Soft X-ray Spectroscopy of a Complex Heterojunction in High-Efficiency Thin-Film Photovoltaics: Intermixing and Zn Speciation at the Zn(O,S)/Cu(In,Ga)Se2 Interface

© 2016 American Chemical Society. The chemical structure of the Zn(O,S)/Cu(In,Ga)Se2interface in high-efficiency photovoltaic devices is investigated using X-ray photoelectron and Auger electron spectroscopy, as well as soft X-ray emission spectroscopy. We find that the Ga/(Ga+In) ratio at the absorber surface does not change with the formation of the Zn(O,S)/Cu(In,Ga)Se2interface. Furthermore, we find evidence for Zn in multiple bonding environments, including ZnS, ZnO, Zn(OH)2, and ZnSe. We also observe dehydrogenation of the Zn(O,S) buffer layer after Ar+ion treatment. Similar to high-efficiency CdS/Cu(In,Ga)Se2devices, intermixing occurs at the interface, with diffusion of Se into the buffer, and the formation of S - In and/or S - Ga bonds at or close to the interface.