Damage-Free Passivation of Ambipolar OECTs with Fluoropolymer Film for Enhanced Performance and Stability Toward Reliable Biosignal Processing.

Organic electrochemical transistor (OECT) is a promising building block for bioelectronic and neuromorphic applications due to its high transconductance and low-voltage operation. However, microstructural instability and irreversible electrochemical degradation of the organic mixed ionic-electronic conductors (OMIECs) are still challenging to achieve high performance of OECTs. Here, we present an ambipolar vertical OECT in which a fluorinated passivation layer is deposited on the OMIEC surface directly by solvent-free initiated chemical vapor deposition (iCVD) method without damaging the channel layer. Vapor-phase infiltration of the fluoropolymer layer followed by thermal annealing induces controlled nanoscale phase separation in the OMIEC layer, enabling efficient ion doping in both p-type and n-type modes. Consequently, fluoropolymer-passivated ambipolar vertical OECTs (FPA-vOECTs) exhibit higher transconductance, far enhanced transient response, and longer operational stability. In particular, the transconductance-a key figure of merit-increased from 12.7 to 73.7 mS in p-type and from 4.1 to 21.4 mS in n-type operation. Leveraging the enhanced performance of the ambipolar vertical OECTs, we also demonstrate, for the first time, a single-channel bipolar event-driven spiking encoder for neuromorphic bioelectronics, enabling electrocardiogram signal encoding and spiking neural network-based arrhythmia classification with 90.5% accuracy.