The diffusion behavior of Se at the CdS/Cu(In,Ga)(S,Se)2 thin film solar cell interface was investigated by X-ray photo-electron spectroscopy and X-ray excited Auger electron spectroscopy. Buffer/absorber structures with S/Se ratios between zero and three at the initial Cu(In,Ga)(S,Se)2 surface were analyzed. Samples from a high-efficiency laboratory process as well as from an industrial large-area process were investigated. Selenium diffusion into the CdS buffer layer was found; the magnitude of which strongly depended upon the S content at the absorber surface. The associated modification of the heterojunction partners had a significant effect upon the electronic structure at the interface.

Sulfur Gradient-Driven Se Diffusion at the CdS/CuIn(S,Se)2 Solar Cell Interface. L.Weinhardt, M.Bär, S.Pookpanratana, M.Morkel, T.P.Niesen, F.Karg, K.Ramanathan, M.A.Contreras, R.Noufi, E.Umbach, C.Heske: Applied Physics Letters, 2010, 96[18], 182102