Home About us Contact
|
Home About us Contact | ||
|
|
||
Maximum External Quantum Efficiency (maximum + external_quantum_efficiency)
Selected AbstractsSynthesis and luminescence of poly(phenylacetylene)s with pendant iridium complexes and carbazole groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2010José Vicente Abstract Poly(phenylacetylene)s containing pendant phosphorescent iridium complexes have been synthesized and their electrochemical, photo- and electroluminescent properties studied. The polymers have been synthesized by rhodium-catalyzed copolymerization of 9-(4-ethynylphenyl)carbazole (CzPA) and phenylacetylenes (C,N)2Ir(,2 - O,O,-MeC(O)CHC(O)C6H4CCH-4) (C,N = ,2 - N,C1 -2-(pyridin-2-yl)phenyl (IrppyPA) or ,2 - N,C1 -2-(isoquinolin-1-yl)phenyl (IrpiqPA)). In addition, organic poly(phenylacetylene)s with pendant carbazole groups have been synthesized by rhodium-catalyzed copolymerization of CzPA and 1-ethynyl-4-pentylbenzene. Complex (C,N)2Ir(,2 - O,O,-MeC(O)CHC(O)Ph) (IrpiqPh; C,N = 2-(isoquinolin-1-yl)phenyl-,2 - N,C1) was prepared and characterized. While the copolymers of the Irppy series were weakly phosphorescent, those of the Irpiq series displayed at room temperature intense emissions from the carbazole (fluorescence) and iridium (phosphorescence) emitters, being the latter dominant when the spectra were recorded using polymer films. Triple layer OLED devices employing copolymers of the Irpiq series or the model complex IrpiqPh yielded electroluminescence with an emission spectra originating from the iridium complex and maximum external quantum efficiencies of 0.46% and 2.99%, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3744,3757, 2010 [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] 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] 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] En Route to High External Quantum Efficiency (,12%), Organic True-Blue-Light-Emitting Diodes Employing Novel Design of Iridium (III) PhosphorsADVANCED MATERIALS, Issue 21 2009Yuan-Chieh Chiu True-blue Ir(III) phosphors are designed, synthesized, and applied to multilayered organic true-blue-light-emitting diodes with CIEx,y color chromaticity of (0.15,0.11) and maximum external quantum efficiency of ,12%, demonstrating unprecedented performance among all blue-phosphorescent OLEDs ever documented. The molecular-design strategy and subsequent device-fabrication protocol reveal a major development in OLEDs. [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] White-Light Emission from a Single Polymer with Singlet and Triplet Chromophores on the BackboneMACROMOLECULAR RAPID COMMUNICATIONS, Issue 24 2006Hongyu Zhen Abstract Summary: A strategy to generate an efficient white-light emission has been developed by mixing fluorescence and phosphorescence emission from a single polymer. Fluorene is used as the blue-emissive component, benzothiadiazole (BT) and the iridium complex [(btp)2Ir(tmd)] are incorporated into a polyfluorene backbone, respectively, as green- and red-emissive chromophores by Suzuki polycondensation. By changing the contents of BT and [(btp)2Ir(tmd)] in the polymer, the electroluminescence spectrum from a single polymer can be adjusted to achieve white-light emission. A white polymeric light-emitting diode (WPLED) with a structure of ITO/PEDOT:PSS/PVK/PFIrR1G03/CsF/Al shows a maximum external quantum efficiency of 3.7% and the maximum luminous efficiency of 3.9 cd,·,A,1 at the current density of 1.6 mA,·,cm,2 with the CIE coordinates of (0.33, 0.34). The maximum luminance of 4,180 cd,·,m,2 is achieved at the current density of 268 mA,·,cm,2 with the CIE coordinates of (0.31, 0.32). The white-light emissions from such polymers are stable in the white-light region at all applied voltages, and the electroluminescence efficiencies decline slightly with the increasing current density, thus indicating that the approach of incorporating singlet and triplet species into the polymer backbone is promising for WPLEDs. Structure of PFIrR1G04 and the EL spectra of its devices under various voltages. Device structure: ITO/PEDOT:PSS/PVK/polymer/CsF/Al. [source] Internal parameters and optical properties of green II-VI heterostructure lasers with active region composed of multi-sheet electronically-coupled CdSe quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2010Aliaksei G. Vainilovich Abstract Optically pumped green-emitting ZnSe-based laser heterostructures of optimized design have been grown by molecular-beam epitaxy and studied. The structures containing five electronically-coupled stacked CdSe quantum dot (QD) sheets demonstrate the minimum threshold power density of 2.2 kW/cm2 and the maximum external quantum efficiency of , 50%. Internal laser characteristics were determined by measuring the differential laser efficiency and laser threshold of a series of samples with different cavity lengths. The characteristic gain and internal quantum efficiency of the structures have been shown to reach the values as high as ,G0 = 114 cm -1 and ,i = 65.4%, while the transparency threshold and internal losses are evaluated as low as IT = 1.22 kW/cm2 and ,i = 2.55 cm -1, respectively. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||