Smart window based on Cu7S4/hydrogel composites with fast photothermal response

Smart windows have attracted much attention owing to their capability of saving energy by modulating sunlight after exerting external stimulus of voltage, light or heat. However, most of these smart windows can only insulate heat by blocking sunlight at high temperature. Herein, we fabricate the Cu7S4/poly(N-isopropylacrylamide) (PNIPAm) composite film with fast optical/thermal response for smart switching to regulate indoor temperature under both low and high temperature. This smart window can save energy smartly and efficiently via integrating the wide absorption of sunlight and excellent photothermal conversion efficiency of Cu7S4 nanoparticles and thermo-responsive effect of PNIPAm. This smart window is transparent (Tlum = 79%, at thickness of 75 μm) and only blocks part of infrared and UV light (TIR = 68.7%, Tsol = 71.9%) at comfortable temperature (20 °C) and low light intensity. However, when temperature is over 32 °C, the smart window can quickly become opaque within 3 min to block more light (Tlum = 41.1%, TIR = 43.0%, Tsol = 40.4%) due to its good photothermal-responsive property. As long as the sunlight is strong enough, the smart window can absorb sunlight and convert it into heat to increase indoor temperature even in cold weather. This smart window can regulate solar radiation dynamically and adapt to surrounding temperature automatically to offer a new strategy to cut down energy consumption of buildings and vehicles smartly.