Chemical Conditions for ZnS Thin Films Preparation by Chemical Bath Deposition

ZnS is a promising material to substitute the CdS layer into the thin film solar cells, given its high reflectance and its wide wavelength to catch the solar radiation. ZnS films prepared by chemical bath technique present a low cost and a simple method to produce controlled films. However, the films quality depends on the chemical reagents and their concentration used. In this work, different chemical conditions are proposed for preparing ZnS films by the chemical bath deposition (CBD) technique. ZnS thin films were deposited at 80 °C by CBD by changing the concentrations of the chemical reagents NH4NO3, KOH, and maintaining the concentrations of ZnCl2 and thiourea (SC(NH2)2) in the chemical bath. The best conditions of the chemical reagents under the different deposition times (60 to 140 min) were obtained as a result of the experimentation done in order to produce ZnS thin films with good optical quality. The mean optical band gap energy measured on the prepared ZnS films was 3.77 eV, with a film thickness between 40 and 63 nm. The crystalline structure of films was amorphous as obtained by x-ray diffraction analysis. The surface roughness measured on the ZnS films was between 5 to 13 nm as obtained from atomic force microscopy images. Energy Dispersive Spectroscopy analysis show a Zn/S atomic ratio between 0.05 to 0.64.