JPH11111462A - Organic electroluminescence device - Google Patents

Abstract

[PROBLEMS] To provide an organic EL device which has high luminous efficiency, long half-life, and maintains stable luminous characteristics. Kind Code: A1 An organic electroluminescent device including at least an anode, a light emitting layer, a hole transport layer and a cathode on a substrate (glass substrate).
In the L element, when the hole transport layer 3 contains the tetrathiafulvalene derivative specified in the present invention, the obtained organic EL element has remarkably excellent luminous efficiency and half-life.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel organic electroluminescent device (hereinafter referred to as "organic EL") used for various products such as flat display (flat display device), flat thin illumination, backlight of liquid crystal display device, decoration and the like. More specifically, the present invention relates to an organic EL device in which a hole transport layer constituting the device has improved luminous efficiency and durability.

[0002]

2. Description of the Related Art In recent years, rapid development of technology in the field of information and communication has been remarkable, and with the progress, flat displays replacing CRTs have been greatly expected. Above all, EL elements have been actively studied because they are excellent in terms of high-speed response, visibility, luminance and the like.

In a ZnS / Mn-based inorganic electroluminescent element that is currently in practical use, a driving voltage of 1
There is a problem that it is as high as about 00 V and sufficient luminance cannot be obtained. On the other hand, the organic EL device reported by Tang et al. Of Kodak Company in the United States in 1987 can be driven at a low DC voltage of 10 V or less, has a high luminance of 1000 cd / m ² or more, and has a luminous efficiency of 1.51 m / W. (Appl. Phys. Lett., Vol.
51, 913 (1987)). This device has an anode, a hole transporting layer, an electron transporting light emitting layer, and a cathode formed on a glass substrate. This presentation showed the advantages of low-voltage driving and multi-coloring by designing organic molecules compared to inorganic electroluminescent devices, and thus many organic EL devices such as new organic materials and new cathode materials Research has begun.

A conventionally known organic EL element has a voltage of 10 V
Light is emitted at a low voltage, and visibility is high. Further, since the color tone and the luminous efficiency of light emission can be easily changed by changing the organic compound used for the light emitting layer, use for thin flat full color display devices, various display devices, flat light sources, etc. has been attempted. I have.

A method using tetrathiafulvalene or bis (ethylenedithio) tetrathiafulvalene as a material for the hole transport layer has been proposed (JP-A-9-13).
See No. 024. Hereinafter, it is referred to as “known tetrathiafulvalene derivative”. ).

[0006] However, all of the conventionally known organic EL elements have disadvantages of low luminous efficiency and short life. One of the causes of this short life is organic EL
It has been pointed out that in the device, the organic substance in the hole transport layer of the device is crystallized during driving, and separation occurs at the interface of the organic layer, resulting in a decrease in luminous efficiency.

[0007]

As described above, conventional organic EL devices have not been sufficiently satisfactory in terms of luminous efficiency and lifetime.

In view of the above, the present invention is directed to solving such a problem, and suppresses the crystallization of the hole transport layer, thereby increasing the luminous efficiency, the luminance, and the half life of the organic compound as compared with the prior art. The purpose is to provide an EL element.

[0009]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, a specific tetrathiafulvalene derivative different from a known tetrathiafulvalene derivative has been added to the hole transport layer of the organic EL device. Thiafulvalene derivative (hereinafter, referred to as “tetrathiafulvalene derivative specified in the present invention”)
It has been found that the use of a compound enhances the hole transporting ability and can significantly increase the luminous efficiency and durability of the obtained device, and have completed the present invention.

That is, the present invention provides an organic EL device including an anode, a hole transport layer, a light emitting layer, and a cathode, wherein the hole transport layer contains a specific tetrafulvalene derivative. It is.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to FIG. 1 showing a configuration of a typical organic EL device.

The organic EL device of the present invention may have a structure including at least an anode, a hole transporting layer, a light emitting layer and a cathode. The light emitting layer can also serve as a hole transporting layer.
In addition, one or more other layers such as an electron transport layer can be included as necessary, and all of the techniques of the organic EL element conventionally known can be used except for the characteristic part of the present invention.

Conventionally known organic EL devices include:
For example, as shown in FIG. 1, a light emitting layer 4 and a hole transport layer 3 are provided between a metal electrode serving as a cathode 5 and a transparent electrode serving as an anode 2.
Is arranged. Here, the hole transport layer 3 has a function of facilitating injection of holes from the anode 2 and a function of blocking electrons. A glass substrate, which is a substrate 1, is disposed outside the transparent electrode, which is the anode 2, and excitons are generated by recombination of electrons injected from the metal electrode and holes injected from the transparent electrode. The element emits light in the process of radiation deactivation, and the light is emitted outside through the transparent electrode and the glass substrate. The light emitting layer is generally composed of an organic phosphor thin film.

In the present invention, the hole transport layer is improved. The hole transport layer contains the tetrathiafulvalene derivative specified in the present invention as a material for the hole transport layer. Indicated by I).

[0015]

Embedded image In the above formula, A represents R ¹ or SR ¹ , B represents R ² or SR ² , or A and B together represent a substituent represented by the following formula (II) or (II ′). D is R ³ or R ³
S represents E, R ⁴ or R ⁴ S, or D and E together represent a substituent represented by the following formula (III) or (III ′).

[0016]

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[0017]

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Here, A is R ¹ , B is R ² , D is R ³ , E
There is represented respectively R ^4, a derivative represented by the following formula (IV), A is the SR ^1, B is ^{SR 2, D R 3 S,} E is R ⁴
S is a derivative represented by the following formula (V), and A and B together form the above formula (II) to give D
And E together represent the above formula (III), the following formula (V
A derivative represented by the formula (II), wherein A and B together form the above formula (II '), and D and E together form the above formula (II
I ′) represents derivatives represented by the following formulas (VII) and (VII ′), and these derivatives are particularly preferable.
Of course, it is included in the tetrathiafulvalene derivative specified in the present invention.

[0019]

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[0020]

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[0021]

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[0022]

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In the above formula, R ^{1 to} R ⁸ are each independently a hydrogen atom, a halogen atom (halogen atom such as fluorine, chlorine and bromine), a substituted or unsubstituted hydroxyl group, a substituted or unsubstituted amino group. And any of substituted or unsubstituted hydrocarbon groups. The hydrocarbon group is a saturated or unsaturated, linear, branched, cyclic or aromatic hydrocarbon residue having 1 to 30 carbon atoms, that is, an alkyl (a carbon-carbon double bond or a triple bond in the substituent). An unsaturated hydrocarbon residue having at least one carbon atom, a cycloalkyl (which may contain at least one carbon-carbon double bond or triple bond in the ring) or an aryl group. Etc. may have a substituent.

[0024] However, in the above formula (IV), not to represent every R ¹ to R ⁴ are hydrogen atom at the same time, in Matashiki (VI), R ¹
All to R ⁸ do not simultaneously represent hydrogen atoms.

Examples of the alkyl group include methyl,
Ethyl, ethenyl, ethynyl, propyl (n-, iso-),
Propenyl, allyl, propynyl, butyl (n-, iso-, se
c-, tert-), butenyl, butadienyl, butynyl, pentyl (n-, iso-, etc.), pentenyl, pentadienyl, hexyl (n-, iso-, etc.), hexenyl, octyl (n-, iso-
And the like, and dodecyl (n-, iso-, etc.). Examples of the cycloalkyl group include cyclopentyl, cyclohexyl, cycloheptyl, cyclohexynyl, cyclic polyacetylene residues, and the like. May be any aromatic compound residue, such as phenyl, naphthyl, and anthracene residues.

Examples of the substituent of the hydrocarbon residue which may have a substituent include a halogen atom such as fluorine, chlorine and bromine, and a linear or branched alkyl or alkoxy group having 1 to 10 carbon atoms. , Phenyl or phenoxy and naphthyl or naphthoxy groups. One or more of these substituents may be substituted. When it has a substituent, the hydrocarbon residue preferably has 1 to 30 carbon atoms including the substituent.

The substituents on the hydroxyl group and the amino group having a substituent are each independently, and include straight-chain and branched-chain alkyl groups having 1 to 10 carbon atoms, phenyl groups and naphthyl groups. it can. In the case of an amino group, two hydrogen atoms can be substituted.

In the above-mentioned substituents of the hydrocarbon residue and the substituents of the hydroxyl group and the amino group, the straight-chain and branched-chain alkyl groups include methyl, ethyl, propyl (n-, iso-
-), Propyl, butyl (n-, iso-, sec-, tert-), pentyl (n-, iso-, etc.), hexyl (n-, iso-, etc.), octyl (n-, iso-, etc.) Can be mentioned.

In the above-mentioned substituent of the hydrocarbon residue, examples of the straight-chain or branched-chain alkoxy group include a hydroxyl group substituted with the above-mentioned alkyl group.

Particularly preferred tetrathiafulvalene derivatives specified in the present invention are, for example, all of A in formula (I)
Derivatives in which at least one of E to E represents a phenyl group and the remainder each represent a hydrogen atom; at least two of A to E each represent a lower (e.g., 5 or less carbon) alkylthio group, and the remainder each represent a hydrogen atom; B and D and E
Are taken together to form formulas (II) and (III), respectively.
A derivative in which at least two of R ^{1 to} R ^{8 each} represent a lower (e.g., 5 or less carbon) alkyloxy group, and the rest each represent a hydrogen atom; and A and B, and D and E each represent And derivatives representing formulas (II ′) and (III ′), respectively.

When the tetrathiafulvalene derivative specified in the present invention is used in a hole transport layer, one kind of the derivative is used.
That is, they can be used alone or in combination of two or more, and can also be used in combination with one or more of conventional light emitting materials and light emitting materials to be found in the future.
In this case, one layer can be formed by mixing a plurality of components, or a plurality of layers, for example, a first hole transport layer, a second hole transport layer, a third layer,... Can also. The use of a plurality of hole transport layers is preferable because the energy barrier for carrier injection can be reduced at the interface between the layers, so that the luminous efficiency is improved and the life is greatly extended. When the hole transport layer is formed of a plurality of layers, at least one of the layers may contain the tetrathiafulvalene derivative specified in the present invention.

When a material other than the present invention is used in combination in the hole transport layer, it is used as a material which is conventionally known as an organic material for the hole transport layer of a photoconductive material or a hole transport layer of an organic EL device. (Japanese Unexamined Patent Publication No.
No. 243393 and JP-A-5-159882, U.S. Pat.
7,450), for example, N, N'-diphenyl-N, N'-
A group of compounds represented by bis (3-methylphenyl)-(1,1′-biphenyl) -4,4′-diamine (hereinafter abbreviated as “TPD”), poly-N-vinylcarbazole, , Amine derivatives and the like, and materials to be developed in the future may be used. In addition, a polymer material such as polyimide, polycarbonate, or polysulfone can be mixed and used as a binder for the hole transporting substance. The thin film may be formed by a method known per se, for example, a vacuum deposition method, a spin coating method, a casting method, an LB method, or the like. The thickness of the thin film layer is 5 to 200 nm, preferably about 20 to 100 nm.

As the organic compound used in the light emitting layer,
Organic compounds conventionally used as a fluorescent material for a light emitting layer of an organic EL device (Japanese Patent Laid-Open No. 5-1598)
No. 82, JP-A-63-295695 and JP-A-3-231970), for example, tris (8-quinolinolato) aluminum (hereinafter abbreviated as "Alq"), distyrylarylene, benzoquinolinol beryllium Complexes and the like can be used in combination. Further, the light emitting layer can be preferably used by doping a dye such as a coumarin derivative, a rubrene derivative, or a quinacridone derivative. Any organic substance that will be developed in the future can be used as long as it exhibits luminous ability. There is no particular difficulty in forming the light emitting layer,
A method known per se, for example, a vapor deposition method, a spin coating method,
What is necessary is just to employ | adopt a casting method, LB method, etc. and to implement. In the future, a method for forming a light emitting layer to be developed can be adopted.

The thickness of the light-emitting layer is not particularly limited, and may also serve as a hole transporting layer and / or an electron transporting layer. The thickness varies depending on the type, but may be appropriately selected as necessary. , Preferably 20-100n
m.

In the present invention, as described above, the electron transporting layer can be used between the light emitting layer and the cathode. In this case, the barrier for injection of the carrier from the electrode is reduced, and the carrier is transported at a low voltage. This is preferable because injection can be performed and penetration of carriers having the opposite polarity can be blocked to increase the recombination probability.

When an electron transport layer (for example, see JP-A-2-16791) is used, the electron transport layer is preferably an oxadiazole derivative or the like. For example, a method of providing an electron transport layer such as phenylbiphenyloxadiazole between the light emitting layer and the electron injection electrode of the cathode (C. Adachi,
S. Tokito, T. Tsutsui, S. Saito., Jpn. J. Appl.Ph
y., vol. 27, L269 (1988)).

As the anode used in the present invention, a conventional transparent electrode may be used. For example, conventionally, as a transparent electrode of an organic EL element, generally, Au, a Group 3B element-doped zinc oxide, a fluorine-doped tin oxide, polyaniline, ITO
(A composite oxide of In ₂ O ₃ -SnO ₂ ) and the like (see Japanese Patent Application Laid-Open Nos. 5-88344 and 5-166414).

In order to extract light emission outside, at least one of the anode 2 and the cathode 5 needs to be transparent or translucent. Usually, the anode is formed on a glass substrate to make it transparent.

As the cathode material, metal electrodes conventionally known as cathode materials for organic EL devices can be employed (Japanese Patent Laid-Open Nos. 6-326354, 5-198380, 63-295695). Reference). For example, a metal or an alloy having a small work function (an alloy such as MgAg, MgAl, AlLi, MgIn, InLi, and AlCa) is used. In particular, as an electron injection electrode,
For example, it is preferable to form and use a silver-doped magnesium electrode, or to use a lithium-doped aluminum electrode instead of the silver-doped magnesium electrode.

There is no particular difficulty in specifically manufacturing the organic EL device of the present invention in accordance with the above description with reference to FIG. 1. For example, as the anode 2, for example, indium-doped tin (the above-described IT)
O) As a hole transport layer 3, a tetrathiafulvalene derivative specified in the present invention is mixed with, for example, TPD on a substrate 1 (glass substrate) provided with a transparent electrode, or as a separate layer, a total thickness of about 10 − A thin film having a thickness of 200 nm is formed, and a light emitting layer 4 is formed thereon to a thickness of about 10 to 100 nm.
An m-thick film may be formed by vapor deposition, and further, for example, a silver-doped magnesium electrode may be formed as the cathode 5. For the device manufactured in this way, for example, a positive
When a direct current is applied, light emission such as green is obtained.

[0041]

Since the hole transport layer of the organic EL device contains the tetrathiafulvalene derivative specified in the present invention, the hole transport ability is large and the crystallization of the hole transport layer is suppressed. An organic EL element having higher luminous efficiency and longer half-life than an organic EL element can be provided.

[0042]

EXAMPLES Next, a method for producing an organic EL device of the present invention and an organic EL obtained by the method according to examples and comparative examples.
The element will be specifically described. However, the present invention is not necessarily limited to these examples.

Example 1 An organic EL device was manufactured based on FIG.

A substrate 1 (glass substrate) provided with a transparent conductive film (sheet resistance 7 Ω / □) of ITO (the above-mentioned tin-doped indium oxide) having a film thickness of 200 nm as an anode 2 was successively washed with an alkaline detergent, ultrapure water and 2- Ultrasonic cleaning with propanol. On this anode 2 (ITO), a methylene chloride solution containing 5 parts by weight of polyether sulfone and 5 parts by weight of 4,4-diphenyltetrathiafulvalene as a hole transport layer 3 was spin-coated. To form a 40 nm layer. Next, Alq was deposited as the light emitting layer 4 to a thickness of 60 nm by a vacuum deposition method at a rate of 0.3 nm / sec. Finally, a MgAg alloy (containing 1 part by weight of silver with respect to 10 parts by weight of magnesium) as a cathode 5 is formed into a film having a thickness of 200 nm at a rate of 1 nm / sec by a vacuum evaporation method.
An organic EL device was manufactured. The degree of vacuum during vacuum deposition is
It was 8.0 × 10 ⁻⁶ torr.

(Comparative Example 1-2) In Example 1, polyether sulfone and tetrathiafulvalene (Comparative Example 1) or TPD (Comparative Example 2) were added to a solution to be spin-coated to form a hole transport layer. Was repeated in the same manner as described above except that a methylene chloride solution containing 5 parts by weight and 5 parts by weight was used, and an organic EL device was manufactured in the same manner.

Comparative Example 3 In the formation of the hole transporting layer of Example 1, bis (ethylenedithio) tetrathiafulvalene was formed by vacuum evaporation at a rate of 0.3 nm / sec to a thickness of 50 nm.
Example 1 was repeated without any change except that a film was formed by vapor deposition to a thickness of 10 nm, and an organic EL device was manufactured in the same manner.

Example 2-3 In the formation of the hole transporting layer of Example 1, bis (4,5-dihydronaphtho [1,2-d]) tetrathiafulvalene represented by the formula (VII) was used. Example 2) or dimethoxybisethylenedithiotetrathiafulvalene (Example 3) represented by the following formula (VIII) was formed by vacuum evaporation at a rate of 0.3 nm / sec.
Example 1 was repeated without any change except that a film was formed by vapor deposition to a thickness of 10 nm, and an organic EL device was manufactured in the same manner.

[0048]

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Example 4 In Example 1, poly-N was used as a solution to be spin-coated to form a hole transport layer.
-Vinylcarbazole and TM represented by the following formula (IX)
Example 1 was repeated without any change except that a methylene chloride solution containing 5 parts by weight of T-TTF and 5 parts by weight of T-TTF was used, and an organic EL device was similarly manufactured.

[0050]

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(Example 5) In the formation of the hole transporting layer of Example 1, a step of further depositing 10 nm of TPD as a second hole transporting layer 3b on the hole transporting layer (3a). Example 1 was repeated without any change except adding, and an organic EL device was manufactured in the same manner.

(Example 6) In the formation of the hole transport layer of Example 2, a step of further depositing a 10 nm thick layer of TPD as a second hole transport layer 3b on the hole transport layer (3a). Example 2 was repeated without any change except adding, and an organic EL device was manufactured in the same manner.

(Example 7) In the formation of the light emitting layer of Example 1, there was no change except that quinacridone was co-evaporated with Alq as a 0.5 part by weight doping dye per 100 parts by weight of Alq to form a layer. Example 1 was repeated to manufacture an organic EL device in the same manner.

(Luminous Efficiency / Drive Stability Test) In order to examine the luminous efficiency and the drive stability of the organic EL devices manufactured in the above Examples and Comparative Examples, the current density was 2
The value of the luminous efficiency at 0 mA / cm ² (1 m / W) and the time (time) required for the luminance to decrease by half when driven at a constant current of 10 mA / cm ^{2 in a} nitrogen atmosphere were measured. The results are shown in Table 1.

[0055]

[Table 1]

From the results shown in Table 1, it was found that the organic EL device of the present invention maintained stable light-emitting characteristics for a long period of time. In particular, considering the comparative examples, it can be seen that the tetrathiafulvalene derivative specified in the present invention has excellent characteristics that cannot be inferred from the known tetrathiafulvalene derivative at all.

[0057]

According to the present invention, the hole transport layer of the organic EL device contains the tetrathiafulvalene derivative specified in the present invention, thereby improving the carrier transport ability of the obtained device and suppressing the crystallization of the hole transport layer. Therefore, the present invention can provide an organic EL device having higher luminous efficiency and longer half-life than conventional organic EL devices. Since the present invention is excellent in luminous efficiency and half-life, various applications of the present invention are possible as long as the effects of the present invention such as various display elements and flat light sources are not impaired.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a typical organic EL element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3 Hole transport layer 3a First hole transport layer 3b Second hole transport layer 4 Light emitting layer 5 Cathode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinji Terazono 1150 Hazawacho, Kanagawa-ku, Yokohama-shi Asahi Glass Co., Ltd.

Claims (6)

[Claims] 1. An organic electroluminescence device comprising an anode, a hole transport layer, a light emitting layer and a cathode, wherein the hole transport layer contains a tetrathiafulvalene derivative represented by the following formula (I). Organic electroluminescent element. Embedded image In the above formula, A represents R ¹ or SR ¹ , B represents R ² or SR ² , or A and B together represent a substituent represented by the following formula (II) or (II ′); Is R ³ or R ³
S represents E, R ⁴ or R ⁴ S, or D and E together represent a substituent represented by the following formula (III) or (III ′). Embedded image Embedded image In the above formula, R ^{1 to} R ⁸ are each independently a hydrogen atom, a halogen atom, a substituted or unsubstituted hydroxyl group, a substituted or unsubstituted amino group and a substituted or unsubstituted hydrocarbon group. A, B, D and E are R ¹ , R ² ,
When R ³ and R ⁴ are represented, all of R ^{1 to} R ⁴ do not represent a hydrogen atom at the same time, and A and B, D and E together form formulas (II) and (III) In the case of representing a substituent represented by, all of R ^{1 to} R ⁸ do not simultaneously represent a hydrogen atom. 2. In R ^{1 to} R ⁸ of the formulas (I) to (III), the hydrocarbon group is a saturated or unsaturated, linear, branched, cyclic or aromatic hydrocarbon group having 1 to 30 carbon atoms. , A hydrocarbon residue, which may have at least one substituent, in which case the substituent is a halogen atom or a group having 1 to 1 carbon atoms.
10, linear and branched alkyl or alkoxy groups,
A phenyl or phenoxy group and either a naphthyl or naphthoxy group, the substituents on a substituted or unsubstituted hydroxyl group and a substituted or unsubstituted amino group are each independently, and a straight or branched chain having 1 to 10 carbon atoms An alkyl group of
The device according to claim 1, wherein the device is any one of a phenyl group and a naphthyl group. 3. In the formula (I), at least one of A to E represents a phenyl group and the remainder represents a hydrogen atom;
At least two of E represent a lower alkylthio group and the rest represent a hydrogen atom; or A and B and D and E together represent formulas (II) and (III), respectively, and R ¹ to At least two of R ⁸ each represent a lower alkyloxy group and the rest each represent a hydrogen atom; or A and B, and D and E together form a group represented by the formula (I
The device according to claim 1, which represents (I ') and (III'). 4. The device according to claim 1, wherein the hole transport layer comprises a plurality of layers, at least one of which contains the tetrathiafulvalene derivative. 5. The device according to claim 1, further comprising an electron transport layer. 6. A display element using the element according to claim 1.