Material For Diodes Research Articles

Evolution of Organic Light Emitting Diode (OLED) Materials and their Impact on Display Technology.

Organic light-emitting diodes (OLEDs) have revolutionized display and lighting technologies, offering unparalleled design, device flexibility, vibrant colors, and energy efficiency. In this comprehensive review we elucidate the evolution of OLED technology, summarizing its progression from the fundamental principles of fluorescence (1st generation) and phosphorescence (2nd generation) to the emergence of thermally activated delayed fluorescence (TADF) (3rd generation), hyper fluorescence (4th generation), and exceptional future generation OLEDs. This review highlights the development and challenges of early-generation OLEDs, scrutinizing their mechanisms, emitters, and limitations. As TADF OLEDs mark a significant paradigm shift, we explore their enhanced efficiency and potential for cost-effective production without the involvement of toxic heavy metals. Building upon this foundation this review explores the burgeoning concepts of hyper-fluorescence and 5th-generation OLEDs, poised to push the boundaries of color purity, efficiency, and operational stability. This consolidated comprehensive exploration described herein may provide enormous information for designing future-generation OLED materials for sustainable development.

Damage mechanisms caused by radiation proton (ion beam) in double interface layer nano-MOS structure

In this study, the effects of ion beam (proton) on the PbO/SnO2/p-Si double interfacial layer MOS Schottky diode material were studied. The parameters of the ionizing radiation detection properties and radiation resistance of using double interfacial oxide layers were analyzed in MOS Schottky diodes. In the analysis, SRIM/TRIM software code was examined theoretically and modeled using simulation. The displacement per atom occurs more in the SnO2 oxide layer than in the other interface layer. This can be explained by the concept of Bragg Curve Peak, which occurs as a result of ion beam induced doping effect. It has been observed that the electrical properties of the PbO/SnO2/p-Si double interface layer MOS Schottky diode structure in terms of sensing ionizing radiation change after ion beam induced doping and the interface states are affected. It has been shown that our double interface layer nano-MOS structure can be used as a ion beam based sensor on these results. In addition to the inelastic collision, without causing ionization NIEL values of PbO and SnO2 layers were found to be 424.88 MeV. cm2/g and 524.9 MeV. cm2/g, respectively. These theoretical results were shown as graphs using the TRIM Monte Carlo simulation program and the behavior of the phonons in the layers was modeled. Additionally, LET values were calculated according to layers and compared with the simulation results of TRIM. While the LET value of the PbO layer was 889.3 MeV. cm2/g, the LET value of the SnO2 layer was determined to be 1639 MeV cm2/g. The LET concept is visually presented with the TRIM software and it is seen that the displacement per atom is highest in the SnO2 layer and the Bragg Curve reaches its maximum point. Thus, it can be seen that the SnO2 layer produces more transient damage and oxide interface traps compared to the PbO layer as ionizing radiation propagates between the oxide layers. By studying the effects of the ion beam source on the MOS Schottky diode structure, it is shown that the double interface layer structure increases the oxide interface traps and the SnO2 material is promising in terms of radiation sensing and detection properties. Moreover, MOS Schottky states that using a double interface layer instead of a single oxide layer in MOS structures positively increases the number of interface traps in the oxide layer for ion beam radiation detection.

Benchmark computations of nearly degenerate singlet and triplet states of N-heterocyclic chromophores. I. Wavefunction-based methods.

In this paper, we investigate the role of electron correlation in predicting the S1-S0 and T1-S0 excitation energies and, hence, the singlet-triplet gap (ΔEST) in a set of cyclazines, which act as templates for potential candidates for fifth generation organic light emitting diode materials. This issue has recently garnered much interest with the focus being on the inversion of the ΔEST, although experiments have indicated near degenerate levels with both positive and negative being within the experimental error bar [J. Am. Chem. Soc. 102, 6068 (1980), J. Am. Chem. Soc. 108, 17(1986)]. We have carried out a systematic and exhaustive study of various excited state electronic structure methodologies and identified the strengths and shortcomings of the various approaches and approximations in view of this challenging case. We have found that near degeneracy can be achieved either with a proper balance of static and dynamic correlation in multireference theories or with state-specific orbital corrections, including its coupling with correlation. The role of spin contamination is also discussed. Eventually, this paper seeks to produce benchmark numbers for establishing cost-effective theories, which can then be used for screening derivatives of these templates with desirable optical and structural properties. Additionally, we would like to point out that the use of domain-based local pair natural orbital-similarity transformed EOM-coupled cluster singles and doubles as the benchmark for ΔEST [as used in J. Phys. Chem. A 126(8), 1378 (2022), Chem. Phys. Lett. 779, 138827 (2021)] is not a suitable benchmark for these classes of molecules.

Influence of carbon dots as modifier and SiO2 shell coating as a protecting layer in YAlO3:Cr3+ phosphors for multimodal applications

This study focuses on the synthesis of SiO2-coated carbon dots (CDs) grafted onto YAlO3:Cr3+ (YAP:Cr3+) nanophosphors (NPs) through a combustion method. The CDs enhance the absorption cross-section of Cr3+ ions, significantly boosting the luminescence of YAP:Cr3+ by 19.29-fold. Further improvement is achieved with a SiO2 coating, leading to a 48.73-fold increase in photoluminescence intensity. The NCs are colour tunable, with emissions ranging from pinkish-red to blue, depending on the concentration of CDs and the excitation wavelength. These properties make them suitable for diverse applications, such as ratio metric fluorescence sensors for detecting Fe3+ ions within the 0–350 µM range, with high sensitivity (0.2 µM) and a low detection limit (4.93 μM). Additionally, they serve as material for white light-emitting diodes (W-LEDs), achieving CIE coordinates of (0.31, 0.30) and a rendering index of 94. The NCs also function as an optical thermometer with a sensitivity of 0.31 % K−1 at 320 K, making them ideal for temperature sensing applications. Moreover, their stability and dual-emissive nature make them highly effective in latent fingerprints (LFPs) detection, enabling high-resolution, level III fingerprint analysis. The dual emission properties of CDs and Cr3+ ions position these NCs as multifunctional materials, suitable for optical sensing, lighting, and security applications.

Enhanced luminescence of CaO:Eu2+ red phosphor in glass for high-power warm LED

Highly emissive and stable red phosphors are vital for the warm Light Emitting Diode (LED). Herein, blue-light-excited CaO:Eu2+ red phosphors were prepared using the carbonation method, coupled with the double crucible carbon reduction technology. The addition of GeO2 and SnO2 significantly enhanced the photoluminescence (PL) intensity and quantum efficiency. Furthermore, a phosphor-in-glass (PiG) made from an improved luminescent CaO:Eu2+ was developed and utilized for LED applications. Such PiG samples considerably improved the stability of CaO:Eu2+ phosphors. The excellent stability, high color rendering index (Ra) value of 87.7 and low correlated color temperature (CCT) of 4469 K confirmed the resulting CaO:Eu2+-based PiG as a promising material for white light-emitting diodes (WLEDs).

Machine Learning-Driven Precise Design of Stable OLED Materials: Predicting and Enhancing Multi-State C-N Bond Dissociation Energies

The intrinsic stability of organic light-emitting diode (OLED) materials critically hinges on the bond dissociation energies (BDEs) of fragile bonds, particularly C-N bonds. Despite the necessity of considering BDEs in multiple electronic states due to the complex working conditions of organic materials in OLED devices, comprehensive exploration remains challenging. Herein, we constructed a high-quality dataset, CNBDE-24, comprising nearly 1500 data points for BDEs across multiple electronic states, obtained through an active learning-guided density functional theory (DFT) calculation strategy. Machine learning models trained on the CNBDE-24 dataset exhibit excellent accuracy in predicting BDEs for OLED materials in neutral, triplet excited (T1), and anionic states, achieving an adjusted coefficient of determination exceeding 0.90 on the test set and bypassing the need for high-cost calculation. Moreover, utilizing neutral state BDEs as pre-training data significantly reduces model error and provides deeper insights into the relationships between different BDEs. We find that BDEs in neutral are influenced by the electronic properties of the nitrogen atom, as indicated by descriptors such as Gasteiger charges. Incorporating C-N bonds into aromatic systems and slightly dispersing N atom charges can inherently increase multi-state BDEs without altering luminescent properties. Additionally, anionic BDEs are determined by the extent of charge transfer during bond cleavage and can be regulated by modifying the C-side fragment. High-throughput virtual screening reveals a new stable purple emitter with a dominant 0–0 transition at 360 nm, which was validated through DFT and excited-state property evaluations. Strategies for enhancing BDEs in multiple resonance thermally activated delayed fluorescence materials without altering excited-state properties are also demonstrated.

Dimesitylborane as Electron Accepting Unit in High Performance Yellow Single-Layer Phosphorescent Organic Light Emitting Diode.

A new host material for Single-Layer Phosphorescent Organic Light-Emitting Diodes (SL-PhOLED) is reported, namely SPA-2-FDMB, using the dimesitylborane (DMB) fragment as an acceptor unit. The molecular design is constructed on the general donor-spiro-acceptor architecture, which consists of connecting, via a spiro bridge, a donor and an acceptor units in order to avoid strong interaction between them. The DMB fragment is known for many electronic applications (notably Aggregation-Induced Emission) but has not been used yet for SL-PhOLED applications. This appears particularly interesting, as the development of this simplified technology has shown that only a few electron-accepting fragments such as diphenylphosphine oxide can provide high-performance devices. Herein, the yellow-emitting SL-PhOLED using SPA-2-FDMB as host presents an External Quantum Efficiency of 8.1% (Current Efficiency of 24.9cd.A-1) with a low threshold voltage of 2.6V. As SPA-2-FDMB presents a sharp HOMO/LUMO difference, the good matching of HOMO and LUMO energy levels with the Fermi level of the electrodes is responsible for these performances. The low LUMO level of -2.61eV also appears particularly important. These performances are, to date, the highest reported for a yellow/orange-emitting SL-PhOLED and show the potential of DMB unit in the single-layer technology.

Interfacial Dipole Engineering for Energy Level Alignment in NiOx-Based Quantum Dot Light-Emitting Diodes.

The solution-derived non-stoichiometric nickel oxide (NiOx) is a promising hole-injecting material for stable quantum dot light-emitting diodes (QLEDs). However, the carrier imbalance due to the misalignment of energy levels between the NiOx and polymeric hole-transporting layers (HTLs) curtails the device efficiency. In this study, the modification of the NiOx surface is investigated using either 3-cyanobenzoic acid (3-CN-BA) or 4-cyanobenzoic acid (4-CN-BA) in the QLED fabrication. Morphological and electrical analyses revealed that both 4-CN-BA and 3-CN-BA can enhance the work function of NiOx, reduce the oxygen vacancies on the NiOx surface, and facilitate a uniform morphology for subsequent HTL layers. Moreover, it is found that the binding configurations of dipole molecules as a function of the substitution position of the tail group significantly impact the work function of underlying layers. When integrated in QLEDs, the modification layers resulted in a significant improvement in the electroluminescent efficiency due to the enhancement of energy level alignment and charge balance within the devices. Specifically, QLEDs incorporating 4-CN-BA achieved a champion external quantum efficiency (EQE) of 20.34%, which is a 1.8X improvement in comparison with that of the devices utilizing unmodified NiOx (7.28%). Moreover, QLEDs with 4-CN-BA and 3-CN-BA modifications exhibited prolonged operational lifetimes, indicating potential for practical applications.

Near Room Temperature Solvothermal Growth of Ferroelectric CsPbBr3 Nanoplatelets with Ultralow Dark Current.

CsPbBr3 exhibits outstanding optoelectronic properties and thermal stability, making it a coveted material for detectors, light-emitting diodes, and solar cells. Despite observations of ferroelectricity in CsPbBr3 quantum dots, synthesizing bulk ferroelectric CsPbBr3 crystals has remained elusive, hindering its potential in next-generation optoelectronic devices like optical switches and ferroelectric photovoltaics. Here, a breakthrough is reported: a novel solvothermal technique enabling the growth of ferroelectric CsPbBr3 nanoplatelets with lateral dimensions in the tens of micrometers. This represents a significant step toward achieving large-area ferroelectric CsPbBr3 crystals. Unlike traditional methods, this approach allows for growth and crystallization of CsPbBr3 in alcohol solutions by enhancing precursor solubility. This study confirms the ferroelectric nature of these nanoplatelets using second harmonic generation, electrical characterizations, and piezoresponse force microscopy. This work paves the way for utilizing ferroelectric CsPbBr3 in novel optoelectronic devices, significantly expanding the potential of this material and opening doors for further exploration in this exciting field.

Suppressing Formation of Buried Defects during Annealing Enables Bright Perovskite Light-Emitting Diodes.

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a promising hole-transporting material for perovskite light-emitting diodes (PeLEDs). However, intrinsic luminance quenching at the PEDOT:PSS/perovskite interface causes deterioration of performance. Here, we develop a facile and effective strategy to passivate the interface defects via the modification of PEDOT:PSS by l-norvaline. As a pre-buried additive, l-norvaline not only reacts with PEDOT:PSS, but also forms the coordination and hydrogen bond with perovskite. We demonstrated that the generation of buried defects at the PEDOT:PSS/perovskite interface originates from the crystallization process of the perovskite film during annealing by in-situ photoluminescence measurements. The surface of l-norvaline-modified PEDOT:PSS can passivate the interfacial defects and inhibit exciton quenching. As a result, the PeLED shows a good device performance with a luminance of 80089 cd m-2 at 509 nm and an external quantum efficiency of 13.04%.

(Invited) Precise Determination of Exciton Binding Energy of Organic Semiconductors

Strongly bound excitons in organic semiconductors are crucial for the operation of organic optoelectronic devices. However, accurate experimental data on the exciton binding energy of organic semiconductors are lacking. In this study, we determine the exciton binding energy as the difference between the optical and transport bandgaps with a precision of 0.1 eV. From the systematic study of the exciton binding energy of 42 organic semiconductors (15 non-fullerene acceptors, 4 fullerene acceptors, 13 low-bandgap polymers, 7 organic light-emitting diode materials, and 3 crystalline materials), we found that the exciton binding energy is a quarter of the transport gap regardless of the material. We interpret this unexpected relationship in terms of a hydrogen atom model.

Effect of the Saccharin Concentration on Electrodeposition of the Fe-Ni Alloy

The FMM (Fine Metal Mask) used in the OLED display manufacturing process is a metal sheet with holes formed to allow the deposition of diode material only in the sub-pixel area. To prevent deformation and misalignment of the FMM (Fine Metal Mask) caused by heat during the RGB organic deposition process, an Invar plate with a thermal expansion coefficient (CTE) close to 0 is used. The Invar sheet applied to the current FMM is manufactured through a metallurgical process, and its final thickness after rolling is 20 micron. However, due to limitations in reducing thickness with the rolling process, for manufacturing FMM with a thickness of under 10 micron for next-generation high-resolution (UHD-level) displays, the bottom-up electroplating process is suitable. However, to maintain the shape of the electroplated Invar sheet while ensuring commercial-grade low CTE, heat treatment at temperatures exceeding 600℃ for an extended period is required, utilizing thermo-mechanical processing methods. If uniformity in the microstructure composed of nano-grains is ensured in the electroplated Invar alloy in the As-deposited, it is possible to increase the efficiency of the process by reducing the heat-treatment processing cost.Therefore, in this study, we investigated the microstructural evolution in the Invar alloy by controlling the surface stress of the electroplated layer during pre-plating. We controlled the key additive, saccharin, in the Fe-Ni alloy electrolyte to assist the diffusion of iron and nickel ions. By examining the relation between microstructural uniformity, determined by the plated layer, and CTE, we propose optimized process conditions for the pre-plated Invar sheet.

Manufacture of the Invar Film Using a Continuous Electrodeposition Technique for the OLED FMM

In the manufacturing processes of red-green-blue (RGB)-type organic light emitting diode (OLED) displays, Invar is used as a material for the fine metal mask (FMM), which guides the evaporated diode materials through its small holes onto the correct positions of the substrate glass. The electroforming of Invar is an immediate hot issue in the RGB-type OLED display industries. Contrary to the conventional top-down method of pyrometallurgically producing Invar, a bottom-up approach of electroforming is a promising technology for producing very thin FMMs to achieve high-quality images in such displays. The present authors have recently presented that the electroformed Invar via sophisticated heat treatment exhibits the coefficient of thermal expansion (CTE) as low as that of the conventional Invar. The current work has been aimed at investigating the effect of the microstructure evolution on the CTE during heat treatment of the electroformed Invar. Finally, we propose optimal process conditions to manufacture the Invar FMM applied for an ultra high definition (UHD) grade of the OLED display.

The experimental and DFT approaches on electronic, thermal and conductivity properties of non-linear optical bearing fused aromatic chalcones towards prospective OLEDs

New derivatives of push-pull chalcone was successfully synthesized to demonstrate as NLO active on the impact of organic light emitting diode (OLED) materials. A total of three fused-aromatic chalcones (AA, AB, AC) with different substituents have been characterized through TGA, Z-scan analysis, 1H & 13C NMR, IR and UV–Vis. All the targeted compounds are nonlinear refraction (NLR) active with the range of χ(3) (∼ × 10–6 esu). AC reveals the highest value of first order hyperpolarizability (βtot) at 528.08 × 10–30 esu upon the substitution of strong electron acceptor. Theoretical investigation was performed by employing the theory of B3LYP/6–31 G (d,p) level via density functional theory (DFT) to optimize the geometries, molecular electrostatic potential (MEP) and frontier molecular orbitals (FMO). The predicted electronic properties of the molecule are supported by the experimental results, confirming the theoretical conclusions. The examination of its potential as emissive layer in OLED application was constructed on ITO substrate for electroluminescence behaviour evaluation under various direct current (DC) voltages supply. The preliminary outcomes reveal that these simple chalcone derivatives are capable of being utilised in any optoelectronic application.

Spatially Resolved Functional Group Analysis of OLED Materials Using EELS and ToF-SIMS.

Electron energy-loss spectroscopy (EELS) is widely used in analyzing the electronic structure of inorganic materials at high spatial resolution. In this study, we use a monochromator to improve the energy resolution, allowing us to analyze the electronic structure of organic light-emitting diode (OLED) materials with greater precision. This study demonstrates the use of the energy-loss near-edge structure to map the nitrogen content of organic molecules and identify the distinct bonding characteristics of aromatic carbon and pyridinic nitrogen. Furthermore, we integrate EELS with time-of-flight secondary ion mass spectrometry for molecular mapping of three different bilayers composed of OLED materials. This approach allows us to successfully map functional groups in the by-layer OLED and measure the thickness of two OLED layers. This study introduces spatially resolved functional group analysis using electron beam spectroscopy and contributes to the development of methods for complete nanoscale analysis of organic multilayer architectures.

Research on structure and optical properties of Tm3+-Tb3+ doped borate glass

In this paper, a series of B2O3–Al2O3–ZnO–BaO–Tm2O3–Tb2O3 glasses were synthesized by high temperature melting method. Under appropriate ultraviolet excitation, Tm3+ ions produce 1D2→3F4 energy level transition and emit blue light. The concentration quenching point is 0.75 % mol, and the color saturation is high. Tb3+ ions produce 5D4→7F5 energy level transition and emit green light, and the concentration quenching point of Tb3+ ions is 0.75 % mol. By characterizing the fluorescence lifetime and luminescence intensity of B2O3–Al2O3–ZnO–BaO–Tm2O3–Tb2O3 glass, the existence of Tm3+→Tb3+ energy transfer in the glass was verified, and the energy transfer efficiency and energy transfer mechanism were studied in detail. It is found that B2O3–Al2O3–ZnO–BaO–Tm2O3–Tb2O3 glass is an ideal material for light-emitting diodes, light-emitting materials and fluorescent display devices.

Uncovering the Aggregation-Induced Emission Mechanisms of Phenoxazine and Phenothiazine Groups.

Molecules with both aggregation-induced emission (AIE) and thermally activated delayed fluorescence (TADF) properties are potential organic light-emitting diode materials; however, the AIE and TADF mechanisms are still debatable. In this work, four molecules incorporating carbazole (Cz), phenoxazine (PXZ), and phenothiazine (PTZ) as donor groups to the diphenylsulfone acceptor were investigated. The experiment results indicate that a molecule containing Cz exhibits solely TADF properties, whereas molecules containing PXZ and PTZ demonstrate both TADF and AIE characteristics. As for DPS-PTZ, the result indicates that the thin-film environment restricts molecular twisting, consequently reducing nonradiative decay, thereby attributing to the AIE property by density functional theory and molecular dynamics simulation. As for DPS-PXZ, the result suggests that the restricted access to a conical intersection in a singlet excited via an expansion in the C-S-C angle is the pivotal factor for the AIE characteristic. The C-S-C angle twist of DPS-PXZ is impeded in the aggregate state and resulted in luminescence. Understanding the mechanisms serves as a valuable guide for the development of new AIE systems, enabling their application in various practical domains.

Synthesis and Electron Transporting Properties of Diblock Copolymers Consisting of Polyfluorene and Polystyrene.

Poly(9,9-di-n-octylfluorene) (PFO) is a promising material for polymer light-emitting diodes (PLEDs) due to its advantageous properties. To enhance its electron transporting capabilities, diblock polymers were synthesized by attaching polystyrene (PSt) chains of varying lengths to one end of the PFO molecule. In a comparative study with PFO homopolymer, the diblock polymers maintained similar thermal properties, absorption spectra, and photoluminescent stability, while exhibiting slightly deeper lowest unoccupied molecular orbital (LUMO) levels and higher crystallinity. Notably, diblock polymers with shorter polystyrene blocks demonstrated higher electron mobility than the PFO homopolymer and diblock polymers with excessively long polystyrene blocks. These findings suggest that the optimal chain length of the polystyrene block is crucial for maximizing electron mobility, thus offering valuable insights for designing high-performance PLED materials.

P‐205: Exploring Potential of Language Models in OLED Materials Discovery

Language Models (LMs) have recently achieved remarkable success in natural language processing and other Artificial Intelligence (AI) applications. In this work, we adopt a language‐like representation of organic molecules and utilize LMs to address two typical tasks in the discovery of Organic Light‐Emitting Diode (OLED) materials: property prediction and structure generation. In the prediction task, the LM serves as a surrogate model of the quantum chemistry simulator for electronic properties prediction. In the generation task, the LM acts as a conditional generator for generating novel molecules with desired properties. This work demonstrates the great potential of LMs in unifying multiple tasks in OLED materials discovery within a simple but efficient framework.

Precise Regulation on the Bond Dissociation Energy of Exocyclic C-N Bonds in Various N-Heterocycle Electron Donors via Machine Learning.

Heterocycles with saturated N atoms (HetSNs) are widely used electron donors in organic light-emitting diode (OLED) materials. Their relatively low bond dissociation energy (BDE) of exocyclic C-N bonds has been closely related to material intrinsic stability and even device lifetime. Thus, it is imperative to realize fast prediction and precise regulation of those C-N BDEs, which demands a deep understanding of the relationship between the molecular structure and BDE. Herein, via machine learning (ML), we rapidly and accurately predicted C-N BDEs in various HetSNs and found that five-membered HetSNs (5-HetSNs) have much higher BDEs than almost all 6-HetSNs, except emerging boron-N blocks. Thorough analysis disclosed that high aromaticity is the foremost factor accounting for the high BDE of 5-HetSNs, and introducing intramolecular hydrogen-bond or electron-withdrawing moieties could also increase BDE. Importantly, the ML models performed well in various realistic OLED materials, showing great potential in characterizing material intrinsic stability for high-throughput virtual-screening and material design efforts.