Theoretical study of Zn and Cd interstitials and substitutional interstitials in CuInSe2 via hybrid functional calculations

We have investigated the formation of Zn and Cd interstitials in the CuInSe₂ solar cell material via density-functional-theory (DFT) calculations by employing the HSE06 hybrid functional. The computed formation energies for Zn interstitials were in the range of 2.09-2.68 e V, and in the range of 2.04-2.25 eV for substitutional interstitials. In constrast, the formation energies of Cd interstitials and substitutional interstitials were between 1.85-2.75 eV and 2.41-2.64 eV, respectively. Thus, these results indicate, that Cd interstitials are more likely to be formed than Zn interstitials, and that in case of Zn inclusion into CuInSe₂ Zn atoms will prefer to adopt substitutional interstitial arrangements.