Selectively emissive fluoropolymer film for passive daytime radiative cooling

Abstract

Passive daytime radiative cooling is an attractive method to reduce overheating and the heat island effect, thus addressing the global warming effect. This technology does not require any input energy, noise, vibrations, and polluting gas to produce sub-ambient temperatures. In this study, we propose a simple passive daytime radiative cooler, composed of a silver back layer and commercial ethylene tetrafluoroethylene film. With many molecular vibration peaks in the sky window and high solar transmittance of ethylene tetrafluoroethylene, the silver-deposited film exhibits only 3.5% solar absorption and 88.6% emissivity in the sky window, resulting in a substantial sub-ambient cooling effect of up to 9.7 °C in outdoor measurements. The theoretical prediction was confirmed to match well with experimental results, and the passive daytime radiative cooling ability of the film was examined using global-scale cooling energy density maps.