Optical and structural constants of CdS thin films grown by electron beam vacuum evaporation for solar cells

The structural and optoelectronic properties of polycrystalline cadmium sulfide (CdS) films grown by electron beam evaporation have been optimized through thermal annealing treatment. The direct band gap is decreased from 2.57 eV to 2.43 eV with the treatment and various optical, dielectric, material characteristic energy parameters/constants have also been determined. X-ray diffraction (XRD) analysis revealed the zinc blende cubic structure of the films and an indication of phase change is observed at 500 °C. The electrical conductivity is found to be increased with annealing temperature while the Fourier transform infrared (FTIR) analysis revealed an increment in IR transmittance. The surface morphology is found to be homogeneous with uniform circle-shaped grains and the presence of Cd and S elements in the grown film is confirmed by the energy-dispersive spectroscopy analysis. From optimized results, it can be figured that the CdS films annealed at 500 °C are suitable for window and hole-blocking layers in CdTe-based and perovskite solar cells respectively.