Conducting Polymer Nanocomposite Films And Its Applications As Electrode Materials

Rencently, electroactive polymer and its nanocomposites based on carbon nanomaterials exhibit excellent electrical and electrochemical performance, and attract more attentions as novel functional materials. In this paper, deposition and characterization of conducting polymer poly(3,4-ethylenedioxythiophene)(PEDOT) and its nanocomposite films was demonstrated. The electrical and electrochemical performance of PEDOT and its nanocomposites were investigated and their applications as electrode film for optoelectronic and energy storage devices was explored, and the related mechanism was also included. The main results are as follows:1. A PEDOT nanocomposite film was constructed on porous tantalum pentoxide surface through electrostatic self-assembly method, and the results indicated that the film was deposited on substrate with a layer-by-layer fashion. The concentration of polycation and pH of solution showed distinct influence on film morphology, electrical and self-assembly performance. The influence of nanocomposites on equivalent series resistance(ESR) of capacitor was studied. It has been found that the Poly(diallyldimethylammonium chloride)(PDDA)/poly(sodium styrene sulfonate)(PSS) films showed more distinct influence on capacitor ESR than PDDA/PEDOT-PSS due to the less conductive performance. For the first time, this electrostatic self-assembly films was constructed on porous Ta2O5 surface as a electrode films for tantalum capacitor and the device performance was investigated. The results indicated that this highly conductive ultrathin film can be the candidate to replace the common PEDOT films as capacitor electrode, and the electrostatic self-assembly film based device exhibited better stability and more simple preparation process.2. A chemical vapor phase polymerization(VPP) deposition of PEDOT/PEDOT-graphene nanocomposites on porous tantalum pentoxide surface as cathode films for a tantalum capacitor was demonstrated and the device performance was studied. The results revealed that a close package of PEDOT on graphene was formed after the VPP depositon, which resulted in good contact performance between conducting polymer and graphene. The improved mechanical performance of nanocomposites was also observed due to the addition of graphene. The VPP PEDOT and PEDOT/grapene exhibit series diffraction peaks at 2θ = 10.8°, 12.3°, 16.5 and 23.7°, indicating the well order structure of nanocomposites constructed from oxidant template. The conductive characterization revealed that high conductivity of PEDOT/graphene nonocomposites about 100.3S/cm was obtained, which comes from good synergistic effect between PEDOT and graphene. For the first time, the performance of tantalum capacitor based on PEDOT/PEDOT-graphene electrode were investigated, and the results indicated that the highly conductive performance of this nanocomposites gives a rise to lower device equivalent series resistance(ESR), lower leakage current and improved voltage withstand performance of device. This novel tantalum capacitor can work at 1MHz frequency with low capacitance loss about 30%, indicating the excellent high frequency characteristics.3. The VPP deposition method was also demonstrated to prepare composites of PEDOT/single-walled carbon nanotubes(SWCNTs) and PEDOT/reduced graphene oxide(RGO), and these nanocomposites as supercapacitor electrode for energy storage applications was explored. These nanocomposites exhibited ordered structure due to the template effect of composite film deposited on a crystal FeCl3 oxidant film, and a close package of PEDOT on carbon nanomaterials was obtained. The electrochemical performance of these nanocomposites was investigated and the approximate rectangular cyclic voltammetry curves indicated the good electrochemical activity of both PEDOT nanocomposites. Compared with pure PEDOT, the PEDOT/SWCNTs and PEDOT/RGO exhibited larger voltammetry curve current, which may comes from the higher specific surface area and conductivity of carbon nanomaterials. Moreover, the PEDOT/RGO composite electrode showed excellent specific capacitance retention about 83%, which can keep a 171 F/g capacitance after the current increasing from 0.2 A/g to 2.0 A/g. The results also indicated that this nanocomposite is suitable as electrode films for large current charging/discharging supercapacitor. The further investigation also revealed that the supercapcitor with PEDOT/RGO as electrode can keep 90% initial capacitance after 1000 cycles, indicating excellent capacitance retention and working stability.4. A layer-ordered PEDOT composite films was constructed on a LB film template through VPP deposition method and this novel composite film was deposited on indium tin oxide(ITO) substrate as hole injection layer for organic lighting emitting diode(OLED). The self-assembly ability investigation of surfactant at air-water interface indicated that the surfactant have different mean molecule area due to the different alkyl chain. Compared with docosoic acid(n-DA), the short alkyl chain of arachic acid(AA) leads to more vertical arrangement of molecules at air-water interface, resulting in smaller mean molecule area and weak matrix steric hindrance between adjacent molecules. The XPS analysis indicated that the PEDOT were well located between adjacent surfactant ultrathin layer and the composite films exhibited well ordered structure. This highly ordered structure can afford possibility for carries jumping from one dimension PEDOT nanostructure to another PEDOT layer. This carries jumping phenomenon between strong relevance PEDOT was also influenced by the insulation steric hindrance of PEDOT molecules. The hole injection performance of this layer-ordered ultrathin films as hole injection layer was also investigated. Compared with common PEDOT films, the OLED with PEDOT:AA film as injection layer exhibited maximum luminance about 3522 cd/m2 and obtained a 3.2 cd/A luminance at 12 V, and lower driving voltage of device was also observed. The excellent luminance performance of device resulted from the well defined structure of layer-ordered PEDOT: AA films, which can supply suitable and layer-ordered structure for further enhanced hole injecting capability from ITO to emitting materials. Moreover, the insertion of ordered and well defined nanostructure layer for hole transferring layer further enhanced the exciton formation from hole-electron combination.