Cd 2 + ∕ N H 3 treatment-induced formation of a CdSe surface layer on CuGaSe2 thin-film solar cell absorbers

Cu Ga Se 2 (CGSe)-based high-gap thin-film solar cells have to date not reached their potential level of electrical performance. In order to elucidate possible shortcomings of the electronic interface structure, we have studied the initial stage of the CdS∕CGSe interface formation by use of a simple Cd2+∕NH3 treatment. As in the case of low-gap chalcopyrites, we find a Cd-containing surface layer, in the present case comprised of approximately one monolayer of CdSe. The results indicate that the CdS∕CGSe interface is not abrupt, but contains intermediate layers. Furthermore, they shed light on possible surface modification schemes to enhance the overall performance of high-gap CGSe chalcopyrite solar cells.