Fabrication of Vertical Organic Electrochemical Transistor from n-Type Ion Gel Based on Benzodifurandione-Based Oligo(p-phenylene vinylene)s

Organic electrochemical transistors (OECTs) using aqueous gate dielectrics have garnered significant interest for bioelectronic applications, but their viability for long-term use in neuromorphic computing and synaptic devices is limited due to their short-term functionality. To address this issue, two benzodifurandione-based oligo (p-phenylene vinylene) polymers, BDOPV-TCNVT and ClBDOPV-TCNVT, were synthesized and their properties were investigated in quasi-solid-state ion gel-gated vertical OECTs (v-OECTs). Compared to BDOPV-TCNVT, the chlorinated ClBDOPV-TCNVT demonstrated lower frontier molecular orbitals and easier electrochemical doping.<br/>The as-spun ClBDOPV-TCNVT exhibited a higher volumetric capacitance (1.94 F cm−3) than as-spun BDOPV-TCNVT (1.49 F cm−3), primarily due to easier ion infiltration resulting from its lower crystallinity and mixed chain orientation. The quasi-solid-state v-OECTs based on both polymers (as-spun) showed transconductance (gm) values of 0.06–0.08 mS. However, following thermal treatments, the gm gradually decreased for both polymers due to enhanced edge-on ordering and tighter interchain packing, which hindered ion penetration. Despite the challenges with electrochemical doping by quasi-solid-state ion gel-gated dielectrics, the enlarged area and decreased channel length in v-OECTs enhanced gm compared to parallel OECTs. This suggests that v-OECTs, with their larger channel area and shorter channel length, can improve transconductance. Additionally, it was found that thermal treatments improved electron mobility in organic field-effect transistors (OFETs) due to enhanced molecular packing, but this packing hindered ion penetration in v-OECTs. The importance of tailored material designs for optimizing v-OECTs, focusing on achieving efficient vertical charge transport and ion infiltration is noticeable. This could address the current limitations and expand the applications of OECTs in bioelectronics and neuromorphic computing.