Electrochromic and structural characteristics of mesoporous WO3 films prepared by a sol-gel method

The preparation of electrochromic films of mesoporous tungsten trioxide from tungstic acid and tungstic hexaethoxide precursors with the addition of an organic stabiliser via a sol-gel method is reported. These films have been structurally characterised and both the film morphology and crystalline composition of the films were found to be significantly dependent on the temperature at which the films were annealed and upon the choice of precursor. Films annealed at lower temperatures consisted of amorphous and hexagonal tungsten trioxide, whereas films annealed above 500 degreesC comprised solely of monoclinic WO3. The electrochromic activity of the films was found to be equally dependent on method of preparation, and both the composition and the structure of the WO3 films were shown to clearly influence the colouration efficiency of the films.