TY - JOUR A1 - Yetkin, Hasan A. A1 - Kodalle, Tim A1 - Bertram, Tobias A1 - Villanueva‐Tovar, Alejandra A1 - Rusu, Marin A1 - Klenk, Reiner A1 - Szyszka, Bernd A1 - Schlatmann, Rutger A1 - Kaufmann, Christian A. T1 - Decay mechanisms in CdS‐buffered Cu(In,Ga)Se2 thin‐film solar cells after exposure to thermal stress: Understanding the role of Na JF - Progress in Photovoltaics: Research and Applications N2 - Due to their tunable bandgap energy, Cu(In,Ga)Se2 (CIGSe) thin‐film solar cells are an attractive option for use as bottom devices in tandem configurations. In monolithic tandem devices, the thermal stability of the bottom device is paramount for reliable application. Ideally, it will permit the processing of a top device at the required optimum process temperature. Here, we investigate the degradation behavior of chemical bath deposited (CBD) CdS‐buffered CIGSe thin‐film solar cells with and without Na incorporation under thermal stress in ambient air and vacuum with the aim to gain a more detailed understanding of their degradation mechanisms. For the devices studied, we observe severe degradation after annealing at 300°C independent of the atmosphere. The electrical and compositional properties of the samples before and after a defined application of thermal stress are studied. In good agreement with literature reports, we find pronounced Cd diffusion into the CIGS absorber layer. In addition, for Na‐containing samples, the observed degradation can be mainly explained by the formation of Na‐induced acceptor states in the TCO front contact and a back contact barrier formation due to the out‐diffusion of Na. Supported by numerical device simulation using SCAPS‐1D, various possible degradation models are discussed and correlated with our findings. KW - CdS buffer layer KW - CIGSe KW - degradation mechanism KW - elemental interdiffusion KW - Na KW - SCAPS KW - simulation KW - thermal stress Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:523-15138 VL - 29 IS - 9 SP - 1034 EP - 1053 PB - Wiley ER - TY - JOUR A1 - Villanueva-Tovar, Alejandra A1 - Kodalle, Tim A1 - Kaufmann, Christian A. A1 - Schlatmann, Rutger A1 - Klenk, Reiner T1 - Limitation of Current Transport across the Heterojunction in Cu(In,Ga)Se2 Solar Cells Prepared with Alkali Fluoride Postdeposition Treatment JF - Solar RRL N2 - Postdeposition treatments (PDTs) of chalcopyrite absorbers with alkali fluorides have contributed to improving the efficiency of corresponding solar cell devices. However, cells prepared with PDTs also tend to exhibit nonideal current–voltage (J–V) characteristics especially at low temperatures. These include blocking of the forward diode current, saturation of the open‐circuit voltage with respect to temperature, a discrepancy between dark and Jsc (Voc) characteristics, and a crossover between dark and light J–V curves. These are typical observations while measuring the temperature‐dependent J–V characteristics. Herein, the influence of electronic material parameters on the blocking of the current across the heterojunction in numerical simulations is reported. It is shown that a low‐doped ZnO window layer, acceptor defects at the CdS/ZnO interface, or a high band offset at that interface lead to similar nonideal J–V characteristics, suggesting that the carrier density in the buffer layer is a crucial parameter for the current limitation. Connections between the effects of PDT previously reported in literature and the electronic material parameters considered in the numerical model are discussed to explain the nonideal J–V characteristics caused by the PDTs. KW - alkali fluoride postdeposition treatments KW - Cu(In,Ga)Se KW - current transports KW - nonideal characteristics KW - numerical simulations Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:523-14503 VL - 4 IS - 4 ER - TY - JOUR A1 - Farias-Basulto, Guillermo A1 - Mehlhop, Thede A1 - Otto, Nicolas J. A1 - Bertram, Tobias A1 - Jäger, Klaus A1 - Gall, Stefan A1 - Weinberger, Nikolaus A1 - Schlatmann, Rutger A1 - Lauermann, Iver A1 - Klenk, Reiner A1 - List-Kratochvil, Emil A1 - Kaufmann, Christian A. T1 - Improving Perovskite/CIGS Tandem Solar Cells for Higher Power Conversion Efficiency through Light Management and Bandgap Engineering JF - ACS Applied Materials & Interfaces N2 - Perovskite and chalcopyrite materials are excellent absorbers for highly efficient, all-thin-film tandem solar cells. This work presents a certified world record for such a device, achieving a power conversion efficiency of 24.6 ± 1.1% under steady-state conditions. The best IV parameters extracted from certified current–voltage measurements presented a short-circuit current density of around 19.3 mA/cm 2 , an open-circuit voltage of 1.765 V, and a fill factor of 71.8%. In comparison to our previous record, the current density improved considerably, mainly due to the lowering of the bandgap of the bottom subcell and the improved optics of the top perovskite cell. KW - Photovoltaic KW - photovoltaic KW - thin-film KW - solar Cell KW - CIGS KW - perovskite KW - tandem KW - record KW - Solar Cell KW - CIGS solar cells KW - Perovskite Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:523-21725 SN - 1944-8244 SN - 1944-8252 VL - 17 IS - 40 SP - 56250 EP - 56255 PB - American Chemical Society ER - TY - JOUR A1 - Farias‐Basulto, Guillermo A1 - Kafedjiska, Ivona A1 - Bertram, Tobias A1 - Riedel, Maximilian A1 - Emery, Quiterie A1 - Remec, Marko A1 - Graniero, Paolo A1 - Khenkin, Mark A1 - Kaufmann, Christian A. A1 - Lauermann, Iver A1 - Klenk, Reiner A1 - Schlatmann, Rutger A1 - Ulbrich, Carolin T1 - Perovskite‐CIGSe Tandem Solar Cell: Over One Year of Outdoor Monitoring JF - Advanced Energy and Sustainability Research N2 - Tandem solar cells can surpass the limitations of single‐junction devices, promising increased performance due to lower thermalization losses. Even though many research and industrial upscaling efforts are based on perovskite‐Si tandems, all‐thin‐film photovoltaic (PV) devices, for instance with chalcopyrite (CIGSe) and perovskite, can offer many advantages such as significant cost and material savings and access to niche markets like building integrated‐ and flexible PV. However, long‐term stability and outdoor performance of perovskite‐based tandem devices is to this day challenging. This work presents the first data analysis of year‐round outdoor measurements (mpp‐tracked) of a perovskite‐chalcopyrite tandem device with a starting efficiency of about 23.14% before encapsulation. The maximum outdoor performance of the tandem device changed during the period of observation, reaching the peak performance in April and then decreased due to the device degradation. At its maximum outdoor performance, the tandem could reach up to 68% higher instantaneous power output, relative to its single‐junction reference (CIGSe‐SJ). In addition, a quantitative time series performance analysis, exemplary qualitative imaging characterization of the tandem before and after outdoor exposure, is shown. Finally, the possibility of predicting the immediate performance of an all‐thin‐film tandem is verified by using a multiple linear regression model with accuracies generally exceeding 90%. KW - Machine learning KW - Cu(In,Ga)Se KW - machine learning KW - perovskite KW - solar energy KW - tandem KW - Perovskite KW - Solar energy Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:523-22159 SN - 2699-9412 VL - 6 IS - 12 ER -