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.