Influence of annealing temperature on properties of Cu(In,Ga)(Se,S)2 thin films prepared by co-sputtering from quaternary alloy and In2S3 targets

Pentanary Cu(In,Ga)(Se,S)2 (CIGSS) thin films were deposited on soda-lime glass substrate by co-sputtering quaternary alloy, and In2S3 targets. In this study, we investigated the influence of post-annealing temperature on structural, compositional, electrical, and optical properties of CIGSS films. Our experimental results show that the CIGS quaternary target had chalcopyrite characteristics. All CIGSS films annealed above 733 K exhibited a polycrystalline tetragonal chalcopyrite structure, with (1 1 2) preferred orientation. The carrier concentration and resistivity of the resultant CIGSS layer annealed above 763 K was 4.86×1016 cm−3 and 32 Ω cm, respectively, and the optical band-gap of the CIGSS absorber layer was 1.18 eV. Raman spectral analysis demonstrated the existence of many different phases, including CuInSe2, CuGaSe2, and CuInS2. This may be because the vibration frequencies of In–Se, In–S bonds are similar to the Ga–Se and Ga–S bonds, causing their absorption bands overlap.

Research Highlights
► We report a chalcopyrite Cu(In,Ga)(Se,S)2 (CIGSS) thin films on soda lime glass substrate by co-sputtering quaternary single-phase chalcopyrite CIGS alloy, and In2S3 targets.
► By incorporating sulfur into partly selenized CIGS films, researchers fabricated a chalcopyrite CIGSS layer with double-graded band-gap structure.
► The CIGS quaternary target and Raman spectra were analyzed for investigating the CIGSS structure and quality.