Study of thermocolored WO3 thin film under direct solar radiation

The effect of vacuum annealing on the spectral response and structure of tungsten oxide films prepared by electron beam evaporation was studied. The temperatures of WO3 and glass heated in vacuum and under solar radiation were investigated. Vacuum annealing WO3 at 450 °C for 1 h was observed to change the film from transparent to a deep shade of blue and to cut off the infrared radiation as a result of increased reflectance and absorbance. The annealing was also observed to decrease the band gap of the WO3 from 3.2 to 2.4 eV, and to change the film from an amorphous to a polycrystalline phase. The colored WO3 film was observed to increase the temperature of the substrate glass at a rate of 0.06 °C (W m−2)−1 due to its solar radiation absorbance. These films were left to self-bleach outside for extended periods of time