Annealing Effect on the Structure and Optical Properties of CBD-ZnS Thin Films for Windscreen Coating

Zinc sulfide (ZnS) thin films were prepared and synthesized by the chemical bath deposition (CBD) technique on microscopic glass substrates using stoichiometric amounts of the precursor materials (ZnSO₄·7H₂O, NH₄OH, and CS(NH₂)₂). Structural, morphological, compositional, and optical characterization of the films were studied. The obtained thin films were found to exhibit polycrystalline possessions. The effect of annealing temperature on the crystallographic structure and optical bandgap of ZnS thin films were both examined. The grain size and unit cell volume were both found to be increased. In addition, the strain, dislocation density, and the number of crystallites were found to be decreased with annealing temperature at 300 °C. However, the annealed sample was perceived to have more Zn content than S. The optical characterization reveals that the transmittance was around 76% of the as-deposited thin film and had been decreased to ~50% with the increasing of the annealing temperature. At the same time, the bandgap energy of the as-deposited film was 3.98 eV and was found to be decreased to 3.93 eV after annealing.