JPH05217675A - Electroluminescence element - Google Patents

Abstract

PURPOSE:To increase the brightness using a simple constitution and enhance the light emission efficiency without change of the light emission wavelength by including metal atoms in a part of a light emission layer. CONSTITUTION:An electroluminescent element is composed of a positive electrode 5, a negative electrode 1, and a light emission layer or layers 2 made of organic compound pinched by the two electrodes, wherein a metal inclusive layer 3 is provided in a part of the light emission layer 2. Examples of the metal are silver, tin, lead, magnesium, and aluminum, or further nickel, gold, plutinum, etc. The metal inclusive layer 3 may be produced through co- evaporation with the material to light emission layer or insertion of a metal thin layer. Thereby the brightness can be increased without changing the light emission wavelength and requiring any complicated constitution, and also the light emission efficiency be enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a light emitting layer made of a light emitting material, and can directly convert electric energy into light energy by applying an electric field, which is different from conventional incandescent lamps, fluorescent lamps or light emitting diodes. Differently, the present invention relates to an electroluminescence device that enables realization of a large-area planar light-emitting body.

[0002]

2. Description of the Related Art An electroluminescence device has an intrinsic electroluminescence device which emits light only in an alternating electric field by (1) exciting a light emitter by local movement of electrons and holes in a light emitting layer due to a difference in emission excitation mechanism. The element is divided into (2) a carrier injection type electroluminescent element that operates by a DC electric field by injecting electrons and holes from an electrode and recombining the electrons and holes in the light emitting layer to excite a luminescent body. The intrinsic electroluminescence type light emitting device of (1) is generally ZnS.
An inorganic compound to which Mn, Cu, etc. are added is used as a light emitter, but it requires a high AC electric field of 200 V or more for driving, high manufacturing cost, insufficient brightness and durability, etc. Has many problems.

In the carrier injection type electroluminescent device (2), a thin film organic compound has been used as a light emitting layer, and a high brightness device has been obtained. For example, JP-A-59-194393, U.S. Pat. No. 4,539,507,
Japanese Patent Laid-Open No. 63-2956695, US Pat. No. 4,720,4
32 and Japanese Patent Laid-Open No. 63-264692 disclose an electroluminescent device comprising an anode, an organic hole injecting and transporting zone, an organic electron injecting luminescent material and a cathode. Examples of materials used for these are organic materials. Aromatic tertiary amines are representative examples of hole injecting and transporting materials, and aluminum trisoxine and the like are representative examples of organic electron injecting light emitting materials.

In addition, Jpn. Journal of A
applied Physicd, vol. 27, p71
3-715 reports an electroluminescent device comprising an anode, an organic hole transport layer, a light emitting layer, an organic electron transport layer and a cathode. Materials used for these are N, N as organic hole transport materials. '-Diphenyl-N,
N′-bis (3-methylphenyl) -1,1′-biphenyl-4,4′-diamine, and as an organic electron transport material, 3,4,9,10-perylenetetracarboxylic acid bisbenzimidazole In addition, phthaloperinone is exemplified as the light emitting material.

In these examples, in order to use an organic compound as a hole transport material, a light emitting material, and an electron transport material, various characteristics of these organic compounds are sought, and these characteristics are effectively combined to form an electroluminescent device. It means that the research and development of a wide range of organic compounds is necessary.

Further, the carrier injection type electroluminescent device using an organic compound as a light emitting body, including the above examples, has a short history of research, and it can be said that research into its materials and devices is still sufficient. However, in reality, there are many problems such as further improvement of brightness, control of emission wavelength, and improvement of durability.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances of the prior art. It has a simple structure without changing the emission wavelength, has improved brightness, and has excellent emission efficiency. An object of the present invention is to provide an electroluminescent device.

[0008]

According to the present invention, in an electroluminescent device comprising an anode and a cathode and a light emitting layer composed of one or a plurality of layers of an organic compound sandwiched therebetween, a light emitting layer is provided. Provided is an electroluminescent device characterized in that metal atoms are mixed in a part thereof, and in particular, an electroluminescent device characterized in that the metal atoms in the light emitting layer are distributed in a thin layer form. To be done.

As a result of intensive studies on the constituent elements of the light emitting layer for solving the above problems, the present inventors have made up of an anode and a cathode and one or a plurality of organic compound layers sandwiched between them. In the electroluminescent device according to the present invention, the electroluminescent device in which a metal atom is mixed in a part of the light emitting layer is found to be effective for the above problems, and the present invention has been completed.

An example of the electroluminescent device of the present invention will be described below with reference to the drawings. In FIGS. 1, 2 and 3, 1 is a cathode, 2 is a light emitting layer, 3 is a metal mixed layer, 4 is a hole transport layer, 5 is an anode,
Reference numeral 6 is a substrate, and 7 is an electron transport layer. The conventional electroluminescent device does not have the metal-mixed layer 3 and cannot obtain sufficient brightness. However, the structure of the present invention can increase the brightness and improve the luminous efficiency. Becomes

In the electroluminescence device of the present invention, silver, tin, lead, magnesium, aluminum or nickel, gold, platinum or the like can be used as the metal atom material mixed in the light emitting layer. The metal-mixed layer 3 can be provided by co-evaporation with the light emitting layer material or by inserting a thin metal layer. In the case of co-deposition, it is preferable that the metal content is 1 to 5 mol%, and in the case of thin layer insertion, the insertion is 2 to 10 Å.

In the electroluminescent device of the present invention, examples of the organic compound forming the light emitting layer include anthracene compounds, naphthalene compounds, phenanthrene compounds,
Any known luminescent compound such as a pyrene compound, a chrysene compound, a perylene compound, a butadiene compound, a coumarin compound, an acridine compound, and a stilbene compound can be used.

The electroluminescent device according to the present invention is constituted by thinning the above-described luminescent compound by a vacuum vapor deposition method, a solution coating method or the like and sandwiching it between an anode and a cathode. At that time, plural kinds of other substances may be added to the compound as additives. Further, a charge injection / transport layer may be separately provided between the electrode and the electrode in order to improve the efficiency of charge injection from the electrode.

As the anode material, nickel, gold, platinum, palladium and alloys thereof, or metals having a large work function such as tin oxide (SnO ₂ ), indium tin oxide (ITO) and copper iodide, alloys and compounds thereof, Furthermore, conductive polymers such as poly (3-methylthiophene) and polypyrrole can be used.

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

The electroluminescent device of the present invention is constructed as a device by sequentially laminating each of the above layers on a transparent substrate such as glass. However, the stability of the device is improved, and particularly protection of moisture in the atmosphere is provided. Therefore, a protective layer may be separately provided, or the entire element may be put in a cell and silicon oil or the like may be enclosed.

[0017]

The present invention will be described in more detail with reference to the following examples. Example 1 A triphenylamine derivative represented by the following chemical formula 1 was vacuum-deposited on a glass substrate having an ITO anode having a surface resistance of 20Ω / □ to form a hole transport layer having a thickness of 500Å. Next, the bisstyrylanthracene derivative 200 shown in Chemical formula 2
Å, 5 Å of aluminum, and 300 Å of the bisstyrylanthracene derivative represented by Chemical formula 3 were sequentially laminated by vapor deposition to form a light emitting layer. Finally, a cathode made of aluminum was vacuum-deposited on 1500 L to prepare an electroluminescence device as shown in FIG. Also, for comparison, a similar device was manufactured except for the metal-mixed layer. The device thus obtained showed a luminance of 580 cd / m ² at a driving current of 50 mA / cm ² , and it was recognized that the luminance was significantly improved as compared with 75 cd / m ² of the comparative device. No change in emission wavelength was observed.

[Chemical 1]

[Chemical 2]

Example 2 As the light emitting layer material, the bisstyrylanthracene derivative represented by Chemical formula 3 was 100 Å, aluminum 5 Å, and Chemical formula 3
An electroluminescent device as shown in FIG. 1 was produced in the same manner as in Example 1 except that the bisstyrylanthracene derivative 400Å shown in FIG. The device thus obtained has a driving current of 50 mA / cm ² of 5
A luminance of 60 cd / m ² was exhibited, and a significant improvement in luminance was recognized as compared with 110 cd / m ² of the element excluding the metal-containing layer prepared for comparison. No change in emission wavelength was observed.

[Chemical 3]

[0019]

In the electroluminescent device of the present invention, since metal atoms are mixed in a part of the light emitting layer made of an organic compound,
Without changing the emission wavelength and without adopting a complicated configuration,
The brightness can be improved and the luminous efficiency is excellent.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an electroluminescent device according to the present invention.

FIG. 2 is a schematic cross-sectional view of another electroluminescent device according to the present invention.

FIG. 3 is a schematic cross-sectional view of another electroluminescent device according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cathode, 2 ... Light emitting layer, 3 ... Metal mixing layer, 4 ... Hole transport layer, 5 ... Anode, 6 ... Substrate, 7 ... Electron transport layer.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Chihaya Adachi 1-3-3 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (2)

[Claims] 1. An electroluminescent device comprising an anode and a cathode, and a light emitting layer composed of one or a plurality of layers of an organic compound sandwiched therebetween, wherein a metal atom is mixed in a part of the light emitting layer. An electroluminescent device characterized by the above. 2. The electroluminescent device according to claim 1, wherein the metal atoms in the light emitting layer are distributed in a thin layer.