Sputtering Flexible VO2 Films for Effective Thermal Modulation

Fast-Developing Dynamic Radiative Thermal Management: Full-Scale Fundamentals, Switching Methods, Applications, and Challenges

Rapid population growth in recent decades has intensified both the global energy crisis and the challenges posed by climate change, including global warming. Currently, the increased frequency of extreme weather events and large fluctuations in ambient temperature disrupt thermal comfort and negatively impact health, driving a growing dependence on cooling and heating energy sources. Consequently, efficient thermal management has become a central focus of energy research. Traditional thermal management systems consume substantial energy, further contributing to greenhouse gas emissions. In contrast, emergent radiant thermal management technologies that rely on renewable energy have been proposed as sustainable alternatives. However, achieving year-round thermal management without additional energy input remains a formidable challenge. Recently, dynamic radiative thermal management technologies have emerged as the most promising solution, offering the potential for energy-efficient adaptation across seasonal variations. This review systematically presents recent advancements in dynamic radiative thermal management, covering fundamental principles, switching mechanisms, primary materials, and application areas. Additionally, the key challenges hindering the broader adoption of dynamic radiative thermal management technologies are discussed. By highlighting their transformative potential, this review provides insights into the design and industrial scalability of these innovations, with the ultimate aim of promoting renewable energy integration in thermal management applications.

Selective Laser Doping and Dedoping for Phase Engineering in Vanadium Dioxide Film

Vanadium dioxide (VO2), renowned for its reversible metal-to-insulator transition (MIT), has been widely used in configurable photonic and electronic devices. Precisely tailoring the MIT of VO2 on micro-/nano-scale is crucial for miniaturized and integrated devices. However, existing tailoring techniques like scanning probe microscopy, despite their precision, fall short in efficiency and adaptability, particularly on complex or curved surfaces. Herein, this work achieves the local engineering of the phase of VO2 films in high efficiency by employing laser writing to assist in the hydrogen doping or dedoping process. The laser doping and laser dedoping technique is also highly flexible, enabling the fabrication of reconfigurable, non-volatile, and multifunctional VO2 devices. This approach establishes a new paradigm for creating reconfigurable micro/nanophotonic and micro/nanoelectronic devices.

Thermochromic Vanadium Dioxide Nanostructures for Smart Windows and Radiative Cooling

The pursuit of energy-saving materials and technologies has garnered significant attention for their pivotal role in mitigating both energy consumption and carbon emissions. In particular, thermochromic windows in buildings offer energy-saving potential by adjusting the transmittance of solar irradiation in response to temperature changes. Radiative cooling (RC), radiating thermal heat from an object surface to the cold outer space, also offers a potential way for cooling without energy consumption. Accordingly, smart window and RC technologies based on thermochromic materials can play a crucial role in improving energy efficiency and reducing energy consumption in buildings in response to the surrounding temperature. Vanadium dioxide (VO2) is a promising thermochromic material for energy-saving smart windows and RC due to its reversible metal-to-insulator transition, accompanying large changes in its optical properties. This review provides a brief summary of synthesis methods of VO2 nanostructures based on nanoparticles and thin films. Moreover, this review emphasizes and summarizes modulation strategies focusing on doping, thermal processing, and structure manipulation to improve and regulate the thermochromic and emissivity performance of VO2 for smart window and RC applications. In last, the challenges and recent advances of VO2-based smart window and RC applications are briefly presented.

A solar/radiative cooling dual-regulation smart window based on shape-morphing kirigami structures

The energy efficiency of buildings has become a critical issue due to their substantial contribution to global energy consumption. Windows, in particular, are often the least efficient component of the building envelope, and conventional smart windows focus solely on regulating solar transmittance while overlooking radiative cooling. Although several recent designs achieved dual-control of solar and radiative cooling, these windows still face limitations in terms of durability, limited modulation ability and energy-saving performance. To address these challenges, we propose a novel dual-control smart window design consisting of a reconfigurable kirigami structure and polydimethylsiloxane-laminated thermochromic hydrogel coated with silver nanowires. In summer, the thermochromic hydrogel turns translucent to suppress the solar heat gain, while the high emissivity kirigami structure covers the exterior surface of the window, promoting radiative cooling. In winter, the hydrogel becomes transparent to allow for solar transmission. Additionally, the kirigami structure undergoes an out-of-plane structural change, opening towards the outside environment to expose the underlying low-emissivity silver nanowires and suppress heat radiation. Our design achieves a promising solar transmittance modulation ability of ∼24% and a good long-wave infrared emissivity regulation ability of 0.5. Furthermore, it exhibits significantly improved durability, which is nine times longer than the lifespan of conventional smart hydrogels. Our novel approach offers a promising solution for constructing energy-efficient and durable smart windows and outperforms existing state-of-the-art solar/radiative cooling dual-regulation smart windows in the literature.

Thermochromic Energy Efficient Windows: Fundamentals, Recent Advances, and Perspectives

Thermochromic energy efficient windows represent an important protocol technology for advanced architectural windows with energy-saving capabilities through the intelligent regulation of indoor solar irradiation and the modulation of window optical properties in response to real-time temperature stimuli. In this review, recent progress in some promising thermochromic systems is summarized from the aspects of structures, the micro-/mesoscale regulation of thermochromic properties, and integration with other emerging energy techniques. Furthermore, the challenges and opportunities in thermochromic energy-efficient windows are outlined to promote future scientific investigations and practical applications in building energy conservation.

Gradient Variation Oxygen-Content Vanadium-Oxygen Composite Films with Enhanced Crystallinity and Excellent Durability for Smart Windows

Vanadium dioxide (VO2)-based smart windows show excellent promise for energy-saving and have been extensively researched. However, for the glass industry-compatible magnetron sputtering process, VO2 films are difficult to obtain and have homogeneous crystalline state, leaving them lacking the ideal solar modulation (ΔTsol) and sensitivity (narrow hysteresis loop). More importantly, the instability of VO2 hinders its commercialization. Multilayer structures have been repeatedly investigated to solve these problems. Unfortunately, the mediocre thermochromic properties as well as the complex and expensive manufacturing steps still hinder its commercialization. In this work, we prepared gradient variation oxygen-content vanadium-oxygen composite films (V2O3/VO2/V2O5, VOgv) with enhanced crystallinity and excellent durability by one-step continuous sputtering. According to optical measurements, the ΔTsol of the VOgv films was significantly increased by 145% (from 6.85 to 16.80%) compared to VO2 films, and the width of the hysteresis loop was reduced by 67% (from 19.34 to 6.36 °C), while the VOgv films exhibited a wider preparation window. The accelerated tests have shown that the film has an equivalent service life of approximately 20 years. We exploited the intrinsic similarity in properties of homologous compounds of vanadium oxide and simplified the preparation process, which is supposed to break the existing application bottlenecks and increase the commercializing possibility of VO2-based thermochromic smart windows.

One-Step Hydrothermal Synthesis, Thermochromic and Infrared Camouflage Properties of Vanadium Dioxide Nanorods

Vanadium dioxide (VO2) has attracted interest from researchers because it undergoes a metal-insulator phase transition (MIT), which is accompanied by a reversible and remarkable change in both electrical and optical properties. VO2 exhibits numerous polymorphs and thus it is essential to control the growth of specific monoclinic VO2 (M) and rutile VO2 (R) phases. In this study, we developed a cost-effective and facile method for preparing VO2 nanorods with a highly crystalline monoclinic phase by one-step hydrothermal synthesis, in which only V2O5 and H2C2O4 are used as raw materials. The phase evolution of VO2 during the hydrothermal process was studied. The obtained VO2 nanorods were thoroughly mixed with fluorocarbon resin and homogeneous emulsifier in an ethanol solution to obtain a VO2 dispersion. To prepare VO2 films, screen printing was performed with a stainless steel screen mesh mask on glasses or fabric substrate. The VO2 coating had good thermochromic performance; the infrared transmittance change was greater than 20% @1.5 μm whilst keeping the visible transmittance greater than 50%. Meanwhile, the polyester base coating on the fabric had an emissivity change of up to 22%, which provides a solution for adaptive IR camouflage.