Yellow Organic Light-emitting Diodes Research Articles

Design and Synthesis of a Y-Type Thioxanthone-Carbazole for the Application in Blue and Yellow Organic Light-Emitting Diodes

Design and Synthesis of a Y-Type Thioxanthone-Carbazole for the Application in Blue and Yellow Organic Light-Emitting Diodes

An electroluminescence efficiency of 30.3% for a yellow thermally activated delayed fluorescence emitter with a high horizontal emitting dipole ratio

The synthesized 3,6,11-triTPA-BPQ yellow dopant exhibits a high horizontal emitting dipole ratio of 92%, leading to a high-performance yellow organic light-emitting diode with an external quantum efficiency of 30.3%.

Observation of Reverse Intersystem‐Crossing From the Upper‐Level Triplet to Lowest Singlet Excitons (T2→S1) in Tetra(t‐butyl)rubrene‐Based OLEDs for Enhanced Light‐Emission

AbstractHigh external quantum efficiency (EQE) up to 25% has recently been reported from tetra(t‐butyl)rubrene (TBRb)‐based organic light‐emitting diodes (OLEDs), but its physical origin is still vague. Herein, using the featured responses of the evolution processes of electron‐hole pairs to an external magnetic field, an unreported high‐level reverse intersystem‐crossing (HL‐RISC) from upper‐level triplet to lowest singlet excitons (T2→S1) is observed when T2 is well confined in the active layer of pure TBRb. This HL‐RISC channel becomes stronger with lowering operational temperatures because it is not an endothermic process. Due to the larger separation distance of TBRb molecules with four tert‐butyl groups, the intersystem‐crossing (ISC) process of polaron pairs is stronger than the singlet fission (SF) process existing in pure TBRb, which is markedly different from the behaviors of excited states in pure rubrene (Rb) with negligible ISC and strong SF. More importantly, HL‐RISC is stronger in TBRb than in Rb‐doped systems, which is consistent with the higher EQE frequently reported from TBRb‐doped OLEDs. Thus, this work deepens the physical understanding of microscopic processes in typical organic multi‐functional semiconductors of TBRb or Rb and paves the way for fabricating further high‐efficiency yellow OLEDs.

Rational molecular design of TADF emitters towards highly efficient yellow electroluminescence with a nearly 30% external quantum efficiency and low roll-off

A boron-based thermally activated delayed fluorescence emitter was developed for highly efficient yellow organic light-emitting diodes by employing a strong donor with large steric hindrance.

Highly efficient yellow organic light-emitting diodes with slow efficiency roll-off by mixing red and green emissions

In this work, we report the design and optimization of yellow organic light-emitting diodes (OLEDs) with tris [2-(p-tolyl)pyridine]iridium (III) (Ir (mppy)3) doped 4,4′,4′-tris(N-carbazolyl)triphenylamine (TCTA) and bis(2-phenylquinoline) (2,2,6,6-tetramethylheptane-3,5-dionate)iridium (III) (PQ2Ir (dpm)) doped 2,6-bis(3-(9H-carbazol-9-yl)phenyl)phyridine (26DCzPPy) films as green and red light-emitting layers (EMLs). Experimental results demonstrated that the designed double EMLs system is beneficial in carriers' distribution, exciton confinement and reducing triplet exciton quenching because of the matched energy levels and triplet energies of hosts and dopants. Finally, the optimal device showed a very maximal current efficiency of 65.51 cd/A, slow roll-off of efficiency with a very high current efficiency of 63.54 cd/A at 5000 cd/m2, and excellent yellow emission with CIE coordinates of (0.468, 0.493) at 10 mA/cm2.

New structure host material for phosphorescent OLED devices

New carbazole and quinoxaline based low molar mass bipolar derivative was synthesized, characterized, and tested as host derivative in phosphorescent organic light emitting diodes (OLEDs). The material could form homogeneous amorphous materials (layers) with very high glass transition temperature of 136 °C and also with very high initial thermal decomposition temperature of about 387 °C. The electron photoemission spectra of the layers of the synthesized compound showed ionization potentials of about 5.85 eV. The compound was tested as host material for green Ir(ppy)3 , blue FIrpic, and yellow PO-01 triplet phosphorescent guests. The device with the yellow PO-01 triplet emitter exhibited the best overall performance. The most efficient yellow OLED demonstrated turn-on voltage of 4.9 V, a maximum brightness exceeding 4050 cd/m2 and current efficiency of 10.8 cd/A with power efficiency of 6.9 lm/W at 100 cd/m2.

Fabrication and characterization of an organic light-emitting diode based on Langmuir–Blodgett films using oligo(phenylenevinylene) derivatives

We present the characterization of oligo(phenylenevinylene) derivatives which contain dendrons of first to third generations with terminal chains of C12H25 and C3H7, then, Langmuir–Blodgett and spin coating films of this compounds were used to make an OLED. To make the films, some previous studies were performed such as the isotherms, the Brewster Angle Microscopy and hysteresis to find which compound forms the most suitable monolayer at the water–air interface so that it can be transferred to an ITO-glass substrate through the Langmuir–Blodgett (LB) technique. Until 30 LB films were transferred to ITO and, then, a metallic electrode was deposited over the film to apply a voltage between ITO and this metallic electrode. As a result, a green–yellow organic light-emitting diode was obtained and it was characterized through UV–Vis spectroscopy, photoluminescence, electroluminescence, lifetime and we compared its performance with other OLED fabricated through the spin coating technique. We concluded that the LB OLED has a lower driving voltage and its lifetime is almost the same for both. In addition, we have calculated through density functional theory the band gaps for the six compounds presented here and we observed that all the six dendrons have band gaps of approximately 2 eV.

Highly efficient thermally activated delayed fluorescence yellow organic light-emitting diodes with a low efficiency roll-off

Highly efficient TADF yellow OLEDs with an extremely low efficiency roll-off have been obtained herein via rational device engineering.

Incorporating Thermally Activated Delayed Fluorescence into Mechanochromic Luminescent Emitters: High‐Performance Solution‐Processed Yellow Organic Light Emitting Diodes

AbstractMultifunctional materials with stimuli‐responsive features are demonstrated to be promising smart materials. In this work, three multifunctional materials, namely 5TzPmPXZ, 7TzPmPXZ, and 5,7TzPmPXZ, are constructed by integrating phenoxazine with electron‐acceptor core [1,2,4]triazolo[1,5‐a]pyrimidine (TzPm). Intriguingly, these materials exhibit not only thermally activated delayed fluorescence but also multicolor luminescence switching which is caused by the phase transitions between microcrystalline and amorphous states upon external stimuli. Moreover, the solution‐processed organic light emitting diodes (OLEDs) fabricated with these materials furnish a high external quantum efficiency up to 14.3% and the Commission Internationale de l'Eclairage coordinates of (0.43, 0.53), which represents the state‐of‐the‐art performance for solution‐processed yellow OLEDs.

Efficient Blue and Yellow Organic Light-Emitting Diodes Enabled by Aggregation-Induced Emission.

A new class of donor-bridge-acceptor (D-π-A) π-conjugated light-emitting molecules comprising carbazole as donor and maleimide (Cbz-MI, Cbz-MI(d)), phthalimide (Cbz-Pth) as acceptor units with phenyl ring as spacer have been synthesized in good yields. These compounds exhibit high quantum yield with three distinct emission colors yellowish-green (Cbz-MI), bright yellow Cbz-MI(d), and sky blue (Cbz-Pth) in the solid state. Single-crystal X-ray and quantum chemical calculations reveals that twisting of the phenyl rings with high torsional angle on maleimide and phthalimide units reduce the effective inter-chromophore electronic coupling, furnish dramatic changes in their photophysical properties in solution and solid states. Intriguingly, Cbz-MI(d) and Cbz-Pth exhibits a unique aggregation-induced blue-shifted emission (AIBSE) due to restricted intramolecular rotation (RIR) process, while Cbz-MI shows red-shifted emission in the solid state. The solvatochromic study reveal that combined RIR and excited state migration augment AIE (aggregation-induced emission) properties. The electrochemical properties reveal that Cbz-MI exhibits high oxidation propensity while Cbz-Pth shows low reduction values. Subsequently, organic light-emitting diodes (OLEDs) were fabricated with a simple three-layer device containing Cbz-Pth and Cbz-MI(d) as emitting layers. Cbz-MI(d) exhibits high performance yellow OLED with an external quantum efficiency exceeding ∼4.1% and a brightness exceeding ∼73915 cd/m2, which is among the best performance reported for bright yellow fluorescence organic light-emitting diodes.

Multiple–color AIE coumarin–based Schiff bases and potential application in yellow OLEDs

Three new coumarin–based derivatives with similar molecular structure were synthesized through a simple Schiff base reaction and their fluorescent properties were investigated in detail. Among of the compounds showed aggregation–induced emission (AIE) characteristics and high quantum efficiency (ΦF), of which compound 1 powder showed the strongest emission peak 570nm (ΦF = 25.3%), compound 2 solid exhibited 610nm fluorescence emission peak (ΦF = 3.3%), while the maximum emission wavelength of compound 3 powder red–shift to 640nm (ΦF = 16.8%). Meanwhile, compounds 1–3 showed long fluorescence lifetimes with respective 8.86μs, 8.97μs and 8.51μs. The appearance of fluorescence properties can be attributed to efficient the excited state intramolecular proton transfer (ESIPT) and the twisted intramolecular charge transfer (TICT). Furthermore, due to the good luminescent properties, high stabilities and the large Stokes–shifts, the three compounds were ideal candidates for promising applications in organic lightemitting diodes (OLEDs).

High efficiency yellow organic light-emitting diodes with a solution-process feasible iridium based emitter

Yellow emission plays an important role in many display and lighting applications, such as RGBY display or blue hazard free lighting sources, while a wet-process enables soft devices to be manufactured cost-effectively.

AZO/Ag/AZO anode for resonant cavity red, blue, and yellow organic light emitting diodes

Indium tin oxide (ITO) is the transparent electrode of choice for organic light-emitting diodes (OLEDs). Replacing ITO for cost and performance reasons is a major drive across optoelectronics. In this work, we show that changing the transparent electrode on red, blue, and yellow OLEDs from ITO to a multilayer buffered aluminium zinc oxide/silver/aluminium zinc oxide (AZO/Ag/AZO) substantially enhances total output intensity, with better control of colour, its constancy, and intensity over the full exit hemisphere. The thin Ag containing layer induces a resonant cavity optical response of the complete device. This is tuned to the emission spectra of the emissive material while minimizing internally trapped light. A complete set of spectral intensity data is presented across the full exit hemisphere for each electrode type and each OLED colour. Emission zone modelling of output spectra at a wide range of exit angles to the normal was in excellent agreement with the experimental data and hence could, in principle, be used to check and adjust production settings. These multilayer transparent electrodes show significant potential for both eliminating indium from OLEDs and spectrally shaping the emission.

Indenocarbazole based bipolar host materials for highly efficient yellow phosphorescent organic light emitting diodes

We report bipolar host materials with robust indenocarbazole and biphenyl moiety as hole-electron-transporting unit for phosphorescent yellow organic light-emitting diodes (OLEDs). New host materials demonstrated an excellent morphological stability with high glass transition temperature of 207 °C. Simultaneously, it also revealed appropriate triplet energy of about 2.6 eV for ideal triplet energy transfer to yellow phosphorescent dopant. A phosphorescent yellow OLED with new host ICBP1 (and ICBP2) and conventional yellow dopant iridium(III)bis(4-(4-t-butylphenyl)thieno[3,2-c]pyridinato-N,C2′)acetylacetonate (Ir(tptpy)2acac) shows a low driving voltage of 3.4 (and 3.6 V) at 1000 cd/m2, and maximum external quantum efficiency as high as 26.4%. Such efficient performance of phosphorescent yellow OLEDs is attributed to a good charge balance and high electron transport properties of host materials.

Highly efficient yellow organic light-emitting diodes based on a hole-dominant host layer co-doped with yellow emitting and electron transporting guests

We fabricated high efficiency yellow-color organic light-emitting diodes (OLEDs) by co-doping 2,8-di(t-butyl)-5,11-di[4-(t-butyl)phenyl]-6,12-diphenylnaphthacene (TBRb) and tris(8-hydroxyquinolinato)aluminum (Alq3) guests in a N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) host. Co-doping of electron-transporting Alq3 with yellow dopant TBRb in hole-dominant NPB layers resulted in substantial luminance-yield improvement compared to TBRb-only counterparts without color contamination from Alq3 green emission. The luminance yield of 11.4 cd/A, corresponding to the co-doping of 8% TBRb and 2% Alq3, is larger than previously reported luminance-yield values of conventional TBRb-based yellow OLEDs. Another advantage of the TBRb-Alq3 co-doped OLEDs is an insignificant roll-off of efficiency at high current-density and/or brightness levels.

An ideal host-guest system to accomplish high-performance greenish yellow and hybrid white organic light-emitting diodes

Greenish yellow organic light-emitting diodes (GYOLEDs) have steadily attracted researcher's attention since they are important to our life. However, their performance significantly lags behind compared with the three primary colors based OLEDs. Herein, for the first time, an ideal host-guest system has been demonstrated to accomplish high-performance phosphorescent GYOLEDs, where the guest concentration is as low as 2%. The GYOLED exhibits a forward-viewing power efficiency of 57.0 lm/W at 1000 cd/m2, which is the highest among GYOLEDs. Besides, extremely low efficiency roll-off and voltages are achieved. The origin of the high performance is unveiled and it is found that the combined mechanisms of host-guest energy transfer and direct exciton formation on the guest are effective to furnish the greenish yellow emission. Then, by dint of this ideal host-guest system, a simplified but high-performance hybrid white OLED (WOLED) has been developed. The WOLED can exhibit an ultrahigh color rendering index (CRI) of 92, a maximum total efficiency of 27.5 lm/W and a low turn-on voltage of 2.5 V (1 cd/m2), unlocking a novel avenue to simultaneously achieve simplified structure, ultrahigh CRI (>90), high efficiency and low voltage.

High efficiency yellow organic light-emitting diodes with optimized barrier layers

High efficiency Iridium (III) bis (4-phenylthieno [3,2-c] pyridinato-N,C2′) acetylacetonate (PO-01) based yellow organic light-emitting devices are fabricated by employing multiple emission layers. The efficiency of the device using 4,4′,4″-tris(N-carbazolyl) triphenylamine (TCTA) as potential barrier layer (PBL) outperforms those devices based on other PBLs and detailed analysis is carried out to reveal the mechanisms. A forward-viewing current efficiency (CE) of 65.21cd/A, which corresponds to a maximum total CE of 110.85cd/A is achieved at 335.8cd/m2 in the optimized device without any outcoupling enhancement structures.

High efficiency yellow fluorescent organic light emitting diodes based on m-MTDATA/BPhen exciplex

High efficient yellow organic light emitting diodes (OLEDs) based on exciplex were reported. The exciplex was formed by 4, 4' ,4 ''-tris (3-methylphenyl (phenyl) amino)-triphenylamine (m-MTDATA) and 4, 7- diphenyl-1, 10-phenanthroline (BPhen). The resulting yellow OLEDs exhibited an external quantum efficiency of over 7%, which is attributed to the effective energy back transfer from exciplex triplet state to exciplex singlet state. The maximum power efficiency of 25 lm/W was achieved. Doping a yellow phosphor Ir(bt)2(acac) into m-MTDATA: BPhen blend, a high efficiency device was achieved with a turn-on voltage of 2.1 V, maximum power efficiency and external quantum efficiency of 86.1 lm/W and 20.7%, respectively.

Mixing of phosphorescent and exciplex emission in efficient organic electroluminescent devices.

We fabricated a yellow organic light-emitting diode (OLED) based on the star-shaped donor compound tri(9-hexylcarbazol-3-yl)amine, which provides formation of the interface exciplexes with the iridium(III) bis[4,6-difluorophenyl]-pyridinato-N,C2']picolinate (FIrpic). The exciplex emission is characterized by a broad band and provides a condition to realize the highly effective white OLED. It consists of a combination of the blue phosphorescent emission from the FIrpic complex and a broad efficient delayed fluorescence induced by thermal activation with additional direct phosphorescence from the triplet exciplex formed at the interface. The fabricated exciplex-type device exhibits a high brightness of 38 000 cd/m(2) and a high external quantum efficiency.

Co‐deposited Cu(I) Complex for Tri‐layered Yellow and White Organic Light‐Emitting Diodes

Four compounds 4‐[3,6‐di(carbazol‐9‐yl)carbazol‐9‐yl]isoquinoline (TCIQ), 3‐[3,6‐di(carbazol‐9‐yl)carbazol‐9‐yl]pyridine (TCPy), 4‐(carbazol‐9‐yl)isoquinoline (4CIQ), and 3‐(carbazol‐9‐yl)pyridine (CPy) containing pyridyl or isoquinolyl were designed and synthesized to co‐deposition with copper iodide (CuI) to form luminescent Cu(I) complex doped film in situ, which could be utilized as the emissive layer in organic light‐emitting diodes (OLEDs). It is found that simple tri‐layered yellow and white OLEDs can be achieved by co‐depositing CuI and TCIQ with tuning ratios. The compound TCIQ serves a dual role as both a ligand for forming the emissive Cu(I) complex and as a host matrix for the formed emitter in yellow OLEDs, and a third role as a blue emitter in white OLEDs.