Improved Thermoelectric Behavior of Nanotube-Filled Polymer Composites with Poly(3,4-ethylenedioxythiophene) Poly(styrenesulfonate)

Abstract

The thermoelectric properties of carbon nanotube (CNT)-filled polymer composites can be enhanced by modifying junctions between CNTs using poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), yielding high electrical conductivities (up to approximately 40000 S/m) without significantly altering thermopower (or Seebeck coefficient). This is because PEDOT:PSS particles are decorated on the surface of CNTs, electrically connecting junctions between CNTs. On the other hand, thermal transport remains comparable to typical polymeric materials due to the dissimilar bonding and vibrational spectra between CNT and PEDOT:PSS. This behavior is very different from that of typical semiconductors whose thermoelectric properties are strongly correlated. The decoupled thermoelectric properties, which is ideal for developing better thermoelectric materials, are believed to be due to thermally disconnected and electrically connected contact junctions between CNTs. Carrier transport at the junction is found to be strongly dependent on the type and concentration of stabilizers. The crucial role of stabilizers was revealed by characterizing transport characteristics of composites synthesized by electrically conducting PEDOT:PSS and insulating gum Arabic (GA) with 1:1-1:4 weight ratios of CNT to stabilizers. The influence of composite synthesis temperature and CNT-type and concentration on thermoelectric properties has also been studied. Single-walled (SW) CNT-filled composites dried at room temperature followed by 80 degrees C exhibited the best thermoelectric performance in this study. The highest thermoelectric figure of merit (ZT) in this study is estimated to be approximately 0.02 at room temperature, which is at least one order of magnitude higher than most polymers and higher than that of bulk Si. Further studies with various polymers and nanoparticles with high thermoelectric performance may result in economical, lightweight, and efficient polymer thermoelectric materials.

Highly anisotropic P3HT films with enhanced thermoelectric performance via organic small molecule epitaxy

“…Previous studies on the TE properties of conducting polymers and their composites revealed that the use of template induction with inorganic nanoparticles (for example, carbon nanotubes, graphene, metal nanowires) increased the degree of ordering of polymer molecular arrangements and therefore improved σ and S, [11][12][13][14][15][16] but a clear explanation for the intrinsic effect of the molecular structure on electron transport is still lacking. The electron transport in a conducting polymer composite containing an inorganic dispersion phase is complex because multiple factors may influence the transport process in diverse ways.…”

Polyvinylidene fluoride (PVDF)/polyacrylonitrile (PAN)/carbon nanotube nanocomposites for energy storage and conversion

“…5 that the value of n was in the range from 0.48993 to 0.8752 for the samples prepared by solution cast method and in the range from 0.861 to 0.90475 for the samples prepared by the electrospinning method. These results reveal the semiconductor behaviors of the composites [44]. It is evident from the results that none of the MWCNTs composites displayed the ideal dielectric behavior exhibited by the pure PVDF/PAN; however, the samples ranged from pure dielectric to clear semiconductor behavior as the content of MWCNTs in the material decreased.…”

Correcting for contact geometry in Seebeck coefficient measurements of thin film devices

“…The results discussed in this paper prove that a detailed specification of the used device geometry is required when reporting the measurement of Seebeck coefficients in films. In for example the references [10,20,23,24] no or an unclear description is given of the tested device. It should be noted that the results shown in this paper are also relevant for devices with non-rectangular electrode geometry, such as finite-sized point contacts.…”

“…In literature different electrode geometries are encountered, e.g. long narrow electrodes [4,[19][20], roughly square electrodes [3], point-like contacts [9,14], and more complex structures [2,11]. One of the considerations when choosing the contact geometry is the conductivity of the studied material.…”

“…[2]. In other cases [3,4,10,[19][20][21], the electrodes are placed on top of or below a larger semiconducting film, enabling additional current flow outside the channel. When a linear temperature gradient is applied in a region that includes the electrodes, as for practical reasons is commonly done, this electrode layout possibly distorts the measured value of S: Fig.…”