JP3605441B2 - Edge emitting organic thin film EL device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an edge emitting organic thin film EL device.
[0002]
[Prior art]
In 1966, Helfrich et al. Injected electronic carriers into a fluorescent organic semiconductor and thought that light would be obtained if the recombination of electrons and holes occurred, and injected carriers into anthracene single crystals. And EL emission corresponding to the fluorescence spectrum was observed.
Later, in 1986, a collaborative research team between Kyushu University and Bell Laboratories in the United States used a perylene vapor-deposited film for the light-emitting layer, and observed EL that was visible to the naked eye even in the daytime.
[0003]
In 1987, according to Tang of Eastman Kodak Company, a pn junction was favorably formed at the interface with the triphenylazisimine derivative by using an Alq3 vapor-deposited film having better electron transportability than a perylene vapor-deposited film. A high-brightness EL (dc 10 V 1000 cd / m 2) using a Mg / In alloy that easily emits electrons as a cathode material has been announced. With this presentation as an opportunity, research on organic thin-film EL devices has progressed rapidly, and the number of research presentations by the Japan Society of Applied Physics, The Chemical Society of Japan, the Society of Polymer Science, etc. has increased.
[0004]
The light emission principle of the organic thin film EL element described above is that electrodes are attached to both ends of an organic dye thin film having strong fluorescence, and by applying a DC voltage, electrons are emitted from a cathode using a material having a small work function, and the work function is reduced. Holes are injected from an anode using a large material, and the injected electrons and holes move in the thin film and emit light by radiative recombination.
The process of radiative recombination at this time is
1) The injected electrons directly recombine with holes in the valence band to emit light,
2) once captured by the emission center, recombine with holes
3) recombine with holes through the non-luminescent center to release heat and enter thermal equilibrium;
It returns to the ground state through one or more of these steps.
The larger the ratio of radiative recombination to non-radiative recombination, the higher the internal quantum efficiency of light emission, and as a result, the higher the luminance.
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]
[Problems to be solved by the invention]
On the other hand, multi-color and full-color EL devices having high luminance have not been achieved.
In particular, the structure of a highly reliable element that emits a plurality of chromatic colors has not been sufficiently studied.
[0006]
On the other hand, general technical problems, such as various problems such as light emission luminance and drive voltage, are being improved, but the biggest problem remaining is improvement of long-term life characteristics of the device. To this end, establishment of element sealing technology is the biggest issue in terms of production technology.
Further, it is desired to search for a structure in which the agglomerated structure is hardly deteriorated with time or chemical deterioration while further improving the external light emission efficiency, and a thin film material suitable for these structures.
It is considered that the cause of the deterioration of the device is a change in the electronic state of the surface due to the adsorption of oxygen and a chemical deterioration due to aggregation of the organic thin film layer due to the adsorption of moisture. In order to prevent this, it is effective to form a moisture-proof layer around the element with a certain inorganic oxide film.
However, there were many unclear points in the material and composition.
[0007]
[Means for Solving the Problems]
l) Improvement of external luminous efficiency FIG. 1 shows an example of the structure of a monochromatic edge emitting organic thin film EL device according to the present invention, and FIG. 2 shows an example of a three-layer edge emitting organic thin film EL device.
These structures are all covered with a reflective metal layer, except for the part that emits light at the edge. By forming such a structure, it has been found that light generated by light emission can be confined as a microcavity, and strong light can be extracted from one side.
[0008]
Microcavities are created by the interference effect of the emitted light, and the increase in brightness due to this interference effect is strongly dependent on the thickness of the organic layer. Specifically, the maximum of the luminance was observed at 0.04 to 0.08 μm.
[0009]
Next, the reflective electrode (1) is made of a material having a large work function, and specifically includes Au, Au: Ag, SnO2, ITO, Pt, Se, Te, and the like. The reflective electrode (2) is made of a material having a small work function, and specifically includes Na, Na: K, Li, Mg, Mg: Ag, Ca, and the like.
[0010]
Based on the results, an edge emitting organic thin film EL device shown in FIG. 1 was prepared, and "luminance-current characteristics" of the device were measured. The results are shown in FIG. As a result of measuring the EL element formed of the same light emitting layer from the surface direction, red and green were 800 cd / m2 and blue were 200 cd / m2 at a current density of 10 mA per unit area.
[0011]
Examples of the material constituting the light emitting layer include Alq3 (Alq3: tris (8-hydroxyquinoline) aluminium), Shinkasha Red B, DCM (DCM: dicyanomethylenepyran derivative), and DPVBi (DPVBi: 4,4′-bis-diphenylvinylphenyl). Can be exemplified. These were able to form a light emitting layer by combining a single or a plurality of light emitting materials.
In addition, it was confirmed that the above-described effect was not changed even if a single color or a plurality of elements were laminated in any order.
[0012]
On the other hand, the hole transport material that constitutes the hole layer used in combination with the light emitting layer is an amorphous material, and at the same time, has a high ability to form a large-area thin film and high carrier mobility in the thin film. Is required. As this material, an electrophotographic photoreceptor material, for example, TPD (m) (TPD (m): N, N'-diphenyl-N, N'-bis (3-methyl-phenyl) -1,1-diphenyl-4,4) '-Diamine) can be used.
If an impurity is contained, it deprives the energy of excitons generated by carrier recombination and acts as a so-called quencher. Therefore, this hole transport material needs to be sufficiently purified by a recrystallization method or a sublimation method.
[0013]
2) Improvement of sealing technology As described above, the cause of device degradation is to focus on the cause of the change in the electronic state of the luminous body surface due to the adsorption of oxygen, and the chemical deterioration due to aggregation in the organic thin film layer due to the adsorption of moisture. Material selection. As a result, it was found that SiO2 was effective in preventing oxygen from entering, and Al2O3 was effective in preventing moisture from entering.
[0014]
With these results as background, these were mixed and the optimum mixing ratio as a sealing layer was examined. The result is shown in FIG. The test contents shown in FIG. 4 are obtained by determining the relationship between the molar mixture ratio and the luminance half-life. The test conditions were such that DC 10 mA / cm 2 was continuously supplied at a constant temperature and humidity of 60 ° C. and 90%.
[0015]
It was found that when the mixing molar ratio of SiO2 and Al2O3 was 2 to 4 to 8 to 6, the characteristics as the sealing layer were particularly excellent, and when it was 3 to 7, it was particularly excellent.
[0016]
It has also been found that the layer structure of the two materials has the same effect in both the laminated structure and the mixed layer structure.
[0017]
【Example】
Further, the present invention will be described with reference to examples in order to clarify the contents of the present invention.
[0018]
Example 1
FIG. 5 shows a flow of assembling the edge emitting organic thin film EL device according to the present invention.
After a glass substrate having a thickness of 1.1 mm was sufficiently cleaned by ultrasonic cleaning, ITO was formed into a film having a thickness of 0.2 μm by sputtering. Patterning was performed by etching to form the ITO electrode.
Next, Au: Ag (10: 1) was formed thereon as a reflective electrode by sputtering to a thickness of 0.1 μm.
[0019]
Next, a hole transport layer and a light emitting layer were formed.
Specifically, TPD (m) purified by a sublimation purification apparatus sufficiently preheated with nitrogen gas under a high vacuum was loaded on a tungsten board and formed into a film having a thickness of 0.05 μm by a resistance heating method. .
Then, a fluorescent dye obtained by adding 1.0 wt% of DCM to Alq3 purified by sublimation was loaded on the quartz board, and a film was formed to 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.
[0020]
Further, a reflective electrode is formed.
Specifically, Mg: Ag (10: 1), which is a material having a small work function, was formed to a thickness of 0.1 μm using a DC sputtering apparatus. The reason why Ag is added to Mg is that there is an effect of improving reflection efficiency and preventing electrode deterioration.
[0021]
Al2O3: SiO2 (7 mol: 3 mol) was formed into a film having a thickness of 0.2 [mu] m by high frequency sputtering for the purpose of improving durability over the entire laminate including the reflection electrode.
[0022]
Finally, the 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.
[0023]
When a voltage was applied to the transparent electrode and the back electrode of the edge emitting organic thin-film EL device thus obtained and driven, a red (x = 0.67, y = 0.33) luminance and a conventional surface emission were obtained. About 100 times the emission of the device was achieved.
[0024]
Example 2
FIG. 6 shows a flow of assembling the edge emitting organic thin-film EL device having a three-layer structure of RGB primary colors according to the present invention.
[0025]
After a glass substrate having a thickness of 1.1 mm was sufficiently cleaned by ultrasonic cleaning, ITO was formed into a film having a thickness of 0.2 μm by sputtering. Patterning was performed by etching to form the ITO electrode.
Next, Au: Ag (10: 1) was formed thereon as a reflective electrode by sputtering to a thickness of 0.1 μm.
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.
On this, SiO2 was formed as an insulating layer to a thickness of 0.2 μm to form a red EL element.
[0026]
The above operation was repeated, and a green EL element and a blue EL element were sequentially stacked.
[0027]
Finally, a film of Al2O3: SiO2 (7 mol: 3 mol) is formed to a thickness of 0.2 μm on the entire EL device of the three primary colors by a high frequency sputtering method, and a film thickness of 0.2 μm is formed except for the light outlet. Covered with a thin film of metallic chromium.
[0028]
When a voltage was applied to the transparent electrode and the back electrode of the edge emitting organic thin film EL device thus obtained and driven, a full-color EL device having chromaticity coordinates as shown in FIG. 7 was obtained. The balance was also (x = 0.36, y = 0.38). Also, in the aspect of luminance, as in the case of the luminance of the single light color, light emission about 100 times that of the conventional surface light emitting device was achieved (FIG. 8).
[0029]
Function and effect of the present invention
According to the present invention, it is possible to obtain an EL device having excellent durability and at the same time having a luminance 100 times higher than that of the conventional surface light emission.
In addition, since light emission of not only a single color but also a plurality of colors can be driven without deteriorating the performance, a full-color display can be obtained.
[0030]
[Brief description of the drawings]
FIG. 1 shows a cross-sectional structure of an edge emitting organic thin-film EL element having a one-layer structure (single color) according to the present invention.
FIG. 2 shows a cross-sectional structure of an edge emitting organic thin-film EL element having a three-layer structure (three primary colors) according to the present invention.
FIG. 3 is a diagram showing “brightness-current density characteristics” of the edge emitting organic thin film EL element having a single layer structure according to the present invention.
FIG. 4 is a diagram showing a relationship of “luminance half-life—mixing molar ratio of SiO 2 and Al 2 O 3” used for a moisture-proof layer.
FIG. 5 is a view showing a flow of assembling an edge emitting organic thin film EL element having a single layer structure according to the present invention.
FIG. 6 is a diagram showing a flow of assembling a three-layer edge emitting organic thin film EL device according to the present invention.
FIG. 7 is a diagram showing the chromaticity of each layer of the three-layer edge emitting organic thin film EL device according to the present invention.
FIG. 8 is a view showing “brightness-current density characteristics” of three colors of the edge emitting organic thin film EL element having a three-layer structure according to the present invention.
[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-proof 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)

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 one or a plurality of end faces of the organic thin film EL element are provided in an organic thin film EL element having an organic thin film layer sandwiched between the electrodes. An edge-emitting organic thin-film EL device characterized in that a metal layer is formed on the EL device. On a glass substrate with a transparent conductive film, a reflective electrode having a large work function and a reflective electrode having a small work function are provided, and one or more of the organic thin film EL elements are provided in an organic thin film EL element in which a plurality of organic thin film layers are sandwiched between the electrodes. A stacked edge-emitting organic thin-film EL device characterized in that a metal layer is formed except for an end face. 3. The organic EL device according to claim 1, further comprising a mixed thin film layer of Al2O3 and SiO2.

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