Preparation And Electrochromic Properties Of Vanadium-doped Tungsten Trioxide Films

Electrochromic materials have the characteristics of dynamically adjusting optical properties.Among various electrochromic materials,tungsten trioxide（WO₃）has always been the most studied and relatively sufficient electrochromic material.However,the manufacturing cost of WO₃ electrochromic devices is high.In this paper,the purpose of constructing low-cost,high-performance WO₃ electrochromic materials is modified and studied by doping,and the preparation of corresponding devices is also explored.Vanadium doping is a common method for modifying WO₃ materials,and it has been proved that it can effectively improve the electrical conductivity of the material and increase the electrochemical active sites on the surface of the material,which is beneficial to improve the electrochemical performance of the material.However,for tungsten trioxide thin film materials,the reported vanadium doping methods generally involve high temperature and high-pressure processes,and the operation is complicated,which is not conducive to large-scale preparation.In order to solve this problem,an electrodeposition method for preparing vanadium-doped tungsten trioxide thin films was developed in this study.The vanadium-doped WO₃ thin film is simply and efficiently prepared after high temperature annealing.The method has the advantages of simplicity,economy,high repeatability and high practical value.Compared with undoped WO₃,it is found that vanadium doping promotes the electrodeposition of WO₃,and the deposition amount per unit time is more,which is beneficial to reduce the industrial production time.A series of vanadium-doped tungsten oxide thin films with controllable vanadium atomic doping amount were prepared by this method,and it was found that the WO₃ thin films with a vanadium-tungsten molar ratio of2%exhibited the best electrochromic properties.Compared with undoped WO₃,the contrast of WO₃ with 2%molar ratio of vanadium to tungsten at 632.8 nm increased from 6.13%to16.46%,the coloring efficiency increased from 22.3 cm²C^-1 to 41 cm²C^-1 and cycle stability increased,and Li⁺was removed more easily..The distribution of vanadium in the WO₃ phase is uniform according to the EDS surface scan.After doping,the surface structure of WO₃becomes rough,the grain size of WO₃ decreases,the grain size is about 30nm,which can provide a large number of reaction sites,and the forbidden band width is reduced from 3.6e V to 3.55e V.Further,we used the optimal molar ratio of 2%vanadium to tungsten to electrodeposit V-doped WO₃ on ITO glass,flexible ITO-PET,flexible graphene-PET substrates,and self-made gel electrolyte and aqueous electrolyte,three kinds of electrochromic devices that can achieve"blue-transparent"reversible color change were prepared,and the color change of the devices was good.We found that the better conductive ITO glass and ITO-PET deposited more uniformly than the flexible graphene-PET substrate.We also found that V-doped WO₃on graphene substrate can change color in Na Cl aqueous solution and the aqueous electrolyte will not generate bubbles,which is of reference significance for the preparation of WO₃devices in the future.