Electrochromics and thermochromics : towards a new paradigm for energy efficient buildings

Modern buildings normally have large windows and glass facades, known jointly as glazings, for achieving good day-lighting and indoors-outdoors contact. However, glazings are challenging for the buildings' energy efficiency and frequently let in or out too much energy, which has to be balanced by active cooling or heating. Cooling requirements, in particular, have soared recently. Emerging technologies based on thermochromics and/or electrochromics can regulate the inflow of visible light and solar energy between widely separated limits and yield better energy efficiency than static solutions. Thermochromic thin layers, based on vanadium dioxide, transmit less infrared solar radiation at high temperature than at low temperature. Electrochromic multilayer structures, normally based on thin films of tungsten oxide and nickel oxide, can regulate the transmittance of visible light and solar energy when a low-voltage is applied for a short time in order to move charge between the two oxide films. Importantly, the new fenestration technologies can improve indoor comfort. This brief review covers thermochromics and electrochromics and emphasizes that they are keys to a new paradigm for energy efficient buildings