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Organic Light-emitting Devices (organic + light-emitting_device)
Selected AbstractsSynthesis, Characterization, and Bipolar Transporting Behavior of a New Twisted Polycyclic Aromatic Hydrocarbon: 1,,4,-Diphenyl-naphtho-(2,.3,:1.2)-pyrene-6,-nitro-7,-methyl CarboxylateCHEMISTRY - A EUROPEAN JOURNAL, Issue 25 2010Qichun Zhang Prof. Abstract An asymmetric twistacene, 1,,4,-diphenyl-naphtho-(2,.3,:1.2)-pyrene-6,-nitro-7,-methyl carboxylate (tetracene 2), was synthesized by using benzyne-trapping chemistry. Its structure, determined by X-ray crystallography, confirmed that this material has a twisted topology with torsion angles as high as 23.8(3)°. Organic light-emitting devices using tetracene 2 as either charge-transporting materials or emitters have been fabricated. The results indicate that this material has bipolar transporting behavior in these devices. [source] SensLED: An Electro-Optical Active Probe for Oxygen DeterminationADVANCED MATERIALS, Issue 34 2009Stefan Sax A novel concept for an electro-optical active gas probe capable of oxygen detection is presented. Based on a modified organic light-emitting device, we demonstrate that a reversible analyte,indicator interaction can be used for analyte determination. [source] White light generation through yellow nanophosphor and blue organic light-emitting diodePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2009Je Hong Park Abstract White light-emitting device (WLED) combining yellow-emitting nanophosphor and blue organic light-emitting diode (LED) was developed. WLED was fabricated by using a spin-coating method. Yellow-emitting nanophosphor was dispersed in the blue-emitting polymer solution for spin-coating. As a variation of mixture ratio of yellow-emitting nanophosphor and blue-emitting polymer in emitting layer, the emission spectra were studied. Our white organic light-emitting device with 30% phosphor mixture ratio and at the driving voltage of 17 V showed the color coordinates of x = 0.266 and y = 0.33. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Correlation Between Triplet,Triplet Annihilation and Electroluminescence Efficiency in Doped Fluorescent Organic Light-Emitting DevicesADVANCED FUNCTIONAL MATERIALS, Issue 8 2010Yichun Luo Abstract Triplet,triplet annihilation (TTA) is studied in a wide range of fluorescent host:guest emitter systems used in organic light-emitting devices (OLEDs). Strong TTA is observed in host:guest systems in which the dopant has a limited charge-trapping capability. On the other hand, systems in which the dopant can efficiently trap charges show insignificant TTA, an effect that is due, in part, to the efficient quenching of triplet excitons by the trapped charges. Fluorescent host:guest systems with the strongest TTA are found to give the highest OLED electroluminescence efficiency, a phenomenon attributed to the role of TTA in converting triplet excitons into additional singlet excitons, thus appreciably contributing to the light output of OLEDs. The results shed light on and give direct evidence for the phenomena behind the recently reported very high efficiencies attainable in fluorescent host:guest OLEDs with quantum efficiencies exceeding the classical 25% theoretical limit. [source] High Efficiency Blue Organic LEDs Achieved By an Integrated Fluorescence,Interlayer,Phosphorescence Emission ArchitectureADVANCED FUNCTIONAL MATERIALS, Issue 4 2010Tianhang Zheng Abstract This paper presents a new strategy to develop efficient organic light-emitting devices (OLEDs) by doping fluorescent- and phosphorescent-type emitters individually into two different hosts separated by an interlayer to form a fluorescence,interlayer,phosphorescence (FIP) emission architecture. One blue OLED with FIP emission structure comprising p -bis(p - N,N -diphenylaminostyryl)benzene (DSA-Ph) and bis[(4,6-di-fluorophenyl)-pyridinate- N,C2']picolinate (FIrpic) exhibiting a peak luminance efficiency of 15.8,cd A,1 at 1.54,mA cm,2 and a power efficiency of 10.2,lm W,1 at 0.1,mA cm,2 is successfully demonstrated. The results are higher than those of typical phosphorescent OLEDs with a single emission layer by 34% and 28%, respectively. From experimental and theoretical investigations on device performance, and the functions of the used emitters and interlayer, such enhancement should ascribe to the appropriate utilization of the two types of emitters. The fluorescent emitter of DSA-Ph is used to facilitate the carrier transport, and thus accelerate the generation of excitons, while the phosphorescent emitter of FIrpic could convert the generated excitons into light efficiently. The method proposed here can be applied for developing other types of red, green, and white OLEDs. [source] Tuning the Optoelectronic Properties of Carbazole/Oxadiazole Hybrids through Linkage Modes: Hosts for Highly Efficient Green ElectrophosphorescenceADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Youtian Tao Abstract A series of bipolar transport host materials: 2,5-bis(2-(9H -carbazol-9-yl)phenyl)-1,3,4-oxadiazole (o -CzOXD) (1), 2,5-bis(4-(9H -carbazol-9-yl)phenyl)-1,3,4-oxadiazole (p -CzOXD) (2), 2,5-bis(3-(9H -carbazol-9-yl)phenyl)-1,3,4-oxadiazole (m -CzOXD) (3) and 2-(2-(9H -carbazol-9-yl)phenyl)-5-(4-(9H-carbazol-9-yl)phenyl)-1,3,4-oxadiazole (op -CzOXD) (4) are synthesized through simple aromatic nucleophilic substitution reactions. The incorporation of the oxadiazole moiety greatly improves their morphological stability, with Td and Tg in the range of 428,464,°C and 97,133,°C, respectively. The ortho and meta positions of the 2,5-diphenyl-1,3,4-oxadiazole linked hybrids (1 and 3) show less intramolecular charge transfer and a higher triplet energy compared to the para-position linked analogue (2). The four compounds exhibit similar LUMO levels (2.55,2.59,eV) to other oxadiazole derivatives, whereas the HOMO levels vary in a range from 5.55,eV to 5.69,eV, depending on the linkage modes. DFT-calculation results indicate that 1, 3, and 4 have almost complete separation of their HOMO and LUMO levels at the hole- and electron-transporting moieties, while 2 exhibits only partial separation of the HOMO and LUMO levels possibly due to intramolecular charge transfer. Phosphorescent organic light-emitting devices fabricated using 1,4 as hosts and a green emitter, Ir(ppy)3 or (ppy)2Ir(acac), as the guest exhibit good to excellent performance. Devices hosted by o -CzOXD (1) achieve maximum current efficiencies (,c) as high as 77.9,cd A,1 for Ir(ppy)3 and 64.2,cd A,1 for (ppy)2Ir(acac). The excellent device performance may be attributed to the well-matched energy levels between the host and hole-transport layers, the high triplet energy of the host and the complete spatial separation of HOMO and LUMO energy levels. [source] Efficient Light-Emitting Devices Based on Phosphorescent Polyhedral Oligomeric Silsesquioxane MaterialsADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Xiaohui 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] Structure,Property Relationship of Pyridine-Containing Triphenyl Benzene Electron-Transport Materials for Highly Efficient Blue Phosphorescent OLEDsADVANCED FUNCTIONAL MATERIALS, Issue 8 2009Shi-Jian Su Abstract Three triphenyl benzene derivatives of 1,3,5-tri(m -pyrid-2-yl-phenyl)benzene (Tm2PyPB), 1,3,5-tri(m -pyrid-3-yl-phenyl)benzene (Tm3PyPB) and 1,3,5-tri(m -pyrid-4-yl-phenyl)benzene (Tm4PyPB), containing pyridine rings at the periphery, are developed as electron-transport and hole/exciton-blocking materials for iridium(III) bis(4,6-(di-fluorophenyl)pyridinato- N,C2,)picolinate (FIrpic)-based blue phosphorescent organic light-emitting devices. Their highest occupied molecular orbital and lowest unoccupied molecular orbital (LUMO) energy levels decrease as the nitrogen atom of the pyridine ring moves from position 2 to 3 and 4; this is supported by both experimental results and density functional theory calculations, and gives improved electron-injection and hole-blocking properties. They exhibit a high electron mobility of 10,4,10,3,cm2,V,1,s,1 and a high triplet energy level of 2.75,eV. Confinement of FIrpic triplet excitons is strongly dependent on the nitrogen atom position of the pyridine ring. The second exponential decay component in the transient photoluminescence decays of Firpic-doped films also decreases when the position of the nitrogen atom in the pyridine ring changes. Reduced driving voltages are obtained when the nitrogen atom position changes because of improved electron injection as a result of the reduced LUMO level, but a better carrier balance is achieved for the Tm3PyPB-based device. An external quantum efficiency (EQE) over 93% of maximum EQE was achieved for the Tm4PyPB-based device at an illumination-relevant luminance of 1000,cd,m,2, indicating reduced efficiency roll-off due to better confinement of FIrpic triplet excitons by Tm4PyPB in contrast to Tm2PyPB and Tm3PyPB. [source] Influences of Connecting Unit Architecture on the Performance of Tandem Organic Light-Emitting Devices,ADVANCED FUNCTIONAL MATERIALS, Issue 14 2007Y. Chan Abstract The present work investigates the influence of the n-type layer in the connecting unit on the performance of tandem organic light-emitting devices (OLEDs). The n-type layer is typically an organic electron-transporting layer doped with reactive metals. By systematically varying the metal dopants and the electron-transporting hosts, we have identified the important factors affecting the performance of the tandem OLEDs. Contrary to common belief, device characteristics were found to be insensitive to metal work functions, as supported by the ultraviolet photoemission spectroscopy results that the lowest unoccupied molecular orbitals of all metal-doped n-type layers studied here have similar energy levels. It suggests that the electron injection barriers from the connecting units are not sensitive to the metal dopant used. On the other hand, it was found that performance of the n-type layers depends on their electrical conductivities which can be improved by using an electron-transporting host with higher electron mobility. This effect is further modulated by the optical transparency of constituent organic layers. The efficiency of tandem OLEDs would decrease as the optical transmittance decreases. [source] Modifying the Output Characteristics of an Organic Light-Emitting Device by Refractive-Index Modulation,ADVANCED FUNCTIONAL MATERIALS, Issue 18 2006T. Höfler Abstract In order to modify the output characteristics of organic light-emitting devices (OLEDs), the optical properties of an active layer within the device are patterned without introducing any thickness modulation. For this purpose a new conjugated copolymer, which serves as a hole-transporting material and at the same time can be index patterned using UV techniques, is synthesized. Poly(VC- co -VBT) (VC: N -vinylcarbazole; VBT: 4-vinylbenzyl thiocyanate) is prepared by free-radical copolymerization of VC and VBT. The material contains photoreactive thiocyanate groups that enable altering of the material's refractive index under UV illumination. This copolymer is employed as a patternable hole-transporting layer in multilayer OLEDs. Refractive-index gratings in poly(VC- co -VBT) are inscribed using a holographic setup based upon a Lloyd mirror configuration. The fourth harmonic of a Nd:YAG (YAG: yttrium aluminum garnet) laser (266,nm) serves as the UV source. In this way 1D photonic structures are integrated in an OLED containing AlQ3 (tris(8-hydroxyquinoline) aluminum) as the emitting species. It is assured that only a periodical change of the refractive index (,n,=,0.006 at ,,=,540,nm) is generated in the active material but no surface-relief gratings are generated. The patterned devices show more forward-directed out-coupling behavior than unstructured devices (increase in luminosity by a factor of five for a perpendicular viewing direction). This effect is most likely due to Bragg scattering. For these multilayer structures, optimum outcoupling was observed for grating periods ,,,,390,nm. [source] Immiscible polymers in double spin-coated electroluminescent devices containing phenyl-substituted tris(8-hydroxyquinoline)aluminum derivatives soluble in a host polymerJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2003E. Shoji Abstract Three new phenyl-substituted tris(8-hydroxyquinoline)aluminum (AlQ3) derivatives have been synthesized: tris(5-phenyl-8-quinolinolate-N1,O8)aluminum, tris(5,7-diphenyl-8-quinolinolate-N1,O8)aluminum, and tris[5,7-bis(p -fluorophenyl)-8-quinolinolate-N1,O8]aluminum. These AlQ3 derivatives are easily soluble in common organic solvents and form solid-phase solutions in a poly(aryl ether ketone) host polymer (A435). These interesting properties allow the use of soluble AlQ3 derivatives in double spin-coated organic light-emitting devices of the type ITO/NPB-QP/A435 + 50 wt % soluble AlQ3 derivative/Mg, where NPB-QP is a hole-transporting polymer insoluble in toluene, the solvent for A435. Typical double spin-coated organic layer devices are characterized by an emission at 530,539 nm, a threshold voltage of 6,9 V, and a maximum luminance of 1800,4000 cd/m2 at 21,25 V. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3006,3016, 2003 [source] Enhanced performance by inserting ultrathin SiO2 layer in organic light-emitting devicesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2007Lianbin Niu Abstract Improved performance of organic light-emitting devices (OLEDs) has been obtained by insertion of an ultrathin film of silicon oxide (SiO2) at the interface of 8-hydroxyquinoline aluminum (Alq3) and N,N ,-bis(1-naphthyl)- N,N ,-diphenyl-1,1,-biphenyl-4,4,-diamine (NPB) layers. When a 1.0 nm SiO2 film was inserted, for an unoptimized indium,tin oxide (ITO)/NPB/SiO2/Alq3/Al device, the current efficiency was as high as 7.35 cd/A. Compared with conventional devices, a higher efficiency has been achieved. The mechanism of performance enhancement is discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Inorganic Layers on Polymeric Films , Influence of Defects and Morphology on Barrier PropertiesCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 5 2003M. Hanika Abstract Flexible polymeric films are not only widely used in conventional packaging as substitute for glass and aluminum foil packaging but are also proposed as encapsulation for novel products, like flexible solar cells or organic light-emitting devices. The two essential properties of the polymeric packaging are flexibility and good permeation barrier properties against gases and vapors. This article deals with vacuum web coating as a common way of increasing barrier properties of polymeric films and the problems related to this procedure. Defects caused by particles and surface imperfections are found to dominate the permeation rate for such coated polymeric films. Atomic force microscopy, electron and also optical microscopy was used for analysis of the coating layer. Three-dimensional numerical simulations were performed for modeling of the influence of defect size, spacing and film thickness. Results of numerical modeling and of many practical experiments show that the permeability is almost independent of the substrate film thickness when a critical thickness is exceeded. In most cases the defects can be treated as independent of each other. The gas permeability of vacuum web-coated polymeric films can be quantitatively predicted by a simple formula. For gases, like oxygen, it is shown that a statistic analysis of the defect sizes by optical microscopy is sufficient. For water vapor transmission, however, the structure of the coating layer itself has also to be taken into account. [source] | ||||||||||||||||