Record Passive Radiative Cooling of over 15 °C by a Micro-Nanoporous Granular Composite Film

Energy-free cooling via passive daytime radiative cooling (PDRC) has great potential for various applications. It is still challenging to develop an inexpensive PDRC material with high temperature reduction. Here, we report a micro-nanoporous granular composite film with an outdoor temperature decrease of over 15 °C. The success relies on the unique micro-nanoporous granular structure that couples strong multiple scattering and surface phonon polariton, leading to a high solar reflectance of 96.2%. Significantly, the thermal emissivity reaches 98.3% within the atmospheric transmittance window, which is the highest value reported to date. Moreover, the film presents a hydrophobicity and mechanical elasticity.