Cadmium sulphide (CdS) thin films have been grown on corning glass substrate by thermal
evaporation technique under base pressure 2 × 105 mbar. In this study we investigate the influence
of Cadmium chloride (CdCl2) heat treatment and argon and oxygen (Ar + O2) annealing on the
structural, morphological optical and electrical properties of CdS thin films to achieve high quality
thin films for solar cells applications. X-ray diffraction (XRD), Field Emission scanning electron
microscope (FE-SEM) and UV–Vis-NIR spectrophotometer were used to confirm and investigate
the different physical properties of CdS films. The quality of CdS thin films crystallinity including the
average grain size (Davg), the average lattice strain (εls) and the dislocation density (ρD) were extracted
via XRD line broadening analysis. XRD analysis revealed that the samples are polycrystalline in
nature with a mixed (hexagonal + cubic) structure and the crystallinity of the films increases with
both (Ar + O2) annealing and CdCl2 heat treatment. After (Ar + O2) annealing and CdCl2 heat
treatment processes the mean values of the grain size indicating the grain growth of CdS films.
The surface morphology of the CdS films was examined by (FE-SEM) analysis; which confirmed
the nano-crystalline nature of the CdS films with uniform coverage of the substrate surface; The
optical properties of as-deposited, (Ar + O2) annealed and CdCl2 treated CdS films were discussed
in detail. The optical energy gap was calculated using Tauc plot extrapolation. It was found to be
increased from 2.43 eV for as-deposited film to 2.45 for CdCl2 treated CdS film. Swanepoel method
was employed to estimate the thicknesses and extract the refractive index of the CdS films. The Room
temperature resistivity decreased from 13.4 Ω cm for as-deposited CdS film to 2 and 0.8 Ω cm for
(Ar + O2) annealed and CdCl2 treated CdS films respectively. The CdCl2 treated CdS film has the
highest figure of merit value of 29 × 10−4 Ω−1. The obtained results confirm that the CdCl2 heat
treatment process in (Ar + O2) atmosphere can enhance the physical properties of CdS thin films as
a promising window layer or buffer layer material for CdS/CdTe and Cu(In,Ga)Se2 solar cells.