Peak External Quantum Efficiency Research Articles

Multivalent-effect immobilization of reduced-dimensional perovskites for efficient and spectrally stable deep-blue light-emitting diodes.

Despite substantial advances in green and red metal halide perovskite light-emitting diodes (PeLEDs), blue PeLEDs, particularly deep-blue ones (defined as Commission International de l'Eclairage y coordinate (CIEy) less than 0.06) that meet the latest Rec. 2020 colour gamut standard, lag dramatically behind owing to a severe phase segregation-induced electroluminescent spectral shift and low exciton utilization in broadened bandgap perovskite emitters. Here we propose a multivalent immobilization strategy to realize high-efficiency and spectrally stable deep-blue PeLEDs by introducing a polyfluorinated oxygen-containing molecule. Systematic experiments and extensive 5,000 fs ab initio molecular dynamics simulations reveal that a crucial role of the multivalent effect stemming from three kinds of interaction of hydrogen bond (F···H-N), ionic bond (F-Pb) and coordination bond (C=O:Pb) with perovskite is to synergistically stabilize the perovskite phase and enhance exciton radiative recombination. The resultant exciton concentration and exciton recombination rate of the deep-blue perovskite emitter are increased by factors of 1.66 and 1.64, respectively. In this context, our target PeLEDs demonstrate a peak external quantum efficiency of up to 15.36% at a deep-blue emission wavelength of 459 nm and a half-lifetime of 144 min at a constant current density of 0.45 mA cm-2. Moreover, the deep-blue PeLEDs maintain a constant spectrum peak with CIE chromaticity coordinates of (0.136, 0.051) under a steady driving current for 60 min.

Enhanced size-dependent efficiency of InGaN/AlGaN near-ultraviolet micro-LEDs

This study presents an approach for enhancing the external quantum efficiency (EQE) of multiple-quantum-well InGaN/AlGaN near-ultraviolet (NUV) micro-light-emitting diodes (micro-LEDs) without changing the epitaxial layer. Unlike the size-dependent EQE reduction observed in blue, green, and red micro-LEDs, the EQE of NUV micro-LEDs at high current densities (≥10 A/cm2) improves as the device dimensions shrink from 500 × 500 μm2 to 20 × 20 μm2. A 20 × 20 μm2 micro-LED achieves a peak EQE of 12.3%, compared to 8.60% for a larger 500 × 500 μm2 micro-LED. Experimental results attribute this EQE enhancement to improved light-extraction efficiency, driven by better current spreading. In larger micro-LEDs, pronounced current crowding causes carrier overflow from the active region, leading to reduced EQE at high current densities. These findings highlight the promising potential of NUV micro-LEDs for diverse applications.

Sulfonic Acid Ligands Promote Surface Reconstruction of Perovskite Quantum Dots for High‐Performance Light‐Emitting Diodes

AbstractPerovskite quantum dots (PQDs) have emerged as promising candidates for next‐generation high‐quality lighting and high‐definition displays due to their outstanding luminescence properties, characterized by a narrow emission spectrum and tunable color. However, during the purification process involving polar solvents, ligand detachment from the quantum dot surface often induces crystal defects, thereby compromising their long‐term stability. Herein, the effects of various post‐processing strategies on PQD performance are systematically explored, including the use of oleic acid (OA), didodecyldimethylammonium bromide (DDAB), and their combinations, alongside OA‐assisted synthesis. Furthermore, a synergistic post‐processing strategy based on DDAB‐NaMeS (sodium methanesulfonate) is proposed to elucidate the mechanism of ligand reconstruction on the quantum dot surface during purification. The resulting PQDs demonstrated excellent stability over a storage period exceeding one month, and the corresponding Quantum Dots Light‐Emitting Diodes (QLEDs) achieved a peak external quantum efficiency (EQE) of 9.82%, representing a 1.91‐fold improvement over standard devices. These QLEDs exhibited exceptional optoelectronic performance, underscoring their potential for application in other sulfonic acid ligands and perovskite‐based materials.

Supercycle Al-Doped ZnMgO Alloys via Atomic Layer Deposition for Quantum Dot Light-Emitting Diodes.

Colloidal quantum-dot light-emitting diodes (QD-LEDs) have been significantly improved in terms of device performance and lifetime by employing zinc oxide (ZnO) as an electron transport layer (ETL). Although atomic layer deposition (ALD) allows fabrication of uniform, high-quality ZnO films with minimal defects, the high conductivity of ZnO has hindered its straightforward application as an ETL in QD-LEDs. Herein, we propose fabrication of Al-doped ZnMgO (Al:ZnMgO) ETLs for QD-LEDs through a supercycle ALD, with alternating depositions of various metal oxides. The supercycle ALD allows for extensive control of compositions, which is not possible in typical hydrolysis-based approaches. ZnMgO alloys produced by ALD adjust the band gap to match the QDs and suppress the electron injection. However, Mg compositions of >10% lead to a reduction in electron conductivity, limiting the charge balance in the QDs. The Al doping provides Al3+ ions, oxygen vacancies, and zinc interstitials to compensate for the reduced conductivity of ZnMgO. Composition tuning based on the supercycle ALD enables to realize the ETLs offering optimal electron injection capability without compromising the electrical conductivity. QD-LEDs with the Al:ZnMgO ETLs exhibit a peak external quantum efficiency of 15.7% and peak luminance of 167,000 cd m-2, on par with typical devices using ZnMgO nanocrystal-based ETLs.

Thianthrene 5,5,10,10-tetraoxide-based phosphorescent platinum(II) complexes for solution-processed organic light-emitting diode (OLED) with external quantum efficiency approach 25 %

Thianthrene 5,5,10,10-tetraoxide-based phosphorescent platinum(II) complexes for solution-processed organic light-emitting diode (OLED) with external quantum efficiency approach 25 %

High external quantum efficiency in InGaN-based green micro-light emitting diodes at ultra-low current density by removing pre-wells

Abstract InGaN-based green light-emitting diodes with different pre-well numbers were grown by organometallic vapor phase epitaxy deposition method on patterned sapphire substrates. Micro-LED chips with a size of 17×20μm² were fabricated, and a peak external quantum efficiency (EQE) of 39% was achieved at ultra-low current density of 0.07A/cm². The EQE variation curves of different samples were studied under different current densities. It was confirmed that by reducing the number of pre-wells the Shockley-Read-Hall non-radiative recombination under ultra-low current density was suppressed, which ultimately results in a high EQE of Micro-LEDs.

Grain engineering for efficient near-infrared perovskite light-emitting diodes

Metal halide perovskites show promise for next-generation light-emitting diodes, particularly in the near-infrared range, where they outperform organic and quantum-dot counterparts. However, they still fall short of costly III-V semiconductor devices, which achieve external quantum efficiencies above 30% with high brightness. Among several factors, controlling grain growth and nanoscale morphology is crucial for further enhancing device performance. This study presents a grain engineering methodology that combines solvent engineering and heterostructure construction to improve light outcoupling efficiency and defect passivation. Solvent engineering enables precise control over grain size and distribution, increasing light outcoupling to ~40%. Constructing 2D/3D heterostructures with a conjugated cation reduces defect densities and accelerates radiative recombination. The resulting near-infrared perovskite light-emitting diodes achieve a peak external quantum efficiency of 31.4% and demonstrate a maximum brightness of 929 W sr−1 m−2. These findings indicate that perovskite light-emitting diodes have potential as cost-effective, high-performance near-infrared light sources for practical applications.

Efficient and Long Lifetime Red InP‐Based QLEDs Enabled by Simultaneously Improved Carrier Injection Balance and Depressed Leakage

AbstractInP quantum dots (QDs), without heavy metals, show great potential for display and lightening applications. However, achieving efficient InP‐based quantum dot light‐emitting diodes (QLEDs) with extended operational lifetime remains challenging due to unbalanced carrier injection within the device. In this study, polyvinyl pyrrolidone (PVP) is introduced as an intermediate layer between the QDs emitting layer (EML) and the ZnMgO electron transport layer (ETL). This intermediate layer is designed to block excess electron injection into the QDs layer and simultaneously reduce leakage current. Additionally, the introduction of PVP can passivate QDs/ETL interface defects and inhibit exciton quenching of QDs by the ZnMgO ETL. The optimized device achieves a peak external quantum efficiency (EQE) of 23.5% and a long T95 operational lifetime of over 800 h at an initial luminance of 1000 cd m−2 for red InP‐based QLEDs emitting at 624 nm. Both the EQE and the T95 operational lifetime represent the highest values achieved for red InP‐based QLEDs to date.

Influence of the AlN-sapphire template on the optical polarization and efficiency of AlGaN-based far-UVC micro LED arrays

Abstract Arrays of far-UVC micro light emitting diodes (LEDs) based on AlGaN and emitting at 233–235 nm have been fabricated on different types of AlN-sapphire templates and the optical polarization, output power, and efficiencies have been studied in dependence of the template technology and the mesa diameter of the micro-pixels. While LEDs fabricated on metal organic vapor phase epitaxy (MOVPE) AlN-sapphire templates show dominant TM polarized emission with a degree of polarization (DoP) of −0.2, LEDs on high temperature annealed AlN-sapphire templates show dominant TE polarized emission with a DoP of 0.2–0.3. The output power and external quantum efficiency increases with decreasing diameter of the slanted and reflective micro LED mesa. Peak output powers of 18 mW at 200 mA and peak external quantum efficiencies of up to 2.7% for mesa diameters of 1.5 µm on annealed templates were measured, corresponding to peak wall plug efficiencies of 1.7%, while conventional LEDs with large mesa areas on the same template showed maximum EQEs of 1.1%. The relative increase in output power by using the micro LED approach as compared to a conventional large area emitter is stronger for LEDs on MOVPE AlN templates than on annealed templates (about a factor of 3.7 vs. 2.3, respectively, at 50 mA) which is attributed to the polarization dependence of the light extraction.

Improving Optical Efficiency and Luminance of GaN-Based Micro-Light-Emitting Diodes for High-Resolution Displays via NH3 Plasma Pretreatment.

GaN-based micro-light-emitting diodes (Micro-LEDs) are regarded as promising light sources for near-eye-display applications such as augmented reality/virtual reality (AR/VR) displays due to their high resolution, high brightness, and low power consumption. However, the application of Micro-LEDs in high-pixel-per-inch (PPI) displays is constrained by the drop in efficiency caused by sidewall defects in small-sized devices. In this study, a process method involving NH3 plasma pretreatment to reduce sidewall defects is proposed and investigated for enhancing the external quantum efficiency (EQE) of small-sized devices. The influence of NH3 plasma pretreatment on the GaN surface is investigated and analyzed by the X-ray photoelectron spectroscopy (XPS) characterizations and compared with H2 plasma pretreatment for further discussions on the mechanism. The enhancement in EQE and luminance of devices with different sizes by NH3 plasma pretreatment is observed and discussed. For the 10 μm Micro-LED, a peak EQE of 20.2% is achieved, representing a 33.8% improvement compared with that of the untreated device. At 200 A/cm2, the luminance of the 10 μm device with NH3 plasma pretreatment is 1.64 × 107 cd/m2, exhibiting a 49% increase compared with the untreated device.

Large Scale Synthesis of Red-Emitting Quantum Dots for Efficient and Stable Light-Emitting Diodes.

It is known that large-scale synthesis of emitters affords colloidal quantum dot (CQD) materials with a great opportunity toward the mass production of quantum dot light-emitting diodes (QLEDs) based commercial electronic products. Herein, an unprecedented example of scalable CQD (> 0.5 kilogram) is achieved by using a core/shell structure of CdZnSe/ZnSeS/CdZnS, in which CdZnSe, ZnSeS, and CdZnS alloys are used as the inner core, transition layer and outermost shell, respectively. It exhibits a high fluorescence quantum yield (>90%), a robust excited state, and a fast radiative transition rate. The investigation of morphology and surface state reveals the possible reasons for such excellent optical properties, which include uniform size distribution, no undesired byproducts, and high defect tolerance. The QLEDs exhibit a peak external quantum efficiency of over 21%, a high luminance of over 9.5×104cd m-2, and a long lifetime of over 1.0×106 h, corresponding to the state-of-the-art performance among the QLEDs based on the large-scale synthesis of CQDs. Therefore, it is believed that an efficient and reliable strategy is provided toward the large-scale synthesis of CQDs, which can be used as emitters in the QLEDs-based commercial electronic devices and make the mass production of these products a reality.

High triplet energy host material with a 1,3,5-oxadiazine core from a one-step interrupted Fischer indolization

Energy-efficient and deep-blue organic light-emitting diode (OLED) with long operating stability remains a key challenge to enable a disruptive change in OLED display and lighting technology. Part of the challenge is associated with a very narrow choice of the robust host materials having over 3 eV triplet energy level to facilitate efficient deep-blue emission and deliver excellent performance in the OLED device. Here we show the molecular design of new 1,3,5-oxadiazines (NON)-host materials with high triplet energy over 3.2 eV, enabling deep-blue OLED devices with a peak external quantum efficiency of 21%. A series of NON-host materials are prepared by the condensation of substituted arylhydrazines and cyclohexylcarbaldehyde in a 2:3 ratio. This straightforward “one-pot” procedure enables the formation of indoline-containing derivatives with three fused heterocyclic rings and two stereogenic centres. All materials emit UV-fluorescence in the range of 315–338 nm while possessing highly desirable characteristics for application in deep-blue OLED devices: good thermal stability, a wide energy gap (3.9 eV), a high triplet energy level of (3.3 eV), and excellent volatility during sublimation.

Bright and Efficient CsSnBr3 Light-Emitting Diodes Enabled by Interfacial Reaction-Assisted Crystallization.

Tin-based perovskites are more environmentally friendly than their lead-based alternatives. Perovskite light-emitting diodes (PeLEDs) using iodide-based tin perovskites have achieved considerable advancements in efficiency. However, PeLEDs using bromide-based tin perovskites have not progressed as rapidly, primarily due to challenges in controlling their crystallization processes. Here, an interfacial reaction-assisted crystallization method is introduced to achieve bright and efficient CsSnBr3 PeLEDs. It is started by forming an intermediate phase through the coordination of SnBr2 with ethylenediamine derivatives. Subsequently, a protonation reaction is designed between the intermediate phase and the acidic polyethylenedioxythiophene: poly(styrene sulfonate) hole-transport layer to generate high-quality CsSnBr3 films. Additionally, the use of potassium thiocyanate additives effectively enhances the photoluminescence efficiency of the CsSnBr3 films. These efforts result in CsSnBr3-based PeLEDs achieving a maximum luminance of 787cdm-2 and a peak external quantum efficiency of 0.91%, demonstrating the most efficient and brightest CsSnBr3-based PeLEDs to date. This work opens an avenue to better control the crystallization of tin-based perovskite.

Chloride Vapor Annealing for Efficient Deep-Blue Perovskite Light-Emitting Diodes.

Achieving deep-blue emission is crucial for the practical application of perovskite light-emitting diodes (LEDs) in displays. Increasing the ratio of chlorine to bromine in the perovskite is a facile method to achieve deep-blue emission. However, the low solubility of chloride in the perovskite precursor solution and the low formation energy of defects present challenges that limit device efficiency. Here, we demonstrate a chloride vapor annealing method utilizing ethylammonium chloride (EAC) to enable in situ halide exchange and defect passivation. We find that the chloride ions from EAC can effectively exchange with the bromide ions in the perovskite, resulting in blue-shifted emission. Additionally, the ammonium group in EAC can coordinate with unsaturated lead, reducing trap-assisted nonradiative recombination. Based on this approach, we achieve efficient deep-blue perovskite LEDs with a peak external quantum efficiency of 6.8% and color coordinates of (0.131, 0.044), which fully meet the Rec. 2020 blue standard.

High-Performance Green and Blue Light-Emitting Diodes Enabled by CdZnSe/ZnS Core/Shell Colloidal Quantum Wells.

The unique anisotropic properties of colloidal quantum wells (CQWs) make them highly promising as components in nanocrystal-based devices. However, the limited performance of green and blue light-emitting diodes (LEDs) based on CQWs has impeded their practical applications. In this study, alloy CdZnSe core CQWs with precise compositions are tailored via direct cation exchange (CE) from CdSe CQWs with specific size, shape, and crystal structure and utilized hot-injection shell (HIS) growth to synthesize CdZnSe/ZnS core/shell CQWs exhibiting exceptional optoelectronic characteristics. This approach enabled the successful fabrication green and blue LEDs manifesting superior performance compared to previously reported solution-processed CQW-LEDs. The devices demonstrated a remarkable peak external quantum efficiency (20.4% for green and 10.6% for blue), accompanied by a maximum brightness 347,683cd m-2 for green and 38,063cd m-2 for blue. The high-performance represents a significant advancement for nanocrystal-based light-emitting diodes (Nc-LEDs) incorporating anisotropic nanocrystals. This work provides a comprehensive synthesis strategy for enhancing the efficiency of Nc-LEDs utilizing anisotropic nanocrystals.

Screening Fluorination Additives for Efficient Perovskite Light-Emitting Diodes.

Fluorinated additives are proposed to address the issue of domain polydispersity in quasi-2D perovskites. However, the lack of established screening criteria for these additives necessitates a laborious and costly trial-and-error process. Herein, this work explores the behind nature for the first time how various fluorination in fluorinated additives affect domain distribution in quasi-2D perovskites. The studies reveal that fully fluorinated additives could suppress undesirable low-dimensional domains, facilitating efficient energy transfer, while partially fluorinated additives adversely cause deteriorated optical properties. The observed trend is ascribed to the molecular dipole moment of the fluorinated additives, offering a reasonable explanation for experimental phenomena that has never been reported before. By employing fully fluorinated additives, the fabricated sky-blue perovskite light-emitting diodes (PeLEDs) deliver a peak external quantum efficiency (EQE) of 20.38% (@488nm), marking as one of the highest efficiencies reported to date. The finding provides a screening criterion for fluorinated additives to realize efficient PeLEDs.

Efficient green InP-based QD-LED by controlling electron injection and leakage.

Green indium phosphide (InP)-based quantum dot light-emitting diodes (QD-LEDs) still suffer from low efficiency and short operational lifetime, posing a critical challenge to fully cadmium-free QD-LED displays and lighting1-3. Unfortunately, the factors that underlie these limitations remain unclear and, therefore, no clear device-engineering guidelines are available. Here, by using electrically excited transient absorption spectroscopy, we find that the low efficiency of state-of-the-art green cadmium-free QD-LEDs (which ubiquitously adopt the InP-ZnSeS-ZnS core-shell-shell structure) originates from the ZnSeS interlayer because it imposes a high injection barrier that limits the electron concentration and trap saturation. We demonstrate, both experimentally and theoretically, that replacing the currently widely used ZnSeS interlayer with a thickened ZnSe interlayer enables improved electron injection and depressed leakage simultaneously, allowing to achieve a peak external quantum efficiency of 26.68% and T95 lifetime(time for theluminance to dropto 95% of the initial value) of 1,241 h at an initial brightness of 1,000 cd m-2 in green InP-based QD-LEDs emitting at 543 nm-exceeding the previous best values by a factor of 1.6 and 165, respectively3,4.

Optimization of P-electrode structures to enhance current spreading uniformity in micro-LEDs.

In this study, we designed and fabricated parallel-connected green micro-LEDs with three different P-electrode configurations: rounded (Sample A), cross-shaped (Sample B), and circular (Sample C). We then systematically evaluated the impact of these electrode shapes on the devices' optoelectronic performance. The results show that the shape of the P-electrode significantly influences the optoelectronic performance of micro-LEDs. With a round mesa, Sample C exhibits the lowest operating voltage and the smallest dynamic resistance and achieves a peak external quantum efficiency (EQE) of 19.57%, which is 25.53% and 11.13% higher than that of Sample A (15.59%) and Sample B (17.61%), respectively. The analysis suggests that this improvement is mainly due to enhanced uniformity in current spreading and shorter current injection paths. COMSOL simulations, along with thermal resistance and surface temperature measurements, confirm that different P-electrode shapes affect the uniformity of current distribution in micro-LEDs, which in turn impacts the device's thermal performance. TracePro simulation results further demonstrated that circular P-electrodes optimize the light output of the device. We believe that this study provides a valuable reference for the design and fabrication of micro-LED chips.

Boosting carrier transport via functionalized short-chain conjugated ligands enables efficient green perovskite quantum dot light-emitting diodes

Boosting carrier transport via functionalized short-chain conjugated ligands enables efficient green perovskite quantum dot light-emitting diodes

Solution Processed Bilayer Metal Halide White Light Emitting Diodes.

Metal halide perovskites and perovskite-related organic metal halide hybrids (OMHHs) have recently emerged as a new class of luminescent materials for light emitting diodes (LEDs), owing to their unique and remarkable properties, including near-unity photoluminescence quantum efficiencies, highly tunable emission colors, and low temperature solution processing. While substantial progress has been made in developing monochromatic LEDs with electroluminescence across blue, green, red, and near-infrared regions, achieving highly efficient and stable white electroluminescence from a single LED remains a challenging and under-explored area. Here, a facile approach to generating white electroluminescence is reported by combining narrow sky-blue emission from metal halide perovskites and broadband orange/red emission from zero-dimensional (0D) OMHHs. For the proof of concept, utilizing TPPcarz+ passivated two-dimensional (2D) CsPbBr3 nanoplatelets (NPLs) as sky blue emitter and 0D TPPcarzSbBr4 as orange/red emitter (TPPcarz+ = triphenyl (9-phenyl-9H-carbazol-3-yl) phosphonium), white LEDs (WLEDs) with a solution processed bilayer structure have been fabricated to exhibit a peak external quantum efficiency (EQE) of 4.8% and luminance of 1507 cd m-2 at the Commission Internationale de L'Eclairage (CIE) coordinate of (0.32, 0.35). This work opens a new pathway for creating highly efficient and stable WLEDs using metal halide perovskites and related materials.