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 2,979 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A novel series of thermally stable blue light emitting quateraryls with a piperidine donor and a nitrile acceptor was prepared from a ketene- S, S-acetal under mild conditions without using an organometal catalyst. The performance of a blue quateraryl 6e was investigated by fabricating a multilayer OLED with a configuration of ITO/PEDOT:PSS (40 nm)/quateraryl (60 nm)/BCP (6 nm)/Alq(3) (20 nm)/LiF (0.5 nm)/Al (200 nm), which exhibited blue emission with a low turn on voltage of 4 V at a brightness of 0.22 cd/m(2).
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PMID:Vapor-phase processable novel nonplanar donor-acceptor quateraryls for blue OLEDs(#). 1849 70

With the increasing development of organic light emitting devices (OLED), interest in the mechanisms of charge carrier photogeneration, separation, transport and recombination continues to grow. Electromodulation of photoluminescence has been used as an efficient probe to investigate the evolution of primary excitation in all electric field. This method can provide useful information on carrier photogeneration, the formation and dissociation of excitons, energy transfer, and exciton recombination in the presence of electric field. The operation of OLED brings electrons and holes from opposite electrodes and generates singlet and triplet excitons. However, triplet excitons are wasted because a radiative transition from triplets is spin-forbidden. Spin statistics predicts that singlet-to-triplet ratio is 1 : 3 in organic semiconductors. One way to harvest light from triplet excitons is to use phosphorescent materials. These materials incorporate a heavy metal atom to mix singlet and triplet states by the strong spin-orbit coupling. As a result, a spin forbidden transition may occur allowing an enhanced triplet emission. Among phosphorescent materials, Ir(ppy)3 has attracted much attention because of its short triplet lifetime to minimize the triplet-triplet annihilation. High quantum efficiencies have been obtained by doping organic molecules and in polymers with Ir(ppy)3. In the present paper, the photoluminescence and electroluminescence spectra of Ir(ppy)3 doped PVK film are measured at room temperature. The device structure is ITO/PEDOT : PSS/PVK Ir(ppy)3/BCP/Alq3/Al. The results show that the luminescence capabilities of devices are different when the concentration of Ir(ppy)3 is different. When the concentration of Ir(ppy)3 is suitable, the luminescence of PVK is lower but that of Ir(ppy)3 is stronger relatively, indicating that the energy transfer from the host materials to the guest materials is sufficient. It is concluded that the device with 5% of Ir(ppy)3 has the best luminescence properties according to its light power-current-voltage curve, meaning that the best concentration of Ir(ppy)3 in such kind of device is 5%.
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PMID:[Luminescence characteristics of PVK doped with Ir(ppy)3]. 1853 1

The changes of exciton generation region are influenced by varying electric field, which affect the color and efficiency performance of devices. Firstly, The authors fabricated two types of phosphorescent light emitting devices, device 1:ITO/PEDOT : PSS/PVK : Ir(ppy)s : DCJTB (100:2:1 wt)/BCP(10 nm)/Alq3 (15 nm)/Al, and device 2: ITO/PEDOT : PSS/ PVK : Ir(ppy)3 (100:2 wt)/BCP (10 nm)/Alq3(15 nm)/Al. The authors investigated the influences of electric field on exciton generation region in single-layer and multi-doped structure devices. Analysis of the electroluminescence spectrum under different voltages indicates that the emitting of Ir(ppy)3, PVK and DCJTB was enhanced with the increase in applied voltages. Compared to Ir(ppy)3, the emitting of PVK and DCJTB was prominently enhanced. This is because under high electric field it is easier high energy carrier to generate high energy exciton, and the emitting of wide-band-gap material PVK is stronger; on the other hand, the authors investigated the results from the aspect of energy band gap. DCJTB is narrow-band-gap material, which can capture carrier comparatively easily and emit stronger light. At the same time, we obtained a new emission peak located at 460 nm, which becomes comparatively weak with increasing voltage. In order to explore the reason, we fabricated the device: ITO/ PEDOT: PSS/PVK : BCP : Ir(ppy)3 (x:y:2 wt)/Alq3 (15 nm)/Al. The 460 nm emission peak doesn't disappear by changing the mass ratio of x and y. The authors speculate that the emission peak relates to PVK and BCP.
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PMID:[Study of exciton generation region of phosphorescent light emitting devices based on the changing electric field]. 1995 Jun 20

Influences of electric fields on the emission from organic light-emitting diodes (OLEDs) based on poly (N-vinylcarbazole) (PVK); 2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline (BCP); and tris (8-hydroxyquinoline) aluminum (Alq3) were studied. There are three emission peaks at 420 nm, 520 nm, and 620 nm of the device ITO/PEDOT: PSS/PVK/BCP/LiF/Al under different driving voltages. The emissions at 420 nm and 520 nm should be from the exciton emission of PVK and Alq3, respectively. The last emission at 620 nm could be attributed to electroplex emission at the interface between the PVK and BCP layers. A high intensity white emission via electroplex formation was obtained with Commission International d'Eclairage (CIE) coordinates (0.33, 0.34) at 15 V, which is very close to the equienergy white point (0.33, 0.33).
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PMID:White emission via electroplex emission from two blue materials. 2035 63

The present work investigates the effects of different buffer layers on the performance of blue organic light-emitting diodes (OLEDs), and compares them with the device with no buffer layer. Two kinds of blue OLEDs with 4,4'-bis(2,2'-diphenyl vinyl)-1,1'-biphenyl (DPVBi) as the emitting layer, N, N'-bis-(1-naphthyl)-N, N'-1-diphenyl-1,1 '-biphenyl-4, 4'-diamine (NPB) as the hole transporting layer, and copper phthalocyanine (CuPc) and poly(3,4-ethylenedioxythiophene) : poly (styrenesulphonate) PEDOT : PSS as the hole injection layer respectively were fabricated with the structures of ITO/CuPc/NPB/DPVBi/BCP/Alq3 /Al and ITO/PEDOT : PSS/NPB/DPVBi/BCP/Alq3/Al. Moreover, the effects of different preparation technology of CuPc on the performance of OLEDs were also investigated. It was found that the performance of the devices with a hole injection layer is better than that of the device without any hole-injection layer. Although the luminance and efficiency of the water-soluble CuPc based device are worse than that of the device with thermally evaporated CuPc, but better than that of the device with water-soluble PEDOT : PSS. So the water-soluble CuPc is a good hole injection material because it is easier to fabricate the film than traditional CuPc.
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PMID:[Effects of hole-injection layers on the performance of blue organic light-emitting diodes]. 2171 21

A new series of thermally stable blue light-emitting nonplanar pyrenylarenes having an amine donor and a nitrile acceptor group was prepared from a ketene-S,S-acetal under conventional heating and/or microwave irradiation. The photophysical, electrochemical, and optical behavior of donor-acceptor pyrenylarenes are demonstrated. The performance of blue light-emitting pyrenylarenes was investigated by fabricating a multilayer device with the device configuration of ITO/PEDOT:PSS (40 nm)/NPB (30 nm)/pyrenylarene (55 nm)/BCP (8 nm)/LiF (0.6 nm)/Al (200 nm), which exhibited low turn-on voltage (5 V) with luminance efficiency of 0.8 Cd/A with nonaggregation behavior in both solution and solid state.
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PMID:Thermally stable nonaggregating pyrenylarenes for blue organic light-emitting devices. 2180 32

In the present work, the photoluminescence (PL) and electroluminescence (EL) characteristics of Tris[2-(2,4-difluorophenyl)pyridine]iridium(III) (Ir(Fppy)3) doped poly(n-vinylcarbazole) (PVK) with different doping concentrations were investigated. And a blue phosphorescent organic light-emitting diode (OLED) with the structures of ITO/PEDOT : PSS/PVK : Ir(Fppy)3/BCP/Alq3/LiF/Al was fabricated. The experimental results show that the luminescence performances of devices are different as the doping concentration of Ir(Fppy)3 is different. When the doping concentration of Ir(Fppy)3 is lower, the luminescence of PVK can be found in EL spectra. When the doping concentration is too high, concentration quenching may occur. As the doping concentration is suitable, the luminescence of PVK can not be found, only the luminescence of Ir(Fppy)3 can be found in EL spectra. It is concluded that the device with doping concentration of 4% has the best photoelectric performance according to its current density-voltage-luminance curve.
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PMID:[Luminescence characteristics of PVK doped with Ir(Fppy)3]. 2209 20

A cyclometalated iridium(II) complex, bis(2-thiophen-2-yl-quinolinato)(acetoacetonate)iridium(II) [(tq)2Ir(III)(acac)] was synthesized for use in phosphorescent organic light-emitting diodes. The photophysical and electrochemical properties of the iridium(Ill) complex were characterized by UV-visible absorption, photoluminescence, and cyclic voltammetry. The maximum UV-visible absorption of (tq)2Ir(acac) was observed at 289 nm. (Tq)2Ir(acac) in dichloromethane showed its maximum photoluminescence (PL) emission at 629 nm. The optical band gap energy of (tq)2Ir(III)(acac) was measured to be 2.11 eV, and the HOMO energy level of (tq)2Ir(Ill)(acac) was calculated to be -5.08 eV. The T1 state of (tq)2Ir(lll)(acac), calculated from the PL emission maximum (2.01 eV), was well matched with the T1 level of CBP (2.6 eV). The phosphorescent organic light-emitting diode with a configuration of ITO/PEDOT:PSS/alpha-NPD/TCTA/CBP:(tq)2Ir(II)(acac)(8 wt%)/BCP/Alq3/LiF/Al was fabricated and characterized. Light emission from the device was observed at a low turn-on voltage of 4.3 V. The device showed a maximum brightness of 24,000 cd/m2 at 16.3 V and an external quantum efficiency of 11.1% with a Commission Internationale de l'Eclairage (CIE) coordinate of (0.690, 0.310).
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PMID:Pure red phosphorescent organic light-emitting diodes made of iridium(III) complex with thiophene-quinoline ligand. 2426 81

Surface plasmonic structure in solution-processable PHOLED was fabricated by blending and spin-coating techniques. ZnO nanoparticles were incorporated into the hole injection layer (PEDOT:PSS) by mixing solutions prior the EML spin-coating. The device structure are ITO/PEDOT:PSS+ ZnO/FIrpic:PVK/BCP/Alq3/LiF/Al. Plasmonic structures in PHOLED can be used for the enhancement of performance in existing device architectures.
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PMID:Surface plasmon resonance enhanced organic light emitting diode. 2473 72

A novel main ligand 2-(2,4-dimethoxyphenyl)-5-trifluoromethylpyridine (MeO2CF3ppy) and its complex bis[2-(2,4-dimethoxy-phenyl)-5-trifluoromethyl pyridinato-N,C2]iridium acetylacetonate (MeO2CF3ppy)2Ir(acac) was synthesized. 2,4-Dimethoxy and 5-trifluoromethyl group were incorporated into main ligand to tune luminescence color. The phosphorescence organic light-emitting diodes (PhOLEDs) based on this complex with the configuration of ITO/PEDOT:PSS (40 nm)/PVK:CBP:Ir(III) complex (50 nm)/BCP (20 nm)/LiF (0.7 nm)/Al (100 nm) were fabricated. The solution-processed PhOLEDs based on (MeO2CF3ppy)2Ir(acac) exhibited a maximum quantum efficiency of 4.18% and luminance efficiency 9.04 cd/A with CIE coordinate of (0.32, 0.64).
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PMID:Synthesis and characterization of phenylpyridine-based iridium(III) complex for solution-processed phosphorescent organic light-emitting diode. 2475 56


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