Tungsten oxide film synthesis by spray pyrolysis of peroxotungstic acid and its electrochromic characterization

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 degrees C and the monoclinic crystalline tungsten oxide at above 400 degrees C. Electrochemical and in-situ optical transmittance analysis showed that amorphous phase tungsten oxide at 250 degrees C 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.The authors gave thanks to Korean Ministry of Commerce, Industry and Energy (MOCIE) for its financial support for this research as a sol-gel next-generation project