JPH11312587A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance blue purity and increase heat resistance by including an aromatic amine compound in a luminescent layer. SOLUTION: A luminescent layer of an organic electroluminescent element contains an aromatic amine compound represented by formula I or formula II. In each formula, Ar<1> and Ar<2> each represents an aromatic hydrocarbon group or an aromatic hetrocyclic group, which may independently have a substitutional group. R<1> to R<14> represent an alkyl group, an aralkyl group, an alkenyl group, an amino group, an amide group, an alkoxy carbonyl group, an alkoxy group, an aryl oxy group, an aromatic hydrocarbon group, or an aromatic heterocyclic group which may independently have a hydrogen atom, a cyano group, a carboxyl group, a hydroxyl group, which may also have a substitutional group. X represents divalent aromatic hydrocarbon group or aromatic heterocyclic group, which may independently have a substitutional group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an organic electroluminescent device. More specifically, the present invention relates to an organic electroluminescent device having a light emitting layer containing a specific aromatic amine compound. The organic electroluminescent device of the present invention can achieve blue emission with good color purity and has improved stability.
It is expected to be applied to a display, a multi-color display element, or a light source utilizing the features of a surface light emitter.

[0002]

2. Description of the Related Art Conventionally, as a thin film type electroluminescent (EL) element, Zn, which is a group II-VI compound semiconductor of an inorganic material, is used.
In general, S, CaS, SrS, and the like are doped with Mn or a rare earth element (Eu, Ce, Tb, Sm, or the like) which is a luminescence center. However, EL devices manufactured from the above inorganic materials include: 1) AC drive is required (50 to 1000 Hz), 2) High drive voltage (up to 200 V), 3) It is difficult to achieve full color (especially blue), and 4) Peripheral drive circuit is expensive. .

However, in recent years, in order to improve the above problems,
Development of EL devices using organic thin films has been started. In particular, in order to enhance the luminous efficiency, the type of the electrode was optimized for the purpose of improving the efficiency of carrier injection from the electrode, and a hole transport layer composed of an aromatic diamine and a luminescent layer composed of an aluminum complex of 8-hydroxyquinoline were used. Of an organic electroluminescent device provided with a device (Appl. Phys. Le)
tt. , Vol. 51, p. 913, 1987), the luminous efficiency has been greatly improved as compared with a conventional EL device using a single crystal such as anthracene. Also, for example,
Doping a fluorescent dye for laser such as coumarin using an aluminum complex of 8-hydroxyquinoline as a host material (J. Appl. Phys., 65, 3610).
1989), the emission efficiency is improved, the emission wavelength is converted, and the like.

In addition to the electroluminescent device using a low molecular material as described above, poly (p-phenylenevinylene) (Nature, 347, 539, 1) may be used as a material for the light emitting layer.
990), poly [2-methoxy-5- (2-ethylhexyloxy) -1,4-phenylenevinylene] (Ap
pl. Phys. Lett. 58, 1982, 1
991 etc.), poly (3-alkylthiophene) (Jp
n. J. Appl. Phys, 30, L1938,
1991) and the development of an electroluminescent device using a polymer material such as a polymer material such as polyvinyl carbazole, and a mixture of a low molecular light emitting material and an electron transfer material (Applied Physics, 61
Volume, p. 1044, 1992).

[0005]

In order to apply an organic electroluminescent device to a display device such as a flat panel display, it is necessary to ensure sufficient reliability of the device. However, the heat resistance of the conventional organic electroluminescent device is insufficient, and the current-voltage characteristic shifts to a higher voltage side due to an increase in the ambient temperature or process temperature of the device, or local Joule heat generated when the device is driven. Deterioration such as shortening of service life and generation and increase of non-light emitting portions (dark spots) was inevitable. In particular, regarding the blue light emitting element, 8-
At present, the stability of the device is inferior to that of a green light-emitting device using an aluminum complex of hydroxyquinoline.

The main cause of the above-mentioned element deterioration is deterioration of the thin film shape of the organic layer. It is considered that the deterioration of the thin film shape is caused by crystallization (or aggregation) of the organic amorphous thin film due to heat generated during driving of the element. This low heat resistance is considered to be due to the low glass transition temperature (hereinafter abbreviated as Tg) of the material. Tg generally has a linear correlation with the melting point. Many of the compounds used for the light emitting layer of the blue light emitting element have a low molecular weight and a low melting point and low Tg because of the restriction that pi electron conjugation cannot be expanded. At present, it is not sufficiently stable chemically.

[0007] As a compound used in a blue organic electroluminescent device, anthracene (Jpn. J. Ap.
pl. Phys. 27, L269, 1988.
Years), tetraphenylbutadiene, pentaphenylcyclopentadiene (Appl. Phys. Lett., 5
6, 799, 1990), distyrylbenzene derivatives (Journal of the Chemical Society of Japan, p. 1162, 1992), oxadiazole derivatives (Jpn. J. Appl. Phy.
s. , 31, 1812, 1992; Journal of the Chemical Society of Japan, 1540, 1991), azomethine zinc complex (Jpn. J. Appl. Phys., 32, L51).
1, 1993), a benzazole metal complex (JP-A-8-81472), a mixed-ligand aluminum complex (JP-A-5-198377; JP-A-5-1983).
JP-A-78-214; JP-A-5-214332; JP-A-6-214332
-172751), N, N'-diphenyl-N,
N '-(3-methylphenyl) -1,1'-biphenyl-4,4'-diamine (Jpn. J. Appl. Phys.
s. 32, L917, 1993), polyvinyl carbazole (Appl. Phys. Lett., 63).
Vol., P. 2627, 1993), 1,2,4-triazole derivatives (Chem. Lett., P. 47, 1996).
Year), aminopyrene dimer (Jpn.J. Appl.P
hys. , 35, 4819, 1996), distyrylbiphenyl derivatives (Applied Physics, 62, 1015).
1993; Appl. Phys. Lett. , 6
7, 3853, 1995), silole derivatives (J. Am. Chem. Soc., 118, 1197).
4, p. 1996). Among the blue light-emitting materials described above, typical compounds whose device characteristics are well studied are shown below.

[0008]

Embedded image

[0009]

Embedded image

[0010]

Embedded image

Distyrylbiphenyl derivative (B-1)
Has a high fluorescence intensity and does not form an exciplex even when used in a device, and emits blue light.
l. Phys. Lett. , 67, 3853, 19
1995), ionization potential in thin film state is 5.9
Because of its high eV, it is difficult to inject holes from the hole transport layer. In addition, the EL spectrum shows a broad peak having a light emission maximum near 480 nm, and the blue color purity is poor. This color purity is not improved by doping. Bis (2-methyl-8-quinolinolato) (p-phenylphenolato) aluminum complex (B
-2), the color purity of blue is also insufficient. Although the color purity is improved by doping with perylene, the stability at the time of driving does not reach a practical level (Japanese Patent Laid-Open No. 5-198377).
No.). N, N'-diphenyl-N, N '-(3-methylphenyl) -1,1'-biphenyl-4,4'-diamine which is an aromatic diamine (commonly called TPD)
Shows an EL spectrum having an emission peak at 464 nm when combined with a triazole derivative as a hole blocking layer (Jpn. J. Appl. Phys., 32).
Volume, L917, 1993), Tg of TPD is 63 ° C.
Therefore, it has thermal instability such as crystallization. From the high-temperature characteristics of the display element for vehicle use, a value of Tg of 85 ° C. or more is required.

[0012] In addition, it has been reported that 4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl is used as a light emitting layer. Blue emission was not obtained because the ionization potential was lower than the ionization potential of the layer and the hole blocking layer was not provided (IEICE technical report, OME)
97-69, 1997; Monthly Display, July,
62, 1996).

For the reasons described above, the blue organic electroluminescent device has a problem of color purity of light emission, and furthermore, has a serious problem in heat resistance and driving life of the device for practical use. The fact that the blue purity of the organic electroluminescent device is not improved and the heat resistance and the driving characteristics are unstable are undesirable characteristics as a display device such as a flat panel display aiming at full color. An object of the present invention is to provide an organic electroluminescent device having high blue purity and heat resistance.

[0014]

Means for Solving the Problems The present inventors have made intensive studies in view of the above situation and found that the above problem can be solved by using a light emitting layer containing a specific aromatic amine compound. The invention has been completed. That is, the gist of the present invention is an organic electroluminescent device including at least a hole transport layer, a light emitting layer, and a hole blocking layer sandwiched between an anode and a cathode on a substrate, wherein the light emitting layer has the following general formula ( An organic electroluminescent device comprising an aromatic amine compound represented by I) or (II),

[0015]

Embedded image

[0016]

Embedded image

(In the formula (I) or (II), Ar ¹ and Ar ² each independently represent an aromatic hydrocarbon group or an aromatic heterocyclic group which may have a substituent. , R
¹ to R ¹⁴ each independently represent a hydrogen atom, a cyano group,
A carboxyl group, a hydroxyl group, or an alkyl group, an aralkyl group, an alkenyl group, an amino group, an amide group, an alkoxycarbonyl group, an alkoxy group, an aryloxy group, an aromatic hydrocarbon group or an aromatic group, each of which may have a substituent; X represents a divalent aromatic hydrocarbon group or an aromatic heterocyclic group each of which may have a substituent.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an organic electroluminescent device according to the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing an example of the structure of a general organic electroluminescent device used in the present invention, wherein 1 is a substrate, 2 is an anode, 4 is a hole transport layer, 5 is a light emitting layer, and 6 is The hole blocking layers, 8 each represent a cathode.

The substrate 1 serves as a support for the organic electroluminescent device, and is made of a quartz or glass plate, a metal plate or a metal foil, a plastic film or a sheet, or the like. Particularly, a glass plate or a plate of a transparent synthetic resin such as polyester, polymethacrylate, polycarbonate, and polysulfone is preferable. When using a synthetic resin substrate, it is necessary to pay attention to gas barrier properties. If the gas barrier property of the substrate is too small, the organic electroluminescent device may be deteriorated by the outside air passing through the substrate, which is not preferable. For this reason, a method of providing a dense silicon oxide film or the like on at least one surface of the synthetic resin substrate to secure gas barrier properties is also a preferable method.

An anode 2 is provided on a substrate 1, and the anode 2 plays a role of injecting holes into a hole transport layer. This anode is usually made of a metal such as aluminum, gold, silver, nickel, palladium and platinum, a metal oxide such as an oxide of indium and / or tin, a metal halide such as copper iodide, carbon black, or poly. (3-methylthiophene), conductive polymers such as polypyrrole and polyaniline. Usually, the formation of the anode 2 is often performed by a sputtering method, a vacuum evaporation method, or the like.
In the case of fine particles of metal such as silver, fine particles of copper iodide or the like, carbon black, fine particles of conductive metal oxide, fine particles of conductive polymer, etc., they are dispersed in an appropriate binder resin solution and To form the anode 2. Further, in the case of a conductive polymer, a thin film can be formed directly on the substrate 1 by electrolytic polymerization, or the conductive polymer can be applied on the substrate 1 to form the anode 2 (Ap).
pl. Phys. Lett. 60, 2711, 1
992). The anode 2 can be formed by laminating different materials. The thickness of the anode 2 depends on the required transparency. When transparency is required, it is desirable that the visible light transmittance is usually 60% or more, preferably 80% or more. In this case, the thickness is usually 5 to 10%.
00 nm, preferably about 10 to 500 nm. If opaque, the anode 2 may be the same as the substrate 1. Further, it is also possible to laminate a different conductive material on the anode 2.

On the anode 2, a hole transport layer 4 is provided. As a condition required for the material of the hole transport layer, it is necessary that the material has a high hole injection efficiency from the anode and can efficiently transport the injected holes. Therefore, the ionization potential is small, the transparency to visible light is high, the hole mobility is large, the stability is further improved, and impurities serving as traps are hardly generated at the time of manufacture or use. Required. In addition to the above general requirements, when considering applications for in-vehicle display, the element is required to have further heat resistance. Therefore, Tg is 85
A material having a value of at least C is desirable.

As such a hole transporting material, for example, aromatic diamine compounds linked with tertiary aromatic amine units such as 1,1-bis (4-di-p-tolylaminophenyl) cyclohexane (particularly, Kaisho 59-194393
Publication), 4,4'-bis [N- (1-naphthyl) -N
[Phenylamino] biphenyl, aromatic amines containing two or more tertiary amines and two or more condensed aromatic rings substituted with nitrogen atoms (JP-A-5-234681); Aromatic triamines having a starburst structure in derivatives (US Pat. No. 4,92
3,774), N, N'-diphenyl-N,
N'-bis (3-methylphenyl) biphenyl-4,
Aromatic diamines such as 4'-diamine (U.S. Pat.
No. 64,625), a triphenylamine derivative which is sterically asymmetric as a whole molecule (JP-A-4-12927).
No. 1), a compound in which a pyrenyl group is substituted with a plurality of aromatic diamino groups (JP-A-4-175395), and an aromatic diamine in which a tertiary aromatic amine unit is linked by an ethylene group (JP-A-4-264189). Japanese Patent Application Laid-Open No. 4-290466), aromatic diamines having a styryl structure (Japanese Patent Application Laid-Open No. Hei 4-290851), those obtained by linking aromatic tertiary amine units with thiophene groups (Japanese Patent Application Laid-Open No. 4-304466), starburst type aromatics Triamines (JP-A-4-308688) and benzylphenyl compounds (JP-A-4-36415)
No. 3), a compound in which a tertiary amine is linked by a fluorene group (Japanese Patent Application Laid-Open No. 5-25473), a triamine compound (Japanese Patent Application Laid-Open No. 5-239455), and a bisdipyridylaminobiphenyl (Japanese Patent Application Laid-Open No. 5-320634). ),
N, N, N-triphenylamine derivatives (Japanese Unexamined Patent Publication No.
No. 972), aromatic diamines having a phenoxazine structure (JP-A-7-138562), diaminophenylphenanthridine derivatives (JP-A-7-25247).
No. 4), silazane compounds (US Pat. No. 4,950,
950), silanamine derivatives (JP-A-6-49)
079), phosphamine derivatives (JP-A-6-25)
659) and quinacridone compounds.
These compounds may be used alone, or may be used as a mixture as necessary.

In addition to the above compounds, polyvinyl carbazole and polysilane (App
l. Phys. Lett. 59, 2760, 19
1991), polyphosphazene (JP-A-5-31094)
No. 9), polyamide (JP-A-5-310949), polyvinyl triphenylamine (JP-A-7-53).
No. 953), a polymer having a triphenylamine skeleton (Japanese Patent Laid-Open No. 4-133065), and a polymer in which triphenylamine units are linked by a methylene group (Synth
etic Metals, 55-57, 4163,
1993), polymethacrylates containing aromatic amines (J. Polym. Sci., Polym. Che.
m. Ed. , 21, 969, 1983).

The hole transport layer 4 is formed by laminating the above hole transport material on the anode 2 by a coating method or a vacuum evaporation method. In the case of the coating method, one or two or more hole transport materials and, if necessary, an additive such as a binder resin or a coatability improver that does not trap holes are added,
The solution is dissolved to prepare a coating solution, applied to the anode 2 by a method such as spin coating, and dried to form the hole transport layer 4. Examples of the binder resin include polycarbonate, polyarylate, and polyester. If the amount of the binder resin is large, the hole mobility is reduced, so that a small amount is desirable, and usually 50% by weight or less is preferable.

In the case of the vacuum evaporation method, the hole transporting material is put into a crucible placed in a vacuum vessel, the inside of the vacuum vessel is evacuated to about 10 ^-4 Pa by a suitable vacuum pump, and then the crucible is heated. Then, the hole transport material is evaporated to form the hole transport layer 4 on the anode 2 on the substrate 1 placed facing the crucible. When the hole transport layer 4 is formed, a metal complex and / or a metal salt of an aromatic carboxylic acid (JP-A-4-320484), a benzophenone derivative and a thiobenzophenone derivative (JP-A-5-295) are further used as acceptors.
361), fullerenes (JP-A-5-33145)
No. 8) is doped at a concentration of 10 ⁻³ to 10% by weight to generate holes as free carriers, thereby enabling low-voltage driving.

The thickness of the hole transport layer 4 is usually from 10 to 30.
0 nm, preferably 30-100 nm. In order to uniformly form such a thin film, generally, a vacuum deposition method is often used. To improve the contact between the anode 2 and the hole transport layer 4, as shown in FIG.
May be provided. The conditions required for the material used for the anode buffer layer are that a uniform thin film can be formed with good contact with the anode and thermally stable, that is, the melting point and the glass transition temperature are high, and the melting point is 300 ° C. or more, A glass transition temperature of 100 ° C. or higher is required. In addition, the ionization potential is low, holes can be easily injected from the anode, and the hole mobility is high. To this end, porphyrin derivatives and phthalocyanine compounds (JP-A-63-29569) and star-bust-type aromatic triamines (JP-A-Hei.
308688), hydrazone compounds (Japanese Unexamined Patent Publication No.
No. 320483), an alkoxy-substituted aromatic diamine derivative (Japanese Patent Application Laid-Open No. 4-220995), p- (9
-Anthryl) -N, N-di-p-tolylaniline (JP-A-3-111485), polythienylenevinylene and poly-p-phenylenevinylene (JP-A-4-145)
192), polyaniline (Appl. Phys.
Lett. 64, p. 1245, 1994), and sputtered carbon films (JP-A-8-3).
No. 1573) and metal oxides such as vanadium oxide, ruthenium oxide, and molybdenum oxide (The 43rd Alliance Lecture on Applied Physics, 27-a-SY-9, 1996)
Year) has been reported.

Examples of the compound often used as the material of the anode buffer layer include a porphyrin compound and a phthalocyanine compound. These compounds may have a central metal or may be non-metallic. Specific examples of preferred such compounds include the following compounds: porphine 5,10,15,20-tetraphenyl-21H, 23
H-porphine 5,10,15,20-tetraphenyl-21H, 23
H-porphine cobalt (II) 5,10,15,20-tetraphenyl-21H, 23
H-porphine copper (II) 5,10,15,20-tetraphenyl-21H, 23
H-porphine zinc (II) 5,10,15,20-tetraphenyl-21H, 23
H-porphine vanadium (IV) oxide 5,10,15,20-tetra (4-pyridyl) -21
H, 23H-porphine 29H, 31H-phthalocyanine copper (II) phthalocyanine zinc (II) phthalocyanine titanium phthalocyanine oxide magnesium phthalocyanine copper phthalocyanine copper (II) 4,4 ′, 4 ″, 4 ″ ″-tetraaza-29
H, 31H-phthalocyanine

In the case of the anode buffer layer, a thin film can be formed in the same manner as in the case of the hole transporting layer. However, in the case of an inorganic substance, a sputtering method, an electron beam evaporation method, or a plasma CVD method is used. The thickness of the anode buffer layer 3 formed as described above is usually 3 to 100 nm, preferably 10 to 100 nm.
５０50 nm.

The light emitting layer 5 is provided on the hole transport layer 4. The light emitting layer 5 is transported between the electrodes to which the electric field is applied, the holes injected from the anode 2 and transported through the hole transport layer, and the holes injected from the cathode 8 and transported through the hole blocking layer 6. It is formed from a compound that emits blue light by efficiently recombining the electrons. Therefore, it is a compound that has both hole transporting properties and electron transporting properties, has high hole mobility and electron mobility, and has excellent stability and is less likely to generate impurities that become traps during production or use. Is required. Further, in order to enable blue light emission, it is necessary that the fluorescence wavelength in a thin film state is in the range of 400 to 500 nm.

In the present invention, a fluorescent aromatic amine compound is used as a material satisfying the above conditions. Conventionally,
Attempts have been made to use an aromatic amine compound as a light-emitting layer having a hole-transporting property. However, no hole-transporting layer is provided between the anode and the anode (Jpn. J. Appl. Phys., 32).
Vol., L917, 1993), the ionization potential of the light emitting layer is higher than the ionization potential of the hole transport layer (Jpn. J. Appl. Phys., 35,
(4819, 1996), the emission efficiency of the device was low, and only a blue light-emitting device with low stability was obtained. In the present invention, in order to effectively use a hole transporting aromatic amine compound as the light emitting layer, it is necessary to use a fluorescent aromatic amine having an ionization potential 0.1 eV or more smaller than the ionization potential of the hole transporting layer. It has been found to be suitable. With this element structure, it is possible to simultaneously increase the hole concentration in the light emitting layer when the element is energized, and to prevent extinction of excitons generated by recombination in the light emitting layer at the anode.

As the material of the light emitting layer in the organic electroluminescent device of the present invention, there is no further limitation on the aromatic amine compound as long as it satisfies the relation of ionization potential with the hole transport layer. Considering stability, it is desirable to have a high glass transition temperature (Tg). From this, the light emitting layer is represented by the general formula (I) or (I)
More preferably, it is selected from the aromatic amine compounds represented by I).

In the above general formulas (I) and (II), preferably, X is each independently a divalent, benzene ring, naphthalene ring, anthracene ring, binaphthyl which may have a substituent. A fluorene ring, a phenanthrene ring, a pyrene ring, an acridine ring, a phenazine ring, a phenanthridine ring, a phenanthroline ring, a pyridyl ring, or a biphenyl, wherein the substituent is a halogen atom; An alkenyl group such as a vinyl group; an alkoxycarbonyl group having 1 to 6 carbon atoms such as a methoxycarbonyl group and an ethoxycarbonyl group; an alkoxy group having 1 to 6 carbon atoms such as a methoxy group and an ethoxy group; a phenoxy group; Aryloxy groups such as benzyloxy group; dialkylamino groups such as diethylamino group and diisopropylamino group A group. As the substituent,
Particularly preferred are a methyl group, a phenyl group and a methoxy group.

Ar ¹ to Ar ⁴ are preferably each independently a phenyl group, a biphenyl group, a naphthyl group, an anthryl group, a phenanthryl group, a pyrenyl group, a pyridyl group, each of which may have a substituent. Triazyl group,
A pyrazyl group, a quinoxalyl group or a thienyl group, wherein the substituent is a halogen atom; an alkyl group having 1 to 6 carbon atoms such as a methyl group or an ethyl group; an alkenyl group such as a vinyl group; a methoxycarbonyl group or an ethoxycarbonyl group A methoxy group having 1 to 6 carbon atoms;
An alkoxy group having 1 to 6 carbon atoms such as an ethoxy 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. As the substituent, particularly preferably,
Examples include a methyl group, a phenyl group, and a methoxy group. The compound represented by the general formula (I) is synthesized, for example, by the following route. A biamine derivative represented by the following general formula (VII) and a biamine derivative represented by the following general formula (VIII)

[0034]

Embedded image

[0035]

Embedded image

The Udmann reaction (Ullmann reaction) (Organic Synthesis, vol. 1, 544)
Page), the resulting compound represented by the following general formula (IX)

[0037]

Embedded image

After the replacement is separated by column chromatography, it is represented by the following general formula (X).

[0039]

Embedded image

The desired aromatic amine compound represented by the general formula (I) is obtained by subjecting the iodine compound to Ullmann reaction in the same manner. The compound represented by the general formula (II) is also synthesized by a similar route. In the present invention, the molecular structure represented by the general formula (I) or (II) allows the Tg to be 85 ° C. or higher, and gives an amorphous thin film that is not easily crystallized due to the improved heat resistance. It is possible to reduce the interdiffusion of molecules between the hole transporting layer and the electron transporting layer by 85 ° C.
Even under the above-mentioned high temperature, it can be sufficiently suppressed. Also,
The ionization potential is 0.1 e more than that of the hole transport layer.
V or more, and 400 to 500 n
A light emitting layer having a fluorescence maximum in a wavelength region of m can be designed.
Preferred specific examples of the aromatic amine compounds represented by the general formulas (I) and (II) are shown in Tables 1 to 4, but are not limited thereto. Unsubstituted substituents in the table represent hydrogen atoms.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

[Table 4]

These compounds may be used alone or, if necessary, may be used as a mixture. The light emitting layer 5 is formed by laminating on the hole transport layer 4 by a coating method or a vacuum deposition method in the same manner as the hole transport layer 4. However, in the case of the coating method, it is necessary to use a solvent that does not dissolve the hole transport layer already formed as a thin film.
The thickness of the light emitting layer 5 is usually 5 to 300 nm, preferably 10 to 100 nm. In order to uniformly form such a thin film, generally, a vacuum deposition method is often used.

In order to improve the luminous efficiency of blue light and the color purity at the same time as to improve the driving life of the device,
Doping a fluorescent dye using the light emitting layer material as a host material is an effective method. As doped dyes having blue fluorescence, condensed polycyclic aromatic rings such as perylene (Japanese Patent Laid-Open No. 5-198377), coumarin derivatives, naphthalic imide derivatives (Japanese Patent Laid-Open No. 4-320486), aromatic amine derivatives ( JP-A-8-199162). The content of these doped dyes in the host material is preferably in the range of 0.1 to 10% by weight. Of course, it is also possible to dope a green fluorescent dye or a red fluorescent dye in order to obtain green or red light emission.
As a method of performing the above-mentioned doping by a vacuum evaporation method, there are a method of co-evaporation and a method of previously mixing an evaporation source at a predetermined concentration.

When each of the above dopants is doped in the light emitting layer, the dopant is uniformly doped in the thickness direction of the light emitting layer.
For example, doping only near the interface with the hole transport layer,
Conversely, doping may be performed near the interface of the electron transport layer.

On the light emitting layer 5, a hole blocking layer 6 is provided. The hole blocking layer 6 has a role of preventing holes moving from the light emitting layer from reaching the cathode, and a compound capable of efficiently transporting electrons injected from the cathode toward the light emitting layer 5. It is formed. The physical properties required for the material constituting the hole blocking layer are that the electron mobility is high and the hole mobility is low, and in order to efficiently confine holes in the light emitting layer, the ionization potential of the light emitting layer is 0.2 eV
It is necessary to have a large value of the ionization potential. Since the hole transporting layer is made of a material having no electron transporting ability, the hole blocking layer has a function of confining holes and electrons in the light emitting layer and improving luminous efficiency. As a hole blocking layer material satisfying such conditions, a mixed ligand complex represented by the following general formula (III):

[0049]

Embedded image

(Wherein R ¹⁵ to R ²⁰ each independently represent a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, an allyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group, Carboxyl group, alkoxy group, alkylsulfonyl group, α-haloalkyl group, hydroxyl group, amide group optionally having substituent (s), aromatic hydrocarbon group optionally having substituent (s) or substituent (s) M represents an Al atom or a Ga atom, and L represents the following general formula (IIIa), (III
b) or (IIIc))

[0051]

Embedded image

(Where Y is any of Si, Ge or Sn
Represents an atom of^ThreeOr Ar ⁷Is a substituent
An aromatic hydrocarbon ring group or an aromatic compound
A dinuclear metal complex represented by the following general formula (IV):

[0053]

Embedded image

(Wherein, R ¹⁵ and R ²⁰ each independently represent a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, an allyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group, Carboxyl group, alkoxy group, alkylsulfonyl group, α-haloalkyl group, hydroxyl group, amide group optionally having substituent (s), aromatic hydrocarbon group optionally having substituent (s) or substituent (s) Represents an aromatic heterocyclic group which may be represented by M, and M represents an Al atom or a Ga atom.) A compound having at least one 1,2,4-triazole ring represented by the following structural formula (IV),

[0055]

Embedded image

A styryl compound represented by the following general formula (V) is exemplified.

[0057]

Embedded image

(Wherein, Ar ⁸ represents a divalent aromatic hydrocarbon group which may have a substituent or an aromatic heterocyclic group which may have a substituent, and Ar ⁹ to Ar ¹² Each independently represents an aromatic hydrocarbon group or an aromatic heterocyclic group, each of which may have a substituent)

Specific examples of the mixed ligand complex represented by the general formula (III) include bis (2-methyl-8-quinolinolato) (phenolato) aluminum, bis (2-methyl-
8-quinolinolato) (ortho-cresolato) aluminum, bis (2-methyl-8-quinolinolato) (meta-cresolato) aluminum, bis (2-methyl-8-quinolinolato) (para-cresolato) aluminum, bis (2-methyl) -8-quinolinolato) (ortho-phenylphenolato) aluminum, bis (2-methyl-8-quinolinolato) (meta-phenylphenolato) aluminum, bis (2-methyl-8-quinolinolato) (para-phenylphenolato) Aluminum, bis (2-methyl-
8-quinolinolato) (2,3-dimethylphenolato) aluminum, bis (2-methyl-8-quinolinolato)
(2,6-dimethylphenolato) aluminum, bis (2-methyl-8-quinolinolato) (3,4-dimethylphenolato) aluminum, bis (2-methyl-8-quinolinolato) (3,5-dimethylphenolato) ) Aluminum, bis (2-methyl-8-quinolinolato) (3,5
-Di-tert-butylphenolato) aluminum, bis (2-methyl-8-quinolinolato) (2,6-diphenylphenolato) aluminum, bis (2-methyl-8)
-Quinolinolato) (2,4,6-triphenylphenolato) aluminum, bis (2-methyl-8-quinolinolato) (2,4,6-trimethylphenolato) aluminum, bis (2-methyl-8-quinolinolato) (2,3
6-trimethylphenolato) aluminum, bis (2-
Methyl-8-quinolinolato) (2,3,5,6-tetramethylphenolato) aluminum, bis (2-methyl-
8-quinolinolato) (1-naphthrat) aluminum,
Bis (2-methyl-8-quinolinolato) (2-naphthrat) aluminum, bis (2-methyl-8-quinolinolato) (triphenylsilanolato) aluminum, bis (2-methyl-8-quinolinolato) (triphenylgermanola) G) aluminum, bis (2-methyl-8-quinolinolato) (tris (4,4-biphenyl) silanolato) aluminum, bis (2,4-dimethyl-8-quinolinolato) (ortho-phenylphenolato) aluminum, bis ( 2,4-dimethyl-8-quinolinolato) (para-phenylphenolato) aluminum, bis (2,4
-Dimethyl-8-quinolinolato) (meta-phenylphenolato) aluminum, bis (2,4-dimethyl-8-)
Quinolinolato) (3,5-dimethylphenolato) aluminum, bis (2,4-dimethyl-8-quinolinolato)
(3,5-di-tert-butylphenolato) aluminum, bis (2-methyl-4-ethyl-8-quinolinolato) (para-cresolato) aluminum, bis (2-methyl-4-methoxy-8-quinolinolato) (Para-phenylphenolato) aluminum, bis (2-methyl-5)
-Cyano-8-quinolinolato) (ortho-cresolate)
Aluminum, bis (2-methyl-6-trifluoromethyl-8-quinolinolato) (2-naphthrat) aluminum, bis (2-methyl-8-quinolinolato) (phenolato) gallium, bis (2-methyl-8-quinolinolato) (Ortho-cresolato) gallium, bis (2-methyl-8-quinolinolato) (para-phenylphenolatogallium, bis (2-methyl-8-quinolinolato) (1-
(Naphtolato) gallium, bis (2-methyl-8-quinolinolato) (2-naphtrato) gallium, bis (2-methyl-8-quinolinolato) (triphenylsilanolato) gallium, bis (2-methyl-8-quinolinolato) ( Tris (4,4-biphenyl) silanolato) gallium and the like.

Particularly preferably, bis (2-methyl-8-
(Quinolinolato) (2-naphthrat) aluminum and bis (2-methyl-8-quinolinolato) (triphenylsilanolato) aluminum. The general formula (IV)
As a specific example of the binuclear metal complex represented by
Methyl-8-quinolato) aluminum-μ-oxo-bis- (2-methyl-8-quinolylato) aluminum, bis (2,4-dimethyl-8-quinolato) aluminum-
μ-oxo-bis- (2,4-dimethyl-8-quinolylato) aluminum, bis (4-ethyl-2-methyl-8)
-Quinolinolato) aluminum-μ-oxo-bis-
(4-ethyl-2-methyl-8-quinolinolato) aluminum, bis (2-methyl-4-methoxyquinolinolato) aluminum-μ-oxo-bis- (2-methyl-
4-methoxyquinolinolato) aluminum, bis (5-
Cyano-2-methyl-8-quinolinolato) aluminum-μ-oxo-bis (5-cyano-2-methyl-8-quinolinolato) aluminum, bis (5-chloro-2-methyl-8-quinolinolato) aluminum-μ- Oxo
Bis- (5-chloro-2-methyl-8-quinolinolato)
Aluminum, bis (2-methyl-5-trifluoromethyl-8-quinolinolato) aluminum-μ-oxo-
Bis- (2-methyl-5-trifluoromethyl-8-quinolinolato) aluminum; Particularly preferably, bis (2-methyl-8-quinolato) aluminum-μ-oxo-bis- (2-methyl-8-quinolate)
Aluminum. Specific examples of the compound having at least one 1,2,4-triazole ring represented by the structural formula (V) are shown below.

[0061]

Embedded image

Specific examples of the styryl compound represented by the general formula (VI) include, for example, a distyrylbiphenyl compound (B-1) exemplified as a conventional blue light-emitting material. The thickness of the hole blocking layer 6 is usually 0.3 to 100 n.
m, preferably 0.5 to 10 nm. The hole blocking layer can be formed in the same manner as the hole transporting layer, but usually, a vacuum evaporation method is used.

It is conceivable to provide an electron transport layer 7 between the hole blocking layer 6 and the cathode 8 for the purpose of further improving the luminous efficiency of the device. The electron transport layer 7 is formed of a compound capable of efficiently transporting electrons injected from the cathode between the electrodes to which an electric field is applied in the direction of the hole blocking layer 6. The electron transport layer has an effect of preventing excitons generated by recombination in the light emitting layer from being diffused and quenched by the cathode 8.

The electron transporting compound used in the electron transporting layer 7 has a high electron injection efficiency from the cathode 8 and
It is necessary that the compound has high electron mobility and can efficiently transport injected electrons. Materials satisfying such conditions include metal complexes such as aluminum complexes of 8-hydroxyquinoline (JP-A-59-19).
No. 4393), metal complexes of 10-hydroxybenzo [h] quinoline (JP-A-6-322362), oxadiazole derivatives (JP-A-2-216791), and distyrylbiphenyl derivatives (JP-A-3-231).
970), silole derivatives (JP-A-9-8761)
No. 6), 3- or 5-hydroxyflavone metal complex (Appl. Phys. Lett., Vol. 71, 3338).
Pp. 1997), benzoxazole metal complex (JP-A-6-336586), benzothiazole metal complex (JP-A-9-279134), and trisbenzimidazolylbenzene (US Pat. No. 5,645,948). ), Quinoxaline compounds (JP-A-6-20716)
No. 9), phenanthroline derivatives (JP-A-5-33)
No. 1449), 2-t-butyl-9,10-N,
N'-dicyanoanthraquinone diimine (Phys. S
tat. Sol. (A), 142, 489, 199
4 years), n-type hydrogenated amorphous silicon carbide, n-type zinc sulfide, n-type zinc selenide, and the like. The thickness of the electron transport layer 7 is generally 5 to 200 nm, preferably 10 to 10 nm.
0 nm.

The cathode 8 plays a role of injecting electrons into the electron transport layer 7. As the material used for the cathode 8, the material used for the anode 2 can be used, but for efficient electron injection, a metal having a low work function is preferable, and tin, magnesium, indium, calcium, A suitable metal such as aluminum or silver or an alloy thereof is used. Specific examples include a low work function alloy electrode such as a magnesium-silver alloy, a magnesium-indium alloy, and an aluminum-lithium alloy. Further, the interface between the cathode and the light emitting layer or the electron transport layer is LiF, LiF.
Inserting an extremely thin film (0.1 to 5 nm) of an alkali metal compound such as ₂ O or an alkaline earth halide is an effective method for improving the efficiency of the device (Appl. P).
hys. Lett. 70, 152, 1997;
IEEE Trans. Electron. Device
es, 44, 1245, 1997; Japanese Patent Application No. 9-8.
No. 6662). The thickness of the cathode 8 is usually the same as that of the anode 2. In order to protect the cathode made of a low work function metal, further laminating a metal layer having a high work function and being stable to the atmosphere increases the stability of the device. For this purpose, metals such as aluminum, silver, nickel, chromium, gold, platinum and the like are used.

The structure opposite to that of FIG. 1, ie, the structure in which the cathode 8, the electron transport layer 7, the light emitting layer 5, the hole transport layer 4, the anode 2
And the organic electroluminescent device of the present invention can be provided between two substrates, at least one of which has high transparency, as described above. Similarly, it is also possible to laminate in a structure opposite to the above-mentioned respective layer constitutions shown in FIGS.

According to the organic electroluminescent device of the present invention, blue light emission with good color purity can be obtained, and not only can it function as a full-color or multi-color blue sub-pixel, but also can be combined with a fluorescent conversion dye to produce a full-color display device. (Japanese Unexamined Patent Publication (Kokai) No. 3-15289).
No. 7).

[0068]

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.

[Production Example of Exemplified Compound (I-2)]
3.38 g of N'-diphenylbenzidine, 2-methyl-
8.61 g of 1-iodonaphthalene, potassium carbonate 2.1
0 g, 2.46 g of copper powder, and 0.25 g of 18-crown-6-ether were added to 25 ml of nitrobenzene, and reacted at 180 ° C. for 20 hours under nitrogen. After completion of the reaction, the reaction solution was released into 100 ml of methanol, and the precipitated dark brown crude product was dissolved in chloroform, and the solvent was distilled off.
Washed with methanol. Thereafter, the product was purified by column chromatography using silica gel to obtain 0.43 g of a tan powder. The yield was 7%. This compound was analyzed by mass spectrometry and found to have a molecular weight of 616 and FT
By -IR and ¹ H-NMR, it was confirmed to be the target compound (I-2). The melting point was measured at 217 ° C. Tg showed a high value of 93 ° C. as measured by differential thermal analysis using a DSC-20 manufactured by Seiko Instruments Inc.

Reference Example 1 A glass substrate was ultrasonically washed with acetone, washed with pure water, ultrasonically washed with isopropyl alcohol, dried with dry nitrogen, and dried.
After performing the V / ozone cleaning, the apparatus was set in a vacuum evaporation apparatus, and evacuated using an oil diffusion pump until the degree of vacuum in the apparatus became 2 × 10 ⁻⁶ Torr or less.

The exemplified compound (I-2) was put in a ceramic crucible, and heated by a tantalum wire heater around the crucible to perform vapor deposition. At this time, the temperature of the crucible was controlled in the range of 200 to 260 ° C. The degree of vacuum during vapor deposition is 1.8 × 10 ^-6 To
rr (about 2.3 × 10 ⁻⁴ Pa) and a deposition rate of 0.3 nm
/ S to obtain a uniform and transparent film having a thickness of 82 nm. The ionization potential of this thin film sample was measured using an ultraviolet electron analyzer (AC-1) manufactured by Riken Keiki Co., Ltd.
It showed a value of 5.06 eV. The maximum of the fluorescence wavelength measured by exciting this vapor-deposited film with a mercury lamp (wavelength 350 nm) was 465 nm, which was blue fluorescence.

Similarly, when the ionization potential, the maximum fluorescence wavelength and the Tg of Exemplified Compound (II-5) were measured, they were 5.08 eV, 445 nm and 88 ° C., respectively. Reference Example 2 As a material for the hole transporting layer, the following 4,4′-bis [N- (1-naphthyl) was used instead of the exemplified compound (I-3).
-N-phenylamino] biphenyl (H-1)

[0073]

Embedded image

A deposition film was prepared in the same manner as in Reference Example 1 except that was used as a deposition source. When the ionization potential of this thin film sample was measured, it showed a value of 5.25 eV. Reference Example 3 As a material for the hole blocking layer, bis (2-methyl-8-quinolinolato) shown below was used in place of the exemplary compound (I-3).
(Triphenylsilanolato) aluminum complex (HB-
A deposited film was prepared in the same manner as in Reference Example 1 except that 1) was used as the deposition source. this

[0075]

Embedded image

The ionization potential of the thin film sample of 5.
It was 51 eV. Example 1 An organic electroluminescent device having a structure shown in FIG. 2 was produced by the following method. Indium tin oxide (ITO) transparent conductive film deposited on a glass substrate with a thickness of 120 nm (Geomatec; electron beam filmed product; sheet resistance 15Ω)
Was patterned into 2 mm-wide stripes using ordinary photolithography and hydrochloric acid etching to form an anode. The patterned ITO substrate is cleaned in the order of ultrasonic cleaning with acetone, water cleaning with pure water, and ultrasonic cleaning with isopropyl alcohol, dried with nitrogen blow, and finally cleaned with ultraviolet and ozone, and placed in a vacuum evaporation apparatus. installed. After the rough exhaust of the above apparatus is performed by an oil rotary pump, the degree of vacuum in the apparatus is 2 × 10 ⁻⁶ Torr (about ^2.10 Torr).
Evacuation was performed using an oil diffusion pump equipped with a liquid nitrogen trap until the pressure became 7 × 10 ⁻⁴ Pa) or less.

As a hole transport layer material, 4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (H-1) was put into a ceramic crucible, and a tantalum wire heater around the crucible was used. Heating was performed for vapor deposition. At this time, the temperature of the crucible was controlled in the range of 250 to 265 ° C. The degree of vacuum at the time of vapor deposition is 1.4 × 10 ⁻⁶ Torr (about 1.9 × 1 Torr).
0 ^-4 Pa) at a deposition rate of 0.3 nm / sec and a film thickness of 60 nm.
Was obtained.

Next, as a material of the light emitting layer 5, the exemplified compound (I-2) was vapor-deposited on the hole transport layer 4 in the same manner. At this time, the temperature of the crucible was controlled in the range of 220 to 260 ° C. The degree of vacuum during vapor deposition is 1.0 × 10 ⁻⁶ Torr
r (about 1.3 × 10 ⁻⁴ Pa) at a deposition rate of 0.1 to 0.1.
At 2 nm / sec, the film thickness was 30 nm. Subsequently, as a material for the hole blocking layer 6, a bis (2-methyl-8-quinolinolato) (triphenylsilanolato) aluminum complex (HB-1) was deposited on the light emitting layer 5 in the same manner. . At this time, the temperature of the crucible was controlled in the range of 180 to 190 ° C. The degree of vacuum during deposition is 1.0 × 10 ⁻⁶ Torr
(About 1.3 × 10 ⁻⁴ Pa), the deposition rate was 0.2 nm / sec, and the film thickness was 20 nm. Further, as a material of the electron transport layer 7, the following 8-hydroxyquinoline complex (E-1) of aluminum was vapor-deposited on the hole blocking layer 6 in the same manner.

[0079]

Embedded image

At this time, the temperature of the crucible was controlled in the range of 310 to 320 ° C. The degree of vacuum during deposition is 7.7 × 10 ^-7 To
rr (about 1.0 × 10 ⁻⁵ Pa) and a deposition rate of 0.3 nm
/ S and the film thickness was 25 nm. The above hole transport layer 4
The substrate temperature at the time of vacuum-depositing the electron transport layer 7 was kept at room temperature.

Here, the element on which the vapor deposition up to the electron transporting layer 7 was performed was once taken out of the vacuum vapor deposition apparatus into the atmosphere, and a stripe-shaped shadow mask having a width of 2 mm was used as a cathode vapor deposition mask. It is closely attached to the element so as to be orthogonal to the stripe, and is placed in another vacuum evaporation apparatus, and the degree of vacuum in the apparatus is 2 × 10 ⁻⁶ as in the case of the organic layer.
Evacuation was performed until the pressure became Torr (about 2.7 × 10 ⁻⁴ Pa) or less. As the cathode 8, first, magnesium fluoride (Mg)
F ₂ ) was deposited on a molybdenum boat at a deposition rate of 0.01
nm / sec, degree of vacuum 2.0 × 10 ⁻⁶ Torr (about 2.7 ×
At 10 ⁻⁴ Pa), a film was formed on the electron transport layer 7 to a thickness of 0.5 nm. Next, aluminum was heated in the same molybdenum boat, deposition rate 0.6 nm / sec, an aluminum layer having a thickness of 40nm in vacuum of 1.0 × 10 ^-5 Torr (about 1.3 × 10 ^-3 Pa) Was formed. Further, copper is further heated thereon using a molybdenum boat in order to increase the conductivity of the cathode, and a deposition rate of 0.6 nm / sec.
Vacuum degree 8.0 × 10 ^-6 Torr (about 1.1 × 10 ^-3 P
A cathode 8 was completed by forming a copper layer having a thickness of 40 nm in a). The substrate temperature during the deposition of the above three-layer cathode 8 was kept at room temperature.

As described above, an organic electroluminescent device having a light emitting area of 2 mm × 2 mm was obtained.
Table 5 shows the light emission characteristics of this device. In Table-5,
The emission luminance indicates a value at a current density of 250 mA / cm ² , the luminous efficiency indicates a value at 100 cd / m ² , the luminance / current indicates a slope of the luminance-current density characteristic, and the voltage indicates a value at 100 cd / m ^2. . The peak maximum wavelength of the EL spectrum and the CIE chromaticity coordinate value (JIS Z8701) are shown together. The emission color was blue. This device did not show a remarkable rise in drive voltage even after storage for a long period of time, and did not decrease in luminous efficiency or luminance, and stable storage stability of the device was obtained.

[0083]

[Table 5]

Example 2 Illustrative compound (II-5) was used as the light-emitting layer.
An element was produced in the same manner as in Example 1 except that the element was used instead of 2). Table 5 shows emission characteristics of the device. Example 3 Example 2 was repeated except that the exemplified compound (II-5) was used as a light emitting layer, and that perylene was uniformly doped in the thickness direction at a concentration of 1.2% by weight in the light emitting layer by a binary vapor deposition method. An element was produced in the same manner. Table 5 shows the light emission characteristics of this device. Due to the perylene doping, the chromaticity coordinates completely entered the blue region.

Comparative Example 1 An element was produced in the same manner as in Example 2 except that the hole blocking layer was not provided and the thickness of the electron transport layer was changed to 45 nm. The light emission of this device was green having a maximum at 530 nm, and light emission was observed from aluminum 8-hydroxyquinoline complex used as the electron transporting layer.

Comparative Example 2 An element was manufactured in the same manner as in Example 2 except that the hole transport layer was not provided and the thickness of the light emitting layer was changed to 60 nm. Although blue light emission was obtained, the light emission luminance was as low as about 300 cd / m ² . Comparative Example 3 An element was produced in the same manner as in Example 3, except that the compound (B-2) having a thickness of 45 nm was used as the light emitting layer, and (E-1) was used as the electron transporting layer. Table 5 shows the light emission characteristics of this device. Both the luminance and the luminous efficiency were low, and the luminescent color was bluish green.

Comparative Example 4 A device was produced in the same manner as in Comparative Example 2 except that perylene was uniformly doped in the light emitting layer at a concentration of 1.0% by weight in the film thickness direction by a binary vapor deposition method. Table 5 shows the light emission characteristics of this device. Although blue light was emitted by doping with perylene, the luminance and the luminous efficiency were not improved.

[0088]

According to the organic electroluminescent device of the present invention, since the device has a light emitting layer containing a specific aromatic amine, blue light with good color purity can be achieved, and a device having improved stability can be obtained. Obtainable. Accordingly, the organic electroluminescent device according to the present invention can be used as a light source (for example, a light source of a copier, a liquid crystal display) such as a flat panel display (for example, for an OA computer or a wall-mounted television), a multi-color display device, or a surface light emitter. And light sources for backlights of instruments and the like, display boards, and marker lights. Particularly, as a display element for a vehicle or an outdoor which requires high heat resistance, its technical value is great.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an example of an organic electroluminescent device.

FIG. 2 is a schematic sectional view showing another example of the organic electroluminescent device.

FIG. 3 is a schematic sectional view showing another example of the organic electroluminescent device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3 Anode buffer layer 4 Hole transport layer 5 Emitting layer 6 Hole blocking layer 7 Electron transport layer 8 Cathode

Claims (6)

[Claims] 1. An organic electroluminescent device comprising at least a hole transport layer, a light emitting layer, and a hole blocking layer sandwiched between an anode and a cathode on a substrate, wherein the light emitting layer has the following general formula (I) or An organic electroluminescent device comprising the aromatic amine compound represented by (II). Embedded image Embedded image (In the formula (I) or (II), Ar ¹ and Ar ² are
Each independently represents an aromatic hydrocarbon group or an aromatic heterocyclic group, each of which may have a substituent, and R ¹ to R ¹⁴
Are each independently a hydrogen atom, a cyano group, a carboxyl group, a hydroxyl group, or an alkyl group, an aralkyl group, an alkenyl group, an amino group, an amide group, an alkoxycarbonyl group, and an alkoxy group, each of which may have a substituent. X represents an aryloxy group, an aromatic hydrocarbon group or an aromatic heterocyclic group, and each X independently represents a divalent aromatic hydrocarbon group or an aromatic group which may have a substituent. Represents a heterocyclic group) 2. The method according to claim 1, wherein the ionization potential of the hole transport layer is 0.1 eV or more higher than the ionization potential of the light emitting layer, and the ionization potential of the hole blocking layer is 0.2 eV or more higher than the ionization potential of the light emitting layer. Item 2. The organic electroluminescent device according to Item 1. 3. The organic electroluminescent device according to claim 1, wherein the hole transport layer is selected from an aromatic amine compound different from the light emitting layer. 4. The method according to claim 1, wherein the hole blocking layer has the following general formula (III) or
A metal complex represented by the formula (IV),
At least one triazole derivative or the following general formula (V
At least one of the styryl compounds represented by I)
4. The method according to claim 1, wherein
3. The organic electroluminescent device according to claim 1. Embedded image(Where R^FifteenOr R²⁰Is independently a hydrogen atom,
Halogen atom, alkyl group, aralkyl group, alkenyl
Group, allyl group, cyano group, amino group, acyl group, alcohol
Xycarbonyl group, carboxyl group, alkoxy group,
Alkylsulfonyl group, α-haloalkyl group, hydroxyl group,
An amide group which may have a substituent,
May have an aromatic hydrocarbon group or a substituent
Represents an aromatic heterocyclic group, M represents an Al atom or a Ga atom
And L represents the following general formula (IIIa), (IIIb) or (IIIc)
Represents one of the following)(Wherein, Y represents any atom of Si, Ge or Sn.
I, Ar^ThreeOr Ar ⁷Are each independently substituted
An aromatic hydrocarbon group or an aromatic compound
Represents a ring group)(Where R^FifteenOr R²⁰Is independently a hydrogen atom,
Halogen atom, alkyl group, aralkyl group, alkenyl
Group, allyl group, cyano group, amino group, acyl group, alcohol
Xycarbonyl group, carboxyl group, alkoxy group,
Alkylsulfonyl group, α-haloalkyl group, hydroxyl group,
An amide group which may have a substituent,
May have an aromatic hydrocarbon group or a substituent
Represents an aromatic heterocyclic group, M represents an Al atom or a Ga atom
(Shown)Embedded image(Wherein, Ar⁸Is a divalent aromatic which may have a substituent
Aromatic hydrocarbon group or divalent aromatic optionally having a substituent
Represents a group heterocyclic group, Ar⁹Or Ar¹²Are independent
And an aromatic hydrocarbon, each of which may have a substituent.
Group or aromatic heterocyclic group) 5. The organic electroluminescent device according to claim 1, wherein an electron transporting layer is provided between the hole blocking layer and the cathode. 6. The film thickness of the hole blocking layer is 0.5 to 30 nm.
The organic electroluminescent device according to any one of claims 1 to 5, wherein