Electron-phonon coupling in crystalline organic semiconductors: Microscopic evidence for nonpolaronic charge carriers

TL;DR

This study uses first-principles calculations to analyze electron-phonon interactions in crystalline organic semiconductors, providing microscopic evidence that band-like carriers are nonpolaronic, contrary to traditional assumptions.

Contribution

It offers the first microscopic evidence supporting the nonpolaronic nature of band-like carriers in organic semiconductors through detailed ab initio calculations.

Findings

Carrier-phonon coupling strengths decrease with molecular size.

Quasiparticle spectral residues indicate nonpolaronic carriers.

First-principles approach confirms nonpolaronic charge transport in naphthalene.

Abstract

We consider electron(hole)-phonon coupling in crystalline organic semiconductors, using naphthalene for our case study. Employing a first-principles approach, we compute the changes in the self-consistent Kohn-Sham potential corresponding to different phonon modes and go on to obtain the carrier-phonon coupling matrix elements (vertex functions). We then evaluate perturbatively the quasiparticle spectral residues for electrons at the bottom of the lowest-unoccupied- (LUMO) and holes at the top of the highest-occupied (HOMO) band, respectively obtaining $Z_e\approx 0.74$ and $Z_h\approx 0.78$. Along with the widely accepted notion that the carrier-phonon coupling strengths in polyacenes decrease with increasing molecular size, our results provide a strong microscopic evidence for the previously conjectured nonpolaronic nature of band-like carriers in these systems.