Chemical engineering of Cu(In,Ga)Se2 surfaces: An absolute deoxidation studied by X-ray photoelectron spectroscopy and Auger electron spectroscopy signatures

CIGS (Cu(In,Ga)Se2) absorbers are among the most efficient for photo-conversion. As part of their manufacturing cycle, absorber surface preparation is crucial for both the success of processes and the outcome of characterizations actions. This work tackles the question of an efficient deoxidation of CIGS surfaces. Chemical composition of surface is investigated thanks to XPS (X-ray Photoelectron Spectroscopy) characterizations. Present study focuses on the possible control of the CIGS absorber surface associated with simple HCl treatment and subsequent atmosphere ageing up to 20 days. Using 1.0 M HCl concentration solution, remarkable oxide elimination is achieved. Starting from an air aged as-grown surface (Cu and Se-poor), this treatment enables the generation of a deoxidized chalcopyrite reference sample. Furthermore, the reoxidation process of the treated surface at ambient atmosphere is studied considering the global evolution of the XPS signals as the best probe of the ageing process. The surface composition evolution represents a key parameter for the achievement of the following interfaces engineering. The main result is that the reoxidation process is not instantaneous (no significant oxide content before 2 days) and involves In, Ga and Se elements while the Cu seems less affected, leading again to a Cu-poor surface different from the initial one.