A low cost preparation of VO₂ thin films with improved thermochromic properties from a solution-based process

This paper describes a solution-based route to synthesize vanadium dioxide (VO₂) thermochromic thin films on glass substrate by spin-coating technology followed by nitrogen-annealing with vanadium pentoxide (V ₂O₅) and oxalic acid (H₂C₂O ₄) as source material, which is fairly economical and practical. Surface morphologies indicate that the films obtained by this method are homogeneous and particulate, irregular prisms emerge as the annealing temperatures increase. X-ray diffractions show that films annealed at relatively low temperature are pure monoclinic phase with a preferred orientation of (011). NaV₄O₇ and NaV₆O₁₅ form along with raising the heating temperatures. VO₂ films obtained exhibit excellent visible transparency and switching property at near-infrared wavelengths across the metal-semiconductor transition. Transmittance change at λ = 2000 nm of VO₂ thin film annealed at 450 C attains as high as 41.5% and its solar modulation efficiency reaches up to 8.8%. The W-doped VO₂ film at a doping level of 1 at.% exhibits a thermochromic switch at 37 C with a narrow hysteresis, which will greatly favor the practical application of VO₂-based smart windows.