ABSTRACT
We investigate high-efficiency CuIn(Ga)Se2 (CIGS) solar cells by transmission electron microscopy (TEM). TEM cross sections of the solar cells reveal a layer sequence Mo-CIGS-CdxSy-ZnO. The CIGS absorbers are subdivided into a layer whose grains reveal an average diameter of ~100 nm containing the elements Cu, In, Ga and Se on a Mo contact and a microcrystalline layer (average grain diameter ~ 2 μm) with the elements Cu, In and Se. These microcrystalline grains exhibit the crystal structure of pure chalcopyrite. A pn junction, which other authors report to be a heterojunction of p-type chalcopyrite and n-type defect-chalcopyrite, is not observed in our study. The nominal CdxSy buffer layer has a thickness of 10–20 nm, but Cd could not be detected or its concentration is at the limit of detectability (1 wt %).
