Effects of Na Incorporation in p-Type CuInS2

Abstract

We have investigated the electronic structures of Na-incorporated In-rich CuInS₂based onab initioelectronic band structure calculations. We find that the formation of ionic Na_Cu–S bonds decreases the Madelung energy, resulting in a shift in the energy levels of S 3porbitals in the vicinity of the Na atoms towards lower energy regions. Forp-type CuInS₂:V_Cu, we find that interstitial Na species, except for Na_Cu, 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 In_Cuand interstitial In.