Abstract
By directly converting heat into electricity, thermoelectric effects provide a unique physical process from heat waste to energy harvesting. Requiring the highest possible power factor defined as α2σ, with the thermopower α and the electrical conductivity σ, such a technology necessitates the best knowledge of transport phenomena in order to be able to control and optimize both α and σ. While conducting polymers have already demonstrated their great potentiality with enhanced thermoelectric performance, the full understanding of the transport mechanisms in these compounds is still lacking. Here we show that the thermoelectric properties of one of the most promising conducting polymer, the poly(3,4-ethylenedioxythiophene) doped with tosylate ions (PEDOT-Tos), follows actually a very generic behavior with a scaling relation as α ∝ σ−1/4. Whereas conventional transport theories have failed to explain such an exponent, we demonstrate that it is in fact a characteristic of massless pseudo-relativistic quasiparticles, namely Dirac fermions, scattered by unscreened ionized impurities.
Highlights
By directly converting heat into electricity, thermoelectric effects provide a unique physical process from heat waste to energy harvesting
The only sizable difference can be seen in the data of the highly oriented samples for which the electrical conductivity is typically enhanced from 2 or 3 orders of magnitude with respect to unoriented samples
The thermoelectric performance is usually quantified with the so called dimensionless figure of merit ZT = α2σT /κ, with the thermal conductivity κ. Another way to probe this efficiency is to consider the power factor, namely α2σ, or more usefully a thermal power factor α2σT which has the same unit than the thermal conductivity
Summary
By directly converting heat into electricity, thermoelectric effects provide a unique physical process from heat waste to energy harvesting. Whereas conventional transport theories have failed to explain such an exponent, we demonstrate that it is a characteristic of massless pseudorelativistic quasiparticles, namely Dirac fermions, scattered by unscreened ionized impurities The understanding of both electrical and thermal transport phenomena in the conducting polymers is a key issue in order to be able to control and to optimize their properties[1,2,3,4,5,6,7,8]. In an effort of clarifying the standard semi classical approach of transport phenomena including both electrical conductivity and thermopower, Kang and Snyder[2] have demonstrated that a scaling law could relate in the degenerate limit the aforementioned transport coefficients such as α ∝ σ−1/s They claimed that the exponent s = 3 gave a superior fit to s = 4 and they highlighted that it was consistent with electrons scattered by unscreened ionized impurities in the frame of a three dimensional (3D) band model.
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