Efficient Energy Transfer Enabled by Dark States in van der Waals Heterostructures

Area of Science:

• Condensed matter physics
• Optoelectronics
• Materials science

Background:

• Dark exciton states possess long lifetimes and rich band structures, making them potential energy reservoirs.
• The optical-transition-forbidden nature of dark excitons limits their experimental study and practical applications.
• Monolayer transition metal dichalcogenides like WS$_{2}$ are crucial for optoelectronic devices.

Purpose of the Study:

• To demonstrate a universal dark state nonlinear energy transfer (ET) mechanism in WS$_{2}$/CsPbBr$_{3}$ van der Waals heterostructures.
• To utilize the energy from dark exciton states in CsPbBr$_{3}$ to enhance the photoelectric performance of monolayer WS$_{2}$.
• To explore the characteristics of this dark state ET, including its mechanism and range.

Main Methods:

• Fabrication of monolayer WS$_{2}$/CsPbBr$_{3}$ van der Waals heterostructures.
• Two-photon excitation to probe dark exciton states.
• Characterization of energy transfer pathways using spectroscopic techniques.
• Analysis of the energy transfer as Förster resonant energy transfer (FRET) and donor-bridge-acceptor hopping.

Main Results:

• Demonstrated a universal dark state nonlinear energy transfer mechanism.
• Identified the energy transfer as 2D-2D Förster resonant energy transfer (FRET).
• Revealed a long-range donor-bridge-acceptor hopping mode with transfer distances exceeding 200 nm.
• Achieved nearly an order of magnitude enhancement in the near-infrared detection performance of monolayer WS$_{2}$.

Conclusions:

• The study establishes a novel energy transfer pathway utilizing dark exciton states in 2D materials.
• This mechanism provides a viable route for harnessing dark exciton energy for practical applications.
• The findings significantly enrich the theoretical understanding of dark exciton dynamics and energy transfer processes.