  Ultrafast charge transfer processes provide a facile way to create interlayer
excitons in directly contacted transition metal dichalcogenide (TMD) layers.
More sophisticated heterostructures composed of TMD/hBN/TMD enable new ways to
control interlayer exciton properties and achieve novel exciton phenomena, such
as exciton insulators and condensates, where longer lifetimes are desired. In
this work, we experimentally study the charge transfer dynamics in a
heterostructure composed of a 1 nm thick hBN spacer between MoSe$_{2}$ and
WSe$_{2}$ monolayers. We observe the hole transfer from MoSe$_{2}$ to WSe$_{2}$
through the hBN barrier with a time constant of 500 ps, which is over 3 orders
of magnitude slower than that between TMD layers without a spacer. Furthermore,
we observe strong competition between the interlayer charge transfer and
intralayer exciton-exciton annihilation processes at high excitation densities.
Our work opens possibilities to understand charge transfer pathways in
TMD/hBN/TMD heterostructures for the efficient generation and control of
interlayer excitons.
