  Organic electrochemical transistors (OECTs) serve as the foundation for a
wide range of emerging applications, from bioelectronic implants and smart
sensor systems to neuromorphic computing. Their ascent originates from a
distinctive switching mechanism based on the coupling of electronic and ionic
charge carriers, which gives rise to a multitude of unique characteristics.
Notably, various OECT systems have been reported with significant hysteresis in
their transfer curve. While being a feature sought after as non-volatile memory
in neuromorphic systems, no universal explanation has yet been given for its
physical origin, impeding its advanced implementation. Herein, we present a
thermodynamic framework that readily elucidates the emergence of bistable OECT
operation through the interplay of enthalpy and entropy. We validate our model
through three experimental approaches, covering temperature-resolved
characterizations, targeted material manipulation, and thermal imaging. In this
context, we demonstrate the exceptional scenario where the subthreshold swing
deviates from Boltzmann statistics, and we provide an alternate view on
existing data in literature, which further supports our model. Finally, we
leverage the bistability in form of a single-OECT Schmitt trigger, thus
compacting the complexity of a multi-component circuit into a single device.
These insights offer a revised understanding of OECT physics and promote their
application in non-conventional computing, where symmetry-breaking phenomena
are pivotal to unlock novel paradigms.
