Surface characterization of epitaxial Cu-rich CuInSe2 absorbers

We investigated the electrical properties of epitaxial Cu-rich CuInSe2 by Kelvin probe force microscopy (KPFM) under ambient and ultra-high vacuum conditions. We first measured the sample under ambient conditions before and after potassium cyanide (KCN) etching. In both cases, we do not see any substantial contrast in the surface potential data; furthermore, after the KCN etching we observed outgrowths with a height around 2nm over the sample surface. On the other hand, the KPFM measurements under ultra-high vacuum conditions show a work function dependence according to the surface orientation of the Cu-rich CuInSe2 crystal. Our results show the possibility to increase the efficiency of epitaxial Cu-rich CuInSe2 by growing the materials in the appropriated surface orientation where the variations in work function are reduced.