Radiative cooling by tailoring surfaces with microstructures: Association of a grating and a multi-layer structure

We propose in this article a method to conceive radiative coolers that are reflective in the solar spectrum and emissive in the transparency window of the atmosphere (8-13 µm). We choose an approach combining thermal control capacities of gratings and multi-layers. It is the first time that simple gratings are used for radiative cooling applications. We use optimized BN, SiC and SiO2 gratings, which have emissivity peaks in the transparency window. We place under these gratings a metal/dielectric multi-layer structure to obtain a near perfect reflectivity in the solar spectrum and to enhance the emissivity in the transparency window. The optimized structures produce a good radiative cooling power density up to 80 W.m−2 at night and a mean daytime radiative cooling power density of 55 W.m−2, with local atmospherical and solar conditions in Poitiers.