A new strategy of nanocompositing vanadium dioxide with excellent durability

Vanadium dioxide has been widely investigated as a thermochromic smart window material. However, it has mediocre thermochromic properties (low solar modulation ability Δ T sol , low luminous transmission T lum and high transition temperature ( τ c )). More importantly, the Achilles heel of VO 2 is its thermodynamically unstable characteristics which severely hinder its commercialization. Different approaches have been investigated to enhance its thermochromic properties and nanocomposites outperformed other methods according to calculations and experiments. The conventional nanocomposite technique is to disperse VO 2 nanoparticles (NPs), usually made by the solution process, into a transparent media and the highest Δ T sol could only reach 20% theoretically. In this report, we employed the glass industry compatible process of magnetron sputtering, followed by rapid thermal annealing (RTA). Instead of the usual continuous films, this thin film process gave a unique structure where VO 2 NPs are dispersed in a V 2 O 5 /V 3 O 7 matrix with a dense thermodynamically stable V 2 O 5 overcoat. This new type of nanocomposite gives a nearly doubled Δ T sol (20%) compared with that of the best reported continuous single vanadium oxide film (10%). The accelerated test suggested that the expected service life of this film is 23 years, which is a breakthrough in VO 2 based thermochromic smart windows. The high durability, due to the encapsulation of V 2 O 5 , together with the significantly enhanced thermochromic properties and facile industry compatible process, provide a new strategy to scale up this technology into real-world applications. We developed a new strategy to fabricate a VO 2 coating with long-term stability, a low τ c (42.4 °C heating, 36.5 °C cooling), significantly enhanced thermochromic performance ( T lum of 35.7% and Δ T sol of 13.2%) and low fabrication cost.