Effect of different precursor sols on the properties of CeO2-TiO2 films for electrochromic window applications

The properties of spin coated CeO2-TiO2 films derived from three different sols containing equimolar quantities of cerium and titanium, fired at 500 degrees C have been investigated. The films have been deposited using cerium chloride and two different alkoxides and the influence of acetic acid added as a catalyst and modifier of microstructure of the coatings has also been studied. Optical, structural, thermal, and electrochemical properties have been studied and compared. Although gelation time of sols is dependent on the precursor material, enhanced transparency is exhibited by the films prepared with all the sols that have reached the state of gelation. The crystallization behavior and the porosity of the films are highly influenced by the precursor material. Acetic acid derived films with the highest porosity exhibit the highest diffusion coefficient for Li ions. Amorphicity prevailing in films derived from Ti propoxide based precursor sol as against the nanocrystalline films derived from the other sols endow higher ion insertion capacity to former films and highest coloration efficiency is attained when these films are incorporated into an electrochromic device. The highest reversibility for the charging and discharging processes and excellent electrochemical properties observed for the film derived from titanium propoxide prove its practical utility in electrochemical applications. Besides, the highest optical modulation for the electrochromic device comprising WO3 (electrochromic electrode) and titanium propoxide derived counter electrode is a manifestation of the suitability of the latter electrode in electrochromic window applications. (c) 2006 Elsevier Ltd. All rights reserved.