Synthesis of ZnS Thin Films by Chemical Bath: From Room Temperature to 90°C

A physicochemical analysis was performed on the solution used for synthetizing zinc sulfide (ZnS) films by chemical bath; such solution contained zinc chloride, potassium hydroxide, ammonium nitrate and thiourea as chemical reagents. Solubility curves and species distribution diagrams were used to obtain the best conditions for ZnS deposition in a wide range of bath temperatures between 25 and 90°C. Solubility curves evidenced the necessity to adjust the thiourea concentration for each bath temperature in order to obtain enough amounts of sulfur ions needed for ZnS formation. The thiourea concentrations were fixed at 0.2 M (90°C), 0.6 M (60°C), 1.25 M (40°C), and 2.25 M (25°C) to get higher quality films. Characterization results of films deposited at the conditions described above showed the films to have a bandgap energy value between 3.65 and 3.72 eV, stoichiometry of [Zn]/[S] ≈1, and homogeneous and agglomerate-free surfaces, which make them proper for solar cells applications.