Side-Chain Grafting Frequency Controls Trap Formation and Polaron Mobility in Organic Mixed Conductors

Organic mixed ionic–electronic conductors (OMIECs) are π-conjugated polymer–electrolyte composites that support coupled ionic and electronic transport, making them candidates for bioelectronics, electrochemical sensors, and energy storage devices. Despite growing interest in these materials, the joint influence of electrolyte composition and polymer side-chain design on OMIEC morphology and charge transport remains poorly understood, owing to the small number of material systems that have been experimentally or computationally characterized. Here, coarse-grained molecular dynamics (CG-MD) and kinetic Monte Carlo (kMC) simulations are used to systematically vary anion size (1–3 Å) and polymer side-chain design (polarity and grafting frequency) across nine OMIEC configurations. The simulations reveal that side-chain frequency is the dominant design lever for polaron mobility, with half-frequency intermediate polar side chains achieving approximately 40% higher mobility than full-frequency configurations owing to a significant reduction in trap-site formation. Smaller anions percolate more readily near polymer side chains, with 1 Å anions achieving roughly 25–50% higher local concentration than 3 Å anions across the studied systems, but this enhanced percolation does not translate into significant differences in backbone organization or mobility. Reduced side-chain frequency also promotes longer-range π–π stacking extending to approximately 14 Å, while anion size and side-chain hydrophilicity exert minimal influence on backbone alignment. These results identify side-chain frequency as a more effective optimization target than anion size or hydrophilicity for improving OMIEC conductivity and provide a computational framework for establishing quantitative design rules across a broader range of mixed conducting polymers and electrolytes.