Quasi-periodic selective multilayer emitter for sub-ambient daytime radiative cooling

Abstract

This work theoretically demonstrates a quasi-periodic selective multilayer emitter for sub-ambient daytime radiative cooling. In the design process, by inserting well-defined materials with different refractive-index profiles in suitable layers, there are absorption bands at different regions and the absorption bands are enhanced and broad in atmospheric transparency windows. Combined with the interference effects of the surface and the high reflectivity of Ag, the solar reflectance of the emitter is maximal in the solar spectrum. The influence of different nonradiative heat exchanges and the ambient air temperatures on the cooling performance of the multilayer emitter are calculated. At the same time, the mechanism of radiative cooling is analyzed. All the results show that the proposed emitter can effectively achieve sub-ambient daytime radiative cooling. Due to the superior durability and mechanical robustness of the multilayer emitter, it may be a key element in the realization of energy-efficient radiative cooling devices.