@article{dong_lee_song_neu_kashani_you_ade_2025, title={Control Over Vertical Composition in Low Complexity Polymer Solar Cells}, volume={1}, ISSN={["1614-6840"]}, url={https://doi.org/10.1002/aenm.202404962}, DOI={10.1002/aenm.202404962}, abstractNote={Abstract Inverted organic solar cells are promising due to their better stability compared to conventional structures. Donors with low synthetic complexity are desirable to lower costs. However, inverted devices are rarely used in low‐complexity systems. To investigate the reasons, the low‐complexity PTQ10:BTP‐eC9 binary system is benchmarked against the high‐complexity PM6:BTP‐eC9 system. In PTQ10:BTP‐eC9, where the efficiency of inverted devices lags the conventional structure significantly, distinct wetting layers are observed in conventional and inverted device structures. Conversely, the vertical distribution of PM6:BTP‐eC9 remains unaffected by changes in interlayer materials. The surface is always enriched in BTP‐eC9, but less for PM6. Importantly, the addition of PC 71 BM reduces the nonuniform vertical composition gradients. As the PC 71 BM concentration increases, the efficiency of the inverted PTQ10 devices approach that of the conventional devices and PTQ10:BTP‐eC9:PC 71 BM (1:1.2:0.4) exhibits negligible efficiency differences between inverted (14.01%) and conventional (14.49%) architectures. The concentration‐gradients aredriven by the interfacial energy between the active layer and interlayer materials and the casting kinetics in the case of the surface. Understanding the thermodynamic and kinetic aspects provides valuable insights for optimizing the performance of inverted organic solar cells, bringing them closer to practical applications.}, journal={ADVANCED ENERGY MATERIALS}, author={Dong, Xinyun and Lee, Byongkyu and Song, Runqiao and Neu, Justin and Kashani, Somayeh and You, Wei and Ade, Harald}, year={2025}, month={Jan} }
 @article{shanahan_yan_olanrewaju_kashani_ade_so_you_2024, title={Acid-Triggered Side Chain Cleavage Leads to Doped Conjugated Polymers of High Conductivity}, volume={10}, ISSN={["1520-5126"]}, DOI={10.1021/jacs.4c09843}, abstractNote={Cleavable side chain based conjugated polymers (CSCPs) represent a unique approach to offering solution processability with added benefits via the elimination of insulating side chains. This work highlights an optimally designed polythiophene-carboxylic acid based CSCP, POET-T2-COOH, which achieves a conductivity exceeding 350 S/cm in molecularly doped and side chain cleaved films, 100-100,000 times higher than three other structurally isomeric CSCPs. The high conductivity of POET-T2-COOH is accomplished via a new "cleavage with doping" methodology, synergistically combining a strong acid and a primary dopant. This hybrid method achieves the greatest conductivity in all isomeric CSCPs over conventional doping or cleavage techniques. The doped and side chain cleaved POET-T2-COOH displays a stable conductivity in inert atmospheres and a high work function of 5.3 eV, opening up new applications.}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Shanahan, Jordan and Yan, Liang and Olanrewaju, Yusuf and Kashani, Somayeh and Ade, Harald and So, Franky and You, Wei}, year={2024}, month={Oct} }
 @article{schrickx_kashani_buck_ding_rech_flagg_li_kudenov_you_richter_et al._2024, title={Exceptional Alignment in a Donor-Acceptor Conjugated Polymer via a Previously Unobserved Liquid Crystal Mesophase}, volume={4}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.202315183}, abstractNote={Abstract Orienting polymer semiconductors is desirable to optimize device characteristics, provide insight into microstructure, and magnify subtle phase behavior. Here, a combination of uniaxial strain and subsequent heating of the donor–acceptor (DA) polymer PBnDT‐FTAZ is discovered to lead to exceptional optical dichroic ratios of up to 38 (and close to 50 near the polymer's absorption edge). This alignment is achieved due to the existence of a previously undetected thermotropic liquid crystal (LC) mesophase. The LC transition, not discernable through calorimetry, is uncovered through a combination of in situ UV–vis spectroscopy, X‐ray scattering, and dynamic mechanical analysis (DMA). Comparing PBnDT‐FTAZ to the non‐fluorinated PBnDT‐HTAZ and the homo polymer PBnDT, all of which show similar thermal transitions, reveals that exceptional alignment is only found in PBnDT‐FTAZ. This is attributed to the PBnDT‐FTAZ film having two distinct liquid crystal populations, and the polymer templating to a highly aligned, high‐clearing temperature population when heated. The DMA thermal relaxation behavior observed here is also seen in other DA conjugated polymers suggesting that such thermotropic LC mesophases may be common in these materials. These findings demonstrate a polymer semiconductor with remarkable alignment and uncover phase behavior with broad implications for process‐structure‐property relationships in polymer semiconductors.}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Schrickx, Harry M. and Kashani, Somayeh and Buck, Lauren and Ding, Kan and Rech, Jeromy J. and Flagg, Lucas Q. and Li, Ruipeng and Kudenov, Michael W. and You, Wei and Richter, Lee J. and et al.}, year={2024}, month={Apr} }
 @article{kwon_giridharagopal_neu_kashani_chen_quezada_guo_ade_you_ginger_2024, title={Quantifying Doping Efficiency to Probe the Effects of Nanoscale Morphology and Solvent Swelling in Molecular Doping of Conjugated Polymers}, volume={2}, ISSN={["1932-7455"]}, DOI={10.1021/acs.jpcc.4c00153}, abstractNote={We study the doping of conjugated polymers from droplets of molecular dopant solutions, as might be used in additive manufacturing approaches. We compare the doping efficiency of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) solutions between two model conjugated polymers, regioregular poly(3-hexylthiophene) (P3HT) and poly(bithiophene-thienothiophene) copolymer with a triethylene glycol side chain (P(g32T-TT)). We find that F4TCNQ dopes P(g32T-TT) more efficiently from solution, producing films with >103 times higher conductivity. Using spectroelectrochemistry to calibrate polaron spectra to known hole injection levels, we quantify the doping efficiency (polarons created/dopant molecule added) to be higher than 170% for P(g32T-TT) but only 47.2% for P3HT. We further explore the differences in molecular doping using a combination of scanning Kelvin probe microscopy (SKPM) and conductive atomic force microscopy (cAFM). We explore doping efficiency and aggregation as a function of the solvent of the dopant solution, side chain, and regioregularity of conjugated polymers; we show that the doping efficiency and dopant aggregation are both correlated with the ability of the dopant/solvent solution to swell the conjugated polymer, with combinations that swell, resulting in more efficient doping and smoother films with less aggregation.}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Kwon, Sung-Joo and Giridharagopal, Rajiv and Neu, Justin and Kashani, Somayeh and Chen, Shinya E. and Quezada, Ramsess J. and Guo, Jiajie and Ade, Harald and You, Wei and Ginger, David S.}, year={2024}, month={Feb} }
 @article{ghaffari_kashani_do_weninger_riehn_2023, title={A nanophotonic interferometer}, volume={34}, ISSN={["1361-6528"]}, url={https://doi.org/10.1088/1361-6528/acb443}, DOI={10.1088/1361-6528/acb443}, abstractNote={The transmission of light through sub-wavelength apertures (zero-mode waveguides, ZMW) in metal films is well-explored. It introduces both an amplitude modulation as well as a phase shift to the oscillating electromagnetic field. We propose a nanophotonic interferometer by bringing two ZMW (∼100 nm diameter) in proximity and monitoring the distribution of transmitted light in the back-focal plane of collecting microscope objective (1.3 N.A.). We demonstrate that both an asymmetry induced by the binding of a quantum dot in one of the two ZMW, as well as an asymmetry in ZMW diameter yield qualitatively similar transmission patterns. We find that the complex pattern can be quantified through a scalar measure of asymmetry along the symmetry axis of the aperture pair. In a combined experimental and computational exploration of detectors with differing ZMW diameters, we find that the scalar asymmetry is a monotonous function of the diameter difference of the two apertures, and that the scalar asymmetry measure is higher if the sample is slightly displaced from the focal plane of the collecting microscope objective. An optimization of the detector geometry determined that the maximum response is achieved at an aperture separation that is comparable to the wavelength on the exit side of the sensor. For small separations of apertures, on the order of a quarter of the wavelength and less, the signal is strongly polarization dependent, while for larger separations, on the order of the wavelength or larger, the signal becomes essentially polarization-independent.}, number={18}, journal={NANOTECHNOLOGY}, author={Ghaffari, Abbas and Kashani, Somayeh and Do, Kevin and Weninger, Keith and Riehn, Robert}, year={2023}, month={Apr} }
 @article{kashani_rech_liu_baustert_ghaffari_angunawela_xiong_dinku_you_graham_et al._2023, title={Exciton Binding Energy in Organic Polymers: Experimental Considerations and Tuning Prospects}, volume={12}, ISSN={["1614-6840"]}, DOI={10.1002/aenm.202302837}, abstractNote={Abstract Discrepancies in reported values of exciton binding energy (E b ) for organic semiconductors (OSs) necessitate a comprehensive study. Traditionally, E b is defined as the difference between the transport gap (E t ) and the optical gap (E opt ). Here, the E b values of PBnDT‐TAZ polymer variants are determined using two commonly employed methods: a combination of ultraviolet photoemission spectroscopy and low‐energy inverse photoemission spectroscopy (UPS‐LEIPS) and solid‐state cyclic voltammetry (CV). E b values obtained by UPS‐LEIPS show low dispersion and no clear correlation with the polymer structure and thedielectric properties. In contrast, CV reveals a larger dispersion (200 meV‐1 eV) and an apparent qualitative E b ‐molecular structure correlation, as the lowest E b values are observed for oligo‐ethylene glycol side chains. This discrepancy is discussed by examining the implications of the traditional definition of E b . Additionally, the impact of both intrinsic and extrinsic factors contributing to the derived experimental values of E t is discussed. The differences in intrinsic and extrinsic factors highlight the context‐dependent nature of measurement when drawing global conclusions. Notably, the observed E b trend derived from CV is not intrinsic to the pure materials but likely linked to electrolyte swelling and associated changes in dielectric environment, suggesting that high‐efficiency single‐material organic photovoltaics with low E b may be possible via high dielectric materials.}, journal={ADVANCED ENERGY MATERIALS}, author={Kashani, Somayeh and Rech, Jeromy James and Liu, Tuo and Baustert, Kyle and Ghaffari, Abbas and Angunawela, Indunil and Xiong, Yuan and Dinku, Abay and You, Wei and Graham, Kenneth and et al.}, year={2023}, month={Dec} }
 @article{ghaffari_do_kashani_weninger_riehn_2022, title={A Nanophotonic Interferometer for small particle detection}, volume={12223}, ISBN={["978-1-5106-5430-3"]}, ISSN={["1996-756X"]}, DOI={10.1117/12.2634318}, abstractNote={The transmission of light through sub-wavelength apertures (zero-mode waveguides, ZMW) in metal films is wellexplored. It introduces both an amplitude modulation as well as a phase shift to the transmitted oscillating electromagnetic field. We propose a nanophotonic interferometer by bringing two zero-mode waveguides in proximity and monitoring the distribution of light in the back-focal plane of the collecting microscope objective. We demonstrate that both an asymmetry induced by the binding of a quantum dot in one of the two ZMW, as well as a asymmetry in ZMW diameter yield qualitatively similar deflection patterns. Using ZMW pairs with diameter asymmetries, we find that the complex pattern of the transmitted light can be quantified through a scalar measure of asymmetry along the symmetry axis of the aperture pair. We find that this scalar asymmetry is a monotonous function of the diameter difference of the two apertures.}, journal={INTERFEROMETRY XXI}, author={Ghaffari, A. and Do, K. and Kashani, S. and Weninger, K. and Riehn, Robert}, year={2022} }
 @article{kashani_wang_risko_ade_2022, title={Relating reorganization energies, exciton diffusion length and non-radiative recombination to the room temperature UV-vis absorption spectra of NF-SMA}, volume={12}, ISSN={["2051-6355"]}, url={https://doi.org/10.1039/D2MH01228F}, DOI={10.1039/d2mh01228f}, abstractNote={Understanding excited-state reorganization energies, exciton diffusion lengths and non-radiative (NR) recombination, and the overall optoelectronic responses of nonfullerene small molecule acceptors (NF-SMAs) is important in order to rationally design new materials with controlled properties. While the effects of structural modifications on the optical gaps and electron affinities of NF-SMAs have been studied extensively, analyses of their absorption spectra that carefully characterize electronic and vibrational contributions that allow comparisons of reorganization energies and their implications for exciton diffusion lengths and NR recombination have yet to be reported. Here, we study the room temperature absorption spectra of three structural classes of NF-SMAs in dilute solutions through multiparameter Franck Condon (MFC) analyses and density functional theory (DFT) calculations. We show that the absorption spectra of these NF-SMAs can be categorized based on molecular structure-spectra correlation. The absorption spectra of curved, Y6-like structures can be described using an MFC model with two electronic transitions and two effective vibrational modes. The results of MFC/DFT analyses reveal that Y6 exhibits the smallest intra-molecular reorganization energy among the materials studied. Linear ITIC-like molecular structures reveal larger reorganization energies and reduced conformational uniformity compared to Y6. Meanwhile structures such as IDTBR and IEICO, which have an extra π-conjugated moiety between the donor and acceptor moieties, have large excited-state reorganization energies and low degrees of conformational uniformity. Since the intra-molecular reorganization energy is correlated with exciton diffusion length and nonradiative voltage losses (ΔVnr), our results highlight the power of RT absorption spectroscopy and DFT calculations as simple tools to designing improved OSCs materials with small reorganization energies, small ΔVnr, large exciton diffusion length and low energetic disorder (due to a strongly dominant conformation).}, journal={MATERIALS HORIZONS}, author={Kashani, Somayeh and Wang, Zhen and Risko, Chad and Ade, Harald}, year={2022}, month={Dec} }
 @article{steckmann_angunawela_kashani_zhu_nahid_ade_gadisa_2022, title={Ultrathin P(NDI2OD-T2) Films with High Electron Mobility in Both Bottom-Gate and Top-Gate Transistors}, volume={3}, ISSN={["2199-160X"]}, url={https://doi.org/10.1002/aelm.202101324}, DOI={10.1002/aelm.202101324}, abstractNote={Abstract Ultrathin organic films (typically < 10 nm) attracted great attention due to their (semi)transparency and unique optoelectronic properties that benefit applications such as sensors and flexible electronics. At the core of that, achieving high mobility in an ultrathin film is essential for the efficient operation of relevant electronic devices. While the state‐of‐the‐art material systems, e.g., P(NDI2OD‐T2) also known as N2200 can achieve high mobility in a thin film (typically > 20 nm), multitudinous challenges remain in processing an ultrathin film exhibiting desired charge transport morphology within a preferred thickness limit. Here, high electron mobility (a tenfold increase compared to annealed spin‐coated films) is reported in both the top and bottom‐gate configuration organic field‐effect transistors comprising ultrathin N2200 films produced with a water‐floating film transfer method. A range of characterization techniques are used to investigate these ultrathin films and their microstructure, and conclude that favorable edge‐on polymer orientation at the top as well as throughout the ultrathin film thickness and the quality of π–π ordering as captured by the largest coherences length resulted in this high mobility in N2200 ultrathin films, in stark contrast to the commonly observed microstructural gradient in spin‐coated thin films. The results provide new insight into the electronic and microstructural properties of thin films of organic semiconductors.}, journal={ADVANCED ELECTRONIC MATERIALS}, author={Steckmann, Thomas and Angunawela, Indunil and Kashani, Somayeh and Zhu, Youqin and Nahid, Masrur M. and Ade, Harald and Gadisa, Abay}, year={2022}, month={Mar} }
 @article{king_melville_rice_kashani_tonnele_raboui_swaraj_grant_mcafee_bender_et al._2021, title={Silicon Phthalocyanines for n-Type Organic Thin-Film Transistors: Development of Structure-Property Relationships}, volume={3}, ISSN={["2637-6113"]}, DOI={10.1021/acsaelm.0c00871}, abstractNote={Silicon phthalocyanines (SiPcs) have shown great potential as n-type or ambipolar organic semiconductors in organic thin-film transistors (OTFTs) and organic photovoltaics. Although properly designed SiPcs rival current state-of-the-art n-type organic semiconducting materials, relatively few structure–property relationships have been established to determine the impact of axial substituents on OTFT performance, hindering the intelligent design of the next generation of SiPcs. To address this omission, we have developed structure–property relationships for vapor-deposited SiPcs with phenoxy axial substituents. In addition to thorough electrical characterization of bottom-gate top-contact OTFTs, we extensively investigated SiPc thin films using X-ray diffraction, atomic force microscopy (AFM), grazing-incidence wide-angle X-ray scattering (GIWAXS), and density functional theory (DFT) modeling. OTFT performance, including relative electron mobility (μe) of materials, was in general agreement with values obtained through DFT modeling including reorganization energy. Another significant trend observed from device performance was that increasing the electron-withdrawing character of the axial pendant groups led to a reduction in threshold voltage (VT) from 47.9 to 21.1 V. This was corroborated by DFT modeling, which predicted that VT decreases with the square of the dipole induced at the interface between the SiPc pendant and substrate. Discrepancies between modeling predictions and experimental results can be explained through analysis of thin-film morphology and orientation by AFM and GIWAXS. Our results demonstrate that a combination of DFT modeling to select prospective candidate materials, combined with appropriate processing conditions to deposit molecules with a favorable thin-film morphology in an "edge-on" orientation relative to the substrate, yields high-performance n-type SiPc-based OTFTs.}, number={1}, journal={ACS APPLIED ELECTRONIC MATERIALS}, author={King, Benjamin and Melville, Owen A. and Rice, Nicole A. and Kashani, Somayeh and Tonnele, Claire and Raboui, Hasan and Swaraj, Sufal and Grant, Trevor M. and McAfee, Terry and Bender, Timothy P. and et al.}, year={2021}, month={Jan}, pages={325–336} }
 @article{balar_siddika_kashani_peng_rech_ye_you_ade_brendan t. o'conner_2020, title={Role of Secondary Thermal Relaxations in Conjugated Polymer Film Toughness}, volume={32}, ISSN={["1520-5002"]}, url={https://publons.com/wos-op/publon/35208553/}, DOI={10.1021/acs.chemmater.0c01910}, abstractNote={Conjugated polymers have proven to be an important class of materials for flexible and stretchable electronics. To ensure long-term thermal and mechanical stability of associated devices, there is a need to determine the origin of the polymer ductility and toughness. In this work, we investigate a variety of high-performance conjugated polymers and relate their thermomechanical behavior to film toughness. Dynamic mechanical analysis (DMA) is used to probe thermomechanical relaxations of the conjugated polymers. Film ductility is measured as a function of temperature to determine the temperature that corresponds to a significant loss in film toughness. We systematically study polymers with changes to the side-chain structure, backbone structure, and crystallinity. We also compare polymers that have a clear glass transition (Tg) to those that do not. It is found that secondary thermal relaxations (sub-Tg) play a critical role in film toughness. This sub-Tg is found to be a local molecular relaxation that appears to relate to side-chain and backbone mobility. We also find that many of the polymers considered continue to show moderate ductility below their sub-Tg, which is attributed to crystallites or aggregates that have active slip systems. These results provide new insights into how conjugated polymer structure and related thermal relaxations influence film toughness that will assist in realizing mechanically robust devices.}, number={15}, journal={CHEMISTRY OF MATERIALS}, author={Balar, Nrup and Siddika, Salma and Kashani, Somayeh and Peng, Zhengxing and Rech, Jeromy James and Ye, Long and You, Wei and Ade, Harald and Brendan T. O'Conner}, year={2020}, month={Aug}, pages={6540–6549} }