Ultrathin and High‐Efficiency Passive Daytime Radiative Cooling Coating via Polymer‐Particle Co‐Design

ABSTRACT Polymer‐based passive daytime radiative cooling (PDRC) coatings can mitigate global warming by reflecting solar radiation and emitting atmospheric transparency window (ATW) band mid‐infrared (MIR) radiation into outer space (∼3 K). However, achieving high solar reflectance ( R _sol ) and MIR emissivity (ε _MIR ) typically requires considerable thickness, which inevitably increases cost and self‐weight. To fabricate ultrathin coatings with superior optical performance, we propose a polymer‐particle co‐design strategy that fully leverages their synergistic contributions. Specifically, polymers and particles containing functional groups with resonance frequencies matching those in the ATW are selected, while Lorenz‐Mie scattering theory is employed to optimize particle sizes, thereby maximizing cooperative absorption in the ATW and complementary scattering in the solar spectrum. The resulting coating exhibits a high R _sol of 93.8% and a ε _MIR of 97.1%, while maintaining a thickness only 40% that of commercial coatings. Compared with commercial coatings, the proposed coating reduces unmanned aerial vehicles (UAVs) surface and simulated indoor temperatures by up to 8.1°C and 5.7°C, and achieves annual energy savings of 27.6, 24.8, and 22.6 MJ/m ² in Haikou, Hong Kong, and Macau. These findings highlight the potential of this designed coating for UAVs thermal management and building energy conservation in low‐ and mid‐latitude regions.