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Electrochemical capacitance-voltage profiling of nonuniformly doped GaAs heterostructures with SQWs and MQWs for LED applications
摘要： Light-emitting heterostructures with single and multiple GaAs/InGaAs quantum wells have been investigated by means of electrochemical capacitance-voltage (ECV) profiling. Capacitance-voltage characteristics were measured; concentration profiles of free charge carriers over the heterostructure depth as well as the intensity of quantum well filling by charge carriers were obtained. In heterostructures with a single quantum well (QW) we considered limitations of capacitance techniques for undoped QW profiling, which is situated near the metallurgic border of the p–n –junction. We made a detailed consideration of phenomena related to Debye smearing and we developed and analyzed the dependence of the space charge region width on the doping. Special attention was paid to investigation of the “blind” area. This was inspired by the practical problem from capacitance spectroscopy of semiconductors, when the researcher poses the task of obtaining a free charge carrier depth distribution profile as deep as possible in the space charge region, i.e. where the intensity of the electric field is maximum. Generally, the active QW of a LED heterostructure is placed deep in the space charge region, so reaching these regions is extremely important for practical problems. We present an evolution of capacitance-voltage characteristics during ECV profiling of nonuniformly doped p – n– heterostructures. For a heterostructure with multiple quantum wells we registered a response from 6 QWs.
关键词： capacitance-voltage profiling,heterostructure,quantum well,nonuniform doping,Electrochemical capacitance-voltage profiling,quantum dot,light-emitting diodes
更新于2025-11-14 17:28:48
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Highly Stable Red Quantum Dot Light Emitting Diodes with Long T <sub/>95</sub> Operation Lifetime
摘要： Quantum dot light-emitting diodes (QLEDs) with excellent performances such as external quantum efficiency (EQE) and lifetime have almost met the requirement of low brightness display. However, the short operation lifetime under high brightness limits the application of QLEDs in outdoor displays and lightings. Herein, we report a highly efficient, stable red QLED by using of lithium and magnesium co-doped as well as magnesium oxide shell-coated zinc oxide nanoparticle layer as electron transport layer (ETL). The optimized QLED has a high peak EQE of 20.6%, a low efficiency roll-off at high current, and a remarkably long lifetime T95 > 11000 h at 1000 cd m-2, which indicates the realization of the most stable red QLED up to now. The improvement in the long-term stability of the QLED is attributed to the use of co-doped and shell-coated zinc oxide ETL with reduced electron injection to improve the charge balance in device.
关键词： EQE,QLEDs,electron transport layer,ETL,magnesium oxide shell-coated zinc oxide,Quantum dot light-emitting diodes,external quantum efficiency,lithium and magnesium co-doped,ZLMO@MO,lifetime
更新于2025-09-23 15:21:01
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High efficiency and stability of ink-jet printed quantum dot light emitting diodes
摘要： The low efficiency and fast degradation of devices from ink-jet printing process hinders the application of quantum dot light emitting diodes on next generation displays. Passivating the trap states caused by both anion and cation under-coordinated sites on the quantum dot surface with proper ligands for ink-jet printing processing reminds a problem. Here we show, by adapting the idea of dual ionic passivation of quantum dots, ink-jet printed quantum dot light emitting diodes with an external quantum efficiency over 16% and half lifetime of more than 1,721,000 hours were reported for the first time. The liquid phase exchange of ligands fulfills the requirements of ink-jet printing processing for possible mass production. And the performance from ink-jet printed quantum dot light emitting diodes truly opens the gate of quantum dot light emitting diode application for industry.
关键词： quantum dot light emitting diodes,ink-jet printing,external quantum efficiency,dual ionic passivation,lifetime
更新于2025-09-23 15:21:01
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Large Performance Enhancement in All-Solution-Processed, Full-Color, Inverted Quantum Dot Light-Emitting Diodes by Using Graphene Oxide-Doped Hole Injection Layer
摘要： Solution-processed hole injection layers (HILs) for full-color, inverted quantum dot light-emitting diodes (QLEDs) are developed by simply incorporating the graphene oxide (GO) into poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). The excellent wettability of the GO-doped PEDOT:PSS mixture facilitates the effective deposition of HIL onto the organic underlayer. Ultraviolet photoelectron spectroscopy and Raman spectroscopy characterization reveal that the GO-doped PEDOT:PSS HIL possesses the advantages of increased work function and improved conductivity. Thus, the GO-doped PEDOT:PSS HIL can promote hole injection from the top anode into the device by reducing the hole injection barrier and sheet resistance. As a result, by using the GO-doped PEDOT:PSS HIL, we have successfully demonstrated highly bright all-solution-processed, full-color, inverted QLEDs showing remarkably enhanced luminance of 142165, 63318, and 3019 cd/m2 for green, red, and blue devices, respectively. To the best of our knowledge, the green device’s luminance is the best for all-solution-processed inverted green QLEDs. These results suggest that the GO-doped PEDOT:PSS is a promising candidate for high-quality HIL in all-solution-processed QLEDs with an inverted structure.
关键词： Optical,Quantum Dot Light-Emitting Diodes,Hole Injection Layer,Plasmonics,Magnetic,Hybrid Materials,Graphene Oxide,PEDOT:PSS
更新于2025-09-23 15:21:01
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Light extraction from quantum dot light emitting diodes by multiscale nanostructures
摘要： Improving the light extraction efficiency by introducing optical–functional structures outside of quantum dot light emitting diodes (QLED) for further enhancing the external quantum efficiency (EQE) is essential for its application in display and lighting industrialization. Although the efficiency of QLED has been optimized by controlling of the synthesis of the quantum dots, the low outcoupling efficiency is indeed unresolved because of total internal reflections, waveguides and metal surface absorptions within the device. Here, we are utilizing multiscale nanostructures attaching to the outer surface of the glass substrate to extract the trapped light from the emitting layers of QLED. The result indicates that both the EQE and luminance are improved from 12.29% to 17.94% and 122400 cd m-2 to 178700 cd m-2, respectively. The maximum EQE and current efficiency improve to 21.3% and 88.3 cd A?1, respectively, which are the best performance among reported green QLED with light outcoupling nanostructures. The improved performance is ascribed to eliminate total internal reflection by multiscale nanostructures attached to the outer surface of the QLED. Additionally, the simulation result of Finite-difference time domain (FDTD) also demonstrates the light trapping effect is reduced by the multiscale nanostructures. The design of the novel light outcoupling nanostructure for further improving the efficiency of QLED can promote its application in display and lighting industrializations.
关键词： quantum dot light emitting diodes,multiscale nanostructures,light extraction efficiency,external quantum efficiency,display and lighting industrialization
更新于2025-09-23 15:19:57
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Solution-processed blue quantum-dot light-emitting diodes based on double hole transport layers: Charge injection balance, solvent erosion control and performance improvement
摘要： Solution processed quantum-dot based light emitting diodes (QLEDs) usually suffer from the issues of imbalanced carrier injection (especially for blue QLEDs) and solvent erosion, which prevents these devices from reaching high performance. Here we report a simple and effective method of promoting hole injection and mitigating solvent erosion simultaneously for fabricating high-performance blue QLEDs. Poly [(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(p-butylphenyl))-diphenylamine)] (TFB)/Lithium bis(trifluoromethanesulfonimide) (Li-TFSI)-doped poly(9-vinlycarbazole) (PVK) bi-layers with smooth surfaces/interfaces, prepared via a solution-process by utilizing 1,4-dioxane as the solvent for PVK, were used as hole transport layers (HTLs) for improving the performance of blue QLEDs. The TFB/Li-doped PVK based QLED records 5829 cd/m2 of maximum brightness and 5.37% of peak EQE, which represents 1.1-fold increase in brightness and ~11.5-fold increase in EQE as compared with the devices based on TFB-only HTLs. The enhanced performance for these TFB/Li-doped PVK based QLEDs can be ascribed to more efficient hole injection offered by Li-doped bilayer HTLs with smooth surfaces/interfaces and stepwise energy level alignment. The CIE 1931 color coordinates (0.15, 0.03) for these TFB/Li-doped PVK based QLEDs are close to the National Television System Committee (NTSC) standard blue CIE coordinates, showing promise for use in next-generation full-color displays. This work provides a facile solution method of fabricating TFB/Li-doped PVK bi-layers with smooth surfaces/interfaces and proves the superiority of these TFB/Li-doped PVK bi-layered HTLs in hole transport and injection for high-performance blue QLEDs.
关键词： double hole transport layers,blue quantum-dot light-emitting diodes,charge injection；Lithium salt doped hole transport layer,solvent erosion,solution processability
更新于2025-09-23 15:19:57
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Highly Efficient Quantum Dot Light‐Emitting Diodes by Inserting Multiple Poly(methyl methacrylate) as Electron‐Blocking Layers
摘要： This work presents a new device architecture integrating multiple poly(methyl methacrylate) (PMMA) electron-blocking layers (EBL) in quantum dot light-emitting diodes (QD-LEDs). The device utilizes red-emitting CdSe/ZnS QD with a novel structure where multiple PMMA EBLs are sandwiched between a pair of QD layers. A systematic optimization of QD-LED structures has shown that a device including two PMMA and three QD layers performs the best, achieving a current efficiency of 17.8 cd A?1 and a luminance of 194 038 cd m?2. Numerical simulation of a simplified model of the proposed QD-LED structure verifies that the structure consisting of two PMMA and three QD layers provides significant improvement in electroluminescent intensity. The simulation provides further insight into the origin of the effect of the PMMA EBL by showing that the addition of PMMA EBL reduces the electron leakage from the active QD region and enhances electron confinement, leading to an increased electron concentration in the QD active layers and a higher radiative recombination rate. The experimental and theoretical studies presented in this work demonstrate that multiple layers of PMMA can act as efficient EBLs in the fabrication of QD-LEDs of improved performance.
关键词： simulation,device architecture,electron-blocking layer,electron leakage,poly(methyl methacrylate) (PMMA),quantum dot light-emitting diodes (QD-LED)
更新于2025-09-19 17:13:59
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One‐Pot Exfoliation of Graphitic C <sub/>3</sub> N <sub/>4</sub> Quantum Dots for Blue QLEDs by Methylamine Intercalation
摘要： Here, a simplified synthesis of graphitic carbon nitride quantum dots (g-C3N4-QDs) with improved solution and electroluminescent properties using a one-pot methylamine intercalation–stripping method (OMIM) to hydrothermally exfoliate QDs from bulk graphitic carbon nitride (g-C3N4) is presented. The quantum dots synthesized by this method retain the blue photoluminescence with extremely high fluorescent quantum yield (47.0%). As compared to previously reported quantum dots, the g-C3N4-QDs synthesized herein have lower polydispersity and improved solution stability due to high absolute zeta-potential (?41.23 mV), which combine to create a much more tractable material for solution processed thin film fabrication. Spin coating of these QDs yields uniform films with full coverage and low surface roughness ideal for quantum dot light-emitting diode (QLED) fabrication. When incorporated into a functional QLED with OMIM g-C3N4-QDs as the emitting layer, the LED demonstrates ≈60× higher luminance (605 vs 11 Cd m?2) at lower operating voltage (9 vs 21 V), as compared to the previously reported first generation g-C3N4 QLEDs, though further work is needed to improve device stability.
关键词： graphitic carbon nitride,quantum dot light-emitting diodes,metal-free semiconductors,hydrothermal exfoliation
更新于2025-09-19 17:13:59
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Efficiency Enhancement of Perovskite CsPbBr <sub/>3</sub> Quantum Dot Light-emitting Diodes by Doped Hole Transport Layer
摘要： Balanced charge injection is essential to high-performance Perovskite CsPbBr3 quantum dot-based light-emitting diodes (QLEDs). However, low mobility of hole-transport materials (HTMs) severely restrict improving performance of QLEDs. Herein, we provide a novel HTMs to improve the highest occupied molecular orbital (HOMO) energy level structure and carrier mobility by doping poly (9-vinlycarbazole) (PVK) and poly [N, N′-bis(4-butylphenyl)-N, N′-bis(phenyl) benzi-dine] (poly-TPD). We also introduce poly (methyl methacrylate) (PMMA) as electron block layer to further achieve charge injection balance. Finally, an enhanced external quantum efficiency (EQE) of 0.53% and 414.83 cd/m2 was obtained. Compared with the untreated QLED, this result has been 8-fold enhanced, provides a new approach to attain better performance.
关键词： Quantum Dot Light-emitting Diodes,Efficiency Enhancement,Perovskite CsPbBr3,Hole Transport Layer
更新于2025-09-19 17:13:59
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All-solution Processed High Performance Inverted Quantum Dot Light Emitting Diodes
摘要： All-solution processed colloidal quantum dot light emitting diodes (QLEDs) with record performance have been successfully realized by introducing dually-doped poly(ethylenedioxythiophene)/polystyrenesulfonate (PEDOT:PSS) hole-injection layer and polyethylenimine (PEI) interfacial layer. Doping PEDOT:PSS with both Zonyl and isopropanol (IPA) significantly improves the wettability of PEDOT:PSS, making coating hydrophilic PEDOT:PSS onto hydrophobic hole-transporting layer poly(9-vinlycarbazole) (PVK) possible. The PEI interlayer between PVK/QD layer not only lowers down the vacuum level, thereby reducing the hole-injection barrier to balance the charge carriers, but also passivates QD surface defects via its amine group to suppress fluorescence quenching. As a result, the peak current efficiency of 28.1 cd/A, 43.1 cd/A, and 1.26 cd/A, the maximum external quantum efficiency (EQE) of 20.6%, 10.4%, and 2.95%, and the maximum luminance of 5.06 × 104 cd/m2, 1.21 × 105 cd/m2, and 2.96 × 103 cd/m2, have been achieved for red, green, and blue QLEDs, respectively. To the best of our knowledge, the red device’s EQE is one of the highest among all inverted red QLEDs. In addition, the extrapolated lifetime of the red QLEDs sets a new record by reaching 8253 h at an initial brightness of 100 cd/m2.
关键词： PEDOT:PSS,inverted structure,QLEDs,all-solution processed,quantum dot light emitting diodes,PEI
更新于2025-09-19 17:13:59