Anisotropic electron-phonon interactions in 2D lead-halide perovskites

TL;DR

This study reveals anisotropic electron-phonon interactions in 2D lead-halide perovskites, showing how crystal structure influences charge dynamics and photoconductivity, with implications for optoelectronic applications.

Contribution

It provides the first detailed experimental and theoretical analysis of anisotropic electron-phonon coupling in 2D perovskites, linking phonon mode directionality to electronic properties.

Findings

In-plane photoconductivity varies by 10% depending on direction.

Anisotropy arises from directional electron-phonon interactions.

Feynman polaron theory explains the observed anisotropy.

Abstract

Two-dimensional hybrid organic-inorganic metal halide perovskites offer enhanced stability for perovskite-based applications. Their crystal structure's soft and ionic nature gives rise to strong interactions between charge carriers and ionic rearrangements. Here, we investigate the interaction of photo-generated electrons and ionic polarizations in single-crystal 2D perovskite butylammonium lead iodide, varying the inorganic lammelae thickness in the 2D single crystals. We determined the directionality of the transition dipole moments of the relevant phonon modes (in the 0.3-3 THz range) by angle-and-polarization dependent THz transmission measurements. We find a clear anisotropy of the in-plane photoconductivity, with a 10% reduction along the axis parallel with the transition dipole moment of the most strongly coupled phonon. Detailed calculations, based on Feynman polaron theory, indicate that the anisotropy originates from directional electron-phonon interactions.