Full daytime sub-ambient radiative cooling in commercial-like paints with high figure of merit

Abstract

We demonstrate remarkable full-daytime subambient cooling performance with CaCO3 and BaSO4 nanoparticle paints. These fillers have a high electron band gap for low solar absorptance and phonon resonance or polymer absorption in the sky window for high sky window emissivity. With an appropriate particle size and a broad particle size distribution, the BaSO4 nanoparticle film reaches an ultrahigh solar reflectance of 97.6% and a high sky window emissivity of 0.96. During field tests, the BaSO4 film stays more than 4.5 °C below ambient temperature or achieves an average cooling power of 117 W/m2. The BaSO4-acrylic paint is developed with a 60% volume concentration to enhance the reliability in outdoor applications, achieving a solar reflectance of 98.1% and a sky window emissivity of 0.95. Field tests indicate similar cooling performance to the BaSO4 films. Overall, our BaSO4-acrylic paint shows a standard figure of merit of 0.77.