Influence of humidity and aging on the optimization of VO₂ sol-gel thin films for thermochromic smart windows

Global energy consumption is severely impacted by inefficient heat management and the loss of energy through windows in buildings. Thermochromic smart materials, such as monoclinic vanadium dioxide (VO₂ M1), can be exploited to reduce energy consumption via a passive solar modulation. The successful fabrication of VO₂ thin films generally requires careful control of stoichiometry and crystalline structure due to the complex phase stability diagram of vanadium oxides. The development of a simple and versatile method, not requiring a protected atmosphere, would boost the applicability of VO₂ thin films for energy-saving devices. Here, VO₂ (M1) thin films are obtained via the sol-gel method, exploiting the advantages of ambient humidity and solution aging to enhance the film formation. The latter influence is assessed through the optical, morphological, and structural properties of the films. The aging of the solution and the humidity during the film deposition are found to remarkably promote thermochromic efficiency, with the best thermochromic performance corresponding to T_lum = 73% and ∆T_sol = 9.1%.