Scalable and all-season passive thermal modulation enabled by radiative cooling, selective solar absorption, and thermal retention

Abstract

Temperature regulation of infrastructures by active heating and cooling approaches consumes about 20% of the total energy across the world, intensifying the energy crisis and exacerbating global warming by greenhouse gas emissions. In this work, we demonstrate a strategy for the all-season passive thermal modulation enabled by its three-mode functionality of radiative cooling, selective solar absorption, and thermal retention in a scalable manner. The radiative cooler consists of a 50μm thick Polydimethylsiloxane (PDMS) film with its back coated by broadband reflective silver (Ag) thin film (200 nm in thickness). The high solar reflectance (Rsolar, 0.95) and thermal emittance (ϵIR, 0.9) of the PDMS-derived radiative cooler facilitate the subambient cooling effect during the hot summer. The selective solar absorber is derived by selective leaching the aluminum (Al) element in the aluminum alloy by the hot alkaline solution to form the solar absorption copper (Cu) nanostructures over the all-wavelength reflective alloy substrate. The high solar absorptance (αsolar, 0.95) and low ϵIR (0.05) of the selective solar absorber assist the efficient solar harvesting during the daytime of the cold winter, meanwhile, its low ϵIR suppresses the radiative heat dissipation helping the thermal retention during the cold nighttime of the winter. The fabrication of the radiative cooler is derived by roll-to-roll casting, while the selective solar absorber can be manufactured by the solution process, which allows the all-season passive temperature regulation in a scalable manner.