  Trapped interlayer excitons (IXs) in MoSe2-WSe2 heterobilayers have generated
interest for use as single quantum emitter arrays and as an opportunity to
study moir\'e physics in transition metal dichalcogenide (TMD)
heterostructures. IXs are spatially indirectly excitons comprised of an
electron in the MoSe2 layer bound to a hole in the WSe2 layer. Previous reports
of spectrally narrow (<1 meV) photoluminescence (PL) emission lines at low
temperature have been attributed to IXs localized by the moir\'e potential
between the TMD layers. Here, we show that spectrally narrow IX PL lines are
present even when the moir\'e potential is suppressed by inserting a bilayer
hexagonal boron nitride (hBN) spacer between the TMD layers. We directly
compare the doping, electric field, magnetic field, and temperature dependence
of IXs in a directly contacted MoSe2-WSe2 region to those in a region separated
by bilayer hBN. Our results show that the localization potential resulting in
the narrow PL lines is independent of the moir\'e potential, and instead likely
due to extrinsic effects such as nanobubbles or defects. We show that while the
doping, electric field, and temperature dependence of the narrow IX lines is
similar for both regions, their excitonic g-factors have opposite signs,
indicating that the IXs in the directly contacted region are trapped by both
moir\'e and extrinsic localization potentials.
