Synthesis of WO2.72:Fe thin films via ammonium tungstate precursor by spray pyrolysis technique and annealing

In this study, WO_2.72:Fe thin films have been prepared on glass substrates heated to a fixed temperature of 350 °C by the spray pyrolysis technique, from an aqueous ammonium tungstate solution (NH₄)₁₀H₂(W₂O₇)₆ with a concentration of 0.005 M. The dopant concentrations were 1, 3 and 5 %. After deposition, the thin films were annealed at 550 °C for 4 h. The characterization results revealed that Fe doping has a significant effect on the morphology of thin films depending on its concentration. In addition, it promotes crystallites growth and improves the surface quality. GIXRD analysis has shown that the thin films obtained after the annealing are polycrystalline in nature, the structure of the WO_2.72 films was monoclinic, with space groups P2/m (10). The growth direction was variable depending on the doping concentration. It was noticed that the peaks positions, the preferential grain orientation and the structural parameters are affected by the doping concentrations, which had no effect on the phase type of the obtained films. The WO_2.72 films have interesting optical properties; high transmittance in the visible range of 75 % as well as high absorption in the ultra-violet range from 1.4 to 0.2 a.u. Moreover, the films exhibit both direct and indirect electronic transitions, which are red-shifted due to Fe-doping.