Using the inelastic background in hard x-ray photoelectron spectroscopy for a depth-resolved analysis of the CdS/Cu(In,Ga)Se2 interface

The inelastic background of hard x-ray photoelectron spectroscopy data is analyzed to paint a depth-resolved picture of the CdS/Cu(In,Ga)Se-2 (CdS/CIGSe) layer structure. The CdS/CIGSe interface is the central component in next-generation chalcopyrite thin-film photovoltaic devices. By analyzing both, the (unscattered) core-level peaks and the inelastic background, and by varying the excitation photon energy from 2.1 up to 14 keV, we can derive photoemission information over a broad range of electron kinetic energies and, hence, sampling depths. With this complementary information, the CdS film thickness of a CdS/CIGSe interface can be accurately determined as a function of the CdS deposition time. For the thinner CdS films, the film thickness can be shown to vary laterally. Furthermore, small amounts of Se and process-related Rb can be detected in a thin (similar to 2 nm) surface layer of all investigated CdS films. (C) 2021 Author(s).

Automated summary

The study analyzes the inelastic background of hard x-ray photoelectron spectroscopy data to provide depth-resolved information on the CdS/CIGSe layer structure. By analyzing core-level peaks and inelastic background, the study accurately determines the CdS film thickness at the CdS/CIGSe interface, observing lateral variations in thickness for thinner CdS films. Additionally, small amounts of Se and process-related Rb are detected in a thin surface layer of all investigated CdS films.