Tunable Segmental Motion of PEDOT:PSS Films under Hydration and Ion Intercalation for Efficient Ionic–Electronic Transport

Organic mixed ionic–electronic conductors (OMIECs), which facilitate both electronic and ionic transport, are gaining increasing attention for their potential in emerging applications and for elucidating fundamental physical processes. Their mixed conduction is often limited by ion transport, which involves an interplay of polymer segmental dynamics and local free volume for ion hopping, both intrinsically linked to the glass transition of the amorphous fraction. Here, we developed an electrochemical cell integrated with the alternating current (ac) chip calorimeter to probe the glass transition behavior of poly(3,4-ethylene dioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) films in dry, hydrated, and electrochemically dedoped states. Our findings reveal that increased film heterogeneity with elongated structures exhibits enhanced segmental motion and a lower glass transition temperature (T_g) under both states. Upon swelling, samples with increased heterogeneity underwent less volumetric deformation and showed a smaller fraction increase in the disordered domain. This preserves electronic pathways while accelerating ion transport in hydration. Furthermore, during electrochemical reduction, the increased interfacial area between the electrolyte and elongated PEDOT-rich domains promotes segmental motion through soft confinement effects, resulting in more pronounced T_g reduction and improved dedoping kinetics. These results demonstrate that morphological optimization enables precise control of segmental motion and the amorphous domain fraction in the OMIECs, thereby simultaneously suppressing disorder upon swelling and enhancing ion transport during dedoping to synergistically optimize ionic–electronic mixed conduction.