Understanding the factors underpinning device switching times is crucial for the implementation of organic electrochemical transistors in neuromorphic computing, bioelectronics 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 organic electrochemical transistors. Here, using operando optical microscopy, we image the local doping level of the transistor channel and show that turn-on occurs in two stages—propagation of a doping front, followed by uniform doping—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 phenomena of carrier-density-dependent mobility. We show that ion transport limits the operation speed in our devices. Our study provides insights into the kinetics of organic electrochemical transistors and guidelines for engineering faster organic electrochemical transistors.

了解影响器件开关时间的因素对于在神经形态计算、生物电子学和实时传感应用中实现有机电化学晶体管至关重要。现有的器件操作模型无法解释实验观察结果，即累积模式有机电化学晶体管的关闭时间通常比开启时间快得多。在这里，我们使用操作光学显微镜对晶体管沟道的局部掺杂水平进行成像，并显示导通发生在两个阶段——掺杂前沿的传播，随后是均匀掺杂——而关断发生在一个阶段。我们将更快的关断归因于工程以及物理和化学因素的组合，包括沟道几何形状、掺杂和去掺杂动力学的差异以及载流子密度依赖的迁移率现象。我们证明离子传输限制了我们设备的运行速度。我们的研究提供了对有机电化学晶体管动力学的见解，并为设计更快的有机电化学晶体管提供了指导。