Switchable selective and broadband passive radiative cooler based on metasurface

Abstract

In recent years, although numerous studies have achieved radiative cooling, they tend to rely on broadband emitter design which has the emissivity comprising over the entire wavelength of the atmosphere. Here, we propose switchable selective emitter mode (i.e., SE mode) or broadband emitter mode (i.e., BE mode) passive radiative cooler, which changes the emission spectrum either selective or broadband based on the metasurface. When the device is at SE mode, it emits heat strongly and selectively only within the wavelength from 8 μm to 13 μm of the atmospheric window. This distinguishes the purpose of each mode of the cooler, which makes possible to demonstrate theoretically and experimentally each emitter’s advantages depending on the situation. When the device is heated, the BE mode shows 50W/m2 higher cooling power than SE mode, while the sample is exposed directly to the rooftop without any extra heat input, the SE mode has 2 ºC superior cooling temperature than BE mode. This work describes a distinguished approach of selective emitter and broadband emitter, which opens up the possibility of not only for sub ambient cooling but also for the optoelectronic devices.