WITHDRAW (NO REG) 5/20/2024 SB02.04.12 Impact of Dielectric Environment and Counterion Size on Polaron Characteristics in Electrochemically Doped π-Conjugated Polymers

Electrochemically doped π-conjugated polymers (CP) are central materials in several emerging applications such as semiconductors in optoelectronic devices, active materials in thermoelectric generators, and electrode or binder materials in batteries. In these systems, electronic transport is controlled by the formation of polarons, which act as charge carriers in the CP. As the CP interacts with counterions from an electrolyte source, the charge associated with the polaron is stabilized. While both the counterion and the solvent environment involved in this interaction can impact the optical and charge-carrier properties of CPs, a clear understanding of the governing mechanisms is still lacking. Here we focus on assessing how single-chain polaron properties are impacted by changes in the surrounding dielectric environment and counterion used. We use first-principles calculations based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT) with a tuned range-corrected hybrid functional to determine various polaron characteristics in the model CP N2200 in assorted dielectric environments with and without counterions of varying sizes present. We find that the Coulomb interactions between the polaron and the counterion lead to smaller, more strongly bound polarons as reflected by changes in charge delocalization, bond distortion, and polaron features of the optical absorption spectra. These data provide valuable insight into how such variables impact the charge transport properties of electrochemically doped CP’s.