Transient electroluminescence from multilayer small organic molecular light-emitting devices

Savvateev, Vadim; Friedl, J. H.; Zou, Lu‐Yi; Christensen, Kenneth A.; Oldham, Warren J.; Rothberg, Lewis J.; Chen-Esterlit, Z.; Kopelman, Raoul; Shinar, J.

doi:10.1117/12.416898

Cited by 3 publications

(3 citation statements)

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“…The luminescence properties of these systems have been studied by several authors. [11][12][13][14][15][16] Stolka et al 2,17,18 investigated films of solid solutions of TPD in bisphenol A polycarbonate with different concentrations and found no crystallization of the TPD at room temperature up to 80%. A high concentration of TPD in the polymer host is preferred because the charge mobility usually increases with the concentration of charge transport molecules as the intermolecular distance between them is decreased.…”

Section: Introductionmentioning

confidence: 99%

Influence of Polycarbonate Flexibility on the Annealing-Induced Phase Separation of the Hole Transport Molecule TPD in a Model Charge Transport Composite

2003

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The depression of glass transition temperature, annealing-induced phase separation, and morphology were investigated in a binary solid solution of N,N‘-diphenyl-N,N‘-bis(3-methylphenyl)-[1,1‘-biphenyl]-4,4‘-diamine (TPD) in bisphenol A polycarbonate (BPAPC) and cyclohexyl polycarbonate (PCZ) with three different molecular weights. Differential scanning calorimetry, X-ray diffraction, microscopy, and FTIR were used to characterize these composites. Molecularly doped TPD in polymers significantly depressed the T g of the host polymers. Although it could be expected that the TPD would disperse well in a flexible polymer and cause a substantial decrease in T g, we find that the extent of depression is more pronounced with the rigid polymer. FTIR studies indicate that a molecular level interaction exists between TPD and the polycarbonates, as shown by the frequency shifts in the aromatic region. Upon annealing, the phase separation and crystallization of TPD lead to a recovery of the T g of the polymer, by 10−20 °C, depending on the temperature and time of annealing. In the case of TPD/BPAPC composites, although the crystallinity of the phase-separated TPD was found to be close to 30%, the extent of recovery of the T g was small. This is attributed to the plasticizing effect of the TPD crystals. A lower degree of crystallinity was observed in the case of TPD/PCZ, which is due to the lower molecular flexibility of the PCZ relative to BPAPC as well as the difference between the T g of the polymer and the annealing temperature. The molecular weight and its dispersion has a significant effect on the recovery of the T g in the case of PCZ, as well as the crystallinity of the phase-separated TPD.

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Section: Introductionmentioning

confidence: 99%

Influence of Polycarbonate Flexibility on the Annealing-Induced Phase Separation of the Hole Transport Molecule TPD in a Model Charge Transport Composite

2003

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“…Niketenko et al assumed that the back flow of the charge accumulation that occurred in the transient layer (or internal interface) for the polymer LEDs during the pulse was responsible for the EL overshoot. 4) A similar assumption was proposed for the low molecular OLEDs, 5) showing that upon the removal of the bias, the accumulated charges in the interface layer recombined, yielding the spike. Some research groups have reported detailed theoretical explanations 6) and numerical modeling 4,7) of the EL spikes from pulsed OLEDs.…”

Section: Introductionmentioning

confidence: 64%

Electroluminescence Spikes of Pulsed Organic Light-Emitting Diodes at Switch-Off Using 1,4-Bis[2-[4-[N,N-di( p-tolyl)amino]phenyl]vinyl]benzene as a Light-Emitting Layer

Wei

Horiba

Furukawa

et al. 2005

Jpn. J. Appl. Phys.

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The electroluminescence (EL) spikes from low-molecular organic light-emitting diodes (OLEDs) at the switch-off of applied pulse voltage using 1,4-bis[2-[4-[N,N-di( p-tolyl)amino]phenyl]vinyl]benzene (DSB) as an emission layer were observed. The characteristics of EL spikes, such as their duration and magnitude, were studied by changing the device structure of the OLEDs and the conditions of the applied voltage. The duration of the EL spikes was found to depend on the species of electron transport layer but to be independent of the amplitude of the applied voltage. The magnitude of the EL spikes increased with the applied time up to a saturated state, which was significantly determined by the thickness of the emitting layer. The trapezoid pulse voltage was found to be an effective tool for predicting the charge accumulation in the interfacial layer.

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“…5,6) In addition, for some organic thin films with a double heterostructure, special transient phenomena such as electroluminescence spikes could also be observed at the switch-on and/or switch-off of the electric pulse. 7,8) The current-voltage characteristics of liquid crystal (LC) cells have been measured under a triangular-wave voltage, for revealing the orientation of LC molecules and impurity ions in the LC cells. 9) However, to date, most of the research on transient response from pulsed OLEDs has employed a rectangular pulse with the effects of the transient time, the rise time and fall time of the voltage pulse, often being ignored.…”

Section: Introductionmentioning

confidence: 99%

Use of Trapezoid Pulse Voltage in Study of Transient Response of Organic Light-Emitting Diodes

Wei

Furukawa

Ichikawa

et al. 2005

Jpn. J. Appl. Phys.

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We investigated the transient electroluminescence (EL) and transient current (TC) of organic light-emitting diodes under a trapezoid electric pulse at a repetition rate of 1 kHz by changing the transient time of the pulse from ∼ ns to ∼ µs. Our data shows that the change in the transient time of the pulse not only affects the delay time and rise time of transient EL, but also changes the temporal evolution of TC. In addition, we studied the charge accumulation in the interfacial layer of organic films with different heterostructures, particularly the EL spike from a pulsed device with 1,4-Bis[2-[4-[N,N-di( p-tolyl)amino]phenyl]vinyl]benzene as a light-emitting layer at switch-off. The dynamic behavior of TC was further analyzed by computational approaches.

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Transient electroluminescence from multilayer small organic molecular light-emitting devices

Cited by 3 publications

References 0 publications

Influence of Polycarbonate Flexibility on the Annealing-Induced Phase Separation of the Hole Transport Molecule TPD in a Model Charge Transport Composite

Influence of Polycarbonate Flexibility on the Annealing-Induced Phase Separation of the Hole Transport Molecule TPD in a Model Charge Transport Composite

Electroluminescence Spikes of Pulsed Organic Light-Emitting Diodes at Switch-Off Using 1,4-Bis[2-[4-[N,N-di( p-tolyl)amino]phenyl]vinyl]benzene as a Light-Emitting Layer

Use of Trapezoid Pulse Voltage in Study of Transient Response of Organic Light-Emitting Diodes

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