Here, we report a selective multilayer emitter for eco-friendly daytime passive radiative cooling. The types of materials and thickness of up to 10 layers of the multilayer structure are optimized by a genetic algorithm. The passive radiative cooler is designed to mainly target low solar absorption, which allows sub-ambient cooling under direct sunlight. We used a custom objective function in the solar region to achieve high-performance daytime radiative cooling to minimize solar absorption. The designed structure minimizes solar absorption with an average absorptivity of 5.0% in the solar region (0.3-2.5 μm) while strongly emitting thermal radiation with an average emissivity of 86.0% in the atmospheric transparency window (8-13 μm). The designed and fabricated structure achieves daytime net cooling flux of 84.8 W m-2 and 70.6 W m-2, respectively, under the direct AM 1.5 solar irradiation (SI) (total heat flux of 892 W m-2 in the 0.3-2.5 μm wavelength region). Finally, we experimentally demonstrate a passive radiative cooling of the fabricated selective emitter through a 72-hour day-night cycle, showing an average and maximum temperature reduction of 3.1 °C and 6.0 °C, respectively. Our approach provides additional degrees of freedom by designing both materials and thickness and thereby is expected to allow high-performance daytime radiative cooling.
Bibliographical noteFunding Information:
Research funding: This work was financially supported by the POSCO-POSTECH-RIST Convergence Research Center program funded by POSCO, and the National Research Foundation (NRF) grants (NRF-2019R1A2C3003129, CAMM-2019M3A6B3030637, NRF-2019R1A5A8080290, NRF-2018M3D1A1058997) funded by the Ministry of Science and ICT of the Korean government. S.S. and D.C. acknowledge the NRF Global Ph.D. fellowships (NRF-2017H1A2A1043322 and NRF-2019H1A2A1076622), respectively, funded by the Ministry of Education (MOE) of the Korean government. Y.Y. acknowledges the Hyundai Motor Chung Mong-Koo fellowship, and the NRF fellowship (NRF-2021R1A6A3A13038935) funded by the MOE of the Korean government.
© 2021 Sunae So et al., published by De Gruyter, Berlin/Boston.
- computational optimization
- multilayer structures
- radiative cooling
- selective emitters
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Atomic and Molecular Physics, and Optics
- Electrical and Electronic Engineering