Band alignment at the i-ZnO/CdS interface in Cu(In,Ga)(S,Se)2 thin-film solar cells

The interface between the i-ZnO layer and the CdS buffer in Cu(In,Ga)(S,Se)2 thin-film solar cells from the Shell Solar baseline process has been investigated using ultraviolet- and x-ray photoelectron spectroscopy and inverse photoemission. Combining both techniques, a direct determination of the conduction and valence band offsets at the interface is possible. Different from existing models, we find a flat conduction band alignment (i.e., a conduction band offset of 0.10±0.15 eV), ∼0.5 eV above the Fermi level, and a valence band offset of 0.96±0.15 eV.