Fused Bithiophene Imide Oligomer and Diketopyrrolopyrrole Copolymers for n‐Type Thin‐Film Transistors

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Diketopyrrolopyrrole (DPP)‐based copolymers have received considerable attention as promising semiconducting materials for high‐performance organic thin‐film transistors (OTFTs). However, these polymers typically exhibit p‐type or ambipolar charge‐transporting characteristics in OTFTs due to their high‐lying highest occupied molecular orbital (HOMO) energy levels. In this work, a new series of DPP‐based n‐type polymers have been developed by incorporating fused bithiophene imide oligomers (BTIn) into DPP polymers. The resulting copolymers BTIn‐DPP show narrow band gaps as low as 1.27 eV and gradually down‐shifted frontier molecular orbital energy levels upon the increment of imide group number. Benefiting from the coplanar backbone conformation, well‐delocalized π‐system, and favorable polymer chain packing, the optimal polymer in the series shows promising n‐type charge transport with an electron mobility up to 0.48 cm2 V−1 s−1 in OTFTs, which is among the highest values for the DPP‐based n‐type polymers reported to date. The results demonstrate that incorporating fused bithiophene imide oligomers into polymers can serve as a promising strategy for constructing high‐performance n‐type polymeric semiconductors.