Scalable and paint-format colored coatings for passive radiative cooling

Abstract

Passive radiative cooling is an innovative way to radiate heat from objects to outer space by reflecting the sunlight and producing emission in the infrared spectrum especially in the atmospheric transparency window without additional energy input, which has received a widespread attention. However, state-of-the-art radiative coolers have a white appearance in the reflection of the total incoming solar radiation, facing inevitable challenges for anti-glare and other aesthetic issues. To address these problems, we have developed scalable colored coatings by using a facile solvothermal reaction. A combination of color and efficient radiative cooling has, thereby, been achieved by sacrificing a part of the reflections in the visible spectrum. The reflectance in the near-infrared spectrum, and emittance in the atmospheric window, were then maximized to 0.99 and 0.97, respectively. Without the contribution of an additional reflective layer, this type of coating has been found to achieve a sub-ambient temperature drop of 2.31°C (under a solar irradiance of 885 Wm -2 ) and a net cooling power of 68 Wm -2 . Due to the low cost of raw oxide materials, and simple preparation process, the present study has demonstrated a novel potential for large-scale practical applications of colored coatings for passive radiative cooling. • Colored coatings were synthesized, characterized and fabricated. • Attained cooling performance by maximizing near-infrared reflectance and emittance in the atmospheric window. • Achieved color performance through sacrificed partial reflection in visible spectrum. • Exhibited a sub-ambient temperature drop of 2.31°C and a net cooling power of 68 Wm -2 .