Investigation of electrochromic properties of nanocrystalline tungsten oxide thin film

Thin films of tungsten oxide were grown by organometallic chemical vapor deposition (OMCVD) using tetra(allyl)tungsten, W(η 3-C 3H 5) 4. X-Ray diffraction (XRD) analyses showed amorphous films at substrate temperatures ( T s) 350°C. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed grain sizes in the range 20–40 nm. In situ electrochemical reduction of WO 3.2/ITO (2.0 M HCl) produced a faint blue color in less than 1 s. The maximum coloration efficiency (CE) was found to be 22 cm 2/mC at 630 nm. The density of the films decreases from 4.53 to 4.29 g/cm 3 after annealing. An optical bandgap ( E g) of ∼3.2 eV was estimated for both as-deposited and annealed films.