Phase-changing NIPAM-AM/ATO hydrogels for thermochromic smart windows with highly adaptive solar modulation

Improving the solar regulation and reducing the response temperature of thermochromic smart windows are pivotal importance for energy-saving buildings. However, these two strategies are challenging to be integrated into one window. Herein, a novel composite hydrogel based on N-isopropylacrylamide (NIPAM) doped with antimony-doped tin oxide (ATO) nanoparticles and acrylamide (AM) was developed for producing a high-performance smart window, which successfully achieved enhanced solar energy regulation and reduced response temperature. This smart window was fabricated by combining a reversible thermoresponsive hydrogel (TAH) that acted as a thermochromic material with a ATO multilayer film that performed as a transparent heater. The as-prepared smart window could modulate solar light over a range from ultraviolet (UV) to infrared (IR) radiation and achieved active responses to high-temperature weather. The smart window showed high luminous transmittance (Tlum, 82.92 %) together with an excellent solar modulation performance (ΔTlum = 73.31 %, ΔTIR = 38.26 %, and ΔTsol = 60.74 %), and a lower critical solution temperature of 32 °C. Even after 120 high- and low-temperature cyclic durability tests, the smart windows still exhibited a high solar modulation capability. In outdoor demonstrations, the as-prepared smart window exhibited a promising temperature regulation ability under strong solar irradiation. Therefore, the present universal modification framework provided some insights for the future design of energy-saving windows.