Why accumulation mode organic electrochemical transistors turn off much faster than they turn on

TL;DR

This study investigates why accumulation mode organic electrochemical transistors (OECTs) turn off faster than they turn on, revealing the underlying physical and chemical factors affecting switching times through operando microscopy.

Contribution

It provides a detailed analysis of the kinetics behind OECT switching, highlighting the roles of device geometry, doping kinetics, and ion transport in the speed difference.

Findings

Turn-off occurs in one stage, while turn-on occurs in two stages.

Ion transport limits device operation speed.

Faster turn-off is due to physical and chemical factors.

Abstract

Understanding the factors underpinning device switching times is crucial for the implementation of organic electrochemical transistors (OECTs) in neuromorphic computing and real-time sensing applications. Existing models of device operation cannot explain the experimental observations that turn-off times are generally much faster than turn-on times in accumulation mode OECTs. Through operando optical microscopy, we image the local doping level of the transistor channel and show that device turn-on occurs in two stages, while turn-off occurs in one stage. We attribute the faster turn-off to a combination of engineering as well as physical and chemical factors including channel geometry, differences in doping and dedoping kinetics, and the physical phenomena of carrier density-dependent mobility. We show that ion transport is limiting the device operation speed in our model devices. Our study provides insights into the kinetics of OECTs and guidelines for engineering faster OECTs.