JPH0812967A - Organic electroluminescent element - Google Patents

Abstract

PURPOSE:To obtain an organic electroluminescent element which can keep stable luminescent characteristics for a long time by adding a 4,4'- bistriazinylstilbene derivative to an organic luminous layer. CONSTITUTION:An electroconductive film of e.g. indium/tin oxide as a 10-500nm anode 2 is built up on a base 1 of e.g. glass or polyester sheet, and a hole- transporting layer 3 in a thickness of 10-300nm is formed by coating with or vacuum-depositing an organic material {e.g. 4,4'-bis[(N-1-naphthyl)-N- phenylaminolbiphenyl(H1)} or an inorganic material (e.g. p-type hydrogenated amorphous silicon) An organic luminous layer 4 is formed by vacuum-depositing a 4,4'-bistriazinylstilbene derivative represented by the formula (-wherein Ar<1> to Ar<4> are each aryl, biphenyl or an aromatic-heterocyclic group) on the hole- transporting layer 4 in a thickness of 10-200nm. A cathode 5 is built up by vacuum-depositing a metallic thin film of e.g. tin in a thickness of 10-500nm.

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, Zn which is a II-VI group compound semiconductor of an inorganic material has been used.
It is general that S, CaS, SrS, etc. are doped with Mn or a rare earth element (Eu, Ce, Tb, Sm, etc.), which is the emission center, but the EL element made from the above inorganic material is 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.

However, 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 electroluminescent device having a layer (Appl. Phy
s. Lett. , 51, p. 913, 1987), the luminous efficiency is greatly improved as compared with the conventional electroluminescent 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) (N
ature, 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
1991; Thin Solid Films, Volume 216,
96, 1992; Nature, 357, 477.
P., 1992), poly (3-alkylthiophene)
(Jpn. J. Appl. Phys, 30 volumes, L193
8 pages, 1991; Appl. Phys. , 72
Vol., P. 564, 1992), etc.
A device in which a low molecular weight light emitting material and an electron transfer material are mixed with a polymer such as polyvinylcarbazole (Applied Physics, 61, 1)
044, 1992) is also being developed.

[0005]

In an organic electroluminescence device using a low molecular weight material, the low molecular weight thin film layer is crystallized with time or thermally, resulting in loss of uniformity of the thin film shape, and A major problem is that a non-light emitting portion called a dark spot is generated or an element is short-circuited. As a solution to this crystallization problem, an organic electroluminescence device using the above-mentioned polymer has been studied, but it is difficult to precisely control the film thickness because the light emitting layer is formed by a wet method such as spin coating. 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 operating life is short.

For the above-mentioned reason, the organic electroluminescence device actually has a problem of instability due to the shape of the thin film in practical use.

[0007]

SUMMARY OF THE INVENTION In view of the above situation, the inventors of the present invention have conducted extensive studies for the purpose of providing an organic electroluminescent device capable of maintaining stable light emitting characteristics over a long period of time, and as a result, organic light emitting We have found that it is preferable for the layer to contain a 4,4'-bis-triazinyl stilbene derivative and have completed the invention.

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

[0009]

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⁴ , 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 characterized by containing a triazinyl stilbene 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 an example of the structure of the organic electroluminescence device of the present invention, in which 1 is a substrate, 2 is an anode, and 3 is a substrate.
Represents a hole transport layer, 4 represents an organic light emitting layer, and 5 represents a cathode. The substrate 1 serves as a support for the organic electroluminescence device of the present invention, and a plate of quartz or glass, a metal plate or a metal foil, a plastic film or a sheet, and the like are used, and a glass plate, polyester, polymethacrylate. A transparent synthetic resin substrate such as polycarbonate, polysulfone, or the like is preferable.

An anode 2 is provided on the substrate 1, which is usually aluminum, gold, silver, nickel,
It is composed of a metal such as palladium or 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). The anode is usually formed by a sputtering method, a vacuum vapor deposition method or the like, but metal fine particles such as silver or copper iodide,
In the case of carbon black, conductive metal oxide fine particles, conductive polymer fine powder, etc., they can be formed by dispersing them in a suitable binder resin solution and applying them 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. 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, but when the transparency is required, it is desirable that the visible light has a transmittance of 60% or more, preferably 80% or more. Is usually 5 to 1000 nm, preferably 10 to 50
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 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. The material used for the cathode 5 may be the material for the anode, but a metal having a low work function is preferable for efficient electron injection, and tin, magnesium, indium, aluminum, silver or the like is preferable. Appropriate metals or their alloys are used. 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 at least one of the anode 2 and the cathode 5 to have good transparency as an organic electroluminescence device. From this, one of the anode 2 and the cathode 5 preferably has a film thickness of 10 to 500 nm, and is desired to have good transparency.

A hole transport layer 3 is provided on the anode 2. As the hole transport layer, holes from the anode are efficiently transported between the electrodes to which an electric field is applied toward the organic light emitting layer. Formed of a material that can. Usually, an organic hole transport material is used for the hole transport layer. As the organic hole transport material, the hole injection efficiency from the anode 2 is high, and
It is necessary that the material is 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 that serve as traps are hard to be generated during manufacturing or use. Examples of such an organic hole transport compound include 1,1-bis (4-di-).
Aromatic diamine compounds in which tertiary aromatic amine units such as p-tolylaminophenyl) cyclohexane are linked (JP-A-59-194393), 4,4'-bis [(N-1-naphthyl) -N- Aromatic amines containing two or more tertiary amines represented by phenylamino] biphenyl and having two or more condensed aromatic rings substituted by nitrogen atoms (Japanese Patent Laid-Open No. 234681/1993), a derivative of triphenylbenzene. Aromatic triamines 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), the molecule as a whole is three-dimensionally Asymmetric triphenylamine derivative
No. 129,271), 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 with an ethylene group (JP-A-4-264189). Gazette),
Aromatic diamine having styryl structure (JP-A-4-29)
No. 0851), one in which an aromatic tertiary amine unit is linked by a thiophene group (JP-A-4-304466), and a starburst type aromatic triamine (JP-A-4-304).
308688), a benzylphenyl compound (JP-A-4-364153), a compound in which a tertiary amine is linked by a fluorene group (JP-A-5-25473), a triamine compound (JP-A-5-239455), Bisdipyridylaminobiphenyl (JP-A-5-32063)
4), N, N, N-triphenylamine derivatives (JP-A-6-1972), aromatic diamines having a phenoxazine structure (Japanese Patent Application No. 5-290728),
Diaminophenylphenanthridine derivative (Japanese Patent Application No. 6-
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, may be mixed and used.

In addition to the above compounds, polyvinyl carbazole and polysilane (App, which are hole-transporting polymers).
l. Phys. Lett. , 59, 2760, 19
9 etc.), polyphosphazene (Japanese Patent Laid-Open No. Hei 5)
-310949), polyamide (JP-A-5-31)
No. 0949), polyvinyl triphenylamine (Japanese Patent Application No. 5-205377), a polymer having a triphenylamine skeleton (Japanese Patent Laid-Open No. 4-133065), a polymer in which triphenylamine units are linked by a methylene group or the like ( S
ynthetic Metals, 55-57, 41
63, 1993), polymethacrylates containing aromatic amines (J. Polym. Sci., Poly.
m. 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 3. In the case of coating, a coating solution prepared by adding one or more organic hole-transporting compounds and a binder resin that does not become a hole trap, if necessary, and an additive such as a coating property improving agent such as a leveling agent, is dissolved. It is adjusted, coated 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, polyester and the like. If the binder resin is added in a large amount, it lowers the hole mobility, so a smaller amount is desirable,
It is preferably 50% by weight or less.

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 placed facing the crucible. When forming the organic hole transport layer, further as an acceptor,
Aromatic carboxylic acid metal complexes and / or metal salts (JP-A-4-320484), benzophenone derivatives and thiobenzophenone derivatives (JP-A-5-29536).
No. 1) and fullerenes (Japanese Patent Laid-Open No. 5-331458) at a concentration of 10 ⁻³ to 10% by weight to generate holes as free carriers and low voltage driving is possible. is there.

The thickness of the hole transport layer 3 is usually 10 to 30.
It is 0 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 3, an inorganic material can be used instead of the organic compound. 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. Examples include type zinc selenide. These inorganic hole transport layers are formed by a CVD method, a plasma CVD method, a vacuum deposition method, a sputtering method, or the like.

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

The compound used for the organic light-emitting layer 4 is required to have high electron injection efficiency from the cathode 5 and to efficiently transport 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. It is also required to play a role of emitting blue light when the holes and the electrons are recombined.

A more important condition required for the compound used for 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 examining the deterioration of the organic electroluminescent device, the present inventor has 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, since many organic compounds are molecular crystals in the solid state, even if they are in the amorphous state immediately after thinning, they should be crystallized with the passage of time. Is a common phenomenon. Whether such crystallization occurs depends largely on the glass transition temperature, and a thin film made of a material having a high glass transition temperature tends to be difficult to crystallize. Generally, since a good correlation is established between the glass transition temperature and the melting point, it can be considered that an organic compound having a high melting point exhibits a high glass transition temperature. As a result of diligent studies for preventing the crystallization of the thin film, the present inventor has found that the 4,4′-bis-triazinyl stilbene derivative has a very high melting point of 300 ° C. or higher and gives a uniform amorphous thin film. It was found that it is hard to crystallize, is thermally stable, and has a favorable effect on the stability of the device.

In the present invention, 4,4 'represented by the above general formula (I) is used as the organic light emitting layer of the organic electroluminescent device.
By using the -bis-triazinyl stilbene derivative, stable device characteristics can be obtained for a long period of time. In the general formula (I), Ar ¹ , Ar ² and A are preferred.
r ³ and Ar ⁴ each independently represent a phenyl group which may have a substituent, a naphthyl group, an anthryl group, a biphenyl group, a pyridyl group or a thienyl group, wherein the substituent is a halogen atom; methyl. Carbon number such as group and ethyl group
~ 6 alkyl groups; alkenyl groups such as vinyl groups; methoxycarbonyl groups, ethoxycarbonyl groups and other carbon atoms 1 to 6
6 alkoxycarbonyl group; C1-6 alkoxy group such as methoxy group and ethoxy group; aryloxy group such as phenoxy group and benzyloxy group; dialkylamino group such as amino group, dimethylamino group and diisopropylamino group; A cyano group and a hydroxyl group.

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

Specific preferred examples of the 4,4'-bis-triazinyl stilbene derivative represented by the general formula (I) are shown in Table 1 below, but the invention is not limited thereto.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

All of the exemplified compounds shown in Tables 1 to 3 above are high melting point compounds. For example, compound (1) is 39
0 ° C or higher, Compound (2) is 373 ° C, Compound (3) is 3
85 ° C, compound (8) 375 ° C, compound (9) 42
The compound (12) has a temperature of 306 ° C at 0 ° C or higher. The thickness of the organic light emitting layer 4 is usually 10 to 200 nm, preferably 30.
-100 nm.

The same method as for the organic hole transport layer is used for the organic light emitting layer.
Can be formed by, but usually vacuum deposition method is not used.
Be done. Improves the luminous efficiency of the device and changes the luminescent color.
For the purpose of obtaining, for example, aluminum 8-hydroxyquinoline
For lasers such as coumarin, using the aluminum complex as a host material
Doping with a fluorescent dye (J. Appl. Phy
s. , 65, 3610, 1989).
You. Also in the present invention, the above 4,4'-bis-triazine
Nylstilbene derivative as host material for laser
10 fluorescent dyes ^-3By doping 10 mol%
Therefore, the light emission characteristics of the device can be further improved.

The structure of the organic electroluminescent device of the present invention includes the following layered structures:

[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. The compounds used in this electron transport layer include
It is required that the electron injection from the cathode be easy and that the electron transporting capacity should be even greater. As such an electron transport material,

[0034]

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[0035]

[Chemical 4]

Oxadiazole derivatives such as (App
l. Phys. Lett. , 55, 1489, 19
1989; Jpn. J. Appl. Phys. , 31 volumes,
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 layer structure, the interface layer is for improving the contact between the cathode and the organic layer, and is an aromatic diamine compound (Japanese Patent Application No. 5-48075).
No.), quinacridone compound (Japanese Patent Application No. 5-116204)
No.), naphthacene derivatives (Japanese Patent Application No. 5-116205)
No.), organosilicon compounds (Japanese Patent Application No. 5-116206)
No.), 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 interface layer material may be provided near the cathode interface of the organic light emitting layer and the electron transport layer.

Incidentally, it is also possible to have a structure opposite to that of FIG. 1, that is, the cathode 5, the organic light emitting layer 4, the hole transport layer 3 and the anode 2 may be laminated in this order on the substrate, and at least as described above. It is also possible to provide the organic electroluminescent element of the present invention between two substrates, one of which is highly transparent. Similarly, it is also possible to stack in a structure opposite to the above-mentioned layer structure.

[0039]

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

An indium tin oxide (ITO) transparent conductive film having a thickness of 120 nm deposited on a glass substrate is ultrasonically cleaned with acetone, washed with pure water, ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen, and UV / ozone. After the 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 the organic hole transport layer material, 4,4'-bis [(N-1-naphthyl) -N-phenylamino] biphenyl (H1) shown below is used.

[0042]

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[0045] was placed in a ceramic crucible in advance, and vapor deposition was performed by heating with a tantalum wire heater around the crucible. The temperature of the crucible at this time was controlled in the range of 150 to 180 ° C. The degree of vacuum during vapor deposition is 1.1 to 0.9 × 10 ^-6 Tor.
The organic hole transport layer 3 having a film thickness of 60 nm was obtained at a deposition time of 2 minutes and 30 seconds at r. Next, as a material of the organic light emitting layer 4, Table 1
The 4,4′-bis-triazinyl stilbene derivative (1) shown in (4) 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 during vapor deposition is 3.7 to 1.1.
× 10 ^-6 Torr, evaporation time 4 minutes 10 seconds, film thickness 60
was nm.

Finally, as a cathode, a mixture of magnesium and silver
Gold electrode is vapor-deposited with a film thickness of 150 nm by the two-source simultaneous vapor deposition method.
did. Vapor deposition uses a molybdenum boat and the degree of vacuum is 4 ×
10 ^-6Torr, vapor deposition time is 2 minutes and 40 seconds, and it is a glossy film.
was gotten. The atomic ratio of magnesium to silver is 10: 1.5.
Met. I of the organic electroluminescent device produced in this way
Plus to TO electrode (anode), magnesium / silver alloy electrode
When a negative DC voltage is applied to the (cathode),
The element emits a uniform yellow-green color, and the peak wavelength of the emission is
It was 560 nm.

Immediately after preparation of the above-mentioned device and in dry nitrogen 5
The results of the emission characteristics after storage for 2 days are shown in the table below.
No remarkable increase in driving voltage was observed, 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 in the organic light emitting layer. Therefore, when a voltage is applied using both conductive layers as electrodes, stable light emission characteristics can be obtained over a long period of time.

Therefore, the EL element 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) making 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.

[Explanation of symbols]

 1 Substrate 2 Anode 3 Hole Transport Layer 4 Organic Light Emitting Layer 5 Cathode

Claims (1)

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