Effects of Na Incorporation in p-Type CuInS2

Abstract

We have investigated the electronic structures of Na-incorporated In-rich CuInS2 based on ab initio electronic band structure calculations. We find that the formation of ionic NaCu–S bonds decreases the Madelung energy, resulting in a shift in the energy levels of S 3p orbitals in the vicinity of the Na atoms towards lower energy regions. For p-type CuInS2:VCu, we find that interstitial Na species, except for NaCu, are very unstable and move easily within the crystal. This indicates that the mobile Na will act as a passivator of donor states such as InCu and interstitial In.