All-day effective radiative cooling by optically selective and thermally insulating mesoporous materials

Due to serious solar absorption and poor thermal insulation on the cold side, current daytime radiative cooling falls far short of the theoretical potential. The mesoporous film can be used for both thermal insulation and optical selection. In this study, the radiative properties of infrared transparent mesoporous materials are investigated. The Diffusion Limited Cluster Aggregation algorithm is employed to reproduce the micro-structures of the mesoporous materials. The structure-dependent normal hemispherical transmittance is predicted by the combination of discrete dipole approximation and Monte Carlo method. The effects of material type and structure characteristics (particle size, volume fraction and cover thickness) on the infrared transmittance and all-day radiative cooling performance are quantified. The results show that the polyethylene (PE) aerogel achieves the best thermal insulation performance and good spectral selectivity. It can work as a thermally insulating barrier and an infrared transparent window for the radiative cooling surface. By integrating with PE aerogel, the radiative cooling surface can enable the passive cooling up to 13 K below the ambient temperature during the day and 15 K below the ambient temperature during the night at a wind speed of 2.8 m/s. This work provides an optimal design of optically selective and thermally insulating mesoporous materials in passive all-day radiative cooling applications.