Effect of annealing on properties of CuInS2 thin films

Surface morphology, structural and optical properties of CuInS2 thin films grown by the single source thermal evaporation in vacuum have been studied. The films were annealed from 250 to 550 degrees C in argon atmosphere with low oxygen concentration (O-2 < 2 ppm). CuInS2 films are characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and optical transmittance and reflectance spectra. The maximum grain size of the sample after annealing at 550 degrees C was over 150 nm. The electron dispersion spectroscopy and X-ray analysis concludes that the polycrystalline CuInS2 thin film after annealing above 200 degrees C were sulphur-poor. We obtain CuInS2 layers with high structural and optical quality at annealing temperature above 450 degrees C with formation of In2O3 as minority phase. The band gap energy of the CuInS2 films after annealing above 450 degrees C was about 1.50 eV which perfectly matches the solar spectrum for energy conversion.