Vanadium dioxide(VO₂) exhibits thermochromic property due to the phase transition at a critical temperature (Tc) of 68^oC. When the temperature lower than Tc, VO₂ is a semiconductor and is transparent to the infrared; while for temperature higher than Tc, the material displays metallic behaviours and reflects a great part of infrared. It is this phase transition that makes VO₂ used as coating material on the intelligent energy-saving window. The intelligent window with VO₂ can control the indoor temperature through the regulation of infrared transmission, reducing the building energy consumption and achieving the purpose of energy saving. Nevertheless, the higher Tc, the smaller solar modulation and lower luminous transmission are three key factors that block the practicle application of VO₂.

To solve these problems, a simple device based on the VO₂ nanoparticles film on ITO glass was fabricated by researchers in Lab of Nanomaterials & Nanostructures, Institute of Solid State Physics (ISSP), Hefei Institutes of Physical Science.

This device utilizes the advantages of thermal sensitive performance of VO₂ and high optical transparency, thermal and electrical conductivities of ITO by which the infrared transmittance can be actively and dynamically controlled by the magnitude of a constant voltage (Figure 1) and the duration of a pulse voltage, respectively. (Figure 2)

The integration of VO₂ and ITO helps to overcome the high Tc limit of VO₂ in practical applications. In addition, the VO₂ film based on nanoparticles possess several attractive characteristics such as the cost effectiveness, convenience and versatility, suitability for arbitrary substrates and ease of large-scale production. And the VO₂ nanoparticles film demonstrates a higher luminous transmittance and solar energy transmittance modulation.

The study findings provide insight into the way to develop an advanced VO₂ electrothermochromic device as well as to apply transparent conductive materials to thermochromic field.

This study entitled Active and dynamic infrared switching of VO₂(M) nanoparticle film on ITO glass was published in J. Mater. Chem. C. And this study was sponsored by the National Natural Science Foundation of China and the Anhui Province Natural Science Foundation.

Figure 1. Dependence of VO₂  infrared transmittance on the applied voltage. (Image by LI Ming) 

Figure 2. Dynamic infrared switching performance of VO₂ (Image by LI Ming)