Fabrication And Electrochromic Properties Of Ti-doped Nanoporous WO₃ Films By Combining Magnetron Sputtering And Anodic Oxidation Techniques

Tungsten oxide(WO₃)is the earliest and most widely studied electrochromic material,which has good electrochromic properties.However,the common WO₃ thin film materials still have some problems in practical application,such as small optical modulation,low coloration efficiency,long response time and poor cycle stability.In order to solve the above problems,WO₃ porous film and Ti doped Ti-WO₃ porous film are prepared by magnetron sputtering and anodic oxidation in this thesis.The crystal structure,surface morphology,elemental composition,optical properties and electrochromic properties of the films are analyzed by XRD,SEM,EDS,electrochemical test and UV-Vis spectrophotometry.The main research contents are as follows:In this thesis,the DC reactive magnetron sputtering method was used to obtain metal W films with different thicknesses by regulating sputtering times,and then the WO₃ films with porous structures were prepared by anodizing method.The pore size was adjusted by changing the oxidation time,and finally the WO₃ porous films with large pore size and different thicknesses were formed.The influence of film thickness on the electrochromic properties of WO₃ was explored.The results show that as the thickness of WO₃ porous film increases from0.12?m to 1.2?m,the charge capacity of the film increases,and the reaction reversibility value increases first and then decreases.When the film thickness is too large,the number of inserted ions is too large,and the film structure is damaged,which is not conducive to the improvement of the electrochromic performance of WO₃ film.In this experiment,the thickness of 0.6?m WO₃porous film electrochromic performance is the best.On the basis of 0.6?m thickness,Ti-WO₃ porous films with different Ti contents were prepared by using tungsten-titanium mixed target.The results show that Ti doping can effectively improve the response speed and cycle stability of WO₃ film.In this experimental range,the electrochromic performance of Ti-WO₃ porous film with Ti content of 1.41 wt.%is the best.CV test results show that Ti doping can improve the ability of the film to accommodate ions and electrons.Excessive doping will lead to similar atomic segregation in the films,and the electrochromic performance is reduced.The results of optical properties show that the crystal structure of Ti-WO₃ porous films changes and the defect concentration increases.Therefore,Ti doping has no obvious effect on the optical modulation and coloration efficiency of WO₃ films.Compared with the undoped WO₃ porous film,the cycle stability of the film is greatly improved.After 200 cycles,the shape and area of the CV curve of the Ti-doped Ti-WO₃ porous film remain basically unchanged,while the CV area of the undoped WO₃ film is significantly reduced.Through the calculation of the amount of inserted charge Q_b and the amount of extracted charge Q_c,the ratio of Q_b/Q_c in the Ti-doped Ti-WO₃ film is about 0.95,while the ratio of Q_b/Q_c in the undoped WO₃ porous film drops to about 0.8,which fully proves that Ti doping can efficiently reduce the accumulation of Li⁺in the film,so that the cycle stability of the film is greatly improved.