JP3235244B2 - 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 (EL) device used for a flat light source and a display.

[0002]

2. Description of the Related Art An EL device using an organic substance is expected to be used as an inexpensive, large-area, full-color display device of a solid light emitting type, and many developments have been made. In general EL element
The element is composed of a light emitting layer and a pair of opposed electrodes sandwiching the layer. In light emission, when an electric field is applied between both electrodes, electrons are injected from the cathode side, holes are injected from the anode side , and the electrons recombine with holes in the light emitting layer, and the energy level is changed to the conduction band. This is a phenomenon in which energy is emitted as light when returning to the valence band from.

[0003] Conventional organic EL devices have a higher driving voltage and lower luminous brightness and luminous efficiency than inorganic EL devices.
In addition, the characteristic deterioration was remarkable, and it had not been put to practical use.
2. Description of the Related Art In recent years, an organic EL in which a thin film containing an organic compound having high fluorescence quantum efficiency that emits light at a low voltage of 10 V or less is laminated.
Devices have been reported and are of interest (see Applied Physics Letters, vol. 51, p. 913, 1987). In this method, the metal chelate complex is converted into a phosphor layer,
High brightness green light emission is obtained by using an amine compound for the hole injection layer, and the brightness is several hundreds at a DC voltage of 6 to 7V.
It achieves cd / m ² and maximum luminous efficiency of 1.5 lm / W, and has performance close to the practical range.

[0004] However, organic EL devices up to now have improved luminous intensity due to the improved structure, but do not yet have sufficient luminous brightness. In addition, there is a major problem that the stability upon repeated use is poor. Therefore, at present, it is desired to develop an organic EL device having higher emission luminance and excellent stability when repeatedly used.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide an organic EL device having a high luminous intensity and excellent stability when used repeatedly. As a result of intensive studies by the present inventors, they have found that an organic EL device using an organic compound represented by the general formula [1] has high emission intensity and excellent stability during repeated use. Reached.

[0006]

That is, the present invention relates to an electroluminescent device having a layer containing at least a phosphor between a pair of electrodes.
An organic electroluminescence device using at least one of the organic compounds represented by

The general formula [1]

[0008]

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(Wherein R ¹ to R ¹⁸ each independently represent a hydrogen atom, a halogen atom, a cyano group, a nitro group, an amino group, a dialkylamino group, a diphenylamino group, a hydroxyl group, an alkoxy group, a mercapto group, a siloxy group) Group, acyl group, cycloalkyl group, carboxylic acid group, sulfonic acid group, substituted or unsubstituted aliphatic hydrocarbon group, substituted or unsubstituted aromatic hydrocarbon group, substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted heterocyclic group, may form an aromatic ring or heterocyclic .A and B between two substituents, represents different oxygen atom, a sulfur atom, an -NR ¹⁹ together .R ¹⁹ may be any substituent.)

Hereinafter, typical examples of the compound of the general formula [1] used in the present invention are specifically exemplified by compounds (a) to (o), but the present invention is limited to the following typical examples. Not something.

Compound (a)

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Compound (b)

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Compound (c)

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Compound (d)

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Compound (e)

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Compound (f)

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Compound (g)

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Compound (h)

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Compound (i)

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Compound (j)

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Compound (k)

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Compound (l)

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Compound (m)

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Compound (n)

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Compound (o)

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FIGS. 1 to 3 show an organic EL used in the present invention.
A schematic diagram of the device is shown. In the figure, generally, electrode A 2
Is an anode, and 6 which is an electrode B is a cathode. Since the compound of the general formula [1] has both strong light emission and large carrier transport ability, the hole injection layer 3, the phosphor layer 4,
It is effective to use any of the electron injection layers 5. For the phosphor layer 4 in FIG. 1, if necessary, a light-emitting auxiliary agent, a hole transport material for transporting carriers, or an electron transport material can be used in addition to the light-emitting substance.

FIG. 2 shows the structure of the phosphor layer 4 and the hole injection layer 3.
Are separated. With this structure, the hole injection efficiency from the hole injection layer 3 to the phosphor layer 4 is improved, and the light emission luminance and the light emission efficiency can be increased.

The structure shown in FIG. 3 has an electron injection layer 5 in addition to the hole injection layer 3 to improve the efficiency of recombination of holes and electrons in the phosphor layer 4. In this manner, by making the organic EL element have a multilayer structure, it is possible to prevent a decrease in luminance and life due to quenching.

As the conductive material used for the anode of the organic EL device, those having a work function of more than 4 eV are preferable, and carbon, aluminum, vanadium, iron, cobalt, nickel, tungsten, silver, gold, etc. Alloys thereof and metal oxides such as tin oxide and indium oxide are used.

As the conductive material used for the cathode, 4
Those having a work function smaller than eV are preferable, and magnesium, calcium, titanium, yttrium, lithium, ruthenium, manganese and the like, and alloys thereof are used, but not limited thereto.

In the organic EL device, it is desirable that at least the electrode A indicated by 2 or the electrode B indicated by 6 be transparent in order to emit light efficiently. Further, it is desirable that the substrate 1 is also transparent. The transparent electrode is set so as to secure a predetermined light transmittance by a method such as vapor deposition or sputtering using the above-described conductive substance.

The substrate 1 is not limited as long as it has mechanical and thermal strengths and is transparent. Examples thereof include a glass substrate, an ITO substrate, a NESA substrate, a polyethylene plate, and a polyether sulfone. And a transparent resin such as a polypropylene plate.

Each layer of the organic EL device according to the present invention can be formed by any of dry film forming methods such as vacuum evaporation and sputtering and wet film forming methods such as spin coating and dipping. The thickness is not particularly limited, but each layer needs to be set to an appropriate thickness. If the film thickness is too large, a large applied voltage is required to obtain a constant light output, resulting in poor efficiency. If the film thickness is too small, pinholes and the like are generated, and sufficient light emission luminance cannot be obtained even when an electric field is applied.

In the case of the wet film forming method, a liquid in which the material for forming each layer is dissolved or dispersed in an appropriate solvent such as chloroform, tetrahydrofuran, dioxane or the like is used, and the solvent may be any one. . Further, an appropriate resin or additive may be used for improving the film forming property, preventing pinholes in the film, and the like.

In the organic EL device shown in FIG.
By using the compound of the general formula [1] as a luminescent substance, high luminescent characteristics can be achieved. In addition, this compound can obtain more efficient light emission luminance by using a light emitting substance auxiliary agent in the same layer.

In the present organic EL device, if necessary, in addition to the compound of the general formula [1], a known luminescent substance, luminescent auxiliary agent, hole transport substance, and electron transport substance can be used.

Examples of such known luminescent substances or luminescent auxiliary substances include anthracene, naphthalene, phenanthrene, pyrene, tetracene, coronene, chrysene, and the like.
Fluorescein, perylene, phthaloperylene, naphthaloperylene, perinone, phthaloperinone, naphthaloperinone, diphenylbutadiene, tetraphenylbutadiene, coumarin, oxadiazole, aldazine, bisbenzoxazoline, bisstyryl, pyrazine, CPD, oxine, aminoquinoline, imine, diphenylethylene, Examples include, but are not limited to, vinylanthracene, diaminocarbazole, pyran, thiopyran, polymethine, merocyanine, imidazole chelated oxinoid compounds, and the like.

As the hole transporting substance, oxadiazole, triazole, imidazolone,
Imidazolethione, pyrazoline, tetrahydroimidazole, oxazole, hydrazone, acylhydrazone, stilbene, butadiene, benzidine-type triphenylamine, styrylamine-type triphenylamine, diamine-type triphenylamine, and the like, and derivatives thereof, and polyvinyl carbazole, polysilane, There is a polymer material such as a conductive polymer, but it is not limited thereto.

As the electron transporting substance, an appropriate substance having an electron accepting property is used. For example, anthraquinodimethane,
Examples include, but are not limited to, diphenylquinone, oxadiazole, perylenetetracarboxylic acid, and the like.

It is also possible to sensitize by adding an electron accepting substance to the hole transporting substance and adding an electron donating substance to the electron transporting substance. Organic EL shown in FIGS. 2 and 3
In the device, the compound of the general formula [1] can be used in any layer, and at least one of a luminescent material, a luminescent auxiliary, a hole transport material, and an electron transport material may be contained in the same layer. . As described above, in the present invention, since the compound of the general formula [1] was used for the organic EL device, the luminous efficiency and the luminous brightness could be increased. In addition, this element was extremely stable against heat and current, and the degradation, which had been a major problem until now, could be greatly reduced. The organic EL device of the present invention can be used as various display devices.

[0041]

The present invention will be described in more detail with reference to the following examples.

Example 1 A compound (e) was dissolved in chloroform on a washed glass plate with an ITO electrode, and a phosphor layer was formed by spin coating to obtain a phosphor layer having a thickness of 0.05 μm. . An electrode having a thickness of 0.2 μm was formed thereon using an alloy in which magnesium and silver were mixed at a ratio of 10: 1 to obtain the organic EL device shown in FIG. This device has a DC voltage of 5 V and
Light emission of 0 m ² was obtained.

Example 2 Organic E was prepared in the same manner as in Example 1 except that a phosphor layer was formed by vacuum evaporation using the compound (g).
An L element was produced. This element has a DC voltage of 5 V and
Light emission of 0 m ² was obtained.

Example 3 N, N'-diphenyl-N, N '-(3-methylphenyl) -1,1' was placed on a washed glass plate with an ITO electrode.
-Biphenyl-4,4'-diamine was vacuum-deposited to obtain a hole injection layer having a thickness of 0.03 μm. Next, the compound (i) was dissolved in chloroform, and a phosphor layer having a thickness of 0.02 μm was obtained by spin coating. An electrode having a thickness of 0.2 μm was formed thereon using an alloy in which magnesium and silver were mixed at a ratio of 10: 1 to obtain the organic EL device shown in FIG. This element has about 290 cd / m ² at a DC voltage of 5 V.
Was obtained.

Example 4 N, N'-diphenyl-N, N '-(3-methylphenyl) -1,1' was placed on a washed glass plate with an ITO electrode.
-Biphenyl-4,4'-diamine was vacuum-deposited to obtain a hole injection layer having a thickness of 0.03 μm. Next, the compound (k) was dissolved in chloroform, and a phosphor layer having a thickness of 0.02 μm was obtained by spin coating. further,
Perylene was vacuum-deposited to obtain an electron injection layer having a thickness of 0.03 μm. An electrode having a thickness of 0.2 μm was formed thereon using an alloy in which magnesium and silver were mixed at a ratio of 10: 1 to obtain an organic EL device shown in FIG. This device emitted light of about 320 cd / m ² at a DC voltage of 5 V.

When all the organic EL devices shown in this example were continuously emitted at 1 mA / cm ² ,
Stable light emission could be observed for 00 hours or more. The organic EL device of the present invention achieves luminous efficiency, improved luminous brightness and longer life, and a luminescent material used in combination therewith,
Luminescence auxiliary substances, hole transport substances, electron transport substances, sensitizers,
It does not limit the resin, the electrode material and the like, and the element manufacturing method.

Comparative Example 1 The following compound (p) was used in place of compound (e).
Outside, an organic EL element was manufactured in the same manner as in Example 1.
Was. This device, calling the 140 cd / m ² at a direct current voltage of 5V
Light brightness was obtained. However, continuous emission at 1 mA / cm ²
Then, the luminance was reduced to half in about 250 hours.
A non-light-emitting portion called a dark spot is located on the light-emitting surface.
Occurred frequently. Compound (p)

Embedded image Comparative Example 2 The following compound (q) was used instead of compound (g).
Outside, an organic EL device was manufactured in the same manner as in Example 2.
Was. This device, calling the 150 cd / m ² at a direct current voltage of 5V
Light brightness was obtained. However, instead of uniform surface emission, 1
After continuous emission at mA / cm ² , it took about 150 hours
The brightness is reduced by half, and the dark spot
Light-emitting sites occurred frequently on the light-emitting surface. Compound (q)

Embedded image Comparative Example 3 The following compound was used as the phosphor layer instead of the compound (i).
Except for using (r), the organic E was prepared in the same manner as in Example 3.
An L element was produced. This element is 90c at 5V DC
An emission luminance of d / m ² was obtained. However, uniform surface emission
Instead, the light and slightly dark areas were seen. Ma
When continuous emission was performed at 1 mA / cm ² , about 200
The brightness decreased by half over time. Compound (r)

Embedded image Comparative Example 4 The following compound was used as the phosphor layer instead of the compound (k).
Except for using (s), the organic E was prepared in the same manner as in Example 4.
An L element was produced. This element is 160 V DC at 5 V.
An emission luminance of cd / m ² was obtained. However, even surface
When emitted continuously at 1 mA / cm ² instead of light ,
In about 200 hours, the brightness was reduced by half. Also a dark spot
The number of non-light-emitting sites, which are referred to as pits, increased over time. Compound (s)

Embedded image In the comparative example, uniform surface light emission was not obtained,
The reason for the short lifetime was that the material used in the comparative example had poor crystallinity.
It is presumed that a uniform film could not be formed due to the high
You.

[Effect of the Invention] Since the symmetry is reduced, the arrangement becomes difficult.
The compound represented by the general formula [1] of the present invention in which crystallinity is suppressed.
By using the compound, it was possible to obtain an organic EL device having higher luminous efficiency and higher luminance than the conventional one and having a long life.

[0048]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic structure of an organic EL device used in Examples 1 and 2.

FIG. 2 is a cross-sectional view illustrating a schematic structure of an organic EL device used in Example 3.

FIG. 3 is a cross-sectional view illustrating a schematic structure of an organic EL device used in Example 4.

[Explanation of symbols]

 1. Substrate 2. Electrode A3. 3. Hole injection layer Phosphor layer 5. Electron injection layer 6. Electrode B

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C09K 11/06 CA (STN) REGISTRY (STN)

Claims (1)

(57) [Claims] 1. An organic electroluminescent device having at least one compound represented by the general formula [1] in an electroluminescent device having a layer containing at least a phosphor between a pair of electrodes. . General formula [1] (Wherein R ¹ to R ¹⁸ each independently represent a hydrogen atom, a halogen atom, a cyano group, a nitro group, an amino group, a dialkylamino group, a diphenylamino group, a hydroxyl group, an alkoxy group, a mercapto group, a siloxy group, an acyl group, Group, cycloalkyl group, carboxylic acid group, sulfonic acid group, substituted or unsubstituted aliphatic hydrocarbon group, substituted or unsubstituted aromatic hydrocarbon group, substituted or unsubstituted aromatic heterocyclic group, substituted or unsubstituted A substituted heterocyclic group, which may form an aromatic ring or a heterocyclic ring between two substituents.
And B are different oxygen atoms, sulfur atoms, -NR
Represents ¹⁹ . R ¹⁹ may be any substituent. )