TY - JOUR A1 - Pranav, Manasi A1 - Benduhn, Johannes A1 - Nyman, Mathias A1 - Hosseini, Seyed Mehrdad A1 - Kublitski, Jonas A1 - Shoaee, Safa A1 - Neher, Dieter A1 - Leo, Karl A1 - Spoltore, Donato T1 - Enhanced charge selectivity via anodic-C60 layer reduces nonradiative losses in organic solar cells JF - ACS applied materials & interfaces N2 - Interfacial layers in conjunction with suitable charge-transport layers can significantly improve the performance of optoelectronic devices by facilitating efficient charge carrier injection and extraction. This work uses a neat C-60 interlayer on the anode to experimentally reveal that surface recombination is a significant contributor to nonradiative recombination losses in organic solar cells. These losses are shown to proportionally increase with the extent of contact between donor molecules in the photoactive layer and a molybdenum oxide (MoO3) hole extraction layer, proven by calculating voltage losses in low- and high-donor-content bulk heterojunction device architectures. Using a novel in-device determination of the built-in voltage, the suppression of surface recombination, due to the insertion of a thin anodic-C-60 interlayer on MoO3, is attributed to an enhanced built-in potential. The increased built-in voltage reduces the presence of minority charge carriers at the electrodes-a new perspective on the principle of selective charge extraction layers. The benefit to device efficiency is limited by a critical interlayer thickness, which depends on the donor material in bilayer devices. Given the high popularity of MoO3 as an efficient hole extraction and injection layer and the increasingly popular discussion on interfacial phenomena in organic optoelectronic devices, these findings are relevant to and address different branches of organic electronics, providing insights for future device design. KW - nonradiative losses KW - molybdenum oxide KW - organic solar cells KW - interfacial layers KW - charge selectivity Y1 - 2021 U6 - https://doi.org/10.1021/acsami.1c00049 SN - 1944-8244 SN - 1944-8252 VL - 13 IS - 10 SP - 12603 EP - 12609 PB - American Chemical Society CY - Washington ER - TY - GEN A1 - Phuong, Le Quang A1 - Hosseini, Seyed Mehrdad A1 - Sandberg, Oskar J. A1 - Zou, Yingping A1 - Woo, Han Young A1 - Neher, Dieter A1 - Shoaee, Safa T1 - Quantifying quasi-fermi level splitting and open-circuit voltage losses in highly efficient nonfullerene organic solar cells T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The power conversion efficiency (PCE) of state-of-the-art organic solar cells is still limited by significant open-circuit voltage (V-OC) losses, partly due to the excitonic nature of organic materials and partly due to ill-designed architectures. Thus, quantifying different contributions of the V-OC losses is of importance to enable further improvements in the performance of organic solar cells. Herein, the spectroscopic and semiconductor device physics approaches are combined to identify and quantify losses from surface recombination and bulk recombination. Several state-of-the-art systems that demonstrate different V-OC losses in their performance are presented. By evaluating the quasi-Fermi level splitting (QFLS) and the V-OC as a function of the excitation fluence in nonfullerene-based PM6:Y6, PM6:Y11, and fullerene-based PPDT2FBT:PCBM devices with different architectures, the voltage losses due to different recombination processes occurring in the active layers, the transport layers, and at the interfaces are assessed. It is found that surface recombination at interfaces in the studied solar cells is negligible, and thus, suppressing the non-radiative recombination in the active layers is the key factor to enhance the PCE of these devices. This study provides a universal tool to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1384 KW - nonfullerene acceptors KW - organic solar cells KW - quasi-Fermi level KW - splitting KW - quasi-steady-state photoinduced absorptions KW - surface KW - recombinations KW - voltage losses Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-570018 SN - 1866-8372 IS - 1 ER - TY - JOUR A1 - Perdigon-Toro, Lorena A1 - Zhang, Huotian A1 - Markina, Anastaa si A1 - Yuan, Jun A1 - Hosseini, Seyed Mehrdad A1 - Wolff, Christian Michael A1 - Zuo, Guangzheng A1 - Stolterfoht, Martin A1 - Zou, Yingping A1 - Gao, Feng A1 - Andrienko, Denis A1 - Shoaee, Safa A1 - Neher, Dieter T1 - Barrierless free charge generation in the high-performance PM6:Y6 bulk heterojunction non-fullerene solar cell JF - Advanced materials N2 - 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. KW - driving force KW - non-fullerene acceptors KW - organic solar cells KW - photocurrent generation Y1 - 2020 U6 - https://doi.org/10.1002/adma.201906763 SN - 0935-9648 SN - 1521-4095 VL - 32 IS - 9 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Phuong, Le Quang A1 - Hosseini, Seyed Mehrdad A1 - Sandberg, Oskar J. A1 - Zou, Yingping A1 - Woo, Han Young A1 - Neher, Dieter A1 - Shoaee, Safa T1 - Quantifying quasi-fermi level splitting and open-circuit voltage losses in highly efficient nonfullerene organic solar cells JF - Solar RRL N2 - The power conversion efficiency (PCE) of state-of-the-art organic solar cells is still limited by significant open-circuit voltage (V-OC) losses, partly due to the excitonic nature of organic materials and partly due to ill-designed architectures. Thus, quantifying different contributions of the V-OC losses is of importance to enable further improvements in the performance of organic solar cells. Herein, the spectroscopic and semiconductor device physics approaches are combined to identify and quantify losses from surface recombination and bulk recombination. Several state-of-the-art systems that demonstrate different V-OC losses in their performance are presented. By evaluating the quasi-Fermi level splitting (QFLS) and the V-OC as a function of the excitation fluence in nonfullerene-based PM6:Y6, PM6:Y11, and fullerene-based PPDT2FBT:PCBM devices with different architectures, the voltage losses due to different recombination processes occurring in the active layers, the transport layers, and at the interfaces are assessed. It is found that surface recombination at interfaces in the studied solar cells is negligible, and thus, suppressing the non-radiative recombination in the active layers is the key factor to enhance the PCE of these devices. This study provides a universal tool to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells. KW - nonfullerene acceptors KW - organic solar cells KW - quasi-Fermi level KW - splitting KW - quasi-steady-state photoinduced absorptions KW - surface KW - recombinations KW - voltage losses Y1 - 2020 U6 - https://doi.org/10.1002/solr.202000649 SN - 2367-198X VL - 5 IS - 1 PB - Wiley-VCH CY - Weinheim ER -