@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{younts_danilov_gundogdu_gautam_2018, title={Charge generation dynamics in polymer nonfullerene solar cells with low energy loss}, volume={8}, ISSN={["1947-7988"]}, DOI={10.1117/1.JPE.8.032209}, abstractNote={Abstract. Polymer nonfullerene solar cells are emerging as an alternative of polymer fullerene solar cells. However, maximizing the short-circuit density and open-circuit voltage is a critical issue in these solar cells. Here, using ultrafast spectroscopy, we measured exciton relaxation and charge separation dynamics in polymer nonfullerene blend with low driving force. Our study indicates high polaron yield despite the energy loss of as low as 0.59 eV. This suggests that the small driving force has minimum detrimental effect in realizing high performance in polymer nonfullerene solar cells.}, number={3}, journal={JOURNAL OF PHOTONICS FOR ENERGY}, author={Younts, Robert and Danilov, Evgeny and Gundogdu, Kenan and Gautam, Bhoj}, year={2018} }
 @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{awartani_gautam_zhao_younts_hou_gundogdu_ade_2018, title={Polymer non-fullerene solar cells of vastly different efficiencies for minor side-chain modification: impact of charge transfer, carrier lifetime, morphology and mobility}, volume={6}, ISSN={["2050-7496"]}, url={https://doi.org/10.1039/C7TA01746D}, DOI={10.1039/c7ta01746d}, abstractNote={The performance of the 11.25% efficient PBDB-T : ITIC system degraded to 4.35% after a minor side-chain modification in PBDB-O : ITIC. In this study, the underlying reasons behind this vast difference in efficiencies are investigated.}, number={26}, journal={JOURNAL OF MATERIALS CHEMISTRY A}, publisher={Royal Society of Chemistry (RSC)}, author={Awartani, Omar M. and Gautam, Bhoj and Zhao, Wenchao and Younts, Robert and Hou, Jianhui and Gundogdu, Kenan and Ade, Harald}, year={2018}, month={Jul}, pages={12484–12492} }
 @article{gautam_younts_carpenter_ade_gundogdu_2018, title={The Role of FRET in Non-Fullerene Organic Solar Cells: Implications for Molecular Design}, volume={122}, ISSN={["1089-5639"]}, url={https://doi.org/10.1021/acs.jpca.7b12807}, DOI={10.1021/acs.jpca.7b12807}, abstractNote={Non-fullerene acceptors (NFAs) have been demonstrated to be promising candidates for highly efficient organic photovoltaic (OPV) devices. The tunability of absorption characteristics of NFAs can be used to make OPVs with complementary donor-acceptor absorption to cover a broad range of the solar spectrum. However, both charge transfer from donor to acceptor moieties and energy (energy) transfer from high-bandgap to low-bandgap materials are possible in such structures. Here, we show that when charge transfer and exciton transfer processes are both present, the coexistence of excitons in both domains can cause a loss mechanism. Charge separation of excitons in a low-bandgap material is hindered due to exciton population in the larger bandgap acceptor domains. Our results further show that excitons in low-bandgap material should have a relatively long lifetime compared to the transfer time of excitons from higher bandgap material in order to contribute to the charge separation. These observations provide significant guidance for design and development of new materials in OPV applications.}, number={15}, journal={JOURNAL OF PHYSICAL CHEMISTRY A}, publisher={American Chemical Society (ACS)}, author={Gautam, Bhoj R. and Younts, Robert and Carpenter, Joshua and Ade, Harald and Gundogdu, Kenan}, year={2018}, month={Apr}, pages={3764–3771} }
 @article{li_zhong_gautam_bin_lin_wu_zhang_jiang_zhang_gundogdu_et al._2017, title={A near-infrared non-fullerene electron acceptor for high performance polymer solar cells}, volume={10}, ISSN={["1754-5706"]}, DOI={10.1039/c7ee00844a}, abstractNote={Low-bandgap polymers/molecules are an interesting family of semiconductor materials, and have enabled many recent exciting breakthroughs in the field of organic electronics, especially for organic photovoltaics (OPVs).}, number={7}, journal={ENERGY & ENVIRONMENTAL SCIENCE}, author={Li, Yongxi and Zhong, Lian and Gautam, Bhoj and Bin, Hai-Jun and Lin, Jiu-Dong and Wu, Fu-Peng and Zhang, Zhanjun and Jiang, Zuo-Quan and Zhang, Zhi-Guo and Gundogdu, Kenan and et al.}, year={2017}, month={Jul}, pages={1610–1620} }
 @article{younts_duan_gautam_saparov_liu_mongin_castellano_mitzi_gundogdu_2017, title={Efficient generation of long-lived triplet excitons in 2D hybrid perovskite}, volume={29}, number={9}, journal={Advanced Materials}, author={Younts, R. and Duan, H. S. and Gautam, B. and Saparov, B. and Liu, J. and Mongin, C. and Castellano, F. N. and Mitzi, D. B. and Gundogdu, K.}, year={2017} }
 @article{nguyen_lee_gautam_park_gundogdu_kim_woo_2017, title={Single component organic solar cells based on oligothiophene-fullerene conjugate}, volume={27}, number={39}, journal={Advanced Functional Materials}, author={Nguyen, T. L. and Lee, T. H. and Gautam, B. and Park, S. Y. and Gundogdu, K. and Kim, J. Y. and Woo, H. Y.}, year={2017} }
 @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{kranthiraja_kim_lee_gunasekar_sree_gautam_gundogdu_jin_kim_2017, title={The impact of sequential fluorination of pi-conjugated polymers on charge generation in all-polymer solar cells}, volume={27}, number={29}, journal={Advanced Functional Materials}, author={Kranthiraja, K. and Kim, S. and Lee, C. and Gunasekar, K. and Sree, V. G. and Gautam, B. and Gundogdu, K. and Jin, S. H. and Kim, B. J.}, year={2017} }
 @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{zhu_xue_he_jiang_hu_bai_zhang_xiao_gundogdu_gautam_et al._2016, title={A PCBM Electron Transport Layer Containing Small Amounts of Dual Polymer Additives that Enables Enhanced Perovskite Solar Cell Performance}, volume={3}, ISSN={["2198-3844"]}, DOI={10.1002/advs.201500353}, abstractNote={A polymer/PCBM hybrid electron transport layer is reported that enables high‐performance perovskite solar cells with a high power conversion efficiency of 16.2% and with negligible hysteresis. Unlike previous approaches of reducing hysteresis by thermal annealing or fullerene passivation, the success of our approach can be mainly attributed to the doping of the PCBM layer using an insulating polymer (polystyrene) and an amine‐containing polymeric semiconductor named PFNOX.}, number={9}, journal={ADVANCED SCIENCE}, author={Zhu, Zonglong and Xue, Qifan and He, Hexiang and Jiang, Kui and Hu, Zhicheng and Bai, Yang and Zhang, Teng and Xiao, Shuang and Gundogdu, Kenan and Gautam, Bhoj Raj and et al.}, year={2016}, month={Sep} }
 @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{uddin_kim_younts_lee_gautam_choi_wang_gundogdu_kim_woo_et al._2016, title={Controlling Energy Levels and Blend Morphology for All-Polymer Solar Cells via Fluorination of a Naphthalene Diimide-Based Copolymer Acceptor}, volume={49}, ISSN={["1520-5835"]}, DOI={10.1021/acs.macromol.6b01414}, abstractNote={We investigate the photovoltaic properties and charge dynamics of all polymer solar cells (all-PSCs) based on poly[(N,N′-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-5,5′-(2,2′-bithiophene)] (P(NDI2OD-T2)) and its fluorinated analogue, poly[(N,N′-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-5,5′-(3,3′-difluoro-2,2′-bithiophene)] (P(NDI2OD-T2F)), as the acceptor polymer and poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-alt-5-octyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione] (PBDTTTPD) as the donor polymer. The PBDTTTPD:P(NDI2OD-T2)-based device has a high open-circuit voltage (VOC) of 1.03 V but suffers from low power conversion efficiency (PCE) of 2.02% with a short-circuit current density (JSC) and fill factor (FF) of 4.45 mA cm–2 and 0.44, respectively. In a stark contrast, the PCE of PBDTTTPD:P(NDI2OD-T2F)-based PSC dramatically increases to 6.09% (VOC = 1.00 V, JSC = 11.68 mA cm–2, and FF = 0.52). These results are attributed...}, number={17}, journal={MACROMOLECULES}, author={Uddin, M. A. and Kim, Y. and Younts, R. and Lee, W. and Gautam, B. and Choi, J. and Wang, C. and gundogdu and Kim, B. J. and Woo, H. Y. and et al.}, year={2016}, month={Sep}, pages={6374–6383} }
 @article{cheema_younts_gautam_gundogdu_el-shafei_2016, title={Design and synthesis of BODIPY sensitizers with long alkyl chains tethered to N-carbazole and their application for dye sensitized solar cells}, volume={184}, ISSN={["1879-3312"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84994504448&partnerID=MN8TOARS}, DOI={10.1016/j.matchemphys.2016.09.024}, abstractNote={In this study, three boron dipyrromethenes (BODIPY) dyes with extended conjugation and electron donating carbazole groups with different alkyl chain lengths tethered to N-carbazole were synthesized and characterized for dye-sensitized solar cells. The goal was to study the effect of different alkyl chain lengths on dye aggregation at TiO2 surface. The proposed molecular strategy resulted in BODIPY dyes which showed interesting electronic absorption and fluorescence properties. It was observed that intramolecular energy transfer decreases with the increase in alkyl chain length possibly due to induced changes in molecular geometry caused by long alkyl chains. Additionally, interface analysis by impedance spectroscopy in comparison to N719 sensitized TiO2 solar cell showed significant charge transport related losses (Nyquist plot) most likely due to impedance resulted from aggregated BODIPY dye on TiO2 surface. Femtosecond transient absorption studies showed the loss of excited electrons by recombination with oxidized ground state of the sensitizers.}, journal={MATERIALS CHEMISTRY AND PHYSICS}, author={Cheema, Hammad and Younts, Robert and Gautam, Bhoj and Gundogdu, Kenan and El-Shafei, Ahmed}, year={2016}, month={Dec}, pages={57–63} }
 @article{dunlap-shohl_younts_gautam_gundogdu_mitzi_2016, title={Effects of Cd Diffusion and Doping in High-Performance Perovskite Solar Cells Using CdS as Electron Transport Layer}, volume={120}, ISSN={["1932-7455"]}, DOI={10.1021/acs.jpcc.6b05406}, abstractNote={Perovskite solar cells with stabilized power conversion efficiency exceeding 15% have been achieved, using a methylammonium lead iodide (MAPbI3) absorber and CdS as the electron transport layer. X-ray photoelectron spectroscopy reveals a small presence of Cd at the surface of most perovskite films fabricated on CdS. Perovskite films were deliberately doped with Cd to understand the possible impacts of Cd diffusion into the perovskite absorber layer. Doping substantially increases the grain size of the perovskite films but also reduces device performance through the formation of an electrical barrier, as inferred by the S-shape of their J–V curves. Time-resolved photoluminescence measurements of the doped films do not indicate substantial nonradiative recombination due to bulk defects, but a secondary phase is evident in these films, which experiments have revealed to be the organic–inorganic hybrid material methylammonium cadmium iodide, (CH3NH3)2CdI4. It is further demonstrated that this compound can for...}, number={30}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Dunlap-Shohl, Wiley A. and Younts, Robert and Gautam, Bhoj and Gundogdu, Kenan and Mitzi, David B.}, year={2016}, month={Aug}, pages={16437–16445} }
 @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{cheema_younts_ogbose_gautam_gundogdu_el-shafei_2015, title={A femtosecond study of the anomaly in electron injection for dye-sensitized solar cells: the influence of isomerization employing Ru(II) sensitizers with anthracene and phenanthrene ancillary ligands}, volume={17}, ISSN={["1463-9084"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84949117754&partnerID=MN8TOARS}, DOI={10.1039/c4cp04741a}, abstractNote={HD-7 is prone to ISC and shows a continuous increase in the triplet TA signal, whereas HD-8 shows enhanced singlet injection, followed by decay in the TA signal.}, number={4}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Cheema, Hammad and Younts, Robert and Ogbose, Louis and Gautam, Bhoj and Gundogdu, Kenan and El-Shafei, Ahmed}, year={2015}, month={Jan}, pages={2750–2756} }
 @article{gautam_lee_younts_lee_danilov_kim_gundogdu_2015, title={Charge Generation Dynamics in Efficient All-Polymer Solar Cells: Influence of Polymer Packing and Morphology}, volume={7}, ISSN={["1944-8244"]}, DOI={10.1021/acsami.5b08531}, abstractNote={All-polymer solar cells exhibit rapid progress in power conversion efficiency (PCE) from 2 to 7.7% over the past few years. While this improvement is primarily attributed to efficient charge transport and balanced mobility between the carriers, not much is known about the charge generation dynamics in these systems. Here we measured exciton relaxation and charge separation dynamics using ultrafast spectroscopy in polymer/polymer blends with different molecular packing and morphology. These measurements indicate that preferential face-on configuration with intermixed nanomorphology increases the charge generation efficiency. In fact, there is a direct quantitative correlation between the free charge population in the ultrafast time scales and the external quantum efficiency, suggesting not only the transport but also charge generation is key for the design of high performance all polymer solar cells.}, number={50}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Gautam, Bhoj R. and Lee, Changyeon and Younts, Robert and Lee, Wonho and Danilov, Evgeny and Kim, Bumjoon J. and Gundogdu, Kenan}, year={2015}, month={Dec}, pages={27586–27591} }
 @article{gautam_barrette_mai_yan_zhang_danilov_you_ade_gundogdu_2015, title={Direct Optical Observation of Stimulated Emission from Hot Charge Transfer Excitons in Bulk Heterojunction Polymer Solar Cells}, volume={119}, ISSN={["1932-7447"]}, DOI={10.1021/acs.jpcc.5b06557}, abstractNote={Charge transfer excitons (CTEs) play an important role in semiconducting polymer-based optoelectronic applications. In organic photovoltaics, they are an intermediate step between tightly bound excitons and free charges. Although CT state energies at the interface of bulk heterojunction organic solar cells have been reported using quantum chemical calculations and by sensitive external quantum efficiency (EQE) measurements, direct optical observation of CT states was limited to relaxed, low energy, CT levels. Here we used polarization anisotropy transient absorption experiments to measure emission from high-energy CT levels. These experimental methods provide means to study high energy CT state dynamics in BHJs with controlled molecular orientations and complement theoretical calculations of interfacial CT state energies.}, number={34}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Gautam, Bhoj R. and Barrette, Andy and Mai, Cong and Yan, Liang and Zhang, Qianqian and Danilov, Eygeny and You, Wei and Ade, Harald and Gundogdu, Kenan}, year={2015}, month={Aug}, pages={19697–19702} }
 @article{cheema_islam_han_gautam_younts_gundogdu_el-shafei_2014, title={Influence of mono versus bis-electron-donor ancillary ligands in heteroleptic Ru(II) bipyridyl complexes on electron injection from the first excited singlet and triplet states in dye-sensitized solar cells}, volume={2}, ISSN={["2050-7496"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84905571530&partnerID=MN8TOARS}, DOI={10.1039/c4ta01942c}, abstractNote={A novel Ru(ii) bipyridyl complex was designed for DSCs.}, number={34}, journal={JOURNAL OF MATERIALS CHEMISTRY A}, author={Cheema, Hammad and Islam, Ashraful and Han, Liyuan and Gautam, Bhoj and Younts, Robert and Gundogdu, Kenan and El-Shafei, Ahmed}, year={2014}, pages={14228–14235} }
 @article{cheema_islam_younts_gautam_bedja_gupta_han_gundogdu_el-shafei_2014, title={More stable and more efficient alternatives of Z-907: carbazole-based amphiphilic Ru(II) sensitizers for dye-sensitized solar cells}, volume={16}, ISSN={["1463-9084"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84911879802&partnerID=MN8TOARS}, DOI={10.1039/c4cp04120h}, abstractNote={Here we report two novel amphiphilic Ru(ii) heteroleptic bipyridyl complexes, HD-14 and HD-15, compared to previously reported NCSU-10.}, number={48}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Cheema, Hammad and Islam, Ashraful and Younts, Robert and Gautam, Bhoj and Bedja, Idriss and Gupta, Ravindra Kumar and Han, Liyuan and Gundogdu, Kenan and El-Shafei, Ahmed}, year={2014}, pages={27078–27087} }