JPH1140369A - Electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroluminescent element with no uneven brightness. SOLUTION: An anode 11 made of ITO (indium tin oxide) and an organic EL layer 13 are formed sequentially on a glass substrate 10. By using the same metal mask, a low resistant metal electrode 12 made of Mg and a cathode 14 are formed by vapor deposition. A contact region 14a of the cathode 14 is connected to a cathode extraction electrode 15 made of ITO formed at the same time as the anode 11. They are sealed with a sealing member 16 except for the anode extraction terminal 14a and a cathode extraction terminal 15a. Voltage applied from the anode extraction terminal 14a is applied to a low resistant metal electrode 12 with almost no drop. Voltage between the electrodes is not varied in any portions, and the organic EL layer 13 emits light in almost the same brightness in any portions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent device, and more particularly to an electroluminescent device which does not cause luminance unevenness even when the area is increased.

[0002]

2. Description of the Related Art An organic EL panel is known as a backlight of a flat display such as a liquid crystal display. Organic E which has been conventionally used as a backlight
The L panel 3 includes, for example, an anode electrode 31 laminated on a transparent glass substrate 30 and an organic
It is composed of an L layer 32 and a cathode electrode 33.
At one end of the anode electrode 31, an anode electrode extraction terminal 31a is provided. At one end of the cathode electrode 33, a cathode electrode extraction terminal 33a is provided.

Here, the anode electrode take-out terminal 31a
A predetermined voltage is applied to each of the cathode electrode take-out terminals 33a and the anode electrode 31 of the organic EL panel 3.
By applying a predetermined voltage equal to or greater than a threshold value between the organic EL layer 32 and the cathode electrode 33, a current flows through the organic EL layer 32, and energy generated by recombination of electrons and holes is transferred to the organic EL layer 3.
2 emits light when absorbed by the light emitting layer.

The light emitted from the organic EL layer 32 passes through the anode electrode 31 and the glass substrate 30 and is displayed. Therefore, the anode electrode 31 is generally made of transparent ITO.
(Indium Tin Oxide), and for the cathode electrode 33, a reflective low-resistance Mg (Magnesium) alloy is used.

However, since the ITO constituting the anode electrode 31 has a higher resistance than the metal material of the cathode electrode 33, the voltage applied from the anode electrode extraction terminal 31a decreases as the distance from the anode electrode extraction terminal 31a increases. For this reason, the voltage between the anode electrode 31 and the cathode electrode 33 decreases as the distance from the anode electrode extraction terminal 31a increases, and the current flowing through the organic EL layer 32 decreases. For this reason, the conventional organic EL panel 3 has a problem that the brightness may be uneven depending on the distance from the anode electrode 31.

In order to solve the uneven brightness of the organic EL panel 3 due to the voltage drop at the anode electrode 31, it is conceivable to form the anode electrode 31 thick. That is, by forming the anode electrode 31 thick, the resistance value of the anode electrode 31 is reduced, and a voltage drop at the anode electrode 31 is prevented.

However, when the anode electrode 31 is formed thick to reduce the resistance, the amount of light absorbed by the anode electrode 31 out of the light emitted from the organic EL layer 32 increases. In particular, when the anode electrode 31 has a thickness longer than the wavelength of the light emitted from the organic EL layer 32, the light absorption increases, and thus the light displayed on the organic EL panel 3 becomes dark. was there.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and has as its object to provide an electroluminescent device having no uneven brightness.

[0009]

In order to achieve the above object, an electroluminescent device according to a first aspect of the present invention comprises a first electrode having a first terminal for applying a voltage, A light emitting layer formed on the first electrode and emitting light in accordance with an applied electric field; and a light emitting layer having a lower sheet resistance than the first electrode formed on the peripheral end of the first electrode. An end electrode; and a second electrode formed to be stacked on the light emitting layer and having a region for applying a voltage, wherein the light emitting layer has a voltage applied to the first and second electrodes. And emits light in accordance with the electric field generated thereby.

In this electroluminescent device, a peripheral electrode having a smaller sheet resistance than the first electrode is provided on a peripheral end of the first electrode, so that the first terminal is connected to the peripheral terminal in the peripheral resistance. The drop of the applied voltage is small. The first
Even if a voltage drop occurs at the first electrode, the voltage drop follows the distance from the peripheral electrode, so that the voltage drop at the first electrode can be prevented to a considerable extent. Therefore, there is no large difference in the voltage between the electrodes depending on the distance from the first terminal, and the light emission luminance does not vary depending on the location.

Here, the peripheral end does not necessarily mean the entire area of the peripheral end. In addition, the first and second
The electric field generated by the voltage between the substrates is determined by the distance between the first and second substrates and the resistance of the light emitting layer. When the voltage between the substrates becomes equal to or higher than a predetermined value, current flows through the light emitting layer, and the light emitting layer emits light.

In the above electroluminescent device, it is preferable that the second electrode is made of the same material as the peripheral electrode.

[0013] The electroluminescent device is further connected to the region of the second electrode, is made of a material having a higher work function than the second electrode, and has a second function for applying a voltage to an end. An extraction electrode having a first terminal and a second electrode.
And a sealing member that seals the first electrode, the light emitting layer, the peripheral electrode, the third electrode, and the removal electrode.

Here, a material having a higher work function is less likely to undergo a chemical change such as oxidation. That is, it means that the extraction electrode is less likely to undergo a chemical change than the second electrode, and that the performance is less deteriorated.

In this case, the second electrode having a low work function and excellent electron emission properties can be sealed with the sealing member, so that a chemical change of members constituting the electroluminescent element is less likely to occur. . For this reason, it is possible to prevent the performance of the electroluminescent device from deteriorating.

In the above-mentioned electroluminescent device, it is preferable that the peripheral electrode is formed in a shape in which a substantially U-shape is opposed.

By configuring the peripheral end electrode in this manner, the supporting force of the metal mask used when forming the peripheral end electrode can be increased. For this reason, the metal mask can be more closely adhered to a substrate or the like on which the electroluminescent element is formed, and a clean electrode pattern can be formed.

In the above-mentioned electroluminescent device, the first electrode may be constituted by, for example, a transparent electrode.

In order to emit the light emitted from the light emitting layer to the outside, at least one of the first and second electrodes must be an IT
It is necessary to be composed of a transparent electrode made of O or the like. However, since a transparent electrode generally has a higher resistance than a metal electrode and a voltage drop is likely to occur, a voltage drop can be prevented by forming a peripheral end electrode at a peripheral end of the transparent first electrode.

In the above electroluminescent device, the light emitting layer may be constituted by an organic electroluminescent layer.

[0021]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In this embodiment, a case will be described in which the present invention is applied to an organic EL panel used as a backlight of a portable information terminal including a liquid crystal panel.

FIG. 1 is a diagram schematically showing the configuration of the organic EL panel 1 of this embodiment. FIG. 2 is a plan view of the organic EL panel 1 of FIG. 1, and FIG. FIG. 4 is a cross-sectional view taken along a line A. 1, the organic EL panel 1 has an anode electrode 11, a low-resistance metal electrode 12, an organic EL layer 13, a cathode electrode 14, and a cathode extraction electrode 15 stacked in a predetermined order on a transparent glass substrate 10. It was formed.

The anode electrode 11 is formed by forming ITO sputtered over the entire surface of the glass substrate 10 into a predetermined shape by photolithography. The anode electrode 11 is made of a transparent I
It is made of TO and transmits light emitted from the organic EL layer 13.
The sheet resistance of the anode electrode 11 is 8Ω / □. At one end of the anode electrode 11, an anode electrode take-out terminal 11a for applying a voltage to the anode electrode 11 is provided.

The low resistance metal electrode 12 is connected to the anode electrode 11
Are formed in such a manner that the U-shape faces each other on the peripheral end portion. The low-resistance metal electrode 12 is formed by vacuum evaporation using the same metal mask as the metal mask for forming the cathode electrode 14. The low-resistance metal electrode 12 is made of Mg, similarly to a cathode electrode 14 described later, and has a sheet resistance of 0.3Ω / □. Low resistance metal electrode 12
Is to prevent a voltage drop of the voltage applied from the anode electrode extraction terminal 11a even in a portion far from the anode electrode extraction terminal 11a.

The organic EL layer 13 emits white light for use as a backlight by vacuum evaporation to form three types of organic E layers for red (R), green (G), and blue (B).
The L layers are formed in a predetermined order. The organic EL layer 13
As shown in FIG. 4, a hole transport layer 13a is formed on the anode electrode 11 in common for R, G, and B. The hole transport layer 13a is formed so that the layer thickness varies depending on the distance from the low-resistance metal electrode 12, as described later. On the hole transport layer 13a, an electron transporting light emitting layer 13r for R,
Electron transporting light emitting layer 13g for G, light emitting layer 13ba for B
And the electron transport layer 13bb are formed in a predetermined order.

The hole transport layer 13a common to R, G, and B has an α
-Consisting of NPD. The electron transporting light emitting layer 13r for R is
DCM1 consists of dispersed Alq3. The electron transporting light emitting layer 13g for G is made of Bebq2. The light emitting layer 13ba for B is composed of 96% by weight of DPVBi and 4% by weight of B
CzVBi. The electron transport layer 13bb for B is made of A
1q3. These electron transporting light emitting layer or electron transporting layer and light emitting layer, by using a mask,
R, G, and B are sequentially formed.

When a voltage equal to or higher than a threshold value is applied between the anode electrode 11 and the cathode electrode 14, holes are injected from the hole transport layer 13a by the energy of the electric field generated thereby, and the electron transporting light emitting layer 13r, Electrons are injected from 13g or the electron transport layer 13bb. The energy excited by the recombination of the holes and the electrons is transferred to the electron transporting light emitting layers 13r and 13g or the light emitting layer 13b.
The light of R, G, and B is emitted by the absorption of a. The organic EL panel 1 emits white light by additively mixing three colors of R, G, and B emitted from the respective organic EL layers for R, G, and B.

The organic EL layer 13 is formed on the anode electrode 1
1 is formed leaving a region where the low-resistance metal electrode 12 is formed. In addition, the organic EL layer 13 includes the anode electrode 11
It is also formed on a portion of the anode electrode 11 where a contact region 14a to be described later is formed so that the electrode 14 and the cathode electrode 14 do not contact each other.

The cathode electrode 14 is a low-resistance metal electrode 12
Is formed on the organic EL layer 13 by a vacuum evaporation method at the same time as the formation. The region where the cathode electrode 14 is formed is
It is much smaller than the region where the organic EL layer 13 is formed. The cathode electrode 14 has a thickness of 5500 °
It is made of Mg or a Mg alloy having a work function lower than 1, and has a sheet resistance of 0.3Ω / □. At one end of the cathode electrode 14, a contact region 14a for connecting to the cathode extraction electrode 15 is provided.

The cathode extraction electrode 15 is formed simultaneously with the anode electrode 11 by a photolithography method. At an end of the cathode extraction electrode 15, a cathode electrode extraction terminal 15a is provided. Since the cathode extraction electrode 15 is made of ITO having the same sheet resistance as the anode electrode 11, the width is increased except for the cathode electrode extraction terminal 15a in order to reduce the resistance value.

As described above, the organic EL panel 1 is used as a backlight of a liquid crystal display of a portable information terminal, and the area of a portion (display area) through which light passes through the glass substrate 10 is 6 ×. It is about 9cm. The thickness of the organic EL layer 13 of the organic EL panel 1 is 10
It is about 00-3000 °.

This organic EL panel 1 has a glass substrate 10
An anode electrode 11, a low resistance metal electrode 12, an organic EL layer 13, and a cathode electrode 14 were formed on the substrate.
These are actually sealed by a sealing member 16 made of resin except for the anode electrode lead-out terminal 11a and the cathode electrode lead-out terminal 15a.

Hereinafter, the organic EL panel 1 of this embodiment will be described.
Will be described with reference to FIGS. 5 (A) to 5 (E). Here, according to the cross section taken along the line BB in FIG.
The manufacturing process of the L panel 1 will be described sequentially.

First, an ITO thin film is deposited on the entire surface of the glass substrate 10 by a sputtering method. Then, unnecessary portions of the deposited ITO, that is, portions other than the portions serving as the anode electrode 11 and the cathode extraction electrode 15 are removed by photolithography. Thus, the anode electrode 11 and the cathode extraction electrode 15 are formed on the glass substrate 10 (step (A)).

Next, a metal mask having a window which is slightly smaller than the anode electrode 11 formed in the step (A) and slightly larger than a portion where the contact region 14a of the cathode electrode 14 overlaps the anode electrode 11 is placed at a predetermined position. At the same time, α-NPD is vacuum deposited. Thus, the hole transport layer 13a is formed by evaporating α-NPD on the window portion of the metal mask.

Next, a window is opened in accordance with the arrangement of the portion where the light emitting layer 13ba for B is to be formed. The metal mask is positioned at a predetermined position, and the hole transport layer 13a is formed on the blue light emitting region. Then, DPVBi and BCzVBi are mixed at a predetermined ratio and vacuum-deposited to form a light-emitting layer 13ba for B. Then, using the same metal mask, Alq
3 is vacuum-deposited to form an electron transport layer 13bb for B. Further, the hole transport layer 1 is formed by aligning metal masks having different windows respectively at predetermined positions.
Alq in which DCM1 is dispersed on the red light emitting region of 3a
3, and Bebq2 was vacuum-deposited on the green light emitting region,
And G electron transporting light emitting layers 13r and 13g are formed. Thereby, the entire organic EL layer 13 is formed (step (B)).

Next, a metal mask having windows opened in the opposed U-shaped low resistance metal electrode 12 and the cathode electrode 14 (including the contact region 14a formed integrally) is positioned at a predetermined position. Then, Mg is vacuum-deposited. Thus, Mg is deposited on the window portion of the metal mask, and the low-resistance metal electrode 12 and the cathode electrode 14 (contact region 1) are formed.
4a) (step (C)).

Then, the anode electrode 11, the low-resistance metal electrode 12, the organic EL layer 13, the cathode electrode 14, and the cathode extraction electrode 15 formed in the steps (A) to (C) are connected to the anode electrode extraction terminal 11a and The organic EL panel 1 is manufactured by sealing with the sealing member 16 except for the portion of the cathode electrode extraction terminal 15a (step (D)).

Hereinafter, the organic EL panel 1 of this embodiment will be described.
Will be described. In order to cause the organic EL panel 1 to emit light, a driver (not shown) applies a voltage of 4 V to the anode electrode extraction terminal 11a. Further, a voltage of 0 V is applied to the cathode electrode extraction terminal 15a.

The voltage applied to the anode electrode extraction terminal 11a is also applied to the low resistance metal electrode 12. Since the sheet resistance of the low-resistance metal electrode 12 is as small as 0.3 Ω / □, even if a current flows through the organic EL layer 13, the applied voltage hardly drops, and the potential of the low-resistance metal electrode 12 increases over the entire surface. It becomes almost 4V. In the anode electrode 11,
Since the sheet resistance is relatively large at 8Ω / □, the voltage drops depending on the distance from the low-resistance metal electrode 12. But,
Since the low-resistance metal electrode 12 is provided almost at the peripheral end of the anode electrode 11, the distance from the low-resistance metal electrode 12 is relatively short even at the center of the anode electrode 11, and the voltage drop is small.

On the other hand, the voltage applied to the cathode electrode extraction terminal 15a is applied to the cathode electrode 14 via the cathode extraction electrode 15 and the contact region 14a.
Here, the sheet resistance of the cathode electrode 14 is 0.3Ω / □.
Therefore, the value of the voltage applied to the cathode electrode take-out terminal 15a is hardly changed by the current flowing through the organic EL layer 13 in the cathode electrode 14. That is, the voltage of the entire cathode electrode 14 is almost 0V.

As a result, the voltage between the anode electrode 11 and the cathode electrode 15 does not significantly differ depending on the location. The organic EL element 13 emits light at a luminance corresponding to the voltage between the anode electrode 11 and the cathode electrode 15 at a corresponding location, but the emission luminance does not change much over the entire surface of the organic EL panel 1.

As described above, in the organic EL panel 1 of this embodiment, the anode electrode 11 made of ITO is used.
Is provided with a low-resistance metal electrode 12 made of Mg. Here, in the low resistance metal electrode 12, the voltage applied from the anode electrode extraction terminal 11a hardly drops. Therefore, even if the anode electrode 11 made of ITO is formed thin, a voltage drop at the anode electrode 11 can be prevented within a considerable range. For this reason, a large voltage difference does not occur depending on the distance from the anode electrode extraction terminal 11a.
The brightness of the L panel 1 does not vary depending on the location.

Further, the organic EL panel 1 of this embodiment
In the manufacturing process, the low-resistance metal electrode 12 and the cathode electrode 1
4 were formed in the same step using the same metal mask. By forming the low-resistance metal electrode 12 and the cathode electrode 14 in the same process as described above, the entire manufacturing process of the organic EL panel 1 can be shortened, and the manufacturing cost can be reduced. Further, by forming the low-resistance metal electrode 12 and the cathode electrode 14 using the same metal mask, precision of fine processing is not required for these two. Furthermore, the low resistance metal electrode 12
Since there is no intersection between the electrode and the cathode electrode 14, the occurrence rate of defective products due to a short circuit between these electrodes can be reduced.

In this embodiment, the metal mask used in the step of forming the low-resistance metal electrode 12 and the cathode electrode 14 has a window in which the U-shaped metal mask is opposed to each other. The resistance metal electrode 12 was formed such that U-shaped ones faced each other. Therefore, the supporting force of the metal mask itself is increased, and the adhesion between the substrate 10 and the metal mask is improved. Therefore, a clean electrode pattern can be formed.

Further, the organic EL panel 1 of this embodiment
In the manufacturing process, the low-resistance metal electrode 12 is formed after the organic EL layer 13 is formed on the anode electrode 11.
For this reason, the luminous characteristics of the organic EL panel 1 can be stabilized without affecting the interface state between the anode electrode 11 and the organic EL layer 13 which has a particularly strong influence on the luminous characteristics of the organic EL panel 1.

Further, the organic EL panel 1 of this embodiment
Then, the cathode extraction electrode 15 made of ITO is used.
And a portion other than the anode electrode extraction terminal 11a and the cathode electrode extraction terminal 15a is sealed with the sealing member 16. For this reason, the portions (the low-resistance metal electrode 12 and the cathode electrode 14) formed of Mg or Mg alloy, which are easily oxidized, can be sealed so as not to come into contact with air, and the performance of the organic EL panel 1 is reduced. There is no deterioration.

In the above embodiment, the anode electrode 11 made of ITO is formed on the glass substrate 10 side, and the organic EL
The light emitted from the layer 13 is applied to the anode electrode 11 and the glass substrate 1.
0 was displayed in a transparent manner. However, the anode electrode made of ITO may be formed farther from the substrate than the cathode electrode. In this case, a low-resistance metal electrode 12 made of Mg or a Mg alloy and a cathode electrode 14 are formed on a substrate, and an electron transporting light emitting layer or an electron transporting layer and a light emitting layer are formed on the cathode electrode 14, and then a metal mask is formed. Is used to form a hole transport layer having a different layer thickness depending on the region, and then the anode electrode 11 made of ITO is formed on the low-resistance metal electrode 12 and the hole transport layer. With this configuration, the light emitted from the organic EL layer is:
The light passes through the anode electrode and is displayed on the opposite side of the substrate. In this case, as the resin used as the sealing member, a transparent resin having light transmittance may be used.

In the above embodiment, the anode electrode 11
And a low-resistance metal such as Mg for the cathode electrode 14. However, ITO may be used for the cathode electrode and low resistance metal may be used for the anode electrode. Also in this case, the light emission luminance in the organic EL panel can be made uniform by the thickness of the low resistance metal electrode and the organic EL layer provided at the peripheral end of the cathode electrode. Further, for the cathode electrode and the low-resistance metal electrode, metals other than Mg having a small sheet resistance, such as Ti (Titanium), can also be used.

In the above embodiment, the cathode electrode 14
The cathode extraction electrode 15 made of ITO was connected to the contact region 14a, and the entire cathode electrode 14a was sealed with the sealing member 16. However, there is no such cathode extraction electrode, and even if the contact region of the cathode electrode is used as the cathode extraction electrode as it is, the organic E
The light emission luminance of the L panel can be made uniform in the same manner.

In the above embodiment, the low-resistance metal electrode 1
Reference numeral 2 denotes a cathode electrode 14 using one metal mask.
Was formed at the same time in the step of forming. However, the low-resistance metal electrode 12 may be formed in a step different from the step of forming the cathode electrode 14. In this case, a voltage drop can be further prevented by increasing the thickness of the low-resistance metal electrode 12.

In the above embodiment, the organic EL panel 1
In addition, three types of organic EL layers of R, G, and B are arranged in a predetermined order, and white light is displayed by additive color mixing of the three colors of R, G, and B. Thus, the three types of organic E of R, G, and B
Instead of disposing the L layer 13, the present invention can be applied to an electroluminescent element having a layer that emits white light. In addition, by arranging three types of organic EL panels for R, G, and B in an overlapping manner, an organic EL panel that emits white light can be formed. In this case, organic EL for R, G, B
The thickness of the organic EL layer can be changed for each of the panels as described above. Further, the present invention can be applied not only to an element emitting white light but also to an electroluminescent element emitting light of any color. Further, the light emitting layer may also serve as a hole transport layer.

In the above embodiment, a case has been described in which the present invention is applied to the organic EL panel 1 used as a backlight of a portable information terminal having a liquid crystal panel. However, the present invention can also be used for an organic EL element used for another purpose that emits light by applying a predetermined voltage between the electrodes. Further, the present invention can be applied to other light-emitting elements that emit light by an electric field, such as an inorganic EL element.
Further, the size can be applied to various sizes.

[0054]

As described above, according to the electroluminescent device of the present invention, luminance unevenness does not occur due to the voltage drop of the voltage applied to the electrode.

Further, by providing an extraction electrode having a work function higher than that of the second electrode and sealing the second electrode with a sealing member, a chemical change of members constituting the electroluminescent element is less likely to occur. In addition, deterioration of the performance of the electroluminescent device can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of an organic EL panel according to an embodiment of the present invention.

FIG. 2 is a plan view of the organic EL panel of FIG.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is a diagram showing the structure of three types of organic EL layers of red, green, and blue for generating white light in the organic EL layer of the organic EL panel of FIG. 1;

FIG. 5 is a view showing a manufacturing process of the organic EL panel of FIG. 1;

FIG. 6 is a view schematically showing a configuration of a conventional organic EL panel.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Organic EL panel, 10 ... Glass substrate, 11 ... Anode electrode, 11a ... Anode extraction terminal, 1
2 ... low resistance metal electrode, 13 ... organic EL layer, 14 ... cathode electrode, 14a ... contact area, 15 ... cathode extraction electrode, 15a ... cathode electrode extraction terminal, 16 ... ..Sealing members

Claims (5)

[Claims] A first electrode having a first terminal for applying a voltage, a light emitting layer laminated on the first electrode and emitting light in accordance with an applied electric field; A peripheral electrode having a lower sheet resistance than the first electrode formed by being laminated on the peripheral end of the first electrode; and a region for applying a voltage which is formed by being laminated on the light emitting layer. And a second electrode, wherein the light emitting layer emits light according to an electric field generated by a voltage applied to the first and second electrodes. 2. The electroluminescent device according to claim 1, wherein the second electrode is made of the same material as the peripheral electrode. 3. An extraction electrode connected to the region of the second electrode, made of a material having a higher work function than the second electrode, and having a second terminal for applying a voltage to an end. And a sealing member that seals the first electrode, the light emitting layer, the peripheral electrode, the third electrode, and the removal electrode, leaving the first and second electrodes. The electroluminescent device according to claim 1, wherein: 4. The electroluminescent device according to claim 1, wherein the peripheral electrode is formed in a shape in which a substantially U-shape is opposed. 5. The electroluminescent device according to claim 1, wherein the light emitting layer is constituted by an organic electroluminescence layer.