A new strategy of nanocompositing vanadium dioxide with excellent durability

Abstract

Vanadium dioxide has been widely investigated as a thermochromic smart window material. However, it has mediocre thermochromic properties (low solar modulation ability ΔT_sol, low luminous transmission T_lum and high transition temperature (τ_c)). More importantly, the Achilles heel of VO₂ 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 VO₂ nanoparticles (NPs), usually made by the solution process, into a transparent media and the highest ΔT_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 VO₂ NPs are dispersed in a V₂O₅/V₃O₇ matrix with a dense thermodynamically stable V₂O₅ overcoat. This new type of nanocomposite gives a nearly doubled ΔT_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 VO₂ based thermochromic smart windows. The high durability, due to the encapsulation of V₂O₅, 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.