Modeling Polaron Excitations and Stabilization Mechanisms in Conjugated Polymers

TL;DR

This paper develops a dielectric-stabilized tight-binding model to accurately describe polaron states in conjugated polymers, matching experimental spectroscopic data and clarifying the dominant stabilization mechanism.

Contribution

It introduces a first-principles parameterized model that explains polaron formation and excitation energies, emphasizing dielectric polarization over local ring distortions.

Findings

Quantitative reproduction of mid-infrared absorption features.

Identification of dielectric polarization as the main stabilization mechanism.

Correlation of polaron energetics with spectroscopic observables.

Abstract

Charge carriers in organic semiconductors form polarons, which are self-localized states stabilized by interactions with their environment. Using a dielectric-stabilized tight-binding model parameterized from first-principles calculations, we compute ground and excited polaron states in poly(3-hexylthiophene) (P3HT). Our results quantitatively reproduce key mid-infrared absorption features, notably the chain-length-dependent shift of the intrachain polaron excitation peak (peak B) and its variation between regioregular and regiorandom P3HT. Comparison to an alternative stabilization mechanism based on local ring distortions reveals that dielectric polarization dominates polaron formation, as ring distortions yield insufficient binding and excitation energies inconsistent with experiments. These findings clarify the microscopic origin of polarons in conjugated polymers and provide a predictive framework linking polaron energetics to spectroscopic observables, advancing the understanding of charge transport in organic semiconductors.