JP3284766B2 - Organic electroluminescent device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescent device, and more particularly to a thin film 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, 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 (50-1000 Hz), 2) High drive voltage (up to 200 V), 3) It is difficult to achieve full color (especially blue), 4) Cost of peripheral drive circuit is high. ing.

However, in recent years, in order to improve the above problems,
Development of EL devices using organic thin films has been started. 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 luminous efficiency, and the organic luminescent layer composed of an organic hole transport layer composed of an aromatic diamine and the aluminum complex of 8-hydroxyquinoline was used. Of an organic electroluminescent device provided with a layer (Appl. Phy
s. Lett. , Vol. 51, p. 913, 1987), the luminous efficiency is greatly improved as compared with a conventional electroluminescent device using a single crystal such as anthracene or the like, and the practical characteristics are approached.

In addition to the above low molecular weight materials, poly (p-phenylenevinylene) (N
atature, 347, 539, 1990; App.
l. Phys. Lett. 61, 2793, 19
1992), poly [2-methoxy, 5- (2'-ethylhexoxy) -1,4-phenylenevinylene] (App
l. Phys. Lett. 58, 1982, 19
91; ThinSolid Films, 216,
96, 1992; Nature, 357, 477.
P. 1992), poly (3-alkylthiophene)
(Jpn. J. Appl. Phys, 30, L193
8, 1991; Appl. Phys. , 72
Vol., P. 564, 1992).
An element in which a low molecular light emitting material and an electron transfer material are mixed with a polymer such as polyvinyl carbazole (Applied Physics, Vol. 61, 1
044, 1992).

[0005]

In an organic electroluminescent device using a low molecular weight material, the low molecular weight thin film layer is crystallized with time or thermally, and as a result, the uniformity of the thin film shape is lost. A major problem is that a non-light emitting portion called a dark spot is generated, or a short circuit of the element is caused. As a solution to the crystallization problem, an organic electroluminescent device using the above-described polymer has been studied. However, since the light-emitting layer is formed by a wet method such as spin coating, precise control of the film thickness is difficult. In addition, it is difficult to control impurities, so that the luminous efficiency is lower than that of the low-molecular type,
In addition, the driving life is short.

[0006] For the reasons described above, in actual use, the organic electroluminescent device has a problem of instability due to the shape of the thin film in practical use.

[0007]

In view of the above situation, the present inventors have made intensive studies with the aim of providing an organic electroluminescent device capable of maintaining stable light emitting characteristics for a long period of time. It has been found that the layer preferably contains a 4,4'-bis-triazinylstilbene derivative, and the present invention has been completed.

That is, the gist of the present invention is an organic electroluminescent device including at least a hole transport layer and an organic light emitting layer sandwiched between an anode and a cathode on a substrate, wherein the organic light emitting layer has the following general formula (I) )

[0009]

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(Wherein, Ar ¹ to Ar ⁴ each independently represent an aryl group, a biphenyl group or an aromatic heterocyclic group which may have a substituent) -An organic electroluminescent device comprising a triazinylstilbene derivative. Hereinafter, the organic electroluminescent device of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a sectional view schematically showing a structural example of an organic electroluminescent device of the present invention, wherein 1 is a substrate, 2 is an anode, and 3 is an anode.
Represents a hole transport layer, 4 represents an organic light emitting layer, and 5 represents a cathode. The substrate 1 serves as a support of the organic electroluminescent device of the present invention, and may be a quartz or glass plate, a metal plate or metal foil, a plastic film or sheet, or the like. Transparent synthetic resin substrates such as polycarbonate, polysulfone and the like are preferable.

An anode 2 is provided on a substrate 1. The anode 2 is usually made of aluminum, gold, silver, nickel,
It is made of a metal such as palladium and tellurium, a metal oxide such as an oxide of indium and / or tin, copper iodide, carbon black, or a conductive polymer such as poly (3-methylthiophene). Usually, the formation of the anode is often performed by a sputtering method, a vacuum evaporation method, or the like, but fine metal particles such as silver or copper iodide,
In the case of carbon black, conductive metal oxide fine particles, conductive polymer fine powder, or the like, it can also be formed by dispersing in an appropriate binder resin solution and applying the solution on a substrate. Further, in the case of a conductive polymer, a thin film can be formed directly on a substrate by electrolytic polymerization or formed by coating on a substrate (Appl. Phys. Let.).
t. 60, 2711, 1992). The above anodes can be laminated with different materials. The thickness of the anode 2 varies depending on the required transparency. If transparency is required, it is desirable that the transmittance of visible light is 60% or more, preferably 80% or more. Is usually 5 to 1000 nm, preferably 10 to 50 nm.
It is about 0 nm.

The anode 2 may be the same as the substrate 1 if it is opaque. Further, it is also possible to stack the above-mentioned anodes with different materials. In the example of FIG. 1, the anode 2 plays a role of hole injection. On the other hand, the cathode 5 plays a role of injecting electrons into the organic light emitting layer 4. As the material used for the cathode 5, the material for the anode can be used. However, for efficient electron injection, a metal having a low work function is preferable, and tin, magnesium, indium, aluminum, silver, or the like is preferable. Suitable metals or their alloys are used. The 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, at least one of the anode 2 and the cathode 5 needs to have good transparency as an organic electroluminescent element. From this, it is preferable that one of the anode 2 and the cathode 5 has a thickness of 10 to 500 nm, and it is desirable that the anode 2 and the cathode 5 have good transparency.

A hole transport layer 3 is provided on the anode 2, and as the hole transport layer, holes from the anode are efficiently transported between the electrodes to which an electric field is applied in the direction of the organic light emitting layer. Formed from materials that can be used. Usually, an organic hole transport material is used for the hole transport layer. As an organic hole transport material, the hole injection efficiency from the anode 2 is high, and
It is necessary that the material be capable of efficiently transporting the injected holes. For that purpose, it is required that the ionization potential is small, the hole mobility is large, the stability is excellent, and impurities serving as traps are hardly generated at the time of manufacture or use. Such organic hole transport compounds include, for example, 1,1-bis (4-di-
Aromatic diamine compounds linked with tertiary aromatic amine units such as p-tolylaminophenyl) cyclohexane (JP-A-59-194393), 4,4'-bis [(N-1-naphthyl) -N- Phenylamino] aromatic amines containing two or more tertiary amines represented by biphenyl and having two or more condensed aromatic rings substituted by nitrogen atoms (JP-A-5-234681), and derivatives of triphenylbenzene Aromatic triamine having a starburst structure (U.S. Pat. No. 4,923,774), N, N'-diphenyl-N, N'-bis (3-methylphenyl)-
Aromatic diamines such as (1,1′-biphenyl) -4,4′-diamine (US Pat. No. 4,764,625);
α, α, α ′, α′-tetramethyl-α, α′-bis (4-di-p-tolylaminophenyl) -p-xylene (JP-A-3-269084) Asymmetric triphenylamine derivatives (Japanese Unexamined Patent Publication No.
No. 129271), 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). Gazette),
Aromatic diamine having a styryl structure (JP-A-4-29
No. 0851), a compound in which an aromatic tertiary amine unit is linked by a thiophene group (Japanese Patent Application Laid-Open No. 4-304466), a starburst type aromatic triamine (Japanese Patent Application Laid-Open No.
308688), a benzylphenyl compound (JP-A-4-364153), a tertiary amine linked by a fluorene group (JP-A-5-25473), a triamine compound (JP-A-5-239455), Bisdipyridylaminobiphenyl (JP-A-5-32063)
No. 4), N, N, N-triphenylamine derivatives (JP-A-6-1972), aromatic diamines having a phenoxazine structure (Japanese Patent Application No. 5-290728),
Diaminophenylphenanthridine derivatives (Japanese Patent Application No. Hei 6
No. 45669), hydrazone compounds (JP-A-2-311591), silazane compounds (US Pat. No. 4,950,950),
Examples thereof include silanamine derivatives (JP-A-6-49079), phosphamine derivatives (JP-A-6-25659), and quinacridone compounds. These compounds are
They may be used alone or, if necessary, mixed.

In addition to the above-mentioned compounds, a hole transporting polymer such as polyvinyl carbazole or polysilane (App
l. Phys. Lett. 59, 2760, 19
9), polyphosphazene (Japanese Unexamined Patent Publication No.
No. 3-194949), polyamide (JP-A-5-31)
No. 0949), polyvinyltriphenylamine (Japanese Patent Application No. 5-205377), a polymer having a triphenylamine skeleton (Japanese Patent Application Laid-Open No. 4-1330065), and a polymer in which triphenylamine units are linked by a methylene group or the like ( S
Synthetic Metals, 55-57, 41
63, 1993), polyamines containing aromatic amines (J. Polym. Sci., Poly).
m. Chem. Ed. , 21, 969, 1983.
Year)).

The hole transport layer 3 is formed by laminating the organic hole transport material on the anode 2 by a coating method or a vacuum evaporation method. In the case of coating, one or more kinds of organic hole transporting compounds and a binder resin which does not trap holes as required and additives such as a coating property improving agent such as a leveling agent are added and dissolved. It is adjusted, applied on the anode 2 by a method such as spin coating, and dried to form the hole transport layer 3. Examples of the binder resin include polycarbonate, polyarylate, and polyester. If the amount of the binder resin is large, the hole mobility is lowered, so that a smaller amount is preferable.
It is preferably at most 50% by weight.

In the case of the vacuum evaporation method, an organic hole transporting material is put into a crucible installed in a vacuum vessel, and the inside of the vacuum vessel 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 placed opposite the crucible. When forming the organic hole transport layer, further, as an acceptor,
Metal complexes and / or metal salts of aromatic carboxylic acids (JP-A-4-320484), benzophenone derivatives and thiobenzophenone derivatives (JP-A-5-29536)
No. 1) and doping fullerenes (JP-A-5-331458) at a concentration of 10 ⁻³ to 10% by weight to generate holes as free carriers, thereby enabling low-voltage driving. is there.

The thickness of the hole transport layer 3 is usually from 10 to 30.
0 nm, preferably 30-100 nm. In order to uniformly form such a thin film, a vacuum deposition method is often used. It is also possible to use an inorganic material instead of an organic compound as the material of the hole transport layer 3. The conditions required for the inorganic material are the same as those for the organic hole transport material. Examples of the inorganic material used for the hole transport layer 3 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. Zinc selenide and the like. These inorganic hole transport layers are formed by a CVD method, a plasma CVD method, a vacuum evaporation method, a sputtering method, or the like.

The film thickness of the inorganic hole transporting layer is, like the organic hole transporting layer, usually 10 to 300 nm, preferably 30 to 1 nm.
00 nm. An organic light emitting layer 4 is provided on the hole transport layer 3, and the organic light emitting layer 4 can efficiently transport electrons from the cathode toward the hole transport layer between electrodes to which an electric field is applied. It is formed from a compound that can be formed.

The compound used for the organic light emitting layer 4 needs to have a high electron injection efficiency from the cathode 5 and to be able to efficiently transport the injected electrons. For this purpose, it is required that the compound has a high electron affinity, a high electron mobility, a high stability, and hardly generates impurities serving as traps during production or use. It is also required to emit blue light upon recombination of holes and electrons.

An even more important condition required for the compound used in the organic light emitting layer is to form a stable amorphous thin film. This is a condition necessary for suppressing the occurrence of film defects in the organic electroluminescent device and for operating the organic electroluminescent device stably for a long period of time. As a result of studying the deterioration of the organic electroluminescent device by the present inventor, it has been found that one of the major causes is that the organic light-emitting layer changes from a uniform film state to an island-like non-uniform state with time.

As in the above example, many organic compounds are molecular crystals in the solid state. Therefore, even if the organic compound is in an amorphous state immediately after being formed into a thin film, it must be crystallized over time. Is a common phenomenon. Whether such crystallization occurs depends greatly on the glass transition temperature, and a thin film made of a material having a high glass transition temperature tends to be hardly crystallized. In general, since a good correlation is established between the glass transition temperature and the melting point, an organic compound having a high melting point may be considered to exhibit a high glass transition temperature. The present inventors have conducted intensive studies to prevent crystallization of this thin film. As a result, the 4,4′-bis-triazinylstilbene derivative showed a very high melting point of 300 ° C. or more, and gave a uniform amorphous thin film. It has been found that it is hardly crystallized, is thermally stable, and has a favorable effect on the stability of the device.

In the present invention, the organic light emitting layer of the organic electroluminescent device is a 4,4 ′ represented by the above general formula (I).
By using the bis-triazinylstilbene derivative, stable device characteristics can be obtained over a long period of time. In the general formula (I), preferably, Ar ¹ , Ar ² , A
r ³ and Ar ⁴ each independently represent a phenyl group, a naphthyl group, an anthryl group, a biphenyl group, a pyridyl group or a thienyl group which may have a substituent, wherein the substituent is a halogen atom; Group, carbon group 1 such as ethyl group
Alkyl groups of 6 to 6; alkenyl groups such as vinyl groups; and 1 to 1 carbon atoms such as methoxycarbonyl groups and ethoxycarbonyl groups.
An alkoxycarbonyl group having 6 carbon atoms; an alkoxy group having 1 to 6 carbon atoms such as a methoxy group and an ethoxy group; an aryloxy group such as a phenoxy group and a benzyloxy group; a dialkylamino group such as an amino group, a dimethylamino group and a diisopropylamino group; A cyano group and a hydroxyl group.

Particularly preferably, Ar ¹ , Ar ² , Ar ³ and Ar ⁴ are each independently phenyl, p-methylphenyl, m-methylphenyl, p-chlorophenyl, m-chlorophenyl, A methoxyphenyl group,
It is selected from a pt-butylphenyl group. The 4,4′-bis-triazinylstilbene derivative represented by the general formula (I) can be synthesized, for example, by a method disclosed in Swiss Patent No. 472,416.

Preferred specific examples of the 4,4'-bis-triazinylstilbene derivative represented by the general formula (I) are shown in Table 1 below, but are not limited thereto.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

The exemplified compounds shown in Tables 1 to 3 are all high melting point compounds. For example, compound (1) is 39
0 ° C. or higher, compound (2) at 373 ° C., compound (3) at 3
85 ° C., compound (8) at 375 ° C., compound (9) at 42
The temperature is 0 ° C. or higher, and the temperature of compound (12) is 306 ° C. The thickness of the organic light emitting layer 4 is usually 10 to 200 nm, preferably 30 to 200 nm.
１００100 nm.

The organic light emitting layer is prepared in the same manner as the organic hole transport layer.
Can be formed, but usually a vacuum evaporation method is used.
It is. Improve the luminous efficiency of the device and change the emission color
For example, 8-hydroxyquinoline aluminum
For lasers, such as coumarin, using an iron complex as a host material
Doping a fluorescent dye (J. Appl. Phy
s. , 65, 3610, 1989).
You. In the present invention, the above 4,4'-bis-triazine is also used.
Nylstilbene derivative as host material for laser
10 fluorescent dyes ^-3By doping 10 mol%
As a result, the light emitting characteristics of the element can be further improved.

The structure of the organic electroluminescent device of the present invention may have the following layer structure:

[0032]

[Table 4] Anode / organic hole transport layer / organic light emitting layer / cathode, anode / organic hole transport layer / organic light emitting layer / electron transport layer / cathode, anode / organic hole transport layer / organic light emitting layer / interface layer / Cathode, anode / organic hole transport layer / organic light emitting layer / electron transport layer / interface layer / cathode.

In the above layer structure, the electron transport layer is for further improving the efficiency of the device, and is laminated on the organic light emitting layer. Compounds used in the electron transport layer include:
It is required that the electron injection from the cathode is easy and the electron transporting ability is further increased. As such an electron transport material,

[0034]

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[0035]

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Oxadiazole derivatives such as (App
l. Phys. Lett. 55, 1489, 19
89; Jpn. J. Appl. Phys. , Volume 31,
1812, 1992) or a system in which they are dispersed in a resin such as PMMA (Appl. Phys. Lett., 61).
Vol., P. 2793, 1992), or n-type hydrogenated amorphous silicon carbide, n-type zinc sulfide, n-type zinc selenide, and the like. The thickness of the electron transport layer is usually 5 to 200
nm, preferably 10 to 100 nm.

Similarly, in the above-mentioned layer structure, the interface layer is for improving the contact between the cathode and the organic layer, and is composed of an aromatic diamine compound (Japanese Patent Application No. 5-48075).
Quinacridone compounds (Japanese Patent Application No. 5-116204)
No.), a naphthacene derivative (Japanese Patent Application No. 5-116205)
No.), organic silicon compounds (Japanese Patent Application No. 5-116206)
No.) and organic phosphorus compounds (Japanese Patent Application No. 5-116207). The thickness of the interface layer is usually 2 to 100 n.
m, preferably 5 to 30 nm. Instead of providing the interface layer, a region containing 50% by weight or more of the above interface layer material may be provided near the cathode interface between the organic light emitting layer and the electron transport layer.

It is to be noted that a structure reverse to that shown in FIG. 1, that is, a cathode 5, an organic light emitting layer 4, a hole transport layer 3, and an anode 2 can be laminated on a substrate in this order. It is also possible to provide the organic electroluminescent device of the present invention between two substrates, one of which is highly transparent. Similarly, it is also possible to laminate in a structure opposite to the above-mentioned respective layer constitutions.

[0039]

Next, the present invention will be described in more detail with reference to Synthesis Examples and Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. Example 1 An organic electroluminescent device having the structure shown in FIG. 1 was produced by the following method.

A transparent conductive film of indium tin oxide (ITO) having a thickness of 120 nm deposited on a glass substrate is subjected to ultrasonic cleaning with acetone, water cleaning with pure water, ultrasonic cleaning with isopropyl alcohol, drying with dry nitrogen, UV / ozone. After the 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.

As an organic hole transporting layer material, 4,4′-bis [(N-1-naphthyl) -N-phenylamino] biphenyl (H1) shown below is used.

[0042]

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Was placed in a ceramic crucible in advance, and was 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 150 to 180 ° C. The degree of vacuum at the time of vapor deposition is 1.1 to 0.9 × 10 ⁻⁶ Torr.
With r, an organic hole transport layer 3 having a film thickness of 60 nm was obtained in a deposition time of 2 minutes and 30 seconds. Next, as a material of the organic light emitting layer 4, Table 1
The 4,4′-bis-triazinylstilbene derivative (1) shown in (1) was vapor-deposited on the organic hole transport layer 3 in the same manner. The temperature of the crucible at this time is 300-350
The temperature was controlled in the range of ° C. The degree of vacuum at the time of vapor deposition is 3.7 to 1.1.
× 10 ^-6 Torr, deposition time: 4 minutes 10 seconds, film thickness: 60
nm.

Finally, as a cathode, a combination of magnesium and silver
A gold electrode is deposited in a thickness of 150 nm by a binary simultaneous vapor deposition method.
did. Vapor deposition was performed using a molybdenum boat and the degree of vacuum was 4 ×
10 ^-6Torr, deposition time: 2 minutes 40 seconds, glossy film
was gotten. The atomic ratio of magnesium to silver is 10: 1.5
Met. The organic electroluminescent device I
Magnesium / silver alloy electrode plus TO electrode (anode)
(Negative DC voltage)
The device showed uniform yellow-green emission, and the emission peak wavelength was
It was 560 nm.

Immediately after the preparation of the above-mentioned device and in dry nitrogen for 5 hours.
The results of the emission characteristics after storage for 2 days are shown in the table below.
No remarkable rise in the driving voltage was observed, and no decrease in luminous efficiency was observed, and stable storage stability of the device was obtained.

[0046]

[Table 5]

[0047]

According to the organic electroluminescent device of the present invention, an anode, a hole transport layer, an organic light emitting layer, and a cathode are sequentially provided on a substrate, and a specific compound is used for the organic light emitting layer. Therefore, when a voltage is applied using both conductive layers as electrodes, stable light-emitting characteristics can be obtained over a long period of time.

Therefore, the EL element of the present invention is a light source (for example, a light source of a copying machine, a liquid crystal display, and instruments) utilizing the features of the field of flat panel displays (for example, for OA computers and wall-mounted televisions) and surface illuminators. It can be applied to backlight light sources, display boards and marker lights, and its technical value is great.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3 Hole transport layer 4 Organic light emitting layer 5 Cathode

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-157473 (JP, A) JP-A-7-188649 (JP, A) JP-A-6-271848 (JP, A) 295359 (JP, A) JP-A-3-223387 (JP, A) JP-A-6-230197 (JP, A) JP-A-56-2354 (JP, A) JP-A-56-98263 (JP, A) JP-A-7-188190 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05B 33/14 C09K 11/06 REGISTRY (STN) CA (STN)

Claims (1)

(57) [Claims] 1. An organic electroluminescent device comprising at least a hole transport layer and an organic light emitting layer sandwiched between an anode and a cathode on a substrate, wherein the organic light emitting layer is represented by the following general formula (I): (Wherein, Ar ¹ to Ar ⁴ each independently represent an aryl group, a biphenyl group or an aromatic heterocyclic group which may have a substituent). An organic electroluminescent device comprising a nilstilbene derivative.