Sub-ambient radiative cooling under tropical climate using highly reflective polymeric coating

Abstract

While passive radiative cooling has shown great potential in temperate regions in lowering surface temperatures, its cooling performance under tropical climate that is characterised by high solar irradiance and humidity still lacks exploration. Herein, we adopt a highly reflective polymeric coating with BaSO 4 particles dispersed in P(VdF-HFP) matrix for radiative cooling in the tropics. Through the strong Mie scattering of sunlight and intrinsic bond vibration, the substrate-independent average solar reflectance and infrared emittance within the 8–13 μm atmospheric window could reach 97% and 94.2%, respectively. For the first time, surfaces could maintain sub-ambient temperatures under direct exposure to the sky and surroundings even when the solar intensity was 1000 W/m 2 and downwelling atmospheric radiation was 480 W/m 2 , while separately achieving 2 °C below ambient during night-time with an effective cooling power of 54.4 W/m 2 . With a scalable fabrication-process, our cost-effective single-layer coating can be easily applied to diverse substrates, which is suitable for real-world applications in the tropics. Radiative cooling is a passive technology that lowers surface temperatures by reflecting solar energy and releasing thermal energy to the cold universe through the atmospheric window. For the first time, sub-ambient temperatures are achieved in tropical daytime by a cost-effective single-layer coating. • For the first time, surfaces could maintain sub-ambient temperatures in tropical daytime. • 2 °C below ambient during night-time, with a cooling power of 54.4 W/m 2 . • Solar reflectance and infrared emittance could reach 97% and 94.2%, respectively. • Cost-effective single-layer coating can be easily applied to diverse substrates.