Multilayered SiO2/Si3N4 photonic emitter to achieve high-performance all-day radiative cooling

Radiative cooling has gained considerable attention recently, mainly due to its spontaneous thermodynamic process of dissipating surplus heat from the terrestrial object to deep space without any external energy. However, challenges still remain to meet better the stringent requirement on spectral selectivity for improving the current unoptimized cooling performance, especially for the multilayer-type radiative coolers. In this work, we proposed a radiative cooler with seven layers of SiO2 and Si3N4 optimized by using the evolutionary algorithm, which firstly facilitates a high reflection of solar irradiation utilizing the optical impedance mismatch, secondly enables a broadband emissivity merely within the atmospheric window by complementary phonon resonances, and thirdly suppresses the emissivity outside the atmospheric window (not only the solar spectral range). The continuous rooftop measurement and the comprehensive calculation collectively demonstrated the excellent capability of the radiative cooler, e.g., a measured temperature drop of 8 °C and a simulated cooling power of 87 W/m2 under the sunlight of ~900 W/m2. Besides, the cooling performance can be further enhanced if exposed to a dry climate due to the high humidity during the test. Our work contributes an alternative candidate to multilayered radiative coolers with cooling performance comparable to the polymer counterparts, and as well as providing a rational design approach exploiting both the structural and material aspects for similar photothermal devices.