Electron Blocking Layer Research Articles

Numerical study and optimization of GO/ZnO based perovskite solar cell using SCAPS

<abstract> <p>This paper focuses on the numerical study of hybrid organic-inorganic perovskite solar cells. It investigates the incorporation of a graphene oxide (GO) thin layer to enhance solar cell efficiency. The study demonstrates that the GO layer improves interaction with the absorber layer and enhances hole transportation, resulting in reduced recombination and diffusion losses at the absorber and hole transport layer (HTL) interface. The increased energy level of the Lower Unoccupied Molecular Orbital (LUMO) in GO acts as an excellent electron-blocking layer, thereby improving the V<sub>OC</sub>. The objective is to explore different structures of perovskite solar cells to enhance their performance. The simulated solar cell comprises a GO/FASnI<sub>3</sub>/TiO<sub>2</sub>/ZnO/ITO sandwich structure, with FASnI<sub>3</sub> and ZnO thicknesses adjusted to improve conversion efficiency. The impact of thickness on device performance, specifically the absorber and electron transport layers, is investigated. The fill factor (FF) changes as the absorber and electron transport layers (ETL) increase. The FF is an important parameter that determines PSC performance since it measures how effectively power is transferred from the cell to an external circuit. The optimized solar cell achieves a short-circuit current density (J<sub>SC</sub>) of 27.27 mA/cm<sup>2</sup>, an open-circuit voltage (V<sub>OC</sub>) of 2.76 V, a fill factor (FF) of 27.05% and the highest power conversion efficiency (PCE) of 20.39% with 400 nm of FASnI<sub>3</sub> and 300 nm of ZnO. These findings suggest promising directions for the development of more effective GO-based perovskite solar cells.</p> </abstract>

Effects of thermal history on the performance of low-temperature solid oxide fuel cells with Sm0.2Ce0.8O2-δ electrolyte and LiNi0.81Co0.15Al0.04O2 electrodes

In this study, low-temperature solid oxide fuel cells with an ∼560 μm thick Sm0.2Ce0.8O2−δ (SDC) electrolyte and ∼890 μm thick LiNi0.81Co0.15Al0.04O2−δ (NCAL) electrodes are constructed and characterized under three experimental conditions. The cell with an NCAL cathode pre-reduced under an H2 atmosphere at 550 °C presents the best electrochemical performance. This is ascribed to facts that the reduction reaction generating Ni–Co alloy particles on the NCAL surface and partial reoxidation of Ni–Co to Ni(Co)O under an air atmosphere during subsequent experiments increase the triple-phase-boundary area, improve the catalytic activity for the oxygen reduction reaction, and cause a low polarization resistance (0.186 Ω cm2). Also, the reduction of the Ni foam–NCAL anode triggers the formation of H+/O2− bi-ionic SDC–Li2CO3–LiOH composite electrolytes. The LiOH–Li2CO3 melt permeates and densifies the electrolyte layer; this significantly increases the electrical conductivity of the electrolyte layer to 0.291 S cm−1 and lowers the ohmic resistance of the cell (0.170 Ω cm2). The Li2CO3–LiOH phases serve as electron-blocking layers to limit the electronic conductivity of the electrolyte layer. This induces a high open-circuit voltage of 1.024 V and a high maximum power density of 611.3 mW·cm−2.

Suppression of polarization effect in deep-ultraviolet light-emitting diodes with composition-graded triangle electron-blocking layer

Impacts of polarization effect and electron-blocking layer (EBL) on the characteristics of deep-ultraviolet (DUV) light-emitting diode (LED) are investigated numerically. Simulation results show that the DUV LED with a bulk AlGaN EBL of high aluminum composition possesses good capability of electron confinement in general, while the characteristics deteriorate dramatically when the degree of polarization is high. Instead, the DUV LED with a composition-graded triangle AlGaN EBL is found to be less sensitive to the variation of polarization effect and possesses superior output performance in comparison with the counterpart LED with a bulk AlGaN EBL under high degree of polarization. The composition-graded triangle AlGaN EBL is beneficial for the DUV LED with high crystalline quality due to the relatively slight energy band deformation under high degree of polarization.

Demonstration of ultraviolet-B AlGaN-based laser diode operation with a peak light output power of 150 mW by improving injection efficiency through polarization charge modulation

In this study, AlGaN-based ultraviolet-B band laser diodes with 150-mW peak output power in pulsed operation were demonstrated at room temperature. The oscillation wavelength, differential quantum efficiency, and slope efficiency of a laser diode were 300 nm, 3.6%, and 0.15 W/A, respectively. These results were obtained by increasing the injection efficiency and decreasing the positive fixed polarization charge formed at the interface between a p-side waveguide layer and an electron blocking layer when polarization doping is formed in a p-AlGaN cladding layer.

Efficiency droop in AlGaN crystal-based UVB LEDs in the context of electron blocking mechanism

Aluminum gallium nitride (AlGaN) based UVB LEDs are delivering an increase in efficiency under low current drive, however, the devices are confronted with high efficiency droop and high operating voltages during the measurement on bare-wafer under high current drive. Such issues in UVB LEDs are attributed to using conventional p-type multi-quantum-barrier electron-blocking layer (p-MQB EBL) and fixed Al-contents in the p-AlGaN hole-source layer (HSL). When the conventional p-MQB EBL and bulk p-AlGaN HSL was replaced by Al-graded ud-AlGaN EBL and Al-graded p-AlGaN HSL, respectively, the efficiency droop has been remarkably suppressed and almost uniform external-quantum efficiency (EQE) under high injection current was confirmed. Also, the operating voltages under 150 mA drive were significantly reduced from 64 V (conventional p-MQB EBL) to 24 V (new polarized ud-AlGaN EBL) in UVB LEDs. These improvements are attributed to the smooth valance band edge without any potential barrier in both Al-graded ud-AlGaN EBL and Al-graded p-AlGaN HSL for efficient injection efficiency. At the same time the new structure was considered useful for both blocking of high energy electron overshooting toward the p-side as well as Mg-diffusion toward the multi-quantum wells (MQWs) under high current drive. These experimental results were also confirmed by simulations.

Simulation and theoretical study of AlGaN-based deep-ultraviolet light-emitting diodes with a stepped electron barrier layer

Owing to the COVID-19 outbreak, sterilization of deep-ultraviolet light-emitting diodes (DUV LEDs) has attracted increasing attention. Effectively improving the radiative recombination efficiency and mitigating the efficiency degradation, mainly caused by electron leakage and nonradiative recombination, have also emerged as two of the main issues to be addressed. In this study, a DUV LED epitaxial structure with a novel electron-blocking layer (EBL) is proposed. The DUV LED with a luminescence wavelength of ∼297 nm was formed by the stepwise variation of the Al component. Through the simulation and analysis of its performance parameters, we found that, compared to the conventional EBL structure, this new EBL structure not only reduces the electron leakage to the p-region effectively but also increases the hole injection into the active region, resulting in an increase in carrier concentration in the active region, a two-to-three-fold increase in the radiative recombination rate, and a 58% increase in the internal quantum efficiency, thus alleviating the efficiency droop and achieving a more efficient operation at high current densities.

Cubic GaN and InGaN/GaN quantum wells

LEDs based on hexagonal InGaN/GaN quantum wells are dominant technology for many lighting applications. However, their luminous efficacy for green and amber emission and at high drive currents remains limited. Growing quantum wells instead in the cubic phase is a promising alternative because, compared to hexagonal GaN, it benefits from a reduced bandgap and is free of the strong polarization fields that can reduce the radiative recombination rate. Initial attempts to grow cubic GaN in the 1990s employed molecular beam epitaxy, but now, metal-organic chemical vapor deposition can also be used. Nonetheless, high phase purity requires careful attention to growth conditions and the quantification of any unwanted hexagonal phase. In contrast to hexagonal GaN, in which threading dislocations are key, at its current state of maturity, the most important extended structural defects in cubic GaN are stacking faults. These modify the optical properties of cubic GaN films and propagate into active layers. In quantum wells and electron blocking layers, segregation of alloying elements at stacking faults has been observed, leading to the formation of quantum wires and polarized emission. This observation forms part of a developing understanding of the optical properties of cubic InGaN quantum wells, which also offer shorter recombination lifetimes than their polar hexagonal counterparts. There is also growing expertise in p-doping, including dopant activation by annealing. Overall, cubic GaN has rapidly transitioned from an academic curiosity to a real prospect for application in devices, with the potential to offer specific performance advantages compared to polar hexagonal material.

AlGaN-Based Deep UV Laser Diodes without an Electron Blocking Layer and with a Reduced Aluminum Composition of Quantum Barriers

AlGaN-Based Deep UV Laser Diodes without an Electron Blocking Layer and with a Reduced Aluminum Composition of Quantum Barriers

AlGaN-Based Deep-Ultraviolet Laser Diodes with Novel Superlattice Electron-Blocking Layers

AlGaN-Based Deep-Ultraviolet Laser Diodes with Novel Superlattice Electron-Blocking Layers

Improvement of the optoelectronic characteristics in deep-ultraviolet laser diodes with tapered p-cladding layer and triangular electron blocking layer

Improvement of the optoelectronic characteristics in deep-ultraviolet laser diodes with tapered p-cladding layer and triangular electron blocking layer

Compositional degradation of the electron blocking layers through solid-solution in GaN-based laser diodes

Electron leakage currents seriously hinder GaN-based blue laser diodes (LDs) from high wall-plug efficiencies. Inserting an ultra-thin AlGaN electron blocking layer (EBL) in the epitaxy structure is a major technique to suppress the leakage currents for which a high Al composition in the EBL is necessary. Despite many studies on the optimization of the compositions of EBLs, it is questionable whether they reach the designed value in real growths by metal-organic vapor phase epitaxy. We investigate the influence of the growth conditions of upper cladding layers (CLs) on the underlying EBLs. A strong composition degradation of the EBL is observed when the growth rate of the CL is low, which drastically reduces the output performance of both LEDs and LDs. A 30-nm fast-growing protecting layer can efficiently prevent the EBL from such degradation. The phenomenon cannot be explained by a composition pulling effect nor an etch effect by hydrogen, but by a mutual solid solution between the EBL and the adjacent CL. The solution process is found thermally favored by calculating the Gibbs energy where strain and entropies are considered. It is inferred that the chemically active Ga adatoms at the surface play an important role in accelerating the solution process. Based on these considerations, we introduce a random walk model to clarify the kinetic influence of CL growth rates on EBL degradation semi-quantitatively. The results help to understand the subtle process in the growth of heterostructures and the transport process of GaN-based LDs.

Color-tunable quantum-dot light emitting diode and its integration with GaN-based blue LED for smart white-light emission

White-light emission with tunable color temperature have potential applications in the fields of smart lighting and backlight. In this study, we introduced an electron blocking layer (EBL) between red and green emission layers (EMLs) in a quantum-dot light-emitting diode (QLED). The emitting color of QLED can be tuned from red to green as the carrier distribution and recombination region are regulated by the applied voltage. In addition, the color tunable QLED device was integrated with a GaN-based blue light emitting diode (LED), achieving a hybrid QLED/LED device for white-light emission. Under the alternate-current (AC) driving method, the QLED was forwardly driven while the LED was reversely biased, and thus, both devices can be independently addressed by the polarity of the AC driving voltage. The results showed that the color temperature of white-light emission can be tuned from 3102K (warm white) to 12853K (cold white) and the highest color rendering index (CRI) of 88.6 can be also achieved, exhibiting great prospects in the application of lighting.

Effects of Ni-NCAL and Ni–Ag electrodes on the cell performances of low-temperature solid oxide fuel cells with Sm0.2Ce0·8O2-δ electrolyte at various temperatures

Three low-temperature solid oxide fuel cells are built using Sm0.2Ce0·8O2-δ (SDC) as the electrolyte. Cell A is symmetrical and features Ni–LiNi0.8Co0·15Al0·05O2 (Ni–NCAL) electrodes, Cell B comprises a Ni–NCAL anode and a Ni–Ag cathode, and Cell C is fabricated using a Ni–NCAL cathode and a Ni–Ag anode. The ohmic resistance and polarization resistance (Rp) of Cells B and C are significantly higher than those of Cell A. The reduction of NCAL at the anodes of Cells A and B yields LiOH and Li2CO3 phases, and the Ni particles generated on the surfaces of the NCAL particles improve the catalytic activity of the cells. Li2CO3–LiOH melts at temperatures >450 °C and penetrates the porous SDC electrolyte layer, causing its densification and abnormal grain growth and increasing its ionic conductivity to >0.2 S/cm at low temperatures. The high open-circuit voltages (OCVs) (0.970–1.113 V) of the cells during electrochemical measurements are ascribed to the Li2CO3–LiOH phase which serves as an electron-blocking layer for the SDC electrolytes. As the reduction of NCAL approaches completion, the anode comprises only Ni phase, which hinders the charge transfer process. The triple-phase-boundary (TPB) area at cathode of Cell B is significantly lower than that of Cell A; therefore, the catalytic activity of Cell B for the oxygen reduction reaction is lower than that of Cell A. Consequently, the maximum power density (MPD) of Cell B is less than half of that of Cell A. The large Rp value of Cell C is ascribed to its low TPB area at Ni–Ag anode which has no reaction with H2 during operation. No visible sintering of the SDC electrolyte layer is observed for Cell C; therefore, its ionic conductivity is considerably smaller than those of the electrolyte layers of Cells A and B. The OCVs of Cell C (0.281–0.495 V) are significantly lower than the typical OCVs of ceria-based SOFCs. This is attributed to the porous SDC electrolyte layer of Cell C. The large Rp values and the low OCVs contribute to the low MPDs of Cell C at various temperatures.

Study of AlGaN-based deep ultraviolet laser diodes using one-way step-shaped quantum barriers and symmetrical step-shaped electron and hole blocking layers

To improve the carrier injection efficiency and optimize the performance of the AlGaN-based deep ultraviolet laser diodes (DUV-LDs), one-way step-shaped quantum barriers (OWS-QBs), a symmetrical step-shaped electron blocking layer (SS-EBL), and a symmetrical step-shaped hole blocking layer (SS-HBL) are proposed. Crosslight software is used to simulate the DUV-LDs with a traditional structure, with OWS-QBs, and with OWS-QBs, a SS-EBL, and a SS-HBL. The simulation results and physical mechanism analysis indicate that the SS-EBL, SS-HBL, and OWS-QBs contribute to the increased carrier concentration in the quantum wells, the reduced carrier leakage in the nonactive regions, the increased stimulated emission rate, the reduced threshold current and threshold voltage, and the enhanced output power and electro-optical conversion efficiency of DUV-LDs.

Compositionally graded quaternary electron blocking layer for efficient deep ultraviolet AlGaN-based light-emitting diodes

Compositionally graded quaternary electron blocking layer for efficient deep ultraviolet AlGaN-based light-emitting diodes

The charging performance in contact electrification of fluorinated ethylene propylene surfaces by electrode bridge

Triboelectricity utilizes triboelectric nanogenerators (TENG) that transfer negative charges between two material surfaces that are in contact. Incomplete flow of charges results in charge accumulation on the material surfaces. In this study, we demonstrated that the accumulated charges could enhance induced output by contact electrification using electrode bridge (EB) to improve charge transfer mechanism. Triboelectric nanogenerator electrode bridge (TENG-EB) was fabricated using synergistic combination of polymer-polymer, polymer-metal, and metal-metal contacts during contact-electrification. Fluorinated ethylene propylene (FEP) film was fabricated using hot pressing technique. FEP crystallinity reached 85.8%, maximum temperature for ε r of FEP was 145 °C, and remanent polarization of FEP polymer was 4.2 µC mm – 2 . The individual events of the charge transfer during contact and separating of TENG-EB could be studied with a single electrode measurement. Separation of FEP, EB and electrode surfaces led to induced output of which signal was 4 times higher than TENG with non-EB. This mechanism utilized DC output that enhanced AC output signal for a given tapping frequency across a rectifier circuit. This new route is proposed for further research, development and invention in alternative energy field including energy harvesting and flexible electronic devices. • Charges event is demonstrated using electrode bridge (EB) induced output performance. • Triboelectric nanogenerator electrode bridge (TENG-EB) was fabricated based on synergistic combination of polymer-polymer, polymer-metal, and metal-metal contacts. • FEP-Al hot pressing is fabricated for electron blocking layer (EBL) has also played a vital role in blocking the electron overflow between a negative material and an electrode. • Output signal of TENG-EB is 4 times higher than that of a TENG non-EB.

Effective interfacial energy band engineering strategy toward high-performance triboelectric nanogenerator

Provided that electron transition ascribed to overlapping electron dominates the mechanism of contact electrification of triboelectric nanogenerators (TENGs), the electron transfer process occurs due to the built-up electric field between the triboelectrification surface and bottom electrode. In this work, we embed a solution-processed high-permittivity electron blocking layer (HPEBL) of LaZrO into the classical contact-separation mode TENG to build an energy barrier (ΔE > 1.3 eV) between ITO and PDMS, which could effectively block the transportation of electrons towards the bottom electrode. The surface potential decline rate of PDMS is obviously suppressed, extending the half-charge decay time by ∼3.1 times. A La0.1Zr0.9Ox HPEBL based TENG (H-TENG) demonstrates the electrical outputs with 215 V, 96.3 mA m−2 and 243.3 μC/m−2. Under the external load of 100 MΩ, the average gravimetric/volumetric power density and energy conversion efficiency can be calculated to be 59.34 μW g−1, 152.5 μW cm−3 and 39.2%, respectively. Furthermore, the dielectric behaviors of LaZrO thin films are investigated by metal–insulator-metal (MIM) devices. The Poole-Frenkel (PF) emission is found to dominate the leakage mechanism of LaZrO during operation. Consequently, increasing the relative permittivity and reducing the trap density could be indicated as the optimization orientation of HPEBL.

Enhanced performance in deep-ultraviolet laser diodes with an undoped BGaN electron blocking layer.

Aluminum-rich p-AlGaN electron blocking layers (EBLs) are typically used for preventing overflow of electrons from the active region in AlGaN-based deep ultraviolet (DUV) laser diode (LD). However, these cannot effectively prevent electron leakage and form barrier layers, which affects the hole injection efficiency. Herein, the traditional p-AlGaN EBL in LD is replaced with an undoped BGaN EBL. The undoped BGaN EBL LD increases the effective barrier height of the conduction band to prevent the leakage of electrons and decreases the energy loss caused by the polarization induced electric field, enhancing the hole injection. The slope efficiency of the undoped BGaN EBL LD is 289% higher than that of the highly doped AlGaN EBL LD, and its threshold current is 51% lower. Therefore, the findings of this study provide insights for solving the problems of electron leakage and insufficient hole injection in high-performance and undoped EBL DUV LDs.

Multidimensional Perovskites for High Detectivity Photodiodes.

Low-dimensional perovskites attract increasing interest due to tunable optoelectronic properties and high stability. Here, it is shown that perovskite thin films with a vertical gradient in dimensionality result in graded electronic bandgap structures that are ideal for photodiode applications. Positioning low-dimensional, vertically-oriented perovskite phases at the interface with the electron blocking layer increases the activation energy for thermal charge generation and thereby effectively lowers the dark current density to a record-low value of 5 × 10-9 mA cm-2 without compromising responsivity, resulting in a noise-current-based specific detectivity exceeding 7 × 1012 Jones at 600nm. These multidimensional perovskite photodiodes show promising air stability and a dynamic range over ten orders of magnitude, and thus represent a new generation of high-performance low-cost photodiodes.

InGaN-based light-emitting diodes with Al content graded p-AlxGa1-xN top contact layer

This study demonstrates a GaN-based light-emitting diode (LED) structure with an Al composition, graded p-Al x Ga 1− x N top contact layer as the electron-blocking layer (EBL). Experimental results showed that the LEDs with graded EBL layer exhibited lower forward voltage ( V f ) and higher output power (L op ) than conventional LEDs with constant Al composition in the EBL. The lower V f is attributed to the relatively higher hole concentration caused by the polarization field in the graded AlGaN EBL. In addition to the improved hole concentration, the higher L op is also due to the improved electron confinement caused by the graded EBL. • GaN-based light-emitting diode (LED) structure possessed an Al composition graded p-AlxGa1-xN top contact layer. • Polarization field in the graded AlxGa1-xN EBL causes the relatively higher hole concentration. • Graded AlGaN EBL could effectively mitigate electrons to overflows to the p-GaN. • LEDs with the graded AlGaN EBL exhibited higher efficiency than conventional LEDs with constant Al in the EBL.