Donor-Unit Engineering of Tetrafluorophenylene-Bridged Diketopyrrolopyrrole Polymers Synergistically Optimizes Intermolecular Coupling and Packing Coherence for Flexible Transistors

Abstract

Conjugated polymer semiconductors have achieved remarkable progress in flexible organic field-effect transistors (OFETs). However, simultaneously optimizing intermolecular electronic coupling and long-range aggregation coherence remains a key challenge. Mobility enhancement is often attributed mainly to reduced π–π stacking distance, whereas the synergistic roles of backbone polarization and stacking coherence length remain insufficiently understood. Here, we report a diketopyrrolopyrrole (DPP)-based molecular engineering strategy by modulating the donor unit within a tetrafluorophenylene-bridged DPP (DTB) backbone. This design enables systematic regulation of electronic delocalization and solid-state aggregation while preserving a highly planar conjugated backbone. Among the three polymers, pDTB-CNTVT exhibits more pronounced backbone polarization and stronger intermolecular electronic coupling. Microstructural characterization further reveals that pDTB-CNTVT forms a more ordered solid-state packing structure with a smoother film morphology and a markedly extended π–π stacking coherence length, despite possessing the largest π–π stacking distance. Flexible top-gate/bottom-contact (TG/BC) OFETs fabricated on polyethylene naphthalate (PEN) substrates deliver a maximum hole mobility of 0.72 cm2 V–1 s–1 for pDTB-CNTVT in air. Our work reveals that synergistic tuning of electron delocalization and mesoscale aggregate coherence, rather than simple spatial packing, is critical to developing high-performance polymer semiconductors.