Ultrahigh Visible-Transparency, Submicrometer, and Polymer-Free Radiative Cooling Meta-Glass Coating for Building Energy Saving

Abstract

Glass windows are the most energy-inefficient part of buildings, which triggers the ongoing chasing of energy-efficient transparent radiative cooling (TRC) metamaterials on glasses that simultaneously maintain high visible (VIS) transparency, block near-infrared (NIR) solar radiation, and emit thermal energy through the atmosphere window (AW). However, the stringent multispectral regulation remains challenging since it involves with huge parameter spaces and significant interactions among different bands. Additionally, most TRC metamaterials require a top ∼50 μm polymer for high emissivity in the AW, which will reduce the VIS transparency and suffer from aging issue. Here, we employ the deep reinforcement learning (DRL) method, leveraging its robust material screening and structure optimization capabilities, to design a five-layer submicrometer dielectric multilayer, composed of two stacked materials, as polymer-free TRC metamaterial on glass or meta-glass for short. Utilizing a plain glass substrate with high emission in the AW, our meta-glass demonstrates an ultrahigh angular-independent (<60°) VIS transmissivity against the state-of-the-art, i.e., 86% (92.7% in theory), with ∼48% NIR reflectivity and ∼89% AW emissivity in experiment. In outdoor experiments at ambient temperatures of ∼10 and ∼20 °C, with solar irradiances reaching around 780 and 850 W/m2, our meta-glass achieves a floor temperature reduction of 8.9 and 12.7 °C, respectively, compared to uncoated glass. Furthermore, we achieved customization of meta-glasses with varying transparency levels while maintaining high NIR reflectance by DRL. Our meta-glass exhibits an extraordinary building energy saving potential in most climate zones. This work provides a valuable reference for the advancement of TRC and the design of multispectral metamaterials.