An analytic theory is presented for dark injection from a metallic electrode into a random hopping system, e.g., a conjugated polymer or a molecularly doped polymer. It encompasses injection of a charge carrier from the Fermi level of the electrode into tail states of the distribution of hopping states of the dielectric followed by either return of the charge carrier to the electrode or diffusive escape from the attractive image potential. The latter process resembles Onsager-type geminate pair dissociation in one dimension. The theory yields the injection current as a function of electric field, temperature and energetic width of the distribution of hopping states. At high electric fields it resembles that the current calculated from Fowler-Nordheim tunneling theory although tunneling transitions are not included in the theory. Good agreement with experimental data obtained for diode structures with conjugated polymers as a dielectric is found.

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Transient electroluminescence (EL) from organic bilayer light emitting diodes addressed by a rectangular voltage pulse often features an overshoot when the voltage is switched off. Experimental results are presented for a variety of hole transporting layers in contact with an oxadiazole layer simultaneously acting both as a blockade for holes and as an electron transport layer. The overshoot occurs in spin coated yet not in vapor deposited samples. A model is developed to rationalize charge recombination under the premise (i) of an interfacial layer of finite thickness between hole and electron transport layers in which both transport molecules coexist and (ii) of interfacial energy barriers impeding both hole and electron passage. It predicts the occurrence of an EL overshoot due to the recombination of stored electrons and holes under the action of their mutual space charge field when the external voltage is switched off. The temporal pattern of the predicted transient EL signal is in good agreement with experiment.

We report a 55-inch OLED TV employing white organic light emitting device (WOLED) and oxide TFT. We fabricated the hybrid tandem structure comprising a phosphorescent R/G stack and a fluorescent blue stack to achieve high current efficiency of 90cd /A at 1,000 nit and white color (0.327, 0.344). 55-inch OLED TV was adjusted to cool white color of (0.285, 0.294). We applied a color layer for large color gamut (118% ATSC ratio) and deep blue expression (0.142, 0.054). We also improved 3 kinds of color shift over viewing angle, aging and gray level.

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++Organic light-emitting diodes based on molecularly doped polymer blends have been fabricated and characterized using donor-acceptor substituted stilbenoids as active dye components for hole transport, electron transport and emission. A comparison of the electrochemically generated luminescence (ECL), the photoluminescence (PL) and the electroluminescence (EL) of the organic light-emitting devices (OLEDs) is given.

Transient electroluminescence (EL) from organic bilayer light emitting diodes featuring an interfacial blockade for holes and electrons was studied. At the end of the driving voltage pulse an EL spike is observed whose magnitude exceeds the cw-EL intensity by up to two orders of magnitude. The effect is attributed to an increase of the recombination probability of minority carriers (electrons) with majority carriers upon switching off the external field.

Diodes consisting of a hole transporting layer containing tri-stilbeneamine as active medium and a hole blocking layer (an oxadiazole blend) sandwiched between indium-tinoxide and aluminium electrodes have been characterized via both their j(F) characteristics and the dependence of intensity, quantum efficiency, and spectrum of the electroluminescence on the thickness Le of the hole blocking layer. The results are discussed within the framework of the analytic model advanced in the preceding paper. Both the decrease of the effect of electric field screening at the anode due to the space charge accumulation at the internal interface as well as the recombination efficiency with decreasing Le is in good agreement with theory.