Hole Injection Research Articles

High-efficiency electroluminescence devices containing Si nanocrystals/SiC multilayers via improved carrier injection and recombination process

Realizing high efficiency of all Si-based light-emitting devices is currently one of interesting issues in order to develop monolithic opto-electronic integration on chips. Here, we report an electroluminescence device based on phosphorus (P)-doped silicon nanocrystals (Si NCs)/silicon carbide (SiC) multilayers by modulating carrier injection and recombination process. The p+-Si substrate is used instead of p-Si substrate for facilitating the hole injection into Si NCs. Additionally, the influences of annealing temperature on the device performance have been studied, and the optimized annealing temperature is achieved by balancing the crystallinity, defect state density, and recombination process.

Combustion instability characteristics via fuel nozzle modification in a hydrogen and natural gas Co-firing gas turbine combustor

In this study, three premixed swirl gas turbine nozzles with different fuel injection hole sizes were designed to optimize combustion characteristics influenced by changes in the hydrogen mixing ratio. Experiments involved increasing the hydrogen volume fraction of the fuel from 0 to 60%. The amount of fuel supplied through the pilot flow was increased to suppress combustion instability. The OH* chemiluminescence technique was introduced to analyze flame structure. To understand combustion instability, time delay and time-delay distribution were derived from flame structure analysis and applied to the 1D thermoacoustic model. The results indicated that the amount of fuel required for pilot injection with increasing hydrogen ratio varied with fuel hole size. It was also observed that changes in fuel hole size significantly affected flame characteristic length. Findings from the 1D thermoacoustic analysis confirmed that fuel hole size variation altered combustion instability characteristics by influencing time delay and time-delay distribution variation.

Impact of Defects and Disorder on the Stability of Ta3N5 Photoanodes

AbstractThe photoelectrochemical performance of Ta3N5 photoanodes is strongly impacted by the presence of shallow and deep defects within the bandgap. However, the role of such states in defining stability under operational conditions is not well understood. Here, a highly controllable synthesis approach is used to create homogenous Ta3N5 thin films with tailored defect concentrations to establish the relationship between atomic‐scale point defects and macroscale stability. Reduced oxygen contents increase long‐range structural order but lead to high concentrations of deep‐level states, while higher oxygen contents result in reduced structural order but beneficially passivate deep‐level defects. Despite the different defect properties, the synthesized photoelectrodes degrade similarly under water oxidation conditions due to the formation of a surface oxide layer that blocks interfacial hole injection and accelerates charge recombination. In contrast, under ferrocyanide oxidation conditions, it is found that Ta3N5 films with high oxygen concentrations exhibit long‐term stability, whereas those possessing lower oxygen contents and higher deep‐level defect concentrations rapidly degrade. These results indicate that deep‐level defects result in rapid trapping of photocarriers and surface oxidation but that shallow oxygen donors can be introduced into Ta3N5 to enable kinetic stabilization of the interface.

Heat transfer measurement near injection hole of supersonic nozzle with a sonic jet injection

Heat transfer measurements were conducted to investigate surface heat transfer characteristics resulting from the interaction between a sonic jet and supersonic nozzle crossflow. A sonic jet was injected into the nozzle where the average Mach number is 2.88. Experiments were carried out for three different momentum flux ratios (J=0.5, 1.0, 1.5). A half-nozzle was introduced to measure heat transfer on the inner walls of the nozzle using Infrared thermography. Pressure measurements using PSP and oil flow visualization were also conducted to understand the heat transfer. From the oil flow visualization and heat transfer results, it was found that the area around the hole influenced by recirculation vortexes exhibited high heat transfer coefficients, showing up to 5 times higher values compared to the freestream. Furthermore, as the momentum flux of the jet increased, both the heat transfer augmentation area and the heat transfer coefficient also increased. To analyze the heat transfer characteristics between the nozzle and flat surface, comparisons were made using dimensionless heat transfer coefficients. The nozzle exhibited higher heat transfer in a smaller interaction area compared to that of a flat surface, but the average heat transfer coefficient near the hole was lower. Accordingly, distinct thermal treatment strategies should be employed for nozzles and flat surfaces, especially near injection holes. These insights could be valuable for the thermal design of rockets and other supersonic/hypersonic mobility systems.

Improved Charge Injection Balance in Quantum Dot Light-Emitting Diodes through Interface Texture.

The existing methods to improve the charge balance of quantum dot light-emitting diodes (QLEDs) rely on energy-level matching, but these approaches have been limited by material availability and Fermi-level pinning. Here, we propose a solution that does not require changes to the materials' electronic properties. By using nanoimprinting technology to texture the interface between the hole-transporting layer (HTL) and colloidal quantum dot (CQD) layer, we can increase the HTL-CQD contact area. This significantly enhances the hole injection rate while keeping the electron injection rate essentially unchanged. Compared with the conventional planar structure, QLEDs with textured HTL exhibit lower luminance threshold voltage, significantly higher external quantum efficiency at low bias voltages, improved operational stability, and a similar Lambertian factor. Comprehensive measurements confirm that the HTL-CQD interface texture allows more efficient hole injection into CQDs to occur under lower bias, resulting in less CQD charging and more efficient exciton recombination.

Enhancing OLED electroluminescence by surface modification and work function adjustment of anode through NiO:Co coating

This study presents an approach to improve the electroluminescence (EL) of organic light-emitting diodes (OLEDs) by coating an ultra-thin NiO:Co (NCO) layer on the anode. The NCO layer was pivotal in modifying anodic properties, including surface roughness, hydrophilicity, and work function, thereby promoting ohmic hole injection from the anode into the NPB layer and enhancing the current density and carrier recombination in OLEDs. Compared to OLEDs with a pristine ITO anode, the OLEDs with an NCO-coated ITO anode showed a significant enhancement in EL performance, including a 24.5 % increase in current density, an 84.9 % enhancement in brightness, and a 48.7 % boost in efficiency. Notably, coating NCO on the anode consistently enhanced hole injection regardless of whether ITO or PEDOT:PSS was used as the anode.

Efficient Quasi-2D Perovskite Based Blue Light-Emitting Diodes with Carbon Dots Modified Hole Transport Layer.

Quasi-2D perovskites based blue light-emitting diodes (LEDs) suffer from its poor electroluminescence performance, mainly caused by the nonradiative recombination in in defect-rich low-n phases and the unbalanced hole-electron injection in the device. Here, we developed a highly efficient quasi-2D perovskite based sky-blue LEDs behaving recorded external quantum efficiency (EQE) of 21.07% by employing carbon dots (CDs) as additives in the hole transport layer (HTL). We ascribe the high EQE to the effective engineering of CDs: (1) The CDs at the interface of HTLs can suppress the formation of low-efficient n = 1 phase, resulting a high luminescence quantum yield and energy transfer efficiency of the mixed n-phase quasi-2D perovskites. (2) The CDs additives can reduce the conductivity of HTL, partially blocking the hole injection, and thus making more balanced hole-electron injection. The CDs-treated devices have excellent Spectral stability and enhanced operational stability and could be a new alternative additive in the perovskite optoelectronic devices.

High-Power and High-Efficiency 221 nm AlGaN Far Ultraviolet Laser Diodes

The optical features of far ultraviolet laser diodes (UV LDs) with peak wavelength emission of 221 nm have been numerically analyzed. Global research teams are developing aluminum gallium nitride (AlGaN)-based farUV LDs on Sapphire and AlN substrates as an alternative to Mercury lamps for air-water purification, polymer curing, and bio-medical devices. In this study, the light output power, internal quantum efficiency, stimulated recombination rate curve, and optical gain curve of the compositionally graded p-cladding layer (p-CL) were studied and show significant improvements. Therefore, the optimized structure can reduce the overflow of electrons and increase the injection of holes. This approach proves to be an efficient method for enhancing farUV LDs’ overall performance when compared to the reference structure.

Elevating standard-red perovskite LED performance: unleashing optimal potential with complex HTL and insert modification layer

In this study, we introduce a novel strategy to improve the productivity of perovskite light-emitting diodes (PeLEDs) by incorporating a KBr interface layer alongside PEDOT:PSS as the hole transport layer (HTL). This innovative approach enables the creation of a standard-red perovskite film emitting light precisely at 630 nm. Our investigation demonstrates that optimizing the concentration of the KBr modified layer (10 mg ml−1), in conjunction with an ethylene glycol (EG)-doped PEDOT:PSS electrode, promotes the growth of CsPbBr1.3I1.7 perovskite phases on the HTL while effectively reducing exciton quenching in PEDOT:PSS-based PeLEDs. Furthermore, these modifications lower the work function of the PEDOT:PSS surface, thus regulating hole injection and improving charge balance within the device. Consequently, our device achieves impressive performance metrics, including a high quantum yield of 68.2%, maximum luminance (L max) of 747 cd m−2, and an External Quantum Efficiency (EQE) of 0.24%, representing significant advancements in red perovskite-based lighting technology.

Efficient and droop-free AlGaN-based UV-C LED using the inverted linearly graded active region and engineered hole source layer

The poor efficiency of the aluminum gallium nitride (AlGaN)-based ultraviolet (UV)-C light emitting diode (LED) remains as the major hindrance towards its commercialization. Thus, to enhance the internal quantum efficiency (IQE) and light output power (LOP) and to mitigate the efficiency droop of AlGaN-based UV-C LED, this simulation work proposes and examines a new engineering strategy, i.e., inverted linearly graded quantum wells along with quantum barriers over a series of samples A, B and C. To further improve the characteristics of AlGaN-based UV-C LED, an engineered linearly graded p-AlGaN layer has been proposed in the device structure. This increases the electron and hole concentrations by ∼2-fold and ∼8-fold, respectively. The 1.2-fold reduction in hole effective potential barrier height improves the hole injection. Also, the 1.5-fold increase in electron effective potential barrier height limits electron spill-off from the active region. The proposed structural-engineering reduces quantum confined stark effect (QCSE) confirmed by the reduction of quantum well slopes. Reducing carrier spill-off and QCSE increases average radiative recombination rate by ∼8-fold. The maximum IQE is improved by ∼44 % and the efficiency droop is also reduced to a promising level of ∼2 % in case of the sample under consideration. Finally, the LOP increases 10-fold, promisingly. Thus, the proposed structure is supposed to be highly potential for improving the UV-C LED performance. The electroluminescence spectra show that despite the gradual differences introduced in the structure, all the samples emit at ∼276 nm with similar full width at half maximum providing a reference for the comparison.

Nanoscale interface engineering for enhanced performance in light-emitting-diode devices: ITO/Ag-SRCOOH

In light-emitting diode (LED) devices, the hole-injection layer (HIL) reduces the hole injection barrier (HIB) between the anode and organic layers to obtain favorable conditions for hole transport, which considerably affects device efficiency and performance. However, the fabrication of ultrathin silver (Ag) films for electron and hole transport layers remains challenging. We demonstrated the design of a nanoscale HIL interface with chemisorption-bonded carboxylic acid-terminated alkanethiol self-assembled layers on ultrathin Ag. The device structure consisted of indium tin oxide (ITO)/Ag-mercaptan acid (Ag-SRCOOH)/N, Nj-Di (1-naphthyl)-N,Nj-diphenyl-(1,1-biphenyl)-4,4-diamine (NPB)/tris-(8-hydroxyquinoline) aluminum (Alq3)/ETL(LiF/Al. Notably, a chemical bond peak was not detected between ITO and ultrathin Ag. However, X-ray photoelectron spectroscopy (XPS) measurements confirmed Ag binding to the thiol group of 3-mercaptopropionic acid (MPA) and 11-mercaptoundecanoic acid (MUA) on the Ag island surface, which is evident from -S-Ag- and -RS-Ag- association peaks. Ultraviolet photoelectron spectroscopy analysis results revealed a reduction in the HIB of device from 0.68 to 0.19 eV. Consequently, the luminance and current density, and current density of the AgNP–MPA device increased by 63-fold, 5.8-fold, and 1.1-fold, respectively. Similarly, the AgNP-MUA device exhibited enhanced performance with a 61-fold increase in luminance, 43-fold increase in current density, and a 1.4-fold increase in current efficiency, respectively. The results of this study not only opened novel avenues for future applications, including operation requiring flexibility and transparency of LEDs, but also proposed the optimization of nanoscale interfaces to enhance LED performance.

Charge transport dynamics and emission response in quantum-dot light-emitting diodes for next-generation high-speed displays

Inorganic quantum-dot light-emitting diodes (QD-LEDs) have gained significant attention as optoelectronic devices for next-generation display systems due to their superior colour properties. A comprehensive understanding of the charge transport dynamics and transient emission responses of the QD-LED is crucial to achieving high motion picture quality next-generation QD-LED display systems. In this study, we investigated the transient emission response of QD-LED devices through an advanced charge transport simulation model tailored to the quantum-dots (QDs). The dynamic response of the QD-LED devices is evaluated using the time-resolved electroluminescence measurement method for both cadmium-based and cadmium-free red, green, and blue QD-LEDs. The QD-LED devices exhibit notable emission drops during pulse voltage application. The charge transport simulation quantitatively reveals that the on and off switching speeds and the emission drops are intricately influenced by the electron and hole injection balance and a combination of carrier recombination factors within the QD layer. The charge transport simulation also shows that space-charge accumulation, due to the combined effects of charge imbalance and Auger recombination, quantitatively explains a potential device degradation mechanism. Therefore, the QD-specified charge transport model provides a crucial approach in designing and optimizing QD-LED devices for next-generation high-speed QD-LED displays with ultimate colour quality and long lifetimes.

Sufficient energy band utilization profited from spatially discrete heterogeneous interfaces to induce efficient photoelectrochemical water splitting for ZnIn2S4 photoanode

The applied possibility of ZnIn2S4 is improved in the photoelectrochemical (PEC) energy transfer filed through elevated light absorption, accelerating charges transfer and suppressed carrier recombination. Consequently, Sb2S3/ZnIn2S4/Cu2S ternary composite photoanode is obtained through the induction of Sb2S3/ZnIn2S4 and ZnIn2S4/Cu2S heterogeneous interfaces at different spatial locations in ZnIn2S4, which enhances photocurrent density of ZnIn2S4-based photoanode to 2.81 mA/cm2 from 0.15 mA/cm2 with the nearly full visible spectrum absorption range of ∼ 776 nm. The deposition of Sb2S3 leads to enhanced quantum efficiencies, carrier diffusion time, and number of surface states. The loading of Cu2S top layer predominantly results in optimized surface states style and holes injection efficiency of SS/ZIS/CS. The comprehensive measurements and density functional theory (DFT) calculation demonstrate Sb2S3 and Cu2S are together employed to enhance the hybridization efficiencies of energy bands, accelerate charge transfer, revise the reaction sites, reduce free energy barrier of rate-determining steps and reaction over potential of ZnIn2S4 to enhance PEC water spitting. This work pioneers the construction of ZnIn2S4-based multijunction photoanodes with sufficient energy band utilization and confirms the conspicuous prospect for remaining photoanodes.

0, 1, 2, and 3-Dimensional zinc oxides enabling high-efficiency OLEDs

In the pursuit of high-efficiency organic light-emitting diodes (OLEDs), this paper unveils the potential of zinc oxide (ZnO) nanostructures of various dimensions (0,1,2, and 3D), doped in hole injection layer (PEDOT:PSS). Unique enhancements were demonstrated in forms from nanoparticles (0D) to nanowires (1D), nanosheets (2D), and nanoflowers (3D), revolutionizing OLED performance. Specifically, the incorporation of 0D-ZnO doped in PEDOT:PSS resulted in remarkable efficiency improvements of 19 % in maximum power efficacy (PEmax), 19 % in maximum current efficacy (CEmax) and 24 % in maximum external quantum efficiency (EQEmax), compared with the undoped counterpart. Elevating the dimensions to 1D-ZnO (20 nm), when doped in PEDOT:PSS, enabled an increment of 46, 54 and 64 % in PEmax, CEmax and EQEmax, respectively. Furthermore, 2D-ZnO (annealed at 400 °C) doped in PEDOT:PSS achieved notable performance improvements, with enhancements of 24 % in PEmax, 23 % in CEmax, and 28 % in EQEmax. Despite size limitations, 3D-ZnO doped in PEDOT:PSS exhibited enhancements of 11 % in PEmax, 15 % in CEmax, and 20 % in EQEmax. We achieved the best results by integrating 1D-ZnO into PEDOT:PSS, which may be attributed to the small diameter of the 1D-ZnO structure when compared to 0D, 2D, and 3D ZnO, resulting in superior OLED performance. These findings demonstrate the significant potential of ZnO nanostructures doped in PEDOT:PSS in enhancing the performance of green OLEDs, and paving the way for more sustainable, cost-effective, and efficient OLEDs for display and lighting applications. Continued research on ZnO and other inorganic materials holds promise for further advancements in OLED technology and a brighter, more energy-efficient future.

Improved Molecular Packing of Self-Assembled Monolayer Charge Injectors for Perovskite Light-Emitting Diodes.

Self-assembled monolayers (SAMs) have shown great potential as hole injection materials for perovskite light-emitting diodes due to their low parasitic absorption and ability to adjust energy level alignment. However, the head and anchoring groups on SAM molecules with significant differences in polarity can lead to the formation of micelles in the commonly used alcoholic processing solvent, inhibiting the formation of an intact SAM. In this work, the introduction of methyl groups on carbazole in the phosphonic-acid-based SAM materials is found to facilitate energy level alignment and promote the formation of compact SAMs. The alternative molecular structure also enhances the solvent resistance of poly(9-vinylcarbazole), suppressing interfacial defect densities and nonradiative recombination processes in the emissive perovskites. PeLEDs based on the methyl-containing SAMs exhibit ∼30% enhancement in efficiency. These findings contribute to a better understanding of the design of SAM materials for PeLED applications.

All‐Solution‐Processed Top‐Emitting InP Quantum Dot Light‐Emitting Diode with Polyethylenimine Interfacial Layer

AbstractRecent studies on top‐emitting structure, which is designed to enhance the color purity and outcoupling efficiency of quantum‐dot light‐emitting diodes (QLEDs), employ commercially unviable methods owing to limited options for applying the hole injection layer through solution processes on the bottom electrode. In this study, all‐solution‐processable conventional top‐emitting QLEDs (TQLEDs) are successfully fabricated by introducing a polyethylenimine (PEI) interlayer, doping isopropyl alcohol (IPA) into the hole‐injection layer (poly (3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate), PEDOT:PSS), and using the dynamic spin‐coating method. The increased hole injection resulting from the tuned anode‐HIL interface by the PEI and IPA‐doped HIL, coupled with the enhanced outcoupling efficiency and full width at half maximum (FWHM) derived from the optimized cavity length through simulation, realizes a red InP QLED with high efficiency and color purity. The optimized TQLED exhibits a maximum current efficiency and FWHM of 28.04 cd A−1 and 36 nm, respectively, which are threefold higher and 8 nm narrower than those of bottom‐emitting QLEDs, marking the highest current efficiency ever reported for top‐emitting red InP QLEDs.

Determination of band offsets at the interfaces of NiO, SiO2, Al2O3, and ITO with AlN

The valence and conduction band offsets at the interfaces between NiO/AlN, SiO2/AlN, Al2O3/AlN, and ITO/AlN heterointerfaces were determined via x-ray photoelectron spectroscopy using the standard Kraut technique. These represent systems that potentially would be used for p-n junctions, gate dielectrics, and improved Ohmic contacts to AlN, respectively. The band alignments at NiO/AlN interfaces are nested, type-I heterojunctions with a conduction band offset of −0.38 eV and a valence band offset of −1.89 eV. The SiO2/AlN interfaces are also nested gap, type-I alignment with a conduction band offset of 1.50 eV and a valence band offset of 0.63 eV. The Al2O3/AlN interfaces are type-II (staggered) heterojunctions with a conduction band offset of −0.47 eV and a valence band offset of 0.6 eV. Finally, the ITO/AlN interfaces are type-II (staggered) heterojunctions with conduction band offsets of −2.73 eV and valence band offsets of 0.06 eV. The use of a thin layer of ITO between a metal and the AlN is a potential approach for reducing contact resistance on power electronic devices, while SiO2 is an attractive candidate for surface passivation or gate dielectric formation on AlN. Given the band alignment of the Al2O3, it would only be useful as a passivation layer. Similarly, the use of NiO as a p-type layer to AlN does not have a favorable band alignment for efficient injection of holes into the AlN.

Improving hole injection with the polarization effect for 279 nm AlGaN-based deep ultraviolet light-emitting diodes

Improving hole injection with the polarization effect for 279 nm AlGaN-based deep ultraviolet light-emitting diodes

Low‐Power Charge Trap Flash Memory with MoS2 Channel for High‐Density In‐Memory Computing

AbstractWith the rise of on‐device artificial intelligence (AI) technology, the demand for in‐memory comptuing has surged for data‐intensive tasks on edge devices. However, on‐device AI requires high‐density, low‐power memory‐based computing to efficiently handle large data volumes. Here, this study proposes a reliable multilevel, high gate‐coupling ratio memory device with MoS2 channel tailored for high‐density 3D NAND Flash‐based in‐memory computing. The MoS2 channel, featured by its small bandgap and high‐mobility, facilitates reliable memory window of approximately 8 V thanks to erase operation through hole injection. This not only suppresses vertical charge loss but also alleviates the burden on voltage generator circuits, indicating the suitability of MoS2 as channel material for 3D NAND Flash architecture. Additionally, a low‐k (≈2.2) tunneling layer deposited via initiated chemical vapor deposition increases the gate‐coupling ratio, thereby reducing the operating voltage. Utilizing Au nanoparticles as the charge storage layer, MoS2 memory devices show synaptic plasticity with 6‐bit, endurance (104 cycles), read disturbance (105 cycles), and retention times (105 s). Furthermore, device‐to‐system simulations for neural networks based on MoS2‐memory devices have successfully achieved a fingerprint recognition of 95.8%. These results provide the foundation to develop multi‐bit MoS2‐memory devices for AI accelerators and 3D NAND Flash memory.

Effects of Current Filaments on IGBT Avalanche Robustness: A Simulation Study

With the increase in voltage level and current capacity of the insulated gate bipolar transistor (IGBT), the avalanche effect has become an important factor limiting the safe operating area (SOA) of the device. The hole injection into the p/n junction on the backside of the IGBT after avalanche is the main feature that distinguishes the avalanche effect from other devices. In this paper, the avalanche breakdown characteristics of IGBT and the nature of current filament are investigated using theoretical analysis and numerical simulation, and the underlying physical mechanism controlling the nature of current filaments is revealed. The results show that the hole injection on the backside of the IGBT leads to an additional negative differential resistance (NDR) branch on the avalanche breakdown curve. The device’s common-base current gain, αpnp, is a crucial factor in determining the current filament. As αpnp increases, the avalanche-induced current filament becomes stronger and slower, resulting in weaker avalanche robustness of the device.