Interfacial Charge Transfer in Atomically Thin 2D Transition-Metal Dichalcogenide Heterostructures

Abstract

Atomically thin transition-metal dichalcogenides (TMDs) exhibit excellent optoelectronic properties and are promising for fundamental investigations and applications in next-generation photovoltaics, photodetectors, quantum sensors, and quantum computers. Combined with other semiconductor materials, TMDs can form heterostructures with improved and even emergent properties. The type of interface between constituent components of the heterostructure ultimately defines the heterostructure's behavior and performance. Understanding charge transfer at the TMD/semiconductor interface is vital to the development of next-generation photovoltaic, photodetector, and quantum materials applications. Here we review recent studies of photoinduced charge transfer in TMD/semiconductor heterostructures, where the semiconductor constituent is a TMD, a colloidal quantum dot (QD), or a hybrid perovskite. We focus on experimental studies that utilize ultrafast optical methods to decipher the charge-transfer kinetics. We present examples of the formation of interlayer excitons as a proof of charge transfer, interlayer excitons trapped in moire potentials, and heterostructures showing spin-valley conservation of interlayer exciton emission. We review TMD/ QD heterostructures where charge transfer is tuned by energy-band-gap matching (engineering) and close the review with a subfield on TMD/perovskite heterostructures.

Optical Time-Resolved Microscopy on Few-Atoms-Thick Materials

“…Transient optical spectra acquired with the pump and probe technique are a consolidated and important experimental tool to study materials’ electron and structural dynamics. Pump-induced modifications in transmission or reflection, i.e., Δ T / T or Δ R / R , are interpreted to show the optical response of 2D films deposited on different substrates, such as the formation of excitons, the electron–phonon coupling or the many-body interactions like bandgap renormalization and trion or biexciton formation. In the interpretation of the pump–probe data, attention should be paid to the presence of the substrate.…”

“…The usual way to interpret data is by studying the kinetics, i.e., the variation rates of various species, identified through specific spectral features. 9 Information is extracted from multiexponential decay dynamics at specific spectral positions. However, despite widespread efforts, there is no consensus on the mechanisms governing the multiexponential decay dynamics.…”

“…The film−substrate models do not take into account the variation of the monolayer properties due to defects or strains induced by the fabrication process 9,11 or the effects due to the finite size of the samples. 13,14 Usually, defects induce small variations in the monolayer intrinsic properties when averaged measurements are used via far-field optical probes.…”

“…As a reference for the discussion, we consider the properties of single-layer transition metal dichalcogenides (TMDs) studied by transient absorption spectroscopy (TAS). The usual way to interpret data is by studying the kinetics, i.e., the variation rates of various species, identified through specific spectral features . Information is extracted from multiexponential decay dynamics at specific spectral positions.…”

“…The film–substrate models do not take into account the variation of the monolayer properties due to defects or strains induced by the fabrication process , or the effects due to the finite size of the samples. , Usually, defects induce small variations in the monolayer intrinsic properties when averaged measurements are used via far-field optical probes. However, due to the strong light–matter interaction in TMD materials, novel optical and electronic states may be revealed if sufficient spatial resolution is available.…”