Centimeter‐Scale and Visible Wavelength Monolayer Light‐Emitting Devices

Abstract

Monolayer 2D transition metal dichalcogenides (TMDCs) have shown great promise for optoelectronic applications due to their direct bandgaps and unique physical properties. In particular, they can possess photoluminescence quantum yields (PL QY) approaching unity at the ultimate thickness limit, making their application in light-emitting devices highly promising. Here, large-area WS 2 grown via chemical vapor deposition is synthesized and characterized for visible (red) light-emitting devices. Detail optical characterization of the synthesized films is performed, which show peak PL QY as high as 12%. Electrically pumped emission from the synthetic WS 2 is achieved utilizing a transient-mode electroluminescence device structure, which consists of a single metal-semiconductor contact and alternating gate fields to achieve bipolar emission. Utilizing this aforementioned structure, a centimeter-scale (≈0.5 cm 2 ) visible (640 nm) display is demonstrated, fabricated using TMDCs to showcase the potential of this material system for display applications.absorbed, and is a key figure of merit as it directly dictates the final efficiency when the materials are made into light-emitting devices or photovoltaics. Various microscale light-emitting devices have been demonstrated using TMDCs. [13][14][15][16] However, a challenge has been the requirement for simultaneous formation of low-resistance contacts to both electrons and holes in the same device. In one specific architecture, we recently demonstrated efficient bipolar carrier injection using transientmode operation through a single Schottky contact. [17] The device effectively acts as a light-emitting capacitor, with minimal dependence on the contact metal to the semiconductor. This device structure was shown to work with exfoliated monolayers of MoS 2 , WS 2 , MoSe 2 , and WSe 2 . Furthermore, large-area (3 mm × 2 mm) emission was demonstrated using WSe 2 monolayers grown by chemical vapor deposition (CVD). Although the WSe 2 devices were bright, their emission is in the near-infrared regime (750 nm peak emission). Recently, millimeter-scale WS 2 devices operated in the visible wavelength regime were demonstrated using a vertical architecture with quantum dots and polymers as electron/hole injection layers, but a more efficient device is still demanded. [18] In this regard, we report a centimeter-scale, bright, visible light-emitting device based on WS 2 monolayers synthesized via CVD [19][20][21] using a simple capacitor structure. The CVD-synthesized material exhibits a respectable peak PL QY of approximately 10%, without a droop at high injection levels. Using this material, we fabricate a transient-electroluminescence (t-EL) device and characterize its performance; in particular, its efficient light emission at high injection levels. Finally, we also fabricate a sixteen-pixel display with bright red EL emission (640 nm, peak output power 14 µW cm −2 ), which is visible in ambient room lighting. Figure 1a shows the PL spectra of the synthesized WS 2 measured over a p...

Performance Limits of an Alternating Current Electroluminescent Device

“…[ 10–12 ] EL has also been demonstrated with a laterally structured capacitive device structure in which materials are deposited on top of a gate oxide layer across which AC voltage is applied. [ 13–15 ] A more complex transistor‐based structure that applies an additional drain–source bias can also be adopted to generate light from various materials. [ 16,17 ] These examples, which use microscale metal contacts to inject carriers, may be sufficient to produce AC EL from materials with relatively high mobility; however, denser electrical contacts are preferable for generating bright AC EL from other kinds of materials, including molecular emitters with poor mobility.…”

A High‐Efficiency Wavelength‐Tunable Monolayer LED with Hybrid Continuous‐Pulsed Injection

“…In a DC LED device, electrons and holes are injected simultaneously, [ 7 ] while in an AC LED, electrons or holes are injected separately under different AC voltage polarities. [ 10 ] This separate injection feature opens a promising way to fabricated pulsed LED devices [ 12 ] and allows us to probe electroluminescence (EL) emission pathway and the carrier dynamic down to each injection cycle. [ 13 ] However, the recombination of electrons and holes can only occur on the contact edge between electrodes and 2D monolayer material, thus EL emission effective area is small.…”

Two-dimensional materials for light emitting applications: Achievement, challenge and future perspectives

“…Although the EL external quantum efficiency for WSe2 LEDs, at current stage, is only 0.01%, the beauty of this AC driven LEDs is that the device does not require complex p-n junctions or heterostructures to achieve light emission, which provides the opportunity to scale up the devices to larger sizes. Based on this structure, centimetre scale monolayer AC driven LEDs have been achieved [126]. In Fig.…”