Effect of S/(S+Se) ratio during the annealing process on the performance of Cu2ZnSn(S,Se)4 solar cells prepared by sputtering from a quaternary target

Abstract Cu2ZnSn(S,Se)4 (CZTSSe) has gained significant attention as a solar cell absorber material owing to its great long-time application potential. In this study, the precursors deposited by single quaternary target sputtering were annealed in different S/S + Se ratios atmosphere and CZTSSe solar cells were prepared. The mechanism of the S/Se replacement process and its effect on the composition, morphology, bandgap, and performance of the CZTSSe solar cells were systematically investigated. It was found that a decrease in the Se content in the annealing atmosphere showed an effect on the growth and properties of the thin films similar to that shown by an increase in the S/(S + Se) ratio. However, this effect was much milder than that of the increase in the S/(S + Se) ratio. The S/(S + Se) ratio of the CZTSSe thin films could be controlled by varying their S and Se contents in the annealing atmosphere and then adjusting their bandgaps. An increase in the bandgap improved the open circuit voltage and efficiency of the resulting solar cells. The cell annealed with the S:Se molar ratio of 1:3 showed an efficiency of 8.41% without anti-reflection coating.