A flexibly hierarchical porous polydimethylsiloxane film for Passive daytime radiative cooling

Passive daytime radiative cooling (PDRC) is a technology without requiring additional energy that cools objects by reflecting sunlight and radiating heat into outer space. However, the design process of PDRC films is relatively complicated or costly, which is not conducive to large-scale fabrication. For this, we fabricated a flexibly hierarchical porous polydimethylsiloxane (PDMS) radiative cooling film, which is simple and fast to fabricate and can be used for efficient large-scale production. It can reach the average emissivity of 0.95 in the transparent atmospheric window (8–13 μm). The average reflectance is above 0.7 in the solar wavelength band (0.3–2.5 μm), which is nearly 9 times of the non-porous structure. Thus, the porous PDMS films realize excellent sub-ambient temperature drop of 14.9 °C at the solar intensity of 910 W/m2.