Optical Attenuation for Complementary Electrochromic Devices: Application to the Tungsten Oxide-Polyaniline System

Abstract

The optical attenuation of complementary electrochromic devices (ECDs) with two reversible electrodes operating in tandem is presented. The transmittances of electrochromic thin film electrodes are related to the electrochemical and optical properties of each coated electrochromic (EC) layer. By combining the electrochemical and optical properties of these two electrodes, a general variable transmittance function suitable for describing the switching characteristics of complementary ECDs is developed. To test the validity of the model, hybrid inorganic/organic complementary ECD, comprising a tungsten oxide (WO3) and polyanilinc (PAni) thin film couple in combination with a proton-conducting polymer electrolyte, is studied. Spectroelectrochemical measurements were performed in order to obtain the coloration efficiencies of both WOJ and PAni thin films. The measured optical attenuation for the ECD is in good agreement with the model prediction using the parameters obtained from the individual thin film measurements. Furthermore, it has been verified, both theoretically and experimentally, that the charge capacities of the two EC layers have to be matched in order to achieve the maximum optical attenuation.