Research On Electrochromic Properties And Optical Properties Of Metal Oxide Thin Films

Tungsten oxide（WO₃）is a material with good photocatalytic,photochromic and electrochromic properties and is currently used in a wide range of applications such as photocatalysts,gas sensors and smart windows.However,the structure and properties of WO3 films are influenced by the preparation process and post-treatment conditions,so it is important to optimize the preparation parameters and control the annealing temperature to improve the properties of WO3 films.In this paper,WO_3-x（0≤x<1）films with different annealing temperatures were prepared by RF magnetron sputtering and analyzed using field emission scanning electron microscopy（FESEM）,X-ray diffraction（XRD）,atomic force（AFM）,ultraviolet-visible spectrophotometer（UV-Vis）,Raman spectrometer and electrochemical testing devices.In this paper,three main aspects have been investigated.First,the effects of different annealing temperatures on the crystal structure and morphology of WO_3-xthin films were investigated.The results show that under high temperature annealing in the annealing furnace,with the increase of annealing temperature,the WO_3-xfilms transformed from amorphous state to monoclinic phase,and the WO₃main crystalline phase was enhanced significantly,and oxygen-deficient phases such as W₁₈O₄₉and W₂₀O₅₈gradually appeared.At the same time,the surface roughness of the WO_3-x.films in the crystalline state increases with increasing annealing temperature.Secondly,the effect of different annealing temperatures on the optical and electrochromic properties of WO_3-xfilms was investigated.The results show that the amorphous WO₃films have a maximum transmittance modulation range of about90%at 550 nm in the visible range,and their electrochromic properties increase with increasing voltage scan rate;in contrast,the crystalline WO₃films have a lower transmittance modulation range and electrochromic properties.In addition,the crystalline WO₃films have a high absorption coefficient in the 300-700 nm band,which increases with annealing temperature,while the amorphous WO_3-xfilms have a low absorption coefficient.Thirdly,Fabry-Perot（F-P）interferometric resonant cavity type polychromatic WO₃films were prepared on the basis of magnetron sputtering deposition and verified by computational experimental fitting using finite difference in time domain（FDTD）and ellipsometry spectroscopy.The crystal structure and optoelectronic properties of the polychromatic WO₃films were investigated before and after annealing.The results show that the colorful WO₃films have significant color variation and their reflectance varies with the angle of incidence and wavelength.The amorphous WO₃films have better electrochromic properties in the UV and visible wavelengths,but their colored and faded states have lower transmittance and reflectance.The crystalline WO₃films have higher reflectivity in both forms,up to 12%in the tinted state and 16%in the faded state,and up to 57.7%in the crystalline state,with significant improvements in optical and electrochromic properties.This paper provides a certain reference for optimizing the preparation process of WO_3-xthin film crystals and improving the optoelectronic properties,as well as new ideas for the design and preparation of new materials with special optical effects and functions.