JPH03163186A - Electroluminescent element - Google Patents

Abstract

PURPOSE:To obtain an electroluminescent element comprising an anode, a cathode, and one or more organic compound layers provided therebetween, which can emit high-luminance light of various luminescent colors and has improved durability, by employing at least one layer made of a specific organic compound as the organic compound layer. CONSTITUTION:An electroluminescent element comprising an anode, a cathode and one or more organic compound layers provided therebetween, wherein at least one of the organic compound layers is a layer made of an organic compound represented by the formula [wherein R is a (substituted) aromatic residue or a heterocyclic residue].

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has a light-emitting layer made of a luminescent substance, and by applying an electric field, the electric field applied energy can be directly converted into light energy, which makes it possible to ．． The present invention relates to an electroluminescent device that, unlike fluorescent lamps or light emitting diodes, enables the realization of large-area planar light emitters.

[Conventional technology]

Electroluminescent elements differ in their luminescence excitation mechanisms; (1) intrinsic electroluminescent elements, which excite a luminescent body by local movement of electrons and holes within the luminescent layer, and emit light only in an alternating electric field;
2) Carrier injection type electroluminescent devices that excite a luminescent material by injecting electrons and holes from an electrode and recombining them within a luminescent layer, and operate in a DC electric field. (1) The intrinsic electroluminescence type light emitting device is generally made of ZnS and Mn-Cu.
The light-emitting body is a Retsuki compound with the addition of
Requiring a high AC electric field of 200V or more for activation;
It has many problems such as high manufacturing cost and insufficient brightness and durability.

The carrier injection type electroluminescent device (2) has become capable of achieving high luminance since thin film-like organic compounds have been used as the light emitting layer. For example, JP-A-59-19
4393. U.S. Patent No. 4,539,507, Japanese Unexamined Patent Publication No. 1983-
No. 295,695, U.S. Pat. Typical examples of such materials include aromatic tertiary amine as an organic hole injection and transport material, and aluminum trisoxine as an organic electron injection luminescent material.

Also, Jpn. Journal of Applied
Physicd, vol. 27, p. 713-715 reports an electroluminescent device consisting of an anode, an organic hole transport layer, a light emitting layer, an organic electron transport layer, and a cathode.
The materials used for these include N,N'-diphenyl-N,N'-bis(3
-methylphenyl)-1,1'-biphenyl-4,4'
- Diamine is also used as an organic electron transport material.
, 4,9.10-perylenetetracarboxylic acid bisbenzimidazole is exemplified, and lid perinone is exemplified as a luminescent material. These examples demonstrate that in order to use organic compounds as hole-transporting materials, luminescent materials, and electron-transporting materials, it is necessary to explore various properties of these organic compounds and effectively combine these properties to create electroluminescent devices. In other words, it shows that research and development of a wide range of organic compounds is necessary.

Furthermore, research on carrier-injection electroluminescent devices using organic compounds as light emitters, including the examples mentioned above, has a short history, and research into materials and device development has not yet been sufficiently conducted. However, there are many issues to be solved, such as further improvement of brightness, diversification of emission wavelengths to enable precise selection of blue, green, and red emission hues when considering application to full-power color displays, and improvement of durability. The reality is that

[Problem to be solved by the invention]

The present invention has been made in view of the above-mentioned state of the prior art, and its purpose is to provide an electroluminescent element that has diversity in emission wavelength, exhibits various emission hues, and has excellent durability.

[Means to solve the problem]

As a result of intensive study on the constituent elements of the light-emitting layer to solve the above problems, the present inventors discovered that an electric field composed of a PJh electrode, a cathode, and one or more organic compound layers sandwiched between them. In the light emitting device, an electroluminescent device characterized in that at least one of the organic compound layers is a layer containing an organic compound represented by the following general formula (1) as a constituent is effective for solving the above problem. We have discovered something and have completed the present invention.

(R represents a substituted or unsubstituted aromatic residue or heterocyclic residue.) In general formula (1), examples of carbocyclic or heterocyclic aromatic rings used as R include phenyl, naphthyl, , anthrinole, acenaphthenyl, fluorenyl, phenanthryl, pyridyl, pyrimidyl, furanyl, virolyl, thiophenyl, ki? Lyle, penzofuranyl, penzothiophenyl, indolyl. Examples include carbazolyl, penzoxazolyl, and quinoxalyl. Moreover, the following can be mentioned as a substituent of R in general formula (1).

(1) Halogen atom, trifluoromethyl group, cyano group, nitro group (2) Alkyl group; preferably C1 to C2. Especially C
1 to C12 linear or branched alkyl group, and these alkyl groups further include a hydroxyl group, a cyano group, and a C1 to C12 alkyl group.
an alkoxy group, phenyl group or halogen atom of tZ,
It may contain a phenyl group substituted with an alkyl group of Ce to Ce2 or an alkoxy group of Ce to Ce2.

(3) Alkoxy group (-OR');R" represents anolekyl group defined in (2).

(4) Aryloxy group: Examples of the aryl group include phenyl and naphthyl groups, which may contain a C1 to CXZ alkoxy group, a C2 to C2 alkyl group, or a halogen atom as a substituent.

(5) Alkylthio group (-SR''): R1 represents the alkyl group defined in (2).

? It represents an acyl group or an aryl group such as an alkyl group, an acetyl group, or a benzoyl group as defined in 2), and examples of the aryl group include a phenyl group, a biphenylyl group, or a naphthyl group, and these are an alkoxy group of 00 to 01■, It may contain a C1 to C12 alkyl group or a halogen atom as a substituent. Furthermore, n2 and R3 may form a ring together with the nitrogen atom, such as in a piperidyl group or a morpholyl group. It may also form a ring jointly with the carbon atom on the aryl group, as in the case of the eurolidyl group. (7) Alkoxy carbonyl group (-COOR');R'
represents an alkyl group defined in (2) or an aryl group defined in (4).

(8) Acyl group (-COR'), sulfonyl group (-SO
, R'), represents the defined meaning. However, this excludes the case where R2 and R3 jointly form a ring with the carbon atoms on the aryl group.

(9) Alkylene dioxy group or alkylene dithio group such as methylene dioxy group or methylene dithio group Next, specific examples of the compound represented by the general formula (I) used in the present invention will be shown. It is not limited.

[Example of Chemical Table of Compound of General Formula (1)] The electroluminescent device of the present invention is produced by applying the organic compound described above by vacuum evaporation, solution coating, etc., so that the total thickness of the organic compound as a whole is smaller than 2, more preferably ,0.05p
It is constructed by forming an organic compound layer by thinning it to a thickness of m-0.5,n and sandwiching it between an anode and a cathode.

Hereinafter, the present invention will be explained in more detail along the drawings.

FIG. 1 shows a typical example of the electroluminescent device of the present invention,
The electroluminescent device according to FIG. 1, which has a structure in which an anode, a light-emitting layer, and an lla electrode are sequentially provided on a substrate, uses a single compound and has hole-transporting properties, electron-transporting properties, and luminescent properties. This is particularly useful when using a mixture of compounds with individual characteristics. FIG. 2 shows a light-emitting layer formed by a combination of a hole-transporting compound and an electron-transporting compound. This configuration combines the favorable properties of organic compounds, and by combining compounds with excellent hole transport properties or electron transport properties, it is possible to smoothly inject holes or electrons from the electrodes to obtain an element with excellent light emitting properties. That is. Note that in the case of this type of electroluminescent device, the luminescent substance differs depending on the organic compound used. It is not possible to unambiguously determine which compound emits light.

Figure 3 shows a light-emitting layer formed by a combination of a hole-transporting compound, a luminescent compound, and an electron-transporting compound, and this can be considered to be a type of layer that further advances the above idea of functional separation. .

This type of electroluminescent device can be obtained by appropriately combining compounds that have hole-transporting properties, electron-transporting properties, and luminescent properties, so the range of compounds that can be used is extremely wide, making it easy to select them. Not only that, but also various compounds having different emission wavelengths can be used, which has many advantages such as diversifying the hue of the emitted light of the device.

All of the compounds of the present invention have excellent luminescent properties, and can have structures as shown in FIGS. 1, 2, and 3, if necessary.

Furthermore, in the present invention, by appropriately selecting R or the type of substituent in the general formula (I), it is possible to provide both a compound with excellent hole transport properties and a compound with excellent electron transport properties.

Therefore, in the case of the configurations shown in FIGS. 2 and 3, two or more types of compounds represented by the general formula (1) may be used as a component of the light emitting layer.

In the present invention, the above general formula (
The compound represented by I) is used, but if necessary, an aromatic tertiary amine or N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1 is used as a hole-transporting compound. .1'-biphenyl-4,4'-diamine, etc., and aluminum trisoxine, perylenetetracarboxylic acid derivatives, etc. can be used as the electron transporting compound.

In the electroluminescent device of the present invention, the light emitting layer is electrically biased. However, a slight pinhole may cause a short circuit and the device may no longer function, so it is desirable to use a compound with excellent emissive layer shape or film-forming properties. Furthermore, a light-emitting layer can be formed by combining such a compound with excellent film-forming properties with, for example, a polymer binder. Polymer binders that can be used in this case include polystyrene, polyvinyltoluene, polyN-vinylcarbazole, polymethyl methacrylate, polymethyl acrylate, polyester, polycarbonate, polyamide, and the like. Further, in order to improve the efficiency of charge injection from the electrode, it is also possible to separately provide a charge injection transport layer between the electrode and the charge injection transport layer.

The anode materials include nickel, gold, platinum, palladium, alloys thereof, metals with large work functions such as oxide (SnQ), indium tin oxide (I-0), copper iodide, alloys and compounds thereof, and For example, conductive bonomers such as poly(3-methylthiophene) and polyvirol can be used.

On the other hand, as the cathode material, silver, tin, lead, magnesium, manganese, aluminum, or an alloy thereof, which has a small work function, is used. It is desirable that at least one of the materials used for the anode and the cathode be sufficiently transparent in the emission wavelength region of the device. Specifically, it is desirable to have a light transmittance of 80% or more.

In the present invention, it is preferable that the transparent anode be formed on a transparent substrate and have the structure shown in FIGS. 1 to 3, but the opposite structure may be used depending on the case. Moreover, glass, plastic film, etc. can be used as the transparent substrate.

In addition, in the present invention, in order to improve the stability of the electroluminescent device obtained in this way, and in particular to protect it from atmospheric moisture, it is possible to provide a separate protective layer, or to place the entire device in a cell using silicone. It is also possible to enclose oil or the like.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Size 3 vs. X 3+u*. on a glass substrate. Thickness 50
An anode made of indium tin oxide (ITO) containing 10% of indium tin oxide (ITO) was formed, and on top of the anode was formed an anode of 500% hole transport consisting of a triphenylamine derivative represented by the following structural formula (a), and an electron transporting material consisting of the compound NQ5 [1000%, 1,500 cathodes made of a silver/magnesium alloy (7.7 atomic percent silver, 99.9% purity) were each formed by vacuum evaporation, and the device shown in FIG. 2 was fabricated. The degree of vacuum during vapor deposition was approximately I x 10-' Torr, and the substrate temperature was room temperature.

A DC power supply was attached to the anode and cathode of the device thus fabricated via lead wires, and when a voltage of 30V was applied, a current with a current density of 67+A/cs+" flowed through the device.
Clear yellow light emission was observed over a long period of time. From this example, it is understood that the compound NQ5 used in the present invention functioned as an electron-transporting luminescent material. Examples 2 to 5 The following results were obtained by carrying out the same operation as in Example 1, except that the compound shown below was used in place of the compound NQ5 used in Example 1.

Examples 6 to 9 Implemented except that the compound shown below was used as the hole transport layer instead of the compound Nl15 used in Example 1, and the oxadiazole derivative represented by the following structural formula (b) was used as the electron transport layer. The procedure was carried out in the same manner as in Example 1, and the following results were obtained.

From this example, the compounds Nα1, Nα2, Na
It is understood that IO, NQ12 functioned as an electron-transporting luminescent material.

Example 10 Using the substrate used in Example 1, the compound Nα was placed on the anode.
Light emission consisting of 1/fi1000. As the 113 electrodes, cathodes made of a silver/magnesium alloy were each manufactured by vacuum evaporation under the same conditions as described above. When this element was opened and operated in the same manner as in Example 1, 30 ll was generated at 30 V.
A current of 1A/c♂ was passed through the device, and clear yellow-green light was observed for a long time.

From this example, it is understood that the compound Nal used in the present invention functioned as a light emitting element even in a single layer.

Example 11 Using the substrate used in Example 1, the above structural formula (
a) Hole transport M made of the triphenylamine derivative shown in 600 pieces, Luminescence 1 made of the compound NQI
600A. 600 electron transport layers made of the oxadiazole derivative represented by the structural formula (b) and a silver/magnesium alloy were successively formed as a cathode by vacuum evaporation under the same conditions as in Example 1, as shown in FIG. We fabricated a device like this. When this device was driven in the same manner as in Example 1, 30
A current of 35 mA/cm'' was passed through the device at V, and clear yellow-green light emission was observed for a long time.

Example 12 Thickness 1. A 1 mm thick alkali-free borosilicate glass was used as a substrate, and after thorough cleaning, an anode made of an ITO thin film with a thickness of about 50 OA was formed on this glass substrate by electron beam evaporation.

Next, the compound kl was vacuum-deposited on this anode to form a hole transport layer with a thickness of 800 mm. Next, 8-hydroxyquinoline aluminum shown below was evaporated to a thickness of about 800 mm on the hole transport layer to form an electron transport layer, and magnesium was further evaporated to a thickness of about 1 mm to form a cathode. An electroluminescent device with the structure shown in Figure 2 was fabricated. Note that the material after the hole transport layer was evaporated by resistance heating. Next, pull out the lead wires from the anode and cathode and apply direct current 7.
When I connected it to the 11 source and passed a current through it, clear light emitted.
It was also confirmed that this electroluminescent device had the following characteristics. Emission color: Yellow-green Emission starting voltage: +5.5ν Intoxicating current: 0.5 to 3 mA/cm” Example 1
3-14 Compound Nα1 which is a hole transport substance in Example 12
Electroluminescent devices of Examples 13 and 14 were obtained in the same manner as in Example I2, except that the compounds shown in Table 1 were used instead of. Table 1 shows the characteristics of these electroluminescent devices.

Table-1 Example 15 Thoroughly cleaned thickness: 1.1! A PJh electrode was formed by vapor-depositing about 200 pieces of gold onto all alkali-free borosilicate glass.

Next, the compound Ma4 was vacuum-deposited on the anode to a thickness of 8.
00 large hole transport layer was provided.

Next, the following 12-phthalobenonone derivative was deposited on the hole transport layer to a thickness of about 1,500 nm to form a light emitting layer.

Further, on top of this, approximately 1,000 ml of the following perylene derivative was deposited to provide an electron transport layer, and on top of this, approximately 1,000 ml of aluminum was evaporated as a cathode to produce an element with a structure as shown in Figure 3. did. All materials were evaporated by resistance heating. When the lead g was pulled out from the cathode and the cathode, and a direct current was applied to it, clear light emission was observed.

Furthermore, it was confirmed that this electroluminescent device had the following characteristics.

Emission color: Yellow-orange Emission starting voltage: +18V Emission starting voltage -5-50 mA/am" Example 16 Compound Na4, which is the hole transport substance in Example 15
An electroluminescent device of Example 16 was obtained in the same manner as Example 15 except that Compound 5 was used instead of Compound 5.

It was confirmed that this electroluminescent element had the following characteristics.

Emission color: Yellow-orange Emission starting voltage: +16 V Intoxicating current: 5 to 50 mA/cm" [Effects of the Invention] The electroluminescent device of the present invention Since the compound represented by the general formula (I) was used as a material,
Even with a low rotational voltage, it is possible to obtain high-brightness light emission for a long period of time, and it is also possible to exhibit various color tones.

Furthermore, since the device can be easily fabricated by vacuum evaporation or the like, it has the advantage of being able to efficiently produce large-area devices at low cost.

[Brief explanation of the drawing]

1 to 3 are schematic cross-sectional views of an electroluminescent device according to the present invention.

Claims (1)

[Claims] (1) In an electroluminescent device composed of an anode and a cathode, and one or more organic compound layers sandwiched between them, at least one of the organic compound layers is represented by the following general formula (I). An electroluminescent device characterized by having a layer containing an organic compound as a constituent component. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (R represents a substituted or unsubstituted aromatic residue or heterocyclic residue.)