JPH09245968A - Organic light emitting element and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize an electrode for elongating a service life, and drive an element at low voltage. SOLUTION: In a light emitting element comprising a transparent electrode 12 formed on a glass substrate 11, a hole transport material layer 13 formed on the transparent electrode 12, an electron transport material layer 14 of organic material formed on the hole transport material layer 13, and a metal electrode 15 formed on the electron transport material layer 14, univalent metal, bivalent metal, or trivalent metal is used as material for the metal electrode 15. In addition, a layer of oxide or hydroxide of the surface of the metal electrode 15 is formed at an interface between the electron transport material layer 14 and the metal electrode 15.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a light emitting element using an organic material and an electrode thereof.

[0002]

2. Description of the Related Art Research on a light emitting device using an organic material has been published for more than 20 years, and anthracene is used as a light emitting material to inject a current into anthracene to recombine electrons and holes. It has been reported to emit light. On the other hand, in 1987, an efficient light emitting device was realized by a research announcement by Kodak Group, and the possibility of practical application increased all at once.

However, from a practical point of view, the life of the above light emitting device is very short and has not reached a practical level. One of the major causes of deterioration of the element is oxidation of electrodes for injecting electrons.

Further, an electrode material having a small work function is required for injecting a current into the device, particularly for injecting electrons into an organic material. In general, examples of materials having a low work function include alkali metals such as sodium, potassium, lithium, and magnesium or alkaline earth metals, and all of these metal materials are unstable in the atmosphere. Among them, it has been found that a magnesium-silver alloy has particularly excellent element characteristics, but even with this material, the element life has not reached the level of practical use.

After that, various metals have been studied as electrodes for the purpose of stability. The electrode materials that have been announced so far are listed as Mg, Mg-Ag, In and Mg-I.
n. Single metals such as Ca and Al or alloys thereof have been announced. As a criterion for selecting these materials, attention has been paid to how current can be efficiently injected without causing a voltage rise.

After that, an aluminum-lithium alloy was announced as an improved electrode material. However, although the use of this electrode lowered the driving voltage, the life of the light emitting device was somewhat extended. After all, it has not reached the level of practical use.

[0007]

Among the factors that determine the life of the organic light emitting device, the stability of the electrode is particularly important.
One of the keys is how to drive the device at low voltage. The specific issue for that purpose is the stable realization of electron injection from the cathode to the organic material. In the reports so far, there have been few reports of stable operation using a single metal, and binary alloys such as Mg-Ag or Al.
-Li electrodes and the like have been reported. However, even elements using these metals are required to have more stable electrodes by reacting with moisture or oxygen in the atmosphere over time to deteriorate the characteristics of the element.

[0008]

DISCLOSURE OF THE INVENTION The present invention is to improve an electrode which has the greatest influence on the deterioration of an organic light emitting device, and is characterized in that the cause of the deterioration of the electrode is removed from the surface of the electrode material. Is. As a means for this, the functions of the respective parts are overlapped by compounding the structure of the electrode material.

Specifically, at the interface between the metal electrode and the organic material, the work function or ionization potential of the family electrode was reduced. As a means for reducing the work function or the ionization potential, the work function of the metal at the interface portion is made smaller by oxidizing or hydroxylating the interface metal portion.

The present invention, which has the above-mentioned structure, has not been put into practical use because it lacks reliability in the related art by using a binary alloy and a ternary alloy for the electrodes of the organic light emitting device.
In the present invention, the bottom electrode can be driven by lowering the work function or ionization potential of the metal in the interface state by oxidizing or hydroxylating the electrode state at the interface with the organic material, and as a result, long life can be realized and practical I was able to approach the change.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, organic light emitting devices according to embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing the structure of an organic light emitting element according to an embodiment of the present invention. In FIG. 1, indium tin oxide, so-called ITO is formed on a glass substrate 11.
An electrode (first electrode) 12 is provided, and a hole transport material layer 13 made of an organic material and an electron transport material layer 14 made of an organic material are provided thereon by a vapor deposition method, a dipping method or a spin coat method,
Further, an electrode 15 (second electrode) is provided on it. The electrode is most easily prepared by vapor deposition or sputtering, and the vapor deposition method is also used in the present invention. By controlling the conditions during the production of the above electrode, a thin oxidation or hydroxide layer is formed between the electrode 15 and the electron transport material layer of the organic material.

Specifically, when forming an electrode, an oxide layer or a hydroxide layer is formed by increasing the concentration of oxygen molecules or hydrogen molecules in the atmosphere as compared with the case of normal film formation. . The thickness of the oxide layer or the hydroxide layer is preferably 50 angstroms or less.

As a metal having a low work function for injecting an electric current into an organic material, an alkali metal such as sodium, potassium or lithium, and an alkaline earth metal such as magnesium, aluminum or calcium are used.

Next, an energy diagram of each material having the structure shown in FIG. 1 is shown in FIG. In FIG. 2, 12 ITO
It can be seen that holes can be easily injected from the electrode into the hole transport material of 13. On the other hand, from 15 electrodes to 14
In the electron injection into the electron transporting material, the electron transporting material aluminum quinoline has a work function of 2.9 eV. In the example shown in FIG. 2, it is easier to inject the electron when the difference from Mg metal 3.7 eV is as small as possible. .

In order to show the effectiveness of the present invention, FIG. 3 shows the measurement results of the work function of the electrode. The measurement was performed using a surface observation device A-1 manufactured by Riken Denshi. The measurement principle is to irradiate the electrodes with light having wavelengths corresponding to various energies and count the number of electrons that are emitted to the outside. In the experiment, the sample is irradiated with light of various wavelengths, the corresponding energy is plotted on the horizontal axis, and the amount of electrons corresponding to the extracted electrons is plotted on the vertical axis, and the work function is extrapolated to the threshold value corresponding to that wavelength. To measure the work function and ionization potential. FIG.
The work function of the Mg electrode used for was measured on the surface 2 hours after the production. From FIG. 3, the work function of this surface can be measured as 4 eV.

Next, FIG. 4 shows an embodiment of the present invention.
It shows the change with time of the work function of the MgAg alloy produced by the vapor deposition method. The experiment is to measure the work function of the Mg electrode formed on the surface of the organic material with the vapor deposition device. Furthermore, both the interface of the organic material of the electrode and the surface in contact with the atmosphere are compared and described. As can be seen from the experimental results, the work function of the interface in contact with the organic material is 3.5 eV and 3.7 of Mg metal.
It can be seen that it is smaller than eV (in this experiment, the change in ionization potential of the interface with time is measured by taking out a new interface after the nuclear measurement time).

From the results of this experiment, it can be seen that the electrode material of the present invention causes an increase in ionization potential on the surface in contact with air, which is also caused by oxidation, but this electrode composition prevents internal oxidation.

As another experimental example, FIG. 5 shows the experimental result when Al is used as the metal electrode. Normally, the work function of Al is about 4.2 eV, but with the structure of the present invention, it is 3.3 eV.
It can be seen that the work function has dropped. Further, it can be seen from this experimental result that this electrode operates stably for 1000 hours or more.

In the present invention, it is desirable to use Mg, Ca, aluminum or aluminum alloy as the electrode material.

[0021]

According to the device structure thus far, an extra applied voltage is required to inject electrons into the organic material. Experimentally, a voltage of 10 V or higher was required. With the configuration of the present invention, the drive voltage can be reduced to 10 V or less, usually to about 5 V. We also confirmed that it operates more stably.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of an organic light emitting device according to an embodiment of the present invention.

FIG. 2 is a diagram showing an energy diagram of a material used for the organic light emitting device in the embodiment of the present invention.

FIG. 3 is a diagram showing a measurement result of a work function of an electrode used for an organic light emitting element in an embodiment of the present invention.

FIG. 4 is a diagram showing a measurement result of a work function of an electrode used for an organic light emitting element in an embodiment of the present invention.

FIG. 5 is a diagram showing measurement results of work functions of electrodes used in the organic light emitting device according to the embodiment of the present invention.

[Explanation of symbols]

 11 Glass Substrate 12 ITO Transparent Electrode 13 Hole Transport Material Layer 14 Electron Transport Material Layer 15 Metal Electrode

Claims (7)

[Claims] 1. A first electrode formed on a substrate, a hole-transporting material layer formed on the first electrode, and an electron-transporting material layer made of an organic material formed on the hole-transporting material layer. And a second electrode formed on the electron transporting material layer, wherein a monovalent metal, a divalent metal or a trivalent metal is used as the material of the second electrode. An organic light-emitting device, which is used and has a layer formed by oxidizing or hydroxylating the surface of the second electrode at the interface between the electron transport material layer and the second electrode. 2. A first electrode formed on a substrate, a hole transport material layer formed on the first electrode, and an electron transport material layer made of an organic material formed on the hole transport material layer. And a second electrode formed on the electron transporting material layer, wherein a monovalent metal, a divalent metal or a trivalent metal is used as the material of the second electrode. A binary or ternary alloy with another metal is used, and a layer formed by oxidizing or hydroxylating the surface of the second electrode is formed at the interface between the electron transport material layer and the second electrode. Characteristic organic light emitting device. 3. The organic light emitting device according to claim 1, wherein Mg, Ca, aluminum or an alloy thereof is used as the second electrode. 4. The organic light emitting device according to claim 1, wherein the oxidized or hydroxylated layer has a thickness of 50 angstroms or less. 5. The work function or ionization potential of the electrode at the interface between the electron transporting material layer and the second electrode is set to be smaller than that of the metal of the second electrode before use. The organic light emitting device according to. 6. A step of forming a first electrode on a substrate, and a step of forming a hole transport material layer on the first electrode,
Manufacture of an organic light emitting device, comprising: forming an electron transporting material layer of an organic material on the hole transporting material layer; and forming a second electrode on the electron transporting material layer by vacuum deposition or spattering. In the method, a monovalent metal, a divalent metal or a trivalent metal is used as a material of the second electrode, and in the step of forming the second electrode, an atmosphere of oxygen molecules or hydrogen is used. A method for manufacturing an organic light emitting device, characterized in that a layer in which the surface of the second electrode is oxidized or hydroxylated is formed at the interface between the electron transport material layer and the second electrode by increasing the concentration of molecules. . 7. A step of forming a first electrode on a substrate, and a step of forming a hole transport material layer on the first electrode,
Manufacture of an organic light emitting device, comprising: forming an electron transporting material layer of an organic material on the hole transporting material layer; and forming a second electrode on the electron transporting material layer by vacuum deposition or spattering. In the method, a binary alloy or a ternary alloy of a monovalent metal, a divalent metal or a trivalent metal and another metal is used as a material of the second electrode, and the second electrode is used. In the step of forming an electrode, a layer obtained by oxidizing or hydroxylating the surface of the second electrode is formed at the interface between the electron transport material layer and the second electrode by increasing the concentration of oxygen molecules or hydrogen molecules in the atmosphere. A method of manufacturing an organic light-emitting device, which comprises forming.