TY - JOUR A1 - Zhang, Shanshan A1 - Hosseini, Seyed Mehrdad A1 - Gunder, Rene A1 - Petsiuk, Andrei A1 - Caprioglio, Pietro A1 - Wolff, Christian Michael A1 - Shoaee, Safa A1 - Meredith, Paul A1 - Schorr, Susan A1 - Unold, Thomas A1 - Burn, Paul L. A1 - Neher, Dieter A1 - Stolterfoht, Martin T1 - The Role of Bulk and Interface Recombination in High-Efficiency Low-Dimensional Perovskite Solar Cells JF - Advanced materials N2 - 2D Ruddlesden-Popper perovskite (RPP) solar cells have excellent environmental stability. However, the power conversion efficiency (PCE) of RPP cells remains inferior to 3D perovskite-based cells. Herein, 2D (CH3(CH2)(3)NH3)(2)(CH3NH3)(n-1)PbnI3n+1 perovskite cells with different numbers of [PbI6](4-) sheets (n = 2-4) are analyzed. Photoluminescence quantum yield (PLQY) measurements show that nonradiative open-circuit voltage (V-OC) losses outweigh radiative losses in materials with n > 2. The n = 3 and n = 4 films exhibit a higher PLQY than the standard 3D methylammonium lead iodide perovskite although this is accompanied by increased interfacial recombination at the top perovskite/C-60 interface. This tradeoff results in a similar PLQY in all devices, including the n = 2 system where the perovskite bulk dominates the recombination properties of the cell. In most cases the quasi-Fermi level splitting matches the device V-OC within 20 meV, which indicates minimal recombination losses at the metal contacts. The results show that poor charge transport rather than exciton dissociation is the primary reason for the reduction in fill factor of the RPP devices. Optimized n = 4 RPP solar cells had PCEs of 13% with significant potential for further improvements. KW - 2D perovskites KW - interface recombination KW - perovskite solar cells KW - photoluminescence KW - V-OC loss Y1 - 2019 U6 - https://doi.org/10.1002/adma.201901090 SN - 0935-9648 SN - 1521-4095 VL - 31 IS - 30 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Caprioglio, Pietro A1 - Stolterfoht, Martin A1 - Wolff, Christian Michael A1 - Unold, Thomas A1 - Rech, Bernd A1 - Albrecht, Steve A1 - Neher, Dieter T1 - On the relation between the open-circuit voltage and quasi-fermi level splitting in efficient perovskite solar cells JF - advanced energy materials N2 - Today's perovskite solar cells (PSCs) are limited mainly by their open‐circuit voltage (VOC) due to nonradiative recombination. Therefore, a comprehensive understanding of the relevant recombination pathways is needed. Here, intensity‐dependent measurements of the quasi‐Fermi level splitting (QFLS) and of the VOC on the very same devices, including pin‐type PSCs with efficiencies above 20%, are performed. It is found that the QFLS in the perovskite lies significantly below its radiative limit for all intensities but also that the VOC is generally lower than the QFLS, violating one main assumption of the Shockley‐Queisser theory. This has far‐reaching implications for the applicability of some well‐established techniques, which use the VOC as a measure of the carrier densities in the absorber. By performing drift‐diffusion simulations, the intensity dependence of the QFLS, the QFLS‐VOC offset and the ideality factor are consistently explained by trap‐assisted recombination and energetic misalignment at the interfaces. Additionally, it is found that the saturation of the VOC at high intensities is caused by insufficient contact selectivity while heating effects are of minor importance. It is concluded that the analysis of the VOC does not provide reliable conclusions of the recombination pathways and that the knowledge of the QFLS‐VOC relation is of great importance. KW - electro-optical materials KW - perovskite solar cells KW - photovoltaic devices KW - thin films Y1 - 2019 U6 - https://doi.org/10.1002/aenm.201901631 SN - 1614-6832 SN - 1614-6840 VL - 9 IS - 33 PB - Wiley-VCH CY - Weinheim ER - TY - GEN A1 - Caprioglio, Pietro A1 - Stolterfoht, Martin A1 - Wolff, Christian Michael A1 - Unold, Thomas A1 - Rech, Bernd A1 - Albrecht, Steve A1 - Neher, Dieter T1 - On the relation between the open‐circuit voltage and quasi‐Fermi level splitting in efficient perovskite solar cells T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe N2 - Today's perovskite solar cells (PSCs) are limited mainly by their open‐circuit voltage (VOC) due to nonradiative recombination. Therefore, a comprehensive understanding of the relevant recombination pathways is needed. Here, intensity‐dependent measurements of the quasi‐Fermi level splitting (QFLS) and of the VOC on the very same devices, including pin‐type PSCs with efficiencies above 20%, are performed. It is found that the QFLS in the perovskite lies significantly below its radiative limit for all intensities but also that the VOC is generally lower than the QFLS, violating one main assumption of the Shockley‐Queisser theory. This has far‐reaching implications for the applicability of some well‐established techniques, which use the VOC as a measure of the carrier densities in the absorber. By performing drift‐diffusion simulations, the intensity dependence of the QFLS, the QFLS‐VOC offset and the ideality factor are consistently explained by trap‐assisted recombination and energetic misalignment at the interfaces. Additionally, it is found that the saturation of the VOC at high intensities is caused by insufficient contact selectivity while heating effects are of minor importance. It is concluded that the analysis of the VOC does not provide reliable conclusions of the recombination pathways and that the knowledge of the QFLS‐VOC relation is of great importance. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 774 KW - electro‐optical materials KW - perovskite solar cells KW - photovoltaic devices KW - thin films Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-437595 SN - 1866-8372 IS - 774 ER - TY - JOUR A1 - Schulze, Patricia S. C. A1 - Bett, Alexander J. A1 - Bivour, Martin A1 - Caprioglio, Pietro A1 - Gerspacher, Fabian M. A1 - Kabaklı, Özde Ş. A1 - Richter, Armin A1 - Stolterfoht, Martin A1 - Zhang, Qinxin A1 - Neher, Dieter A1 - Hermle, Martin A1 - Hillebrecht, Harald A1 - Glunz, Stefan W. A1 - Goldschmidt, Jan Christoph T1 - 25.1% high-efficiency monolithic perovskite silicon tandem solar cell with a high bandgap perovskite absorber JF - Solar RRL N2 - Monolithic perovskite silicon tandem solar cells can overcome the theoretical efficiency limit of silicon solar cells. This requires an optimum bandgap, high quantum efficiency, and high stability of the perovskite. Herein, a silicon heterojunction bottom cell is combined with a perovskite top cell, with an optimum bandgap of 1.68 eV in planar p-i-n tandem configuration. A methylammonium-free FA(0.75)Cs(0.25)Pb(I0.8Br0.2)(3) perovskite with high Cs content is investigated for improved stability. A 10% molarity increase to 1.1 m of the perovskite precursor solution results in approximate to 75 nm thicker absorber layers and 0.7 mA cm(-2) higher short-circuit current density. With the optimized absorber, tandem devices reach a high fill factor of 80% and up to 25.1% certified efficiency. The unencapsulated tandem device shows an efficiency improvement of 2.3% (absolute) over 5 months, showing the robustness of the absorber against degradation. Moreover, a photoluminescence quantum yield analysis reveals that with adapted charge transport materials and surface passivation, along with improved antireflection measures, the high bandgap perovskite absorber has the potential for 30% tandem efficiency in the near future. KW - heterojunction silicon solar cells KW - interfaces KW - perovskite solar cells KW - tandem solar cells KW - thin films Y1 - 2020 VL - 4 IS - 7 PB - John Wiley & Sons, Inc. CY - New Jersey ER - TY - JOUR A1 - Wolff, Christian Michael A1 - Zu, Fengshuo A1 - Paulke, Andreas A1 - Perdigon-Toro, Lorena A1 - Koch, Norbert A1 - Neher, Dieter T1 - Reduced Interface-Mediated Recombination for High Open-Circuit Voltages in CH3NH3PbI3 Solar Cells JF - Advanced materials N2 - Perovskite solar cells with all-organic transport layers exhibit efficiencies rivaling their counterparts that employ inorganic transport layers, while avoiding high-temperature processing. Herein, it is investigated how the choice of the fullerene derivative employed in the electron-transporting layer of inverted perovskite cells affects the open-circuit voltage (V-OC). It is shown that nonradiative recombination mediated by the electron-transporting layer is the limiting factor for the V-OC in the cells. By inserting an ultrathin layer of an insulating polymer between the active CH3NH3PbI3 perovskite and the fullerene, an external radiative efficiency of up to 0.3%, a V-OC as high as 1.16 V, and a power conversion efficiency of 19.4% are realized. The results show that the reduction of nonradiative recombination due to charge-blocking at the perovskite/organic interface is more important than proper level alignment in the search for ideal selective contacts toward high V-OC and efficiency. KW - electron-transport layers KW - nonradiative recombination KW - open-circuit voltage KW - perovskite solar cells Y1 - 2017 U6 - https://doi.org/10.1002/adma.201700159 SN - 0935-9648 SN - 1521-4095 VL - 29 PB - Wiley-VCH CY - Weinheim ER -