Abstract
AbstractHighly oriented polymer films can show considerable anisotropy in the thermoelectric properties leading to power factors beyond those predicted by the widely obeyed power law linking the thermopower S and the electrical conductivity σ as S ∝ σ−1/4. This has led to encouraging practical results with respect to the electrical conductivity, notwithstanding that the conditions necessary to enhance σ and S simultaneously are less clear. Here, kinetic Monte Carlo simulations are used to study the impact of structural anisotropy on the thermoelectric properties of disordered organic semiconductors. It is found that stretching is a suitable strategy to improve the conductivity along the direction of strain, whereas the effect on the power factor depends on the morphology the polymer crystallizes. In general, crystalline polymers show a simultaneous increase in σ and S which is not the case for amorphous polymers. Moreover, it is shown that the trends resulting from simulations based on variable‐range hopping are in good agreement with experiments and can describe the different functional dependencies in the S versus σ behavior of different directions.
Highlights
Semiconducting organic materials have attracted increasing interest as thermoelectric (TE) converters in the recent years due to their potentially low fabrication costs and non-toxicity
With the help of kinetic Monte Carlo simulations we systematically investigated the impact of structural anisotropy in disordered organic semiconductors
By analyzing the impact of the parameters affecting the length scales and the structural order of such systems we examine under which conditions creating structural anisotropy by e.g. rubbing or drawing, is a suitable strategy to enhance the power factor of organic thermoelectric materials
Summary
Semiconducting organic materials have attracted increasing interest as thermoelectric (TE) converters in the recent years due to their potentially low fabrication costs and non-toxicity. Vijayakumar et al experimentally studied the anisotropy in the thermoelectric properties of highly oriented films based on PBTTT and P3HT, respectively.[4] Based on different functional dependencies of S(σ) in the different directions, the authors concluded that two different charge transport behaviors may govern the parallel and perpendicular directions.
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