Phase transition mechanism and application of silicon-doped VO2 thin films to smart windows

It is important to examine the mechanism of the metal-insulator transition (MIT) of vanadium dioxide (VO2), which is of great significance, to understand the considerably related properties required for developing smart window applications. Here, we investigated the effect of the MIT on the thermochromic performance of VO2. We prepared Si-doped VO2 thin films and then used the sol-gel approach to deposit these thin films on Al2O3. X-ray diffraction (XRD) results showed that there was a metastable phase M2 in the VO2 film, which is classified as a Mott insulator owing to electron correlation between the undimerized V ions. Additionally, we found that 3% Si-doped VO2 thin films exhibited good thermochromic performance with a luminous transmittance (Delta T-lum) of 54.7% and a sol modulation efficiency (Delta T-sol) of 13.9%, which is superior to that of undoped VO2 films with Delta T-lum of 37.2% and Delta T-sol of 7.3%. This can be attributed to simultaneous control of the transmittance in the visible and near-infrared regions of Si-doped VO2 thin films. Therefore, this study provides a novel method of tuning the optical and electrical characteristics of VO2 thin films.