V. Alberts

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 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.

Structural and in-depth compositional features of homogeneous pentenary chalcopyrite alloys prepared with a reproducible deposition technology

Homogeneous single-phase Cu(In0.75Ga0.25)(Se1−ySy)2 alloys were prepared by the reaction of magnetron sputtered CuIn0.75Ga0.25 precursors to a H2Se/Ar and H2S/Ar gaseous atmosphere under well-defined experimental conditions. X-ray diffraction analysis of the films showed characteristic chalcopyrite peaks with a high degree of symmetry, indicative of homogeneous rather than compositionally graded material. Glancing incident angle x-ray diffraction revealed virtually no variation in the lattice parameters through the entire depth of the alloys. X-ray photoelectron spectroscopy depth profiling confirmed the homogeneous distributions of the respective elements through the entire depth of the pentenary semiconductor alloy under optimized selenization/sulfurization conditions.