Achieving Element Homogeneity for Excellent Kesterite Devices through Regulating the Se Amount

Uniform distribution of elements in the kesterite absorption layer is known to play an important role in the photoelectric conversion efficiency of devices. Here, through regulating the placed Se amount in the graphite box during the selenization process, enhanced element homogeneity within kesterite (Cu,Ag)2ZnSn(S,Se)4 (ACZTSSe) films can be obtained. An appropriate Se amount (7.5 mmol) can decrease the cation element migration ratio to the surface from the bottom of the film, reduce cation enrichment at the grain boundary, and decrease the unfavorable defects of the films. The uniform distribution of elements can optimize the band tail states and improve the electrical properties of the absorption layer. Finally, the photoelectric conversion efficiency of solar cells can be increased from 7.9% (RSe-2.5) to 11.3% (RSe-7.5). Our conclusions can provide insights regarding the role played by the placed Se content in the ACZTSSe thin-film solar cells.