Key Takeaways & Executive Findings
- •• Spectrally selective daytime radiative cooling (SSDRC) materials achieve superior cooling performance by emitting predominantly within the atmospheric transmission window while suppressing non-ATW thermal radiation absorption. • The review systematically categorizes SSDRC materials into fibrous materials, membranes, and particle coatings, detailing their fabrication principles and operational mechanisms. • SSDRC materials demonstrate significant potential in personal thermal management, outdoor building cooling, and energy harvesting, offering eco-friendly and passive cooling solutions. • Future development of SSDRC materials faces challenges such as scalability, durability, and cost-effectiveness, which must be addressed for widespread practical implementation.
Abstract
Daytime radiative cooling is an eco-friendly and passive cooling technology that operates without external energy input. Materials designed for this purpose are engineered to possess high reflectivity in the solar spectrum and high emissivity within the atmospheric transmission window. Unlike broadband-emissive daytime radiative cooling materials, spectrally selective daytime radiative cooling (SSDRC) materials exhibit predominant mid-infrared emission in the atmospheric transmission window. This selective mid-infrared emission suppresses thermal radiation absorption beyond the atmospheric transmission window range, thereby improving the net cooling power of daytime radiative cooling. This review elucidates the fundamental characteristics of SSDRC materials, including their molecular structures, micro- and nanostructures, optical properties, and thermodynamic principles. It also provides a comprehensive overview of the design and fabrication of SSDRC materials in three typical forms, i.e., fibrous materials, membranes, and particle coatings, highlighting their respective cooling mechanisms and performance. Furthermore, the practical applications of SSDRC in personal thermal management, outdoor building cooling, and energy harvesting are summarized. Finally, the challenges and prospects are discussed to guide researchers in advancing SSDRC materials.
1. Introduction
Human activities and technological advancements have culminated in persistent global warming, a challenge that is anticipated to intensify in the coming decade [1]. The quest for effective cooling solutions has emerged as a critical global priority among sustainability experts. Traditional cooling technologies, predominantly air conditioning systems, not only consume substantial electricity, thereby contributing to heightened greenhouse gas emissions, but also exacerbate global warming due to the use of refrigerants. Consequently, there is an urgent need to identify innovative green cooling technologies.
Daytime radiative cooling (DRC) is emerging as a passive cooling technique without any energy consumption [2–4]. This approach facilitates the dissipation of thermal radiation from objects into the universe via the atmospheric transmission window (ATW) while simultaneously rejecting solar irradiation to reduce photothermal load [5–7]. Heat escapes from surfaces as thermal radiation into the cold vacuum of space, resulting in a spontaneous temperature drop.
A diverse array of materials, including polymers [8–10], ceramic particles [11–13], photonic crystals [14–17], metamaterials [18–20], and fibrous materials [10, 21–23], have been reported for DRC applications. These materials usually present broadband-emissive characteristics due to their non-selective emissivity within the mid-infrared (MIR) wavelength range. Hence, the high non-ATW emissivity of MIR broadband-emissive materials results in the absorption of excessive thermal radiation from the surrounding environment, which affects their daytime radiative cooling. Spectrally selective daytime radiative cooling (SSDRC) materials are characterized by their dominant emission in the ATW wavelength bands while exhibiting low emission in the non-ATW ranges [24, 25]. Notably, SSDRC materials have three typical spectrum properties: (1) high reflectivity in the solar wavelength range to minimize sunlight absorption and mitigate photothermal effect; (2) high emissivity in the ATW range to facilitate thermal radiation dissipation into outer space; and (3) low emissivity in the non-ATW wavelength ranges to reduce thermal radiation absorption from the surrounding environment. In recent years, numerous reviews have summarized the principles [5, 26], materials [27–29], fabrication methods [2, 30, 31], and practical applications [28, 30] of DRC materials, offering valuable insights.
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An-Quan Xie, Hui Qiu, Wangkai Jiang, Yu Wang, Shichao Niu, Ke-Qin Zhang, Ghim Wei Ho, Xiao-Qiao Wang (2025). Recent Advances in Spectrally Selective Daytime Radiative Cooling Materials. Nano-Micro Letters. https://doi.org/10.1007/s40820-025-01771-8
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Frequently Asked Questions
What is spectrally selective daytime radiative cooling (SSDRC)?
SSDRC is an advanced passive cooling technology that uses materials with high solar reflectivity and high emissivity specifically within the atmospheric transmission window (ATW), while suppressing emission outside this range. This selectivity enhances net cooling power by reducing thermal radiation absorption from the environment.
What are the typical forms of SSDRC materials?
SSDRC materials are typically fabricated in three forms: fibrous materials, membranes, and particle coatings. Each form has distinct structural and optical properties that influence its cooling performance and application suitability.
What are the main applications of SSDRC materials?
SSDRC materials are primarily applied in personal thermal management (e.g., cooling textiles), outdoor building cooling (e.g., roof coatings), and energy harvesting (e.g., thermoelectric generators). These applications leverage passive cooling to reduce energy consumption and improve thermal comfort.
How do SSDRC materials differ from broadband-emissive radiative cooling materials?
Broadband-emissive materials emit across the entire mid-infrared spectrum, including non-ATW ranges, which can absorb excess environmental thermal radiation. SSDRC materials selectively emit only within the ATW, minimizing unwanted absorption and thereby achieving higher net cooling power.
What are the current challenges in SSDRC material development?
Key challenges include scalability of fabrication, long-term durability, cost-effectiveness, and integration into practical systems. Future research aims to address these issues to enable widespread adoption of SSDRC technology.
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