Fast Photo‐Heat‐Response Cu ₇ S ₄ /PNIPAM Composite Hydrogels Real‐Timely Adjusting the Incident Light Transmittance Rate for Smart Windows

Smart windows are emerging energy‐saving approaches for buildings, dynamically adjusting light transmittance based on weather changes to maintain indoor comfort. However, conventional thermochromic (TC) materials have slow response rates and poor optical sensitivity. Herein, hollow Cu 7 S 4 nanomaterials with broad spectral absorption and high photothermal conversion efficiency are combined with thermoresponsive PNIPAM hydrogel to create a Cu 7 S 4 /PNIPAM hydrogel. This composite enables fast transmittance conversion via photothermal response. The smart window, designed with a glass interlayer, can adaptively adjust transmittance according to real‐time light intensity. It is transparent at low light intensity ( T 550 nm = 70.2%) and quickly becomes translucent ( T 550 nm = 39.8%) within 3 min under high light intensity, blocking excess light. This design can reduce indoor temperature by up to 16 °C compared to ordinary glass. Additionally, in cold climates, the smart window can provide heat through photothermal conversion. This approach offers a new way to enhance the performance of traditional TC materials.