The development of unipolar n-type semiconducting polymers with electron mobility (µe ) over 5 cm2 V-1 s-1 remains a massive challenge in organic semiconductors. Diketopyrrolopyrrole (DPP) has proven to be a successful unit for high-performance p-type and ambipolar polymers. However, DPP's moderate electron-accepting capability leads to the shallow frontier molecular orbital (FMO) levels of the resultant polymers and hence limit the µe in unipolar n-type organic transistors. Herein, this issue has been addressed by using a hybrid acceptor-modulation strategy based on DPP-containing "fluorinated triple-acceptor architecture", namely DPP-difluorobenzothiadiazole-DPP (DFB). Compared with DFB's non-fluorinated counterpart, DFB features deeper FMO levels and a shape-persistent framework. Therefore, a series of DFB-based polymers demonstrate planar backbones and lowered FMO levels by ≈0.10 to 0.25 eV versus that of the control polymer. Intriguingly, all DFB-polymers exhibit excellent unipolar n-type transistor performances. Notably, a full-locked backbone conformation and high crystallinity with crystalline coherence length of 524 Å are observed for pDFB-TF, accounting for its high µe of 5.04 cm2 V-1 s-1 , which is the highest µe value for DPP-based unipolar n-type polymers reported to date. This work demonstrates that the strategy of "fluorinated triple-acceptor architecture" opens a new path towards high-performance unipolar n-type semiconducting polymers.
Keywords: acceptor-modulation strategy; diketopyrrolopyrrole; fluorination; n-type semiconducting polymers; triple-acceptor architecture.
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