Cyano‐Functionalized Fused Bithiophene Imide Dimer‐Based n‐Type Polymers for High‐Performance Organic Thermoelectrics

Abstract Doped n‐type polymers usually exhibit low electrical conductivities and thermoelectric power factors (PFs), restricting the development of high‐performance p–n‐junction‐based organic thermoelectrics (OTEs). Herein, the design and synthesis of a new cyano‐functionalized fused bithiophene imide dimer (f‐BTI2), CNI2, is reported, which synergistically combines the advantages of both cyano and imide functionalities, thus leading to substantially higher electron deficiency than the parent f‐BTI2. On the basis of this novel building block, a series of n‐type donor–acceptor and acceptor–acceptor polymers are successfully synthesized, all of which show good solubility, deep‐lying frontier molecular orbital levels, and favorable polymer chain orientation. Among them, the acceptor–acceptor polymer PCNI2‐BTI delivers an excellent electrical conductivity up to 150.2 S cm −1 and a highest PF of 110.3 µW m −1 K −2 in n‐type OTEs, attributed to the optimized polymer electronic properties and film morphology with improved molecular packing and higher crystallinity assisted by solution‐shearing technology. The PF value is the record of n‐type polymers for OTEs to date. This work demonstrates a facile approach to designing high‐performance n‐type polymers and fabricating high‐quality films for OTE applications.