Molecular Understanding of Thermo-Electric Properties in Organic Polymers

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Any energy transformation from primary sources is accompanied by heat losses. An efficient and environmental friendly way to reutilize the waste heat is thermoelectrics. Thermoelectricity converts temperature differences and thus heat into electricity. As a material property it is determined by the electrical (s) and thermal (k) conductivity and the Seebeck coefficient (a). The thermoelectric efficiency can be quantified with the figure-of-merit zT = (sa^2/k)T. Optimal thermoelectric materials posses a zT of about 1 (at or below 250°C). Emerging candidates for low cost, environmental friendly, solution-processable and flexible thermoelectric modules, are pi-conjugated, semiconducting polymers. However, they exhibit low electrical conductivity, leading to very low zT of 10^-5 (at room temperature). Doping can increase the electrical conductivity up to metallic-like values, but lower the Seebeck coefficient. An optimum balance can be achieved by reducing the dopants volume and controlling the oxidation state of the polymer, leading to zT~1. Despite this recent progress, there is still no fundamental understanding of the effects induced by different dopants that determine the supramolecular polymer-dopant structures, as well as charge and the heat transfer properties.This project is aimed at the molecular understanding of thermal and electrical properties of polymer-dopant blends, using multiscale atomistic simulations. The following properties will be modelled for state-of-the-art p- and n-type organic thermoelectrics: 1) structure, 2) spectroscopic properties, 3) charge transport regimes, 4) electrical conductivity, 5) Seebeck coefficient and 6) thermal conductivity to address the interplay between dopants and semiconducting polymer chains. The ultimate goal is to understand the structure-function relationships that rule thermoelectric phenomena, from the molecular up to the microscopic scale, in polymer semiconductors materials. This project will be the first systematic molecular driven investigation, combining atomistic simulations with charge and thermal transport theories in (semi)conducting polymers and complex polymer-dopant blends. It will also pave the way toward a physical-chemical understanding of emerging technologies such as organic spintronics and organic batteries.