Anisotropic porous designed polymer coatings for high-performance passive all-day radiative cooling

Radiative Cooling Properties of Portlandite and Tobermorite: Two Cementitious Minerals of Great Relevance in Concrete Science and Technology

Although concrete and cement-based materials are the most engineered materials employed by mankind, their potential for use in daytime radiative cooling applications has yet to be fully explored. Due to its complex structure, which is composed of multiple phases and textural details, fine-tuning of concrete is impossible without first analyzing its most important ingredients. Here, the radiative cooling properties of Portlandite (Ca(OH)2) and Tobermorite (Ca5Si6O16(OH)2·4H2O) are studied due to their crucial relevance in cement and concrete science and technology. Our findings demonstrate that, in contrast to concrete (which is a strong infrared emitter but a poor sun reflector), both Portlandite and Tobermorite exhibit good radiative cooling capabilities. These results provide solid evidence that, with the correct optimization of composition and porosity, concrete can be transformed into a material suitable for daytime radiative cooling.

Humidity-tolerant porous polymer coating for passive daytime radiative cooling

Coating building envelopes with a passive daytime radiative cooling (PDRC) material has attracted enormous attention as an alternative cooling technique with minimal energy consumption and carbon footprint. Despite the exceptional performance and scalability of porous polymer coating (PPC), achieving consistent performance over a wide range of drying environments remains a major challenge for its commercialization as a radiative cooling paint. Herein, we demonstrate the humidity vulnerability of PPC during the drying process and propose a simple strategy to greatly mitigate the issue. Specifically, we find that the solar reflectance of the PPC rapidly decreases with increasing humidity from 30% RH, and the PPC completely losses its PDRC ability at 45% RH and even become a solar-heating material at higher humidity. However, by adding a small amount of polymer reinforcement to the PPC, it maintains its PDRC performance up to 60% RH, resulting in a 950% increase in estimated areal coverage compared to PPC in the United States. This study sheds light on a crucial consistency issue that has thus far been rarely addressed, and offers engineering guidance to handle this fundamental threat to the development of dependable PDRC paint for industrial applications.

Integrating Light Diffusion and Conversion Layers for Highly Efficient Multicolored Fiber-Dye-Sensitized Solar Cells

Fiber solar cells as promising wearable power supplies have attracted increasing attentions recently, while further breakthrough on their power conversion efficiency (PCE) and realization of multicolored appearances remain urgent needs particularly in real-world applications. Here, a fiber-dye-sensitized solar cell (FDSSC) integrated with a light diffusion layer composed of alumina/polyurethane film on the outmost encapsulating tube and a light conversion layer made from phosphors/TiO2/poly(vinylidene fluoride-co-hexafluoropropylene) film on the inner counter electrode is designed. The incident light is diffused to more surfaces of fiber electrodes, then converted on counter electrode and reflected to neighboring photoanode, so the FDSSC efficiently takes advantage of the fiber shape for remarkably enhanced light harvesting, producing a record PCE of 13.11%. These efficient FDSSCs also realize color-tunable appearances, improving their designability and compatibility with textiles. They are further integrated with fiber batteries as power systems, providing a power solution for wearables and emerging smart textiles.

Porous Structure of Polymer Films Optimized by Rationally Tuning Phase Separation for Passive All-Day Radiative Cooling

Passive all-day radiative cooling (PARC) films with porous structures prepared via nonsolvent-induced phase separation (NIPS) have attracted considerable attention owing to their cost-effectiveness and wide applicability. The PARC performances of the films correlate with their porous structures. However, the porous structure formed using the NIPS process cannot be finely regulated. In this study, we prepared polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) films with porous structures optimized by rationally tuning the phase separation, which was achieved by adjusting the proportions of two good solvents with varying solubility parameters. The optimized PVDF-HFP film with a hierarchically porous structure exhibited a high solar reflectance of 97.7% and an infrared emissivity of 96.7%. The film with excellent durability achieved an average subambient cooling temperature of approximately 5.4 °C under a solar irradiance of 945 W·m-2 as well as a temperature of 11.2 °C at nighttime, thus demonstrating all-day radiative cooling. The results indicate that the proposed films present a promising platform for large-scale applications in green building cooling and achieving carbon neutrality.

Radiative Cooling for Energy Sustainability: From Fundamentals to Fabrication Methods Toward Commercialization

Radiative cooling, a technology that lowers the temperature of terrestrial objects by dissipating heat into outer space, presents a promising ecologically-benign solution for sustainable cooling. Recent years witness substantial progress in radiative cooling technologies, bringing them closer to commercialization. This comprehensive review provides a structured overview of radiative cooling technologies, encompassing essential principles, fabrication techniques, and practical applications, with the goal of guiding researchers toward successful commercialization. The review begins by introducing the fundamentals of radiative cooling and the associated design strategies to achieve it. Then, various fabrication methods utilized for the realization of radiative cooling devices are thoroughly discussed. This discussion includes detailed assessments of scalability, fabrication costs, and performance considerations, encompassing both structural designs and fabrication techniques. Building upon these insights, potential fabrication approaches suitable for practical applications and commercialization are proposed. Further, the recent efforts made toward the practical applications of radiative cooling technology, including its visual appearance, switching capability, and compatibility are examined. By encompassing a broad range of topics, from fundamental principles to fabrication and applications, this review aims to bridge the gap between theoretical research and real-world implementation, fostering the advancement and widespread adoption of radiative cooling technology.