P-Type Chemical Doping-Induced High Bipolar Electrical Conductivities in a Thermoelectric Donor–Acceptor Copolymer

Typically, conducting polymers transfer either electrons or holes. It is rare to see high bipolar (p- and n-type) electrical conductivities within a single bulk doped organic polymer without the assistant of gate voltage. Herein, we report that FeCl₃-doped solution-processable D–A copolymer poly (2,5-bis(2-octyldo decyl)-3,6-di(thiophen-2-yl)diketopyrrolo[3,4-c]pyrrole-1,4-dione-alt-thieno[3,2-b]thiophen) (DPPTTT) could exhibit a high p-type electrical conductivity of 130.6 S/cm and a good n-type electrical conductivity of 14.2 S/cm by engineering the doping level. Both p- and n-type electrical conductivities were superior to most solution-processable D–A copolymers, in cluding monopolar polymers. The high electrical conductivity resulted in high thermoelectric performance of DPPTTT in both p- and n-type, leading to a high current density of 3 A/cm² for a fully organic planar p–n junction created with only one material. Structural and spectroscopic tests were performed to provide a fundamental understanding of the polarity-switch mechanism. Our results open up an opportunity of making p- and n-type modules with a single conducting polymer for modern organic electronics in the future and might arouse research interest in exploring novel conducting polymers to enrich the knowledge of charge transport in organic materials.