A Dual Photonic Structure with Beaded Networks and Core–Shell Nanoparticles for Ultrathin yet High-Performance Passive Daytime Radiative Cooling Coatings

Developing energy-free passive daytime radiative cooling (PDRC) coatings has broad application prospects, which is of practical significance to alleviate the issues of energy shortages and global warming. However, conventional thick PDRC coatings suffer from high material consumption, leading to elevated costs and higher thermal resistance, underscoring the need for ultrathin alternatives. Fabricating ultrathin films (<200 μm) both with high solar reflectance ( R solar, 0.28–2.5 μm) and atmospheric transparent window emissivity (ε LWIR, 8–13 μm) remains challenging. To address this challenge, we designed a dual photonic structure consisting of a porous poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) film with a beaded network, integrated with Al 2 O 3 @SiO 2 core–shell nanoparticles. At a thickness of only ∼150 μm, the film achieves a R solar of 94.2% and ε LWIR of 0.972. Under solar irradiance 850–900 W/m 2, outdoor tests demonstrate a maximum cooling effect of 18.8 °C relative to the blank control. Meanwhile, the film achieved a net radiative cooling power of 206–216 W/m 2 under 418–510 W/m 2 solar irradiance, with a surface temperature equal to the blank control (44–47 °C). Moreover, the superhydrophobic surface endows excellent self-cleaning capability, maintaining stable optical performance after two months of outdoor exposure. The dual photonic structure provides an innovative approach for ultrathin, high-performance, and durable radiative cooling materials.