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 - Krückemeier, Lisa A1 - Rau, Uwe A1 - Stolterfoht, Martin A1 - Kirchartz, Thomas T1 - How to report record open-circuit voltages in lead-halide perovskite solar cells JF - Advanced energy materials N2 - Open-circuit voltages of lead-halide perovskite solar cells are improving rapidly and are approaching the thermodynamic limit. Since many different perovskite compositions with different bandgap energies are actively being investigated, it is not straightforward to compare the open-circuit voltages between these devices as long as a consistent method of referencing is missing. For the purpose of comparing open-circuit voltages and identifying outstanding values, it is imperative to use a unique, generally accepted way of calculating the thermodynamic limit, which is currently not the case. Here a meta-analysis of methods to determine the bandgap and a radiative limit for open-circuit voltage is presented. The differences between the methods are analyzed and an easily applicable approach based on the solar cell quantum efficiency as a general reference is proposed. KW - bandgap KW - fill factor losses KW - nonradiative voltage losses KW - photovoltaics KW - radiative limit KW - recombination KW - Shockley-Queisser model Y1 - 2019 U6 - https://doi.org/10.1002/aenm.201902573 SN - 1614-6832 SN - 1614-6840 VL - 10 IS - 1 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Kegelmann, Lukas A1 - Tockhorn, Philipp A1 - Wolff, Christian Michael A1 - Márquez, José A. A1 - Caicedo Dávila, Sebastián A1 - Korte, Lars A1 - Unold, Thomas A1 - Loevenich, Wilfried A1 - Neher, Dieter A1 - Rech, Bernd A1 - Albrecht, Steve T1 - Mixtures of Dopant-Free Spiro-OMeTAD and Water-Free PEDOT as a Passivating Hole Contact in Perovskite Solar Cells JF - ACS applied materials & interfaces N2 - Doped spiro-OMeTAD at present is the most commonly used hole transport material (HTM) in n-i-p-type perovskite solar cells, enabling high efficiencies around 22%. However, the required dopants were shown to induce nonradiative recombination of charge carriers and foster degradation of the solar cell. Here, in a novel approach, highly conductive and inexpensive water-free poly(3,4-ethylenedioxythiophene) (PEDOT) is used to replace these dopants. The resulting spiro-OMeTAD/PEDOT (SpiDOT) mixed films achieve higher lateral conductivities than layers of doped spiro-OMeTAD. Furthermore, combined transient and steady-state photoluminescence studies reveal a passivating effect of PEDOT, suppressing nonradiative recombination losses at the perovskite/HTM interface. This enables excellent quasi-Fermi level splitting values of up to 1.24 eV in perovskite/SpiDOT layer stacks and high open-circuit voltages (V-OC) up to 1.19 V in complete solar cells. Increasing the amount of dopant-free spiro-OMeTAD in SpiDOT layers is shown to enhance hole extraction and thereby improves the fill factor in solar cells. As a consequence, stabilized efficiencies up to 18.7% are realized, exceeding cells with doped spiro-OMeTAD as a HTM in this study. Moreover, to the best of our knowledge, these results mark the lowest nonradiative recombination loss in the V-OC (140 mV with respect to the Shockley-Queisser limit) and highest efficiency reported so far for perovskite solar cells using PEDOT as a HTM. KW - perovskite solar cell KW - selective contact KW - spiro-OMeTAD KW - PEDOT KW - recombination KW - passivation KW - quasi-Fermi level splitting Y1 - 2019 U6 - https://doi.org/10.1021/acsami.9b01332 SN - 1944-8244 SN - 1944-8252 VL - 11 IS - 9 SP - 9172 EP - 9181 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Gao, Feng A1 - Wang, Jianpu A1 - Blakesley, James C. A1 - Hwang, Inchan A1 - Li, Zhe A1 - Greenham, Neil C. T1 - Quantifying loss mechanisms in polymer Fullerene photovoltaic devices JF - dvanced energy materials KW - organic photovoltaics KW - recombination KW - bulk heterojunctions KW - loss mechanisms KW - drift-diffusion models Y1 - 2012 U6 - https://doi.org/10.1002/aenm.201200073 SN - 1614-6832 VL - 2 IS - 8 SP - 956 EP - 961 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Baunach, Martin A1 - Chowdhury, Somak A1 - Stallforth, Pierre A1 - Dittmann-Thünemann, Elke T1 - The landscape of recombination events that create nonribosomal peptide diversity JF - Molecular biology and evolution : MBE N2 - Nonribosomal peptides (NRP) are crucial molecular mediators in microbial ecology and provide indispensable drugs. Nevertheless, the evolution of the flexible biosynthetic machineries that correlates with the stunning structural diversity of NRPs is poorly understood. Here, we show that recombination is a key driver in the evolution of bacterial NRP synthetase (NRPS) genes across distant bacterial phyla, which has guided structural diversification in a plethora of NRP families by extensive mixing andmatching of biosynthesis genes. The systematic dissection of a large number of individual recombination events did not only unveil a striking plurality in the nature and origin of the exchange units but allowed the deduction of overarching principles that enable the efficient exchange of adenylation (A) domain substrates while keeping the functionality of the dynamic multienzyme complexes. In the majority of cases, recombination events have targeted variable portions of the A(core) domains, yet domain interfaces and the flexible A(sub) domain remained untapped. Our results strongly contradict the widespread assumption that adenylation and condensation (C) domains coevolve and significantly challenge the attributed role of C domains as stringent selectivity filter during NRP synthesis. Moreover, they teach valuable lessons on the choice of natural exchange units in the evolution of NRPS diversity, which may guide future engineering approaches. KW - evolution KW - recombination KW - structural diversity KW - natural products KW - nonribosomal peptide synthetases KW - microbial ecology Y1 - 2021 U6 - https://doi.org/10.1093/molbev/msab015 SN - 0737-4038 SN - 1537-1719 VL - 38 IS - 5 SP - 2116 EP - 2130 PB - Oxford Univ. Press CY - Oxford ER -