Sn-Se Binary and Cu-Sn-Se Ternary Thin Films Grown by Co-Evaporation Process

Abstract

Unfavorable secondary phases like binaries and ternaries are often observed in synthesizing Cu2ZnSnSe4 (CZTSe) quaternary crystal due to its narrow phase space, which strongly limits the performance of Kesterite solar cells. To identify the growth parameters against the stability of these secondary phases, we systematically studied the growth process of Sn-Se binaries and Cu-Sn-Se ternaries using co-evaporation method. We found that the compositions of Sn-related binary and ternary phases were strongly dependent on the substrate temperature and Se flux during deposition, which will be helpful in designing formation paths for quaternary system. Growth temperature of CZTSe higher than 490 °C will make the thin film free of Cu2SnSe3 phase. Our experiments also suggest that formation pathways in the Cu2SnSe3-ZnSe pseudobinary phase diagram at a slightly lower substrate temperature deserve more experimental and theoretical considerations because of its easier composition control.