Colored Radiative Cooling Coatings with Nanoparticles

Abstract

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.

Photonics Empowered Passive Radiative Cooling

“…As the radiative cooling materials are usually integrated with the exterior of terrestrial objects, such as building facades, where aesthetic color designs are important. [ 14,102–105 ] The commonly used white and silvery reflectance surfaces are not likely to be adopted in those scenarios. Therefore, developing radiative coolers with aesthetic surface color is a pressing research field.…”

Colorful surfaces for radiative cooling

“…Photonic structural colors received extensive interests in recent decades due to their unique coloration mechanism that is different from conventional pigments. [91][92][93][94][95][96][97][98][99][100] Intriguingly, the color of photonic structures can be designed using engineered subwavelength features to minimize the solar heating effect. For instance, owing to controlled thin film interference (e.g., Fabry-Pérot interference), layered photonic structures can generate designated color within the full visible range.…”

“…4(f)], 98 and metallic nanoparticle resonances. 100 The major target for these works is to realize narrowband optical absorption (i.e., structure-induced colors) and keep the strong thermal emission simultaneously for radiative cooling. However, solarabsorption-induced heating is still inevitable.…”

“…Photonic structural colors received extensive interests in recent decades due to their unique coloration mechanism that is different from conventional pigments [91][92][93][94][95][96][97][98][99][100]. Intriguingly, the color of photonic structures can be designed using engineered subwavelength features to minimize the solar heating effect.…”

“…The different thermal loads of these two materials resulted in drastically different temperatures when placed under direct sunlight. Other strategies include silicon nanowire arrays on Ag film [Fig.4(d)],94 metal-insulator-metal cavity structures [Fig.4(e)],97 engineered multilayered films [Fig.4(f)],98 and metallic nanoparticle resonances 100. The major target for these works is to realize narrowband optical absorption (i.e., structure-induced colors) and keep the strong thermal emission simultaneously for radiative cooling.…”