JPH1154287A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the continuation of short circuit between a negative electrode and a positive electrode by the action of internal stresses, even in the case of the generation of short circuit due to dust and a flaw by making the internal stresses of a first negative electrode different from that of a second negative electrode. SOLUTION: A metal electrode 1a between metal electrodes 1a, 1b is formed of aluminum into a film state, and the metal electrode 1b is formed of copper into a film state on the metal electrode 1a. Aluminum is smaller in tensile stress than copper of the metal electrode 1b. In thin parts of an organic layer 3 between the metal electrodes 1a, 1b to be negative electrodes and a transparent electrode 2 to be a positive electrode due to dust and flaws, a drive current is concentrated on these thin parts, and the organic layer 3 is evaporated by heating, so as to generate short circuit between the metal electrodes 1a, 1b and the transparent electrode 2. The metal electrodes 1a, 1b at these parts are ruptured to form holes, and the metal electrodes 1a, 1b are curved out in a direction opposite to the transparent electrode 2 side, so as to dissolve a short-circuited state and to prevent emission failure. It can also be so constituted that the compressive stress of the metal electrode 1b is smaller than that of the metal electrode 1a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence device.

[0002]

2. Description of the Related Art Conventionally, an organic electroluminescence device (hereinafter, referred to as an organic EL (Electro-luminescence) device) which emits light by passing an electric current through a phosphor formed on a glass plate or a transparent organic film.
ectroluminecsence elements) are known.
As shown in FIG. 3, a transparent electrode 2 serving as a plurality of anodes made of ITO or the like, as shown in FIG.
An organic layer 3 including a hole transport layer and a light emitting layer, and a plurality of metal electrodes 1 serving as cathodes crossing the transparent electrode 2 are sequentially deposited and laminated. The transparent electrode 2 and the metal electrode 1 which face each other with the organic layer 3 interposed therebetween form a light emitting portion which is an organic EL light emitting element, and the transparent electrode 2 and the metal electrode 1
Are formed as one unit with the light emitting portion of the intersection region where each of the light emitting portions crosses each other so as to face each other.

Further, in order to supplement the conductivity of the transparent electrode 2 having a high electric resistance, a bus line 7 of a low resistance portion made of a metal film is used.
Are partially laminated between the transparent electrode 2 and the organic layer 3.
In the organic EL element having such a configuration, each layer is arranged in a matrix.

The metal electrode 1 includes Cr, Al, an alloy of Mo (molybdenum) and Ta (tantalum), Al, Cu and Si.
A low-resistance material having good conductivity such as an alloy of ITO is used, and a conductive material (I) having a large work function such as ITO is used for the transparent electrode 2.
For example, TO work function = about 5.0 eV or gold (Au work function = about 5.1 eV) is used. When gold is used as an electrode material, the electrode is in a translucent state.

The bus line 7 laminated on a part between the transparent electrode 2 and the organic layer 3 is made of Cr, Al, an alloy of Mo and Ta, an alloy of Al, Cu and Si, or the like. The cost is reduced by using the same material for the metal electrode 1 and the bus line 7.

In manufacturing such an organic EL device, if two electrodes of an anode and a cathode of the organic EL device are short-circuited (short-circuited) due to dust or scratches, the pixel becomes defective in light emission, and the whole line becomes undesired. Light emission failure may occur. The anode and the cathode are short-circuited due to dust on the anode and before and after the organic layer is formed, and when a current is concentrated there, the current generates heat and a part of the organic layer evaporates. The short circuit continues, resulting in a light emission failure of the display panel of the organic EL element. This is shown in FIG. That is, the resistance becomes small near the scratch on the left side of FIG. 4 on the transparent electrode 2 and near the dust (particles) on the right side of FIG. Therefore, the current is concentrated on a portion where the resistance is small, so that a short circuit occurs.

[0007]

As described above, the organic E
In the L element, the above-described problem occurs when the short circuit between the anode and the cathode due to dust or scratches continues. However, if the short circuit can be prevented from continuing, the light emission failure is suppressed to a narrow range. be able to. The present invention has been made in view of the above problems, and has as its object to provide an organic EL element having few light-emission defects.

[0008]

According to a first aspect of the present invention, there is provided an organic EL device comprising at least an anode, a luminescent layer, a first cathode and a second cathode on a transparent substrate. Are sequentially laminated, wherein the internal stress of the first cathode and the internal stress of the second cathode are made different.

The invention described in claim 2 is the first invention.
Wherein the tensile stress of the second cathode is greater than the tensile stress of the first cathode.

[0010] Further, the invention according to claim 3 is based on claim 1.
Wherein the compressive stress of the second cathode is smaller than the compressive stress of the first cathode.

[0011]

In the present invention, the cathode is constituted by the first and second cathodes having different internal stresses in the organic EL element. Therefore, even if a short circuit occurs due to the presence of dust or scratches, the cathode and the anode are acted on by the internal stress. Continuation of the short circuit with the user can be prevented.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to FIGS. FIG. 1 is a sectional view showing the structure of each layer constituting the organic EL device according to the present invention. FIG. 2 shows the internal stress of the metal electrodes constituting the first and second cathodes of the organic EL device according to the present invention. It is sectional drawing explaining. FIG. 1 is the same as the structure described for the structure of the conventional organic EL element.
Since some of the materials are different, portions corresponding to the respective portions in FIG. 3 are given the same numbers.

As shown in FIG. 1, a plurality of transparent electrodes 2, such as ITO, serving as a first electrode, an organic layer 3, and a plurality of second electrodes intersecting the transparent electrode 2 are formed on a glass transparent substrate 6. A metal electrode 1a as a second cathode having a different internal stress from a metal electrode 1a as a first cathode and a metal electrode 1a as a first cathode
b. The transparent electrode 2 and the metal electrodes 1a, 1a, 1
b, a light-emitting portion serving as an organic EL light-emitting element is formed, and the light-emitting portion in an intersection region where the transparent electrode 2 and the metal electrodes 1a and 1b face each other and cross each other is defined as 1 unit.
Pixels are formed.

In order to supplement the conductivity of the transparent electrode 2 having a high electric resistance, a bus line (not shown) of a low-resistance portion having a width smaller than that of the transparent electrode 2 made of a metal film having a larger work function than the transparent electrode is provided. It is laminated on a part between the transparent electrode 2 and the organic layer 3, and the respective layers are arranged in a matrix.

As the metal electrode 1a, a metal having a small work function (for example, an Al-Li alloy) such as aluminum, magnesium, indium, silver, or an alloy of each is used. For the metal electrode 1b, a metal material or a manufacturing method having an internal stress different from that of the metal electrode 1a is used as described later. In addition, for the transparent electrode 2, a conductive material having a large work function, such as ITO, or gold can be used. When gold is used as an electrode material, the electrode is in a translucent state.

A bus line (not shown) laminated on a part between the transparent electrode 2 and the organic layer 3 includes gold having a large work function:
Au, platinum: Pt, selenium: Se, nickel: Ni, or an alloy material containing these metals is used.

The metal electrodes 1a and 1b are, for example,
a is formed of aluminum (Al), and the metal electrode 1b is formed of copper (Cu) on the metal electrode 1a. Metal electrode 1a
Al is known to have a smaller tensile stress than Cu of the metal electrode 1b.

Therefore, since the tensile stress of the Cu metal electrode is larger than the tensile stress of the Al metal electrode, the organic layer between each metal electrode that becomes a cathode due to dust and scratches and the transparent electrode that becomes an anode is formed. In a thin portion, the driving current is concentrated in this portion, and the heat generated causes the organic layer to evaporate, causing a short circuit between the cathode and the anode, and the cathode in that portion is broken to form a hole. Therefore, a force acts to warp in the direction opposite to the side of the transparent electrode serving as the anode due to internal stress. As a result, the metal electrode
In a state where a hole is formed in a portion such as dust or a scratch, the portion warps to the side opposite to the transparent electrode and the short-circuit state is eliminated.

The above-mentioned internal stress is aluminum: A
It is reported that l, silver: Ag, gold: Au, lead: Pb, and copper: Cu are larger in this order, so that they can be appropriately selected and used as each metal electrode.

FIG. 2 shows the metal electrodes 1a,
Reference numeral 1b denotes a warped portion that partially bends due to a difference in tensile internal stress between each other. That is, after the heat generated causes the organic layer to evaporate and break the portion that was short-circuited with the transparent electrode of the cathode, S1 in the diagram showing the tensile internal stress of the metal electrode 1a, whereas S1 in the diagram showing the tensile internal stress of the metal electrode 1b Since S2 is large, the metal electrode 1a
As shown in the figure, a force is applied to the b to contract, and the short-circuit state is eliminated by warping to the opposite side to the transparent electrode.

In the above description, the case where each metal electrode is made of a different kind of metal has been described. However, even if the same material is used, the internal stress varies depending on the thin film forming process. Therefore, for example, a metal electrode serving as a first cathode is formed by vapor deposition by resistance heating with Al, and a metal electrode serving as a second cathode is formed on the same A electrode.
The vapor deposition by EB (electron beam) is performed with l.

By using different film forming methods for forming the respective metal electrodes as described above, the internal stresses of the respective metal electrodes serving as the first and second cathodes can be made different, and the above-mentioned materials are made different. The same effect as in the case can be obtained.

Further, in the film forming process, there are various parameters such as a processing time and a processing temperature which influence the film forming state. Therefore, the same effect can be obtained by changing the parameters to form the film.

As described above, by forming the respective electrodes by making the film forming processes of the first and second metal electrodes different from each other, the same effect as when the above-mentioned different materials are formed can be obtained. Is possible. In the above description, the tensile stress was used. However, even if the compressive stress is applied, the action of the force is opposite to the tensile stress, so that the compressive stress of the metal electrode serving as the second cathode is reduced by that of the metal electrode serving as the first cathode. If it is smaller than the compressive stress, the same effect can be obtained.

In the above description, an example of a two-layer metal electrode has been described, but it goes without saying that three or more layers may be used.

As described above, by forming the first metal electrode and the second metal electrode having different internal stresses by making the material or the forming process of the thin film different from each other, the dust can be reduced. After the electrical short between the cathode and the anode in the area where there is damage or damage is broken by heat, etc., the internal electrode displaces the cathode electrode to the opposite side to the opposite anode, causing an electrical short. Can be eliminated.

The part of the electrode constituting the cathode that has short-circuited with the anode at a part having dust or scratches is broken, and the internal stress warps to the opposite side of the anode to eliminate the short-circuit state with the anode. Although this may occur during energized light emission aging during the manufacturing process, it can also be expected when the user energizes during use.

In the above description, the difference between the internal stresses of the two layers constituting the cathode is used. However, the same effect can be expected by using magnetic attraction as another method. For example, the first cathode is formed of an aluminum thin film on the organic layer, and a second material containing a magnetic material or a magnetic material is formed on the first cathode.
Is formed by vapor deposition or the like.

Next, after the entire laminated portion on the transparent glass substrate is sealed with a protective film, a magnet is disposed outside the protective film, whereby a magnet disposed on the side opposite to the transparent glass substrate is provided.
A magnetic attraction force acts between the sealed inner magnetic material forming the second cathode, and the second portion of the portion that is short-circuited with the anode of the electrode constituting the cathode in a portion having dust and scratches. The cathode is broken by the magnetic attraction with the first cathode to the side opposite to the anode, and a short circuit with the anode can be eliminated.

In addition, the entire pixel or its entire line does not fail to emit light, and if the short-circuit state is eliminated, only a part of the pixel having dust or scratches may cause the failure of light emission. Can be significantly reduced, and an organic EL element with improved quality can be obtained.

[0031]

As described above, according to the present invention,
In the organic EL device, the cathode is constituted by the first cathode and the second cathode having different internal stresses. Therefore, even if a short circuit occurs due to the presence of dust or scratches, the cathode and the anode are connected by the action of the internal stress. Continuation of the short circuit can be prevented, and an organic EL element having few defective light emission portions can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration of each layer constituting an organic EL device according to the present invention.

FIG. 2 is a cross-sectional view illustrating the internal stress of a metal electrode constituting each of the first and second cathodes of the organic EL device according to the present invention.

FIG. 3 is a diagram showing a structure of an organic EL element.

FIG. 4 is a cross-sectional view showing a structure of a portion of a conventional organic EL element such as dust and scratches.

[Explanation of symbols]

 1, 1a, 1b ··· Metal electrode 2 ··· Transparent electrode 3 ··· Organic layer 6 ··· Glass transparent substrate 7 ··· Bus line

Continued on the front page (72) Inventor Tatsufumi Murayama 4- 3146-7, Yawatahara, Yonezawa-shi, Yamagata Prefecture Inside Yonezawa Plant, North Pioneer Co., Ltd. (72) Yasuhiko Sawada 4- 3146-7, Yawatahara, Yonezawa-shi, Yamagata East Kita Pioneer Co., Ltd. Yonezawa Plant (72) Inventor Teruo Toma 4- 3146-7, Yawatahara, Yonezawa City, Yamagata Prefecture East Kita Pioneer Co., Ltd. Yonezawa Plant (72) Inventor Hitoshi Nakata 4- 3146, Yawatahara, Yonezawa City, Yamagata Prefecture 7 Tohoku Pioneer Co., Ltd. Yonezawa Plant (72) Inventor Hirofumi Kubota 6-1, 1-1 Fujimi, Tsurugashima-shi, Saitama Pref.

Claims (3)

[Claims] 1. A transparent substrate comprising at least an anode, a light-emitting layer,
An organic electroluminescence device comprising a first cathode and a second cathode which are sequentially laminated, wherein the internal stress of the first cathode is different from the internal stress of the second cathode. element. 2. The organic electroluminescent device according to claim 1, wherein the tensile stress of the second cathode is greater than the tensile stress of the first cathode. 3. The organic electroluminescence device according to claim 1, wherein the compressive stress of the second cathode is smaller than the compressive stress of the first cathode.