Defect-Driven Polaron Localization in π-Conjugated Systems: The Role of Spatial Correlation and Coulomb Binding.

Abstract

Defect engineering offers a powerful strategy to modulate polaron delocalization in π-conjugated materials; however, the complex interplay between different types of defects and dopant-induced Coulomb binding remains insufficiently understood. Here, we present a comprehensive theoretical investigation of hole-polaron transport using a Holstein-style Hamiltonian applied to π-conjugated lattices such as polymers and covalent organic frameworks (COFs) that incorporate vacancy and linker defects, a disorder framework encompassing distributions of disordered sites, and dopant-induced Coulomb binding effects. Simulated mid-infrared signatures and polaron coherence numbers uncover distinct and nuanced behaviors, revealing how the spatial correlation (random vs correlated) of different defect types governs polaron delocalization pathways. While dopant counterions strongly localize polarons, their precise positioning relative to crystalline versus disordered domains critically modulates transport efficiency. To establish experimental relevance, we compare our simulations with polarized intrachain and interchain mid-infrared spectra of doped P3HT films, providing fundamental insights into how specific dopant-polymer configurations give rise to anisotropic spectroscopic signatures and their direct correlation with anisotropic polaron transport. The strong agreement between theory and experiment validates our predictions and establishes guiding principles for optimizing polaron transport in disordered π-conjugated materials.