Excitonic Emission in Atomically Thin Electroluminescent Devices

Abstract

2D layered materials derived from their bulk counterparts are intriguing platforms for the exploration of novel optoelectronic applications and fundamental physical phenomena. Among the 2D family, 2D semiconductors with sizable bandgaps, such as transitional metal dichalcogenides and black phosphorus, are promising building blocks for next‐generation light‐emitting applications due to their extraordinary optical and photoelectrical properties. Originating from the combined effect of quantum confinement and reduced dielectric screening, the excitonic effect is dominant in ultrathin 2D semiconductors and of essential importance for the performance of 2D light‐emitting diodes (2DLEDs). Herein, a systematic summary and review is presented, where excitonic properties and the main influencing factors, including Coulomb interactions, band structures, carrier dynamics, and external electrical fields, are first analyzed. The recent progress of 2DLEDs as well as their excitonic emission features and electroluminescence manipulation are then introduced. Lastly, the ongoing challenges and future prospects of 2DLEDs are discussed.

One‐Step Exfoliation Method for Plasmonic Activation of Large‐Area 2D Crystals

“…2D materials and their heterostructures offer a unique platform for the exploration of different physical phenomena at the atomic-scale limit, including quantum Hall effects, [1,2] moiré heterostructures related physics, [3,4] superconductivity, [5] charge density waves (CDW) [6] and magnetism. [7] These intriguing properties are enabling diverse device applications such as field effect transistors, [8,9] quantum emitters, [10][11][12] memory devices, [13] optoelectronic devices, [14][15][16][17] and energy storage units. [18] The continuous improvement of 2D material fabrication methods plays a crucial role in enabling the discovery of novel properties and device applications of 2D materials.…”

“…But despite CVD methods showing a clear advantage for preparing waferscale monolayers, [19,20] or even twisted heterobilayers, [21] the in-plane strain, higher density of defects and impurities in CVD-grown samples are still challenging to control. [12,22,23] As one of the most widely used "top-down" 2D materials fabrication strategy, mechanical exfoliation shows advantages in feasibility and cost-effectiveness for exploring their novel properties. Traditional exfoliation methods via scotch tape or polydimethylsiloxane (PDMS) tape can be employed for getting highquality 2D monolayer crystals, but are limited in terms of sample size (≈10-100 μm) and exfoliation yield.…”

“…But despite CVD methods showing a clear advantage for preparing wafer‐scale monolayers, [ 19,20 ] or even twisted heterobilayers, [ 21 ] the in‐plane strain, higher density of defects and impurities in CVD‐grown samples are still challenging to control. [ 12,22,23 ]…”

Electroluminescence from Megasonically Solution-Processed MoS2 Nanosheet Films

“…Electroluminescence (EL), which is the conversion of an electrical current into light, is central to diverse technologies such as lighting, displays, data communication, and sensing. − Over the past decade, two-dimensional (2D) monolayer semiconductors have been widely studied for electroluminescent devices due to their diverse and tunable optoelectronic and photonic properties. In particular, transition metal dichalcogenides (TMDs) have been of interest due to their layer-dependent bandstructure, direct bandgap at the monolayer limit, strong light–matter interactions, tightly bound excitons, trions, and multiexcitons that can be controlled by strain , and doping, − solution-processability for printed optoelectronics, − high carrier mobility, , and mechanical flexibility .…”

Defect-Enhanced Exciton–Exciton Annihilation in Monolayer Transition Metal Dichalcogenides at High Exciton Densities

“…Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) with the chemical structure of MX 2 (M: Mo or W; X: S, Se, or Te) have garnered significant interest in the past decade owing to their many unique optical and electronic properties, such as layer-dependent bandgap, high electron mobility, high third-order nonlinear polarizability and susceptibility, and spin–valley interactions. − Compared to multilayer TMDs, the bandgap in monolayer TMDs becomes a direct bandgap in the visible to near-IR region, and the exciton binding energy in the material increases to approximately 300 meV. − The reason is that the dielectric screening effect of the exciton is weakened and the spatial confinement effect of the wave function is enhanced. − The enhanced stability of the excitons in monolayer materials not only improves the photoluminescence quantum yield (PLQY) at room temperature, making these materials efficient light emitters and single-photon sources ,, but also provides an opportunity to study the steady-state and dynamic physical properties of excitons to explore new applications, − ,− such as field-effect transistors and ultrasensitive photodetectors. − …”