The design of ultra-broadband selective near-perfect absorber based on photonic structures to achieve near-ideal daytime radiative cooling

Publication date: 5 February 2018
Source:Materials & Design, Volume 139
Author(s): Dong Wu, Chang Liu, Zenghui Xu, Yumin Liu, Zhongyuan Yu, Li Yu, Lei Chen, Ruifang Li, Rui Ma, Han Ye
Passive cooling, which cools without any electricity input, has had a great impact on global energy consumption. The recent progress on radiative cooling has many potential applications in efficient passive cooling. During the day, this strategy uses the maximized infrared emissivity via the atmospheric transparency windows for radiating heat and minimizing solar absorption. However, the realization of daytime radiative coolers with ideal selective mid-infrared emissivity is still a great challenge. Here, we firstly design and numerically demonstrate a near-ideal radiative cooler operating below the ambient temperature, achieving both broadband selective emissivity in the infrared atmospheric window and extremely low absorption in the entire solar spectrum, realizing a net cooling power exceeding 122W/m² at ambient temperature. The cooling effect can still persist under significant nonradiative heat exchange conditions. The design of multi-layer all-dielectric micropyramid structure in this work not only solves the shortcoming of poor mid-infrared selectivity in planar photonics device, but also overcomes the disadvantage of high solar absorption in metal/dielectric metamaterials. The comparisons of physics mechanism between this multi-layer all-dielectric structure and previously reported multi-layer metal/dielectric structure also are investigated clearly. Thus, this study can help pave the way for designing ideal daytime radiative coolers.

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