Cu₂ZnSnSe₄ thin-film solar cells by thermal co-evaporation with 11.6% efficiency and improved minority carrier diffusion length

11.6%-efficiency Cu2ZnSnSe4 (CZTSe) thin-film solar cells are fabricated via a thermal co-evaporation method. The CZTSe thin film with improved microstructure exhibits a minority carrier diffusion length over 2 μm, resulting in efficient photogenerated carrier collection in the device. A comparative study of photoluminescence in pure selenide and pure sulfide devices shows reduced band-tailing for the pure selenide phase.