JP3158600B2 - Organic electroluminescent 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 electroluminescent device and, more particularly, to a thin film type device which emits light by applying an electric field by a combination of a hole transporting layer composed of an organic compound and a light emitting layer. Things.

[0002]

2. Description of the Related Art Conventionally, as a thin film type electroluminescent device,
ZnS, Ca, which are II-VI compound semiconductors of inorganic materials
In S, SrS, etc., Mn as a luminescence center and rare earth elements (E
u, Ce, Tb, Sm, etc.) are generally used. However, electroluminescent devices made from the above inorganic materials require: 1) AC drive (50 to 1000 Hz); 2) High drive voltage (Up to 200 V), 3) it is difficult to achieve full color (particularly, blue is a problem), and 4) the cost of peripheral driving circuits is high.

However, in recent years, in order to improve the above problems,
Electroluminescent devices using organic materials have been developed. As the light emitting layer material, in addition to anthracene and pyrene which have been known for a long time, a cyanine dye (J. Chem. S)
oc., Chem. Commun., 557, 1985), pyrazoline (Mol. Crys. Liq. Cryst., 135, 355,
1986), perylene (Jpn. J. Appl. Phys., 25).
Vol. L773, 1986) or a coumarin compound or tetraphenylbutadiene (JP-A-57-5178).
No. 1) has been reported.

Further, in order to improve the efficiency of injecting carriers from the electrodes in order to increase the luminous efficiency, the type of the electrodes is optimized, and a device for providing a luminescent layer composed of a hole transport layer and an organic phosphor is disclosed (Japanese Patent Application Laid-open No. Sho. No. 57-51781, JP-A-59
194393, JP-A-63-29569, Appl. Phys. Lett., 51, 913, 1987.
Year). Further, for the purpose of improving the luminous efficiency of the device and changing the luminescent color, doping a fluorescent dye for laser such as coumarin using an aluminum complex of 8-hydroxyquinoline as a host material (J. Appl.
hys., 65, 3610, 1989).

[0005]

However, the organic electroluminescent devices disclosed in these publications still have insufficient light-emitting performance, especially long-term stability of the device, and further improvement has been desired. In view of the above situation, the present inventors have conducted intensive studies with the aim of providing an organic electroluminescent device that can be driven stably, and as a result, found that a specific compound was suitable, and completed the present invention. .

[0006]

That is, the gist of the present invention is to provide an anode, an organic hole transport layer, an organic electron transport layer,
In an organic electroluminescent device having a cathode laminated, an organic hole transport material and / or an organic electron transport material in an organic hole transport layer are provided.
An organic electron transporting material in the transport layer as a host material;
A compound represented by the following general formula (I) is added to the material.
The organic electroluminescent device characterized by being over-flop.

[0007]

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(Wherein, R ¹ , R ² , R ³ and R ⁴ each independently represent an aromatic hydrocarbon group which may have a substituent, and X represents an aromatic hydrocarbon group which may have a substituent. A good nitrogen atom, a sulfur atom which may have a substituent, an oxygen atom which may have a substituent or a selenium atom which may have a substituent, Y is a hydrogen atom, a cyano group, Carboxyl group,
An amide group which may have a substituent, an ester group which may have a substituent, an alkyl group which may have a substituent, and an aromatic hydrocarbon group which may have a substituent Or a heterocyclic group which may have a substituent. )Less than,
The organic electroluminescent device of the present invention will be described with reference to the attached drawings.

FIG. 1 is a sectional view schematically showing an example of the structure of an organic electroluminescent device of the present invention, wherein 1 is a substrate, 2a and 2b are conductive layers, 3 is an organic hole transport layer, and 4 is an organic electron transport. Each layer is represented. The substrate 1 serves as a support for the organic electroluminescent device of the present invention, and may be a quartz or glass plate, a metal plate or metal foil, a plastic film or sheet, or the like. Transparent synthetic resin substrates such as polymethacrylate, polycarbonate, and polysulfone are preferred.

A conductive layer 2a is provided on the substrate 1,
The conductive layer 2a is usually made of a metal such as aluminum, gold, silver, nickel, palladium, and tellurium, a metal oxide such as an oxide of indium and / or tin, copper iodide, carbon black, or poly (3-methylthiophene). )
And the like. The formation of the conductive layer 2a is usually performed by a sputtering method, a vacuum deposition method, or the like, but metal fine particles such as silver or copper iodide, carbon black, conductive metal oxide fine particles,
In the case of a conductive resin fine powder or the like, it can also be formed by dispersing in an appropriate binder resin solution and applying it on a substrate. Further, in the case of a conductive resin, a thin film can be formed directly on a substrate by electric field polymerization. The above conductive layer can be formed by stacking different substances.

The thickness of the conductive layer 2a varies depending on the required transparency. If transparency is required, the visible light transmittance is desirably 60% or more, preferably 80% or more. In this case, the thickness is usually 50 to 1000
0 °, preferably about 100 to 5000 °. If opaque, the conductive layer 2a may be the same as the substrate 1. Further, the conductive layer 2a can be stacked with a different material.

In the example shown in FIG. 1, the conductive layer 2a functions as an anode (anode) for injecting holes. on the other hand,
The conductive layer 2b serves as a cathode (cathode) as the organic electron transport layer 4
Plays the role of injecting electrons into As the material used for the conductive layer 2b, the material for the conductive layer 2a can be used. However, for efficient electron injection, a metal having a low work function is preferable, and tin, magnesium,
A metal such as indium, aluminum, silver, or an alloy thereof is used. The thickness of the conductive layer 2b is generally the same as that of the conductive layer 2a, and can be formed by the same method as the conductive layer 2a.

Although not shown in FIG. 1, a substrate similar to substrate 1 can be further provided on conductive layer 2b. However, as the electroluminescent element, at least one of the conductive layer 2a and the conductive layer 2b needs to have good transparency. From this, one of the conductive layers 2a and 2b
The thickness is preferably 100 to 5000 °, and good transparency is desired.

An organic hole transport layer 3 is provided on the conductive layer 2a. The organic hole transport layer 3 efficiently transports holes from the anode between the electrodes to which an electric field is applied. Formed from compounds that can be transported in the direction of The organic hole transport compound needs to be a compound having a high hole injection efficiency from the conductive layer 2a and capable of efficiently transporting the injected holes. For this purpose, it is required that the compound has a small ionization potential, a large hole mobility, and a trap which is excellent in stability and positive and hardly occurs during production or use.

Examples of such hole transport compounds include those described on pages 5 to 6 of JP-A-59-194393 and columns 13 and 14 of US Pat. No. 4,175,960. Can be Preferred specific examples of these compounds include N, N'-diphenyl-N, N'-
(3-methylphenyl) -1,1′-biphenyl-4,
Aromatic amine compounds such as 4'-diamine, 1,1'-bis (4-di-p-tolylaminophenyl) cyclohexane, and 4,4'-bis (diphenylamino) quadrophenyl. Other than the aromatic amine compounds,
Hydrazone compounds disclosed in JP-A-2-311591 can be mentioned. These aromatic amine compounds or hydrazone compounds may be used alone or, if necessary, as a mixture.

The organic hole transport layer 3 is formed by laminating on the conductive layer 2a by a coating method or a vacuum evaporation method. For example, in the case of a coating method, one or more organic hole transporting compounds are added and, if necessary, an additive such as a binder resin which does not trap holes and an additive such as a coating agent such as a repelling agent are dissolved. The applied coating solution is prepared, applied to the conductive layer 2a by a method such as spin coating, and dried to form the organic hole transporting layer 3. Examples of the binder resin include polycarbonate, polyacrylate, and polyester. Since a large amount of the binder resin decreases the hole mobility, a small amount is desirable, and the amount is preferably 50% by weight or less.

In the case of the vacuum evaporation method, the organic hole transporting material is put in a crucible provided in a vacuum vessel, and the inside of the vacuum vessel is evacuated to 10 ^-6 Torr by a suitable vacuum pump. Is heated to evaporate the hole transport material and form a layer on the substrate placed opposite the crucible. The thickness of the organic hole transport layer 3 is usually 100 to 3000 °, preferably 300 to 1000 °. In order to uniformly form such a thin film, a vacuum deposition method is often used.

An organic electron transporting layer 4 is provided on the organic hole transporting layer 3. The organic electron transporting layer 4 efficiently transfers electrons from a cathode between electrodes to which an electric field is applied. It is formed from a compound that can be transported in three directions. The organic electron transport compound needs to be a compound having high electron injection efficiency from the conductive layer 2b and capable of efficiently transporting injected electrons. For this purpose, it is required that the compound has a high electron affinity, a high electron mobility, a high stability, and hardly generates impurities serving as traps during production or use.

Materials satisfying such conditions include aromatic compounds such as tetraphenylbutadiene (Japanese Patent Application Laid-Open No.
And metal complexes such as aluminum complexes of 8-hydroxyquinoline (JP-A-59-1943).
No. 93), cyclopentadiene derivatives (Japanese Unexamined Patent Publication No.
289675), perinone derivatives (JP-A 2-2)
No. 89676), oxadiazole derivatives (Japanese Patent Application Laid-Open No. 2-216991), and bisstyrylbenzene derivatives (Japanese Patent Application Laid-Open Nos. 1-245087 and 2-222448).
No. 4), perylene derivatives (JP-A-2-189890)
JP-A-3-7991), coumarin compounds (JP-A-2-191694 and JP-A-3-792), rare-earth complexes (JP-A-1-256584), and distyrylpyrazine derivatives (JP-A-Heisei 2). No. 252793). When these compounds are used, the organic electron transport layer 4 simultaneously plays the role of transporting electrons and the role of emitting light when holes and electrons recombine.

The thickness of the organic electron transporting layer 4 is usually 100
Å2000Å, preferably 300〜1000Å.
The organic electron transporting layer 4 can be formed in the same manner as the organic hole transporting layer 3, but usually, a vacuum evaporation method is used. Further, in order to further improve the luminous efficiency of the organic electroluminescent element, another organic electron transport layer 5 can be further laminated on the organic electron transport layer 4 as shown in FIG. The compound used for the organic electron transport layer 5 is required to be capable of easily injecting electrons from the cathode and to have a higher electron transport ability. Examples of such an organic electron transporting compound include nitro-substituted fluorenone derivatives such as a compound represented by the following structural formula (D9), and a compound represented by the following structural formula (D10)
Thiopyran dioxide derivative such as a compound represented by the following formula, diphenylquinone derivative such as a compound represented by the following structural formula (D11), perylene tetracarboxylic acid derivative such as a compound represented by the following structural formula (D12) (Jp
n. J. Appl. Phys. 27, L269, 1988
Oxadiazole derivatives such as compounds represented by the following structural formula (D13) (Appl. Phys. Lett. 55,
1489, 1989).

[0021]

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The film thickness of the organic electron transport layer 5 is as follows.
Usually 100 to 2000 °, preferably 300 to 100
0 °. In addition, it is also possible to stack the conductive layer 2b, the organic electron transport layer 4, the organic hole transport layer 3, and the conductive layer 2a in this order on the substrate, that is, at least as described above. It is also possible to provide the electroluminescent element of the present invention between two substrates, one of which is highly transparent. Also,
Similarly, the structure may be reversed from that of FIG.

Conventionally, various fluorescent dyes have been doped with an 8-hydroxyquinoline aluminum complex as a host material for the purpose of improving the luminous efficiency of an organic light emitting device and changing the luminescent color (US). Japanese Patent No. 4,769,292) has the advantages of this doping method that the luminous efficiency is improved by using a high-efficiency fluorescent dye, the emission wavelength is checked by selecting the fluorescent dye, and a fluorescent dye that causes concentration quenching can also be used. Fluorescent dyes having poor film properties can also be used.

In the present invention, when the organic electron transporting layer plays a role, the host material includes the above-mentioned organic electron transporting compound. When the organic hole transporting layer plays a role, the host material serves as the host material. And the aforementioned aromatic amine compounds and hydrazone compounds. In the present invention, the region doped with the compound represented by the general formula (I) may be the whole or a part of the organic hole transport layer 3 and / or the organic electron transport layer 4. . The amount of the compound represented by the general formula (I) doped with respect to the host material is preferably 10 ⁻³ to 10 mol%.

The compound represented by the general formula (I) shows strong fluorescence in a solid state and a solution state, does not have the above-described problem of concentration quenching, and has no limitation on the concentration range of doping. In addition, since it itself has the ability to form a stable amorphous film, when doped into a host material, the thin film state of the host material can be structurally stabilized, and the organic electroluminescent device can be used for a long time. It is possible to provide stability.

As a method of doping the compound represented by the general formula (I) into the organic hole transporting layer 3 and / or the organic electron transporting layer 4, for example, in the case of a coating method, an organic hole transporting compound is used. Alternatively, an organic electron transporting compound, a compound represented by the general formula (I), and if necessary, an additive such as a binder resin which does not trap holes or electrons as necessary, or a coating improver such as a repelling agent. The coating solution added and dissolved is adjusted, applied by a method such as spin coating, and dried to form a coating solution. Examples of the binder resin include polycarbonate, polyarylate, and polyester. If the amount of the binder resin is large, the mobility of holes or electrons is reduced. In the case of the vacuum evaporation method, an organic hole transporting compound or an organic electron transporting compound is put in a crucible placed in a vacuum vessel, and the compound represented by the general formula (I) is put in another crucible, After the inside is evacuated to about 10 ^-6 Torr by an appropriate vacuum pump, each crucible is heated and evaporated at the same time to form a layer on the substrate placed facing the crucible. As another method, a mixture of the above materials at a predetermined ratio may be evaporated using the same crucible.

In the general formula (I), R ¹ , R ² , R
³ and R ⁴ represent an aromatic hydrocarbon group which may have a substituent, and is preferably selected from a phenyl group, a naphthyl group, a phenanthrene group and the like. Examples of the substituent include a halogen atom such as a chlorine atom, a bromine atom and an iodine atom; an alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group; an alkoxy group having 1 to 6 carbon atoms such as a methoxy group and an ethoxy group; 1 carbon atom such as methoxycarbonyl group and ethoxycarbonyl group
To 6; an alkoxysulfonyl group such as a methoxysulfonyl group and an ethoxysulfonyl group; a cyano group, an amino group, a dimethylamino group and a nitro group.

X is a nitrogen atom which may have a substituent,
Indicate sulfur, oxygen and selenium atoms. Examples of the substituent include an alkyl group such as an alkyl group having 1 to 28 carbon atoms; an alkoxyalkyl group such as a methoxyethyl group and an ethoxyethyl group; an alkoxyalkoxyalkyl group such as a methoxyethoxyethyl group and an n-butoxyethoxyethyl group; Alkoxyalkoxyalkoxyalkyl groups such as ethoxyethoxyethyl group and ethoxyethoxyethoxyethyl group; aryloxyalkyl groups such as phenyloxyethyl group, naphthyloxyethyl group and p-chlorophenyloxyethyl group; benzyl group, phenethyl group and p-chloro Arylalkyl groups such as benzyl group and p-nitrobenzyl group; cycloalkylalkyl groups such as cyclohexylmethyl group, cyclohexylethyl group and cyclopentylethyl group; allyloxyethyl group and 3-bromoallyloxy Alkenyloxyalkyl groups such as tyl group; cyanoalkyl groups such as cyanoethyl group and cyanomethyl group; hydroxyalkyl groups such as hydroxyethyl group and hydroxymethyl group; substitution of tetrahydrofurylalkyl group such as tetrahydrofuryl group and tetrahydrofurylethyl group. Or an unsubstituted alkyl group, an allyl group, a substituted or unsubstituted alkenyl group such as a 2-chloroallyl group, a phenyl group,
Examples include a substituted or unsubstituted aryl group such as a p-methylphenyl group, a naphthyl group, and an m-methoxyphenyl group, and a cycloalkyl group such as a cyclohexyl group and a cyclopentyl group.

Y is a hydrogen atom, a cyano group, a carboxyl group, an amide group; CONH ₂ , CONHR, CONRR '
(Wherein R and R 'each represent an aromatic hydrocarbon group such as a phenyl group or an alkyl group which may be substituted); an ester group; COOR "(where R" represents an aromatic hydrocarbon group such as a phenyl group). A hydrogen group or an optionally substituted alkyl group), an optionally substituted alkyl group having 1 to 28 carbon atoms, an optionally substituted phenyl group, a naphthalene group, an aromatic group such as a phenanthrene group A hydrocarbon group; an optionally substituted thiophene ring group, a pyrrole ring group, a thiazole ring group, a furan ring group, an oxazole ring group, a benzothiophene ring group, a benzofuran ring group, an indole ring group,
It is selected from a heterocyclic group such as a pyridine ring group.

The synthesis of these compounds is described by Magaga et al. In J. Heterocyclic. Chem.
981); 26: 215, 1989 (1989). Specific examples of the compound thus obtained are described below.

[0031]

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[0032]

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[0033]

In the present invention, by using the fluorescent compound represented by the general formula (I) as a doping material for the organic electron transporting layer and / or the organic hole transporting layer,
Excellent light-emitting characteristics and long-term stability can be provided.

[0034]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the description of the following examples unless it exceeds the gist. Example 1 An organic electroluminescent device having the structure shown in FIG. 1 was produced by the following method.

A transparent conductive film of indium tin oxide (ITO) deposited on a glass substrate at 1200.degree. Was washed with water and ultrasonically washed with isopropyl alcohol, and then placed in a vacuum evaporation apparatus to reduce the degree of vacuum in the apparatus. 2 × 10 ^-6 T
The gas was exhausted using an oil diffusion pump until the pressure became orr or less.
As the organic hole transport layer material, the following structural formulas (XIX) and (X
X) is a hydrazone compound represented by the following formula:
And mixed.

[0036]

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These ceramic crucibles were put into a crucible and heated by a Ta wire heater around the crucible to evaporate in a vacuum vessel. The temperature of the crucible was in the range of 130 to 150 ° C., and the degree of vacuum during evaporation was 7 × 10 ⁻⁷ Torr. An organic hole injecting and transporting layer was thus deposited to a thickness of 520 °. The deposition time was 2 minutes and 30 seconds. Next, an 8-hydroxyquinoline complex of aluminum represented by the following structural formula (E1) is used as a material for the organic electron transport layer.

[0038]

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The compound (1) as a fluorescent dye to be doped was simultaneously heated and deposited in separate crucibles. At this time, the temperature of each crucible was set at 22 for the 8-hydroxyquinoline complex of aluminum.
0 to 240 ° C, 110 to 120 for compound (1)
Controlled at ° C. The degree of vacuum at the time of vapor deposition is 6 × 10 ⁻⁷ Torr
The deposition time was 2 minutes. As a result, the film thickness 525
In Å, an organic electron transporting layer doped with 4 mol% of the compound (1) was obtained.

Finally, as a cathode, an alloy electrode of magnesium and silver was deposited to a thickness of 1500 ° by a binary simultaneous vapor deposition method. The evaporation was performed using a molybdenum boat, the degree of vacuum was 6 × 10 ⁻⁶ Torr, and the evaporation time was 8 minutes. A glossy film was obtained. The atomic ratio of magnesium to silver is 1
The range was 0: 3. The results of the emission characteristics measured by applying a positive DC voltage to the ITO electrode (anode) and a negative DC voltage to the magnesium / silver electrode (cathode) of the organic electroluminescent device thus manufactured are shown in Table 1 below. This device emitted green uniform light.

Comparative Example 1 An organic electroluminescent device was produced in the same manner as in Example 1 except that the organic electron transporting layer was not doped with the compound (1). Table 1 shows the measurement results of the light emission characteristics of this device. This device emitted green uniform light.

[0042]

[Table 1]

Example 2 and Comparative Example 2 Each element produced in Example 1 and Comparative Example 1 was stored in a vacuum, and the change with time in the practical driving voltage (V ₁₀₀ ) at which the luminance became 100 cd / m ² was measured. The results obtained are shown in FIG. While the device of Example 1 exhibited long-term stability, the device of Comparative Example 1 showed a significant increase in driving voltage and a significant decrease in luminance after 30 days or more.

[0044]

According to the organic electroluminescent device of the present invention, an anode (anode), an organic hole injecting and transporting layer, an organic electron injecting and transporting layer, and a cathode (cathode) are sequentially provided on a substrate.
Since the organic hole injection transport layer and / or organic electron injection transport layer, or a part thereof is doped with a specific fluorescent dye, when a voltage is applied using both conductive layers as electrodes,
Light emission with practically sufficient luminance can be obtained at a low drive voltage, and the initial light emission characteristics can be maintained even after long-term storage.

Therefore, the electroluminescent device of the present invention can be used as a light source (for example, a light source of a copier, a backlight of a liquid crystal display or an instrument) utilizing the characteristics of a flat panel display (for example, a wall-mounted television) and a surface light emitting element. It can be applied to light sources, display boards, and marker lights, and its technical value is great.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of one embodiment of the organic electroluminescent device of the present invention.

FIG. 2 is a sectional view of another embodiment of the organic electroluminescent device of the present invention.

FIG. 3 is a diagram showing the results of measuring the change over time of the practical driving voltage of the organic electroluminescent devices manufactured in Examples and Comparative Examples of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2a, 2b Conductive layer 3 Organic hole transport layer 4 Organic electron transport layer 5 Organic electron transport layer comprised of a compound different from 4

Continuation of front page (56) References JP-A-3-37293 (JP, A) JP-A-63-264692 (JP, A) Appl. Phys. 65 (9), 1989, p. 3610-3616 (58) Field surveyed (Int. Cl. ⁷ , DB name) C09K 11/06 CA (STN) REGISTRY (STN)

Claims (3)

(57) [Claims] 1. An organic electroluminescent device in which an anode, an organic hole transport layer, an organic electron transport layer, and a cathode are sequentially laminated, wherein an organic hole transport material and / or organic hole transport material in the organic hole transport layer is provided.
The organic electron transporting material in the organic electron transporting layer is used as a host material, and the host material is represented by the following general formula (I).
An organic electroluminescent device, wherein the compound is doped . Embedded image (Wherein, R ¹ , R ² , R ³ and R ⁴ each independently represent an aromatic hydrocarbon group which may have a substituent, and X represents a nitrogen atom which may have a substituent. Represents a sulfur atom which may have a substituent, an oxygen atom which may have a substituent or a selenium atom which may have a substituent,
Has a hydrogen atom, a cyano group, a carboxyl group, an amide group which may have a substituent, an ester group which may have a substituent, an alkyl group which may have a substituent, Represents an aromatic hydrocarbon group which may be substituted or a heterocyclic group which may have a substituent. ) 2. The method according to claim 1, wherein
The doping amount of the represented compound is 10 to the host material.
^-3 Organic electroluminescent element characterized by being 10 mol% to 10 mol%
Child. 3. The organic electroluminescent device according to claim 1, wherein the host material is an organic electron transporting material comprising a metal complex.