Highly suppressed solar absorption in a daytime radiative cooler designed by genetic algorithm
Sunae So, Younghwan Yang, Soomin Son, Dasol Lee, Dongwoo Chae, Heon Lee, Junsuk Rho
Abstract
Abstract 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.