Hole Injection Research Articles

Enhanced Charge Balance for Efficient Electroluminescence from Cesium Copper Halides.

Cesium copper halides have the advantages of high photoluminescence quantum efficiency and good stability, making them attractive for replacing toxic lead halides in the field of perovskite light-emitting diodes (LEDs). However, due to their shallow conduction band and the lack of electron transport layers compatible with it, it remains a great challenge to achieve charge balance in LED devices. This drawback manifests as the accumulation of holes at the interface between the emitting layer and electron transport layer, resulting in nonradiative recombination. Here, we demonstrate an effective approach to address this issue by suppressing hole injection, which is realized through modification of the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) layer with polyethylenimine. This leads to cesium-copper-halide LEDs with a high external quantum efficiency of 5.6%, representing an advance in device architecture for efficient electroluminescence from cesium copper halides.

Numerical Investigation of Combustion Mechanism with Multi-Position Injection in a Dual-Mode Combustor

To improve the flame propagation, combustion stability, and uniformity of the temperature field, multi-position injection is applied in a dual-mode combustor by controlling heat release in different locations. Using the chemical reaction of the finite rate combustion model and the detailed reaction mechanism of hydrogen combustion as described by Jachimowski, the influence of different multi-position injection patterns in a dual-mode combustor is analyzed. The one-equation Large Eddy Simulation (LES) turbulence model was chosen to define the sublattice turbulent viscous terms in a three-dimensional scramjet model. Based on a combustion chamber, the effect of the injection equivalent ratio (0.35–0.70), the relative position of the nozzle holes, and the injection pressure on the combustion process and flow field characteristics are analyzed with multi-position injection. The combustion efficiency, total pressure recovery coefficients, and pressure distribution under different operation conditions are compared. We observed that the combustion intensity increases and the upstream combustion shock string distance becomes greater with increased equivalent ratios. When the global equivalent ratio of multi-position injection remains unchanged, the arrangement of nozzles with the small injection spacing, i.e., two injection holes arranged face to face on the upper and lower walls, or the setting of multiple injection holes with the same pressure, can effectively increase the stability rate of the combustion flow field. In addition, the combustion efficiency at the outlet and the internal pressure of the combustion chamber in the stable state are also improved, relative to the increased total pressure loss.

Improved Hole Injection in Hybrid Light‐Emitting Transistors Incorporating Lithium and Copper(II) Poly(Styrene Sulfonate)

AbstractLight‐emitting transistors (LETs) are optoelectronic devices that perform switching and light‐emitting functions in a single device. Hybrid LETS (HLETs) using inorganic metal oxide semiconductors as the transport layer with organic emissive layers and hole‐injection layers (HILs) combine the excellent switching performance of metal oxides with the flexibility and tunability of organic semiconductors. However, the efficiency of n‐HLETs typically suffers from unbalanced electron and hole injection. To overcome this issue, two hybrid polyelectrolytes—lithium poly(styrene sulfonate) (Li:PSS) and copper(II) poly(styrene sulfonate) (Cu:PSS)—are investigated as HILs in HLETs. HLETs employing Cu:PSS interlayers exhibit significantly enhanced brightness values of up to 4.89 × 103 cd m−2 and an external quantum efficiency (EQE) of 0.45%, compared to HLETs without HIL (no emission) and pristine poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) (2.17 × 102 cd m−2 with an EQE of 0.01%). To understand how the HILs influence the performance, ultraviolet photoelectron spectroscopy (UPS) analysis and photoluminescence (PL) quenching studies are performed, which reveal improved energy band structure and reduced quenching using metal:PSS HILs. This work provides useful information about the function that polyelectrolyte HILs perform in HLET devices which may be exploited to develop new materials and applied in other types of optoelectronic devices.

Revisiting Hole Injection in Quantum Dot Light‐Emitting Diodes

AbstractInjecting holes from the hole transport layer (HTL) into the quantum dot (QD) emitting layer in quantum dot light‐emitting diodes (QLEDs) is considered challenging due to the presence of a relatively high hole injection barrier at the HTL/QD interface. However, QLEDs with exceptional brightness and efficiency are achieved, prompting a reevaluation of the traditional hole injection mechanisms. This study examines the hole injection mechanism in QLEDs using a combination of experiments and simulations. The results demonstrate that the applied bias significantly reduces the barrier height between the highest occupied molecular orbital level of the HTL and the valence band (VB) of the QDs, facilitating hole injection. The bending of the lowest unoccupied molecular orbital energy level of the HTL at the HTL/QD interface confines electrons within the QD, effectively minimizing leakage current. Additionally, the triangle‐shaped potential barrier arising from the bending of the VB energy level of the QDs creates favorable conditions for hole–tunneling injection. Moreover, both simulations and experiments consistently demonstrate that the predominant pathway for hole injection from the HTL to the QDs in the QLED device involved thermally assisted tunneling. This study is important to understand the hole injection mechanism in QLEDs.

A Method for Measuring Parameters of Defective Ellipse Based on Vision.

Ellipse detection has a very wide range of applications in the field of object detection, especially in the geometric size detection of inclined microporous parts. However, due to the processing methods applied to the parts, there are certain defects in the features. The existing ellipse detection methods do not meet the needs of rapid detection due to the problems of false detection and time consumption. This article proposes a method of quickly obtaining defective ellipse parameters based on vision. It mainly uses the approximation principle of circles to repair defective circles, then combines this with morphological processing to obtain effective edge points, and finally uses the least squares method to obtain elliptical parameters. By simulating the computer-generated images, the results demonstrate that the center fitting error of the simulated defect ellipses with major and minor axes of 600 and 400 pixels is less than 1 pixel, the major and minor axis fitting error is less than 3 pixels, and the tilt angle fitting error is less than 0.1°. Further, experimental verification was conducted on the engine injection hole. The measurement results show that the surface size deviation was less than 0.01 mm and the angle error was less than 0.15°, which means the parameters of defective ellipses can obtained quickly and effectively. It is thus suitable for engineering applications, and can provide visual guidance for the precise measurement of fiber probes.

Electron and hole injection barriers between silicon substrate and RF magnetron sputtered In2O3 : Er films

In2O3 : Er films have been synthesized on silicon substrates by RF magnetron sputter deposition. The currents through the synthesized metal/oxide/semiconductor (MOS) structures (Si/In2O3 : Er/In-contact) have been measured for n and p type conductivity silicon substrates and described within the model of majority carrier thermoemission through the barrier, with bias voltage correction to the silicon potential drop. The electron and hole injection barriers between the silicon substrate and the film have been found to be 0.14 and 0.3 eV, respectively, by measuring the temperature dependence of the forward current at a low sub-barrier bias. The resulting low hole injection barrier is accounted for by the presence of defect state density spreading from the valence band edge into the In2O3 : Er band gap to form a hole conduction channel. The presence of defect state density in the In2O3 : Er band gap is confirmed by photoluminescence data in the respective energy range 1.55–3.0 eV. The band structure of the Si/In2O3 : Er heterojunction has been analyzed. The energy gap between the In2O3 : Er conduction band electrons and the band gap conduction channel holes has been estimated to be 1.56 eV.

Ultrastable and High-Efficiency Deep Red QLEDs through Giant Continuously Graded Colloidal Quantum Dots with Shell Engineering.

Quantum dot (QD) based light-emitting diodes (QLEDs) hold great promise for next-generation lighting and displays. In order to reach a wide color gamut, deep red QLEDs emitting at wavelengths beyond 630 nm are highly desirable but have rarely been reported. Here, we synthesized deep red emitting ZnCdSe/ZnSeS QDs (diameter ∼16 nm) with a continuous gradient bialloyed core-shell structure. These QDs exhibit high quantum yield, excellent stability, and a reduced hole injection barrier. The QLEDs based on ZnCdSe/ZnSeS QDs have an external quantum efficiency above 20% in the luminance range of 200-90000 cd m-2 and a record T95 operation lifetime (time for the luminance to decrease to 95% of its initial value) of more than 20000 h at a luminance of 1000 cd m-2. Furthermore, the ZnCdSe/ZnSeS QLEDs have outstanding shelf stability (>100 days) and cycle stability (>10 cycles). The reported QLEDs with excellent stability and durability can accelerate the pace of QLED applications.

Synthesis and Properties of Bipolar Ladder-Like Polysiloxane with Carbazole and Triphenylphosphine Oxygen Groups.

In this study, a series of ladder-like polysiloxanes are synthesized by introducing double-chain Si-O-Si polymer as the backbone and the carbazole and triphenylphosphine oxide with high triplet energy as side groups. The ladder-like structures of polysiloxanes are achieved through a controlled polymerization method that involves the monomer self-assembly and subsequent surface-restricted solid-phase in situ condensation through freeze-drying. The introduction of siloxane improves thermal stability of the polymers and inhibits the conjugation of the polymers between the side groups, leading to an increase in the triplet energy level. Therefore, all these polymers perform higher triplet energy levels than phosphorescent emitter (FIrpic). The cyclic voltammetry measurements demonstrate that the bipolar polymer exhibits a high highest occupied molecular orbital (HOMO) value of -5.32eV, which is consistent with the work function of ITO/PEDOT:PSS, consequently facilitating hole injection. Furthermore, the incorporation of triphenylphosphine oxide promotes electron injection. Molecular simulations reveal that the frontier orbital distributions of the bipolar polymer are located on the carbazole and triphenylphosphine groups, respectively, which facilitate the transport of electrons and holes.

Electron and hole injection barriers between silicon substrate and RF magnetron sputtered In2O3 : Er films

In2O3 : Er films have been synthesized on silicon substrates by RF magnetron sputter deposition. The currents through the synthesized metal/oxide/semiconductor (MOS) structures (Si/In2O3 : Er/In-contact) have been measured for n and p type conductivity silicon substrates and described within the model of majority carrier thermoemission through the barrier, with bias voltage correction to the silicon potential drop. The electron and hole injection barriers between the silicon substrate and the film have been found to be 0.14 and 0.3 eV, respectively, by measuring the temperature dependence of the forward current at a low sub-barrier bias. The resulting low hole injection barrier is accounted for by the presence of defect state density spreading from the valence band edge into the In2O3 : Er band gap to form a hole conduction channel. The presence of defect state density in the In2O3 : Er band gap is confirmed by photoluminescence data in the respective energy range 1.55–3.0 eV. The band structure of the Si/In2O3 : Er heterojunction has been analyzed. The energy gap between the In2O3 : Er conduction band electrons and the band gap conduction channel holes has been estimated to be 1.56 eV.

Formation of Single‐Chain Anionic Bolaamphiphiles on Indium Tin Oxide Surfaces through Self‐Assembly To Improve Optoelectronic Device Performance

AbstractThe surface of indium tin oxide (ITO) was modified with bolaamphiphilic (BA) materials to tune the energy‐level alignment of electrodes in optoelectronic devices (OEDs). Tuning the energy‐level alignment of the electrode is crucial for enhancing OED efficiency by improving carrier injection. Although the dielectric properties of organic solvents influence the formation of BA self‐assembled monolayers (SAMs), our study found that the intermolecular forces of the dissolved BA materials and the solution medium are more important for the formation of a well‐ordered film on the electrode. Our results also showed efficient tunneling phenomenon between the electrode and the hole transport layer (HTL) using BA material. The holes were transported to the tunnel junctions where the Fermi energy was sufficiently close to the HOMO band of the BA. Therefore, the tunnel barrier height of the ITO/HTL of the OED was reduced, and favorable conditions for hole injection was created, resulting in a 2–3 times increase in luminance and current density. It is believed that the larger area of interface contact between electrode/BA/HTL and the formation of well‐ordered BA layers are responsible for the improved performance of the BA‐modified electrode surface and OED.

Impact Analysis of Off-State Avalanche-Breakdown Stress on 650 V-Class Superjunction MOSFET

In this work, the reliability degradation of a 650 V-class superjunction (SJ) MOSFET under continuous violent OFF-state avalanche-breakdown stress is studied. Decreased threshold voltage and increasing saturation current have been observed which are attributed to the injection of hot holes below the trench bottom into the gate oxide layer. High-energy electrons and holes are generated under OFF-state avalanche stress leading to accelerated and violent collision ionization. The body diode suffers from severe avalanche breakdown leading to heat generation by collision ionization. In addition, the injection of hot holes is further enhanced with the assistance of the electrical field at the bottom of the gate. These phenomena are further analyzed by experimental characterizations and theoretical simulation using TCAD tools. Our comprehensive study on the reliability degradation behaviors of SJ devices under OFF-state avalanche-breakdown stress can be instructive in future device optimization and failure analysis.

Evaluation of Trapping Behaviors in Forward Biased Schottky-Type p-GaN Gate HEMTs

In this work, we investigated the trapping behaviors in the Schottky-type p-GaN gate high-electron-mobility transistors (HEMTs) under positive gate bias using the current-transient method. By excluding the trapping effect introduced by the measurement voltages, the actual recovery curves of drain transient current under different gate filling voltages and temperatures were extracted. The impacts of electron trapping, hole injection, and electron–hole recombination on the threshold voltage instability can be effectively distinguished according to the results of drain current variations under different gate stresses. In addition, the dynamic drain leakage current was monitored to confirm the electron–hole recombination and optical pumping of trapped electrons. The properties of three electron traps can be obtained based on the time constant spectrum (TCS), and a database of the gate-trapping behaviors in the GaN-based devices was constructed. The combined results may provide a basis for a better understanding of the threshold voltage instability under positive gate stress in the p-GaN gate HEMTs.

High Hole Injection for Nitrogen-Polarity AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes

High hole injection is desired for improving the performance of AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs). In this work, we adopted a compositionally graded p-Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y1</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-y1</sub> N/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.85</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.15</sub> N superlattice (SL) structure in a nitrogen-polarity DUV LED. Our numerical simulation results show that this SL structure is very beneficial to the hole injection into the active region, and leads to a low turn-on voltage and device resistance. This is significant because a low device resistance means a low power consumption and a high wall-plug efficiency. Meanwhile, a DUV LED with compositionally graded SL has a peak internal quantum efficiency (72%) that is much higher than that of the reference DUV LED without an SL (56%). This work provides an attractive approach to effectively injecting holes into the active region of a nitrogen-polarity AlGaN-based DUV LED.

Hot Carrier Degradation Accompanied by Recovery in InSnZnO Thin-Film Transistors

In this letter, the reliability of InSnZnO thin-film transistors (TFTs) under hot carrier (HC) stress is systematically studied. HC degradation accompanied by recovery is observed for the first time in InSnZnO TFTs. The acceptor-like trap state generation and electron trapping into gate insulator (GI) jointly degenerate the device, and electron detrapping from GI and hole injection into GI jointly recover the device meanwhile. The self-weakening of HC effect with stress time and the vertical electric field enhancement jointly trigger the domination of the recovery effect.

Heat-transfer modeling of the gas gap under a wafer

The wafer temperature is a critical observable in semiconductor manufacturing. One of the various mechanisms determining this temperature is the heat transfer in a gas gap between the wafer and the electrostatic chuck (ESC). Various correlations for this heat transfer are available. However, to calculate more accurately the spatial distribution of this temperature, computing the flow in this gap is necessary. With this motivation in mind, this paper presents a computational fluid dynamics model (CFD) for the flow in the wafer-ESC gap that is designed to be easy to implement in industrial CFD codes. This model is tested in various channel-flow problems and then applied to a generic wafer-ESC configuration. For this configuration, CFD results show that varying the flow rate split between three zones, or the total flow rate, or the rugosity of the wafer affect the heat transfer coefficient and its spatial variation. This is important since controlling this variation would allow to maintain a uniform wafer temperature. The model could be used in more realistic wafer-ESC configurations to consider many other parameter variations, such as the size of injection holes, a radially varying gap distance, or the use of many injection zones. From a broader viewpoint, the model is applicable to vacuum problems other than the wafer-ESC configuration.

Perovskite Light-Emitting Diodes with an External Quantum Efficiency Exceeding 30.

Perovskite light-emitting diodes (PeLEDs) are strong candidates for next-generation display and lighting technologies due to their high color purity and low-cost solution-processed fabrication. However, PeLEDs are not superior to commercial organic light-emitting diodes (OLEDs) in efficiency, as some key parameters affecting their efficiency, such as the charge carrier transport and light outcoupling efficiency, are usually overlooked and not well optimized. Here, ultrahigh-efficiency green PeLEDs are reported with quantum efficiencies surpassing a milestone of 30% by regulating the charge carrier transport and near-field light distribution to reduce electron leakage and achieve a high light outcoupling efficiency of 41.82%. Ni0.9 Mg0.1 Ox films are applied with a high refractive index and increased hole carrier mobility as the hole injection layer to balance the charge carrier injection and insert the polyethylene glycol layer between the hole transport layer and the perovskite emissive layer to block the electron leakage and reduce the photon loss. Therefore, with the modified structure, the state-of-the-art green PeLEDs achieve a world record external quantum efficiency of 30.84% (average= 29.05±0.77%) at a luminance of 6514cdm-2 . This study provides an interesting idea to construct super high-efficiency PeLEDs by balancing the electron-hole recombination and enhancing the light outcoupling.

Enhanced Performances of Quantum Dot Light-Emitting Diodes with an Organic–Inorganic Hybrid Hole Injection Layer

PEDOT:PSS (polyethylene dioxythiophene:polystyrenesulfonate) is a commonly used hole injection layer (HIL) in optoelectronic devices due to its high conductive properties and work function. However, the acidic and hygroscopic nature of PEDOT:PSS can be problematic for device stability over time. To address this issue, in this study we demonstrated the potential of an organic–inorganic hybrid HIL by incorporating solution-processed WOx nanoparticles (WOx NPs) into the PEDOT:PSS mixture. This hybrid solution was found to have a superior hole transport ability and low Ohmic contact resistance contributing to higher brightness (~62,000 cd m−2) and current efficiency (13.1 cd A−1) in the manufactured quantum-dot-based light-emitting diodes (QLEDs). In addition, the resulting devices achieved a relative operational lifetime of 7071 h, or approximately twice that of traditional QLEDs with PEDOT:PSS HILs. The proposed method is an uncomplicated, reliable, and low-cost way to achieve long operational lifetimes without sacrificing efficiency in optoelectronic devices.

Enhancing the performance of Quasi-2D perovskite blue light emitting diodes via a WS2 energy matching layer

Due to the deep energy levels, the external quantum efficiency (EQE) of the blue perovskite light-emitting diode (PeLED) is far lower than its green, red, and near-infrared counterparts, which has exceeded 20%. The mismatched energy levels between perovskites and the hole transporting layer (HTL) still hinder the hole injection and consequent improvement of blue PeLED device performance. Here, a two-dimensional material, WS2 (Tungsten disulfide), was introduced to match the energy levels between perovskites and HTL and enhanced the hole injection. The WS2 HTL-based perovskite FAPbBr3-xClx blue LED achieved a luminance of 990 cd/m2 with an EQE of 3.24%, which surpasses the performance of previously reported for the formamidinium (FA) based system, indicating the potential of WS2 for PeLEDs.

Threshold voltage shift model for p-GaN gate enhancement mode HEMT

In this paper, we based on the gate structure of p-GaN HEMT connected with Schottky diode and PIN diode and analyzed the threshold voltage shift mechanism under the influence of gate voltage. Based on the carrier transport mechanism, the electron injection current and hole injection current of the p-GaN layer is discussed and calculated, while the gate current model and threshold voltage shift model of the p-GaN HEMT are analyzed. The accuracy of the model is verified by comparing with the experimental data. The effects of p-GaN doping concentration, AlGaN barrier layer thickness and Al component on the gate current and VTH shift are discussed based on the model. By optimizing the device structure and process parameters, the gate current of HEMT can be reduced and the stability of VTH can be improved.

Tunable charge injection from graphene to halide perovskite induced by reversible ion segregation

Migration of point defects can result in various performance instabilities in organometal halide perovskite devices. In particular, the segregation of charged defects can influence the electron transport, but the correlation between ionic and electronic transports remains elusive. In this work, we use a graphene/methylammonium lead iodide capacitor to probe the effect of ion segregation on the charge injection behavior at the graphene/perovskite junction. In our samples, the ion segregation in the perovskite film is induced by a controllable electric field applied through an electrostatic gate. At the same time, the charge injection from graphene to the perovskite is probed by monitoring changes in the graphene conductivity. It is found that a positive (negative) defect accumulation layer near the graphene/perovskite interface can facilitate electron (hole) injection from the graphene electrode to the perovskite. Because the polarity of the defect accumulation layer is switchable by changing the direction of the applied electric field, the graphene/perovskite interface behaves like a Schottky junction with a tunable charge injection barrier height. This behavior should be generally found in other metal/halide perovskite interfaces as well.