JP2010027524A - Organic el element, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element which is excellent in light-emitting characteristics and low-voltage light-emitting characteristics and can achieve high reliability and is excellent in economical efficiency, and to provide a manufacturing method thereof. <P>SOLUTION: In the organic EL element 10 having an anode 2 arranged on a substrate (Base body) 1, an organic light-emitting layer 3 arranged on the anode 2 and a cathode 4 arranged on the organic light-emitting layer 3 so as to face the anode 2 via the organic light-emitting layer 3, the anode 2 includes a first ZnO transparent conductive film layer 2a doped with a group III element and having a crystal structure where C-axes are oriented in mutually different directions, and the first ZnO transparent conductive film layer 2a forms an interface between the organic light-emitting layer 3. A doping amount of the group III element to ZnO is set to be 6-40 at%. The anode 2 is formed with a double-layered structure having the first ZnO transparent conductive film layer 2a and a second ZnO transparent conductive film layer 2b where 3-8 at% group III element is doped into the ZnO. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an organic EL element and a method for manufacturing the same, and more specifically, in an organic EL element using a ZnO transparent conductive film as an anode, the emission efficiency with respect to current density is improved and the emission luminance peak is shifted to a lower voltage side (that is, The present invention relates to an organic EL element intended to enable low voltage light emission and the like and a method for manufacturing the same.

In recent years, attention has been focused on organic EL elements capable of obtaining high emission luminance of several hundreds to several 10,000 cd / m ² at a low voltage of about 10 V, for example.
This organic EL element usually has an anode disposed on a substrate, an organic light emitting layer disposed on the anode, and a principal surface opposite to a principal surface bonded to the anode of the organic light emitting layer. And a cathode provided to be joined to the organic light emitting layer. The organic light emitting layer is generally composed of a hole transport material layer such as triphenyldiamine (TPD), a fluorescent material such as an aluminum quinolinol complex (Alq3), or a phosphorescent material such as an iridium complex (Ir (ppy) ₃ ). A layered light emitting layer is used.

  By the way, as a material used as an anode of such an organic EL element, it is considered effective to inject a large number of holes into a light emitting layer, a hole injection transport layer, or the like. Further, it is often configured to take out emitted light from the substrate side, and it is necessary to be a transparent conductive material.

  Conventionally, ITO (tin-added indium oxide) has been widely used as a material for such transparent electrodes.

  However, since indium (In) is expensive and is a substance that may be depleted of resources, there is an increasing demand for transparent electrodes using other materials, and ZnO (zinc oxide) is expected as an alternative material. ing.

And the organic EL element which used the ZnO transparent conductive film as an anode has also been proposed (patent document 1).
However, the work function of the conventional ZnO transparent conductive film is about 4.5 eV, and the actual situation is that further improvement is required in order to further improve the characteristics and improve the light emission efficiency with respect to the current density.
Japanese Patent Laid-Open No. 11-067459

  The present invention has been made in view of the above circumstances, and a ZnO transparent conductive film that has high light emission efficiency with respect to current density and can shift a light emission luminance peak to a low voltage side without using ITO is an anode. An object of the present invention is to provide an organic EL device used in the above and a method for producing the same.

In order to solve the above problems, the organic EL device of the present invention is
An anode disposed on a substrate, an organic light emitting layer disposed on the anode, and a cathode disposed on the organic light emitting layer so as to face the anode through the organic light emitting layer. In the organic EL element provided,
The anode includes a first ZnO transparent conductive film layer doped with a group III element and having a crystal structure in which c-axis is oriented in a plurality of different directions,
The first ZnO transparent conductive film layer forms an interface with the organic light emitting layer.

Also, an anode disposed on the substrate, an organic light emitting layer disposed on the anode, and a cathode disposed on the organic light emitting layer so as to face the anode through the organic light emitting layer In an organic EL device comprising:
The anode includes a first ZnO transparent conductive film layer doped with a group III element and having a ZnO (002) rocking curve half-width of 13.5 ° or more,
The first ZnO transparent conductive film layer forms an interface with the organic light emitting layer.

Also, an anode disposed on the substrate, an organic light emitting layer disposed on the anode, and a cathode disposed on the organic light emitting layer so as to face the anode through the organic light emitting layer In an organic EL device comprising:
The anode includes a first ZnO transparent conductive film layer doped with 6 to 40 at% of a group III element,
The first ZnO transparent conductive film layer forms an interface with the organic light emitting layer.

  In the organic EL device of the present invention, it is preferable that the first ZnO transparent conductive film layer is doped with a group III element of 6 to 20 at%.

  The anode preferably further includes a second ZnO transparent conductive film layer doped with 3 to 8 at% of a group III element.

  The group III element is preferably at least one selected from the group consisting of Ga, Al, and In.

  The substrate on which the anode is disposed is made of glass, quartz, sapphire, Si, SiC, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), polyimide, cycloolefin polymer, It is preferable that at least one selected from the group consisting of polycarbonate and the main component is used.

Moreover, the manufacturing method of the organic EL element of this invention is as follows.
Forming an anode on a substrate;
Forming an organic light emitting layer on the anode;
In the manufacturing method of an organic EL device comprising a step of forming a cathode on the organic light emitting layer,
The step of forming the anode uses a raw material containing ZnO and a group III element oxide, and forms a film by a thin film formation method so that the doping amount of the group III element is in the range of 6 to 40 at%. And a step of forming a first ZnO transparent conductive film layer having a crystal structure in which the c-axis is directed to a plurality of different directions and forming an interface with the organic light emitting layer. Yes.

Moreover, the manufacturing method of the organic EL element of this invention is as follows.
Forming an anode on a substrate;
Forming an organic light emitting layer on the anode;
In the manufacturing method of an organic EL device comprising a step of forming a cathode on the organic light emitting layer,
The step of forming the anode uses a raw material containing ZnO and a group III element oxide, and forms a film by a thin film formation method so that the doping amount of the group III element is in the range of 6 to 40 at%. ZnO (002) has a step of forming a first ZnO transparent conductive film layer having a rocking curve half-width of 13.5 ° or more and forming an interface with the organic light emitting layer. Yes.

  In the step of forming the first ZnO transparent conductive film layer, the thin film forming method is selected from the group consisting of sputtering, vapor deposition, vapor deposition ion plating, laser ablation, and arc plasma vapor deposition. This is one type of method, and it is desirable to use a sintered body target made of a composition containing ZnO and a group III element oxide.

  Further, the thin film forming method in the step of forming the first ZnO transparent conductive film layer is selected from the group consisting of a sputtering method, a vapor deposition method, a vapor deposition ion plating method, a laser ablation method, and an arc plasma vapor deposition method. It is desirable to use one method and to apply a bias voltage to the substrate during film formation.

Further, the step of forming the anode uses a raw material containing ZnO and a group III element oxide, and a second thin film forming method is used so that the doping amount of the group III element is in the range of 3 to 8 at%. A step of forming a ZnO transparent conductive film layer;
It is desirable that the first ZnO transparent conductive film layer is formed on the second transparent conductive film layer so that the anode has a multi-layer structure.

The group III element is preferably at least one selected from the group consisting of Ga, Al, and In.

  The substrate is at least selected from the group consisting of glass, quartz, sapphire, Si, SiC, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), polyimide, cycloolefin-based polymer, and polycarbonate. It is preferable that one type is a main component.

  As in the present invention, the first ZnO transparent conductive film layer is provided with a first ZnO transparent conductive film layer doped with a group III element and having a crystal structure oriented in a plurality of directions different from each other as the c-axis. However, by using a material that forms an interface with the organic light emitting layer, the work function of the anode is increased, the light emission efficiency with respect to the current density is improved, and the light emission luminance peak is shifted to the low voltage side. Is possible. As a result, an organic EL element having high characteristics can be obtained without using ITO.

In the organic EL element, the organic light emitting layer is excited by exciton in which holes and electrons are recombined, and emits light when returning to the ground state. The wavelength depends on the material. When an n-type conductive ITO film or ZnO film is used as the anode forming the interface with the hole transport layer, the hole injection efficiency is improved when the anode is less likely to emit electrons, that is, the work function is higher. , Leading to improved characteristics such as low-voltage light emission.
The first ZnO transparent conductive film layer doped with a group III element and having a crystal structure oriented in a plurality of directions different from each other as the anode has a high work function. By using it as the anode, it is possible to provide an organic EL element excellent in characteristics such as light emission efficiency and low voltage light emission.
The reason why the work function is improved in the first ZnO transparent conductive film layer is not necessarily clear, but the crystal orientation is disturbed by the high concentration doping of group III elements such as Ga, and the amorphous and crystalline phases are mixed. It is presumed that this is because a deep localized level is formed and the Fermi level is lowered.

Moreover, since the first ZnO transparent conductive film layer having the above-mentioned requirements has a practical level of moisture resistance and the raw material is inexpensive, it can realize excellent reliability and economy.
Further, in the first ZnO transparent conductive film layer, excellent moisture resistance can be obtained because, as in the prior art, crystals have a columnar growth and have a single orientation structure in which the c-axis is directed in the same direction. In the case of the conductive film layer, moisture enters the inside through the grain boundary (boundary) and deteriorates the moisture resistance, whereas the present invention has a crystal structure in which the c-axis is directed to a plurality of different directions. In the transparent conductive film layer having a region, it is considered that the change in the film structure is due to suppressing reoxidation of oxygen deficiency due to moisture.
In addition, in the transparent conductive film layer constituting the anode in the organic EL element of the present invention, the main part, which is a part in contact with the organic light emitting layer, has a crystal structure in which the c-axis is directed to a plurality of different directions. In other regions, there may be an amorphous region, a region having a so-called quasicrystalline structure such as an intermediate between amorphous and crystalline, and the like.

Further, the anode includes a first ZnO transparent conductive film layer doped with a group III element and having a half width of ZnO (002) rocking curve of 13.5 ° or more, and the first ZnO transparent conductive film layer includes: Even when the interface is formed with the organic light emitting layer, the same effect as described above can be obtained.
In the present invention, the requirement that the ZnO (002) rocking curve half-value width is 13.5 ° or more is the requirement for a ZnO film layer having a ZnO (002) rocking curve half-value width of 13.5 ° or more. This is because the degree to which the c-axis is directed in the same direction is sufficiently low to suppress or prevent reoxidation of oxygen deficiency.

Further, when the anode is configured to include the first ZnO transparent conductive film layer obtained by doping ZnO with a group III element of 6 to 40 at%, the same effect as described above can be obtained.
Note that the first ZnO transparent conductive film layer doped with 6 to 40 at% of a group III element usually has a crystal structure in which the c-axis is oriented in a plurality of different directions, and a ZnO (002) rocking curve half The value width is 13.5 ° or more.

  In addition, since the first ZnO transparent conductive film layer obtained by doping ZnO with a group III element at 6 to 20 at% has a relatively low doping concentration, ionized impurity scattering is suppressed. Therefore, in addition to the effect that the work function is high, the effect that the resistance value is low is obtained.

  Further, when the anode further includes a second ZnO transparent conductive film layer doped with 3 to 8 at% of a group III element, the first ZnO transparent conductive film layer allows light emission efficiency and low voltage. The improvement of desired characteristics such as light emission is promoted, and this second ZnO transparent conductive film layer makes it possible to reduce the resistance of the anode, which is significant.

In addition, by using at least one selected from the group consisting of Ga, Al and In as a group III element, it has high characteristics such as light emission efficiency and low voltage light emission, has a practical level of moisture resistance, and is economical. An anode having excellent properties can be formed more reliably.
As the type of group III element (doping element), it is most preferable to use Ga which has a high vapor pressure of oxide and can be easily doped at a high concentration, but other group III elements Al or In were used. Even in this case, an effect equivalent to that obtained when Ga is used can be obtained.

  In addition, as a substrate on which the anode is disposed, glass, crystal, sapphire, Si, SiC, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), polyimide, cycloolefin polymer, and polycarbonate By using a material mainly comprising at least one selected from the group consisting of: an anode having high characteristics such as luminous efficiency and low voltage light emission, practical level of moisture resistance, and excellent economy Can be formed more reliably.

In addition, the organic EL device manufacturing method of the present invention uses a raw material containing ZnO and a group III element oxide in the step of forming the anode, and the doping amount of the group III element is in the range of 6 to 40 at%. As described above, since the film is formed by the thin film forming method, a region having a crystal structure in which the c-axis is oriented in a plurality of directions different from each other easily and reliably without requiring a complicated process is provided. The first ZnO transparent conductive film layer can be formed on the substrate, has a high characteristic, has a practical level of moisture resistance, and has an economically efficient anode. An organic EL element having excellent characteristics such as voltage emission can be efficiently manufactured.
As a method for forming the first ZnO transparent conductive film layer, by using off-axis sputtering, collision of high energy particles with the ZnO film can be avoided, and a transparent conductive film layer having a low resistivity can be obtained. It becomes possible.

  Further, in the step of forming the anode, a thin film forming method is performed by using a raw material containing ZnO and a group III element oxide so that the doping amount of the group III element is in the range of 6 to 40 at%. When the film is formed by the above, a ZnO (002) rocking curve half-width is 13.5 ° or more, and a first ZnO transparent conductive film layer that forms an interface with the organic light emitting layer is formed on the substrate. Organic EL elements with excellent characteristics such as light emission efficiency and low voltage light emission that have high characteristics, high levels of moisture resistance, practical use, and excellent economic efficiency. Can be manufactured.

  Moreover, using a sintered compact target made of a composition containing ZnO and a group III element oxide, a sputtering method, a vapor deposition method, and so on so that the doping amount of the group III element oxide is in the range of 6 to 40 at%. By forming a film on a substrate by one method selected from the group consisting of vapor deposition ion plating method, laser ablation method, and arc plasma vapor deposition method, it is easy and reliable without requiring any complicated process. , It becomes possible to form a transparent conductive film layer having a region having a crystal structure in which the c-axis is directed in a plurality of directions different from each other on the substrate, has high characteristics, has a practical level of moisture resistance, and It is possible to efficiently produce an organic EL device having an anode that is excellent in economic efficiency and excellent in characteristics such as light emission efficiency and low voltage light emission.

  Moreover, using a sintered compact target made of a composition containing ZnO and a group III element oxide, a sputtering method, a vapor deposition method, and so on so that the doping amount of the group III element oxide is in the range of 6 to 40 at%. Even when the film is formed on the substrate by one method selected from the group consisting of vapor deposition ion plating, laser ablation, and arc plasma vapor deposition, the ZnO (002) rocking curve half width is 13. It becomes possible to form a first ZnO transparent conductive film layer having a region having a crystal structure in which the c-axis is oriented in a plurality of directions different from each other at 5 ° or more on the substrate, and has high characteristics and practical level. It is possible to efficiently produce an organic EL device having an anode having excellent moisture resistance and excellent economy, and having excellent characteristics such as light emission efficiency and low voltage light emission.

  In the step of forming the anode, a second ZnO transparent conductive film is formed by a thin film forming method using a raw material containing ZnO and a group III element oxide so that the group III element doping amount is in the range of 3 to 8 at%. A step of forming a film layer, and when the first ZnO transparent conductive film layer is formed on the second transparent conductive film layer so that the anode has a multi-layer structure, the characteristics of the anode That is, it is possible to sufficiently exhibit the characteristics of low resistance and high work function, and it becomes possible to efficiently manufacture an organic EL element having good characteristics.

By using at least one selected from the group consisting of Ga, Al, and In as a group III element, a ZnO-based transparent conductive film layer having a practical level of moisture resistance and excellent in economic efficiency can be efficiently obtained. An organic EL device that can be formed well, has high characteristics, has a practical level of moisture resistance, has an anode that is economical, and has excellent characteristics such as luminous efficiency and low-voltage light emission. It can be manufactured efficiently.
As the type of group III element (doping element), it is most preferable to use Ga which has a high vapor pressure of oxide and can be easily doped at high concentration. However, when Al or In, which is another group III element, is used, it is possible to obtain the same effect as when Ga is used.

  As the substrate, at least one selected from the group consisting of glass, quartz, sapphire, Si, SiC, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), polyimide, cycloolefin polymer, and polycarbonate. Can be used as the main component, has high characteristics, has a practical level of moisture resistance, and has an economically efficient anode, and has excellent characteristics such as luminous efficiency and low voltage light emission. The organic EL element can be efficiently manufactured.

  The features of the present invention will be described in more detail below with reference to examples of the present invention.

A glass substrate made of non-alkali glass was prepared as a substrate (base), and cleaning with isopropyl alcohol and UV irradiation was performed as a pretreatment to obtain a clean surface.
Moreover, a ZnO mixed sintered body target containing 5 to 37 at% Ga and having a sintering density of 80% or more was prepared as a sputtering target.

Then, the glass substrate is set in a sputtering vacuum chamber, evacuated to 5.5 × 10 ⁻⁵ Pa, and then subjected to sputtering to form a ZnO film (first ZnO transparent conductive film layer). went.
The set film thickness of the ZnO film was 400 nm. Then, after patterning by wet etching on the formed ZnO film, it was confirmed by using a stylus type step gauge that the film thickness was ± 15% with respect to the set film thickness.
Further, the resistivity of this ZnO film was examined by four-probe measurement. As a result, when the Ga doping amount was 5.0 at%, the resistivity was 5.0 × 10 ⁻⁴ Ωcm. The resistivity increased as the Ga doping amount increased, and it was confirmed that the resistivity became 5.0 × 10 ⁻² Ωcm when the Ga doping amount reached 37 at%.
Moreover, as a result of conducting a composition analysis about this ZnO film, it was confirmed that the Ga doping amount was the same as the target composition. The average light transmittance in the visible region was 80% or more.

Furthermore, the work function was measured using an atmospheric photoelectron spectrometer. The measurement results are shown in FIG.
As shown in FIG. 1, it was confirmed that the work function increased as the Ga doping amount increased. Although not particularly shown, it was confirmed that the work function was saturated even when Ga was doped at 20 at% or more and was almost constant up to 37 at%.

It is known that increasing the Ga doping amount disturbs the crystal structure and increases the ZnO (002) rocking curve half width.
In this Example 2, various ZnO films (first ZnO transparent conductive film layers) having different Ga doping amounts were prepared by the method according to the above Example 1, and (002) rocking curve half for each ZnO film. The relationship between price range and work function was investigated. The relationship is shown in FIG.
As shown in FIG. 2, it was confirmed that the work function increased as the ZnO (002) rocking curve half-width increased, and exceeded the ITO work function of 4.8 eV at a half-width of 13.5 ° or more.

  A second ZnO film (second ZnO transparent conductive film layer) having a Ga doping amount of 5.0 at% and a thickness of 300 nm is formed on the same glass substrate as that used in Example 1, and further, A first ZnO film (first ZnO transparent conductive film layer) having a Ga doping amount of 13.3 at% and a thickness of 5 nm was formed to form a second ZnO film formed on the glass substrate 1 as shown in FIG. An anode 2 having a two-layer structure including the ZnO transparent conductive film layer 2b and the first ZnO transparent conductive film layer 2a formed thereon was formed.

The thickness (300 nm) of the second ZnO transparent conductive film layer 2b with Ga doping amount of 5.0 at% is larger than the thickness (5 nm) of the first ZnO transparent conductive film layer 2a with Ga doping amount of 13.3 at%. Therefore, the resistivity of the two-layered anode 2 was almost the same as that of the second ZnO transparent conductive film layer 2b having a Ga doping amount of 5.0 at%. On the other hand, the work function was the same as in the case of only the first ZnO transparent conductive film layer 2a having a Ga doping amount of 13.3 at%.
That is, it was confirmed that both the low resistivity and the high work function can be realized simultaneously by forming the anode 2 in a two-layer structure as in Example 2.
When the anode has a two-layer structure of the second ZnO transparent conductive film layer and the first ZnO transparent conductive film layer as described above, the second ZnO transparent conductive film layer has a viewpoint of realizing low resistance. Therefore, the film thickness is preferably about 50 to 300 nm, and the first ZnO transparent conductive film layer is preferably about 1 to 5 nm from the viewpoint of realizing a high work function.

FIG. 4 is a diagram schematically showing a configuration of an organic EL element according to Example 4 of the present invention.
As shown in FIG. 4, the organic EL element 10 includes a glass substrate 1, an anode 2 formed on the glass substrate 1, an organic light emitting layer 3 formed on the anode 2, and an organic light emitting layer 3. And a formed cathode 4.

Next, the manufacturing method of this organic EL element is demonstrated.
(1) First, by a method according to Example 1 described above, an anode (a single-layered anode made of the first ZnO transparent conductive film layer) 2 having a Ga doping amount of 8.8 at% and a thickness of 400 nm is made of alkali-free glass. It formed on the glass substrate 1.
(2) Then, an organic layer (organic light emitting layer) was formed on the anode 2 by the following method.
(a) As a light emitting layer material, poly (N-vinylcarbazole) (PVCz: made by Aldrich),
(b) As an electron transport material, 2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole (PBD: manufactured by Aldrich),
(c) Tris (2-phenylpyridine) iridium (Ir (ppy) ₃ : manufactured by Dojindo) as a green phosphorescent material
1,2-dichloroethane solution (light emitting layer solution) containing 2.0% by weight in a weight ratio of 50: 40: 3 was prepared.
(3) Then, after washing the glass substrate on which the Ga-doped ZnO film was formed in (1) above, UV ozone treatment was performed to remove trace amounts of organic substances remaining on the substrate surface.
Then, immediately after the UV ozone treatment, the above solution (light emitting layer solution) was spin-coated under the conditions of a rotation speed of 3500 rpm and a rotation time of 60 s, and dried at 110 ° C. for 10 minutes to form a 90 nm organic light emitting layer 3. .
(4) Next, on this organic light emitting layer 3,
(a) an electron injection layer (CsF: thickness 3 nm) (not shown),
(b) Cathode (Mg: Ag alloy film: thickness 250 nm, and Ag film: thickness 50 nm) 4
Was deposited at a rate of CsF film: 0.1 nm / s, Mg: Ag alloy film 1 nm / s, and Ag film 0.1 nm / s under conditions of a vacuum degree of 2.8 × 10 ⁻⁴ Pa.

As a result, as shown in FIG. 4, a ZnO film having a Ga doping amount of 8.8 at% and a thickness of 400 nm is formed on the glass substrate 1 as the anode (a single-layered anode composed of the first ZnO transparent conductive film layer) 2. Thus, an organic EL element 10 having a structure in which the organic light emitting layer 3 and the cathode 4 were sequentially formed thereon was obtained.
And the produced organic EL element was taken out from the vapor deposition apparatus and sealed in a glove box, and then the light emission characteristics were evaluated.
For comparison, an organic EL element having an anode of an ITO film having a thickness of 150 nm was fabricated instead of the ZnO film. The organic EL element of this comparative example was also taken out of the vapor deposition apparatus and sealed in a glove box, and then the light emission characteristics were evaluated.

The light emission characteristics of the organic EL device produced in Example 4 and the organic EL device of the comparative example are shown in FIGS. 5 shows the relationship between voltage and light emission luminance, and FIG. 6 shows the relationship between current density and light emission efficiency.
As shown in FIGS. 5 and 6, by using the first ZnO transparent conductive film layer having the c-axis grown in a plurality of directions and having a high work function as the anode, the peak top of the light emission luminance is on the low voltage side. It was confirmed to shift. It was also confirmed that the luminous efficiency with respect to the current density was also improved.

In Example 5, an organic EL element having an organic light emitting layer different from the organic EL element of Example 4 was prepared as the organic light emitting layer.
Below, the manufacturing method of the organic EL element of this Example 5 is demonstrated.

(1) First, a ZnO film (anode) having a Ga doping amount of 8.8 at% and a thickness of 400 nm (a single-layered anode made of the first ZnO transparent conductive film layer) is made alkali-free by the method according to Example 1 above. It formed on the glass substrate 1 which consists of glass.
After cleaning the glass substrate on which the ZnO film was formed, UV ozone treatment was performed in order to remove a trace amount of organic substances remaining on the substrate surface.
(2) Then, as described above, the substrate that has been subjected to the UV ozone treatment is immediately placed in a vacuum deposition apparatus, and on the anode having a single-layer structure composed of the first ZnO transparent conductive film layer,
(a) hole injection layer N, N′-di-1-naphthyl-N, N′-diphenylbenzidine (a-NPD: manufactured by Dojin Chemical Co., Ltd., sublimation purified product), thickness: 50 nm, and
(b) Light-emitting layer Tris (8-hydroxyquinoline) aluminum (Alq3: manufactured by Dojin Chemical Co., Ltd., sublimation product), thickness: 50 nm
Were stacked in the above order at a rate of 0.1 nm / s under the condition of a vacuum degree of 1.0 × 10 ⁻⁴ Pa to form an organic light emitting layer.
(3) Next, on this organic light emitting layer,
(a) Electron injection layer (LiF): thickness: 0.5 nm,
(b) Cathode (Al film: thickness 50 nm and Ag film: thickness 100 nm)
Were vapor-deposited at a rate of 0.1 nm / s under conditions of a degree of vacuum of 2.4 × 10 ⁻⁴ Pa.

As a result, as shown in FIG. 4, a single-layered anode 2 made of the first ZnO transparent conductive film layer was formed on the glass substrate 1, and the organic light emitting layer 3 and the cathode 4 were sequentially formed thereon. The organic EL element 10 having a structure was obtained.
And the produced organic EL element was taken out from the vapor deposition apparatus and sealed in a glove box, and then the light emission characteristics were evaluated.
For comparison, an organic EL element having an anode of an ITO film having a thickness of 150 nm was fabricated instead of the ZnO film. The organic EL element of this comparative example was also taken out of the vapor deposition apparatus and sealed in a glove box, and then the light emission characteristics were evaluated.

The light emission characteristics of the organic EL element of Example 5 and the organic EL element of the comparative example are shown in FIGS. 7 shows the relationship between voltage and light emission luminance, and FIG. 8 shows the relationship between current density and light emission efficiency.
As shown in FIGS. 7 and 8, the organic EL device of Example 5 did not reach the comparative example in which the ITO film was used as the anode in terms of the luminous efficiency, but the peak top of the luminous luminance shifted to the low voltage side. Confirmed to do.

In Example 6, the following three types of organic EL elements (1), (2), and (3) were produced.
(1) An organic EL device having a single-layered anode composed of a first ZnO transparent conductive film layer (thickness: 300 nm) having a Ga doping amount of 5.0 at% (see FIG. 4 for the structure),
(2) On the ZnO film (thickness: 300 nm) (second ZnO transparent conductive film having a low resistivity) of Ga doping amount of 5.0 at% (1) above, further, Ga doping amount of 13.3 at% An organic EL element having a two-layered anode in which a ZnO film (first ZnO transparent conductive film layer having a high work function) is formed under the condition of thickness: 5 nm.
As shown in FIG. 9, the organic EL element includes a glass substrate 1, a second ZnO transparent conductive film layer 2 b formed on the glass substrate 1 having a low resistivity, and a first ZnO transparent film having a high work function. A two-layered anode 2 composed of a conductive layer 2a, an organic light emitting layer 3 formed on the first ZnO film 2a on the anode 2, and a cathode 4 formed on the organic light emitting layer 3 are provided. Yes. ,
(3) On the ZnO film (thickness: 300 nm) (second ZnO transparent conductive film having a low resistivity) of the Ga doping amount of 5.0 at% (1) above, a ZnO film having a Ga doping amount of 13.3 at% An organic EL device having a two-layered anode in which (a first ZnO transparent conductive film layer having a high work function) is formed under the condition of a thickness of 1 nm. This organic EL element also has the same configuration as the organic EL element (2) shown in FIG. However, the thickness of the first ZnO transparent conductive film layer 2a having a large work function is different.

In addition, each organic EL element of said (2) and (3) was specifically produced by the method demonstrated below.
(1) First, a glass substrate made of non-alkali glass was prepared as a substrate, and cleaning by isopropyl alcohol and UV irradiation was performed as a pretreatment to obtain a clean surface.

  (2) Further, as a sputtering target, a ZnO mixed sintered body target containing 5.0 at% Ga and having a sintering density of 80% or more, and a sintering density 80% or more containing 13.3 at% Ga. A ZnO mixed sintered body target was prepared.

(3) Then, the glass substrate was set in a sputtering vacuum chamber, and after evacuation to 5.5 × 10 ⁻⁵ Pa, sputtering was performed to form a ZnO film.
As the sputtering apparatus, a multi-target type sputtering apparatus capable of installing a plurality of targets in the same chamber was used. A ZnO target having a Ga content of 5.0 at% was used to form a film with a set film thickness of 300 nm to form a second ZnO transparent conductive film layer which is a low resistivity layer.
Further, the oxygen flow rate was set to 1 sccm in vacuum, and a film was formed with a set film thickness of 5 nm (or 1 nm) using a target with a Ga concentration of 13.3 at%, and the first ZnO transparent, which is a high work function layer, was formed. A conductive layer was formed.
As described above, it is possible to increase the work function of the formed ZnO film layer by introducing oxygen gas when forming the first ZnO transparent conductive film layer. This is because oxygen vacancies in the ZnO film layer are reduced by introducing oxygen, and a thin insulating layer is formed at the interface, causing band bending at the interface, and banding of the valence band and conduction band bends to the high energy side. It is estimated that the work function is improved by shifting the Fermi level.

(4) Next, after patterning by wet etching, the film thickness was measured using a stylus-type step gauge, and it was confirmed that the film thickness was ± 15% with respect to the set film thickness.
The resistivity of the two-layered anode provided with the first and second ZnO transparent conductive film layers was 5.9 × 10 ⁻⁴ Ωcm, and the average light transmission in the visible region was obtained by four-probe measurement. The rate was 83%. As a result of the composition analysis, it was confirmed that the Ga doping amount was the same as that of the target composition in both the first and second ZnO transparent conductive film layers.

  (5) Next, the glass substrate on which the anode having the two-layer structure was formed as described above was washed, and then UV ozone treatment was performed to remove a trace amount of organic substances remaining on the substrate surface.

(6) Then, after UV ozone treatment, immediately install it in a vacuum evaporation system and place it on the anode with a two-layer structure.
(a) Hole injection layer N, N′-di-1-naphthyl-N, N′-diphenylbenzidine (a-NPD: manufactured by Tokyo Chemical Industry Co., Ltd., sublimation product), thickness: 50 nm, and
(b) Light emitting layer tris (8-hydroxyquinoline) aluminum (Alq3: manufactured by Tokyo Chemical Industry Co., Ltd., sublimation product), thickness: 50 nm
Were stacked in the above order at a rate of 0.1 nm / s under the condition of a vacuum degree of 1.0 × 10 ⁻⁴ Pa to form an organic light emitting layer.

(7) Then, on the light emitting layer (organic light emitting layer) formed as described above,
(a) Electron injection layer (LiF): thickness: 0.5 nm,
(b) Cathode (Al film: thickness 100 nm)
Vapor deposition was performed at a rate of 0.1 nm / s and 0.5 nm / s under conditions of a vacuum degree of 2.4 × 10 ⁻⁴ Pa, respectively, and an organic EL device having a Ga-doped ZnO film as an anode was produced. .

And the produced organic EL element was taken out from the vapor deposition apparatus and sealed in a glove box, and then the light emission characteristics were evaluated.
The light emission characteristics of the organic EL device of Example 6 are shown in FIG.

As shown in FIG. 10, a first ZnO transparent conductive film layer with a Ga doping amount of 13.3 at% is added on a second ZnO transparent conductive film layer with a Ga doping amount of 5.0 at% to form a two-layer structure. It was confirmed that the emission luminance profile shifted to the low voltage side by forming the anode.
From Example 6, it was confirmed that a high work function layer was formed on the outermost surface and disposed so as to be in contact with the organic light emitting layer, so that both the function as electrode (low resistance) and the improvement of the light emitting characteristics can be achieved. .

  Although not shown in the above embodiment, when the film is formed while applying a bias voltage to the substrate in the step of forming the ZnO film serving as the anode, the doping amount of the group III element oxide is reduced. However, it becomes possible to improve moisture resistance, and an anode having low resistance and excellent moisture resistance can be reliably manufactured.

  In each of the above embodiments, the case where a glass substrate is used as the substrate has been described. However, it is also possible to use a PEN substrate, a PET substrate, or the like, and a single crystal substrate such as crystal, sapphire, or Si. It is also possible to use.

In each of the above-described embodiments, the case where the ZnO film is formed directly on the substrate has been described. However, when the ZnO film is formed on a substrate that allows moisture to pass therethrough such as a flexible substrate, SiNx is used. By forming the ZnO film on the substrate through the thin film, the moisture resistance of the formed ZnO film can be further improved.
Although not shown in the above embodiment, an ITO film is used as a transparent conductive film layer having a low resistivity, and this ITO film and a ZnO transparent conductive film layer having a large work function and a large amount of doping of a group III element (first film) are used. Even when an anode having a multi-layer structure is configured by combining a single ZnO transparent conductive film layer), an anode having both low resistivity and high work function characteristics can be realized.

  The present invention is not limited to the above embodiments in other respects as well. The type of material used for the light emitting layer, the type and amount of group III element doped in the ZnO film, and the specifics of the ZnO film Various film forming conditions and the like can be applied within the scope of the invention.

As described above, according to the present invention, as the anode of the organic EL element, the first ZnO transparent conductive film layer doped with a group III element and having a crystal structure in which the c-axis is directed to a plurality of different directions is provided. Since the first ZnO transparent conductive film layer is used to form an interface with the organic light emitting layer, it has high characteristics and reliability without using ITO, and is excellent in economic efficiency. An organic EL element can be provided.
Moreover, by forming the anode into a two-layer structure further including a second ZnO transparent conductive film layer in which ZnO is doped with 3 to 8 at% of a group III element, both a low resistivity and a high work function are realized simultaneously. It becomes possible.
Therefore, the present invention can be widely applied to organic EL elements that are required to have high luminous efficiency and low resistance.

It is a figure which shows the relationship between the doping concentration of Ga and a work function in a ZnO transparent conductive film. It is a figure which shows the relationship between a ZnO (002) rocking curve half value width, and a work function in a ZnO transparent conductive film. It is a figure which shows the structure of the anode which has a 2 layer structure provided with the 1st and 2nd ZnO transparent conductive film layer. It is a figure which shows typically the structure of the organic EL element concerning the Example (Example 4) of this invention. It is a figure which shows the relationship between a voltage and light emission luminance of the organic EL element of FIG. It is a figure which shows the relationship between the current density of the organic EL element of FIG. 4, and luminous efficiency. It is a figure which shows the relationship between the voltage of the organic EL element concerning Example 5, and light emission luminance. It is a figure which shows the relationship between the current density of the organic EL element concerning Example 5, and luminous efficiency. It is a figure which shows the structure of the organic EL element of Example 6 typically. It is a figure which shows the relationship between the voltage of the organic EL element of Example 6, and light emission luminance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2a 1st ZnO transparent conductive film layer 2b 2nd ZnO transparent conductive film layer 2 Anode 3 Organic light emitting layer 4 Cathode 10 Organic EL element

Claims (14)

An anode disposed on a substrate, an organic light emitting layer disposed on the anode, and a cathode disposed on the organic light emitting layer so as to face the anode through the organic light emitting layer. In the organic EL element provided,
The anode includes a first ZnO transparent conductive film layer doped with a group III element and having a crystal structure in which c-axis is oriented in a plurality of different directions,
An organic EL element, wherein the first ZnO transparent conductive film layer forms an interface with the organic light emitting layer. An anode disposed on a substrate, an organic light emitting layer disposed on the anode, and a cathode disposed on the organic light emitting layer so as to face the anode through the organic light emitting layer. In the organic EL element provided,
The anode includes a first ZnO transparent conductive film layer doped with a group III element and having a ZnO (002) rocking curve half-width of 13.5 ° or more,
An organic EL element, wherein the first ZnO transparent conductive film layer forms an interface with the organic light emitting layer. An anode disposed on a substrate, an organic light emitting layer disposed on the anode, and a cathode disposed on the organic light emitting layer so as to face the anode through the organic light emitting layer. In the organic EL element provided,
The anode includes a first ZnO transparent conductive film layer doped with 6 to 40 at% of a group III element,
An organic EL element, wherein the first ZnO transparent conductive film layer forms an interface with the organic light emitting layer.   The organic EL device according to claim 3, wherein the first ZnO transparent conductive film layer is doped with a group III element of 6 to 20 at%.   5. The organic EL device according to claim 1, wherein the anode further includes a second ZnO transparent conductive film layer doped with 3 to 8 at% of a group III element.   6. The organic EL element according to claim 1, wherein the group III element is at least one selected from the group consisting of Ga, Al, and In.   The substrate on which the anode is disposed is glass, quartz, sapphire, Si, SiC, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), polyimide, cycloolefin-based polymer, and polycarbonate. The organic EL device according to claim 1, wherein at least one selected from the group consisting of: Forming an anode on a substrate;
Forming an organic light emitting layer on the anode;
In the manufacturing method of an organic EL device comprising a step of forming a cathode on the organic light emitting layer,
The step of forming the anode uses a raw material containing ZnO and a group III element oxide, and forms a film by a thin film formation method so that the doping amount of the group III element is in the range of 6 to 40 at%. And a step of forming a first ZnO transparent conductive film layer having a crystal structure in which the c-axis is directed in a plurality of different directions and forming an interface with the organic light emitting layer. A method for manufacturing an organic EL element. Forming an anode on a substrate;
Forming an organic light emitting layer on the anode;
In the manufacturing method of an organic EL device comprising a step of forming a cathode on the organic light emitting layer,
The step of forming the anode uses a raw material containing ZnO and a group III element oxide, and forms a film by a thin film formation method so that the doping amount of the group III element is in the range of 6 to 40 at%. ZnO (002) has a step of forming a first ZnO transparent conductive film layer having a rocking curve half width of 13.5 ° or more and forming an interface with the organic light emitting layer. A method for manufacturing an organic EL element.   In the step of forming the first ZnO transparent conductive film layer, the thin film forming method is selected from the group consisting of sputtering, vapor deposition, vapor deposition ion plating, laser ablation, and arc plasma vapor deposition 10. The method for producing an organic EL device according to claim 8, wherein a sintered compact target comprising a composition containing ZnO and a group III element oxide is used.   In the step of forming the first ZnO transparent conductive film layer, the thin film forming method is selected from the group consisting of the sputtering method, vapor deposition method, vapor deposition ion plating method, laser ablation method, and arc plasma vapor deposition method. 11. The method of manufacturing an organic EL element according to claim 10, wherein a bias voltage is applied to the substrate during film formation. The step of forming the anode uses a raw material containing ZnO and a group III element oxide, and a second ZnO transparent film is formed by a thin film forming method so that the doping amount of the group III element is in the range of 3 to 8 at%. Further comprising forming a conductive film layer,
9. The anode is configured to have a multi-layer structure by forming the first ZnO transparent conductive film layer on the second transparent conductive film layer. The manufacturing method of the organic EL element in any one of 11.   The method for producing an organic EL element according to claim 8, wherein the group III element is at least one selected from the group consisting of Ga, Al, and In.   The substrate is at least selected from the group consisting of glass, quartz, sapphire, Si, SiC, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), polyimide, cycloolefin-based polymer, and polycarbonate. The method for producing an organic EL element according to any one of claims 8 to 13, wherein one type is a main component.

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