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 -