Regulation of Zn/Sn ratio in kesterite absorbers to boost 10% efficiency of Cu_2ZnSn(S,Se)_4 solar cells

The Zn/Sn ratio in Cu_2ZnSn(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.