Fabry–Perot resonance assisted dual-layer coating with enhanced wavelength-selective refection and emission for daytime radiative cooling

Abstract Radiative cooling has significant potential for application in the cooling of buildings, thermoelectric and photovoltaic owing to its no energy consumption and emission of harmful gases. In this paper, a daytime radiative cooling emitter (DRCE) consists of a dual-layer coating made of aluminum oxynitride (ALON) and silicon dioxide (SiO2) on an aluminum (Al) substrate is proposed to achieve daytime radiative cooling. The thicknesses of the ALON and SiO2 are respectively optimized to 10.23 and 7.40 μ m by variable metric method and genetic algorithm, and the transfer matrix method is used to calculate the radiative properties of the optimized DRCE. At a temperature of 30 ° C , the optimized DRCE achieves a high average total hemispherical emissivity (about 70%) in the wavelength band of atmospheric window, owing to the combining of the emissivities of the ALON and SiO2 in this wavelength band and the help of the Fabry–Perot (F-P) resonance. Owing to the high spectral directional transmissivity of only the dual-layer coating and high spectral directional reflectivity of bulk Al in the wavelength band of solar radiation, a high average total hemispherical reflectivity (about 98%) can be achieved in the wavelength band of solar radiation. When the power of solar radiation is about 900 W/m2, the cooling power of the optimized DRCE is about 110 W/m2 at the ambient air temperature ( T a m b = 30 ° C ), and the steady-state temperature of the optimized DRCE can be about 7 ° C lower than the ambient air temperature. This study shows that by selecting suitable materials and utilizing the F-P resonance, even a simple dual-layer structure can achieve high-performance daytime radiative cooling. Furthermore, it is also demonstrated that ALON may be a good candidate material for the DRCE, providing more material choices for improving its performance.