Operando High-Resolution Swell Mapping for Mixed Ionic-Electronic Channel

Organic electrochemical transistors (OECTs) and related bioelectronics operate through ionic (de)doping of organic mixed ionic-electronic (semi)conductor (OMIEC) channels with concomitant swelling. However, operando swelling monitoring with high spatiotemporal resolution has remained a challenge owing to the inherent limitations of existing techniques. Here, we introduce an in-situ characterization platform for real-time swelling monitoring of OECT channels by incorporating a laser Doppler vibrometer with a customized testing module. This approach enables dynamic reconstruction of the swelling process with sub-nanometer and sub-microsecond spatiotemporal resolution, revealing apparent inhomogeneity in swelling magnitudes (4 nm ~ 400 nm) in different OMIECs and channel locations, along with distinct ionic (de)doping paths originating from vertical channel edge. Moreover, we identify the Coulomb force between vertically stacked source/drain electrodes as an effective factor for swelling suppression, which enables the demonstration of high-fidelity OECTs (> 15 million full switching cycles) and organic artificial neurons (> 15-day stable operation in 1×PBS). Our work provides a brand-new route for guiding OMIEC synthesis, elucidating underlying mechanisms, and advancing the design of robust (bio)electronic devices.