A hierarchically structured self-cleaning energy-free polymer film for daytime radiative cooling

Radiative cooling without using electricity represents an ideal green solution for air-conditioning. Despite exciting progress made so far, most of the radiative cooling materials are vulnerable to outdoor contamination, which leads to decreased performance. Herein, we fabricate a hierarchically structured PVDF/PDMS porous film which integrates strong sunlight reflectance (97%), high thermal-infrared emittance (96%) and robust super hydrophobicity (160.2). The synergy of the effective solar reflection and thermal-infrared emission enables the film to yield a sub-ambient temperature drop of 12.3 degrees C under strong sunlight. More importantly, the super hydrophobicity keeps the film away from contamination by self-cleaning, maintaining well the radiative cooling performance for a long-term outdoor use. Additionally, the as-obtained film shows excellent chemical durability after exposure to different pH solutions and UV light irradiation. This work provides a new strategy to integrate self-cleaning with radiative cooling, showing great potential to advance energy-free cooling materials toward real-world applications.