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

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 (Delta T-sol=9.5%) and an applicable luminous transmittance (T-lum=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.