  Vertically stacked van der Waals heterostructures constitute a promising
platform for providing tailored band alignment with enhanced excitonic systems.
Here we report observations of neutral and charged interlayer excitons in
trilayer WSe2-MoSe2-WSe2 van der Waals heterostructures and their dynamics. The
addition of a WSe2 layer in the trilayer leads to significantly higher
photoluminescence quantum yields and tunable spectral resonance compared to its
bilayer heterostructures at cryogenic temperatures. The observed enhancement in
the photoluminescence quantum yield is due to significantly larger
electron-hole overlap and higher light absorbance in the trilayer
heterostructure, supported via first-principle pseudopotential calculations
based on spin-polarized density functional theory. We further uncover the
temperature- and power-dependence, as well as time-resolved photoluminescence
of the trilayer heterostructure interlayer neutral excitons and trions. Our
study elucidates the prospects of manipulating light emission from interlayer
excitons and designing atomic heterostructures from first-principles for
optoelectronics.
