Comparative study of thermochromic properties on fresh and aged vanadium dioxide films

Vanadium dioxide (VO2) thin films were fabricated by means of DC reactive magnetron sputtering at low temperature, and then were aged in air for 5 years. The thermochromic properties of the fresh VO2 film and aged one were investigated by UV–visible spectrophotometer. The experimental results show that the fresh VO2 film shows excellent thermochromic properties with a high visible transmittance of 40.8% and a large switching efficiency of 73% at 2500 nm. For the film aged in ambient air for 5 years, the visible transmittance is increased to 54.0% due to a blue-shift of absorption edge and a decrease in luminous absorbance. More interestingly, the aged VO2 film still keeps a relatively large switching efficiency of 51% at 2500 nm, suggesting the deposited VO2 film has a good thermochromic stability in ambient air. These characteristics indicate the practical applications of VO2 film to smart optical devices.