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ABSTRACT: Internal potential distribution of organic light-emitting diodes (OLEDs) is an essential problem. By using dc bridge to eliminate errors due to high resistance of the devices at low bias, the potential distribution has been accurately measured for both double-layer and single-layer OLEDs. It is found that the electric field inside the device is not uniform, and the potential distribution changes with external bias. This phenomenon could be the effect of space charge originating from the unequal injections of holes and electrons, which is confirmed by the results of the device with modified work function of the anode.
Applied Physics Letters 10/2010; 97(15):153305-153305-3. · 3.84 Impact Factor
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B. F. Ding,
Y Yao,
X. Y. Sun,
Z. Y. Sun, X. D. Gao,
Z. T. Xie,
Z. J. Wang,
X. M. Ding,
Y Z Wu,
X F Jin,
C. Q. Wu,
X. Y. Hou
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ABSTRACT: Magnetoelectroluminescence (MEL) of organic semiconductor has been experimentally tuned by adopting blended emitting layer consisting of both hole and electron transporting materials. A theoretical model considering intermolecular quantum correlation is proposed to demonstrate two fundamental issues: (1) two mechanisms, spin scattering and spin mixing, dominate the two different steps respectively in the process of the magnetic field modulated generation of exciton; (2) the hopping rate of carriers determines the intensity of MEL. Calculation successfully predicts the increase of singlet excitons in low field with little change of triplet exciton population. Comment: 16 pages, 4 figures
11/2009;
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ABSTRACT: Synchrotron radiation photoemission study showed that the energy level alignment at the interface between N , N<sup>′</sup> -bis(naphthalene-1-y1)- N , N<sup>′</sup> -bis(phenyl) benzidine (NPB), a typical hole transport material, and Al could be adjusted by precovering a thin C <sub>60</sub> layer on Al. The interface dipoles so formed could shift both the highest occupied molecular orbital level of NPB and the secondary electron cutoff measured at the early stage of the NPB deposition. The barrier height for hole injection from Al to NPB could thus be lowered by as much as 0.98 eV, and the optimal thickness of the inserted C <sub>60</sub> layer was found to be 8–12 Å.
Journal of Applied Physics 06/2009; · 2.17 Impact Factor
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Journal of Applied Physics 05/2009; 105:106105. · 2.17 Impact Factor
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ABSTRACT: High-resolution synchrotron radiation photoemission spectroscopy was used to investigate the chemical properties of Al–LiF interfaces. An electronic state appeared at the Al/LiF interface with a binding energy 4.8 eV higher than that of the metallic Al 2p core level, but the state was hardly found to be present at the LiF/Al interface. This indicates that intensive chemical reaction could occur at the Al/LiF interface, while the reaction occurring at the LiF/Al interface would be weak. This result explains well the unsymmetrical electron injection from different sides of the symmetrical device of indium-tin-oxide\Al\LiF\tris(8-hydroxyquinoline) aluminum\LiF\Al showing unsymmetrical current-voltage characteristics.
Applied Physics Letters 02/2009; 94(6):063302-063302-3. · 3.84 Impact Factor
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Applied Physics Letters. 01/2009; 94:063302.
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Applied Physics Letters 01/2009; 94:063302. · 3.84 Impact Factor
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Applied Physics Letters 01/2009; 94:063302. · 3.84 Impact Factor
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ABSTRACT: We report a delayed-switch-on effect in organic memories; i.e., the organic memory devices can automatically switch from off state to on state after a certain period of time when biased at voltages below the threshold voltage. Meanwhile, the lower the voltage is, the longer the switching time will be. The time scales from milliseconds to about 104 s with decreasing voltage. Moreover, by applying a certain voltage between threshold voltage and Vmax, intermediate states are also obtained. The existence of filamentary microconducting channels in the organic layer is proposed to be responsible for the observed switching phenomenon.
Applied Physics Letters 10/2007; 91(14):143511-143511-3. · 3.84 Impact Factor
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ABSTRACT: High contrast organic light-emitting devices with low-reflection cathodes are fabricated. The cathode consists of a semitransparent metal layer, a phase-changing (PC) layer, and a reflective metal layer. With Al doped tris(8-hydroxyquinoline) aluminum as PC layer, devices exhibit the average reflectivity of the ambient light as low as about 13%. And its electrical characteristics are almost identical to that of a conventional device, although the thickness is increased by 70%. The improvement in conductivity could be attributed to the conductive Al cluster distributed in the organic matrix.
Applied Physics Letters 06/2006; 88(23):233505-233505-3. · 3.84 Impact Factor
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ABSTRACT: By adopting C60/Al composite anode and an inverted device structure of ITO/Alq3/C60/CuPc/C60/Al, we have achieved a power conversion efficiency of 0.78% under 75 mW/cm2 AM1.5G simulated illumination and a shelf lifetime of 950 h from unencapsulated organic solar cells. The improved stability is attributed to efficient protection of the C60 layer in the inverted structure. Replacing the C60/Al anode with C60/Au anode in the inverted structure, produces a power conversion efficiency of 0.64%, comparable to that of the device with C60/Al anode. This indicates that the property of the composite electrode is mainly determined by the thin C60 layer. Use of C60/Al composite anode to fabricate inverted organic light-emitting devices gives rise to an efficiency of the device comparable to that of conventional devices.
Organic Electronics.
