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  Ruiz-Perona, A.; Palma-Lafuente, D.; Sánchez, Y.; Guc, M.; Kodalle, T.; Salem, M.O.; Placidi, M.; Serna, R.; Pérez-Rodríguez, A.; Merino, J.M.; Caballero, R.: Semitransparent Wide Bandgap Cu₂ZnGe(S,Se)₄ Thin-Film Solar Cells: Role of the Sulfurization Process. Solar RRL 8 (2024), p. 2300947/1-9

10.1002/solr.202300947
Open Access Version

Abstract:
Semitransparent solar cells are very attractive due to the increasing integration in daily life. Kesterite-type based thin-film solar cells stand out because of its environmentally benign composition and outstanding stability. Herein, the influence of the back contact (Mo/V2O5/FTO or Mo/FTO) and thickness of Cu2ZnGe(S,Se)4 (CZGSSe) absorber layer, grown by sulfurization of coevaporated CZGSe, is investigated. To increase the transparency, thinner absorber layers with higher bandgap energy are produced. A double sulfur gradient through the CZGSSe layer with a considerable S content near the back contact and the formation of Mo(S,Se)2 phase at the back interface is detected for an absorber of only 400 nm thickness. Efficiencies of 3.1% and 2.7% are achieved for 1.2 μm CZGSSe-based devices with Eg of 1.73 and 1.86 eV, respectively, while enabling transmittance values higher than 20% in the near-infrared (NIR). The highest transmittance, 40% in the NIR, is achieved for the 400 nm CZGSSe-based solar cells with Eg of 2.1 eV; however, a significant reduction of these devices’ performance is obtained due to the presence of ZnS secondary phase and a different back-contact interface formation. This work presents the first promising semitransparent CZGSSe solar cells, opening new paths of applications.