Multimodal operando characterization unravels polaron accumulation and ion dynamics in high-stability ambipolar OECTs

Achieving both high performance and stability in ambipolar organic electrochemical transistors (OECTs) remains challenging, largely due to limited understanding of how polymer structure and doping mechanisms interplay. Addressing this requires operando techniques that capture both structural and charge dynamics. In this study, we use a multimodal operando approach to investigating P-6O, a naphthalenediimide and dialkoxybithiazole copolymer with oligo(ethylene glycol) side chains. Operando electron paramagnetic resonance (EPR) and x-ray photoelectron spectroscopy (XPS), supported by density functional theory, reveal the formation of localized p- and n-polarons due to low backbone planarity, a characteristic often considered a design challenge for achieving robust transport and stability. However, P-6O-based OECTs exhibit pulsing stability. attenuated total reflection Fourier transform infrared and temperature-dependent EPR indicate strong polymer-electrolyte interactions, while operando XPS and grazing incidence wide-angle x-ray scattering reveal bidirectional ion motion that preserves film morphology. Collectively, these results underscore the critical role of ion dynamics in stabilizing OECTs, even in less planar polymers, and offer design guidelines for stable ambipolar transport.