High-sulfur Cu2ZnSn(S,Se)4 films by sulfurizing as-deposited CZTSe film: The evolutions of phase, crystallinity and S/(S+Se) ratio

Abstract

High-sulfur Cu2ZnSn(S,Se)4 (CZTSSe) films were prepared by sulfurizing as-deposited Cu2ZnSnSe4 (CZTSe) films sputtered from a quaternary target. In this work, we investigated the evolutions of phase, crystallinity and S/(S+Se) of films from as-deposited CZTSe to CZTSSe during sulfurization. During heat treatment, two critical temperatures are found, namely, the formation temperature of CZTSSe between 300 °C and 380 °C and the recrystallization temperature of CZTSSe at around 580 °C. Annealed at above 380 °C, the phase of film transforms from CZTSe to CZTSSe with increasing sulfur content. A high sulfurization temperature is beneficial to grain growth of CZTSSe due to recrystallization. The S/(S+Se) ratio in CZTSSe (typically around 0.8) varies within 0.1 with different sulfurization temperature and time. S/(S+Se) ratio from 0.49 to 0.88 can be obtained by varying H2S volume percentage. In order to obtain wide variation of S/(S+Se) ratio in CZTSSe film, H2S volume percentage is the key parameter. This work demonstrates a promising method for high-S CZTSSe film and the tunability of sulfurization parameters on S/(S+Se) ratio by this method.