DEVELOPMENT OF ELECTROCHROMIC CELLS BY THE SOL-GEL PROCESS

These investigations have the development of electrochromic cells via the sol-gel process as their objective. Syntheses routes for tungsten oxide. WO3, coa.ting sols and cerium oxide-titanium oxide sols, CeO2-T iO2, were developed, which enabled indium-tin oxide (ITO) coated glass substrates to be coated homogeneously and without visible cracking. O ptoelectrochemical measurements were employed to determine the variati on of the electrochromic properties (change in optical density, Delta OD, and switching times) of WO3, layers, investigated as a function of coating parameters, such as chamber humidity and the temperature of h eat treatment, A novel nanocomposite electrolyte system, based on orga nically modified silanes, was developed, which has an ionic conductivi ty of 10(-4)-10(-5) S cm(-1) at 25 degrees C, Values of diffusion coef ficients for lithium ions in tungsten oxide layers could be determined by electrochemical impedance spectroscopy (EIS) and lie in the range 10(-11)-10(-12) cm(2)/s. The values obtained are comparable with liter ature values for WO3 layers deposited by sputtering. The cells which h ave 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 transmis sion to be obtained, i.e. from 80% to 50%. (C) 1998 Elsevier Science B .V. All rights reserved.