Sn Substitution by Ge: Strategies to Overcome the Open-Circuit Voltage Deficit of Kesterite Solar Cells

• DOI: 10.1021/acsaem.0c00763
• Publication Date: 2020-05-12T16:32:45Z
• Authors: Leo Choubrac; Marcus Bär; Xeniya Kozina; Roberto Félix; Regan G. Wilks; Guy Brammertz; Sergiu Levcenko; Ludovic Arzel; Nicolas Barreau; Sylvie Harel; Marc Meuris; Bart Vermang
• Keywords: Kesterite; Substitution (logic); Open-circuit voltage

Current state-of-the-art Cu2ZnSn(S,Se)4 kesterite solar cells are limited by low open-circuit voltages (VOC). In order to evaluate what extent the substitution of Sn Ge is able result in higher VOC values, this article focuses on Cu2ZnGeSe4 "CZGSe" devices. To reveal their full potential, different strategies explored that, particular, aim at optimization CZGSe/buffer heterojunction. Here, employing hard X-ray photoelectron spectroscopy, it evidenced that only a combination surface treatments remove all detrimental secondary phases. Further improvements achieved establishing cell heat treatment air. A systematic study impact annealing temperatures and durations determines best parameters be 60 min 200 °C. Also, Zn(O,S,OH) as more transparent alternative heavy-metal compound CdS buffer layer has been realized. Combining strategies, with 8.5 7.5% total area efficiency have prepared, which record for Sn-free any buffer, respectively. Beyond these records, work clearly confirms emerging trend Ge-for-Sn successful strategy improve cells.