Improved Efficiency of CuInS2-Based Solar Cells without Potassium Cyanide Process

Abstract
A high open-circuit voltage (V oc) exceeding 0.80 V was obtained by adding Ga to Na-incorporated CuInS2 thin films. Cu(In, Ga)S2 films were fabricated by sulfurization of Na-containing Cu-In-Ga precursors in H2S atmosphere. The inclining Ga profile resulted in a graded band gap. Therefore, the enhancements of cell performance by Ga addition were not only increase in Voc but also that in short-circuit current density (J sc). We achieved an efficiency of 11.2% with V oc=0.802 V, J sc=20.9 mA/cm2 and FF=0.667. This is the highest efficiency reported for CuInS2 solar cells fabricated without the potassium cyanide (KCN) process.