JP3300065B2 - Organic electroluminescence device - Google Patents

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 (hereinafter, referred to as an organic EL device).

[0002]

2. Description of the Related Art As shown in FIG. 1, for example, an organic EL device comprises an organic compound and an organic compound laminated on a glass substrate 1 between a transparent electrode 2 as an anode and a metal electrode 3 as a cathode. It has a two-layer structure in which a hole transport layer 4 and an organic phosphor thin film 5 as a light emitting layer are formed. here,
The organic hole transport layer 4 has a function of easily injecting holes from the transparent electrode 2 and a function of blocking electrons.
In the light emitting layer, excitons are generated by recombination of the electrons injected from the metal electrode 3 and the holes injected from the organic hole transport layer 4, and the excitons emit light in the process of radiation deactivation. Is emitted outside through the transparent electrode 2 and the glass substrate 1.

Since such an organic EL device is a current injection type device, its luminous efficiency greatly depends on the work function of each of the electrodes 1 and 2. Therefore, many studies have been made on the metal electrode 1 for injecting electrons, that is, the cathode. However, at least one side of the electrode, that is, the transparent electrode 2 in FIG. 1 has to transmit at least light generated in the light-emitting layer, and is mainly made of ITO (Indium Tin).
Oxide) or tin oxide (SnO ₂ ) in many cases, and the effect of injecting the transparent electrode 2 into the carrier was not so much a problem.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an organic EL device having a structure which has a high luminous efficiency while maintaining the transmittance of the electrode by focusing on an electrode which transmits light.

[0005] The organic EL device of the present invention is formed by laminating at least a light emitting layer made of an organic compound and an electrode layer facing each other with the light emitting layer interposed therebetween , on which light is emitted from the light emitting layer. an organic electroluminescent device is a transparent electrode layer allowed to transmit the light of the electrode layer, trace the additive metal a metal having a different work function conductive metal oxide as the main component and the metal oxide Containing , the transparent electrode layer is an anode layer,
The added metal has a work function of 5.0 eV or more .
Further, the organic EL device of the present invention comprises at least an organic compound
And a light-emitting layer made of
An electrode layer and a light emitting layer
Organic electroluminescent device that emits light from
Wherein the electrode layer is transparent to transmit the light.
The electrode layer contains a conductive metal oxide as a main component and the metal oxide
Metal having a work function different from that of the
The transparent electrode is an anode layer and a cathode layer,
The additive metal of the anode layer has a work function of 5.0 eV or more.
The work function of the additive metal of the cathode layer is 4.3 eV or less.
It has.

[0006]

In the organic EL device of the present invention, the work function of the transparent electrode through which light passes is controlled by the type and content of the additional metal contained in the conductive metal oxide. The injection efficiency of at least one of electrons and holes can be increased, and the light emission efficiency of the organic EL element can be improved without lowering the light transmittance.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. In the organic EL device according to the present embodiment, a transparent electrode 2, an organic compound layer, and an electrode 3 facing the transparent electrode 2 are sequentially formed on a glass substrate 1 in the same manner as the conventional organic EL device shown in FIG. These electrodes 2 and 3 have a structure connected to a DC power supply 6. For example, when the transparent electrode 2 is formed as an anode as shown in FIG. 1, for example, N, N′-diphenyl-N, N
An organic hole transport layer 4 made of '-bis (3-methylphenyl) -1,1'-biphenyl-4,4'-diamine (TPD) and an organic material made of, for example, tris (8-quinolinol) aluminum (Alq ₃ ) A phosphor thin film 5 is laminated and formed, and light emitted from the light emitting layer is applied to the anode 2 and the glass substrate 1.
And is emitted to the outside of the device.

The anode 2 is made of, for example, ITO, SnO ₂ ,
Zinc oxide (ZnO), indium cadmium oxide (CdI
n ₂ O _2), a conductive metal oxide such as tin oxide cadmium (Cd ₂ SnO ₄₎ as a main component, a high work function has a work function example shown in Table 1 platinum (Pt), gold (Au), It is made of a metal having a large work function such as palladium (Pd), that is, a metal containing a trace amount of 5.0 eV or more as an additional metal.

[0009]

[Table 1]

The anode 2 is formed by, for example, doping the inside of the conductive film with a metal shown in Table 1 after performing a binary sputtering method, a co-evaporation method, or forming a conductive film made of a conductive metal oxide on the glass substrate 1 in advance. It is manufactured by a suitable method such as a method so as to have a desired metal content. Therefore, anode 2
Since the work function varies depending on the type and content of the added metal, the type and content can be adjusted so that holes are efficiently injected from the anode 2 into the light emitting layer.

Next, a specific example will be described. [Specific example 1] ITO was formed on a glass substrate 1 by a binary sputtering method.
Then, Pt is deposited to a thickness of 1000 Å to form an anode 2 made of ITO containing 0.10 wt% of Pt. On the anode 2, TPD is deposited to a thickness of 500 angstroms to form a hole transport layer 4, and Alq ₃ is deposited on the hole transport layer 4 to form a phosphor layer 5. Mg and Al were co-deposited on the phosphor layer 5 at an atomic ratio of 10: 1 to a thickness of 1500 angstroms to form a cathode 3, thereby producing an organic EL device. When a current of 7.5 mA / cm ² was passed through the device, the luminance was 508 cd / m ² and the voltage was 4.5 V.

[Comparative Example] Anode 2 of ITO was applied to glass substrate 1
Was prepared. On the anode 2, TPD is deposited to a thickness of 500 angstroms to form a hole transport layer 4, and Alq ₃ is deposited on the hole transport layer 4 to form a phosphor layer 5. Mg and Al were co-deposited on the phosphor layer 5 at an atomic ratio of 10: 1 to a thickness of 1500 angstroms to form a cathode 3, thereby producing an organic EL device. When a current of 7.5 mA / cm ² was passed through the device, the luminance was 310 cd / m ² and the voltage was 5.0 V.

Thus, comparing Example 1 and Comparative Example, it can be seen that the device according to the present invention has improved luminous efficiency. Therefore, when the present invention is applied to the anode 2, holes can be efficiently injected from the anode 2 into the light emitting layer, and the luminous efficiency of the organic EL device can be improved. Next, a case where the electrode 2 is formed as a cathode will be described. In this device, as shown in FIG. 2, a transparent electrode 3a and an organic phosphor thin film 5 as a light emitting layer are sequentially formed on a glass substrate 1.
Further, the light emitting layer has a structure in which the organic hole transport layer 4 and the electrode 2a serving as an anode are laminated, and the light emitted from the light emitting layer passes through the cathode 3a and the glass substrate 1 and is emitted to the outside of the device.

The cathode 3a is made of the same conductive metal oxide as the anode 2, for example, aluminum (Al), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), lithium (Li). )), A metal having a small work function, that is, a metal having a work function of 4.3 eV or less;
Alternatively, it is composed of an oxide such as aluminum oxide (Al ₂ O ₃ ), magnesium oxide (MgO 2) or barium oxide (BaO 2) as an additive metal, that is, a material containing a small amount as a dopant. The cathode 3a is formed by a suitable method similar to that of the anode 2 so as to have a desired metal content.

The work function of the cathode 3a changes depending on the type and content of the dopant to be added.
The type and content can be adjusted so that electrons are efficiently injected from the cathode 3a into the light emitting layer. Next, a specific example will be described. [Specific Example 2] ITO is deposited on a glass substrate 1 by a binary sputtering method.
And a cathode 3a containing 0.08 wt% of BaO 2 in ITO by vapor deposition of BaO 2 to a thickness of 1000 Å.
Is prepared. Alq ₃ as a phosphor layer 5 is formed on the cathode 3a.
Is deposited to a thickness of 500 angstroms, TPD is deposited on the phosphor layer 5 to a thickness of 350 angstroms to form a hole transport layer 4, and the following is further formed on the hole transport layer 4: Cu-Pc represented by the chemical formula

[0016]

Embedded image

Is deposited to a thickness of 350 angstroms (not shown), and Pt is applied thereon as an anode 2a.
Organic EL by vapor deposition with a thickness of 500 angstroms
An element was manufactured. When a current of 7.5 mA / cm ² was passed through the device, the luminance was 620 cd / m ² and the voltage was 4.8 V. As described above, when the specific example 2 is compared with the comparative example, it is understood that the luminous efficiency is improved in the device according to the present invention.

Since the cathode 3a is transparent for transmitting light, the anode 2a may be opaque.
The thickness of the anode 2a made of a metal having a large work function such as t or Pd can be made thick and uniform. Therefore, in such an element structure, the range of selection of the material and the film thickness of the anode 2a is expanded. Therefore, when the present invention is applied to the cathode 3a, the efficiency of hole injection from the anode 2a can be improved, and electrons can be efficiently injected from the cathode 3a into the light emitting layer. Can be improved.

In the organic EL device according to the present invention, the content of the additive metal contained in the transparent electrodes serving as the electrodes 2 and 3a is such that a desired work function can be obtained without impairing the light transmittance. 0.01wt% ~ 10wt% for
Is preferred. When the amount is out of this range, that is, when the amount of the added metal exceeds 10% by weight, the light transmittance is reduced and the luminous efficiency of the device is reduced. On the other hand, when the amount of the added metal is less than 0.01% by weight. In such a case, it becomes difficult to control the work function, and the luminous efficiency of the device becomes low.

Further, in the organic EL device of the present invention,
The anode 2 is made of a metal having a large work function, that is, a transparent electrode containing a metal having a work function of 5.0 eV or more as an additive metal.
When a transparent electrode containing a metal of V or less as an additive metal is used, light of the light emitting layer can be extracted from both electrode sides of the device. Therefore, for example, as shown in FIG. 3, the organic EL element having the above structure is formed in a three-layer structure and each light emitting layer emits blue (B), red (R), and green (G) in order from the substrate side. Then, a color light-emitting display element can be manufactured.

As shown in FIG. 4, both electrodes 2, 3a
Are formed of transparent electrodes each containing a metal exhibiting a desired work function as an additive metal, and a black dye is applied and formed on the back surface of the electrode 3a opposed to the glass substrate 1 via the light emitting layer to form an anti-reflection film 7. The contrast of light emitted to the outside of the device can be improved as compared with a device having a conventional structure in which a cathode facing the glass substrate 1 via a light emitting layer functions as a reflection film.

[0022]

According to the present invention, the transparent electrode that transmits light among the electrode pairs sandwiching the light emitting layer has a conductive metal oxide as a main component and has a work function different from that of the conductive metal oxide. Since a small amount of metal is contained as an additive metal, the work function of this transparent electrode can be controlled according to the type and content of the additive metal contained, so that at least one of electrons and holes can be efficiently injected into the light emitting layer, and In addition, the hole injection efficiency can be increased, and the light emission efficiency of the element can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an organic EL element.

FIG. 2 is a configuration diagram showing one embodiment of an organic EL device according to the present invention.

FIG. 3 is a configuration diagram of a light emitting display element to which the organic EL element according to the present invention is applied.

FIG. 4 is a configuration diagram showing another embodiment of the organic EL device according to the present invention.

[Explanation of Signs of Main Parts]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode as transparent electrode 3 Cathode as electrode pair 2a Anode as electrode pair 3a Cathode as transparent electrode 4,5 Light emitting layer

Claims (4)

(57) [Claims] 1. An organic electroluminescent element in which at least a light emitting layer made of an organic compound and an electrode layer facing each other with the light emitting layer interposed therebetween are formed on a substrate, and light is emitted from the light emitting layer. there, the transparent electrode layer allowed to transmit the light of the electrode layer,
Contains a trace amount of a metal having a work function different from that of the metal oxide containing a conductive metal oxide as a main component as an additive metal ,
The transparent electrode layer is an anode layer, and the added metal is 5.0 eV
An organic electroluminescence device having the above work function . 2. The content of the additive metal in the anode layer is set to be 0.
The content according to claim 1, wherein the content is from 01 wt% to 10 wt%.
Electroluminescent element. 3. A light-emitting layer comprising at least an organic compound
And an electrode layer facing each other via the light emitting layer.
The light emitting layer emits light from the light emitting layer.
Organic electroluminescent device, A transparent electrode layer that transmits the light among the electrode layers,
Conductive metal oxide as the main component and different from the metal oxide
A small amount of a metal having a work function
The transparent electrode is an anode layer and a cathode layer, the anode layer
The additive metal has a work function of 5.0 eV or more, the cathode
The additive metal of the layer has a work function of 4.3 eV or less
An organic electroluminescence device characterized by the following. 4. The additive of the anode layer and the cathode layer
The genus has a content of 0.01 wt% to 10 wt%.
The organic electroluminescence device according to claim 3.