An n‐type Polymer with High‐Performance Thermoelectric Properties by Solvent‐Mediated Oxidation

Abstract Organic thermoelectric (OTE) materials are interesting because they can have the merits of high mechanical flexibility, lightweight, and low or no toxicity over inorganic thermoelectric (TE) materials. Both p ‐ and n ‐type OTE materials are required for efficient TE conversion. But the performance of n ‐type OTE materials lags well behind their p ‐type counterparts. Herein, the great enhancement in the TE properties of poly(benzodifurandione) (PBFDO) films through a treatment with a solution of FeCl ₃ with dimethyl sulfoxide (DMSO) as the solvent is reported. This can greatly enhance the Seebeck coefficient and thus the power factor of PBFDO. The optimal power factor is 306.1 ± 8.7 µW m ⁻¹ K ⁻² , and the corresponding electrical conductivity and Seebeck coefficient are 970 ± 26 S cm ⁻¹ and −56.2 ± 1.6 µV K ⁻¹ , respectively. This is the highest power factor for n ‐type OTEs. The corresponding ZT value is 0.27 ± 0.01 at room temperature. The TE properties depend on the solvent of the FeCl ₃ solution. A solvent with a high donor number, like DMSO, can share its electrons with PBFDO. It can hinder the dedoping of PBFDO by Fe ³⁺ and thus greatly enhance the Seebeck coefficient while not lowering the electrical conductivity too much.