Solvent-controlled crystalline beta-phase formation in electrospun P(VDF-TrFE) fibers for enhanced piezoelectric energy harvesting

Electrospun piezoelectric polymer fibers, which offer mechanical flexibility, light weight, and relatively low temperature processing, have emerged as a strong solution to shape-adaptive energy harvesting and sensing applications for smart electronics at multi-scales. In this work, we aim to enhance the electrospun fiber-based piezoelectric energy harvesting performance by elucidating the role of the solvent in crystallization kinetics and fiber formation during electrospinning as well as its influence on harvesting performance. Two key solvent characteristics, surface tension and evaporation rate, are found to play a role in determining uniform fiber formation with controllable diameters, degree of crystallization, and electroactive β-phase content, which are primarily responsible for the piezoelectric performance of the electrospun poly(vinylidene fluoride-trifluroethylene) P(VDF-TrFE). A substantial difference in the piezoelectric output performance is clearly observed depending on the choice of solvent. Indeed, N,N-dimethylformamide with a low evaporation rate enables piezoelectric output voltage generation of a thermally annealed P(VDF-TrFE) fiber-based device up to 139.5 V, while the device with as-spun fibers in the other solvent case, methyl ethyl ketone, yields a much lower voltage of 75.3 V. This study demonstrates that the tailoring capability of the solvent should be carefully considered together with other processing and operating conditions (e.g., thermal annealing, bending frequency, and electrical resistances) in order to realize enhanced piezoelectric energy harvesting performance of electrospun fibers for versatile potential applications.