Origin of high piezoelectricity in carbon nanotube/halide nanocrystal/P(VDF-TrFE) composite nanofibers designed for bending-energy harvesters and pressure sensors

Diverse nanostructures have been applied in piezoelectric energy harvesters for efficient energy conversion. Here, nanofiber composites composed of two fillers of inorganic perovskite halide CsPbBr3 nanocrystals and carbon nanotubes (CNTs) in a matrix of poly(vinylidene fluoride–trifluoroethylene) (P(VDF-TrFE)) were investigated to explore high-performance bending-driven power-generation and physiological current-sensing. An optimized harvester with 5 wt% CsPbBr3 and 0.3 wt% CNTs demonstrated impressive peak outcomes of ~15.9 V and ~1128 nA as a result of periodic bending at a bending strain of 1.19% and a bending frequency of 2.5 Hz, which are ~17.6 and ~10.5 times better than the results achieved for the P(VDF-TrFE) nanofiber harvester. As the origin of the substantial enhancements, extra dipolar polarization by embedded CsPbBr3 nanocrystals and space-charge polarization by dispersed CNTs contacting with the polymer matrix were assumed to be responsible for the high electromechanical coupling under the bending motion. The optimized composite structure was also successfully applied as wearable pressure sensors to convert various mechanical inputs exerted by physiological motions into electrical signals with competitive sensing characteristics.