Band gap modification of spray pyrolysed ZnS films by doping and thermal annealing

ZnS thin films are widely used in solar cells as window material. Optical and electrical properties of the films such as band gap energy and resistivity directly affect device performance. In this work it was shown that properties of ZnS films can be changed by doping and thermal annealing. Therefore, films with convenient parameters can be chosen for the fabrication of any device. ZnS films were fabricated by spray pyrolysis technique. Zinc chloride and thiourea used as sources of Zn and S respectively. Films were grown on 350oC hot substrates. Furthermore 1, 5, 10, 15 % doped films prepared by addition of boric acid into the solution. Structural, optical and electrical properties of the films were examined by SEM, XRD, optical transmission and resistivity measurements. Later on all films annealed in air at 350oC for 30 min. All measurements were done also for annealed films. Effects of doping and thermal annealing on the band gap energy and resistivity of the films were shown. Band gap energies of the films were between 3.37-3.82 eV and surface resistivities were between 257.2-12.5 MΩ.