JPH097762A - Edge emitting organic thin film EL device - Google Patents

Abstract

(57) [Summary] [Purpose] High-brightness organic thin film E with excellent reliability and durability.
Obtain the L element. [Structure] A light emitting layer was provided on a reflective electrode having a large work function and a reflective electrode having a small work function to obtain an edge emitting type chromatic organic thin film EL device. Further, by stacking these layers, an organic thin film EL element of a plurality of colors such as R, G and B is obtained. Furthermore, by stacking Al2O3 and SiO2 with a constant mixing ratio on the edge emitting organic EL device, the durability was remarkably improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge emitting organic thin film EL device.

[0002]

BACKGROUND OF THE INVENTION 1966 Helfrich et al. Considered that an electron carrier is injected into a fluorescent organic semiconductor, and if recombination of electrons and holes occurs therein, light emission can be obtained. We succeeded in injecting the carrier and observed EL emission that matched the fluorescence spectrum. Then 19
In 1986, a joint research team between Kyushu University and Bell Laboratories in the United States
The perylene vapor-deposited film was used for the light-emitting layer, and the EL that was visible to the naked eye was observed even in the daytime.

1987, Eastman Kodak Company, Tang, et al.
High brightness EL (dc l0V l0) using a Mg / In alloy, which has a good pn junction at the interface with the triphenylazisimine derivative and is easy to emit electrons to the cathode material by using the q3 vapor deposition film.
00cd / m2) was announced. Taking this opportunity to use organic thin films
Research on EL devices has progressed rapidly, and the number of research presentations by the Japan Society of Applied Physics, the Chemical Society of Japan, and the Polymer Society of Japan has increased.

The principle of light emission of the organic thin film EL element described above is that electrodes are attached to both ends of a thin film of an organic dye having strong fluorescence, and a DC voltage is applied, whereby electrons are emitted from a cathode using a material having a small work function. Holes are injected from the anode using a material having a large work function, and the injected electrons and holes move in the thin film and emit light by recombining with light emission. The process of radiative recombination at this time is as follows: 1) the injected electrons are directly recombined with holes in the valence band to emit light, 2) once captured by the emission center, and then radiatively recombined with holes. 3) Recombines with holes through the non-radiative center to release heat and enter a thermal equilibrium state, and returns to the ground state through any one or more of these processes. The larger the ratio of radiative recombination to non-radiative recombination, the higher the internal quantum efficiency of luminescence, resulting in higher brightness. Then, this light emission appears as surface light emission through the end face of the thin film organic thin film EL element or the transparent electrode.

[0005]

On the other hand, multi-colorization and full-colorization of EL elements having large brightness have not been achieved. In particular, the structure of a highly reliable device capable of emitting a plurality of chromatic colors has not been sufficiently studied.

On the other hand, general technical problems, such as various problems such as light emission brightness and driving voltage, are being improved, but the remaining major problem is improvement of long-term life characteristics of the device.
For this purpose, establishment of a device sealing technology is the most important issue in terms of production technology. Further, it is desired to search for a structure that is less likely to cause deterioration over time or chemical deterioration of the agglomerated structure while further improving the external light emission efficiency, and a thin film material suitable for these structures. It is considered that the above-mentioned deterioration of the element is caused by a change in the electronic state of the surface due to the adsorption of oxygen and a chemical deterioration due to the aggregation of the organic thin film layer due to the adsorption of water. In order to prevent this, it is effective to form a moisture-proof layer on the outer periphery of the element with a constant inorganic oxide film. However, there were many unclear points in terms of its material and composition.

[0007]

[Means for Solving the Problems]

l) Improvement of external light emission efficiency FIG. 1 shows an example of the structure of a monochromatic edge emitting organic thin film EL element according to the present invention, and FIG. 2 shows an example of a three-layer edge emitting organic thin film EL element. All of these structures are covered with the reflective metal layer except for the area where the edge light is emitted. It has been found that by forming such a structure, light generated by light emission can be confined as a microcavity, and strong light can be extracted from one side.

The microcavity is caused by the interference effect of emitted light, and the increase in brightness due to this interference effect is strongly dependent on the thickness of the organic layer. Specifically, 0.04 to 0.08 μm
The maximum brightness was recognized at.

Next, the reflective electrode (1) is made of a material having a large work function, specifically Au, Au: Ag, SnO2, ITO, Pt,
Se, Te, etc. are applicable. The reflective electrode (2) is made of a material with a low work function, specifically Na, Na: K, Li, Mg, Mg: A.
g, Ca, etc. are applicable.

Based on these results, the edge emitting organic thin film EL device of FIG. 1 was prepared, and the "brightness-current characteristic" of this device was obtained.
Was measured and the results are shown in FIG. E formed from the same light emitting layer
The result of measuring the L element from the surface direction is 10mA per unit area.
The current densities were 800 cd / m2 for red and green and 200 cd / m2 for blue.

As a material forming the light emitting layer, Alq3 (Alq
3: tris (8-hydroxyquinoline) aluminum), Shinkashared B, DCM (DCM: dicyanomethylenepyran derivative) and DPVBi (DPVBi: 4,4'-bis-diphenylvinylbi)
phenyl) can be exemplified. These can be used alone or in combination of a plurality of light emitting materials to form a light emitting layer.
In addition, it was confirmed that the above-mentioned effect does not change even if monochromatic or plural elements are laminated in any order.

On the other hand, the requirements for the hole transport material constituting the hole layer used in combination with the light emitting layer are amorphous materials, and at the same time, the ability to form a large-area thin film is high, and the carrier mobility in the thin film is high. Is required to be high. As this material, an electrophotographic photosensitive material such as TPD (m) (TPD
(m): N, N'-diphenyl-N, N'-bis (3-methyl-phenyl)-
1,1-diphenyl-4,4'-diamine) can be used. When impurities are contained, the energy of excitons generated by carrier recombination is deprived and acts as a so-called quencher.
This hole transport material needs to be sufficiently purified by a recrystallization method or a sublimation method.

2) Improvement of sealing technology As described above, the cause of the deterioration of the device is that the change in the electronic state of the surface of the light emitter due to the adsorption of oxygen and the chemical deterioration due to the aggregation of the organic thin film layer due to the adsorption of moisture. The material was selected focusing on. As a result, Si is used to prevent the entry of oxygen.
It has been found that O2 is effective and Al2O3 is effective for preventing the ingress of water.

With these results as the background, these were mixed and the optimum mixing ratio for the sealing layer was investigated. The result is shown in FIG. The content of the test according to FIG. 4 is to obtain the relationship between the mixing molar ratio and the luminance half-life. The test conditions are that a current of 10 mA / cm2 is continuously applied under constant temperature and humidity of 60 ° C and 90%.

When the mixing molar ratio of SiO2 and Al2O3 is 2 to 4 to 8 to 6, the characteristics as a sealing layer are particularly excellent,
It has been found to be particularly excellent when the ratio is desirably 3 to 7.

The layer structure of the two materials is a laminated structure.
It was also found that the mixed layer structure has the same effect.

[0017]

EXAMPLES In order to clarify the contents of the present invention, examples will be further described.

Example 1 FIG. 5 shows a flow of assembling an edge emitting organic thin film EL device according to the present invention. After thoroughly cleaning a 1.1 mm-thick glass substrate by ultrasonic cleaning, ITO was sputtered to a film thickness of 0.2 μm. Patterning was performed by etching to form this ITO electrode. Then, Au: Ag (10: 1) was sputter-deposited thereon with a film thickness of 0.1 μm as a reflective electrode.

Next, a hole transport layer and a light emitting layer were formed. Specifically, TPD (m) purified by a sublimation purification device that sufficiently preheated nitrogen gas under high vacuum was loaded on a tungsten board, and a film having a thickness of 0.05 μm was formed by a resistance heating method. Then, for Alq3 sublimated and refined on this, D
A fluorescent dye containing 1.0 wt% of CM was loaded on a quartz board to form a film with a thickness of 0.04 μm by a resistance heating method. In order to form the hole transport layer and the light emitting layer into a predetermined shape, masking is performed with a thin plate such as stainless steel.

Further, a reflective electrode is formed. In particular,
A material with a low work function, Mg: Ag (10: 1), was deposited to a film thickness of 0.1 μm using a DC sputtering device. Mg to Ag
Is added because it has an effect of improving reflection efficiency and preventing electrode deterioration.

Al2O3: SiO2 (7 mol: 3 mol) was formed into a film having a thickness of 0.2 μm by a high frequency sputtering method for the purpose of improving durability on the entire laminated body including the reflective electrode.

Finally, except the light outlet, it was covered with a thin film made of metallic chromium so as to have a thickness of 0.2 μm.

The edge-emitting organic thin film E thus obtained
When a voltage was applied to the transparent electrode and the back electrode of the L element to drive them, a red light emission (x = 0.67, y = 0.33) with a brightness of about 100 times that of the conventional surface emitting device was achieved.

Example 2 FIG. 6 shows a flow of assembling an edge emitting organic thin film EL device having a three-layer structure of RGB primary colors according to the present invention.

After thoroughly cleaning a 1.1 mm-thick glass substrate by ultrasonic cleaning, ITO was sputtered to a film thickness of 0.2 μm. Patterning was performed by etching to form this ITO electrode. Then, Au: Ag (10: 1) was sputter-deposited thereon with a film thickness of 0.1 μm as a reflective electrode. Further, a hole transport layer and a red light emitting layer were formed in the same manner as in Example 1, and a reflective electrode was formed thereon. An SiO2 film with a thickness of 0.2 μm is formed on top of this as an insulating layer, and the red EL
The device was formed.

By repeating the above operation, the green EL element,
Blue EL elements were sequentially laminated.

Finally, Al is applied to the entire EL elements of the above three primary colors.
2O3: SiO2 (7 mol: 3 mol) was formed into a film having a thickness of 0.2 μm by a high frequency sputtering method, and a portion other than the light outlet was covered with a thin film made of metallic chromium so as to have a thickness of 0.2 μm.

The edge-emitting organic thin film E thus obtained
When a voltage is applied to the transparent electrode and the back electrode of the L element to drive them, a full-color EL having chromaticity coordinates as shown in FIG.
The element is obtained, and at the same time, the overall white balance (x = 0.
36, y = 0.38). Also, in terms of brightness, as in the case of single-light color, light emission of about 100 times that of conventional surface-emitting devices was achieved (FIG. 8).

[0029]

EFFECTS OF THE INVENTION According to the present invention, E which is excellent in durability and at the same time has a brightness 100 times higher than that of conventional surface emission.
An L element can be obtained. Further, not only a single color, but also a plurality of colors of light can be driven without deteriorating the performance thereof, so that it is possible to obtain a full-color display.

[0030]

[Brief description of drawings]

FIG. 1 shows a cross-sectional structure of an edge emitting organic thin film EL device having a one-layer structure (monochrome) according to the present invention.

FIG. 2 shows a sectional structure of an edge emitting organic thin film EL device having a three-layer structure (three primary colors) according to the present invention.

FIG. 3 is a diagram showing “luminance-current density characteristics” of an edge emitting organic thin film EL device having a single layer structure according to the present invention.

[Figure 4] "Brightness half-life-SiO2 and Al2O" used for moisture barriers
FIG. 3 is a diagram showing a relationship of “mixing molar ratio of 3”.

FIG. 5 is a view showing a flow of assembling an edge emitting organic thin film EL device having a single layer structure according to the present invention.

FIG. 6 is a diagram showing a flow of assembling an edge emitting organic thin film EL device having a three-layer structure according to the present invention.

FIG. 7 is a diagram showing the chromaticity of each layer of an edge emitting organic thin film EL device having a three-layer structure according to the present invention.

FIG. 8 is a diagram showing “luminance-current density characteristics” in which three colors of the edge emitting organic thin film EL element having a three-layer structure according to the present invention are combined.

[Explanation of symbols]

 11 glass substrate 12 transparent conductive film 13 reflective electrode (1) 14 hole transport layer 15 light emitting layer 16 reflective electrode (2) 17 moisture barrier layer 18 reflective metal 21 glass substrate 22 transparent conductive film 23 reflective electrode (1) 24 hole transport Layer 25 R Light-Emitting Layer 26 Reflective Electrode (2) 27 Insulating Film 28 G Light-Emitting Layer 29 B Light-Emitting Layer 210 Moisture-Proof Layer 211 Reflective Metal

Claims (3)

[Claims] 1. An organic thin-film EL element in which a reflective electrode having a large work function and a reflective electrode having a small work function are provided on a glass substrate with a transparent conductive film, and an organic thin-film layer is sandwiched between the electrodes. Alternatively, an edge emitting organic thin film EL element is characterized in that a metal layer is formed excluding a plurality of edge surfaces. 2. An organic thin film EL element having a reflective electrode having a large work function and a reflective electrode having a small work function provided on a glass substrate with a transparent conductive film, and a plurality of organic thin film layers sandwiched between the electrodes. 1. A laminated edge emitting organic thin film EL device, characterized in that a metal layer is formed except for one or a plurality of end faces. 3. The organic thin film EL device according to claim 1, wherein Al2O3 and SiO
2. A mixed thin film layer of 2 is provided.
Alternatively, the edge emitting organic thin film EL device according to claim 2.