Optically switchable coatings: Paper presented at 4th Power Electronics for Plasma Engineering Konferenz 2013, Freiburg, Germany, 22.05.2013-23.05.2013

For modern buildings with large glazing areas solar irradiation helps to reduce the energy demand for heating and lighting, but also leads to overheating and in consequence to high cooling loads. Optically switchable windows allow a variable transmittance of sunlight, and therefore minimize the overall consumption of energy keeping the visual contact to the environment. This paper wants to give a short introduction of electrochromic and gasochromic devices, including electrochromic devices with redox electrolyte. For such devices, tungsten oxide is an outstanding electrochromic material, and therefore some parameters have to be optimized by the deposition process, which are usually not in the scope of coatings for architectural glazings, as there are redox potential or diffusion constant. A nice review about optically switchable technologies for architectural glazings was already given in “Properties, requirements and possibilities of smart windows for dynamic daylight and solar energy control in buildings: A state-of-the-art review”, by Ruben Baetens, Bjørn Petter Jelle, and Arild Gustavsen, Solar Energy Materials & Solar Cells 94 (2010) 87–105. This includes also other technologies beyond electrochromic devices, like suspended particle devices or liquid crystal devices. There are also thermochromic (organic and inorganic) and thermotropic systems, but out all of these the electrochromic devices still seem to be the most interesting ones for architectural glazings. Still under investigation are photoelectrochromic and photochromic devices (“Switchable windows with tungsten oxide”, Andreas Georg, Anneke Georg, Wolfgang Graf, Volker Wittwer, Vacuum 82 (2008) 730–735)