High Reflectivity Modulation Electrochromic Windows

Abstract

ABSTRACTIn this paper we report the fabrication of high reflectivity modulation electrochromic Windows (ECW's) which have exhibited a colored state reflectivity of more than 50% for the wavelength range of 1 to 2.5 µm with an average bleached state reflectivity of 20%. The transmissivity of these ECW's in the colored state was less than 5% and in the bleached state it averaged 60%. The materials employed were tungsten oxide (nominally WO3) for the first electrochromic electrode, lithium cobalt oxide (nominally LiCoO2) for the second, complementary, electrochromic electrode, lithium phosphorus oxynitride (Lipon) for the ionic conductor (electrolyte), and indium tin oxide (ITO) and indium oxide (In2O3) for the two transparent electronic conductors. The predicted and measured reflectivity of the ECW's were influenced by the first transparent conductor (TM) in relation to its thickness and optical properties. Devices without a TC1 exhibited the highest reflectivity modulation, It was also concluded that two of the main limitations to the degree of reflectivity modulation attainable with the ECW's were lithium insertion into TC1 and electronic transport through the electrolyte.