Daytime Radiative Cooling Using Near-Black Infrared Emitters

Abstract

Recent works have demonstrated that daytime radiative cooling under direct sunlight can be achieved using multilayer thin films designed to emit in the infrared atmospheric transparency window while reflecting visible light. Here, we demonstrate that a polymer-coated fused silica mirror, as a near-ideal blackbody in the mid-infrared and near-ideal reflector in the solar spectrum, achieves radiative cooling below ambient air temperature under direct sunlight (8.2 °C) and at night (8.4 °C). Its performance exceeds that of a multilayer thin film stack fabricated using vacuum deposition methods by nearly 3 °C. Furthermore, we estimate the cooler has an average net cooling power of about 127 W m –2 during daytime at ambient temperature even considering the significant influence of external conduction and convection, more than twice that reported previously. Our work demonstrates that abundant materials and straightforward fabrication can be used to achieve daytime radiative cooling, advancing applications such as dry cooling of thermal power plants.