Applications In Light-emitting Devices Research Articles

Properties of Multistranded Twisted Graphene Fibers and Their Application in Flexible Light-Emitting Devices.

As a typical carbon-based material electrode, graphene fiber exhibits many advantages, such as good electrical conductivity, lightweight, and strong structural designability. Its demand is increasing in the wearable display field. With the help of fine denier fiber spinning combined with multistranded graphene fibers prepared via twisting and drafting, their petal-like twisted structure endows the fibers with a high specific surface area, enabling them to complete dye adsorption within 30 min. Simultaneously, compared with that of a single fiber with the same thickness, the volume specific resistance of a multistranded twisted graphene fiber is reduced by 2.4 times. During force sensing, the twisted structure of multistranded fibers exhibits varying simultaneity of fiber fracture with excellent resistance sensitivity reaching up to 55%. The multistranded twisted flexible graphene fibers demonstrate excellent robustness. Electroluminescent flexible devices prepared with graphene fibers and fiber braided fabrics with different organizational structures as electrodes emit highly saturated short-wave blue light during long-term multiple use. Therefore, multistranded twisted graphene fibers exhibit considerable potential for future applications in wearable multicolor smart displays and flexible optical signal electronics.

Synthesis and characterization of UV organic light-emitting electrochemical cells (OLECs) using phenanthrene fluorene derivatives for flexible applications

This paper details how two new small molecules, based on phenanthrene, were developed, and tailored for light-emitting device applications. An account is provided of both the compound synthesis and the methodologies employed in device fabrication. The ink formulation was improved by the use of triflate counterions. Standard bottom emitting devices were constructed on ITO glass along with top emitting devices on a sputter coated silver on glass substrate. Both structures exhibit UV emissions from the synthesized molecules. Successful EL emission within the UV spectrum range has been achieved by spray coating these active molecules onto glass slides. The optimized solution-processed devices produce UV emission using a semi-transparent silver nanowire top electrode. This results in electroluminescence (EL) peaking at 398 nm, with a maximum EL emission intensity of 20.5 μW/cm2.

Regioisomerism vs Conformation: Impact of Molecular Design on the Emission Pathway in Organic Light-Emitting Device Emitters.

Despite the design and proposal of several new structural motifs as thermally activated delayed fluorescent (TADF) emitters for organic light-emitting device (OLED) applications, the nature of their interaction with the host matrix in the emissive layer of the device and their influence on observed photophysical outputs remain unclear. To address this issue, we present, for the first time, the use of up to four regioisomers bearing a donor-acceptor-donor electronic structure based on the desymmetrized naphthalene benzimidazole scaffold, equipped with various electron-donating units and possessing distinguished conformational lability. Quantum chemical calculations allow us to identify the most favorable conformations adopted by the electron-rich groups across the entire pool of regioisomers. These conformations were then compared with conformational changes caused by the interaction of the emitter with the Zeonex and 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) matrices, and the correlation with observed photophysics was monitored by UV-vis absorption and steady-state photoluminescence spectra, combined with time-resolved spectroscopic techniques. Importantly, a CBP matrix was found to have a significant impact on the conformational change of regioisomers, leading to unique TADF emission mechanisms that encompass dual emission and inversion of the singlet-triplet excited-state energies and result in the enhancement of TADF efficiency. As a proof of concept, regioisomers with optimal donor positions were utilized to fabricate an OLED, revealing, with the best-performing dye, an external quantum emission of 11.6%, accompanied by remarkable luminance (28,000 cd/m2). These observations lay the groundwork for a better understanding of the role of the host matrix. In the long term, this new knowledge can lead to predicting the influence of the host matrix and adopting the structure of the emitter in a way that allows the development of highly efficient and efficient OLEDs.

Solid-State Photochemical Cascade Process Boosting Smart Ultralong Room-Temperature Phosphorescence in Bismuth Halides.

Molecular ultralong room-temperature phosphorescence (RTP), exhibiting multiple stimuli-responsive characteristics, has garnered considerable attention due to its potential applications in light-emitting devices, sensors, and information safety. This work proposes the utilization of photochemical cascade processes (PCCPs) in molecular crystals to design a stepwise smart RTP switch. By harnessing the sequential dynamics of photo-burst movement (induced by [2+2] photocycloaddition) and photochromism (induced by photogenerated radicals) in a bismuth (Bi)-based metal-organic halide (MOH), a continuous and photo-responsive ultralong RTP can be achieved. Furthermore, utilizing the same Bi-based MOH, diverse application demonstrations, such as multi-mode anti-counterfeiting and information encryption, can be easily implemented. This work thus not only serves as a proof-of-concept for the development of solid-state PCCPs that integrate photosalient effect and photochromism with light-chemical-mechanical energy conversion, but also lays the groundwork for designing new Bi-based MOHs with dynamically responsive ultralong RTP.

In-Situ passivation of mixed-halide perovskite nanocrystals for high-performance blue light-emitting diodes

In halide perovskite nanocrystals (NCs), insulating long chain ligands such as oleic acid (OA) and oleylamine (OAm) often remove the halide ions during the purification process, leading to surface vacancy defects. This hinders their application in light-emitting devices. Herein, we report an in-situ passivation strategy using ethyl trifluoroacetate, which is hydrolyzed to trifluoroacetic acid, as an antisolvent in the purification process to passivate defects by reacting with uncoordinated Pb2+ and OAm on the surface of NCs, thus anchoring Br− to the surface of NCs. This achieves a mild removal of OAm and OA while passivating both anionic and cationic vacancies. Consequently, we achieved high-performance blue perovskite light-emitting diodes (PeLEDs). The PeLEDs based on these NCs exhibit pure blue electroluminescence at 463 nm with an external quantum efficiency of 4.14 % and a luminance of 1035 cd m−2. This study provides insights and a foundation for the development of high-performance PeLEDs.

Analysis of Wet-Etched Structures on R-Plane Substrates of Sapphire in the Etchant of Sulfuric Acid and Phosphoric Acid

The occurrence and variation of wet-etched structures on R-plane substrates of sapphire were analyzed according to the distribution of drilling rates of typical crystal planes. First, the experiment for etching the sapphire hemisphere was conducted to obtain the distribution of etching rates with C-plane as the rotation center in the experimental etchant (236 °C, three parts H2SO4 and one part H3PO4 in terms of volume). Then, the transfer matrix was applied to transform the distribution of etching rates with C-plane as the rotation center in the experimental etchant (236 °C, three parts H2SO4 and one part H3PO4 in terms of volume) into the distribution of etching rates with R-plane as the rotation center. The positive curvature maximum identification method was then applied to obtain the distribution of drilling rates of typical crystal planes on R-plane substrates. Finally, the occurrence and variation of polygonal grooves with different mask configurations on R-plane substrates in the experimental etchant (236 °C, three parts H2SO4 and one part H3PO4 in terms of volume) were analyzed based on the distribution of drilling rates of typical crystal planes. This provides a basis for the application and development of GaN-based light-emitting diode devices.

Fabrication of crack-free strained SiGe/Ge multiple quantum wells on Ge-on-Si(111) by the patterning method

We fabricate strained SiGe/Ge multiple quantum well (MQW) structures on Ge-on-Si(111). It is clearly found that high-density crystal cracks are generated in the MQW due to the accumulated tensile strain when the total thickness of the MQW increases beyond the critical thickness. In this study, we determine the critical thickness of the strained SiGe/Ge (111) MQW. Moreover, we demonstrate the mesa-patterning of the Ge-on-Si prior to the MQW growth can drastically suppress the crack formation, leading to the significant increase in the critical thickness. As a result, we find that room-temperature photoluminescence from the crack-suppressed MQW is highly enhanced. This indicates that the suppression of crack formation by the patterning method is very promising toward SiGe/Ge MQW embedded light-emitting device applications.

Understanding Defects in Perovskite Solar Cells through Computation: Current Knowledge and Future Challenge.

Lead halide perovskites with superior optoelectrical properties are emerging as a class of excellent materials for applications in solar cells and light-emitting devices. However, perovskite films often exhibit abundant intrinsic defects, which can limit the efficiency of perovskite-based optoelectronic devices by acting as carrier recombination centers. Thus, an understanding of defect chemistry in lead halide perovskites assumes a prominent role in further advancing the exploitation of perovskites, which, to a large extent, is performed by relying on first-principles calculations. However, the complex defect structure, strong anharmonicity, and soft lattice of lead halide perovskites pose challenges to defect studies. In this perspective, on the basis of briefly reviewing the current knowledge concerning computational studies on defects, this work concentrates on addressing the unsolved problems and proposing possible research directions in future. This perspective particularly emphasizes the indispensability of developing advanced approaches for deeply understanding the nature of defects and conducting data-driven defect research for designing reasonable strategies to further improve the performance of perovskite applications. Finally, this work highlights that theoretical studies should pay more attention to establishing close and clear links with experimental investigations to provide useful insights to the scientific and industrial communities.

Instigating the Asymmetry of Dy3+ Ions Doped in Borate Glasses for Photonic Device w-LED Applications

For usage in solid state white light emitting device applications, dysprosium-activated calcium aluminum barium sodium borate glass was synthesized. The detailed understanding of physical, optical, structural, and photo-luminescence characteristics was examined and compared. To comprehend the oscillator strength of the ligands in the prepared glasses, the Judd-Ofelt intensity characteristics were assessed. The Ω2 greater relative oscillator strength value shows highest for the prepared glasses suggesting their cause due to hypersensitive transitions. In comparison to other glasses in the research, the potential radiative transition probabilities, branching ratios, and stimulated emission cross-section for 575 nm emission all exhibited higher values. The stimulated emission cross-section shows highest for 0.3 mol% Dy2O3 content in the present glasses. The asymmetry of synthesizedglass sample ratio has been evaluated and compared using Yellow to Blue (Y/B) emission ratio. Study of the emission spectra and assessment of CCT and DUV values for the glasses reveal emission in the CIE diagram's white light zone.

Thermally activated delayed fluorescence tetradentate ligand-containing gold(III) complexes with preferential molecular orientation and their application in organic light-emitting devices.

A new class of thermally activated delayed fluorescence (TADF) pyridine-/pyrazine-containing tetradentate C^C^N^N gold(III) complexes have been designed and synthesized. Displaying photoluminescence quantum yields (PLQYs) of up to 0.77 in solid-state thin films, these complexes showed at-least a six-fold increase in the radiative decay rate constant (kr) in toluene upon increasing temperature from 210 to 360 K. Using variable-temperature (VT) ultrafast transient absorption (TA) spectroscopy, the reverse intersystem crossing (RISC) processes were directly observed and the activation parameters were determined, in line with the results of the Boltzmann two-level model fittings, in which the energy separation values between the lowest-lying singlet excited state (S1) and the lowest-lying triplet excited state (T1), ΔE(S1-T1), of these complexes were estimated to be in the range of 0.16-0.18 eV. Through strategic modification of the position of the electron-donating -tBu substituent in the cyclometalating ligand, the permanent dipole moments (PDMs) of these tetradentate gold(III) emitters could be manipulated to enhance their horizontal alignment in the emitting layer of organic light-emitting devices (OLEDs). Consequently, the resulting vacuum-deposited OLEDs demonstrated a 30% increase in the theoretical out-coupling efficiency (ηout), as well as promising electroluminescence (EL) performance with maximum external quantum efficiencies (EQEs) of up to 15.7%.

Investigation of Photoluminescence and Optoelectronics Properties of Transition Metal-Doped ZnO Thin Films.

Thin films of zinc oxide (ZnO) doped with transition metals have recently gained significant attention due to their potential applications in a wide range of optoelectronic devices. This study focuses on ZnO thin films doped with the transition metals Co, Fe, and Zr, exploring various aspects of their structural, morphological, optical, electrical, and photoluminescence properties. The thin films were produced using RF and DC co-sputtering techniques. The X-ray diffraction (XRD) analysis revealed that all the doped ZnO thin films exhibited a stable wurtzite crystal structure, showcasing a higher structural stability compared to the undoped ZnO, while the atomic force microscopy (AFM) imaging highlighted a distinctive granular arrangement. Energy-dispersive X-ray spectroscopy was employed to confirm the presence of transition metals in the thin films, and Fourier-transform infrared spectroscopy (FTIR) was utilized to investigate the presence of chemical bonding. The optical characterizations indicated that doping induced changes in the optical properties of the thin films. Specifically, the doped ZnO thin film's bandgap experienced a significant reduction, decreasing from 3.34 to 3.30 eV. The photoluminescence (PL) analysis revealed distinguishable emission peaks within the optical spectrum, attributed to electronic transitions occurring between different bands or between a band and an impurity. Furthermore, the introduction of these transition metals resulted in decreased resistivity and increased conductivity, indicating their positive influence on the electrical conductivity of the thin films. This suggests potential applications in solar cells and light-emitting devices.

Light emission, structure-phase evolution, and photocatalytic behavior in full-series multilayered GaTe1−xSx (0 ≤ x ≤ 1) with direct-transition edge

The crystal structures and optical properties of full-series multilayered GaTe1−xSx (0 ≤ x ≤ 1) are examined. The results reveal that the monoclinic (M) phase dominates for 0 ≤ x ≤ 0.4, and the hexagonal (H) phase dominates for 0.425 ≤ x ≤ 1. The full-series multilayer GaTe1−xSx exhibited strong photoluminescence. The emission range of M-GaTe1−xSx (0 ≤ x ≤ 0.4) layers displays 1.65–1.77 eV (700–750 nm) and that of the H-GaTe1−xSx (0 ≤ x ≤ 1) layers is 1.588–2.5 eV (496–780 nm). Micro-time-resolved photoluminescence (μTRPL) revealed that the M-phase had a shorter PL recombination lifetime than H-phase because the surface effect. The multilayer GaTe1−xSx (0 ≤ x ≤ 1) exhibited superior light emission and absorption capabilities for application in light-emitting and photocatalytic devices. The GaTe0.5S0.5 nanosheet photocatalyst demonstrated the best photocatalytic performance because its abundant surface state and mixed phases to enhance the photo-degradation ability.

A multifunctional emitter with synergistical adjustment of rigidity and flexibility for high-performance data-recording and organic light-emitting devices with “hot exciton” channel

An intramolecular dual-locking design is proposed for organic luminescent materials, aiming at synergistically adjusting the molecular rigidity and flexibility for applications in data storage and light-emitting devices. According to this concept, a multifunctional donor–acceptor type emitter, LPCz-TRZ, is developed, featuring a “soft” diphenylmethane lock and a “hard” single-bond lock in its donor moiety. The highly locked structure results in appreciable rigidity that endows LPCz-TRZ with high luminescence efficiency, narrow emission, promoted charge conductivity and triplet harvesting “hot exciton” channels, allowing high-performance deep-blue organic light-emitting diodes (OLEDs) with an external quantum efficiency as high as 7.88%, which is among the best deep-blue “hot exciton” OLEDs. Notably, the structure of LPCz-TRZ is semi-flexible, leading to unique mechanochromic luminescence (MCL) behavior. Compared to the conventional MCL emitters, the orchestration of rigidity and flexibility in LPCz-TRZ affords high-contrast, fatigue-resistance MCL, as evidenced by a simple, rewritable data-recording demonstration with negligible fatigue after up to 15 wiring-erasing cycles.

Solution-processed CsPbBr3 perovskite LEDs using blended-polymer additives for nearly 100% surface coverage

The all-inorganic perovskite material (CsPbBr3) is a promising light-emitting material due to its narrow color spectrum, wet solution processability, and cost-effectiveness. Despite such advantages, pinholes, poor surface coverage, and stability issues limit widespread applications of perovskite light-emitting devices (PeLEDs) in solid-state lighting applications. The performance of PeLEDs depends strongly on the morphological characteristics of the perovskite layer, with low surface coverage and surface roughness observed to lead to higher current leakage and lower current efficiency. We find that perovskite thin films blended with polymers to form composite layers effectively enhance the thin film’s surface coverage and uniformity, improving performance. We report CsPbBr3 PeLEDs with dual polymer additives, with a 12.1% reduction in the turn-on voltage (Von), a 97.21% reduction in leakage current density, a 200%+ enhancement in maximum brightness, and a 700% increase in power efficiency compared to a control CsPbBr3 device. To study the likely source of these enhancements, we have conducted a comparative film analysis of test and control devices using field-emission scanning electron microscopy and atomic force microscopy. A reduced crystal grain size (∼204nm to ∼101nm) and a nearly 100% (99.79%) surface coverage (compared to 79.53% found for control devices) suggest that the improved overall morphology and surface coverage likely play a significant role in the improved performance. Further, a reduction in surface roughness (∼45%) and the formation of a nearly pinhole-free film are observed to increase yield by 20%.

Effect of substituting on the transition dipole moment of the double perovskite Cs2AgInCl6

The all-inorganic double perovskite Cs2AgInCl6 with three dimensional structure has attracted much attention due to its direct bandgap property and particular luminescence mechanism, which is self-trapped exciton emission. However, it is a pity that Cs2AgInCl6 exhibits low photoluminescence quantum yield, which affects its application for light-emitting devices. In this paper, the band structure and transition dipole moment of Cs2AgIn(1−x)Sb x Cl6 (x = 0, 0.25, 0.5, 0.75) are calculated using first principle calculation. The calculated results shows that the pure material Cs2AgInCl6 not only has a large band gap but also has the dipole forbidden transition, which means that the electrons cannot be excited from the valence band maximum to the conduction band minimum. However, the substituted Cs2AgIn0.75Sb0.25Cl6 have a good property for the band gap about 3.066 eV and break forbidden transition at point X. The reason for its change is due to the overlap of electron and hole for charge density. Our work provides theoretical guidance for the design of more efficient light-emitting devices.

Ink formulation of phosphorescent emitter with mixed host and its application in inkjet-printed organic light-emitting devices

Ink formulation of phosphorescent emitter with mixed host and its application in inkjet-printed organic light-emitting devices

Multicolor emission tuning of ZnS@SiO2-Eu3+ composite as potential application in light-emitting devices

Multicolor emission tuning of ZnS@SiO2-Eu3+ composite as potential application in light-emitting devices

Stability Optimization of 0D Cs3Cu2Cl5 Single Crystal with High Green Emission for Optoelectronics

Cs3Cu2Cl5 is unstable owing to ionic migration and lattice decomposition in the atmosphere. In addition, obtaining large bulk single crystals of Cs3Cu2Cl5 is challenging. Herein, a novel strategy is proposed for synthesizing a Cs3Cu2Cl5 single crystal that exhibits excellent crystallinity and photoluminescence (PL) properties using an antisolvent‐assisted method. Na+ is doped into the Cs3Cu2Cl5 lattice to replenish the lattice defects caused by chlorine vacancies, thus leading to stronger chemical interactions between Cu+ and Cl− ions. Moreover, Na+ doping circumvents ionic migration and lattice decomposition, thereby enhancing the PL intensity and maintaining the long‐term stability of Cs3Cu2Cl5 in the atmosphere. Incorporating 10% Na+ into the Cs3Cu2Cl5 lattice enhances the PL intensity by 18%, and the high‐stability PL can maintain more than 48.5% of the PL intensity after 90 d in an atmospheric environment. In addition, a white light‐emitting device (LED) is fabricated using the 10% Na+‐doped Cs3Cu2Cl5 crystal powder and it exhibits a high color‐rendering index (93.7) and correlated color temperature (7120 K). Additionally, it exhibits superior stability, even at a high temperature of 120 °C. Thus, the excellent high‐temperature stability of Cs3Cu2Cl5 can promote its practical application in LED.

Exceptional Thermochemical Stability of Graphene on N-Polar GaN for Remote Epitaxy.

In this study, we investigate the thermochemical stability of graphene on the GaN substrate for metal-organic chemical vapor deposition (MOCVD)-based remote epitaxy. Despite excellent physical properties of GaN, making it a compelling choice for high-performance electronic and light-emitting device applications, the challenge of thermochemical decomposition of graphene on a GaN substrate at high temperatures has obstructed the achievement of remote homoepitaxy via MOCVD. Our research uncovers an unexpected stability of graphene on N-polar GaN, thereby enabling the MOCVD-based remote homoepitaxy of N-polar GaN. Our comparative analysis of N- and Ga-polar GaN substrates reveals markedly different outcomes: while a graphene/N-polar GaN substrate produces releasable microcrystals (μCs), a graphene/Ga-polar GaN substrate yields nonreleasable thin films. We attribute this discrepancy to the polarity-dependent thermochemical stability of graphene on the GaN substrate and its subsequent reaction with hydrogen. Evidence obtained from Raman spectroscopy, electron microscopic analyses, and overlayer delamination points to a pronounced thermochemical stability of graphene on N-polar GaN during MOCVD-based remote homoepitaxy. Molecular dynamics simulations, corroborated by experimental data, further substantiate that the thermochemical stability of graphene is reliant on the polarity of GaN, due to different reactions with hydrogen at high temperatures. Based on the N-polar remote homoepitaxy of μCs, the practical application of our findings was demonstrated in fabrication of flexible light-emitting diodes composed of p-n junction μCs with InGaN heterostructures.

A rational strategy for directly synthesizing strongly yellow solid-state fluorescent-emitting carbon nanodots composite microparticles by structure regulation

Carbon nanodots (CDs) have received huge attention of researchers due to their good optical properties. However, CDs generally suffer from severely fluorescence self-quenching once they are aggregated or in solid state, limitating their applications in light-emitting devices. In this work, we report a rational strategy for synthesis of yellow fluorescent carbon nanodots (Y-CDs)-based microparticles with a high solid-state photoluminescence quantum yield (32.02%). It is the first report on designing a lamellar structured matrix to disperse CDs to realize long-wavelength solid fluorescence. The matrix is confirmed as p-phenylenediamine dihydrochloride by X-ray diffraction (XRD). 3-glycidyloxypropyltrimethoxysilane (KH-560) acts as a bridge to connect CDs to the matrix based on epoxy-amine reaction and silane hydrolysis condensation for uniform dispersion of CDs and high solid-state luminescence can be easily achieved. Meanwhile, through adjusting the amount of KH-560, the morphology of Y-CDs-based microparticles can be controlled from cube to layered structure and the fluorescence intensity can be significantly improved. Importantly, the optimal Y-CDs particles can be combined with blue chips (450 nm) to fabricate high-performance white light-emitting diodes (WLEDs) without using commercial phosphor, and the constructed WLEDs exhibit a high color rendering index (CRI) of 84.2.