A Literature Study on Electrochromic and Thermochromic Materials: Final Report

Materials are known as chromogenic when they change their color in response to some stimulus. In thermochromic (TC), electrochromic (EC) and photochromic (PC) materials the stimuli are temperature, electric field and photons respectively. Scientists at the Energy Efficient Buildings Program at the Lawrence Berkeley Laboratory, University of California have led the efforts to study the solar energy applications of these materials. (Refs. 1-4). The objectives of this program were to investigate the literature, analyze and report on the properties of EC and TC materials that may be useful for solar energy conversion and building glazing applications. The intent was to emphasize, but not limit the study to, the oxides of vanadium and niobium.

Materials for use in building glazing applications have to perform in the -30 °C to 40 °C range and they have to be nonlinear with respect to solar energy transmittance. A similar performance except for operation at much higher temperatures (up to 300 °C) would be of interest in solar collector glazing. Also of interest is a material that can operate up to 600 °C and switch between being a solar absorber and reflector.