@article{HosseiniTokmoldinLeeetal.2020,
  author    = {Hosseini, Seyed Mehrdad and Tokmoldin, Nurlan and Lee, Young Woong and Zou, Yingping and Woo, Han Young and Neher, Dieter and Shoaee, Safa},
  title     = {Putting order into PM6:Y6 solar cells to reduce the langevin recombination in 400 nm thick junction},
  series = {Solar RRL},
  volume    = {4},
  journal   = {Solar RRL},
  number    = {11},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {2367-198X},
  doi       = {10.1002/solr.202000498},
  pages     = {7},
  year      = {2020},
  abstract  = {Increasing the active layer thickness without sacrificing the power conversion efficiency (PCE) is one of the great challenges faced by organic solar cells (OSCs) for commercialization. Recently, PM6:Y6 as an OSC based on a non-fullerene acceptor (NFA) has excited the community because of its PCE reaching as high as 15.9\%; however, by increasing the thickness, the PCE drops due to the reduction of the fill factor (FF). This drop is attributed to change in mobility ratio with increasing thickness. Furthermore, this work demonstrates that by regulating the packing and the crystallinity of the donor and the acceptor, through volumetric content of chloronaphthalene (CN) as a solvent additive, one can improve the FF of a thick PM6:Y6 device (approximate to 400 nm) from 58\% to 68\% (PCE enhances from 12.2\% to 14.4\%). The data indicate that the origin of this enhancement is the reduction of the structural and energetic disorders in the thick device with 1.5\% CN compared with 0.5\% CN. This correlates with improved electron and hole mobilities and a 50\% suppressed bimolecular recombination, such that the non-Langevin reduction factor is 180 times. This work reveals the role of disorder on the charge extraction and bimolecular recombination of NFA-based OSCs.},
  language  = {en}
}
@article{PerdigonToroZhangMarkinaetal.2020,
  author    = {Perdigon-Toro, Lorena and Zhang, Huotian and Markina, Anastaa si and Yuan, Jun and Hosseini, Seyed Mehrdad and Wolff, Christian Michael and Zuo, Guangzheng and Stolterfoht, Martin and Zou, Yingping and Gao, Feng and Andrienko, Denis and Shoaee, Safa and Neher, Dieter},
  title     = {Barrierless free charge generation in the high-performance PM6:Y6 bulk heterojunction non-fullerene solar cell},
  series = {Advanced materials},
  volume    = {32},
  journal   = {Advanced materials},
  number    = {9},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {0935-9648},
  doi       = {10.1002/adma.201906763},
  pages     = {9},
  year      = {2020},
  abstract  = {Organic solar cells are currently experiencing a second golden age thanks to the development of novel non-fullerene acceptors (NFAs). Surprisingly, some of these blends exhibit high efficiencies despite a low energy offset at the heterojunction. Herein, free charge generation in the high-performance blend of the donor polymer PM6 with the NFA Y6 is thoroughly investigated as a function of internal field, temperature and excitation energy. Results show that photocurrent generation is essentially barrierless with near-unity efficiency, regardless of excitation energy. Efficient charge separation is maintained over a wide temperature range, down to 100 K, despite the small driving force for charge generation. Studies on a blend with a low concentration of the NFA, measurements of the energetic disorder, and theoretical modeling suggest that CT state dissociation is assisted by the electrostatic interfacial field which for Y6 is large enough to compensate the Coulomb dissociation barrier.},
  language  = {en}
}
@article{SamsonRechPerdigonToroetal.2020,
  author    = {Samson, Stephanie and Rech, Jeromy and Perdigon-Toro, Lorena and Peng, Zhengxing and Shoaee, Safa and Ade, Harald and Neher, Dieter and Stolterfoht, Martin and You, Wei},
  title     = {Organic solar cells with large insensitivity to donor polymer molar mass across all acceptor classes},
  series = {ACS applied polymer materials},
  volume    = {2},
  journal   = {ACS applied polymer materials},
  number    = {11},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {2637-6105},
  doi       = {10.1021/acsapm.0c01041},
  pages     = {5300 -- 5308},
  year      = {2020},
  abstract  = {Donor polymer number-average molar mass (M-n) has long been known to influence organic photovoltaic (OPV) performance via changes in both the polymer properties and the resulting bulk heterojunction morphology. The exact nature of these M-n effects varies from system to system, although there is generally some intermediate M-n that results in optimal performance. Interestingly, our earlier work with the difluorobenzotriazole (FTAZ)-based donor polymer, paired with either N2200 (polymer acceptor) or PC61BM (fullerene acceptor), PcBm demonstrated <10\% variation in power conversion efficiency and a consistent morphology over a large span of M-n (30 kg/mol to over 100 kg/mol). Would such insensitivity to polymer M-n still hold true when prevailing small molecular acceptors were used with FTAZ? To answer this question, we explored the impact of FTAZ on OPVs with ITIC, a high-performance small-molecule fused-ring electron acceptor (FREA). By probing the photovoltaic characteristics of the resulting OPVs, we show that a similar FTAZ mn insensitivity is also found in the FTAZ:ITIC system. This study highlights a single-donor polymer which, when paired with an archetypal fullerene, polymer, and FREA, results in systems that are largely insensitive to donor M. Our results may have implications in polymer batch-to-batch reproducibility, in particular, relaxing the need for tight M-n control during synthesis.},
  language  = {en}
}
@article{PerdigonToroLeQuangPhuongElleretal.2022,
  author    = {Perdigon-Toro, Lorena and Le Quang Phuong, and Eller, Fabian and Freychet, Guillaume and Saglamkaya, Elifnaz and Khan, Jafar and Wei, Qingya and Zeiske, Stefan and Kroh, Daniel and Wedler, Stefan and Koehler, Anna and Armin, Ardalan and Laquai, Frederic and Herzig, Eva M. and Zou, Yingping and Shoaee, Safa and Neher, Dieter},
  title     = {Understanding the role of order in Y-series non-fullerene solar cells to realize high open-circuit voltages},
  series = {Advanced energy materials},
  volume    = {12},
  journal   = {Advanced energy materials},
  number    = {12},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1614-6832},
  doi       = {10.1002/aenm.202103422},
  pages     = {13},
  year      = {2022},
  abstract  = {Non-fullerene acceptors (NFAs) as used in state-of-the-art organic solar cells feature highly crystalline layers that go along with low energetic disorder. Here, the crucial role of energetic disorder in blends of the donor polymer PM6 with two Y-series NFAs, Y6, and N4 is studied. By performing temperature-dependent charge transport and recombination studies, a consistent picture of the shape of the density of state distributions for free charges in the two blends is developed, allowing an analytical description of the dependence of the open-circuit voltage V-OC on temperature and illumination intensity. Disorder is found to influence the value of the V-OC at room temperature, but also its progression with temperature. Here, the PM6:Y6 blend benefits substantially from its narrower state distributions. The analysis also shows that the energy of the equilibrated free charge population is well below the energy of the NFA singlet excitons for both blends and possibly below the energy of the populated charge transfer manifold, indicating a down-hill driving force for free charge formation. It is concluded that energetic disorder of charge-separated states has to be considered in the analysis of the photovoltaic properties, even for the more ordered PM6:Y6 blend.},
  language  = {en}
}