Here, we report the use of two high-spin pro-quinoid benzo[1,2-c;4,5-c′]bisthiadiazole (BBT) polymers for high-performance solution-processable polymer thermoelectrics. Sequential solution-phase doping using FeCl3 as p-dopant results in very high electrical conductivities of over 300 S cm–1, even though these BBT polymers take on face-on orientation. By optimizing the level of doping, we achieved the best thermoelectric performance with an average electrical conductivity of 232.7 ± 23.7 S cm–1, Seebeck coefficient of 49.4 ± 3.6 μV K–1, and power factor of 56.5 ± 4.3 μW m–1 K–2. The importance of polaron/bipolarons delocalization and triplet bipolarons to achieve high electrical conductivity and Seebeck coefficient simultaneously is rationalized.
We thank Ms. Jozel Tan and Dr. Martin Van Meurs from ICES and A*STAR for their help in the high-temperature GPC measurements. J.X. would like to acknowledge the A*STAR, SERC Thermoelectric Materials Program (Grants 1527200019 and 1527200021).