Photonic structures in radiative cooling

Abstract

Radiative cooling is a passive cooling technology without any energy consumption, compared to conventional cooling technologies that require power sources and dump waste heat into the surroundings. For decades, many radiative cooling studies have been introduced but its applications are mostly restricted to nighttime use only. Recently, the emergence of photonic technologies to achieves daytime radiative cooling overcome the performance limitations. For example, broadband and selective emissions in mid-IR and high reflectance in the solar spectral range have already been demonstrated. This review article discusses the fundamentals of thermodynamic heat transfer that motivates radiative cooling. Several photonic structures such as multilayer, periodical, random; derived from nature, and associated design procedures were thoroughly discussed. Photonic integration with new functionality significantly enhances the efficiency of radiative cooling technologies such as colored, transparent, and switchable radiative cooling applications has been developed. The commercial applications such as reducing cooling loads in vehicles, increasing the power generation of solar cells, generating electricity, saving water, and personal thermal regulation are also summarized. Lastly, perspectives on radiative cooling and emerging issues with potential solution strategies are discussed.

Functional Radiative Cooling: Basic Concepts, Materials, and Best Practices in Measurements

“…Previous studies on RC materials have mostly focused on enhancing cooling performance, which makes it important to fabricate these materials having a white color. ,, However, because the final application of RC is the coating of building exteriors, the incorporation of colors into RC materials cannot be overlooked from the perspective of aesthetics. Recently, the number of studies addressing this issue has gradually increased. − In the following sections, we review the colored RC materials by categorizing them according to their coloration mechanisms.…”

Suitability of Anodic Porous Alumina as a Passive Radiative Cooler: An In-Depth Study

“…Therefore, developing a cooling technology which cools without any power input can make a significant difference in energy savings by reducing the use of air conditioners. Multiple applications − can take advantage of this cooling method beyond building cooling, such as improvements in the thermal comfort of textiles for personal thermal management − or improvements in the efficiency of electronic devices by avoiding overheating. , Different approaches have been explored, such as multilayers, , paints, , photonic structures, ,, porous − or metallized polymers, polymer dielectric composites, and natural materials. , The porous nanostructures have shown the best results, , becoming an interesting characteristic to improve the cooling performance of a material. This has encouraged scientific research on porous anodic aluminum oxide (AAO) nanostructures, which is an amorphous material with an isotropic permittivity, a strong acoustic resonance absorption at the far IR (15–25 μm), and high transparency in the UV–vis–NIR range …”

“…Multiple applications 9−12 can take advantage of this cooling method beyond building cooling, 13 such as improvements in the thermal comfort of textiles for personal thermal management 14−18 or improvements in the efficiency of electronic devices by avoiding overheating. 19,20 Different approaches have been explored, such as multilayers, 7,21 paints, 22,23 photonic structures, 7,24,25 porous 26−28 or metallized polymers, 29 polymer dielectric composites, 30 and natural materials. 31,32 The porous nanostructures have shown the best results, 33,34 becoming an interesting characteristic to improve the cooling performance of a material.…”

Coral-Inspired Asymmetrically Porous Radiative Cooling Biofilm with Thermoplastic Polyurethane-Enhanced Mechanical Tolerance as Building Energy-Saving Envelope

“…Porous structures can be meticulously designed at the micro-and nano-scale through photonics and bionics to achieve excellent optical properties. 25,26 Ni et al utilized a scalable melt processing method to manufacture a porous poly(vinylidene fluoride) composite sheet (PPCS) which exhibits a high solar reflectivity of 91.8% and a high infrared emissivity of 94.3%. 27 Park et al prepared an ecofriendly polymer structure for effective radiative cooling by thermotropic phase separation.…”

“…Several common structures of PRC films can be broadly categorized as multilayer structures, − metamaterials, − randomly distributed particle structures, − and porous structures. − The first three structures achieve high solar reflectivity mainly through a reflective metal layer placed at the bottom of the material, which has certain limitations in structural design. Porous structures can be meticulously designed at the micro- and nano-scale through photonics and bionics to achieve excellent optical properties. , Ni et al utilized a scalable melt processing method to manufacture a porous poly­(vinylidene fluoride) composite sheet (PPCS) which exhibits a high solar reflectivity of 91.8% and a high infrared emissivity of 94.3% . Park et al prepared an ecofriendly polymer structure for effective radiative cooling by thermotropic phase separation.…”