JP2010108652A - Manufacturing method of organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of an organic electroluminescent element in which light emission having high brightness and high efficiency is made possible, an increase of a driving voltage, the generation of an undesirable voltage rise and generation of defects such as short circuiting can be suppressed, and which has superior productivity. <P>SOLUTION: The manufacturing method of the organic electroluminescent element is formed with a plurality of light-emitting layers laminated between a cathode and an anode via an intermediate layer. The intermediate layer is formed by a process to form a layer having a conductor of 1×10<SP>5</SP>Ω or less with energy of 10eV or less by gas phase method, to be adjoined to a layer at least containing one of from alkali metal, alkali earth metal, alkali metal oxide, and alkali earth metal oxide. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing an organic electroluminescent device that can be used for an illumination light source, a backlight for a liquid crystal display, a flat panel display, and the like, and more specifically, includes a plurality of organic light emitting layers and emits light with high brightness and high efficiency. The present invention relates to a method for manufacturing an organic electroluminescence element.

  As an organic light-emitting element called an organic electroluminescence element, a transparent electrode serving as an anode, a hole transport layer, a light-emitting layer (organic light-emitting layer), an electron injection layer, and an electrode serving as a cathode are laminated on the surface of one side of a transparent substrate. An example of such a configuration is known. Then, by applying a voltage between the anode and the cathode, electrons injected into the light emitting layer through the electron injection layer and holes injected into the light emitting layer through the hole transport layer are generated in the light emitting layer. Light is emitted by recombination, and thus the light emitted from the light emitting layer is extracted through the transparent electrode and the transparent substrate.

  The organic electroluminescence element is characterized by being self-luminous, exhibiting relatively high-efficiency light emission characteristics, and capable of emitting light in various colors, such as a display device such as a flat panel display. It is expected to be used as a light emitter or as a light source, for example, a backlight for a liquid crystal display or illumination, and some of them are already in practical use.

  However, the organic electroluminescence element has a trade-off relationship between the luminance and the lifetime, and has a problem that the lifetime is shortened when the luminance is increased in order to obtain a clearer image or bright illumination light.

  In order to solve this problem, an organic electroluminescence element having a structure in which a plurality of light-emitting layers are provided between an anode and a cathode and each light-emitting layer is electrically connected by an intermediate layer has recently been proposed (for example, Patent Documents). 1-5).

  FIG. 4 shows an example of the structure of such an organic electroluminescence element. A plurality of light emitting layers 4a and 4b are provided between an electrode to be the anode 1 and an electrode to be the cathode 2, and the adjacent light emitting layer 4a. , 4b, with the intermediate layer 3 interposed therebetween, and this is laminated on the surface of the transparent substrate 5. The anode 1 is formed as a light transmissive electrode, and the cathode 2 is formed as a light reflective electrode. In FIG. 4, the illustration of the electron injection layer and the hole transport layer provided on both sides of the light emitting layers 4a and 4b is omitted.

  In this example, when the voltage is applied between the anode 1 and the cathode 2 by dividing the plurality of light emitting layers 4a and 4b by the intermediate layer 3, the plurality of light emitting layers 4a and 4b are connected in series. Since light is emitted simultaneously in the state and the light from each of the light emitting layers 4a and 4b is added, it is possible to emit light with higher luminance than a conventional organic electroluminescence element when a constant current is applied, and the luminance-lifetime as described above It is possible to avoid this trade-off.

Here, the general ones currently known as the configuration of the intermediate layer 3 are, for example, (1) BCP: Cs / V ₂ O ₅ , (2) BCP: Cs / NPD: V ₂ O ₅ , (3) In-situ reaction product of Li complex and Al, (4) Alq: Li / ITO / hole transport material, (5) Metal-organic mixed layer, (6) Oxide containing alkali metal and alkaline earth metal Etc. In addition, description of ":" represents mixing of 2 types of materials, and description of "/" represents lamination | stacking of the composition before and behind.
Japanese Patent Laid-Open No. 11-329748 JP 2003-272860 A JP 2005-135600 A JP 2006-332048 A JP 2006-173550 A

  However, if an intermediate layer that partitions a plurality of light emitting layers is provided as in the above-described prior art, there is a risk that an increase in driving voltage and an undesirable increase in voltage may occur, and defects such as short circuits due to poor film quality occur. In addition, there is a possibility that the above-described problem may occur, and further, there arises a manufacturing problem that it is necessary to combine the vapor deposition process and the sputtering process.

For example, in the intermediate layer of the system shown in (1) above, there is a possibility that a short circuit problem may occur due to the film quality of the V ₂ O ₅ layer.

  In the system shown in (2), there is a problem of voltage increase due to a side reaction occurring between two layers. In other words, it has been reported that Lewis acid molecules react with electron transport materials, and alkali metals react with hole transport materials as Lewis bases, and these reactions cause an increase in driving voltage (Reference: Society of Polymer Science, Japan). Organic EL Study Group Lecture on December 9, 2005 Multiphoton organic EL lighting).

  Moreover, in the system shown in (3) above, there is a problem that the organic ligand component of the Li complex used for obtaining the in-situ reaction product may adversely affect the device characteristics.

  In the system (4), since ITO is used as the intermediate layer, depending on the film formation technique, the influence on the film quality of the base film (Alq: Li, etc.) and the ITO film is large.

  For example, since a conductor such as ITO is a refractory metal oxide, it is difficult to form a film by a resistance heating vapor deposition method that has little influence on the base film and can control film formation particles with low energy. Therefore, these films are generally formed by EB vapor deposition or sputtering. However, in that case, X-rays or electrons emitted from the electron beam source, or high-energy particles caused by plasma or sputtering, may damage the underlying film, which adversely affects device characteristics. It has become.

  Further, in this system, hole injection from the ITO as the intermediate layer into the hole transport material is not always good, and there is a problem in terms of driving voltage and element characteristics. Furthermore, due to the small resistivity of ITO, when the thickness of the ITO layer is reduced, charges may be transmitted through the ITO surface to places where it is not desired to emit light, and light is emitted from portions other than the intended light emitting region. It becomes a problem to occur.

  In the above system (5), since the intermediate layer is formed by mixing a metal containing a metal compound such as a metal oxide and an organic substance, the thermal stability of the intermediate layer is lowered, and particularly when a large current is applied. There was a problem that the stability of the intermediate layer was inferior to the heat generation.

  In the system (6), the function as an intermediate layer of a metal oxide containing an alkali metal or an alkaline earth metal is not necessarily sufficient, and other than the metal oxide containing an alkali metal or an alkaline earth metal. There is a problem that it is substantially necessary to use a layer made of a material, and the structure of the intermediate layer is complicated.

  Furthermore, in the systems (1) and (4) described above, there is a possibility that defects around the intermediate layer may occur due to the stress in the film constituting the intermediate layer, particularly when the device is a large area device.

  Patent Document 3 describes a method of forming an intermediate layer by adding an additive to one kind of matrix so that its concentration does not become zero at any position in the film. In addition, it is impossible to solve all the problems described in the above-mentioned reference.

  Therefore, in forming an organic electroluminescence device including a plurality of light emitting layers stacked via an intermediate layer as described above, it is desired to realize an intermediate layer that overcomes the various problems described above. It has become to.

  The present invention has been made in view of the above points, and can emit light with high luminance and high efficiency, and can increase driving voltage, cause an undesirable increase in voltage, and cause defects such as short circuits. It is an object of the present invention to provide a method for producing an organic electroluminescence device which can be suppressed and has good productivity.

A method for producing an organic electroluminescent element according to claim 1 of the present invention is a method for producing an organic electroluminescent element in which a plurality of light emitting layers are formed between an anode and a cathode via an intermediate layer, the intermediate layer comprising However, at least one of an alkali metal, an alkaline earth metal, an alkali metal oxide, and an alkaline earth metal oxide is used to form a layer in which a conductor having a size of 1 × 10 ⁵ Ωcm or less is formed by a vapor phase method with an energy of 10 eV or less. It is characterized by being provided with a step of forming adjacent to the layer including one.

In addition to the above-described structure, a method for manufacturing an organic electroluminescent element according to claim 2 is a method in which a layer in which a conductor having a density of 1 × 10 ⁵ Ωcm or less is formed by a vapor phase method with an energy of 10 eV or less is formed by an electron beam evaporation method or an ion It is characterized in that it is formed by a sputtering method or a sputtering method that does not use plasma.

In addition to the above-described structure, the method for manufacturing an organic electroluminescent element according to claim 3 forms a layer in which a conductor of 1 × 10 ⁵ Ωcm or less is formed by a vapor phase method with an energy of 10 eV or less in the presence of oxygen. It is characterized by.

  According to the method for manufacturing an organic electroluminescent element according to the first aspect of the present invention, the conductive layer having a low specific resistance is contained in the intermediate layer, so that the driving voltage of the organic electroluminescent element can be lowered. Further, since this layer is formed by a vapor phase method with a low energy of 10 eV or less, it is possible to reduce the influence (damage) on the layer to be the base film. Further, since this layer and a layer containing at least one of alkali metal, alkaline earth metal, alkali metal oxide, and alkaline earth metal oxide are formed adjacent to each other, they are adjacent to the intermediate layer. Therefore, it is possible to reduce the charge injection barrier to the electron transporting layer, and as a result, it is possible to manufacture an organic electroluminescence device having a low voltage drive and a long lifetime.

According to the method for manufacturing an organic electroluminescent element according to claim 2, an electron beam evaporation method, an ion plating method, or a sputtering method that does not use plasma in the presence of oxygen on a layer containing a metal oxide of 1 × 10 ⁵ Ωcm or less. Therefore, it is possible to form a highly transparent intermediate layer with less adverse effects on the layer to be the base film, and to improve the device characteristics of organic electroluminescence.

According to the method for manufacturing an organic electroluminescent element according to claim 3, since the layer for forming a conductor of 1 × 10 ⁵ Ωcm or less by a vapor phase method with an energy of 10 eV or less is formed in the presence of oxygen, The transmittance can be further increased, and the device characteristics of organic electroluminescence can be improved.

  Hereinafter, the best mode for carrying out the present invention will be described.

  FIG. 1 shows an example of the structure of the organic electroluminescence element of the present invention, in which a light emitting layer 4 and an intermediate layer 3 are provided between an electrode to be an anode 1 and an electrode to be a cathode 2. The light emitting layer 4 is composed of a plurality of light emitting layers 4a and 4b. The light emitting layers 4a and 4b are stacked in the stacking direction of the anode 1 and the cathode 2, and an intermediate between the light emitting layer 4a and the light emitting layer 4b. Layer 3 is interposed. One electrode (anode 1) is laminated on the surface of the transparent substrate 5. In the embodiment of FIG. 1, the anode 1 is formed as a light transmissive electrode, and the cathode 2 is formed as a light reflective electrode.

  In the form shown in FIG. 1, two light emitting layers 4 a and 4 b are provided as the light emitting layer 4 via the intermediate layer 3, but the light emitting layer 4 is further laminated in multiple layers via the intermediate layer 3. There may be. The number of stacked light emitting layers 4 is not particularly limited. However, since the difficulty of optical and electrical element design increases as the number of layers increases, it is preferably within 5 layers. In addition, a hole injection layer, a hole transport layer, an electron transport layer, an electron injection layer, etc. are provided between the organic light emitting layer 4 and the anode 1 or the cathode 2 as necessary, as in a general organic electroluminescence device. In FIG. 1, these layers are not shown.

The intermediate layer 3 includes a layer (hereinafter referred to as the intermediate layer 3A) in which a conductor of 1 × 10 ⁵ Ωcm or less is formed by a gas phase method with an energy of 10 eV or less, an alkali metal, an alkaline earth metal, an alkali metal oxide, And a layer containing at least one of alkaline earth metal oxides (hereinafter referred to as intermediate layer 3B).

The intermediate layer 3A is not particularly limited as long as it is a layer made of a material generally known as a conductive material. For example, a material appropriately selected from metals, metal oxides, electrically conductive compounds, and the like is available. It is used as a conductor. By way of example, Al, Cu, Ni, Ag , Au, a metal such as Ti, CuI, ZnSe, ZnS, metal compounds such as CuSe, ITO (indium - tin _{oxide), SnO 2, ZnO, IZO} ( indium - Zinc Metal oxides such as oxides) and carbon compounds such as carbon nanotubes and fullerenes. One of these materials may be used, or a plurality of these materials may be used in combination. For example, indium and tin, indium and zinc, aluminum and gallium, gallium and zinc, titanium and niobium, or any other metal containing any of the above metals, or a metal oxide or a mixture of other combinations. Good. The oxidation number of each metal and the mixing ratio of a plurality of metals can be arbitrarily set so that the film quality, stability, and electrical characteristics of the metal oxide are within preferable ranges. The intermediate layer 3A preferably contains a metal oxide because the transparency of the film is improved and, as a result, the efficiency as a device is also improved.

  The intermediate layer 3A is formed by depositing film-forming particles with an energy of 10 eV or less by a vapor phase method. As a result, it is possible to eliminate the influence on the layer serving as the base film. Furthermore, it is preferable to form this layer in the presence of oxygen. By forming the film in the presence of oxygen, the permeability of the film can be improved, and as a result, the optical characteristics of the device on which the organic light emitting electroluminescent element is mounted can be improved. In general, when vapor-depositing / sputtering a highly transparent metal oxide material or the like, the actual film may become a lower oxide to become an absorption film (brown film) and the transmittance may be reduced. However, according to the method of forming a film in the presence of oxygen as described above, the transmittance can be improved by suppressing the intermediate layer 3A from becoming an absorption film. Note that, depending on the film formation method, there is a distribution of energy when forming particles. In this case, it means that the maximum value of energy in the energy distribution is 10 eV or less.

  In forming the intermediate layer 3A in the presence of oxygen, the flow rate of oxygen is controlled to the extent that oxygen does not affect the base film, or the film formation chamber is partitioned so that the influence of oxygen inflow does not affect the base film. It is preferable to do. Thereby, it is possible to prevent the base film from being damaged. At this time, it is preferable that the inflow amount of oxygen is extremely small (partial pressure is about 0.001 to 0.0001 Pa) so as not to affect the base film.

  The method for forming the intermediate layer 3A is not particularly limited as long as it can be formed with the energy as described above. For example, the resistance heating evaporation method, the electron beam evaporation method, and the ion beam sputtering method are used. It is preferable to form by a method that does not use plasma such as an ion plating method, and among these, an electron beam evaporation method, an ion plating method, or a sputtering method that does not use plasma is more preferable. According to such a method that does not use plasma, it is possible to form the intermediate layer 3A with less adverse effects on the layer serving as the base film and a highly transparent film quality, and to form the intermediate layer 3A as a thin film. It becomes possible to do. The resistance heating evaporation can be controlled to 0.01 eV or less, the electron beam evaporation can be controlled to 0.1 eV or less, the ion beam sputtering can be controlled to 10 eV or less, and the ion plating can be controlled to 10 eV or less. It is preferred to carry out the membrane.

  The energy of the particles during the formation of the intermediate layer 3A can be controlled by determining the energy value using a plasma monitor, an energy analyzer, or the like, and controlling the film forming process based on this value.

  The intermediate layer 3A can further contain metals and compounds other than those described above. When the intermediate layer 3A includes a hole-injecting metal oxide layer, the intermediate layer 3A may contain a metal or metal oxide having hole-injecting properties. Examples of the metal having hole injecting properties include, but are not limited to, molybdenum, rhenium, tungsten, vanadium, nickel, ruthenium, and aluminum. Whether or not these materials have hole injection properties can generally be determined on the basis of whether or not they can be used as hole injection layers. For example, formation of charge transfer complexes with materials used as hole injection layers Can be determined from optical means such as a change in absorption spectrum or a change in emission intensity.

Further, the intermediate layer 3A may further contain an insulator such as an organic compound or a non-conductive inorganic substance. The inorganic insulator is not particularly limited as long as it can be formed into a mixed film with a conductor. For example, metal fluorides such as lithium fluoride and magnesium fluoride, metal chlorides represented by sodium chloride, magnesium chloride and the like. And metal oxides such as aluminum, cobalt, zirconium, titanium, vanadium, niobium, chromium, tantalum, tungsten, manganese, molybdenum, ruthenium, iron, nickel, copper, gallium, zinc, etc. Insulators such as Al ₂ O ₃ , MgO, iron oxide, AlN, SiN, SiC, SiON, BN, etc. that is and, selecting silicon compounds including such SiO 2, _SiO, etc. carbon compound optionally It can be used Te.

  These insulators are preferably selected from those having low absorption in the visible light region or low refractive index. As a result, the light absorption rate and refractive index of the intermediate layer 3A can be reduced, and as a result, reflection and absorption inside the device are reduced, and loss caused when light generated in the light emitting layer 4 is emitted to the outside. Can be reduced. In particular, any one of metal oxides, metal halides, metal nitrides, metal carbides, carbon compounds, and silicon compounds having no electrical conductivity is preferable from the viewpoints of heat resistance, stability, and optical properties.

When the intermediate layer 3A is formed as a mixture layer made of a plurality of materials as described above, the mixing ratio of the conductor and other substances in the layer is such that the specific resistance of the intermediate layer 3A is 1 × 10 ⁵ Ωcm or less. As long as it becomes, it can be arbitrarily set.

The thickness of the intermediate layer 3A is preferably 10 nm or less, more preferably 5 nm or less. By setting the thickness of the intermediate layer 3A to 10 nm or less, the current conduction in the lateral direction in the film is reduced to a negligible level, and unintentional light emission from a part other than the light emitting region described as the disadvantage of the prior art is performed. It becomes possible to suppress more. In particular, as the relationship between the thickness (nm) and the specific resistance (Ωcm), the value of thickness (nm) / specific resistance (Ωcm) is preferably in the range of 10 ⁴ or less. The lower limit of the thickness of the intermediate layer 3A is preferably 2 nm. If the thickness of the intermediate layer 3A is thinner than this, the layer may not be formed uniformly and stably.

  The intermediate layer 3B includes at least one of an alkali metal (Group I metal), an alkaline earth metal (Group II metal), an alkali metal oxide, and an alkaline earth metal oxide.

  The metal or metal oxide contained in the intermediate layer 3B is not particularly limited. For example, lithium, cesium, sodium, strontium, magnesium, calcium, yttrium, samarium, alkali metals, alkaline earth metals, Examples include rare earth metal oxides, iridium, and nickel oxides. These may be used alone or in combination of two or more. The oxidation number of each metal and the mixing ratio of a plurality of metals can be arbitrarily set so that the film quality, thermal stability, and electrical characteristics of a layer formed of these metals or metal oxides are within preferable ranges. Is possible. The intermediate layer 3A may be made of substantially the same material.

  The material used for the intermediate layer 3B is preferably an electron injecting material. Whether or not the material used for the intermediate layer 3B is electron-injectable can generally be determined based on the same criteria as whether or not it can be used as an electron-injection layer. For example, charge transfer with the material used as the electron-injection layer The formation of the complex may be judged from optical means such as a change in absorption spectrum or a change in emission intensity.

The intermediate layer 3B may contain an insulator such as an organic compound or a nonconductive inorganic substance in addition to the metal or metal oxide. The inorganic insulator is not particularly limited as long as it can form a mixed film with an alkali metal, an alkaline earth metal, an alkali metal oxide, and an alkaline earth metal oxide. For example, lithium fluoride or magnesium fluoride Metal halides such as metal fluorides such as sodium chloride, sodium chloride, magnesium chloride, etc., aluminum, cobalt, zirconium, titanium, vanadium, niobium, chromium, tantalum, tungsten, manganese, molybdenum, ruthenium, Various metal oxides such as iron, nickel, copper, gallium and zinc (excluding those included in the hole-injecting metal oxide), nitrides, carbides, oxynitrides, etc., for example, Al ₂ O ₃ , MgO, iron oxide, AlN, SiN, SiC, SiON, BN and other insulators, It can be arbitrarily selected from silicon compounds such as SiO ₂ and SiO, and carbon compounds.

  These insulators are preferably selected from those having low absorption in the visible light region or low refractive index. As a result, the light absorptance and refractive index of the intermediate layer 3B can be reduced, and as a result, reflection and absorption inside the device are reduced, and loss caused when light generated in the light emitting layer 4 is emitted to the outside. Can be reduced. In particular, any one of metal oxides, metal halides, metal nitrides, metal carbides, carbon compounds, and silicon compounds having no electrical conductivity is preferable from the viewpoints of heat resistance, stability, and optical properties.

  The thickness of the intermediate layer 3B is preferably 0.5 to 2 nm. If the thickness of the intermediate layer 3B is thinner than this range, the voltage may increase and the life may be shortened. On the other hand, even if the thickness of the intermediate layer 3B is thicker than this range, there is a possibility that the voltage is increased and the life is shortened.

  Further, as in the embodiment of FIG. 2, the intermediate layer 3B is a transparent metal oxide layer 3B-1 on the anode 1 side, and an alkali metal, alkaline earth metal, alkali metal oxide on the anode 1 side, and It is also preferable that the layer 3B-2 containing at least one of the alkaline earth metal oxides is constituted by two layers. Thereby, it can drive with a lower voltage. Further, the thickness ratio between the layer 3B-1 and the layer 3B-2 is preferably in the range of 1: 4 to 1:10. If the thickness of the layer 3B-2 is thinner than this range with respect to the thickness of the layer 3B-1, the life and efficiency may be reduced. On the other hand, even if the thickness of the layer 3B-2 is thicker than this range with respect to the thickness of the layer 3B-1, the life and efficiency may be reduced.

  The intermediate layer 3A and the intermediate layer 3B are formed adjacent to each other. As a result, the driving voltage of the organic electroluminescence element can be lowered, and the charge injection barrier from the intermediate layer to the adjacent electron transporting layer can be reduced. A luminescence element can be manufactured. In the example of FIG. 1, the intermediate layer 3A is disposed on the cathode 1 side, and the intermediate layer 3B is disposed on the anode side. That is, in the case of stacking from the anode 1 side, after forming the intermediate layer 3B, the intermediate layer 3A is formed in contact with the intermediate layer 3B. According to such an arrangement of the intermediate layer 3A and the intermediate layer 3B, it is possible to improve the characteristics of electron transfer and hole transfer, and to obtain an organic electroluminescence element with good light emission.

  It is also preferable to introduce a charge transfer complex layer into the organic electroluminescence device of the present invention, if necessary. Thereby, the characteristics of electron movement and hole movement can be further improved, and the light emission of the element can be further improved.

When a charge transfer complex layer is used for hole injection, it is introduced between the intermediate layer 3 and the hole injection layer located on the cathode 2 side. Examples of such a layer include a system in which a metal, a metal oxide semiconductor, an inorganic acceptor, an organic acceptor, or the like is added to a hole transporting material or a material from which electrons are easily extracted. As the metal, a metal having a high work function, for example, gold having a work function of 5 eV or more, or a metal such as vanadium, molybdenum, rhenium, tungsten, or nickel can be used. Further, the metal oxide is not particularly limited, but for example, metal oxides such as vanadium, molybdenum, rhenium, tungsten, nickel, zinc, tin, niobium are preferably used. Examples of the inorganic acceptor include iron chloride, iron bromide, copper iodide, bromine and iodine. As the organic acceptor, fluorine-containing organic compounds, cyano group-containing organic compounds such as F ₄ -TCNQ, DDQ, CF ₃ TCNQ, 2-TCNQ, or derivatives thereof can be used. Derivatives containing fluorine or a cyano group can also be preferably used.

  The organic acceptor includes an organic substance and a material that accepts electrons from the organic substance. The mixing ratio of the organic substance and the material that accepts electrons from the organic substance can be appropriately set according to the type of the material, but preferably the material that accepts electrons from the organic substance is 0.1% relative to the organic substance. It is in the range of ˜80 mol%, more preferably in the range of 1 to 50 mol%.

  As the organic substance used for the organic acceptor, a hole transport material or a material that easily extracts electrons is preferably used. Examples of the hole transporting material include generally known triarylamine derivatives such as NPD, TPD, 2-TNATA and the like. Moreover, even if it is a material other than a triarylamine derivative, for example, an aromatic derivative such as a biphenyl derivative, an anthracene derivative, or a naphthalene derivative, or a material that can easily extract electrons such as an aniline derivative or a thiophene derivative is appropriately used. Can be used.

  When a charge transfer complex layer is used for electron injection, a material system generally known as a charge transfer complex system and contributing to electron injection can be used. Such a material system is not particularly limited. For example, a metal having a work function of 3.7 eV or less in the electron transport material, for example, cerium, lithium, sodium, magnesium, potassium, rubidium, samarium, yttrium. And a layer formed by mixing an electron transport material with an organic material or an inorganic material having an energy level capable of donating electrons to the electron transport material, and the like. .

  As an organic material or an inorganic material having an energy level capable of donating electrons to an electron transport material, for example, an organic material generally known as an organic donor, for example, a ruthenium complex, or a work function of 3.7 eV or less is used. Examples thereof include metals and metal oxide semiconductors containing these metals. The metal layer having a work function of 3.7 eV or less is not particularly limited, but contains a metal selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals including the metals exemplified above. Preferably, the layer is

  The thickness of the charge transfer complex layer is not particularly limited, but is generally preferably about 1 to 20 nm. If the thickness of the charge transfer complex layer is thinner than this range, the voltage may be increased. On the other hand, if the thickness of the charge transfer complex layer is larger than this range, the light transmittance may be lowered.

In addition, the layer of the charge transfer complex may include other organic compounds and inorganic substances such as metals such as Al, Cu, Ni, Ag, Au, Ti, LiF, Li ₂ O, NaF, CsF, SiO ₂ , SiO ₂ It is preferable to contain a metal halide or a metal oxide. Mixing two or more materials can improve the stability of materials that are not stable by themselves, or improve the film formability of materials that are poor in film quality and adhesion to adjacent layers. Is possible.

  As a material of the light emitting layer 4, any material known as a material for an organic electroluminescence element can be used. For example, anthracene, naphthalene, pyrene, tetracene, coronene, perylene, phthaloperylene, naphthaloperylene, diphenylbutadiene, tetraphenylbutadiene, coumarin, oxadiazole, bisbenzoxazoline, bisstyryl, cyclopentadiene, quinoline metal complex, tris (8-hydroxyxyl) Norinato) aluminum complex, tris (4-methyl-8-quinolinato) aluminum complex, tris (5-phenyl-8-quinolinato) aluminum complex, aminoquinoline metal complex, benzoquinoline metal complex, tri- (p-terphenyl- 4-yl) amine, 1-aryl-2,5-di (2-thienyl) pyrrole derivative, pyran, quinacridone, rubrene, distyrylbenzene derivative, distyrylarylene derivative, distili Amine derivatives and various fluorescent dyes, but include those including a material system and its derivatives of the foregoing, the present invention is not limited to these. Moreover, it is also preferable to mix and use the light emitting material selected from these compounds suitably. Further, not only a compound that emits fluorescence, typified by the above-described compound, but also a material system that emits light from a spin multiplet, for example, a phosphorescent material that emits phosphorescence, and a part thereof are included in a part of the molecule. A compound can also be used suitably. The light emitting layer 4 made of these materials may be formed by a dry process such as vapor deposition or transfer, or may be formed by a wet process such as spin coating, spray coating, die coating, or gravure printing. .

  Moreover, what was used conventionally can be used as it is for the board | substrate 5, the anode 1, the cathode 2, etc. which hold | maintain the laminated | stacked element | device which is another member which comprises an organic electroluminescent element.

  That is, the substrate 5 is light-transmitting when light is emitted through the substrate 5, and has a frosted glass-like shape in addition to being colorless and transparent. There may be. For example, a transparent glass plate such as soda lime glass or non-alkali glass, a plastic film or a plastic plate produced by an arbitrary method from a resin such as polyester, polyolefin, polyamide, or epoxy, or a fluorine resin can be used. . Furthermore, it is also possible to use a material having a light diffusing effect by containing particles, powder, bubbles or the like having a refractive index different from that of the substrate matrix in the substrate 5 or imparting a shape to the surface. Further, when light is emitted without passing through the substrate 5, the substrate 5 does not necessarily have to be light transmissive, and any substrate 5 is used as long as the light emission characteristics, life characteristics, etc. of the element are not impaired. be able to. In particular, the substrate 5 having high thermal conductivity can be used in order to reduce a temperature rise due to heat generation of the element during energization.

The anode 1 is an electrode for injecting holes into the light emitting layer 4, and an electrode material made of a metal, an alloy, an electrically conductive compound, or a mixture thereof having a large work function is preferably used. It is preferable to use a voltage of 4 eV or more. Examples of the material of the anode 1 include metals such as gold, conductive materials such as CuI, ITO (indium-tin oxide), SnO ₂ , ZnO, IZO (indium-zinc oxide), PEDOT, and polyaniline. Examples thereof include a conductive polymer doped with a polymer and an optional acceptor, and a conductive light-transmitting material such as a carbon nanotube. The anode 1 can be produced, for example, by forming these electrode materials on the surface of the substrate 5 in a thin film by a method such as vacuum deposition, sputtering, or coating. In order to transmit the light emitted from the light emitting layer 4 to the outside through the anode 1, the light transmittance of the anode 1 is preferably set to 70% or more. Further, the sheet resistance of the anode 1 is preferably several hundred Ω / □ or less, and particularly preferably 100 Ω / □ or less. Here, the film thickness of the anode 1 varies depending on the material in order to control the light transmittance, sheet resistance, and other characteristics of the anode 1 as described above, but is set to a range of 500 nm or less, preferably 10 to 200 nm. It is good.

Further, the cathode 2 is an electrode for injecting electrons into the light emitting layer 4, and it is preferable to use an electrode material made of a metal, an alloy, an electrically conductive compound and a mixture thereof having a small work function, and the work function is It is preferably 5 eV or less. Examples of the electrode material for the cathode 2 include alkali metals, alkali metal halides, alkali metal oxides, alkaline earth metals and the like, and alloys thereof with other metals such as sodium, sodium-potassium alloys, Examples include lithium, magnesium, a magnesium-silver mixture, a magnesium-indium mixture, an aluminum-lithium alloy, and an Al / LiF mixture. Aluminum, Al / Al ₂ O ₃ mixture, etc. can also be used. Further, an alkali metal oxide, an alkali metal halide, or a metal oxide may be used as the base of the cathode 2, and one or more conductive materials such as metals may be stacked and used. For example, an alkali metal / Al laminate, an alkali metal halide / alkaline earth metal / Al laminate, an alkali metal oxide / Al laminate, and the like can be given as examples. Moreover, it is good also as a structure which takes out light from the cathode 2 side using the transparent electrode represented by ITO, IZO, etc. FIG. The organic layer at the interface of the cathode 2 may be doped with an alkali metal such as lithium, sodium, cesium, or calcium, or an alkaline earth metal.

  Moreover, the said cathode 2 can be produced by forming these electrode materials in a thin film by methods, such as a vacuum evaporation method and sputtering method, for example. When light emitted from the light emitting layer 4 is extracted from the anode 1 side, the light transmittance of the cathode 2 is preferably 10% or less. On the other hand, when light is extracted from the cathode 2 side using the transparent electrode as the cathode 2 (including the case where light is extracted from both the anode 1 and the cathode 2), the light transmittance of the cathode 2 is set to 70% or more. It is preferable. In this case, the thickness of the cathode 2 varies depending on the material in order to control characteristics such as light transmittance of the cathode 2, but it is usually 500 nm or less, preferably 100 to 200 nm.

  Any element configuration of the organic electroluminescence element of the present invention can be used as long as it is not contrary to the gist of the present invention. For example, as described above, FIG. 1 omits the description of the hole injection layer, the hole transport layer, the electron transport layer, and the electron injection layer, but these layers can be provided as needed.

  The material used for the hole transport layer can be selected from, for example, a group of compounds having hole transport properties. Examples of this type of compound include 4,4′-bis [N- (naphthyl) -N-phenyl-amino] biphenyl (α-NPD), N, N′-bis (3-methylphenyl)-(1 , 1′-biphenyl) -4,4′-diamine (TPD), 2-TNATA, 4,4 ′, 4 ″ -tris (N- (3-methylphenyl) N-phenylamino) triphenylamine (MTDATA) 4,4′-N, N′-dicarbazole biphenyl (CBP), spiro-NPD, spiro-TPD, spiro-TAD, TNB, and the like, arylamine compounds, amine compounds containing a carbazole group, An amine compound containing a fluorene derivative can be exemplified, and any generally known hole transporting material can be used.

The material used for the electron transport layer can be selected from the group of compounds having electron transport properties. Examples of this type of compound include metal complexes known as electron transporting materials such as Alq ₃ and compounds having a heterocyclic ring such as phenanthroline derivatives, pyridine derivatives, tetrazine derivatives, oxadiazole derivatives, etc. Instead, any generally known electron transport material can be used.

  In the organic electroluminescence element of the present invention formed as described above, since the plurality of light emitting layers 4 are provided via the intermediate layer 3, the plurality of light emitting layers 4 are formed by the intermediate layer 3. It emits light in a state where it is electrically connected in series, and can emit light with high luminance.

  Next, the present invention will be specifically described with reference to examples.

Example 1
As an example, an organic electroluminescence element having the layer configuration shown in FIG. 1 and the pattern shown in FIG. 3 was produced.

First, a 0.7 mm thick glass substrate 5 on which an ITO film having a thickness of 110 nm, a width of 5 mm, and a sheet resistance of about 12 Ω / □ was formed as the anode 1 as shown in the pattern of FIG. 3 was prepared. The substrate 5 was subjected to ultrasonic cleaning with a detergent, ion-exchanged water, and acetone for 10 minutes each, then subjected to steam cleaning with IPA (isopropyl alcohol), dried, and further subjected to UV / O ₃ treatment.

Next, this substrate 5 is set in a vacuum deposition apparatus, and 4,4′-bis [N- (naphthyl) as a hole injection layer is formed on the anode 1 under a reduced pressure atmosphere of 1 × 10 ⁻⁴ Pa or less. A co-evaporated body (molar ratio 1: 1) of -N-phenyl-amino] biphenyl (α-NPD) and molybdenum oxide (MoO ₃ ) was deposited to a thickness of 30 nm. Next, α-NPD was vapor-deposited thereon with a thickness of 40 nm as a hole transport layer.

Next, a layer obtained by co-evaporating 7% by mass of rubrene on Alq ₃ was formed as a light emitting layer 4a on the hole transport layer with a thickness of 40 nm. Then, on the light-emitting layer 4a, to form a film with a thickness of 30nm to Alq ₃ alone as an electron transport layer, _Li 2 _MoO 4 ((Ltd.) Kojundo Chemical Laboratory, Ltd.) as an electron injection layer with a thickness of 3nm A film was formed.

Next, as an intermediate layer 3B, Mg was formed with a thickness of 1 nm by specific resistance heating vapor deposition. Subsequently, as the intermediate layer 3A, ITO, which is a conductor of 1 × 10 ⁵ Ωcm or less, was formed in a thickness of 3 nm by electron beam evaporation (vapor phase method) in an oxygen atmosphere. At that time, film formation was performed using an energy analyzer (manufactured by Pfeiffer: model number PPM442) while confirming that the kinetic energy of the particles in the atmosphere during film formation was 10 eV or less.

Subsequently, MoO ₃ which is a hole-injecting metal oxide was formed into a film having a thickness of 1 nm by resistance heating vapor deposition, and α-NPD was deposited in a thickness of 40 nm as a hole transport layer.

Then, on the hole transport layer to form a layer by depositing rubrene 7 wt% both in Alq ₃ as a light-emitting layer 4b with a thickness of 40 nm. Next, Alq ₃ was deposited as an electron transport layer alone on the light emitting layer 4b to form a film having a thickness of 30 nm. Subsequently, LiF was deposited with a thickness of 0.5 nm.

  Thereafter, aluminum serving as the cathode 2 was deposited at a deposition rate of 0.4 nm / s to a width of 5 mm and a thickness of 100 nm as shown in the pattern of FIG.

  Thus, the organic electroluminescent element which has the light emitting layer 4 as shown in FIG. 1 having a two-layer structure and the pattern shown in FIG. 3 was obtained. In FIG. 1, the hole injection layer, the hole transport layer, and the electron transport layer are not shown.

(Example 2)
The intermediate layer 3A was formed by depositing ITO, which is a conductor of 1 × 10 ⁵ Ωcm or less, to a thickness of 3 nm by ion beam sputtering. At that time, film formation was performed using an energy analyzer (manufactured by Pfeiffer: model number PPM442) while confirming that the kinetic energy of the particles in the atmosphere during film formation was 10 eV or less. Others were the same materials and methods as in Example 1 to obtain an organic electroluminescence element.

(Example 3)
The intermediate layer 3B was formed by depositing Li with a thickness of 1 nm. Others were the same materials and methods as in Example 1 to obtain an organic electroluminescence element.

Example 4
The intermediate layer 3A was formed as a 10 nm layer made of a mixture of ITO by electron beam evaporation and Na by heat evaporation (weight ratio 95: 5, specific resistance 9 × 10 ⁻³ Ωcm). At that time, film formation was performed using an energy analyzer (manufactured by Pfeiffer: model number PPM442) while confirming that the kinetic energy of the particles in the atmosphere during film formation was 10 eV or less. Others were the same materials and methods as in Example 1 to obtain an organic electroluminescence element.

(Conventional example 1)
As Conventional Example 1, an organic electroluminescent element having a single light emitting layer 4 was produced.

First, on the anode 1 of the glass substrate 5 provided with the same ITO film (anode 1) as in Example 1, as a hole injection layer, α-NPD and MoO ₃ co-evaporated body (molar ratio 1: 1). ) Was vapor-deposited with a film thickness of 30 nm, and α-NPD was vapor-deposited with a film thickness of 40 nm thereon as a hole transport layer.

Next, on the hole transport layer, a layer in which 7% by mass of rubrene was co-evaporated on Alq ₃ as a light emitting layer 4 was formed to a thickness of 40 nm.

Next, an Alq ₃ film having a thickness of 30 nm alone was formed thereon as an electron transport layer, and subsequently, LiF was formed to a thickness of 0.5 nm.

  Thereafter, aluminum serving as the cathode 2 was vapor-deposited at a deposition rate of 0.4 nm / s to a width of 5 mm and a thickness of 100 nm, thereby obtaining an organic electroluminescence element having a single-layer structure of the light-emitting layer 4.

(Comparative Example 1)
The intermediate layer 3A was formed by depositing ITO, which is a conductor of 1 × 10 ⁵ Ωcm or less, to a thickness of 20 nm by magnetron sputtering (sputtering using plasma). There were many particles having an energy value exceeding 10 eV in the magnetron sputtering method. Others were the same materials and methods as in Example 1 to obtain an organic electroluminescence element.

(Comparative Example 2)
Without providing the intermediate layer 3B, the intermediate layer 3A was formed by depositing Au, which is a conductor of 1 × 10 ⁵ Ωcm or less, to a thickness of 2 nm by vapor deposition. Others were the same materials and methods as in Example 1 to obtain an organic electroluminescence element.

(Comparative Example 3)
The intermediate layer 3A was formed by depositing SiO (estimated 1 × 10 ¹⁰ Ωcm) having a high specific resistance to a thickness of 10 nm by vapor deposition. Others were the same materials and methods as in Example 1 to obtain an organic electroluminescence element.

(Comparative Example 4)
On the layer of Alq ₃ (30 nm) provided as the electron transport layer, the intermediate layer 3B was formed with a thickness of 2 nm from an electron injecting metal oxide made of Li ₂ O, and the intermediate layer 3A was not provided. Others were the same materials and methods as in Example 1 to obtain an organic electroluminescence element.

(Comparative Example 5)
On the Alq ₃ (30 nm) layer provided as the electron transport layer, the intermediate layer 3A is not provided with the intermediate layer 3B, and the intermediate layer 3A is made of ITO and Al, which are conductors of 1 × 10 ⁵ Ωcm or less, in a weight ratio of 9: 1 was co-evaporated to form a film having a thickness of 10 nm. Others were the same materials and methods as in Example 1 to obtain an organic electroluminescence element.

(Evaluation)
A current of 15 mA / cm ² was passed through the organic electroluminescence elements obtained in each of the examples, conventional examples, and comparative examples, and the voltage and luminance at that time were measured. At this time, the maximum voltage was 20V. The results are shown in Table 1.

  As can be seen in Table 1, the organic electroluminescence elements of the respective examples are approximately twice as large as the conventional example 1 in which the light emitting luminance and the driving voltage are provided, and the presence of the intermediate layer 3. It was confirmed that the electrical connection between the two organic light emitting layers 4a and 4b was satisfactorily performed.

On the other hand, in Comparative Example 1, a layer made of ITO, which is a conductor of 1 × 10 ⁵ Ωcm or less, was formed by sputtering using plasma, so that damage to the organic film interface of the underlying film was caused by damage from the plasma. It can be seen that the drive voltage increases and the light emission efficiency decreases.

In Comparative Example 2, only a current of about 10 mA / cm ² flowed even at 20 V, and no light emission was obtained. In Comparative Example 3, almost no current flowed even at 20V. In Comparative Example 2, the hole injection barrier from the intermediate layer is large, and in Comparative Example 3, the conductivity of the intermediate layer is low. Therefore, it is considered that sufficient current does not flow even when a high voltage is applied.

  In Comparative Examples 4 and 5, almost no current flowed even at 20V. Since Comparative Example 4 does not include a conductive layer, Comparative Example 5 does not have an electron injecting layer, and thus it is considered that no current flows.

It is a schematic sectional drawing which shows the layer structure in an example of embodiment of this invention. It is a schematic sectional drawing which shows the layer structure in another example of embodiment of this invention. 2 is a plan view showing an outline of a pattern of an organic electroluminescence element produced in Example 1. FIG. It is a schematic sectional drawing which shows the layer structure in a prior art.

Explanation of symbols

1 Anode 2 Cathode 3, 3A, 3B Intermediate layer 4, 4a, 4b Light emitting layer 5 Substrate

Claims (3)

A method for manufacturing an organic electroluminescent element comprising a plurality of light-emitting layers formed between an anode and a cathode via an intermediate layer, wherein the intermediate layer comprises a conductor having a energy of 1 × 10 ⁵ Ωcm or less at an energy of 10 eV or less. Forming a layer formed by a vapor phase method adjacent to a layer containing at least one of alkali metal, alkaline earth metal, alkali metal oxide, and alkaline earth metal oxide. A method for producing an organic electroluminescent element, comprising: The layer for forming a conductor of 1 × 10 ⁵ Ωcm or less by a vapor phase method with an energy of 10 eV or less is formed by an electron beam evaporation method, an ion plating method, or a sputtering method without using plasma. 2. A method for producing an organic electroluminescent element according to 1. 3. The method for producing an organic electroluminescent element according to claim 1, wherein a layer for forming a conductor having a density of 1 × 10 ⁵ Ωcm or less by a gas phase method with an energy of 10 eV or less is formed in the presence of oxygen. .

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