Electronic level alignment at the deeply buried absorber/Mo interface in chalcopyrite-based thin film solar cells

We have investigated the electronic structure of the absorber/back contact interface for S-free [Cu(In,Ga)Se2 (“CIGSe”)] and S-containing [Cu(In,Ga)(S,Se)2 (“CIGSSe”)] chalcopyrites with direct and inverse photoemission. Comparison of the electronic levels of the cleavage planes reveals a pronounced cliff in the conduction band at the CIG(S)Se∕Mo interface. For the valence band, we find a flat alignment and a small spike for the CIGSe- and CIGSSe-based structures, respectively.