Heat resistant polymer electrolyte for enhanced organic electrochromic windows based on poly (3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine)

Abstract

Electrochromic Windows(ECWs) have the potential to save energy through dynamic control of light and solar energy entering a room (via solar heat gain coefficient control). ECWs have been developed as an optical shutter in airplane, building and automobile applications. An ECW is composed of three components, a working electrode based on electrochromic materials, a counter electrode based on ion storage materials and the electrolyte as an ionic conducting layer. Organic ECWs have been gaining popularity due to easy and cost effective manufacturing, availability of wide range of colors, high optical contrast and flexibility in design. However there are challenges in commercialization and application of organic ECWs. The application of ECWs as a sunroof in automobiles demands operation in harsh environment conditions like elevated temperature. Consequently the University of Washington, Center for Intelligent Materials and Systems has been developing a heat resistant organic ECW that can be operated at elevated temperatures maintaining high optical contrast, fast switching speed, optical color memory and electrochemical stability. The proposed design is an ECW based on poly (3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine),PPRODOT-Me2 as a working electrode, V<super>2</super>O<super>5</super>-TiO<super>2</super> composite materials as a counter electrode and poly(ethylene imine) based electrolyte. The ionic conductivity of the electrolyte was calculated through complex impedance method and temperature dependence of the electrolyte was determined using environment test chamber to control a temperature range of 15 to 80<super>o</super> Celsius for 100 hours. A 76 × 76 mm<super>2</super> ECW was developed and the optical transmittance change was observed by Chronoamperomerty and Time course measurement. The electrochemical stability of the window was monitored using cyclic voltammetry. The developed electrochromic window showed good optical contrast, electrochemical stability and fast response time after testing at elevated temperatures for 100 hours.