Spatially Decoupled Ionic Pathways for Preserved Energetic Disorder of Organic Mixed Conductors

Abstract

Organic mixed ionic–electronic conductors (OMIECs) combine facile volumetric ion transport with robust electronic conduction, yet enhancing ionic accessibility through polar side chains often forces polar moieties into the ordered domains that govern charge transport, largely broadening the energetic landscape and eroding carrier mobility. Cross-linking with polar networks can improve ion transport without altering conjugated backbones, but how it reshapes the ionic–electronic balance has remained unresolved. Here, we address this question using length-modulated nitrene-induced photo-cross-linkers (n-NIPS) in indacenodithiophene–benzothiadiazole (IDTBT), chosen as a high-mobility yet ionically nonconductive representative. We found that phase-selective partitioning confines the n-NIPS network to the amorphous free volume, providing predefined, length-tunable ionic pathways while preserving the ordered aggregates for charge pathways, confirmed by the preserved ultralow energetic disorder of IDTBT. Transient organic electrochemical transistor measurements, analyzed through a Chapman–Richards growth framework, resolve the effect into separable capacitive and kinetic contributions, revealing that cross-linking collapses the initial ion-injection barrier once the cross-linker exceeds the anion size and isolates electrical conduction from the progressive degradation seen in pristine films. Cyclic spectroelectrochemistry attributes this protection to mechanical suppression of microstructural rearrangement, which suppresses irreversible interchain disruption and widens the reversible doping window. This work provides a mechanistic design principle of disorder-free OMIECs applicable to neuromorphic and bioelectronic devices.