What Can We Learn about PEDOT:PSS Morphology from Molecular Dynamics Simulations of Ionic Diffusion?

Abstract

Poly­(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is one of the most important mixed electron-ion conducting polymers, where the efficiency of the ion transport is crucial for many of its applications. Despite the impressive experimental progress in the determination of ionic mobilities in PEDOT:PSS, the fundamentals of ion transport in this material remain poorly understood, and the theoretical insight into the ion diffusion on the microscopical level is completely missing. In the present paper, a Martini 3 coarse-grained molecular dynamics (MD) model for PEDOT:PSS is developed and applied to calculate the ion diffusion coefficients and ion distribution in the film. We find that the ion diffusion coefficients for Na+ ions are practically the same in the PEDOT-rich and PSS-rich regions and do not show sensitivity to the oxidation level. We compare the calculated diffusion coefficients with available experimental results. Based on this comparison and based on the MD morphology simulation of PEDOT:PSS revealing the formation of pores inside the film, we revise a commonly accepted granular morphological model of PEDOT:PSS. Namely, we argue that PEDOT:PSS films, in addition to PEDOT-rich and PSS-rich regions, must contain a network of pores where the ion diffusion takes place.

Proton Conducting Neuromorphic Materials and Devices

“…The potential models such as AMBER, CHARMM, and OPLS thus approximate complex molecular behaviors in polymers and other soft-matter system by assigning parameters to atoms and modeling forces between them, enabling the exploration of biomolecular structures and interactions. Numerous studies using these potential models have explored combinations of PEDOT to examine self-assembly, electronic transportation attributes, interactions between the electrolyte and polymer, and alterations in morphology to mimic conditions in operating devices. − The oversimplified treatment of electrostatic interaction in these classical models necessitates a multiscale approach where these models are often combined with quantum mechanical approaches. For example, the OPLS models was combined with quantum mechanical calculations by Landi et al to simulate polymeric mixed ionic and electronic conductors .…”

Microscopic Insights of Electrochemical Switching of Poly(benzimidazobenzophenanthroline) (BBL) Thin Film: A Molecular Dynamics Study

“…The p-type CPs have been identified as an efficient OMIEC to be used in numerous applications . One of the widely studied p-type OMIECs is poly­(3,4-ethylenedioxythiophene:polystyrenesulfonate (PEDOT:PSS), where hydrated ions are believed to be transported through the hydrophilic PSS – phase whereas holes are transported through the hydrophobic PEDOT backbone. , However, the recent microscopic insights obtained from the molecular dynamics (MD) study reveal that the transport mechanism of hydrated ions is actually because of water channel formation into the PEDOT:PSS film . The polymer film structure and morphology influence the ion-electron coupling in the films and affect OMIEC’s performance as the ion-electron coupling inside the channel enhances the film’s capacitance and electron mobility, resulting in high-gain organic electrochemical transistors (OECTs) .…”