Abstract
Radiative cooling can make the selective emitter cool below ambient temperature without any external energy. Recent advances in photonic crystal and metamaterial technology made a high-efficiency selective emitter achievable by precisely controlling the emitter’s Infrared emission spectrum. However, the high cost of the photonic crystals and meta-materials limit their application. Herein, an efficient bilayer selective emitter is prepared based on the molecular vibrations of functional nanoparticles. By optimizing the volume fraction of the functional nanoparticles, the bilayer selective emitter can theoretically cool 36.7 °C and 25.5 °C below the ambient temperature in the nighttime and daytime, respectively. Such an efficient cooling performance is comparable with the published photonic crystal and metamaterial selective emitters. The rooftop measurements show that the bilayer selective emitter is effective in the ambient air even under direct sunlight. The relatively low cost and excellent cooling performance enable the bilayer selective emitter to have great potential for a practical purpose.
Highlights
Cooling, as one of the major end-uses of electricity, triggers massive amounts of energy consumption
The passive radiative cooling can make the temperature of the radiators‘ surface decrease below ambient temperature without external energy
Spectral analysis of the samples with a different volume fraction of the functional nanoparticle illustrates that the selectivity of the emitter’s IR emission reduces with the increase of the particle’s volume fraction, which can degrade the performance of the selective emitter
Summary
As one of the major end-uses of electricity, triggers massive amounts of energy consumption. The passive radiative cooling can make the temperature of the radiators‘ surface decrease below ambient temperature without external energy. Radiaive cooling has the potential to lower the emissions of greenhouse gases as well as optimize the existing structure of the energy source [2]. The efficient radiative cooling devices are expected to have near unity infrared (IR) emissivity within. The daytime radiative cooling, is still a great challenge since solar energy is absorbed intensively by these emitters, which generates massive heat on the surface of the emitters [2,10]. The effecient daytime cooling process requires selective emitters to have near unity solar reflectivity while emitting selectively and significantly within 8–14 μm in the IR region
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