Thermoelectric Performance of an Open-Shell Donor-Acceptor Conjugated Polymer Doped with a Radical-Containing Small Molecule

Thermoelectric devices based on conducting polymers are promising energy conversion systems; however, the intrinsic semiconducting nature inherent to the macromolecular architecture of common conjugated polymers (CPs) in their neutral form requires doping to impart electrical conductivity and requires optimization of the complex dopant-polymer interactions in order to enhance thermoelectric performance. Therefore, designing and synthesizing CPs that have readily tunable properties and that can be doped in a facile manner using stable and noncorrosive dopants is a significant opportunity in the field. Here, we report the expedient synthesis of a donor-acceptor CP based on an alternating cyclopentadithiophene and thiadiazoloquinoxaline framework that exhibits a narrow band gap, an open-shell electronic ground state, intrinsic electrical conductivity (sigma similar to 10(-3) S cm(-1)), and a large Seebeck coefficient (S > 1000 mu V K-1) in the absence of dopants. The addition of a tailored open-shell dopant significantly increases sigma and allows for the systematic manipulation of the thermoelectric properties, resulting in an optimized power factor of >10 mu W m(-1) K-2, one of the largest values reported for nontraditional CP thermoelectric systems. This combination of a next-generation, radical-containing macromolecule with an open-shell small molecule dopant opens a new pathway by which to control charge transport and enable improved behavior in next-generation polymer thermoelectric systems.