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

The reaction of dc sputtered metallic CuIn alloys to a reactive H ₂Se/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.