Experimental and First-Principles Investigation of PDA@KNN/P(VDF-TrFE) Composite Films: Interfacial Effects and Piezoelectric Enhancement

Flexible piezoelectric sensors with high output and long-term stability are critically limited by low polar phase content and inefficient interfacial electromechanical coupling in polymer-based systems. Here, we report a high-performance flexible piezoelectric sensor based on a PDA-engineered PDA@KNN/P(VDF-TrFE) electrospun composite, achieving simultaneous enhancement of β-phase crystallinity, interfacial stress transfer, and piezoelectric output. Owing to the bioinspired PDA interfacial layer and electrospinning-induced chain alignment, the optimized composite exhibits an ultrahigh β-phase fraction of 85.5%, significantly higher than pristine P(VDF-TrFE) (∼51%). The piezoelectric sensor delivers a high output voltage of 30 V, an ultrasensitive pressure response of 0.48 V·kPa–1, and excellent durability with <3% signal degradation over 3000 loading cycles, outperforming most reported PVDF-based piezoelectric sensors. First-principles density functional theory (DFT) calculations reveal that PDA-mediated interfacial coupling significantly lowers the interfacial formation energy (−3.27 eV), induces directional charge transfer, and reduces the work function, thereby enhancing interfacial polarization and electromechanical response. Furthermore, the sensor is successfully integrated into a self-powered smart wrist pressure monitoring system, enabling real-time detection of mechanical stimuli during fitness training. This work demonstrates a performance-driven interfacial engineering strategy for high-output, durable, and lead-free flexible piezoelectric sensors, with strong potential for wearable electronics and self-powered sensing applications.