Aligning spectral emissivity profiles to the atmospheric transmission window for radiative cooling using layered dielectrics augmented with metamaterial interfaces

Abstract

Passive radiative cooling, an innovative approach for cooling buildings and devices, has attracted considerable attention in recent years. One significant challenge in radiative cooling is the need for surfaces with selective spectral emissivity that aligns with the atmospheric transmission of earth. The spectral emissivity of the surface in the 8–13 μm serves as a crucial factor in enhancing the net cooling capacity of the surface. In this study, we achieved a spectral surface emissivity that is aligned with the atmospheric transmission window using layered dielectrics augmented with a metamaterial interface. By harnessing the strong coupling within the gap of a bowtie antenna resulting from the interaction of light with metallic surfaces, we achieve a broadband absorption around a resonance frequency within the atmospheric window spectrum. Additionally, we successfully attained broadband reflection in the visible region with a reflectivity of more than approximately 97 % and in the near-infrared spectra through the design and optimization of alternating layers with high and low refractive indices (SiO₂–TiO₂) deposited on a thin silver layer. Our results indicate that merging the metamaterial surface with dielectric layers eliminates the need for thick layers in conventional radiative cooling structures. This configuration significantly improves cooling performance, and it results in a more compact and thinner stack.