Synthesis and optical properties of Cu2SnZnS4 films under different sulfur atmospheres

The electrodeposited precursor is a mixture of Cu, Sn, and Zn alloys, these elements form Cu6Sn5 and CuZn binary phases, and subsequently these phases transform into many binary and ternary intermediates, such as CuS, ZnS, Cu2SnS3, and Cu2ZnSnS4 (CZTS) at low annealing temperature in pure sulfur and H2S atmospheres. Finally, CZTS films can be completely formed by sulfidizing at 550 °C for 1 h in pure sulfur and H2S atmospheres. However, the initial temperature of synthesizing CZTS in H2S atmosphere is higher than that in pure sulfur atmosphere, but the highest temperature of synthesizing CZTS in H2S atmosphere is lower than that in pure sulfur atmosphere. The direct band gaps of the CZTS films synthesized at 550 °C for 1 h in pure sulfur and H2S atmospheres are about 1.54 and 1.52 eV, respectively.