Ultra-Efficient Passive Daytime Radiative Cooling Enabled by Dual-Selective Inorganic SiO2/Si3N4 Photonic Emitter

Abstract

Radiative cooling is a zero-energy technology that enables subambient cooling by emitting heat into outer space (≈3K) via the atmospheric transparent windows. However, existing designs predominantly focus only on the primary atmospheric window (8–13 µm) and neglect another window (16–25 µm), underutilizing their cooling potential. Moreover, widely utilized organic radiative cooling metamaterials face significant challenges, including oxidation, degradation, and delamination, which ultimately reduce their operational lifespan. In this work, a dual-selective emitter is demonstrated based on an inorganic multilayer SiO₂/Si₃N₄ photonic structure. Outdoor experiments demonstrate that the emitter achieves notable subambient cooling (≈12.6 °C) and a cooling power of 141.4$\mathrm{W}{\mathrm{m}}^{-2}$ under a solar irradiance of over 900$\mathrm{W}{\mathrm{m}}^{-2}$, exceeding the performance of existing inorganic multilayer thermal emitters. Moreover, this emitter's substantial application potential is revealed in building cooling energy conservation with estimated annual energy savings of ≈129.1$\mathrm{MJ}{\mathrm{m}}^{-2}$ in hot climates through numerical simulations, thereby facilitating meaningful reductions in fossil fuel consumption and greenhouse gas emissions. This work offers a scalable and practical radiative cooling solution for sustainable thermal management with superior performance.