Joule heating driven infrared switching in flexible VO2 nanoparticle films with reduced energy consumption for smart windows

Vanadium dioxide (VO2) is emerging as the most promising candidate for next-generation smart windows. However, the applications of VO2-based films encounter the bottleneck of its optimal thermochromic property being unable to be retained as the modulating phase transition temperature approaches the ambient temperature. Joule heating is an effective approach to maintain the infrared switching ability of pristine VO2 films, but the accompanied energy consumption and its effects on the infrared switching ability of flexible VO2 films are still unexplored. Here, we fabricated flexible VO2 nanoparticle films via a scalable blade-coating process and investigated the effects of Joule heating on the infrared switching of flexible VO2 films. Infrared switching triggered by Joule heating can be effectively managed by the input voltages with high stability and exhibited no obvious degradation even after 10 000 bending cycles, suggesting excellent flexibility. Importantly, we found that maximum infrared switching ability could be sustained with a dramatically reduced power, 15% of the threshold power (224 mW cm−2), by utilizing the hysteresis behaviour of the as-prepared VO2 films. This study provides a practical strategy for utilizing hysteresis behaviour to maintain the optimal infrared switching ability of flexible VO2 films with low energy consumption, substantially promoting the development of flexible smart devices.