Electroluminescent arrangement using doped blend systems

Details Electroluminescent arrangement using doped blend systems Electroluminescent arrangement using doped blend systems

1999-01-25

2002-04-23

Yamnitzky, Marie (Department: 1774)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S917000, C313S504000, C313S506000, C427S066000

Reexamination Certificate

active

06376107

ABSTRACT:

This application claims priority to German Patent Application 198 03 889.5 filed Jan. 31, 1998 which is incorporated by reference in its entirety for all purposes.
An electroluminescent (EL) arrangement is characterized in that, with application of an electric voltage, it emits light with a flow of current. Such arrangement has long been known in industry by the name “light emitting diodes” (LEDs). The emission of light occurs as result of positive charges (holes) and negative charges (electrons) recombining with emission of light.
In the development of light-emitting components for electronics or photonics, mainly inorganic semiconductors, such as gallium arsenide, are used today. Point-like display elements can be produced on the basis of such substances. Extensive arrangements are not possible.
In addition to the semiconductor light emitting diodes, electroluminescent arrangements based on low molecular weight organic compounds applied by vapour deposition are known (U.S. Pat. No. 4,539,507, U.S. Pat. No. 4,769,262, U.S. Pat. No. 5,077,142, EP-A 406,762, EP-A 278,758, EP-A 278,757).
Furthermore, polymers such as poly-(p-phenylene) and poly-(p-phenylenevinylene) (PPV) are described as electroluminescent polymers: G. Leising et al., Adv. Mater. 4 (1992) No. 1; Friend et al., J. Chem. Soc., Chem. Commun. 32 (1992); Saito et al., Polymer, 1990, Vol. 31, 1137; Friend et al., Physical Review B, Vol. 42, No. 18, 11670 or WO 90/13148. Further examples of PPV in electroluminescent displays are described in EP-A 443 861, WO-A-9203490 and 92003491.
EP-A 0 294 061 presents an optical modulator based on polyacetylene.
For the production of flexible polymer LEDs, Heeger et al., have proposed soluble conjugated PPV derivatives (WO 92/16023).
Polymer blends of different compositions are likewise known: M. Stolka et al., Pure and Appl. Chem., Vol. 67, No. 1, pp 175-182, 1995; H. Bässler et al., Adv. Mater. 1995, 7, No. 6, 551; K. Nagai et al., Appl. Phys. Lett. 67 (16), 1995, 2281; EP-A 532 798.
The organic EL arrangements contain, as a rule, one or more layers of organic charge-transporting compounds. The basic structure in the sequence of the layers is as follows:
1 Carrier, substrate
2 Base electrode
3 Hole-injecting layer
4 Hole-transporting layer
5 Light-emitting layer
6 Electron-transporting layer
7 Electron-injecting layer
8 Top electrode
9 Contacts
10 Envelope, encapsulation.
The layers 3 to 7 constitute the electroluminescent element.
This structure represents the most general case and can be simplified by omitting individual layers so that one layer performs several functions. In the simplest case, an EL arrangement consists of two electrodes between which is located an organic layer which performs all functions —including the function of light emission. Such systems are described, for example, in the application WO 90/13148, on the basis of poly-(p-phenylenevinylene).
Tang et al. state that the efficiency of electroluminescent arrangements can be improved by using an emitter layer which consists of organic matrix material with which a small amount of a dopant has been mixed (U.S. Pat. No. 4,769,292). Preferred material is aluminium 8-hydroxyquinoline (Alq
3
). The dopants can be chosen from a number of different classes of intensely fluorescent substances. Preferred examples of these are coumarins and rhodamines.
Murayama et al. describe insoluble quinacridone pigments as dopants (U.S. Pat. No. 5,227,252) which is incorporated by reference in its entirety for all purposes. Further, substituted but insoluble quinacridone pigments are described, all of which are applied by vapour deposition methods, together with the electroluminescent component (generally Alq
3
) (covaporization) (EP 0 766 498 A2 and Tang, Information Display 10/96, C. W. Tang, Information Display 10/96, 16 (1996), T. Wakimoto, S. Kawami, K. Nagayania, Y. Yonemoto, R. Murayama, J. Funaki, H. Sato, H. Nakada, K. Imai, International Symposium of Inorganic and Organic Electroluminescence 1994, Hamamatsu, Japan 1994, Conference Volume S. 77, J/.Shi, C. W. Tang, Appl. Phys. Lett. 70 (13), 1665 (1997), U.S. Pat. No. 005,616,427 A). It was found that EL arrangements having a dopant in the organic emitter layer also had improved long-term behaviour during operation in addition to an increased efficiency.
Multilayer systems can be built up by vapour deposition methods, in which the layers are applied successively from the gas phase, or by casting methods. Owing to the higher process speeds, casting methods are preferred. However, the surface dissolution process of an already applied layer during overcoating with the next layer may present a difficulty in certain cases.
The object of the present invention is the provision of electroluminescent arrangements having high luminous density and improved stability, it being possible to use a casting method to apply the doped mixture to be applied.
For this purpose, it was necessary to synthesize specially substituted quinacridone derivatives which have sufficient solubility for the casting process in the solvents used. Cast, doped systems are said to have improved long-term behaviour compared with undoped systems.
It was found that electroluminescent arrangements which contain the blend system stated below meet these requirements. Below, the term zone is also equivalent to layer.
The present invention therefore relates to electroluminescent arrangements containing a substrate, an anode, an electroluminescent element and a cathode, at least one of the two electrodes being transparent in the visible spectral range and it being possible for the electroluminescent element to contain in sequence:
A hole-injecting zone, hole--transporting zone, electroluminescent zone, electron-transporting zone and/or an electron-injecting zone, characterized in that the hole-injecting and/or hole-transporting zone is an optionally substituted tris-1,3,5-(aminophenyl)benzene compound A or a mixture thereof and the electroluminescent element optionally contains a further functionalized compound from the group consisting of the hole-transporting materials, a luminescent material B and optionally electron-transporting materials, it being possible for the hole-injecting and hole-transporting zone to contain one or more further hole-transporting compounds in addition to the component A, at least one zone being present, it being possible to omit individual zones and it being possible for the zone(s) present to perform several functions, the electroluminescent element containing a substituted quinacridone compound C as a dopant in at least one zone.
A zone may perform several functions, that is to say that a zone may contain, for example, hole-injecting, hole-transporting, electroluminescent, electron-injecting and/or electron-transporting substances and dopant.
The electroluminescent element may furthermore contain one or more transparent polymeric binders D.
The optionally substituted tris-1,3,5-(aminophenyl)benzene compound A represents an aromatic tertiary amino compound of the general formula (I)
in which
R
2
represents hydrogen, optionally substituted alkyl or halogen, wherein the substituent is alkoxy, aryl, OH or halogen,
R
3
and R
4
, independently of one another, represent hydrogen, optionally substituted C
1
-C
10
-alkyl, alkoxycarbonyl-substituted C
1
-C
10
-alkyl, or aryl, aralkyl or cycloalkyl, each of which is optionally substituted with a hydrocarbon, halogen heteroatom, hydroxy or alkoxy.
R
3
and R
4
, independently of one another, preferably represent C
1
-C
6
-alkyl, in particular methyl, ethyl, n- or iso-propyl, n-, iso-, sec- or tert-butyl, C
1
-C
4
-alkoxycarbonyl-C
1
-C
6
-alkyl, such as, for example, methoxy-, ethoxy-, propoxy- or butoxycarbonyl-C
1
-C
4
-alkyl, or phenyl-C
1
-C
4
-alkyl, naphthyl-C
1
-C
4
-alkyl, cyclopentyl, cyclohexyl, phenyl or naphthyl, each of which is optionally substituted by C
1
-C
4
-alkyl and/or C
1
-C
4
-alkoxy.
R
3
and R
4
, independently of one another, particularly preferably represent unsubstituted phenyl or naphthyl or phenyl or naphthyl, each of

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