Dissecting Interlayer Hole and Electron Transfer in Transition Metal Dichalcogenide Heterostructures via Two-Dimensional Electronic Spectroscopy.

Monolayer transition metal dichalcogenides (ML-TMDs) are two-dimensional semiconductors that stack to form heterostructures (HSs) with tailored electronic and optical properties. TMD/TMD-HSs like WS2/MoS2 have type II band alignment and form long-lived (nanosecond) interlayer excitons following sub-100 fs interlayer charge transfer (ICT) from the photoexcited intralayer exciton. While many studies have demonstrated the ultrafast nature of ICT processes, we still lack a clear physical understanding of ICT due to the trade-off between temporal and frequency resolution in conventional transient absorption spectroscopy. Here, we perform two-dimensional electronic spectroscopy (2DES), a method with both high frequency and temporal resolution, on a large-area WS2/MoS2 HS where we unambiguously time resolve both interlayer hole and electron transfer with 34 ± 14 and 69 ± 9 fs time constants, respectively. We simultaneously resolve additional optoelectronic processes including band gap renormalization and intralayer exciton coupling. This study demonstrates the advantages of 2DES in comprehensively resolving ultrafast processes in TMD-HS, including ICT.