Cd2+/NH3-treatment of high-gap CuGaSe2 thin film solar cell absorbers

For chalcopyrite-based solar cells with conventional CdS buffers (prepared in a chemical bath), the Cd²⁺/NH₃-treatment can be used as a tool to visualize the processes during the initial stages of interface formation in the chemical bath. For high-gap CuGaSe₂ (CGSe) - an absorber material which has not yet shown its full potential in terms of solar cell performance - a CdSe surface compound was recently identified at the CGSe absorber surface after this kind of simple surface conditioning. In this contribution, we will clarify whether the [Ga]/[Cu]-ratio of the CGSe absorber has an impact on the formation of this non-abrupt interface. In addition, the lateral variation of the observed absorber surface modification will be investigated. Thus, as-deposited and Cd²⁺/NH₃-treated CGSe surfaces were characterized by X-ray excited Auger and photoelectron spectroscopy using Mg Kα and/or tuneable monochromatized synchrotron radiation.