Improvement of the Electrical Properties of Cu-Poor CuInS2 Thin Films by Sodium Incorporation

Abstract
We investigated the effects of intentional sodium incorporation on the electrical conductivity of Cu-poor CuInS2 thin films. CuInS2 films were fabricated by sulfurization of In–S/Cu/Na2S/In precursors. Sodium incorporation resulted in a remarkable increase in the lateral conductivity and the cell efficiency of CuInS2-based solar cells. Photoluminescence measurements revealed that the enhancements were attributed to the annihilation of donor states, most likely In interstitials, by sodium incorporation.