Local environment surrounding S and Cd in CdS : O thin film photovoltaic materials probed by X-ray absorption fine structures

Local environments surrounding Cd and S in CdS:O thin films have been determined using extended x-ray absorption fine structure (EXAFS) and near-edge x-ray absorption fine structure (NEXAFS). As indicated by the Cd EXAFS, Cd atoms remain predominantly bonded with S. The S EXAFS and NEXAFS clearly demonstrate the presence of S–O bonds. The oxygen atoms actually combine with S to form SO3 and SO4 complexes. Combined with the transmission electron micrograph, these x-ray results suggest formation of oxygen-free CdS nanocrystals and provide an unambiguous explanation for the mystery of increased band gap that appears to violate the band anticrossing model.