Glass plays a crucial role in the energy efficiency and daylight comfort of buildings. As the glass industry is developing insulating glass with enhanced insulation properties and implementing this more and more in buildings, a trend of declining heating demand in the building sector has been initiated to comply with energy efficiency regulation. However, at the same time, with increasing temperatures in summer, another problem appears: our buildings are getting too hot and airconditioning use is increasing. This trend asks for the next innovation in adaptive glazing which blocks sunlight on sunny days to prevent overheating and excessive amounts of daylight, whilst allowing sunlight on cloudy days. However, current glazing does not adapt to these changes in weather conditions and thus does not always contribute to an optimal indoor climate.
Here we present a novel photochromic smart glass film. The film self-regulates both solar heat rejection and daylight comfort based on the outdoor sunlight intensity. The technology is based on a light-sensitive pigment simply produced in solution and applied using a scalable roll-to-roll coating technique, which changes its absorption of sunlight when irradiated with UV-light. At first the film highly transparent with a visible light transmission (Tvis) of 87% when adhered to a single glass plate. Unlike other self-adaptive films, this technology allows a significant change in both the visible as well as the invisible near-IR sunlight range, achieving a solar heat (g-value) modulation of 0.33, whilst showing a visible light change of 48% between the transparent and tinted state. Simulations on a model office show that this large g-value modulation causes an annual energy saving potential up to 35% compared to the same glazing without the film.