Spectrally designed photonic film with heat conducting pathways for efficient daytime radiative cooling and thermal dissipation

Daytime radiative cooling enables passive cooling of objects without consuming energy. However, it is a challenge for most radiative cooling films to achieve exceptional solar reflectivity , infrared emissivity and thermal conductivity simultaneously, which limits their applications in above-ambient conditions such as electrical equipment . Herein, we prepare highly solar-reflective β -Si 3 N 4 dielectric particles with solar reflectivity exceeding 0.91 and atmospheric window emissivity of 0.93 by one-step combustion synthesis . The radiative cooling film consisted of β -Si 3 N 4 particles and PVDF matrix achieves a subambient cooling performance of 11.63 °C and theoretically yields a radiative cooling power of 45.41 W m −2 in the daytime. Futhermore, the film exhibits high thermal conductivity of 3.19 W m −1  K −1 due to the heat conducting pathways constructed by elongated rod-like β -Si 3 N 4 particles, which leads to a remarkable temperature drop of 5.00 °C when be applied on the surface of 5 W LED. The film reported here provides a practical option for the efficient radiative cooling and heat dissipation of electrical equipment.