Pyramid Textured Photonic Films with High‐Refractive Index Fillers for Efficient Radiative Cooling

Abstract Sub‐ambient cooling technologies relying on passive radiation have garnered escalating research attention owing to the challenges posed by global warming and substantial energy consumption inherent in active cooling systems. However, achieving highly efficient radiative cooling devices capable of effective heat dissipation remains a challenge. Herein, by synergic optimization of the micro‐pyramid surface structures and 2D hexagonal boron nitride nanoplates ( h ‐BNNs) scattering fillers, pyramid textured photonic films with remarkable solar reflectivity of 98.5% and a mid‐infrared (MIR) emittance of 97.2% are presented. The h ‐BNNs scattering filler with high thermal conductivity contributed to the enhanced through‐plane thermal conductivity up to 0.496 W m −1 K −1 and the in‐plane thermal conductivity of 3.175 W m −1 K −1 . The photonic films exhibit an optimized effective radiative cooling power of 201.2 W m −2 at 40 °C under a solar irradiance of 900 W m −2 and a daily sub‐ambient cooling effect up to 11 °C. Even with simultaneous internal heat generation by a 10 W ceramic heater and external solar irradiance of 500 W m −2 , a sub‐ambient cooling of 5 °C can be realized. The synergic matching strategy of high thermal conductivity scattering fillers and microstructured photonic surfaces holds promise for scalable sub‐ambient radiative cooling technologies.