Enhanced contrast ratio of an electrochromic window (ECW) based on a V2O5-TiO2 composite thin film as a counter electrode

Abstract

An Electrochromic window (ECW) is a strong candidate for an optical shutter. An ECW is composed of the conductive polymer as a working electrode and V₂O₅ as a counter electrode. The ECW technology switches between colored and bleached stages. In this paper the modification of a V₂O₅ thin film as a counter electrode is studied to increase contrast ratio of ECWs by adding TiO₂ into V₂O₅. The dependence of the intercalation properties and transmissivity of V₂O₅-TiO₂ composite films on various chemical compositions, a preparation and characterization of the films for use as a transparent ion storage layer in organic ECWs are focused on in this paper. A V₂O₅-TiO₂ composite film was synthesized with sol-gel electrophoresis deposition method. Indium Tin Oxide (ITO) coated glass was used as an electrically conductive and transparent substrate. A V₂O₅-TiO₂ composite film with V/Ti ratio of 70/30 in the reduced state showed 6 to 13improvement of transmissivity between 380 nm and 800 nm wavelengths as compared to a V₂O₅ thin film in the same state. Li⁺ intercalation rate was also observed to be higher. The composite film exhibited twice of capacitance than that of the V₂O₅ film. An ECW with the composite film exhibited 6higher contrast ratio than that with the V₂O₅ film. The contrast ratio of the ECW, measured as Δ%T, was equal to 56%, and ranged from 2to 58between the colored and bleached state measured at 580 nm wavelength. The color change response speed was also faster, i.e., only two seconds between fully colored and bleached stages.