Efficient realization of daytime radiative cooling with hollow zigzag SiO2 metamaterials.

A tunable selective emitter with hollow zigzag SiO₂ metamaterials, which are deposited on Si₃N₄ and Ag film, is proposed and numerically investigated for achieving excellent radiative cooling effects. The average emissivity reaches a high value of 98.7% in the atmospheric window and possesses a high reflectivity of 92.0% in the solar spectrum. To reveal the enhanced absorptivity, the confined electric field distribution is investigated, and it can be well explained by moth eye effects. Moreover, tunable emissivity can also be initiated with different incident angles and it stays above 83% when the incident angle is less than 80°, embodying the excellent cooling performance in the atmospheric transparency window. Its net cooling power achieves 100.6 W⋅m⁻², with a temperature drop of 13°, and the cooling behavior can persist in the presence of non-radiative heat exchange conditions. Therefore, high and tunable selective emitters based on our designed structure could provide a new route to realizing high-performance radiative cooling. This work is also of great significance for saving energy and environmental protection. [ABSTRACT FROM AUTHOR]