Influence of the Mobility Ratio and Density of States Width on the Thermoelectric Properties of Polymer Blends

Conjugated polymers can be used in mechanically flexible and low cost thermoelectric (TE) devices, but their thermoelectric performance must be improved to make them commercially viable. The performance of thermoelectric materials depends on the electrical conductivity, Seebeck coefficient and thermal conductivity. The higher the doping concentration, the more electrically conductive the material becomes, but generally at the cost of a decrease in the Seebeck coefficient. Blending of π-conjugated polymers has been proposed as a method to minimize the tradeoff between electrical conductivity and the Seebeck coefficient. By blending two polymers, the total density of states (D.O.S.) will be manipulated, which may be used to alter the charge transport in the TE material. The major parameters that we expect to impact the power factor in polymer blends are the mobility ratios between the two polymers and the shape of D.O.S. Here, we use a model introduced by Bässler and Arkhipov to theoretically probe how these two parameters impact the thermoelectric performance. We find that a narrower D.O.S. and lower mobility of the added polymer with respect to host polymer can lead to an enhancement in the Power factor of the TE material.