A New Strategy of Nanocompositing Vanadium Dioxied with Excellent Durability

Vanadium dioxide is widely investigated as a thermochromic smart window material. However its mediocre thermochromic property (low solar modulation ability ΔTsol, low luminous transmission Tlum, and high transition temperature (τc)) and thermodynamically unstable characteristics hinder its commercialization. Different approaches have been investigated to enhance its thermochromic property and nanocomposition outperformed other methods by calculation and experiment. The conventional nanocomposite was to disperse VO2 nanoparticles (NP) usually made by the solution process into a transparent media and the highest ΔTsol could only reach 20% theoretically. In this report we employed glass industry compatible process magnetron sputtering followed by rapid thermal annealing (RTA), instead of usual continuous films, such a thin film process gave a unique structure where VO2 NP is dispersed in V2O5/V3O7 matrix with a dense thermodynamic stable V2O5 overcoat. The new type of nanocomposite gives nearly doubled ΔTsol (20%) compared with the best reported continuous vanadium oxides films (10%). Simulation suggested the ΔTsol and Tlum could be further improved to 21.1% and 41.2% by modulating the thickness of V2O5 layer. Simulation suggested that by replacing the conventional transparent matrix, ΔTsol could be further improved from 20.9% to 29.6%. Such combination of ΔTsol (29.6%) and a Tlum (63.8%) outperforms any other theoretical calculation by various surface modifications. The accelerated test suggested that the expected service life of such films is 23 years, which is a breakthrough in VO2 based thermochromic smart window. The high durability due to the encapsulation of V2O5 together with much enhanced thermochromic properties and facile industry compatible process provides a new strategy to scale up this technology into real-world applications.