JP2005071696A - Organic EL device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the luminous performance and reliability of an organic EL device using a negative electrode having a metal layer and an oxide conductive layer. <P>SOLUTION: This organic EL device 100 comprises: an anode 2; a translucent cathode 5; and an organic EL layer 9 formed between the positive electrode 2 and the negative electrode 5 and containing at least a luminous layer 4. The negative electrode 5 comprises: a first metal layer 6 containing a first metal; a second metal layer 7 containing a second metal; and an oxide conductive layer 8 containing an oxide in this order from the side of the organic EL layer 9. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an organic electroluminescence (EL) device.

  Since organic EL elements can be driven at a low voltage and can emit light with high luminance, research and development on organic EL elements have been actively conducted. In general, an organic EL element has a structure in which a light emitting layer formed using an organic material is sandwiched between a pair of electrodes, at least one of which has translucency. A hole injecting and transporting layer, an electron injecting and transporting layer, and the like are provided between the pair of electrodes as necessary.

  The organic EL element can be used for a display device, for example. There are a simple matrix method and an active matrix method for driving the display device. In the display device of the simple matrix method, it is necessary to increase the instantaneous luminance of each pixel as the duty ratio increases. When the panel becomes large, there is a problem that power consumption increases. Therefore, particularly when a large display panel is required, an active matrix system is mainly employed.

  An active matrix display device using an organic EL element has a substrate on which a plurality of thin film transistors (hereinafter may be abbreviated as “TFT”) is formed, and an organic EL element formed on the substrate. ing. The TFT is formed for each of a plurality of pixels arranged in a matrix. By turning on / off the TFT of each pixel by the control signal, the light emission state of the organic EL element can be controlled for each pixel, and as a result, an image can be displayed. The display device having such a structure includes a method of taking out light from the organic EL element from the substrate surface opposite to the surface on which the TFT is formed (bottom emission method), a TFT formed on the substrate, and the organic EL element. There is a method of taking out from above (top emission method).

  A TFT usually has a semiconductor layer made of polysilicon, amorphous silicon or the like, an electrode made of metal, and the like, but such a semiconductor layer or electrode does not have sufficient light transmittance. Therefore, the bottom emission method in which light is extracted through the TFT has a problem that the ratio of the light emission area to the pixel area (aperture ratio) is small. In the organic EL display device, the current driving method is preferably adopted because the variation in display performance of each pixel is suppressed and the change in panel display luminance due to the deterioration of the organic EL material can be further reduced. If adopted, four transistors are required for each pixel. Therefore, the aperture ratio is further reduced as compared with a case where a voltage driving method which is simpler but inferior in display variation or the like for each pixel (two transistors in each pixel) (Non-Patent Document 1).

  In the top emission method, it is possible to prevent the problem of the aperture ratio. However, in this method, the upper electrode of the organic EL element needs to be light transmissive. The upper electrode usually has a laminated structure of an electron injection electrode (cathode) made of a sufficiently thin metal film so that light can be transmitted and a transparent conductive film formed on the electron injection electrode. The transparent conductive film is provided to protect the electron injection electrode, which is a thin metal film, and to reduce wiring resistance. For the formation of this transparent conductive film, a method of generating relatively high energy particles such as sputtering and ion plating is usually used, so that the electron injection electrode and the light emitting layer in the lower layer are damaged, As a result, device characteristics may be deteriorated.

In order to prevent damage to the lower layer when forming the transparent conductive film, as the structure of the upper electrode, for example, a laminated structure of an electron injection cathode layer (metal film) and an amorphous transparent conductive film (Patent Document 1), A laminated structure of a low work function insulating layer (LiO ₂ ) / cathode (Ag) / transparent conductive film (Patent Document 2) is disclosed.

  However, the structure of the upper electrode disclosed in these patent documents has the following problems.

  As the transparent conductive film, an oxide conductive layer containing indium tin oxide (ITO) or indium zinc oxide (IZO) as a main component from the viewpoint of translucency and resistivity is used. A good oxide conductive layer made of ITO or IZO is generally formed while introducing oxygen gas into the film forming apparatus. On the other hand, the upper electrode has a metal layer for injecting electrons into the organic EL layer. As a material for such a metal layer, a metal having a low work function, for example, magnesium, is used to improve the electron injection efficiency. In many cases, an alkaline earth metal such as (Mg), calcium (Ca), or barium (Ba), an alkali metal, indium (In), or an alloy containing these metals is used. Therefore, when a metal layer made of a low work function metal is formed and an oxide conductive layer is formed using the metal layer as a base, the low work function metal is easily oxidized by the oxygen gas introduced into the film forming apparatus. There is a problem of deteriorating element characteristics. Even in the case where the oxide conductive layer is formed while introducing only Ar gas into the film formation apparatus without introducing oxygen gas, the oxide conductive layer is a metal oxide and thus included in the oxide conductive layer. Since the low work function metal is oxidized by the generated oxygen, the device characteristics may be deteriorated.

As described above, in particular, when an oxide conductive layer such as ITO is formed on a metal layer made of a low work function metal, oxidation of the metal layer becomes a problem. When in contact with the oxide conductive layer, there is a problem of deterioration in characteristics or reliability due to oxidation of the metal layer.
Japanese Patent Laid-Open No. 10-162959 JP 2001-85163 A Shang-Li Chen et al. IDW '01, p.399

  An object of the present invention is to improve the light emission efficiency and reliability of an organic EL element in an organic EL element using a cathode having a metal layer and an oxide conductive layer.

  The organic EL device of the present invention includes an anode, a light-transmitting cathode, and an organic EL layer that is formed between the anode and the cathode and includes at least a light-emitting layer. A first metal layer containing a metal, a second metal layer containing a second metal, and an oxide conductive layer containing an oxide are provided in this order from the organic EL layer side.

  In a preferred embodiment, the work function of the second metal is greater than the work function of the first metal.

  The second metal layer preferably has a visible light transmittance of 10% or more.

  It is preferable that the second metal layer substantially completely covers the surface of the first metal layer.

  In a preferred embodiment, the thickness of the second metal layer is 10 nm or more and 30 nm or less.

  The total thickness of the first metal layer and the second metal layer is preferably 35 nm or less.

  The oxide conductive layer contains the oxide as a main component, and the oxide may be indium tin oxide (ITO) or indium zinc oxide (IZO).

  The second metal may include at least one metal selected from the group consisting of Ni, Os, Pt, Pd, Al, Au, and Rh.

  The oxide conductive layer may be formed by sputtering using a sputtering gas containing oxygen gas.

  The organic EL layer may include an organic layer formed using a solution containing a polymer material.

  A display device of the present invention includes any one of the organic EL elements described above and a thin film transistor.

  Another organic EL device of the present invention includes an anode, a light-transmitting cathode, and an organic EL layer formed between the anode and the cathode and including at least a light-emitting layer. A layer, a conductive layer capable of suppressing oxidation of the metal layer, and an oxide conductive layer containing an oxide are provided in this order from the organic EL layer side.

  According to the present invention, in the cathode of the organic EL element, the second metal layer is provided between the first metal layer and the oxide conductive layer, and the first metal layer is directly connected to the oxide conductive layer. Since it is not in contact, the oxidation of the first metal layer can be suppressed. In the case where the oxide conductive layer is formed after the first metal layer is formed, oxidation of the first metal layer when the oxide conductive layer is formed can be suppressed.

  Thus, since the oxidation of the first metal layer is suppressed, a decrease in the electron injection efficiency of the first metal layer can be suppressed, and as a result, the light emission efficiency of the organic EL element can be improved. Moreover, since the deterioration of the characteristics of the organic EL element can be suppressed, the reliability of the organic EL element is improved.

  Hereinafter, embodiments of the organic EL element according to the present invention will be described with reference to the drawings.

(Embodiment 1)
An organic EL element 100 shown in FIG. 1 includes an anode 2, an organic EL layer 9, and a cathode 5 that are sequentially formed on a substrate 1. In the present embodiment, the organic EL layer 9 is formed of the light emitting layer 4 and the hole transport layer 3, but the organic EL layer 9 only needs to include at least the light emitting layer 4, and is not limited to the configuration of FIG. In the organic EL element 100 of the present embodiment, the light from the light emitting layer 4 is extracted from above the cathode 5 (top emission type), so the cathode 5 has translucency. The cathode 5 has a three-layer structure in which a first metal layer 6, a second metal layer 7, and an oxide conductive layer 8 containing an oxide are stacked in this order on an organic EL layer 9. The first metal layer 6 includes a first metal, and the second metal layer 7 includes a second metal.

  In the organic EL element 100 of FIG. 1, the first metal layer 6 is disposed between the first metal layer 6 and the oxide conductive layer 8 to form the first conductive layer 8 when the oxide conductive layer 8 is formed. It is possible to prevent the metal layer 6 from being oxidized. Accordingly, it is possible to suppress a decrease in the light emission efficiency of the organic EL element due to the oxidation of the first metal layer 6. In this specification, “light emission efficiency” is the luminance (light flux) of extracted light with respect to the electric power input to the organic EL element. If the decrease in light emission efficiency can be suppressed, the power input to the organic EL element can be reduced in order to achieve the required luminance. Therefore, since the current or voltage applied to the organic EL element can be reduced, deterioration of the organic EL element can be suppressed, and as a result, the reliability of the organic EL element can be improved. In addition, even after the organic EL element is formed, the first metal layer 6 is not directly in contact with the oxide conductive layer 8, so that it is difficult to be oxidized by oxygen contained in the oxide conductive layer 8. Therefore, it is possible to suppress deterioration of the organic EL element due to an increase in resistance of the first metal layer 6 and a decrease in electron injection efficiency, and it is possible to improve the reliability of the organic EL element.

  The work function of the second metal is preferably larger than the work function of the first metal. As described above, a metal having a low work function, that is, a metal having a high electron injection efficiency is used as the material of the first metal layer 6, and a metal having a high work function, that is, a metal that is not easily oxidized. By using, oxidation of the first metal layer 6 can be prevented without lowering the electron injection efficiency of the first metal layer 6. The second metal includes at least one metal selected from the group consisting of Ni, Os, Pt, Pd, Al, Au, and Rh, for example.

  The second metal layer 7 only needs to have a function of suppressing the oxidation of the first metal layer 6 when or after the oxide conductive layer 8 is formed. The second metal layer 7 preferably has a visible light transmittance of 10% or more. When the second metal layer 7 has a visible light transmissivity of 10% or more, a transparent organic EL panel or an organic EL panel having a top emission structure can be realized. The second metal layer 7 preferably covers the surface of the first metal layer 6 almost completely. Thereby, the oxidation of the 1st metal layer 6 can be prevented more effectively. In addition, since the 2nd metal layer 7 can suppress the oxidation of the 1st metal layer 6 partially, if the surface of the 1st metal layer 6 is at least partially covered, for example, the 2nd metal layer Layer 7 may be a porous film. The thickness of the second metal layer 7 is preferably 10 nm or more. If the thickness of the 2nd metal layer 7 is 10 nm or more, the oxidation of the 1st metal layer 6 can be prevented more reliably. On the other hand, the thickness of the second metal layer 7 is preferably 30 nm or less. If the thickness of the second metal layer 7 exceeds 30 nm, the light absorption of the second metal layer 7 increases, and there is a possibility that sufficient translucency for visible light cannot be ensured.

  The total thickness of the first metal layer 6 and the second metal layer 7 is preferably 35 nm or less. If the total of these thicknesses is 35 nm or less, a transparent organic EL panel or a top emission structure organic EL panel can be realized.

  The oxide conductive layer 8 contains an oxide as a main component. For example, the oxide conductive layer 8 is formed of substantially only 100% oxide except for a small amount of impurities.

  Instead of the second metal layer 7, a conductive layer (such as a layer made of a conductive oxide) other than the metal layer that can exhibit the function of preventing the oxidation of the first metal layer 6 may be provided. Alternatively, an insulating layer having such a function may be used. In the case of using an insulating layer, the thickness of the insulating layer is preferably sufficiently small so that the conductivity between the first metal layer 6 and the oxide conductive layer 8 is maintained.

  The organic EL layer 9 may include an organic layer formed from a solution using a polymer material. Thereby, since the thin film formation method which does not use vacuum, such as a printing method and an inkjet method, can be used, an organic EL element can be produced at a lower cost.

The organic EL layer 9 only needs to include the light emitting layer 4 and may have a single layer structure or a multilayer structure. The organic EL layer 9 in the present embodiment has, for example, the following configuration, but the present invention is not limited to these.
(1) Organic light emitting layer (2) Hole transport layer / organic light emitting layer (3) Organic light emitting layer / electron transport layer (4) Hole transport layer / organic light emitting layer / electron transport layer (5) Hole injection layer / Hole transport layer / organic light emitting layer / electron transport layer The light emitting layer 4 contained in the organic EL layer 9 may be a single layer or may have a multilayer structure. The light emitting layer 4 may be a layer in which a base material is doped with a dopant.

  As the light emitting material contained in the light emitting layer 4, a known light emitting material for an organic LED element can be used. Known light emitting materials can be classified into low molecular light emitting materials, polymer light emitting materials, precursors of polymer light emitting materials, and the like. Specific compounds of the respective light emitting materials are exemplified below, but the present invention is not limited thereto.

  As low molecular weight light emitting materials, aromatic dimethyldiene compounds such as 4,4′-bis (2,2′-diphenylvinyl) -phenyl ((DPVBi)), 5-methyl-2- [2- [4- (5- Oxadiazole compounds such as methyl-2-benzoxaziryl) phenyl] vinyl] benzoxazole, 3- (4-biphenylyl) -4-phenyl-5-t-butylphenyl-1,2,4-triazole (TZA) ) And other triazole compounds, styryl bezene compounds such as 4-bis (2-methystyryl) benzene, fluorescent organic materials such as thiovirazine dioxide derivatives, benzoquinone derivatives, naphthoquinone derivatives, anthraquinone derivatives, azomethine zinc complexes, (8- Fluorescent organometallic compounds such as hydroxynolinato) aluminum complexes can be used.

Polymer light-emitting materials include poly (2-decyloxy-1,4-phenylene) (DO-PPP), poly [2,5-bis- [2- (N, N, N-triethylammonium) ethoxy] -1 4-phenyl-alt-1,4-phenyllene] dibromide (PPP-NEt ³⁺ ), poly [2- (2′-ethylhexyloxy) -5-methoxy-1,4-phenylenevinylene] (MEH-PPV) ) Etc. can be used.

  Moreover, a poly (P-phenylene vinylene) precursor (Pre-PPV), a poly (P-naphthalene vinylene) precursor (Pre-PNV), etc. can be used as a precursor of the polymer light emitting material.

  The light emitting layer 4 can be formed by a known method. For example, the light emitting layer can be formed by depositing an organic light emitting material using a dry process such as a direct vacuum evaporation method, an EB method, or an MBE method. Instead, a solution for forming an organic light emitting layer containing an organic light emitting material is applied to a spin coating method, a doctor blade method, a discharge coating method, a spray coating method, an ink jet method, a relief printing method, an intaglio printing method, a screen printing method, a micro gravure coating. The light emitting layer may be formed by applying using a wet process such as a method.

  In the case of using a wet process, the organic light emitting layer forming solution may be a solution containing at least one kind of light emitting material, and may contain two or more kinds of light emitting materials. Further, in addition to the light emitting material, a leveling agent, a light emission assisting agent, an additive (donor, acceptor, etc.), a charge transport agent, a light emitting dopant, and the like may be included. Further, the solvent of the organic light emitting layer forming solution may be any solvent that can dissolve or disperse the light emitting material, such as pure water, methanol, ethanol, THF (tetrahydrofuran), chloroform, toluene, xylene, trimethylbenzene and the like. May be.

  Each of the hole transport layer and the electron transport layer (collectively referred to as “charge transport layer”) may have a single layer structure or a multilayer structure. The charge transport layer can be formed, for example, by a known method (dry process, wet process) as described above as a method for forming the light emitting layer. When the charge transport layer is formed by a wet process, the solvent of the charge transport layer forming solution may be any solvent that can dissolve or disperse the charge transport material, and the solvent exemplified above as the solvent of the light emitting layer forming solution. It may be.

  As the charge transport material contained in the charge transport layer, a known material can be used. Although these specific compounds are shown below, this invention is not limited to this.

  Examples of hole transport materials contained in the hole transport layer include porphyrin compounds, N, N′-bis- (3-methylphenyl) -N, N′-bis- (phenyl) -benzidine (TPD), N, Aromatic tertiary amine compounds such as N′-di (naphthalen-1-yl) -N, N′-diphenyl-benzidine (NPD), low molecular materials such as hydrazone compounds, quinacridone compounds and stilamine compounds, polyaniline, 3 , 4-polyethylenedioxythiophene / polystyrene sulfonate (PEDT / PSS), poly (triphenylamine derivative), polyvinylcarbazole (PVCz) and other polymer materials, poly (P-phenylene vinylene) precursor, poly (P A polymer material precursor such as a (naphthalene vinylene) precursor can be used.

  As an electron transport material included in the electron transport layer, for example, a low molecular material such as an oxadiazole derivative, a triazole derivative, a benzoquinone derivative, a naphthoquinone derivative, or a fluorenone derivative, or a polymer material such as poly [oxadiazole] is used. it can.

  The first and cathodes 2 and 5 can be formed from known electrode materials as exemplified below.

The anode (anode) 2 may be a layer made of an electrode material such as a metal material having a large work function such as Au, Ni or Pt or a conductive metal oxide such as ITO, IZO or SnO _2. . Moreover, you may have a multilayer structure containing the layer which consists of the said electrode material. For example, the anode 2 has a structure in which an SiO ₂ layer having a thickness (for example, about 1 nm) is provided on the organic EL layer 9 side of the layer made of the above electrode material so as not to greatly hinder the conductivity of this layer. Also good. Since the surface of the SiO ₂ layer is excellent in affinity (wetting property) with the organic light emitting layer forming solution and the charge transport layer forming solution, the addition of the SiO ₂ layer causes the anode 2 and the organic EL layer 9 to be in contact with each other. Adhesion can be improved.

  Of the cathode (cathode) 5, the layer (first metal layer) 6 in contact with the organic EL layer 9 preferably contains at least a metal having a low work function, and as a material of the first metal layer 6, Ca, Ce Yb, Cs, Rb, Ba, Al, an alloy of Mg and Ag, an alloy of Al and Li, or the like can be used. Among the cathodes 2, a layer (second metal layer) 7 located between the first metal layer 6 and the oxide conductive layer 8 is a chemically relatively stable metal such as Ni, Os, Pt, It is preferably formed using Pd, Al, Au, Rh. As a result, not only the oxidation of the first metal layer 6 is suppressed, but also the second metal layer 7 itself is not oxidized, and the second metal layer 7 and the first metal layer 6 do not react. The deterioration of the cathode 2 can be suppressed. Moreover, it is preferable that the 2nd metal layer 7 has the transmittance | permeability of 10% or more over the visible light whole region. Furthermore, in order to prevent oxidation of the first metal layer 6, it is preferable that the second metal layer 7 has excellent coverage with respect to the first metal layer 6. For example, a Ni film (thickness: 35 nm) formed on a synthetic quartz substrate by an electron beam evaporation method exhibits a transmittance of about 10% over the entire visible light region, and is not an island in surface morphology observation by scanning electron microscopy. Since it does not show a shape, it was confirmed that the covering property was also excellent. It was confirmed that the films made of the other materials described above also have good transmittance and covering properties, although there are differences in degree. In this specification, a film that does not have an island-like structure generally includes a wide range of continuous films, and may be, for example, a film having pinholes or a porous film. In order to form a film that does not have an island structure as the second metal layer 7, a material that does not easily form an island structure is selected as the material of the second metal layer 7, depending on the formation method and film thickness. It is preferable. It has been confirmed in the above-described experiment that, for example, when Ni, Al, or the like is used as the material of the second metal layer 7, a film that does not have an island-like structure can be formed even if the thickness is small. In addition, materials (Os, Pd, etc.) that are generally used for thin film coating are also materials that are unlikely to have an island structure, and therefore can be used as the material for the second metal layer 7.

  The organic EL element 100 of FIG. 1 is a top emission type, but by using a transparent substrate such as a glass substrate as the substrate 1, light from the light emitting layer 4 can be extracted from the lower side of the substrate 1 (bottom emission). . Even in this case, the same effect as described above can be obtained by preventing oxidation of the first metal layer 6 by the second metal layer 7.

  The cathode 5 only needs to include at least one conductive layer 8 including first and second metal layers 6 and 7 and an oxide, and each layer may have a stacked structure. Further, other layers having different functions from these layers may be further included.

  Hereinafter, the result of evaluating the characteristics of the organic EL element of the present embodiment will be described.

  First, the organic EL element (FIG. 1) of Example 1 is produced.

A striped Pt electrode (width: 2 mm, length: 5 cm, thickness: about 150 nm) 2 is formed on a 5 cm square insulating substrate 1 using an electron beam evaporation apparatus. Next, an NPD (hole transport) layer 3 (thickness: about 60 nm) and an Alq ₃ (light emission) layer 4 (thickness: about 60 nm) are formed in this order on the Pt electrode 2 by resistance heating vapor deposition. To do. The shapes of the NPD layer 3 and the Alq ₃ layer 4 are both 3 cm square. Thereafter, a translucent cathode 5 composed of an alloy layer 6 of Mg and Ag, a Ni layer 7 and an ITO layer 8 is formed by the method described below. The shape of the cathode 5 is a stripe shape (width: 2 mm, length: 5 cm) along the direction orthogonal to the Pt electrode 2. First, an alloy layer 6 of Mg and Ag having a thickness of about 5 nm is formed as the first metal layer. The alloy layer 6 of Mg and Ag is formed by resistance heating co-evaporation using a metal mask while controlling the deposition rate of Mg and Ag so that the molar concentration ratio is about 10: 1. Subsequently, a Ni layer 7 (thickness: 10 nm, transmittance: 60%) is formed as a third metal layer by an electron beam evaporation method using the same metal mask as the alloy layer 6 of Mg and Ag. Finally, an ITO layer 8 having the same stripe pattern as that of the alloy layer 6 of Mg and Ag and the Ni layer is formed as a transparent electrode layer by a DC sputtering method. The thickness of the ITO layer 8 is 100 nm. In the DC sputtering method, an ITO sintered target is used as a target, and a mixed gas of Ar and O ₂ is used as a sputtering gas. Note that the substrate 1 is not particularly heated when any of the alloy layer 6 of Mg and Ag, the Ni layer 7 and the ITO layer 8 is formed. Thereby, the organic EL element of Example 1 is completed.

  Next, in order to compare with the organic EL element of Example 1, the organic EL element of Comparative Example 1 is produced as shown in FIG. The organic EL element of Comparative Example 1 has the same configuration as that of the organic EL element of Example 1 except that the cathode 5 does not have the Ni layer 7 and is composed only of the alloy layer 6 of Mg and Ag and the ITO layer 8. And is produced by a similar method.

When a direct current voltage is applied to each of the organic EL elements of Example 1 and Comparative Example 1 obtained above so that the Pt electrode 2 is positive and the ITO layer 8 is negative, the light emission occurs in any of the organic EL elements. Green light emission was observed from the Alq ₃ layer 4 as a layer. At this time, in the organic EL element of Example 1, the luminance of light from the Alq ₃ layer 4 observed above the ITO layer 8 was 100 cd / m ² at an applied voltage of 10V. On the other hand, in the organic EL element of Comparative Example 1, the luminance of light from the Alq ₃ layer 4 observed above the ITO layer 8 is 10 cd / m ² at an applied voltage of 10 V. Compared to the luminance of the EL element, it was greatly reduced. The cause is considered as follows. In the organic EL element of Comparative Example 1, the alloy layer 6 of Mg and Ag is partially oxidized by the oxygen in the sputtering gas used at the time of forming the ITO layer 8 to become an oxide. Electron injection efficiency is reduced. Therefore, sufficient light emission cannot be obtained in the light emitting layer 4. On the other hand, in the organic EL device of Example 1, the oxygen in the sputtering gas used when forming the ITO layer 8 does not react with the relatively stable Ni layer, and is blocked by the Ni layer to form Mg and Ag. Since it is difficult to reach the alloy layer 6, it is difficult to react with the alloy layer 6 of Mg and Ag. That is, since oxygen in the sputtering gas does not damage the cathode 5 (particularly, the alloy layer 6 of Mg and Ag), the cathode 5 can inject electrons into the organic EL layer 9 with high efficiency.

(Embodiment 2)
Hereinafter, the configuration of a display device using the organic EL element will be described with reference to FIG.

  In the display device 200 of FIG. 3, the organic EL element 100 is formed on the active matrix substrate 101. The active matrix substrate 101 includes a substrate 1, a plurality of TFTs formed for each pixel on the substrate 1, and a planarization film 14 that covers these TFTs. Each TFT is provided so as to cover the gate electrode 12, an island-like semiconductor layer (not shown) formed on the gate electrode 12 via the gate insulating film 13, and both ends of the island-like semiconductor layer. TFT electrodes (source and drain electrodes) 10 (bottom gate structure). Each TFT is connected to the source line 11 ′ and the gate line 11. A through hole 15 reaching the drain electrode 10 of each TFT is provided in the planarizing film 14. An organic EL element 100 is formed on the planarization film 14. The anode 2 of the organic EL element 100 is formed for each pixel by patterning a conductive layer deposited on the planarizing film 14 and inside the through hole 15. Each anode 2 is connected to the corresponding drain electrode 10 of the TFT via a through hole 15. These anodes 2 are insulated from each other by an insulating film 16 formed so as to cover the respective edge portions and through holes 15 of each anode 2. On the anode 2 and the insulating film 16, a hole injection layer 3a, a light emitting layer 4, a first metal layer 6, a second metal layer 7 and an oxide conductive layer 8 are formed in this order.

  Since the display device 200 in FIG. 3 has the above-described configuration, the display device 200 has high luminous efficiency and can realize a high-definition and bright display. Moreover, since deterioration of the cathode 5 in the organic EL element 100 can be suppressed, the reliability is high.

  The configuration of the display device according to the present invention is not limited to the above. For example, the TFT may have a top gate structure. The configuration of the organic EL element 100 is not limited to the above, and various configurations as described with reference to FIG. 1 can be applied. In addition, a simple matrix display device can be formed using the organic EL element 100. Further, the display device 200 may adopt a voltage driving method that requires two TFTs for each pixel, or may adopt a current driving method that requires four TFTs for each pixel. .

  Hereinafter, the result of evaluating the characteristics of the organic EL display device of the present embodiment will be described.

  First, an organic EL display device (FIG. 3) of Example 2 is manufactured.

A TFT using polysilicon as a semiconductor layer is formed on the insulating substrate 1, and then covered with a planarizing film 14 in order to eliminate unevenness on the surface of the substrate 1. Next, the Ni electrode (anode) 2 is formed on the planarizing film 14 and inside the through hole 15 provided in the planarizing film 14. The Ni electrode 2 is connected to the drain electrode 10 of the TFT by a through hole 15. The thickness of the Ni electrode 2 formed on the planarizing film 14 is 150 nm. Thereafter, an SiO ₂ film is formed so as to cover the through hole 15 and the edge portion of the Ni electrode 2. Subsequently, a mixed aqueous solution of polyethylene dioxythiophene (PEDOT) and polystyrene sulfonic acid (PSS) is applied to the substrate by a spin coat method, and dried at 150 ° C. for 20 minutes, thereby forming the hole injection layer 3a. At this time, the thickness of the hole injection layer 3a is set to about 60 nm by controlling the concentration of the solution, the number of rotations during spin coating, and the like. Next, similarly to the hole injection layer 3a, a light emitting layer 4 is formed by applying and drying a solution of a polyfluorene derivative by a spin coating method. A Ca layer (thickness: 5 nm) 6, an Os layer (thickness: 10 nm) 7, and an ITO layer (thickness: 150 nm) 8 are used as the translucent cathode 5 on the light emitting layer 4 with the same mask. Are sequentially formed. In this embodiment, the Ca layer 6 is formed by resistance heating vapor deposition, the Os layer 7 is formed by plasma coating, and the ITO layer 8 is formed by sputtering. The transmittance of the Os layer 7 is 50%. Thereby, an organic EL display device is obtained.

  Next, for comparison with Example 2, an organic EL display device (not shown) of Comparative Example 2 is produced. The organic EL display device of Comparative Example 2 has a cathode 5 composed of a Ca layer (thickness: 10 nm) 6 and an ITO layer (thickness: 150 nm) 8 (that is, an Os layer which is a second metal layer). The organic EL display device has the same configuration as that of the organic EL display device according to the second embodiment except that the manufacturing method is the same.

In each of the display devices of Example 2 and Comparative Example 2, when a control signal was applied to the TFT, a voltage was applied to the light emitting layer 4 of the organic EL element 100 located in the same pixel as the TFT to emit light. In the display device of Example 2, when the applied voltage to the organic EL element 100 was 10 V, the luminance of the light from the light emitting layer 4 observed on the ITO layer 8 was about 100 cd / m ² . On the other hand, in the display device of Comparative Example 2, light emission was observed by applying a voltage to the light emitting layer 4, but it was difficult to measure the luminance because the area of uniform light emission was small.

  The cause is considered as follows. In the organic EL display device in Comparative Example 2, the Ca layer 6 is oxidized by the oxygen gas used when forming the ITO layer 8 and functions as an insulating layer. As a result, electrons are transferred from the Ca layer 6 to the organic EL. It becomes difficult to be injected. Therefore, sufficient light emission cannot be obtained in the light emitting layer 4. On the other hand, in the organic EL element 100 in Example 2, since the Ca layer 6 is not oxidized by the oxygen gas used when forming the ITO layer 8 as described in Example 1, the electrode 5 is higher than the organic EL layer 9. Electrons can be injected efficiently. Therefore, in the display device according to the second embodiment, a high luminance display can be stably obtained. In addition, variation in luminance for each organic EL element 100 is small, and high-quality display can be obtained.

  According to the present invention, since the oxidation of the first metal layer in the cathode having the first metal layer and the oxide conductive layer can be suppressed, a highly reliable and highly efficient organic EL element can be provided.

  The present invention can be suitably applied particularly to a top emission type organic EL element. Further, when such an organic EL element is used in an active matrix display device, a remarkable effect is sometimes obtained.

It is sectional drawing which shows typically the structure of the organic EL element of embodiment by this invention. It is sectional drawing which shows the structure of the organic EL element of the comparative example 1 typically. It is sectional drawing which shows typically the structure of the organic electroluminescence display of embodiment by this invention.

Explanation of symbols

1 Substrate 2 Anode (Anode)
3 hole transport layer 3a hole injection layer 4 light emitting layer 5 cathode (cathode)
6 First metal layer 7 Second metal layer 8 Oxide conductive layer 9 Organic EL layer 10 Source and drain electrodes 11, 11 ′ wiring 12 Gate metal 13 Gate insulating film 14 Planarizing film 15 Through hole 16 Insulating film 100 Organic EL element 101 Active matrix substrate 200 Organic EL display device

Claims (12)

The anode,
A light-transmitting cathode;
An organic EL layer formed between the anode and the cathode and including at least a light emitting layer;
The cathode has a first metal layer containing a first metal, a second metal layer containing a second metal, and an oxide conductive layer containing an oxide in this order from the organic EL layer side. Organic EL element.   The organic EL element according to claim 1, wherein a work function of the second metal is larger than a work function of the first metal.   The organic EL element according to claim 1, wherein the second metal layer has a visible light transmittance of 10% or more.   The organic EL device according to claim 1, wherein the second metal layer substantially completely covers the surface of the first metal layer.   The organic EL element according to any one of claims 1 to 4, wherein the thickness of the second metal layer is 10 nm or more and 30 nm or less.   The organic EL element according to claim 1, wherein the total thickness of the first metal layer and the second metal layer is 35 nm or less.   The organic EL according to claim 1, wherein the oxide conductive layer contains the oxide as a main component, and the oxide is indium tin oxide (ITO) or indium zinc oxide (IZO). element.   The organic EL device according to any one of claims 1 to 7, wherein the second metal includes at least one metal selected from the group consisting of Ni, Os, Pt, Pd, Al, Au, and Rh.   The organic EL element according to claim 1, wherein the oxide conductive layer is formed by sputtering using a sputtering gas containing oxygen gas.   The organic EL element according to claim 1, wherein the organic EL layer includes an organic layer formed using a solution containing a polymer material. The organic EL element according to any one of claims 1 to 10,
A display device including a thin film transistor. The anode,
A light-transmitting cathode;
An organic EL layer formed between the anode and the cathode and including at least a light emitting layer;
The cathode includes a metal layer, a conductive layer capable of suppressing oxidation of the metal layer, and an oxide conductive layer containing an oxide in this order from the organic EL layer side.

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