Abstract
Tungsten oxide (WO3) thin films with various thicknesses of approximately 36, 72, 108, and 180nm were prepared using radio frequency sputtering method. Film thickness can be controlled at nanoscale. In addition, X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy were utilized for investigating morphologies and microstructures of as-prepared WO3 thin films. Moreover, optical properties of the WO3 nanofilms were characterized using ultraviolet-visible-near infrared spectroscopy. Transmittance of WO3 films changed during the electrochemical cycles. WO3 films with various thicknesses give various transmittance modulation between colored and bleached states. WO3 films with a thickness of approximately 108nm had the largest transmittance modulation among various film thicknesses, about 66% measured at 550nm. Results showed that the value of transmittance of colored samples decreased with increasing film thickness. However, transmittance of bleached samples was not influenced significantly by their thickness.
Highlights
Energy consumption and greenhouse gas emission of buildings account for a large part of total energy consumption and CO2 emissions in both developed and developing countries in the world
X-ray diffraction (XRD) results showed that as-prepared WO3 films with various thickness of 36, 72, 108, and 180 nm had the same monoclinic crystal structure
The absorption peak at about 980 cm–1 is related to W = O stretching vibrations, whereas the absorption peak at about 585 cm–1 is corresponding to O-W-O stretching vibrations from the crystalline WO3.18,26 Fourier transform infrared (FTIR) results showed that as-prepared WO3 films with various thickness of 36, 72, 108, and 180 nm had similar crystalline structure
Summary
Energy consumption and greenhouse gas emission of buildings account for a large part of total energy consumption and CO2 emissions in both developed and developing countries in the world. A building may lose about 30% of its heat or air conditioning energy through its windows, because windows have usually poor thermal insulation properties and high radiation transmittance. Chromogenic smart windows have been used for regulating solar radiation transmitted through the windows into buildings. Nowadays, chromogenic smart windows are not widely utilized in normal buildings. Chromogenic smart windows can adjust solar radiation transmitted through windows by regulating transmittance value. Glass with functional film of chromogenic smart windows can change windows transmittance value if functional film materials of glass are sensitive to voltage, solar radiation, heat, and so on. The role of the film thickness on structural and optical properties of WO3 films was investigated. Ultraviolet-visible-near infrared (UV-VisNIR) spectroscopy was utilized to analyze optical properties of WO3 films
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