Low temperature synthesis of nanocrystalline WO3 films by sol–gel process

Tungsten oxide (WO3) is one of the most promising materials for electrochromic devices. In this paper, we report on a simple route for the low temperature synthesis of nanocrystalline WO3 films involving treatment of tungsten hexachloride and non-ionic tri-block copolymer surfactant at 100 °C. The films were studied by Raman spectroscopy and transmission electron microscopy (TEM) for their structural properties and also by scanning electron microscopy (SEM) to understand it’s microstructure. Raman studies show the presence of different nanocrystalline phases (m-WO3, and WO3 · 1/3 H2O) embedded in an amorphous matrix. A TEM diffraction pattern shows the nanocrystalline nature and a preferred growth direction for the crystallites. An electrochromic system using the low temperature WO3 film as an active electrode was fabricated and tested.