JP2010033973A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent element in which light emission is possible at high luminance and high efficiency, in which the occurrence of faults such as increase of driving voltage, the occurrence of an undesirable voltage rise and a short circuit or the like are suppressed, and which has superior productivity. <P>SOLUTION: In the organic electroluminescent element A, between an anode 1 and a cathode 2, a plurality of light-emitting layers 4 equipped with organic light-emitting layers are laminated via an intermediate layer 3. The intermediate layer 3 is constituted of a first layer 3a including a conductive body of which specific resistance at 23°C is 1×10<SP>5</SP>Ωcm or less, a second layer 3b composed of a metal compound film-formed by a gas phase method of film-forming energy of 10 eV or less, and a third layer 3c containing at least one of alkaline metal, alkaline-earth metal, and these oxides. Then, the first layer 3a, the second layer 3b, and the third layer 3c are laminated in this order from the cathode 2 side. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an organic electroluminescence element used for an illumination light source, a backlight for a liquid crystal display, a flat panel display, and the like. Specifically, the present invention relates to an organic electroluminescence element that includes a plurality of organic light emitting layers and emits light with high brightness and high efficiency. .

  As an example of an organic light-emitting device called an organic electroluminescence device, a transparent electrode (anode 1), a hole transport layer, an organic light-emitting layer (organic organic light-emitting layer), an electron injection layer, and an electrode (cathode 2) are provided on one surface of a transparent substrate. Are formed by sequentially laminating. When a voltage is applied between the anode 1 and the cathode 2 of the organic electroluminescence element A, electrons injected into the organic light emitting layer through the electron injection layer and injected into the organic light emitting layer through the hole transport layer. The holes recombine in the organic light emitting layer to emit light, and this light is emitted to the outside through the transparent electrode and the transparent substrate.

  The organic electroluminescence element A has features such as self-emission, relatively high-efficiency emission characteristics, and capable of emitting light in various colors, and emits light from a display device such as a flat panel display. It is expected to be used as a body or as a light source, for example, a backlight for a liquid crystal display or illumination, and a part thereof has already been put into practical use.

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

  In order to solve this problem, in recent years, an organic light emitting device having a plurality of organic light emitting layers between the anode 1 and the cathode 2 and electrically connecting each organic light emitting layer has been proposed (for example, Patent Document 1). 5).

  FIG. 3 shows an example of the structure of such an organic electroluminescence element A. In the illustrated example, a plurality of light emitting layers 4a and 4b including an organic light emitting layer are provided between an anode 1 and a cathode 2 provided on one surface of a transparent substrate 5, and between adjacent light emitting layers 4a and 4b. The intermediate layer 3 is interposed between the two. The anode 1 is formed as a light transmissive electrode, and the cathode 2 is formed as a light reflective electrode. In FIG. 3, the electron injection layer and the hole transport layer provided on both sides of the organic light emitting layer in the light emitting layers 4a and 4b are not shown.

  In this example, the plurality of light emitting layers 4 a and 4 b are electrically connected via the intermediate layer 3, so that the light emitting layers a and 4 b are connected in series, and a voltage is applied between the anode 1 and the cathode 2. When applied, the organic light emitting layers in the light emitting layers 4a and 4b emit light simultaneously. For this reason, from the organic electroluminescent element A, the light which the light from the organic light emitting layer in each light emitting layer 4a, 4b adds is radiate | emitted, and the light-emission brightness with respect to the amount of electricity supply improves rather than the conventional organic electroluminescent element A To do. This avoids the brightness-lifetime tradeoff in the organic electroluminescent element A as described above.

Commonly known configurations of the intermediate layer 3 include, 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. (":" Represents a mixture of two materials, and "/" represents a stack of preceding and following compositions).

  However, if the intermediate layer 3 for partitioning a plurality of organic light emitting layers is provided as in the above prior art, an increase in driving voltage and an undesirable increase in voltage may occur.

Moreover, in the organic electroluminescent element which has an intermediate | middle layer, there also exists a problem of the damage generate | occur | produced in the interface of an intermediate | middle layer and the light emitting layer adjacent to this intermediate | middle layer. That is, when high energy particles collide with the surface of the light emitting layer by sputtering or the like when forming the intermediate layer, the particles penetrate into the organic layer, the organic material is decomposed and the layer structure of the light emitting layer is destroyed, Side reactions between organic materials and particles may occur, resulting in an increase in current injection barrier at the interface between the intermediate layer and the light emitting layer, resulting in an increase in driving voltage, a decrease in device lifetime, and emission characteristics. Or drop.
Japanese Patent Laid-Open No. 11-329748 JP 2003-272860 A JP 2005-135600 A JP 2006-332048 A JP 2006-173550 A

  The present invention has been made in view of the above points, and can emit light with high luminance and high efficiency, and can suppress an increase in driving voltage and an undesirable voltage increase, and also extend the lifetime of the element. An object of the present invention is to provide an organic electroluminescence device that can have a long lifetime.

In the organic electroluminescent element A according to the present invention, a plurality of light emitting layers 4 each including an organic light emitting layer are laminated via an intermediate layer 3 between an anode 1 and a cathode 2. The intermediate layer 3 includes a first layer 3a containing a conductor having a specific resistance of 1 × 10 ⁵ Ωcm or less at 23 ° C. and a metal compound formed by a vapor phase method having a film formation energy of 10 eV or less. The first layer 3a and the second layer 3b are composed of a two-layer 3b and an alkali metal, an alkaline earth metal, and a third layer 3c containing at least one of these oxides. And the 3rd layer 3c is laminated | stacked.

  According to the present invention, the first layer 3a having a small specific resistance constituting the intermediate layer 3 functions as a charge separation layer and the third layer 3c functions as an electron injection layer, so that light emission from the intermediate layer 3 on both sides thereof can be achieved. Good charge transfer to the layer 4 can be ensured. Further, when the intermediate layer 3 is formed, the second layer 3b formed with low energy can be provided by being stacked on the third layer 3c. When the second layer 3b is formed, the light emitting layer 4 serving as a base is the first layer 3b. It is protected by the three layers 3c and damage to the base is suppressed, and further, the first layer 3a can be provided by being laminated on the second layer 3b. Damage to the layer 3c is protected by the second layer 3b, and damage to the base is suppressed. For this reason, when the intermediate layer 3 is formed, damage to the intermediate layer and the light emitting layer adjacent to the intermediate layer is suppressed, and charge transfer from the intermediate layer 3 and from the intermediate layer 3 to the light emitting layer 4 is favorably maintained. .

  The second layer 3b preferably contains a molybdenum compound. In this case, the film formation energy required when the second layer 3b is formed is further reduced, and damage to the base during the formation of the second layer 3b is further suppressed, and film formation damage during the formation of the first layer 3a is further suppressed. Is further suppressed, and the charge transport property at the interface between the layers is further maintained.

  The second layer 3b preferably contains a titanium compound. In this case, the titanium compound having a large energy gap makes the second layer 3b optically excellent, and the second layer 3b becomes a dense film, which causes film formation damage when the first layer 3a is formed. Further, the charge transfer in the intermediate layer 3 and from the intermediate layer 3 to the light emitting layer 4 is further maintained.

  The second layer 3b preferably contains a boron compound. In this case, the film formation energy required when the second layer 3b is formed is further reduced, and damage to the base during the formation of the second layer 3b is further suppressed, and film formation damage during the formation of the first layer 3a is further suppressed. Is further suppressed, and the charge transfer in the intermediate layer 3 and from the intermediate layer 3 to the light emitting layer 4 is maintained at a higher level.

  According to the present invention, it is possible to emit light with high brightness and high efficiency, and it is possible to suppress an increase in driving voltage and an undesirable voltage increase and to extend the lifetime of the element.

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

  An example of the structure of the organic electroluminescence element A is shown in FIG. In the illustrated example, a light emitting layer 4 and an intermediate layer 3 including an organic light emitting layer are interposed between an electrode to be the anode 1 and an electrode to be the cathode 2. As the light-emitting layer 4, a plurality of light-emitting layers 4a and 4b are stacked in the electrode stacking direction, and the intermediate layer 3 is interposed between the light-emitting layers 4a and 4b adjacent to each other. Furthermore, one electrode (anode 1) 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 the present embodiment, the two light emitting layers 4 a and 4 b are provided as the light emitting layer 4, but a larger number of light emitting layers 4 may be laminated via the intermediate layer 3. The number of stacked light emitting layers 4 is not particularly limited. However, the increase in the number of layers increases the difficulty of designing optical and electrical elements. As in the general organic electroluminescence device A, the light emitting layers 4a and 4b include a hole injection layer, a hole transport layer, an electron transport layer, an electron injection layer, etc. between the organic light emitting layer and the anode 1 or the cathode 2. These layers may be provided, but these layers are not shown in FIG.

The intermediate layer 3 includes a first layer 3a containing a conductor having a specific resistance at 23 ° C. of 1 × 10 ⁵ Ωcm or less, a second layer 3b made of a metal compound formed with low energy, and an alkali metal or alkali The third layer 3c containing an earth metal and at least one of these oxides has a structure in which the cathode 2 is sequentially laminated in this order.

The conductor having a specific resistance of 1 × 10 ⁵ Ωcm or less constituting the first layer 3a is not particularly limited as long as it is a material generally known as a conductive material. For example, a metal, a metal oxide, an electrically conductive compound, etc. Selected. Specific examples of this conductor include metals such as Al, Cu, Ni, Ag, Au, and Ti, metal compounds such as CuI, ZnSe, ZnS, and CuSe, ITO (indium-tin oxide), SnO ₂ , ZnO, Examples thereof include metal oxides such as IZO (indium-zinc oxide), carbon compounds such as carbon nanotubes and fullerenes. Moreover, the conductor which comprises the 1st layer 3a is not limited to 1 type. For example, the first layer 3a may be composed of a plurality of metals selected from any one of the above metals such as indium and tin, indium and zinc, aluminum and gallium, gallium and zinc, titanium and niobium, or the like. Or a mixture of two or more conductors selected from metal oxides, metal oxides, metal compounds, and other conductors. The oxidation number of the metal in the conductor constituting the first layer 3a, the mixing ratio of the plurality of conductors, etc. are appropriately set so that the film quality, thermal stability and electrical characteristics of the first layer 3a are good. Is set.

The thickness of the first layer 3a is preferably 10 nm or less, more preferably 5 nm or less. By forming the first layer 3a as a thin film in this manner, the lateral direction of the first layer 3a (the direction orthogonal to the stacking direction of the organic electroluminescence element A), although the specific resistance of the first layer 3a is small. ) Is reduced to a negligible level, and light emission in a region other than the intended light-emitting region is suppressed. In particular, the value obtained by dividing the thickness (nm) of the first layer 3a by the specific resistance (Ωcm) of the first layer 3a is preferably 10 ⁴ (nm / Ωcm) or less.

The first layer 3a may contain a metal or a compound thereof as an additive in addition to the conductor having a specific resistance of 1 × 10 ⁵ Ωcm or less. The specific resistance of the additive is not particularly limited. The metal is preferably at least one selected from tungsten, molybdenum, rhenium, vanadium, ruthenium, and aluminum. By containing these metals or compounds thereof in the first layer 3a, the charge injection property of the first layer 3a is improved, and the carrier injection property of the intermediate layer 3 is further improved. The content of the metal or the compound thereof in the first layer 3a is not particularly limited as long as the specific resistance of the first layer 3a does not depart from the spirit of the present invention, but is usually in the range of 0.1 to 20% by weight. Is preferred.

The first layer 3a may further contain an organic compound, a nonconductive inorganic insulator, or the like. The inorganic insulator is not particularly limited as long as it can be mixed with a conductor constituting the first layer 3a and formed into a film. For example, a metal fluoride such as lithium fluoride or magnesium fluoride; Metal halides such as metal chlorides typified by magnesium chloride; aluminum, cobalt, zirconium, titanium, vanadium, niobium, chromium, tantalum, tungsten, manganese, molybdenum, ruthenium, iron, nickel, copper, gallium, zinc, etc. And various metal oxides, nitrides, carbides, oxynitrides, etc. (excluding those corresponding to the conductor having a specific resistance of 1 × 10 ⁵ Ωcm or less). Specific examples of the inorganic insulator include, for example, Al ₂ O ₃ , MgO, iron oxide, AlN, SiN, SiC, SiON, BN, SiO ₂ , SiO, etc. It is used by appropriately selecting from carbon compounds and the like.

These insulators are preferably selected from those having low absorption in the visible light region or having a low refractive index. In this case, the light absorption rate and the refractive index of the first layer 3a are reduced, and as a result, Reflection and absorption inside the device are reduced. For this reason, the loss when the light generated in the light emitting layer 4 is emitted to the outside is 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 mixing ratio of the conductive metal oxide and other substances in the layer is arbitrarily set as long as the specific resistance of the first layer 3a is in the range of 1 × 10 ⁵ Ωcm or less.

  The second layer 3b is formed by a vapor phase method with a film formation energy of 10 eV or less. The film formation energy is derived by analyzing the kinetic energy of gas molecules in the atmosphere during film formation using an energy analyzer such as model number PPM442 manufactured by Pfeiffer. When molecules other than the film forming material such as argon and oxygen coexist in the atmosphere during film formation such as sputtering, the energy of the molecule having the highest energy among the various molecules in the atmosphere is set. Deposition energy is assumed. Examples of the vapor phase method with a film formation energy of 10 eV or less include resistance heating evaporation, EB evaporation, laser heating evaporation, and sputtering using a counter target.

Examples of the metal compound constituting the second layer 3b include Li ₂ MoO ₄ , Na ₂ MoO ₄ , MoO ₃ , TiO ₂ , LiBO ₂ , Li ₂ B ₄ O ₇ , B ₂ O ₃ , LiAlO ₂ , LiNBO ₃ , ZnSe. , ZnS, ZnTe, Bi ₂ Se ₃ , Li ₂ GeO ₃ , LiTaO ₃ , LiSiO _3, etc., compounds showing semiconductivity, compounds containing alkali metals, alkaline earth metals or rare earth metals and other metals It is selected as appropriate. In particular, the metal compound is preferably a metal compound of any one of Mo, Ti, and B. When the metal compound is a Mo compound or a B compound, the second layer 3b can be formed with lower film formation energy, and the second layer 3b can form the first layer 3a. The effect of suppressing damage at the time is further improved. On the other hand, when the metal compound is a Ti compound, the energy gap of the metal compound is increased, so that the second layer 3b becomes an optically superior layer, and the second layer 3b becomes a dense film. As a result, the effect of suppressing damage during film formation of the first layer 3a is further improved, and the charge transport property at the interface can be kept high.

  The thickness of the second layer 3b is preferably in the range of 1 nm to 100 nm, more preferably in the range of 1 nm to 50 nm. If the thickness of the second layer 3b is too thin, there is a possibility that actions such as damage reduction at the time of forming the first layer 3a may not be sufficiently exhibited. If the thickness is too thick, the driving voltage may not be sufficiently reduced. .

  The third layer 3c contains at least one of alkali metals, alkaline earth metals, and oxides thereof. Specifically, for example, the third layer 3c contains a metal such as lithium, cesium, sodium, strontium, magnesium, calcium, yttrium, and samarium, and an oxide of these metals. The said metal and oxide are used individually by 1 type, or 2 or more types are used together. The oxidation number of the metal in the oxide constituting the third layer 3c, the mixing ratio of plural kinds of metals and oxides, etc., so that the film quality, thermal stability and electrical characteristics of the third layer 3c are good. Is set as appropriate.

  Although the thickness of the 3rd layer 3c is set suitably, when the 3rd layer 3c is comprised with a metal, it is preferable that the said thickness is the range of 0.1-5 nm, and the 3rd layer 3c is a metal oxide. In the case where the thickness is comprised, the thickness is preferably in the range of 0.5 nm to 20 nm.

The third layer 3c may contain an organic compound or an inorganic substance other than the metal and oxide. For example, the third layer 3c contains a metal such as Al, Cu, Ni, Ag, Au, or Ti, a metal halide such as LiF, Li ₂ O, NaF, CsF, SiO ₂ , or SiO, or a metal oxide. May be. As described above, the third layer 3c contains two or more kinds of components, so that the stability of a component that is not stable by itself is improved, or the properties such as film quality and adhesion to an adjacent layer are obtained by a single component. The above-described characteristics can be improved when the film becomes worse, or the film forming property can be improved.

  In producing the organic electroluminescent element A, after forming an electrode (anode 1) on a substrate, a light emitting layer 4 is formed, and a predetermined number of intermediate layers 3 and light emitting layers are stacked, An electrode (cathode 2) is formed on the upper stage. Each electrode and the light emitting layer are formed by an appropriate method such as a coating method or a vapor deposition method which has been conventionally performed for producing the organic electroluminescence element A.

  When the intermediate layer 3 is formed, the third layer 3c, the second layer 3b, and the first layer 3a are sequentially stacked on the light emitting layer.

  Although the method for forming the third layer 3c is not limited, an evaporation method is particularly preferably employed. As a vapor deposition source, a crucible containing a metal, a cell or boat, a vapor deposition source generally known as an alkali metal dispenser, or the like is used.

  The second layer 3b is formed by a vapor phase method having a film formation energy of 10 eV or less as described above. When the second layer 3b is formed in this manner, the light emitting layer 4 as the base is protected by the third layer 3c when the second layer 3b is formed, and the film formation energy during the film formation of the second layer 3b is low. For this reason, damage to the light emitting layer 4 that is the base during the formation of the second layer 3b is suppressed.

  Further, the first layer 3a is formed, for example, by forming a conductor constituting the first layer 3a into a thin film by an appropriate method such as vacuum deposition, sputtering, or coating. When the first layer 3a is formed in this way, the underlying light emitting layer 4 is protected by the third layer 3c and the second layer 3b, and damage to the underlying light emitting layer 4 during the formation of the first layer 3a. Is suppressed.

  In the intermediate layer 3 formed in this way, the first layer 3a having a small specific resistance functions as a charge separation layer and the third layer 3c functions as an electron injection layer. Good charge transfer to 4 can be ensured. In particular, since damage to the underlayer is suppressed when the intermediate layer 3 is formed as described above, the first layer having a low specific resistance is maintained in the intermediate layer 3 while maintaining good electron transport properties and electron injection properties in the intermediate layer 3. Since 3a is included, the electrical resistance of the intermediate layer 3 is reduced.

  A configuration other than the intermediate layer 3 in the organic electroluminescence element A will be described.

  The light emitting layer disposed on the cathode side with respect to the first layer 3a may be provided with a hole injection layer containing a hole injecting metal oxide adjacent to the intermediate layer. Examples of the hole-injecting metal oxide include metal oxides containing any of molybdenum, rhenium, tungsten, vanadium, zinc, indium, tin, gallium, titanium, and aluminum. In addition, the metal oxide is not limited to a single oxide, for example, binary oxide containing any of the above metals such as indium and molybdenum, vanadium and zinc, aluminum and gallium, gallium and zinc, titanium and niobium, and the like. Or higher multi-element oxides. The oxidation number of the metal in this layer, the mixing ratio of a plurality of metals, and the like are appropriately set so that the film quality, thermal stability, and electrical characteristics of this layer are good.

  The hole injection layer may be made of a conductor (metal oxide) that can form the first layer 3a as long as the layer exhibits hole injection properties.

  The thickness of the hole injection layer is not particularly limited, but is preferably in the range of 1 nm to 20 nm.

  The light emitting layer disposed on the cathode side with respect to the first layer 3a may be provided with a hole injection layer containing a hole injection charge transfer complex adjacent to the intermediate layer. This hole injection layer is composed of, for example, a system in which an organic material such as a hole transporting material or a material from which electrons are easily extracted and a material that accepts electrons from the organic material are added.

  As the hole transporting material, generally used triarylamine derivatives such as α-NPD (4,4′-bis [N- (naphthyl) -N-phenyl-amino] biphenyl), TPD (N, N′-bis) are used. (3-methylphenyl)-(1,1′-biphenyl) -4,4′-diamine), 2-TNATA (4 ′, 4 ″ -tris [N, N- (2-naphthyl) phenylamino] triphenyl) In addition, examples of materials that easily extract electrons include aromatic derivatives such as biphenyl derivatives, anthracene derivatives, and naphthalene derivatives, aniline derivatives, and thiophene derivatives.

Examples of the material that accepts electrons from the organic material include metals, metal oxide semiconductors, inorganic acceptors, and organic acceptors. Examples of the metal include a metal having a high work function, for example, gold having a work function of 5 eV or more, and metals such as vanadium, molybdenum, rhenium, tungsten, and nickel. The metal oxide is not particularly limited, but for example, metal oxides of vanadium, molybdenum, rhenium, tungsten, nickel, zinc, tin, and niobium are preferable. Examples of the inorganic acceptor include iron chloride, iron bromide, copper iodide, bromine and iodine. Examples of the organic acceptor include fluorine-containing organic compounds and cyano group-containing organic compounds. Specifically, for example, F ₄ -TCNQ (tetrafluorotetracyanoquinodimethane), DDQ (dichlorodicyanoquinone), CF ₃ TCNQ (Trifluoromethyltetracyanoquinodimethane), 2-TCNQ, or derivatives thereof are exemplified, but derivatives containing a larger number of fluorine, cyano groups and the like in the molecule are also preferably used.

  The mixing ratio of the material that accepts electrons from the organic material to the organic material is appropriately set according to the type of the material, but is preferably in the range of 0.1 mol% to 80 mol%, more preferably 1 mol% to 50 mol%. Range.

  The thickness of the hole injection layer is not particularly limited, but is preferably in the range of 1 nm to 20 nm.

In addition, the hole injection layer containing the hole injection charge transfer complex is composed of other organic compounds and inorganic substances other than the components constituting the charge transfer complex, such as metals such as Al, Cu, Ni, Ag, Au, and Ti. , LiF, Li ₂ O, NaF, CsF, SiO ₂ , SiO ₂ , or other metal halides or metal oxides may be contained. By containing two or more components in this way, the stability of components that are not stable by themselves is improved, or the properties such as film quality and adhesion to adjacent layers are deteriorated by a single component. The characteristics can be improved, and the film formability can be improved.

  Moreover, as a material which comprises the organic light emitting layer in the light emitting layers 4a and 4b, the arbitrary materials known as a material for the organic electroluminescent elements A can be used. Examples of such materials include, but are not limited to, anthracene, naphthalene, pyrene, tetracene, coronene, perylene, phthaloperylene, naphthaloperylene, diphenylbutadiene, tetraphenylbutadiene, coumarin, oxadiazole, bisbenzoxazoline, bisstyryl, cyclohexane Pentadiene, quinoline metal complex, tris (8-hydroxyquinolinato) aluminum complex, tris (4-methyl-8-quinolinato) aluminum complex, tris (5-phenyl-8-quinolinato) aluminum complex, aminoquinoline metal complex, benzo Quinoline metal complex, tri- (p-terphenyl-4-yl) amine, 1-aryl-2,5-di (2-thienyl) pyrrole derivative, pyran, quinacridone, rubrene, distyrylbenzene Conductor, distyryl arylene derivatives, distyrylamine derivatives, and various fluorescent pigments, etc., and derivatives thereof. A plurality of materials selected from the above materials may be used in combination. In addition to a material that emits fluorescence such as the above materials, a material system that emits light from a spin multiplet, for example, a phosphorescent material that emits phosphorescence, and a portion made of the material are included in a part of the molecule. Compounds and the like are also preferably used. The organic layer made of these materials is formed by a dry process such as vapor deposition or transfer, or by a wet process such as spin coating, spray coating, die coating, or gravure printing.

  Further, as other members constituting the organic electroluminescence element A, that is, the substrate 5, the anode 1, the cathode 2, and the like holding the stacked elements, the conventional structure can be applied as it is.

  That is, the substrate 5 needs to have light transmittance when light is emitted from the organic electroluminescence element A through the substrate 5. Such a light-transmitting substrate may be slightly colored in addition to being colorless and transparent, or may be in the form of frosted glass. As such a substrate, for example, a transparent glass plate such as soda lime glass or alkali-free glass, a resin such as polyester, polyolefin, polyamide, epoxy, or a plastic film or plastic produced by an arbitrary method from a fluorine resin, etc. A board etc. are mentioned. In addition, the substrate 5 may contain particles, powder, bubbles, etc. having a refractive index different from that of the base material constituting the substrate 5, and the surface is processed into an appropriate shape to provide a light diffusion effect. May be.

  Further, in the case where light is emitted from the organic electroluminescence element A without passing through the substrate 5, the substrate 5 does not necessarily need to have a light transmission property, as long as the light emission characteristics, life characteristics, etc. of the element are not impaired. Made of material. In particular, it is preferable to use the substrate 5 having high thermal conductivity 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 organic light emitting layer in the light emitting layer 4, and is formed of an electrode material made of a metal, an alloy, an electrically conductive compound, or a mixture thereof having a high work function. In particular, it is preferably formed of a material having a work function of 4 eV or more. Examples of the material of the anode 1 include metals such as gold; conductive metal oxides such as CuI, ITO (indium-tin oxide), SnO ₂ , ZnO, and IZO (indium-zinc oxide); PEDOT And conductive polymers such as polyaniline; conductive polymers doped with an arbitrary acceptor; and conductive light-transmitting materials such as carbon nanotubes. The anode 1 is formed, for example, by forming the electrode material as described above into a thin film on the surface of the substrate 5 by a method such as vacuum deposition, sputtering, or coating. In addition, when light emitted from the light emitting layer 4 is extracted through the anode 1, the light transmittance of the anode 1 is preferably 70% or more. The sheet resistance of the anode 1 is preferably several hundred Ω / □ or less, and particularly preferably 100 Ω / □ or less. The film thickness of the anode 1 is appropriately set according to the material constituting the anode 1 so that the characteristics such as light transmittance and sheet resistance of the anode 1 are as desired, but preferably 500 nm or less. Preferably, it is set in the range of 10 to 200 nm.

The cathode 2 is an electrode for injecting electrons into the organic light emitting layer in the light emitting layer 4, and is formed of an electrode material made of a metal, an alloy, an electrically conductive compound, or a mixture thereof having a low work function. It is particularly preferable that the material is formed of a material having a work function of 5 eV or less. Examples of the electrode material of 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 and sodium-potassium alloys. , Lithium, magnesium, magnesium-silver mixture, magnesium-indium mixture, aluminum-lithium alloy, Al / LiF mixture, and the like. Aluminum, Al / Al ₂ O ₃ mixture, etc. can also be used as the electrode material of the cathode 2. Alternatively, the cathode 2 may be formed by forming a base with an alkali metal oxide, an alkali metal halide, or a metal oxide, and laminating one or more conductive materials such as metal on the base. . Examples of such a laminated structure of the base and the cathode 2 include an alkali metal / Al laminated structure, an alkali metal halide / alkaline earth metal / Al laminated structure, and an alkali metal oxide / Al laminated structure. Etc. Alternatively, the cathode 2 may be formed of a transparent electrode material typified by ITO, IZO, etc., and light emitted from the organic electroluminescence element A may be extracted from the cathode 2 side. Further, an interface portion with the cathode 2 in the organic layer in contact with the cathode 2 may be doped with an alkali metal or alkaline earth metal such as lithium, sodium, cesium, or calcium. The cathode 2 is formed, for example, by forming an electrode material constituting the cathode 2 on a thin film by a method such as a vacuum evaporation method or a sputtering method. In addition, when light emitted from the light emitting layer 4 is extracted through the anode 1, the light transmittance of the cathode 2 is preferably 10% or less. Conversely, when light emitted from the light emitting layer 4 is extracted through the cathode 2 (including the case where light is extracted through both the anode 1 and the cathode 2), the light transmittance of the cathode 2 is 70. % Or more is preferable. The film thickness of the cathode 2 is appropriately set according to the material constituting the cathode 2 so that the characteristics such as light transmittance of the cathode 2 become a desired level, preferably 500 nm or less, more preferably 100 to 100 nm. It is set in the range of 200 nm.

  The element structure of the organic electroluminescence element A according to the present invention is not limited to the above-described form, and any structure can be adopted as long as it is not contrary to the gist of the present invention. For example, in FIG. 1, the hole injection layer, the hole transport layer, the electron transport layer, and the electron injection layer in the light emitting layer 4 are omitted, but these configurations may be appropriately provided as necessary.

  The material constituting the hole transport layer is appropriately selected from, for example, a group of compounds having hole transport properties. Examples of this type of compound include arylamine compounds, amine compounds containing a carbazole group, amine compounds containing a fluorene derivative, and typical examples of these compounds include α-NPD (4,4′-bis [ N- (naphthyl) -N-phenyl-amino] biphenyl), TPD (N, N′-bis (3-methylphenyl)-(1,1′-biphenyl) -4,4′-diamine), 2-TNATA (4 ′, 4 ″ -tris [N, N- (2-naphthyl) phenylamino] triphenylamine), 4,4 ′, MTDATA (4 ″ -tris (N- (3-methylphenyl) N-phenylamino) ) Triphenylamine), CBP (4,4′-N, N′-dicarbazolebiphenyl), spiro-NPD, spiro-TPD, spiro-TAD, TNB, and the like. That. Moreover, not only the said material but the arbitrary generally known hole transport material may be used.

Moreover, the material which comprises an electron carrying layer is suitably selected, for example from the group of compounds which have electron transport property. Examples of this type of compound include metal complexes known as electron transporting materials such as Alq ₃ (tris (quinolin-8-yloxy) aluminum), and heterocycles such as phenanthroline derivatives, pyridine derivatives, tetrazine derivatives, and oxadiazole derivatives. However, the present invention is not limited to this, and any generally known electron transporting material can be used.

  In the organic electroluminescent element A configured as described above, since the plurality of light emitting layers 4 are laminated, high luminance light emission is possible.

  Next, the present invention will be specifically described with reference to examples. The film formation energy in each example and comparative example is a value derived by analyzing the kinetic energy of gas molecules in the atmosphere during film formation using model number PPM422 manufactured by Pfeiffer.

Example 1
A glass substrate 5 having a thickness of 0.7 mm, on which an ITO film (anode 1) having a thickness of 150 nm, a width of 5 mm, and a sheet resistance of about 10Ω / □ was formed as shown in the pattern of FIG. The substrate 5 was subjected to ultrasonic cleaning with a detergent, ion-exchanged water, and acetone for 10 minutes each, then subjected to vapor cleaning with IPA (isopropyl alcohol), dried, and further subjected to UV / O ₃ treatment.

Next, this substrate 5 was set in a vacuum deposition apparatus, and 4,4′-bis [N- (naphthyl)-as a hole injection layer 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, on the hole transport layer, a layer obtained by co-evaporating 3% by mass of quinacridone on Alq ₃ as an organic light emitting layer was formed with a thickness of 30 nm. Next, Alq ₃ alone as an electron transport layer is formed on the organic light emitting layer to a thickness of 35 nm, and subsequently, an alloy film having a molar ratio of Al to Li of 1: 1 is formed as an electron injection layer to a thickness of 3 nm. Filmed. Thereby, the light emitting layer 4a was formed.

Next, Li ₂ O is deposited by resistance heating vapor deposition to form a third layer 3c having a thickness of 5 nm, and then MoO ₃ is deposited by resistance heating vapor deposition (deposition energy 0.001 eV) to form a second layer having a thickness of 10 nm. The layer 3b is formed, and subsequently ITO, which is a conductor having a specific resistance of 1 × 10 ⁵ Ωcm or less, is formed by sputtering to form the first layer 3a having a thickness of 5 nm. The intermediate layer 3 composed of the layer 3b and the third layer 3c was formed.

Next, α-NPD and MoO ₃ are co-deposited (molar ratio 1: 1) on the intermediate layer 3 to form a 20 nm-thick hole injection layer, and then α-NPD is deposited to a thickness of 30 nm. A hole transport layer is formed, and then Alq ₃ and quinacridone are co-evaporated so that the ratio of quinacridone is 7% by mass to form an organic light-emitting layer having a thickness of 30 nm. Alq ₃ alone is formed on the organic light-emitting layer. Evaporation was performed to form an electron transport layer having a thickness of 35 nm.

  Next, LiF was deposited to a thickness of 0.5 nm by resistance heating vapor deposition, and then aluminum was deposited to a thickness of 5 mm and a thickness of 100 nm at a deposition rate of 0.4 nm / s as shown in the pattern of FIG. Formed.

  Thereby, the organic electroluminescent element A provided with the light emitting layer 4 of a double structure as shown in FIG. 2 was obtained. The hole injection layer, the hole transport layer, and the electron transport layer are not shown.

(Example 2)
The electron injection layer was formed of a 1 nm thick Na vapor deposition film. Also in forming the intermediate layer 3, the second layer 3b is a Li ₂ MoO ₄ and the resistance heating vapor deposition (deposition energy 0.001EV) was formed to a thickness 5 nm, the first layer 3a resistivity 1 × 10 ⁵ Ωcm or less ZnO, which is a conductive material, was formed by resistance heating vapor deposition to a thickness of 5 nm. Other than that was carried out similarly to Example 1, and obtained the organic electroluminescent element A. FIG.

(Example 3)
In forming the intermediate layer 3, the third layer 3c is formed in a thickness 2nm by depositing by sputtering MgO, forming the second layer 3b is a TiO ₂ EB vapor deposition (film formation energy 0.02 eV) and thickness 5nm Then, as the first layer 3a, ITO was EB evaporated and SiO was heated by resistance heating to form a 5 nm thick mixture layer (ITO: SiO weight ratio 8: 2, specific resistance 1 × 10 ³ Ωcm). . Other than that was carried out similarly to Example 1, and obtained the organic electroluminescent element A. FIG.

Example 4
The electron injection layer was formed of a Cs vapor deposition film having a thickness of 1 nm. In forming the intermediate layer 3, the third layer 3c is formed by resistance heating vapor deposition of Na ₂ O to a thickness of 5 nm, and the second layer 3b is formed by resistance heating vapor deposition of LiBO ₂ (film formation energy: 0.001 eV). The first layer 3a was formed to a thickness of 5 nm by sputtering ZnO, which is a conductor of 1 × 10 ⁵ Ωcm or less. Other than that was carried out similarly to Example 1, and obtained the organic electroluminescent element A. FIG.

(Example 5)
In forming the second layer 3b in the intermediate layer 3, a layer of Li ₂ MoO _{4 having} a thickness of 5 nm was formed by resistance heating vapor deposition (film formation energy 0.001 eV). Other than that was carried out similarly to Example 1, and obtained the organic electroluminescent element A. FIG.

(Example 6)
In forming the second layer 3b in the intermediate layer 3, a TiO ₂ layer having a thickness of 5 nm was formed by EB vapor deposition (deposition energy: 0.02 eV). Other than that was carried out similarly to Example 1, and obtained the organic electroluminescent element A. FIG.

(Example 7)
In forming the second layer 3b in the intermediate layer 3, a layer of LiBO _{2 having} a thickness of 2 nm was formed by resistance heating vapor deposition (film formation energy: 0.001 eV). Other than that was carried out similarly to Example 1, and obtained the organic electroluminescent element A. FIG.

(Example 8)
In forming the second layer 3b in the intermediate layer 3, a LiWO ₄ layer having a thickness of 2 nm was formed by resistance heating vapor deposition (film formation energy: 0.001 eV). Other than that was carried out similarly to Example 1, and obtained the organic electroluminescent element A. FIG.

(Conventional example)
In the same manner as in Example 1, a hole injection layer, a hole transport layer, an organic light emitting layer, and an electron transport layer were sequentially formed on the anode 1 of the glass substrate 5 provided with the ITO film (anode 1). An electron injection layer was not formed. Thereby, the light emitting layer 4 was formed.

  Next, without forming the intermediate layer 3, LiF was deposited on the electron transport layer by resistance heating vapor deposition to a thickness of 0.5 nm, and then aluminum was added at a thickness of 0.4 nm / nm as in the pattern of FIG. The cathode 2 was formed by vapor deposition to a width of 5 mm and a thickness of 100 nm at a vapor deposition rate of s.

  Thereby, the organic electroluminescent element A provided with only one light emitting layer 4 was obtained.

(Comparative Example 1)
In forming the intermediate layer 3, the second layer 3b was formed to a thickness of 10 nm by sputtering MoO ₃ (film formation energy 300 eV). Other than that was carried out similarly to Example 1, and obtained the organic electroluminescent element A. FIG.

(Comparative Example 2)
In forming the intermediate layer 3, the second layer 3b (Li ₂ MoO ₄ layer) was not provided. Other than that was carried out similarly to Example 2, and obtained the organic electroluminescent element A. FIG.

(Comparative Example 3)
In forming the intermediate layer 3, the third layer 3c (a mixture layer of ITO and SiO) was not provided. Other than that was carried out similarly to Example 3, and obtained the organic electroluminescent element A. FIG.

(Comparative Example 4)
In forming the intermediate layer 3, the second layer 3b was formed to a thickness of 5 nm by sputtering TiO ₂ (deposition energy: 420 eV). Other than that was carried out similarly to Example 3, and obtained the organic electroluminescent element A. FIG.

(Evaluation test)
The organic electroluminescence element A obtained in each example, conventional example and comparative example was connected to a power source (source meter manufactured by Keithley Instruments Inc., model number 2400), and 10 mA / cm ² between the anode 1 and the cathode ^2. Then, the light emission luminance of the organic electroluminescent element A and the voltage (drive voltage) between the anode 1 and the cathode 2 were measured. The upper limit voltage for securing the constant current value was 20V. Moreover, Topcon Co., Ltd. "BM-9" was used for the brightness | luminance measurement. The results are shown in Table 1.

  As can be seen from Table 1, the organic electroluminescence elements A of Examples 1 to 8 have a drive voltage that is approximately twice that of the conventional example, and the light emission luminance is approximately twice that of the conventional example 1, with an intermediate It was confirmed that the electrical connection between the two light-emitting layers 4 due to the presence of the layer 3 was maintained well.

  On the other hand, in Comparative Examples 1 to 4, the driving voltage greatly exceeded twice that of the conventional example, the light emission luminance was low, and the light emission efficiency was poor.

It is a schematic sectional drawing which shows an example of embodiment of this invention. The schematic structure of the organic electroluminescent element A for a test produced in the Example is shown, (a) is a top view, (b) is a B-B 'sectional view of (a). It is a schematic sectional drawing which shows an example of a prior art.

Explanation of symbols

A organic electroluminescence device 1 anode 2 cathode 3 intermediate layer 3a first layer 3b second layer 3c third layer 4 light emitting layer 4a light emitting layer 4b light emitting layer

Claims (4)

An organic electroluminescence device in which a plurality of light emitting layers including an organic light emitting layer are laminated via an intermediate layer between an anode and a cathode,
The intermediate layer includes a first layer containing a conductor having a specific resistance of 1 × 10 ⁵ Ωcm or less at 23 ° C., and a second layer made of a metal compound formed by a vapor phase method with a film formation energy of 10 eV or less. And an alkali metal, an alkaline earth metal, and a third layer containing at least one of these oxides, and the first layer, the second layer, and the third layer are laminated in order from the cathode side. An organic electroluminescence device characterized by comprising:   The organic electroluminescence device according to claim 1, wherein the second layer contains a molybdenum compound.   The organic electroluminescence device according to claim 1 or 2, wherein the second layer contains a titanium compound.   The organic electroluminescence device according to any one of claims 1 to 3, wherein the second layer contains a boron compound.

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