Enhanced thermal stability and thermochromic properties of VOx-based thin films by room-temperature magnetron sputtering

- VOx-based thin films with high thermal stability were prepared.
- High thermochromic properties of the films can be obtained by film design.
- Interfacial stress and oxygen vacancies accelerated degradation of films.
- Annealing period was shortened by 75% due to cooling in air.

In order to enhance the thermal stability and thermochromic properties, three kinds of VOx-based thin films with different structures (single-layer, triple-layer and multi-layer, respectively) were designed in this study. All of them were prepared by room-temperature reactive magnetron sputtering and subsequently rapid thermal annealing (RTA) in nitrogen atmosphere. The optical properties and microstructure of VOx-based thin films were investigated. The results reveal that all samples are ascribed to pure VO2 (M), and the VOx-based thin films exhibit superior thermochromic properties with the solar modulation (ΔTsol) up to 12.75%, 15.65% and 18.02%, respectively. The phase transition temperature (Tc) is as low as 54 °C for multi-layer thin films without doping, which indicates that the film design could effectively enhance optical switching and depress the Tc. After thermal treatment in the air, the phase of V2O5 appeared at 325 °C, 275 °C and 375 °C for single-layer, triple-layer and multi-layer thin films, respectively, which indicates the multi-layer thin films show the best thermal stability. According to the degradation mechanism in this paper, the unbalance of interfacial stress and oxygen vacancies in VOx thin film accelerated the oxidation process, which results in the disappearance of thermochromic properties. Furthermore, the multi-layer thin films still show superior ΔTsol of 16.56% and Tc of 56 °C, when it was taken out at 400 °C and cooled quickly in air. Meanwhile, the annealing period could be reduced by 75% in comparison to cooling in vacuum chamber. Our research set forth a new avenue in enhancing the thermal stability and production efficiency, which can promote the practical applications of VOx-based thin films.