Preparation And Thermoelectric Properties Of Composites Based On Polythiophene Derivatives With Donor-Acceptor Structure Or Low Bandgap

As a possible means of energy conversion between heat and electricity without moving mechanical components or hazardous working fluids, thermoelectric(TE) materials have attracted a significant amount of attention. Organic or polymer TE materials exhibit special inherent advantages, such as a potentially low cost because of the abundance of carbon resources, an overall simple synthesis, simple processing into versatile forms and low thermal conductivity. Owing to these advantages, more and more attention has recently been focused on polymer TE materials.In this paper, a series of polythiophene derivatives, such as poly-Schiff base(PSB) with donor-acceptor(D-A) structue containing thiophene units, low-bandgap poly(3,4-ethylenedioxythiophene methine)s with different side groups, were synthesized for use as thermoelectric materials. All these synthesized polymers were blended with corresponding inorganic fillers to prepare polymer-inorganic composites. The effects of polymer structures(ig.D-A structure, different side group) on TE performances of the polymer-based composites were investigated. The main contents of this paper are summarized below.1) PSB with a D-A structure containing thiophene units(PSB(A)) was synthesized and was blended with different fillers to prepare polymer-inorganic TE composites. For comparison, PSB with the common structure(PSB(B)) was also synthesized, and PSB(B)-graphite(G) composites were fabricated. The PSB(A)/G composites exhibited a higher power factor of 10.2 μWm-1K-2 compared with that of 4.5 μWm-1K-2 for the PSB(B)/G composites at the same doping level. The results show that the excellent TE materials could be produced by preparing polymer-inorganic TE composites using novel conducting polymers with a special structure(e.g., donor-acceptor structure) and conducting fillers. The effects of different fillers on the TE properties of the PSB(A)-based composites were investigated in detail, and the highest TE figure of merit, ZT=2.53×10-3, was obtained(PSB(A)/80%G).2) A series of low-bandgap poly(3,4-ethylenedioxythiophene methine)s(PEDOT-M) with different side groups were synthesized for use as thermoelectric materials. The structure of PEDOT-M were evidenced by 1H-NMR and FTIR. The Seebeck coeffcients and bandgap of PEDOT-M were obtained by corresponding method. The PEDOT-M with strongly electron-withdrawing and electron-donating groups exhibited the highest Seebeck coefficients and the lowest bandgaps.3)(PEDOT-M)-related composites were prepared via solution mixing followed by mechanical ball milling and cold pressing and these composites were characterized by SEM, TGA, FTIR, XRD, Raman. The effects of different side groups(donor and acceptor side groups) on the TE properties of PEDOT-M/multi-walled carbon nanotubes(MWNT) and PEDOT-M/G ccomposites were studied. The highest ZT value at 120 °C for PEDOT-M/G composite that contained 80 wt% G was 6.75×10-3. The highest ZT value at 120 °C for PEDOT-M/MWNT composite containing 80 wt% MWNT was 9.5×10-4.