Designer SiO₂ Metasurfaces for Efficient Passive Radiative Cooling

Abstract

In recent years, an increasing number of passive radiative cooling materials are proposed in the literature, with several examples relying on the use of silica (SiO2) due to its unique stability, non‐toxicity, and availability. Nonetheless, due to its bulk phonon‐polariton band, SiO2 presents a marked reflection peak within the atmospheric transparency window (8‐13 µm), leading to an emissivity decrease that poses a challenge to fulfilling the criteria for sub‐ambient passive radiative cooling. Thus, the latest developments in this field are devoted to the design of engineered SiO2 photonic structures, to increase the cooling potential of bulk SiO2 radiative coolers. This review seeks to identify the most effective photonic design and fabrication strategies for SiO2 radiative emitters by evaluating their cooling efficacy, as well as their scalability, providing an in‐depth analysis of the fundamental principles, structural models, and results (both numerical and experimental) of various types of SiO2 radiative coolers.

Radiative Cooling Potential of a Water-Based Paint Formulation under Realistic Application Conditions

“…The concept of daytime passive radiative cooling (PRC) has recently emerged as a promising strategy to reduce cooling-related energy consumption in a fully passive way. , The PRC effect exploits the sky transparency window (STW) between 8 and 13 μm, at which infrared radiation can escape the Earth and dissipate into the heat sink of outer space. Combined with a high solar reflectance, the overall heat balance of a PRC coating can lead to its spontaneous cooling even during the day, thus providing a net electricity-free cooling power. − A schematic illustration related to the incoming solar radiation and the physical mechanism that provides a radiative exchange toward outer space through the STW is reported in Figure a.…”

Assembly of Hollow Yttrium Oxide Spheres from Nano-Sized Yttrium Oxide for Advanced Passive Radiative Cooling Materials

“…Further developments include crafting covers that inhibit thermal exchange between the emitter and environment [ 15 , 16 ]. When crafting PRC films, incorporating a significant volume of filler (over a 50 vol.%) into the emitter enhances the film’s cooling performance but complicates the production process due to the increased viscosity, making the blending of fillers and the creation of uniform films challenging [ 17 ]. Conversely, emitters with low filler content show reduced efficiency, necessitating the use of Supplementary Materials .…”

“…Conversely, emitters with low filler content show reduced efficiency, necessitating the use of Supplementary Materials . Previous studies have utilized glass bubbles (GBus) and barium sulfate (BaSO 4 ), known for their theoretically high solar reflectance and radiative capabilities within the atmospheric window, as fillers for emitters [ 17 , 18 ].…”

Radiative cooling performance of a modified paint formulation with an integrated UV and convection shielding layer

“…This requires materials that are engineered to exhibit high reflectivity (larger than 95%) over the whole solar spectrum, combined with a high thermal emission capacity in the atmospheric transparency window (ε ∼ 1) [11,12]. Hence, the concept of daytime passive radiative cooling (DPRC) with a high solar reflectance can lead to its spontaneous cooling even during the day [13,14], thus providing a net electricity-free cooling power [15][16][17]. A large interest in PRC materials moved towards manufacturing paint-like systems that represent a more versatile and cost-effective solution.…”