Smart window of large transparency-tuning capacity

Windows are one of the least energy-efficient components of a building. It allows energy to escape, leading to high cooling demand in summer and energy loss in winter. Sunlight and temperature in the building also affect people’s health, comfort, and even productivity. As a result, controlling the heat and light entering the building dynamically is critical for improving the comfort of building occupants and reducing energy consumption. In this work, we develop a tunable smart window based on transparent dielectric elastomer actuators (DEAs) as an alternative solution to sunlight and temperature control. The transparency-tuning is achieved by creating wrinkles in a soft elastomer film made of waterborne polyurethane (WPU). The actuation mechanism is based on highly transparent dielectric elastomer actuators that use all solid-state stretchable transparent conductive polymer poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)/(PEDOT:PSS/WPU) as compliant electrodes. The modulation range of the smart tunable window with direct viewing is achieved to be 35% to 90%, which is one of the largest among existing tunable windows. At the low-transparency state, the window can also effectively block the heat and decrease the temperature rise to 2°C over 200 s, while the ambient temperature rises by 6°C with direct sunlight. We anticipate that this transparency-tuning mechanism is potentially useful for privacy protection, smart glass, projector screens, displays, and camouflage. The heat isolation feature also has the potential to reduce carbon emissions and improve the sustainability of buildings and greenhouses.