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Stability of VO2 Thermochromic Films is Enhanced Through Interfacial Encapsulation

Update time:2019-08-10
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Due to the excessive use of lighting, air-conditioning and heating, buildings account for about 40% of total world energy consumption every year. With the increasing demands for reducing the building energy consumption, an effective way is to apply the chromogenic coatings on building fenestration to control the solar radiation entering or blackbody radiation leaving the buildings. As one of the typical thermochromic materials, vanadium dioxide (VO2) can initiate an automatic reversible semiconductor-metal transition (SMT), which can give rise to a dramatic modification of the optical properties from infrared (IR) transmitting to IR shielding in the near-infrared region. Thus, VO2 is suitable for the application of energy-efficient windows.

With the continuous research progress in VO2 smart windows, breakthroughs were obtained in phase transition temperature, optical performance and large-scale preparation. However, the instability and deterioration of the VO2 remains one of the biggest challenges for its commercialization. Since Vanadium is a multivalent element, the VO2 can be oxidized by moisture and oxygen in the air, thereby causing failure of the thermochromic film.

Recently, researchers from Shanghai Institute of Ceramics of the Chinese Academy of Sciences designed VO2 thermochromic films with various exposed interfaces and demonstrated that the cross-section plays an important role in the deterioration process of VO2 films. Meanwhile, greatly enhanced stability of VO2 thermochromic films was achieved by interfacial encapsulation. The result was published in Matter (DOI: 10.1016/j.matt.2019.04.004), entitled “Mitigating Deterioration of Vanadium Dioxide Thermochromic Films by Interfacial Encapsulation”.

The researchers incorporated hydrophobic and stable hafnium dioxide (HfO2) layers with VO2 films for encapsulated surfaces and cross-sections. With modified thickness and structure of HfO2 layers, the degradation process of VO2 can be effectively suppressed. The proposed films can retain stable phase transition performances under high relative humidity (90%) and temperature (60℃) over 100 days, which is equal to ~16 years in the real environment. Meanwhile, the encapsulation structure also shows significant enhanced stability in the boiling water test and the thermal stability test. Improving the stability of VO2 materials is a necessary step towards commercializing production of high-performance films for long-term use.

This study was supported by the National Natural Science Foundation of China, the Youth Innovation Promotion Association of the Chinese Academy of Sciences, the Science Foundation for Youth Scholar of State Key Laboratory of High Performance Ceramics and Superfine Microstructures, the Shanghai Pujiang Program, and the Key Research and Development Plan of Anhui Province.

 

Schematic figure of the proposed VO2/HfO2 encapsulation structure and corresponding transmittance spectra, while VO2 shows a hydrophilic surface and HfO2 shows a hydrophobic surface.

 

Contact:

CAO Xun

Shanghai Institute of Ceramics

E-mailcxun@mail.sic.ac.cn.

 

Reference:

DOI:https://doi.org/10.1016/j.matt.2019.04.004

 

 
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