  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.
