Organic Light-emitting Diode Technology Research Articles

Exciplex-driven blue OLEDs: unlocking multifunctionality applications

We present the development of multifunctional blue-emission organic light-emitting diodes (OLEDs) using TADF-exciplex materials. These OLEDs exhibit sensitivity to external stimuli and achieve a maximum external quantum efficiency (EQE) of 11.6% through partly liquid processing. This technique allows for large-scale production on arbitrary geometries.The potential multifunctionality of the devices arises from their response to low external magnetic fields (up to 100 mT) with an efficiency up to 2.5% for magnetoconductance, while maximum magneto-electroluminescence effects of 4.1% were detected. We investigated novel aspects, including the utilization of two organic materials without further doping and the investigation of the impact of 2,2ʹ,2″-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) processing in liquid and vapor form. The insights gained provide a fundamental understanding regarding the applicability of exciplex (EX) materials for fully solution-processed OLEDs through a deliberate omission of doping. Our work represents a significant advancement on the path towards multifunctional OLED technology, with potential applications in cost-efficient, scalable organic full-color displays and advanced sensing system.

Boosting Organic Light-Emitting Diodes Technology Using Thermally Activated Delayed Fluorescent Emitters: A Review

Boosting Organic Light-Emitting Diodes Technology Using Thermally Activated Delayed Fluorescent Emitters: A Review

Unraveling Degradation Processes and Strategies for Enhancing Reliability in Organic Light-Emitting Diodes

Organic light-emitting diodes (OLEDs) have emerged as a promising technology for various applications owing to their advantages, including low-cost fabrication, flexibility, and compatibility. However, a limited lifetime hinders the practical application of OLEDs in electronic devices. OLEDs are prone to degradation effects during operation, resulting in a decrease in device lifetime and performance. This review article aims to provide an exciting overview of OLED degradation effects, highlighting the various degradation mechanisms. Subsequently, an in-depth exploration of OLEDs degradation mechanisms and failure modes is presented. Internal and external processes of degradation, as well as the reactions and impacts of some compounds on OLED performance, are then elucidated. To overcome degradation challenges, the review emphasizes the importance of utilizing state-of-the-art analytical techniques and the role of these techniques in enhancing the performance and reliability of OLEDs. Furthermore, the review addresses the critical challenges of lifetime and device stability, which are crucial for the commercialization of OLEDs. This study also explores strategies to improve OLEDs’ lifetime and stability, such as using barrier layers and encapsulation techniques. Overall, this article aims to contribute to the advancement of OLED technology and its successful integration into diverse electronic applications.

Recent research on the status and advances of OLED

Organic Light-Emitting Diodes (OLEDs) have already been a prominent display technology in various applications for many decades, ranging from smartphones and televisions to wearable devices and lighting. It is important to understand the current state of OLED research in order to assess its progress, identify challenges, and explore more potential ways for further development. In this paper, the significance and widespread adoption of OLED technology are briefly introduced, and its advantages over traditional display technologies are highlighted. The paper then provides a concise overview of the major components and working principles of OLEDs without delving into basic notions. The paper discusses both small molecule OLEDs (SMOLEDs) and polymer OLEDs (POLEDs), emphasizing their unique structure, characteristics and properties. Different strategies employed to enhance OLED performance is investigated, including the regulation of band gaps that influence the efficiency and brightness. This paper also focuses on the evaluation of device reliability and stability aspects. The techniques and materials employed in studies related to OLED development are also discussed with many searched experimental data and ongoing research activities. Furthermore, the research content covered the aspects of recent commercial advancements in OLED technology, such as Active matrix OLEDs (AMOLED) and Passive matrix (PMOLED). The review provides a guideline for researchers, industry professionals, and enthusiasts to better understand the OLED technology into its details, potential, and the areas that require further exploration.

A Magnetic field sensor based on OLED / organic photodetector stack.

In this study an all-organic magnetic field sensor based on an organic light emitting diode (OLED) and organic photodetector (OPD) layer stack is presented. This sensor opens possibilities to create printable, flexible magnetic field sensors using commercially viable components, allowing magnetic field sensors to be simply integrated into existing OLED technology. The sensor function is driven by the large magneto-electroluminescence (MEL) of a thermally activated delayed fluorescence (TADF)-emitter based OLED, which in reference devices have shown an MEL of about 60% for magnetic fields on the order of 10 mT. Maximum sensitivity of about 0.15 nA/mT (150 μV/mT or 15 mV/kG with amplification) is achieved at a magnetic field of 3 mT to 4 mT. While the detectivity is limited to ~ 10-3 T·Hz-1/2, we show this can be improved upon on as the magnetic field detection sensitivity of OLEDs measured by an external Si-detector is about an order of magnitude higher. Sensitivity of 2 nA/mT and detectivities better than 10-5 T·Hz -1/2 are demonstrated, and the intrinsic detectivity limit is estimated to be on the order of 10-9 T·Hz -1/2.

Flexible Organic Light-Emitting Diodes: Structure and Fabrication

Flexible organic light-emitting diodes (OLED) technology with thin, light in weight, and free in design have been developed and perfected rapidly. The versatility of flexible OLED technology has been effectively proved in the sectors of displays, lighting, and medicine. In this article, the structure and fabrication of flexible OLED were introduced. Normal flexible OLED device construction includes flexible OLED substrate, barrier layers, electrode and organic layer. The flexible OLED is made on the substrate. The barrier layer is used to shield the OLED material from airborne oxygen and humidity. The electrodes are used for electricity, and the organic layer is used for light. The production processes of flexible OLED include coat-debond with advantages such as good stability and thermal conductivity, bond-debond with the advantage of simple and convenient and roll-to-roll [R2R] method with advantages of low cost, and mass production. Additionally, the application fields of these methods have been highlighted.

High-efficiency blue-emission crystalline organic light-emitting diodes sensitized by “hot exciton” fluorescent nanoaggregates

Sensitizing fluorescent materials is an effective way to maximally use excitons and obtain high-efficiency blue organic light-emitting diodes (OLEDs). However, it is a persistent challenge for present amorphous thin-film OLEDs to improve photon emission under low driving voltage, severely impeding the development of OLED technology. Here, we propose a novel OLED architecture consisting of a crystalline host matrix (CHM) and embedded "hot exciton" nanoaggregates (HENAs), which effectively sensitize blue dopant (D) emission. Owing to the advantages of the crystalline thin-film route, the device exhibits largely enhanced blue photon output [Commission International de L'Eclairage coordinates of (0.15, 0.17)], with a low turn-on/operation voltage of 2.5 V (at 1 cd/m2)/3.3 V (at 1000 cd/m2), an extremely low Joule heat loss ratio (7.8% at 1000 cd/m2), and a maximum external quantum efficiency (EQE) up to 9.14%. These areal photon output features have outperformed the present amorphous thin-film blue OLEDs with high EQE, demonstrating that the CHM-HENA-D OLED is promising for future OLEDs.

Decorated pyridine as hole transporting material (HTM) for solution-processed OLEDs

While organic light emitting diodes (OLEDs) technology is evolving at a fast pace, the development of flexible and full-color display panels with low power consumption provides superiority to these devices as eco-friendly lighting sources. Several strategies and methods have been attempted to improve the OLED device performance, especially in light-emitting materials. Even though, with significant advancements in efficiency, OLED technology demonstrates the feasibility to enhance further without saturation, thus attracting researchers to develop new materials with an effective device strategy. In this work, we report an integrated hole transporting material, 3,6-bis(4,6-diphenylpyridin-2-yl)-9-ethyl-9H-carbazole (CDP) with functionalization of carbazole unit with pyridine substituents. CDP adopted a moderately high triplet energy (2.61 eV), high thermal stability, and high hole transportability. Solution-processed CDP-based OLEDs were fabricated containing phosphorescent green emitter (Ir(PPy)3) and compared with conventional N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) based OLEDs. The CDP-based device exhibited a high performance with decreased layer thickness from ∼25 nm to ∼5 nm, with maximum external quantum efficiency, power efficiency, current efficiency, and brightness of 17.2 %, 66.8 lm/W, 64.0 cd/A, and 18,740 cd/m2, respectively which was superior to the NPB-based control device. Enhancement in device performance with reduced thickness of hole transport layer in CDP-based OLEDs distinctly demonstrates the effective potential of the designed material.

Nitrogen-modified a-C:H layers applied for light emitting diodes

The main problem of organic light-emitting diodes (OLEDs) is their degradation caused by the interaction of the polymer with atmospheric factors. The development of new encapsulation methods and materials for OLEDs can solve this problem. In this work prompted us to investigate the possibility of using hydrogenated amorphous carbon nitrogen-modified (a-C:N:H) layer as protective passive coatings. The layers were deposited on the active polymer layer and as a stand-alone active layer in the devices by radio frequency plasma assisted chemical vapor deposition (13.56 MHz). Different types of the diodes architectures (glass/ITO/PVK/Ca/Al, diodes with glass/ITO/PVK/a-C:N:H/Ca/Al and glass/ITO/a-C:N:H/Ca/Al) were prepared for which specified of the current-voltage and electroluminescent-voltage characteristics. The layers structure and morphology were assessed by X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX). The UV Vis spectroscopy studies have been carried out for the a-C:N:H layer and absorption bands were determined. The photoluminescence and fluorescence of the layers were confirmed. The optical properties and chemical stability were measured by spectroscopic ellipsometry. The influence of solvents on the dispersion dependence of the refractive index and extinction coefficient was also determined. The obtained results are promising in the context of the layers applications in OLEDs technology.

ILLUMINAZIONE: EVOLUZIONE TECNOLOGICA SOSTENIBILE TRA PASSATO, PRESENTE E FUTURO

The concern about environmental problems, in recent years, greatly encouraged and fostered the development of innovative energy saving systems (lighting and sensors) and effective energy conversion devices using renewable sources (solar, geothermal, wind); those technologies are now largely employed both at industrial and domestic levels. This note illustrates the emblematic case of light manipulation and lighting systems. Artificial light, being often assumed for granted, do not only allow us to see and move in our surroundings, but it also helps us to interact with the environment and live better. It is truly considered a form of physical and mental well-being. After a brief historical overview on the lighting system evolution during the last 150 years, starting from the lamps developed by Edison, we will discuss the current revolution of the OLED (organic light emitting diodes) technology. Focusing on OLEDs perspectives and challenges, it will be highlighted the fundamental contribution given by the chemistry and the steering effect on the physics and engineering fields.

Effects of hole transport and energy barrier on the width of the exciton formation zone in organic light-emitting diodes

Phosphorescent organic light-emitting diodes (OLEDs) have been fabricated based on MoO[Formula: see text]-doped [Formula: see text],[Formula: see text]-bis-(1-naphthyl)-diphenyl-1,1[Formula: see text] -biphenyl-4,4[Formula: see text]-diamine (NPB:MoO[Formula: see text] and 4,4[Formula: see text]-[Formula: see text],[Formula: see text]-dicarbazole-biphenyl (CBP:MoO[Formula: see text]. The device using 20 nm NPB:MoO3/10 nm CBP:MoO3 shows increased width of the exciton formation zone and thereby relieved efficiency roll-off than the one using 30 nm CBP:MoO3. This is mostly because the NPB:MoO3/CBP:MoO3 reduces the transit time for holes from anodes to emissive layers than the CBP:MoO3, as a result of the higher hole mobility of NPB:MoO3 than that of CBP:MoO3. Although the energy barrier from NPB:MoO3 to CBP:MoO3 markedly affects the current density versus voltage characteristics of a device, it barely alters the width of the exciton formation zone. This is ascribed to the instantaneous passage of holes through the interfacial barrier, regardless of its magnitude, thereby offering little effect on the transit time for holes from the anode to the emissive layer. The current research provides novel insight into the working mechanism of OLED, hopefully pushing forward OLED technology towards high-luminance applications.

Applications and Future Developments of Flexible Organic Light-emitting Diode

With the rapid development of display technology, human beings have more and more stringent requirements for display products, e.g., their light weight, thinness, flexible performances, and versatility. Contemporarily, the flexible organic light-emitting diode (OLED) technology and its derived multi-layer structure tend to be wearable, light, and responsive in a short time. Although flexible OLED technology is popular, there are still many problems that needs to be addressed, e.g., new raw materials, rough flexible substrate, and low efficiency in workmanship, resulting in poor luminescence, rough and inflexible products. In this paper, a new type of flexible fiber display system is proposed by combining OLED with conductive optical fiber. This paper comprehensively introduces the mechanism, manufacturing technology and structure of this new type of flexible OLED. It covers various scopes like Internet information communication, real-time positioning, and medical assistance, etc. Despite some challenges and limitations, this product possesses a variety of advantages in terms of its convenience and flexibility, which makes the exploitation of a large range of applications probable. Therefore, it is highly expected that these promising prospects of development will stimulate the further progress in display fabrication, which helps to facilitate people’s lives in the future. These results shed light on the significance of developments of flexible OLED technology.

Advancing Near-Infrared Phosphorescence with Heteroleptic Iridium Complexes Bearing a Single Emitting Ligand: Properties and Organic Light-Emitting Diode Applications

Cyclometalated iridium complexes, emitters of choice in organic light-emitting diodes (OLEDs), hold great potential for near-infrared (NIR) applications. Upon increasing the conjugation size and chemical complexity of the ligands, as required to push the emission toward the NIR), overall high-molecular-weight complexes (both homoleptic and heteroleptic β-diketonate ones) are obtained, posing related issues in OLED processing. One, so far barely explored, question arises: “Why endow Ir(III) with three or two emissive ligands when one might work just as well?” Herein, as proof of concept for OLED technology, we disclose three novel deep-red to NIR emitters of formula Ir(C^N)2(iqbt), with a single iqbt (1-(benzo[b]thiophen-2-yl)-isoquinolinate) ligand responsible for the emission in the NIR range. (C^N) are cyclometalated ligands with higher triplet energy than that of iqbt. We demonstrate that the presence of a single iqbt ligand is sufficient to enable efficient phosphorescence matching that of homoleptic Ir(iqbt)3; moreover, the Ir(C^N)2(iqbt) based OLEDs display efficiency exceeding the one of Ir(iqbt)3. These compounds offer several important benefits: (i) advantageous synthetic protocols limiting to the last step of the use of novel and synthetic costly NIR ligands (implying a lower amount of ligand required), (ii) commercially available (C^N) to prepare the starting Ir chloro-dimers, and (iii) lower molecular weight of the complexes compared to that of the homoleptic parent ones fruitful for easier vacuum thermal processing of the emitters.

Dipole Moment‐ and Molecular Orbital‐Engineered Phosphine Oxide‐Free Host Materials for Efficient and Stable Blue Thermally Activated Delayed Fluorescence (Adv. Sci. 3/2022)

Organic Light-Emitting Diodes In many thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs), efficiency and lifespan have shown a trade-off relationship. In article number 2102141, Soo-Ghang Ihn and coworkers present phosphine oxide-free hosts designed via a dipole moment- and molecular orbital-engineering, which enhance the device efficiency and stability simultaneously. This approach paves the way for the commercialization of TADF OLED technology.

Blue Light Intensity in Organic Light-Emitting Diode and Liquid-Crystal Display Televisions

Exposure to artificial blue light from screens, especially at evening or nighttime hours, can suppress melatonin production, throw the circadian rhythm off balance, and lead to general difficulty falling asleep. This study sought to investigate the difference in blue light intensity in organic light-emitting diode (OLED) and liquid-crystal display (LCD) screens, specifically in the form of televisions. An observational and quasi-experimental method was used, using a photometer to measure light intensity and a longpass optical filter to block out light ranging from 415 to 515 nanometers, serving as the wavelength of blue light for this study. Two televisions—one OLED and one LCD—were used, with five colors being displayed on each one, one at a time. The LCD television contained more relative blue light than the OLED television for four out of the five colors displayed. On average for all colors, the LCD television emitted 24.92% more blue light than the OLED television, relative to their overall brightnesses. Limitations in scope and the potential of confounding variables interfering with data prevent any definitive conclusions from being drawn, however this study still contributes to the current body of knowledge with evidence towards a trend of lessened blue light intensity in OLED screens compared to LCD screens, which correlates with speculation by other researchers. This study sets the ground for future research investigating the potential of OLED technology in lowering exposure to blue light, thus lessening the negative impacts it can have on individuals.

Investigating the exciton formation zone and its roles in phosphorescent organic light emitting diodes

The exciton formation zone has been studied in phosphorescent organic light emitting diodes (OLEDs). It is found that the width (W) of the exciton formation zone can be increased by reducing the transit time for holes (electrons) from the anode (cathode) into the emissive layer (EML) by decreasing the thickness of the hole (electron) transport layer. The increase in the thickness of the EML enables the exciton formation zone to be widened. The efficiency roll-off of the device is relieved when W increases. The device stability is found to be directly proportional to the product of W and the thickness of the electron transport layer. A thicker electron transport layer better suppresses diffusion of the metal cathode into the EML, increasing device stability but simultaneously decreasing the transit time for electrons from the cathode into the EML, and thereby W, so decreasing device stability. We also investigated the effect of charge carrier mobilities in the EML, modified by dye concentration, on W. The current research provides novel insights into guiding the delicate designs of OLEDs, hopefully pushing OLED technology towards high-luminance applications.

(Invited) Flexible, Stretchable and Healable Electronics

Organic electronics, based on semiconducting and conducting polymers, have been extensively investigated in the past decades and have found commercial applications in lighting panels, smartphone and TV screens using OLEDs (organic light emitting diodes) technology. Many other applications are foreseen to reach the commercial maturity in future in areas such as transistors, sensors and photovoltaics.Organic electronic devices, apart from consumer applications, are paving the path for key applications at the interface between electronics and biology, such as in polymer electrodes for recording and stimulating neural activity in neurological diseases. In such applications, organic polymers are very attractive candidates due to their distinct property of mixed conduction: the ability to transport both electron/holes and ionic species. Additionally, conducting polymers offer the possibility to tune their surface properties (e.g., wettability or chemical reactivity) by changing their oxidation state, thus promoting or hindering the adhesion of biomolecules. This feature can be particularly useful for enhancing the biocompatibility of implantable electrodes.My talk will deal with processing and characterization of conducting polymer films and devices for flexible, stretchable and healable electronics.Self-healing electronic materials are highly relevant for application in biology and sustainable electronics. We observed mechanical and electrical healability of PEDOT:PSS thin films. Upon reaching a certain thickness (about 1 µm), PEDOT:PSS thin films damaged with a sharp blade can be healed by simply wetting the damaged area with water. The process is rapid, with a response time on the order of 150 ms. Significantly, by blending with other polymers, the films are transformed into autonomic self-healing materials without the need of external stimulation. This reveals a new property of PEDOT:PSS and enables its immediate use in flexible and biocompatible electronics, such as electronic skin and bio-implanted electronics, placing conducting polymers on the front line for healing applications in bioelectronics.

Solid-state nuclear magnetic resonance study of polymorphism in tris(8-hydroxyquinolinate)aluminium.

Tris(8-hydroxyquinolinate)aluminium (Alq3 ) is a metal-organic coordination complex, which is a widely used electroluminescent material in organic light-emitting diode technology. Crystalline Alq3 is known to occur in five polymorphic forms (denoted α, β, γ, δ, and ε), although the structures of some of these polymorphs have been the subject of considerable debate. In particular, the structure of α-Alq3 , which is a model for the local structure in amorphous films used in devices, is highly complex and has never been conclusively solved. In this work, we use solid-state nuclear magnetic resonance (NMR) and density functional theory (DFT) calculations to investigate the local structure of four Alq3 samples. We find that the first structure proposed for α-Alq3 is inconsistent with all of the samples studied, and DFT calculations further suggest that this structure is energetically unfavourable. Instead, samples containing the meridional (mer) isomeric form are found to contain local structures consistent with ε-Alq3 , and a sample containing the facial (fac) isomeric form is consistent with a mixture of γ-Alq3 and δ-Alq3 . We also investigate the influence of different strategies for dispersion correction in DFT geometry optimisations. We find that a recently proposed modified semiempirical dispersion correction scheme gives good agreement with experiment. Furthermore, the DFT calculations also show that distinction between mer and fac isomers on the basis of ηQ that has been assumed in previous work is not always justified.

Application of inkjet printing in the large area display of organic light-emitting diode

<p indent=0mm>As the interaction media between human beings and electronic devices, display technology has become more and more important in our daily life with the development of modern information technology such as big data technology and artificial intelligence, which also brings the huge demands on the market of large area display. Active organic light-emitting diode (OLED) is one of the most competitive candidates for the next-generation display, fulfilling the demand of vivid color, wide view angle, flexible stretchability and high contrast. Thus, OLED devices have already been widely applied in small-size displays such as smart watches, smart phones, tablet computers and automobile monitor and so on. However, currently most commercialized OLED devices are still fabricated by high-cost methods, greatly hindering their application in large area display. For example, in the commercial large area display, only white OLED technology has been practically employed regardless of its high fabrication cost which is the reason of its less sharing market occupancy. White OLED technique faces some difficulties that can hardly be solved perfectly for adopting thermal deposition process, such as poor utilization of organic materials, expensive deposition facilities and low product yields, etc. The technique of QD-OLED is another alternative method for large area display, which is the upcoming scheme Samsung promotes firmly, but it has been repeatedly delayed in the mass production because there are still some unconquered barriers in materials and manufacturing processes. According to the announcement of Samsung display company, in the next half year of 2021, the commodity of QD-OLED will be appeared finally, but it could not be sold in large quantities, which will be with high price exceeding expectation of consumer. Therefore, including TV, phone and monitor, the retail price of OLED products is much higher than that of liquid crystal display (LCD) all the time, impeding the commercial application of large area OLED. With the advantages of effective material utilization, low cost and convenient fabrication of large area panel, inkjet printing is relatively suitable for the manufacture of large area OLED display, which is the crucial developing technique to the display companies and researching institutes. Except the immaturity of industrial inkjet machine and process, the efficiency and stability of OLED based on inkjet printing can’t satisfy the requirements of commercialized application. Consequently, it is significant that OLED based on inkjet printing with high efficiency and long lifetime is realized and marketed by improving ink materials, devices and processes to achieve low price and outstanding performance. In this paper, starting with descripting the current status of large area OLED display, we briefly introduce the recent progresses of inkjet printing OLED and relevant materials and devices, as well as their applications in large area display. Finally, we present our ideas about the future developing direction of new display of OLED based on inkjet printing technology.

Zapata Computing

When computational chemist Alán Aspuru-Guzik told his business partner Christopher Savoie that he had an idea for a quantum computing software company, Savoie was skeptical, he admits. This was 2017, and quantum computing was (and arguably still is) in its infancy. Savoie asked Aspuru-Guzik what a state-of-the-art quantum computer could do. Not much more than a pocket calculator, Aspuru-Guzik told him. But the two had worked together successfully at Kyulux on machine-learning methods to advance organic light-emitting diode technology, so Savoie visited Aspuru-Guzik’s lab, then at Harvard University. By the time they’d finished lunch, Savoie says, he was convinced that Aspuru-Guzik and his collaborators—Yudong Cao, Peter Johnson, Jonathan P. Olson, and Jhonathan Romero Fontalvo—were on to something. By the afternoon, Aspuru-Guzik was calling quantum computing researchers to introduce Savoie as the new CEO of Zapata Computing. Quantum computing proponents have made huge promises, especially in chemistry. A traditional computer represents