Hydrothermal deposition and photochromic performances of three kinds of hierarchical structure arrays of WO3 thin films

Three kinds of tungsten oxide (WO3) thin films have been fabricated by a simple hydrothermal deposition method. Scanning electron microscopy images of the products revealed that the capping agents did impact the microstructure of WO3 films. Films prepared without capping agents were ordered nanorod arrays, while the ones obtained with ethanol and oxalic acid revealed peeled-orange-like and cauliflower-like hierarchical structure arrays, respectively. Both of the two hierarchical structures were composed of much thinner nanorods compared with the one obtained without capping agents. All the WO3 films exhibited good photochromic properties and the two with inducers performed even better, which could be due to the changes in the microstructure that increased the amount of photogenerated electron–hole pairs and the proton diffusion rates.