Thermochromic VO2-SiO2composite coating from ammonium citrato-oxovanadate(IV)

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.

Active optical modulation of quasi-BICs in Si-VO2 hybrid metasurfaces

Active optical modulation breaks the limitation of a passive device, providing a new, to the best of our knowledge, alternative to achieve high-performance optical devices. The phase-change material vanadium dioxide (VO₂) plays an important role in the active device due to its unique reversible phase transition. In this work, we numerically investigate the optical modulation in resonant Si-VO₂ hybrid metasurfaces. The optical bound states in the continuum (BICs) in an Si dimer nanobar metasurface are studied. The quasi-BICs resonator with high quality factor (Q-factor) can be excited by rotating one of the dimer nanobars. The multipole response and near-field distribution confirm that magnetic dipoles dominate this resonance. Moreover, a dynamically tunable optical resonance is achieved by integrating a VO₂ thin film to this quasi-BICs Si nanostructure. With the increase of temperature, VO₂ gradually changes from the dielectric state to metal state, and the optical response exhibits a significant change. Then, the modulation of the transmission spectrum is calculated. Situations where VO₂ is located in different positions are also discussed. A relative transmission modulation of 180% is achieved. These results fully confirm that the VO₂ film shows an excellent ability to modulate the quasi-BICs resonator. Our work provides a route for the active modulation of resonant optical devices.

Influence of VO2 based structures and smart coatings on weather resistance for boosting the thermochromic properties of smart window applications

Vanadium dioxide (VO₂)-based energy-saving smart films or coatings aroused great interest in scientific research and industry due to the reversible crystalline structural transition of VO₂ from the monoclinic to tetragonal phase around room temperature, which can induce significant changes in transmittance and reflectance in the infrared (IR) range. However, there are still some obstacles for commercial application of VO₂-based films or coatings in our daily life, such as the high phase transition temperature (68 °C), low luminous transmittance, solar modulation ability, and poor environmental stability. Particularly, due to its active nature chemically, VO₂ is prone to gradual oxidation, causing deterioration of optical properties during very long life span of windows. In this review, the recent progress in enhancing the thermochromic properties of VO₂-hybrid materials especially based on environmental stability has been summarized for the first time in terms of structural modifications such as core–shell structures for nanoparticles and nanorods and thin-films with single layer, layer-by-layer, and sandwich-like structures due to their excellent results for improving environmental stability. Moreover, future development trends have also been presented to promote the goal of commercial production of VO₂ smart coatings.

VO₂ based energy saving smart coatings are of great interest in research and industry due to the reversible crystalline structural transition of VO₂ which can induce significant transmittance and reflectance changes in the infrared range.