Photochromic Film a.k.a. Chameleon film(tentative name), auto-tinting films

S. Hong
Korea Institute of Energy Research(KIER),

Keywords: flexible photochromic film, building energy efficiency, thin film coating


Through the cooperated works with companies in developing new chromogenic materials that can be deposited below 150oC, we successfully demonstrate the flexible photochromic film that can reversibly tune its transmittance in response to sun light. While it has an average transmittance of 70% at 600 ~ 700nm at its original state, it turns to greenish blue with 20% transmittance at 600 ~ 700nm upon exposure to sunlight. As the previously fabricated photochromic glass, photo-switching time of this photochromic films are not affected by their dimension. Switching time for coloring and bleaching is not the same. While the former is about 5min, the latter takes much longer time, about 5 hours. Now we focus on optimizing switching time for bleaching under dark condition by carefully tuning material’s composition. Our photochromic film does not need external power to operate that can greatly reduce expenditure of installation and maintenance. Electrochromic applications have found widespread success in smart windows for architectural buildings (SageGlass), auto-dimming rear view mirrors (Gentex), thermal control in space satellites, and camouflage applications. EC smart window are highly valued for their aesthetic glazing, low energy consumption, and a good coloration memory effect, which can reduce glare and incoming solar irradiation into the buildings, thereby lowering the energy consumption of air conditioning in the building. However, most of EC technologies are built in on rigid substrate. Currently there is an urgent need for flexible auto-tinting devices that can provide energy savings by retrofitting of existing window or sunroofs. Therefore, our technology of photochromic film is well suited for this purpose. Moreover, our photochromic film can be fabricated by roll-to-roll process that can significantly reduce the manufacturing cost. Furthermore, no need of external power supply to operate our photochromic films can provide a freedom of their application either on existing or planned buildings window as well as sunroofs.