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

Highlight absorption (similar to 15%) and strong photoluminescence(PL) emission in monolayer (1L) transition metal dichalcogenides (TMDs)make them ideal candidates for optoelectronic device applications.Competing interlayer charge transfer (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 ofnm, unlike the CT process. Our experiment shows that an efficientET occurs from the 1Ls WSe2-to-MoS2 with aninterlayer hexagonal boron nitride (hBN), due to the resonant overlappingof the high-lying excitonic states between the two TMDs, resultingin enhanced HS MoS2 PL emission. This type of unconventionalET from the lower-to-higher optical bandgap materialis not typical in the TMD HSs. With increasing temperature, the ETprocess becomes weaker due to the increased electron-phononscattering, destroying the enhanced MoS2 emission. Ourwork provides new insight into the long-distance ET process and itseffect on the photocarrier relaxation pathways.