Characterization of chemically deposited ZnS thin films on bare and conducting glass

Zinc sulfide (ZnS) thin films are deposited onto both bare and ITO coated glass by low-cost and simple aqueous chemical bath deposition (CBD) method for using it in thin film solar cells. The optimized growth conditions are chosen for deposition of ZnS thin films by investigating photo-electrochemical (PEC), optical, structural and morphological properties of both as-deposited and annealed films. PEC measurements of the films show n-type electrical conductivity. Optical measurements show that the films have higher transmittance and lower absorbance above 700 nm. The band gap of the films lies in the range 3.67–3.68 eV for bare glass substrates and 3.62–3.65 eV for ITO coated conducting glass substrates. From the X-ray diffraction (XRD) study, as-deposited films are found to be polycrystalline with (1 1 1) and (2 2 0) preferential orientations of the cubic structure. The XRD results show that the average crystallite size is estimated to 40.41 nm for as-deposited films and 50.59 nm for annealed films deposited on to bare glass substrates. For ITO coated conducting glass substrates it is estimated to 43.23 nm for as-deposited films and to 53.32 nm for annealed films. The XRD results also show that lattice constant of ZnS is observed to 0.5626–0.5671 nm. From Scanning Electron Microscopy (SEM) study it is found that the films appeared dense crack-free surfaces with regular granular shaped grains. Comparing the results of the deposited ZnS thin films on bare and ITO coated glass substrates, it is observed that the properties of the deposited films are not substrate dependent.