Optical Properties of Zinc Sulphide Thin Films Coated with Aqueous Organic Dye Extract for Solar and Optoelectronic Device Applications

Optical properties of ZnS thin films coated with organic dye extract on different Zn2+ concentrations from ZnSO4 are presented in this study. The effects of concentration and post-deposition annealing temperatures on the optical properties of the films were investigated. Aqueous dye extract-coated ZnS nanocrystals, were prepared by a simple and low-cost chemical bath deposition method. Results obtained revealed that optical properties of the films were modified by concentration and post-deposition annealing temperature. Increasing concentration reduced the transparency of the films. Annealing increased the transparency of the films except for films deposited with 0.1M concentration of ZnSO4. In general, the heat-treated layers were found to transmit better than the as-deposited layers. The analysis of energy band gap showed a reduction in band gap with increasing Zn2+ concentration of the as-deposited films. It also indicated that post-deposition annealing, increased energy band gap except for films deposited with 0.1M concentration of ZnSO4. The relationship between the energy band gap with both concentration and post-deposition annealing fit into the quadratic model with high R2 values. The range of values of 3.889–3.981eV recorded for the band gaps is within the range for application in diverse solar architecture and optoelectronic devices.