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He L.,Xi'an Jiaotong University | Liu J.,Xi'an Jiaotong University | Wu Z.,Key Laboratory for Physical Electronics and Devices | Wang D.,Xi'an Jiaotong University | And 5 more authors.
Thin Solid Films | Year: 2010

Thin films of N,N′-bis-(3-Naphthyl)-N,N′-biphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB), tris-(8-hydroxyquinoline)-aluminum (Alq3) and their blends prepared by spin-coating process were investigated. Experimental results revealed that the NPB films prepared by spin-coating process have smoother surface than that of Alq3, which was attributed to their different molecular structures. Organic light-emitting devices (OLEDs) with emitting layer prepared by spin-coating the blends of NPB and Alq3 exhibited a maximum luminance and a current efficiency over 10,000 cd/m2 and 3.8 cd/A respectively, and when 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-[l]benzopyrano[6,7,8-ij]quinolizin-11-one was doped in, a current efficiency of 8 cd/A can be obtained. Comparative device performance to the vapor-deposited OLEDs suggested that solution-process could be an alternative route for the fabrication of OLEDs based on Alq3. © 2009 Elsevier B.V. All rights reserved.


Wang D.,Xi'an Jiaotong University | Wu Z.,Key Laboratory for Physical Electronics and Devices | Zhang X.,Key Laboratory for Physical Electronics and Devices | Jiao B.,Key Laboratory for Physical Electronics and Devices | And 4 more authors.
Organic Electronics: physics, materials, applications | Year: 2010

We investigated characteristics of solution-processed films of 4,4′-bis(2,2-diphenylvinyl)-1,1′-bibenyl (DPVBi), N,N′-bis(naphthalene-1-yl)-N,N′-bis(phenyl)-benzidine (NPB), and their blends, and it was found that the spin-coated films of NPB, and blends of NPB and DPVBi, though having lower densities, were more uniform than their vacuum-deposited counterparts. Using the spin-coated films of NPB:DPVBi as mixed host, doped with blue dye (4,4′-bis[2-(4-(N,N-diphenylamino)phenyl)vinyl]biphenyl) and yellow dye (5,6,11,12-tetraphenylnaphacene), new white organic light-emitting devices (WOLEDs) were demonstrated. The luminance (maximum luminance of 35822 cd/m2), efficiency (5.3 lm/W (100 cd/m2) and 8.3 cd/A (1000 cd/m2)) and stability of these solution-processed devices are better than or equivalent to the vacuum-deposited one, which was expected as an alternative route to the fabrication of small-molecular WOLEDs, reducing the cost of devices and avoiding the complexities of the co-evaporation of multiple dopants and host materials in the vacuum deposition. © 2010 Elsevier B.V. All rights reserved.


Wang F.,Key Laboratory for Physical Electronics and Devices | Zhang H.-B.,Key Laboratory for Physical Electronics and Devices | Cao M.,Key Laboratory for Physical Electronics and Devices | Nishi R.,Osaka University | Takaoka A.,Osaka University
Ultramicroscopy | Year: 2010

Multiple scattering has an important influence on the analysis of microns-thick specimens with MeV electrons. In this paper, we report on effects of multiple scattering of MeV electrons on electron transmission and imaging of tilted and thick amorphous film specimens by experiment and theoretical analysis. Electron transmission for microns-thick epoxy-resin and SiO2 specimens calculated by the multiple elastic-scattering theory is in good agreement with measurements in the ultrahigh voltage electron microscope (ultra-HVEM) at Osaka University. Electron transmission and electron energy are then presented in an approximate power law. The bright-field ultra-HVEM images of gold particles on the top or bottom surfaces of 5 and 15 μm thick specimens further illustrate the effect of multiple scattering on image quality. The observed top-bottom effect for the very thick specimens appears to be mainly caused by multiple elastic scattering. With increase in the accelerating voltage from 1 to 2 MV, image blurring, contrast, the signal-to-noise ratio, and the top-bottom effect are improved because of reduction in the influence of multiple scattering. However, the effect of specimen thickness on image blurring is shown to be stronger than that of accelerating voltage. At the 2 MV accelerating voltage, the 100 nm gold particle can be imaged with less blurring of ∼4 nm when located at the bottom surface of a 15 μm thick epoxy-resin specimen. © 2009 Elsevier B.V. All rights reserved.


Hu W.-B.,Key Laboratory for Physical Electronics and Devices | Yang M.,Key Laboratory for Physical Electronics and Devices | Liu Z.,Key Laboratory for Physical Electronics and Devices
IEEE Transactions on Plasma Science | Year: 2011

The microdischarge process and the vacuum ultraviolet (VUV) emission properties of dielectric-barrier-discharge-type flat fluorescent lamps (FFLs) are investigated by shooting the spatiotemporally resolved images of a microdischarge in an FFL filled with Ne-Xe (10%) gas mixture of 85 kPa with a high-speed intensified charge-coupled device camera and by measuring the VUV emission spectra at various gas pressures and driving parameters with a vacuum monochromator and a photomultiplier tube. It was found that a microdischarge was generated at a protrusion on the cathode at first, diffused to the anode side afterward, and exhibited a uniform glow discharge pattern. The measured results of the VUV spectra show that, as the total gas pressure increases, the 147-nm resonance emission gradually decreases, while the continuum emission centered at 173 nm rapidly increases, which cause both of the intensity and the efficiency of the VUV emission to increase. As the driving voltage amplitude increases, there exists a maximum VUV emission efficiency value. At a total gas pressure of 70 kPa, as the driving pulse frequency increases from 50 to 130 kHz, the spectral intensities of the VUV emission initially increase and then gradually tend to saturate at 90 kHz. © 2006 IEEE.


Li W.-Q.,Key Laboratory for Physical Electronics and Devices | Zhang H.-B.,Key Laboratory for Physical Electronics and Devices
Applied Surface Science | Year: 2010

Space charge and surface potential profiles are investigated with numerical simulation for dielectric films of SiO2 positively charged by a focused electron beam. By combining the Monte Carlo method and the finite difference method, the simulation is preformed with a newly developed comprehensive two-dimensional model including electron scattering, charge transport and trapping. Results show that the space charge is distributed positively, like a semi-ellipsoid, within a high-density region of electrons and holes, but negatively outside the region due to electron diffusion along the radial and beam incident directions. Simultaneously, peak positions of the positive and negative space charge densities shift outwards or downwards with electron beam irradiation. The surface potential, along the radial direction, has a nearly flat-top around the center, abruptly decreases to negative values outside the high-density region and finally increases to zero gradually. Influences of electron beam and film parameters on the surface potential profile in the equilibrium state are also shown and analyzed. Furthermore, the variation of secondary electron signal of a large-scale integration sample positively charged in scanning electron microscopic observation is simulated and validated by experiment. © 2009 Elsevier B.V. All rights reserved.


Wang D.,Xi'an Jiaotong University | Wu Z.,Key Laboratory for Physical Electronics and Devices | Zhang X.,Key Laboratory for Physical Electronics and Devices | Wang D.,Key Laboratory for Physical Electronics and Devices | Hou X.,Key Laboratory for Physical Electronics and Devices
Journal of Luminescence | Year: 2010

We investigated solution-processed films of 4,4′-bis(2,2-diphenylvinyl)-1,1′-bibenyl (DPVBi) and its blends with N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD) by atomic force microscopy (AFM). The AFM result shows that the solution-processed films are pin-free and their morphology is smooth enough to be used in OLEDs. We have developed a solution-processed white organic light-emitting device (WOLEDs) based on small-molecules, in which the light-emitting layer (EML) was formed by spin-coating the solution of small-molecules on top of the solution-processed hole-transporting layer. This WOLEDs, in which the EML consists of co-host (DPVBi and TPD), the blue dopant (4,4′-bis[2-(4-(N,N-diphenylamino)phenyl)vinyl]biphenyl) and the yellow dye (5,6,11,12-tetraphenylnaphtacene), has a current efficiency of 6.0 cd/A at a practical luminance of 1000 cd/m2, a maximum luminance of 22500 cd/m2, and its color coordinates are quite stable. Our research shows a possible approach to achieve efficient and low-cost small-molecule-based WOLEDs, which avoids the complexities of the co-evaporation process of multiple dopants and host materials in vacuum depositions. © 2009 Elsevier B.V. All rights reserved.

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