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.
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