Interfaces of chalcogenide solar cells: a study of the composition at the Cu(In,Ga)Se2/CdS contact

The chemical composition of the Cu(In,Ga)Se2/CdS interface is studied using photoelectron spectroscopy, with monochromatized Al Kα and synchrotron radiation as excitation source. The samples were prepared by the decapping of Se layers, yielding a Cu-poor surface composition. CdS deposition and photoemission were performed in the same vacuum system. An excess of sulfur is detected at very low CdS thickness. However, reference experiments suggest that the interface is atomically abrupt. In contrast to the interface of CdS with a stoichiometric CuInSe2 single-crystal surface, the formation of CuxS at elevated temperatures is suppressed by the Cu-poor surface phase.