A structural study of Cu–In–Se compounds by x-ray absorption fine structure

The local structures about Cu, In, and Se atoms in a series of Cu2Se–In2Se3pseudobinary compounds have been investigated by x-ray absorption fine structure (XAFS). In K-edge XAFS and L3-edge x-ray absorption near-edge structure (XANES) suggest that CuInSe2, Cu0.9InSe1.95, Cu0.82InSe1.91, and Cu2In3Se5.5have a nominally four-coordinated InSe4structure, whereas CuIn3Se5and CuIn5Se8possess two different InSe4structures. Cu K-edge XAFS also showed that CuIn3Se5and CuIn5Se8possess two different CuSe4structures, whereas others have a CuSe4structure. Se K-edge XANES and curve fitting analysis reveal that the Cu vacancy (VCu) gradually forms with decreasing Cu/In ratio. Moreover, the substitution of In for VCu(InCu) is observed in CuIn3Se5and CuIn5Se8. These results were compared to the previously proposed Cu–In–Se models. We conclude that Cu0.9InSe1.95and Cu0.82InSe1.91have a chalcopyrite structure with VCuand that the structure of CuIn3Se5and CuIn5Se8is a stannite-like structure with VCuand InCudefects.