All-Day Passive Radiative Cooling for Future Clean Energy Technology

With the ever-increasing consciousness of the energy crisis and global warming issues, passive cooling methods that use free and renewable energy sources have been pursued recently. Radiative cooling is an efficient passive cooling strategy that dissipates excessive heat to the universe through thermal radiation. In particular, all-day passive radiative cooling has offered an even larger spectrum of energy-saving applications by suppressing solar absorptivity under solar irradiation. In this talk, we present our recent research progress on all-day passive radiative cooling for practical applications as well as for improved cooling performance. Firstly, we discuss the inverse design of daytime radiative cooling for high performance [1]. The design of a selective multilayer emitter was optimized by a genetic algorithm, and we achieved highly suppressed solar absorption, thereby, high-performance radiative cooling under direct sunlight. We then discuss the efforts to promote the implementation of radiative cooling for real-world applications. We first discuss the realization of all-day radiative cooling devices on a large scale to address practical issues [2-4]. By using silica-coated porous anodic aluminum oxide, we developed a centimeter-scale radiative cooling device demonstrating a maximum cooling of 6.1 °C below ambient during the daytime [2]. We also developed large-scale radiative cooling devices in particle mixture coating format [3]. By further analyzing the effect of each particle on radiative cooling performance, we report a large-scale paint-format radiative cooling device with high performance [4]. Such particle-based devices allow the use of facile one-step and cost-effective fabrication methods, providing the potential for large-scale production and applications. Finally, we present radiative cooling devices with practical functionalities, including transparency [5] and switchability [6]. We discuss a transparent radiative cooling device that transmits visible light reflects near-infrared light and radiates thermal energy to lower the temperature during the daytime while maintaining transparency [5]. Such a transparent can be used for eco-friendly cooling windows in vehicles or buildings. We then discuss a switchable radiative cooling device according to temperature [6]. By exploiting the changeable material properties of vanadium dioxide in response to temperature, we achieved a temperature-adaptive radiative cooling device that radiates thermal energy only when the temperature is above the phase transition temperature.<br/><br/><b>References</b><br/>[1] So, S. et al., <i>Nanophotonics</i>, <b>2022</b>, 11, 2107-2115<br/>[2] Lee, D. et al., <i>Nano Energy</i>, <b>2021</b>, 79, 105426<br/>[3] Chae, D. et al.,<i> ACS Applied Materials and Interfaces</i>, <b>2021</b>, 13, 21119-21126<br/>[4] Yun, J. et al., Submitted<br/>[5] Kim, M. et al., <i>Advanced Optical Materials</i>, <b>2021</b>, 9, 2170047<br/>[6] Kim, M. et al., <i>Opto-Electronic Advances</i>,<b> 2021</b>, 4, 200006