JP3328731B2 - Organic electroluminescence device - Google Patents

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 (hereinafter referred to as an organic EL device).
Specifically, the present invention relates to an organic EL device using substituted poly (p-phenylenevinylene) as a light emitting material.

[0002]

2. Description of the Related Art A conventionally used inorganic electroluminescent element requires a high voltage to emit light. Recently, Tang et al. Used an organic fluorescent dye as a light emitting layer,
In addition, an organic EL device having a two-layer structure in which an organic charge transporting compound used for an electrophotographic photoreceptor or the like is laminated is manufactured, and a low voltage driving is performed as compared with a device having only a light emitting layer.
A high-efficiency, high-brightness organic EL device has been realized (Japanese Unexamined Patent Publication No.
No. 9-194393). Compared to inorganic EL devices, organic EL devices have the features of low-voltage driving, high luminance, and easy emission of many colors. Attempts have been reported [Japanese Journal of Applied Physics (Jpn. J. Appl.
Phys. 27, L269 (1988)], [Journal of Applied Physics (J. Ap)
pl. Phys. 65, 3610 (1989)
]. Until now, low-molecular-weight organic fluorescent dyes have been generally used as light-emitting materials, and high-molecular-weight light-emitting materials have been described in WO 9013148, Japanese Patent Laid-Open Publication No.
No. 126787, Applied Physics Letters (Appl. Phys. Lett.) 58, 19
82 (1991) and the like.

[0003]

However, the organic EL devices using the polymer light emitting materials which have been reported so far have a high driving voltage and cannot always be said to have sufficient luminance. The polymer light-emitting material is thermally stable and can easily form a light-emitting layer having excellent uniformity by a coating method. Therefore, an organic EL device having a lower driving voltage and a higher luminance while utilizing these advantages. Is required.

An object of the present invention is to provide a low-voltage driven, high-brightness organic EL device using a polymer light-emitting material as a light-emitting layer.

[0005]

Means for Solving the Problems The present inventors have intensively studied low voltage driving and high luminance of an organic EL device using a polymer light emitting material as a light emitting layer. As a result, as the polymer light-emitting material, with a substituted poly -p- phenylene vinylene, thereto, by a Turkey used after adding an electron-transporting compound as a light-emitting layer, when using the polymer light emitting material alone As a result, it has been found that lower voltage driving and higher luminance can be realized, and the present invention has been achieved.

That is, the present invention provides an organic electroluminescent device having at least a light emitting layer between a pair of anodes and cathodes, at least one of which is transparent or translucent, wherein the light emitting layer is

[0007]

Embedded image (Wherein, R ₁ , R ₂ , R ₃ , and R ₄ are each independently selected from hydrogen, an alkyl group having 1 to 20 carbon atoms, an alkoxy group, an alkylthio group, and an aromatic hydrocarbon group having 6 to 20 carbon atoms. And at least one is an alkyl group, an alkoxy group, or an alkylthio group having 4 to 20 carbon atoms, and n represents a number of 10 to 30,000), and a substituted poly (p-phenylenevinylene). to provide an organic EL element characterized in it to contain an electron transport compound.

Hereinafter, the organic EL device of the present invention will be described in detail. The substituted poly (p-phenylenevinylene) represented by the above formula 2 used in the present invention is soluble in a solvent. Here, R ₁ , R ₂ , R ₃ and R ₄ are each independently selected from hydrogen, an alkyl group having 1 to 20 carbon atoms, an alkoxy group and an alkylthio group, and an aromatic hydrocarbon group having 6 to 20 carbon atoms. In order to show a group and to provide solubility, at least one of them needs to be an alkyl group, an alkoxy group or an alkylthio group having 4 to 20 carbon atoms. Among these, an alkyl group or an alkoxy group having a good film-forming property is particularly preferable. Here, as the alkyl group having 1 to 20 carbon atoms, for example, methyl group, ethyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, decyl group, lauryl group, 2-ethyl-
Examples include a hexyl group, a 3-methyl-butyl group, and an isopropyl group, and a pentyl group, a hexyl group, a heptyl group, an octyl group, a decyl group, a 2-ethyl-hexyl group, and a 3-methyl-butyl group are preferable. Alternatively, as the alkoxy group having 1 to 20 carbon atoms, methoxy group, ethoxy group, butoxy group, pentyloxy group, hexyloxy group, heptyloxy group, octyloxy group, decyloxy group, lauryloxy group, 2-ethyl-hexyloxy A 3-methyl-butoxy group, an isopropyloxy group, and the like, and a pentyloxy group, a hexyloxy group, a heptyloxy group,
Octyloxy, decyloxy, 2-ethyl-hexyloxy and 3-methyl-butoxy are preferred. Examples of the alkylthio group include a methylthio group, an ethylthio group,
Butylthio group, pentylthio group, hexylthio group, heptylthio group, octylthio group, decylthio group, laurylthio group, 2-ethyl-hexylthio group, 3-methyl-butylthio group, isopropylpropylthio group, etc., and pentylthio group, hexylthio group, heptylthio group, Octylthio, decylthio, 2-ethyl-hexylthio, 3
-A methyl-butylthio group is preferred. Examples of the aromatic hydrocarbon group include a phenyl group, a 4-alkoxyphenyl group,
Examples thereof include an alkylphenyl group, a 1-naphthalene group, and a 2-naphthalene group.

Specific examples of the substituted poly (p-phenylenevinylene) include poly (2,5-dipentyl-p-phenylenevinylene), poly (2,5-dihexyl-p-phenylenevinylene), and poly (2,5). -Diheptyl-p-phenylenevinylene), poly (2,5-dioctyl-p-)
Phenylene vinylene), poly (2,5-didecyl-p-)
Phenylenevinylene), poly (2,5-dipentyloxy-p-phenylenevinylene), poly (2,5-dihexyloxy-p-phenylenevinylene), poly (2,5
-Diheptyloxy-p-phenylenevinylene), poly (2,5-dioctyloxy-p-phenylenevinylene), poly (2,5-didecyloxy-p-phenylenevinylene), poly (2,5-dipentylthio-p) -Phenylenevinylene), poly (2,5-dihexylthio-p)
-Phenylenevinylene), poly (2,5-diheptylthio-p-phenylenevinylene), poly (2-methoxy-
5-heptyloxy-p-phenylenevinylene), poly (2-methoxy-5-lauryloxy-p-phenylenevinylene), poly (2-methoxy-5- (2′-ethyl-hexyloxy) -p-phenylenevinylene) ), Poly (2-methoxy-5-heptylthio-p-phenylenevinylene), poly (2-methoxy-5-laurylthio-p)
-Phenylene vinylene), poly (2-methoxy-5-)
(3′-methyl-butoxy) -p-phenylenevinylene) and the like. Among them, poly (2,5-
Dipentyl-p-phenylenevinylene), poly (2.5)
-Dihexyl-p-phenylenevinylene), poly (2,
5-diheptyl-p-phenylenevinylene), poly (2,5-dioctyl-p-phenylenevinylene), poly (2,5-dipentyloxy-p-phenylenevinylene), poly (2,5-dihexyloxy-p- Phenylenevinylene), poly (2,5-diheptyloxy-p-)
Phenylenevinylene), poly (2,5-dioctyloxy-p-phenylenevinylene), poly (2,5-didecyloxy-p-phenylenevinylene), poly (2-methoxy-5-hexyloxy-p-phenylenevinylene), Poly (2-methoxy-5- (3'-methyl-butoxy) -p-phenylenevinylene) is preferred. These substituted poly (p-phenylenevinylenes) may be used alone or in combination of two or more.

[0010] In formula 2, n represents the number of repeating units, may be difficult to obtain a uniform film when surplus Linimo too small, also be too large to decrease solubility, uniform manufacturing since it may be film becomes difficult range of n is from 10 to 30000, 10-10000 virtuous better <br/> physician.

These substituted organic solvent-soluble substituted poly (p-
When using phenylene vinylene) to form a film from a solution, it is only necessary to remove the solvent by drying after coating this solution, and the same method can be applied when an electron transporting compound is mixed, Above is very advantageous.

The method for synthesizing the substituted poly (p-phenylenevinylene) represented by the above formula (2) is not particularly limited.
For example, Japanese Patent Application Laid-Open Nos.
No. 217, for example. That is, for example, a corresponding bis (methyl halide) compound, more specifically, for example, 2,5-diheptyloxy-p-xylylenedibromide is converted to a tertiary butyl alcohol in a mixed solvent of xylene / tertiary butyl alcohol. A dehydrohalogenation method in which polymerization is performed using potassium butoxy potassium. Examples thereof include a Wittig method in which a corresponding phosphonium salt and an aldehyde are reacted with a lithium alcoholate as a catalyst, and a sulfonium salt decomposition method in which a corresponding sulfonium salt is polymerized in the presence of an alkali, followed by desulfonium salt treatment. . In addition, when these polymer compounds are used as a light emitting layer of an organic EL device, since their purity affects the light emitting characteristics, it is desirable to purify the compound after synthesis, such as reprecipitation purification and separation by chromatography.

The electron-transporting compound used in the present invention is not particularly limited as long as it has a high electron-transporting property with respect to substituted poly (p-phenylenevinylene) used as a light-emitting material. Examples include benzoquinone-based compounds, naphthoquinone-based compounds, anthraquinone-based compounds, tetracyanoanthraquinodimethane-based compounds, diphenyldicyanoethylene-based compounds, fluorenone-based compounds, diphenoquinone-based compounds, and metal complexes of 8-hydroxyquinoline and derivatives thereof. .
Specifically, JP-A-63-70257 and JP-A-63-175
860, JP-A-2-135361, 2-135
Known compounds such as those described in U.S. Pat. No. 359 and No. 3-152184 can be used, but oxadiazole compounds, benzoquinone compounds, anthraquinone compounds, 8-hydroxyquinoline and metal complexes of derivatives thereof can be used. Is preferable, and in particular, 2- (4-biphenylyl)-
5- (4-t-butylphenyl) -1,3,4-oxadiazole, benzoquinone, anthraquinone, and tris (8-quinolinol) aluminum are preferred. These electron transporting compounds may be used alone or as a mixture of two or more. When an electron transporting compound is used as a mixture with substituted poly (p-phenylenevinylene), if the amount is too small, the effect is small, and if the amount is too large, the current that does not contribute to light emission increases. , Brightness and the like are deteriorated. The mixing ratio varies depending on the molecular weight of the electron transporting compound used, but the mixing ratio is 1 to 1 based on the long-chain group-substituted poly (p-phenylenevinylene).
40 wt% is preferable, and 2 to 30 wt% is more preferable.
It is.

In the present invention, the use of a material obtained by dispersing a known luminescent material in the substituted poly (p-phenylenevinylene) represented by Chemical Formula 2 as a luminescent layer is also included. The light-emitting material is not particularly limited. For example, naphthalene derivatives, anthracene and its derivatives, perylene and its derivatives, polymethine-based, xanthene-based, coumarin-based, cyanine-based dyes, and metal complexes of 8-hydroxyquinoline and its derivatives , Aromatic amines, tetraphenylcyclopentadiene and its derivatives, tetraphenylbutadiene and its derivatives, and the like. Specifically, for example, Japanese Patent Application Laid-Open No. 57-51781, 5
Known ones such as those described in JP-A-9-194393 can be used.

The structure of the organic EL device of the present invention will be described below. As a pair of electrodes composed of an anode and a cathode, a transparent or translucent electrode having a transparent or translucent electrode formed on a transparent substrate such as glass or transparent plastic is used. As the material of the anode, a conductive metal oxide film, a translucent metal thin film, or the like is used. Specifically, indium tin oxide (ITO), tin oxide (NESA), Au, Pt, Ag, Cu and the like are used. As a manufacturing method, a vacuum evaporation method, a sputtering method,
A plating method or the like is used.

Next, a light emitting layer containing a substituted poly (p-phenylenevinylene) and an electron transporting compound is formed on the anode. Examples of the film forming method include a coating method such as a spin coating method, a casting method, a dipping method, a bar coating method, a roll coating method, or a vacuum deposition method using a mixed solution of these materials. It is particularly preferable to form a film by a coating method such as a method, a casting method, a dipping method, a bar coating method, and a roll coating method.

The thickness of the light emitting layer is 5 to 10 μm, preferably 10 to 1 μm. In order to increase the current density and the luminous efficiency, the range of 100 to 5000 ° is preferable. In the case where the film is formed into a thin film by a coating method, the solvent is removed.
Preferably from 60 to 300 ° C, more preferably from 100 to 300 ° C.
It is desirable to heat-treat at a temperature of 250 ° C. The heat treatment time is at least one for removing the solvent.
The treatment is preferably performed for 0 minutes or more, and practically 1 to 24
Time is more preferred.

In another embodiment, when the light emitting layer does not contain an electron transporting compound, the light emitting layer is provided by the above-described film forming method, and the electron transporting layer is formed thereon. As the material of the electron transport layer, the above-described electron transport compound is used.

The method for forming the film of the electron transporting compound is not particularly limited, but is a vacuum evaporation method from a powder state, or a spin coating method after dissolving in a solvent, a casting method, a dipping method, a bar coating method, a roll coating method. After mixing and dispersing a long-chain-group-substituted poly (p-phenylenevinylene) or a polymer compound different therefrom and an electron-transporting compound in a solution state or a molten state. Coating methods such as spin coating, casting, dipping, bar coating, and roll coating can be used. The polymer compound to be mixed is not particularly limited, but those which do not extremely inhibit charge transport are preferable, and those which do not strongly absorb visible light are suitably used. For example, long-chain group-substituted poly (p-phenylenevinylene), poly (p-phenylenevinylene), poly (2,5-dimethoxy-p-phenylenevinylene), poly (2,5-dimethyl-p- Phenylene vinylene), polythiophene and its derivatives, poly (2,5-thienylene vinylene) and its derivatives, polycarbonate, polymethacrylate,
Examples thereof include polymethyl methacrylate, polystyrene, polyvinyl chloride, and polysiloxane. It is preferable to use a coating method in that the film can be easily formed.

The thickness of the electron transporting layer is required to be at least such that no pinholes are generated. However, if the thickness is too large, the resistance of the element increases and a high driving voltage is required, which is not preferable. Therefore, the thickness of the electron transport layer is 50 to 20.
00 °.

Next, when the light-emitting layer is a mixed layer of substituted poly (p-phenylenevinylene) and an electron-transporting compound, the light-emitting layer is formed on this layer. When the light-emitting layer and the electron-transport layer are laminated, the electron-transport layer is formed. An electrode is provided on the layer. This electrode becomes an electron injection cathode. The material is not particularly limited, but a material having a small ionization energy is preferable. For example, Al, In, Mg, an alloy of Mg and Ag (Mg-Ag
Alloy), In-Ag alloy, Mg-
An In alloy, a graphite thin film or the like is used. Among them, an alloy of Mg and Ag is preferable. As a method for manufacturing the cathode, a known method such as a vacuum evaporation method and a sputtering method is used.

The structure of the EL device of the present invention is as follows.
In addition to the structure of the anode / light-emitting layer / cathode (/ indicates that the layers are stacked) or the structure of the anode / light-emitting layer / electron transport layer / cathode described above, between the anode and the light-emitting layer or between the cathode and the electron transport A combination structure having a polymer compound buffer layer between the layers, that is, anode / buffer layer / light-emitting layer / cathode, anode / buffer layer / light-emitting layer / electron transport layer / cathode, anode / light-emitting layer / buffer layer / Cathode, anode / light-emitting layer / electron transport layer / buffer layer / cathode, anode / buffer layer / light-emitting layer / buffer layer / cathode, anode / buffer layer / light-emitting layer / electron transport layer / buffer layer / cathode can also be used. . The polymer compound used for the buffer layer is not particularly limited, but those that do not extremely inhibit charge transport are preferable, and those that do not strongly absorb visible light are suitably used. For example, poly (N-vinylcarbazole), polyaniline and its derivatives, polythiophene and its derivatives, poly (2,5-thienylenevinylene) and its derivatives, polysilane and its derivatives, and the like are exemplified. It is preferable to use a coating method in that the film can be easily formed. The thickness of the buffer layer is usually 5 to 10 μm, preferably 10 to 5000 °, more preferably 2 to 10 μm to increase the current density and increase the luminous efficiency.
0-1000 °.

[0023]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1 A glass substrate provided with an ITO film having a thickness of 200 ° by sputtering was used in Example 6 of JP-A-1-79217, instead of 2,5-diheptyl-p-xylylenedibromide. Poly (2,5-diheptyloxy-p-phenylenevinylene) synthesized by the method described in Example 6 using 5-diheptyloxy-p-xylylene dibromide [gel permeation chromatography (GPC)
The number average degree of polymerization in terms of polystyrene is about 360], and 2- (4-biphenylyl) -5- as an electron transporting compound.
0.6% of (4-t-butylphenyl) -1,3,4-oxadiazole (the mixing ratio to poly (2,5-diheptyloxy-p-phenylenevinylene) is 5 wt%)
Using a 7 wt% toluene / chloroform (3/2 weight ratio) solution, a film was formed to a thickness of 800 ° by spin coating. Then, after drying this at 60 ° C. under reduced pressure for 1 hour,
Then, 3000 nm of In was deposited thereon as a cathode to produce an organic EL device. The degree of vacuum at the time of vapor deposition is 3 × 10 ^-6
Torr or less. When a voltage of 19.4 V was applied to this device, a current having a current density of 275 mA / cm ² flowed and orange EL light emission with a luminance of 160.6 cd / m ² was observed. In addition, the voltage for achieving a luminance of ²⁰ cd / m ² was 13.2 V.

Example 2 2- (4-biphenylyl) -5- (4-t-butylphenyl) -1,3,4-oxadiazole was converted to poly (2,5
-Diheptyloxy-p-phenylenevinylene) in the same manner as in Example 1, except that the amount was 890 ° C.
An organic EL device having a light-emitting layer having a thickness of 3 mm was produced. When a voltage of 26.0 V was applied to this element, a current density of 21
A current of 9 mA / cm ² flows, and a luminance of 71.9 cd / m ²
Orange EL emission was observed. 20 cd /
The voltage for obtaining a luminance of m ² was 19.6 V.

Example 3 2- (4-biphenylyl) -5- (4-t-butylphenyl) -1,3,4-oxadiazole was converted to poly (2,5
-Diheptyloxy-p-phenylenevinylene) in the same manner as in Example 1 except that the content was 2.5 wt%.
An organic EL device having a light emitting layer having a thickness of 10 ° was produced. When a voltage of 19.4 V was applied to this device, a current having a current density of 56 mA / cm ² flowed and luminance of 46.8 cd
/ M ² was observed. 20
The voltage for obtaining a luminance of cd / m ² was 17.5 V.

Comparative Example 1 Poly (2,5-diheptyloxy-p-phenylenevinylene) was added to 2- (4-biphenylyl) -5- (4-t-butylphenyl) -1,3,4-oxadiazole. Was prepared in the same manner as in Example 1 except that the light-emitting layer was not mixed. When a voltage of 33.3 V was applied to this device, a current density of 617 mA / c
Although a current of m ² flowed, only orange EL emission with a luminance of 26.4 cd / m ² was observed. 20
The voltage for obtaining a luminance of cd / m ² was 32.9 V.

Example 4 Poly (2,5-diheptyloxy-p-phenylenevinylene) was used in place of 2,5-diheptyl-p-xylylene dibromide in Example 6 of JP-A-1-79217. Poly (2,5-dihexyloxy-p-phenylenevinylene) synthesized by the method described in Example 6 using 2,5-dihexyloxy-p-xylylene dibromide (polystyrene-equivalent number average polymerization degree by GPC of about 1).
60) to give 2- (4-biphenylyl) -5- (4-
Example 1 except that t-butylphenyl) -1,3,4-oxadiazole was mixed at 10 wt% with respect to poly (2,5-dihexyloxy-p-phenylenevinylene) and chloroform was used as a solvent. 1300Å in the same way
An organic EL device having a light-emitting layer having a thickness of 3 mm was produced. When a voltage of 25.0 V was applied to this element, a current density of 34
A current of 6 mA / cm ² flows, and a luminance of 44.6 cd / m ²
Orange EL emission was observed. 20 cd /
The voltage for obtaining a luminance of m ² was 23.5 V.

Example 5 Poly (2,5-diheptyloxy-p-phenylenevinylene) was used instead of 2,5-diheptyl-p-xylylene dibromide in Example 6 of JP-A-1-79217. Poly (2,5-dipentyloxy-p-phenylenevinylene) synthesized by the method described in Example 6 using 2,5-dipentyloxy-p-xylylene dibromide (polystyrene-equivalent number average polymerization degree by GPC of about 4).
00) to give 2- (4-biphenylyl) -5- (4-
Example 1 was repeated except that 10% by weight of t-butylphenyl) -1,3,4-oxadiazole was mixed with poly (2,5-dipentyloxy-p-phenylenevinylene) and chloroform was used as a solvent. 1400Å in the same way
An organic EL device having a light-emitting layer having a thickness of 3 mm was produced. When a voltage of 23.3 V was applied to this element, a current density of 38
A current of 6 mA / cm ² flows, and a luminance of 51.4 cd / m ²
Orange EL emission was observed. 20 cd /
The voltage for obtaining a luminance of m ² was 22.5 V.

Comparative Example 2 2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole was converted to poly (2,5
-Diheptyloxy-p-phenylenevinylene) was prepared in the same manner as in Example 1 except that 44.4 wt% was mixed with respect to -diheptyloxy-p-phenylenevinylene) to produce an organic EL device having a light-emitting layer having a thickness of 2600 °. When a voltage of 40.0 V was applied to this element, a current having a current density of 1360 mA / cm ² flowed.
Only an orange EL emission of 3.4 cd / m ² was observed. In addition, when the voltage is increased, 20
It was not possible to achieve a luminance of cd / m ² .

Example 6 An ITO film having a thickness of 200 ° was formed by sputtering.
Synthesized on the attached glass substrate in the same manner as in Example 1.
Poly (2,5-diheptyloxy-p-phenylenevinyl)
And anthraquinone [poly
(2,5-diheptyloxy-p-phenylenevinylene
0.67 wt% toluene
Spin / chloroform (3/2 weight ratio) solution
A film having a thickness of 1100 ° was formed by coating. Then,
After drying at 60 ° C. for 1 hour under reduced pressure, the cathode and
Then, In is deposited at 3000 ° to produce an organic EL device.
did. The degree of vacuum during evaporation is 3 × 10^-6Under Torr
there were. When a voltage of 20.8 V was applied to this element,
Current density 165.2 mA / cm ^TwoCurrent flows and the brightness is 1
46 cd / m^TwoOrange EL emission was observed.
In addition, 20 cd / m^TwoThe voltage for achieving the luminance of 16.
It was 8V.

Example 7 Except that a layer composed of a mixture of poly (2,5-thienylenevinylene) and poly (p-phenylenevinylene) in a ratio of 7: 3 (weight ratio) was provided as a buffer layer on an ITO film.
The light-emitting layer and the cathode were manufactured in the same manner as in Example 6 to produce an organic EL device in which the total thickness of the buffer layer and the light-emitting layer was 1500 °. Here, a layer composed of a mixture of poly (2,5-thienylenevinylene) and poly (p-phenylenevinylene) in a ratio of 7: 3 was obtained by the method described in Example 1 of JP-A-1-9221. Poly (2,5-thienylenevinylene) (P
TV) intermediate with N, N-dimethylformamide (DM
F) and a Br ^- salt of a poly (p-phenylenevinylene) (PPV) intermediate synthesized by the method described in Example 1 of JP-A-59-199746. Was added to a large amount of aqueous NaBF ₄ solution to exchange the counter ion (Br ⁻ ) for BF ₄ ^−, and the BF ₄ ⁻ salt of the PPV intermediate recovered as a precipitate was dissolved in DMF to give a PPV intermediate solution. A solution was prepared by spin-coating a solution in which both polymers produced after the heat treatment were mixed at a weight ratio of 7: 3, and heat-treated at 200 ° C. When a voltage of 24.4 V was applied to this device, a current having a current density of 70.8 mA / cm ² flowed and orange EL emission with a luminance of 120 cd / m ² was observed. In addition, the voltage for achieving a luminance of ²⁰ cd / m ² was 18.2 V.

Example 8 An organic EL device having a light-emitting layer having a thickness of 630 ° was produced in the same manner as in Example 6 except that benzoquinone was mixed instead of anthraquinone. A voltage of 18.3 is applied to this element.
When V was applied, the current density was 163.4 mA / cm ²
And the EL of orange with a luminance of 63 cd / m ²
Luminescence was observed. Also, the voltage required to achieve a luminance of ²⁰ cd / m ^{2 was} 14.8 V.

Example 9 A glass substrate provided with an ITO film in the same manner as in Example 1
0.75 wt% of poly (2,5-diheptyloxy-p-phenylenevinylene) [number-average degree of polymerization in terms of polystyrene by gel permeation chromatography (GPC) of about 360] synthesized by the same method as in Example 1. A film was formed by dipping using a chloroform solution. Then, this was dried at 60 ° C. for 1 hour under reduced pressure, and then tris (8-quinolinol) aluminum was deposited thereon at 700 ° as an electron transporting layer, and then Mg-A was used as a cathode.
A g alloy (weight ratio 10: 1) was deposited at 1500 ° and Ag was further deposited thereon at 1000 ° to produce an organic EL device. The total thickness of the organic layer was 910 °. The degree of vacuum at the time of vapor deposition was 3 × 10 ⁻⁶ Torr or less. When a voltage of 17.8 V was applied to this element, a current having a current density of 420 mA / cm ² flowed and a luminance of 2290
An orange EL emission of cd / m ² was observed. The emission spectrum was consistent with the fluorescence spectrum of poly (2,5-diheptyloxy-p-phenylenevinylene).

Comparative Example 3 An organic EL device was manufactured in the same manner as in Example 9 except that the electron transport layer was not provided. When a voltage of 9.2 V was applied to this device, a current having a current density of 569 mA / cm ² flowed and orange EL emission with a luminance of 1189 cd / m ² was observed. Further, even if the voltage was further increased, the luminance did not improve, and light emission stopped at 11.7 V due to destruction of the element.

[0036]

As described above, the organic EL of the present invention
The element is driven at a lower voltage and has improved brightness as compared with the conventional one, and a planar light source as a backlight,
It can be used as a device such as a flat panel display.

Continuation of the front page (56) References JP-A-3-244630 (JP, A) JP-A-2-250292 (JP, A) JP-A-2-209988 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) H05B 33/14 C09K 11/06

Claims (2)

(57) [Claims] 1. An organic electroluminescence device having at least a light emitting layer between a pair of anodes and cathodes, at least one of which is transparent or translucent, wherein the light emitting layer is represented by the following formula: (Wherein, R ₁ , R ₂ , R ₃ , and R ₄ are each independently selected from hydrogen, an alkyl group having 1 to 20 carbon atoms, an alkoxy group, an alkylthio group, and an aromatic hydrocarbon group having 6 to 20 carbon atoms. And at least one is an alkyl group, an alkoxy group, or an alkylthio group having 4 to 20 carbon atoms, and n represents a number of 10 to 30,000), and a substituted poly (p-phenylenevinylene). An organic electroluminescence device comprising an electron transporting compound. 2. The organic electroluminescent device according to claim 1, wherein the cathode is characterized by comprising an alloy of Mg and Ag.