Elucidating the Piezoelectric, Ferroelectric, and Dielectric Performance of Lead-Free KNN/PVDF and Its Copolymer-Based Flexible Composite Films

Ecofriendly, reliable, and high-performance piezoelectric materials are drawing huge interest in resolving the environmental problems arising due to consumption of fossil fuel energy. Among the lead-free ferroelectrics, potassium sodium niobate (KNN, (K,Na)NbO 3 ) is one of the most promising piezoelectric ceramics that can replace Pb(Zr,Ti)O 3 . In the present work, the piezoelectric performance of KNN incorporated in poly(vinylidene fluoride) (PVDF) and its copolymers, polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) and poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), has been compared. The films were fabricated by a solution casting method and were further polarized by a corona poling technique. The results confirmed that the nanocomposite film with 8 wt % KNN filler in PVDF-TrFE (PTK8) exhibited the highest F (β) value, maximum remnant polarization, and dielectric constant value than other nanocomposites. The relative β-phase contents in PTK8, PHK8, and PK8 composite films reached 85, 76, and 75.8%, respectively, indicating that KNN acts as the most suitable nucleating agent in PVDF-TrFE. Also, the piezoelectric voltage output of the PTK8-based nanogenerator was found to be remarkably higher (∼20 V) as compared to other nanocomposite-based piezoelectric nanogenerators. It also exhibited a maximum power density of 0.54 μW/cm 2 that was significantly improved in comparison to other composites. This nanogenerator was found to be a promising power generation device promoting miniaturization of self-powered systems.