OLED Materials Research Articles

Optical spectrum of OLED materials by time-dependent density functional theory

Optical spectrum of OLED materials by time-dependent density functional theory

Cellulose-Templated Stable Foldable Oriented Films with Polarized RGB Luminescence

Solution processing in a vacuum-free system is highly advantageous because printing, coating, and roll-to-roll processes can be used for large-area and scalable manufacturing. However, producing a flat surface with high orientation is challenging. In addition, high folding stability is essential for building a basis for foldable devices. Herein, we present a valuable method to obtain oriented films of π-conjugated polymers, which we describe as a “Simple way of Orienting Films prepared by Templating cellulose,” abbreviated as SOFT. In this method, a glass or flexible substrate was uniaxially coated by a single-sweep process using a wet cloth containing a cellulose solution. A conjugated polymer solution, an OLED material, was deposited onto the cellulose film by spin coating, followed by thermal annealing. A uniaxially oriented film was obtained with orientation factors up to 0.9, and its polarized fluorescence was verified for red/green/blue colors. The oriented films were stable at various positions and showed no degradation of orientation factors after folding 100–500 times at a folding angle of 320°. The homogeneous area and surface roughness of the films were approximately 2 × 3 cm2 and 50 nm, respectively, with an orientation reproducibility of ∼96%. A high tensile strength of 30 MPa was measured on the oriented films. The orientation mechanism was attributed to the alignment of the backbone structure of the conjugated polymers along the surface anisotropy of a uniaxially coated cellulose film.

Solution-processable organic light-emitting diodes utilizing electroluminescent perylene tetraester-based columnar liquid crystals.

Herein, we reveal a homologous series of liquid crystals involving perylene tetraesters as the core connected to the four trialkoxyphenyl units at the periphery using the triazole moiety as the linker. A thorough analysis using differential scanning calorimetry, polarized optical microscopy, and small- and wide-angle X-ray scattering studies confirm that all the mesogens 1a-c hold a stable enantiotropic columnar mesophase. Suitable molecular orbital levels and excellent material photophysical and thermal properties encouraged the study of their electroluminescent properties. Due to this, a well designed solution-processable organic light emitting diode device structure is configured as ITO (125 nm)/poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) (35 nm)/host: x wt% emitter (x = 0.5, 1.0, 3.0, 5.0) (20 nm)/2,2'2''-(1,3,5-benzinetriyl)tris(1-phenyl-1-H-benzimidazole) (TPBi) (40 nm)/lithium fluoride (LiF) (1 nm)/aluminium (Al) (200 nm) using compounds 1a-c as emitters. 4,4',4''-Tris[phenyl(m-tolyl)amino]triphenylamine (m-MTDATA) and 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) were chosen as two different host materials. The current density-voltage-luminance and current efficacy-luminance-power efficacy plots suggest that m-MTDATA is a better host than CBP. Amongst, device based on 1 wt% emitter 1c doped in the m-MTDATA host matrix displayed the best performance, with a maximum power efficacy of 17.2 lm W-1, current efficacy of 18.5 cd A-1, and external quantum efficiency of 6.3%.

Understanding excited state properties of host materials in OLEDs: simulation of absorption spectrum of amorphous 4,4-bis(carbazol-9-yl)-2,2-biphenyl (CBP).

4,4-Bis(carbazol-9-yl)-2,2-biphenyl (CBP) is widely used as a host material in phosphorescent organic light-emitting diodes (PhOLEDs). In the present study, we simulate the absorption spectra of CBP in gas and condensed phases, respectively, using the efficient time-dependent long-range corrected tight-binding density functional theory (TD-LC-DFTB). The accuracy of the condensed-phase absorption spectra computed using the structures obtained from classical molecular dynamics (MD) and quantum mechanical/molecular mechanical (QM/MM) simulations is examined by comparison with the experimental absorption spectrum. It is found that the TD-LC-DFTB gas-phase spectrum is in good agreement with the GW-BSE spectrum, indicating TD-LC-DFTB is an accurate and robust method in calculating the excitation energies of CBP. For the condensed-phase spectrum, we find that the electrostatic embedding has a minor influence on the excitation energy. Computing accurate absorption spectra is a particular challenge since static and dynamic disorders have to be taken into account. The static disorder results from the molecular packing in the material, which leads to molecule deformations. Since these structural changes sensitively impact the excitation energies of the individual molecules, a proper representation of this static disorder indicates that a reasonable structural model of the material has been generated. The good agreement between computed and experimental absorption spectra is therefore an indicator for the structural model developed. Concerning dynamic disorder, we find that molecular changes occur on long timescales in the ns-regime, which requires the use of fast computation approaches to reach convergence. The structural models derived in this work are the basis for future studies of charge and exciton transfer in CBP and related materials, also concerning the degradation mechanisms of CBP-based PhOLEDs.

Latest Development of Soluble OLED Materials and its Application to Mid- to Large-sized Panel Production.

Latest Development of Soluble OLED Materials and its Application to Mid- to Large-sized Panel Production.

2,7-Carbazole Derived Organoboron Compounds: Synthesis and Molecular Fluorescence.

Triarylboranes have drawn much attention in OLEDs owing to their remarkable solid-state luminescence properties. Here two new A-D-A type compounds, 2,7-bis(dimesitylboryl)-N-ethyl-carbazole (BCz) using triarylborane as electron acceptor and carbazole as electron donor while 2,7-bis((4-(dimesitylboryl)phenyl)ethynyl)-9-ethyl-carbazole (BPACz) using phenylacetylene as extra conjugated bridge, have been synthesized and their photoluminescence related properties in various states have been investigated both experimentally and theoretically. Both compounds show blue emission with high quantum yields, being potential candidates for blue OLED materials.

Role of Dysprosium in In2-xDyxO3 to Enhance White Light Emission in OLED

Background: OLED material is always having much science to explore in them. The role of rare earth Dy as a dopant material in well studied In2O3 is studied. Objective: The candidature of the white light emission from the Organic light emitting diode is explored in the present work. Methods: The doping concentration effect and the corresponding emission is shown in the present work. It is emphasized that the doping at nearly x = 1 mol% of dysprosium could alter the transition states and the output of the emission is pure white which is corresponds to the luminescence peaks. Color purity and co-related color temperature was calculated by CIE technique. Results: The spectroscopic parameters are calculated by Judd-Oflet approaches which is suitable for RE3+ (RE= rare earth) ions. Conclusion: The present prepared phosphor is suitable for white light emission and used in display devices applications.

24.5: High‐Performance Electron‐Blocking Layer Materials for OLED

This paper reports our recent R&D efforts in developing electron‐blocking layer (EBL) materials for OLEDs. Materials of superior performance were developed by judicial selection of building blocks and substituents, in conjunction with careful optimization of energy levels.

The structural studies of 2-[(4-tert-butylphenyl)-5–(4-biphenyl)]-1, 3, 4- oxadiazole (PBD) incorporated γ ray irradiated chitosan films for optoelectronic applications

Herein, versatile biopolymer chitosan films doped with 2-[(4-‑tert-butylphenyl)-5–(4-biphenyl)]-1, 3, 4- oxadiazole (PBD) a known OLED material were prepared by intercalation method. These films witnessed crosslinking which in turn exhibited exciting properties due to gamma irradiation with varied dosages. The radical mediated crosslinking of NH2 group with t‑butyl group was envisaged by the increased crystallinity of the films. The XPS analysis showed the formation of the bond between dopant and polymer backbone. The changes in binding energies of unirradiated and irradiated CHPBD films for N1s from 399.08 eV (1° amine) to 400.7 eV (2°amine), supported reaction of NH2 group with t‑butyl group of PBD in crosslinking of dopant and polymer matrix with the formation of CN linkage. In PXRD, peaks centered around 21.24° for pristine chitosan film, but for the unirradiated CHPBD, it was shifted to the lower angle16.09° to form amorphous film. However, for the irradiated CHPBD shifting to the higher angle 22.9°, 23.08°, 27.23° suggesting that dopant had chemically interacted with the polymer matrix. The Young's modulus, tensile strength indicated supportive properties. An interesting change in UV absorption behavior was observed for the unirradiated CHPBD exhibiting λmax at 290 nm with a hypsochromic shift with respected to dopant (λmax,309 nm). This indicated weak head-to-head alignment of dyes in an unirradiated matrix; whereas irradiation brought about changes through chemical crosslinking in the architecture of films with a redshift to 309 nm. Hyperchromism was also the effect of irradiation on films. The unirradiated films exhibited emission maxima around 369 nm whereas irradiated films showed 412 nm. Hence, a simple method was developed for the preparation of blue emissive biopolymeric materials.

Synthesis of 1H‐Pyrazolo[3,4‐b]quinoxaline Derivatives by Modification of the Regiospecific Reaction – the Influence of the Microwave Field

AbstractThe microwave‐assisted reductive cyclization reaction with the use of triphenylphosphine as a reducing agent in the synthesis of 1H‐pyrazolo[3,4‐b]quinoxaline derivatives was investigated. Contrary to the conventional method of conducting the reaction, the process in the reactor takes 25 minutes with moderate yields (30–38 %). This procedure was used to obtain three new 1,3‐dimethyl‐1H‐pyrazolo[3,4‐b]quinoxaline derivatives with substituents at position 6 of different donor‐acceptor character, which were used to determine the basic photophysical properties (UV‐Vis absorption spectra, fluorescence emission spectra) and the quantum yields of fluorescence were appointed. The measurement results indicate the possible use of new compounds as materials for OLEDs. The conducted research brings new knowledge in the field of 1H‐pyrazolo[3,4‐b]quinoxaline derivative systems and provides an alternative to conventional synthesis of pyrazoloquinoxalines.

P‐116: TADF OLED Emission Zone and Stability Analysis with Water Exposure to Different Layers During Deposition

Reliable devices are essential for the commercialization of OLED technology. OLED materials are notorious for their sensitivity to various substances such as water. For thermally activated delayed emission (TADF) OLEDs, which layers are most water‐sensitive is unknown. Work towards understanding how water affects OLED performance is shown. Surprisingly, it is shown that the water effect on the emission layer is negligible compared to other layers in this stack. The emission zone is measured for fresh and degraded OLEDs deposited under different water partial pressures. Using a novel highly sensitive measurement method, a shift to the anode side was observed.

PPG and Universal Display to add OLED materials plant in Ireland

PPG and Universal Display to add OLED materials plant in Ireland

Improvements of Organic Light‐Emitting Diodes Using Graphene as an Emerging and Efficient Transparent Conducting Electrode Material

AbstractOrganic light emitting diodes (OLEDs) have received wide attention and progress in impacting the electronics market. The progress of OLEDs in the market over their inorganic counterpart is principally due to their cost savings, flexibility, and excellent performance. As a result of the rising demands for next‐generation electronic devices with increased efficiency, high flexibility, reduced cost, and stretchability, there is a need for improvements of OLEDs. In order to fulfill these requirements, it is necessity to replace the transparent conductive electrode (TCE) with a better alternative. The conventionally used TCE, indium tin oxide (ITO), suffers from the scarcity of indium, increased cost, instability, and brittleness. Graphene is recognized as a suitable alternative to ITO because of its excellent properties including high optical transmittance, outstanding electrical conductivity, stability, and great mechanical flexibility. However, the performance of graphene as the TCE material in OLEDs is limited. Several efforts have been made to improve graphene's performance through electrode modifications. This review covers a summary of fabrication techniques for graphene‐based TCEs and their improvements. Finally, the application and performance of graphene‐based TCEs in OLED devices and the performance of such OLEDs are discussed.

P‐13.9: Developing High‐Performance OLED Materials with Diverse Properties for Various Display Makers

Our efforts in developing novelhigh‐performance ETL and R prime materials are presented. These new materials are tailor‐designed for our customers to improve the performance of their AMOLED display products.

P‐226: Late‐News‐Poster: Degradation and Impurity Analysis of Organic Materials for OLED Application by Laser Desorption/Ionization Time of Flight‐Mass Spectrometry

We demonstrate the performance of the degradation analysis of N,N″‐Di(1‐naphthyl)‐N,N″‐diphenyl‐(1,1″‐biphenyl)‐4,4″‐diamine (NPB) by laser desorption/ionization time of flight mass spectrometry (LDI‐TOF MS), which is a rapid and accurate technique for material identification. The difference of normal and degraded areas of NPB was clearly shown in mass spectra. Degraded areas were visualized by using LDI‐TOF MS imaging with high spatial resolution of 5 μm. Positive and negative mass spectra of 9,10‐Di(1‐naphthyl)anthracene (α‐ADN) with 98%(HPLC) purity were obtained to determine impurities in OLED materials. The bromine ion that generated impurities during the synthetic process was detected in the negative spectrum of α‐ADN. This technique provides a convenient method to validate the performance and stability of OLED device.

High Triplet Energy Host Materials for Blue TADF OLEDs-A Tool Box Approach.

The synthesis of stable blue TADF emitters and the corresponding matrix materials is one of the biggest challenges in the development of novel OLED materials. We present six bipolar host materials based on triazine as an acceptor and two types of donors, namely, carbazole, and acridine. Using a tool box approach, the chemical structure of the materials is changed in a systematic way. Both the carbazole and acridine donor are connected to the triazine acceptor via a para- or a meta-linked phenyl ring or are linked directly to each other. The photophysics of the materials has been investigated in detail by absorption-, fluorescence-, and phosphorescence spectroscopy in solution. In addition, a number of DFT calculations have been made which result in a deeper understanding of the photophysics. The presence of a phenyl bridge between donor and acceptor cores leads to a considerable decrease of the triplet energy due to extension of the overlap electron and hole orbitals over the triazine-phenyl core of the molecule. This decrease is more pronounced for the para-phenylene than for the meta-phenylene linker. Only direct connection of the donor group to the triazine core provides a high energy of the triplet state of 2.97 eV for the carbazole derivative CTRZ and 3.07 eV for the acridine ATRZ. This is a major requirement for the use of the materials as a host for blue TADF emitters.

Transition-Metal-Free Synthesis of Heterobiaryls through 1,2-Migration of Boronate Complex.

The synthesis of a diverse range of heterobiaryls has been achieved by a transition-metal-free sp2 -sp2 cross-coupling strategy using lithiated heterocycle, aryl or heteroaryl boronic ester and an electrophilic halogen source. The construction of heterobiaryls was carried out through electrophilic activation of the aryl-heteroaryl boronate complex, which triggered 1,2-migration from boron to the carbon atom. Subsequent oxidation of the intermediate boronic ester afforded heterobiaryls in good yield. A comprehensive 11 B NMR study has been conducted to support the mechanism. The cross coupling between two nucleophilic cross coupling partners without transition metals reveals a reliable manifold to procure heterobiaryls in good yields. Various heterocycles like furan, thiophene, benzofuran, benzothiophene, and indole are well tolerated. Finally, we have successfully demonstrated the gram scale synthesis of the intermediates for an anticancer drug and OLED material using our methodology.

Synthesis and Characterization of High-Efficiency Red Phosphorescent Iridium(III) Complexes with 1-(4-(Trifluoromethyl)phenyl)isoquinoline Ligand

Two new tfmpiq-based bis-cyclometalated iridium(III) complexes, [(tfmpiq)2Ir(imdzppo)] (2a) and [(tfmpiq)2Ir(idzpo)] (2b) (where tfmpiq = 1-(4-(trifluoromethyl)phenyl)isoquinoline, imdzppo = 2-(imidazo[1,2-a]pyridin-2-yl)phenol, idzpo = 2-(2H-indazol-2-yl)phenol), have been synthesized and fully characterized. The single crystal structure of 2b has been determined. The relationship between the structures and photophysical properties of both complexes are considered, and the DFT calculations have been used to further support the deduction. These Ir(III) complexes emit red light with quantum yields of 39.9-51.9% in degassed CH2Cl2 solution at room temperature. Also, their emission originates from a hybrid 3MLCT/3LLCT/3LC excited state. All these results show that iridium(III) complexes 2a-2b are suitable for red-phosphorescent materials in OLEDs.

New pyrene-based butterfly-shaped blue AIEgens: Synthesis, structure, aggregation-induced emission and their nondoped blue OLEDs

Developing the blue emitters with excellent electroluminescence (EL) performance is crucial for full-color displays and solid-state lighting. Based on the synthetic strategy for exploring highly efficient luminescent solids by constructing aggregation-induced emission (AIE) systems, two new pyrene-based butterfly-shaped blue AIEgens, Py(5,9)BTPE and Py(5,9)BTriPE, have been successfully designed and synthesized by integrating two tetraphenylethylene (TPE) or triphenylethylene (TriPE) groups into pyrene ring. The adoption of the pyrene unit with a large optical bandgap, the use of the TPE or TriPE group with AIE characteristic, the integration of the TPE or TriPE group into pyrene ring at 5,9-positions, and the highly twisted molecular conformations of present AIE systems endow the two compounds with bright blue emission in the solid state. These foregoing features ensure that the new pyrene-based compounds can serve as excellent blue-emitting materials in OLEDs. A non-doped OLED based on Py(5,9)BTPE exhibited a sky-blue emission (Von: 3.2 V) with a CIE coordinates of (0.19, 0.28), a maximum external quantum efficiency (EQEmax) of 3.35%, a current efficiency (CE) of 6.51 cd A−1 with a low efficiency roll-off that represents one of the highest value reported for sky-blue AIE-based OLEDs. An analogous device with Py(5,9)BTriPE as an emitting layer displayed a pure-blue emission (CIE: 0.16, 0.17) with a moderate EQEmax of 1.27% and a CE of 1.63 cd A−1 with a low efficiency roll-off. Furthermore, the EL emissions of the two devices display almost no change with the increasing of the current density, indicating their good color stability.

10.2: Invited Paper: Quantum Dots as a new generation of emitting materials in OLEDs

Colloidal quantum dots (QDs)‐based light‐emitting diodes (QD‐LEDs) has been actively researched due to the potential impacts to the display and lighting industry base on the unique properties of QDs itself such as size‐dependent bandgap tuneability, narrow emission spectrum, and low‐cost solution‐based processing. However, the most of promising results in the past used cadmium (Cd) contained II‐VI semiconductor nanocrystals. Therefore, a considerable future task is to substitute Cd‐containing QDs with less toxic materials. InP‐based QDs is a promising material among the III‐V semiconductor nanocrystals and it has been already applied in conventional and inverted QD‐LED structure.