Brønsted Acid Doping with Soluble B(C ₆ F ₅ ) ₃ -H ₂ O Boosts Responsivity in PBTTT-C14/PCBM Phototransistors

The controlled doping of organic semiconductors is a promising strategy for optimizing the charge transport and optoelectronic performance in organic devices. Herein, we report a Brønsted acid doping method using the tris(pentafluorophenyl)borane–water complex [B(C6F5)3-H2O] to modulate the molecular ordering and charge dynamics of PBTTT-C14/PCBM heterojunctions. The air-exposed B(C6F5)3 (BCF) forms a stable Brønsted acid complex capable of protonating PBTTT-C14, leading to enhanced charge delocalization and reduced trap density. The optimized 2 wt % BCF-H2O-doped PBTTT-C14/PCBM film exhibited a carrier mobility of 6.89 × 10–2 cm2V–1s–1, a responsivity of 343.57 A/W, and a photocurrent-to-dark-current ratio of 2.3 × 105, representing nearly a 3-fold improvement over the pristine film. Spectroscopic analysis (11B NMR, EPR, and UV–vis-NIR) confirms successful doping, while transient absorption and GIXRD measurements reveal a prolonged exciton lifetime, enhanced crystallinity, and improved molecular orientation. This work provides a straightforward approach to high-performance phototransistors via Brønsted acid doping of conjugated polymers.