Radiative Cooling Research Articles

Nanoporous Film Layers to Enhance the Performance of Passive Radiative Cooling Paint Mixtures

Nanoporous Film Layers to Enhance the Performance of Passive Radiative Cooling Paint Mixtures

Transparent and Thermally Stable Rare-Earth-Doped Luminescent Gallate Glass toward Passive Daytime Radiative Cooling Applications.

Currently, the implementation of passive daytime radiative cooling based on zero-energy cooling methodologies primarily focuses on polymers and composite materials, whereas the available literature on all-inorganic materials is relatively few. Here, we present a novel microcrystalline glass material CaGa0.5Al1.5O4 (CGAO), doped with rare-earth elements and prepared by the high-temperature melting method. This material exhibits long-term stability at 200 °C, coupled with an effective infrared radiation cooling function, demonstrating a 4.9 °C temperature reduction at solar noon. The energy transfer and luminescence mechanisms of Tb3+ and Sm3+ doped CGAO glass have been thoroughly investigated, along with thorough assessments of its thermal stability and hardness. The glass exhibits ultrahigh light transmission in the ultraviolet to near-infrared range, with the transmittance reaching 98% in specific spectral bands. Furthermore, it demonstrates superior luminescent thermal stability, retaining 85.6% and 71.2% of its initial luminescence intensity at 423 and 523 K, respectively. The high-temperature resistance and stability and long-term cooling properties render CGAO glass as an optimal candidate for integration into future energy-efficient and sustainable building designs.

Boosting self-powered wearable thermoelectric generator with solar absorber and radiative cooler

The electrical output of wearable thermoelectric generators (wTEGs) has traditionally been constrained by small temperature differentials when powering microelectronics. In this study, we innovatively combine photothermal and radiative cooling mechanisms within a single wTEGs system, enabling substantial, uninterrupted power generation. Specifically, we designed a multilayer selective solar absorber (m-SSA) composed of flexible dielectric-metal stacks. This absorber demonstrates exceptional solar absorption efficiency of 93 % and significantly low thermal emissivity of 10 %. In practical outdoor conditions, it achieves a temperature increase of up to 108 °C under solar irradiation. Concurrently, we developed a flexible hierarchically porous radiative cooler (HP-RC), which reflects 96 % of solar energy and emits 97 % of thermal energy, achieving a cooling differential of up to 10 °C, even at ambient temperatures of 42 °C. Integration of the m-SSA and HP-RC with wTEGs allows for the simultaneous harvesting of heat from solar, cold space, and earth (robots or human body). This novel energy capture mechanism yielded a notable power density of 198 mW/m² for human body and 52 mW/m2 for steel robots in outdoor wearable applications. This significant advancement promotes the field toward high-performance, integrated green power technologies and holds promise for next-generation wearable self-powered devices.

Pushing Radiative Cooling Technology to Real Applications.

Radiative cooling is achieved by controlling surface optical behavior toward solar and thermal radiation, offering promising solutions for mitigating global warming, promoting energy saving, and enhancing environmental protection. Despite significant efforts to develop optical surfaces in various forms, five primary challenges remain for practical applications: enhancing optical efficiency, maintaining appearance, managing overcooling, improving durability, and enabling scalable manufacturing. However, a comprehensive review bridging these gaps is currently lacking. This work begins by introducing the optical fundamentals of radiative cooling and its potential applications. It then explores the challenges and discusses advanced solutions through structural design, material selection, and fabrication processes. It aims to provide guidance for future research and industrial development of radiative cooling technology.

Molecularly and Structurally Designed Polyimide Nanofiber Radiative Cooling Films for Spacecraft Thermal Management

AbstractRadiative cooling films (RCFs) are crucial for spacecraft thermal management, but their optical performance is currently limited by their structures and intrinsic high absorption at short wavelengths. In this study, a novel RCF using electrospun polyimide nanofibers optimized at both the molecular and microscale levels is developed. The newly designed polyimide molecules significantly decrease visible and ultraviolet (UV) light absorption while maintaining excellent thermal radiation properties in the infrared spectrum. By optimizing the diameter and orientation of the nanofibers using Monte Carlo simulations, the resulting film achieves a solar reflectivity of 99.6% and a mid‐infrared emissivity of 0.93. Its physical structures and optical properties remain stable under exposure to UV light, atomic oxygen, and extreme temperature changes. Further vacuum radiative cooling tests reveal that the thermal equilibrium temperature of this film is approximately 28 °C lower than that of Kapton‐based RCFs currently used in spacecraft. These results provide a new approach for creating efficient thermal management materials for space applications, with potential for broader use in architecture, electronic devices, and outdoor equipment.

Alumina Fiber Membrane Prepared by Electrospinning Technology for Passive Daytime Radiative Cooling

Alumina Fiber Membrane Prepared by Electrospinning Technology for Passive Daytime Radiative Cooling

Scalable Film Based on Thermochromic and Radiative Cooling Effects for Anti-Counterfeiting and Low Temperature Preservation

Scalable Film Based on Thermochromic and Radiative Cooling Effects for Anti-Counterfeiting and Low Temperature Preservation

Artificial Intelligence‐Enhanced Metamaterial Bragg Multilayers for Radiative Cooling

A full numerical study combining artificial intelligence (AI) methods and electromagnetic simulation software on a multilayered structure for radiative cooling (RC) is investigated. The original structure is made of SiO2/Si nanometer‐thick layers that make a Bragg mirror for wavelengths in the solar irradiance window (0.3–4 μm). The structures are then optimized in terms of the calculated net cooling power and characterized via the reflected and absorbed incident light as a function of their structural parameters. This investigation provides with optimal designs of beyond‐Bragg, all‐dielectric, ultra‐broadband mirrors that provide net cooling powers in the order of ≈100 W m−2, similar to the best‐performing structures in literature. Furthermore, it explains AI's success in producing these structures and enables the analysis of resonant conditions in metal‐free multilayers with unconventional layer thickness distributions, offering innovative tools for designing highly efficient structures in RC.

A Mussel-Inspired and Recyclable Coating with Integrated Daytime Radiative Cooling and Triboelectric Energy Harvesting for Intelligent and Sustainable Buildings.

Carbon neutrality necessitates new technologies for renewable energy utilization, active regulation of heat exchange, and material recycling to promote green and intelligent building development. Currently, the integration of these functions and characteristics into a single coating material presents a significant challenge. Here, we demonstrate a novel triboelectric and radiative cooling coating with mussel-inspired architectures, fabricated using cellulose nanofibers and Mica-TiO2 as a functional mortar and brick, respectively. The abundant polar groups and specific surface area of cellulose nanofibers enable a high accumulation of induced electrostatic charges, allowing the coating to act as a tribolayer to generate triboelectric outputs. The regularly layered arrangement of Mica-TiO2 endows fire resistance to the coating, which exhibits self-extinguishing properties and maintains 45% of its original electrical output even after direct exposure to flame for 20 s. Additionally, the created multilayered stacking morphology, as well as intense group vibrations of Mica-TiO2, facilitates high reflectivity (Rsolar = 0.9) and long-wave infrared emissivity (ϵLWIR = 0.94), achieving a daytime subambient temperature drop of 5.3 °C. Notably, the coating can be recycled easily while maintaining its triboelectric, radiative cooling, and fire-resistant properties. This work provides an innovative strategy for unifying triboelectric and radiative cooling functions, as well as recyclability, into a single coating material, offering new insights for future sustainable and energy-efficient buildings.

Macro-Nanoporous Film with Cauliflower-Shaped Fibers for Highly Efficient Passive Daytime Radiative Cooling.

Passive daytime radiative cooling (PDRC) is a simple and effective cooling approach that does not consume any extra energy just by highly reflecting shortwave sunlight and highly radiating infrared heat through the atmospheric windows. In recent years, the application of photonic coolers and metamaterials for PDRC has been studied. However, they usually have complex processes and high precision requirements, which seriously limit large-scale fabrication. In this paper, a high-performance polyvinylidene difluoride-hexafluoropropylene (PVDF-HFP) PDRC fiber film was prepared by a simple and efficient electrospinning method combined with phase separation, and the obtained PVDF-HFP fibers have a cauliflower-shaped macro-nanoporous structure. The cauliflower-shaped structure provides more scattering sites of the fibers, and the fiber film with the macro-nanoporous morphology has a high scattering ability in the solar region, resulting in a high solar reflectivity of 99.65%. The PVDF-HFP porous film possesses an emissivity of 90.44% in the atmospheric window, and it can reach a maximum cooling temperature of 10.2 °C during the daytime. In addition, the excellent mechanical strength provides a guarantee for its large-scale practical application. This study offers an effective improvement strategy for the spectral performance of polymer fiber films, which is meaningful for green cooling management and reduction of carbon emission.

A High-Power, Flexible, and Magnetically Attachable Radiative Cooling Film

Radiative cooling is an environmentally friendly, passive cooling technology that operates without energy consumption. Current research primarily focuses on optimizing the optical properties of radiative cooling films to enhance their cooling performance. In practical applications, thermal contact between the radiative cooling film and the object significantly influences the ultimate cooling performance. However, achieving optimal thermal contact has received limited attention. In this study, we propose and experimentally demonstrate a high-power, flexible, and magnetically attachable and detachable radiative cooling film. This film consists of polymer metasurface structures on a flexible magnetic layer. The monolithic design allows for convenient attachment to and detachment from steel or iron surfaces, ensuring optimal thermal contact with minimal thermal resistance and uniform temperature distribution. Our magnetic radiative cooling film exhibits superior cooling performance compared to non-magnetic alternatives. It can reduce the temperature of stainless-steel plates under sunlight by 15.2 °C, which is 3.6 °C more than that achieved by non-magnetic radiative cooling films. The radiative cooling power can reach 259 W∙m−2 at a working temperature of 70 °C. Unlike other commonly used attachment methods, such as thermal grease or one-off tape, our approach allows for detachment and reusability of the cooling film according to practical needs. This method offers great simplicity, flexibility, and cost-effectiveness, making it promising for broad applications, particularly on non-horizontal irregular surfaces previously considered challenging.

Core-Shell Composite Nanofibers with High Temperature Resistance, Hydrophobicity and Breathability for Efficient Daytime Passive Radiative Cooling.

Radiative cooling technology, which is renowned for its ability to dissipate heat without energy consumption, has garnered immense interest. However, achieving high performance, multifunctionality, and smart integration while addressing challenges such as film thickness and enhancing anisotropic light reflection remains challenging. In this study, a core-shell composite nanofiber, PVDF@PEI, is introduced and designed primarily from a symmetry-breaking perspective to develop highly efficient radiative cooling materials. Using a combination of solvent-induced phase separation (EIPS) inverse spinning and (aggregation) self-assembly methods (EISA or EIAA) and coaxial electrostatic spinning (ES), superconformal surface anisotropic porous nanofiber membranes are fabricated. These membranes exhibit exceptional thermal stability (up to 210°C), high hydrophobicity (contact angle of 126°), robust UV protection (exceeding 99%), a fluorescence multiplication effect (with a 0.6% increase in fluorescence quantum efficiency), and good breathability. These properties enable the material to excel in a wide range of application scenarios. Moreover, this material achieved a remarkable daytime cooling temperature of 8°C. The development of this fiber membrane offers significant advancements in the field of wearables and the multifunctionality of materials, paving new paths for future research and innovation.

Self-adaptive radiation recuperator with double phase transition temperature switches based on VO2 intelligent films

Developing renewable energy for heating and cooling to achieve carbon neutrality and environmental protection is of great significance. The combination of photothermal (PT) and radiative cooling (RC) technology to continuously obtain energy throughout the day is gradually attracting interest, in which vanadium dioxide (VO2) intelligent phase transition film serves as a bridge between the daytime PT mode and the nighttime RC mode. The high phase transition temperature of VO2 poses a challenge to environmental adaptability and dynamic switching in practical applications. In this work, a novel self-adaptive radiation recuperator with double phase transition temperature (37 °C and 68 °C) switches is proposed to exchange energy from the sun and outer space by radiation. Compared with VO2 and W-doped VO2 single-layer structure, this method has a higher self-adaptability to easily achieve the phase transition temperature of mode switching. The absorptivity of the radiation recuperator is 0.75 in the solar band (0.3–2.5 μm), and the emissivity switching capability is present from 0.3 to 0.86 in the atmospheric window band (8–14 μm). The transition mode generated by the presence of double phase transition temperature improves temperature self-adaptability and improves energy collection efficiency in dynamic environments.

A UV-resistant porous composite film for radiative cooling and enhanced hydrophobicity

Passive Daytime Radiative Cooling (PDRC) offers a promising strategy to reduce surface heat by reflecting solar radiation and emitting long-wave infrared radiation into space. However, the widespread application of PDRC is currently limited by challenges such as complex fabrication processes, high costs, and the materials’ susceptibility to outdoor aging. In this work, we fabricated a cost-effective, ultraviolet (UV)-resistant porous composite (UPC) film by phase separation technology. UPC films achieve high solar reflectance (0.92) and outstanding broadband longwave infrared thermal emissivity (0.975) by adjusting particle size and mass fractions of TiO2 particles embedded in Poly (methyl methacrylate) (PMMA). When applied to a drone, the films achieve a cooling effect of 12.6°C. Notably, the mid-infrared emissivity of UPC films remained stable after prolonged exposure to UV radiation (360 hours at an irradiance of 1 W/m2), with the reflectance decreasing by only 1.3 %. Software simulations were employed to evaluate the energy savings performance of UPC films in various urban environments, showing significant energy-saving benefits. Furthermore, after treatment with the modified solution, the surface contact angle of UPC films reaches 152.5°, providing excellent resistance to contamination. This work contributes to the advancement of low-cost, durable, and energy-efficient cooling solutions.

Energy saving potential of passive radiative cool coating in high-rise data center with neighboring infrastructure

To coordinate with the evolution of I&T, it is indicated to enhance the number of data center (DC) worldwide, which involves enormous cooling demand that may lead to energy wastage if the facility is not constructed energy-efficiently, impeding decarbonization. Passive radiative cooler (PRC) have exhibited their energy-saving capability in many studies. Being a windowless building, DC has extensive coverage area for PRC comparing to other buildings that require outdoor visual access. The power-saving potential of a dual-layer daytime radiative cooling paint (DDRCC) in a high-rise DC was investigated at multi-building scale using a self-created site model under Hong Kong's humid subtropical climate. Besides the roof, which has been the target PRC-employed surface in previous studies, this work deployed DDRCC on roof and vertical façade of the DC, attaining optimal saving of 652–821 kW and cooling power of 23.4–29.5 W/m2, demonstrating its practicability in high-rise building. DDRCC accomplished cooling power of 2.5–48.0 W/m2 in scenarios with various configuration of PRC-utilized envelope. Additionally, for the site studied, the cooling power of DDRCC enhanced with aspect ratio when the height of adjacent buildings was comparable to the DC. DDRCC was competent to achieve power-saving with walls of different thermal resistances.

Particle-Solid Transition Architecture for Efficient Passive Building Cooling.

Electricity consumption for building cooling accounts for a significant portion of global energy usage and carbon emissions. To address this challenge, passive daytime radiative cooling (PDRC) has emerged as a promising technique for cooling buildings without electricity input. However, existing radiative coolers face material mismatch issues, particularly on cementitious composites like concrete, limiting their practical application. Here, we propose a cementitious radiative cooling armor based on a particle-solid transition architecture (PSTA) to overcome these challenges. The PSTA design features an asymmetric yet monolithic morphology and an all-inorganic nature, decoupling radiative cooling from building compatibility while ensuring UV resistance. In the PSTA design, nanoparticles on the surface serve as sunlight scatterers and thermal emitters, while those embedded within a cementitious substrate provide build compatibility and cohesiveness. This configuration results in enhanced interfacial bonding strength, high solar reflectance, and strong mid-infrared emittance. Specifically, the PSTA delivers an enhanced interfacial shear strength (0.93 MPa), several-fold higher than that in control groups (metal, glass, plastic) along with a cooling performance (a subambient temperature drop of ∼6.6 °C and a cooling power of ∼92.8 W under a direct solar irradiance of ∼680 W/m2) that rivals or outperforms previous reports. Importantly, the design concept of the PSTA is applicable to various particles and solids, facilitating the practical application of PDRC technology in building scenarios.

Bioinspired all-day adaptive radiative cooler with high-power cooling and efficient suppressing overcooling

This research presents a design in the bionic on-off switch layer and thermal insulation layer, crucial for the cooling power adjustment of the radiative cooler. The design features a change in the upper surface area of the on-off switch layer, inspired by the unfolding and folding behaviors of pinto peanut leaves in day and night, which enables high-power cooling during the day and suppresses overcooling at night. The introduction of a bulge-pit structure in the thermal insulation layer reduces the heat exchange between the cooler and the outside. The novelty of this research lies in the integration of a bionic design, an innovative bulge-pit structure, and an optimized polyacrylonitrile spinning layer on the surface of green balsa wood. The study examines the cooling properties of the cooler under simulated day and night conditions. Key findings reveal that day subambient radiative cooling of 6.6 °C, which is slightly better than a passive radiative cooler. At night, it elevates the ambient temperature by 3.4 °C compared to a passive radiative cooler. The total energy savings applied in a specified area for all day are estimated to reach up to 770 kJ. This design marks a significant advancement in the radiative cooling field.

Regulating Cold Energy from the Universe by Bifunctional Phase Change Materials for Sustainable Cooling

AbstractHarvesting cold energy from the universe by radiative cooling (RC) is a promising zero‐carbon route for green cooling. However, low power density and spatiotemporal energy mismatch of RC are great challenges for realizing efficient space cooling. Herein, a facile strategy for regulating cold energy from the universe by bifunctional phase change materials (PCM) for sustainable cooling is proposed. A bifunctional phase‐change composite film (PCCF) by integrating RC coating with PCM for 24‐h cold energy harvesting, storage, and utilization is demonstrated. The bifunctional PCCF can harvest cold energy from the universe and regulate the redundant cold energy generated by nighttime RC to compensate for the cold shortage of daytime RC, realizing flexible regulation of all‐day RC and setting new records of cooling power up to 180 W m−2 with sub‐ambient temperature drop of 11.95 °C. The work offers a promising strategy for zero‐carbon sustainable cooling by maximizing RC with cold energy storage.

Feasibility of realizing photothermal, photovoltaic, and radiative cooling with a flexible structure

The escalating energy demands and the imperative of environmental conservation necessitate advanced sustainable energy solutions. This study introduces a novel nanofluid spectrum-splitting photovoltaic/thermal system integrated with radiative cooling (RC) technology, termed NSS-RC-PV/T. This system optimizes solar spectrum utilization, enhances thermal management, and significantly improves the efficiency and flexibility of heat, electricity, and cooling outputs. Employing a reversible PV-Ag panel, the system adapts between PV/T and RC modes based on energy demands. A comprehensive mathematical model is established to evaluate its performance under realistic environmental conditions across China. Results indicate the maximum energy output of the system is 6438 MJ/m2, which is a 33.4% increase in annual energy output compared to the conventional PV/T system. The dynamic power response model also shows an increase of 5.8% (266 MJ/m2) compared to the daylight response model. This research underscores the potential of NSS-RC-PV/T systems in advancing renewable energy technologies and meeting modern energy needs.

Rational Design and Fine Fabrication of Passive Daytime Radiative Cooling Textiles Integrate Antibacterial, UV-Shielding, and Self-Cleaning Characteristics.

Passive daytime radiative cooling (PDRC) textiles hold substantial potential for localized outdoor cooling of the human body without additional energy consumption, but their limited multifunctional integration severely hinders their practical application. Herein, aluminum-doped zinc oxide (AZO) nanoparticles were purposefully introduced into poly(vinylidene fluoride) (PVDF) nanofibers via a facile electrospinning process, forming a large-scale and flexible PDRC textile with the desired antibacterial, UV-shielding, and self-cleaning capabilities. These prepared PDRC textiles present a weighted sunlight reflection rate of 92.3% and a weighted emissivity of 89.5% in the mid-infrared region. Furthermore, outdoor tests with an average solar intensity of ∼715 W/m2 demonstrated that a skin simulator temperature could be cooled by ∼16.1 °C below the ambient temperature, outperforming cotton fabric by ∼6.3 °C. Owing to the outstanding photocatalytic properties of the AZO nanoparticles, these prepared PVDF textiles exhibit antibacterial properties (Escherichia coli: 99.99%), UV-shielding performance (UPF > 50+), and superior self-cleaning capabilities, providing a cost-effective and eco-friendly avenue for daytime personal thermal management.