A comparative study of Cu–Se and In–Se bond length distributions in CuInSe2 with related In-rich compounds

The local atomic structure around the Cu and In atoms of CuInSe2 (CIS), Cu2In4Se7 and CuIn3Se5 was studied using Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy at the Cu and In K-edges. Room and low-temperature EXAFS measurements were performed at beamline BM29 at the European Synchrotron Radiation Facility (ESRF) and collected data were analysed using the freely available IFEFFIT package. The analysis assumed a chalcopyrite structure for the CuInSe2 samples while different structures (Cahlcopyrite and P-chalcopyrite) were tried for Cu2In4Se7 and CuIn3Se5. The results show that the In–Se bond length remains constant in the CuInSe2 samples within the experimental uncertainty but slight differences are observed in the Cu–Se bond lengths. These decrease with the Cu content in accordance with previous X-ray diffraction (XRD) results on the same samples. The values obtained for the Debye–Waller factors in the CuInSe2 samples are lower for the In–Se bond compared to Cu–Se, which is consistent with a higher ionicity in the former bond.