Coupling of Ionic and Electronic Dynamics in Doped Semiconducting Polymers

A new model of charge transport in organic polymeric materials with mixed ionic and electronic conduction (OMIEC) is proposed. The excess charge in doped polymers is very mobile and the dynamics of the polymer chain cannot be accurately described with a model including only fixed point charges. We are mainly interested in describing the morphological change upon charging and the slow polymeric and ionic dynamics over hundreds of nanoseconds while we are forced to take into account rapid rearrangements of the excess charge in the picosecond timescale. We introduced a new scheme based on the combination of MD and QM/MM to evaluate the classical dynamics of polymer, water and ions, while allowing the excess charge of the polymer chains to rearrange following the external electrostatic potential. We deployed this method on a range of systems and drew some general conclusions on the coupling between electronic and ionic motions. Alongside very fast modes (<5 ps important for the polaronic effects) and very slow dynamic (>500 ns, responsible for the static disorder), both already expected, we discovered a highly important dynamical effect in the intermediate timescale (5-500 ps). The energy of the localized carrier states evolves in time: the trap states are short lived and energy barriers evolve over times. In other words ionic and nuclear dynamics are therefore driving the electronic dynamics rather than providing a static disordered landscape.

C Burke, A Landi, A Troisi, Mater. Horiz. 2024, https://doi.org/10.1039/D4MH00706A