Cu<inf>2</inf>SrSnS<inf>4</inf> absorber based efficient heterostructure single junction solar cell: a hybrid-DFT and macroscopic simulation studies

The Quaternary Chalcogenide material Cu2ZnSn(S,Se)4 showed all the optimum material properties suitable for photovoltaic application. Yet, the current development has slowed down due to band-tailing issues and challenges to overcome. It causes the potential fluctuation for conduction band minima and valence band maxima. We introduced large ionic radii Sr in place of Zn to address the band tailing issue and demonstrated that Cu2SrSnS4 (CSTS) material is a promising alternative of Cu2ZnSn(S,Se)4 for solar cell application using a hybrid computational approach. The structural and optoelectronic properties of Cu2SrSnS4 are computed using the density functional approach. The direct bandgap of Cu2SrSnS4 of ~ 1.78 eV and significant absorption coefficient in the desired spectral range makes it a suitable absorber material for heterojunction solar cell. The computed materials properties are used to investigate the single junction photovoltaic device performance by introducing the realistic defect densities, recombination rate, electron affinity, and back electrode work function with two different buffer layers (CdS and ZnS). The devices, i.e., AZO/ZnO/CdS/CSTS/Mo and AZO/ZnO/ZnS/CSTS/Mo showed > 17.71% and > 20.12% photoconversion efficiency under optimized conditions. These devices exhibit nearly identical Jsc, whereas the device with ZnS buffer layer showed relatively larger Voc. Further, graphene as the ETL layer is evaluated and showed possible alternative to the conventional AZnO/ZO layers. This study shows the potential of Cu2SrSnS4 (CSTS) for an alternative absorber-based single heterojunction photovoltaic device with a large efficiency.