Fully Printed Ionic Diodes from Polymerizable Ionic Liquids.

Soft ionic diodes (SIDs) comprising p- and n-type polyelectrolytes are fundamental components of bioinspired iontronic devices. However, traditional ionic diode fabrication techniques require low-throughput, manual processes to interface electrodes and electrolytes and are typically limited to producing planar geometries. Moreover, hydrogels commonly used as SID electrolytes lose water over time, which leads to device instability and loss of performance. In this work, we present a method for fully 3D printing ionic diodes from solvent-free, polymerizable ionic liquids (pILs) that enables rapid and scalable manufacturing of SIDs. Four inks, including p- and n-type electrode and electrolyte inks, are used to print SIDs with 2D to 3D geometries and rectification ratios of up to 46. The geometry-, scan rate-, and time-dependent performance of SIDs are characterized via cyclic voltammetry and chronoamperometry. Leveraging the flexibility of 3D printing, we demonstrate current and voltage scaling relationships in multidiode arrays printed in parallel or series, respectively. We also highlight a dense multidiode crossbar array (≈100 SIDs/cm2) that can be quickly and uniquely achieved with our 3D printing approach. We anticipate the materials and methods reported in this work will enable opportunities for fabricating ionic diodes and multifunctional iontronic devices critical to advancing applications in bioelectronics, neuromorphics, and soft robotics.