Some Aspects Of Electrochromism Of Wo Filmsfilms Prepared By A Chemical Deposition Method

Abstract

ABSTRACT Tungsten tri-oxide thin films were prepared by deposition from a solution of tungsten chloride, and, for comparison, by the acidification of a solution of sodium tungstate. The mechanism of the formation of HWQ« is explained in terms of oxidation of WClfi by 0^ followed by chlorination of alcohol and formation of EL which reduces WQQ to HWQo. The electrochromic behavior of these films was investigated by studying their current-voltage behavior, absorbance spectra, response time, and the diffusion coefficient of lithium ions in the film.Systems with variable light absorption, transmission, or reflection are of great importance for the construction of smart windows with controllable light transmission or glare free automotive rearview mirrors with adjustable reflectance. This phenomenon of variable optical properties, commonly known as electrochromism is usually initiated by the electrochemical injection into or depletion of charges from the material in contact with an ionic conductor. Electrochromism is based on the unique property of a number of transition metal oxides, organic polymers, or inorganic complexes which have different colors in different or mixed oxidation states. Transition metal oxides such as the oxides of iridium, rhodium, nickel and cobalt are colored in their higher oxidation states, and are known as anodically coloring materials. The oxides of tungsten, molybdenum, vanadium and niobium are colored in their lower oxidation states, and are, thus, known as cathodically coloring materials.The most widely investigated electrochromic substance is tungsten tri- oxide, WOo This material is blue when it is reduced and transparent when it is oxidized. The electrochromic activity exhibited by WOo thin films vary depending on the methods used for their preparation. W0« film is usually prepared by vacuum evaporation or rf sputtering. Instead, we prepared the film in a simple way, by deposition from solution of tungsten chloride, and, for comparison, by the sol-gel method, as reported previously . We report here our results on the electrochromic properties of these films as studied electrochemically and spectroscopically.Thin films of tungsten oxide were deposited on fluorine-doped tin- oxide (FTO) coated glass substrates (Johnson-Watkins) using the