Peroxotungstic acid precursor solution was sprayed on indium-doped tin oxide (ITO) glass substrates to synthesize amorphous and crystalline phase tungsten oxide thin films by changing heating temperature. We could synthesize the amorphous phase at below 400 oC and the monoclinic crystalline tungsten oxide at above 400 oC. Electrochemical and in-situ optical transmittance analysis showed that amorphous phase tungsten oxide at 250 oC had a good electrochromic property with a large optical transmittance change between its bleached and colored states. The coloration mechanisms are due to polaron generation by inserting ions and electrons to change W+6 state to W+5 or W+4 state.
Keywords: Peroxotungstic acid, Electrochemical, Electrochromic, Spray pyrolysis, Tungsten oxide