Synthesis And Electrochromic Properties Of Polythiophene Derivatives And Their Application In Electrochromic Devices

The electrochromic phenomenon refers to the reversible and visible change in transmittance and/or reflectance that is associated with an electrochemically induced oxidation-reduction reaction after the application of an appropriate electrode potential. Electrochromic materials have attracted wide attention due to their potential application to the fields of smart window,display devices,automotive rear-view mirrors and so on.Conducting polymers stand for a family of important electrochromic materials due to their unique advantages of chemistry and physics.Polythiophene and its derivatives are considered to be a significant class of electrochromic materials that have gained popularity because of their easy preparation,high electrical conductivity and great environmental and thermal stability.Conducting polymers were generally prepared either by a chemical or an electrochemical method in organic solutions. However,it is difficult to obtain their high quality films in traditional organic solutions.Compared with traditional solvents,room temperature ionic liquids have many advantages such as non-flammability,non-volatility,high electric conductivity,wide potential windows(typically over 4 V wide)and excellent thermal and chemical stability.They also are excellent solvents for a wide range of organic and inorganic materials.The ionic liquids as "green solvents" could be a promising medium for electrochemical synthesis.In this paper,different polythiophene's derivatives as electrochromic materials were prepared in a "green solvent" ionic liquid.The electrochromism was discussed. And the films of polythiophene's derivatives were composited with metal oxides nanocomposite films to improve their electrochromic properties.Corresponding electrochromic devices were also constructed.With various experiment techniques such as cyclic voltammetry,scanning electron microscopy,chronoabsorptometry, UV-Vis spectral analysis,spectroelectrochemistry and electrochromic properties of the electrochromic films and devices were characterized.The results showed that the electrochromic films and devices exhibited high chromatic contrast,comparative switching time and excellent electrochemistry stability for application.Chapter 1 The development,mechanism and applications of electrochromism, electrochromic material and device were described in detail.Chapter 2 Electrochemical polymerization in a room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate([BMIM]PF₆),was used to prepare electrochromic poly(3-hexylthiophene)(PHexT).Characterization of the resulting polymer was performed by cyclic voltammetry(CV)and scanning electron microscopy(SEM)analyses.Spectroelectrochemistry and electrochromic properties were also characterized using various experiment techniques in the same pure ionic liquid.The thin film of PHexT was orange red in its fully reduced state.After oxidization of the undoped polymer,the film underwent a reversible change to the blue form.The PHexT film exhibited high chromatic contrast(40%),comparative switching time(2.5 s)and great electrochromic efficiency(230 cm²C^-1).A PHexT-based electrochromic device(ECD)was constructed and its electrochromic properties were also investigatedChapter 3 Poly(3-chlorothiophene)(PC1T)was electrochemically synthesized on a nanoporous TiO₂ surface in ionic liquid[BMIM]PF₆ by galvanostat methods to control charge densities of 93 mC cm^-2.Spectroelectrochemical analysis presented that the PC1T/TiO₂ nanocomposite film had an electronic bandgap of 1.80 eV with a bordeaux color in the reduced form and a dark blue color in the oxidized form.The switching ability of the PC1T/TiO₂ nanocomposite film was monitored and the percent transmittance(%T)was measured as 12%at 555 nm and 25%at 770 nm.Moreover,a PC1T/TiO₂ composite film based electrochromic device(ECD)was constructed and its electrochromic properties were also investigated.Chapter 4 In this chapter,a film of Ag nano-particles was deposited throgh the method of vacuum evaporation,and characterized with scanning electron microscopy (SEM)and UV-Vis spectrophotometry.And then the Ag film was composed with the inorganic electrochromic film WO₃ produced by the constant potential method in the sol-gel solution to create a new kind of electrochromic material.Various experiment techniques such as UV-Vis spectrophotometry,chronoamperometry were employed to detect the nanocomposite film's electrochromic properties.The Ag-WO₃ film was colorless at 0.8 V and changed to blue at -1.0 V reversibly with high transmittance, comparative switching time and great switching stability.The 5-layer electrochromic device:ITO/Ag-WO₃ nanocomposite film/solid electrolyte/poly(3-methythiophene)/ ITO was also constructed and appeared good electrochromic properties.