Full and In Situ Printing of Nanogenerators that Are Based on an Inherently Viscous Piezoelectric Polymer: An Effort to Minimize “Coffee Ring Effect” and Nonprinting Operations

Abstract

Among various printing technologies for fabrication of electronic devices, microplotter printing and inkjet printing provide the best printing resolution. For inkjet printing, which is compatible with only low-viscosity inks, the "coffee ring effect" and time-/labor-consuming nonprinting operations are among the most that impose challenges to its applications for rapid and large-scale fabrication of electronic devices. When printing a flexible electronic device that tends to bend spontaneously, relocating an unfinished/undried workpiece for postprinting treatments usually causes ink diffusion, resulting in deteriorated printing resolution, nonuniformity, and defects. Taking the printing of a poly(vinylidene fluoride)-(PVDF-) based flexible nanogenerator as an example, this work utilized a high-viscosity compatible microplotter printer and a concentrated/viscous PVDF ink (which minimized the "coffee ring effect)" and an in situ fabrication process (which not only maximally facilitated and minimized the nonprinting operations but also avoided the deterioration of the printing resolution and the nonuniformity/defects). A morphological comparison investigation showed that a PVDF patch printed (for only two passes with a concentrated 7 wt % PVDF ink) with a microplotter was morphologically homogeneous with no observable defects, while a PVDF patch printed (for 80 passes with a diluted 0.5 wt % PVDF ink) with a typical inkjet printer exhibited conspicuous nonuniformity and defects like grooves, pits, and cracks. Performance characterization of such a nanogenerator showed that it generated negative− positive twin pulses of short-circuit current during its cyclic bending and unbending, with a short-circuit current density magnitude up to ∼0.4 μA/cm 2 . A flexible carbon nanotube-based chemiresistive gas sensor was also fully printed in situ, in order to demonstrate that the in situ printing method utilized in this work is also compatible with fine features and low-viscosity inks.