Preparation And Properties Of Multi-color Mo-doped Vanadium Pentoxide Electrochromic Thin Films

Oxide electrochromic thin films have drawn great attention due to their numerous potential applications. Electrons and ions can be reversibly transported in layered V₂O₅.Vanadium oxide thin films have gained great interest, owing to their multi-color electrochromic characteristics. Meanwhile, V₂O₅ can not only be used as cathode material, but also be used as anode material. Additionally, the optical and electrical properties of V₂O₅ thin films can be effectively modulated by Mo doping. In this thesis, investigation on the preparation and properties of Mo-doped V₂O₅ thin films are performed. The main conclusions are listed as follows:1. The uniform and stable V₂O₅ sol was synthesized by sol-gel technique. The V₂O₅ thin films were prepared under different voltages（4 V, 6 V, 8 V and 10 V） by electrodeposition.The V₂O₅ thin films with layered structure were characterized by X-ray diffraction（XRD）.These results show that no distinct difference of the interlayer distance, about 1nm, is observed significantly with the increase of applied voltage. Moreover, vibration modes of layered V₂O₅ are observed in Raman spectra. The layered structure of V₂O₅ thin films prepared by elecrodeposition has been proven further by means of optical properties. In this paper, the effect of deposition voltage on electrochromic properties of V₂O₅ thin films and Mo-doped V₂O₅ thin films are systematically investigated. At an optimum deposited voltage of 10 V, a good performance with the high cycle stability and short response time is obtained for the V₂O₅ thin films.2. The Mo-doped V₂O₅ hybrid sol was synthesized by hydrothermal method. Uing electrodeposition, Mo-doped V₂O₅ thin films were prepared under different voltages（4 V, 6 V,8 V and 10 V）. The Mo-doped V₂O₅ thin films have a（001） plane layered characteristic byXRD analysis. It is obvious that layered characteristic of V₂O₅ is not significantly affected by Mo doping. Moreover, the interlayer distance of Mo-doped V₂O₅ is 1.11 nm, 1.31 nm, 1.27 nm and 1.14 nm, respectively, which are 0.1 0.3 nm wider than V₂O₅. These results confirmed that the interlayer distance is enlarged by Mo-doping, which provides wider transport channel for the intercalation / deintercalation behavior of Li+ion, and better performance of electrochromic of Mo-doped V₂O₅ thin films is observed. Two clear crystallization areas with a fringe spacing of 0.28 nm and 0.36 nm are observed in the HRTEM images of the thin film, which is in a good agreement with the XRD results. The AFM images of Mo-doped V₂O₅ thin films reveal that the surface is smooth, and the mean roughness is less than 20 nm. The cycle stability of the Mo-doped V₂O₅ thin films deposited under 10 V is better than the undoped ones. The Mo-doped V₂O₅ thin films can display five coloration states（light yellow, deep orange, light green, blue-green and blue） at various applied voltates of 1.0 V, 1.5 V,-0.3 V,-0.5 V,-1.0 V, respectively, less than 2 V.3. The effect of post-annealing on the structural and electrochromic properties of the Mo-doped V₂O₅ thin films is investigated. By varying the annealing temperature, the interlayer distance is increased from 1.16 nm（as-deposited） to 1.38 nm, and the enlarged interlayer spacing would facilitate ion movement between interlayers inside the electrochromic matrix. In addition, the coloration efficiency of the Mo-doped V₂O₅ thin films annealed at 250 ℃ was 42.7 cm2C-1, while that of the as-deposited thin films was 22.2 cm2C-1.Therefore, both the optical modulation and color efficiency of the Mo-doped V₂O₅ thin films are greatly enhanced under an optimum post-annealing condition.