Influence of twist angle on ultrafast charge separation in WS2-graphene heterostructures

TL;DR

This study uses advanced spectroscopy to show that the twist angle in WS2-graphene heterostructures critically influences ultrafast charge separation, impacting optoelectronic device design.

Contribution

It provides direct experimental evidence on how twist angle affects charge transfer dynamics in vdW heterostructures, a topic with previously conflicting results.

Findings

Charge separation is efficient at 0° twist angle.

At 30°, electrons and holes transfer at similar rates.

Twist angle controls charge separation efficiency.

Abstract

Van der Waals (vdW) heterostructures, formed by stacking two-dimensional materials, offer highly tunable electronic and optical properties, with the twist angle between layers acting as a critical tuning parameter. While its impact on moir\'e patterns, band structure, and correlated states is well-established, the influence of twist angle on ultrafast charge transfer remains controversial. Here, we employ time- and angle-resolved photoemission spectroscopy (trARPES) to directly probe ultrafast charge transfer in epitaxially grown WS\textsubscript{2}-graphene heterostructures with twist angles of 0$^{\circ}$ and 30$^{\circ}$. Upon photoexcitation at $\hbar\omega = 3.1\,\mathrm{eV}$, we observe efficient charge separation at 0$^{\circ}$, while at 30$^{\circ}$, electron and hole transfer occur at similar rates. Our results highlight the crucial role of the twist angle in controlling charge separation efficiency, offering valuable insights for designing vdW heterostructures for applications in photovoltaics and optoelectronics.