Regulation of Zn/Sn ratio in kesterite absorbers to boost 10% efficiency of Cu2ZnSn(S, Se)4 solar cells*

The Zn/Sn ratio in Cu2ZnSn(S, Se)4 (CZTSSe) films has been regulated to control the composition-related phase, defect, and photoelectric properties for high performance kesterite solar cells. It is found that the increase in the Zn/Sn ratio can slightly narrow the energy band gap to extend the light absorption range and improve the photocurrent. Optimal Zn/Sn ratio of 1.39 in CZTSSe film is obtained with the least secondary phase, the lowest defect density, and the longest charge recombination lifetime. Up to 10.1% photoelectric conversion efficiency has been achieved by this composition regulation.