Effects of Heat Treatment Temperature on the Microstructure and Photochromic Properties of WO3 Films

WO3 thin films were prepared via sol-gel dip-coating method. The photochromic properties of the WO3 thin films were characterized by color difference meter; effects of heat treatment temperature on its microstructure and photochromic properties were investigated by XRD, AFM, SEM, TEM and UV-Vis. The results show that the photochromic properties of the WO3 thin films are enhanced with the rise of heat treatment temperature. When it is 350 degrees C, the color difference reaches to the top of 2.2462, which is because the conduction electron concentration increasing with the rise of heat treatment temperature is propitious to produce photo-generated electron hole pairs. And it is easy to promote the electrons to conduction band at the narrowest band gap. When it is 400 degrees C, the sample obtains depressed photochromic properties resulting from crassitude grains and decreasing specific surface area. When it is up to 450 degrees C, the photochromic properties are further reduced, as lattice distortion goes against the separation of electron hole pairs.