Homotrilayer MoSe2 for increased lifetime and oscillator strength of hybridised interlayer excitons

Two-dimensional semiconductors offer a compelling platform for excitons with robust interaction with light, owing to their confined nature and their numerous manipulable degrees of freedom. In bilayers, interlayer excitons (IX) combine these degrees of freedom with high interactions due to their out-of-plane alignment. However, their oscillator strength is often negligible. Interlayer hybridization provides IX with a significant oscillator strength. Here, we examine the ultrafast dynamics of these hybrid IX in bilayer and trilayer MoSe2. We find that IX are particularly strong in trilayers. These unexplored excitonic species exhibit fundamentally different dynamics from IX in bilayers, with delayed rise times of over 2 ps and significantly longer lifetimes. We attribute this to the origin of this excitonic species and confirm it with theory. Our findings offer insights into high oscillator strength, long-living interlayer excitons in trilayers, superior to their bilayer counterparts.