High-Performance Stretchable Field-Effect Transistors Based on Intrinsically Flexible n-Type Partially Conjugated...

Two intrinsically flexible conjugated polymers, PBT-90 and PFBT-90, were designed and synthesized via aldol polycondensation. Both polymers incorporate a novel double-flexible-node unit, 5,5'-bis(1,1,2,2-tetrafluoro-2-(thiophen-2-yl)ethyl)-2,2'-bithiophene, which can reduce brittleness and enhance recoverability in both bulk polymers and processed films. Both polymers displayed n-type charge transport in transistors fabricated on a polyethylene terephthalate substrate, achieving high electron mobilities (µ_e) of 3.85 and 4.56 cm² V^-1 s^-1 for PBT-90 and PFBT-90, respectively, only slightly inferior to 5.44 and 6.37 cm² V^-1 s^-1 of their fully conjugated analogues, PBT-100 and PFBT-100. Utilizing a self-developed PET/CYTOP/AlO_x three-layer thin film transfer process, combined with orthogonal solvent design and interlayer protection strategies, we fabricated high-performance stretchable transistors. The PFBT-90-based devices exhibited a record-high µ_e of 3.51 cm² V^-1 s^-1 in the pristine state. Under 100% strain, they retained a µ_e > 2.86 cm² V^-1 s^-1 (>80% retention). The remarkable device performance originates from its suitable frontier molecular orbitals structure, low backbone glass transition temperature, and well-balanced finitely conjugated backbone, where rigid conjugated segments ensure highly efficient charge carrier transport and flexible nonconjugated segments dissipate stress. Our findings offer a pivotal molecular design strategy and a versatile fabrication process for advanced stretchable organic electronics.