JPH0468076A - Electroluminescent element - Google Patents

Abstract

PURPOSE:To prepare an electroluminescent element emitting various hues of light and improved in durability by holding an org. compd. layer constituted of a specified org. compd. between an anode and a cathode. CONSTITUTION:An org. compd. of formula I [wherein Ar is an (un)substd. carbocyclic or heterocyclic arom. ring (e.g. phenyl, naphthyl, biphenyl, pyridyl or thiophenyl); (n) is 3-6] (e.g. the compd. of formula II) is made into a thin film by vacuum evaporation or soln. coating to prepare a mono- or multi-layered org. compd. layer (0.05-0.5mum in thickness) contg. a layer constituted at least of the compd. I. The org. compd. layer is held between an anode and a cathode formed on a substrate.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has a light-emitting layer made of a light-emitting substance, and by applying an electric field, the applied energy of the electric field can be directly converted into light energy. 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) Intrinsic electroluminescence type light emitting device is generally made of ZnS with Mn and Cu.
The luminescent material is an inorganic compound added with
Requiring a high alternating current electric field of 200μ or more for driving;
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. 4,539,5Q7, JP-A-63-
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, an electroluminescent device consisting of an anode, an organic hole transport layer, a light emitting layer, an organic electron transport layer, and a cathode is reported, and the materials used for these include N as the organic hole transport material. .

N'-diphenyl-N,N'-bis(3-methylphenyl)-1゜1'-biphenyl-4,4'-diamine,
In addition, as organic electron transport materials, 3, 4, 9.10
-perylenetetracarboxylic acid bisbenzimidazole and phthaloperinone are exemplified as luminescent materials.

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 in brightness, diversification of emission wavelengths to enable precise selection of blue, green, and red emission hues when considering application to full-color displays, and improvement of durability. The reality is that there are.

[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 diversity in emission wavelengths.

It is an object of the present invention to provide an electroluminescent element that exhibits various luminescent hues and has excellent durability.

[Means to solve the problem]

As a result of intensive studies on the constituent elements of a light-emitting layer to solve the above problems, the present inventors found that an electroluminescent layer composed of an anode, a cathode, and one or more organic compound layers sandwiched between the anode and cathode. An electroluminescent device is effective for solving the above problem, in which 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 component. This discovery led to the completion of the present invention.

◎HA r). (1) (However, Ar represents a substituted or unsubstituted carbocyclic aromatic ring or a substituted or unsubstituted heterocyclic aromatic ring.

Further, n represents an integer of 3 to 6. ) In the general formula (1), examples of Ar include phenyl group, naphthyl group, biphenyl group, pyridyl group, and thiophenyl group.

Next, specific examples of the compound represented by the general formula (1) used in the present invention will be shown, but the present invention is not limited thereto.

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 less than 2 tones, more preferably 0.05p.
It is constructed by forming an organic compound layer by thinning it to a thickness of m-0.5 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,
It has a structure in which an anode, a light-emitting layer, and a cathode are sequentially provided on a substrate.

The electroluminescent device shown in FIG. 1 is particularly useful when a single compound is used that has hole-transporting properties, electron-transporting properties, and luminescent properties, or when a mixture of compounds having each of these properties is used. .

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, since the light-emitting substances differ depending on the organic compounds used in combination, 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 as a further advancement of the above-mentioned concept 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.

It not only makes selection easy, but also allows the use of various compounds with different emission wavelengths, which has many advantages, such as diversifying the emission hues 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.

Further, in the present invention, Ar in the general formula (1)
Alternatively, by appropriately selecting the type of substituent, 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 components for forming the light emitting layer.

In the present invention, one light-emitting layer forming component is the general formula (
The compound shown in 1) is used, but if necessary, an aromatic tertiary amine or N,N'-diphenyl-N,N'-bis(3-methylgenyl)-1 is used as a hole-transporting compound. , 1'-biphenyl-4,4'-diamine, etc., and as an electron transporting compound, aluminum trisoxine or a perylentitracarboxylic acid derivative can be used.

The electroluminescent device of the present invention emits light by applying an electrical bias to the light-emitting layer, but a slight pinhole may cause a short circuit and cause the device to no longer function, so film formation is necessary to form the light-emitting layer. It is desirable to use compounds with excellent 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, poly-N-vinylcarbazole, polymethyl methacrylate, polymethyl acrylate, polyester,
Examples include polycarbonate and polyamide. In addition, in order to improve the charge injection efficiency from the electrode,
It is also possible to separately provide a charge injection transport layer between the electrodes.

The anode materials include nickel, gold, platinum, palladium, their alloys, metals with large work functions such as tin oxide (SnO□), indium tin oxide (ITO), iodide steel, their alloys and compounds, and even polyester. (3-methylthiophene), a conductive polymer such as polypyrrole, etc. 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.6 In the present invention, it is preferable that a transparent anode be formed on a transparent substrate and configured as shown in FIGS. 1 to 3. In some cases, the opposite configuration may be used. Moreover, glass, plastic film, etc. can be used as the transparent substrate.

Furthermore, in the present invention, a separate protective layer is provided in order to improve the stability of the electroluminescent device obtained in this manner, particularly for protection against atmospheric moisture.

The entire device may be placed in a cell and silicone oil or the like may be sealed therein.

〔Example〕

The present invention will be described in more detail below based on Examples.

Example 1 Size 3mm x 3m+++, thickness 5 on a glass substrate
A hole transport system consisting of an anode made of indium tin oxide (ITO) and a benzidine derivative represented by the following structural formula (a) on top of the anode is made of indium tin oxide (ITO). F 500 layers, a light emitting layer of 1000 layers made of the above compound Not, and a cathode made of 1500 layers of silver/magnesium alloy (silver 7.7 atomic percent, purity 99.9%) were each formed by vacuum evaporation, as shown in FIG. A device like this was fabricated. The degree of vacuum during vapor deposition is approximately 1X
10-' Torr, and the substrate temperature is room temperature. When a DC power source was connected to the anode and cathode of the device thus fabricated via lead wires and a voltage of 30 V was applied, a current with a current density of 70 mA/ci was applied to the device, and clear blue light was emitted for a long time. confirmed over the years.

From this example, it is understood that the compound NQI used in the present invention functioned as an electron transporting luminescent material.

Example 2 The anode and A device as shown in FIG. 2 was produced by sandwiching the material between cathodes. When this element was driven in the same manner as in Example 1, 2
A current of 30 mA/j was passed through the device at 0 V, and clear blue light emission was observed for a long time.

From this example, it is understood that the compound Nα2 used in the present invention functioned as a hole-transporting luminescent material.

Examples 3 to 4 The following results were obtained in the same manner as in Example 2, except that the compound shown below was used in place of Compound Ma 2 used in Example 2.

Example 5 Using the substrate used in Example 1, the compound Nα was placed on the anode.
A light emitting layer of 1,000 layers consisting of 2, an anode, and a cathode of 1,500 layers of silver/magnesium alloy were each fabricated by vacuum evaporation under the same conditions as described above. When this device was driven in the same manner as in Example 1, a current of 20 mA/d at 20 V flowed through the device, and clear blue light emission was observed over a long period of time.

From this example, it is understood that the compound Na2 used in the present invention functioned as a light emitting element even in a single layer.

〔Effect of the invention〕

Since the electroluminescent device of the present invention uses the compound represented by the general formula (I) as a constituent material of the organic compound layer,
Even with a low driving 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.

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

[Brief explanation of drawings]

1 to 3 are schematic cross-sectional views of an electroluminescent device according to the present invention. Patent applicant Rico Co., Ltd.

Claims (3)

[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.▼ (However, Ar represents a substituted or unsubstituted carbocyclic aromatic ring, a substituted or unsubstituted heterocyclic aromatic ring, and n represents an integer from 3 to 6. .) (2) In general formula (I), Ar is a phenyl group,
The electroluminescent device according to claim 1, which is a naphthyl group, a biphenyl group, a pyridyl group, or a thiophenyl group. (3) The electroluminescent device according to claim 1 or claim 2, wherein the organic compound layer has a thickness of 0.05 to 0.5 μm.