Sulfur gradient-driven Se diffusion at the CdS / CuIn ( S , Se ) 2 solarcell interface

The diffusion behavior of Se at the CdS / Cu ( In , Ga ) ( S , Se ) 2 thin film solar cell interface was investigated by x-ray photoelectron 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 (NREL) as well as from an industrial large-area process (AVANCIS) were investigated. We find selenium diffusion into the CdS buffer layer, the magnitude of which strongly depends on the S content at the absorber surface. The associated modification of the heterojunction partners has significant impact on the electronic structure at the interface.