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Mixed-dimensional van der Waals heterojunctions involve interfacing materials with different dimensionalities, such as a 2D transition metal dichalcogenide and a 0D organic semiconductor. These heterojunctions have shown unique interfacial properties not found in either individual component. Here, we use femtosecond transient absorption to reveal photoinduced charge transfer and interlayer exciton formation in a mixed-dimensional type-II heterojunction between monolayer MoS 2 and vanadyl phthalocyanine (VOPc). Selective excitation of the MoS 2 exciton leads to hole transfer from the MoS 2 valence band to VOPc highest occupied molecular orbit in ∼710 fs. On the contrary, selective photoexcitation of the VOPc layer leads to instantaneous electron transfer from its excited state to the conduction band of MoS 2 in less than 100 fs. This light-initiated ultrafast separation of electrons and holes across the heterojunction interface leads to the formation of an interlayer exciton. These interlayer excitons formed across the interface lead to longer-lived charge-separated states of up to 2.5 ns, longer than in each individual layer of this heterojunction. Thus, the longer charge-separated state along with ultrafast charge transfer times provide promising results for photovoltaic and optoelectronic device applications.
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Electron dynamics in MoS 2 -graphite heterostructures
The electron dynamics in heterostructures formed by multilayer graphite and monolayer or bulk MoS 2 were studied by femtosecond transient absorption measurements. Samples of monolayer MoS 2 -multilayer graphite and bulk MoS 2 -multilayer graphite were fabricated by exfoliation and dry transfer techniques. Ultrafast laser pulses were used to inject electron–hole pairs into monolayer or bulk MoS 2 . The transfer of these photocarriers to the adjacent multilayer graphite was time resolved by measuring the differential reflection of a probe pulse. We found that photocarriers injected into monolayer MoS 2 transfer to graphite on an ultrafast time scale shorter than 400 fs. Such an efficient charge transfer is key to the development of high performance optoelectronic devices with MoS 2 as the light absorbing layer and graphite as electrodes. The absorption coefficient of monolayer MoS 2 can be controlled by the carriers in graphite. This process can be used for interlayer coupling and control. In a bulk MoS 2 -graphite heterostructure, the photocarrier transfer time is about 220 ps, due to the inefficient interlayer charge transport in bulk MoS 2 . These results provide useful information for developing optoelectronic devices based on MoS 2 -graphite heterostructures.
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- Award ID(s):
- 1505852
- PAR ID:
- 10058211
- Date Published:
- Journal Name:
- Nanoscale
- Volume:
- 9
- Issue:
- 38
- ISSN:
- 2040-3364
- Page Range / eLocation ID:
- 14533 to 14539
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1039/C7NR04763K
