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Organic Light-emitting Diodes (organic + light-emitting_diode)
Kinds of Organic Light-emitting Diodes Selected AbstractsAn Alternative Approach to Constructing Solution Processable Multifunctional Materials: Their Structure, Properties, and Application in High-Performance Organic Light-Emitting DiodesADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Shanghui Ye Abstract A new series of full hydrocarbons, namely 4,4,-(9,9,-(1,3-phenylene)bis(9H -fluorene-9,9-diyl))bis(N,N -diphenylaniline) (DTPAFB), N,N,-(4,4,-(9,9,-(1,3-phenylene)bis(9H -fluorene-9,9-diyl))bis(4,1-phenylene))bis(N -phenylnaphthalen-1-amine) (DNPAFB), 1,3-bis(9-(4-(9H -carbazol-9-yl)phenyl)-9H -fluoren-9-yl)benzene, and 1,3-bis(9-(4-(3,6-di- tert -butyl-9H -carbazol-9-yl)phenyl)-9H -fluoren-9-yl)benzene, featuring a highly twisted tetrahedral conformation, are designed and synthesized. Organic light-emitting diodes (OLEDs) comprising DNPAFB and DTPAFB as hole transporting layers and tris(quinolin-8-yloxy)aluminum as an emitter are made either by vacuum deposition or by solution processing, and show much higher maximum efficiencies than the commonly used N,N,-di(naphthalen-1-yl)- N,N,-diphenylbiphenyl-4,4,-diamine device (3.6 cd A,1) of 7.0 cd A,1 and 6.9 cd A,1, respectively. In addition, the solution processed blue phosphorescent OLEDs employing the synthesized materials as hosts and iridium (III) bis[(4,6-di-fluorophenyl)-pyridinato-N, C2] picolinate (FIrpic) phosphor as an emitter present exciting results. For example, the DTPAFB device exhibits a brightness of 47 902 cd m,2, a maximum luminescent efficiency of 24.3 cd A,1, and a power efficiency of 13.0 lm W,1. These results show that the devices are among the best solution processable blue phosphorescent OLEDs based on small molecules. Moreover, a new approach to constructing solution processable small molecules is proposed based on rigid and bulky fluorene and carbazole moieties combined in a highly twisted configuration, resulting in excellent solubility as well as chemical miscibility, without the need to introduce any solubilizing group such as an alkyl or alkoxy chain. [source] Stable, Glassy, and Versatile Binaphthalene Derivatives Capable of Efficient Hole Transport, Hosting, and Deep-Blue Light EmissionADVANCED FUNCTIONAL MATERIALS, Issue 15 2010Bin Wei Abstract Organic light-emitting diodes (OLEDs) have great potential applications in display and solid-state lighting. Stability, cost, and blue emission are key issues governing the future of OLEDs. The synthesis and photoelectronics of a series of three kinds of binaphthyl (BN) derivatives are reported. BN1,3 are "melting-point-less" and highly stable materials, forming very good, amorphous, glass-like films. They decompose at temperatures as high as 485,545,°C. At a constant current density of 25,mA,cm,2, an ITO/BN3/Al single-layer device has a much-longer lifetime (>80,h) than that of an ITO/NPB/Al single-layer device (8,h). Also, the lifetime of a multilayer device based on BN1 is longer than a similar device based on NPB. BNs are efficient and versatile OLED materials: they can be used as a hole-transport layer (HTL), a host, and a deep-blue-light-emitting material. This versatility may cut the cost of large-scale material manufacture. More importantly, the deep-blue electroluminescence (emission peak at 444 nm with CIE coordinates (0.16, 0.11), 3.23 cd A,1 at 0.21,mA cm,2, and 25200,cd,m,2 at 9,V) remains very stable at very high current densities up to 1000,mA,cm,2. [source] Highly Efficient Non-Doped Blue Organic Light-Emitting Diodes Based on Fluorene Derivatives with High Thermal Stability,ADVANCED FUNCTIONAL MATERIALS, Issue 10 2005L. Tao Abstract A new series of blue-light-emitting fluorene derivatives have been synthesized and characterized. The fluorene derivatives have high fluorescence yields, good thermal stability, and high glass-transition temperatures in the range 145,193,°C. Organic light-emitting diodes (OLEDs) fabricated using the fluorene derivatives as the host emitter show high efficiency (up to 5.3,cd,A,1 and 3.0,lm,W,1) and bright blue-light emission (Commission Internationale de L'Eclairage (CIE) coordinates of x,=,0.16, y,=,0.22). The performance of the non-doped fluorene-based devices is among the best fluorescent blue-light-emitting OLEDs. The good performance of the present blue OLEDs is considered to derive from: 1),appropriate energy levels of the fluorene derivatives for good carrier injection; 2),good carrier-transporting properties; and 3),high fluorescence efficiency of the fluorene derivatives. These merits are discussed in terms of the molecular structures. [source] Vertical-type organic device using thin-film ZnO transparent electrodeELECTRICAL ENGINEERING IN JAPAN, Issue 2 2007Hiroyuki Iechi Abstract We propose a double heterojunction organic light-emitting diode (OLED) using a zinc oxide (ZnO) film, which works as a transparent and electron injection layer. The crystal structure of the ZnO films as a function of Ar/O2 flow ratio and the basic characteristics of the OLED depending on the ZnO sputtering conditions are investigated. Excellent characteristics of the novel OLED were obtained, as high as 470 cd/m2 at 22 V and 7.6 mA/cm2. The results obtained here demonstrate that the vertical organic light-emitting transistor (OLET) using a ZnO layer as an electron injection layer is promising as a key element for flexible sheet displays. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(2): 49,55, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20151 [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] An Organic Light-Emitting Diode with Field-Effect Electron Transport,ADVANCED FUNCTIONAL MATERIALS, Issue 1 2008S. Schols Abstract We describe an organic light-emitting diode (OLED) using field-effect to transport electrons. The device is a hybrid between a diode and a field-effect transistor. Compared to conventional OLEDs, the metallic cathode is displaced by one to several micrometers from the light-emitting zone. This micrometer-sized distance can be bridged by electrons with enhanced field-effect mobility. The device is fabricated using poly(triarylamine) (PTAA) as the hole-transport material, tris(8-hydroxyquinoline) aluminum (Alq3) doped with 4-(dicyanomethylene)-2-methyl-6-(julolindin-4-yl-vinyl)-4H-pyran (DCM2) as the active light-emitting layer, and N,N,-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13H27), as the electron-transport material. The obtained external quantum efficiencies are as high as for conventional OLEDs comprising the same materials. The quantum efficiencies of the new devices are remarkably independent of the current, up to current densities of more than 10 A cm,2. In addition, the absence of a metallic cathode covering the light-emission zone permits top-emission and could reduce optical absorption losses in waveguide structures. These properties may be useful in the future for the fabrication of solid-state high-brightness organic light sources. [source] Organic Infrared Upconversion DeviceADVANCED MATERIALS, Issue 20 2010Do Young Kim Novel infrared-to-visible light upconversion devices are demonstrated by fabricating an organic light-emitting diode with an infrared-sensitizing layer. With a SnPc:C60 mixed layer as an infrared absorber and fac-tris(2-phenylpyridinato) iridium (III) (Irppy3) as an emitter, an infrared-to-green up-conversion device is demonstrated under 830-nm irradiation (see figure, ITO=indium tin oxide). The maximum photon-to-photon conversion efficiency is 2.7% at 15V. [source] A Lasing Organic Light-Emitting DiodeADVANCED MATERIALS, Issue 4 2010Bodo H. Wallikewitz Direct structuring of photocrosslinkable polyspirobifluorene copolymers by holographic lithography to yield insoluble, organic, distributed feedback (DFB) lasers with thresholds as low as 2,µJ,cm,2 is reported (see figure). These DFB lasers (X-LEP layer in figure) are embedded in the first optimized, multilayered slab-waveguide organic light-emitting diode with good luminance efficiency of ,6,cd A,1 and concomitant low laser thresholds. The effect of electrical excitation on the optically pumped laser is investigated for the first time. [source] Highly Efficient and Color-Stable Deep-Blue Organic Light-Emitting Diodes Based on a Solution-Processible DendrimerADVANCED MATERIALS, Issue 47 2009Lei Wang A color-stable blue organic light-emitting diode is obtained utilizing a solution-processible fluorescent , -conjugated dendrimerG0 (see image), with a maximum luminance efficiency of 5.3,cd A,1. Efficient green, red, and white OLEDs are also demonstrated by doping G0 with phosphorescent dyes. Combining high device efficiency with solution processibility, G0 becomes one of the best blue-emitting materials for fabricating flat-panel displays and white-light lighting panels via solution processing. [source] Synthesis of bipolar charge transporting block copolymers and characterization for organic light-emitting diodeJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2010Kousuke Tsuchiya Abstract A series of hole and electron transporting random and block copolymers consisting of triphenylamine moiety as a hole transporting unit and oxadiazole moiety as an electron transporting unit have been prepared via a nitroxide mediated radical polymerization. Oxadiazole monomers with t -butyl or trifluoromethyl groups, 2 and 7, respectively, were used for copolymerization. Photoluminescent measurements of polymers revealed that the formation of the exciplex between triphenylamine and oxadiazole units tends to occur in the order of random copolymers, block copolymers, and polymer blends, implying phase-separated morphologies in block or blend systems. The polymers were applied for OLED devices, and we found that the morphology in the polymer layer critically affected device performance. The block copolymer comprising hole and electron transporting units with the composition of 14/86 showed the highest external quantum efficiency over 10%. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1461,1468, 2010 [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] Effective Manipulation of the Electronic Effects and Its Influence on the Emission of 5-Substituted Tris(8-quinolinolate) Aluminum(III) ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2006Victor A. Montes Abstract The unique electron-transport and emissive properties of tris(8-quinolinolate) aluminum(III) (Alq3) have resulted in extensive use of this material for small molecular organic light-emitting diode (OLED) fabrication. So far, efforts to prepare stable and easy-to-process red/green/blue (RGB)-emitting Alq3 derivatives have met with only a limited success. In this paper, we describe how the electronic nature of various substituents, projected via an arylethynyl or aryl spacer to the position of the highest HOMO density (C5), may be used for effective emission tuning to obtain blue-, green-, and red-emitting materials. The synthetic strategy consists of four different pathways for the attachment of electron-donating and electron-withdrawing aryl or arylethynyl substituents to the 5-position of the quinolinolate ring. Successful tuning of the emission color covering the whole visible spectrum (,=450,800 nm) was achieved. In addition, the photophysical properties of the luminophores were found to correlate with the Hammett constant of the respective substituents, providing a powerful strategy with which to predict the optical properties of new materials. We also demonstrate that the electronic nature of the substituent affects the emission properties of the resulting complex through effective modification of the HOMO levels of the quinolinolate ligand. [source] A Transparent, Flexible, Low-Temperature, and Solution-Processible Graphene Composite ElectrodeADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Haixin Chang Abstract The synthesis and preparation of a new type of graphene composite material suitable for spin-coating into conductive, transparent, and flexible thin film electrodes in ambient conditions is reported here for the first time. Solution-processible graphene with diameter up to 50 ,m is synthesized by surfactant-assisted exfoliation of graphite oxide and in situ chemical reduction in a large quantity. Spin-coating the mixing solution of surfactant-functionalized graphene and PEDOT:PSS yields the graphene composite electrode (GCE) without the need for high temperature annealing, chemical vapor deposition, or any additional transfer-printing process. The conductivity and transparency of GCE are at the same level as those of an indium tin oxide (ITO) electrode. Importantly, it exhibits high stability (both mechanical and electrical) in bending tests of at least 1000 cycles. The performance of organic light-emitting diodes based on a GCE anode is comparable, if not superior, to that of OLEDs made with an ITO anode. [source] Multifunctional 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] The Role of Transition Metal Oxides in Charge-Generation Layers for Stacked Organic Light-Emitting DiodesADVANCED FUNCTIONAL MATERIALS, Issue 11 2010Sami Hamwi Abstract The mechanism of charge generation in transition metal oxide (TMO)-based charge-generation layers (CGL) used in stacked organic light-emitting diodes (OLEDs) is reported upon. An interconnecting unit between two vertically stacked OLEDs, consisting of an abrupt heterointerface between a Cs2CO3 -doped 4,7-diphenyl-1,10-phenanthroline layer and a WO3 film is investigated. Minimum thicknesses are determined for these layers to allow for simultaneous operation of both sub-OLEDs in the stacked device. Luminance,current density,voltage measurements, angular dependent spectral emission characteristics, and optical device simulations lead to minimum thicknesses of the n-type doped layer and the TMO layer of 5 and 2.5,nm, respectively. Using data on interface energetic determined by ultraviolet photoelectron and inverse photoemission spectroscopy, it is shown that the actual charge generation occurs between the WO3 layer and its neighboring hole-transport material, 4,4',4"-tris(N -carbazolyl)-triphenyl amine. The role of the adjacent n-type doped electron transport layer is only to facilitate electron injection from the TMO into the adjacent sub-OLED. [source] Highly Efficient p-i-n and Tandem Organic Light-Emitting Devices Using an Air-Stable and Low-Temperature-Evaporable Metal Azide as an n-DopantADVANCED FUNCTIONAL MATERIALS, Issue 11 2010Kyoung Soo Yook Abstract Cesium azide (CsN3) is employed as a novel n-dopant because of its air stability and low deposition temperature. CsN3 is easily co-deposited with the electron transporting materials in an organic molecular beam deposition chamber so that it works well as an n-dopant in the electron transport layer because its evaporation temperature is similar to that of common organic materials. The driving voltage of the p-i-n device with the CsN3 -doped n-type layer and a MoO3 -doped p-type layer is greatly reduced, and this device exhibits a very high power efficiency (57,lm W,1). Additionally, an n-doping mechanism study reveals that CsN3 was decomposed into Cs and N2 during the evaporation. The charge injection mechanism was investigated using transient electroluminescence and capacitance,voltage measurements. A very highly efficient tandem organic light-emitting diodes (OLED; 84,cd A,1) is also created using an n,p junction that is composed of the CsN3 -doped n-type organic layer/MoO3 p-type inorganic layer as the interconnecting unit. This work demonstrates that an air-stable and low-temperature-evaporable inorganic n-dopant can very effectively enhance the device performance in p-i-n and tandem OLEDs, as well as simplify the material handling for the vacuum deposition process. [source] Interface Engineering for Organic ElectronicsADVANCED FUNCTIONAL MATERIALS, Issue 9 2010Hong Ma Abstract The field of organic electronics has been developed vastly in the past two decades due to its promise for low cost, lightweight, mechanical flexibility, versatility of chemical design and synthesis, and ease of processing. The performance and lifetime of these devices, such as organic light-emitting diodes (OLEDs), photovoltaics (OPVs), and field-effect transistors (OFETs), are critically dependent on the properties of both active materials and their interfaces. Interfacial properties can be controlled ranging from simple wettability or adhesion between different materials to direct modifications of the electronic structure of the materials. In this Feature Article, the strategies of utilizing surfactant-modified cathodes, hole-transporting buffer layers, and self-assembled monolayer (SAM)-modified anodes are highlighted. In addition to enabling the production of high-efficiency OLEDs, control of interfaces in both conventional and inverted polymer solar cells is shown to enhance their efficiency and stability; and the tailoring of source,drain electrode,semiconductor interfaces, dielectric,semiconductor interfaces, and ultrathin dielectrics is shown to allow for high-performance OFETs. [source] Phenylcarbazole-Based Phosphine Oxide Host Materials For High Efficiency In Deep Blue Phosphorescent Organic Light-Emitting DiodesADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Soon Ok Jeon Abstract Highly efficient deep blue phosphorescent organic light-emitting diodes are developed using novel phenylcarbazole-based phosphine oxide host materials (PPO1 and PPO2). A deep blue phosphorescent dopant, tris((3,5-difluoro-4-cyanophenyl)pyridine) iridium, is doped into PPO1 and PPO2 at a doping concentration of 15% and a high quantum efficiency of 18.4% is obtained with color coordinates of (0.14, 0.15). [source] A Bipolar Host Material Containing Triphenylamine and Diphenylphosphoryl-Substituted Fluorene Units for Highly Efficient Blue ElectrophosphorescenceADVANCED FUNCTIONAL MATERIALS, Issue 17 2009Fang-Ming Hsu Abstract Highly efficient blue electrophosphorescent organic light-emitting diodes incorporating a bipolar host, 2,7-bis(diphenylphosphoryl)-9-[4-(N,N -diphenylamino)phenyl]-9-phenylfluorene (POAPF), doped with a conventional blue triplet emitter, iridium(III) bis[(4,6-difluoro-phenyl)pyridinato- N,C2´]picolinate (FIrpic) are fabricated. The molecular architecture of POAPF features an electron-donating (p-type) triphenylamine group and an electron-accepting (n-type) 2,7-bis(diphenyl-phosphoryl)fluorene segment linked through the sp3 -hybridized C9 position of the fluorene unit. The lack of conjugation between these p- and n-type groups endows POAPF with a triplet energy gap (ET) of 2.75,eV, which is sufficiently high to confine the triplet excitons on the blue-emitting guest. In addition, the built-in bipolar functionality facilitates both electron and hole injection. As a result, a POAPF-based device doped with 7,wt% FIrpic exhibits a very low turn-on voltage (2.5,V) and high electroluminescence efficiencies (20.6% and 36.7,lm W,1). Even at the practical brightnesses of 100 and 1000,cd m,2, the efficiencies remain high (20.2%/33.8,lm W,1 and 18.8%/24.3,lm W,1, respectively), making POAPF a promising material for use in low-power-consumption devices for next-generation flat-panel displays and light sources. [source] Versatile, Benzimidazole/Amine-Based Ambipolar Compounds for Electroluminescent Applications: Single-Layer, Blue, Fluorescent OLEDs, Hosts for Single-Layer, Phosphorescent OLEDsADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Chih-Hsin Chen Abstract A series of compounds containing arylamine and 1,2-diphenyl-1H -benz[d]imidazole moieties are developed as ambipolar, blue-emitting materials with tunable blue-emitting wavelengths, tunable ambipolar carrier-transport properties and tunable triplet energy gaps. These compounds possess several novel properties: (1) they emit in the blue region with high quantum yields; (2) they have high morphological stability and thermal stability; (3) they are capable of ambipolar carrier transport; (4) they possess tunable triplet energy gaps, suitable as hosts for yellow-orange to green phosphors. The electron and hole mobilities of these compounds lie in the range of 0.68,144,×,10,6 and 0.34,147,×,10,6,cm2 V,1 s,1, respectively. High-performance, single-layer, blue-emitting, fluorescent organic light-emitting diodes (OLEDs) are achieved with these ambipolar materials. High-performance, single-layer, phosphorescent OLEDs with yellow-orange to green emission are also been demonstrated using these ambipolar materials, which have different triplet energy gaps as the host for yellow-orange-emitting to green-emitting iridium complexes. When these ambipolar, blue-emitting materials are lightly doped with a yellow-orange-emitting iridium complex, white organic light-emitting diodes (WOLEDs) can be achieved, as well by the use of the incomplete energy transfer between the host and the dopant. [source] Phosphorescent OLEDs: Synthesis and Characterization of Red-Emitting Iridium(III) Complexes for Solution-Processable Phosphorescent Organic Light-Emitting Diodes (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 14 2009Mater. On page 2205, S.H. Jin and co-workers report on the development of red-emitting iridium(III) complexes for solution-processable phosphorescent organic light-emitting diodes (PhOLEDs). This frontispiece image shows the fabrication of full-color PhOLEDs by an inkjet printing method. The combination of good efficiency and color purity identifies this material as a promising candidate for red phosphorescent doping of PhOLEDs. Structure-property relationships for improving the performance of such devices are also investigated. [source] Synthesis and Characterization of Red-Emitting Iridium(III) Complexes for Solution-Processable Phosphorescent Organic Light-Emitting DiodesADVANCED FUNCTIONAL MATERIALS, Issue 14 2009Seung-Joon Lee Abstract A new series of highly efficient red-emitting phosphorescent Ir(III) complexes, (Et-CVz-PhQ)2Ir(pic-N-O), (Et-CVz-PhQ)2Ir(pic), (Et-CVz-PhQ)2Ir(acac), (EO-CVz-PhQ)2Ir(pic-N-O), (EO-CVz-PhQ)2Ir(pic), and (EO-CVz-PhQ)2Ir(acac), based on carbazole (CVz)-phenylquinoline (PhQ) main ligands and picolinic acid N-oxide (pic-N-O), picolinic acid (pic), and acetylacetone (acac) ancillary ligands, are synthesized for phosphorescent organic light-emitting diodes (PhOLEDs), and their photophysical, electrochemical, and electroluminescent (EL) properties are investigated. All of the Ir(III) complexes have high thermal stability and emit an intense red light with an excellent color purity at CIE coordinates of (0.65,0.34). Remarkably, high-performance solution-processable PhOLEDs were fabricated using Ir(III) complexes with a pic-N-O ancillary ligand with a maximum external quantum efficiency (5.53%) and luminance efficiency (8.89,cd,A,1). The novel use of pic-N-O ancillary ligand in the synthesis of phosphorescent materials is reported. The performance of PhOLEDs using these Ir(III) complexes correlates well with the results of density functional theory calculations. [source] Characteristics of Solution-Processed Small-Molecule Organic Films and Light-Emitting Diodes Compared with their Vacuum-Deposited CounterpartsADVANCED FUNCTIONAL MATERIALS, Issue 10 2009Tae-Woo Lee Abstract Although significant progress has been made in the development of vacuum-deposited small-molecule organic light-emitting diodes (OLEDs), one of the most desired research goals is still to produce flexible displays by low-cost solution processing. The development of solution-processed OLEDs based on small molecules could potentially be a good approach but no intensive studies on this topic have been conducted so far. To fabricate high-performance devices based on solution-processed small molecules, the underlying nature of the produced films and devices must be elucidated. Here, the distinctive characteristics of solution-processed small-molecule films and devices compared to their vacuum-deposited counterparts are reported. Solution-processed blue OLEDs show a very high luminous efficiency (of about 8.9,cd A,1) despite their simplified structure. A better hole-blocking and electron-transporting layer is essential for achieving high-efficiency solution-processed devices because the solution-processed emitting layer gives the devices a better hole-transporting capability and more electron traps than the vacuum-deposited layer. It is found that the lower density of the solution-processed films (compared to the vacuum-deposited films) can be a major cause for the short lifetimes observed for the corresponding devices. [source] Synthesis, Photophysical, and Electroluminescent Device Properties of Zn(II)-Chelated Complexes Based on Functionalized Benzothiazole DerivativesADVANCED FUNCTIONAL MATERIALS, Issue 10 2009Soo-Gyun Roh Abstract New Zn(II)-chelated complexes based on benzothiazole derivatives, including substituted functional groups such as methyl (MeZn), methoxy (MeOZn), or fluorenyl unit (FuZn), are investigated to produce white-light emission. 2-(2-Hydroxyphenyl)benzothiazole derivatives in toluene and DMSO exhibit excited-state intramolecular proton transfer (ESIPT), leading to a large Stokes shift of the fluorescence emission. However, in methanol they exhibit no ESIPT due to the intermolecular hydrogen bonding between the 2-(2-hydroxyphenyl)benzothiazole derivative and methanol. Their Zn(II)-chelated complexes exhibit the absorption band red-shifted at 500,nm in nonpolar solvent and the absorption band blue-shifted at about 420,nm in protic solvent. In multilayer electroluminescent devices, methyl-substituted Zn(II)-chelated complex (MeZn) exhibits excellent power efficiency and fluorene-substituted Zn(II)-chelated complex (FuZn) has a high luminance efficiency (1,cd,m,2 at 3.5,V, 10,400,cd,m,2 at 14,V). The EL spectra of Zn(II)-chelated complexes based on benzothiazole derivatives exhibit broad emission bands. In addition, their electron-transport property for red,green,blue (RGB) organic light-emitting diodes (OLEDs) is systematically studied, in comparison with that of Alq3. The results demonstrate the promising potential of MeZn as an electron-transporting layer (ETL) material in preference to Alq3, which is widely used as an ETL material. [source] Triplet Harvesting in Hybrid White Organic Light-Emitting DiodesADVANCED FUNCTIONAL MATERIALS, Issue 9 2009Gregor Schwartz Abstract White organic light-emitting diodes (OLEDs) are highly efficient large-area light sources that may play an important role in solving the global energy crisis, while also opening novel design possibilities in general lighting applications. Usually, highly efficient white OLEDs are designed by combining three phosphorescent emitters for the colors blue, green, and red. However, this procedure is not ideal as it is difficult to find sufficiently stable blue phosphorescent emitters. Here, a novel approach to meet the demanding power efficiency and device stability requirements is discussed: a triplet harvesting concept for hybrid white OLED, which combines a blue fluorophor with red and green phosphors and is capable of reaching an internal quantum efficiency of 100% if a suitable blue emitter with high-lying triplet transition is used is introduced. Additionally, this concept paves the way towards an extremely simple white OLED design, using only a single emitter layer. [source] Multifunctional Deep-Blue Emitter Comprising an Anthracene Core and Terminal Triphenylphosphine Oxide GroupsADVANCED FUNCTIONAL MATERIALS, Issue 4 2009Chen-Han Chien Abstract A highly efficient blue-light emitter, 2- tert -butyl-9,10-bis[4,-(diphenyl-phosphoryl)phenyl]anthracene (POAn) is synthesized, and comprises electron-deficient triphenylphosphine oxide side groups appended to the 9- and 10-positions of a 2- tert -butylanthracene core. This sophisticated anthracene compound possesses a non-coplanar configuration that results in a decreased tendency to crystallize and weaker intermolecular interactions in the solid state, leading to its pronounced morphological stability and high quantum efficiency. In addition to serving as an electron-transporting blue-light-emitting material, POAn also facilitates electron injection from the Al cathode to itself. Consequently, simple double-layer devices incorporating POAn as the emitting, electron-transporting, and -injecting material produce bright deep-blue lights having Commission Internationale de L'Eclairage coordinates of (0.15,0.07). The peak electroluminescence performance was 4.3% (2.9 cd A,1). For a device lacking an electron-transport layer or alkali fluoride, this device displays the best performance of any such the deep-blue organic light-emitting diodes reported to date. [source] Highly Efficient Red Phosphorescent OLEDs based on Non-Conjugated Silicon-Cored Spirobifluorene Derivative Doped with Ir-ComplexesADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Yi-Yeol Lyu Abstract A novel host material containing silicon-cored spirobifluorene derivative (SBP-TS-PSB), is designed, synthesized, and characterized for red phosphorescent organic light-emitting diodes (OLEDs). The SBP-TS-PSB has excellent thermal and morphological stabilities and exhibits high electroluminescence (EL) efficiency as a host for the red phosphorescent OLEDs. The electrophosphorescence properties of the devices using SBP-TS-PSB as the host and red phosphorescent iridium (III) complexes as the emitter are investigated and these devices exhibit higher EL performances compared with the reference devices with 4,4,- N,N,-dicarbazole-biphenyl (CBP) as a host material; for example, a (piq)2Ir(acac)-doped SBP-TS-PSB device shows maximum external quantum efficiency of ,ext,=,14.6%, power efficiency of 10.3 lm W,1 and Commission International de L'Eclairage color coordinates (0.68, 0.32) at J,=,1.5,mA cm,2, while the device with the CBP host shows maximum ,ext,=,12.1%. These high performances can be mainly explained by efficient triplet energy transfer from the host to the guests and improved charge balance attributable to the bipolar characteristics of the spirobifluorene group. [source] Highly Efficient Hole Injection Using Polymeric Anode Materials for Small-Molecule Organic Light-Emitting DiodesADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Kaushik Roy Choudhury Abstract A novel, highly efficient hole injection material based on a conducting polymer polythienothiophene (PTT) doped with poly(perfluoroethylene-perfluoroethersulfonic acid) (PFFSA) in organic light-emitting diodes (OLEDs) is demonstrated. Both current,voltage and dark-injection-current transient data of hole-only devices demonstrate high hole-injection efficiency employing PTT:PFFSA polymers with different organic charge-transporting materials used in fluorescent and phosphorescent organic light-emitting diodes. It is further demonstrated that PTT:PFFSA polymer formulations applied as the hole injection layer (HIL) in OLEDs reduce operating voltages and increase brightness significantly. Hole injection from PTT:PFFSA is found to be much more efficient than from typical small molecule HILs such as copper phthalocyanine (CuPc) or polymer HILs such as polyethylene dioxythiophene: polystyrene sulfonate (PEDOT-PSS). OLED devices employing PTT:PFFSA polymer also demonstrate significantly longer lifetime and more stable operating voltages compared to devices using CuPc. [source] Solution-Processible Phosphorescent Blue Dendrimers Based on Biphenyl-Dendrons and Fac -tris(phenyltriazolyl)iridium(III) Cores,ADVANCED FUNCTIONAL MATERIALS, Issue 19 2008Shih-Chun Lo Abstract Solution-processible saturated blue phosphorescence is an important goal for organic light-emitting diodes (OLEDs). Fac -tris(5-aryltriazolyl)iridium(III) complexes can emit blue phosphorescence at room temperature. Mono- and doubly dendronized fac -tris(1-methyl-5-phenyl-3- n -propyl-1H -[1,2,4]triazolyl)iridium(III) 1 and fac -tris{1-methyl-5-(4-fluorophenyl)-3- n -propyl-1H -[1,2,4]triazolyl}iridium(III) 4 with first generation biphenyl-based dendrons were prepared. The dendrimers emitted blue light at room temperature and could be solution processed to form thin films. The doubly dendronized 3 had a film photoluminescence quantum yield of 67% and Commission Internationale de l'Eclairage (CIE) coordinates of (0.17, 0.33). OLEDs comprised of a neat film of dendrimer 3 and an electron transport layer achieved a brightness of 142,cd m,2 at 3.8,V with an external quantum efficiency of 7.9%, and CIE coordinates of (0.18, 0.35). Attachment of the fluorine atom to the emissive core had the effect of moving the luminescence to shorter wavelengths but also quenched the luminescence of the mono- and doubly dendronized dendrimers. [source] Novel Heteroleptic CuI Complexes with Tunable Emission Color for Efficient Phosphorescent Light-Emitting Diodes,ADVANCED FUNCTIONAL MATERIALS, Issue 15 2007Q. Zhang Abstract A series of orange-red to red phosphorescent heteroleptic CuI complexes (the first ligand: 2,2,-biquinoline (bq), 4,4,-diphenyl-2,2,-biquinoline (dpbq) or 3,3,-methylen-4,4,-diphenyl-2,2,-biquinoline (mdpbq); the second ligand: triphenylphosphine or bis[2-(diphenylphosphino)phenyl]ether (DPEphos)) have been synthesized and fully characterized. With highly rigid bulky biquinoline-type ligands, complexes [Cu(mdpbq)(PPh3)2](BF4) and [Cu(mdpbq)(DPEphos)](BF4) emit efficiently in 20,wt,% PMMA films with photoluminescence quantum yield of 0.56 and 0.43 and emission maximum of 606,nm and 617,nm, respectively. By doping these complexes in poly(vinyl carbazole) (PVK) or N -(4-(carbazol-9-yl)phenyl)-3,6-bis(carbazol-9-yl) carbazole (TCCz), phosphorescent organic light-emitting diodes (OLEDs) were fabricated with various device structures. The complex [Cu(mdpbq)(DPEphos)](BF4) exhibits the best device performance. With the device structure of ITO/PEDOT/TCCz:[Cu(mdpbq)(DPEphos)](BF4) (15,wt,%)/TPBI/LiF/Al (III), a current efficiency up to 6.4,cd,A,1 with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.61, 0.39) has been realized. To our best knowledge, this is the first report of efficient mononuclear CuI complexes with red emission. [source] | ||||||||||||||||||||||||||||