OLED Structure Research Articles

Charge Mobility of Substituted Donor-Acceptor Compounds Based on Diphenylamines and Dibenzothiophene Dioxides in OLED Structures

Charge Mobility of Substituted Donor-Acceptor Compounds Based on Diphenylamines and Dibenzothiophene Dioxides in OLED Structures

Recent Progress in Blue Thermally Activated Delayed Fluorescence Emitters and Their Applications in OLEDs: Beyond Pure Organic Molecules with Twist D-π-A Structures.

Thermally activated delayed fluorescence (TADF) materials, which can harvest all excitons and emit light without the use of noble metals, are an appealing class of functional materials emerging as next-generation organic electroluminescent materials. Triplet excitons can be upconverted to the singlet state with the aid of ambient thermal energy under the reverse inter-system crossing owing to the small singlet-triplet splitting energy (ΔEST). This results from a specific molecular design consisting of minimal overlap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, due to the spatial separation of the electron-donating and electron-releasing part. When a well-designed device structure is applied, high-performance blue-emitting TADF organic light-emitting diodes can be realized with an appropriate molecular design. Unlike the previous literature that has reviewed general blue-emitting TADF materials, in this paper, we focus on materials other than pure organic molecules with twist D-π-A structures, including multi-resonance TADF, through-space charge transfer TADF, and metal-TADF materials. Cutting-edge molecules with extremely small and even negative ΔEST values are also introduced as candidates for next-generation TADF materials. In addition, OLED structures used to exploit the merits of the abovementioned TADF emitters are also described in this review.

52‐4: Novel Polarizer‐Free OLED Structure with High Optical Gain

With the recent increase in OLED usage, the size and shape of devices are diversifying. In addition, portability is becoming more important along with product performance and improvement. In order to enhance portability, it is necessary to improve battery performance and increase the time available without charging. To this end, it is required to reduce display power consumption, and various methods and structures for reducing power consumption by improving the efficiency of many OLED products have been proposed.Most OLED displays have a polarizer film applied to secure black viewing in the off‐state. However, this reflectance‐reducing film has a transmittance 50% or less, thus the light extraction efficiency is very bad.This paper introduces a simulation‐based design methodology of a new display that is devoid of polarizer film. It required the task of obtaining high outdoor contrast by reducing reflectance of external light with improved light efficiency. By separating the panel structure and optimizing optical filters and OLED devices, reflection reduction, efficiency improvement, and viewing angle characteristics were secured at the same time.The simulation‐based optical design methodology is an important technology that can simultaneously optimize the optical characteristics of new type of display, and is expected to be applied to various product developments in the future.

Modeling of organic light emitting structures

The paper has been shown the results of the study of the parameters of organic light-emitting structures based on the SPICE (Simulation Program with Integrated Circuit Emphasis) model studies. A SPICE model of diode structure has been developed, which is implemented in the form of a substitution scheme based on the basic components of the simulator. This model can be extended by introducing additional components of the substitution scheme, which provides higher accuracy in representing the structure specifics. Graphical results of researches of the model of OLED structure at the change of internal parameters have been presented. The obtained data well represent the parameters of real structures and are characterized by a fairly effective adaptation to the experimental data of specific samples.

Role of MEH:PPV polymer in single layer OLEDs with its optoelectronic characteristics

In this article the main emphasis is given on optoelectronic characteristics of a single layer OLED with taken into account the MEH:PPV polymer, which is chemically known as Poly [2-methoxy-5(2′-ethylhexyloxy)-1, 4-phenylenevinylene], as an emissive layer. The reason behind selection of this polymer is its main particular features such as hydrophobic characteristics with good light emitting capacity and better conversion efficiency as compared to the other conjugated polymers. For the ITO/MEH:PPV/Au OLED structure, we have computed the I-V characteristics, behaviour of anode current with variation in electric field, Excitons density as a function of transient time and finally the luminescent power as a function of applied voltage ranging from 0 to 10 V. In addition, the response of anode current to the transient time (of the order of µs) has also been studied.

26‐4: Late‐News Paper: Development of Positive‐type Photoresists Based on Polyorganosilsesquioxanes for the Pixel Defining Layer (PDL) in OLED Structures

Silicone‐based positive‐type photoresists for the pixel defining layer (PDL) in OLED Structures have been developed. Silicone binder based on polyorganosilsesquioxane resin for the PDL has been synthesized by using a well‐known sol‐gel reaction. Also, photoresist characteristics based on silicone resin such as film retention rate, patterning profile, thermal stability, out‐gas, and transmittance have been investigated. In particular, thermal stability at high temperature (400°C), transmittance at 400 nm, and out‐gas properties were highly effective for the PDL application in OLED devices.

60‐2: Panel Design Technology for a 31‐inch GOA Drived AMOLED Display with BYYB OLED Structure and Slim Border

A much complicated structure, where GOA circuits were placed at the bottom side, was proposed for a 31‐inch AMOLED display. This structure contributed significantly to border reduction and reliability improvement. What's more, amorphous‐indium‐gallium‐zinc‐oxide (a‐IGZO) thin‐film‐transistors (TFTs) with top‐gate structure exhibited high performance and the GOA circuits could operate well.

FDTD modelling of nanostructured OLEDs: analysis of simulation parameters for accurate radiation patterns

Nanostructures in OLEDs allow to manipulate the radiation pattern and direct light of a specific wavelength into a specific angle in the far field by resonant light outcoupling. We present a theoretical study investigating simulation conditions for accurate radiation patterns employing the FDTD method. Radiation patterns of single dipole emitters placed in a sufficiently large simulation domain are superimposed to model the incoherent emission of a continuous emission layer. The necessary simulation domain size is derived by considering propagation length and field profile of the guided mode of a corresponding unstructured OLED. A 5 nm mesh resolution is determined as a good compromise between accuracy and simulation time. The position of an emitter with respect to the grating has a large influence on the radiation pattern. Nevertheless, we demonstrate for nine different OLED structures that the radiation pattern of a homogeneous emission layer is approximated with an amplitude error of less than 5% by superimposing only four equally spaced dipoles at positions pm ,(1/8, 3/8, 5/8, 7/8) cdot varLambda /2, which avoid points of high symmetry.

OLED-LC structures for primary transducers of optical temperature sensors

The work is devoted to the creation of OLED structures, as a light source for optical temperature sensors, and to the study of their optical characteristics. We have carried out the modeling of light-emitting structures in order to select the materials of layers and a technology for their production based on the necessity of obtaining the appropriate spectral characteristics. The optical characteristics of OLEDs and OLED-LC structures are also studied.

Creation and investigation of OLED-structures with inclusion of colloidal quantum dots

During the work organic light-emitting structures FTO/PEDOT:PSS//TPD/TPD+CQD CdSe(650)/Alq3/Al with an efficiency value of about 2% were created. The technique for introducing CdSe CQD (650) into the structure of OLED was developed. The change in the electroluminescence spectra in structures with colloidal quantum dots is demonstrated. The decrease in OLED switching on voltage in structures with the PEDOT: PSS layer is demonstrated.

35‐1: Strategy for Developing an Ultra‐High‐Luminance AMOLED Display

To obtain a high‐luminance active‐matrix organic light‐emitting diode (AMOLED) display compatible with the high‐dynamic‐range (HDR) technology, we investigated the effect of basic components, e.g., field‐effect transistor, pixel circuit, OLED structure, and organic material. Combining these technologies, we fabricated a high‐luminance display with a peak luminance exceeding 3,000 cd/m2.

Yellow emitting Iridium (III) phenyl-benzothiazole complexes with different β-diketone ancillary ligands as dopants in white organic light-emitting diodes

We discuss the influence of the type of β-diketone ancillary ligand in Iridium (III) bis phenyl-benzothiazole complexes ((bt)2Ir(β-diketone)) on their photophysical and electroluminescent properties when they are used as dopants in white organic light-emitting diodes (WOLED). For this purpose, we investigated four novel yellow cyclometalated complexes: (bt)2Ir(dbm), (bt)2Ir(fmtdbm), (bt)2Ir(tta) and (bt)2Ir(bsm), where dbm = 1,3-diphenylpropane-1,3-dionate; fmtdbm = 1-(4-fluorophenyl)-3-(4-methoxyphenyl)propane-1,3-dionate; tta = 4,4,4-trifluoro-1-(thiophene-2-yl)butane-1,3-dionate; and bsm = 1-phenylicosane-1,3-dionate). To obtain white light by mixing emissions of two complementary colors (yellow emitted by the dopant and blue, by another emitter), we chose the following OLED structure: ITO/doped HTL/ElL/ETL/M, where ITO was a transparent anode of In2O3:SnO2; M, a metallic Al cathode; HTL, 4,4’-Bis(9H-carbazol-9-yl)biphenyl (CBP) involved in a poly(N-vinylcarbazole) (PVK) matrix; ElL, an electroluminescent layer of aluminum(III)bis(2-methyl-8-quninolinato)-4-phenylphenolate (BAlq); and ETL, an electron-transporting layer of zinc(II)bis(2-2-hydroxyphenyl)benzothiazole. We found that all complexes are suitable candidates for fabrication of WOLED. The best results were demonstrated by the device doped with 2 wt % of (bt)2Ir(bsm), which had twice as high luminescence (1100 cd/m2) and one-and-a-half as high current efficiency (5 cd/A) as the device doped with 1.25 wt % of the known (bt)2Ir(acac), with its 580 cd/m2 and 3.4 cd/A at approximately the same CIE (Commission Internationale de L’Eclairage) (x/y) coordinates of the warm white light emitted by the two devices.

Design of highly efficient RGB top-emitting organic light-emitting diodes using finite element method simulations.

In this paper, we present finite element method simulations of top-emitting organic light-emitting diodes for designing optimized red, green, and blue full-color device structures. The OLED structures in the simulation are used to evaluate the device parameters, such as the outcoupling efficiency, electroluminescence spectra, and angular emission characteristics on organic layers with varying thickness and different cathodes. The numerical study also extracts these parameters for nano-structured devices. By observing the agreement between the simulated and measured data precisely, our simulations show capability of predicting the fabricated device results.

Force-field parameters for beryllium complexes in amorphous layers.

Unknown force-field parameters for metal organic beryllium complexes used in emitting and electron transporting layers of OLED structures are determined. These parameters can be used for the predictive atomistic simulations of the structure and properties of amorphous organic layers containing beryllium complexes. The parameters are found for the AMBER force field using a relaxed scan procedure and quantum-mechanical DFT calculations of potential energy curves for specific internal (angular) coordinates in a series of three Be complexes (Bebq2; Be(4-mpp)2; Bepp2). The obtained parameters are verified in calculations of some molecular and crystal structures available from either quantum-mechanical DFT calculations or experimental data. Graphical Abstract Beryllium complexes in amorphous layersᅟ.

An Organic Device with Thin Film Transistor Merged with Light Emitting Diode through Use of an Accumulation Layer in TFT As an Electrode

A light-emitting device structure is proposed which includes an organic thin-film structure merged with an organic light-emitting diode structure by utilizing a part of the electron accumulation layer in the organic thin-film transistor as a common electrode for each structure. The organic thin-film structure and the organic light-emitting diode structure each include an organic semiconductor material in which hole mobility is greater in bulk region of the material than electron mobility in the bulk region but less in the channel region. The advantages of such a light-emitting device include less complex processing and a simpler pixel circuit structure in comparison to separately fabricating OTFT and OLED structures and subsequently interconnecting them to form a pixel. Furthermore, relative to a light-emitting transistor, the proposed structure offers the advantage of a broader light emission area which is more suitable for use in display devices.

70.1: Touch‐Interactive High Power Efficiency AMOLED Display with Energy Recycling and Self‐Calibration Capabilities

AbstractA polarizer‐less OLED is introduced with 30% improvement in efficiency. Also, the new OLED structure provides integrated multi‐touch, power recycling/generating, and non‐uniformity /aging self‐calibration capabilities.

Electroluminescent nanocomposites based on molecular crystals for polymer optoelectronics. Part 1

Experimental data on electroluminescence of new light emitting materials, semiconducting organic polymers doped with nanosized J-aggregates of cyanine dyes, are described. OLED structures are considered. New light-emitting diode structures are developed. Polyaniline electroluminescence band is observed. High-resolution atomic force microscopy (AFM) is used to study J-aggregate structures. The AFM procedure is improved to increase accuracy in determination of J-aggregate dimensions. Certain supramolecular species are long ribbons with high flexibility.

Electroluminescent nanocomposites based on molecular crystals for polymer optoelectronics. Part 2

Experimental data on electroluminescence of new light emitting materials, semiconducting organic polymers doped with nanosized J-aggregates of cyanine dyes, are described. OLED structures are considered. New light-emitting diode structures are developed. Polyaniline electroluminescence band is observed. High-resolution atomic force microscopy (AFM) is used to study J-aggregate structures. The AFM procedure is improved to increase accuracy in determination of J-aggregate dimensions. Certain supramolecular species are long ribbons with high flexibility.

Transient electroluminescence spikes in small molecular organic light-emitting diodes

We present a comprehensive study of transient nanosecond electroluminescence (EL) spikes that exceed the dc level and microseconds-long EL tails following a bias pulse in guest-host small molecular organic light-emitting diodes (SMOLEDs), including relatively efficient devices, which elucidates carrier and exciton dynamics in such devices. The transient EL is strongly dependent, among other parameters, on device materials and structure. At low temperatures, all measured devices, with the exception of Pt octaethylporphyrin (PtOEP)-doped tris(8-hydroxyquinoline) Al (Alq${}_{3}$) SMOLEDs, exhibit the spikes at \ensuremath{\sim}70--300 ns. At room temperature (RT), however, only those with a hole injection barrier, carrier-trapping guest-host emitting layer, and no strong electron-transporting and hole-blocking layer [such as 4,7-diphenyl-1,10-phenanthroline (BPhen)] exhibit strong spikes. These narrow and appear earlier under postpulse reverse bias. To further elucidate the origin of the spikes, we monitored their dependence on the pulsed bias width and voltage, the doped layer thickness, and its location within the OLED structure. The characteristics of the microseconds-long tails were also evaluated through the effect of the postpulse voltage. A model based on the recombination of correlated charge pairs (CCPs) and on charge detrapping is presented; the model agrees well with the experimental data. The results suggest that reduced electric-field-induced dissociative quenching of singlet excitons is responsible for the spikes' amplitude exceeding the on-pulse dc EL level. The long tails are attributed to recombination of charges detrapped from a distribution of shallow, mostly host, sites, reminiscent of the detrapping and recombination processes that yield the thermally stimulated luminescence of such materials. The comprehensive transient EL measurements in guest-host devices demonstrate the generality of the strong spike phenomenon in devices with charge trapping in the emitting guest molecules. Hence the transient EL can serve as an important tool to identify the dominant emitting mechanisms in the guest-host systems.

66.2: Efficiency Enhancement in White PIN OLEDs by Simple Internal Outcoupling Methods

AbstractHighly efficient white PIN OLED structures based on internal outcoupling approaches using vacuum processable materials have been developed. In combination with external MLA outcoupling films an efficiency enhancement of 1.8 can be achieved resulting in a power efficiency of 50 lm/W at color coordinates x,y = 0.46/0.41 for a tandem OLED using fluorescent blue and phosphorescent green and red emitter systems. In a single unit 2‐color fluorescent white system with the same combination of internal and external outcoupling methods an efficiency of 37 lm/W at a color x,y = 0.48/0.42 is reached. This is to our knowledge the highest power efficiency reported for a fluorescent white OLED with a flat light extraction method. A similar approach using a vacuum processable scattering material in top emission OLED architectures on metal substrates allows to reach efficiencies of 36.5 lm/W with a CRI of 75 at a color x,y = 0.45/0.41.