OLED Devices Research Articles

Efficient Greenish-Blue Thermally Activated Delayed Fluorescence Zn Complex for Organic Light Emitting Devices

A greenish-blue zinc complex Zn(PhOBz)-PXZ with enhanced thermally activated delayed fluorescence (TADF) properties has been prepared from Zn(OAc)2 and 4PXZ2OHBz, a 2-(1H-benzimidazol-2-yl)phenol-based TADF ligand. The TADF phenomenon has been confirmed by time-resolved photoluminescence (TrPL) studies. The DFT calculations show spatially well-separated HOMO and LUMO in their ground states, along with a small energy splitting between the excited singlet (S1) and triplet (T1) states, in a good agreement with the TADF mechanism. Due to the high thermal stability of Zn(PhOBz)-PXZ, OLED devices can be fabricated by vacuum vapor deposition, and greenish-blue OLEDs with the maximum emission at 521 nm were successfully demonstrated. The maximum external quantum efficiency (EQEmax) of 10.6%, with Commission Internationale de l’Eclairage (CIE) coordinates of (0.28, 0.47) were recorded. Zinc TADF complexes have the advantages of cost-effectiveness, greater abundance of natural resources, environmentally friendly metals, making them potential replacements for future precious metal emitters.

Substituent groups effects on AIEgens of fluorenone derivatives: Optical properties, bioimaging, and LED devices

Understanding structure-property relationships is crucial for developing materials with a high fluorescence quantum yield (ΦF) and optimizing their performance. In this study, three fluorenone-carbazole-based molecules (FO-Cz1, FO-Cz2, and FO-Cz3) were synthesized, which have similar structures but varying substituent groups (carbazole, 3,6-di‑tert‑butyl‑9H-carbazole, and 3,6-diphenyl-9H-carbazole). The different substituent groups significantly changed the optical properties of the luminogens. The experimental results confirmed that FO-Cz1, FO-Cz2, and FO-Cz3 were AIEgens, and the introduction of a phenyl group gave FO-Cz3 strong αAIE(I/I0) and greater solid fluorescence quantum yields than FO-Cz1 and FO-Cz2. Analysis of photophysical properties, theoretical calculations, and X-ray crystallography revealed that the emission properties of FO-Cz1, FO-Cz2, and FO-Cz3 were influenced by the use of flexible substituent groups. The substituent groups avoided π-π stacking, reduced non-radiative transitions, and enhanced fluorescence in the aggregated state. Substituent groups on the benzene ring gave FO-Cz3 a tightly-packed structure and strong emission. It was used for cancer cell imaging and LED devices, in which FO-Cz3 exhibited high photostability and biocompatibility, making it a superior photosensitizer for bioimaging and applications in OLED devices. This research sheds light on the AIE behaviors of fluorenone complexes and offers valuable insights for the development of organic luminescent materials.

Nature-Inspired Synthesis of Yeast Capsule Replicas Encased with Silica-Vinyl Functionality: New Fluorescent Hollow Hybrid Microstructures.

Yeast capsules (YCs) produced from Saccharomyces cerevisiae with encapsulated fluorescent phenosafranin and azure dyes were used as catalytic template guides for developing hybrid functional organic/inorganic hollow microstructures with silica (SiO2) deposited on their surface generated in the imidazole-buffered system without the addition of any cationic surfactant. YCs-doped with SiO2 act as fluorescence emitters maintaining dye-loaded materials by sealing the microporous surface of YCs. We used vinyltrimethoxysilane as a precursor of SiO2 endowed with functional vinyl groups facilitating their further modification without disturbing the polysaccharide wall integrity. Consequently, the hybrid fluorescent polysaccharide/silica microcapsules (YC@dye@SiO2) are promising for wide-ranging optoelectronic applications in electrochromic and OLED devices with biocompatibility and biodegradability properties.

SOGCN: Prediction of key properties of MR-TADF materials using graph convolutional neural networks

The exploration of the structure and properties of the luminescent materials in OLED devices using Multiple Resonance Thermally Activated Delayed Fluorescence (MR-TADF) is constrained by challenges related to long cycles and high experimental costs, making it a key obstacle in the development of new materials. In response to this challenge, we propose an innovative approach by constructing a graph convolutional neural network model named SOGCN to quickly determine whether an unsynthesized material has the potential to become an MR material, and accurately predict its energy gap and half-peak width, thereby expediting the development process of MR-TADF materials. We constructed the MR220 dataset for training the model based on 220 MR-TADF molecules reported in experiments. To ensure the reliability of the SOGCN model in predicting new samples, we have established a rigorous set of theoretical calculation evaluation standards, providing crucial references for the model. In the prediction of the properties of 37 new samples of MR-TADF molecules, SOGCN successfully predicted the singlet–triplet energy gap (ΔEST) of some samples, demonstrating a good trend in FWHM prediction as well. Finally, we have synthesized our designed molecule, Design3 (DtCzB-Boz), the organic light-emitting diodes based on DtCzB-Boz exhibit an emission peak at 508 nm, with the FWHM is 27 nm. The result of photophysical characterization is highly consistent with the predicted value of SOGCN. Notably, the mean absolute errors (MAE) between our model predictions and experimental/computational values were as low as 0.037 eV and 10 nm, respectively. This indicates that SOGCN exhibits higher efficiency and accuracy in predicting the properties of MR-TADF materials.

Synthesis, enantiomeric separation and (chir)optical properties of [7]helicene derivatives for OLED applications. A comprehensive experimental and computational investigation

A two–step photochemical process was employed to synthesize new racemic [7]helicenes with appropriate functional groups, resulting in an overall yield of 61 % to 74 %. These helical species showed good solubility in common solvents and confirmed structurally through various spectroscopic methods. In solution, they exhibited strong absorption (λabs = 250–500 nm) and blue light emission with a fluorescence quantum yield (Φ) ranging from 7 % to 26 %. Experimental analysis of their HOMO and LUMO energy levels highlighted an irreversible electrochemical behavior and a band gap (Eg–el) of 2.60 eV to 2.64 eV. The helicenes were successfully separated by chiral HPLC, yielding P and M–enantiomers in high optical purity (>98.5 % up to >99.5 % ee) that demonstrated substantial optical rotations (e.g., +3700–5000 for the P–enantiomer at λ = 589 nm) and notable electronic circular dichroism (ECD) signals. Density functional theory (DFT) was undertaken to establish connections between diverse structure-properties relationships and precisely replicate the experimental findings. Ultimately, these helical species, with notable performance in emission, electrochemical behavior, and thermal stability, can effectively serve as blue-emitting chiral dopants in OLED devices and as hole-transport units.

New Strategies to Improve the Efficiency of Curcumin‐Based Iridium Complexes for OLED Devices

AbstractAmong the solid‐state lighting technologies, OLEDs occupy a prominent position for the high efficiencies associated with the low CO2 emissions. In line with the recent studies aimed at designing sustainable and biodegradable devices, herein we report on the synthesis of a series of iridium(III) complexes featuring, as β‐diketone ligands, curcumin and 6‐dehydrogingerdione, two natural compounds found in the rhizome of Curcuma longa and Zingiber officinale. To improve the solubility of both the ligands and prevent the aggregation of the complexes, oleoyl residues were inserted on the phenolic −OH groups. The resulting complexes exhibited a green emission with quantum yields as high as 2.8 % (relative to fluorescein). OLED devices were fabricated by using, as emitting layer, a host‐guest blend of the iridium complex in 4,4’‐bis(N‐carbazolyl)‐1,1’‐biphenyl (CBP). The morphological analysis revealed that thin films of the emitting layer were homogeneous. The devices fabricated with iridium complexes from 6‐dehydrogingerdione exhibited higher luminance, efficiency and power efficiency with respect to the corresponding devices obtained from curcumin; also the functionalization of the β‐diketone unit with the oleoyl residue proved to increase significantly the performance of the device. Overall, these data suggest that aggregation is a key factor that compromise the performances of the corresponding OLEDs.

Highly Efficient Blue Host Compound Based on an Anthracene Moiety for OLEDs

We designed and successfully synthesized a novel anthracene-based host material, 10-(4-(naphthalen-1-yl)phenyl)-9-(naphthalen-3-yl)anthracene (2-NaAn-1-PNa). The 2-NaAn-1-PNa exhibited a PL max at 440 nm in film state and demonstrated a wide band gap of 2.95 eV, indicating its suitability as a blue host material. In an OLED device using 2-NaAn-1-PNa as the host and 3Me-1Bu-TPPDA as the dopant, real blue emission was achieved with an electroluminescence maximum (ELmax) at 460 nm and Commission Internationale de L’Eclairage coordinates of (0.133, 0.141). The device exhibited excellent EL characteristics, with an external quantum efficiency of 8.3% and a current efficiency of 9.3 cd/A at 10 mA/cm2. Furthermore, the efficiency roll-off was limited to only 1.9% up to 4000 nits, demonstrating exceptional performance.

Exploring the Feasibility of Eu(TTA)3TPPO as Pigment for Fluorescent Paint

We outline the synthesis of rare earth hybrid organic β-diketonate Eu(TTA)3TPPO complex [Eu: Europium, TTA: Thenoyl Trifluoro Acetone, TPPO: Triphenylphosphine oxide] pigment to formulate luminous paints. Epoxy and urea formaldehyde resins were synthesized by catalytic homo polymerization and solution polymerization technique, respectively. The fluorescent pigment was synthesized at ambient temperature by solution technique, maintaining the stoichiometric ratio at pH 7. Nextly, fluorescent paint was developed on glass substrate with epoxy (E) and urea formaldehyde (UF) resins and toluene as solvent with thickness 0.1 mm, respectively. Photoluminescence (PL) spectra and photometric assessment of the complex were carried out to probe its photophysical parameters. The excitation spectra of the synthesized complex depicts a wide-ranging excitation peak at 466 nm with a wide shoulder at 538 nm, while emission spectra discloses an intense peak, recorded at 617 nm which portrays colour in the reddish-orange region of the visible spectrum. The paint compositions were checked for tack-free, hard dry, adhesion, water, salt, alkali and acid spray test to study their resistance against distinct surroundings. The painted panels also portrayed reddish orange emission at a unique wavelength of 617 nm. Amid all the paint compositions, the intensity of the painted panel with urea formaldehyde as a binder was found to be maximum, followed by the painted panel with epoxy as the binder. Photometric evaluation revealed reddish-orange emission from pure pigment as well as painted panels, which portrayed in the visible spectrum. This proposes a way to develop fluorescent paints that find applications in several areas such as flexible displays, glow-in-dark road paints, OLED devices, automotive rare lighting, fluorescent sensors, aircraft cabin and floor lighting, architectural and interior decorations and many more.

64‐5: Virtual ESD Failure Detection Methodology for Oxide TFT Based OLED Panels

As the screen size and pixel resolution increase, electrostatic discharging (ESD) problems have become the most detrimental issue for the next‐level OLED devices such as IT‐OLED, and QD‐OLED. Electrostatic discharging (ESD) is a well‐known phenomenon in the semiconductor and display industry. For its catastrophic failure, lots of effort has been made over the last three decades to predict ESD failures systematically in display panels, but proper methodologies for ESD hotspot prediction have not developed due to its complicated physical behaviors. Especially for the oxide TFT‐based OLED devices, the Bottom Metal Layer (BML) is introduced to shield the electric field from the external light‐induced charging and enhance the output characteristics of oxide TFT. However, this large area of the BML layer can cause serious electrostatic charging (ESD) issues during the fabrication process. In this work, we analyzed five different types of temporal charging injection mechanisms and three types of failure phenomena. To simulate the multi‐scale time‐dependent full panel ESD models, we developed simplified OLED panel design verification models by using advanced numerical techniques such as perfect boundary approximation and thin sheet metal approximation. Based on the newly developed simulation methodology, robust OLED panel designs are suggested and experimentally verified..

80‐3: Distinguished Paper: 47.5 inch 8K Inkjet Printing AMOLED MNT with Local Boosting GOA Design

In this paper, we presented a 47.5 inch 8K2K AMOLED MNT employing a LTPS backplane, top emissive inkjet printing (IJP) OLED devices and gate driver on array (GOA) supporting independent 32*9 zone control and internal compensation driving. It is so far the first prototype AMOLED MNT integrating inkjet printing process and local high frame rate (up to 960Hz) driving. Thanks to the high resolution, local frame rate data processing and superior IJP OLED EL, it shows a brand new approach to deliver a premium display.

47.5‐inch 8K inkjet printing AMOLED monitor with local boosting gate driver on array design

AbstractIn this paper, we presented a 47.5 in. 8K2K AMOLED MNT employing a low temperature poly‐silicon (LTPS) backplane, top emissive inkjet printing (IJP) OLED devices, and gate driver on array (GOA) supporting independent 32 * 9 zone control and internal compensation driving. By combining printed RGB units with a common evaporative blue stack, we proposed the hybrid tandem IJP devices that improved both device efficiency and operation load balance. In the local boosting GOA design, a novel architecture for independent display partition control was developed. The GOA cascading and timing scheme was carefully considered by reusing several clock signals to support both TFT internal compensation and display zone control. It is so far the first prototype AMOLED MNT integrating inkjet printing process and local high frame rate (up to 960 Hz) driving. Thanks to the 8K2K high resolution, local frame rate data processing, and IJP OLED EL reaching HDR brightness up to 580 nits with superior optical performance, it shows a brand‐new approach to deliver a premium display.

Synthesis of new [6]helicene derivatives for OLED applications. Experimental photophysical and chiroptical properties and theoretical investigation

Six-membered helicenes with specific functionalities were synthesized in good overall yields (40 %-73 %) through a concise photochemical method, allowing for their comprehensive characterization. The racemic mixtures were effectively resolved into their P- and M-enantiomers with high optical purity (97.56 %-100 % ee) by using chiral HPLC. This separation showcased remarkable optical activity, revealing substantial optical rotations (e.g., +2500–3000 for the (P)-enantiomer at λ = 589 nm) and notable electronic circular dichroism (ECD) signals. The organic helical species showed a strong absorption in the UV region and exhibited a red shifted emission, resulting in a quantum yield of 0.12–0.21. Moreover, they demonstrated irreversible one-electron oxidation and reduction processes, and their HOMO and LUMO energy levels were estimated via electrochemical methods. Utilizing DFT and TD–DFT computational approaches, we accurately predicted the electronic absorption and ECD spectra, as well as the frontier molecular orbitals (FMOs), aligning closely with experimental observations. Furthermore, in-depth analyses of absorption and ECD spectra, molecular electrostatic potential (MEP), and reduced density gradient (RDG) through quantum chemical calculations offered insights into the fundamental characteristics of these materials. The collective properties strongly indicate the potential application of these helicenes in electroluminescent and OLED devices, underscoring their promise as candidates in optoelectronic applications.

Polyimides with ultra-low coefficient of thermal expansion derived from diamine containing bisbenzimidazole and bisamide

To provide polyimide (PI) with high heat resistance and ultra-low coefficient of thermal expansion (CTE) for use in flexible display substrates, a novel diamine with bisbenzimidazole and bisamide groups, namely N,N'-(1H,1'H-[5,5'-bibenzo[d]imidazole]-2,2'-diyl)bis(4-aminobenzamide) (BZBA), was designed and successfully synthesized. Several poly(benzimidazole-amide-imide) (PBIAI) films were prepared by thermal imidization with 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 4,4'-oxydiphthalic anhydride (ODPA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), and 4,4'-(hexafluoroisopropylindene)-diphthalic anhydride (6FDA), respectively. Among them, BZBA-BPDA has a high glass transition temperatures ( Tg = 345 °C) while achieving an extremely low coefficients of thermal expansion (CTE = 1.9 ppm K−1), meeting the processing requirements of polymer flexible substrates in OLED devices. The effects of different dianhydrides on the performance of PBIAIs were compared, providing a meaningful reference for further adjusting the PI molecular structure to meet specific requirements for industrial polymer films.

Aqueous solution processed transition-metal-doped ZnO as electron injection layers for efficient inverted organic light emitting diodes

Zinc oxide (ZnO) has attracted lots of attention to be used as interfacial materials in organic optoelectronic devices owing to its attractive properties. In this work, a series of transition-metal-doped ZnO thin films were prepared by using a facile aqueous solution process, thereafter these films were employed as electron injection layers (EILs) combined with the tris-(8-hydroxyquinoline) aluminum (Alq3) emitting layer to construct the inverted organic light-emitting diodes (IOLEDs). The transition-metal-doped ZnO EIL-based IOLEDs demonstrate markedly improved device performance compared to the reference neat ZnO EIL-based IOLED. However, different transition-metal ions have much different doping effect on the device performance. CoCl2 doped ZnO EIL based IOLED device possesss an optimal current efficiency of 5.52 cd A−1, which is increased about 40% compared to the device with the neat ZnO as EIL. The enhancement might be attributed to the increased electron mobility and favorable interfacial energy level alignment of the transition-metal doped ZnO EIL for more efficient electron injection. Our findings may provide a promising strategy to improve the electron injection properties of ZnO film in the OLED devices.

Fabrication of high performance based deep-blue OLED with benzodioxin-6-amine-styryl-triphenylamine and carbazole hosts as electroluminescent materials

The present study reports synthesis of phenathroimidazole derivatives structures following donor–acceptor relation for high performance deep-blue light emitting diodes. Herein, methyl substituted benzodioxin-6-amine phenanthroimidazoles Cz-SBDPI and TPA-SBDPI derivatives that provide the blue light were designed and synthesized. These Cz-SBDPI and TPA-SBDPI show higher glass transition (Tg) temperatures of 199 and 194 °C and demonstrate enhanced thermal properties. Apart from enhanced thermal stability these compounds also exhibit superior photophysical, electrochemical and electroluminescent properties. The non-doped carbazole based device display improved electroluminescent performances than those of TPA-based devices. The strong orbital-coupling due to decreased energy barrier between Cz-SBDPI transitions result in deep blue emission with CIE—0.15, 0.06. For non-doped Cz-SBDPI device; high L (brightness):12,984 cd/m2; ηc (current efficiency): 5.9 cd/A; ηp (power efficiency): 5.7 lm/W and ηex (external quantum efficiency): 6.2% was observed. The results show that the D–A emitters can serve as simple but also as an effective approach to devise cheap electroluminescent materials that has high efficiency and can serve as OLED devices.

Bicarbazole-Benzophenone-Based Twisted Donor-Acceptor-Donor Derivatives as Blue Emitters for Highly Efficient Fluorescent Organic Light-Emitting Diodes.

This paper delves into the development of a group of twisted donor-acceptor-donor (D-A-D) derivatives incorporating bicarbazole as electron donor and benzophenone as electron acceptor for potential use as blue emitters in OLEDs. The derivatives were synthesized in a reaction of 4,4'-difluorobenzophenone with various 9-alkyl-9'H-3,3'-bicarbazoles. The materials, namely, DB14, DB23, and DB29, were designed with different alkyl side chains to enhance their solubility and film-forming properties of layers formed using the spin-coating from solution method. The new materials demonstrate high thermal stabilities with decomposition temperatures >383 °C, glass transition temperatures in the range of 95-145 °C, high blue photoluminescence quantum yields (>52%), and short decay times, which range in nanoseconds. Due to their characteristics, the derivatives were used as blue emitters in OLED devices. Some of the OLEDs incorporating the DB23 emitter demonstrated a high external quantum efficiency (EQEmax) of 5.3%, which is very similar to the theoretical limit of the first-generation devices.

Graphene on quartz modified with rhenium oxide as a semitransparent electrode for organic electronics

Our research shows that commercially available graphene on quartz modified with rhenium oxide meets the requirements for its use as a conductive and transparent anode in optoelectronic devices. The cluster growth of rhenium oxide enables an increase in the work function of graphene by 1.3 eV up to 5.2 eV, which guarantees an appropriate adjustment to the energy levels of the organic semiconductors used in OLED devices.

Slow magnetic relaxation and luminescence properties in β-diketonate lanthanide(iii) complexes. Preparation of Eu(iii) and Yb(iii) OLED devices

Six β-diketonate compounds [Ln(btfa)3(4,4′-dinonylbipy)] Ln = Sm, Eu, Tb, Dy, Er and Yb are reported. Magnetic and Luminescence study is also filed. The Eu and Yb complexes were successfully used as emitters in multilayer vacuum-deposited OLEDs.

An unprecedented {Y2⊂Y10} type disk-like Y12 nanocluster featuring electroluminescence property in OLED device

An unprecedented disk-like Y12 cluster with unique Y2⊂Y10 type structure was achieved successfully, which is the largest non-brucite type disk-like RE cluster and exhibits obvious electroluminescence performance in OLED device.

Synthesis, characterization, optical properties, and solvatochromism of highly fluorescent benzotriazolyl vinyl aniline based D-π-A fluorophores

Two solvatochromic benzotriazolyl vinyl aniline derivatives have been synthesized via the Krapcho decarboxylation with chemical yields of 43% and 47%. Single crystal X-ray diffraction confirmed that the (E)-isomer was preferentially obtained. Experimental and theoretical studies were performed for both compounds. Photophysical properties were evaluated: in solution fourteen solvents were used and quantum yields of 15.8–34.0% were reached, and in thin films, a bathochromic phenomenon was observed. DFT calculations were also performed to analyze the electronic properties and cyclic voltammetry helped to evaluate the behavior of both compounds in thin films. Furthermore, the compounds were employed in a concept test to study their application in OLED devices.