Free-standing SWNTs/VO2/Mica hierarchical films for high-performance thermochromic devices

Vanadium dioxide (VO2) with reversible metal-insulator transition (MIT) is a promising energy-saving material for next-generation smart windows and infrared devices. However, the specific applications are largely limited by the relatively high critical temperature as well as the non-transferable grown-substrate. Herein, we report such limitations can be overcome by directly growing VO2 on layered mica sheets and integrating with high transparent single-walled carbon nanotube (SWNT) films. The SVVNTs/VO2/mica hierarchical films can be peeled-off to form a free-standing ultra-thin optical window and can further be transferred to other substrates with high flexibility and transparency. By heating the SWNTs/VO2 layer with a bias current, the MIT process of VO2 film can be facilely modulated, achieving the reversible and dynamical regulation of the infrared transmission. Furthermore, by adjusting the bias current, it is possible to change the starting local temperature and shift the initial situation close to the phase transition boundary, resulting in the decreased energy barrier to-trigger the MIT behavior. This fascinating strategy overcomes the high critical temperature limit of VO2 and avoids the bottle-neck problem in practical applications of VO2 material, which demonstrates wide applications of this kind of device in the future.