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排序方式: 共有307条查询结果,搜索用时 171 毫秒
131.
Varatharajan Sivasubramaniam Florian Brodkorb Stephanie Hanning Oliver Buttler Hans Peter Loebl Volker van Elsbergen Herbert Boerner Ullrich Scherf Martin Kreyenschmidt 《Solid State Sciences》2009,11(11):1933-1940
Different analytical tools and methodologies are currently employed to determine degradation products of organic blue light emitting devices in order to identify the failure mechanisms which determine the lifetime of these devices. This article provides a deeper understanding of degradation mechanisms of organic light emitting diodes (OLEDs) during device operation. Degradation products of blue emitting devices containing 8% of the phosphorescent emitter iridium(III)bis(4,6-difluorophenyl)-pyridinato-N,C2′ picolinate (FIrpic) in a matrix containing bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminium (BAlq) as electron transport layer (ETL), 4,4′,4″-tri(N-carbazolyl)triphenylamine (TCTA) and N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4″-diamine (α-NPD) were investigated using laser desorption ionization (LDI) coupled with a time of flight mass spectrometry (TOF/MS). Especially chemical degradation pathways of the hole transport materials TCTA and α-NPD were investigated. The comparison of experimental data of unstressed and stressed device revealed that new reaction products are formed during the device operation. The linkage of TCTA fragments to the α-NPD core in an interfacial reaction as well as a dimerization of TCTA itself was observed. Ten new reaction products could be characterized via LDI-TOF-MS. Some of these compounds might possess a negative influence on the drop of efficiency and lifetime of blue light emitting devices based on FIrpic. 相似文献
132.
Concentration quenching effect of organic light‐emitting devices using DCM1‐doped tetraphenylgermole
Young H. Park Yongmin Kim Honglae Sohn Ki‐Seok An 《Journal of Physical Organic Chemistry》2012,25(3):207-210
We examine the concentration quenching of a 4‐(dicyanomethylene)2‐methyl‐6‐(p‐dimethylaminostyryl)‐4H‐pyran (DCM1)‐doped 1,1‐bis(2‐phenylethynyl)‐2,3,4,5‐tetraphenylgermole (HPAG)‐based light‐emitting diode. Originally, HPAG emits in the ~500‐nm (green) region, which can be converted to a red‐emission material by using DCM1 doping. As the DCM1 concentration increased from 1 to 10 wt%, the electroluminescence peak positions are red‐shifted from 604 to 644 nm, respectively. Increasing doping density not only shows the red‐shift but also shows decreasing luminance efficiency. Förster energy transfer between the HPAG host material and the DCM1 guest material is responsible for the strong red‐emission behavior. The calculated Förster radius (4.0 nm) for excellent Förster energy transfer characteristics with increasing doping concentration of DCM1 is consistent with experimental results. The maximum luminance efficiency was 6.64 cd/A at 11.0 mA/cm2. The HPAG germole compound shows excellent red‐emission host–guest system properties for red organic light‐emitting device applications. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
133.
Silsesquioxane-based nanocomposite dendrimers with photo-luminescent and charge transport properties
The synthesis and characterization of octavinylsilsesquioxane (OVS)-based nanocomposite dendrimers with luminescent and charge transport properties are reported. The nanocomposite dendrimers were prepared in high yield using mild Heck chemistry of mono-haloaromatic compounds with the peripheral vinylsilane groups of OVS. Attachment of 2-naphthalene, 2-(9,9-dimethyl)fluorene, and 2-(4-phenyl)-5-(1-naphthyl)-1,3,4-oxadiazole resulted in materials with blue-violet emission (360-380 nm) and photo-luminescent quantum efficiencies (PLQEs) from 1 to 26%. Blue-green emission was observed for attachment of 1-pyrene, 9-anthracene, and N1-(4-phenyl)-N1,N4,N4-triphenylbenzene-1,4-diamine with PLQEs ranging from 23 to 50%. Despite the planar characteristics of the organic dendrons, the nanocomposite dendrimers are completely amorphous and have high glass transition temperatures (Tg) ranging from 115 to 186 degrees C with decomposition temperatures (Td) exceeding 450 degrees C. Matrix-assisted laser desorption ionization-time of flight shows that unlike traditional Heck chemistry, haloaromatic compounds are adding twice across the vinylsilane groups. Finally, organic light emitting diodes using the aromatic amine-based dendrimer as hole injection layers show 55% improvement in device efficiency over traditional materials (5.16 vs. 3.24 cd A(-1)) with brightness levels exceeding 40,000 cd m(-2). 相似文献
134.
135.
Chul Yoon 《Applied Surface Science》2010,256(23):6951-6955
Investigations were carried out on the changes in the electrical and optical properties and surface roughness of the indium-tin oxide (ITO) anode as a function of DC pulse frequency during facing-target sputtering. The current density-voltage-luminescence (J-V-L) characteristics of organic light emitting diodes (OLEDs) developed on the anodes were measured and analyzed in relation to the properties of ITO. When the pulsed DC frequency was less than 120 kHz, the resistivity of ITO was maintained well below 4.3 × 10−4 Ω cm and the optical energy band gap was greater than 4.1 eV, but these properties changed abruptly at 150 kHz with the morphological transition from columnar to equi-axed. Meanwhile, the surface roughness decreased continuously with increasing pulsed DC frequency up to 150 kHz. The J-V characteristics of the built-up OLED deteriorated slightly as the pulsed DC frequency increased to 120 kHz and then deteriorated rapidly at 150 kHz. The L-V curves, however, showed an improvement of luminescence as the frequency increased up to 120 kHz. These J-V-L characteristics imply that ITO which is more conductive and with a higher band gap can be obtained at the lower pulsed DC frequencies, which is desirable for higher current flow; however, better luminescence is closely related to smoother surfaces. Therefore, for the optimized J-V-L performance of OLEDs, a moderate pulse DC frequency, below the morphological transition of ITO, is desirable. 相似文献
136.
Myeon‐Cheon Choi Jae‐Chul Hwang Chiwan Kim Youngkyoo Kim Chang‐Sik Ha 《Journal of polymer science. Part A, Polymer chemistry》2010,48(22):5189-5197
We synthesized new polynorbornene dicarboximide (PCaNI) functionalized with hole‐transporting carbazole moieties and its copolymer (PCaNA) by ring‐opening metathesis polymerization (ROMP), where the PCaNA was further reacted with 3‐amino‐triethoxysilane to prepare PCaNI/silica hybrid. We also investigated the feasibility of PCaNI and PCaNI/silica hybrid (PCaSi) as a hole‐transporting material for hybrid organic light emitting devices (HOLEDs). To improve the performance of the PCaNI‐based HOLEDs, N,N′‐diphenyl‐N,N′‐(3‐methylphenyl)‐[1,1′‐biphenyl]‐4‐4′‐diamine (TPD) was also introduced into the PCaNI matrix. Results showed that PCaNI exhibited high glass transition temperature (~260 °C) and high optical transparency in the visible region. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of PCaNI were measured as 5.6 and 2.2 eV, while the TPD‐doped PCaNI showed 5.7 eV (HOMO) and 2.6 eV (LUMO). The PCaNI/silica hybrid nanolayers showed excellent solvent resistance due to the formation of covalent bonds between ITO and PCaNI. The HOLEDs with PCaNI/TPD or PCaSi/TPD hybrid nanolayers exhibited relatively higher luminance (~10,000 cd/m2), lower operating voltage (~6.5 V at 300 cd/m2), and higher current efficiency (~2.7 cd/A). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
137.
138.
E. Hartmann P. Boher Ch. Defranoux L. Jolivet M.-O. Martin 《Journal of luminescence》2004,110(4):407-412
We report on the analysis of layer materials commonly used for the fabrication of organic light-emitting diodes (OLEDs) by means of spectroscopic ellipsometry operating in the ultraviolet–visible (UV–VIS) and in the mid-infrared (mid-IR) range of the electromagnetic spectrum. On covering a wide spectral range, these non-destructive, non-contact techniques offer a huge potential in characterizing thin films in terms of layer thickness values, optical indices, absorption properties modified by incorporating optically active dopant molecules, and, finally, electrical layer properties. Individual absorption bands of single organic films can significantly affect the luminance and performance efficiency of OLEDs when building multi-layer stacks. Using mid-IR spectroscopic ellipsometry, the resistance of as-deposited and annealed indium–tin oxide (ITO) layers on glass is determined and compared with values obtained by four-point probe techniques. 相似文献
139.
Monocyclometalated Gold(III) Monoaryl Complexes—A New Class of Triplet Phosphors with Highly Tunable and Efficient Emission Properties
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Alexander Szentkuti Michael Bachmann Dr. Jai Anand Garg Dr. Olivier Blacque Dr. Koushik Venkatesan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(9):2585-2596
Highly tunable and rich phosphorescent emission properties based on the stable monocyclometalated gold(III) monoaryl structural motif are reported. Monochloro complexes of the type cis‐[(N^C)Au(C6H2(CF3)3)(Cl)] N^C=2‐phenylpyridine (ppy)] ( 1 ), [N^C=benzo[h]quinoline (bzq)] ( 2 ), [N^C=2‐(5‐Methyl‐2‐thienyl)pyridine (5m‐thpy)] ( 3 ) were successfully prepared in modest to good yields by reacting an excess of 2, 4, 6‐tris(trifluoromethyl)phenyl lithium (LiFmes) with the corresponding dichloride complexes cis‐[(N^C)AuCl2]. Subsequent replacement of the chloride ligand in 1 with strong ligand field strength such as cyanide and terminal alkynes resulted in complexes of the type cis‐[(ppy)Au(Fmes)(R)] R=CN ( 4 ), I ( 5 ), C?C?C6H5 ( 6 ) and C?C?C6H4N(C6H5)‐p ( 7 ). Single crystal X‐ray diffraction studies of all the complexes except 7 were performed to further corroborate their chemical identity. Thermogravimetric analysis (TGA) studies of the uncommon cis configured aryl alkyne complex 7 confirmed the high stability of this complex. Detailed photophysical investigations carried out in solution at room temperature, at 77 K (2‐MeTHF) in rigidified media, solid state and 5 wt % PMMA revealed the phosphorescent nature of emission in these complexes. Additionally, their behavior was found to be governed based on both the nature of the cyclometalated ligand and the electronic properties of the ancillary ligands. Highly efficient interligand charge transfer in complex 7 provides access to a wide range of emission colors (solvent‐dependent) from deep blue to red with phosphorescence emission quantum yield of 30 % (441 nm) and 39 % (622 nm) in solution and solid state, respectively, and is the highest reported for any AuIII complexes. DFT and TDDFT calculations carried out further validated the observations and assignments based on the photophysical experimental findings. 相似文献
140.
Two novel thermally activated delayed fluorescence (TADF) materials (PTZ-XTN and 2PTZ-XTN), with phenothiazine (PTZ) as an electron donor and xanthenone derivatives (XTN) as electron acceptors, were designed and theoretically investigated as blue OLED emitters. We used density functional theory (DFT) and time dependent DFT (TD-DFT) calculations to determine the electron distribution of HOMO and LUMO and the energy of the lowest singlet (S1) and the lowest triplet (T1) excited states. The large dihedral angle between the electron donor and the electron acceptor imparted a small spatial overlap between HOMO and LUMO in all the materials. This charge separation of the HOMO and LUMO leads to a small energy gap between the S1 state and T1 state, thereby leading to TADF emission. Among the materials studied, PTZ-XTN has the most suitable properties for a blue TADF OLED emitter, even though 2PTZ-XTN has the smallest energy gap between the S1 and T1 states. 相似文献