JPH0337994A - Organic thin film luminous element - Google Patents

Abstract

PURPOSE:To obtain electrodes low in the deterioration of luminous characteristics and allowing formation with good repeatability by applying the chemical composition of Mg1-xInx(0.01<=x<=0.13) to one of the electrodes. CONSTITUTION:In an organic thin film luminous element made of a pair of electrodes 2 and 5 with at least one thereof transparent and clamping a luminous layer 4 made of one or more organic phosphors, the chemical composition of one 5 of the electrodes is Mg1-xInx(0.01<=x<=0.13). For film formation on the Mg1-xInx electrode, a co-deposition process may be used, but a normal vacuum deposition process can also be applied, using an alloy pellet. A slight deviation appears between the compositions of the pellet as a source and a formed alloy electrode film, but not so remarkable as in the case of magnesium and silver. Also, deposition controllability is substantially better than in the case of the co-deposition process, and excellent repeatability and uniformity are available. The Mg1-xInx cathode shows stable characteristics in the atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an organic thin film light emitting device used for flat light sources and displays.

(Conventional technology) EL (electroluminescent) devices made from organic materials are attracting attention as a means of realizing inexpensive large-area film-like full-color display devices due to their abundant materials and molecular-level synthesis technology. There is. For example, DC-driven organic thin-film light-emitting devices have been produced using fused polycyclic aromatic systems such as anthracene and perylene as raw materials and made into thin films by the LB method, vacuum evaporation method, etc., and their light-emitting characteristics have been studied. Furthermore, a new type of organic thin film light emitting device having a two-layer organic thin film structure has recently been reported and is attracting strong interest (Applied Physics Letters, Vol. 51, p. 913, 1987). As shown in FIG. 2, it has been reported that bright green light was obtained by using a metal chelate compound that emits strong fluorescence in the light emitting layer 24 and an amine material in the hole injection layer 23 of a conductive organic material on the front plate.

Finally, a metal cathode 25 is deposited to complete the organic thin film EL device. A brightness of several 100 cd/m2 was obtained by applying a direct current of 6 to 7 cm. The maximum luminous efficiency is 1.51m/W, which is close to the practical level.

In order to facilitate charge injection into the light-emitting layer 24 of this organic thin-film light-emitting device, a metal having a work function as low as possible is often used as the cathode 25, and magnesium is excellent in this respect. Although it is difficult to deposit magnesium due to a small deposition rate, by adding fa'ft silver by co-evaporation method, it becomes possible to form an electrode more uniformly than when magnesium is used alone. Adding too little silver will have no effect;
Moreover, if it is too large, the work function will increase, which is undesirable. Usually about 10 atom % of silver is added.

(Problems to be Solved by the Present Invention) However, it has been difficult to form a magnesium/silver cathode in which about 10 atomic % of silver is contained in magnesium by a co-evaporation method, as in conventional organic thin film light emitting devices. This is because magnesium has a relatively high vapor pressure and is sublimable.
This is because it is difficult to control the evaporation rate of magnesium at a constant rate, and it is not possible to obtain a uniform composition with good reproducibility. As a result, it has been difficult to produce electrodes that are stable for long periods of time even in the atmosphere with good reproducibility.

If there is only one evaporation source, it will be relatively easy to control the evaporation, but
Since silver hardly dissolves in solid solution in magnesium, even if magnesium/silver (10 atomic %) pellets were forcibly made, compositional deviations occurred during vapor deposition, making it difficult to form electrodes stably and with good reproducibility.

Furthermore, conventional cathodes are easily oxidized in the atmosphere, resulting in accelerated deterioration of the light emitting characteristics of the device and non-uniform light emission.

It is extremely important to reduce the rate of deterioration and to form a stable #, ultra-gold metal, including reproducibility, for the practical application of this organic thin film light emitting device. However, it has been difficult to solve these problems with conventional techniques.

An object of the present invention is to provide an organic thin film light-emitting element having electrodes that can be formed with good reproducibility and less deterioration in light-emitting characteristics.

(Means for Solving the Problems) Means provided by the present invention to solve the above-mentioned problems are as follows:
In an organic thin film light emitting device in which a light emitting layer made of at least one organic phosphor is sandwiched between a pair of electrodes, at least one of which is transparent, one of the electrodes is made of Mg1-, In.
This is an organic thin film light emitting device characterized by x (0,01≦x≦0.13).

(Function) When a magnesium/silver cathode is used by co-evaporation as in conventional organic thin film light emitting devices, it is difficult to produce an electrode that is stable for a long time even in the atmosphere with good reproducibility. The main causes of the above problems are that magnesium is sublimable and has a high vapor pressure, that the deposited film is chemically unstable, and that silver does not uniformly enter magnesium. On the other hand, it has been found that the chemical instability of deposited magnesium films can be largely resolved by appropriate alloying. Therefore, we searched for a metal that would be easy to vapor deposit and chemically stable, as an alternative to magnesium and silver, without sacrificing the advantages of magnesium, which is an excellent cathode material. The metal preferably has a high adhesion rate, a low work function, and can form an alloy with magnesium. As a result, it was discovered that Mg1-xInx (0,01≦x≦0.13) has excellent properties as a cathode of an organic thin film light emitting device, resulting in the present invention.

The Mg1-xInx (0,01≦x≦0.13) electrode may be formed by co-evaporation, or by ordinary vacuum evaporation using an alloy pellet. Although there is a slight difference in composition between the pellet serving as the source and the alloy electrode film formed, magnesium and silver are not included, and the vapor deposition controllability is much better than that of the co-evaporation method. Furthermore, the reproducibility and uniformity were excellent. Its work function was almost the same as that of magnesium and silver, and it did not deteriorate the light-emitting characteristics of organic thin-film light-emitting devices. Furthermore, M
g1-xIn! The cathode showed stable characteristics even in the atmosphere. This is thought to be because magnesium and indium form an alloy, resulting in a dense and uniform film.

If the Mg1-xInx (0,01≦x≦0.13) electrode is formed by sputtering, a dense electrode with less deviation in composition can be obtained. Like those formed by electron beam evaporation, the material exhibited stable properties even in the atmosphere.

In this way, Mg1-xInx (0,01≦x≦0.1
3) was used as a deposition source to form a cathode, the problems associated with conventional electrodes could be solved.

(Example) The present invention will be explained in detail below with reference to Examples.

(Example 1) As shown in FIG. 1, an ITO transparent electrode 2 was placed on a glass substrate 1.
While forming poly(methylphenylsilylene) about 60
N, N, N', N'-tetraphenyl- in weight%
An organic hole injection layer 3 made of polysilylene mixed with about 40% by weight of 4,4'-diaminobiphenyl was prepared by 1000 people.
It was formed by dip coating method using toluene solvent. After sufficiently drying, the organic luminescent material tris(8-hydroxyquinoline) aluminum was added as the luminescent layer 4.
It was formed using the 00A vacuum evaporation method. The substrate was not heated during vapor deposition, and the degree of vacuum was on the order of 10-6 [torr]. Finally, Mg
The back metal electrode 5 is formed into a 1500A shape by electron beam evaporation using an alloy pellet containing a mixture of In and In in a ratio of 10=1 to complete an organic thin film light emitting device. The degree of vacuum is 10-6 [torr]
There was one r.

When the luminescent properties of this element were measured in dry nitrogen, green luminescence of 300 cd/m2 was obtained by applying a DC voltage of about 8 cm. This organic thin film light-emitting element is used at a current density of 0.5 m.
When an aging test was conducted under the condition of A/am2, the luminance half-life was over 1000 hours. In conventional elements, 1
00 to 300 hours, the reliability of this device is significantly improved.

The present invention applies not only to tris(8-hydroxyquinoline)aluminum organic phosphors but also to anthracene, pyrene,
Similar effects were also observed with other organic substances such as tetracene, stilbene, perylene, quinone, phenanthrene, and naphthane derivatives. In addition, this organic phosphor has 10-5 to 1
By further adding other highly fluorescent organic molecules such as rhodamine, cyan, picun, coumarin, fluorene, POPOP, etc. in an amount of about 0-2 mo1, various luminescent colors can be obtained. In addition to ITO, the transparent electrode is made of ZnO:Al or 5n02:
Sb, Au, etc. may also be used.

Appropriate amount of indium to be mixed into magnesium was about 10 atomic %. If indium is 13 atomic % or more, it will not be a complete solid solution and a uniform composition will not be obtained. Furthermore, if the amount of indium is less than 1 atomic %, it will be easily oxidized in the atmosphere and will not exhibit stable characteristics.

(Example 2) Tritzelniamine and 12-phthaloperinone at 1O-6
Continuously 750A each in a vacuum of 1torr
.

It is formed by vacuum evaporation using resistance heating of about 800A. Thereafter, a cathode is formed by RF sputtering using a target of magnesium-indium alloy (In: 13 atomic %). The film thickness is approximately 150 OA. When the cathode was formed using this method, a film with good adhesion could be formed, and it was observed that the stability of the device was improved and the rate of brightness deterioration was reduced.

(Effects of the Invention) As explained above, the reliability could be significantly improved by the present invention.

The effects obtained by the present invention are as follows: ■Provide an element that exhibits little deterioration even when stored in the atmosphere.

■ Vapor deposition controllability, which was difficult with conventional vacuum evaporation methods for magnesium, has been significantly improved.

■We were able to improve the stability and reproducibility of device characteristics compared to conventional ones.

As described above, the present invention makes it possible to provide a practical level low voltage direct current driven thin film light emitting device, which has high industrial value.

[Brief explanation of drawings]

FIG. 1 shows a cross-sectional structure of an organic thin film light emitting device used in an example of the present invention. FIG. 2 shows a cross-sectional structure of a conventional organic thin film light emitting device. 1.22...Glass substrate, 2,22...ITO transparent electrode, 3.23-1. Organic hole injection layer, 24,4...
Light emitting layer, 25... Back electrode, 5... Mg:In alloy.

Claims (1)

[Claims] In an organic thin film light-emitting element in which a light-emitting layer made of at least one organic phosphor is sandwiched between a pair of electrodes, at least one of which is transparent, one of the electrodes is Mg_1_
An organic thin film light emitting device characterized in that -_xIn_x (0.01≦x≦0.13).