Electrochromic properties of tungsten oxide films prepared by sparking method using external electric field

In this paper, high porous tungsten oxide (WO3) films were prepared onto indium-doped tin oxide glass substrates by a sparking method, which is a simple and cost-effective technique. An external electric field of 6 kV/cm was applied to the sparking system in order to increase a dense surface morphology and the deposition rate of the films. In experiments, the films were deposited for 20 min at room temperature and post-annealed from 200 to 500 °C for 1 h under atmospheric pressure. High porosity of the WO3 films was fabricated by the sparking method and confirmed by scanning with electron microscopy. Raman spectra and X-ray diffraction patterns show the monoclinic phase of WO3 when the annealing temperature is higher than 300 °C. In addition, the electrochemical analysis was carried out by using a 0.05 M H2SO4 electrolyte solution, Pt as a counter electrode, and Ag/AgCl as a reference electrode. The fast switching speeds of 1.2 s and 2.6 s (for the coloration and bleaching state respectively), optical modulation of 16.3%, and coloration efficiency of 49.6 cm2/C were achieved for annealed films at 300 °C.