Chemical and electronic structure of the heavily intermixed (Cd,Zn)S:Ga/CuSbS2 interface

The interface formation and chemical and electronic structure of the (Cd,Zn)S:Ga/CuSbS2 thin-film solar cell heterojunction were studied using hard X-ray photoelectron spectroscopy (HAXPES) of the bare absorber and a buffer/absorber sample set for which the buffer thickness was varied between 1 and 50 nm. We find a heavily intermixed interface, involving Cu, Zn, and Cd as well as significant Ga and Cu profiles in the buffer. The valence band (VB) offset at the buffer/absorber interface was derived as (-1.3 +/- 0.1) eV, which must be considered an upper bound as the Cu diffused into the buffer might form a Cu-derived VB maximum located closer to the Fermi level. The estimated conduction band minimum was 'cliff'-like; a situation made more severe considering the Cu-deficiency found for the CuSbS2 surface. The complex interface structure's effect on the performance of (Cd,Zn)S:Ga/CuSbS2-based solar cells and its limitation is discussed together with possible mitigation strategies.

Automated summary

The interface formation, chemical, and electronic structure of the (Cd,Zn)S:Ga/CuSbS2 thin-film solar cell heterojunction were studied using HAXPES. A heavily intermixed interface was found, involving Cu, Zn, Cd, Ga, and Cu profiles in the buffer. The effect of the complex interface structure on the performance of the solar cells and possible mitigation strategies were discussed.