Development of electrochromic cells by the sol-gel process

Abstract

These investigations have the development of electrochromic cells via the sol-gel process as their objective. Syntheses routes for tungsten oxide, WO3, coating sols and cerium oxide-titanium oxide sols, CeO2-TiO2, were developed, which enabled indium-tin oxide (ITO) coated glass substrates to be coated homogeneously and without visible cracking. Optoelectrochemical measurements were employed to determine the variation of the electrochromic properties (change in optical density, ΔOD, and switching times) of WO3 layers, investigated as a function of coating parameters, such as chamber humidity and the temperature of heat treatment. A novel nanocomposite electrolyte system, based on organically modified silanes, was developed, which has an ionic conductivity of 10-4-10-5 S cm-1 at 25°C. Values of diffusion coefficients for lithium ions in tungsten oxide layers could be determined by electrochemical impedance spectroscopy (EIS) and lie in the range 10-11-10-12 cm2/s. The values obtained are comparable with literature values for WO3 layers deposited by sputtering. The cells which have been constructed to date show a typical reduction in transmission from 80% to 20% with a half-life of less than 30 s, where half-life is here defined as the time necessary for half of the change in transmission to be obtained, i.e. from 80% to 50%.