CdS/Low-Band-Gap Kesterite Thin-Film Solar Cell Absorber Heterojunction: Energy Level Alignment and Dominant Recombination Process

High Resolution Image Download MS PowerPoint Slide The chemical and electronic interface structure (including energy level alignment) between wet-chemical deposited CdS and low-band-gap Cu 2 ZnSn(S,Se) 4 (CZTSSe) thin-film solar cell absorbers was studied using direct and inverse photoemission. Complementarily, the activation energy ( E a ) of the dominant charge carrier recombination process of related solar cell devices was derived by temperature-dependent current–voltage [ I ( V, T )] measurements. We find the CZTSSe surface to be free of any significant amount of sulfur and the formation of Cd–Se bonds at the interface. A small, positive (“spike”-like) conduction band offset of 0.21 ± 0.28 eV between CZTSSe and CdS was measured. In conjunction with the I ( V, T ) derived E a of 1.09 ± 0.07 eV, which is in excellent agreement with the CZTSSe bulk band-gap energy of 1.07 eV, this reveals that high-rate charge carrier recombination at the CdS/CZTSSe interface can mainly be excluded as the performance-limiting factor in corresponding solar cells.