An ab-initio study of CuInSe2 based ordered defect compounds

We have used the Vienna ab-initio Simulation Package (VASP) to study the electronic and optical properties of ordered defect compounds (ODC's) CuIn5Se8 and CuIn3Se5. The supercells are generated with the parent chalcopyrite structure of CuInSe2. The defect pair (2VCu−+InCu2+) in CuInSe2 plays an important role in the electronic and optical properties of the ODC's are investigated. The band structure and density of states of ODC's are discussed in terms of the parent chalcopyrite compound CuInSe2. The calculated low defect formation energy explains the existence of the ODC's CuIn5Se8 and CuIn3Se5. The optical absorption peaks in the ε2(ω) are explained in the terms of band structure and density of states. The upper valence band of ODC is exclusively formed by the p-d hybridization of Cu-3d and Se-4p states. The obtained results are in good agreement with the available experimental data. The calculated threshold values for CuInSe2 and ODC's are underestimated.