PHOTOEMISSION-STUDIES OF THE ZNO CDS INTERFACE

The highest conversion efficiencies of solar cells based on Cu(In,Ga)S e-2 have been achieved using multilayer CdS/ZnO front contacts. The fo rmation of the heterojunction interface between polycrystalline ZnO an d CdS has been studied with x-ray and ultraviolet photoemission spectr oscopy. The valence band offset between ZnO and CdS has been determine d to be 1.2 eV. No chemical reactions at the interface between ZnO and CdS have been detected up to 200 degrees C. In order to obtain a stan dard reference for the band discontinuities the valence band offsets o f ZnO and CdS relative to Ge have been measured.