang, Sai-Wing and Chen, Song and So, Franky}, year={2013}, month={Feb}, pages={2434–2439} }
 @article{tsang_chen_so_2013, title={Energy Level Alignment and Sub-Bandgap Charge Generation in Polymer:Fullerene Bulk Heterojunction Solar Cells (Adv. Mater. 17/2013)}, volume={25}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/ADMA.201370113}, DOI={10.1002/ADMA.201370113}, abstractNote={A novel technique – charge modulated electro-absorption spectroscopy (CEMAS) – is reported by Franky So and co-workers on page 2434 and used to determine the energy-level alignment and the effective bandgap of organic heterojunctions. What makes CMEAS unique is that it can directly determine the interface energetics of donor–acceptor blends, not possible using conventional electro-chemical methods.}, number={17}, journal={Advanced Materials}, publisher={Wiley}, author={Tsang, Sai-Wing and Chen, Song and So, Franky}, year={2013}, month={May}, pages={2433–2433} }
 @article{chen_jiang_so_2013, title={Hole injection polymer effect on degradation of organic light-emitting diodes}, volume={14}, ISSN={1566-1199}, url={http://dx.doi.org/10.1016/J.ORGEL.2013.06.023}, DOI={10.1016/J.ORGEL.2013.06.023}, abstractNote={Polythienothiophene:poly(perfluoroethylene-perfluoroethersulfonic acid) (PTT:PFFSA) has been used to enhance hole injection into small molecule OLEDs. Compared to devices with polyethylene dioxythiophene polystyrene sulfonate (PEDOT:PSS) as the hole injection layer (HIL), the OLED using PTT:PFFSA as a HIL gives enhanced efficiency and a slower luminance decay as well as a slower rise in operating voltage. Further studies of capacitance–voltage characteristics reveal that positive trapped charges accumulate in the hole transporting layer during operation. These results thus highlight the significance of hole injection layer to OLED operational stability.}, number={10}, journal={Organic Electronics}, publisher={Elsevier BV}, author={Chen, Song and Jiang, Xuezhong and So, Franky}, year={2013}, month={Oct}, pages={2518–2522} }
 @article{casalini_tsang_deininger_arroyave_reynolds_so_2013, title={Investigation of the Role of the Acceptor Molecule in Bulk Heterojunction Photovoltaic Cells Using Impedance Spectroscopy}, volume={117}, ISSN={1932-7447 1932-7455}, url={http://dx.doi.org/10.1021/JP401435S}, DOI={10.1021/JP401435S}, abstractNote={An investigation of the recombination kinetics and the density of states distribution in bulk heterojunction organic photovoltaic cells was undertaken using impedance spectroscopy measurements under varying levels of illumina- tions. Three organic polymer solar cells were investigated which differed only by the p-type polymer used in the active layers while the device architecture and acceptor molecule (PC70BM) were kept the same. We found that the density of states profiles for the three cells are similar and can be superimposed by a horizontal shift due to a difference between the polymers' HOMO and the PC70BM's LUMO levels. The recombination mechanisms for the three cells showed the same behavior, suggesting an important role of the acceptor in this process; however, large differences in the absolute value of carrier lifetime τeff related to the choice of the polymer are evident, indicating that the recombination kinetics depends on a combination of the properties of both materials and the morphology of their blend.}, number={27}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Casalini, Riccardo and Tsang, Sai Wing and Deininger, James J. and Arroyave, Frank A. and Reynolds, John R. and So, Franky}, year={2013}, month={Jun}, pages={13798–13804} }
 @article{small_tsang_chen_baek_amb_subbiah_reynolds_so_2013, title={Loss Mechanisms in Thick-Film Low-Bandgap Polymer Solar Cells}, volume={3}, ISSN={1614-6832}, url={http://dx.doi.org/10.1002/AENM.201201114}, DOI={10.1002/AENM.201201114}, abstractNote={Abstract}, number={7}, journal={Advanced Energy Materials}, publisher={Wiley}, author={Small, Cephas E. and Tsang, Sai-Wing and Chen, Song and Baek, Sujin and Amb, Chad M. and Subbiah, Jegadesan and Reynolds, John R. and So, Franky}, year={2013}, month={Mar}, pages={909–916} }
 @article{lai_tsang_manders_chen_so_2013, title={Properties of interlayer for organic photovoltaics}, volume={16}, ISSN={1369-7021}, url={http://dx.doi.org/10.1016/J.MATTOD.2013.10.001}, DOI={10.1016/J.MATTOD.2013.10.001}, abstractNote={Interfacial materials play an important role in determining the efficiency of an organic photovoltaic (OPV) cell. They are not only responsible for establishing ohmic contact, but also determining different device parameters such as the internal electric field, the film morphology, and the carrier recombination rate which are important to the device performance. Here, we will present the material properties and requirements for these interlayers used in high efficiency OPV cells. This paper aims to reveal the different roles of interlayers, introduce techniques for characterizing their properties, and provide an insight into the future development of novel interlayers for high efficiency organic photovoltaic cells.}, number={11}, journal={Materials Today}, publisher={Elsevier BV}, author={Lai, Tzung-Han and Tsang, Sai-Wing and Manders, Jesse R. and Chen, Song and So, Franky}, year={2013}, month={Nov}, pages={424–432} }
 @article{manders_tsang_hartel_lai_chen_amb_reynolds_so_2013, title={Solution-Processed Nickel Oxide Hole Transport Layers in High Efficiency Polymer Photovoltaic Cells}, volume={23}, ISSN={1616-301X}, url={http://dx.doi.org/10.1002/adfm.201202269}, DOI={10.1002/adfm.201202269}, abstractNote={Abstract}, number={23}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Manders, Jesse R. and Tsang, Sai-Wing and Hartel, Michael J. and Lai, Tzung-Han and Chen, Song and Amb, Chad M. and Reynolds, John R. and So, Franky}, year={2013}, month={Jan}, pages={2993–3001} }
 @article{amb_craig_koldemir_subbiah_choudhury_gevorgyan_jørgensen_krebs_so_reynolds_2012, title={Aesthetically Pleasing Conjugated Polymer:Fullerene Blends for Blue-Green Solar Cells Via Roll-to-Roll Processing}, volume={4}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/am300156p}, DOI={10.1021/am300156p}, abstractNote={The practical application of organic photovoltaic (OPV) cells requires high throughput printing techniques in order to attain cells with an area large enough to provide useful amounts of power. However, in the laboratory screening of new materials for OPVs, spin-coating is used almost exclusively as a thin-film deposition technique due its convenience. We report on the significant differences between the spin-coating of laboratory solar cells and slot-die coating of a blue-green colored, low bandgap polymer (PGREEN). This is one of the first demonstrations of slot-die-coated polymer solar cells OPVs not utilizing poly(3-hexylthiophene):(6,6)-phenyl-C(61)-butyric acid methyl ester (PCBM) blends as a light absorbing layer. Through synthetic optimization, we show that strict protocols are necessary to yield polymers which achieve consistent photovoltaic behavior. We fabricated spin-coated laboratory scale OPV devices with PGREEN: PCBM blends as active light absorbing layers, and compare performance to slot die-coated individual solar cells, and slot-die-coated solar modules consisting of many cells connected in series. We find that the optimum ratio of polymer to PCBM varies significantly when changing from spin-coating of thinner active layer films to slot-die coating, which requires somewhat thicker films. We also demonstrate the detrimental impacts on power conversion efficiency of high series resistance imparted by large electrodes, illustrating the need for higher conductivity contacts, transparent electrodes, and high mobility active layer materials for large-area solar cell modules.}, number={3}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Amb, Chad M. and Craig, Michael R. and Koldemir, Unsal and Subbiah, Jegadesan and Choudhury, Kaushik Roy and Gevorgyan, Suren A. and Jørgensen, Mikkel and Krebs, Frederik C. and So, Franky and Reynolds, John R.}, year={2012}, month={Feb}, pages={1847–1853} }
 @article{stalder_grand_subbiah_so_reynolds_2012, title={An isoindigo and dithieno[3,2-b:2′,3′-d]silole copolymer for polymer solar cells}, volume={3}, ISSN={1759-9954 1759-9962}, url={http://dx.doi.org/10.1039/c1py00402f}, DOI={10.1039/c1py00402f}, abstractNote={The conjugated copolymer of isoindigo and dithienosilole was synthesized and studied in bulk heterojunction solar cells with fullerene derivatives.}, number={1}, journal={Polym. Chem.}, publisher={Royal Society of Chemistry (RSC)}, author={Stalder, Romain and Grand, Caroline and Subbiah, Jegadesan and So, Franky and Reynolds, John R.}, year={2012}, pages={89–92} }
 @article{chan_tsang_lee_so_so_2012, title={Charge injection and transport studies of poly(2,7-carbazole) copolymer PCDTBT and their relationship to solar cell performance}, volume={13}, ISSN={1566-1199}, url={http://dx.doi.org/10.1016/j.orgel.2012.01.030}, DOI={10.1016/j.orgel.2012.01.030}, abstractNote={The charge injection and transport properties of a high performance semiconducting polymer for organic photovoltaic (OPV) applications, poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT), are investigated by time-of-flight (TOF) and dark-injection space-charge-limited current (DI-SCLC) techniques. OPV cells employing PCDTBT are known to possess power conversion efficiency (PCE) exceeding 6% [1], [2]. While TOF probes only the hole mobilities of a thick film, DI-SCLC is shown to be useful down to a sample thickness of ∼200 nm, which is comparable to thicknesses used in OPV cells. We show that for pristine PCDTBT, the hole mobilities for both thick used in TOF and thin films for DI-SCLC are essentially the same, and they are in the range of 0.4–3.0 × 10−4 cm2/Vs at room temperature. Both poly(3,4-ethylene dioxythioplene) doped with poly(strenesulfonate) (PEDOT:PSS) and molybdenum (VI) oxide (MoO3) form quasi-Ohmic contacts to PCDTBT with better hole injection from MoO3. Furthermore, the Gaussian Disorder Model (GDM) was employed to analyze the hopping transport of PCDTBT thin films. We show that PCDTBT possesses a relatively large energetic disorder (σ) of ∼129 meV, which is significantly higher than the σ of poly(3-hexylthiophene) (P3HT) processed under similar conditions. The correlation between σ and OPV device performance is addressed.}, number={5}, journal={Organic Electronics}, publisher={Elsevier BV}, author={Chan, Kevin K.H. and Tsang, S.W. and Lee, Harrison K.H. and So, Franky and So, S.K.}, year={2012}, month={May}, pages={850–855} }
 @article{subbiah_amb_reynolds_so_2012, title={Effect of vertical morphology on the performance of silole-containing low-bandgap inverted polymer solar cells}, volume={97}, ISSN={0927-0248}, url={http://dx.doi.org/10.1016/j.solmat.2011.09.028}, DOI={10.1016/j.solmat.2011.09.028}, abstractNote={The vertical distribution of blended components in the active layer of a bulk heterojunction solar cell composed of poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl] (PDTS-BTD) and [6,6]-phenyl-C71 butyric acid methyl ester (PC71BM) was studied using X-ray photoemission spectroscopy (XPS) and Auger electron spectroscopy (AES) depth profile. We found that the vertical profile of the PDTS-BTD:PC71BM thin films varies, with a PC71BM rich region near the bottom surface and a polymer rich on the top surface. This suggests that the inverted device geometry may be superior to the conventional device geometry for the fabrication of efficient polymer solar cells. Significant enhancement in the power conversion efficiency (PCE) of an inverted polymer solar cell was observed compared to the conventional cell. The enhancement in device performance is attributed to the efficient charge extraction due to the exploitation of vertical morphology of the active layer using the inverted device geometry.}, journal={Solar Energy Materials and Solar Cells}, publisher={Elsevier BV}, author={Subbiah, Jegadesan and Amb, Chad M. and Reynolds, John R. and So, Franky}, year={2012}, month={Feb}, pages={97–101} }
 @article{subbiah_amb_irfan_gao_reynolds_so_2012, title={High-Efficiency Inverted Polymer Solar Cells with Double Interlayer}, volume={4}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/am201537p}, DOI={10.1021/am201537p}, abstractNote={We have studied the performance of normal and inverted bulk-heterojunction solar cells with an active layer composed of a blend of poly[(4,4'-bis(2-ethylhexyl)dithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl] (PDTS-BTD) and {6,6}-phenyl-C71 butyric acid methyl ester (PC(71)BM). For inverted cells, a thin layer of ZnO nanoparticles and MoO(3) were used as interlayers for the bottom cathode and the top anode respectively. To enhance the device performance, a thin film of 4,4',4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (MTDATA) was used along with MoO(3) as an anode interlayer to improve the hole extraction from the photoactive layer to the anode. The inverted polymer solar cells with double interlayer exhibit a higher power conversion efficiency of 6.45% compared to the conventional cell of 4.91% due to efficient charge extraction and favorable vertical morphology of active layer blend. Our ultraviolet photoemission spectroscopy results indicate that the formation of band bending due to interlayer leads to the enhancement in hole extraction.}, number={2}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Subbiah, Jegadesan and Amb, Chad M. and Irfan, Irfan and Gao, Yongli and Reynolds, John R. and So, Franky}, year={2012}, month={Jan}, pages={866–870} }
 @article{graham_wieruszewski_stalder_hartel_mei_so_reynolds_2012, title={Improved Performance of Molecular Bulk-Heterojunction Photovoltaic Cells through Predictable Selection of Solvent Additives}, volume={22}, ISSN={1616-301X}, url={http://dx.doi.org/10.1002/adfm.201102456}, DOI={10.1002/adfm.201102456}, abstractNote={Abstract}, number={22}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Graham, Kenneth R. and Wieruszewski, Patrick M. and Stalder, Romain and Hartel, Michael J. and Mei, Jianguo and So, Franky and Reynolds, John R.}, year={2012}, month={Jul}, pages={4801–4813} }
 @article{irfan_graber_so_gao_2012, title={Interplay of cleaning and de-doping in oxygen plasma treated high work function indium tin oxide (ITO)}, volume={13}, ISSN={1566-1199}, url={http://dx.doi.org/10.1016/j.orgel.2012.05.036}, DOI={10.1016/j.orgel.2012.05.036}, abstractNote={Indium tin oxide (ITO) is extensively used as a transparent electrode in photovoltaic cells and organic light emitting diodes. High surface work function (WF) of ITO is a crucial parameter for enhanced device performance. The ITO WF is usually around 4.3 eV without any surface treatment. With surface treatments ITO WF, as high as 5.4 eV has been reported. We designed a surface treatment method with which we achieved substantially high ITO surface work function of over 6.1 eV. We observed changes in valence electronic structure and core levels, apart from surface cleaning. We also investigated interface formation of copper phthalocyanine (CuPc) on the high WF ITO. In the proximity of the interface the highest occupied energy level of CuPc was observed to be almost pinned to the Fermi level. We fabricated three simple devices with no to high treatment. The device results were observed to be consistent with the findings of electronic energy level alignment.}, number={10}, journal={Organic Electronics}, publisher={Elsevier BV}, author={Irfan, Irfan and Graber, Sachiko and So, Franky and Gao, Yongli}, year={2012}, month={Oct}, pages={2028–2034} }
 @article{chen_small_amb_subbiah_lai_tsang_manders_reynolds_so_2012, title={Inverted Polymer Solar Cells with Reduced Interface Recombination}, volume={2}, ISSN={1614-6832}, url={http://dx.doi.org/10.1002/aenm.201200184}, DOI={10.1002/aenm.201200184}, abstractNote={Conjugated polymer solar cells are attractive as a source of renewable energy due to their compatibility with low cost rollto-roll printing processes. [ 1 ] The most effi cient of these polymer cells utilize a bulk heterojunction (BHJ) morphology, most often fabricated by blending a light-absorbing, electron-donating, and hole-transporting polymer with an electron-accepting fullerene derivative to form an active layer, which separates and transports charge carriers to the electrodes. While conventional BHJ cells are fabricated with a top cathode which requires a low work function metal for effi cient electron extraction, [ 2–5 ] this device architecture is not viable for large area processing due to the poor stability of these cathode materials. To circumvent this problem, an inverted cell geometry is a more practical architecture for existing roll-to-roll processes with a bottom cathode prepared using a modifi ed transparent electrode. [ 6 ]}, number={11}, journal={Advanced Energy Materials}, publisher={Wiley}, author={Chen, Song and Small, Cephas E. and Amb, Chad M. and Subbiah, Jegadesan and Lai, Tzung-han and Tsang, Sai-Wing and Manders, Jesse R. and Reynolds, John R. and So, Franky}, year={2012}, month={May}, pages={1333–1337} }
 @article{koo_youn_zhu_li_tansu_so_2012, title={Light Extraction of Organic Light Emitting Diodes by Defective Hexagonal-Close-Packed Array}, volume={22}, ISSN={1616-301X}, url={http://dx.doi.org/10.1002/adfm.201200876}, DOI={10.1002/adfm.201200876}, abstractNote={Abstract}, number={16}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Koo, Won Hoe and Youn, Wooram and Zhu, Peifen and Li, Xiao-Hang and Tansu, Nelson and So, Franky}, year={2012}, month={May}, pages={3454–3459} }
 @article{koo_youn_zhu_li_tansu_so_2012, title={Light Extraction: Light Extraction of Organic Light Emitting Diodes by Defective Hexagonal-Close-Packed Array (Adv. Funct. Mater. 16/2012)}, volume={22}, ISSN={1616-301X}, url={http://dx.doi.org/10.1002/adfm.201290095}, DOI={10.1002/adfm.201290095}, abstractNote={On page 3454, Franky So and co-workers report the preparation of defective hexagonal-close-packed arrays to extract the waveguide modes trapped in an organic light-emitting diode. The broadening of the periodicity and the lack of long-range ordering in the defective array pattern allow effective extraction of the waveguide modes over all emission wavelengths and angles, resulting in non-directional light emission with insignificant spectral changes.}, number={16}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Koo, Won Hoe and Youn, Wooram and Zhu, Peifen and Li, Xiao-Hang and Tansu, Nelson and So, Franky}, year={2012}, month={Aug}, pages={3453–3453} }
 @article{chen_manders_tsang_so_2012, title={Metal oxides for interface engineering in polymer solar cells}, volume={22}, ISSN={0959-9428 1364-5501}, url={http://dx.doi.org/10.1039/c2jm33838f}, DOI={10.1039/c2jm33838f}, abstractNote={Significant progress in power conversion efficiencies and stabilities of polymer solar cells has been achieved using semiconducting metal oxides as charge extraction interlayers. Both n- and p-type transition metal oxides with good transparency in the visible as well as infrared region make good Ohmic contacts to both donors and acceptors in polymer bulk heterojunction solar cells. Their compatibility with roll-to-roll processing makes them very attractive for low cost manufacturing of polymer solar cells. In this review, we will present the recent results on synthesis and characterization of these metal oxides along with the device performance of the solar cells using these metal oxides as interlayers.}, number={46}, journal={Journal of Materials Chemistry}, publisher={Royal Society of Chemistry (RSC)}, author={Chen, Song and Manders, Jesse R. and Tsang, Sai-Wing and So, Franky}, year={2012}, pages={24202} }
 @article{small_tsang_kido_so_so_2012, title={Origin of Enhanced Hole Injection in Inverted Organic Devices with Electron Accepting Interlayer}, volume={22}, ISSN={1616-301X}, url={http://dx.doi.org/10.1002/adfm.201200185}, DOI={10.1002/adfm.201200185}, abstractNote={Abstract}, number={15}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Small, Cephas E. and Tsang, Sai-Wing and Kido, Junji and So, Shu Kong and So, Franky}, year={2012}, month={Apr}, pages={3261–3266} }
 @article{koo_yun_zhu_li_tansu_so_2012, title={P-110: Light extraction of Phosphorescent OLEDs by Defective Hexagonal-Close-Packed Array}, volume={43}, ISSN={0097-966X}, url={http://dx.doi.org/10.1002/j.2168-0159.2012.tb06089.x}, DOI={10.1002/j.2168-0159.2012.tb06089.x}, abstractNote={Abstract}, number={1}, journal={SID Symposium Digest of Technical Papers}, publisher={Wiley}, author={Koo, Wonhoe and Yun, Wooram and Zhu, Peifen and Li, Xiao-Hang and Tansu, Nelson and So, Franky}, year={2012}, month={Jun}, pages={1474–1476} }
 @article{chen_small_amb_subbiah_lai_tsang_manders_reynolds_so_2012, title={Solar Cells: Inverted Polymer Solar Cells with Reduced Interface Recombination (Adv. Energy Mater. 11/2012)}, volume={2}, ISSN={1614-6832}, url={http://dx.doi.org/10.1002/aenm.201290053}, DOI={10.1002/aenm.201290053}, abstractNote={Due to intrinsic defects, zinc oxide nanoparticles may induce interfacial recombination when used as the electron extraction layer in an inverted polymer solar cell. On page 1333, Franky So, John R. Reynolds, and co-workers demonstrate that UV-ozone treatment is an effective way to passivate defects in ZnO NPs and reduce interface recombination in a polymer solar cell. As a result, the power conversion efficiency of inverted PDTGTPD: PC71BM cells is improved to 8.1%.}, number={11}, journal={Advanced Energy Materials}, publisher={Wiley}, author={Chen, Song and Small, Cephas E. and Amb, Chad M. and Subbiah, Jegadesan and Lai, Tzung-han and Tsang, Sai-Wing and Manders, Jesse R. and Reynolds, John R. and So, Franky}, year={2012}, month={Nov}, pages={1281–1281} }
 @article{xiang_koo_chen_so_liu_kong_wang_2012, title={Solution processed multilayer cadmium-free blue/violet emitting quantum dots light emitting diodes}, volume={101}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4738375}, DOI={10.1063/1.4738375}, abstractNote={We demonstrate blue/violet emitting devices based on cadmium-free zinc selenide/zinc sulfide core/shell quantum dots. Using poly(N-vinylcarbazole) with a low lying highest occupied molecular orbital energy for the hole transporting layer, enhanced hole injection was observed, resulting in efficient blue/violet emitting devices. The device charge balance was further enhanced by tuning the thicknesses of the hole transporting layer and quantum dot emitting layer.}, number={5}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Xiang, Chaoyu and Koo, Wonhoe and Chen, Song and So, Franky and Liu, Xiong and Kong, Xiangxing and Wang, Yunjun}, year={2012}, month={Jul}, pages={053303} }
 @article{beaujuge_tsao_hansen_amb_risko_subbiah_choudhury_mavrinskiy_pisula_brédas_et al._2012, title={Synthetic Principles Directing Charge Transport in Low-Band-Gap Dithienosilole–Benzothiadiazole Copolymers}, volume={134}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja301898h}, DOI={10.1021/ja301898h}, abstractNote={Given the fundamental differences in carrier generation and device operation in organic thin-film transistors (OTFTs) and organic photovoltaic (OPV) devices, the material design principles to apply may be expected to differ. In this respect, designing organic semiconductors that perform effectively in multiple device configurations remains a challenge. Following "donor-acceptor" principles, we designed and synthesized an analogous series of solution-processable π-conjugated polymers that combine the electron-rich dithienosilole (DTS) moiety, unsubstituted thiophene spacers, and the electron-deficient core 2,1,3-benzothiadiazole (BTD). Insights into backbone geometry and wave function delocalization as a function of molecular structure are provided by density functional theory (DFT) calculations at the B3LYP/6-31G(d,p) level. Using a combination of X-ray techniques (2D-WAXS and XRD) supported by solid-state NMR (SS-NMR) and atomic force microscopy (AFM), we demonstrate fundamental correlations between the polymer repeat-unit structure, molecular weight distribution, nature of the solubilizing side-chains appended to the backbones, and extent of structural order attainable in p-channel OTFTs. In particular, it is shown that the degree of microstructural order achievable in the self-assembled organic semiconductors increases largely with (i) increasing molecular weight and (ii) appropriate solubilizing-group substitution. The corresponding field-effect hole mobilities are enhanced by several orders of magnitude, reaching up to 0.1 cm(2) V(-1) s(-1) with the highest molecular weight fraction of the branched alkyl-substituted polymer derivative in this series. This trend is reflected in conventional bulk-heterojunction OPV devices using PC(71)BM, whereby the active layers exhibit space-charge-limited (SCL) hole mobilities approaching 10(-3) cm(2) V(-1) s(-1), and yield improved power conversion efficiencies on the order of 4.6% under AM1.5G solar illumination. Beyond structure-performance correlations, we observe a large dependence of the ionization potentials of the polymers estimated by electrochemical methods on polymer packing, and expect that these empirical results may have important consequences on future material study and device applications.}, number={21}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Beaujuge, Pierre M. and Tsao, Hoi Nok and Hansen, Michael Ryan and Amb, Chad M. and Risko, Chad and Subbiah, Jegadesan and Choudhury, Kaushik Roy and Mavrinskiy, Alexei and Pisula, Wojciech and Brédas, Jean-Luc and et al.}, year={2012}, month={May}, pages={8944–8957} }
 @article{lee_chopra_bera_maslov_eom_zheng_holloway_xue_so_2011, title={DOWN-CONVERSION WHITE OLEDS: Down-Conversion White Organic Light-Emitting Diodes Using Microcavity Structure (Adv. Energy Mater. 2/2011)}, volume={1}, ISSN={1614-6832}, url={http://dx.doi.org/10.1002/aenm.201190010}, DOI={10.1002/aenm.201190010}, abstractNote={Franky So and co-workers report on a high effi ciency microcavity downcon-version white organic light-emitting diodes. By incorporating a film of down-conversion phosphors within the device, a luminous efficiency of 99 lm/W at 30 cd/m2 can be obtained, paving the way for more effi cient solid-state lighting devices. On p. 174}, number={2}, journal={Advanced Energy Materials}, publisher={Wiley}, author={Lee, Jaewon and Chopra, Neetu and Bera, Debasis and Maslov, Sergey and Eom, Sang-Hyun and Zheng, Ying and Holloway, Paul and Xue, Jiangeng and So, Franky}, year={2011}, month={Mar}, pages={173–173} }
 @article{amb_chen_graham_subbiah_small_so_reynolds_2011, title={Dithienogermole As a Fused Electron Donor in Bulk Heterojunction Solar Cells}, volume={133}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja204056m}, DOI={10.1021/ja204056m}, abstractNote={We report the synthesis and bulk heterojunction photovoltaic performance of the first dithienogermole (DTG)-containing conjugated polymer. Stille polycondensation of a distannyl-DTG derivative with 1,3-dibromo-N-octyl-thienopyrrolodione (TPD) results in an alternating copolymer which displays light absorption extending to 735 nm, and a higher HOMO level than the analogous copolymer containing the commonly utilized dithienosilole (DTS) heterocycle. When polyDTG-TPD:PC(70)BM blends are utilized in inverted bulk heterojunction solar cells, the cells display average power conversion efficiencies of 7.3%, compared to 6.6% for the DTS-containing cells prepared in parallel under identical conditions. The performance enhancement is a result of a higher short-circuit current and fill factor in the DTG-containing cells, which comes at the cost of a slightly lower open circuit voltage than for the DTS-based cells.}, number={26}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Amb, Chad M. and Chen, Song and Graham, Kenneth R. and Subbiah, Jegadesan and Small, Cephas E. and So, Franky and Reynolds, John R.}, year={2011}, month={Jul}, pages={10062–10065} }
 @article{lee_chopra_bera_maslov_eom_zheng_holloway_xue_so_2011, title={Down-Conversion White Organic Light-Emitting Diodes Using Microcavity Structure}, volume={1}, ISSN={1614-6832}, url={http://dx.doi.org/10.1002/aenm.201000014}, DOI={10.1002/aenm.201000014}, abstractNote={the down-conversion effi ciency, our fabricate FIrpic OLEDs in a microcavity structure The microcavity serves two First, the FIrpic emission can be tuned to shorter wavelengths to better match the phosphor excitation spectra, resulting in higher down-conversion effi ciency. the microcavity redistributes the optical modes in the device such fl at-panel phosphor substrate to eliminate refl ection and scattering of light at the interface between the OLED glass and the phosphors substrate.}, number={2}, journal={Advanced Energy Materials}, publisher={Wiley}, author={Lee, Jaewon and Chopra, Neetu and Bera, Debasis and Maslov, Sergey and Eom, Sang-Hyun and Zheng, Ying and Holloway, Paul and Xue, Jiangeng and So, Franky}, year={2011}, month={Jan}, pages={174–178} }
 @article{small_chen_subbiah_amb_tsang_lai_reynolds_so_2011, title={High-efficiency inverted dithienogermole–thienopyrrolodione-based polymer solar cells}, volume={6}, ISSN={1749-4885 1749-4893}, url={http://dx.doi.org/10.1038/nphoton.2011.317}, DOI={10.1038/nphoton.2011.317}, number={2}, journal={Nature Photonics}, publisher={Springer Science and Business Media LLC}, author={Small, Cephas E. and Chen, Song and Subbiah, Jegadesan and Amb, Chad M. and Tsang, Sai-Wing and Lai, Tzung-Han and Reynolds, John R. and So, Franky}, year={2011}, month={Dec}, pages={115–120} }
 @article{kim_choudhury_lee_song_sarasqueta_so_2011, title={PbSe Nanocrystal-Based Infrared-to-Visible Up-Conversion Device}, volume={11}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl200704h}, DOI={10.1021/nl200704h}, abstractNote={Low-cost hybrid up-conversion devices with infrared sensitivity to 1.5 μm were obtained by integrating a colloidal PbSe nanocrystal near-infrared sensitizing layer on a green phosphorescent organic light emitting diode. A ZnO nanocrystal hole blocking layer is incorporated in the devices for keeping the device off in the absence of IR excitation. The maximum photon (1.3 μm)-to-photon (0.52 μm) conversion efficiency is 1.3%. The extension (until 1.5 μm) of the near-infrared wavelengths, which can be converted to visible light, may be able to improve night vision.}, number={5}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Kim, Do Young and Choudhury, Kaushik Roy and Lee, Jae Woong and Song, Dong Woo and Sarasqueta, Galileo and So, Franky}, year={2011}, month={May}, pages={2109–2113} }
 @article{chen_choudhury_subbiah_amb_reynolds_so_2011, title={Photo-Carrier Recombination in Polymer Solar Cells Based on P3HT and Silole-Based Copolymer}, volume={1}, ISSN={1614-6832}, url={http://dx.doi.org/10.1002/aenm.201100300}, DOI={10.1002/aenm.201100300}, abstractNote={Abstract}, number={5}, journal={Advanced Energy Materials}, publisher={Wiley}, author={Chen, Song and Choudhury, Kaushik Roy and Subbiah, Jegadesan and Amb, Chad M. and Reynolds, John R. and So, Franky}, year={2011}, month={Sep}, pages={963–969} }
 @article{graham_mei_stalder_shim_cheun_steffy_so_kippelen_reynolds_2011, title={Polydimethylsiloxane as a Macromolecular Additive for Enhanced Performance of Molecular Bulk Heterojunction Organic Solar Cells}, volume={3}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/am2000328}, DOI={10.1021/am2000328}, abstractNote={The effect of the macromolecular additive, polydimethylsiloxane (PDMS), on the performance of solution processed molecular bulk heterojunction solar cells is investigated, and the addition of PDMS is shown to improve device power conversion efficiency by ∼70% and significantly reduce cell-to-cell variation, from a power conversion efficiency of 1.25 ± 0.37% with no PDMS to 2.16 ± 0.09% upon the addition of 0.1 mg/mL PDMS to the casting solution. The cells are based on a thiophene and isoindigo containing oligomer as the electron donor and [6,6]-phenyl-C61 butyric acid methyl ester (PC(61)BM) as the electron acceptor. PDMS is shown to have a strong influence on film morphology, with a significant decrease in film roughness and feature size observed. The morphology change leads to improved performance parameters, most notably an increase in the short circuit current density from 4.3 to 6.8 mA/cm(2) upon addition of 0.1 mg/mL PDMS. The use of PDMS is of particular interest, as this additive appears frequently as a lubricant in plastic syringes commonly used in device fabrication; therefore, PDMS may unintentionally be incorporated into device active layers.}, number={4}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Graham, Kenneth R. and Mei, Jianguo and Stalder, Romain and Shim, Jae Won and Cheun, Hyeunseok and Steffy, Fred and So, Franky and Kippelen, Bernard and Reynolds, John R.}, year={2011}, month={Mar}, pages={1210–1215} }
 @article{mccarthy_liu_jayaraman_gilbert_kim_so_rinzler_2011, title={Reorientation of the High Mobility Plane in Pentacene-Based Carbon Nanotube Enabled Vertical Field Effect Transistors}, volume={5}, ISSN={1936-0851 1936-086X}, url={http://dx.doi.org/10.1021/nn102721v}, DOI={10.1021/nn102721v}, abstractNote={The large current densities attained by carbon nanotube enabled vertical field effect transistors using crystalline organic channel materials are somewhat unexpected given the known large anisotropy in the mobility of crystalline organics and their conventional ordering on dielectric surfaces which tends to orient their high mobility axes parallel to the surface. This seeming contradiction is resolved by the finding that the nanotubes induce a molecular ordering that reorients the high mobility axes to favor current flow in a direction perpendicular to the substrate surface.}, number={1}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={McCarthy, Mitchell A. and Liu, Bo and Jayaraman, Ramesh and Gilbert, Stephen M. and Kim, Do Young and So, Franky and Rinzler, Andrew G.}, year={2011}, month={Jan}, pages={291–298} }
 @article{choudhury_subbiah_chen_beaujuge_amb_reynolds_so_2011, title={Understanding the performance and loss-mechanisms in donor–acceptor polymer based solar cells: Photocurrent generation, charge separation and carrier transport}, volume={95}, ISSN={0927-0248}, url={http://dx.doi.org/10.1016/j.solmat.2011.04.042}, DOI={10.1016/j.solmat.2011.04.042}, abstractNote={Advances in bandgap and molecular spectral engineering have led to color-tunable donor–acceptor (DA) polymers for use in esthetically colored bulk-heterojunction (BHJ) photovoltaic devices where control and optimization of the physical processes governing their operation is necessary to realize high efficiency. We detail a study of the processes of photogeneration of charge carriers, their separation at the DA heterojunctions and their transport in solar cells fabricated from a series of dioxythiophene–benzothiadiazole (DOT–BTD) copolymers (PG1–PG3) as the electron donor and methanofullerene (PCBM) derivatives as the electron acceptor. We also examine the effect of the blend composition on carrier transport and photoresponse. The photogeneration of carriers and their dissociation increases with increase in concentration of the acceptor and peaks at ∼88% of PCBM. Measurements on single-carrier devices show that hole mobility in the polymer phase of the blends is enhanced by up to two orders at compositions having >80% of PCBM by weight. However, even at the optimized composition, the electron mobility in the blend is two orders of magnitude higher than the hole mobility. This largely imbalanced carrier transport results in the build-up of space-charges, limiting the efficiency of charge separation at short-circuit (∼53%) and the fill factor (<45%). To highlight the importance of attaining charge balance in BHJ DA blends for photovoltaics, we further investigate and compare solar cells from two model polymers, a low bandgap DA polymer (PSBTBT) and poly-3-hexylthiophene (P3HT), blended with PCBM. Our findings indicate that, in contrast to the DOT–BTD copolymers, carrier transport is significantly more balanced in these model systems, preventing space-charge build-up and reducing recombination, which results in a markedly improved charge separation efficiency and fill factor.}, number={8}, journal={Solar Energy Materials and Solar Cells}, publisher={Elsevier BV}, author={Choudhury, Kaushik Roy and Subbiah, Jegadesan and Chen, Song and Beaujuge, Pierre M. and Amb, Chad M. and Reynolds, John R. and So, Franky}, year={2011}, month={Aug}, pages={2502–2510} }
 @article{stalder_mei_subbiah_grand_estrada_so_reynolds_2011, title={n-Type Conjugated Polyisoindigos}, volume={44}, ISSN={0024-9297 1520-5835}, url={http://dx.doi.org/10.1021/ma2012706}, DOI={10.1021/ma2012706}, abstractNote={The conjugated electron acceptor isoindigo was used to synthesize two conjugated polymers with backbones composed exclusively of electron-deficient units. Suzuki polycondensation afforded the homopolymer of isoindigo and a copolymer with 2,1,3-benzothiadiazole as repeat unit. The materials are thermally stable up to 380 °C, along with being soluble in and processable from common organic solvents. The polymers absorb light broadly throughout the visible spectrum, with optical bandgaps of 1.70 and 1.77 eV, respectively. Both polymers reduce reversibly with LUMO energy levels at −3.84 and −3.90 eV for the homopolymer and the copolymer, respectively, close to the value of −4.10 eV found for fullerenes such as PC60BM when measured under identical conditions. The polymers HOMO levels were calculated at −5.54 and −5.67 eV, respectively, based on their optical band gaps. Spectroelectrochemical measurements on thin films of the homopolymer showed the generation of stable negative charge carriers, accompanied by co...}, number={16}, journal={Macromolecules}, publisher={American Chemical Society (ACS)}, author={Stalder, Romain and Mei, Jianguo and Subbiah, Jegadesan and Grand, Caroline and Estrada, Leandro A. and So, Franky and Reynolds, John R.}, year={2011}, month={Aug}, pages={6303–6310} }
 @article{subbiah_beaujuge_choudhury_ellinger_reynolds_so_2010, title={Combined effects of MoO3 interlayer and PC70BM on polymer photovoltaic device performance}, volume={11}, ISSN={1566-1199}, url={http://dx.doi.org/10.1016/j.orgel.2010.02.006}, DOI={10.1016/j.orgel.2010.02.006}, abstractNote={The performance of bulk-heterojunction solar cells fabricated from a donor–acceptor structured polymer designed to exhibit the color green (PGREEN) as the electron-donor, along with [6,6]-phenyl-C71 butyric acid methyl ester (PC70BM) as the electron-acceptor, are demonstrated with power conversion efficiency (PCE) up to 3.2% under air mass 1.5G, 100 mW/cm2. The effects of anode interface layers (PEDOT:PSS, MoO3) and different acceptors (PC60BM, bis-PC60BM, PC70BM) on the cell performance were investigated. We found that the combined effect of PC70BM and a MoO3 anode interlayer exhibits a 69% enhancement in PCE compared to cells with PEDOT:PSS and PC60BM. This enhancement in PCE is attributed to combined effects of improved charge transport and strong light absorption by PC70BM, and efficient hole extraction by the MoO3 interlayer.}, number={5}, journal={Organic Electronics}, publisher={Elsevier BV}, author={Subbiah, Jegadesan and Beaujuge, Pierre M. and Choudhury, Kaushik Roy and Ellinger, Stefan and Reynolds, John R. and So, Franky}, year={2010}, month={May}, pages={955–958} }
 @article{so_kondakov_2010, title={Degradation Mechanisms in Small-Molecule and Polymer Organic Light-Emitting Diodes}, volume={22}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/adma.200902624}, DOI={10.1002/adma.200902624}, abstractNote={Abstract}, number={34}, journal={Advanced Materials}, publisher={Wiley}, author={So, Franky and Kondakov, Denis}, year={2010}, month={Jun}, pages={3762–3777} }
 @article{sarasqueta_choudhury_so_2010, title={Effect of Solvent Treatment on Solution-Processed Colloidal PbSe Nanocrystal Infrared Photodetectors}, volume={22}, ISSN={0897-4756 1520-5002}, url={http://dx.doi.org/10.1021/cm1006229}, DOI={10.1021/cm1006229}, abstractNote={PbSe colloidal nanocrystals were used to fabricate infrared photodetectors. Low dark currents were obtained by using chemical treatments to improve the nanocrystal film quality and passivate traps in the nanocrystals. The effects of different nanocrystal capping groups, including oleic acid, octylamine, ethanedithiol, and benzenedithiol, on the nanocrystal film quality and the photodiode characteristics were studied. The spectral responsivities and quantum efficiencies of the photodetectors were also measured. We found that the physical quality of the films was very sensitive to the capping groups used for the nanocrystals as well as the specific exchange reactions. Specifically, the dithiol capping groups were found to enhance the rectification of the photodetectors and significantly reduce the dark current in the devices by effectively passivating the surface traps.}, number={11}, journal={Chemistry of Materials}, publisher={American Chemical Society (ACS)}, author={Sarasqueta, Galileo and Choudhury, Kaushik Roy and So, Franky}, year={2010}, month={Jun}, pages={3496–3501} }
 @article{choudhury_song_so_2010, title={Efficient solution-processed hybrid polymer–nanocrystal near infrared light-emitting devices}, volume={11}, ISSN={1566-1199}, url={http://dx.doi.org/10.1016/j.orgel.2009.09.017}, DOI={10.1016/j.orgel.2009.09.017}, abstractNote={We report solution-processed hybrid LEDs, emitting infrared light with enhanced efficiency, based on PbSe nanocrystal (NC) lumophores embedded a conjugated polymer forming the nanocomposite active layer. The effect of device geometry and the NC-polymer blend composition on device performance is studied in detail. Increasing the PbSe NC concentration leads to a substantial decrease in device current, and an increase in efficiency and turn-on voltage. Analysis of the device data indicates that the PbSe NCs act as carrier traps and radiative recombination centers. With optimized concentration of NC emitters and active layer thickness, the devices exhibit an external electroluminescence quantum efficiency of 0.83% at a peak emission wavelength of 1280 nm.}, number={1}, journal={Organic Electronics}, publisher={Elsevier BV}, author={Choudhury, Kaushik Roy and Song, Dong Woo and So, Franky}, year={2010}, month={Jan}, pages={23–28} }
 @article{qian_zheng_choudhury_bera_so_xue_holloway_2010, title={Electroluminescence from light-emitting polymer/ZnO nanoparticle heterojunctions at sub-bandgap voltages}, volume={5}, ISSN={1748-0132}, url={http://dx.doi.org/10.1016/j.nantod.2010.08.010}, DOI={10.1016/j.nantod.2010.08.010}, abstractNote={The turn-on voltage of a light-emitting diode is generally equal to or greater than its bandgap voltage (or the bandgap energy divided by the electron charge). In contrast, we have found that electroluminescence at sub-bandgap voltages can be observed in polymer light-emitting devices with a heterojunction based on ZnO nanoparticles (NPs). This sub-bandgap electroluminescence is attributed to an Auger-assisted energy up-conversion process at the polymer/ZnO NPs interface, the observation of which depends strongly on the size of the nanoparticles.}, number={5}, journal={Nano Today}, publisher={Elsevier BV}, author={Qian, Lei and Zheng, Ying and Choudhury, Kaushik R. and Bera, Debasis and So, Franky and Xue, Jiangeng and Holloway, Paul H.}, year={2010}, pages={384–389} }
 @article{irfan_ding_gao_small_kim_subbiah_so_2010, title={Energy level evolution of air and oxygen exposed molybdenum trioxide films}, volume={96}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3454779}, DOI={10.1063/1.3454779}, abstractNote={The evolution of electronic energy levels of controlled air and oxygen exposed molybdenum trioxide (MoO3) films has been investigated with ultraviolet photoemission spectroscopy, inverse photoemission spectroscopy, and x-ray photoemission spectroscopy. We found that while most of the electronic levels of as deposited MoO3 films remained largely intact, the reduction in the work function (WF) was substantial. The gradual surface WF change from 6.8 to 5.3 eV was observed for air exposed film, while oxygen exposed film the surface WF saturated at ∼5.7 eV. Two distinct stages of exposure are observed, the first dominated by oxygen adsorption for <1013 Langmuir (L) exposure and at the final step moisture absorption >1013 L.}, number={24}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Irfan and Ding, Huanjun and Gao, Yongli and Small, Cephas and Kim, Do Young and Subbiah, Jegadesan and So, Franky}, year={2010}, month={Jun}, pages={243307} }
 @article{irfan_ding_gao_kim_subbiah_so_2010, title={Energy level evolution of molybdenum trioxide interlayer between indium tin oxide and organic semiconductor}, volume={96}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3309600}, DOI={10.1063/1.3309600}, abstractNote={The thickness dependance of molybdenum trioxide (MoO3) interlayer between conducting indium tin oxide (ITO) and chloro-aluminum pthalocyanine (AlPc-Cl) has been investigated with ultraviolet photoemission spectroscopy (UPS) and inverse photoemission spectroscopy. It was found that the MoO3 interlayer substantially increased the surface workfunction (WF). The increase was observed to saturate at 20 A of MoO3 coverage. The increased WF results in hole accumulation and a band-bendinglike situation in the subsequently deposited AlPc-Cl. From these observations, a possible explanation is deduced for the observed reduction in series resistance by the insertion of the MoO3 insulating layer.}, number={7}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Irfan and Ding, Huanjun and Gao, Yongli and Kim, Do Young and Subbiah, Jegadesan and So, Franky}, year={2010}, month={Feb}, pages={073304} }
 @article{beaujuge_subbiah_choudhury_ellinger_mccarley_so_reynolds_2010, title={Green Dioxythiophene-Benzothiadiazole Donor−Acceptor Copolymers for Photovoltaic Device Applications}, volume={22}, ISSN={0897-4756 1520-5002}, url={http://dx.doi.org/10.1021/cm903495b}, DOI={10.1021/cm903495b}, abstractNote={With the perspective of producing power-generating displays of various colors based on π-conjugated semiconducting polymers, we have developed a synthetic design aimed at addressing color states commonly difficult to attain. Herein, we report on the structure−property relationships and performance in photovoltaic devices of a series of green-colored donor−acceptor (DA) π-conjugated polymers comprised of electron-rich 3,4-dioxythiophenes (DOTs) and the electron-deficient 2,1,3-benzothiadiazole (BTD). In particular, the synthesis and chemical polymerization of two DOT-BTD regiosymmetric oligomers (pentamers M2 and M3), that can be chemically oxidized to yield two-band absorbing polymers with a transmission window in the 480−560 nm range hence reflecting/transmitting the color green (P2 and P3), is reported. The optical and electrochemical properties of P2 and P3 are described and compared to those of a blue-colored parent polymer (P1) obtained via the polymerization of a smaller DOT-BTD oligomeric precursor...}, number={6}, journal={Chemistry of Materials}, publisher={American Chemical Society (ACS)}, author={Beaujuge, Pierre M. and Subbiah, Jegadesan and Choudhury, Kaushik Roy and Ellinger, Stefan and McCarley, Tracy D. and So, Franky and Reynolds, John R.}, year={2010}, month={Mar}, pages={2093–2106} }
 @article{chopra_swensen_polikarpov_cosimbescu_so_padmaperuma_2010, title={High efficiency and low roll-off blue phosphorescent organic light-emitting devices using mixed host architecture}, volume={97}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3464969}, DOI={10.1063/1.3464969}, abstractNote={We report high efficiency and low roll-off for blue electrophosphorescent organic light emitting devices based on a mixed host layer architecture. The devices were fabricated using a mixed layer of di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane, a hole transport material, and 2,8-bis(diphenylphosphoryl)dibenzothiophene, an electron transport material, as the host layer doped with the blue phosphor iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate. Using a mixed layer as the host allowed us to achieve high power efficiency (59 lm/W at 100 cd/m2), low turn-on voltage (2.7 V for >10 cd/m2), and low roll-off in these devices.}, number={3}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Chopra, Neetu and Swensen, James S. and Polikarpov, Evgueni and Cosimbescu, Lelia and So, Franky and Padmaperuma, Asanga B.}, year={2010}, month={Jul}, pages={033304} }
 @article{subbiah_kim_hartel_so_2010, title={MoO3/poly(9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine) double-interlayer effect on polymer solar cells}, volume={96}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3310013}, DOI={10.1063/1.3310013}, abstractNote={A double interlayer composed of MoO3 and poly(9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine) (TFB) was used as an anode contact for bulk heterojunction polymer solar cells. Using this strategy, photovoltaic cells with poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene]: [6,6]-phenyl-C61 butyric acid methyl ester (MDMO-PPV:PCBM) blend as a photoactive layer were fabricated. An enhancement in power conversion efficiency of 53% was observed in cells with a double interlayer compared with cells having a PEDOT: PSS interlayer. The enhancement is attributed to the combined effects of electron blocking and enhanced charge extraction from the photoactive layer to the anode.}, number={6}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Subbiah, Jegadesan and Kim, Do Young and Hartel, Michael and So, Franky}, year={2010}, month={Feb}, pages={063303} }
 @article{so_kondakov_2010, title={OLEDs: Degradation Mechanisms in Small-Molecule and Polymer Organic Light-Emitting Diodes (Adv. Mater. 34/2010)}, volume={22}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/adma.201090111}, DOI={10.1002/adma.201090111}, abstractNote={Abstract}, number={34}, journal={Advanced Materials}, publisher={Wiley}, author={So, Franky and Kondakov, Denis}, year={2010}, month={Sep}, pages={n/a-n/a} }
 @article{kim_song_chopra_de somer_so_2010, title={Organic Infrared Upconversion Device}, volume={22}, ISSN={0935-9648 1521-4095}, url={http://dx.doi.org/10.1002/adma.200903312}, DOI={10.1002/adma.200903312}, abstractNote={In addition to low efficiencies, inorganic orhybrid upconversion devices are expensive to fabricate forlarge-area applications.In recent years, both high-efficiency OLEDs and high-efficiency organic photodetectors have been demonstrated. Allorganic upconversion devices can be realized by integrating anOLED and an organic photodetector into one device. Because oftheir compatibility with lightweight, ruggedness, and flexibleplastic substrates, all organic upconversion devices open upmany applications that cannot be realized using conventionaltechnologies. Yase and co-workers reported that fluorescentOLEDs with titanyl phthalocyanine (TiOPc) as a photosensitivehole injection layer exhibited NIR-to-blue as well as red-to-greenupconversion.}, number={20}, journal={Advanced Materials}, publisher={Wiley}, author={Kim, Do Young and Song, Dong Woo and Chopra, Neetu and De Somer, Pieter and So, Franky}, year={2010}, month={May}, pages={2260–2263} }
 @article{sarasqueta_choudhury_subbiah_so_2010, title={Organic and Inorganic Blocking Layers for Solution-Processed Colloidal PbSe Nanocrystal Infrared Photodetectors}, volume={21}, ISSN={1616-301X}, url={http://dx.doi.org/10.1002/adfm.201001328}, DOI={10.1002/adfm.201001328}, abstractNote={Abstract}, number={1}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Sarasqueta, Galileo and Choudhury, Kaushik Roy and Subbiah, Jegadesan and So, Franky}, year={2010}, month={Nov}, pages={167–171} }
 @article{harding_poplavskyy_choong_so_campbell_2010, title={Variations in Hole Injection due to Fast and Slow Interfacial Traps in Polymer Light-Emitting Diodes with Interlayers}, volume={20}, ISSN={1616-301X 1616-3028}, url={http://dx.doi.org/10.1002/adfm.200900352}, DOI={10.1002/adfm.200900352}, abstractNote={Abstract}, number={1}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Harding, M. James and Poplavskyy, Dmitry and Choong, Vi-En and So, Franky and Campbell, Alasdair J.}, year={2010}, month={Jan}, pages={119–130} }
 @article{kim_so_gao_2009, title={Aluminum phthalocyanine chloride/C60 organic photovoltaic cells with high open-circuit voltages}, volume={93}, ISSN={0927-0248}, url={http://dx.doi.org/10.1016/j.solmat.2009.04.003}, DOI={10.1016/j.solmat.2009.04.003}, abstractNote={Small molecule organic planar and bulk heterojunction photovoltaic cells were fabricated using aluminum phthalocyanine chloride (AlPcCl) or copper phthalocyanine (CuPc) as a donor. While both AlPcCl and CuPc cells have similar short-circuit current, the power conversion efficiency of the AlPcCl cells is about 1.8 times higher than that of the CuPc cells because of the higher open-circuit voltage in the AlPcCl cells. The large open-circuit voltage is due to the large highest occupied molecular orbital (HOMO) energy of AlPcCl. The maximum power conversion efficiency is 2.0% under 1 sun standard AM1.5G solar illumination of 100 mW/cm2.}, number={9}, journal={Solar Energy Materials and Solar Cells}, publisher={Elsevier BV}, author={Kim, Do Young and So, Franky and Gao, Yongli}, year={2009}, month={Sep}, pages={1688–1691} }
 @article{polikarpov_swensen_chopra_so_padmaperuma_2009, title={An ambipolar phosphine oxide-based host for high power efficiency blue phosphorescent organic light emitting devices}, volume={94}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3148642}, DOI={10.1063/1.3148642}, abstractNote={We report blue electrophosphorescent organic light emitting devices with an ambipolar host material, 4-(diphenylphosphoryl)-N,N-diphenylaniline (HM-A1), doped with FIrpic (iridium (III)bis[(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate). The ambipolar nature of the host was verified using single carrier devices. The power efficiency of devices with PO15 (2,8-bis(diphenylphosphoryl)dibenzothiophene) electron transport layer (ETL) showed optimized performance when the ETL thickness was 500 Å, giving a peak power efficiency of 46 lm/W (corresponding external quantum efficiency (EQE) of 17.1%). The EQE and power efficiency at the brightness of 800 cd/m2 were measured with no light outcoupling enhancement and found to be 15.4% and 26 lm/W, respectively.}, number={22}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Polikarpov, Evgueni and Swensen, James S. and Chopra, Neetu and So, Franky and Padmaperuma, Asanga B.}, year={2009}, month={Jun}, pages={223304} }
 @article{eom_zheng_wrzesniewski_lee_chopra_so_xue_2009, title={Effect of electron injection and transport materials on efficiency of deep-blue phosphorescent organic light-emitting devices}, volume={10}, ISSN={1566-1199}, url={http://dx.doi.org/10.1016/j.orgel.2009.03.002}, DOI={10.1016/j.orgel.2009.03.002}, abstractNote={We investigate the performance of FIr6-based deep-blue phosphorescent organic light-emitting devices (PHOLEDs) with three different electron transport materials, bathocuproine (BCP), 4,7-diphenyl-1,10-phenanthroline (BPhen), and tris[3-(3-pyridyl)mesityl]borane (3TPYMB), and study the effect of doping alkaline metals (Li and Cs) into these charge transport materials. External quantum efficiency (ηEQE) of (20 ± 1)% and peak power efficiency (ηP) of (36 ± 2) lm/W were achieved maintaining Commission Internationale de L’Eclairage (CIE) coordinates of (x = 0.16, y = 0.28) in p-i-n dual-emissive-layer (D-EML) deep-blue PHOLEDs with 3TPYMB as the electron transport material and 3TPYMB:Cs as the electron injection layer. The high efficiencies are attributed to the high triplet energy of 3TPYMB as well as the increased conductivity of 3TPYMB:Cs.}, number={4}, journal={Organic Electronics}, publisher={Elsevier BV}, author={Eom, Sang-Hyun and Zheng, Ying and Wrzesniewski, Edward and Lee, Jaewon and Chopra, Neetu and So, Franky and Xue, Jiangeng}, year={2009}, month={Jul}, pages={686–691} }
 @article{chopra_lee_zheng_eom_xue_so_2009, title={Effect of the Charge Balance on High-Efficiency Blue-Phosphorescent Organic Light-Emitting Diodes}, volume={1}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/am900228b}, DOI={10.1021/am900228b}, abstractNote={The charge balance in blue-phosphorescent devices was studied using single-carrier devices, and the results show that the transport is highly hole dominant. The effect of the charge balance on the device performance was further demonstrated using different electron-transport materials with different electron mobilities. By optimization of the charge balance, a maximum current efficiency of 60 Cd A(-1) at a luminance of 500 cd m(-2) was achieved.}, number={6}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Chopra, Neetu and Lee, Jaewon and Zheng, Ying and Eom, Sang-Hyun and Xue, Jiangeng and So, Franky}, year={2009}, month={May}, pages={1169–1172} }
 @article{subbiah_beaujuge_choudhury_ellinger_reynolds_so_2009, title={Efficient Green Solar Cells via a Chemically Polymerizable Donor−Acceptor Heterocyclic Pentamer}, volume={1}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/am900116p}, DOI={10.1021/am900116p}, abstractNote={In this contribution, we report on bulk-heterojunction solar cells using a solution-processable neutral green conjugated copolymer based on 3,4-dioxythiophene and 2,1,3-benzothiadiazole as the donor and [6,6]phenyl-C61 butyric acid methyl ester (PCBM) as the acceptor. We have found that the short-circuit current is very sensitive to the composition of the donor-acceptor blend and it increases with increasing acceptor concentration. The device with a donor-acceptor ratio of 1:8 gives the best performance with a short-circuit current of 5.56 mA/cm(2), an open-circuit voltage of 0.77 V, and a power conversion efficiency of 1.9% under AM 1.5 solar illumination. The incident photon-to-current efficiency (IPCE) of the green solar cells shows two bands, one with a maximum of 57% in the UV region corresponding to absorption of PCBM and a second one with a maximum of 42% at longer wavelengths corresponding to the absorption of the green polymer.}, number={6}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Subbiah, Jegadesan and Beaujuge, Pierre M. and Choudhury, Kaushik Roy and Ellinger, Stefan and Reynolds, John R. and So, Franky}, year={2009}, month={May}, pages={1154–1158} }
 @article{ding_park_gao_kim_so_2009, title={Electronic structure and interactions of LiF doped tris (8-hydroxyquinoline) aluminum (Alq)}, volume={473}, ISSN={0009-2614}, url={http://dx.doi.org/10.1016/j.cplett.2009.03.065}, DOI={10.1016/j.cplett.2009.03.065}, abstractNote={The electronic structure of co-evaporated LiF and tris (8-hydroxyquinoline) aluminum (Alq) films with different weight ratios have been investigated with ultraviolet and X-ray photoemission spectroscopy (UPS and XPS). The results indicate that pristine LiF has only a small n-doping effect. However, Alq films doped with freshly crushed LiF powder source show a much larger shift in the frontier orbital, suggesting that the doping is most probably induced by defects, as such effect disappears after several evaporations. The interactions of the LiF doped Alq with metal overlayers have also been investigated. Al causes significant n-doping of Alq, while Au does not, due to its inertness and p-doping nature.}, number={1-3}, journal={Chemical Physics Letters}, publisher={Elsevier BV}, author={Ding, Huanjun and Park, Kiwan and Gao, Yongli and Kim, Do Young and So, Franky}, year={2009}, month={Apr}, pages={92–95} }
 @article{choudhury_lee_chopra_gupta_jiang_amy_so_2009, title={Highly Efficient Hole Injection Using Polymeric Anode Materials for Small-Molecule Organic Light-Emitting Diodes}, volume={19}, ISSN={1616-301X 1616-3028}, url={http://dx.doi.org/10.1002/adfm.200801368}, DOI={10.1002/adfm.200801368}, abstractNote={Abstract}, number={3}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Choudhury, Kaushik Roy and Lee, Jaewon and Chopra, Neetu and Gupta, Alok and Jiang, Xuezhong and Amy, Fabrice and So, Franky}, year={2009}, month={Feb}, pages={491–496} }
 @article{kim_sarasqueta_so_2009, title={SnPc:C60 bulk heterojunction organic photovoltaic cells with MoO3 interlayer}, volume={93}, ISSN={0927-0248}, url={http://dx.doi.org/10.1016/j.solmat.2009.03.011}, DOI={10.1016/j.solmat.2009.03.011}, abstractNote={Infrared sensitive small molecule organic photovoltaic cells were fabricated using a tin (II) phthalocyanine (SnPc) and C60 bulk heterojunction layer. Molybdenum oxide (MoO3) was used as an interlayer between the ITO anode and light absorbing layers. We found that the short-circuit current of the photovoltaic cells with MoO3 interlayer was substantially enhanced, resulting in a 45% enhancement in power conversion efficiency. The maximum power conversion efficiency is 1.31% under 1 sun standard AM1.5G solar illumination of 100 mW/cm2.}, number={8}, journal={Solar Energy Materials and Solar Cells}, publisher={Elsevier BV}, author={Kim, Do Young and Sarasqueta, Galileo and So, Franky}, year={2009}, month={Aug}, pages={1452–1456} }
 @article{kim_subbiah_sarasqueta_so_ding_irfan_gao_2009, title={The effect of molybdenum oxide interlayer on organic photovoltaic cells}, volume={95}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3220064}, DOI={10.1063/1.3220064}, abstractNote={Both small molecule and polymer photovoltaic cells were fabricated with molybdenum oxide interlayer at the indium tin oxide electrode. Enhancement in power efficiencies was observed in both small molecule and polymer cells. Specifically, the power conversion efficiencies of small molecule cells with the molybdenum oxide interlayer were enhanced by a maximum of 38% due to a significant enhancement in the fill factor. The improved fill factor is attributed to the reduction in series resistance. Our ultraviolet photoemission spectroscopy data indicate that the formation of band bending and the built-in field at the interface due to the interlayer leads to enhancement in hole extraction from the photoactive layer toward the anode.}, number={9}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Kim, Do Young and Subbiah, Jegadesan and Sarasqueta, Galileo and So, Franky and Ding, Huanjun and Irfan and Gao, Yongli}, year={2009}, month={Aug}, pages={093304} }
 @article{eom_zheng_wrzesniewski_lee_chopra_so_xue_2009, title={White phosphorescent organic light-emitting devices with dual triple-doped emissive layers}, volume={94}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3120276}, DOI={10.1063/1.3120276}, abstractNote={We demonstrate high efficiency white organic light-emitting devices with two adjacent emissive layers each doped with three phosphorescent emitters (blue, green, and red). Efficient charge and exciton confinement is realized by employing charge transport layers with high triplet energy, leading to a maximum external quantum efficiency of (19±1)%. Using the p-i-n device structure, we have achieved a peak power efficiency of (40±2) lm/W and (36±2) lm/W at 100 cd/m2, a color rendering index of 79, and Commission Internationale de L’Eclairage coordinates of (0.37, 0.40) for the white light emission.}, number={15}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Eom, Sang-Hyun and Zheng, Ying and Wrzesniewski, Edward and Lee, Jaewon and Chopra, Neetu and So, Franky and Xue, Jiangeng}, year={2009}, month={Apr}, pages={153303} }
 @article{liu_mccarthy_yoon_kim_wu_so_holloway_reynolds_guo_rinzler_2008, title={Carbon-Nanotube-Enabled Vertical Field Effect and Light-Emitting Transistors}, volume={20}, ISSN={0935-9648 1521-4095}, url={http://dx.doi.org/10.1002/adma.200800601}, DOI={10.1002/adma.200800601}, abstractNote={By experiment and supporting theory we demonstrate the facile modulation of the electronic contact-barrier across the junction between single wall carbon nanotubes (SWNTs) and two distinct organic semiconductors demonstrating a new realm of application for carbon nanotubes. We exploit this ability to enable two devices: a vertical field-effect transistor and a vertical light-emitting transistor. The vertical architecture, which is readily facilitated by the specific properties of the nanotubes, allows the use of low mobility semiconductors that would otherwise be considered unsuitable for field effect transistors, thereby expanding the range of potential active materials. For the light-emitting transistor the gate control should permit new pixel drive schemes and affords the potential for increased device lifetimes.}, number={19}, journal={Advanced Materials}, publisher={Wiley}, author={Liu, Bo and McCarthy, Mitchell A. and Yoon, Youngki and Kim, Do Young and Wu, Zhuangchun and So, Franky and Holloway, Paul H. and Reynolds, John R. and Guo, Jing and Rinzler, Andrew G.}, year={2008}, month={Oct}, pages={3605–3609} }
 @article{lee_chopra_so_2008, title={Cavity effects on light extraction in organic light emitting devices}, volume={92}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2830820}, DOI={10.1063/1.2830820}, abstractNote={We have demonstrated that the light extraction efficiency of an organic light emitting device is a strong function of device geometry. Specifically, we have found that the ratio of the extracted mode to the substrate-guided mode varies from 22% to 55% depending on the location of the recombination zone. Our simulation results also indicate that more light is trapped in the substrate as the optical length of device increases. We further show that the light intensity profile varies from a Lambertian shape to a non-Lambertian shape depending on the device geometry due to the cavity effect.}, number={3}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Lee, Jaewon and Chopra, Neetu and So, Franky}, year={2008}, month={Jan}, pages={033303} }
 @article{harding_poplavskyy_choong_campbell_so_2008, title={Effects of solution-processed polymer interlayers on hole injection and device performance of polymer light-emitting diodes}, volume={9}, ISSN={1566-1199}, url={http://dx.doi.org/10.1016/j.orgel.2007.09.003}, DOI={10.1016/j.orgel.2007.09.003}, abstractNote={We present studies of current density and photometric efficiency using three well known, commercially available polyphenylenevinylene and polyfluorene based light-emitting polymers (LEPs) with different interlayers. The thin, spin-coated interlayers of poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine) (TFB) and poly[9,9-dioctyl-fluorene-co-(bis-N,N′-(3-carboxyphenyl)-bis-N,N′-phenylbenzidine)] (BFA) are placed between the poly(3,4-ethylenedioxythiophene)/polystyrenesulphonic acid (PEDOT:PSS) anode and the LEP. It is found that despite having very similar HOMO levels (±0.1 eV) to the LEPs, the interlayers alter both the hole injection efficiency and the photometric efficiency of PLED devices. The increase or decrease of these depends on the particular interlayer-LEP combination involved, but there is a strong, general correlation between poorer hole injection resulting in a higher photometric efficiency. We attribute the variation in hole injection to the altered morphology and contact area at the anode interfaces, with the possible involvement of mobility-dependant space-charge effects or charge trapping. The dominant process in improving the photometric efficiency must be better electron-hole current balance, and/or the shift of the recombination zone to a more favourable position with less exciton quenching. The interlayers do not act as electron blocking layers, but hole injection enhancement by electron injection does seem to occur. These results show that interlayers can both increase and decrease device performance, depending on the interlayer-LEP combination involved.}, number={2}, journal={Organic Electronics}, publisher={Elsevier BV}, author={Harding, M. James and Poplavskyy, Dmitry and Choong, V.-E. and Campbell, Alasdair J. and So, Franky}, year={2008}, month={Apr}, pages={183–190} }
 @article{lee_chopra_eom_zheng_xue_so_shi_2008, title={Effects of triplet energies and transporting properties of carrier transporting materials on blue phosphorescent organic light emitting devices}, volume={93}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2978235}, DOI={10.1063/1.2978235}, abstractNote={We have studied the effects of the hole transporting layers and electron transporting layers on the device efficiencies of iridium(III) bis[(4,6-di-fluorophenyl)-pyridinato-N,C2′] picolinate (FIrpic) doped 3,5′−N,N′-dicarbazole-benzene (mCP) host blue phosphorescent organic light emitting diodes. We found that the device efficiency is very sensitive to the hole transporting materials used and both the triplet energy and carrier transport properties affect the device efficiency. On the other hand, there is no apparent correlation between the device efficiency and the triplet energy of the electron transporting material used. Instead, the device efficiency is affected by the electron mobility of the electron transporting layer only.}, number={12}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Lee, Jaewon and Chopra, Neetu and Eom, Sang-Hyun and Zheng, Ying and Xue, Jiangeng and So, Franky and Shi, Jianmin}, year={2008}, month={Sep}, pages={123306} }
 @article{zheng_eom_chopra_lee_so_xue_2008, title={Efficient deep-blue phosphorescent organic light-emitting device with improved electron and exciton confinement}, volume={92}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2937403}, DOI={10.1063/1.2937403}, abstractNote={We report a significant improvement in the efficiency of deep-blue phosphorescent organic light-emitting devices based on the electrophosphorescent dye bis(4′,6′-difluorophenylpyridinato)tetrakis (1-pyrazolyl) borate (FIr6). Using 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) as the hole transport layer (HTL), we achieved a maximum external quantum efficiency of ηEQE=(18±1)%, which is approximately 50% higher than ηEQE=12% in a previously reported device with bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl as the HTL. The maximum luminous power efficiency was also improved from (14±1)lm∕W to (18±1)lm∕W. We attribute this efficiency improvement to the enhanced electron and exciton confinement provided by TAPC.}, number={22}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Zheng, Ying and Eom, Sang-Hyun and Chopra, Neetu and Lee, Jaewon and So, Franky and Xue, Jiangeng}, year={2008}, month={Jun}, pages={223301} }
 @article{chopra_lee_zheng_eom_xue_so_2008, title={High efficiency blue phosphorescent organic light-emitting device}, volume={93}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3000382}, DOI={10.1063/1.3000382}, abstractNote={We have demonstrated a substantial enhancement in the efficiency of iridium (III) bis[(4,6-di-fluorophenyl)-pyridinate-N,C2′]picolinate based blue phosphorescent organic light-emitting devices (PHOLEDs). The efficiencies of PHOLEDs with conventional electron transport materials are low due to their low electron mobilities as well low triplet energies. High triplet energy electron transporting material with high electron mobility was used as a hole blocker to achieve efficient exciton confinement and good charge balance in the device thereby achieving a high current efficiency of 49cd∕A and an external quantum efficiency of 23%.}, number={14}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Chopra, Neetu and Lee, Jaewon and Zheng, Ying and Eom, Sang-Hyun and Xue, Jiangeng and So, Franky}, year={2008}, month={Oct}, pages={143307} }
 @article{choudhury_yoon_so_2008, title={LiF as an n-Dopant in Tris(8-hydroxyquinoline) Aluminum Thin Films}, volume={20}, ISSN={0935-9648 1521-4095}, url={http://dx.doi.org/10.1002/adma.200701657}, DOI={10.1002/adma.200701657}, abstractNote={Owing to their ease of processing and potential for inexpensive fabrication on low-cost substrates, organic semiconductors have emerged as a novel class of materials for next-generation electronic and optoelectronic devices. The field of organic electronics has generated intense research efforts, spurred on by the promise of a viable alternative to the inorganic materials platform, especially for large-area, flexible electronics applications. Significant progress has been demonstrated towards the realization of efficient organic lightemitting diodes (OLEDs) for flat-panel displays and lighting, thin-film field-effect transistors (TFTs), photodetectors for large-area detector arrays, and organic photovoltaic cells for low-cost solar energy generation. In all of these organic device embodiments, optimization of charge injection/extraction and carrier transport is critically important towards their technological success. Efficient injection or extraction requires low energetic barriers while competent transport demands highly conductive transport layers. Organic semiconductors have low carrier concentration and low carrier mobility. Because of these properties, operating voltages of organic devices are generally higher than their inorganic counterparts. Voltage drop in organic transport layers has typically been minimized by using extremely thin structures, which are inevitably more vulnerable to shorts and therefore detrimental to device stability. In addition, because of the low carrier concentration, carrier transport in this class of materials is space charge limited. Similar to inorganic semiconductors, electrical doping can be an approach to enhance the carrier transport, resulting in enhanced device performance. Specifically, doping in organic semiconductors has been employed in organic light-emitting diodes and promised to be an effective way to lower the device operating voltages. To dope organic semiconductors, typically electron acceptors such as F4-TCNQ are used as p-dopants [10] and electron donors such as alkaline metals are used as n-dopants. While reduced drive voltage and increased brightness have been observed in OLED devices by electrical doping, n-dopants are particularly problematic because of}, number={8}, journal={Advanced Materials}, publisher={Wiley}, author={Choudhury, Kaushik Roy and Yoon, Jong-hyuk and So, Franky}, year={2008}, month={Apr}, pages={1456–1461} }
 @article{eom_zheng_chopra_lee_so_xue_2008, title={Low voltage and very high efficiency deep-blue phosphorescent organic light-emitting devices}, volume={93}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2996274}, DOI={10.1063/1.2996274}, abstractNote={We report on very high efficiency deep-blue phosphorescent organic light-emitting devices (PHOLEDs) based on iridium(III) bis(4′,6′-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate (FIr6). Dual emissive layers consisting of an N,N′-dicarbazolyl-3,5-benzene layer doped with 4wt% FIr6 and a p-bis(triphenylsilyly)benzene layer doped with 25wt% FIr6 were employed to maximize exciton generation on FIr6 molecules. Combined with the p-i-n device structure, we achieved a low turn-on voltage of 3.2V and very high power efficiencies of 25±2lm∕W at 100cd∕m2 and 20±2lm∕W at 1000cd∕m2 for such deep-blue PHOLEDs with peak emission at a wavelength of 458nm.}, number={13}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Eom, Sang-Hyun and Zheng, Ying and Chopra, Neetu and Lee, Jaewon and So, Franky and Xue, Jiangeng}, year={2008}, month={Sep}, pages={133309} }
 @article{sarasqueta_roy choudhury_kim_so_2008, title={Organic/inorganic nanocomposites for high-dielectric-constant materials}, volume={93}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2963193}, DOI={10.1063/1.2963193}, abstractNote={A different approach to fabricate metallic nanostructures in an insulating organic matrix in situ using thermal coevaporation is demonstrated. The method is used to fabricate metal-organic percolative nanocomposite capacitors. Thermal annealing of the nanocomposite films results in a dramatic enhancement (>50 times at 10kHz) of the dielectric constant accompanied by significant lowering (approximately four times) of conductivity and dissipation loss, especially at low frequencies. The improved performance is attributed to structural modifications in the films resulting from enhanced phase segregation of constituents, induced by annealing at optimized temperatures.}, number={12}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Sarasqueta, Galileo and Roy Choudhury, Kaushik and Kim, Do Young and So, Franky}, year={2008}, month={Sep}, pages={123305} }
 @article{niemeyer_campbell_so_crone_2007, title={High quantum efficiency polymer photoconductors using interdigitated electrodes}, volume={91}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2779102}, DOI={10.1063/1.2779102}, abstractNote={In this letter the authors investigate photoconductivity in interdigitated lateral photoconductors with aluminum contacts, and a poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene]/ {6}-1-(3-(methoxycarbonyl)propyl)-{5}-1-phenyl-[6,6]-C61 blend as the active layer. They demonstrate quantum efficiencies over 70% in 5μm devices. The quantum efficiency spectra follow the absorbance spectra and are not corrected for incomplete absorption of the films. The quantum efficiency is a monotonically increasing function of applied field. The field dependence can be explained with a modified Onsager model for charge dissociation.}, number={10}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Niemeyer, A. C. and Campbell, I. H. and So, F. and Crone, B. K.}, year={2007}, month={Sep}, pages={103504} }
 @article{so_krummacher_mathai_poplavskyy_choulis_choong_2007, title={Recent progress in solution processable organic light emitting devices}, volume={102}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2804122}, DOI={10.1063/1.2804122}, abstractNote={Organic light emitting devices (OLEDs) have been the subject of intense research because of their potential for flat panel display and solid state lighting applications. While small molecule OLEDs with very high efficiencies have been demonstrated, solution processable devices are more desirable for large size flat panel display and solid state applications because they are compatible with low cost, large area roll-to-roll manufacturing process. In this review paper, we will present the recent progress made in solution processable OLEDs. The paper will be divided into three parts. In the first part of the paper, we will focus on the recent development of fluorescent polymer OLEDs based on conjugated polyfluorene copolymers. Specifically, we will present results of carrier transport and injection measurements, and discuss how the charge transport and injection properties affect the device performance. In the second part of the paper, we will focus on the recent progress on phosphorescent dye-dispersed nonconjugated polymer OLEDs. Specifically, we will present our recent results on high efficiency green and blue emitting devices based on the dye-dispersed polymer approach. Similar to fluorescent conjugated polymer OLEDs, charge transport and injection properties in dye-dispersed polymer OLEDs also play an important role in the device performance. In the third part of this paper, we will present our results on white emitting phosphorescent OLEDs. Two approaches have been used to demonstrate white emitting OLEDs. First, white emitting OLEDs were made using blue emitting OLEDs with downconversion phosphors. Second, white emitting OLEDs were made by dispersing red, green, and blue phosphorescent dyes into the light emitting layer. High efficiency devices have been demonstrated with both approaches.}, number={9}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={So, Franky and Krummacher, Benjamin and Mathai, Mathew K. and Poplavskyy, Dmitry and Choulis, Stelios A. and Choong, Vi-En}, year={2007}, month={Nov}, pages={091101} }
 @article{poplavskyy_so_2006, title={Bipolar carrier transport in a conjugated polymer by complex admittance spectroscopy}, volume={99}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2149495}, DOI={10.1063/1.2149495}, abstractNote={We report the bipolar transport properties of the LUMATION™ (Sumitomo Chemical) 1300 Series green-emitting polymer investigated by means of admittance spectroscopy. Analysis of the inductive response in single-carrier polymer diodes yields electron and hole mobilities which are in excellent agreement with the results of independent measurements. Admittance measurements in dual injection diodes, in combination with the analysis of current-voltage characteristics, provide evidence that the dual injection diodes operate in space-charge-limited regime, indicative of strong recombination within the material. Our results provide strong evidence that the space-charge-related admittance response of dual-carrier diodes is dominated by combined electron-hole response, which corresponds to the sum of electron and hole mobilities. This implies that electron and hole mobilities cannot be obtained separately from admittance measurements in space-charge-limited dual-carrier devices.}, number={3}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Poplavskyy, Dmitry and So, Franky}, year={2006}, month={Feb}, pages={033707} }
 @article{krummacher_mathai_choong_choulis_so_winnacker_2006, title={General method to evaluate substrate surface modification techniques for light extraction enhancement of organic light emitting diodes}, volume={100}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2234550}, DOI={10.1063/1.2234550}, abstractNote={The external light output of organic light emitting diodes (OLEDs) can be increased by modifying the light emitting surface. The apparent light extraction enhancement is given by the ratio between the efficiency of the unmodified device and the efficiency of the modified device. This apparent light extraction enhancement is dependent on the OLED architecture itself and is not the correct value to judge the effectiveness of a technique to enhance light outcoupling due to substrate surface modification. We propose a general method to evaluate substrate surface modification techniques for light extraction enhancement of OLEDs independent from the device architecture. This method is experimentally demonstrated using green electrophosphorescent OLEDs with different device architectures. The substrate surface of these OLEDs was modified by applying a prismatic film to increase light outcoupling from the device stack. It was demonstrated that the conventionally measured apparent light extraction enhancement by means of the prismatic film does not reflect the actual performance of the light outcoupling technique. Rather, by comparing the light extracted out of the prismatic film to that generated in the OLED layers and coupled into the substrate (before the substrate/air interface), a more accurate evaluation of light outcoupling enhancement can be achieved. Furthermore we show that substrate surface modification can change the output spectrum of a broad band emitting OLED.}, number={5}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Krummacher, B. C. and Mathai, M. K. and Choong, V. and Choulis, S. A. and So, F. and Winnacker, A.}, year={2006}, month={Sep}, pages={054702} }
 @article{choulis_mathai_choong_so_2006, title={Highly efficient organic electroluminescent device with modified cathode}, volume={88}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2204840}, DOI={10.1063/1.2204840}, abstractNote={One of the key parameters for high efficiency organic electrophosphorescent light emitting diodes is charge injection into the phosphorescence compound. By introducing a hybrid device architecture, and incorporating electron and hole interfacial layers with lowest unoccupied molecular orbital and highest occupied molecular orbital levels similar to that of the phosphorescence compound, on the cathode and the anode side of the device, respectively, charge injection properties were improved. A green electrophosphorescence device with luminous efficacy of 50lm∕W at luminance efficiency reaching 55cd∕A was demonstrated.}, number={20}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Choulis, Stelios A. and Mathai, Mathew K. and Choong, Vi-En and So, Franky}, year={2006}, month={May}, pages={203502} }
 @article{mathai_choong_choulis_krummacher_so_2006, title={Highly efficient solution processed blue organic electrophosphorescence with 14lm∕W luminous efficacy}, volume={88}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2212060}, DOI={10.1063/1.2212060}, abstractNote={We report highly efficient solution processed blue electrophosphorescent organic light emitting diodes (PHOLEDs) utilizing a phosphorescent dye and a nonconjugated polymer host, molecularly doped with electron transporting molecules. Based on a bilayer device architecture blue PHOLEDs with luminous efficacy of 14lm∕W at luminous efficiency reaching 22cd∕A are demonstrated. Analysis of device performance indicates that this high efficiency is achieved by a combination of improved charge balance and light outcoupling efficiency. Our results demonstrate that simple solution processed devices can have efficiencies similar to those published to date for small molecule multilayer PHOLEDs based on the same emitter.}, number={24}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Mathai, Mathew K. and Choong, Vi-En and Choulis, Stelios A. and Krummacher, Benjamin and So, Franky}, year={2006}, month={Jun}, pages={243512} }
 @article{krummacher_choong_mathai_choulis_so_jermann_fiedler_zachau_2006, title={Highly efficient white organic light-emitting diode}, volume={88}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2186080}, DOI={10.1063/1.2186080}, abstractNote={We present a highly efficient white electroluminescence device by the combination of a solution processed blue organic phosphorescence light-emitting diode with appropriate down-conversion phosphor system. The use of this down-conversion system produced an extraordinary enhancement on device performance, resulting in a white electroluminescence device with luminance efficacy of 25lm∕W at luminance efficiency reaching 39cd∕A. The extraordinary enhancement on device performance is attributed to isotropic radiation pattern of the excited phosphor particles, leading to high light extraction properties.}, number={11}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Krummacher, Benjamin C. and Choong, Vi-En and Mathai, Mathew K. and Choulis, Stelios A. and So, Franky and Jermann, Frank and Fiedler, Tim and Zachau, M.}, year={2006}, month={Mar}, pages={113506} }
 @article{krummacher_mathai_choong_choulis_so_winnacker_2006, title={Influence of charge balance and microcavity effects on resultant efficiency of organic-light emitting devices}, volume={7}, ISSN={1566-1199}, url={http://dx.doi.org/10.1016/j.orgel.2006.03.011}, DOI={10.1016/j.orgel.2006.03.011}, abstractNote={The contribution of charge balance and optical microcavity effects in solution processed OLEDs cannot be easily quantified due to the absence of a well defined location for the emission zone. In this paper, we study the device efficiency of a solution processed blue electrophosphorescent OLED where the relative electron–hole balance is varied by means of molecular doping with an electron transport material. Changes in the electroluminescent spectra for the device series indicate the presence of optical microcavity effects, which we quantify by means of optical simulation. Furthermore, this enables us to factor out the contribution of microcavity effects on device efficiency enabling the quantification of the charge balance effect on device performance.}, number={5}, journal={Organic Electronics}, publisher={Elsevier BV}, author={Krummacher, Benjamin and Mathai, Mathew K. and Choong, Vi-En and Choulis, Stelios A. and So, Franky and Winnacker, Albrecht}, year={2006}, month={Oct}, pages={313–318} }
 @article{choulis_choong_patwardhan_mathai_so_2006, title={Interface Modification to Improve Hole-Injection Properties in Organic Electronic Devices}, volume={16}, ISSN={1616-301X 1616-3028}, url={http://dx.doi.org/10.1002/adfm.200500443}, DOI={10.1002/adfm.200500443}, abstractNote={Abstract}, number={8}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Choulis, S. A. and Choong, V.-E. and Patwardhan, A. and Mathai, M. K. and So, F.}, year={2006}, month={May}, pages={1075–1080} }
 @article{poplavskyy_su_so_2005, title={Bipolar charge transport, injection, and trapping studies in a model green-emitting polyfluorene copolymer}, volume={98}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.1941482}, DOI={10.1063/1.1941482}, abstractNote={Experimental studies of charge injection and transport of holes and electrons in LUMATION™ Green 1300 Series light-emitting polymer (LEP) by a combination of experimental techniques are reported. It is found that hole mobility is lower than electron mobility and the former exhibits steeper electric-field dependence thus reducing the misbalance between charge mobilities at higher device operating voltages. An approach to quantitatively analyze charge injection and trapping in organic semiconductors is proposed. Based on our analysis, hole current is limited by injection from the anode and trapping in the bulk of the polymer. Further, we found that hole trapping is approximately independent of electric field and injection efficiency increases with increasing electric field. Injection limitation of holes from poly(3,4-ethylenedioxythiophene)/polystyrenesulphonic acid (PEDOT:PSS) electrode is believed to be the result of nonuniform contact between the PEDOT:PSS and LEP rather than the energy barrier. On the other hand, electron injection is close to ohmic and the steady-state electron current is affected by trapping, mainly due to deep traps prevailing at low electric fields and with an estimated concentration of 1016cm−3. Electron trapping is found to be significantly reduced in dual-carrier devices, which is believed to be the effect of faster exciton formation and recombination rates, compared to electron trapping processes.}, number={1}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Poplavskyy, Dmitry and Su, Wencheng and So, Franky}, year={2005}, month={Jul}, pages={014501} }
 @article{choulis_choong_mathai_so_2005, title={The effect of interfacial layer on the performance of organic light-emitting diodes}, volume={87}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2042635}, DOI={10.1063/1.2042635}, abstractNote={We demonstrate high efficiency organic light-emitting devices by incorporation of a nanoscale interfacial layer between a hole-conducting layer (PEDOT:PSS) and a light-emitting polymer layer (LEP) to improve hole injection. The interfacial layer has appropriate highest occupied molecular orbital level in order to act as a bridge for efficient hole injection from the PEDOT:PSS into the LEP. As an example we have incorporated a suitable interfacial layer into a green-emitting single-layer electrophosphorescent light-emitting diode. Devices with the interfacial layer show a peak efficiency of 41lm∕W, an improvement of more than 25% in their performance over comparable devices without the interfacial layer. The results presented here introduce a novel method to improve hole injection and thus efficiency in organic electroluminescent devices.}, number={11}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Choulis, Stelios A. and Choong, Vi-En and Mathai, Mathew K. and So, Franky}, year={2005}, month={Sep}, pages={113503} }