Transparent radiative cooling films containing poly(methylmethacrylate), silica, and silver

Window is the least energy-efficient part of buildings or cars; however radiative cooling, as an efficient energy-zero technology, is rarely used in window films of buildings or cars. Therefore, we in this work fabricated a transparent dual-layer film for daytime radiative cooling, which contained a layer of polymethyl methacrylate (PMMA) uniformly mixed with modified silica nanoparticles (SiO2 NPs) and a layer of silver. The dispersion of the modified SiO2 NPs in PMMA was notably improved through in-site grafting PMMA, which resulted in a high transparency of the radiative cooling film even at a high filling fraction of SiO2 (20 wt%). Owing to the strong broadband IR absorbance/emittance (εAW = 94.3%) and high sunlight reflectance (ρ ≈ 50%), the dual-layer film possessed a high cooling capacity and could achieve an average temperature drop of 1.4 °C than pure PMMA film in the daytime outdoor cooling measurement. In the simulated automotive cooling test, the dual-layer film cooled the interior space up to 6 °C below ambient temperature during peak solar hours. The excellent optical property and cooling capability exhibit a promising application of building and car windows for cooling their interior spaces.