Thermochromic Film of Vanadium Dioxide Having Heat Reflection and Anti-Glare Properties

Abstract

This research aims to study and develop films to exhibit two main functions which are heat reflection of infrared radiation and glare reduction. The heat-reflecting monoclinic vanadium dioxide film was synthesized by a sol-gel dip coating on glass slides followed by a 2-step heat treatment at vacuum base pressure before sintering of 2x10-3 mbar, a furnace temperature of 500oC. The resulting film comprises of particles of irregular shape with size range of approximately 220-380 nm and thickness of 69-74 nm. The vanadium dioxide, which is the main constituent, contains valence electrons V4+2p3/2 and V4+2p1/2. Vanadium pentoxide and vanadium trioxide are also present in small quantities. The electrical property of the vanadium dioxide, determined by the transition temperature, is about 68oC. The optical property, tested when the film temperature is changed from 25oC to 80oC, results in light transmittance in the visible wavelength of 40-50%. At a near-infrared region, the transmittance at 25oC tends to increase as the wavelength increase and is higher than that at 80oC which tends to decrease as the wavelength increases. For the dip-coating fabrication of glare-reduced multilayer films, the three-layer film (Glass/TiO2/SiO2/TiO2) comprises of the first layer (TiO2) next to glass slide with thickness of about 41 nm in thickness, the second layer (SiO2) of about 11 nm and the third layer (TiO2) of about 45 nm. The film’s transmittance in the visible light wavelength is about 70-85%, and in the near-infrared wavelength tends to be constant at 90%. For the fabrication of a multilayer film with both heat-reflecting and glare-reducing properties, the one with the vanadium trioxide and anti-glare multilayer on the same side (Glass/TiO2/SiO2/TiO2/V2O3) is selected. The thickness of the first layer next to glass slide (TiO2) is about 42 nm, the second layer (SiO2) is about 49 nm, the third layer (TiO2) is about 42 nm and the fourth layer (V2O3) is about 82 nm. Light transmittance is approximately 40-50% in the visible light wavelength, and the transmittance in the near-infrared wavelength tends to be constant at about 50%. The findings of this study can be further developed to contain the monoclinic vanadium dioxide phase rather than the vanadium trioxide phase so as to improve reflection property.