Among the various categories of thermoelectric materials, significant attention has been devoted to polymer thermoelectric materials that particularly enjoy low thermal and high electrical conductivities while being solution processable and flexible. Case of study, poly(3, 4-ethylenedioxythiophene) –PEDOT as a conducting polymer has been shown to possess figure of merit (ZT) values as high as 0.42 and promises to rival their inorganic thermoelectric counterparts. Although PEDOT enjoys low thermal conductivities, the electrical conductivity spans a wide range from 10-8 to 103 Scm-1. The ability to increase the electrical conductivity without sacrificing the thermopower is imperative for promoting the use of PEDOT as a thermoelectric material. PEDOT –in particular has been shown to possess high thermopowers (≈100-500 μV K-1) due to electron-phonon scattering in the crystalline grains and electron-phonon coupling in the counter ion introduced to control its crystallinity and processability. On the other hand, the charge transport in PEDOT is typically dominated by phonon-assisted hopping between the metallic domains within the polymer chains which turns out to be a less effective charge transport mechanism than that observed in inorganic materials. Consequently, the electrical conductivity and thermopower are strongly affected by the morphology, composition, temperature, dopant levels, and orientation of this conducting polymer. Herein, we will discuss how the various effects mentioned above affect the thermoelectric properties of PEDOT. We will also present experimental details on an electrically detected magnetic resonance (EDMR) study of the spin dynamics in assembled devices comprised of PEDOT thin films having different counter ions and dopant levels. Finally, we will discuss how our findings can used to predict and understand the thermoelectric properties of other polymer semiconductors.

Manipulating the thermoelectric properties of polymer semiconductors

255th National Meeting (2018)

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