Publication date: 15th December 2025
Already the drain current transients in organic electrochemical transistors hint for not yet fully understood underlaying device physics, as they show a generally slower turn on compared to turn off, with the difference between these on- and off-switching times varying over orders of magnitude between materials and driving voltages. Tracking the charge carrier concentration during switching then completes this asymmetric picture: A sharp doping front entering the device during turn on, followed by gradual bulk de-doping during turn off. We measure these concentration transients optically, using the red-shifted absorption in the doped state of the redox active polymers we investigated. Comparison of this data with drift-diffusion simulations revealed a strong dependence of this asymmetry on the broadness of the density of states, which in our simulations both modulates the carrier density dependence of hole mobilities and influences the maximum charge carrier concentration for a set gate voltage. Our simulation framework also allowed us to study the surprisingly small effect of ionic mobilities in the semiconductor on switching times, above a device specific mobility threshold. The results can be used to guide the rational design of improved devices.
T.K. acknowledges funding by the German Research Foundation (DFG) via Research Training Group GRK 2948/1. M.K. thanks the Carl Zeiss Foundation for financial support
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