Thermo‐Optically Designed Scalable Photonic Films with High Thermal Conductivity for Subambient and Above‐Ambient Radiative Cooling

Abstract Radiative cooling is a promising passive cooling technology that reflects sunlight and emits heat to deep space without any energy consumption. Current research mainly focuses on cooling non‐heat‐generating objects (e.g., water) to a deep subambient temperature under sunlight. Toward real‐world applications, however, cooling outdoor objects that generate tremendous heat and have a temperature higher than ambient (e.g., communication base stations and data centres) remains a challenge. Herein, a scalable photonic film is prepared by introducing 2D dielectric nanoplates with high backward scattering efficiency into a polymer using a simulation aided thermo‐optical design. It is demonstrated that the dielectric nanoplates can break the trade‐off between optical reflection and thermal dissipation of conventional radiative coolers. The photonic film exhibits superior solar reflectance (98%) and has a stronger heat dissipation ability compared to the matrix. It exhibits ≈4 °C subambient cooling performance under direct sunlight and ≈9 °C cooling performance at night. Moreover, it also demonstrates remarkable above‐ambient cooling performance by reducing the underlying heater temperature of ≈18 °C in comparison with traditional polymers under sunlight. The dielectric nanoplates reported here provide an innovative strategy for applications related to light management beyond subambient and above‐ambient radiative cooling.