Polyethylene terephthalate-based colored emitters for efficient daytime radiative cooling

Passive daytime radiant cooling is the process of transferring excess heat to cold spaces. Conventional radiant-cooling devices are usually colored white or silver to achieve high reflectivity in the solar spectrum range; these devices are limited by the high cost of materials and the difficulty of their preparation. Herein, we present a color-tunable radiative cooler consisting of an Ag/SiO2/Ag layer reverse-vaporized on a high-emissivity polymer, namely, polyethylene terephthalate. Because of the materials’ optical properties and synergism, the radiative cooler exhibits a high selective emissivity of 85 % within an atmospheric transparency window. Outdoor experiments in Xiamen, Fujian Province, China showed that the prepared optical films can counter solar heating while achieving color and can realize cooling of up to 6.92 °C below the ambient temperature. This ability was demonstrated by calculating the net cooling power. In addition, the cooling performance of the developed device is better than that of commercial coatings in the same color family, making the use of these colored radiant coolers in the fields of architecture and electronics feasible.