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Electrophosphorescent Devices (electrophosphorescent + device)

Distribution by Scientific Domains

Polymers and Materials Science	87%

Selected Abstracts

Nearly 100% Internal Quantum Efficiency in an Organic Blue-Light Electrophosphorescent Device Using a Weak Electron Transporting Material with a Wide Energy Gap

ADVANCED MATERIALS, Issue 12 2009
Lixin Xiao
A blue-light electrophosphorescence with an internal quantum efficiency of nearly 100%, much higher than that of a stronger electron transporting (ET) material, was achieved with a weak ET silane. This result contradicts the conventional notion that weak ET materials result in low efficiency. [source]

Confinement of Charge Carriers and Excitons in Electrophosphorescent Devices: Mechanism of Light Emission and Degradation,

ADVANCED MATERIALS, Issue 16 2007
D. Chin
Charge-carrier and exciton confinement is essential for efficiency and stability enhancment of electrophosphorescent devices. Emission-layer lifetimes of a 4,4,- N,N,-dicarbazole-biphenyl host doped with either a red- or green- emitting dye (upper and lower figures) show a strong dependence and near independence, respectively, on the type of exciton blocking layer used (four are shown). This is explained using energy- level differences and corresponding charge-trapping behavior. [source]

Bifunctional Green Iridium Dendrimers with a "Self-Host" Feature for Highly Efficient Nondoped Electrophosphorescent Devices,

ANGEWANDTE CHEMIE, Issue 36 2009
Junqiao Ding Dr.
Besser undotiert: Ein Dendron mit einer hohen Carbazoldichte um einen Iridiumkern verbessert die Leistung nichtdotierter elektrophosphoreszenter Einheiten effektiver als Dendrimere höherer Generationen. Eine vielversprechende Effizienz von 45.7,cd,A,1 (13.4,%) und eine hohe Luminanz zeigt 6,B-G1 (siehe Bild). Diese Werte liegen sehr nahe an denen der entsprechenden dotierten Einheit. [source]

Multifunctional Triphenylamine/Oxadiazole Hybrid as Host and Exciton-Blocking Material: High Efficiency Green Phosphorescent OLEDs Using Easily Available and Common Materials

ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010
Youtian Tao
Abstract A new triphenylamine/oxadiazole hybrid, namely m -TPA- o -OXD, formed by connecting the meta -position of a phenyl ring in triphenylamine with the ortho -position of 2,5-biphenyl-1,3,4-oxadiazole, is designed and synthesized. The new bipolar compound is applicable in the phosphorescent organic light-emitting diodes (PHOLEDs) as both host and exciton-blocking material. By using the new material and the optimization of the device structures, very high efficiency green and yellow electrophosphorescence are achieved. For example, by introducing 1,3,5-tris(N -phenylbenzimidazol-2-yl)benzene (TPBI) to replace 2, 9-dimethyl-4,7-diphenyl-1, 10-phenanthroline (BCP)/tris(8-hydroxyquinoline)aluminium (Alq3) as hole blocking/electron transporting layer, followed by tuning the thicknesses of hole-transport 1, 4-bis[(1-naphthylphenyl)amino]biphenyl (NPB) layer to manipulate the charge balance, a maximum external quantum efficiency (,EQE,max) of 23.0% and a maximum power efficiency (,p,max) of 94.3 lm W,1 are attained for (ppy)2Ir(acac) based green electrophosphorescence. Subsequently, by inserting a thin layer of m -TPA- o -OXD as self triplet exciton block layer between hole-transport and emissive layer to confine triplet excitons, a ,EQE,max of 23.7% and ,p,max of 105 lm W,1 are achieved. This is the highest efficiency ever reported for (ppy)2Ir(acac) based green PHOLEDs. Furthermore, the new host m -TPA- o -OXD is also applicable for other phosphorescent emitters, such as green-emissive Ir(ppy)3 and yellow-emissive (fbi)2Ir(acac). A yellow electrophosphorescent device with ,EQE,max of 20.6%, ,c,max of 62.1 cd A,1, and ,p,max of 61.7 lm W,1, is fabricated. To the author's knowledge, this is also the highest efficiency ever reported for yellow PHOLEDs. [source]

Efficient Light-Emitting Devices Based on Phosphorescent Polyhedral Oligomeric Silsesquioxane Materials

ADVANCED FUNCTIONAL MATERIALS, Issue 16 2009
Xiaohui Yang
Abstract Synthesis, photophysical, and electrochemical characterizations of iridium-complex anchored polyhedral oligomeric silsesquioxane (POSS) macromolecules are reported. Monochromatic organic light-emitting devices based on these phosphorescent POSS materials show peak external quantum efficiencies in the range of 5,9%, which can be driven at a voltage less than 10,V for a luminance of 1000,cd m,2. The white-emitting devices with POSS emitters show an external quantum efficiency of 8%, a power efficiency of 8.1,lm W,1, and Commission International de'lÉclairage coordinates of (0.36, 0.39) at 1000,cd m,2. Encouraging efficiency is achieved in the devices based on hole-transporting and Ir-complex moieties dual-functionalized POSS materials without using host materials, demonstrating that triplet-dye and carrier-transporting moieties functionalized POSS material is a viable approach for the development of solution-processable electrophosphorescent devices. [source]

Effect of Electric Field on Coulomb-Stabilized Excitons in Host/Guest Systems for Deep-Blue Electrophosphorescence

ADVANCED FUNCTIONAL MATERIALS, Issue 15 2009
Stephan Haneder
Abstract Here, a study of the electric field induced quenching on the phosphorescence intensity of a deep-blue triplet emitter dispersed in different host materials is presented. The hosts are characterized by a higher triplet excitonic level with respect to the emitter, ensuring efficient energy transfer and exciton confinement, whereas they differ in the highest occupied molecular orbital (HOMO) alignment, forming type I and type II host/guest heterostructures. While the type I structure shows negligible electric field induced quenching, a quenching up to 25% for the type II at a field of 2,MV/cm is reported. A similar quenching behaviour is also reported for thin films of the pure emitter, revealing an important luminescence loss mechanism for aggregated emitter molecules. These results are interpreted by considering Coulomb stabilized excitons in the type II heterostructure and in the pure emitter, that become very sensitive to dissociation upon application of the field. These results clarify the role of external electric field quenching on the phosphorescence of triplet emitters and provide useful insights for the design of deep-blue electrophosphorescent devices with a reduced efficiency roll-off. [source]

Solution-Processible Red Iridium Dendrimers based on Oligocarbazole Host Dendrons: Synthesis, Properties, and their Applications in Organic Light-Emitting Diodes,

ADVANCED FUNCTIONAL MATERIALS, Issue 18 2008
Junqiao Ding
Abstract A series of novel red-emitting iridium dendrimers functionalized with oligocarbazole host dendrons up to the third generation (red-G3) have been synthesized by a convergent method, and their photophysical, electrochemical, and electroluminescent properties have been investigated. In addition to controlling the intermolecular interactions, oligocarbazole-based dendrons could also participate in the electrochemical and charge-transporting process. As a result, highly efficient electrophosphorescent devices can be fabricated by spin-coating from chlorobenzene solution in different device configurations. The maximum external quantum efficiency (EQE) based on the non-doped device configuration increases monotonically with increasing dendron generation. An EQE as high as 6.3% was obtained as for the third generation dendrimer red-G3, which is about 30 times higher than that of the prototype red-G0. Further optimization of the device configuration gave an EQE of 11.8% (13.0,cd A,1, 7.2,lm W,1) at 100,cd m,2 with CIE coordinates of (0.65, 0.35). The state-of-the-art performance indicated the potential of these oligocarbazole-based red iridium dendrimers as solution processible emissive materials for organic light-emitting diode applications. [source]