Charge state-dependent ion condensation near conjugated polymer backbones

Organic mixed ionic/electronic conductors (OMIECs) have shown promise for myriad applications. However, there remain clear gaps in the precise understanding of the fundamental mechanisms of mixed conduction/charging. Among these is the knowledge of the counterion position within crystallites as a function of the distance from the electronic charge transporting backbone. Here, operando experimental data and molecular dynamics simulations show that the counterion position within a prototypical OMIEC poly(2-(4,4′-bis(2-methoxyethoxy)-5′-methyl-[2,2′-bithiophen]-5-yl)-5-methylthieno[3,2-b]thiophene) (pgBTTT) changes as a function of the polymer charge state. Specifically, we show that the counterions reside far away from the backbone at low doping, and condense to positions near the backbone at increased potentials. This dataset can be broadly grouped into 1) experimental data (spectroelectrochemistry, resonant, and non-resonant diffraction), 2) molecular dynamics simulations (structure generation and analysis), and 3) calculated grazing-incidence resonant X-ray diffraction (GIRXRD) data based on the molecular dynamics simulations. Detailed methods associated with generation and collection of the data can be found in the supporting information of the main manuscript.