JP2010135097A - Organic el element, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element with low contact resistance between a cathode and an auxiliary electrode, and driving at low voltage with high current efficiently, without drastically changing a cathode material, kinds of auxiliary electrode materials or present manufacturing processes, in a manufacturing method of the organic EL element. <P>SOLUTION: The manufacturing method of the organic EL element provided with an anode 4, an organic light-emitting layer 6 and a cathode 7 on a substrate 1 in this order, and further provided with an auxiliary electrode 2 for supplying driving current to the cathode 7, includes a process forming the auxiliary electrode 2 on the substrate 1, a process of irradiating gas plasma inactive to all of an auxiliary electrode material, a cathode material and oxygen, on a surface of the auxiliary electrode 2, a process of forming the anode 4 on the substrate 1 so as not to short circuit with the auxiliary electrode 2, a process of forming the organic light-emitting layer 6 on the anode 4, and a process of forming the cathode 7 on upper surfaces of the organic light-emitting layer 6 and the auxiliary electrode 2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a configuration of an organic EL element. In more detail, it is related with the processing method of the auxiliary electrode surface of an organic EL element.

  In recent years, the speed of information communication and the application range have been rapidly increasing. Among these, for display devices, high-definition display devices having low power consumption and high-speed response that can meet the demands of portability and moving image display have been widely devised.

Since organic electroluminescence (hereinafter referred to as organic EL) elements have been reported by Tang et al. As a stacked EL element that emits light with a high luminance of 100 Cd / m ² or more at an applied voltage of 10 V (see, for example, Non-Patent Document 1). Expected to be applied to flat panel displays that take advantage of superior features compared to liquid crystal display elements such as high contrast, low voltage drive, high viewing angle, and high-speed response, and research for practical application is active Has been done. Green monochrome organic EL displays and the like have already been commercialized, and the completion of high-definition full-color displays is awaited.

  Generally, an organic EL element has an organic light emitting layer between electrodes. Among these, a transparent electrode such as IZO or ITO is used as the electrode from which light is extracted, and a metal electrode having a high reflectance such as Al is used for the electrode opposite to the transparent electrode (hereinafter referred to as a back electrode) in order to increase the light extraction efficiency. Is used. Furthermore, in order to supply power to the light emitting layer, a method of controlling light emission by connecting the back electrode to an external drive circuit via an auxiliary electrode is widely used.

  The auxiliary electrode material may be any material that has a low electrical resistance with respect to the back electrode, and metals such as Mo and Al, and Al—Mo, Al—Ti, and Al—Cr alloys can be used. Since it is required to have high reflectance and good electrical conductivity, Al-based metal is often used for the back electrode and Mo-based metal is used for the auxiliary electrode.

  When the Mo-based metal is used for the auxiliary electrode, there arises a problem that the Mo surface is easily oxidized at the time of sputtering film formation or organic layer film formation pretreatment. Previous investigations have shown that the surface of the Mo-based metal auxiliary electrode is oxidized by the organic film pre-treatment process (hereinafter referred to as pre-film formation) after forming the auxiliary electrode, transparent electrode, and shadow mask. .

  When an Al-based metal is stacked on the upper surface of the Mo metal thus oxidized, Al donates electrons to the Mo oxide film, Mo is reduced to Al, and between the Al-based metal layer and the Mo-based metal layer. Then, an Al oxide layer having a high electric resistance is formed. As a result, the resistance between the back electrode and the auxiliary electrode increases, and the current efficiency of the organic EL element is deteriorated.

  On the other hand, the pre-film-forming treatment is performed by performing high-temperature drying (150 ° C.) and UV treatment (heating to 150 ° C. after room temperature) of the substrate immediately before the organic film is formed for the purpose of removing residues and dust on the surface of the transparent electrode. ing. It has been found that when a contamination such as a residue is present at the interface between the transparent electrode and the organic film, a dielectric breakdown occurs due to an increase in driving voltage or an abnormal interface. For this reason, in order to reduce the voltage and improve the reliability of the organic EL element, the film formation pretreatment is a desirable process.

Under such circumstances, some proposals for reducing the resistance between the back electrode and the auxiliary electrode of the organic EL element have been raised. For example, a method has been proposed in which a barrier layer having good anti-modification properties such as noble metals, nitrides, and oxides is used on the upper surface of the auxiliary electrode material (see Patent Documents 1 and 2).
AppL. Phys. Lett. , 51, 913 (1987) JP 2001-351778 A JP 2004-158199 A

  However, since noble metals such as Au are much more expensive than Al, the cost of organic EL products is problematic. Further, when an oxynitride film or a nitride film is manufactured, the manufacturing conditions and manufacturing process of the film are complicated, so that the number of manufacturing steps increases and an increase in manufacturing time can be considered.

  The object of the present invention is to provide a contact resistance between the cathode and the auxiliary electrode without significantly changing the type of the cathode material and the auxiliary electrode material and the current manufacturing process in the manufacture of the organic EL element in view of the above-mentioned present situation. An object of the present invention is to provide an organic EL element which is low and driven at a low voltage with high current efficiency.

For example, in order to use, for example, Al having good reflectivity and low cost as the back electrode, and to prevent an increase in contact resistance, it is necessary to prevent oxidation of the auxiliary electrode surface in contact with the back electrode. For this purpose, the atmosphere during the film-forming pretreatment process may be blocked from the auxiliary electrode surface. Therefore, after the auxiliary electrode is fabricated, it is proposed to coat the auxiliary electrode with an antioxidant adsorption film that is inert to any of the cathode material, auxiliary electrode material, and oxygen, that is, a fluorine-containing film or a fluorine adsorption film. .
Furthermore, since this antioxidant film has a role of blocking the contact between the auxiliary electrode surface and the atmosphere during the pretreatment process for film formation, it is indispensable that the contact resistance with the back electrode is not increased. A thin film is required. Therefore, as a method for coating the auxiliary electrode, it is proposed to expose the cathode material, the auxiliary electrode material, and oxygen to an inert gas plasma atmosphere so that the gas components adhere to the surface of the auxiliary electrode very slightly. With this method, it is possible to form an ultrathin film by adjusting the gas blowing conditions.

The organic EL device of the present invention is also an organic EL device comprising an anode, an organic light emitting layer and a cathode on a substrate in this order, and further comprising an auxiliary electrode for supplying a driving current to the cathode. A fluorine-containing film that is inert to any of the cathode material, auxiliary electrode material, and oxygen is provided between the electrode and the cathode.
The method for producing an organic EL device of the present invention is a method for producing an organic EL device comprising an anode, an organic light emitting layer and a cathode on a substrate in this order, and further comprising an auxiliary electrode for supplying a drive current to the cathode. A step of forming the auxiliary electrode on the substrate; a step of irradiating the surface of the auxiliary electrode with gas plasma inert to any of the auxiliary electrode material, the cathode material, and oxygen; In addition, a step of forming an anode so as not to be short-circuited with the auxiliary electrode, a step of forming an organic light emitting layer on the anode, and a step of forming a cathode on the upper surface of the organic light emitting layer and the auxiliary electrode are included in this order. It is a waste.

In the present invention, (1) by attaching a gas component inert to oxygen, that is, a fluorine gas component and a fluorine compound, to the auxiliary electrode surface, the auxiliary electrode surface is shielded from the atmosphere in the subsequent process. Surface oxidation can be prevented, an increase in contact resistance can be suppressed, and a simple method for producing an organic EL element with high current efficiency and low voltage can be provided.
(2) Since the current cathode material, auxiliary electrode material, and current manufacturing process are not significantly changed, it is possible to simplify the organic EL device with high current efficiency and low voltage while taking advantage of existing facilities and materials. A manufacturing method can be provided.

  First, the cross-sectional schematic diagram of one Embodiment of the organic EL element in this invention is shown in FIG. The organic EL element mainly includes a substrate 1 that is a base that supports the element, an auxiliary electrode 2 that supplies current from the outside, an anode 4, an insulating layer 5, an organic light emitting layer 6, and a cathode (back electrode) 7 that reflects light. Prepare.

The schematic diagram of the organic EL element manufacturing process in this invention is shown in FIG.
First, the auxiliary electrode 2 is formed on the substrate 1 by sputtering.
The auxiliary electrode 2 can be made of a metal having high conductivity such as Al, Cu, Cr, and Mo, and can use a low-resistance metal. The auxiliary electrode 2 is in contact with the back electrode 6 at the end of the organic EL element, and an external driving voltage is organic. Supply to EL element.
For example, after depositing a Mo film using a DC sputtering method, the auxiliary electrode 2 can be patterned by photolithography and patterning a resist.
A preferred thickness of the auxiliary electrode 2 is 50 to 1000 nm.

Next, the substrate on which the auxiliary electrode 2 is patterned is placed in a vacuum apparatus and irradiated with gas plasma 8. As a result, the gas plasma material is adsorbed on the surface of the auxiliary electrode 2 by one to several layers of molecules. This is the antioxidant adsorption film 3. It can be confirmed that the gas plasma material is adsorbed by one layer or several layers by depth direction analysis by XPS capable of analyzing several nm level.
Moreover, when the film thickness of the antioxidant adsorption film 3 increases, the contact resistance may increase due to this thin film. In order to prevent this, it is desirable that the film thickness is one molecule to several layers, less than 10 nm and 0.1 nm or more in terms of thickness.
The antioxidant film is preferably a fluorine-containing film. In the surface analysis by XPS, the fluorine-containing film is a film in which, for example, fluorine is detected with respect to the base material at a composition ratio of F / Mo of 0.008 or more.

The gas species that is the gas plasma material is required to be inert to any of the cathode material, the auxiliary electrode material, and oxygen. “Inert to any of the cathode material, auxiliary electrode material, or oxygen” means that the gas species reacts with the cathode material or the like during manufacturing or driving of the device, for example, to change the structure of the cathode material itself. It means things that do n’t happen.
The gas species is preferably one that can adsorb one layer or several layers on the surface of the auxiliary electrode and can protect the surface of the auxiliary electrode from the atmosphere during sputtering or pretreatment for film formation. The gas species preferably includes one or more gases selected from the group consisting of fluorine (F ₂ ) and fluorine compound gases.
Examples of the fluorine compound include CF ₄ and SF ₆ .
The gas plasma generation method is not particularly limited, and methods such as RF discharge, magnetron discharge, and microwave discharge can be employed.
The type of gas and the gas plasma irradiation conditions are preferably selected as appropriate according to the auxiliary electrode material.
For example, when Mo is used as the auxiliary electrode material, CF ₄ , SF ₆ or a mixed gas thereof can be used as the gas type, the plasma system is inductively coupled plasma [ICP], the RF power is 1000 W to 10,000 W, the atmosphere The pressure can be 150 mTorr.

The ratio of the gas element to the base material on the auxiliary electrode surface after gas plasma irradiation is preferably 0.008 or more.
The elemental composition is a value obtained by measurement by X-ray photoelectron spectroscopy [XPS].

After the gas plasma irradiation, the anode 4 is formed by patterning so that the auxiliary electrode 2 and the anode 4 are not short-circuited.
The anode 4 is made of a transparent conductive material in order to extract light generated in the organic light emitting layer 6 described later. More specifically, the conductive material is preferably a conductive material that transmits 80% or more of the wavelength in the visible light region, and IZO (In—Zn-based oxide) or ITO (In—tin-based oxide) is used.
The anode can be formed by, for example, DC sputtering, magnetron sputtering, or the like. A preferable thickness of the anode is 30 to 1000 nm.
As a method for avoiding electrical contact between the anode 4 and the auxiliary electrode 2, for example, there is a method of forming an anode through an insulating layer 5. The insulating layer 5 is preferably formed of an inorganic oxide or a resin material. For example, SiO ₂ can be used. The insulating layer can be formed by a method such as vapor deposition sputtering, for example. A preferable thickness of the insulating layer is 50 to 1000 nm.

After the patterning of the anode 4 and the insulating layer 5 is completed, a film formation pretreatment for removing residues and dust on the anode surface in a vacuum atmosphere can be performed.
As the pre-film formation treatment, it is desirable to perform room temperature UV treatment, high temperature drying treatment of the substrate, and / or heating UV treatment.
The room temperature UV treatment is usually performed at 10 to 30 ° C. for 1 to 10 minutes. The high temperature drying treatment of the substrate is usually performed at 100 ° C. to 200 ° C. for 30 minutes to 120 minutes. The heating UV treatment is usually performed for 1 minute to 10 minutes by heating to 100 ° C. to 200 ° C.

After the film formation pretreatment, the organic light emitting layer 6 is deposited without breaking the vacuum.
The organic light emitting layer 6 includes at least an organic light emitting layer that emits light by recombination of holes and electrons generated when a voltage is applied to the anode and the cathode, and has a basic structure of anode / organic light emitting layer / cathode. As described above, those provided with a hole injecting and transporting layer and an electron injecting and transporting layer, specifically, those having the following layer structure are employed.
(1) Anode / organic light emitter layer / cathode (2) Anode / hole injection layer / organic light emitter layer / cathode (3) Anode / organic light emitter layer / electron injection layer / cathode (4) Anode / hole injection Layer / hole transport layer / organic light emitter layer / cathode (5) anode / hole injection layer / hole transport layer / organic light emitter layer / electron transport layer / cathode (6) anode / hole injection layer / hole Transport layer / organic phosphor layer / electron transport layer / electron injection layer / cathode

The material of each layer in the organic light emitting layer is not particularly limited, and known materials can be used. The material of the organic light-emitting layer can be selected according to the desired color tone. For example, in order to obtain light emission from blue to blue-green, fluorescence enhancement such as benzothiazole, benzimidazole, and benzoxazole is possible. Whitening agents, metal chelated oxonium compounds, styrylbenzene compounds, aromatic dimethylidin compounds, and the like can be used.
Materials for the electron injection layer include alkali metals such as Li, Na, K, or Cs; alkaline earth metals such as Ba and SI; rare metals; or their fluorides, aluminum chelates (Alq), etc. However, the present invention is not limited to these. Furthermore, Alq3 and benzazul can be used as the material for the electron transport layer, but the material is not limited to these.
As the hole injection layer, copper phthalocyanine can be used, but is not limited thereto. As the hole transporting layer, 4,4′-bis [N- (l-naphthyl) -N-phenylamino] biphenyl (α-NPD), triphenyldiamine (TPD), or the like can be used. However, the present invention is not limited to this.
A method for forming each layer in the organic light emitting layer depends on whether the material is a polymer or a low molecular material. For example, a vacuum deposition method, an ionization deposition method, an MBE method, an inkjet method, or the like can be employed.
A preferable thickness of the organic light emitting layer is 30 nm to 300 nm.

Finally, the back electrode 6 that is a cathode is deposited on the top surfaces of the organic light emitting layer 6 and the auxiliary electrode 2. Thereby, the above-mentioned auxiliary electrode 2 and the back electrode 6 are connected.
The back electrode 6 is preferably a metal or alloy having a work function of less than 4.8 eV and good reflectivity, and Al, Ag, Mg, Mn, or an Al—Li alloy or Mg—Ag alloy containing these metals, or A laminated electrode of these metals such as LiF / Al can also be used.
As a method for forming the back electrode 6, a mask method, a cathode partition wall method, a laser ablation method, or the like can be employed.
A preferable thickness of the back electrode 6 is 30 nm to 300 nm.

First, the gas plasma effect on Mo surface oxidation was verified based on the embodiment of the invention.
First, a Mo pattern serving as an auxiliary electrode was formed. Specifically, after depositing a 300 nm Mo film at room temperature using DC sputtering, the resist was patterned by photolithography, and a Mo pattern a having a wiring width of 7 μm was formed by etching.
Next, gas plasma was exposed to the surface of the Mo pattern a under the following conditions to obtain a Mo pattern b. The gas type was a mixed gas of CF ₄ and Ar, and the gas flow rate ratio was CF ₄ / Ar = 300 sccm / 200 sccm. The plasma method was inductively coupled plasma [ICP], the RF power was 3000 W, and the atmospheric pressure was 1.33 Pa.
Thereafter, on the glass substrate having Mo patterns a and b, IZO as an anode and SiO ₂ as an insulating layer were formed by sputtering and photolithography, respectively, at 220 nm and 400 nm, respectively. ), High-temperature drying treatment (150 ° C., 1 hour) of the substrate, and heating UV treatment (heating to 150 ° C. for 6 minutes) were performed to obtain a substrate having Mo patterns d and c.
The surface state of each Mo pattern thus produced was analyzed. The Mo surface state was evaluated by calculating the composition ratio of carbon (Cls), oxygen (O1s), Mo (Mo3d), and fluorine (Fls) using X-ray photoelectron spectroscopy (XPS, Quantum 2000 manufactured by ULVAC-PHI). Table 1 shows a list of composition ratios.

From Table 1, although there is no fluorine in the Mo pattern a immediately after patterning, 0.9 at% fluorine was present on the Mo surface in the Mo pattern b after the gas plasma exposure process. In addition, the Mo pattern c that has undergone the gas plasma exposure step and the pre-film formation treatment was not significantly different from the Mo pattern b in the state before the film pre-treatment, that is, the Mo pattern b, but the gas plasma exposure was performed. In the Mo pattern d that was not performed, the oxygen composition ratio clearly increased and the Mo composition ratio decreased compared to the state before the film formation pretreatment, that is, the Mo pattern a. This result suggested that the progress of oxidation on the surface of the Mo pattern d was remarkable.
Next, the degree of oxidation of Mo was investigated. FIG. 3 shows the XPS spectrum of Mo (Mo3d). In the figure, the horizontal axis represents binding energy [eV], and the vertical axis represents photoelectron intensity [a. u. ]. The right peak with a low binding energy is a peak derived from metal Mo (near 228 eV), and the left peak with a high binding energy is a peak derived from Mo oxide (231 to 238 eV).
From FIG. 3, the Mo pattern a immediately after patterning and the Mo patterns b and c after the gas plasma exposure process showed a tendency that the peak of metal Mo was larger than the peak of oxidized Mo. On the other hand, in the Mo pattern d that did not go through the gas plasma exposure step, the peak of oxidized Mo was clearly larger than the peak of metal Mo, suggesting that the oxidation progress was remarkable as in Table 1.
Therefore, in order to quantitatively evaluate the degree of oxidation of the Mo pattern surface, the ratio of metal Mo to oxidized Mo was quantified. Specifically, the Mo3d peak was separated into peaks derived from metal Mo and Mo oxide, and each peak area ratio was calculated and evaluated when the entire peak area was 100 [%}.
Table 2 shows the ratio of metal Mo to oxidized Mo.

From Table 2, regarding the ratio of metal Mo to oxidized Mo, the Mo pattern c that has undergone the gas plasma exposure step is close to the Mo pattern b before the film formation pretreatment or the Mo pattern a immediately after patterning, and the gas plasma exposure step. This supported the protection of the Mo surface from oxidation. On the other hand, it was found that the Mo pattern d that did not go through the gas plasma exposure step had a significantly increased ratio of oxidized Mo, and the progress of oxidation on the Mo surface was remarkable.
From the above, it was found that gas plasma exposure is effective in preventing Mo surface oxidation.

Hereinafter, based on the embodiment of the invention, an organic EL element A in which gas plasma was exposed to the Mo surface and an organic EL element B in which gas plasma was not exposed to the Mo surface were produced.
First, an Mo pattern was formed as an auxiliary electrode. After depositing a 300 nm Mo film at room temperature using DC sputtering, the resist was patterned by photolithography, and a pattern with a wiring width of 7 μm was formed by etching.
Next, the organic EL element A was exposed to gas plasma on the Mo surface. The gas type was a mixed gas of CF ₄ and Ar, and the gas flow rate ratio was CF ₄ / Ar = 300 sccm / 200 sccm. The plasma method was ICP, the RF power was 3000 W, and the atmospheric pressure was 1.33 Pa. On the other hand, the organic EL element B did not perform this step.
Next, IZO was produced on a glass substrate by a DC sputtering method in a vacuum sputtering apparatus, and an anode was produced by patterning. At this time, the film thickness of IZO was 220 nm.
Next, as film formation pretreatment for removing dust on the IZO surface, room temperature UV treatment (6 minutes), substrate high temperature drying treatment (150 ° C., 1 hour), heating UV treatment (heating to 150 ° C.) 6 minutes).
Thereafter, an organic light emitting layer was formed. As the hole injection layer, 100 nm of copper phthalocyanine (CuPc) was laminated. As the hole transport layer, 4,4′-bis [N (1-naphthyl) -N-phenylamino] biphenyl (α-NPD) was laminated to 20 nm. The organic light emitting layer was formed by laminating 30 nm of 4,4′-bis (2,2′-diphenylvinyl) biphenyl (DPVBi). The electron injection layer was formed by laminating 20 nm of aluminum chelate (Alq). The deposition rate of each layer was 0.2 to 0.4 nm / second. Then, aluminum (Al) was produced as a cathode with an aluminum vapor deposition apparatus. At this time, the film thickness of Al was 100 nm, and the deposition rate was about 1 nm / second.
Then, the element was conveyed to the glove box and the element was sealed using sealing glass. The sealing glass and the substrate were fixed and sealed through an adhesive.
With respect to the organic EL elements A and B produced as described above, the contact resistance between the cathode and the auxiliary electrode was measured by a four-terminal method by applying a terminal to the lead portion of the cathode and the auxiliary electrode.
Table 3 shows the results of contact resistance measurement.

  From Table 3, it was found that the contact resistance of the organic EL element A exposed to the gas plasma on the Mo surface was clearly lower than that of the organic EL element B not exposed to the gas plasma.

It is typical sectional drawing of the one aspect | mode of the organic EL element of this invention. It is typical sectional drawing which shows the manufacturing process of the organic EL element of this invention. It is an XPS spectrum of the auxiliary electrode surface after passing through each process.

Explanation of symbols

1 Substrate 2 Auxiliary electrode 3 Ultrathin film 4 Anode (transparent electrode)
5 Insulating layer 6 Organic light emitting layer 7 Cathode (back electrode)
10 Organic EL device A
20 Organic EL element B

Claims (3)

An organic EL device comprising an anode, an organic light emitting layer and a cathode on a substrate in this order, and further comprising an auxiliary electrode for supplying a driving current to the cathode,
An organic EL device comprising a fluorine-containing film that is inert to any of a cathode material, an auxiliary electrode material, and oxygen between the auxiliary electrode and the cathode. A method for producing an organic EL device comprising an anode, an organic light emitting layer and a cathode on a substrate in this order, and further comprising an auxiliary electrode for supplying a driving current to the cathode,
Forming the auxiliary electrode on the substrate;
Irradiating the surface of the auxiliary electrode with gas plasma inert to any of the auxiliary electrode material, the cathode material or oxygen;
Forming an anode on the substrate so as not to short-circuit the auxiliary electrode;
Forming an organic light emitting layer on the anode;
And a step of forming a cathode on the upper surface of the organic light emitting layer and the auxiliary electrode in this order. The method of manufacturing an organic EL element according to claim 2, wherein the gas plasma is generated using fluorine (F ₂ ) or a fluorine compound gas as a material.

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