Study On Preparation And Optical Properties Of Warm/Cool-Tone Switchable VO₂-Based Smart Window Films

Vanadium dioxide（VO₂）is a transition metal oxide.Its VO₂（M/R）can undergo reversible transformation around 68℃with excellent near-infrared band regulation characteristics,which makes it a hot research topic in the field of smart window materials.However,when it is applied to the smart windows,there are some problems,such as high phase transition temperature,low solar modulation efficiency,and the yellow color of the film.Based on this,W-Fe and W-Mn co-doping were used to prepare VO₂powder with low phase transition temperature,and the influence of doping elements on the synthesis of M-phase VO₂was studied.Furthermore,the thermochromic microcapsules and VO₂powder were prepared into thin films,which improved the solar modulation efficiency and could control the color-change.The main research work of this thesis is as follows:（1）Study on the characterization and optical properties of VO₂films.M-phase VO₂powders were successfully prepared by the one-step hydrothermal method,and the effects of vanadium source,reaction time and proportion of precursor on the synthesis of M-phase VO₂were investigated.The powders were characterized by XRD,SEM,XPS and DSC.The effects of doping elements on the phase transition temperature and the synthesis of M-phase VO₂were further investigated.Based on this,the films of VO₂were prepared by the scrap-coating method,and the characterization and optical properties of the films were tested.The results showed that the M-phase VO₂was relatively pure when the vanadium source was ammonium metavanadate,and the time cost can be reduced as well.In the process of doping modification,it was found that 1at.%W/1at.%Fe co-doping can not only reduce the phase transition temperature of the powder,but also promote the conversion of A-phase VO₂to M-phase VO₂.The optical properties of VO₂films are related to the amount of VO₂added and the thickness of the film.When the amount of VO₂added was 3%and the thickness of the film was 500μm,the solar modulation efficiency can reach 13.38%when the visual transmittance was above 60%.（2）Study on the characterization and optical properties of warm/cool-tone switchable VO₂films.The high solar modulation efficiency VO₂composite film was prepared by combining VO₂with thermochromic microcapsules,and the effects of film thickness and thermochromic microcapsules on the optical properties of the composite film were studied.The results showed that these three thicknesses of yellow-green composite film can be adjusted in warm and cold tones,and the solar modulation efficiency can be increased to 15.95%when the thickness of the yellow-green composite film was 250μm.When the thickness of the yellow-to-blue composite film was 250μm,the solar modulation efficiency can be increased to5.96%,which is three times of that of the single VO₂film,while the visual transmittance was 70%.These results indicate that the smart window film with warm and cool tones can greatly improve the solar modulation efficiency and has important application value in the field of smart window.