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排序方式: 共有399条查询结果,搜索用时 15 毫秒
31.
Recently, significant efforts have been made to develop highly efficient organic light-emitting diodes (OLEDs) employing reverse intersystem crossing (RISC) owing to its capability of harvesting non-emissive triplet states. Up to date, most of such emitters were small-molecular-weight materials that needed to be doped into a host material. Due to the advantages of ease device fabrication and excellent photoluminescent properties, polymer-based RISC emitters should be developed. In this study, we reported a polyfluorene-based copolymer of poly[{9,9-dioctyl-2,7-divinylene-fluorenylene-alt-co-{2-methoxy-5-(2-ethylhexyloxy)-1,4-phenyene}] (PFOPV), which is a solution-processable, non-doped, high-molecular-weight material exhibiting RISC characteristics. A systematical magneto-electroluminescence study joint by time-resolved spectra revealed that charge transfer (CT) states would be generated between PFO and MEH-PPV components of PFOPV, and triplet CT states can participate in RISC process and contribute significantly to the emission. The PFOPV device shows excellent EL performance with EL efficiency of 12.7 cd/A and EQE of 2.2%, which is about 10–15 times and 2–4 times higher than those of PFO (0.9 cd/A, 0.63%) and MEH-PPV (1.2 cd/A, 1.1%) homopolymer devices, respectively. 相似文献
32.
The impact of defect concentration and current density on the effective singlet exciton diffusion length in 4’-bis(carbazol-9-yl)biphenyl (CBP) is quantified by analyzing the electroluminescent characteristics of several sets of OLEDs. The defect concentration and effective diffusion length are determined through fitting of the defect and CBP emission bands in the electroluminescence spectra under constant current operation using an analytical model derived based on the competition between exciton diffusion and energy transfer to defects. Defect concentrations of 3 ± 1 × 1018 cm−3, 2 ± 1 × 1018 cm−3 and 0.3 ± 0.7 × 1018 cm−3 are calculated in three sets of OLEDs, in which the effective diffusion length decreases as the defect concentration increases. Modelling the dependence of the effective diffusion length on defect concentration a “defect free” diffusion length of 4.5 ± 0.3 nm is obtained for CBP singlet excitons in these devices operated under low current density. We also show that the driving voltage scales linearly with the defect concentration. 相似文献
33.
R.-Y. Wang W.-L. Jia H. Aziz G. Vamvounis S. Wang N.-X. Hu Z. D. Popović J. A. Coggan 《Advanced functional materials》2005,15(9):1483-1487
A new organic blue‐light emitter 1‐methyl‐2‐(anthryl)‐imidazo[4,5‐f][1,10]‐phenanthroline ( 1 ) has been synthesized and fully characterized. The utility of compound 1 as a blue‐light emitter in electroluminescent (EL) devices has been evaluated by fabricating a series of EL devices A where compound 1 functions as an emitter. The EL spectrum of device series A has the emission maximum at 481 nm with the CIE (Commission Internationale de l'Eclairage) color coordinates 0.198 and 0.284. The maximum luminance of devices in series A is 4000 cd m–2 and the best external quantum efficiency of device series A is 1.82 %. The utility of compound 1 as an electron injection–electron transport material has been evaluated by constructing a set of EL devices B where 1 is used as either the electron‐injection layer or the electron injection–electron transport layer. The performance of device series B is compared to the standard device in which Alq3 (tris(8‐hydroxyquinoline) aluminum) is used as the electron injection–electron transport layer. The experimental results show that the performance of 1 as an electron injection–electron transport material is considerably better than Alq3. The stability of device series B is comparable to that of the standard Alq3 device. The excellent performance of 1 as an electron injection/transport material may be attributed to the strong intermolecular interactions of 1 in the solid state as revealed by single‐crystal X‐ray diffraction analysis. In addition, compound 1 is a colorless material with a much larger highest occupied molecular orbital–lowest unoccupied molecular (HOMO–LUMO) gap than Alq3, which renders it potentially useful for a wide range of applications in EL devices. 相似文献
34.
This paper reports the photo- and electroluminescence studies of emitting species of one of the first reported blue emitters, the conjugated-non-conjugated multi-block copolymer, poly[1,8-octanedioxy-2,6-dimethoxy-1,4-phenylene-1,2-ethenylene-1,4-phenylene-1,2-ethenylene-3,5-dimethoxy-1,4-phenylene]. Because the conjugation length of the emissive center is very well defined (two and half phenylene-vinylene units) the differences found between the fluorescence profile of the fluorophore in solution, at several concentrations and that in the solid state allowed us to conclude that in solid the emission comes from associated forms, such as ground-state dimers and/or excimers. Time-resolved fluorescence in a nanosecond time scale recorded at ?em=24,096 cm−1 showed a monoexponential decay of 1.5 ns, which is compatible with rigid forms of stilbene derivatives. 相似文献
35.
Ch. Buchal S. Wang F. Lu R. Carius S. Coffa 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2002,190(1-4):40-46
We discuss the excitation and deexcitation processes for solid state optical emitters. At present, there is considerable interest in depositing a material system, which is compatible to silicon microelectronics processing and which emits electroluminescence (EL). We will compare the EL results of rare earth doped transistors in silicon with doped insulators and doped wide bandgap semiconductors, especially Er in Si (a source for 1.5 μm) as well as Er and Tb in SiO2, Si3N4 and AIN, which are sources for infrared and visible light. The most impressive results are achieved by RE doped GaN film devices, which cover the entire visible spectrum. 相似文献
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38.
Kapoor SinghAmit Kumar Ritu Srivastava Partap S. KadyanModeeparampil N. Kamalasanan Ishwar Singh 《Optical Materials》2011,34(1):221-227
Bis(5,7-dimethyl-8-hydroxyquinolinato)zinc(II) (Me2q)2Zn and 5,7-dimethyl-8-hydroxyquinolinato(2-(2-pyridyl)benzimidazole) zinc(II) Me2q(pbi)Zn have been synthesized and characterized by various techniques. These metal complexes have high thermal stability (>300 °C) and high glass transition temperatures (>150 °C). The vacuum deposited films of these materials show good film forming property and are suitable for opto-electronic applications. Multilayered organic electroluminescent (EL) devices have been fabricated having structure ITO/α-NPD/zinc complex/BCP/Alq3/LiF/Al, which produce emission with chromaticity having Commission Internationale d’Eclairage (CIE) coordinates x = 0.506 and y = 0.484 for (Me2q)2Zn; x = 0.47 and y = 0.52 for (Me2q)(pbi)Zn complex. The electroluminescence spectra show peak emission centered at 572 and 561 nm respectively for these materials. 相似文献
39.
Kyoung Soo YookJun Yeob Lee 《Thin solid films》2011,519(13):4342-4346
The effect of the host structure on the optimum doping concentration in red phosphorescent organic light-emitting diodes (PHOLEDs) was investigated. A mixed host of the phosphine oxide derivative (SPPO21) and 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA) was used as the host in the red PHOLED and the device performances were studied according to the doping concentration. The device performance of the red PHOLED was optimized at a doping concentration of 2% in the SPPO21 rich red PHOLED, while the device performance was optimized at a doping concentration of 6% in the device with 50% TCTA content. It was found that the optimum doping concentration was determined by the energy transfer and charge trapping. 相似文献
40.
Myriam Paire Laurent Lombez Jean-François GuillemolesDaniel Lincot 《Thin solid films》2011,519(21):7493-7496
A spatially resolved electroluminescence (EL) imaging experiment is developed to measure the local sheet resistance of the window layer, directly on the completed CIGS cell. Our method can be applied to the EL imaging studies that are made in fundamental studies as well as in process inspection. The EL experiment consists in using solar cell as a light emitting device: a voltage is applied to the cell and its luminescence is detected. We develop an analytical and quantitative model to simulate the behavior of CIGS solar cells based on the spread sheet resistance effect in the window layer. We determine the repartition of the electric potential on the ZnO, for given cell's characteristics such as sheet resistance and contact geometries. Knowing the repartition of the potential, the EL intensity is measured and fitted against the model. The procedure allows the determination of the window layer sheet resistance. 相似文献