JPH06204556A - Organic electroluminescence element - Google Patents

Abstract

PURPOSE:To obtain an organic electroluminescence element having emission of high lumunance, by doping 8-hydroxyquinoline aluminum of a light-emitting layer with a condensed polycyclic aromatic compound. CONSTITUTION:An 8-hydroxyquinoline aluminum layer being a light-emitting layer is doped with a condensed polycyclic aromatic compound which improves an emission efficiency and brings about a sensitizing effect. As for the condensed polycyclic aromatic compound, phenanthrene, anthracene, pyrene, naphthacene, fluorene, acenaphthylene, etc., are mentioned, for instance. This compound is used by 0.5 to 10mol%, preferably, for doping the the light-emitting layer of the 8-hydroxyquinoline aluminum. The doping can be executed by simultaneous evaporation of the 8-hydroxyquinoline aluminum and the compound.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence device used for a flat light source, a display and the like.

[0002]

2. Description of the Related Art Electroluminescent devices (hereinafter referred to as
(EL element) has high visibility because it is a self-luminous type,
Since it is a completely solid-state device, it has excellent impact resistance and can produce a large-area surface light-emitting device. Currently, an EL device using ZnS: Mn, which is an inorganic phosphor, has been put into practical use. . However, the inorganic EL element requires a high applied voltage of about 200 V to emit light, and the driving method is complicated.

On the other hand, the organic EL device can significantly reduce the applied voltage, and recently, a new type of organic thin film having a two-layer structure, a relatively high brightness (1000 cd / d) at a lower voltage application (10 V or less). m ² or more) of the resulting organic E
L element has been reported (Applied Physics
Letters 51, 913, 1987).

Further, JP-A-2-8287 and JP-A-2-82.
88, Japanese Patent Application Laid-Open No. 2-8289, and the like, by developing new organic phosphors and changing the layer structure (Chemicals and Industry, Vol. 42, page 2023, 1989), etc., to red light to blue light. Examples of light emission in various wavelength regions have been reported. As described above, the organic EL element is capable of emitting light of each color, has a simple structure, and can be easily manufactured. Therefore, it is attracting attention as an inexpensive large-area full-color display element or the like.

However, sufficient brightness has not been obtained yet, and the emission brightness is still about several thousand cd / m ² . Although the brightness can be slightly increased by increasing the driving voltage, there is a limit, and application of a high voltage causes damage to the device, and it is difficult to obtain high brightness.

[0006] The 8-hydroxyquinoline aluminum luminescent layer is doped with a fluorescent dye (J. Appl. P.
hys. , 65 (9), 3610-3616), doping with dyes (50th Annual Meeting of the Applied Physics Society of Japan (1989) 29P-ZP-11), and doping with styryl dyes (51st Applied Physics). The luminous efficiency may be improved by the academic conference (1990) 28a-PB-6), but in these cases, the light is emitted from the doping substance, and 8-hydroxyquinoline aluminum is used only as an electron transfer agent. It functions and does not act as a luminescent agent.

[0007]

The organic EL device is characterized by being driven at a low voltage, and since the device is destroyed, a high voltage cannot be applied. Alternatively, since a more efficient element structure of a material having a high luminous efficiency has not been found, an organic EL element that emits light with high brightness has not been obtained yet. An object of the present invention is to provide an organic EL device that emits light with high brightness.

[0008]

Means for Solving the Problems The present inventors
As a result of diligent studies for improving the brightness of the device, the inventors have found that there is a group of compounds that improve the luminous efficiency and have a sensitizing effect by coexisting with an 8-hydroxyquinoline aluminum layer which is a light emitting layer, and arrived at the present invention. It was That is, the present invention is characterized in that an 8-hydroxyquinoline aluminum layer, which is a light emitting layer, is doped with a condensed polycyclic aromatic compound which improves the light emitting efficiency and brings about a sensitizing effect. Type organic electroluminescent device.

There are two-layer structure and three-layer structure of organic EL elements. These layer structures are provided on a transparent electrode which is a substrate, and a counter electrode is provided thereon to manufacture an organic EL element. In the case of a two-layer structure, it consists of a combination of a hole-transporting layer and an electron-transporting light-emitting layer or a combination of an electron-transporting layer and a hole-transporting light-emitting layer. In the case of a three-layer structure, it consists of a hole-transporting layer and an electron-transporting layer. The light emitting layer is sandwiched.

The structure according to the present invention has a two-layer structure of a hole transport layer and an 8-hydroxyquinoline aluminum layer which is an electron transport luminescent agent, or a three layer structure in which an electron transport layer is further laminated thereon.

Examples of the condensed polycyclic aromatic compound used in the present invention include phenanthrene, 9-methylphenanthrene, anthracene, 1-methylanthracene, and 2
-Methylanthracene, 9-methylanthracene, benz [a] anthracene, pyrene, 1-methylpyrene, naphthacene, perylene, chrysene, triphenylene, benzophenanthrene, fluorene, as-indacene, s
-Indacene, acenaphthylene, acephenanthrylene, aceanthrylene, azulene, heptalen, pleiaden, picene and the like. These compounds are preferably used in the light emitting layer of 8-hydroxyquinoline aluminum in an amount of 0.5.
It is used after being doped with 10 mol%. Further, the doping can be generally performed by co-evaporating 8-hydroxyquinoline aluminum and these compounds.

As the charge transfer agent, compounds used in organic photoconductors for electrophotography and compounds having charge transfer ability can be used. Examples of the hole transfer agent include porphyrin compounds such as porphine, tetraphenylporphine copper, phthalocyanine, copper phthalocyanine, and titanium phthalocyanine oxide, 1,1-bis {4- (di-p
-Tolylamino) phenyl} cyclohexane, 4,
4 ', 4 "-trimethyltriphenylamine, N, N,
N ', N'-tetrakis (p-tolyl) -p-phenylenediamine, 1- (N, N-di-p-tolylamino) naphthalene, 4,4'-bis (dimethylamino) -2,
2'-dimethyltriphenylmethane, N, N, N ',
Aromatic tertiary such as N'-tetraphenyl-4,4'-diaminobiphenyl, N, N'-diphenyl-N, N'-di-m-tolyl-4,4'-diaminobiphenyl, N-phenylcarbazole Amine, 4-di-p-tolylaminostilbene, 4- (di-p-tolylamino) -4 '
Examples include stilbene compounds such as [4- (di-p-tolylamino) styryl] stilbene.

Examples of electron transfer agents include 2- (pt)
ert-Butylphenyl) -5- (p-biphenylyl)
-1,3,5-oxadiazole, tetracyanoquinodimethane, 3,5-dimethyl-3 ', 5'-di-tert
-Butyl-4,4'-diphenoquinone and the like.

Examples of the electron transfer agent include 2- (4-
tert-Butylphenyl) -5- (4-phenylphenyl) -1,3,5-oxadiazole, 2,4,7-
Trinitro-9-fluorenone, 4-butoxycarbonyl-9-dicyanomethylidenefluorene, 3,3'-bis (tert-butyl) -5,5'-dimethyl-diphenoquinone-4,4 ', 3,5'-bis (Tert-butyl) -5,3'-dimethyl-diphenoquinone-4,
4 ', 3,5'-bis (tert-butyl) 3', 5 '
-Dimethyl-diphenoquinone-4,4 'and the like.

Glass, plastic, quartz, etc. are used for the support of the organic EL element, and metal such as gold, aluminum, indium, silver, magnesium, etc., indium-tin-oxide (ITO), tin oxide is formed on this substrate. , An ultra-thin electrode made of zinc oxide, etc.
Use semi-transparent or transparent electrodes. An organic EL element is manufactured by stacking a charge transport layer and a light emitting layer on this, and further forming the same electrode as described above on it. A direct current voltage is applied to this to emit light.

[0016]

EXAMPLES The present invention will be specifically described below with reference to examples.

Example 1 A commercially available ITO glass electrode (transparent conductive film (standard type) manufactured by Matsuzaki Vacuum Co., Ltd.) was fixed to a substrate holder of a vapor deposition apparatus (LC-6F type manufactured by Vacuum Instrument Co., Ltd.) and heated. The boat was charged with N, N'-diphenyl-N, N'-bis (3-tolyl) -4,4'-diamino-1,1'-biphenyl, and the pressure was reduced to 1 × 10 ^-5 Torr. The heating boat is heated to perform vapor deposition at a vapor deposition rate of 120 Å / min, and N, N′-diphenyl-N, N′-bis (3-tolyl) -4,4′-diamino-1,1 having a film thickness of 1000 Å. A hole injection layer of'-biphenyl was formed on the ITO glass electrode.
Next, 8-hydroxyquinoline aluminum is put in a heating boat, anthracene is put in another heating boat, and heating is performed while adjusting the doping concentration of anthracene to 7 mol%, and vapor deposition is performed at a deposition rate of 400 Å / min. Then, a light emitting layer having a film thickness of 1000 Å was formed on the hole injection layer.

Further, a magnesium vapor-deposited film having a thickness of 1500 Å was formed thereon with a size of 3 mm × 8 mm to form a counter electrode, and an organic EL device was prepared. When a direct current of 26 Volt was applied with the ITO electrode as the positive electrode and the magnesium electrode as the negative electrode, a bright green light was emitted, and the luminance was measured using a luminance meter (LS-110 type manufactured by Minolta Camera Co., Ltd.) to show 11000 cd / m ² . It was

Further, the organic EL device was prepared in the same manner except that the doping concentration of anthracene was adjusted to 3.6 mol%, and the doping concentration of anthracene was adjusted to 1.3 mol%, and the same preparation was carried out. Luminance of the organic EL device was measured and found to be 11000 cd / m 2 when a direct current of 26 Volt was applied.
² and 6000 cd / m ² . The emission brightness increases as the anthracene is doped. These organic E
The luminance-driving voltage characteristics of the L element are shown collectively in FIG.

FIG. 1 also collectively shows the luminance-current density characteristics of these organic EL devices.

FIG. 2 shows that by doping anthracene, the luminance is increased and the luminous efficiency is increased even when the current density is constant.

Further, the emission spectrum of the organic EL device doped with anthracene (FIG. 3)

FIG. 3 is an emission spectrum of an undoped organic EL device (FIG. 4)

FIG. 4 is the same as that of FIG. 4, there is no change in the emission spectrum due to doping, and the doped organic EL device is
It can be seen that the light is emitted from hydroxyquinoline aluminum.

Comparative Example 1 An organic EL device was prepared in the same manner as in Example 1 except that the anthracene was doped in Example 1. DC 24
It is clear that the application of Volt shows only a brightness of 2800 cd / m ² and the effect of anthracene doping is remarkable. The luminance-driving voltage characteristics and the luminance-current density characteristics of the organic EL device not doped with anthracene are shown in FIGS.

Example 2 The doping concentration of anthracene in Example 1 was 7 mol%.
An organic EL device was manufactured in the same manner as in Example 1 except that the chrysene was co-deposited at a doping concentration of 8 mol% instead of being co-deposited. DC 24V
When olt was applied, it emitted bright green light with a brightness of 10000 cd / m ² .

Example 3 The doping concentration of anthracene in Example 1 was 7 mol%.
An organic EL device was produced in the same manner as in Example 1 except that 2-methylanthracene was co-deposited at a doping concentration of 5 mol% instead of being co-deposited. When a direct current of 25 Volt is applied, 7,000 cd /
It emitted a bright green light with a brightness of m ² .

Example 4 In Example 1, the doping concentration of anthracene was 7 mol%.
An organic EL device was manufactured in the same manner as in Example 1 except that benzophenanthrene was co-deposited at a doping concentration of 5 mol% instead of being co-deposited as described above. 6500 cd / when applying DC 26 Volt
It emitted a bright green light with a brightness of m ² .

[Brief description of drawings]

FIG. 1 shows a luminance-driving voltage characteristic when anthracene is used.

FIG. 2 shows luminance-current density characteristics when anthracene is used.

FIG. 3 shows an emission spectrum of an EL device doped with anthracene.

FIG. 4 shows an emission spectrum of an EL device not doped with anthracene.

[Explanation of symbols]

 1 Doping concentration 0 mol% 2 Doping concentration 1.3 mol% 3 Doping concentration 3.6 mol% 4 Doping concentration 7 mol%

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[Procedure amendment]

[Submission date] December 7, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Added

[Correction content]

[Figure 1]

[Fig. 2]

[Figure 3]

[Figure 4]

Claims (1)

[Claims] 1. An organic electroluminescence device comprising a stack of organic thin films, wherein 8-hydroxyquinoline aluminum of the light emitting layer is doped with a condensed polycyclic aromatic compound.