Effect of duty cycle on the thermochromic properties of VO2 thin-film fabricated by high power impulse magnetron sputtering

Abstract

Thermochromic VO2 thin films are fabricated by using high power impulse magnetron sputtering. The effect of the duty cycle with different on/off time ratios on the thermochromic properties is investigated. Though the transmittance increases with decreasing duty cycle, a moderate duty cycle is suggested. It is found that V2O3 crystallinities appear at a low duty cycle, while the inter-diffusion between TiO2 and VO2 layers becomes worse at a high duty cycle. In this study, the VO2/TiO2/glass stacked structures reach a solar regulation efficiency (ΔTsol = 9.5%) and an applicable luminous transmittance (Tlum = 43.1%) in a low-temperature state under the duty cycle of 2.5%. The crystalline behavior of the monoclinic phase shown in the x-ray diffraction pattern is further examined by a high resolution transmission electron microscope. The changes in binding energies of V 2p and O 1s orbits are compared throughout the films. The thermochromic properties as a function of TiO2 thickness are also discussed.