Ashkan Abtahi3 4 Yadong Zhang2 Xuyi Luo1 Jianguo Mei1 Seth Marder2 Kenneth Graham4

3, Physics and Astronomy, University of Kentucky, Lexington, Kentucky, United States
4, Chemistry, University of Kentucky, Lexington, Kentucky, United States
2, Chemistry, Georgia Institute of Technology, Atlanta, Georgia, United States
1, Chemistry, Purdue University, West Lafayette, Indiana, United States

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. In polymer based TE materials the polymer needs to be doped to become electrically conductive. 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, thus potentially allowing higher power factors to be reached. By blending two polymers, the total density of states (D.O.S.) will be manipulated, which may be used to alter the energy dependence of 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 pure polymers and the shape of the D.O.S. (i.e., the disorder and the energy offsets between the D.O.S. distributions of each polymer). Here, we modified a model introduced by Bässler and Arkhipov to theoretically probe how these two parameters impact thermoelectric performance. These calculations are then used to fit experimental data of various polymer blends with varying mobility ratios and D.O.S. distributions. We find that adding a polymer with a narrower D.O.S. and higher mobility with respect to host polymer can lead to an enhancement in the power factor.