Organic Light-emitting Diodes Research Articles

Switchable Topologically Chiral [2]Catenane as Multiple Resonance Thermally Activated Delayed Fluorescence Emitter for Efficient Circularly Polarized Electroluminescence.

Aiming at the fabrication of circularly polarized organic light-emitting diodes (CP-OLEDs) with high dissymmetry factors (gEL) and color purity through the employment of novel chiral source, topologically chiral [2]catenanes were first utilized as the key chiral skeleton to construct novel multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters. Impressively, the efficient chirality induction and unique switchable feature of topologically chiral [2]catenane not only lead to a high |gPL| value up to 1.6 × 10-2 but also facilitate in situ dynamic switching of the full-width at half-maximum (FWHM) and circularly polarized luminescence (CPL). Furthermore, the solution-processed CP-OLEDs based on the resultant topologically chiral emitters exhibit reveal narrow FWHM of 36 nm, maximum external quantum efficiency of 17.6%, and CPEL with |gEL| of 2.1 × 10-3. This study demonstrates the successful construction of the first CP-MR-TADF emitters based on topological chirality with the highest |gPL| among the reported CP-MR-TADF emitters and excellent device performance to the best of our knowledge. Moreover, it endowed the MR-TADF emitter with distinctive switchable CPL performances, thus providing a novel design strategy as well as a promising platform for developing intelligent CP-OLEDs.

The Influence of Thickness and Spectral Properties of Green Color-Emitting Polymer Thin Films on Their Implementation in Wearable PLED Applications.

A systematic investigation of optical, electrochemical, photophysical, and electrooptical properties of printable green color-emitting polymer (poly(9,9-dioctylfluorene-alt-bithiophene)) (F8T2) and spiro-copolymer (SPG-01T) was conducted to explore their potentiality as an emissive layer for wearable polymer light-emitting diode (PLED) applications. We compared the two photoactive polymers in terms of their spectral characteristics and color purity, as these are the most critical factors for wearable lighting sources and optical sensors. Low-cost, solution-based methods and facile architecture were applied to produce rigid and flexible light-emitting devices with high luminance efficiencies. Emission bandwidths, color coordinates, operational characteristics, and luminance were also derived to evaluate the device's stability. The tuning of emission's spectral features by layer thickness variation was realized and was correlated with the interplay between H-aggregates and J-aggregates formations for both conjugated polymers. Finally, we applied the functional green light-emitting PLED devices based on the two studied materials for the detection of Rhodamine 6G. It was determined that the optical detection of the R6G photoluminescence is heavily influenced by the emission spectrum characteristics of the PLED and changes in the thickness of the active layer.

Inverted All-Inorganic Nanorod-Based Light-Emitting Diodes via Electrophoretic Deposition.

High performance and high stability in all-inorganic solution processed nanocrystal-based light-emitting diodes (LEDs) are highly attractive for large area devices compared to organic material-based LEDs. In this work, an inverted all-inorganic LED structure is designed to have an easy integration with thin-film transistors. Adopting robust inorganic materials such as Ni1-x O nanoparticle films as a hole transport layer (HTL) is beneficial for the performance of LED. Herein, we have optimized the HTL by introducing Mg into Ni1-x O to bridge the difference in energy offset between the nanorod emissive layer and the HTL, in addition to the advantages of low temperature solubility of Ni1-x O:Mg nanoparticles. Furthermore, CdSe/CdS-based nanorods via electrophoretic deposition (EPD) are amassed in a vertically aligned (VA-NR) fashion as an emissive layer to facilitate the carrier transportation. Fostering these approaches enabled an EQE of 1.2% of the fabricated device, establishing the viability for further development of efficient and highly stable nanocrystal-based LEDs.

Dendritic Oligomers‐Based Exciplex Emitters Realizing Solution‐Processed Organic Light‐Emitting Diodes with Nearly 30% External Quantum Efficiency

AbstractDue to the feature of the strong intermolecular interactions causing aggregation‐caused excitons quenching (ACQ) of solution process, realizing high‐performance solution‐processed organic light‐emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) emitters remains a formidable challenge nowadays. To address this issue, herein, a novel strategy is proposed to construct solution‐processable ternary exciplex emitters by utilizing the dendritic oligomer as the substrate, simultaneously realizing excellent solution‐process adaptability, good dispersibility to restrain harmful ACQ, and improved exciton utilization with multiple reverse intersystem crossing channels. Accordingly, dendritic oligomer‐based exciplex systems are constructed by combining small‐molecule donor and acceptor components with the multi‐carbazole‐substituted tetraphenylsilane‐core analog as substrate. And their film morphologies, photoluminescence quantum yields (ΦPLs), and non‐radiative decay rates of triplet excitons (knrTs) are significantly improved. Among them, DMAC‐DPS:PO‐T2T:SimCP3 exhibits the highest ΦPL of 97.5% and the lowest knrT of 1.0 × 103 s−1, and realizes the best maximum external quantum efficiency of 29.7% in solution‐processed OLED, which is comparable with the highest electroluminescence efficiencies of all solution‐processable emitters. Therefore, this work will provide a prospective pathway to develop efficient solution‐processable exciplex emitters and promote the progress of solution‐processed OLEDs.

The Rise of Tandem Perovskite Light-Emitting Diode.

In 2024, tandem perovskite light-emitting diodes (tandem-PLEDs) achieved a breakthrough external quantum efficiency of 43.42%, with an organic electroluminescence (EL) unit stacked atop a perovskite EL unit, surpassing the previous single-junction perovskite LEDs. This innovative design enables a higher brightness at lower currents, enhancing the longevity and efficiency of the tandem-PLEDs. Additionally, the tandem-PLEDs can also be fabricated by combining a perovskite EL unit with a perovskite quantum dot unit. In this perspective, the key advancements in tandem-PLEDs are highlighted, focusing on the development of perovskite-organic materials, perovskite-perovskite quantum dots, and the design principles for obtaining efficient and stable charge generation layers. But more importantly, the challenges and solutions are discussed in fabricating all-perovskite tandem LEDs using strongly polar solvents that have yet to be reported nowadays. This comprehensive guide aims to support researchers in advancing the practical deployment of tandem-PLED technology.

Defect Engineering in ZnO and Ni-Doped ZnO Nanostructures for Efficient Organic Light Emitting Diode (OLED) Application

Defect Engineering in ZnO and Ni-Doped ZnO Nanostructures for Efficient Organic Light Emitting Diode (OLED) Application

Characteristics Study of OLED Materials

Abstract Organic Light Emitting Diodes (OLEDs) are emerging as promising alternatives to conventional lighting and display technologies due to their unique properties and potential energy efficiency. This study conducts a comprehensive investigation into OLED materials, focusing on their optical, electrical, and structural characteristics. Through experimental analysis and theoretical modeling, the study delves into the performance and behaviour of various OLED materials, including organic semiconductors, charge transport layers, and emissive materials. Critical aspects such as charge carrier mobility, exciton formation, and device stability are examined to understand the mechanisms governing OLED operation. The findings offer valuable insights into optimizing OLED devices for applications ranging from consumer electronics to lighting and signage. This research contributes fundamental knowledge and practical guidelines for material selection, device fabrication, and performance assessment, thereby advancing OLED technology. The insights provided pave the way for future innovations in OLED materials and device design, potentially leading to improvements in efficiency, brightness, and longevity.

Enhanced Emitting Dipole Orientation Based on Asymmetric Iridium(III) Complexes for Efficient Saturated-Blue Phosphorescent OLEDs.

Three novel asymmetric Ir(III) complexes have been rationally designed to optimize their emitting dipole orientations (EDO) and enhance light outcoupling in blue phosphorescent organic light-emitting diodes (OLEDs), thereby boosting their external quantum efficiency (EQE). Bulky electron-donating groups (EDGs), namely: carbazole (Cz), di-tert-butyl carbazole (tBuCz), and phenoxazine (Pxz) are incorporated into the tridentate dicarbene pincer chelate to induce high degree of packing anisotropy, simultaneously enhancing their photophysical properties. Angle-dependent photoluminescence (ADPL) measurements indicate increased horizontal transition dipole ratios of 0.89 and 0.90 for the Ir(III) complexes Cz-dfppy-CN and tBuCz-dfppy-CN, respectively. Analysis of the single crystal structure and density functional theory (DFT) calculation results revealed an inherent correlation between molecular aspect ratio and EDO. Utilizing the newly obtained emitters, the blue OLED devices demonstrated exceptional performance, achieving a maximum EQE of 30.7% at a Commission International de l'Eclairage (CIE) coordinate of (0.140, 0.148). Optical transfer matrix-based simulations confirmed a maximum outcoupling efficiency of 35% due to improved EDO. Finally, the tandem OLED and hyper-OLED devices exhibited a maximumEQE of 44.2% and 31.6%, respectively, together with good device stability. This rational molecular design provides straightforward guidelines to reach highly efficient and stable saturated blue emission.

Pyrene-encapsulated light-emitting π-conjugated polymer with excellent ozone tolerance capacity for large-area and flexible ultra-deep-blue PLEDs with CIEy = 0.08

Emerging flexible polymer light-emitting diodes (PLEDs) are crucial for the development of information display and solid lighting. However, achieving ultrastable light-emitting polymers with robust emissions and outstanding chem-physic stabilities, remains a serious challenge due to the intrinsic oxidative and degrading properties of aromatic units. Herein, we present a universal and convenient pyrene-encapsulation strategy to enhance the ozone tolerance capacity of deep-blue light-emitting conjugated polymers (PPyDPF) for the narrowband flexible PLEDs. More intestingly, compared to the comparison polymers, PPyDPF showed a lower free volume ratio of 71.78 %, facilitating dense interchain packing, which contributes to its excellent ozone tolerance capacity. Large-area PLEDs were fabricated, which exhibit ultra-deep-blue emission with a FWHM of 40 nm and Commission internationale de l’éclairage (CIE) coordinates of (0.16, 0.08). The demonstrated potential for application in light-emitting devices underscores the significance of this approach, providing an effective strategy for developing aging-resistant light-emitting conjugated polymers for optoelectronic applications.

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.

An efficient thermally activated delayed fluorophore featuring an oxygen-locked azaryl ketone acceptor

Thermally activated delayed fluorescence (TADF) dyes are promising for applications like bioimaging, sensing, and optoelectronic devices due to their efficient exciton utilization without noble metals, making them ideal for organic light-emitting diodes (OLEDs). In this contribution, we introduce a new TADF emitter, 3-(9,9-dimethylacridin-10(9H)-yl)-12H-chromeno[2,3-b]quinolin-12-one (CQLO-DMAC), which incorporates an intramolecular oxygen-locked azaryl ketone acceptor, CQLO. This design enhances molecular rigidity and electron-accepting strength. The CQLO-DMAC compound, featuring a bulky donor, shows significant intramolecular charge transfer and TADF emission. Comprehensive analyses, including spectroscopic studies and theoretical calculations, reveal high luminescence efficiency and reduced non-radiative losses. Utilizing CQLO-DMAC in OLEDs, we achieved a green-yellow emission peak at 548 nm and a maximum external quantum efficiency of 17.4%. The findings highlight the potential of CQLQ as a highly effective acceptor in designing of TADF electroluminescent dyes.

Geometrically isomeric [Ir(C^N)(C’^N’)(N’’^O)-tris-heteroleptic [Ir(dFppy)(CN-ppz)(pic)] Ir(III)-complexes with blue-light: Forwards to efficient blue organic light-emitting diodes

Despite the great success of Ir(III)-complex-based green/red-light OLEDs (OLED = organic light-emitting diode), the realization of their efficient blue-OLEDs is far behind and challenging. Herein, using HdFppy (2-(2,4-difluorophenyl)pyridine) and CN-ppzH (4-(1H-pyrazol-1-yl)benzonitrile) as the HC^N/HC’^N’ ligands and Hpic (2-picolinic acid) as the N’’^O-ancillary ligand, the [Ir(C^N)(C’^N’)(N’’^O)]-tris-heteroleptic molecular design strategy was adopted, obtaining the two [Ir(dFppy)(CN-ppz)(pic)]-configured blue-emitting (λPL (photoluminescence emission peak) = 466, 496(sh) nm; ΦPL (photoluminescence quantum efficiency) = 0.41–0.46) geometrical isomers 1a and 1b. Further through the doped and vacuum-deposited fabrication, their blue-OLEDs-1A/1B with the LMax (maximum luminance) values up to 18090–22528 cd/m2 and the ηEQEMax (maximum external quantum efficiency) sizes of 7.99–8.42 %, were realized, respectively. This study result shows that [Ir(dFppy)(CN-ppz)(pic)]-included [Ir(C^N)(C’^N’)(N’’^O)]-tris-heteroleptic Ir(III)-complexes can be used as the attractive blue-phosphor candidates forwards to efficient blue-OLEDs.

Current density–voltage characteristics of exciplex-type organic light-emitting diodes expressed by a simple analytic equation

Exciplex-type bilayer organic light-emitting diodes (OLEDs) with ohmic contacts exhibited current density–voltage (J–V) characteristics that closely matched a simplified analytical model proposed by Nikitenko and Bässler. The analytical model is based on the following key assumptions: (i) complete hole–electron recombination at the interface between a hole transport layer (HTL) and an electron transport layer (ETL), (ii) ohmic contacts at the interfaces between metal electrodes and carrier transport layers, and (iii) electric-field-independent carrier mobilities in both HTL and ETL. The excellent matching shows that the simplified analytical model is sufficient to describe the J–V characteristics of the OLEDs. We also demonstrated that if the carrier mobility of one carrier transport layer is known, that of the other transport layer can be estimated using the equation derived by the simplified analytical model. The simplified analytical model provides a useful method to estimate carrier mobilities within carrier transport layers themselves in OLEDs.

Unveiling the potential: Gallium-doped zinc oxide/silver-nanoparticles/glass structure for superior anode performance in polymer light-emitting diodes

This study examines the effectiveness of gallium-doped zinc oxide (GZO) combined with silver nanoparticles (Ag-NPs) on glass substrates as anodes for polymer light-emitting diodes (PLEDs). The proposed GZO/Ag-NPs/glass structure achieved superior electrical and optical properties, with a peak luminance of 5834 cd/m2 and an average current efficiency of 1.91 cd/A, significantly outperforming the conventional GZO/Ag-NPs/GZO/glass anode. The GZO/Ag-NPs/glass anode enhanced electroluminescence intensity by 379 % compared to the GZO/glass anode, while the GZO/Ag-NPs/GZO/glass anode showed a 196 % enhancement. This highlights the potential for improved PLED performance through enhanced anode conductivity and localized surface plasmon resonance effects.

Charge generation layer with octylamine assistant layer for efficient tandem organic light-emitting diodes

Charge generation layer with octylamine assistant layer for efficient tandem organic light-emitting diodes

Unveiling the ligand effects on Pt(Ⅱ) carbene complexes for rapid, efficient and narrow-spectra blue phosphorescence

Tetradentate Pt(II) complexes, comprising of benzoimidazolyl N-heterocyclic carbene (BI-NHC) coordination, have shown superior performance in blue phosphorescent organic light-emitting diodes (PhOLEDs). Here, four frame-structured complexes were synthesized to explore the intrinsic ligand effect for rapid, efficient and narrow-spectra blue phosphorescence through experimental analyses and theoretical calculations. We found carbazolylpridine (CzPy) chelating part in Pt(II) BI-NHC complexes dominates the phosphorescence with the suppression of metal-centered transition and electron-vibration coupling. Consequently, the CzPy chelated complexes (PtN-dip and PtN-dtb) achieved high luminescent efficiency, rapid radiative decay rate (kr) and narrow emission spectra. The peripheral substituent 2,6-di-iso-propylphenyl (dip) on NHC of PtN-dip constrains the molecule, significantly reducing the non-radiative decay rate (knr) and enhancing the efficiency. The 3,5-di-tert-butylphenyl (dtb) in PtN-dtb could enhances low-frequency vibration coupling that could expedite the excitons decay, resulting in higher kr and knr. This work unveils the intrinsic factors behind the ligand effects of Pt(II) BI-NHC based complexes, leading to a rapid, efficient and narrow-spectra phosphorescence.

Ultrafast dynamics and electroluminescence performance of a novel tetraphenylethylene-based aggregation induced emission luminogen

Efficient emission and confined molecular conjugation in aggregated/solid form, are two beneficial characteristics of blue organic light-emitting materials (OLEMs). Aggregation-induced emission molecules (AIEgens) have evolved as auspicious OLEMs that possess these properties. Herein, we discover an innovative sky-blue tetraphenylethene-based AIEgen, 4′,4‴-(1-phenyl-2-(4-(1,2,2-triphenylvinyl)phenyl)-1H-imidazole-4,5-diyl)bis(N,N-diphenyl-[1,1′-biphenyl]-4-amine) (2TPA-ITPE), with high thermal stability. By employing this AIEgen as a non-doped emitter, the constructed organic light-emitting diode demonstrates a maximum external quantum efficiency of 3.35 % with a power efficiency of 4.1 lm/W and high luminescence of 15896.92 cd/m2 2TPA-ITPE exhibits a weak donor-acceptor character. Moreover, to probe the photo-physical nature of this AIEgen, its excited-state dynamics are examined through ultrafast transient absorption spectroscopy (TAS). The TAS results of this OLEM unveil the generation of a resonant structure species owing to the elongation of C=C double bond. The excited state dynamics reveal that 2TPA-ITPE undergoes three processes after excitation (internal conversion, C=C elongation and vibrational cooling). These findings offer innovative insights into the ultrafast mechanisms underlying excited TPE-based OLEMs.

Low-voltage operatable top-gated organic transistors based on the solution-processed binary polymers dielectric for simplifying the manufacturing flow of arrayed AMOLED

The complex process flow is an important factor that hinders the development of active-matrix organic light-emitting diode (AMOLED) displays. Organic thin-film transistors (OTFTs) are one of the promising candidates as the pixel circuits for AMOLEDs. Both the architecture and the fabrication of OTFTs are crucial elements to determine the process flow and cost of the AMOLEDs. In this Letter, we develop a strategy to significantly simplify the process flow and reduce the cost of AMOLEDs by constructing top-gated OTFTs with a solution-processed vertically phase separated binary polymer dielectric as the pixel circuits. The design on the OTFTs considers both the process flow and the device performance in terms of mobility and operating voltages. The mechanism to improve device performances is discussed. Finally, a 3 × 4 arrayed AMOLED is demonstrated, in which a high mobility over 0.3 cm2/Vs is obtained on the switching and driving OTFTs, and luminance over 300 cd/m2 is achieved on the OLEDs at the supplied low operating voltages of 10 V. This strategy provides a competitive technological route for the manufacturing of AMOLEDs.

High-Performance perovskite quantum dots light-emitting diodes with hole transport layer engineering and synergetic outcoupling enhancement

Perovskite quantum dot light-emitting diodes (PeQLEDs) are frequently considered as the most promising alternatives to organic light-emitting diodes (OLEDs). However, the efficiency of PeQLEDs remains inferior to OLEDs due to suboptimal charge carrier transport and intrinsic light outcoupling efficiency (ηout). Herein, a combination of hole transport layer (HTL) engineering and substrate engineering is demonstrated to improve the charge injection and ηout of PeQLEDs. To replace the conventional PEDOT:PSS, a novel HTL bilayer based on modified PEDOT:PSS and PVK with a lower refractive index and fewer trap densities at the HTL-QDs interface is developed. Additionally, this study identifies the ideal thickness of ITO for achieving optimal ηout of PeQLEDs through optical simulations and experimental validation. Based on the synergistic use of HTL bilayer and 70-nm-thick ITO, the PeQLEDs achieved an optimal external quantum efficiency of 17.96 % at a luminance of 1763 cd/m2 and 15.19 % at 8300 cd/m2 without using any external outcoupling structure, indicating a low efficiency roll-off.

Controlling Drying Conditions in Vacuum for Uniform Film Formation in Inkjet-Printed OLEDs.

The drying process of inkjet-printed organic light-emitting diodes (OLEDs) is influenced by both ink properties and external environmental factors, which ultimately affect the film profile. First, we conducted a detailed investigation of the drying time based on changes in the boiling point (BP) of mixed solvents and analyzed the correlation with the film profile. Under atmospheric drying conditions in a nitrogen (N2) atmosphere, the increased drying time under capillary-driven flow leads to greater particle movement toward the edges, significantly increasing the coffee-ring effect. Additionally, using a high-boiling-point solvent mixture of ethyl 4-methylbenzoate (EMB) and 2-ethylhexyl benzoate (EHB), we produced uniform thin films both between and within pixels (inter and intrapixel uniformity) through a vacuum drying process. In particular, we proposed a drying process model that divides the drying of inkjet pixels into a microfluidic phase and a gelation phase. Through five gelation phase-controlled vacuum drying experiments, the morphology within the pixels was precisely investigated. By sufficiently removing residual solvents after the microfluidic phase and then proceeding with heating, we produced uniform thin films. Furthermore, we fabricated OLED devices using this gelation phase-controlled vacuum drying process, achieving uniform pixel emission and improved device performance.