Fabrication of Cu2ZnSn(S,Se)4 thin film solar cells by selenization of reactively sputtered precursors

Cu2ZnSn(S,Se)4 thin films were fabricated by selenization of reactively sputtered precursors. The precursors showed a fully sulfurized Cu2ZnSnS4 phase with compact surface and columnar structure. The evolutions of composition, morphology and phases for the selenized films were investigated. The selenization resulted in dramatic changes in morphologies, but demonstrated excellent stability on metallic composition and negligible volume expansion of the selenized films. The selenized films show densely packed large grains and single kesterite Cu2ZnSn(S,Se)4 phase. The solar cell with the structure of ITO/i-ZnO/CdS/CZTSSe/Mo/Glass presents the highest power conversion efficiency of 4.3%. The key limitation factor is due to low fill factor, which is mainly caused by a low shunt resistance and severe voltage-dependent photocurrent collection.