NaF/KF post-deposition treatments and their influence on the structure of Cu(In, Ga)Se 2 absorber surfaces

To determine the influence of NaF/KF-post-deposition treatments (PDT) on the chemical and topographical surface structure of Cu(In, Ga)Se 2 (CIGSe) solar cell absorbers, we have used synchrotron-based hard x-ray photoelectron spectroscopy (HAXPES) and scanning electron microscopy (SEM). Variations of the PDT parameters can be used to tune thickness and degree of surface nanopatterning; here we find that the nanopatterning is more pronounced on CIGSe surfaces having more potassium and less copper and gallium. Detailed analysis of Se 3d and In 4d photoemission spectra reveals the presence of (at least) two different species, which indicate the formation of a (nanopatterned) K-In-Se-type surface layer.