Majority carrier injection from ITO anodes into organic light-emitting diodes based upon polymer blends

Vestweber, H.; Pommerehne, J.; Sander, R.; Mahrt, Rainer F.; Greiner, Andreas; Heitz, Walter; Bäßler, H.

doi:10.1016/0379-6779(94)02301-e

Cited by 77 publications

(44 citation statements)

References 17 publications

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“…Metal-organic contacts in organic LEDs have been reported to be ohmic [6] or contact limited with charge injection by a combination of tunneling and thermionic emission [7,8]. The electrical injection properties of the metalorganic contact dominate organic device performance and reliability [9].…”

Section: Metal-polymer Contactsmentioning

confidence: 99%

Measuring internal electric fields in organic light-emitting diodes using electroabsorption spectroscopy

Campbell

Ferraris

Hagler

et al. 1997

Polym. Adv. Technol.

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A widely applicable electroabsorption technique to measure internal electric fields in organic light‐emitting diodes is presented. The technique exploits the change in the a.c. electroabsorption response in the presence of a d.c. electric field. The electroabsorption signal is modulated at the fundamental frequency of the a.c. test signal, in addition to the usual modulation at the second harmonic frequency, when a d.c. bias is present. In metal/organic film/metal devices employing different metal contacts there is a built‐in electric field in the organic film caused by the difference in work function between the two contacts. The electroabsorption response at the fundamental frequency of the applied a.c. bias is measured as a function of an external d.c. bias. The electroabsorption signal is nulled when the applied d.c. bias cancels the built‐in electric field established by the different metals. We apply this technique to measure changes in metal–polymer Schottky barrier heights as a function of the contact metal. In metal/multiple organic films/metal structures the electroabsorption signals from the constituent organic films are identified spectroscopically and measured at both the fundamental and second harmonic frequency of the a.c. test signal. The amplitudes of the electroabsorption responses are then used to determine the a.c. and d.c. electric fields present in the organic layers. We apply this technique to determine the d.c. electric field distribution within a multi‐layer organic light‐emitting diode. These results highlight the general applicability of electroabsorption methods to probe internal electric fields in organic light‐emitting diodes. © 1997 John Wiley & Sons, Ltd.

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Section: Metal-polymer Contactsmentioning

confidence: 99%

Measuring internal electric fields in organic light-emitting diodes using electroabsorption spectroscopy

Campbell

Ferraris

Hagler

et al. 1997

Polym. Adv. Technol.

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“…(4) at high electric fields and the barrier heights derived from ln(j/F 2 ) v. F À1 plots correlated reasonably well with barrier values estimated on the basis of workfunctions. The temperature independence of the injection current observed in systems with large barrier for hole injection lent further support to the concept [33]. At lower fields deviations from FNbehavior are usually noted, though, and currents become temperature-activated, suggesting that at lower fields thermionic emission prevails.…”

Section: à3mentioning

confidence: 78%

Injection, transport and recombination of charge carriers in organic light-emitting diodes

Bäßler

1998

Polym. Adv. Technol.

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Depending on the magnitude of the energy barrier for charge carrier injection from the electrode(s) the current flowing through a light‐emitting diode (LED) can be either space charge‐limited or injection‐limited. The first alternative, reflected in j(E) characteristics obeying Child’s law, requires the electrode to be ohmic. Various injection models are discussed, favoring a hopping description for the escape of a charge carrier from the image charge potential in an energetically disordered system. Information concerning the mobility of charge carriers can be inferred from time of flight studies, from space charge limited currents, as well as from transient absorption due to the momentary space charge stored inside the sample. A simple model, building on the proven validity of Langevin‐type electron hole recombination in organic solids, is able to explain the recombination yield in single‐layer LEDs as a function of the cell current. A more elaborate analytic theory is described for bilayer systems in which internal energy barriers give rise to charge accumulation and to a concomitant redistribution of the electric field. © 1998 John Wiley & Sons, Ltd.

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“…Following Vestweber et al [9], we first have considered the thermionic emission model, which takes Richardson-Schottky emission into account. In this model, tunnelling through barriers is ignored, while field-induced barrier lowering is considered, and the current density at a field (F) is given by [9] J AT 2 exp Àf À bF 1=2 =kT ;…”

Section: Resultsmentioning

confidence: 99%

Charge Injection Mechanisms in Solid State Organic Light-Emitting Devices Based on Alizarin Violet

Das

Chowdhury

Roy

et al. 2000

phys. stat. sol. (a)

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Light-emitting devices utilizing a dye-insulating matrix blend have been fabricated. The emitting dye material used was alizarin, while poly(methylmethacrylate) has been used as the insulating matrix material. Current±voltage and luminance±current characteristics have been studied for different molar concentrations of alizarin. Luminance has been observed in both bias directions in devices with lower alizarin concentration. Luminance under forward bias has been independent of alizarin molar concentration, while it decreased with molar concentration under reverse bias. Fowler-Nordheim tunnelling mechanism and Richardson-Schottky thermionic emission have been shown to be applicable in different ranges and directions of fields. Parameters of the device-like dielectric constant of the emitting layer, and barrier height for holes have been calculated from the models and compared in terms of different injection mechanisms operative in the devices.

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Majority carrier injection from ITO anodes into organic light-emitting diodes based upon polymer blends

Cited by 77 publications

References 17 publications

Measuring internal electric fields in organic light-emitting diodes using electroabsorption spectroscopy

Measuring internal electric fields in organic light-emitting diodes using electroabsorption spectroscopy

Injection, transport and recombination of charge carriers in organic light-emitting diodes

Charge Injection Mechanisms in Solid State Organic Light-Emitting Devices Based on Alizarin Violet

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