Preparation Of PEDOT:PSS-based Composite Materials And Their Thermoelectric Properties

Due to the world’s demand for energy and the environmental impact of global climate change caused by the combustion offossil fuels, thermoelectric (TE) materials, which allow direct con-version between thermal energy and electricity without pollution, have received considerable attention recently as a green option forvarious energy-harvesting applications ranging from power gener-ation to microprocessor cooling. Conducting polymers have been paid much attention because of their low density, low cost, relatively simple synthesis, and easy processing into versatile forms.Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) will be a promising candidate for organic TE materials because of its high electrical conductivity, low thermal conductivity, facile processing and good environmental stability. Nevertheless, the ZT value of PEDOT:PSS is still much lower than that of inorganic thermoelectric materials, mainly due to its lower Seebeck coefficient. Various attempts have been made to enhance the ZT value of PEDOT:PSS. Synthesizing composites was considered an effective strategy to improve materials performances by combining the advantages of each component. These reports have proved that conducting polymer/inorganic TE materials can improve the electrical conductivity of the composite materials and the Seebeck coefficient can be kept at a stable level or can be improved to some extent. Besides, the thermal conductivity of these composite is still consistent with that of conducting polymers. Therefore, this synthesis effect has provided a new approach to improve the TE properties of conducting polymers. Consequently, we believe that it is greatly significant to investigate the TE performances of PEDOT:PSS and their composeite materials. This dissertation mainly detected and discussed the preparation of PEDOT:PSS/inorganic composite materials. The major contents and conclusions are as follows:1. Paper as an effective substrate has been introduced into the thermoelectric field in this work. We have developed a novel strategy to prepare free-standing PEDOT:PSS/paper composite films by a one-step method of directly writing PEDOT:PSS solution on paper, making the process simple, rapid, and facile. The films showed excellent flexibility, light weight, soaking stability in water, and great potential in large-scale production, which could greatly expand their applications in thermoelectric generators. More importantly, the free-standing PEDOT:PSS/paper composite films exhibited great enhancements in both Seebeck coefficient (30.6 μV/K) and electrical conductivity together with a low thermal conductivity (0.16 W/mK). The results indicate that paper as an effective substrate is suitable for the preparation of high-performance and flexible thermoelectric materials. 2. In conclusion, a novel working electrode of PEDOT:PSS film was raised for the electrodeposition of Bi2Te3, and a sandwich-like structured Bi2Te3/PEDOT:PSS/ Bi2Te3 composite film was formed. The structures and surface morphologies were systematically investigated. The composite films exhibited TE properties of a favourable low thermal conductivity (0.169-0.179 W/mK) and a high electrical conductivity (403.5 S/cm), and their ZT value reached a maximum of 1.72 × 10-2. Most importantly, this approach may provide a facile and general method for the electrodeposition of materials with better performance for a wider array of application.3. A novel working electrode of PEDOT:PSS film was raised for the electrodeposition of Te, and a sandwich-like structured Te/PEDOT:PSS/Te composite film was formed. The structures and surface morphologies were systematically investigated. The composite films exhibited TE properties of a favourable low thermal conductivity (0.170-0.175 W/m/K) and a high electrical conductivity (503.5 S/cm), and their ZT value reached a maximum of 2.1 × 10-2.4. A flexible PEDOT:PSS/SWCNTs composite films were obtained by a rapid direct suction-filtration with common organic solvents. The pure PEDOT:PSS films shows maximum electrical conductivity of 1203.5 S/cm and the Seebeck coefficient of composite film reached 46.11 μV/K, respectively, and the maximum ZT value could be up to 0.16, about two orders of magnitude higher than the pure PEDOT:PSS. This study suggests that direct suction-filtration method might be a novel and effective way for improving the thermoelectric properties of PEDOT:PSS.