Excitation-Dependent High-Lying Excitonic Exchange via Interlayer Energy Transfer from Lower-to-Higher Bandgap 2D Material

TL;DR

This study demonstrates an unconventional energy transfer from lower- to higher-bandgap 2D materials in TMD heterostructures, enhancing photoluminescence through resonant excitonic states, with temperature affecting the transfer efficiency.

Contribution

It reveals a novel long-distance energy transfer mechanism from WSe2 to MoS2 via interlayer hBN, which is atypical in TMD heterostructures and impacts photocarrier relaxation.

Findings

Efficient energy transfer from WSe2 to MoS2 enhances PL emission.

Resonant overlap of high-lying excitonic states enables this transfer.

Temperature increase weakens the energy transfer due to electron-phonon scattering.

Abstract

High light absorption (~15%) and strong photoluminescence (PL) emission in monolayer (1L) transition metal dichalcogenide (TMD) make it an ideal candidate for optoelectronic applications. Competing interlayer charge (CT) and energy transfer (ET) processes control the photocarrier relaxation pathways in TMD heterostructures (HSs). In TMDs, long-distance ET can survive up to several tens of nm, unlike the CT process. Our experiment shows that an efficient ET occurs from the 1Ls WSe2-to-MoS2 with an interlayer hBN, due to the resonant overlapping of the high-lying excitonic states between the two TMDs, resulting in enhanced HS MoS2 PL emission. This type of unconventional ET from the lower-to-higher optical bandgap material is not typical in the TMD HSs. With increasing temperature, the ET process becomes weaker due to the increased electron-phonon scattering, destroying the enhanced MoS2 emission. Our work provides new insight into the long-distance ET process and its effect on the photocarrier relaxation pathways.