JPH10199678A - Electroluminescence element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroluminescence element of high reliability in which growth of a non-light emitting part is restrainted. SOLUTION: A first anode electrode 13 comprising ITO, a first organic electroluminescence layer 16, a cathode electrode 17 comprising MgIn, a second organic electroluminescence layer 20, and a second anode electrode 21 comprising ITO are formed on a substrate 12. In above constitution, the cathode electrode 17 comprising MgIn which is easy to be oxidized is held between the first organic electroluminescence layer 16 and the second organic electroluminescence layer 20, so invasion of air or water into the cathode electrode 17 can be prevented to restrain growth of a non-light emitting part. Since a voltage to be applied to each organic electroluminescence layer can be low, deterioration of the organic electroluminescence layer by application of the voltage can be restrained to restrain growth of the non-light emitting part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an electroluminescent device, and more particularly, to an electroluminescent device using an organic electroluminescent material for a light emitting layer.

[0002]

2. Description of the Related Art An electroluminescent element (EL light emitting element) utilizing electroluminescence has an advantage of high visibility since it emits light by itself. In addition, such an electroluminescent device has attracted attention as a device for realizing a large-screen full-color display. Further, the electroluminescent element has an advantage that it is excellent in impact resistance and can be supplied at a low cost because it is a solid-state element. As this type of electroluminescent element, inorganic EL
There are an inorganic electroluminescent device having a layer and an organic electroluminescent device having an organic EL layer.

As an organic electroluminescent device, recently, a device capable of emitting light with high luminous efficiency and a long life at a low driving voltage has been developed. The structure of the organic electroluminescent device includes a structure in which the organic material layer is a single layer, and a structure in which the organic material layer has two, three, or more layers. For example, it is known that an organic EL light emitting device having an organic material layer having a two-layer structure includes an electron transport layer and a hole transport layer, and emits light near an interface between both layers. Further, as an organic EL light emitting device having a three-layer structure, a device having an electron transport layer, a light emitting layer, and a hole transport layer is known. Further, a material in which different organic materials are laminated or mixed in each of these layers is known.

FIG. 5 shows a sectional structure of an organic electroluminescent device having an organic material layer having a two-layer structure. In this organic electroluminescent device, a plurality of anode electrodes 2 are formed on a glass substrate 1 so as to be parallel, and a hole transport layer 3 and an electron transport layer 4 are sequentially formed on the glass substrate 1 and the anode electrode 2. A plurality of cathode electrodes 5 are formed on the electron transport layer 4 so as to be parallel to each other along a direction perpendicular to the anode electrode 2.

[0005]

However, in the conventional electroluminescent device described above, in order to obtain a good light emission amount, the organic EL layer needs to be formed due to the voltage applied between the anode electrode 2 and the cathode electrode 5. There is a problem of deterioration.
When the organic EL layer deteriorates, for example, the organic EL layer
Since the adhesion between the layer and the electrode is reduced, or the efficiency of injecting electrons or holes from the electrode to the organic EL layer is reduced, the non-light-emitting portion (dark spot) increases, and the life of the electroluminescent element is extended Is shortened. In particular, a large-screen electroluminescent device has a problem that the yield is greatly reduced due to the generation of non-light emitting portions. In addition, the cathode electrode of the electroluminescent element is formed of a material having a property of easily injecting electrons into the organic EL layer (electron injecting property). Such materials include MgIn, AlLi, and the like. However, these materials have a problem of low transparency and a problem of being easily oxidized by oxygen or water in the air. As described above, since the cathode electrode is easily oxidized, there is a problem that a non-light emitting portion grows and the reliability of the electroluminescent device is reduced.

The problem to be solved by the present invention is that what means should be taken to suppress the growth of the non-light emitting portion and obtain a highly reliable electroluminescent device.

[0007]

According to the first aspect of the present invention,
A first anode electrode, a first organic EL layer, a light-transmissive cathode electrode, a second organic EL layer,
It is characterized in that an anode electrode and a second anode electrode driven simultaneously corresponding to the anode electrode are laminated. In the invention described in claim 1, the first organic EL layer sandwiched between the cathode electrode and the first anode electrode and the second organic EL layer sandwiched between the cathode electrode and the second anode electrode are the same. Light is emitted in the area. Therefore, in order to obtain a predetermined light emission amount in this region, the light emission amount in each organic EL layer may be small, and a low voltage may be applied to each of the first and second organic EL layers. As described above, since the voltage applied to each organic EL layer is reduced, deterioration of the organic EL layer can be suppressed. Further, the cathode electrode is generally made of a material that is easily oxidized, but has a structure sandwiched between the first organic EL layer and the second organic EL layer, so that the cathode electrode is not exposed to oxygen or water in the air. Deterioration of the cathode electrode due to oxidation can be prevented. By suppressing the deterioration of both the organic EL layer and the cathode electrode, it is possible to suppress the growth of a non-light emitting portion (dark spot) in the electroluminescent element. Therefore, a highly reliable electroluminescent element having a long lifetime can be realized.

In the invention according to a second aspect, an electron transport layer is interposed between the cathode electrode and the first organic EL layer, and between the cathode electrode and the second organic EL layer. It is characterized by: The invention according to claim 3, wherein the electron transport layer is a MgIn film, an AlLi film,
It is characterized by being composed of a metal selected from one of a stacked film of an MgIn film and an Al film or these films and an electron transporting organic material. Claim 2 and Claim 3
In the invention described in (1), by interposing the electron transport layer between the cathode electrode and each organic EL layer, it is possible to easily inject electrons from the cathode electrode to each organic EL layer. For this reason, even if a material having a high work function, such as ITO, is used as the material of the cathode electrode, the efficiency of electron injection from the cathode electrode to the organic EL layer can be ensured.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the electroluminescent device according to the present invention will be described below based on embodiments shown in the drawings. (Embodiment 1) FIG. 1 is a sectional view showing Embodiment 1 of an electroluminescent device according to the present invention. In the figure, reference numeral 11 denotes an electroluminescent element. In the electroluminescent device 11, a plurality of first anode electrodes 13 made of transparent ITO are formed on a substrate 12 having light reflectivity and electrical insulation so as to be parallel to a predetermined direction. Is formed. On the first anode electrode 13 and the substrate 12, a first hole transport layer 14 and a first electron transport layer 15 each having a thickness of 50 nm are sequentially laminated. The first hole transport layer 14 and the first electron transport layer 15 constitute a first organic EL layer 16. The first hole transport layer 14 is made of N, N'-di (α-naphthyl) -N, N'-diphenyl-1,1'-biphenyl-4,4'-
Formed of diamine (hereinafter referred to as α-NPD);
The electron transport layer 15 is formed of beryllium bis (10-hydroxybenzo [h] quinoline) (hereinafter referred to as Bebq2). The structural formulas of α-NPD and Bebq2 are shown below.

[0010]

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On the first electron transport layer 15, Mg
The plurality of cathode electrodes 17 composed of a mixed layer in which In (Mg: In ratio is 10: 1) and Bebq2 are mixed at a molar ratio of 1:20 or a 3 nm-thick MgIn layer are the first anode electrodes described above. 13 are formed so as to be parallel to each other along a direction perpendicular to the direction of the reference numeral 13. The thickness of the cathode electrode 17 is set to be small enough to transmit the light generated in the first organic EL layer 16.

Further, on the cathode electrode 17 and the first electron transport layer 15, a second electron transport layer 18, a second
The hole transport layer 19 is laminated. The second electron transport layer 18 and the second hole transport layer 19 are made of the same material and have the same thickness as the first electron transport layer 14 and the first hole transport layer 15, respectively. The second electron transport layer 18 and the second hole transport layer 19 form a second organic EL layer 20. Further, on the second hole transport layer 19, the second anode electrode 2 made of ITO corresponding to the first anode electrode 13 is formed.
1 are formed so as to be parallel to each other in a direction orthogonal to the above-described cathode electrode 17. Note that the second anode electrode 21 is set to have the same width as the first anode electrode 13. That is, the first anode electrode 13
And the second anode electrode 21 via the first organic EL layer 16, the cathode electrode 17, and the second organic EL layer 20,
They are opposed to each other so as to be overlapped in a plan view.

Next, the operation and operation of the above-described electroluminescent device 11 of the present embodiment will be described. Note that, in the present embodiment, the first anode electrodes 13 which face each other in pairs
The second anode electrode 21 and the second anode electrode 21 are simultaneously selected when scanning and driving are performed in a line-sequential manner. When the first anode electrode 13 and the second anode electrode 21 forming a predetermined pair with the predetermined cathode electrode 17 are selected, the first organic EL layer 16 and the second organic EL layer 20 are connected as shown in FIG. Light is generated at the same time. At this time, between the first anode electrode 13 and the cathode electrode 17 sandwiching the first organic EL layer 16 and between the cathode electrode 17 and the second anode electrode 21,
Have the same value. The driving voltage is one for the organic EL layer (including the electron transport layer and the hole transport layer).
When only the layers are provided, the voltage is lower than the voltage required to output a predetermined luminance. Then, the sum of the amount of light output from the first organic EL layer 16 and the amount of light output from the second organic EL layer 20 is the amount of light output in the light emitting region (dot portion). The light generated in the first organic EL layer 16 is reflected by the substrate 12 and emitted forward (not shown) without transmitting through the substrate 12 having no transparency. Further, since the cathode electrode 17 has a sufficiently small thickness for light transmission, light generated in the first organic EL layer 16 is easily transmitted. The sum of the light transmitted through the cathode electrode 17 (indicated by the symbol L1 in FIG. 1) and the light generated in the second organic EL layer 20 (indicated by the symbol L2 in FIG. 1) is the display light.

In the present embodiment, since the voltage applied to the first organic EL layer 16 and the voltage applied to the second organic EL layer 20 are low, respectively,
Deterioration of the layer due to application of a voltage can be suppressed. Further, since the cathode electrode 17 is sandwiched between the first organic EL layer 16 and the second organic EL layer 20 and does not come into contact with the outside air, a non-light-emitting portion (dark spot) due to the deterioration of the cathode electrode 17 Can be prevented from growing. Therefore, the display life of the electroluminescent element 11 can be improved, and the reliability can be improved.

(Embodiment 2) FIG. 2 is a cross-sectional view showing an embodiment 2 of the electroluminescent device according to the present invention. In the electroluminescent device 11 according to the present embodiment, as in the first embodiment, the substrate 12 having light reflectivity and electrical insulation is used.
A plurality of first anode electrodes 13 made of transparent ITO are formed in parallel on a predetermined direction. On the first anode electrode 13 and the substrate 12, a first hole transport layer 14 and a first electron transport layer 15 each having a thickness of 50 nm are sequentially laminated. These first hole transport layer 14 and first electron transport layer 15 are
6. Note that the first hole transport layer 14 is formed of α-
The first electron transport layer 15 is formed of NPD, and is formed of Bebq2
It is formed with.

In particular, in the present embodiment, the first electron transport layer 1
A plurality of first electron injection layers 22 are formed on 5 in a direction orthogonal to the first anode electrode 13. Also,
On these first electron injection layers 22, a cathode electrode 23 made of transparent ITO is formed. Further, a second electron injection layer 24 facing the first electron injection layer 22 is formed on the cathode electrode 23. That is, the first electron injection layer 22 and the second electron injection layer 24 are formed on the front and back surfaces of the cathode electrode 23. The first electron injection layer 22 and the second electron injection layer 24 are made of MgIn (M
The ratio of g: In is 10: 1) and a mixed layer of Bebq2 mixed at a molar ratio of 1:20 or 3 nm thick MgIn.
Selected from layers. Therefore, light generated in the first organic EL layer 16 can be sufficiently transmitted.

The first electron injection layer 22, the cathode electrode 23,
On the second electron injection layer 24 and the first electron transport layer 15, as in the first embodiment, the second electron transport layer 1
8, a second hole transport layer 19 and a second anode electrode 21 are formed.

In the electroluminescent device 11 according to the present embodiment having such a configuration, as in the first embodiment, the first
Light can be simultaneously generated from the organic EL layer 16 and the second organic EL layer 20. At this time, the first organic EL layer 1
The drive voltages applied between the first anode electrode 13 and the cathode electrode 23 and between the cathode electrode 23 and the second anode electrode 21 with the same value 6 are the same. Each drive voltage is lower than the voltage required to output a predetermined luminance when there is only one organic EL layer (including the electron transport layer and the hole transport layer). And the first organic E
The sum of the amount of light output from the L layer 16 and the amount of light output from the second organic EL layer 20 is the amount of light output in the light emitting area (dot portion). Light generated in the first organic EL layer 16 is reflected by the substrate 12 and emitted forward without transmitting through the substrate 12 having no transparency. further,
Since the first and second electron injection layers 22 and 24 are thin enough to transmit light, light generated in the first organic EL layer 16 can be easily transmitted. The first made of MgIn,
Since the work functions of the second electron transport layers 22 and 24 are smaller than those of the cathode electrode 23 made of ITO, the cathode electrode 2
3 facilitates the injection of electrons into the first electron transport layer 15 and the second electron transport layer 18. Therefore, the cathode electrode 23
Can be improved even if is formed of ITO having a high work function.

Also in the present embodiment, the first organic E
Since the voltage applied to the L layer 16 and the voltage applied to the second organic EL layer 20 are low voltages, it is possible to suppress the deterioration of each organic EL layer due to the application of the voltage. . Further, the first electron injection layer 22 and the second electron injection layer 24 made of MgIn which are easily oxidized are sandwiched between the first organic EL layer 16 and the second organic EL layer 20 and do not come into contact with the outside air. Therefore, the first and second electron injection layers 2
It is possible to prevent a non-light emitting portion (dark spot) from growing due to oxidation of 2, 24. Therefore, the display life of the electroluminescent element 11 can be improved, and the reliability can be improved.

(Embodiment 3) FIG. 3 is a sectional view showing Embodiment 3 of an electroluminescent device according to the present invention. As shown in the figure, in the electroluminescent device 31 of the present embodiment, a plurality of anode electrodes 33 made of transparent ITO are formed on a glass substrate 32 so as to be parallel in a predetermined direction. Further, the anode electrode 33 and the glass substrate 32
Are sequentially formed on the hole transport layer 34 made of α-NPD, B
The electron transport layer 35 made of ebq2 is laminated to form an organic EL.
A layer 36 is formed. The thickness of each of the hole transport layer 34 and the electron transport layer 35 is set to 50 nm. Further, a plurality of cathode electrodes 37 are formed on the electron transport layer 35 in parallel along a direction orthogonal to the anode electrode 33. This cathode electrode 37
Is formed of MgIn, and its film thickness is set relatively thick so as not to transmit light. Further, a copper phthalocyanine layer 38 is formed so as to cover the cathode electrode 37 and the electronic organic 35. The structural formula of copper phthalocyanine is shown below.

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The operation and operation of the electroluminescent device 31 having the above configuration will be described. First, holes are injected from the anode electrode 33 to the hole transport layer 34 in the organic EL layer 36 sandwiched between the two electrodes at the intersection of the selected anode electrode 33 and cathode electrode 37. The electrons are injected into the electron transport layer 35 from. These holes and electrons recombine near the hole transport layer 34 in the electron transport layer 35 to generate display light. As shown in FIG. 3, the display light L passes through the anode electrode 33 and the glass substrate 32 and is emitted downward from the glass substrate 32 in the drawing. The light emitted to the cathode electrode 37 side cannot be transmitted through the cathode electrode 37, and is reflected to the glass substrate 32 side to be used as display light.

In this embodiment, the copper phthalocyanine layer 38
However, by forming a phthalocyanine complex such as iron phthalocyanine so as to cover the surface of the cathode electrode 37, it is possible to prevent the surface of the cathode electrode 37 made of MgIn from being oxidized. These phthalocyanine complexes, particularly those in which copper, iron, nickel, cobalt and the like are bonded, are linked by a coordination bond and a covalent bond, and are stable to strong acids and extremely stable to light. In addition, since the copper phthalocyanine layer 38 is formed by vapor deposition, it is densely crystallized and adheres to the surface of the cathode electrode 37, so that it is possible to reliably prevent the cathode electrode 37 from coming into contact with the outside air. is there. For this reason, the copper phthalocyanine layer 38 has a high effect of preventing the cathode electrode 37 from being oxidized by invasion of outside air or water. Therefore, in the present embodiment, the growth of the non-light-emitting portion (dark spot) due to the oxidation of the cathode electrode 37 can be suppressed, and the highly reliable electroluminescent device 31 can be obtained.

(Embodiment 4) FIG. 4 is a sectional view showing Embodiment 4 of the electroluminescent device according to the present invention. As shown in the figure, in the electroluminescent device 41 of the present embodiment, a plurality of first cathode electrodes 43 made of ITO are formed on a glass substrate 42 so as to be parallel in a predetermined direction. On the surface of the first cathode electrode 43, M
An electron injection layer 44 made of a gIn film is formed. On the electron injection layer 44 and the glass substrate 42, a first electron transport layer 45 and a first hole transport layer 46 are sequentially laminated to form a first organic EL layer 47. An anode electrode 48 made of ITO is formed on the first electron transport layer 45 so as to be parallel to a direction orthogonal to the first cathode electrode 43. On the anode electrode 43 and the first hole transport layer 46, the second hole transport layer 4
9. The second organic EL layer 51 is formed by laminating the second electron transport layer 50. Furthermore, a second cathode electrode 52 is formed of MgIn on the second electron transport layer 50 so as to be parallel to the first cathode electrode 43. The second cathode electrode 52 is set to a thickness that does not allow light to pass through. Further, the second cathode electrode 5
A copper phthalocyanine layer 53 is formed so as to cover the second and second electron transport layers 50.

In this embodiment, the anode electrode 48
Organic EL layer 4 interposed between the first organic EL layer 4 and the first cathode electrode 43
7 and the second organic EL layer 51 sandwiched between the anode electrode 48 and the second cathode electrode 52, light emission occurs, and the first cathode electrode 43 and the second cathode electrode 52 corresponding to the upper and lower sides.
Are set so that they are selected simultaneously by line-sequential scanning. Therefore, in the same light emitting area (dot portion), the first
The sum of the light generated by the organic EL layer 47 and the second organic EL layer 51 is the light emission amount. In FIG. 4, the first organic EL layer 4
7, light L1 is generated, and light L2 is generated in the second organic EL layer 51. The light L1 and the light L2 together become display light. Also in the present embodiment, since the voltage applied to each organic EL layer may be low, it is possible to prevent the organic EL layer from deteriorating due to the voltage, and to prevent the non-light emitting portion from growing. be able to. In addition, since the electron injection layer 44 made of MgIn which is easily oxidized is covered with the first electron transport layer 45, the electron injection layer 44 does not come into contact with the outside air, and is prevented from being oxidized due to air or water. Can be. Furthermore, since the second cathode electrode 52 is covered with the copper phthalocyanine layer 53, oxidation can be effectively prevented for the same reason as in the third embodiment.

Although the first to fourth embodiments have been described above, the present invention is not limited to these, and various modifications accompanying the gist of the configuration are possible. For example, in each of the above embodiments, Bebq2 was used as the electron transport layer, but the present invention is not limited to this. Of course, Alq3 or the like may be used. Further, as the hole transport layer, α-NPD
In addition, it is of course possible to use PVCz, TPD, or a mixture of PVCz and TPD. Furthermore, the configuration of the organic EL layer is not limited to the two-layer structure as in each of the above-described embodiments, but may be a single-layer structure or a multi-layer structure of three or more layers. In the above-described embodiment, the electron injection layer is formed of MgIn.
A stacked film of an i film, a MgIn film and an Al film may be used, and the material can be appropriately changed in consideration of the work function of the cathode electrode.

[0026]

As is apparent from the above description, according to the present invention, the deterioration of the organic EL layer is suppressed, the oxidation of the cathode electrode is suppressed, and the growth of the non-light emitting portion is suppressed. A high electroluminescent element can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an electroluminescent device according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing an electroluminescent device according to a second embodiment of the present invention.

FIG. 3 is a sectional view showing Embodiment 3 of the electroluminescent device according to the present invention.

FIG. 4 is a sectional view showing an electroluminescent device according to a fourth embodiment of the present invention.

FIG. 5 is a sectional view showing a conventional electroluminescent element.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 electroluminescent element 13 first anode electrode 16 first organic EL layer 17 cathode electrode 20 second organic EL layer 21 second anode electrode 22 first electron injection layer 23 cathode electrode 24 second electron injection layer 31 electroluminescent element 38 53 Copper phthalocyanine layer

Claims (3)

[Claims] A first anode electrode and a first organic electrode;
L layer, light-transmissive cathode electrode, and second organic EL
An electroluminescent device comprising: a layer; and a second anode electrode that is simultaneously driven in correspondence with the first anode electrode. 2. An electron transport layer is interposed between the cathode electrode and the first organic EL layer and between the cathode electrode and the second organic EL layer. Item 2. An electroluminescent device according to item 1. 3. The electron transport layer according to claim 1, wherein the electron transport layer comprises a MgIn film, an AlL
3. The electroluminescent device according to claim 2, wherein the electroluminescent device is made of one of an i film, a MgIn film, and a laminated film of an Al film, or a metal selected from these films and an electron transporting organic material.