Preparation and characterization of pyrolytic spray deposited electrochromic tungsten trioxide films

Tungsten trioxide (WO3) thin films were prepared by spray pyrolysis under v arious conditions using, for the first time, tungsten chloride (WCl6) disso lved in 50% ethanol-50% wafer. All the as-deposited films were amorphous an d dark. When annealed, they became crystallized and transparent. The struct ure and the composition of these films, before and after annealing, were st udied. The X-ray diffraction diagrams revealed that all the annealed films consisted of the monoclinic WO3 phase. The X-ray photoelectron spectroscopy studies of the VV,, doublet showed the W6+ oxidation state: for all the fi lms. The electron probe microanalysis revealed an over, stoichiometry of ox ygen for the unannealed films. The optical properties as well as the struct ure of the annealed, therefore transparent, films prepared at different spr ay rates were also determined. The optical gap was determined from reflecti on and transmission spectra, All annealed samples exhibited a reversible el ectrochromic effect in the presence of an acid electrolyte as demonstrated by cyclic voltammetry and optical transmission measurements. (C) 2000 Elsev ier Science S.A. All rights reserved.