Advancing Multiscale Modeling Approaches to Examine the Physicochemical Characteristics of Organic Mixed Ionic and Electronic Conductors

The continued advance of bioelectronic and electrochemical energy storage and conversion applications requires materials that efficiently transport both electrons and ions. Organic mixed ionic and electronic conductors (OMIEC) have emerged as a promising class of soft conductive materials for these applications. Developing a deep physicochemical understanding of OMEIC behavior is complicated by the intricate interplay of semiconductor morphology, which changes as a function of swelling by the electrolyte, electronic properties, and ion transport. Here we use density functional theory (DFT) calculations to investigate the conditions under which bipolarons form, as opposed to maintaining two (or more) isolated polarons, revealing the impact of counterion size and spacing along a polythiophene homopolymer chain on the preferred charge-carrier state. We also implement a molecular dynamics (MD) modeling framework for polymer-based OMIEC, highlighting a boost in performance. This work lays the foundation for future developments of multiscale OMEIC models.