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Today, SoA energy-efficient windows are based on low-E and/or solar-control coatings. However, these static windows are not efficient enough throughout the season and cannot get rid of the excess of visible radiation in a dynamic way. The energy savings can be much higher if a switchable (dynamic or smart) window is used rather than a static one. Unfortunately, these windows are still rare in buildings because today’s commercially available SW are based on electrochromic devices, which consist of five layers, two electrodes and an electrolyte together with the electrochromic and ion storage films. The complexity of the fabrication process makes SoA SW costly up-to 950 EUR/m2. The implementation of SW based on materials with a thermochromic or photochromic effect i.e., exhibiting reversible colour change because of the temperature or absorption of electromagnetic radiation, allow the development of passive devices, without the need for any extra layers or sensors. Such windows will be activated by solar light and will need neither electricity nor control unit to function and switch automatically on-demand without need for human intervention.

Silver coated glass is used in the market. However, light reflection in visible wavelength range is very strong whereas the largest light transmittance is ~70% through the coating, which creates discomfort in users. Furthermore, Ag is one of the very expensive materials. The most successful thermochromic material that is entering the window market is VO2. However, when transparent to visible light, VO2 exhibits switching of its optical properties at temperatures exceeding 30°C. Furthermore, V is a toxic element, and the largest transparency of VO2 is < 75%, which makes the material less attractive from commercialization point of view. To make the material attractive in the market, one should increase transmittance of the material to < 85%, reduce reflectivity switching temperature to < 25°C by keeping the switching speed at the same level at least and increase durability to at least 20 years. In the proposal we will implement it by applying the concept of doping-induced electronic structure engineering and composite material-induced band gap engineering. Small area and large area depositions of VO2 will be performed, prototype windows with VO2 coating will be fabricated and tested in indoor and outdoor conditions, as well as research environmentally friendly utilization approach. Accelerated testing will be performed and durability will be estimated with objective to develop advanced non-toxic material for SW.