@article{sakorikar_mihaliak_krisnadi_ma_kim_kong_awartani_dickey_2024, title={A Guide to Printed Stretchable Conductors}, volume={1}, ISSN={["1520-6890"]}, url={https://doi.org/10.1021/acs.chemrev.3c00569}, DOI={10.1021/acs.chemrev.3c00569}, abstractNote={Printing of stretchable conductors enables the fabrication and rapid prototyping of stretchable electronic devices. For such applications, there are often specific process and material requirements such as print resolution, maximum strain, and electrical/ionic conductivity. This review highlights common printing methods and compatible inks that produce stretchable conductors. The review compares the capabilities, benefits, and limitations of each approach to help guide the selection of a suitable process and ink for an intended application. We also discuss methods to design and fabricate ink composites with the desired material properties (e.g., electrical conductance, viscosity, printability). This guide should help inform ongoing and future efforts to create soft, stretchable electronic devices for wearables, soft robots, e-skins, and sensors.}, journal={CHEMICAL REVIEWS}, author={Sakorikar, Tushar and Mihaliak, Nikolas and Krisnadi, Febby and Ma, Jinwoo and Kim, Tae-il and Kong, Minsik and Awartani, Omar and Dickey, Michael D.}, year={2024}, month={Jan} }
 @article{shukla_wang_awartani_dickey_zhu_2024, title={Surface Embedded Metal Nanowire-Liquid Metal-Elastomer Hybrid Composites for Stretchable Electronics}, volume={16}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.4c00318}, DOI={10.1021/acsami.4c00318}, abstractNote={Both liquid metal (LM) and metallic filler-based conductive composites are promising stretchable conductors. LM alloys exhibit intrinsically high deformability but present challenges for patterning on polymeric substrates due to high surface tension. On the other hand, conductive composites comprising metallic fillers undergo considerable decrease in electrical conductivity under mechanical deformation. To address the challenges, we present silver nanowire (AgNW)-LM-elastomer hybrid composite films, where AgNWs and LM are embedded below the surface of an elastomeric matrix, using two fabrication approaches, sequential and mixed. We investigate and understand the process-structure-property relationship of the AgNW-LM-elastomer hybrid composites fabricated using two approaches. Different weight ratios of AgNWs and LM particles provide tunable electrical conductivity. The hybrid composites show more stable electromechanical performance than the composites with AgNWs alone. In particular, 1:2.4 (AgNW:LMP w/w) sequential hybrid composite shows electromechanical stability similar to that of the LM-elastomer composite, with a resistance increase of 2.04% at 90% strain. The sequential approach is found to form AgIn2 intermetallic compounds which along with Ga-In bonds, imparts large deformability to the sequential hybrid composite as well as mechanical robustness against scratching, cutting, peeling, and wiping. To demonstrate the application of the hybrid composite for stretchable electronics, a laser patterned stretchable heater on textile and a stretchable circuit including a light-emitting diode are fabricated.}, number={11}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Shukla, Darpan and Wang, Hongyu and Awartani, Omar and Dickey, Michael D. and Zhu, Yong}, year={2024}, month={Mar}, pages={14183–14197} }
 @article{ma_krisnadi_vong_kong_awartani_dickey_2023, title={Shaping a Soft Future: Patterning Liquid Metals}, volume={3}, ISSN={["1521-4095"]}, url={https://doi.org/10.1002/adma.202205196}, DOI={10.1002/adma.202205196}, abstractNote={Abstract}, journal={ADVANCED MATERIALS}, author={Ma, Jinwoo and Krisnadi, Febby and Vong, Man Hou and Kong, Minsik and Awartani, Omar M. and Dickey, Michael D.}, year={2023}, month={Mar} }
 @article{zhong_kirmani_lan_carpenter_rong-hui chew_awartani_yu_niazi_voznyy_hu_et al._2022, title={Conjugated polymers with controllable interfacial order and energetics enable tunable heterojunctions in organic and colloidal quantum dot photovoltaics}, volume={10}, ISSN={2050-7488 2050-7496}, url={http://dx.doi.org/10.1039/D1TA09544G}, DOI={10.1039/d1ta09544g}, abstractNote={Top and bottom surfaces of polymer films are used to construct interfaces in heterojunction based devices, affecting device figure of merit significantly with their different aggregation states.}, number={4}, journal={Journal of Materials Chemistry A}, publisher={Royal Society of Chemistry (RSC)}, author={Zhong, Yufei and Kirmani, Ahmad R. and Lan, Xinzheng and Carpenter, Joshua and Rong-Hui Chew, Annabel and Awartani, Omar and Yu, Liyang and Niazi, Muhammad R. and Voznyy, Oleksandr and Hu, Hanlin and et al.}, year={2022}, pages={1788–1801} }
 @article{balar_rech_siddika_song_schrickx_sheikh_ye_bonilla_awartani_ade_et al._2021, title={Resolving the Molecular Origin of Mechanical Relaxations in Donor-Acceptor Polymer Semiconductors}, volume={32}, ISSN={["1616-3028"]}, url={https://doi.org/10.1002/adfm.202105597}, DOI={10.1002/adfm.202105597}, abstractNote={Abstract}, number={4}, journal={ADVANCED FUNCTIONAL MATERIALS}, publisher={Wiley}, author={Balar, Nrup and Rech, Jeromy James and Siddika, Salma and Song, Runqiao and Schrickx, Harry M. and Sheikh, Nadeem and Ye, Long and Bonilla, Anthony Megret and Awartani, Omar and Ade, Harald and et al.}, year={2021}, month={Oct} }
 @article{duan_peng_colberts_pang_ye_awartani_hendriks_ade_wienk_janssen_et al._2019, title={Efficient Thick-Film Polymer Solar Cells with Enhanced Fill Factors via Increased Fullerene Loading}, volume={11}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.9b00337}, DOI={10.1021/acsami.9b00337}, abstractNote={Developing effective methods to make efficient bulk-heterojunction polymer solar cells at roll-to-roll relevant active layer thickness is of significant importance. We investigate the effect of fullerene content in polymer:fullerene blends on the fill factor (FF) and on the performance of thick-film solar cells for four different donor polymers PTB7-Th, PDPP-TPT, BDT-FBT-2T, and poly[5,5′-bis(2-butyloctyl)-(2,2′-bithiophene)-4,4′-dicarboxylate-alt-5,5′-2,2′-bithiophene] (PDCBT). At a few hundreds of nanometers thickness, increased FFs are observed in all cases and improved overall device performances are obtained except for PDCBT upon increasing fullerene content in blend films. This fullerene content effect was studied in more detail by electrical and morphological characterization. The results suggest enhanced electron mobility and suppressed bimolecular recombination upon increasing fullerene content in thick polymer:fullerene blend films, which are the result of larger fullerene aggregates and improved interconnectivity of the fullerene phases that provide continuous percolating pathways for electron transport in thick films. These findings are important because an effective and straightforward method that enables fabricating efficient thick-film polymer solar cells is desirable for large-scale manufacturing via roll-to-roll processing and for multijunction devices.}, number={11}, journal={ACS APPLIED MATERIALS & INTERFACES}, publisher={American Chemical Society (ACS)}, author={Duan, Chunhui and Peng, Zhengxing and Colberts, Fallon J. M. and Pang, Shuting and Ye, Long and Awartani, Omar M. and Hendriks, Koen H. and Ade, Harald and Wienk, Martijn M. and Janssen, Rene A. J. and et al.}, year={2019}, month={Mar}, pages={10794–10800} }
 @article{ye_zhao_li_mukherjee_carpenter_awartani_jiao_hou_ade_2017, title={High-Efficiency Nonfullerene Organic Solar Cells: Critical Factors that Affect Complex Multi-Length Scale Morphology and Device Performance}, volume={7}, ISSN={["1614-6840"]}, url={https://publons.com/wos-op/publon/5290907/}, DOI={10.1002/aenm.201602000}, abstractNote={Organic solar cells (OSCs) made of donor/acceptor bulk‐heterojunction active layers have been of widespread interest in converting sunlight to electricity. Characterizing of the complex morphology at multiple length scales of polymer:nonfullerene small molecular acceptor (SMA) systems remains largely unexplored. Through detailed characterizations (hard/soft X‐ray scattering) of the record‐efficiency polymer:SMA system with a close analog, quantitative morphological parameters are related to the device performance parameters and fundamental morphology–performance relationships that explain why additive use and thermal annealing are needed for optimized performance are established. A linear correlation between the average purity variations at small length scale (≈10 nm) and photovoltaic device characteristics across all processing protocols is observed in ≈12%‐efficiency polymer:SMA systems. In addition, molecular interactions as reflected by the estimated Flory–Huggins interaction parameters are used to provide context of the room temperature morphology results. Comparison with results from annealed devices suggests that the two SMA systems compared show upper and lower critical solution temperature behavior, respectively. The in‐depth understanding of the complex multilength scale nonfullerene OSC morphology may guide the device optimization and new materials development and indicates that thermodynamic properties of materials systems should be studied in more detail to aid in designing optimized protocols efficiently.}, number={7}, journal={ADVANCED ENERGY MATERIALS}, author={Ye, Long and Zhao, Wenchao and Li, Sunsun and Mukherjee, Subhrangsu and Carpenter, Joshua H. and Awartani, Omar and Jiao, Xuechen and Hou, Jianhui and Ade, Harald}, year={2017}, month={Apr} }
 @article{guo_li_awartani_han_zhao_ade_yan_zhao_2017, title={Improved Performance of All-Polymer Solar Cells Enabled by Naphthodiperylenetetraimide-Based Polymer Acceptor}, volume={29}, ISSN={["1521-4095"]}, DOI={10.1002/adma.201700309}, abstractNote={A new polymer acceptor, naphthodiperylenetetraimide‐vinylene (NDP‐V), featuring a backbone of altenating naphthodiperylenetetraimide and vinylene units is designed and applied in all‐polymer solar cells (all‐PSCs). With this polymer acceptor, a new record power‐conversion efficiencies (PCE) of 8.59% has been achieved for all‐PSCs. The design principle of NDP‐V is to reduce the conformational disorder in the backbone of a previously developed high‐performance acceptor, PDI‐V, a perylenediimide‐vinylene polymer. The chemical modifications result in favorable changes to the molecular packing behaviors of the acceptor and improved morphology of the donor–acceptor (PTB7‐Th:NDP‐V) blend, which is evidenced by the enhanced hole and electron transport abilities of the active layer. Moreover, the stronger absorption of NDP‐V in the shorter‐wavelength range offers a better complement to the donor. All these factors contribute to a short‐circuit current density (J
sc) of 17.07 mA cm−2. With a fill factor (FF) of 0.67, an average PCE of 8.48% is obtained, representing the highest value thus far reported for all‐PSCs.}, number={26}, journal={ADVANCED MATERIALS}, author={Guo, Yikun and Li, Yunke and Awartani, Omar and Han, Han and Zhao, Jingbo and Ade, Harald and Yan, He and Zhao, Dahui}, year={2017}, month={Jul} }
 @article{ghasemi_ye_zhang_yan_kim_awartani_you_gadisa_ade_2017, title={Panchromatic Sequentially Cast Ternary Polymer Solar Cells}, volume={29}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/ADMA.201604603}, DOI={10.1002/adma.201604603}, abstractNote={A sequential-casting ternary method is developed to create stratified bulk heterojunction (BHJ) solar cells, in which the two BHJ layers are spin cast sequentially without the need of adopting a middle electrode and orthogonal solvents. This method is found to be particularly useful for polymers that form a mechanically alloyed morphology due to the high degree of miscibility in the blend.}, number={4}, journal={Advanced Materials}, publisher={Wiley}, author={Ghasemi, Masoud and Ye, Long and Zhang, Qianqian and Yan, Liang and Kim, Joo-Hyun and Awartani, Omar and You, Wei and Gadisa, Abay and Ade, Harald}, year={2017}, month={Jan}, pages={1604603} }
 @article{guo_li_awartani_han_zhang_ade_yan_zhao_2017, title={Side-chain engineering of perylenediimide-vinylene polymer acceptors for high-performance all-polymer solar cells}, volume={1}, ISSN={["2052-1537"]}, DOI={10.1039/c6qm00355a}, abstractNote={The performance of a PDI-vinylene polymer acceptor in an all-PSC is optimized by side-chain engineering. The best average PCE of 7.40% is obtained with a medium side-chain length.}, number={7}, journal={MATERIALS CHEMISTRY FRONTIERS}, author={Guo, Yikun and Li, Yunke and Awartani, Omar and Han, Han and Zhang, Guangye and Ade, Harald and Yan, He and Zhao, Dahui}, year={2017}, month={Jul}, pages={1362–1368} }
 @article{chen_yao_li_awartani_liu_wang_yang_zhang_ade_yan_2017, title={Surprising Effects upon Inserting Benzene Units into a Quaterthiophene-Based D-A Polymer-Improving Non-Fullerene Organic Solar Cells via Donor Polymer Design}, volume={7}, ISSN={["1614-6840"]}, DOI={10.1002/aenm.201602304}, abstractNote={S. Chen, H. Yao, Z. Li, Y. Liu, Z. Wang, G. Yang, J. Zhang, Prof. H. Yan Department of Chemistry and Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction Hong Kong University of Science and Technology Clear Water Bay, Kowloon, Hong Kong E-mail: hyan@ust.hk S. Chen, H. Yao, Z. Li, Prof. H. Yan Hong Kong University of Science and Technology-Shenzhen Research Institute No. 9 Yuexing 1st RD, Hi-tech Park, Nanshan, Shenzhen 518057, P. R. China Dr. O. M. Awartani, Prof. H. Ade Department of Physics and Organic and Carbon Electronics Laboratory North Carolina State University Raleigh, NC 27695, USA E-mail: harald_ade@ncsu.edu Prof. H. Yan Institute of Polymer Optoelectronic Materials and Devices State Key Laboratory of Luminescent Materials and Devices South China University of Technology Guangzhou 510640, P. R. China}, number={12}, journal={ADVANCED ENERGY MATERIALS}, author={Chen, Shangshang and Yao, Huatong and Li, Zhengke and Awartani, Omar M. and Liu, Yuhang and Wang, Zheng and Yang, Guofang and Zhang, Jianquan and Ade, Harald and Yan, He}, year={2017}, month={Jun} }
 @article{guo_li_awartani_zhao_han_ade_zhao_yan_2016, title={A Vinylene-Bridged Perylenediimide-Based Polymeric Acceptor Enabling Efficient All-Polymer Solar Cells Processed under Ambient Conditions}, volume={28}, ISSN={["1521-4095"]}, DOI={10.1002/adma.201602387}, abstractNote={All-polymer solar cells with 7.57% power conversion efficiency are achieved via a new perylenediimide-based polymeric acceptor. Furthermore, the device processed in ambient air without encapsulation can still reach a high power conversion efficiency (PCE) of 7.49%, which is a significant economic advantage from an industrial processing perspective. These results represent the highest PCE achieved from perylenediimide-based polymers.}, number={38}, journal={ADVANCED MATERIALS}, author={Guo, Yikun and Li, Yunke and Awartani, Omar and Zhao, Jingbo and Han, Han and Ade, Harald and Zhao, Dahui and Yan, He}, year={2016}, month={Oct}, pages={8483–8489} }
 @article{zhao_awartani_o'connor_zikry_2016, title={A direct correlation of x-ray diffraction orientation distributions to the in-plane stiffness of semi-crystalline organic semiconducting films}, volume={108}, ISSN={["1077-3118"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84968866659&partnerID=MN8TOARS}, DOI={10.1063/1.4948533}, abstractNote={Large charge mobilities of semi-crystalline organic semiconducting films could be obtained by mechanically aligning the material phases of the film with the loading axis. A key element is to utilize the inherent stiffness of the material for optimal or desired alignment. However, experimentally determining the moduli of semi-crystalline organic thin films for different loading directions is difficult, if not impossible, due to film thickness and material anisotropy. In this paper, we address these challenges by presenting an approach based on combining a composite mechanics stiffness orientation formulation with a Gaussian statistical distribution to directly estimate the in-plane stiffness (transverse isotropy) of aligned semi-crystalline polymer films based on crystalline orientation distributions obtained by X-ray diffraction experimentally at different applied strains. Our predicted results indicate that the in-plane stiffness of an annealing film was initially isotropic, and then it evolved to transverse isotropy with increasing mechanical strains. This study underscores the significance of accounting for the crystalline orientation distributions of the film to obtain an accurate understanding and prediction of the elastic anisotropy of semi-crystalline polymer films.}, number={18}, journal={APPLIED PHYSICS LETTERS}, author={Zhao, Bingxiao and Awartani, Omar and O'Connor, Brendan and Zikry, Mohammed A.}, year={2016}, month={May} }
 @article{awartani_zhao_currie_kline_zikry_brendan t. o'connor_2016, title={Anisotropic Elastic Modulus of Oriented Regioregular Poly(3-hexylthiophene) Films}, volume={49}, ISSN={["1520-5835"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84954288748&partnerID=MN8TOARS}, DOI={10.1021/acs.macromol.5b02680}, abstractNote={Specific morphological features of polymer semiconductors are often promoted in devices to optimize optoelectronic behavior. Less studied is the role of morphology on the mechanical properties of the film, such as elastic modulus, which is an important property for the development of flexible and stretchable devices. To gain insight into the morphological origin of elasticity in polymer semiconductors and its relationship to charge transport, we study the anisotropic in-plane elastic modulus of strain-aligned regioregular poly(3-hexylthiophene) (P3HT) films and compare the results to previously measured field effect charge mobility. The film morphology is varied through the amount of applied strain and post strain thermal annealing. Morphological characterization includes UV–vis optical spectroscopy and X-ray diffraction. The elastic modulus is measured using a buckling-based measurement technique. The elastic modulus of the film is found to decrease as the film is plastically strained. Thermally annealin...}, number={1}, journal={MACROMOLECULES}, author={Awartani, Omar M. and Zhao, Bingxiao and Currie, Tyler and Kline, R. Joseph and Zikry, Mohammed A. and Brendan T. O'Connor}, year={2016}, month={Jan}, pages={327–333} }
 @article{zheng_awartani_gautam_liu_qin_li_bataller_gundogdu_ade_hou_et al._2016, title={Efficient Charge Transfer and Fine-Tuned Energy Level Alignment in a THF-Processed Fullerene-Free Organic Solar Cell with 11.3% Efficiency}, volume={29}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/adma.201604241}, DOI={10.1002/adma.201604241}, abstractNote={Fullerene-free organic solar cells show over 11% power conversion efficiency, processed by low toxic solvents. The applied donor and acceptor in the bulk heterojunction exhibit almost the same highest occupied molecular orbital level, yet exhibit very efficient charge creation.}, number={5}, journal={Advanced Materials}, publisher={Wiley}, author={Zheng, Z. and Awartani, O. M. and Gautam, B. and Liu, D. L. and Qin, Y. P. and Li, W. N. and Bataller, Alexander and gundogdu and Ade, H. and Hou, J. H. and et al.}, year={2016}, month={Nov}, pages={1604241} }
 @article{roy_awartani_sen_o'connor_kudenov_2016, title={Intrinsic coincident linear polarimetry using stacked organic photovoltaics}, volume={24}, ISSN={["1094-4087"]}, DOI={10.1364/oe.24.014737}, abstractNote={Polarimetry has widespread applications within atmospheric sensing, telecommunications, biomedical imaging, and target detection. Several existing methods of imaging polarimetry trade off the sensor's spatial resolution for polarimetric resolution, and often have some form of spatial registration error. To mitigate these issues, we have developed a system using oriented polymer-based organic photovoltaics (OPVs) that can preferentially absorb linearly polarized light. Additionally, the OPV cells can be made semitransparent, enabling multiple detectors to be cascaded along the same optical axis. Since each device performs a partial polarization measurement of the same incident beam, high temporal resolution is maintained with the potential for inherent spatial registration. In this paper, a Mueller matrix model of the stacked OPV design is provided. Based on this model, a calibration technique is developed and presented. This calibration technique and model are validated with experimental data, taken with a cascaded three cell OPV Stokes polarimeter, capable of measuring incident linear polarization states. Our results indicate polarization measurement error of 1.2% RMS and an average absolute radiometric accuracy of 2.2% for the demonstrated polarimeter.}, number={13}, journal={OPTICS EXPRESS}, author={Roy, S. Gupta and Awartani, O. M. and Sen, P. and O'Connor, B. T. and Kudenov, M. W.}, year={2016}, month={Jun}, pages={14737–14747} }
 @article{zhao_awartani_o'connor_zikry_2016, title={Microstructural Behavior and Failure Mechanisms of Organic Semicrystalline Thin Film Blends}, volume={54}, ISSN={["1099-0488"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84954289843&partnerID=MN8TOARS}, DOI={10.1002/polb.23991}, abstractNote={Organic thin film blends of P3HT semiconducting polymers and PCBM fullerenes have enabled large-scale semiconductor fabrication pertaining to flexible and stretchable electronics. However, molecular packing and film morphologies can significantly alter mechanical stability and failure behavior. To further understand and identify the fundamental mechanisms affecting failure, a multiphase microstructurally based formulation and nonlinear finite-element fracture methodology were used to investigate the heterogeneous deformation and failure modes of organic semicrystalline thin film blends. The multiphase formulation accounts for the crystalline and amorphous behavior, polymer tie-chains, and the PCBM aggregates. Face-on packing orientations resulted in extensive inelastic deformation and crystalline rotation, and this was characterized by ductile failure modes and interfacial delamination. For edge-on packing orientations, brittle failure modes and film cracking were due to lower inelastic deformation and higher film stress in comparison with the face-on orientations. The higher crystallinity of P3HT and larger PCBM aggregates associated with larger domain sizes, strengthened the film and resulted in extensive film cracking. These predictions of ductile and brittle failure are consistent with experimental observations for P3HT:PCBM films. The proposed predictive framework can be used to improve organic film ductility and strength through the control of molecular packing orientations and microstructural mechanisms. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 896–907}, number={9}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, author={Zhao, Bingxiao and Awartani, Omar and O'Connor, Brendan and Zikry, Mohammed A.}, year={2016}, month={May}, pages={896–907} }
 @article{roy_awartani_sen_o'connor_kudenov_2015, title={Complete Intrinsic Coincident Polarimetry using Stacked Organic Photovoltaics}, volume={9613}, ISSN={["0277-786X"]}, DOI={10.1117/12.2188972}, abstractNote={Measuring the 2 dimensional Stokes vector, to determine the polarization state of light, finds application in multiple areas, including the characterization of aerosol size distributions, target identification, quality control by evaluating the distribution of stress birefringence, resolving data channels in telecommunications, and for evaluating biological tissues in medical imaging. Conventional methods, such as channeled and division of focal plane polarimeters, usually limit spatial resolution, while others, like division of aperture or division of amplitude polarimeters, have higher complexity and less compactness. To help solve these issues, we have developed a system that uses semitransparent organic photovoltaics (OPVs) as photodetectors. The active area of the devices consist of biaxially oriented polymer films, which enables the device to preferentially absorb certain polarized states of incident light, depending on the orientation of the polymer chains. Taking advantage of the cells’ transparency and ease of processing, compared to inorganic materials, enables multiple devices to be “stacked” along the optical axis. Presently, experiments have been conducted to detect linear polarization states of light. We use three stacked OPVs, where each device can measure one of the first three Stokes parameters simultaneously, thereby ensuring high spatial and temporal resolution with inherent spatial registration. In this paper, the fabrication of the OPVs and the design and calibration technique is documented, along with experimental data, supporting the hypothesis.}, journal={POLARIZATION SCIENCE AND REMOTE SENSING VII}, author={Roy, S. Gupta and Awartani, O. M. and Sen, P. and O'Connor, B. T. and Kudenov, M. W.}, year={2015} }
 @article{awartani_kudenov_kline_brendan t. o'connor_2015, title={In-Plane Alignment in Organic Solar Cells to Probe the Morphological Dependence of Charge Recombination}, volume={25}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.201403377}, abstractNote={Bulk heterojunction (BHJ) organic solar cells are fabricated with the polymer semiconductor aligned in the plane of the film to probe charge recombination losses associated with aggregates characterized by varying degrees of local order. 100% uniaxial strain is applied on ductile poly(3‐hexylthiophene):phenyl‐C61‐butyric acid methyl ester (P3HT:PCBM) BHJ films and characterize the resulting morphology with ultraviolet‐visible absorption spectroscopy and grazing incidence X‐ray diffraction. It is found that the strained films result in strong alignment of the highly ordered polymer aggregates. Polymer aggregates with lower order and amorphous regions also align but with a much broader orientation distribution. The solar cells are then tested under linearly polarized light where the light is selectively absorbed by the appropriately oriented polymer, while maintaining a common local environment for the sweep out of photogenerated charge carriers. Results show that charge collection losses associated with a disordered BHJ film are circumvented, and the internal quantum efficiency is independent of P3HT local aggregate order near the heterojunction interface. Uniquely, this experimental approach allows for selective excitation of distinct morphological features of a conjugated polymer within a single BHJ film, providing insight into the morphological origin of recombination losses.}, number={8}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Awartani, Omar and Kudenov, Michael W. and Kline, R. Joseph and Brendan T. O'Connor}, year={2015}, month={Feb}, pages={1296–1303} }
 @article{kitchen_awartani_kline_mcafee_ade_brendan t. o'connor_2015, title={Tuning Open-Circuit Voltage in Organic Solar Cells with Molecular Orientation}, volume={7}, ISSN={["1944-8244"]}, DOI={10.1021/am508855s}, abstractNote={The role of molecular orientation of a polar conjugated polymer in polymer-fullerene organic photovoltaic (OPV) cells is investigated. A planar heterojunction (PHJ) OPV cell composed of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) is used as a model system to isolate the effect of the interfacial orientation on the photovoltaic properties. The molecular orientation of the aggregate P3HT relative to the PCBM layer is varied from highly edge-on (conjugated ring plane perpendicular to the interface plane) to appreciably face-on (ring plane parallel to the interface). It is found that as the P3HT stacking becomes more face-on there is a positive correlation to the OPV open-circuit voltage (V(OC)), attributed to a shift in the highest occupied molecular orbital (HOMO) energy level of P3HT. In addition, the PHJ OPV cell with a broad P3HT stacking orientation distribution has a V(OC) comparable to an archetypal bulk heterojunction (BHJ) device. These results suggest that, in the BHJ OPV cell, the hole energy level in the charge transfer state is defined in part by the orientation distribution of the P3HT at the interface with PCBM. Finally, the photoresponses of the devices are also shown to have a dependence on P3HT stacking orientation.}, number={24}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Kitchen, Brent and Awartani, Omar and Kline, R. Joseph and McAfee, Terry and Ade, Harald and Brendan T. O'Connor}, year={2015}, month={Jun}, pages={13208–13216} }
 @article{awartani_kudenov_brendan t. o'connor_2014, title={Organic photovoltaic cells with controlled polarization sensitivity}, volume={104}, ISSN={["1077-3118"]}, DOI={10.1063/1.4868041}, abstractNote={In this study, we demonstrate linearly polarized organic photovoltaic cells with a well-controlled level of polarization sensitivity. The polarized devices were created through the application of a large uniaxial strain to the bulk heterojunction poly(3-hexylthiophene):Phenyl-C61-butyric acid methyl ester (P3HT:PCBM) film and printing the plastically deformed active layer onto a PEDOT:PSS and indium tin oxide coated glass substrate. The P3HT:PCBM layer is processed such that it is able to accommodate high strains (over 100%) without fracture. After printing the strained films, thermal annealing is used to optimize solar cell performance while maintaining polarization sensitivity. A dichroic ratio and short circuit current ratio of ≈6.1 and ≈1.6 were achieved, respectively.}, number={9}, journal={APPLIED PHYSICS LETTERS}, author={Awartani, Omar and Kudenov, Michael W. and Brendan T. O'Connor}, year={2014}, month={Mar} }
 @article{awartani_lemanski_ro_richter_delongchamp_brendan t. o'connor_2013, title={Correlating Stiffness, Ductility, and Morphology of Polymer:Fullerene Films for Solar Cell Applications}, volume={3}, ISSN={["1614-6840"]}, DOI={10.1002/aenm.201200595}, abstractNote={Abstract}, number={3}, journal={ADVANCED ENERGY MATERIALS}, author={Awartani, Omar and Lemanski, Bethany I. and Ro, Hyun Wook and Richter, Lee J. and DeLongchamp, Dean M. and Brendan T. O'Connor}, year={2013}, month={Mar}, pages={399–406} }