JP4573592B2 - ORGANIC ELECTROLUMINESCENT ELEMENT, ITS MANUFACTURING METHOD, AND ORGANIC ELECTROLUMINESCENT DISPLAY - Google Patents

Description

The present invention relates to an organic electroluminescence element, a manufacturing method thereof, and an organic electroluminescence display device. More specifically, the present invention relates to an organic electroluminescent element suitable as a top emission type electroluminescent element, a manufacturing method thereof, and an organic electroluminescent display device.

An organic electroluminescence (hereinafter also referred to as “EL”) element has a light emitting layer made of an organic compound between a pair of electrodes, at least one of which has translucency, and, if necessary, hole injection and transport. It has a structure in which a layer, an electron injecting and transporting layer, etc. are sandwiched. Such organic EL devices are actively researched and developed because they can be driven at a low voltage and emit light with high luminance.

Display devices using organic EL elements are classified into a simple matrix system and an active matrix system depending on the driving method of the elements. In the simple matrix method, it is necessary to increase the instantaneous light emission luminance of each pixel in accordance with an increase in the duty ratio, which causes an increase in power consumption in a large panel. For this reason, the active matrix method is becoming the mainstream especially for large panels.

In the active matrix method, a thin film transistor (hereinafter also referred to as “TFT”) provided in each pixel arranged in a matrix is turned on and off by a control signal to control the light emission state of the organic EL element. In this method, an image is displayed. However, TFTs essential for the active matrix method are formed using polysilicon, amorphous silicon, or the like that does not transmit light, and wiring is also formed of a metal that does not transmit light, so that light is emitted from the conventional substrate side. In the extraction method (bottom emission method), the ratio of the light emission area to the pixel area (aperture ratio) becomes small. In particular, the current drive method, which is considered suitable for display panels using organic EL elements, is adopted to suppress variations in display performance from pixel to pixel and to reduce changes in panel display brightness due to deterioration of organic EL materials. In this case, the number of transistors for each pixel is required to be about four, which is twice the number of transistors (two) required in a voltage driving method that is simpler but inferior in variations in display performance for each pixel. The aperture ratio is further reduced.

As a technique for solving this problem, a method of taking out light emission from the side opposite to the substrate (top emission method) has been devised. In the top emission method, the upper electrode needs to be formed of a light-transmitting material, but in general, indium tin oxide (hereinafter also referred to as “ITO”) or indium zinc oxide ( Zinc-doped Indium Oxide; hereinafter also referred to as “IZO”) or the like is used. Generally, a sputtering method or an ion plating method is used to form an ITO film or an IZO film. However, since these methods generate relatively high energy particles, the previously formed organic layer is damaged and the device characteristics are deteriorated.

On the other hand, as a technique for preventing damage to the organic layer or the like in the process of forming the transparent conductive film, an organic EL element in which the cathode has a stacked structure of an electron injection electrode layer and an amorphous transparent conductive film (see, for example, Patent Document 1). In the initial stage of film formation of the transparent conductive film, the electric power required for sputtering is set low, and the electric power is set high as the film formation proceeds (see, for example, Patent Document 2). ) Is disclosed. However, even with this technique, it is difficult to sufficiently prevent deterioration of the characteristics of the organic EL element. The cause is that when a transparent cathode (transparent conductive film) is formed by sputtering or ion plating, plasma is generated using a mixed gas of argon (Ar) and oxygen (O ₂ ). It is conceivable that the organic layer is oxidized by active oxygen atoms in the plasma that is sometimes generated. Therefore, there is still room for improvement in terms of effectively reducing the oxidation of the organic layer in the process of forming the transparent conductive film, thereby improving the light emission luminance of the device.

Regarding the prevention of the deterioration of the organic layer, the structure of an organic EL light emitting element including an organic EL light emitting layer (organic layer), a low resistance transparent oxide layer functioning as an upper electrode, and a high resistance transparent oxide layer Is disclosed (for example, see Patent Document 3). However, this configuration is intended to prevent the deterioration of the organic EL light emitting layer due to intrusion of oxygen, moisture, and the like from the upper electrode. Patent Document 3 discloses a high resistance covering the entire surface of the low resistance oxide layer. It is described that a transparent oxide layer is formed, and a highly resistive transparent oxide layer having high transparency increases the thickness of the transparent oxide layer to prevent oxygen and moisture from entering. For this reason, deterioration of device characteristics due to the oxidation of the organic layer in the process of forming the transparent conductive film is not particularly considered. In Patent Document 3, the low resistance oxide layer has an oxygen partial pressure of 5% or less of the total pressure. It is described that the high resistance oxide layer is formed in an atmosphere having an oxygen partial pressure of 20 to 60% of the total pressure. Low oxygen is introduced. Therefore, the oxidation of the organic layer formed previously is inevitable, and the oxidation of the organic layer in the process of forming the transparent conductive film has not been sufficiently reduced.

In addition, regarding the configuration of the transparent electrode that achieves both the resistivity and the hole injection property, the resistivity is formed so that the resistivity gradually decreases from the surface in contact with the organic material layer (organic layer) toward the other surface. The structure of the transparent electrode is disclosed (for example, refer to Patent Document 4). Patent Document 4 states that “the lower the mixing ratio of oxygen gas to argon gas, the lower the resistivity of the transparent electrode can be lowered, and the higher the mixing ratio of oxygen gas to argon gas can improve the hole injection efficiency. In the formation of the transparent electrode, in the vicinity of the surface in contact with the organic layer, a condition with a high ratio of oxygen gas is applied in order to increase the hole injection efficiency. On the other side of the contacting surface, a condition with a low oxygen gas ratio is applied in order to lower the resistivity. Therefore, this technique is not intended to reduce the oxidation of the organic layer in the process of forming the transparent conductive film.
JP 10-162959 A (pages 1, 10 and 1) JP 2001-85163 A (pages 1, 7 and 7) JP 2004-31102 A (2nd, 3rd, 6th, 11th pages, FIG. 2) Japanese Patent Laying-Open No. 2003-297585 (pages 1, 2, 7)

This invention is made | formed in view of the said present condition, and it aims at providing the organic electroluminescent element excellent in luminous efficiency, its manufacturing method, and an organic electroluminescent display apparatus.

The inventors of the present invention have various organic electroluminescence (EL) elements in which a first electrode, an organic layer including a light emitting layer, and a translucent second electrode are essential and are stacked in this order on a substrate. As a result of investigation, attention was focused on the process of forming a transparent electrode made of a metal oxide constituting the second electrode. Then, when forming this electrode by sputtering or ion-plating, it was found that the light emitting layer was damaged by active oxygen atoms in the generated plasma. Therefore, by forming the organic layer side of the transparent electrode under an atmosphere in which oxygen is not substantially introduced, and providing a portion having a relatively high resistivity on the organic layer side of the transparent electrode, the oxidation of the light emitting layer can be prevented. Thus, the inventors have found that the light emission efficiency of the organic EL element can be improved, and have conceived that the above-mentioned problems can be solved brilliantly, and have reached the present invention.

That is, the present invention is an organic electroluminescence element that includes a first electrode, an organic layer including a light emitting layer, and a translucent second electrode, and is laminated on the substrate in this order. The second electrode includes a transparent electrode made of a metal oxide, and the transparent electrode has a portion having a relatively high resistivity on the organic layer side, and the resistivity is relatively high. The high portion is an organic electroluminescent device that contains more oxygen vacancies than the portion with a relatively low resistivity.
The present invention also provides an organic electroluminescence element comprising a first electrode, an organic layer including a light emitting layer, and a translucent second electrode, which are laminated on a substrate in this order. The two electrodes are configured to include a transparent electrode made of a metal oxide, and the transparent electrode has a portion having a relatively high resistivity on the organic layer side, and the resistivity is relatively high. The portion is formed under a condition in which oxygen is not substantially introduced, and the portion having a relatively low resistivity is also an organic electroluminescence element formed under a condition in which oxygen is introduced.
The present invention is described in detail below.

The organic electroluminescence (EL) element of the present invention includes a first electrode, an organic layer including a light emitting layer, and a translucent second electrode, and is laminated on a substrate in this order. . The first electrode preferably functions as an anode of the organic EL element, and the second electrode preferably functions as a cathode. The light emitting layer emits energy released by recombination of holes injected from the anode and electrons injected from the cathode by applying an electric field between the first electrode and the second electrode. It is a layer that includes a material (light emitting material) that can be used for the above. The light emitting layer may have a single layer structure composed of one layer, or may have a laminated structure composed of two or more layers. The organic layer is not particularly limited as long as it includes at least one light emitting layer, but preferably further includes a hole injection layer and the like. Although it does not specifically limit as said board | substrate, A glass substrate is preferable. As a preferable form of the organic EL element of the present invention, a first electrode, an organic layer including a light emitting layer and a hole injection layer, and a translucent second electrode are essential, and are laminated on a substrate in this order. And the like.
In the organic EL element of the present invention, since the second electrode has translucency, light can be extracted from the second electrode. As a method of taking out light emission of such an organic EL element, a method of taking out light emission from both the first and second electrodes (dual emission method), a method of taking out light emission from only the second electrode (top emission method), and the like can be mentioned. Of these, the top emission method is preferable.
The organic electroluminescent element of the present invention may or may not contain other components as long as such components are essential, and is not particularly limited. .

The second electrode includes a transparent electrode made of a metal oxide. Examples of the metal oxide include indium zinc oxide (indium oxide doped with zinc), zinc oxide doped with gallium, zinc oxide doped with aluminum, and similar compounds. Examples of the method for forming the transparent electrode include sputtering, ion plating, chemical vapor deposition (hereinafter also referred to as “CVD”), vapor deposition, and the like. Is preferred.

The transparent electrode has a portion having a relatively high resistivity on the organic layer side. That is, in the present invention, a portion having a relatively higher resistivity than other portions of the transparent electrode is formed on at least a part of the organic layer side of the transparent electrode. Preferably, in the transparent electrode, the side close to the organic layer (the whole interface on the organic layer side) is constituted by a portion having a relatively high resistivity, and the side far from the organic layer is constituted by a portion having a relatively low resistivity. Composed. The resistivity at 25 ° C. of the portion having a relatively high resistivity is preferably 1 × 10 ⁻³ Ω · cm at the lower limit and 1 × 10 ⁻² Ω · cm at the upper limit, and has a relatively high resistivity. The lower part of the resistivity at 25 ° C. preferably has a lower limit of 1 × 10 ⁻⁴ Ω · cm and an upper limit of 1 × 10 ⁻³ Ω · cm. The upper limit of the resistivity of the transparent electrode is preferably 1 × 10 ⁻³ Ω · cm at 25 ° C. Note that the host metal may be the same or different between the relatively high resistivity portion and the low resistivity portion.

As a form of the present invention, (1) the part where the resistivity is relatively high includes more oxygen vacancies than the part where the resistivity is relatively low, and (2) the resistivity is relatively high A form in which the high part is formed under conditions in which oxygen is not substantially introduced, and the part having a relatively low resistivity is formed under conditions in which oxygen is introduced. In addition, regarding the portion where the resistivity of the transparent electrode is relatively high, the form of (1) is grasped from the configuration (composition), and the form of (2) is grasped from the manufacturing process side. is there. In this invention, it has at least any one form among the form of said (1) and the form of said (2).
In the present invention, oxygen vacancies refer to lattice points that are vacant due to lack of oxygen atoms (ions) that should be periodically arranged in a crystal lattice.
Further, the partial pressure of oxygen under the condition in which oxygen is not substantially introduced is only required to be evaluated to be substantially 0, and within the range in which the effect of preventing deterioration of the organic layer of the present invention can be obtained. If it exists, it may exceed zero. The partial pressure of oxygen at 25 ° C. when forming the portion having a relatively low resistivity is preferably 1 × 10 ⁻⁴ Pa at the lower limit and 1 × 10 ⁻² Pa at the upper limit.

Note that the relationship between the resistivity (specific resistance) and oxygen partial pressure in the transparent electrode formation of the transparent electrodes, as shown in FIG. 2, the oxygen partial pressure is 9 × 10 ^-3 normalized at a deposition rate ( In the present invention, the portion having a relatively high resistivity is formed under a condition in which oxygen is not substantially introduced, and the resistivity is low in the vicinity of Pa / (nm / min)). Since the relatively low portion is formed under the condition where oxygen is introduced, the oxygen partial pressure (the region on the left side of the minimum point in FIG. 2) lower than the minimum point of the specific resistance or the vicinity of the minimum point of the specific resistance. A transparent electrode is formed under the condition of oxygen partial pressure. On the other hand, the transparent electrode described in Patent Document 4 has a high resistivity on the surface side in contact with the organic layer (organic layer) and a low resistivity on the other surface side in contact with the organic layer. Although it is in common with the characteristics of the transparent electrode in the invention, it is formed under conditions opposite to each other in terms of oxygen partial pressure (oxygen gas concentration), and the structure (composition) is different. That is, in the transparent electrode described in Patent Document 4, the other surface side (resistivity) of the surface in contact with the organic layer under the condition of oxygen partial pressure higher than the minimum point of specific resistance (the region on the right side of the minimum point in FIG. 2). Is formed on the surface side in contact with the organic layer under a higher oxygen partial pressure (a portion with a relatively high resistivity).

According to the present invention, when the transparent electrode is formed by sputtering or ion plating, a portion having a relatively high resistivity on the organic layer side is formed without substantially introducing oxygen. Therefore, damage (oxidation) of the organic layer due to active oxygen atoms can be reduced. Then, after forming the relatively high resistivity portion, the resistivity is placed on the relatively high resistivity portion (on the side opposite to the organic layer) in order to reduce the overall resistivity of the transparent electrode. When forming a relatively low portion, even if oxygen gas is introduced, the portion formed earlier with a relatively high resistivity serves as a barrier and can prevent damage to the organic layer. Therefore, in the organic EL device of the present invention, it is possible to reduce the resistivity of the transparent electrode as a whole, and to reduce the voltage drop due to the electrode. It is possible to reduce the power required to obtain the element, suppress the deterioration of the element, obtain high reliability, and the like. The organic EL element of the present invention excellent in luminous efficiency can be suitably used as an electroluminescent element in an organic EL display device or the like.

Hereinafter, the preferable form of the organic electroluminescent element of this invention is demonstrated in detail.
The transparent electrode has at least a relatively high resistivity selected from the group consisting of indium zinc oxide (indium oxide doped with zinc), zinc oxide doped with gallium, and zinc oxide doped with aluminum. It is preferably formed of a material containing at least one kind. According to this, since a transparent electrode having a relatively low resistance can be formed even under a condition where oxygen is not introduced, it is possible to obtain a highly efficient organic EL element by reducing the overall resistance of the second electrode. it can. In addition, it is preferable that the lower limit of the doping amount of zinc in indium oxide doped with zinc is 5 mass% and the upper limit is 15 mass%. Moreover, it is preferable that the lower limit of the doping amount of gallium in zinc oxide doped with gallium is 5 mass% and the upper limit is 15 mass%. Furthermore, it is preferable that the lower limit of the aluminum doping amount in zinc oxide doped with aluminum is 5% by mass and the upper limit is 15% by mass. In addition, from the viewpoint of simplification of the manufacturing process, it is more preferable that not only a portion having a relatively high resistivity but also a portion having a relatively low resistivity be formed of the above-described material.

The transparent electrode preferably has a thickness of a portion having a relatively high resistivity of 5 to 100 nm. As a result, the organic layer can be sufficiently prevented from being damaged, the second electrode having a sufficiently large transmittance and a sufficiently small resistivity can be formed, and a highly efficient organic EL element can be obtained. . If the thickness of the portion having a relatively high resistivity is less than 5 nm, damage to the organic layer due to active oxygen atoms may not be sufficiently prevented in the electrode formation process by sputtering, ion plating, or the like. When the thickness exceeds 100 nm, the light transmittance of the transparent electrode is lowered, the resistivity of the second electrode as a whole is increased, and the voltage drop in the second electrode may be increased. The thickness of the portion having a relatively high resistivity is more preferably a lower limit of 5 nm and the upper limit is 50 nm. The thickness of a portion having a relatively low resistivity is 50 nm and the upper limit is 500 nm. Preferably there is.

The organic electroluminescent element preferably has an electron injection layer made of an insulator between the organic layer and the transparent electrode. Thereby, when the second electrode is a cathode, the efficiency of injecting electrons into the organic layer when an electric field is applied between the electrodes is increased, and thus a highly efficient organic EL element can be provided.

The organic electroluminescent element preferably has a light-transmitting metal layer between the organic layer and the transparent electrode, or between the electron injection layer and the transparent electrode. Thus, when the second electrode is a cathode, the efficiency of electron injection into the organic layer when an electric field is applied between the electrodes by using a low work function metal or an alloy containing the same as the material of the metal layer Can be increased, and a highly efficient organic EL element can be provided. Moreover, in this invention, the oxidation of a metal layer can be suppressed by the part with relatively high resistivity which the transparent electrode of a 2nd electrode has. The metal layer preferably has a lower limit of 1 nm and an upper limit of 20 nm. If the thickness of the metal layer is less than 1 nm, the efficiency of electron injection into the organic layer may not be sufficiently improved, and if it exceeds 20 nm, the transparency may not be sufficiently obtained. .

The present invention also provides an organic electroluminescent device including a step of forming a first electrode on a substrate, a step of forming an organic layer including a light emitting layer, and a step of forming a translucent second electrode. In the method, the step of forming the second electrode includes a step of forming a transparent electrode made of a metal oxide, and the step of forming the transparent electrode made of the metal oxide substantially includes oxygen gas. It is also a method for producing an organic electroluminescent element in which an electrode is formed under conditions where oxygen gas is introduced after the electrode is formed under conditions that are not introduced.
In the first electrode formation step, a metal film or a conductive metal oxide film is formed using an electron beam (EB) method or the like. In addition, the organic layer forming process includes a dry process such as a direct vacuum deposition method, an EB method, a molecular beam epitaxy (MBE) method, a spin coating method, a doctor blade method, a discharge coating method, a spray coating method, Using a wet process such as an inkjet method, a relief printing method, an intaglio printing method, a screen printing method, or a micro gravure coating method, a light emitting layer, or a hole injection layer, an electron injection layer, a charge transport layer (positive Hole transport layer and electron transport layer) and the like. The formation process of the second electrode includes a process of forming a transparent electrode made of a metal oxide. In the formation process of the transparent electrode, a sputtering method, an ion plating method, a CVD method, a vapor deposition method, or the like is used. .

According to the method for producing an organic EL device of the present invention, in the step of forming a transparent electrode made of a metal oxide, the transparent electrode is formed under the condition that oxygen is not substantially introduced at the initial stage of formation, and then oxygen is introduced. Therefore, a highly efficient organic EL element in which oxidation of the organic layer is sufficiently suppressed can be manufactured.
As a preferable form of the method for producing an organic EL element of the present invention, a form in which the step of forming the first electrode, the step of forming the organic layer including the light emitting layer, and the step of forming the translucent second electrode are performed in this order. Is mentioned.

It is preferable that the manufacturing method of the said organic electroluminescent element includes the process of forming the electron injection layer which consists of an insulator between the process of forming an organic layer, and the process of forming a transparent electrode. According to this, it is possible to manufacture a highly efficient organic EL element in which the efficiency of electron injection into the organic layer when an electric field is applied between the electrodes is improved. In the step of forming the electron injection layer, resistance heating vapor deposition, EB vapor deposition, or the like is used.

The method for producing an organic electroluminescent element includes a step of forming an organic layer and a step of forming a transparent electrode, or a step of forming an electron injection layer made of an insulator and a step of forming a transparent electrode. It is preferable to include the process of forming a translucent metal layer in between. As a result, when the second electrode is a cathode, the efficiency of injecting electrons into the organic layer when an electric field is applied between the electrodes is improved by using a metal material having a low work function as the material of the metal layer. A highly efficient organic EL element can be manufactured. Moreover, in this invention, since the electrode part formed on the conditions which do not introduce | transduce oxygen gas substantially is provided in the process of forming the transparent electrode which comprises a 2nd electrode, the oxidation of a metal layer is suppressed. be able to. In the step of forming the metal layer, DC (direct current) or RF (high frequency) sputtering, ion plating, CVD, vapor deposition or the like is used.

The present invention is also an organic electroluminescence display device comprising the organic electroluminescence element or the organic electroluminescence element produced by the method for producing the organic electroluminescence element. Since the organic EL display device of the present invention includes a high-efficiency organic EL element, it is possible to realize a good display with high luminance and small variation in luminance for each pixel (each organic EL element). As a preferable form of the organic EL display device of the present invention, for example, a form in which the organic EL element of the present invention or the organic EL element manufactured by the method of manufacturing the organic EL element of the present invention is provided in a matrix form, etc. Can be mentioned. Note that examples of the driving method of the organic EL display device of the present invention include an active matrix method and a passive matrix method, and among them, the active matrix method is preferable.

According to the organic electroluminescence (EL) element of the present invention, damage to the organic layer in the transparent electrode forming step is reduced, and the overall resistivity of the transparent electrode can be sufficiently reduced. An organic EL device having excellent luminous efficiency can be provided. Such an organic EL element can be suitably used as an electroluminescent element in an organic EL display device or the like.

Embodiments will be described below, and the present invention will be described in more detail with reference to the drawings. However, the present invention is not limited only to these embodiments.

Embodiment 1 Organic Electroluminescence (EL) Element FIG. 1 is a cross-sectional view schematically showing a configuration of an organic EL element according to Embodiment 1 of the present invention. In addition, the white arrow direction in FIG. 1 represents the direction which takes out light emission.
An organic EL element 100 shown in FIG. 1 has an anode (first electrode) 2, an organic EL layer (organic layer) 9, and a cathode (second electrode) 5 in this order on a substrate 1. The organic EL layer 9 only needs to have at least the light emitting layer 4, and may have a single layer structure or a laminated structure. In the present embodiment, the organic EL layer 9 has a structure in which the hole injection layer 3 and the light emitting layer 4 are laminated in this order from the substrate 1 side. Since the organic EL element 100 of this embodiment is a top emission type in which light from the light emitting layer 4 is extracted from the cathode 5 side, the cathode 5 has translucency. The cathode 5 is formed on the organic EL layer 9 and has at least two oxide conductive layers 7 (parts having a relatively high resistivity among the transparent electrodes) and 8 (relative resistivity among the transparent electrodes). The lower portion of the substrate 1 is laminated in this order from the substrate 1 side.
In the present embodiment, an Al: Ca alloy layer (metal layer) 6 is provided between the oxide conductive layer 7 and the light emitting layer 4. The film thickness of the Al: Ca alloy layer 6 is preferably 1 nm for the lower limit and 20 nm for the upper limit, more preferably 10 nm for the upper limit, and 5 nm for the upper limit in order to provide translucency. Further preferred. As a material of the metal layer 6, in addition to an Al: Ca alloy, a low work function metal having a work function of 4 eV or less (for example, Ce, Yb, Cs, Rb, Sr, Ba, Mg, Li, etc.) or an alloy containing them. May be used. When a polymer material is used as the material of the light emitting layer 4, Ca and Ba are preferably used for the metal layer 6 as a low work function metal. Although it is possible to form the metal layer 6 using a single low work function metal, the metal layer 6 can also be formed by doping the host metal with the low work function metal described above. In this case, the host metal is preferably a chemically relatively stable metal (for example, Ni, Os, Pt, Pd, Al, Au, Rh, etc.). Thereby, the oxidation of the low work function metal contained in the metal layer 6 can be suppressed.

FIG. 2 is a diagram showing the relationship between oxygen partial pressure and film resistivity when forming an oxide transparent conductive film (ITO film).
As shown in FIG. 2, in general, an oxide transparent conductive film has too much oxygen vacancies in the film when the oxygen partial pressure during film formation is 0 or small, so that the crystallinity is low. Unfortunately, the carrier mobility decreases, and oxygen vacancies cannot effectively generate carriers, so that the carrier density is low and the resistance of the film increases. Increasing the oxygen partial pressure during film formation reduces crystal defects, increases carrier mobility, enables oxygen vacancies to generate carriers effectively, and increases carrier density. This reduces the resistance of the film. When the oxygen partial pressure during film formation is further increased, the carrier mobility is saturated, while the oxygen vacancy donor itself decreases, so that the carrier density decreases and the resistance of the film increases again. In this embodiment, the oxide conductive layer 7 is formed under the condition of an oxygen partial pressure of 0, and the oxide conductive layer 8 is formed under an appropriate oxygen partial pressure of which the resistance of the film is reduced.

In the organic EL element 100, the oxide conductive layer 7 on the side close to the organic EL layer 9 is manufactured under the condition that oxygen is not introduced. Therefore, there is no oxidation of the organic EL layer 9 by active oxygen atoms, and the organic EL element A decrease in luminous efficiency of 100 can be suppressed. In the present specification, “luminescence efficiency” refers to the luminance of extracted light with respect to the power input to the organic EL element or the current required for driving. If the decrease in luminous 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 the organic EL element 100, it is preferable to form an electron injection layer made of an insulating film (insulator) between the light emitting layer 4 and the cathode 5. By providing the electron injection layer, the light emission efficiency can be further improved. The insulating film of the electron injection layer _{(insulator), BaO, BaF 2, CaO} , CaF 2, Cs 2 O, CsF, Li 2 O, LiF, is selected from the group consisting of _Ce 2 O _3, CeF 3 One kind of compound or a mixture of two or more kinds is preferable.

Examples of the method for forming the light-transmitting oxide conductive layers 7 and 8 included in the cathode 5 include a sputtering method, an ion plating method, a CVD method, and a vapor deposition method. The oxide conductive layer 7 (part formed without introducing oxygen) and the oxide conductive layer 8 (part formed by introducing oxygen) may be formed by the same manufacturing method or by different manufacturing methods. Also good. The materials may be the same or different.

In addition, as a material for the oxide conductive layer 7 (portion formed without introducing oxygen), indium zinc oxide or gallium doped that can form a film having a relatively low resistivity even under the condition where oxygen is not introduced. If zinc oxide, zinc oxide doped with aluminum, or the like is used, the resistivity of the entire cathode 5 can be lowered.

The organic EL layer 9 preferably includes an organic layer formed from a solution using a polymer material. Thereby, since the thin film formation method which does not require vacuum conditions, such as a printing method and the inkjet method, can be used, an organic EL element can be manufactured more cheaply.

The light emitting layer 4 in the organic EL layer 9 may have a single layer structure or a multilayer structure. The light emitting layer 4 may be a layer in which a base material is doped with a dopant.
As shown in FIG. 1, the organic EL layer 9 in the present embodiment has the hole injection layer 3 and the light emitting layer 4 in this order from the anode 2 side. It is not limited to the configuration shown in FIG. For example, the organic EL layer 9 can have the following configuration.
(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 material included in the light emitting layer 4 may be a polymer material or a low molecular material, and a conventionally known light emitting material for an organic EL element can be used. Conventionally 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 each light emitting material are exemplified below, but the light emitting material is not particularly limited thereto.

Examples of the low-molecular light emitting material include 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) ), Triazole compounds such as 1,4-bis (2-methyryl) benzene, styryl bezene compounds such as thiovirazine dioxide, benzoquinone derivatives, naphthoquinone derivatives, fluorescent organic materials such as anthraquinone derivatives, azomethine zinc complexes, (8- Fluorescent organometallic compounds such as hydroxynolinato) aluminum complexes can be used.
As the polymer light emitting material, poly (2-decyloxy-1,4-phenylene) (DO-PPP), poly [2,5-bis- [2- (N, N, N-triethylammonium) ethoxy] -1 , 4-Phenyl-alt-1,4-phenylylene] dibromide (PPP-NEt ³⁺ ), poly [2- (2′-ethylhexyloxy) -5-methoxy-1,4-phenylenevinylene] (MEH-PPV ) Etc. can be used.
As a precursor of the polymer light-emitting material, a poly (p-phenylene vinylene) precursor (Pre-PPV), a poly (p-naphthalene vinylene) precursor (Pre-PNV), or the like can be used.

The light emitting layer 4 can be formed by a conventionally known method. For example, it can be formed by depositing an organic light emitting material using a dry process such as a resistance heating vapor deposition method, an electron beam (EB) method, or a molecular beam epitaxy (MBE) method. In addition, 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 method. It may be formed by applying using a wet process such as.

When using a wet process, the organic light emitting layer forming solution may contain at least one kind of light emitting material, and may contain two or more kinds of light emitting materials. In addition to the light emitting material, a leveling agent, a light emission assist agent, an additive (donor, acceptor, etc.), a charge transport agent, a light emitting dopant, and the like may be contained. The solvent for the organic light emitting layer forming solution may be any solvent that can dissolve or disperse the light emitting material. For example, pure water, methanol, ethanol, tetrahydrofuran (Tetrahhydrofuran; THF), chloroform, toluene, xylene Or trimethylbenzene.

Each of the hole transport layer and the electron transport layer (hereinafter, collectively referred to as “charge transport layer”) may have a single layer structure or a multilayer structure. The charge transport layer can be formed by, for example, a conventionally known method (dry process or wet process) exemplified as a method for forming the light emitting layer 4. When the charge transport layer is formed by a wet process, the solvent for the charge transport layer forming solution may be any solvent that can dissolve or disperse the charge transport material, and is exemplified as the solvent for the organic light emitting layer forming solution. It may be a solvent. As the charge transport material contained in the charge transport layer, conventionally known materials can be used. Specific examples of these compounds are shown below, but the charge transport material is not particularly limited thereto.

Examples of the hole transport material contained in the hole transport layer include porphyrin compounds, N, N′-bis- (3-methylphenyl) -N, N′-bis- (phenyl) -benzidine (TPD), N , N′-di (naphthalen-1-yl) -N, N′-diphenyl-benzidine (NPD) and other aromatic tertiary amine compounds, hydrazone compounds, quinacridone compounds, styrylamine compounds and other low molecular materials, polyaniline, Polymer materials such as 3,4-polyethylenedioxythiophene / polystyrene sulfonic acid (PEDOT / PSS), poly (triphenylamine derivatives), polyvinyl carbazole (PVCz), and polymer material precursors such as Pre-PPV and Pre-PNV The body 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. Can do.

The anode 2 and the cathode 5 can be formed from electrode materials as exemplified below.
The anode 2 may have a single layer structure 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. It may have a multilayer structure including a layer made of the electrode material. Further, on the side of the layer of the organic EL layer 9 of the above-mentioned electrode material, or may be a structure in which a SiO ₂ layer having a thickness enough not greatly hindered the conductivity of this layer (for example, about 1 nm). 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, by adding the SiO ₂ layer, the anode 2 and the organic EL layer 9 Adhesion can be improved.

Example 1
The organic EL element (FIG. 1) of Example 1 according to the present invention is manufactured by the following method.
On a 5 cm square insulating substrate 1, as an anode 2, a striped Pt electrode (anode, first electrode) 2 (width: 2 mm, length: 5 cm, thickness: with an electron beam (EB) deposition apparatus. About 150 nm). Next, a mixed aqueous solution of PEDOT and PSS is applied on the anode 2 by spin coating, and dried at 150 ° C. for 20 minutes, thereby forming the hole injection layer 3. At this time, the thickness of the hole injection layer 3 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 3, the light emitting layer 4 is formed by applying a polyfluorene derivative solution by spin coating and drying.

Subsequently, a cathode (second electrode) 5 is formed on the light emitting layer 4. First, the metal layer 6 (thickness: 5 nm) is formed by resistance heating vapor deposition using Al containing 5 mass% of Ca as a vapor deposition source (starting material). The shape of the metal layer 6 is a striped layer (width: 2 mm, length: 5 cm) along the direction orthogonal to the anode 2. Thereafter, IZO layers 7 and 8 are formed as an oxide conductive layer by DC sputtering using an IZO sintered target. At this time, sputtering is performed using only Ar gas at the initial stage of IZO formation, and the IZO layer 7 (a portion of the transparent electrode having a relatively high resistivity) is formed without using oxygen gas. Thereafter, an IZO layer 8 (a portion of the transparent electrode having a relatively low resistivity) is formed using Ar gas and oxygen gas. The IZO layers 7 and 8 are formed to have the same stripe pattern as that of the metal layer 6. Thereby, the organic EL element of Example 1 is obtained. Note that when the metal layer 6 and the oxide conductive (IZO) layers 7 and 8 are formed, neither of the processes for heating the substrate is performed.

(Comparative Example 1)
FIG. 4 is a cross-sectional view schematically showing the configuration of the organic EL element of Comparative Example 1. In addition, the white arrow direction in FIG. 4 represents the direction which takes out light emission.
In order to compare with the organic EL element 100 of Example 1, an organic EL element 300 of Comparative Example 1 is produced as shown in FIG. The organic EL element 300 of this comparative example has the same configuration as that of the organic EL element 100 of Example 1 except that the IZO layer is formed entirely using Ar gas and oxygen gas (only the IZO layer 8 is formed). And is produced by a similar method. Note that the organic EL element 300 of Comparative Example 1 is not included in the present invention.

(Emission characteristic evaluation)
A DC voltage was applied to each of the organic EL elements of Example 1 and Comparative Example 1 so that the Pt electrode 2 was positive and the IZO layer 8 was negative, and light emission from the top of the IZO layer 8 was observed. As a result, in the organic EL element 100 of Example 1, green light emission from the light emitting layer 4 was observed even under a fluorescent lamp. However, in the organic EL element 300 of Comparative Example 1, the brightness (luminance that can only be confirmed in a dark place) Only small light emission). Therefore, the light emission luminance of the organic EL element 300 of Comparative Example 1 is significantly smaller than the light emission luminance of the organic EL element 100 of Example 1. That is, the light emission efficiency of the organic EL element 300 of Comparative Example 1 is significantly lower than the light emission efficiency of the organic EL element 100 of Example 1.

The cause is considered as follows.
In the organic EL element 300 of Comparative Example 1, it is considered that the metal layer 6 and the light emitting layer 4 were oxidized by active oxygen atoms (or ions) in the plasma generated when the IZO layer 8 was formed. When the metal layer 6 is oxidized, the efficiency of electron injection from the cathode 5 to the light emitting layer 4 is reduced. Therefore, sufficient light emission cannot be obtained in the light emitting layer 4. Further, when the light emitting layer 4 is oxidized, the light emitting layer 4 itself deteriorates and the light emission efficiency is lowered.
On the other hand, in the organic EL device 100 of Example 1, since the oxygen gas is not used at the initial stage of formation of the IZO layer (when the IZO layer 7 is formed), the metal layer 6 and the light emitting layer 4 are not oxidized. After that, even if the IZO layer 8 is formed using oxygen gas, the IZO layer 7 formed without using oxygen gas first becomes a barrier (barrier layer), so that the metal layer 6 and the light emitting layer 4 are oxidized. Absent. For this reason, since the electron injection efficiency decreases due to oxidation of the metal layer 6 and deterioration due to oxidation of the light emitting layer 4 does not occur, a highly efficient organic EL element can be provided.

<Embodiment 2> Organic EL Display Device FIG. 3 is a cross-sectional view schematically showing a configuration of an organic EL display device according to a second embodiment of the present invention on which the organic EL element 100 according to the first embodiment of the present invention is mounted. is there. 3 indicates a direction in which light emission from the organic EL element 100 is extracted.
In the organic EL display device 200 shown in FIG. 3, the organic EL element 100 is formed on an active matrix substrate 101. The active matrix substrate 101 includes a substrate 1, a plurality of thin film transistors (TFTs) formed on the substrate 1 for each pixel, and a planarization film 14 that covers these TFTs. Each TFT includes a gate electrode 12, an island-like semiconductor layer 17 formed on the gate electrode 12 via a gate insulating film 13, and electrodes provided so as to cover both ends of the island-like semiconductor layer 17 ( Source / drain electrode) 10, a so-called bottom gate structure. Each TFT is connected to a source wiring (not shown) and a gate wiring 11 by a source electrode 10 and a gate electrode 12, respectively. 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 planarizing film 14. The anode (first electrode) 2 of the organic EL element 100 is formed for each pixel by patterning the conductive layers 20 and 21 deposited on the planarizing film 14 and inside the through hole 15. Each anode 2 is connected to the drain electrode 10 of the corresponding TFT through the through hole 15. These anodes 2 are insulated from each other by an insulating film 16 formed so as to cover the edge portion and the through hole 15. On the anode 2 and the insulating film 16, a hole injection layer 3, a light emitting layer 4, a metal layer 6, an oxide conductive layer (IZO layer 7 formed without using oxygen gas and IZO formed using oxygen gas). A laminated film with the layer 8 and a transparent electrode) are formed in this order.

The organic EL display device 200 shown in FIG. 3 has the above-described configuration and is equipped with the organic EL element 100 of the present invention, so that the electron injection efficiency is reduced due to the oxidation of the metal layer 6 and the light emitting layer. By suppressing the decrease in the light emission efficiency due to oxidation, the light emission efficiency is high. Therefore, high definition and bright display can be realized. In addition, variation in luminance between pixels (that is, for each organic EL element 100) is small, and high-quality display can be obtained.

The configuration of the organic EL display device 200 of the present embodiment is not particularly limited to the configuration described above. For example, the TFT may have a top gate structure. Further, the configuration of the organic EL element 100 to be mounted is not particularly limited to the above-described configuration, and various configurations as described in the first embodiment can be applied. Furthermore, as a driving method of the display device, a voltage driving method that requires two TFTs for each pixel may be adopted, or a current driving method that requires four TFTs for each pixel may be adopted. Also good. Alternatively, a simple matrix display device can also be configured using the organic EL element 100.

(Example 2)
The organic EL display device (FIG. 3) of Example 2 according to the present invention is manufactured by the following method.
After forming a bottom-gate TFT using polysilicon as the semiconductor layer 17 on the insulating substrate 1, the TFT is covered with a planarization film 14 in order to eliminate unevenness on the surface of the substrate 1. Next, an Al layer 20 and an IZO layer 21 are formed as the anode (first electrode) 2 on the planarizing film 14 and in the through hole 15 provided in the planarizing film 14. The Al layer 20 and the IZO layer 21 are connected to the drain electrode 10 of the TFT through the through hole 15. Of the Al layer 20 and the IZO layer 21, the thickness of the portion formed on the planarizing film 14 is 150 nm. Next, an SiO ₂ film 16 is formed so as to cover the through hole 15 and the edge portion of the anode 2. Subsequently, the hole injection layer 3 (thickness: about 60 nm) and the light emitting layer 4 are formed in this order on the substrate in the same manner as in Example 1. A light-transmitting metal layer 6 (thickness: 15 nm, for example) is formed on the light emitting layer 4 by co-evaporation of Al and Ca. Al is deposited by the EB method, and Ca is deposited by the resistance heating deposition method. Next, the IZO layers 7 (parts with relatively high resistivity among the transparent electrodes) and 8 (parts with relatively low resistivity among the transparent electrodes) are formed by DC sputtering. When the IZO layers 7 and 8 are formed, the initial 10 nm is formed without introducing oxygen gas (forms the IZO layer 7), and then oxygen gas is introduced to form the IZO layer 8 (total thickness: 100 nm). Form.

(Emission characteristic evaluation)
When a control signal was applied to the TFT of the organic EL display device manufactured in Example 2, green light emission from the light emitting layer 4 was observed from the upper part of the IZO layer 8. Therefore, it was confirmed that the oxidation of the metal layer 6 and the light emitting layer 4 of the organic EL element 100 was sufficiently suppressed.

It is sectional drawing which shows typically the structure of the organic EL element of Example 1 which concerns on this invention. It is a figure which shows the relationship between the oxygen partial pressure at the time of oxide transparent conductive film (ITO film) formation, and film | membrane resistivity. It is sectional drawing which shows typically the structure of the organic electroluminescent display apparatus of Example 2 which concerns on this invention. It is sectional drawing which shows the structure of the organic EL element of the comparative example 1 typically.

Explanation of symbols

1: Substrate 2: Anode (first electrode)
3: Hole injection layer 4: Light emitting layer 5: Cathode (second electrode)
6: Alloy layer (metal layer)
7: Oxide conductive layer (part of transparent electrode having relatively high resistivity)
8: Oxide conductive layer (part of transparent electrode having relatively low resistivity)
9: Organic EL layer (organic layer)
10: source and drain electrodes 11: wiring 12: gate electrode 13: gate insulating film 14: planarizing film 15: through hole 16: insulating film 17: semiconductor layer 20: Al layer 21: IZO layer 100, 300: organic EL element 101: Active matrix substrate 200: Organic EL display device

Claims (16)

An organic electroluminescence device comprising a first electrode, an organic layer including a light emitting layer, and a translucent second electrode, which are laminated in this order on a substrate,
The second electrode includes a transparent electrode made of a metal oxide.
The transparent electrode has a portion having a relatively high resistivity on the organic layer side,
The resistivity is relatively high portion, all SANYO resistivity rich in oxygen vacancies than relatively low portion,
The organic electroluminescence element , wherein the portion having a relatively high resistivity is formed of a material different from that of the portion having a relatively low resistivity . An organic electroluminescence device comprising a first electrode, an organic layer including a light emitting layer, and a translucent second electrode, which are laminated in this order on a substrate,
The second electrode includes a transparent electrode made of a metal oxide.
The transparent electrode has a portion having a relatively high resistivity on the organic layer side,
The portion having a relatively high resistivity is formed under conditions where oxygen is not substantially introduced, and the portion having a relatively low resistivity is formed under conditions where oxygen is introduced. The
The organic electroluminescence element , wherein the portion having a relatively high resistivity is formed of a material different from that of the portion having a relatively low resistivity . The transparent electrode is formed of a material including at least one selected from the group consisting of indium zinc oxide, gallium-doped zinc oxide, and aluminum-doped zinc oxide at least in a portion having a relatively high resistivity. The organic electroluminescent element according to claim 1, wherein the organic electroluminescent element is formed. The organic electroluminescent element according to any one of claims 1 to 3, wherein the transparent electrode has a thickness of a portion having a relatively high resistivity of 5 to 100 nm. The organic electroluminescent element according to any one of claims 1 to 4, wherein the organic electroluminescent element has an electron injection layer made of an insulator between the organic layer and the transparent electrode. The said organic electroluminescent element has a translucent metal layer between an organic layer and a transparent electrode, or between an electron injection layer and a transparent electrode, The any one of Claims 1-5 characterized by the above-mentioned. The organic electroluminescent element of description. The lower limit of the resistivity at 25 ° C. of the relatively high resistivity is 1 × 10 ^-3 Ω · cm, upper limit is 1 × 10 ^-2 The organic electroluminescent element according to claim 1, wherein the organic electroluminescent element is Ω · cm. The lower limit of the resistivity at 25 ° C. at the relatively low resistivity is 1 × 10 ^-4 Ω · cm, upper limit is 1 × 10 ^-3 The organic electroluminescent element according to claim 1, wherein the organic electroluminescent element is Ω · cm. The overall resistivity of the transparent electrode is 25 ° C. and the upper limit is 1 × 10 ^-3 It is (omega | ohm) * cm, The organic electroluminescent element in any one of Claims 1-8 characterized by the above-mentioned. A method for producing an organic electroluminescent element, comprising: a step of forming a first electrode on a substrate; a step of forming an organic layer including a light emitting layer; and a step of forming a translucent second electrode.
The step of forming the second electrode includes a step of forming a transparent electrode made of a metal oxide,
Step, after formation of the high resistivity is relatively electrode by conditions that do not substantially introduce oxygen gas, the resistivity is relatively the conditions of introducing the oxygen gas to form a transparent electrode made of the metal oxide all SANYO forming the lower electrode, and an organic electroluminescent resistivity is relatively high electrode resistivity is characterized <br/> that is intended to form the different materials relatively low electrode Sense element manufacturing method. Method of manufacturing the organic electroluminescent device according to claim 10, wherein further comprising the step of forming the electron injection layer made of an insulating material between the step of forming a step and a transparent electrode forming the organic layer The manufacturing method of organic electroluminescent element of this. The manufacturing method of the organic electroluminescence element includes a step of forming an organic layer and a step of forming a transparent electrode, or a step of forming an electron injection layer made of an insulator and a step of forming a transparent electrode. during manufacturing method of the organic electroluminescent element according to any one of claims 10 or 11, characterized in that it comprises a step of forming a light-transmitting metal layer. The lower limit of the resistivity at 25 ° C. of the electrode having a relatively high resistivity is 1 × 10 ^-3 Ω · cm, upper limit is 1 × 10 ^-2 It is (omega | ohm) * cm, The manufacturing method of the organic electroluminescent element in any one of Claims 10-12 characterized by the above-mentioned. The lower limit of the resistivity at 25 ° C. of the electrode having a relatively low resistivity is 1 × 10 ^-4 Ω · cm, upper limit is 1 × 10 ^-3 It is (omega | ohm) * cm, The manufacturing method of the organic electroluminescent element in any one of Claims 10-13 characterized by the above-mentioned. The overall resistivity of the transparent electrode is 25 ° C. and the upper limit is 1 × 10 ^-3 It is (omega | ohm) * cm, The manufacturing method of the organic electroluminescent element in any one of Claims 10-14 characterized by the above-mentioned. Organic electroluminescent device according to any one of claims 1 to 9 or includes an organic electroluminescent element manufactured by the manufacturing method of the organic electroluminescent element according to any one of claims 10-15 An organic electroluminescence display device characterized by comprising:

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