Colored Radiative Cooling Coatings with Nanoparticles

Daytime radiative cooling under sunlight can be achieved by reflecting solar irradiation and emitting infrared thermal radiation in the transparency regions of earth atmosphere. For the sake of aestheticism, control over coloration would be a clear added value for the automobile body or walls of a building. Since coloration decreases cooling performances because of solar absorption in the visible range, mitigating the loss in radiative cooling power requires selective narrowband absorption in the visible range. In order to make a compromise between aestheticism and energetic efficiency, we aim in this paper to obtain colored surfaces with mitigated sunlight absorption and high emission in the infrared. In this numerical study, we demonstrate that appropriate optical properties can be achieved with plasmonic core–shell nanoparticles (silica core, silver shell) and plain silver nanoparticles embedded in a silica and polydimethylsiloxane matrix. Spectral properties of the composites are obtained by Monte Carlo method. Varying the radii of the core and shell allows tuning the spectral position of the surface plasmon resonance, leading to different colors. It is possible to obtain multiple absorption peaks and therefore additional colors by mixing particles with different geometries. Eventually, increasing the volume fraction of nanoparticles leads to more vivid colors but also to a decrease of radiative cooling power. In conclusion, the structure that is proposed can be used for daytime radiative cooling with large control over the coloration.