Simple sol–gel process and one-step annealing of vanadium dioxide thin films: Synthesis and thermochromic properties

A simple and cost effective sol–gel process for producing vanadium dioxide thin films was developed via thermolysis of V2O5·nH2O (n ≈ 2) VV precursors prepared by dissolving vanadium powder or V2O5 powder in 30% hydrogen peroxide solutions. After spin-coating on fused silica substrates and annealing at 750 °C in vacuum, without any intermediate gas reducing step, the major phase VO2(M, monoclinic phase) was found in both of the films based on V–H2O2 and V2O5–H2O2 precursor, exhibiting large transmittance changes (> 40%) in the IR region (> 2000 nm) and small hysteresis loop width (< 5 °C) which were comparable to reported epitaxial VO2 films. The two films have similar metal-to-insulator transition temperature τC = 62.5 °C, lower than the classical value of 68 °C for VO2 thin films. In addition, the method enables simple doping, as found for 0.56 at.% W-doped VO2 films. This intrinsically simple solution process followed by one-step annealing makes it potentially useful in smart window applications.