Au is not a suitable cathode material of organic light-emitting device because of its high work function resulting in poor electron injection. However, in present work, it is found that the performance of Au-cathode OLEDs can be efficiently improved by introducing a LiF buffer layer and with its optimal thickness can even be comparable to that of conventional Alcathode device. The relationship between the thickness of LiF layer and the performance improvement is investigated. The experimental results indicate a quite different mechanism of LiF thin layer from that of Al-cathode device, which is not chemicalreaction-mechanism-dominant. Other insulator material buffer layers such as Al 2 O 3 and BCP are also investigated.

Single-layer organic memories made of organic material with good conductance have been characterized. Asymmetrical bistable behaviors under biases of opposite polarities are observed for devices with asymmetric electrodes. It is experimentally confirmed that a close correlation exists between the conductivity of the organic layer and the asymmetric bistability of the device under opposite biases. Inserting a block layer or thickening the organic layer will result in negative differential resistance under positive biases, leading to reversible symmetrical bistability. The phenomena are ascribed to the presence of filamentary microconducting channels in the organic layer.

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The interfaces of poly (p -phenylene vinylene) and fullerene derivatives with Al, LiF, and Al/LiF studied by secondary ion mass spectroscopy and x-ray photoelectron spectroscopy: Formation of AlF 3 disproved

The effect of electric field and temperature on bistable characteristics of indium tin oxide/tris-(8-hydroxyquinoline) aluminum (Alq3)/aluminum (Al) device has been investigated. The switching time, during which the device turns from a high resistive (OFF) state to a low resistive (ON) state, increases with decreasing field and temperature. The observed phenomena are accounted for by a phenomenological model that metallic nano-tips may evolve under the influence of the electric field and temperature.

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We present a combined experimental and theoretical study to get insight into both memory and negative differential resistance (NDR) effect in organic memory devices. The theoretical model we propose is simply a one-dimensional metallic island array embedding within two electrodes. We use scattering operator method to evaluate the tunneling current among the electrode and islands to establish the basic bistable I-V curves for several devices. The theoretical results match the experiments very well, and both memory and NDR effect could be understood comprehensively. The experimental correspondence, say, the experiment of changing the pressure of oxygen, is addressed as well.PACS numbers: 73.40.Gk Memory devices based on metal-insulator-metal resistive structure with organic materials are promising in application.1 The underlying mechanism in these devices is not very clear up to now due to the complicated phenomena observed, say for example, the memory effect and the negative differential resistance (NDR) in ON state, making an obstacle for controllable improvement of the performance.2,3 Two different but correlated mechanisms have been addressed. The first one is the SimmonsVerderber (SV) model based on the space charge accumulated on some penetrated metallic islands.4 This model could be proposed to explain NDR, which is also closely related to the memory effect.2 In addition to it, electron tunneling and Coulomb blockade were also proposed, 3 indicating that the different spatial distribution of the space charge gave rise to the transition between ON and OFF state. The admittance spectroscopy provided another evidence to the SV model.5 Whereas, the basic drawback of this mechanism is that, the OFF state is always observed, in practice, during the first scanning of bias voltage, while SV model predicts the sample is initially in ON state.6 The second mechanism is the filamentary conduction, stating that there would be some penetration of metal atoms into organic layer during the deposition of top electrode, which forms some conducting filaments under relative large bias voltage, and the trap-controlled tunneling between different filaments dominates the NDR effect.7,8 The direct experimental evidence for this mechanism is from the transmission electron microscopy image, which shows the metallic filaments are formed in ON state.9 Meanwhile, the temperature insensitivity of ON state current, 10 the time dependent switch-on behavior, 11-13 and the scanning voltage and conductance dependence 14 all go together to support the filamentary mechanism. However, it is still hard to imagine the destruction and recovery of an atomic filament could respond so fast to the scanning voltage. Combining the above two mechanisms, we can get a common idea that, during the deposition of the electrode, the metallic atoms could go deeply into the organic layer and form some islands in the film, 3,15 which is crucial to the NDR effect no matter it originates from space charge or filaments.Another experiments were focusing on the ro...

Synchrotron radiation photoemission study showed that the energy level alignment at the interface between N, N′-bis(naphthalene-1-y1)-N, N′-bis(phenyl) benzidine (NPB), a typical hole transport material, and Al could be adjusted by precovering a thin C60 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 C60 layer was found to be 8–12 Å.