Deposition of single-phase CuIn(Se,S)2thin films from the sulfurization of selenized CuIn alloys

The reaction of dc sputtered metallic CuIn alloys to a reactive H2Se/Ar/H2S gaseous atmosphere is an attractive industrial production process to produce CuIn(Se,S)2 chalcopyrite absorber films for applications in photovoltaic modules. However, the obvious technological advantages of this deposition technology are overshadowed by growth-related anomalies such as the separation or at least partial separation of the ternary phases (i.e. CuInSe2 and CuInS2) during the high temperature selenization/sulphurization of the metallic alloy. This in turn prevents the effective band gap widening of the semiconductor alloys in order to achieve open-circuit voltages in excess of 600 mV, which is a critical prerequisite for the optimal performance of thin film solar modules. In this contribution, the material properties of homogeneous single-phase CuIn(Se,S)2 alloys are discussed, produced with a novel two-stage deposition process.