Circularly Polarized Light-Sensing Artificial Synapses Enabled by a Single p-type Polymer Channel in Organic Electrochemical Transistors

Artificial synapses are key building blocks of neuromorphic systems, integrating information processing and memory at the device level. Incorporating optical inputs further extends their functionality toward visual information processing. Circularly polarized light (CPL) carries handedness as an additional information dimension, yet exploiting it usually demands external optical systems. Here, we demonstrate CPL-sensing artificial synapses built on organic electrochemical transistors (OECTs) that employ a single p-type semiconducting polymer as the active layer. A chiral templating strategy imparts intrinsic chirality to the film, allowing the channel itself to discriminate left- and right-handed CPL without external optics. However, how such a chiral-templated structure responds when subjected to electrochemical reactions has remained largely unexplored. Through morphological analysis and in-operando circular dichroism, we show that the chiral structure is preserved under moderate doping but irreversibly collapses upon over-oxidation. By tracking the interplay between the chiral structure and ion kinetics within the OECT, we identify the operating conditions under which an intrinsically chiral channel enables stable CPL detection. Under left-/right-handed CPL illumination, the devices generate polarization-dependent photocurrents driven by asymmetric light-matter interactions coupled to ion-driven doping. These responses translate into synaptic behaviors, including paired-pulse facilitation, light-intensity- and gate-voltage-dependent potentiation, and persistent (memory) photocurrents, where identical stimuli of opposite handedness yield distinct postsynaptic currents. Polarization-encoded visual information can thus be sensed, processed, and stored within a single device, offering a route to neuromorphic visual systems with enhanced information density.