Robust Stacking-Independent Ultrafast Charge Transfer in MoS₂/WS₂ Bilayers

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Van der Waals-coupled 2D heterostructures show promise for advanced photodetectors and solar cells.
• Understanding interlayer charge transfer is crucial for optimizing device performance, including response speed and efficiency.
• Current understanding suggests charge transfer is highly sensitive to interlayer configurations, posing design challenges.

Purpose of the Study:

• To investigate the ultrafast dynamics of interlayer charge transfer in MoS2/WS2 heterostructures.
• To determine the influence of varying stacking configurations on charge transfer behavior.
• To elucidate the mechanisms behind charge transfer robustness in 2D heterostructures.

Main Methods:

• Optical two-color ultrafast pump-probe spectroscopy to study charge transfer dynamics.
• Atomic-resolved transmission electron microscopy for structural characterization.
• Time-dependent density functional theory (TD-DFT) simulations for theoretical insights.

Main Results:

• Charge transfer in MoS2/WS2 bilayers occurs on an ultrafast timescale of approximately 90 femtoseconds.
• Charge transfer was found to be robust and largely independent of interlayer twist angles and coupling strength.
• Heterogeneous interlayer stretching and sliding were identified as novel pathways facilitating efficient charge transfer.

Conclusions:

• The robustness of ultrafast charge transfer in 2D heterostructures is attributed to previously unrecognized heterogeneous interlayer dynamics.
• These findings simplify the design of 2D heterostructure-based devices by reducing sensitivity to stacking uncertainties.
• The study facilitates the development of next-generation ultrafast and high-efficiency optoelectronic and photovoltaic devices.