Hierarchically porous polymer coatings for highly efficient passive daytime radiative cooling

Abstract

Passive daytime radiative cooling (PDRC) involves spontaneously cooling a surface by reflecting sunlight and radiating heat to the cold outer space. Current PDRC designs are promising alternatives to electrical cooling but are either inefficient or have limited applicability.We present a simple, inexpensive, and scalable phase inversion-based method for fabricating hierarchically porous poly(vinylidene fluoride-co-hexafluoropropene) [P(VdF-HFP)HP] coatings with excellent PDRC capability. High, substrate-independent hemispherical solar reflectances (0.96 ± 0.03) and long-wave infrared emittances (0.97 ± 0.02) allow for subambient temperature drops of ∼6°C and cooling powers of ∼96 watts per square meter (Wm-2) under solar intensities of 890 and 750 Wm-2, respectively.The performance equals or surpasses those of state-ofthe-art PDRC designs, and the technique offers a paint-like simplicity.