BCF Doping Effect Amplified via Elastomer Blending: Microstructure Modulation for Achieving Excellent Mobility and Stretchability in Brittle Conjugated Polymer-Based Transistors

The application of conjugated polymers (CPs) with high charge carrier mobility in stretchable electronics is often limited by their inherent brittleness. To overcome this trade-off, we propose a synergistic toughening strategy for the brittle polymer poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b′]dithiophen-2-yl)-alt-[1,2,5]thia-diazolo [3,4-c] pyridine] (PCDTPT) by combining elastomer blending with polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) and doping with Lewis acid tris(pentafluorophenyl)borane (BCF). Blending with SEBS induces phase separation and reduces PCDTPT crystallinity, resulting in an optimized microstructure that promotes the dispersion of BCF in the PCDTPT. This microstructure enables high doping efficiency with BCF while retaining the favorable charge transport properties and effective stress dissipation capability imparted by elastomer blending. BCF doping enhances the π–π stacking order, coherence length, and crystallinity while reducing both the contact resistance and glass transition temperature, thereby collectively improving the carrier mobility and crack onset strain (COS). The synergy between the two methods yields effects beyond simple summation. Specifically, SEBS blending creates an optimized microstructure of PCDTPT that amplifies the BCF doping efficiency, while BCF-induced plasticization strengthens the COS enhancement of PCDTPT from SEBS. As a result, the ternary PCDTPT/SEBS-BCF films achieve outstanding performance, with one reaching a mobility of 2.60 ± 0.06 cm2 V–1 s–1 at a COS of 133 ± 13% and another attaining a COS of 176 ± 19% with a mobility of 2.35 ± 0.08 cm2 V–1 s–1. These values rank among the best-performing stretchable CP films and represent one of the highest performances reported for stretchable organic field-effect transistors (OFETs) based on intrinsically brittle CPs (original COS < 10%). Furthermore, these PCDTPT/SEBS-BCF films retain excellent stability of the carrier mobility under strain owing to the well-preserved crystalline structures and robust charge transport pathways enabled by the combined effects of elastomer blending and BCF doping. This study provides novel insights and methodologies for toughening CPs, successfully establishing a viable approach to apply brittle CPs in high-performance stretchable semiconductors that overcome conventional limitations, opening new avenues for material selection in advanced stretchable electronic devices.