Impact of Cation Species and Concentrations on the Performance of N-type Vertical OECTs

Abstract

Due to their exceptionally high performance and small footprint, vertical organic electrochemical transistors (vOECTs) have attracted significant attention for next-generation bioelectronics and biosensors. However, the influence of ionic species and concentrations in the electrolytes on vOECT performance, especially for cycling stabilities, remains unclear. This study systematically investigates the influence of alkali cation species and concentrations in aqueous chloride electrolytes on the performance of n-type Homo-gDPP-based vOECTs. By adopting electrolytes with different alkali metal cations (including Li+, Na+, K+, and Rb+) and concentrations (from ~0.01 to ~1000 mM), transfer and transient characteristics, along with cycling stability of vOECTs, are investigated. It is found that with higher electrolyte concentrations and cations with larger crystallographic radius, higher channel currents, larger transconductances, and shorter transient times are obtained. It is speculated that higher ionic concentration and larger crystallographic radius would lead to smaller solution resistance and reduced hydration shells, which then enhance ionic diffusion and improve transistor performance. However, the cycling stability of vOECT exhibits a trade-off with electrolyte concentration, where both excessively high and low concentrations result in inferior stability, which is suggested to be affected by enhanced side reactions and extensive swelling, respectively. This work demonstrates that the performance of vOECTs can be significantly influenced by both the concentration and type of cations, and offers valuable insights into OECT performance optimization by simply adjusting electrolyte contents.