Exciton-phonon coupling induces new pathway for ultrafast intralayer-to-interlayer exciton transition and interlayer charge transfer in WS2-MoS2 heterostructure: a first-principles study

TL;DR

This study uses first-principles calculations to reveal how exciton-phonon interactions enable ultrafast charge transfer and new transfer pathways in WS2-MoS2 heterostructures, advancing understanding of their optoelectronic dynamics.

Contribution

It introduces a first-principles approach that explicitly includes excitons and phonons to explain ultrafast charge transfer mechanisms in 2D heterostructures, highlighting the role of exciton-phonon coupling.

Findings

Exciton-phonon interaction induces ultrafast exciton relaxation times (15-67 fs).

Electron-hole correlations enable novel charge transfer pathways.

Results are consistent with experimental charge transfer times.

Abstract

Despite the weak, van-der-Waals interlayer coupling, photoinduced charge transfer vertically across atomically thin interfaces can occur within surprisingly fast, sub-50fs timescales. Early theoretical understanding of the charge transfer is based on a noninteracting picture, neglecting excitonic effects that dominate the optical properties of such materials. Here, we employ an ab initio many-body perturbation theory approach which explicitly accounts for the excitons and phonons in the heterostructure. Our large-scale first-principles calculations directly probe the role of exciton-phonon coupling in the charge dynamics of the WS$_2$/MoS$_2$ heterobilayer. We find that the exciton-phonon interaction induced relaxation time of photo-excited excitons at the $K$ valley of MoS$_2$ and WS$_2$ is 67 fs and 15 fs at 300 K, respectively, which sets a lower bound to the intralayer-to-interlayer exciton transfer time and is consistent with experiment reports. We further show that electron-hole correlations facilitate novel transfer pathways which are otherwise inaccessible to non-interacting electrons and holes.