JPH0888083A - Organic electric field light-emitting device - Google Patents

Abstract

PURPOSE: To maintain light emitting characteristics stably for a long period of time by interposing a layer including a compound having N-phenyl carbazole skeleton between an organic light emitting layer and a negative electrode, and letting the negative electrode be formed into a mixed constituent film including silver equal to or more than a specified atomic %. CONSTITUTION: ITO transparent conductive films are piled up 120nm thick over a glass substrate 1 so as to be formed into a positive electrode 2. An aromatic amine compound as organic electron hole transporting layer material and Al (C9 H6 NO)3 as organic electron transporting layer material are deposited in order thereon 60nm and 75nm thick respectively by means of vacuum deposition so as to be formed into an organic light emitting layer 3. Next, as a surface phase 4, a compound having N-phenyl carbazole skeleton is deposited thereon 15nm thick by means of vacuum deposition. Finally, an alloy electrode in which an atomic ratio of silver to magnesium is 10:1.52 is deposited thereon as a negative electrode 5 70nm thick by means of binary simultaneous deposition. In this case, the negative electrode is formed into a mixed constituent film which shall include silver equal to or more than 50% of atoms.

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, and more particularly, to a thin film type device which emits light by applying an electric field to a light emitting layer made of an organic compound.

[0002]

2. Description of the Related Art Conventionally, as a thin film type electroluminescent (EL) element, Z which is a II-VI group compound semiconductor of an inorganic material has been used.
In general, nS, CaS, SrS, etc. are doped with Mn or a rare earth element (Eu, Ce, Tb, Sm, etc.), which is the emission center, but EL elements made from the above inorganic materials are 1). AC drive is required (50 to 1000 Hz), 2) high drive voltage (up to 200 V), 3) full colorization is difficult (especially blue is a problem), and 4) peripheral drive circuit costs are high. ing.

In recent years, in order to improve the above problems, EL devices using organic thin films have been developed. In particular, the electrode type was optimized for the purpose of improving the efficiency of carrier injection from the electrode in order to increase the light emission efficiency, and the organic hole transport layer made of an aromatic diamine and the organic light emission made of an aluminum complex of 8-hydroxyquinoline. Of an organic electroluminescence device having a layer (Appl. Phys. Let
t. , 51, p. 913, 1987), the luminous efficiency has been greatly improved as compared with the conventional EL device using a single crystal such as anthracene, and is close to practical characteristics.

In addition to the above low molecular weight materials, poly (p-phenylene vinylene) is used as a material for the organic light emitting layer.
(Nature, 347, 539, 1990; A
ppl. Phys. Lett. , 61, 2793,
1992), poly [2-methoxy, 5- (2'-ethylhexoxy) -1,4-phenylenevinylene] (Ap
pl. Phys. Lett. , 58, 1982, 1
991; ThinSolid Films, 216
Volume, 96 pages, 1992; Nature, 357, 4
77, 1992), poly (3-alkylthiophene) (Jpn. J. Appl. Phys, vol. 30, L1.
938, 1991; Appl. Phys. , 7
Vol. 2, p. 564, 1992), etc., and development of devices such as polyvinylcarbazole and other polymers in which low-molecular light emitting materials and electron transfer materials are mixed (Applied Physics, 61).
Vol., P. 1044, 1992).

In the organic electroluminescent device as described above, indium tin oxide (IT) is usually used as the anode.
A transparent electrode such as O) is used, but as a cathode, a metal electrode having a low work function for efficiently injecting electrons,
For example, magnesium alloy or calcium is used. The biggest problem of the organic electroluminescence device is the life of the device, and one factor that limits the life is the occurrence of dark spots (portions that do not emit light in the light emitting portion of the device) derived from the cathode material. The dark spot refers to a non-light emitting portion generated in the light emitting surface in the organic electroluminescent element when the organic electroluminescent element is stored for a long period of time or is driven for a long period of time. The number and size of the dark spots increase during storage and driving, resulting in a decrease in emission brightness, and as a result, the life of the device is limited. On the other hand, for the purpose of improving the adhesion with the cathode, an interface layer made of an aromatic amine compound is provided between the cathode and the organic light emitting layer,
Attempts to reduce dark spots have been made (JP-A-5-04).
The current situation is that it has not reached a practical level.

[0006]

In the organic electroluminescent devices disclosed so far, electroluminescence is brought about by the recombination of holes injected from the anode and electrons injected from the cathode. In general, the injection of carriers is
It must be done by overcoming the injection barrier at the interface between the cathode and the organic light emitting layer. In order to lower the electron injection barrier and improve the injection efficiency, a metal electrode having a low work function such as magnesium alloy or calcium is used as the cathode. However, since these metal materials have poor adhesion to the organic light emitting layer, they are peeled from the organic light emitting layer, or when the cathode is vapor-deposited on the organic light emitting layer or after vapor deposition, the cathode material and the organic light emitting layer material are A reaction occurs between them, which causes deterioration of the light emitting characteristics of the device and generation of dark spots during long-term storage.

[0007]

In view of the above situation, the inventors of the present invention provide an organic electroluminescent device capable of maintaining stable light emitting characteristics for a long period of time and suppressing the generation of dark spots. As a result of earnest studies for the purpose, it is preferable to provide an interface layer containing a compound having an N-phenylcarbazole skeleton between the organic light emitting layer and the cathode, and use a mixed component film containing 50 atomic% or more of silver as the cathode. After finding out that there is something, the present invention has been completed.

That is, the gist of the present invention is an organic electroluminescence device comprising an organic light emitting layer sandwiched between an anode and a cathode on a substrate, wherein N-phenyl is provided between the organic light emitting layer and the cathode. An organic electroluminescent device characterized in that a layer containing a compound having a carbazole skeleton is provided, and the cathode is a mixed component film containing 50 atomic% or more of silver.

The organic electroluminescent device of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view schematically showing a structural example of the organic electroluminescent device of the present invention, in which 1 is a substrate, 2 is an anode, 3 is an organic light emitting layer, 4 is an interface layer, and 5 is a cathode. The substrate 1 serves as a support for the organic electroluminescent element of the present invention, and a plate of quartz or glass, a metal plate or metal foil, a plastic film or sheet, or the like is used, but a glass plate, polyester, polymethyl A transparent synthetic resin substrate such as methacrylate, polycarbonate and polysulfone is preferable.

An anode 2 is provided on the substrate 1, and the anode 2 plays a role of injecting holes into the organic light emitting layer. This anode is usually a metal such as aluminum, gold, silver, nickel, palladium, tellurium, a metal oxide such as an oxide of indium and / or tin, copper iodide, carbon black, or poly (3-methylthiophene). It is composed of a conductive polymer or the like. The anode is usually formed 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, conductive polymer fine powder, etc. In this case, disperse in a suitable binder resin solution,
It can also be formed by coating on a substrate. Further, in the case of a conductive polymer, a thin film can be directly formed on the substrate by electrolytic polymerization, or can be formed by coating on the substrate (Appl. Phys. Lett., Volume 60, 2).
711, 1992). The above anodes can be laminated with different materials. The thickness of the anode 2 depends on the required transparency, but when transparency is required,
Generally, visible light transmittance is 60% or more, preferably 80%
It is desirable that the light is transmitted as described above. In this case, the thickness is usually 5 to 1000 nm, preferably 10 to 500 nm.

If it is opaque, the anode 2 may also serve as the substrate 1. Further, it is also possible to stack different conductive materials on the anode. An organic light emitting layer 3 is provided on the anode 2, and the organic light emitting layer 3 efficiently transports holes injected from the anode and electrons injected from the cathode between the electrodes to which an electric field is applied. It is made of a material that is recombined and emits light efficiently by the recombination. Usually, in order to improve the luminous efficiency, the organic light emitting layer 3 is divided into a hole transport layer 3a and an electron transport layer 3b as shown in FIG.
pl. Phys. Lett. , 51, 913, 19
1987).

In the above-mentioned function-separated device, the hole transport material must have a high hole injection efficiency from the anode 2 and can efficiently transport the injected holes. Is. For that purpose, it is required that the ionization potential is small, the hole mobility is large, the stability is excellent, and the impurities serving as traps are not easily generated during manufacturing or use.

As such a hole transport material, for example, an aromatic diamine compound in which a tertiary aromatic amine unit such as 1,1-bis (4-di-p-tolylaminophenyl) cyclohexane is linked (Japanese Patent Application Laid-Open No. 2000-242242) Sho 59-19439
3), 4,4'-bis [(N-1-naphthyl)-
Aromatic amines containing two or more tertiary amines represented by N-phenylamino] biphenyl and having two or more condensed aromatic rings substituted with nitrogen atoms (Japanese Patent Laid-Open No. 5-234681) and triphenylbenzene. An aromatic triamine having a starburst structure as a derivative (US Pat.
3,774), N, N'-diphenyl-N, N'-bis (3-methylphenyl)-(1,1'-biphenyl)
Aromatic diamines such as -4,4'-diamine (U.S. Pat. No. 4,764,625), α, α, α ', α'-tetramethyl-α, α'-bis (4-di-p- Tolylaminophenyl) -p-xylene (JP-A-3-269084), sterically asymmetric triphenylamine derivative as a whole molecule (JP-A-4-12971), pyrenyl group and a plurality of aromatic diamino groups. Substituted compound (JP-A-4-175395) and aromatic diamine in which a tertiary aromatic amine unit is linked with an ethylene group (JP-A-4-175395).
264189), aromatic diamines having a styryl structure (JP-A-4-290851), those in which aromatic tertiary amine units are linked by a thiophene group (JP-A-4-304466), and starburst type aromatics. Triamine (JP-A-4-308688), benzylphenyl compound (JP-A-4-364153), and tertiary amine linked by a fluorene group (JP-A 5-2).
5473), triamine compounds (JP-A-5-23)
9455), bisdipyridylaminobiphenyl (JP-A-5-320634), N, N, N-triphenylamine derivative (JP-A-6-1972),
Aromatic diamine having phenoxazine structure (Japanese Patent Application No.
-290728) and diaminophenylphenanthridine derivatives (Japanese Patent Application No. 6-45669), hydrazone compounds (Japanese Patent Application Laid-Open No. 2-311).
591), a silazane compound (US Pat. No. 4,955).
No. 0,950), silanamin derivatives (JP-A-6-4).
No. 9079), phosphamine derivatives (JP-A-6-2).
5659), quinacridone compounds and the like. These compounds may be used alone, or may be used as a mixture if necessary.

In addition to the compounds mentioned above, polyvinyl carbazole and polysilane (App
l. Phys. Lett. , 59, 2760, 19
1991, etc.), polyphosphazene (JP-A-5-310949), polyamide (JP-A-5-3).
No. 10949), polyvinyl triphenylamine (Japanese Patent Application No. 5-205377), a polymer having a triphenylamine skeleton (Japanese Patent Laid-Open No. 1333065), and a polymer in which triphenylamine units are linked by a methylene group or the like ( Synthetic Metals, 55-57,
4163, 1993), polymethacrylates containing aromatic amines (J. Polym. Sci., Pol.
ym. Chem. Ed. , 21: 969, 1983
Years) and other polymeric materials.

The above organic hole transport material is laminated on the anode 2 by a coating method or a vacuum deposition method to form a hole transport layer 3a. In the case of a coating method, a coating solution prepared by adding and dissolving one or more organic hole transporting compounds, if necessary, a binder resin that does not trap holes and a coating property improving agent such as a leveling agent. Is prepared and applied onto the anode 2 by a method such as spin coating,
The organic hole transport layer 3a is formed by drying. Examples of the binder resin include polycarbonate, polyarylate, polyester and the like. If the addition amount of the binder resin is large, the hole mobility is lowered.

In the case of the vacuum deposition method, the organic hole transporting material is placed in a crucible installed in a vacuum container, the interior of the vacuum container is evacuated to 10 ^-6 Torr by an appropriate vacuum pump,
The crucible is heated to evaporate the hole transport material and form a layer on the substrate that faces the crucible. When forming the hole transport layer 3a, further, as an acceptor,
Aromatic carboxylic acid metal complex and / or metal salt (JP-A-4-320484), benzophenone derivative and thiobenzophenone derivative (JP-A-5-295361).
No.), fullerenes (Japanese Patent Laid-Open No. 5-331458) are doped at a concentration of 10 ⁻³ to 10% by weight to generate holes as free carriers, and low voltage driving is possible. .

The thickness of the hole transport layer 3a is usually 10-3.
00 nm, preferably 30 to 100 nm. In order to uniformly form such a thin film, the vacuum evaporation method is often used. As the material of the hole transport layer 3a, it is possible to use an inorganic material instead of the organic compound. The conditions required for the inorganic material are the same as those for the organic hole transport compound. Examples of the inorganic material used for the hole transport layer 3a include p-type hydrogenated amorphous silicon, p-type hydrogenated amorphous silicon carbide, p-type hydrogenated microcrystalline silicon carbide, p-type zinc sulfide, and p-type zinc sulfide. Examples include type zinc selenide.
These inorganic hole transport layers are formed by CVD method, plasma CVD
Method, vacuum deposition method, sputtering method or the like.

The thickness of the inorganic hole transporting layer is usually 10 to 300 nm, preferably 30 to 1 like the organic hole transporting layer.
00 nm. The electron transport layer 3 is formed on the hole transport layer 3a.
b is provided, but the electron transport layer 3b is formed of a compound capable of efficiently transporting electrons from the cathode toward the hole transport layer 3a between the electrodes to which an electric field is applied.

The organic electron transport compound needs to be a compound having a high electron injection efficiency from the interface layer 4 and capable of efficiently transporting the injected electrons. For that purpose, it is required that the compound has a high electron affinity, a high electron mobility, excellent stability, and an impurity that becomes a trap and is less likely to be generated at the time of production or use.

As a material satisfying such a condition, an aromatic compound such as tetraphenyl butadiene (Japanese Patent Laid-Open No. Sho 57-57)
No. 51781), a metal complex such as an aluminum complex of 8-hydroxyquinoline (JP-A-59-194393).
JP), a cyclopentadiene derivative (JP-A-2-28)
9675), perinone derivatives (JP-A-2-289)
676), oxadiazole derivatives (JP-A-2-
No. 216791), and bisstyrylbenzene derivatives (JP-A Nos. 1-245087 and 2-222484).
No.), perylene derivatives (JP-A-2-189890, JP-A-3-791), coumarin compounds (JP-A-2-191694, JP-A-3-792), and rare earth complexes (JP-A-1-256584). JP-A No. 2-252793), p.
A phenylene compound (JP-A-3-33183),
Thiadiazolopyridine derivative (JP-A-3-37292), pyrrolopyridine derivative (JP-A-3-37293)
JP), naphthyridine derivatives (JP-A-3-20398).
No. 2) and the like.

Electron transport layer 3b using these compounds
Simultaneously plays a role of transporting electrons and a role of causing light emission upon recombination of holes and electrons. When the organic hole transport layer 3a has a light emitting function, the electron transport layer 3b serves only to transport electrons. For the purpose of improving the luminous efficiency of the device and changing the luminescent color, for example, by doping an aluminum complex of 8-hydroxyquinoline as a host material with a fluorescent dye for laser such as coumarin (J. Appl. Phys., Vol. 65). , 3610, 1
989) is also being conducted. Also in the present invention, various fluorescent dyes can be used as a host material by using the above-mentioned organic electron transport material as a host material.
By doping 0 ⁻³ to 10 mol%, the emission characteristics of the device can be further improved. The thickness of the electron transport layer 3b is usually 10 to 200 nm, preferably 30 to 1
00 nm.

The organic electron transport layer can be formed in the same manner as the organic hole transport layer, but the vacuum vapor deposition method is usually used. As a method for further improving the luminous efficiency of the organic electroluminescent device, it is conceivable to stack another electron transport layer 3c on the electron transport layer 3b as shown in FIG. 3 (see FIG. 3). The compound used for the electron transport layer 3c is required to be capable of easily injecting electrons from the cathode and have a higher electron transport capability. As such an electron transport material,

[0023]

[Chemical 4]

[0024]

[Chemical 5]

Oxadiazole derivatives such as (Appl.
Phys. Lett. , 55, 1489, 1989
Year; Jpn. J. Appl. Phys. , Volume 31, 18
P. 12, 1992) or a system (Appl. Phys. L) in which they are dispersed in a resin such as polymethylmethacrylate.
ett. , 61, 2793, 1992), or n
Examples include hydrogenated amorphous silicon carbide, n-type zinc sulfide, and n-type zinc selenide. The thickness of the electron transport layer 3c is usually 5 to 200 nm, preferably 10 to 100 nm.

As the single-layer type organic light emitting layer 3 which does not perform the function separation, the above-mentioned poly (p-phenylene vinylene) (Nature, 347, 539, 1990) is used.
Year; Appl. Phys. Lett. , Volume 61, 279
P. 3, 1992), poly [2-methoxy, 5- (2 '
-Ethylhexoxy) -1,4-phenylene vinylene]
(Appl. Phys. Lett., 58, 1982.
P., 1991; Thin Solid Films,
216, 96, 1992; Nature, 357.
Vol., 477, 1992), poly (3-alkylthiophene) (Jpn. J. Appl. Phys, vol. 30,
L 1938, 1991; Appl. Phy
s. , Vol. 72, p. 564, 1992), or a system in which a light emitting material and an electron transfer material are mixed with a polymer such as polyvinylcarbazole (Applied Physics, 61, 1044).
Page, 1992) etc.

An interface layer 4 is provided on the organic light emitting layer.
The role of the interface layer is that it has an affinity with the organic light-emitting layer and at the same time has good adhesion to the cathode, and is chemically stable to allow the reaction between the organic light-emitting layer and the cathode during and / or after formation of the cathode. It has a suppressing effect. It is also important to provide a uniform thin film shape from the viewpoint of adhesion with the cathode. An N-phenylcarbazole skeleton is used as a material that plays such a role.

The interface layer made of a compound having an N-phenylcarbazole skeleton is formed by a coating method or a vacuum vapor deposition method, like the organic hole transport material described above. N-
Suitable compounds having a phenylcarbazole skeleton include those represented by the following general formula (I).

[0029]

[Chemical 6]

In the above general formula (I), Ar ¹ and A
Each r ² is independently a group having at least one N-phenylcarbazole skeleton selected from the following general formula (III).

[0031]

[Chemical 7]

In the above general formula (III), R ^{1 to} R ¹² are each independently preferably a hydrogen atom, a nitro group, a halogen atom; a C ¹ -C 1 group such as a methyl group or an ethyl group.
6 alkyl group; α-haloalkyl group; alkenyl group such as vinyl group; alkoxycarbonyl group having 1 to 6 carbon atoms such as methoxycarbonyl group and ethoxycarbonyl group; alkoxy having 1 to 6 carbon atoms such as methoxy group and ethoxy group Group;
An aryloxy group such as a phenoxy group and a benzyloxy group; a dialkylamino group such as a diethylamino group and a diisopropylamino group, a diarylamino group such as a diphenylamino group and a hydroxyl group, and R ⁴ and R ⁵ , R ⁵ and R ⁶ , R ⁷ and R ⁸ , R ⁸ and R ⁹ may be bonded to each other to form a ring, for example, preferably an aromatic ring such as a benzene ring, a pyridine ring or a pyrrole ring may be formed. Good.

Specific examples of the main group having an N-phenylcarbazole skeleton represented by the general formula (III) are shown in the following table, but not limited thereto.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

[0037]

[Table 4]

[0038]

[Table 5]

[0039]

[Table 6]

[0040]

[Table 7]

[0041]

[Table 8]

[0042]

[Table 9]

In the above general formula (I), Ar ¹ and A
When r ² is not a group having an N-phenylcarbazole skeleton, it represents a group having a nitrogen atom and at least three aromatic rings, and the following groups are preferable.

[0044]

Embedded image

X is preferably --CH.₂-, -CH₂
CH₂-, -CH₂CH₂CH₂Has a substituent such as-
Optionally an alkylene group; cyclo such as cyclohexylene group
Alkylene group; -CH = CH-, -C (CH₃) = CH
-, -CH₂-CH = CH-CH ₂-, -CH = CH-
Alkenylene which may have a substituent such as CH = CH-
Group; phenylene group, naphthylene group, phenanthrene group
An arylene group which may have a substituent such as
It represents a carbonyl group or a direct bond.

Next, the main specific examples of the compound represented by the general formula (I) are shown in Table 1 below, but the invention is not limited thereto.

[0047]

[Table 10]

[0048]

[Table 11]

[0049]

[Table 12]

Other suitable compounds having an N-phenylcarbazole skeleton include compounds represented by the following general formula (II).

[0051]

[Chemical 9]

In the above general formula (II), Ar ³ , A
r ⁴ and Ar ⁵ each independently represent a group having at least one N-phenylcarbazole skeleton selected from the general formula (III), and when it is not an N-phenylcarbazole skeleton, a nitrogen atom and at least Represents a group having three aromatic rings, and in any case,
It is preferably selected from the groups shown for Ar ¹ and Ar ² in the general formula (I).

In the above general formula (II), Y represents a trivalent aromatic ring, a trivalent cycloalkyl ring or a nitrogen atom, preferably -CH =; The removed benzene residue; the cyclohexane residue from which the hydrogen atoms at the 1, 3, 5 positions have been removed; and the nitrogen atom. next,
Specific examples of the compound represented by the general formula (II) are shown below, but the invention is not limited thereto.

[0054]

[Table 13]

[0055]

[Table 14]

[0056]

[Table 15]

When the compound having the N-phenylcarbazole skeleton shown above is formed as the interface layer, two or more kinds of these compounds may be mixed and used. Further, other fluorescent dyes, light emitting materials and the like may be mixed for the purpose of improving the stability of the film of the interface layer. These mixed fluorescent dyes,
Examples of the light emitting material and the like include a compound composed of an aromatic amine, a laser dye such as a coumarin derivative, and perylene,
Examples thereof include polycyclic aromatic dyes such as rubrene, organic pigments such as quinacridone, and 8-hydroxyquinoline metal complex.

The organic electroluminescent element of the present invention having an interface layer containing a compound having an N-phenylcarbazole skeleton has the following layer structure. Anode / organic light emitting layer / interface layer / cathode Anode / polymer organic light emitting layer / interface layer / cathode Anode / polymer dispersed organic light emitting layer / interface layer / cathode Anode / hole transport layer / organic electron transport Light emitting layer / interface layer / cathode Anode / organic hole transporting light emitting layer / organic electron transporting layer / interface layer / cathode Anode / hole transporting layer / organic electron transporting light emitting layer / interface layer / cathode anode / hole transporting Layer / organic electron-transporting light-emitting layer / electron-transporting layer / interface layer / cathode The thickness of the interface layer 4 is usually 1 to 100 nm, preferably 5 to 50 nm.

When the interface layer 4 is formed, a portion containing the components of the organic light emitting layer or the electron transport layer may be provided to change the composition stepwise or continuously to provide the interface layer. Similarly, a cathode may be formed by providing a component containing a cathode component and changing the composition stepwise or continuously. Interface layer 4
A cathode 5 is provided on top of the. The role of the cathode is to efficiently inject electrons into the device, but it is required to have a stable film in order to obtain uniform light emission. The present inventors have found that as a material that plays such a role, a mixed component film containing 50 atomic% or more of silver and mixed with another substance is suitable. As the other substance mixed with silver, a conductive organic compound, resin, inorganic compound or the like can be used, but a simple substance (element) is preferably used and is not particularly limited as long as it does not interfere with electron injection. Are preferably Group IIA, Group IIIA, Group IVA, Group VIA, V of the Periodic Table
An element selected from the group consisting of Group IIA, Group VIII, Group IB, Group IIB, Group IIIB and Group IVB,
More preferred is an element selected from the group consisting of magnesium, calcium, strontium, barium, scandium, yttrium, titanium, aluminum, indium, tin, chromium, manganese, zinc and gold. The cathode may be a simple mixture of silver and these elements, or may be an alloy or the like, and its form is not limited. It is also possible to mix two or more of these elements with silver and use them as a cathode.

In the present invention, as described above, a compound having an N-phenylcarbazole skeleton is used as an interface layer material between the organic light emitting layer and the cathode in the organic electroluminescent element, and the cathode contains 50 atomic% or more of silver. By using the mixed film, excellent device stability is achieved. The film thickness of the cathode 5 is usually the same as that of the anode 2. Although not shown in FIG. 1, a substrate similar to the substrate 1 may be further provided on the cathode 5. However, it is necessary for the EL element that at least one of the anode 2 and the cathode 5 has good transparency. From this, it is preferable that one of the anode 2 and the cathode 5 usually has a film thickness of 10 to 500 nm and good transparency.

It is also possible to stack the cathode 5, the interface layer 4, the organic light-emitting layer 3 and the anode 2 in this order on the substrate in the opposite structure to that of FIG. It is also possible to provide the organic electroluminescent element of the present invention between two highly transparent substrates. Similarly, FIG. 2 and FIG.
It is also possible to stack in the opposite structure.

[0062]

EXAMPLES Next, the present invention will be described more specifically by way of 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. 2 was produced by the following method.

An indium tin oxide (ITO) transparent conductive film deposited to a thickness of 120 nm on a glass substrate was ultrasonically washed with acetone, washed with pure water, washed with isopropyl alcohol and dried with dry nitrogen. After performing UV / ozone cleaning, it was installed in a vacuum vapor deposition apparatus and evacuated using an oil diffusion pump until the degree of vacuum in the apparatus became 2 × 10 ⁻⁶ Torr or less.

As an organic hole transport layer material, an aromatic amine compound (H1) represented by the following structural formula

[0065]

[Chemical 10]

[0066] was put in a ceramic crucible and heated by a tantalum wire heater around the crucible for vapor deposition. The temperature of the crucible at this time was controlled in the range of 170 to 180 ° C. The degree of vacuum during vapor deposition was 1.5 × 10 ⁻⁶ Torr, and the vapor deposition time was 2 minutes and 15 seconds to obtain an organic hole transport layer 3a having a film thickness of 60 nm. Next, as a material for the organic electron transport layer 3b, an aluminum 8-hydroxyquinoline complex represented by the following structural formula, Al (C ₉ H ₆ NO) ₃ (E1)

[0067]

[Chemical 11]

The above was vapor-deposited on the organic hole transport layer 3a in the same manner. The temperature of the crucible at this time is 390-4
Control was performed in the range of 00 ° C. The degree of vacuum during vapor deposition is 7 × 10 ^-7
Torr, vapor deposition time was 1 minute 50 seconds, and film thickness was 75 nm. This layer serves as a light emitting layer. Next, as the interface layer 4, the compound (I-1) having the N-phenylcarbazole skeleton shown in the above table is vapor-deposited on the organic electron transporting light emitting layer 3b in the same manner as the organic hole transporting layer 3a. I went. The degree of vacuum during vapor deposition was 6 × 10 ⁻⁷ Torr, the vapor deposition time was 1 minute 30 seconds, and the film thickness was 15 nm.

Finally, as a cathode, an alloy electrode of silver and magnesium was vapor-deposited to a thickness of 70 nm by the binary vapor deposition method. Deposition is performed using a molybdenum boat, and the degree of vacuum is 1.
A glossy film was obtained at × 10 ⁻⁵ Torr and a vapor deposition time of 3 minutes and 10 seconds. The atomic ratio of silver to magnesium contained in the cathode was 10: 1.52 (mixing ratio [= ratio of atoms other than silver contained in the cathode] = 13.2%).

Measurement was carried out by applying a positive DC voltage to the ITO electrode (anode) and a negative DC voltage to the silver-magnesium alloy electrode (cathode) of the organic electroluminescent device thus produced. A current density of 2.1 mA / cm ² was obtained when 10 V was applied to this device, and the brightness at that time was 78 cd / m ² . Example 2 In the same manner as in Example 1, an ITO transparent conductive film, an organic hole transport layer, an organic electron transport layer organic layer, and an interface layer were laminated on a glass substrate, and silver and indium were used as a cathode by a co-evaporation method. It was deposited to a thickness of 150 nm. The vacuum degree at this time is 6
It was × 10 ^-6 Torr, and the vapor deposition time was 3 minutes. The atomic ratio of silver to indium contained in the cathode is 10:
It was 0.85 (mixing ratio = 7.9%).

This device is 2.8 mA /
A current density of cm ² was obtained, and the brightness at that time was 90 cd /
m ² . Example 3 In the same manner as in Example 1, an ITO transparent conductive film, an organic hole transport layer, an organic electron transport layer organic layer, and an interface layer were laminated on a glass substrate, and silver and tin were used as a cathode by a co-evaporation method to form 150 layers.
Evaporated to a thickness of nm. The degree of vacuum at this time is 7 × 10 ^-6
Torr, and the vapor deposition time was 2 minutes. The atomic ratio of silver and tin contained in the cathode was 10: 0.6 (mixing ratio = 5.7%).

This device has a voltage of 3.6 mA / V when a voltage of 15 V is applied.
A current density of cm ² was obtained, and the brightness at that time was 121 cd.
/ M ² . Example 4 In the same manner as in Example 1, an ITO transparent conductive film, an organic hole transport layer, an organic electron transport layer organic layer, and an interface layer were laminated on a glass substrate, and silver and tin were used as a cathode by a co-evaporation method to form 150
Evaporated to a thickness of nm. The vacuum degree at this time is 2 × 10 ^-5
Torr, and the vapor deposition time was 4 minutes and 30 seconds. The atomic ratio of silver and tin contained in the cathode is 10: 4.44.
Was (mixing ratio = 30.8%).

This element is 4.2 mA /
A current density of cm ² was obtained, and the brightness at that time was 91 cd /
m ² . Example 5 In the same manner as in Example 1, an ITO transparent conductive film, an organic hole transport layer, an organic electron transport layer organic layer, and an interface layer were laminated on a glass substrate, and silver and manganese were used as a cathode by a co-evaporation method.
It was deposited to a thickness of 50 nm. The degree of vacuum at this time is 2 × 1
It was 0 ⁻⁵ Torr, and the vapor deposition time was 3 minutes and 30 seconds.
The atomic ratio of silver to manganese contained in the cathode is 10 :.
It was 0.85 (mixing ratio = 7.8%).

This element is 3.5 mA /
A current density of cm ² was obtained, and the brightness at that time was 85 cd /
m ² . Example 6 In the same manner as in Example 1, an ITO transparent conductive film, an organic hole transport layer, an organic electron transport layer organic layer, and an interface layer were laminated on a glass substrate, and silver and zinc were used as a cathode by a co-evaporation method to form 150
Evaporated to a thickness of nm. The degree of vacuum at this time is 1 × 10 ^-5
Torr, and the vapor deposition time was 2 minutes and 30 seconds. The atomic ratio of silver to manganese contained in the cathode is 10: 1.
It was 98 (mixing ratio = 16.6%).

This element has a voltage of 3.0 mA /
A current density of cm ² was obtained, and the brightness at that time was 94 cd /
m ² . Example 7 In the same manner as in Example 1, an ITO transparent conductive film, an organic hole transport layer, an organic electron transport layer organic layer, and an interface layer were laminated on a glass substrate, and silver and zinc were used as a cathode by a co-evaporation method.
Evaporated to a thickness of nm. The vacuum degree at this time is 9 × 10 ^-6
Torr, and the vapor deposition time was 2 minutes. The atomic ratio of silver to zinc contained in the cathode was 10: 9.4 (mixing ratio = 48.4%).

This device has a voltage of 4.3 mA / V when a voltage of 19 V is applied.
A current density of cm ² was obtained, and the brightness at that time was 113 cd.
/ M ² . Comparative Example 1 In the same manner as in Example 1, an ITO transparent conductive film, an organic hole transport layer, an organic electron transport layer organic layer, and an interface layer were laminated on a glass substrate, and silver was used as a cathode to a thickness of 120 nm. It was vapor-deposited. A vacuum degree of 5 × 10 ⁻⁶ Torr and a vapor deposition time of 4 minutes gave a glossy film. A current density of 2.9 mA / cm ² was obtained when 10 V was applied to this element, and the brightness at that time was 93 cd / m ² .

Comparative Example 2 In the same manner as in Example 1, an ITO transparent conductive film, an organic hole transport layer, an organic electron transport layer organic layer, and an interface layer were laminated on a glass substrate, and silver and magnesium were used as a cathode. It was vapor-deposited to a thickness of 150 nm by the vapor deposition method. Vacuum degree is 5 × 10 ^-6
A glossy film was obtained with Torr and vapor deposition time of 4 minutes.
The atomic ratio of silver to magnesium contained in the cathode is 1
It was 0: 1.1 (mixing ratio = 90.1%).

This device was 3.7 mA / V when 11 V was applied.
A current density of cm ² was obtained, and the brightness at that time was 120 cd.
/ M ² . Table-1 shows the characteristics of the organic electroluminescent elements obtained in Examples 1 to 7 and Comparative Examples 1 and 2.

[0079]

[Table 16] Mixing ratio: The ratio of the number of atoms of elements other than silver contained in the cathode. Vth [V]: Voltage when the brightness exceeds 1 cd / m ² . η100 [lm / W]: Efficiency at 100 cd / m ² light emission. L-J slope [cd / A]: slope when L and J are linearly approximated.

Table 2 shows how the dark spots change when these devices are stored in dry nitrogen. The area ratio of the dark spots is the value obtained by image analysis of the light emitting surface of the CCD camera.

[0081]

[Table 17]

Example 8 An element was manufactured in the same manner as in Example 1. This device was driven under the condition that the current density was 15 mA / cm ^{2 and} the current density was constant. The luminance of this element gradually decreased and was 80 cd / m ² after 500 hours.

Comparative Example 3 In the same manner as in Example 1, an ITO transparent conductive film, an organic hole transport layer, an organic electron transport layer organic layer, and an interface layer were laminated on a glass substrate, and silver was used as a cathode to a thickness of 120 nm. It was vapor-deposited on.
This device was driven under the condition that the current density was 15 mA / cm ^{2 and} the current density was constant. The brightness of this device rapidly decreased after 200 hours, and after 500 hours, 20 cd /
It decreased to m ² . FIG. 4 shows changes in luminance of the devices of Example 8 and Comparative Example 3.

[0084]

According to the organic electroluminescent device of the present invention, an anode, an organic light emitting layer, an interface layer and a cathode are sequentially provided on a substrate, and a specific compound is used in the interface layer, and a silver cathode is used as the cathode. Since the mixed film is used, a uniform light emitting surface can be obtained over a long period of time, and stable light emitting characteristics can be obtained.

Therefore, the EL device of the present invention is used in the field of flat panel displays (for example, for OA computers and wall-mounted televisions) and light sources (for example, light sources for copiers, liquid crystal displays and instruments) that make the most of the characteristics as a surface light emitter. It can be applied to backlights, display boards, and marker lights, and its technical value is great.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of an organic electroluminescence device of the present invention.

FIG. 2 is a schematic cross-sectional view showing another example of the organic electroluminescent element of the present invention.

FIG. 3 is a schematic cross-sectional view showing another example of the organic electroluminescent element of the present invention.

FIG. 4 shows the devices of Example 9 and Comparative Example 3 at 15 mA / cm ^2.
FIG. 6 is a diagram showing a luminance characteristic when driven at a constant current density of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3 Organic light emitting layer 3a Hole transport layer 3b Organic electron transport layer 3c Organic electron transport layer 4c composed of a compound different from 3b 4 Interface layer 5 Cathode

Claims (4)

[Claims] 1. An organic electroluminescent device comprising an organic light emitting layer sandwiched between an anode and a cathode on a substrate, comprising a compound having an N-phenylcarbazole skeleton between the organic light emitting layer and the cathode. An organic electroluminescent device, comprising a layer containing the cathode, and the cathode being a mixed component film containing 50 atomic% or more of silver. 2. The organic electroluminescent device according to claim 1, wherein the compound having an N-phenylcarbazole skeleton is a compound represented by the following general formula (I) or (II). Embedded image (In the formula, at least one of Ar ¹ and Ar ² represents a group having an N-phenylcarbazole skeleton represented by the following general formula (III), and when it is not a group having an N-phenylcarbazole skeleton, a nitrogen atom and Represents a group having at least three aromatic rings, and X represents an alkylene group, a cycloalkylene group, an alkenylene group, an arylene group which may have a substituent, or a direct bond. (In the formula, R ^{1 to} R ¹² are each independently a hydrogen atom, a nitro group, a cyano group, a halogen atom, a hydroxyl group, a saturated or unsaturated aliphatic hydrocarbon group which may have a substituent, An aromatic hydrocarbon group which may have a substituent, an alkoxy group which may have a substituent, an aryloxy group which may have a substituent, an amino group, which has a substituent Represents a dialkylamino group which may be substituted or a diarylamino group which may have a substituent, R ⁴ and R ⁵ , R
⁵ and R ⁶ , R ⁷ and R ⁸ , R ⁸ and R ⁹ may be bonded to each other to form an aromatic ring. ) [Chemical 3] (In the formula, Ar ³ , Ar ⁴ and Ar ⁵ are each independently
At least one is represented by the general formula (III) N-
Represents a group having a phenylcarbazole skeleton, and when it is not an N-phenylcarbazole skeleton, represents a group having a nitrogen atom and at least three aromatic rings, Y represents a trivalent aromatic ring, a trivalent cycloalkyl ring or Represents a nitrogen atom. ) 3. The substance mixed with silver is II of the periodic table.
Group A, Group IIIA, Group IVA, Group VIA, Group VIIA,
Group VIII, Group IB, Group IIB, Group IIIB and IVB
The organic electroluminescent element according to claim 1, which is an element selected from the group consisting of the group. 4. The substance mixed with silver is magnesium, calcium, strontium, barium, scandium,
Yttrium, titanium, aluminum, indium,
The organic electroluminescent element according to claim 1, which is an element selected from the group consisting of tin, chromium, manganese, zinc and gold.