Eco‐Friendly and Scalable Preparation of High‐Efficiency Passive Daytime Radiative Cooling Film Based on Dual‐Layer Strategy

Abstract Passive daytime radiative cooling (PDRC), as a zero‐energy cooling technology, has attracted wide attention. It achieves high reflectivity in the solar band by scattering the incoming sunlight. According to Mie's theory, attaining elevated scattering efficiency necessitates a substantial refractive index disparity between the matrix material and the scattering particles in the PDRC film. Here, the study introduces barium titanate (BTO) nanoparticles as scattering particles, which have the highest theoretical refractive index among dielectric nanoparticles reported in the literature. A two‐layer strategy is implemented to mitigate the strong absorption of BTO nanoparticles in the ultraviolet (UV) band. Furthermore, using a liquid material as the matrix for the film and fabricating it via scrape coating technology enables an eco‐friendly and scalable preparation process. Ultimately, the obtained high‐efficiency PDRC (HE‐PDRC) film exhibits superb solar reflectance (0.948) and infrared atmospheric window emissivity (0.964). The HE‐PDRC film can achieve a cooling effect of ≈8 °C below the ambient temperature under clear weather conditions. The theoretical maximum cooling power is 87.5 W m ^{− 2} during the daytime and 125.2 W m ^{− 2} at night, respectively. This work paves the way for practical large‐scale applications of HE‐PDRC for human thermal comfort in buildings.