Electrochromism

Electrochromism is the phenomenon where the color of a material changes by applying a voltage. By doing so, an electrochromic window can block UV, visible or (near) infrared light by the push of a button. The ability to control transmittance of (near) infrared light limits the amount of energy needed to cool during summer and heat during winter. For this reason it is researched for use in smart windows to increase energy efficiency of buildings. Electrochromism is the phenomenon where the color of a material changes by applying a voltage. By doing so, an electrochromic window can block UV, visible or (near) infrared light by the push of a button. The ability to control transmittance of (near) infrared light limits the amount of energy needed to cool during summer and heat during winter. For this reason it is researched for use in smart windows to increase energy efficiency of buildings. As the color change is persistent and energy need only be applied to affect a change, electrochromic materials are used to control the amount of light and heat allowed to pass through windows ('smart windows'), One popular application is in the automobile industry where it is used to automatically tint rear-view mirrors in various lighting conditions. Among the metal oxides, tungsten oxide (WO3), has been the most extensively studied material. For organic materials, viologens have been commercialized on small scale. A variety of conducting polymers are also of interest, including polypyrrole, PEDOT, and polyaniline. Viologen is used in conjunction with titanium dioxide (TiO2) in the creation of small digital displays. It is hoped that these displays will replace liquid crystal displays as the viologen, which is typically dark blue, has a high contrast compared to the bright white of the titania, thereby providing the display high visibility. Rdot (rdotdisplays.com) is offering flexible displays based on similar materials. Many methods have been used to synthesize tungsten oxide such as chemical vapor deposition (CVD), sputtering, thermal evaporation, spray pyrolysis from vapor–phase based method and sol-gel process, hydrothermal from liquid-phase based method. In industry, sputtering is the most common method for the deposition of tungsten oxide. For material synthesis, sol-gel process is widely used due to its advantages of simple process, low cost and easy control.