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Emissive Layer (emissive + layer)
Selected AbstractsMultifunctional Triphenylamine/Oxadiazole Hybrid as Host and Exciton-Blocking Material: High Efficiency Green Phosphorescent OLEDs Using Easily Available and Common MaterialsADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Youtian 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] High-Performance All-Polymer White-Light-Emitting Diodes Using Polyfluorene Containing Phosphonate Groups as an Efficient Electron-Injection LayerADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Baohua Zhang Abstract We report an efficient non-doped all-polymer polymer white-light-emitting diode (PWLED) with a fluorescent three-color, white single polymer as an emissive layer, an ethanol-soluble phosphonate-functionalized polyfluorene (PF-EP) as an electron-injection/electron-transport layer, and LiF/Al as a cathode, respectively. The all-polymer PWLED achieves a peak external quantum efficiency of 6.7%, a forward viewing luminous efficiency of 15.4 cd A,1 and a power efficiency of 11.4 lm W,1, respectively, at a brightness of 347 cd m,2 with Commission Internationale d'Eclairage coordinates of (0.37, 0.42) and color rendering index of 85, which is the best results among the non-doped PWLEDs. Moreover, this kind of PWLED not only shows excellent color stability, but also achieves high brightness at low voltages. The brightness reaches 1000, 10000, and 46830 cd m,2 at voltages of 4.5, 5.4, and 7.5 V, respectively. The significant enhancement of white-single-polymer-based PWLEDs with PF-EP/LiF/Al to replace for the commonly used Ca/Al cathode is attributed to the more efficient electron injection at PF-EP/LiF/Al interfaces, and the coordinated protecting effect of PF-EP from diffusion of Al atoms into the emissive layer and exciton-quenching near cathode interfaces. The developed highly efficient non-doped all-polymer PWLEDs are well suitable for solution-processing technology and provide a huge potential of low-cost large-area manufacturing for PWLEDs. [source] Harvesting Excitons Via Two Parallel Channels for Efficient White Organic LEDs with Nearly 100% Internal Quantum Efficiency: Fabrication and Emission-Mechanism AnalysisADVANCED FUNCTIONAL MATERIALS, Issue 1 2009Qi Wang Abstract By incorporating two phosphorescent dyes, namely, iridium(III)[bis(4,6-difluorophenyl)-pyridinato-N,C2,]picolinate (FIrpic) for blue emission and bis(2-(9,9-diethyl-9H -fluoren-2-yl)-1-phenyl-1H -benzoimidazol-N,C3)iridium(acetylacetonate) ((fbi)2Ir(acac)) for orange emission, into a single-energy well-like emissive layer, an extremely high-efficiency white organic light-emitting diode (WOLED) with excellent color stability is demonstrated. This device can achieve a peak forward-viewing power efficiency of 42.5,lm,W,1, corresponding to an external quantum efficiency (EQE) of 19.3% and a current efficiency of 52.8,cd,A,1. Systematic studies of the dopants, host and dopant-doped host films in terms of photophysical properties (including absorption, photoluminescence, and excitation spectra), transient photoluminescence, current density,voltage characteristics, and temperature-dependent electroluminescence spectra are subsequently performed, from which it is concluded that the emission natures of FIrpic and (fbi)2Ir(acac) are, respectively, host,guest energy transfer and a direct exciton formation process. These two parallel pathways serve to channel the overall excitons to both dopants, greatly reducing unfavorable energy losses. It is noteworthy that the introduction of the multifunctional orange dopant (fbi)2Ir(acac) (serving as either hole-trapping site or electron-transporting channel) is essential to this concept as it can make an improved charge balance and broaden the recombination zone. Based on this unique working model, detailed studies of the slight color-shift in this WOLED are performed. It is quantitatively proven that the competition between hole trapping on orange-dopant sites and undisturbed hole transport across the emissive layer is the actual reason. Furthermore, a calculation of the fraction of trapped holes on (fbi)2Ir(acac) sites with voltage shows that the hole-trapping effect of the orange dopant is decreased with increasing drive voltage, leading to a reduction of orange emission. [source] Continuous, Atmospheric Process to Create Organic Clusters and Nanostructured, Functional Films,ADVANCED FUNCTIONAL MATERIALS, Issue 5 2006R. Jagannathan Abstract An atmospheric process based on compressed CO2 is used to create stable clusters of small organic molecules. These clusters, 1,10,nm in size, are used as building blocks to assemble thin films on various substrates. Cluster assembly of these films is verified by using low-angle X-ray diffraction. The surface quality of these cluster-assembled films is similar to that of films usually prepared via the vacuum process. Several functional organic light-emitting diode devices have been prepared, in which only the doped emissive layer has been deposited by our process. The radiometric features and efficiencies of these devices match those of vacuum-built devices. Atomic force microscopy of these molecular clusters reveals that they are liquid-like at standard atmospheric conditions. Coatings of these clusters on cloth and stainless steel have been found to be superhydrophobic in nature. [source] Solvent Effects on the Architecture and Performance of Polymer White-Light-Emitting Diodes with Conjugated Oligoelectrolyte Electron-Transport LayersADVANCED MATERIALS, Issue 5 2009Yunhua Xu Polymer-based white-light-emitting diodes are fabricated using conjugated oligoelec trolytes as effective electron-injection layers. However, the choice of solvent used to deposit the conjugated oligoelectrolyte bears a strong influence on the final composition of the emissive layer. Inclusion of water decreases the contact with hydrophobic underlying coatings, and minimizes the extraction of one of the molecular components required for function. [source] Poly(triarylamine): Its synthesis, properties, and blend with polyfluorene for white-light electroluminescenceJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2007Hung-Yi Lin Abstract A new high-molecular-weight poly(triarylamine), poly[di(1-naphthyl)-4-anisylamine] (PDNAA), was successfully synthesized by oxidative coupling polymerization from di(1-naphthyl)-4-anisylamine (DNAA) with FeCl3 as an oxidant. PDNAA was readily soluble in common organic solvents and could be processed into freestanding films with high thermal decomposition and softening temperatures. Cyclic voltammograms of DNAA and PDNAA exhibited reversible oxidative redox couples at the potentials of 0.85 and 0.85 V, respectively, because of the oxidation of the main-chain triarylamine unit. This suggested that PDNAA is a hole-transporting material with an estimated HOMO level of 5.19 eV. The absorption maximum of a PDNAA film appeared at 370 nm, with an estimated band gap of 2.86 eV from the absorption edge. Unusual multiple photoluminescence maxima were observed at 546 nm, and this suggested its potential application in white-light-emission devices. Nearly white-light-emission devices could be obtained with either a bilayer-structure approach {indium tin oxide/poly(ethylenedioxythiophene):poly(styrene sulfonate)/PDNAA/poly[2,7-(9,9-dihexylfluorene)] (PF)/Ca} or a polymer-blend approach (PF/PDNAA = 95:5). The luminance yield and maximum external quantum efficiency of the light-emitting diode with the PF/PDNAA blend as the emissive layer were 1.29 cd/A and 0.71%, respectively, and were significantly higher than those of the homopolymer. This study suggests that the PDNAA is a versatile material for electronic and optoelectronic applications. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1727,1736, 2007 [source] Role of bathocuproine as hole-blocking and electron-transporting layer in organic light emitting devicesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010Reni Tomova Abstract In this paper we present our results concerning the role of 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine, BCP) in OLED structures with emissive layer of Tris-(8-hydroxyquinoline) aluminum (Alq3). It is established that instead of the higher working voltage of devices with bathocuproine their current efficiency significantly increased. This higher efficiency indicates strong hole-blocking nature of bathocuproine (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Multifunctional Crosslinkable Iridium Complexes as Hole Transporting/Electron Blocking and Emitting Materials for Solution-Processed Multilayer Organic Light-Emitting DiodesADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Biwu Ma Abstract Here, a new series of crosslinkable heteroleptic iridium (III) complexes for use in solution processed phosphorescent organic light emitting diodes (OLEDs) is reported. These iridium compounds have the general formula of (PPZ-VB)2Ir(C,N), where PPZ-VB is phenylpyrazole (PPZ) vinyl benzyl (VB) ether; and the C,N ligands represent a family of four different cyclometallating ligands including 1-phenylpyrazolyl (PPZ) (1), 2-(4,6-difluorophenyl)pyridyl (DFPPY) (2), 2-(p-tolyl)pyridyl (TPY) (3), and 2-phenylquinolyl (PQ) (4). With the incorporation of two crosslinkable VB ether groups, these compounds can be fully crosslinked after heating at 180,°C for 30,min. The crosslinked films exhibit excellent solvent resistance and film smoothness which enables fabrication of high-performance multilayer OLEDs by sequential solution processing of multiple layers. Furthermore, the photophysical properties of these compounds can be easily controlled by simply changing the cyclometallating C,N ligand in order to tune the triplet energy within the range of 3.0,2.2,eV. This diversity makes these materials not only suitable for use in hole transporting and electron blocking but also as emissive layers of several colors. Therefore, these compounds are applied as effective materials for all-solution processed OLEDs with (PPZ-VB)2IrPPZ (1) acting as hole transporting and electron blocking layer and host material, as well as three other compounds, (PPZ-VB)2IrDFPPY (2), (PPZ-VB)2IrTPY(3), and (PPZ-VB)2IrPQ(4), used as crosslinkable phosphorescent emitters. [source] | ||||||||||