Chemical bath method for ZnS thin films preparation

We report a chemical bath method to prepare ZnS thin films on glass substrates for solar applications. The proposed method is based on the experience to deposit CdS thin films by chemical bath but replacing some chemical reagents. The bath is composed of zinc chloride, potassium hydroxide, ammonium nitrate, and thiourea. During films deposition, the chemical bath is agitated with a magnetic stirrer; meanwhile its temperature is maintained at 90°C. The critical parameter of the bath for obtaining high quality films is the pH, with 11.5 as initial value. Obtained ZnS films were optically transparent with band gap energies values between 3.5-3.7 eV. Zn:S (1.0:1.2) stoichiometry ratio of films was measured by energy dispersive spectroscopy (EDS). By x-ray diffraction analysis, a sphalerite-type cubic structure with a (111) as main diffraction peak were found in films. Subsequent annealing process of the ZnS films at 200°C and 400°C in Argon atmosphere maintains the films crystalline structure and diminishes their optical band gap energy value.