  Hysteresis in organic electrochemical transistors (OECT) is a basic effect in
which the measured current depends on the voltage sweep direction and velocity.
This phenomenon has an important impact on different aspects of the application
of OECT, such as the switching time and the synaptic properties for
neuromorphic applications. Here we address the combined ionic and electronic
kinetic effects that cause the dominant hysteresis effects. We use a
combination of tools consisting on basic analytical models, advanced 2D
drift-diffusion simulation, and the experimental measurement of a
Poly(3-hexylthiophene) (P3HT) OECT, working in an accumulation mode. We develop
a general transmission line model considering drift electronic transport and
ionic injection and diffusion from the electrolyte. We provide a basic
classification of the transient response to a voltage pulse, according to the
dominant ionic or electronic relaxation time, and the correspondent hysteresis
effects of the transfer curves according to the general categories of inductive
and capacitive hysteresis. These are basically related to the main control
phenomenon, either the vertical diffusion of ions during doping and dedoping,
or the equilibration of electronic current along the channel length.
