Electroluminescence Research Articles

Perovskite Light-Emitting Diodes with Quantum Wires and Nanorods.

Perovskite materials, celebrated for their exceptional optoelectronic properties, have seen extensive application in the field of light-emitting diodes (LEDs), where research is as abundant as the proverbial "carloads of books." In this review, the research of perovskite materials is delved into from a dimensional perspective, with a focus on the exemplary performance of low-dimensional perovskite materials in LEDs. This discussion predominantly revolves around perovskite quantum wires and perovskite nanorods. Perovskite quantum wires are versatile in their growth, compatible with both solution-based and vapor-phase growth, and can be deposited over large areas-even on spherical substrates-to achieve commendable electroluminescence (EL). Perovskite nanorods, on the other hand, boast a suite of superior characteristics, such as polarization properties and tunability of the transition dipole moment, endowing them with the great potential to enhance light extraction efficiency. Furthermore, zero-dimensional (0D) perovskite materials like nanocrystals (NCs) are also the subject of widespread research and application. This review reflects on and synthesizes the unique qualities of the aforementioned materials while exploring their vital roles in the development of high-efficiency perovskite LEDs (PeLEDs).

Yolo Based Defects Detection Algorithm for EL in PV Modules with Focal and Efficient IoU Loss

Considering the defect detection issues in electroluminescence (EL) of photovoltaic (PV) cell systems, lots of factors result in performance degradation, including defect diversity, data imbalance, scale difference, etc. Focal-EIoU loss, an effective defect detection solution for EL, is proposed based on the improved YOLOv5. Firstly, by analyzing the detection background and scale characteristics of EL defects, a binary classification is carried out in the system. Subsequently, a cascade detection network based on YOLOv5 is designed to further extract features from the binary-classified defects. The defect localization and classification are achieved in this way. To address the problem of imbalanced defect samples, a loss function is designed based on EIoU and Focal-F1 Loss. Experimental results are illustrated to show the effectiveness. Compared with the existing CNN-based deep learning approaches, the proposed focal loss calculation-based method can effectively improve the performance of handling sample imbalance. Moreover, in the detection of 12 types of defects, the Yolov5 algorithms can always obtain higher MAP (mean average precision) even with different parameter levels (Yolov5m: 0.791 vs. 0.857, Yolov5l: 0.798 vs. 0.862, Yolov5x: 0.802 vs. 0.867, Yolov5s: 0.793 vs. 0.865).

Enhanced performance of ambient-air processed CsPbBr3 perovskite light-emitting electrochemical cells via synergistic incorporation of dual additives

Metal halide perovskite light-emitting electrochemical cells (MHP-LECs) are promising due to their facile solution processability and exceptional optoelectrical properties. However, commercialization is hindered by poor thin-film coverage and the need for glovebox processing. This study addresses these issues by incorporating poly(ethylene oxide) (PEO) and potassium hexafluorophosphate (KPF6) into cesium lead bromide perovskite (CsPbBr3) emitting layers (EML), processed under ambient-air conditions. These perovskite composite thin films were spin-coated on a preheated substrate, and the device structure was ITO/PEDOT:PSS/EML/Al. Notably, the MHP-LEC based on CsPbBr3:PEO:KPF6 (100:65:0.2, weight ratio) exhibited pure-green emission with a peak at 524 nm and a narrow full width at half-maximum of 27 nm. Compared to a reference device (CsPbBr3:PEO (100:65, weight ratio)), the new device showed 1.5-, 4-, and 5-fold improvements in current density, electroluminescence (EL) intensity, and lifetime, respectively. These enhancements are attributed to reduced non-radiative current leakage, improved film surface coverage and passivation, and balanced charge carrier injection and transportation. This study offers a straightforward approach for processing CsPbBr3 thin films under ambient-air conditions, enhancing the EL performance of MHP-LECs.

Body Diode Reliability of 4H-SiC MOSFETs as a Function of Epitaxial Process Parameter

In this paper, the authors continue the experimental evaluation of bipolar degradation for different 1.2 kV SiC MOSFETs. All the devices are stressed by pulsed repetitive forward current through the body diode with current densities varying from 1000 A/cm2 up to 5000A/cm2. The 1.2 kV SiC MOSFETs are split into two major groups based on the differences in epitaxial material (Type A and Type B) that are subjected to the pulsed forward current stress through the body diode. Additionally, there is a third group with Type B epitaxial material, where p+ implantation process at different temperature is applied to evaluate potential impact on bipolar degradation. Devices are electrically characterized on the Keysight B1505A power device analyzer, both before and after stress testing to trace the drift in the electric parameters. Lastly, the drift in parameters observed in some of the devices, are additionally correlated by an electroluminescence (EL) and scanning acoustic tomography (SAT) analysis.

Dicyanoimidazole-based organic small molecule fluorophores: Synthesis and luminescent properties

Four new organic D-π-A fluorophores consisting of different electron donors (carbazole and diphenylamine) and acceptors (4,5-dicyanoimidazole and 5,6-dicyanobenzo[d]imidazole), i.e., DCI-Cz, DCI-TPA, DCBI-Cz and DCBI-TPA, were synthesized to obtain deep-blue organic light-emitting diodes (OLEDs). These compounds exhibited good solubility and excellent thermal stability as well as strong deep-blue and blue emission in solution and solid states. With mCP (1,3-di(9H-carbazol-9-yl)benzene) as the host material, the doped devices with a configuration of ITO/PEDOT:PSS (30 nm)/mCP:dopant (x wt%) (25 nm)/TPBi (35 nm)/Liq (2 nm)/Al (150 nm) were fabricated by solution-processing the emitting layers to evaluate their electroluminescence (EL) performances. The devices using the blend of mCP with DCI-TPA as emitting layers exhibited the best electroluminescent performance with a maximum external quantum efficiency (EQEmax) of 4.39 % and a maximum current efficiency of 3.04 cd/A.

Molecular Engineering Towards Efficient Aggregation-Induced Delayed Fluorescence Luminogens as Emitters and Sensitizers for High-Performance Organic Light-Emitting Diodes.

Exploring efficient thermally-activated delayed fluorescence materials having maximum external quantum efficiencies (ηext,maxs) exceeding 30 % for organic light-emitting diodes (OLEDs) still remains challenging because it generally requires efficient reverse intersystem crossing (RISC), high photoluminescence quantum yield (ΦPL), and large optical out-coupling efficiency (Φout) simultaneously. Herein, two green aggregation-induced delayed fluorescence (AIDF) luminogens, named XTCz-2 and XTCz-3, are designed and constructed by using xanthone (XT) as electron acceptor and phenylcarbazole-substituted carbazole as donors. XTCz-2 and XTCz-3 exhibit distinguished advantages of high thermal stability (439-560 °C), excellent ΦPLs (84-88 %) and fast RISC rates (1.9×105-4.2×105 s-1), and prefer horizontal dipole orientation and thus have high Φouts. Consequently, they can achieve the state-of-the-art electroluminescence (EL) performances with ηext,maxs of up to 35.0 %. Moreover, XTCz-3 is selected as a sensitizer for sky-blue multi-resonance delayed fluorescence emitter in hyperfluorescence OLEDs, providing narrow EL spectra and excellent ηext,maxs of up to 33.8 % with low efficiency roll-offs. The splendid comprehensive performances demonstrate the significant application potential of these AIDF luminogens as both light-emitting materials and sensitizers for OLEDs.

Room-temperature electroluminescence in the InAsSbP/InAs0.95Sb0.05/InAsSbP single quantum well

The electrical and luminescent characteristics of the heterostructure with a 20 nm-wide n-InAsSbP/n-InAs0.95Sb0.05/p-InAsSbP single quantum well, grown on an n-InAs substrate by the MOVPE method, have been studied. An intense room temperature electroluminescence (EL) with a maximum near the photon energy of 0.34 eV and a FWHM of 32 meV was discovered. It was established that the EL in such single quantum well has been emitted due to type I radiative transitions between the ground levels of electrons and holes both at forward and reverse bias. The characteristics of heterostructures with a single quantum well and the active region based on a bulk InAsSb layer of the same composition have been compared.

Organic polaritonic light-emitting diodes with high luminance and color purity toward laser displays

Achieving high-luminescence organic light-emitting devices (OLEDs) with narrowband emission and high color purity is important in various optoelectronic fields. Laser displays exhibit outstanding advantages in next-generation display technologies owing to their ultimate visual experience, but this remains a great challenge. Here, we develop a novel OLED based organic single crystals. By strongly coupling the organic exciton state to an optical microcavity, we obtain polariton electroluminescent (EL) emission from the polariton OLEDs (OPLEDs) with high luminance, narrow-band emission, high color purity, high polarization as well as excellent optically pumped polariton laser. Further, we evaluate the potential for electrically pumped polariton laser through theoretical analysis and provide possible solutions. This work provides a powerful strategy with a material–device combination that paves the way for electrically driven organic single-crystal-based polariton luminescent devices and possibly lasers.

Short-Wave Infrared Light-Emitting Diodes Using Colloidal CuInS2 Quantum Dots with ZnI2 Dual-Passivation.

Short-wave infrared (SWIR) light-emitting diodes (LEDs) have emerged as promising technologies for diverse applications such as optical communication, biomedical imaging, surveillance, and machine vision. Colloidal quantum dots (QDs) are particularly attractive for SWIR LEDs due to their solution processability, compatibility with flexible substrates, and tunable absorption and luminescence. However, the presence of toxic elements or precious metals in most SWIR-emitting QDs poses health, environmental, and cost challenges. In this context, CuInS2 (CIS) QDs are known for low toxicity, cost-effective fabrication, and SWIR-light emitting capability. However, CIS QDs have not yet been directly utilized to fabricate SWIR LEDs to date, which is due to low particle stability, inefficient charge carrier recombination, and significantly blue-shifted luminescence after integrating into LED devices. To address challenges, we propose a dual-passivation strategy using ZnI2 as a chemical additive to enhance both the optical property of plain CIS QDs and charge carrier recombination upon LED device implementation. The resulting CIS-QD-based LEDs exhibit a stable SWIR electroluminescence (EL) peak (over 1000 nm) with a high EL radiance and a record external quantum efficiency in the SWIR region. Our study represents a significant step forward in SWIR-QLED technology, offering a pathway for the development of high-performance, low-cost, and nontoxic SWIR light sources.

DUV electroluminescence from Bi3+-doped bi-phase yttrium phosphate

Trivalent-doped tetragonal xenotime yttrium orthophosphate phosphors have attracted significant attention as promising materials for deep ultraviolet (DUV) luminescence. In this study, we achieved DUV electroluminescence (EL) using Bi3+-doped bi-phase yttrium phosphate (YPB) phosphor under an AC-driven sinusoidal waveform. Phosphor powder was synthesized via a solid-state reaction with an optimal Bi3+ concentration. The phosphor exhibited a mixed phase of xenotime tetragonal YPO4 and monoclinic Y(PO3). We suggest that the mixed phase within the phosphor particles plays a crucial role in enhancing light generation via a bipolar field emission mechanism in the developed powder-based EL device. It emitted a narrow-band DUV emission spectrum peaking at 243 nm, which was attributed to the 3P1 → 1S0 transition of the Bi3+ ions within the mixed host lattices. Moreover, it has a lower voltage application than the excimer lamp DUV sources. The application of the YPB phosphor in EL devices presents an appealing outlook for future advancements in the development of DUV sources.

Patterned flexible Silver Nanowire/2D MXene transparent conducting electrode for organic light-emitting diodes

With the advent of numerous flexible optoelectronic applications, the importance of flexible and stable transparent conducting electrodes (TCEs) has been considerable. The conventional silver nanowire (AgNW) is a promising candidate as TCEs due to its decent opto-electrical properties and solution processibility. However, AgNW's high surface root mean square (RMS) roughness, relatively high sheet resistance, and low work function (∼4.5 eV) limit the usage for display applications. In this work, we design and study the AgNW and MXene (Ti3C2Tx) hybrid TCEs for flexible organic light-emitting diodes (OLEDs) to enhance the optoelectrical properties and the hole injection within the device. Experiment investigation is carried out via an application of AgNW/MXene (AgMX) hybrid TCEs as a bottom electrode for OLEDs devices in which the photolithography process and lift-off technique are employed for such fabrication. The hybrid TCEs indicate high optical transparency (86.8 % at 550 nm) and low sheet resistance (24.1 Ω/cm2) as well as improved surface morphology, enabling the efficient OLEDs operation. The optimized OLEDs exhibit a clear and stable red electroluminescence (EL) peak with an improved maximum external quantum efficiency (EQE) and luminance of 5.25 % and 3421.7 cd/m2, respectively. Furthermore, the hybrid TCEs are readily formed on poly(ethylene terephthalate) (PET) substrate, showing high durability under the bending test up to 100,000 cycles. The results demonstrate that adopting AgMX TCEs is a reasonable strategy for obtaining proper flexible optoelectronic devices.

On the Electroluminescence of InP Quantum Dots with Varied ZnSe/ZnS Shell Thickness

Quantum dots (QDs) have emerged as a highly promising material for future display applications, offering advantages such as tunable emission wavelengths, narrow linewidths, and the ability to cover a broad color gamut. Traditionally, cadmium selenide (CdSe) QDs have dominated the electroluminescence (EL) QD light-emitting Diode (QLED) landscape. However, the presence of toxic metal cadmium in CdSe QDs has raised environmental and safety concerns. In recent years, indium phosphide (InP) materials, free from heavy metals, have become a focal point in EL QLED research. For InP EL QLED, the shell structure of InP/ZnSe/ZnS core/shell/shell QDs plays a crucial role in influencing carrier behavior and device performance. In this study, we prepare InP QDs with three different shell thickness, including ZnSeS shell with thickness of more than 6 nm (InP/ZnSe/ZnS QD size > 15 nm), and explore their EL properties. The research aims to investigate the potential mechanisms governing the interplay between shell thickness and carrier recombination, contributing to the optimization of InP QLEDs. Figure 1

Photoluminescence and Electroluminescence Confocal Imaging of an OLED

In recent years organic light-emitting diodes (OLEDs) have become one of the leading technologies for full-colour display panels in high-end smartphones and televisions. This rapid growth in use has occurred because OLEDs offer an all-around superior performance to liquid crystal displays (LCDs). For example, they are thinner, lighter, more flexible, less power consumptive, and brighter.When new OLEDs are developed, the optoelectronic properties of individual components and the complete device can be characterised using photoluminescence (PL) and electroluminescence (EL) spectroscopy. In this poster presentation, we use a confocal Raman microscope to characterise and spatially resolve the optoelectronic properties of a fabricated OLED device with four imaging modalities: PL, EL, time-resolved PL (TRPL), and time-resolved EL (TREL). Using a confocal microscope to characterise an OLED's spectral and time-resolved properties provides much greater detail than bulk measurements. Figure 1

(Invited) Colloidal Quantum Dot Laser Diodes: Three Decades in the Making

It has been 30 years since the first demonstration of lasing with semiconductor nanocrystals embedded in glass matrices1 – the samples akin to standard colored glass filters. Following this discovery, it took three years to realize lasing with epitaxial QDs2 and six more years to demonstrate the effect of amplified spontaneous emission (ASE) – a precursor of lasing – with colloidal QDs.3 So far, all reported studies into colloidal QD lasing have utilized optically excited samples. However, most of the prospective technological applications require electrically pumped devices, that is, laser diodes. The realization of such devices is complicated by multiple problems, widely deemed insurmountable. These include extremely fast nonradiative Auger recombination of optical-gain-active multicarrier states, poor stability of QD films under high current densities required for lasing, and unfavorable balance between optical gain and optical losses in electroluminescent (EL) devices wherein a gain-active QD medium is a small fraction of an overall device stack comprising multiple optically lossy charge-transport layers.Here we resolve these problems and achieve strong ASE with electrically driven QDs.4 To demonstrate this effect, we employ compact, continuously graded QDs with strongly suppressed Auger recombination incorporated into a low-loss photonic waveguide integrated into a pulsed light-emitting diode capable of operating at current densities of up to ~2000 A cm-2. These prototype ASE-type laser diodes exhibit strong, broad-band optical gain and demonstrate low-threshold, room-temperature ASE which leads to intense, edge-emitted EL whose instantaneous power reaches ~200 mW. 1. Vandyshev, Y. V., Dneprovskii, V. S., Klimov, V. I. & Okorokov, D. K. Lasing on a transition between quantum-well levels in a quantum dot. JETP Lett. 54, 442-445 (1991).2. Kistaedter, N., Ledentsov, N. N., Grundmann, M., Bimberg, D., Ustinov, V. M., Ruvimov, S. S., Maximov, M. V., Kopev, P. S., Alferov, Z. I. & Richter, U. Low threshold, large To injection laser emission from (InGa)As quantum dots. Electron. Lett. 30, 1416 (1994).3. Klimov, V. I., Mikhailovsky, A. A., Xu, S., Malko, A., Hollingsworth, J. A., Leatherdale, C. A., Eisler, H. J. & Bawendi, M. G. Optical gain and stimulated emission in nanocrystal quantum dots. Science 290, 314-317 (2000).4. Ahn, N., Livache, C., Pinchetti, V., Jung, H., Jin, H., Hahm, D., Park, Y.-S. & Klimov, V. I. Electrically driven amplified spontaneous emission from colloidal quantum dots. Nature 617, 79-85 (2023).

Limited impact of the sidewall effect in dependence of temperature for InGaN-based blue micro-LEDs grown on a silicon substrate.

The electroluminescence (EL) properties of InGaN-based micro-LEDs grown on a silicon substrate are investigated in this Letter to reveal the dominant mechanism in dependence on different temperatures and dimensions. The invalidation of sidewall nonradiative recombination and the impact of localization-induced carrier tunneling on the external quantum efficiency (EQE) are analyzed systematically to realize high performance silicon-based micro-LEDs. Microscopic EL mapping exhibits that the localized carriers in the silicon-grown micro-LED mainly recombine in the central region of mesa. The defects in the multiple quantum wells (MQWs) grown on the silicon substrate can lead to carrier tunneling and EQE reduction at cryogenic temperatures below 200 K, which is more conspicuous for the 30 μm device with a larger inner area ratio. The low-temperature EQE evolution can be attributed to the trade-off between localization-induced tunneling and Shockley-Read-Hall (SRH) recombination.

AC‐Driven Plasmon Waveguide Integrated Electroluminescent Device

AbstractPhotonic elements have greater information‐carrying capabilities compared to electronic components, making the development of high‐speed, chip‐integrated optical communication devices crucial for addressing interconnect bottlenecks in high‐speed computing systems. Significant progress has been made in studying light sources and their transmission. Despite these advancements, achieving a satisfactory integration of photonic circuits with both light source and optical waveguide functions has remained a challenge. Here, a silver nanowire (AgNW) waveguide‐integrated light source is demonstrated driven by alternating current (AC) voltage. AgNW functions as both the electrode and waveguide to simplify the device structure, and the 2D transition metal dichalcogenides (TMDs) monolayer acts as the gain media in device. The electroluminescence (EL) can be tunably modulated via adjusting the frequency and voltage of the AC in this device, and it is also successfully coupled into the waveguide with its transmission distance up to 25 µm. The experiments of electroluminescence and waveguide transmission of different materials and their interlayer excitons have made a preliminary exploration of multiple wavelength transmission. It provides a new research platform forward in the development of chip‐integrated optical communication devices, thereby hopefully addressing the interconnect bottleneck and unlocking the potential for enhanced performance and efficiency in high‐speed computing systems.

Achieving white electroluminescence and low current consumption in devices based on graphene oxide and silicon

This work reports the emission of white electroluminescence (EL) in devices based on silicon. These devices are formed by a heterostructure of porous silicon (PSi), graphene oxide (GO), silicon-rich-oxide (SRO) thin films, and zinc oxide (ZnO) as a transparent conductor oxide (contact). The current consumption in these devices has been reduced by approximately three orders of magnitude compared to the current currents commonly reported for electroluminescent devices. The white EL emission is corroborated by the EL spectra, which are very broad (from 400 to 750 nm) and are attributed to the different nanostructured defects present in the materials that make up the heterostructures. The devices exhibited EL only in negative bias. According to our analysis of the I–V curves, the space-charge limited current conduction mechanism is the dominant carrier conduction mechanism in the region where the EL takes place. The electroluminescence exhibited by these devices starts at a current of 1.1 μA and is the entire area electroluminescent at approximately 3 μA reaches its maximum value at 9 μA. We demonstrated that producing LEDs on a Si substrate can result in significant energy savings.

Quantum Dot-Based Three-Stack Tandem Near-Infrared-to-Visible Optoelectric Upconversion Devices.

Quantum dots (QDs) exhibit size-tunable optical properties, making them suitable for efficient light-sensing and light-emitting devices. Tandem devices that can convert near-infrared (NIR) to visible (Vis) signals can be fabricated by integrating an NIR-sensing QD device with a Vis electroluminescence (EL) QD device. However, these devices require delicate control of the QD layer during processing to prevent damage to the predeposited QD layers in tandem devices during the subsequent deposition of other functional layers. This has restricted attainable device structures for QD-based upconversion devices. Herein, we present a modular approach for fabricating QD-based optoelectric upconversion devices. This approach involves using NIR QD-absorbing (Abs) and Vis QD-EL units as building modules, both of which feature cross-linked functional layers that exhibit structural tolerance to dissolution during subsequent solution-based processes. Tandem devices are fabricated in both normal (EL unit on Abs unit) and inverted (Abs unit on EL unit) structures using the same set of NIR QD-Abs and Vis QD-EL units stacked in opposite sequences. The tandem device in the normal structure exhibits a high NIR photon-to-Vis-photon conversion efficiency of up to 1.9% in a practical transmissive mode. By extending our modular approach, we also demonstrate a three-stack tandem device that incorporates a single NIR-absorbing unit coupled with two EL units, achieving an even higher conversion efficiency of up to 3.2%.

Tunable Ag Nanocavity Enhanced Green Electroluminescence from SiNx:O Light-Emitting Diode.

As the driving source, highly efficient silicon-based light emission is urgently needed for the realization of optoelectronic integrated chips. Here, we report that enhanced green electroluminescence (EL) can be obtained from oxygen-doped silicon nitride (SiNx:O) films based on an ordered and tunable Ag nanocavity array with a high density by nanosphere lithography and laser irradiation. Compared with that of a pure SiNxO device, the green electroluminescence (EL) from the SiNx:O/Ag nanocavity array device can be increased by 7.1-fold. Moreover, the external quantum efficiency of the green electroluminescence (EL) is enhanced 3-fold for SiNx:O/Ag nanocavity arrays with diameters of 300 nm. The analysis of absorption spectra and the FDTD calculation reveal that the localized surface plasmon (LSP) resonance of size-controllable Ag nanocavity arrays and SiNx:O films play a key role in the strong green EL. Our discovery demonstrates that SiNx:O films coupled with tunable Ag nanocavity arrays are promising for silicon-based light-emitting diode devices of the AI period in the future.

Anomalous Electroluminescence Characteristics of Perovskite Modules.

Spatially resolved photoluminescence (PL) and electroluminescence (EL) imaging technologies play a crucial role in evaluating the performance and stability of photovoltaic devices. However, their application in perovskite devices presents unique challenges. In this study, we report a discrepancy between the electrical performance of perovskite solar modules (PSMs) and the EL images. Following the application of a reverse bias voltage, we observed an increase in EL brightness associated with prolonged carrier lifetime and transport length. Furthermore, cross-sectional Kelvin probe force microscopy identified a significant potential increase primarily at the electron-transport layer (ETL) side after reverse bias, suggesting the presence of defective ETL/perovskite interfaces with filled hole traps. To address this EL mismatch, we proposed a mild reverse current recovery method aimed at aligning EL images with the cell performance without compromising device efficiency. This approach effectively mitigates discrepancies, ensuring alignment between the device performance and EL imaging. Our study underscores that caution is required when utilizing EL imaging to monitor spatial homogeneity in PSMs for future industrial production.