Face-On Orientation Matches Vertical Organic Electrochemical Transistors for High Transconductance and Superior Non-Volatility

The recently developed vertical structure of organic electrochemical transistors (OECTs) can integrate volatile (sensing) and non-volatile (memory) functions into one reconfigurable device, making it highly promising. However, compared with the conventional planar OECT (c-OECT), the understanding of vertical OECT (v-OECT) working principles and device engineering strategies is still lacking, impeding rational optimization. Since a major difference between c- and v-OECTs is their charge transport directionality, which is highly influenced by crystallite orientations, the orientation–device structure match thus becomes an important yet outstanding topic for OECTs. Herein, using a newly synthesized n-type small molecule IDIC-MEG, we investigate how much impact such a match can have on OECT performance. The IDIC-MEG c-OECT fails to work due to the seriously hindered in-plane electron transport by face-on orientation. Surprisingly, simply changing the device structure from planar to vertical allows the resultant v-OECT to exhibit the highest reported transconductance (46.3 mS) among all small-molecule OECTs, thanks to the match between face-on orientation and the vertical structure. Such a match also leads to excellent non-volatility, including good conductance state retention, highly predictable programmability, and nice operational stability. This work, for the first time, explicitly demonstrates the significance of orientation–device structure match for OECT optimization. We envisage that this device engineering strategy may provide a new pathway to achieve high-performance, reconfigurable v-OECTs for homogenous in-memory sensing and computing systems, which entail volatile and non-volatile functions alike.