Charge Transport Framework for Crystalline pi-Conjugated Materials

Abstract

Quantitative charge-transport modelling in crystalline pi-conjugated polymers requires an electronic representation that captures extended conjugation and material-specific electron-phonon interactions on equal footing. We present a Wannier-orbital-based formulation of the transient-polaron-localization (TPL) framework for quantitative charge-transport simulations in crystalline pi-conjugated polymers. By expressing all interactions directly in a Wannier representation derived from first-principles calculations, the approach avoids artificial fragmentation of polymer backbones and enables a consistent, material-specific description of electronic couplings and electron-phonon interactions. Low- and high-frequency vibrational modes are incorporated within a mode-resolved TPL formalism, yielding an effective electronic Hamiltonian that captures both dynamic disorder and polaronic renormalization. The methodology is demonstrated for the ambipolar crystalline naphthalenediimide-bithiophene copolymer, enabling a direct comparison of electron and hole transport along the polymer backbone and pi-stacking directions. The simulations reproduce key transport features, including pronounced anisotropy and higher electron than hole mobility. Additional studies on single- and bi-chain systems reveal the essential role of inter-chain coherence in supporting efficient transport along the polymer backbone. Beyond this specific system, the Wannier-orbital-based TPL framework provides a transferable route to disentangle intrinsic charge-transport mechanisms in crystalline pi-conjugated materials and establishes a foundation for future work.