Flexible nanogenerator with 3D-printed ferroelectrets

Flexible ferroelectret-polymer films are piezoelectric due to macro-dipoles that consist of charge layers with opposite polarity across deformable internal cavities and can thus be suitable for wearable energy-harvesting devices. 3D printing of ferroelectrets could increase the design variability of cavity structures, enhance performance and extend application possibilities. In this work, three polypropylene (PP) ferroelectrets with ellipsoidal cavities, but different in porosity and sample thickness were printed by means of Fused Filament Fabrication. After the samples had been polarized via a corona discharge, their piezoelectric performance was characterized by measuring short-circuit current (Isc) and open-circuit voltage (Voc) responses under the same cyclic compressive force. It was found that the PP ferroelectret with a porosity of 25% performed best with Isc of 0.65 μA and Voc of 65 V, and that the peak-to-peak output power decreases with decreasing porosity. A clear influence of sample thickness and cavity geometry was not observed. Our results provide design guidance for the future optimization of the porous structure of ferroelectrets and promote the development of energy harvesting devices for wearable electronics.