JPH08330073A - Organic luminous element and manufacture thereof - Google Patents

Abstract

PURPOSE: To prevent deterioration of a recoupling portion by using an AlZn alloy or a MgAlZn alloy for a negative electrode injecting a current into an organic luminous element. CONSTITUTION: An ITO electrode 12 is provided on a glass substrate 11 as a positive electrode, and an organic material hole transportation material 13 and an electron transportation material are provided on it by a vapor deposition method or an immersion method. A negative electrode injecting a current into an organic luminescent element is provided on it, and a binary alloy or a ternary alloy, e.g. an AlZn alloy or a MgAlZn alloy, is used for the material. When Al and Mg are used, the Al component is set to 20-50% of the sum of Al and Mg. An alkaline metal, e.g. sodium, and an alkaline earth metal, e.g. magnesium, are used as a metal injecting a current into the organic material and having a small work function for the material of the negative electrode 15. The luminous region can be expanded from a single plane to a three-dimensional region, the luminous density of the luminous region is reduced, and the life characteristic is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device using an organic material.

[0002]

2. Description of the Related Art Studies on light emitting devices using organic materials have been published for more than 20 years, and anthracene is used as a light emitting material. This anthracene means that when a current is injected into anthracene, electrons and ho
Recombination occurs, and this recombination causes light emission.

In addition, as to its excellent characteristics as compared with the conventional light emitting element, a device can be formed only by a simple vapor deposition process because of its easy manufacturing method, and further, the characteristics are excellent. It is a self-luminous element and is characterized by high emission brightness and high uniformity. Furthermore, it is a high-brightness light source and its luminous efficiency is large, so that it can reach several percent in power efficiency.

However, from a practical point of view, the life of the light emitting element is very short, and it has not reached a practical level. As described above, oxidation of the electrode for injecting electrons is one of the causes of the deterioration of the element that causes the short life, and it is considered that the cause is the greatest due to the oxidation of the electrode. An electrode material having a low work function is necessary for injecting a current into an element (in particular, injecting an electron into an organic material). Here, as a material having a small work function, an alkali metal such as sodium, potassium, lithium, or magnesium or an alkaline earth metal is generally mentioned. However, all of these metal materials are unstable in the atmosphere. Therefore, this instability is closely linked to the life of the device. Among them, it has been found that the magnesium-silver alloy exhibits relatively excellent element characteristics, but even with this material, the element life has not reached the level of practical use.

Various metals have been studied as electrodes for the purpose of stability, and the electrode materials that have been published so far are listed as Mg, Mg-Ag, In,
Mg-In. It contains simple metals such as Ca and Al, or alloys thereof. As a standard for selecting these materials, attention has been paid to how stable current can be injected in the air without causing voltage rise and efficient current injection.
After that, as a further improved electrode material, aluminum-
An alloy of lithium was announced.

However, even though the driving voltage was lowered by using this electrode, the life of the light emitting element was not so long as the life was slightly extended.

Further, one of the causes of deterioration of the light emitting device is
The decomposition of the organic material due to the bond between the electron and the electron.
This is due to the light emitting mechanism itself, and how to prevent the deterioration is the most important issue for practical use of the light emitting device.

Generally, the deterioration of organic materials is larger than that of inorganic materials, and it is not possible to directly compare the lives under the same conditions. It is required to reduce the deterioration by investigating the deterioration mechanism and taking an appropriate usage method. Furthermore, although the range of research on organic materials has expanded due to the variety of materials, and the characteristics or functions have expanded significantly, the current situation is that efforts to improve the emission lifetime have not been developed.

[0009]

FIG. 4 shows the degree of electrode deterioration due to the oxidation of the electrodes of a conventional light emitting element, and shows the ionization potential of the prepared electrode (representing the ease with which electrons are emitted and having a small numerical value). Which is more effective as an electrode).

In FIG. 4, (1) shows the characteristics of the Mg electrode used as the most standard electrode material, and the ionization potential of the surface of the electrode (the side in contact with air) immediately after preparation of the electrode. Shows the change over time. In the case of an electrode containing only Mg metal, deterioration starts immediately after the electrode is manufactured.
The ionization potential approaches saturation already within 0 minutes. As a result, it can be seen that when the device is operated, the operating voltage rises as the ionization potential increases.

In FIG. 4, (2) is the time change of the ionization potential at the interface with the organic material and at the interface between the metal electrode and the organic material, and it can be seen that there is a time lag than the surface, but it also changes. . In addition, this measurement is performed with the electrode peeled off at the boundary surface between the organic material and the electrode interface (electrode film thickness is a measured value at 1500 A).

Among the factors that determine the life of the organic light emitting device, the stability of the electrode is particularly important. An electrode using Mg-Ag or Al-Li metal, which has been considered to have good characteristics in the past, reacts with moisture or oxygen in the atmosphere over time to deteriorate the characteristics of the element.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems, and particularly to provide an organic light emitting device having a long life which is not deteriorated by oxidation or the like.

Further, among the factors that determine the life of the organic light emitting device, the light emitting material and its structure of the direct conversion portion for converting current into light are particularly important. Specifically, it is particularly important to prevent the deterioration of the part that becomes the excitation part of electrons and the part where the holes and electrons are recombined. The excitation part composed of an organic material is generally a distance between single molecules or tens of tens of molecules, and preventing deterioration of the recombination part is a key to practical use of the organic light emitting device.

[0015]

SUMMARY OF THE INVENTION The present invention is to improve the electrode that has the greatest influence on the deterioration of the organic light emitting device, and removes the cause of the deterioration of the electrode from the surface of the electrode material. As a means for this, the electrode material is compounded on the surface of the material and alloyed with two or more kinds of metals, or layered and layered, and the characteristics of the respective metal materials are used.

As a basis for selecting the electrode material in that case, one is an electrode material having a small work function, and the other is a function of preventing invasion of moisture and oxygen in the atmosphere so as not to reach the current injection interface. Is to have.

As another method, the structure of the element is changed from the conventional one so that the metal electrode portion is not exposed on the surface.

In the present invention, the width of the bonding region is widened from a few molecules to a few hundred molecules in the region which becomes the recombination part of the holes and electrons, which has the greatest influence on the deterioration of the organic light emitting device. This makes it possible to extend the life of the light emitting element.

Further, the bonding force between the electrode and the organic material is generally weak because it is connected only by the Van der Waals force, whereas the ordinary bonding between metals is more than the Van der Waals force due to mutual diffusion. Very big. Therefore, in order to supplement the binding force, the mutual compositions are mixed to compensate.

[0020]

By using a binary alloy or a ternary alloy for the electrodes of the organic light emitting element, the life of the organic light emitting element, which has not been put into practical use due to lack of reliability as a light emitting element due to peeling of the electrode or the like, has been conventionally extended. You can

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Light emitting devices according to embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a structural sectional view of an organic light emitting device according to a first embodiment of the present invention. In FIG. 1, indium oxide tin oxide, a so-called ITO electrode 12, is provided as an anode electrode on a glass substrate 11, and an organic material hole transport material 13 and an electron transport material 14 are deposited thereon by a vapor deposition method, a dipping method or a spin coat method. Method, and the electrode 15 is further provided thereon as an electrode. A binary alloy or a ternary alloy is used as the material of the electrode. In this embodiment, A is a particularly preferable material.
1Zn alloy or MgAlZn alloy is used. When Al and Mg are used, the Al component is preferably 20% to 50% of the total amount of Al and Mg.

The electrode is most easily prepared by vapor deposition or sputtering, and the vapor deposition method is also used in this embodiment.

Further, as a metal having a small work function for injecting a current into the organic material, an alkali metal such as sodium, potassium, lithium, or an alkaline earth metal such as magnesium, aluminum or calcium is used.

Next, the characteristics of the light emitting device of this embodiment will be described with reference to FIG. In FIG. 2, (1) is a time change of the ionization potential (work function, electron emission easiness, a smaller numerical value effectively acts as an electrode) on the surface of the electrode material in contact with air, and (2) ) Indicates the change with time of the value of the boundary surface between the organic material and the electrode. As is clear from FIG. 2, in the electrode material of this example, the surface in contact with air also causes an increase in ionization potential due to oxidation, but the electrode composition according to this example prevents internal oxidation and ionizes the boundary surface. There is no increase in potential.

Particularly, as a selection criterion of other metals added to the material having a small ionization potential, gold and platinum palladium are used as materials having a dense composition of the formed film and having a large internal protection effect (preventing oxidation inside the electrode). It is valid. Furthermore, there is a minimum film thickness for this metal to exert its function effectively, and 0 to 2 microns is the minimum film thickness for exerting the effect. If the film thickness is less than that, diffusion to the electrode material or in the atmosphere The effect diminishes because oxygen and water penetrate.

Further, it was confirmed that, in addition to noble metals such as gold, platinum and palladium, general metals such as aluminum, iron, stainless steel and copper have equivalent functions by increasing the film thickness. At this time, it should be noted that the use of a large film thickness causes a mismatch of expansion coefficients and the like, which causes a problem of electrode separation.

The structure of the light emitting device shown in FIG. 3 is also effective for extending the life. In FIG. 3, reference numeral 31 is made of a material having good heat conduction and having a function of blocking oxygen moisture in the air. As a material having such a function, a substrate material such as aluminum, iron, copper, and stainless is used, and the electrode material 32 having a small ionization potential is provided on the substrate material. Further, an organic material hole transport material 33, an electron transport material 34, a transparent electrode 35 are constituted, and an element protective film 36 is provided.

In FIG. 3, the substrate is made of metal, but plastics other than metal, ceramics and the like can be used if a material having low gas permeability is used.

Specifically, the electrode 15 is made of Mg of 500.
Using at least angstroms, gold Au, platinum Pt, and palladium Pd are provided at 1000 angstroms or more on the Mg electrode as materials impermeable to oxygen and moisture.

These electrodes may be made by either vapor deposition or sputtering. Instead of first depositing magnesium Mg and then depositing a metal of gold, platinum, or palladium, Mg and other metals are removed. You may create them at the same time.

(Embodiment 2) FIG. 5 is a sectional view showing the structure of an organic light emitting device according to a second embodiment of the present invention. Glass substrate 1
1 so-called ITO electrode of indium oxide tin oxide on 1
2, an organic material hole transporting material 13 and an electron transporting material 14 are formed thereon by a vapor deposition method, an immersion method or a spin coat method, and an electrode 15 is provided thereon. The electrode is most easily prepared by vapor deposition or sputtering, and the vapor deposition method is also used in the present invention.

A metal having a small work function is used as an electrode for injecting a current into an organic material. Specifically, alkali metals such as sodium, potassium and lithium, and alkaline earth metals such as magnesium, aluminum and calcium are used. To use. Furthermore, the alloy is used.

In the structure shown in FIG. 5, in the light emitting portion, an organic hole transporting material is vapor-deposited on an ITO substrate, and an electron transporting material is further vapor-deposited thereon to form a PN junction surface at the boundary surface to emit light. . A part of the hole transport material and the electron transport material are mixed with each other to have a wide structure, and in the constitution of this embodiment shown in FIG. 5, the mixed layer is a mixture of the electron transport layer and the hole transport layer. Take 50% each ratio.

Here, the mixed region is formed by a so-called co-evaporation method. The thickness of the co-deposited layer has a great influence on the characteristics, and if it is too thick, it becomes impossible to supply electrons or holes to the entire layer, and the efficiency decreases. On the other hand, if it is too thin, the effect of providing the mixed layer is low and is the same as the conventional light emitting device.

In the device structure of FIG. 5, the thickness of the co-deposition layer was changed from 50 Å to 1000 Å, and the characteristics were examined. As a result, the range of 50 Å to 250 Å was the most effective. It was
The electron transport layer and the hole transport layer themselves are preferably 100 angstroms to 400 angstroms.

The thickness of the mixed layer is an important design factor for the characteristics of the light emitting device. In contrast to a normal semiconductor, the conventional structure of the organic light emitting device is to form a step-shaped junction surface at the PN junction surface. In the semiconductor element made of an inorganic material, the bond between the electron and the hole has no problem particularly in the step-like bonding surface because the electron diffusion region is wide. On the other hand, the junction surface of the organic light emitting device has a small diffusion length in the recombination region of the hole and the electron, and therefore usually has only a few molecules, so that the molecules in the coupling region are largely deteriorated.

By providing the organic light emitting element with a structure corresponding to the tilted impurity doping of the inorganic semiconductor element, the light emitting region can be expanded. In the organic light emitting device, the thickness of the depletion layer is usually about several 300 angstroms, and a recombination region of about 50 angstroms exists therein. Now, if the recombination region is averaged over the entire depletion layer, the life can be expected to be 6 times as long as a simple calculation.

To show the effectiveness of the present invention, FIG. 6 shows the relationship between the luminous efficiency and the thickness of the mixed layer when the mixed layer is provided. FIG. 6 shows the thickness of the mixed layer in the organic material having a thickness of 1000 angstroms. Experimental results show that when the thickness of the mixed layer is 1000 angstroms as a whole, it shows a constant efficiency up to 250 angstroms. This corresponds to a thickness of 5 times that of the conventional light emitting region of 50 Å.

The interface between the organic material and the metal material is usually connected by the so-called Van der Waals coupling force. Since this force is generally small, the metal easily peels off. When stress is applied due to a difference in expansion coefficient, the metal electrode peels off. Therefore, in order to firmly attach the metal electrode to the organic material, it is possible to increase the adhesive force by forming a region in which both materials are mixed with each other, which is desirable.
Also, a mixed film can be prepared by co-evaporating an organic material and an electrode material. Furthermore, the same effect can be realized for the ITO transparent electrode and the organic material, and the adhesion to the substrate can be increased.

[0041]

According to the electrode structure of the present invention, in the conventional electrode structure, when the element life is the shortest, it is several minutes and the longest is 300 hours, but it can be increased to 2000 hours or more. Became.

Further, by adopting the light emitting device structure of the present invention, it becomes possible to expand the light emitting region from a single plane to three dimensions. Therefore, it has been a problem in practical use that the life characteristic is short. However, by adopting the structure of the present invention, it is possible to realize a device life characteristic of 5 times or more by lowering the light emission density of the light emitting region. The application range of the organic light emitting device is very wide and can be expected from a simple flat light source to a flat self-luminous full-color display.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of a light emitting device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing characteristics of the light emitting element in the first embodiment of the present invention.

FIG. 3 is a sectional view showing a structure of a light emitting device according to a first embodiment of the present invention.

FIG. 4 is a diagram showing characteristics of a conventional light emitting element.

FIG. 5 is a sectional view showing a structure of a light emitting device according to a second embodiment of the present invention.

FIG. 6 is a diagram showing the relationship between the luminous efficiency of the light emitting device and the thickness of the mixed layer in the second embodiment of the present invention.

[Explanation of symbols]

 11 glass substrate 12 ITO transparent electrode 13 hole transporting material 14 electron transporting material 15 metal electrode 16 mixed layer 31 element substrate 32 electrode material 33 hole transporting material 34 electron transporting material 35 transparent electrode 36 element protective film

Claims (12)

[Claims] 1. A substrate, an anode-side electrode formed on the substrate, a hole-transporting material layer and an electron-transporting material layer formed of an organic material on the anode-side electrode, the hole-transporting material layer, or An organic light emitting device having a cathode side electrode formed on an electron transporting material layer, characterized in that an AlZn alloy or a MgAlZn alloy is used for the cathode side electrode for injecting current into the organic light emitting device. Light emitting element. 2. A substrate, an anode-side electrode formed on the substrate, a hole-transporting material layer and an electron-transporting material layer formed of an organic material on the anode-side electrode, the hole-transporting material layer, or An organic light emitting device having a cathode side electrode formed on an electron transporting material layer, wherein an alloy in which Mg, Zn and Li are added to Al is used for the cathode side electrode for injecting current to the organic light emitting device, Furthermore, the organic light emitting element is characterized in that the amount of Al is 20% to 50% of the total amount of Al and Mg. 3. Au, Pt or Pd is formed on the cathode side electrode.
3. A layer made of is provided.
The organic light-emitting device described. 4. The organic light emitting device according to claim 1, wherein Au, Pt or Pd is added in the cathode side electrode. 5. The organic light emitting device according to claim 3, wherein the thickness of the layer made of Au, Pt or Pd is 0.2 μm or more. 6. The organic light emitting device according to claim 1, further comprising a protective layer covering the cathode side electrode. 7. The organic light emitting device according to claim 1, wherein the substrate is aluminum, copper, iron, stainless steel, glass, or ceramic plastic, and a material layer having a small ionization potential is formed on the substrate. 8. A substrate, an anode-side electrode formed on the substrate, a hole-transporting material layer and an electron-transporting material layer formed of an organic material on the anode-side electrode, the hole-transporting material layer, or An organic light emitting device having a cathode-side electrode formed on an electron transporting material layer, wherein a mixed layer of the hole transporting material and the electron transporting material is formed between the hole transporting material layer and the electron transporting material layer. An organic light emitting device characterized by the above. 9. The hole transport material layer and the electron transport material layer have a thickness of 100 Å to 400 Å, and the mixed layer of the hole transport material and the electron transport material has a thickness of 50 Å to 500 Å. The organic light-emitting device according to claim 8, wherein the organic light-emitting device is a film. 10. The organic light-emitting device according to claim 8, wherein a mixed layer of the cathode-side electrode material and the electron-transporting material is formed at least between the cathode-side electrode and the electron-transporting material layer. 11. The organic light emitting device according to claim 8, wherein a mixed layer of the anode side electrode material and the hole transport material is formed at least between the anode side electrode and the hole transport material layer. 12. A substrate, an anode-side electrode formed on the substrate, a hole-transporting material layer and an electron-transporting material layer formed of an organic material on the anode-side electrode, the hole-transporting material layer, or An organic light emitting device having a cathode side electrode formed on an electron transporting material layer, wherein a mixed layer of the hole transporting material and the electron transporting material is formed between the hole transporting material layer and the electron transporting material layer. A method of manufacturing an organic light emitting device, wherein the mixed layer is formed by a co-evaporation method.