The effect of annealing on the physical properties of thermally evaporated CuIn2n+1S3n+2 thin films (n=0, 1, 2 and 3)

In this study, the annealing effect on structural, electrical and optical properties of CuIn_2n+1S_3n+2 thin films (n=0, 1, 2 and 3) are investigated. CuIn_2n+1S_3n+2 films were elaborated by vacuum thermal evaporation and annealed at 150 and 250 °C during 2 h in air atmosphere. XRD data analysis shows that CuInS₂ and CuIn₃S₅ (n=0 and 1) crystallize in the chalcopyrite structure according to a preferential direction (112), CuIn₅S₈ and CuIn₇S₁₁ (n=2 and 3) crystallize in the cubic spinel structure with a preferential direction (311). The optical characterization allowed us to determine the optical constants (refractive indexes 2.2–3.1, optical thicknesses 250–500 nm, coefficients of absorption 10⁵ cm^?1, coefficients of extinction <1, and the values of the optical transitions 1.80–2.22 eV) of the samples of all materials. We exploited the models of Cauchy, Wemple–DiDomenico and Spitzer–Fan for the analysis of the dispersion of the refractive index and the determination of the optical and dielectric constants.