TY - JOUR A1 - Ran, Niva A. A1 - Love, John A. A1 - Heiber, Michael C. A1 - Jiao, Xuechen A1 - Hughes, Michael P. A1 - Karki, Akchheta A1 - Wang, Ming A1 - Brus, Viktor V. A1 - Wang, Hengbin A1 - Neher, Dieter A1 - Ade, Harald A1 - Bazan, Guillermo C. A1 - Thuc-Quyen Nguyen, T1 - Charge generation and recombination in an organic solar cell with low energetic offsets JF - dvanced energy materials N2 - Organic bulk heterojunction (BHJ) solar cells require energetic offsets between the donor and acceptor to obtain high short-circuit currents (J(SC)) and fill factors (FF). However, it is necessary to reduce the energetic offsets to achieve high open-circuit voltages (V-OC). Recently, reports have highlighted BHJ blends that are pushing at the accepted limits of energetic offsets necessary for high efficiency. Unfortunately, most of these BHJs have modest FF values. How the energetic offset impacts the solar cell characteristics thus remains poorly understood. Here, a comprehensive characterization of the losses in a polymer:fullerene BHJ blend, PIPCP:phenyl-C61-butyric acid methyl ester (PC61BM), that achieves a high V-OC (0.9 V) with very low energy losses (E-loss = 0.52 eV) from the energy of absorbed photons, a respectable J(SC) (13 mA cm(-2)), but a limited FF (54%) is reported. Despite the low energetic offset, the system does not suffer from field-dependent generation and instead it is characterized by very fast nongeminate recombination and the presence of shallow traps. The charge-carrier losses are attributed to suboptimal morphology due to high miscibility between PIPCP and PC61BM. These results hold promise that given the appropriate morphology, the J(SC), V-OC, and FF can all be improved, even with very low energetic offsets. KW - energetic offset KW - fill factor KW - morphology KW - organic solar cells KW - recombination Y1 - 2018 U6 - https://doi.org/10.1002/aenm.201701073 SN - 1614-6832 SN - 1614-6840 VL - 8 IS - 5 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Ran, Niva A. A1 - Roland, Steffen A1 - Love, John A. A1 - Savikhin, Victoria A1 - Takacs, Christopher J. A1 - Fu, Yao-Tsung A1 - Li, Hong A1 - Coropceanu, Veaceslav A1 - Liu, Xiaofeng A1 - Bredas, Jean-Luc A1 - Bazan, Guillermo C. A1 - Toney, Michael F. A1 - Neher, Dieter A1 - Thuc-Quyen Nguyen, T1 - Impact of interfacial molecular orientation on radiative recombination and charge generation efficiency JF - Nature Communications N2 - A long standing question in organic electronics concerns the effects of molecular orientation at donor/acceptor heterojunctions. Given a well-controlled donor/acceptor bilayer system, we uncover the genuine effects of molecular orientation on charge generation and recombination. These effects are studied through the point of view of photovoltaics-however, the results have important implications on the operation of all optoelectronic devices with donor/ acceptor interfaces, such as light emitting diodes and photodetectors. Our findings can be summarized by two points. First, devices with donor molecules face-on to the acceptor interface have a higher charge transfer state energy and less non-radiative recombination, resulting in larger open-circuit voltages and higher radiative efficiencies. Second, devices with donor molecules edge-on to the acceptor interface are more efficient at charge generation, attributed to smaller electronic coupling between the charge transfer states and the ground state, and lower activation energy for charge generation. Y1 - 2017 U6 - https://doi.org/10.1038/s41467-017-00107-4 SN - 2041-1723 VL - 8 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Love, John A. A1 - Chou, Shu-Hua A1 - Huang, Ye A1 - Bazan, Guillermo C. A1 - Thuc-Quyen Nguyen, T1 - Effects of solvent additive on "s-shaped" curves in solution-processed small molecule solar cells JF - Beilstein journal of organic chemistry N2 - A novel molecular chromophore, p-SIDT(FBTThCA8)(2), is introduced as an electron-donor material for bulk heterojunction (BHJ) solar cells with broad absorption and near ideal energy levels for the use in combination with common acceptor materials. It is found that films cast from chlorobenzene yield devices with strongly s-shaped current-voltage curves, drastically limiting performance. We find that addition of the common solvent additive diiodooctane, in addition to facilitating crystallization, leads to improved vertical phase separation. This yields much better performing devices, with improved curve shape, demonstrating the importance of morphology control in BHJ devices and improving the understanding of the role of solvent additives. KW - current voltage analysis KW - morphology KW - organic solar cells Y1 - 2016 U6 - https://doi.org/10.3762/bjoc.12.249 SN - 1860-5397 VL - 12 SP - 2543 EP - 2555 PB - Beilstein-Institut zur Förderung der Chemischen Wissenschaften CY - Frankfurt, Main ER - TY - JOUR A1 - Proctor, Christopher M. A1 - Albrecht, Steve A1 - Kuik, Martijn A1 - Neher, Dieter A1 - Thuc-Quyen Nguyen, T1 - Overcoming geminate recombination and enhancing extraction in solution-processed small molecule solar cells JF - dvanced energy materials Y1 - 2014 U6 - https://doi.org/10.1002/aenm.201400230 SN - 1614-6832 SN - 1614-6840 VL - 4 IS - 10 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Proctor, Christopher M. A1 - Kim, Chunki A1 - Neher, Dieter A1 - Thuc-Quyen Nguyen, T1 - Nongeminate recombination and charge transport limitations in diketopyrrolopyrrole-based solution-processed small molecule solar cells JF - Advanced functional materials N2 - Charge transport and nongeminate recombination are investigated in two solution-processed small molecule bulk heterojunction solar cells consisting of diketopyrrolopyrrole (DPP)-based donor molecules, mono-DPP and bis-DPP, blended with [6,6]-phenyl-C71-butyric acid methyl ester (PCBM). While the bis-DPP system exhibits a high fill factor (62%) the mono-DPP system suffers from pronounced voltage dependent losses, which limit both the fill factor (46%) and short circuit current. A method to determine the average charge carrier density, recombination current, and effective carrier lifetime in operating solar cells as a function of applied bias is demonstrated. These results and light intensity measurements of the current-voltage characteristics indicate that the mono-DPP system is severely limited by nongeminate recombination losses. Further analysis reveals that the most significant factor leading to the difference in fill factor is the comparatively poor hole transport properties in the mono-DPP system (2 x 10(-5) cm(2) V-1 s(-1) versus 34 x 10(-5) cm(2) V-1 s(-1)). These results suggest that future design of donor molecules for organic photovoltaics should aim to increase charge carrier mobility thereby enabling faster sweep out of charge carriers before they are lost to nongeminate recombination. KW - charge transport KW - solar cells KW - photovoltaic devices KW - organic electronics KW - characterization tools Y1 - 2013 U6 - https://doi.org/10.1002/adfm.201202643 SN - 1616-301X SN - 1616-3028 VL - 23 IS - 28 SP - 3584 EP - 3594 PB - Wiley-VCH CY - Weinheim ER -