Photonics Empowered Passive Radiative Cooling

Passive radiative cooling has recently received renewed interest because of its unprecedented capabilities in cooling terrestrial objects below ambient air temperature without external energy consumption and greenhouse gas emission. This technology has been demonstrated as promising as replacements/complements of conventional compressed air‐based active cooling systems, which can significantly impact the global energy landscape by providing a green and efficient cooling way. The key to this success is judiciously designed photonic micro/nanostructures, which simultaneously reflect solar irradiation and emit thermal infrared emission across the atmospheric transparency window 8–13 μm. Herein, an introduction of the fundamental principles of passive radiative cooling is given, discussing the critical factors associated with the net cooling power of radiative cooling. Following this, the recently emerged photonic materials and structures (e.g., multilayer thin films, micro/nanoparticles, photonic crystals, metamaterials, metasurfaces, etc.) that facilitate radiative cooling are reviewed and fruitfully analyzed and discussed. Some possible scale‐up manufacturing ways toward the practical deployment of this energy‐efficient technology in real‐world applications are then discussed. The potential applications are also summarized and envisioned. Finally, perspectives on the future development in conjunction with artificial intelligent design of photonic structures and materials are presented and discussed.