Fabrication Of Light-emitting Diodes Research Articles

STUDYING ZINC OXIDE/COPPER OXIDE/CADMIUM SELENIDE NANOSTRUCTURES FOR LIGHT EMITTING DIODES

The synthesis of zinc oxide, copper oxide, and cadmium selenide as a heterostructure was conducted using a simple co-precipitation method. Structural, optical, and electrical properties were investigated. XRD patterns show hexagonal form for ZnO, cubic for CuO, and wurtzite for CdSe, with an average particle size of 18.5, 22.3, and 38.2 nm for ZnO, CuO, and CdSe, respectively. SEM images show ZnO crystals with a nanorod shape and CuO and CdSe nanoparticles with nano-branch agglomerations in all directions. Optical properties exhibit a redshift in absorbance (460 nm) with photoluminescence peaks at 500 nm for the heterostructure and a broadened band gap (2.5 eV). In light, the heterostructure shows increased light absorption, leading to enhanced electron-hole production and an exponential increase in forward current. These results enhance the success of fabrication of high-amplification light-emitting diodes.

Greater Influence of Density on the Electrical Properties of an Organic Semiconductor Glass Compared to Molecular Orientation.

Physical vapor deposition is widely used in the fabrication of organic light-emitting diodes and has the potential to adjust the density and orientation through substrate temperature control, which may lead to enhanced electrical performance. However, it is unclear whether this enhanced property is because of the horizontal molecular orientation or the increased density. The effects of the density and orientation on the electrical properties of a potential electron transport material, (3-dibenzo[c,h]acridin-7-yl)phenyl)diphenylphosphine oxide (TPPO-dibenzacridine), were investigated. According to the gyration tensor analysis, TPPO-dibenzacridine resembled an oblate ellipsoid. Furthermore, these films exhibited the highest density when prepared at a substrate temperature of 87.5% of the glass transition temperature with an increase in density of approximately 1.5%. Variable angle spectroscopic ellipsometry measurements confirmed that the transition dipole moment direction of the dibenzacridine moiety, which is involved in the electrical properties, remained isotropic at this temperature. Although horizontal orientations are known to optimize their π-π overlap and improve the electrical properties, the lowest driving voltage was observed under these conditions, which led to the conclusion that the enhanced electrical properties of TPPO-dibenzacridine are greatly influenced by the increased density rather than by the molecular orientation.

Metal-organic-frameworks (MOFs) advanced synthetic strategies and applications, including light emitting diodes, solar cells and photodetectors

Abstract Several synthetic approaches, such as solvothermal, microwave-assisted, electrochemical, and mechanochemical techniques, are used in the creation of metal-organic frameworks (MOFs). The resulting MOFs can be tailored for particular purposes by utilizing the distinct benefits that each of these approaches offers in terms of managing their size, shape, and functional qualities. The most recent developments in MOF synthesis are examined in this study along with how they are being used in optoelectronic devices such as photodiodes, solar cells, and light-emitting diodes (LEDs). MOFs are potential candidates for these applications because of their special qualities, which include their capacity to host light-emitting guest molecules, promote charge transport, and improve light absorption. MOFs effectively house luminescent centers in LEDs, improving brightness and color purity. MOFs improve charge separation and light collecting efficiency in solar cells. The customizable band gaps of MOFs, which may be designed to maximize their performance in photodetection, are advantageous to photodiodes. Advances in MOFs could revolutionize future optoelectronics. Finally, MOFs are based on the ongoing development of advanced synthetic methods that allow for the fabrication of LEDs, solar cells and photodetectors at higher levels of technological innovation and application. Additionally, MOFs in photodetectors, are thought to be active material and their special capacity to interact at various wavelengths may pave the way for more sensitive and adaptable application-specific sensors in a range of areas, including high-speed communication technologies and environmental monitoring.

Aggregation suppression and enhanced blue emission of perylene in zinc-based coordination polymer glass.

Reducing aggregation caused quenching and enhancing stability is crucial in the fabrication of organic light-emitting diodes. Herein, we successfully fabricated blue-emitting coordination polymer glasses using perylene dye and a zinc-based coordination glass. The aggregation of perylene monomers in the solid state was significantly suppressed, and the hybrid glass demonstrated high stability and strong photoluminescent quantum yield (75.5%) under ambient conditions.

Encapsulating Gold Nanoclusters into Melamine–Formaldehyde Polymer Nanoparticles for Confinement Induced Enhanced Emission toward Ratiometric Sensing and Light-Emitting Diode Fabrication

Encapsulating Gold Nanoclusters into Melamine–Formaldehyde Polymer Nanoparticles for Confinement Induced Enhanced Emission toward Ratiometric Sensing and Light-Emitting Diode Fabrication

Short-Wave Infrared Optoelectronics with Colloidal CdHgSe/ZnCdS Core/Shell Nanoplatelets.

Colloidal semiconductor nanocrystals (NCs) are an efficient and cost-effective class of nanomaterials for optoelectronic applications. Advancements in NC-based optoelectronic devices have resulted from progress in synthetic chemistry, adjustable surface properties, and optimized device architectures. Semiconductor nanoplatelets (NPLs) stand out among other NCs due to their precise growth control, yielding uniform thickness with submonolayer roughness. In this study, we demonstrate the versatility of core/shell Cd x Hg1-x Se/Zn y Cd1-y S NPLs for optoelectronic applications in the short-wave infrared (SWIR) spectral range. We employed the very same core/shell NPLs for the fabrication of light-emitting diodes and photodetectors alike, achieving significant performance in both electroluminescence (external quantum efficiency ranging from 7.5% at 1280 nm to 3.8% at 1550 nm) and detection (responsivity of 0.24 A W-1 at 1200 nm).

Tunable Optical Properties, Enhanced Photoluminescence, and Thermostability of CaO: Eu2+/3+ Phosphors by Codoping Cl- Ions.

Europium-activated calcium oxide (CaO: Eu) phosphor shows great potential in the fabrication of light-emitting diodes (LEDs). However, its luminescent intensity and thermostability still need to be further enhanced. In this work, the photoluminescence property and thermostability of CaO: Eu2+/3+ were improved significantly by codoping a few of Cl- ions into it. Compared with CaO: Eu2+/3+ samples, CaO: Eu2+/3+, Cl- phosphors not only have tunable luminescence but also show stronger luminescence intensity and thermal stability. The emission color of phosphors can be tuned by changing the excitation wavelength; typically, strong red/blue light can be displayed under 250/362 nm excitation. More importantly, both the red and blue emissions will increase simultaneously with increasing codoped Cl- content. When the Cl- ion content is 0.06, the emission intensity of CaO: 0.01Eu2+/3+, 0.06Cl- reaches its maximum and its red and blue emission intensities increase by approximate 2.5 times and 13.2 times, respectively. The results show that CaO: Eu2+/3+, Cl- phosphors have potential application value in LEDs and anti-counterfeiting.

A well-performed green-emitting Lu1.5Ca1.5Al3.5Si1.5O12:Ce3+ garnet phosphor for high-quality pc-WLEDs

High-brightness and thermally-stable broadband green-emitting phosphors are highly demanded for the fabrication of high-quality phosphor-converted white light-emitting diodes (pc-WLEDs) with high color rendering index (CRI) and low correlated color temperature (CCT). Herein, we report on the synthesis, luminescent properties, thermal stability and application of a novel highly efficient green-emitting Lu1.5Ca1.5Al3.5Si1.5O12:Ce3+ garnet-type phosphor for blue-chip-pumped high-CRI pc-WLEDs. A series of Lu1.5Ca1.5Al3.5Si1.5O12:Ce3+ green phosphors doped with various Ce3+ concentrations (0.5–4 mol%) have been prepared by a conventional high-temperature solid-state reaction approach. Impressively, the composition-optimized Lu1.5Ca1.5Al3.5Si1.5O12:2%Ce3+ sample exhibits a broad excitation band in the 400–500 nm spectral range with an excitation peak around 451 nm, and it gives rise to a bright broad green emission band in the 470–700 nm wavelength region (emission peak: 533 nm; bandwidth: 108 nm) with CIE color coordinates of (0.3361, 0.5640). Notably, high luminescence efficiency is obtained for Lu1.5Ca1.5Al3.5Si1.5O12:2%Ce3+ phosphor (internal quantum efficiency: 92.2%; external quantum efficiency: 50.7%). Moreover, it is also found that Lu1.5Ca1.5Al3.5Si1.5O12:2%Ce3+ shows excellent resistance to thermal quenching, while its emission intensity at 423 K remains 76% of the initial value at room temperature. Amazingly, the color stability of Lu1.5Ca1.5Al3.5Si1.5O12:2%Ce3+ is also outstanding, and only a very small chromaticity shift (3.99 × 10−3) is observed at 423 K. A high-performance pc-WLED device has been fabricated by using a 450 nm blue-emitting LED chip and as-prepared Lu1.5Ca1.5Al3.5Si1.5O12:2%Ce3+ green phosphor as well as commercial CaAlSiN3:Eu2+ red phosphor. Such device produces a bright warm-white emission under 280 mA driving current, demonstrating super CIE chromaticity coordinates (0.3870, 0.3818), high CRI of 93.8, low CCT of 3865 K, and high luminous efficacy (51.86 lmW−1).

Effect of magnesium doping on NiO hole injection layer in quantum dot light-emitting diodes

Abstract This study reports on the fabrication of quantum dot light-emitting diodes (QLEDs) with an ITO/Ni1−x Mg x O/SAM/TFB/QDs/ZnMgO/Al structure and investigates the effects of various Mg doping concentrations in NiO on device performance. By doping Mg into the inorganic hole-injection layer NiO (Ni1−x Mg x O), we improved the band alignment with the hole-injection layer through band tuning, which enhanced charge balance. Optimal Mg doping ratios, particularly a Ni0.9Mg0.1O composition, have demonstrated superior device functionality, underscoring the need for fine-tuned doping levels. Further enhancements were achieved through surface treatments of Ni0.9Mg0.1O with UV-Ozone (UVO) and thermal annealing (TA) of the ZnMgO electron transport layer. Consequently, by optimizing Mg-doped NiO in QLED devices, we achieved a maximum external quantum efficiency of 8.38 %, a brightness of 66,677 cd/m2, and a current efficiency of 35.31 cd/A, indicating improved performance. The integration of Mg-doped NiO into the QLED structure resulted in a device with superior charge balance and overall performance, which is a promising direction for future QLED display technologies.

Recent Advances in Fluorescent Polyimides.

Polyimide (PI) refers to a type of high-performance polymer containing imide rings in the main chain, which has been widely used in fields of aerospace, microelectronic and photonic devices, gas separation technology, and so on. However, traditional aromatic PIs are, in general, the inefficient fluorescence or even no fluorescence, due to the strong inter- and intramolecular charge transfer (CT) interactions causing unavoidable fluorescence quenching, which greatly restricts their applications as light-emitting functional layers in the fabrication of organic light-emitting diode (OLED) devices. As such, the development of fluorescent PIs with high fluorescence quantum efficiency for their application fields in the OLED is an important research direction in the near future. In this review, we provide a comprehensive overview of fluorescent PIs as well as the methods to improve the fluorescence quantum efficiency of PIs. It is anticipated that this review will serve as a valuable reference and offer guidance for the design and development of fluorescent PIs with high fluorescence quantum efficiency, ultimately fostering further progress in OLED research.

Bidirectional UV/violet heterojunction light-emitting diode with In0.27Al0.73N alloy film as electron transport layer

In this paper, the p-GaN/n-In0.27Al0.73N heterojunction light-emitting diode (LED) was fabricated by radio frequency magnetron sputtering (RF-MS) and the electroluminescence (EL) characteristics of the p-GaN/n-In0.27Al0.73N heterojunction diode was investigated. Based on the preparation of the InXAl1-XN thin films at different substrate temperatures (Ts), the crystal structure, optical and electrical properties were investigated by XRD, SEM and other material characterization techniques. With increasing Ts, the grain size and surface morphology of the InXAl1-XN thin films change dramatically. The film has the best optical and electrical properties when the Ts is 300℃. On the basis of this, the compositional content of indium in the InXAl1-XN film was calculated to be 0.27. The heterojunction LED was fabricated on a commercial p-GaN substrate and the In0.27Al0.73N alloy film. The EL was successfully achieved at various forward and reverse voltages at room temperature and the temperature-dependent EL has been investigated. Furthermore, research is being conducted on the characteristics of the interface of p-GaN/n-In0.27Al0.73N heterojunction and the elucidation of the light-emitting mechanism of diode. The present work uses a simple and low-cost RF-MS method to fabricate UV/Violet bidirectional drive p-GaN/n-In0.27Al0.73N heterojunction LED, which provides a new reference for the fabrication of LED using InXAl1-XN alloy material.

Defects in Nitrogen-Doped ZnO Nanoparticles and Their Effect on Light-Emitting Diodes.

In this study, the effect of defects on the acceptor properties of nitrogen-doped ZnO nanoparticles (NPs) was investigated through the fabrication of light-emitting diodes (LEDs). Nitrogen-doped ZnO NPs were synthesized by an arc discharge in-gas evaporation method and post-annealed at 800 °C in an oxygen and nitrogen atmosphere. The annealed ZnO NPs were characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and photoluminescence spectroscopy. It was found that the annealing of nitrogen-doped ZnO NPs in a nitrogen environment increased the number of zinc vacancies, while annealing in an oxygen environment increased the number of oxygen vacancies due to nitrogen desorption. The output characteristics of LEDs fabricated with oxygen-annealed NPs were degraded, while those with nitrogen-annealed NPs were significantly improved. From these results, the contribution of zinc vacancies to acceptor formation in ZnO NPs was confirmed for the first time in actual pn junction devices.

화합물 반도체 기반의 유연 발광소자 및 디스플레이 제작

This article presents a review of research activities over past decades focused on the fabrication of flexible light-emitting diodes (LEDs) and micro-LED displays. LEDs exhibit excellent material characteristics, including high radiative recombination rates, high carrier mobility, and ultra-long-term stability. These features make LEDs promising candidates for not only the future metaverse display but flexible display applications. However, the brittleness of compound semiconductor thin films poses challenges for creating deformable LED devices. Consequently, significant efforts have been dedicated to imparting deformability to LED devices and displays. We initially discuss a display prepared using a nanowire-assembly process, followed by a strategy involving thin film LEDs for flexible device fabrication. Vertical nanowire LED arrays are presented, along with a discussion of their advantages for flexible devices and displays. Furthermore, we review the selective-area epitaxy of vertical nanowire LED arrays. Finally, we briefly introduce the assembly methods of LEDs onto backplane circuits, addressing several important issues, including the misalignment of LED transfers onto backplane circuits. We conclude with personal remarks on the challenges and future perspectives for research on flexible micro-LED displays.

Vacuum-Boosting Precise Synthetic Control of Highly Bright Solid-State Carbon Quantum Dots Enables Efficient Light Emitting Diodes.

Carbon quantum dots (C-dots) have emerged as efficient fluorescent materials for solid-state lighting devices. However, it is still a challenge to obtain highly bright solid-state C-dots because of the aggregation caused quenching. Compared to the encapsulation of as-prepared C-dots in matrices, one-step preparation of C-dots/matrix complex is a good method to obtain highly bright solid-state C-dots, which is still quite limited. Here, an efficient and controllable vacuum-boosting gradient heating approach is demonstrated for in situ synthesis of a stable and efficient C-dots/matrix complex. The addition of boric acid strongly bonded with urea, promoting the selectivity of the reaction between citric acid and urea. Benefiting from the high reaction selectivity and spatial-confinement growth of C-dots in porous matrices, in situ synthesize C-dots bonded can synthesized dominantly with a crosslinked octa-cyclic compound, biuret and cyanuric acid (triuret). The obtained C-dots/matrix complex exhibited bright green emission with a quantum yield as high as 90% and excellent thermal and photo stability. As a proof-of-concept, the as-prepared C-dots are used for the fabrication of white light-emitting diodes (LEDs) with a color rendering index of 84 and luminous efficiency of 88.14lm W-1, showing great potential for applications in LEDs.

A Conjugated Carboranyl Main Chain Polymer with Aggregation-Induced Emission in the Near-Infrared.

Materials exhibiting aggregation-induced emission (AIE) are both highly emissive in the solid state and prompt a strongly red-shifted emission and should therefore pose as good candidates toward emerging near-infrared (NIR) applications of organic semiconductors (OSCs). Despite this, very few AIE materials have been reported with significant emissivity past 700 nm. In this work, we elucidate the potential of ortho-carborane as an AIE-active component in the design of NIR-emitting OSCs. By incorporating ortho-carborane in the backbone of a conjugated polymer, a remarkable solid-state photoluminescence quantum yield of 13.4% is achieved, with a photoluminescence maximum of 734 nm. In contrast, the corresponding para and meta isomers exhibited aggregation-caused quenching. The materials are demonstrated for electronic applications through the fabrication of nondoped polymer light-emitting diodes. Devices employing the ortho isomer achieved nearly pure NIR emission, with 86% of emission at wavelengths longer than 700 nm and an electroluminescence maximum at 761 nm, producing a significant light output of 1.37 W sr-1 m-2.

Thermally Induced Phase Separation of the PEDOT:PSS Layer for Highly Efficient Laminated Polymer Light-Emitting Diodes.

Among various conductive polymers, the poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) film has been studied as a promising material for use as a transparent electrode and a hole-injecting layer in organic optoelectronic devices. Due to the increasing demand for the low-cost fabrication of organic light-emitting diodes (OLEDs), PEDOT:PSS has been employed as the top electrode by using the coating or lamination method. Herein, a facile method is reported for the fabrication of highly efficient polymer light-emitting diodes (PLEDs) based on a laminated transparent electrode (LTE) consisting of successive PEDOT:PSS and silver-nanowire (AgNW) layers. In particular, thermally induced phase separation (TIPS) of the PEDOT:PSS film is found to depend on the annealing temperature (Tanneal) during preparation of the LTE. At Tanneal close to the glass transition temperature of the PSS chains, a PSS-rich phase with a large number of PSS- molecules enhances the work function of the PEDOT:PSS on the glass-side surface relative to the air side. By using the optimized LTEs, bidirectional laminated PLEDs are obtained with a total external quantum efficiency of 2.9% and a turn-on voltage of 2.6 V, giving a comparable performance to that of the reference bottom-emitting PLED based on a costly evaporated metal electrode. In addition, an analysis of the angular characteristics, including the variation in the electroluminescence spectra and the change in luminance according to the emission angle, indicates that the laminated PLED with the LTE provides a more uniform angular distribution regardless of the direction of emission. Detailed optical and electrical analyses are also performed to evaluate the suitability of LTEs for the low-cost fabrication of efficient PLEDs.

Perfluorooctanoic acid interface modification enabling efficient true-blue perovskite light-emitting diodes and air-processing compatibility

The pure-bromide quasi-2D perovskite has shown advantages in fabrication of blue perovskite light-emitting diodes (PeLEDs) due to its relatively good color stability and capability of moisture resistance. However, the performances of efficiency and luminance of pure-bromide quasi-2D PeLEDs with true-blue (470 nm−480 nm) emission are still inferior. Here, we show a interfacial modification strategy of involving perfluorooctanoic acid (PFOA) to a hole transport layer of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), to improve the performances of the true-blue PeLEDs. The PFOA regulates the molecular conformation of PEDOT:PSS, forming ordered PEDOT domains that improves the carrier transport and a more favorable band alignment with the perovskite emissive layers. The achieved true-blue PeLEDs show peak EQE of 6.86 % and maximum luminance of 854.10 cd/m2 at wavelength of 478 nm, which are the record values for the pure-bromide quasi-2D PeLEDs in true-blue region. Moreover, owing to the hydrophobic fluorine-carbon (C-F) chains of PFOA, we successfully fabricate the blue PeLEDs in air condition without inert gas protection. This work paves the way for commercial applications in next-generation display technologies.

Direct Evidence of the Effect of Water Molecules Position in the Spectroscopy, Dynamics, and Lighting Performance of an Eco-Friendly Mn-Based Organic-Inorganic Metal Halide Material for High-Performance LEDs and Solvent Vapor Sensing.

Luminescent Mn(II)-based organic-inorganic hybrid halides have drawn attention as potential materials for sensing and photonics applications. Here, the synthesis and characterization of methylammonium (MA) manganese bromide ((MA)nBrxMn(H2O)2, (n = 1, 4 and x = 3, 6)) with different stoichiometries of the organic cation and inorganic counterpart, are reported. While the Mn2+ centers have an octahedral conformation, the two coordinating water molecules are found either in cis (1) or in trans (2) positions. The photophysical behavior of 1 reflects the luminescence of Mn2+ in an octahedral environment. Although Mn2+ in 2 also has octahedral coordination, at room temperature dual emission bands at ≈530 and ≈660nm are observed, explained in terms of emission from Mn2+in tetragonally compressed octahedra and self-trapped excitons (STEs), respectively. Above the room temperature, 2 shows quasi-tetrahedral behavior with intense green emission, while at temperatures below 140K, another STE band emerges at 570nm. Time-resolved experiments (77-360K) provide a clear picture of the excited dynamics. 2 shows rising components due to STEs formation equilibrated at room temperature with their precursors. Finally, the potential of these materials for the fabrication of color-tunable down-converted light-emitting diode (LED) and for detecting polar solvent vapors is shown.

B‒N covalent bond-involved π-extension of multiple resonance emitters enables high-performance narrowband electroluminescence.

Multi-boron-embedded multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters show promise for achieving both high color-purity emission and high exciton utilization efficiency. However, their development is often impeded by a limited synthetic scope and excessive molecular weights, which challenge material acquisition and organic light-emitting diode (OLED) fabrication by vacuum deposition. Herein, we put forward a B‒N covalent bond-involved π-extension strategy via post-functionalization of MR frameworks, leading to the generation of high-order B/N-based motifs. The structurally and electronically extended π-system not only enhances molecular rigidity to narrow emission linewidth but also promotes reverse intersystem crossing to mitigate efficiency roll-off. As illustrated examples, ultra-narrowband sky-blue emitters (full-width at half-maximum as small as 8nm in n-hexane) have been developed with multi-dimensional improvement in photophysical properties compared to their precursor emitters, which enables narrowband OLEDs with external quantum efficiencies (EQEmax) of up to 42.6%, in company with alleviated efficiency decline at high brightness, representing the best efficiency reported for single-host OLEDs. The success of these emitters highlights the effectiveness of our molecular design strategy for advanced MR-TADF emitters and confirms their extensive potential in high-performance optoelectronic devices.

High-brightness thermally evaporated perovskite light-emitting diodes via dual-interface engineering

Thermal evaporation emerges as a promising method for the scale-up fabrication of perovskite light-emitting diodes (PeLEDs) due to its superior repeatability and compatibility with the existing display industry compared to conventional solution process. However, the brightness of current high-efficiency thermally evaporated PeLEDs is generally constrained to a range of thousands of cd/m2. Herein, we propose a dual-interface engineering strategy to modulate the charge injection properties and passivate surface defects in the co-evaporated Cs–Pb–Br perovskite emitter. Our findings demonstrate that introducing 4,4′-Cyclohexylidenebis [N, N-bis(4-methylphenyl) benzenamine] additive to the bottom hole transport layer poly (9-vinylcarbazole) not only facilitates hole injection but also increases the conductivity. Meanwhile, the deposition of functionalized phenylethylammonium bromide salts with a specific number of fluorine atoms passivates the top surface defects and enhances the charge transport simultaneously. Consequently, the optimal PeLEDs achieve a maximum luminance of 75,012 cd/m2, marking one of the brightest thermally evaporated PeLEDs reported to date. The proposed strategy holds significant potential to guide the preparation of high-performance thermally evaporated PeLEDs for high-radiance display applications.