Thermoelectric Performances Of Poly(3,4-ethylenedioxythiophene): Poly(Styrenesulfonate) And Its Composites

Thermoelectric (TE) material is a kind of"green"and functional material employed in refrigeration and power generation, which can directly achieve the conversion of thermal energy and electrical energy taking advantage of industrial waste heat and renewable energy, have good energy saving and environmental benefits. Compared with the traditional inorganic TE materials, the organic conducting polymers (CPs) as novel TE materials have been paid much attention because of that they have attractive features for use including their potential low cost due to abundance of carbon resources, easy processing into versatile forms, low thermal conductivity and good environmental stability. Among numerous CPs, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is the most widely used application of CPs, owing to several advantages such as high electrical conductivity, low thermal conductivity, good environmental stability, and their unique"metallic and non-metallic"performance. Therefore, PEDOT:PSS will be a promising candidate for organic TE materials owing to these advantages. Consequently, it is greatly significant to investigate the TE performances of PEDOT:PSS. This dissertation mainly detected and discussed the intrinsic TE performance of PEDOT:PSS films treated by secongd-doping and PEDOT:PSS/inorganic composites. The major contents and conclusions include:1. Firstly, highly conducting free-standing PEDOT:PSS films with room-temperature conductivity of about 300 S·cm^-1 were successfully prepared from PEDOT:PSS solution containing additives (DMSO or EG) on the smooth and flexible polypropylene (PP) film substrate with contact angle of 87°. The contact angle of substrate has significant effect on the preparation of free-standing PEDOT:PSS films. Additionally, the process of adding DMSO or EG did not result in the change of carrier concentration but the increase of carrier mobility. The free-standing PEDOT:PSS film showed high electrical conductivity and stable Seebeck coefficient and its figure of merit (ZT) with high environment stability can be up to 10^-22. Secondly, PEDOT:PSS/MWNT composite films have been successfully prepared by mechanically blending MWCNTs powders and PEDOT:PSS solution and casting the mixed solution on polypropylene (PP) film substrates. The transmission electron microscopy (TEM) and scanning electron microscopy (SEM) characterization indicated that the MWNTs were composited well together with PEDOT:PSS. TE measurements revealed that the electrical conductivity of the composite films decrease with increasing the MWNTs content, and there is no significant changes for the Seebeck coefficient of the composite films. The maximum value of power factorσS²of the composites is 3.2×10^-7 W·m^-1·K^-2;3. Thirdly, Free-standing PEDOT:PSS/Ca₃Co₄O₉ composite films have been successfully prepared by mechanically blending Ca₃Co₄O₉ powders and PEDOT:PSS solution and casting the mixed solution on polypropylene (PP) film substrates. TE measurements revealed that the Seebeck coefficient can be improved with an increase of the Ca₃Co₄O₉ content in the composite films, and the largest enhancement of Seebeck coefficient for the composite film is 24.8% compared with the free-standing PEDOT:PSS film. The maximum value of power factorσS²of the composites is 3.2×10^-7 W·m^-1·K^-2; However, it is also shown that the power factors of the composite films decrease with increasing the Ca₃Co₄O₉ content, mainly due to the decline of electrical conductivity and the limited improvement of Seebeck coefficient.4. The electrical conductivity and Seebeck coefficient of PEDOT:PSS films were simultaneously improved by adding ionic liquid (IL) into polymer solution. The maximum electrical conductivity of PEDOT:PSS/IL films reaches 174 S·cm^-1, more than one order of magnitude higher than that of pure PEDOT:PSS film, and the maximum Seebeck coefficient is up to 30μV·K^-1, almost twice the value of the pure PEDOT:PSS film. The atomic force microscopy images of PEDOT:PSS/IL films indicated that the ILs induced the formation of a special three-dimensional structure of highly conducting PEDOT grains, and result the improvement of thermoelectric performances of PEDOT:PSS films.