Preparation And Infrared/Visible Light Control Properties Of New Titanium Based Thin Films

Electrochromic material can change its optical properties(transmissivity,reflectance and absorptivity)through applied voltage changes,which has application potential in intelligent window,infrared camouflage,display and other fields,with adjustable spectral range mainly including visible light(400-800nm),near-infrared(800-2000nm),mid-infrared(3-5?m)and far-infrared(8-14?m).Anatase,a phase of titanium dioxide,is a kind of tetragonal lattice composed of[TiO₆]octahedral elements,belonging to the wide gap band n-type semiconductor,which can achieve a reversible change from colorless to blue through the embedding of metal ions(usually Li⁺ions).In the process of studying the above reactions,it was found that Li₄Ti₅O₁₂(LTO),which could achieve reversible changes from white to blue under applied voltage,and had electrochromic properties in mid and far infrared ranges.Both of these materials have the advantages of being abundant in the earth and non-toxic.However,TiO₂ electrochromic film usually requires high temperature(500?)heat treatment to fabricate,and we have only few research on LTO electrochromic thin film process.In this thesis,we improve the process to solve the problems above.Firstly,a new hydrothermal method was designed,which could grow TiO₂ electrochromic films directly on the surface of FTO in a simple and rapid way under the combined action of glycerine and(NH₄)₂SO₄.The feasibility of this strategy was proved by studying the crystal growth process and electrochemical behavior of the film.The thin films were assembled into simple devices by a gel electrolyte based on UV-curable adhesive to prove the application prospect.On this basis,the electrochromic properties of TiO₂ semiconductor materials were further improved by Nb doping.Finally,the fabrication of LTO films is explored,with a kind of LTO electrochromic film based on flexible porous conductive working electrode,where LTO can be prepared directly from powder.The electrochromic ability of middle and far infrared band is verified.The specific research contents are as follows:(1)With the assistance of glycerin and(NH₄)₂SO₄,anatase TiO₂ electrochromic film was directly grown on the surface of FTO conductive glass in a strong acidic environment by one-step hydrothermal process,avoiding the process of high temperature heat treatment.The formation of anatase phase crystal was proved,and the porous structure of the surface was observed.The effects of glycerin and(NH₄)₂SO₄ on the growth process and morphology of thin films were further studied by quantitative experiments to understand the growth mechanism of thin films.In the end,the prepared TiO₂electrochromic films showed obvious light transmission modulation ability in the band of350-1100nm,and had fast coloring and fading time(5.7s,4.1s).Simple solid-state electrochromic devices were prepared from the above samples,which showed obvious electrochromic ability,indicating that this process has a certain application potential.(2)Hydroxy-rich Nb precursor was prepared by hydrolysis of NbCl₅,then been mixed with Ti precursor,to prepare Nb-doped TiO₂ thin fims.It was observed that trace Nb doping had almost no effect on the crystal structure of TiO₂,but the effect on crystal growth resulted in a dense structure instead of a porous surface.At this time,the excessive addition of(NH₄)₂SO₄ affects the degree of dense stacking of grains and increases the crystallinity.Under the influence of Nb doping,the overall current density increases,and the overall electrochromic performance improves in the 300-1100nm band.The corresponding wavelength of the maximum modulation range moves to the near-infrared region,possibly due to the accumulation of surface charges.However,due to the dense surface morphology,reduced specific surface area and greater electrostatic repulsion of Nb⁵⁺,it is more difficult to embed Li⁺,and the reduction current density of the doped film is lower,and the response time is greatly increased.(3)LTO electrochromic films were prepared directly on ITO surface by simple coating process.The films had good electrochromic properties.By comparing terpinol with N-methylpyrrolidone(NMP),it was found that terpinol was expected to replace toxic NMP as a new dispersant in the preparation of LTO films.The porous conductive film with good surface morphology and large pore size can be obtained by electrodeposition of gold on nylon membrane.This structure is beneficial to electrolyte infiltration during operation.LTO flexible electrochromic film was prepared by the electrode,and LTO powder was deposited directly on the conductive surface of the gold film by simple filtration method.The LTO thin films were further assembled as simple devices,and it was proved that the LTO thin films obtained by this process showed obvious infrared modulation performance in wide band.