JP2008293895A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent element making possible high luminance light emission by forming an intermediate layer between light-emitting layers, using a simple structure. <P>SOLUTION: The intermediate layer in the organic electroluminescent element is constituted of a laminate laminating an organometallic complex of electron releasing metal with work function which is 3.7 eV or lower or a mixed layer of metal carbonates and reducing metal and a layer of metal oxides. Here, the intermediate layer is the layer arranged in between the light-emitting layers for carrying out transfer of charges for the light-emitting layers arranged on both sides. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an organic electroluminescence element, and more particularly to an organic electroluminescence element including a plurality of light emitting layers used for an illumination light source, a backlight for a liquid crystal display, a flat panel display, and the like.

  As an example, an organic light-emitting element called an organic electroluminescence element includes a light-transmitting electrode serving as an anode, a hole transport layer, an organic light-emitting layer, an electron injection layer, and an electrode serving as a cathode in this order. A structure laminated on the surface is known. In such an organic light emitting device, 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 used. However, light is emitted by recombination in the light emitting layer, and light emitted from the light emitting layer is extracted through the light transmitting electrode and the light transmitting substrate.

  Organic electroluminescence elements have such characteristics as being self-luminous, exhibiting relatively high-efficiency emission characteristics, and being capable of emitting light in various colors, so that they can be used for display devices such as flat panel displays. Or, it is expected to be used as a light source, for example, a backlight for a liquid crystal display or illumination, and some of them are already put into practical use. However, the organic electroluminescence element has a trade-off relationship between the luminance and the lifetime, and has a property that 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 in which a plurality of light emitting layers are provided between an anode and a cathode, and a conductive layer, a layer forming an equipotential surface, or a charge generation layer is provided between the light emitting layers. Elements have been proposed (see, for example, Patent Documents 1 and 2).

  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 serving as the anode 1 and an electrode serving as the cathode 2, and the light emitting layers 4a and 4b adjacent to each other. Are laminated with a conductive layer (or charge generation layer) 10 interposed therebetween, and this is laminated on the surface of a light-transmitting substrate 5. The anode 1 is a light-transmitting electrode and the cathode 2 is a light reflecting member. It forms so that it may become a conductive electrode. In FIG. 4, a hole transport layer and an electron injection layer are provided on both sides of the light emitting layers 4a and 4b, but the hole transport layer and the electron injection layer are not shown.

  Then, by dividing the plurality of light emitting layers 4a and 4b by the conductive layer (or charge generation layer) 10 as described above, when a voltage is applied between the anode 1 and the cathode 2, the plurality of light emitting layers 4a and 4b are as if Since light is emitted simultaneously in a state of being connected in series, and the light from each of the light emitting layers 4a and 4b is added, it can emit light with higher brightness than a conventional organic electroluminescence element when a constant current is applied. Thus, it is possible to avoid the brightness-lifetime trade-off.

  However, the conductive layer or the charge generation layer that partitions the plurality of light emitting layers has a relatively complicated structure. Further, as described below, there are problems such as an undesired voltage rise problem or a process problem.

As the conductive layer or the charge generation layer, general structures currently known 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, etc. (“:” is a mixture of two materials, “/” is the composition before and after.) Represents a stack of).

Here, it is known that Lewis acid molecules react with an electron transport material, and alkali metals react with a hole transport material as a Lewis base, and these reactions cause an increase in driving voltage (Reference: High Molecular ELECTRONIC EL ELECTRONICS ELECTRONICS ELECTRONICS EL ELECTROLOGY ELECTRONICS ELECTRO-EL LIGHTING), and when ITO is sputtered on organic layers, it is known that device efficiency may decrease due to sputter damage. These are the above problems (1) to (4). Specifically, the system (1) has a problem of short circuit due to the film quality of the V ₂ O ₅ layer, the system (2) has a problem of voltage increase due to side reaction of both layers, and the system (3) Al thin film is deposited to obtain reaction products, but the film thickness is very thin and Al atoms cause migration, so they are not in the form of a continuous film but in the form of islands. Can be considered. As a result, there was a problem in life and reliability (see Patent Document 2). Furthermore, in the system (4), there is a problem in the manufacturing process that it is necessary to deposit ITO as a conductive layer or a charge generation layer instead of vapor deposition. Patent Document 3 describes a method of forming a conductive layer or a charge generation 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 this case as well, the problem described in the above reference cannot be solved.

Japanese Patent Laid-Open No. 11-329748 JP 2003-272860 A JP 2005-135600 A

  When a conductive layer or a charge generation layer is formed as an intermediate layer between the light emitting layers as described above, there are various problems. Such an intermediate layer can be easily formed by vapor deposition, and the secondary characteristics cause deterioration of device characteristics. It has been desired to realize an intermediate layer that can suppress the reaction and has a relatively simple structure.

  The present invention has been made in view of the above points, and an object of the present invention is to provide an organic electroluminescence device capable of forming an intermediate layer between light emitting layers with a simple structure and capable of high luminance light emission. To do.

  In the organic electroluminescence device of the present invention, the intermediate layer is a laminate of an electron-donating metal organometallic complex or metal carbonate having a work function of 3.7 eV or less and a reducing metal, and a metal oxide layer. It consists of the laminated body which was made. Here, the intermediate layer is a layer disposed between the light emitting layers in order to transfer charges to the light emitting layers arranged on both sides.

  According to this configuration, the intermediate layer can be formed using a low damage process, for example, a vapor deposition process. In addition, a metal compound (an electron-donating metal organometallic complex or metal carbonate having a work function of 3.7 eV or less) in the mixed layer sufficiently reacts to obtain a high-luminance light-emitting organic electroluminescence device. Furthermore, when forming a metal ultrathin film (see Patent Document 2), the reproducibility is poor due to reasons such as metal migration, but according to the present invention, the thickness of the mixed layer can be stably and uniformly formed. High reproducibility and excellent mass productivity. In addition, even if this mixed layer is thick, there is a level in which electrons flow, so that the thickness of the mixed layer can be increased. Metal complexes are easier to handle and share than simple metals such as cesium. High vapor deposition.

  In the organic electroluminescent element, the present invention is characterized in that a metal layer is sandwiched between a mixed layer constituting the intermediate layer and a metal oxide layer.

  According to this configuration, the organic electroluminescence device has an improved electrical connection state (contact property) between the mixed layer and the metal oxide layer, promotes charge separation in the intermediate layer, and has improved life and reliability. Can be obtained.

  In the organic electroluminescent element, the present invention is characterized in that the metal layer is an alloy composed of two or more kinds of metals.

  According to this configuration, since migration can be suppressed, it is possible to obtain an organic electroluminescence element having an extended lifetime and improved reliability. For example, in the case of Al alone or when Al and Li are laminated, Al tends to cause migration, but when Li and Al are alloyed, it becomes stable and a long life can be achieved.

  According to the present invention, in the above organic electroluminescent element, the metal oxide layer is composed of a laminate of an ambipolar conductive metal oxide and a conductive metal oxide. Here, the ambipolar conductive metal oxide means a compound whose carrier transport ability changes depending on film forming conditions or a mixture, and means only an oxide such as aluminum known as an amphoteric metal in a commonly used term. Not what you want.

  According to this configuration, it is possible to obtain an organic electroluminescent device in which the carrier transport property from the intermediate layer to the light emitting layer becomes smoother, the driving voltage is reduced, the lifetime is increased, and the reliability is improved.

  In the organic electroluminescent element, the present invention is characterized in that the reducing metal is a metal selected from the group consisting of aluminum, titanium, tungsten, platinum, palladium, zirconium, and hafnium.

  According to this configuration, an electron-donating metal having a free work function of 3.7 eV or less can be formed by sufficiently reacting an organometallic complex of an electron-donating metal, a metal carbonate, and a reducing metal. A high-luminance light-emitting organic electroluminescence element that is easy to enter, has improved injectability, and has a long life and improved reliability can be obtained.

  Further, the present invention provides the above organic electroluminescent device, wherein the ambipolar conductive metal oxide is a metal selected from vanadium, molybdenum, rhenium, tungsten, nickel, zinc, copper, indium, strontium, tin, niobium, and tantalum. It is characterized by being an oxide.

  According to this configuration, in particular, the hole injection property into the light emitting layer becomes smooth, and high luminance light emission becomes possible.

  According to the present invention, the intermediate layer is a laminate in which an organic metal complex or metal carbonate of an electron donating metal having a work function of 3.7 eV or less and a mixed layer of a reducing metal and a metal oxide layer are laminated. By comprising the body, it is possible to obtain an organic electroluminescence element capable of emitting light with high luminance and having a long life and improved reliability.

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

  FIG. 1 shows an example of the structure of an organic electroluminescence device according to the present invention. A plurality of light emitting layers 4a and 4b are provided between an electrode serving as an anode 1 and an electrode serving as a cathode 2, and adjacent light emitting layers 4a, 4a, The light-transmitting intermediate layer 3 is interposed between the light-transmitting intermediate layers 3 and laminated on the surface of the light-transmitting substrate 5. The anode 1 is a light-transmitting electrode, and the cathode 2 is It is formed as a light reflective electrode. In the embodiment of FIG. 1, the light emitting layer 4 is formed in a laminated structure of two layers of the light emitting layers 4 a and 4 b, but may be a laminated structure in which the light emitting layer 4 is further laminated in multiple layers via the intermediate layer 3. The range of the number of stacked light emitting layers 4 is not particularly limited, but the upper limit is about 5 layers because the difficulty of optical and electrical element design increases as the number of layers increases. In FIG. 1, a hole injection layer, a hole transport layer, an electron transport layer and an electron injection layer may be provided between the light emitting layers 4a and 4b and the anode 1 and the cathode 2, but these are not shown. .

  In the organic electroluminescence device of the present invention, the intermediate layer 3 is selected from an organometallic complex of an electron donating metal having a work function of 3.7 eV or less and a metal carbonate of an electron donating metal having a work function of 3.7 eV or less. It consists of a laminated body in which a mixed layer of any of these and a reducing metal and a metal oxide layer are laminated.

  A metal layer may be sandwiched between the mixed layer and the metal oxide layer. Although the thickness of the said mixed layer is not specifically limited, For example, it is the range of 1 nm-100 nm, and the range of 5 nm-50 nm is especially preferable. Here, the mixing ratio between the reducing metal and the organometallic complex or metal carbonate of an electron donating metal having a work function of 3.7 eV or less (hereinafter referred to as a metal compound) is not particularly limited. Although there is no, for example, molar ratio, the range of reducing metal: metal compound = 1: 0.05 to 2.0, preferably the range of reducing metal: metal compound = 1: 0.1 to 1.5 Particularly preferred is a range of reducing metal: metal compound = 1: 0.1 to 1.0 containing the reducing metal as a main component. By using the reducing metal as the main component, the reaction of the metal compound is promoted, and the reducing metal and the electron-donating metal are mixed, and in particular, the life extension and the reliability are improved. Although the thickness of the said metal oxide layer is not specifically limited, For example, it is the range of 1 nm-50 nm, and the range of 5 nm-30 nm is especially preferable. The thickness of the metal layer is not particularly limited, but may be a thickness that does not impair the light transmittance (for example, a visible light transmittance of 75% or more), for example, in the range of 0.1 nm to 10 nm. In particular, a range of 0.5 nm to 5 nm is particularly preferable.

  The reducing metal contained in the mixed layer constituting the intermediate layer 3 is preferably selected from the group of aluminum, titanium, tungsten, platinum, palladium, zirconium, and hafnium.

The metal compound contained in the mixed layer constituting the intermediate layer 3 is selected from an organometallic complex containing an electron-donating metal having a work function of 3.7 eV or less, and a metal carbonate. The electron donating metal is selected from the group of alkali metals and alkaline earth metals, and specific examples thereof are not particularly limited, but lithium, sodium, potassium, cesium, beryllium, magnesium, calcium, etc. As an example. Specific examples of the organometallic complex and the metal carbonate are not particularly limited. Examples of the organometallic complex include quinoline complexes such as (8-quinolinolato) lithium complexes, dibivaloylmethanatolithium complexes (Lidpm), and dibivalo. Dibivaloylmethanato complex (dpm complex) such as ilmethanato potassium complex (Kdpm), acetylacetonate complex (acac complex) such as acetylacetonate lithium complex (Liacac), metal carbonate compounds such as cesium carbonate and sodium carbonate Can be mentioned. In addition, an inclusion compound such as a crown ether and a derivative thereof (Chemical Formula 1) that includes an electron-donating metal can also be exemplified as an organometallic complex.

Of the laminated body constituting the intermediate layer 3, specific examples of the metal oxide layer are not particularly limited. For example, ITO (indium-tin oxide), IZO (indium-zinc oxide), AZO (aluminum) -Zinc oxide) Various metal oxides mainly composed of indium oxide, tin oxide, zinc oxide and gallium zinc oxide can be mentioned.
Of the laminate constituting the intermediate layer 3, the specific example of the metal layer is not particularly limited. An alloy, an alloy composed of a reducing metal, a light reflecting metal, and an electron donating metal can be used. Furthermore, the alloy etc. which consist of a metal (or alloy) which is hard to raise | generate a migration, and an electron-donating metal are mentioned. Here, the light reflective metal has a reflectance of 70% or more over the visible light region, and examples thereof include aluminum, silver, and rhodium. Examples of the metal that hardly causes migration include gold, tin, and copper, and examples of the alloy that hardly causes migration include silver-palladium and silver-copper alloys.

  The metal oxide layer constituting the intermediate layer 3 is preferably a laminate of an ambipolar conductive metal oxide and a conductive metal oxide. Specific examples of the ambipolar conductive metal oxide constituting the intermediate layer 3 are not particularly limited, but vanadium, molybdenum, rhenium, tungsten, nickel, zinc, copper, indium, strontium, tin, niobium, tantalum And metal oxides containing an element selected from the group. Specific examples of the conductive metal oxide laminated with the ambipolar conductive metal oxide are not particularly limited, but ITO (indium-tin oxide), IZO (indium-zinc oxide), AZO (aluminum) -Zinc oxide).

  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. As described above, although the hole injection layer, the hole transport layer, the electron transport layer, and the electron injection layer are omitted as an example of the element configuration in FIG. 1, they can be used as needed.

As a material that can be used for 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 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 organic layer 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. . The substrate side, that is, the lower layer side, is composed of a polymer light emitting layer that can be formed by a wet process such as spin coating, spray coating, die coating, gravure printing, and the like. That is, it is desirable to use a low molecular light emitting layer that can be formed by a dry process such as vapor deposition on the upper layer side. Here, the “lower layer side” indicates the entire ITO side unit in the two-stage multi-unit structure (that is, not only the light emitting layer of the ITO side unit).
Further, a light emitting layer 4 that emits light itself, a charge injection layer that injects charges such as electrons or holes into the light emitting layer 4, and a charge transport layer may be required. It will be treated as a functional layer including the transport layer. Here, depending on the selection of the intermediate layer, the charge transport layer and the charge injection layer can be omitted, and the functional layer itself can be made thin.

  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.

  The substrate 5 is light-transmitting when light is emitted through the substrate 5, and may be slightly colored or ground glass in addition to being colorless and transparent. Good. For example, a translucent 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, epoxy, or a fluorine resin is used. be able to. 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 base material 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 light transmittance, and an arbitrary 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 organic 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. Is preferably 4 eV or more. Examples of the material of the anode 1 include, for example, metals such as gold, CuI, ITO (indium-tin oxide), SnO2, ZnO, IZO (indium-zinc oxide), PEDOT, polyaniline, and the like. Examples thereof include conductive light-transmitting materials such as conductive polymers doped with molecules and arbitrary acceptors, and carbon nanotubes. The anode 1 can be produced, for example, by forming these electrode materials into a thin film on the surface of the substrate 5 by a method such as vacuum deposition, sputtering, or coating. Further, in order to irradiate the light emitted from the organic 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.

  The cathode 2 is an electrode for injecting electrons into the organic 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 low work function. 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. Further, an alkali metal oxide, an alkali metal halide, or a metal oxide may be used as the base of the cathode, 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 translucent 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 organic light emitting layer 4 is extracted from the anode 1 side, the light transmittance of the cathode 2 is preferably 10% or less. Conversely, when light is extracted from the cathode 2 side using the translucent 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 70% or more. It is preferable to make it. 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 is usually 500 nm or less, preferably 100 to 200 nm.

  In addition, each member and structure of the organic electroluminescence element can be used in combination as long as the gist of the present invention is not impaired.

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

Prior to the description of the embodiments of the present invention, a conventional organic electroluminescence element will be described as a reference example. 2 and 3 are a top view and an AA cross-sectional view of the organic electroluminescent element of the embodiment of the present invention. Although the details are omitted in FIG. 3, it has a layered structure similar to that shown in FIG. 1, and includes a light emitting layer 4 (4a, 4b), a functional layer including a charge transport layer, a charge injection layer, and the like; The intermediate layer 3 is formed to have the same pattern shape.
[Reference example]
A 0.7 mm thick glass substrate 5 in which ITO having a thickness of 110 nm was formed as an anode 1 as in the pattern of FIG. 2 was prepared. The sheet resistance of ITO (indium tin oxide) forming the anode 1 is about 12Ω / □. This was subjected to ultrasonic cleaning for 10 minutes each with detergent, ion-exchanged water, and acetone, then steam-washed with IPA (isopropyl alcohol), dried, and further treated with UV / O ₃ .

Next, this substrate was set in a vacuum deposition apparatus, and 4,4′-bis [N- (naphthyl) -N— as a hole transport layer on ITO under a reduced pressure atmosphere of 1 × 10 ⁻⁴ Pa or less. Phenyl-amino] biphenyl (α-NPD) was deposited to a thickness of 80 nm.

  Next, on the hole transport layer, a mixed film of TBADN (Chemical Formula 2) and sty-NPD (Chemical Formula 3) (mass ratio; TBADN: sty-NPD = 96: 4) is formed as a light emitting layer with a thickness of 50 nm. Filmed. Next, bathocuproine with a film thickness of 15 nm was formed thereon as an electron transport layer.

［比較例１］ Subsequently, BCP and Cs are formed to a thickness of 5 nm at a molar ratio of 1: 0.25, and aluminum is further formed to a thickness of 80 nm at a deposition rate of 0.4 nm / s. Thus, a cathode was formed, and an organic electroluminescence device having a single light emitting layer was obtained. The shape of the organic electroluminescence element is as shown in FIG. 2 (in FIG. 2, the organic film is composed of a hole injection layer, a hole transport layer, a light emitting layer, and an electron transport layer).

[Comparative Example 1]

  Using a substrate with an ITO anode equivalent to the above reference example, α-NPD was formed to a thickness of 80 nm to form a hole transport layer in the same manner as in the reference example. Next, on the hole transport layer, a mixed film of TBADN and sty-NPD (mass ratio; TBADN: sty-NPD = 96: 4) is formed to a thickness of 50 nm as the first light emitting layer. A BCP film having a thickness of 15 nm was formed thereon as an electron transport layer.

  Next, a mixed film of tris (8-quinolinolato) aluminum (Alq3) and Li (molar ratio; Alq3: Li = 1: 1) was formed to a thickness of 10 nm, and then an IZO film was formed to a thickness of 11 nm. An intermediate layer was formed by forming a film.

  Next, in the same manner as described above, an α-NPD hole transport layer is formed to a thickness of 60 nm on the intermediate layer, and then a mixed film of TBADN and sty-NPD (as a second light emitting layer) ( A mass ratio; TBADN: sty-NPD = 96: 4) is formed with a film thickness of 50 nm, and then a mixed film of BCP and Cs (molar ratio; BCP: Cs = 1: 0.25) is formed with a film thickness of 5 nm. Then, aluminum is further deposited at a film thickness of 80 nm at a deposition rate of 0.4 Å / s, a cathode is formed with the pattern of FIG. 2, and an organic electroluminescence device having a two-layered light emitting layer is obtained. It was. The shape of the organic electroluminescence element is as shown in FIG. 2 (in FIG. 2, the organic film is composed of a hole injection layer, a hole transport layer, a light emitting layer, and an electron transport layer).

Comparative Example, except that a mixed film of Liq (Chemical Formula 4) and Al (molar ratio; Al: Liq = 1: 0.5) was formed to a thickness of 5 nm and then V ₂ O ₅ was formed to a thickness of 5 nm In the same manner as in Example 1, an organic electroluminescence element was obtained.

The intermediate layer was formed in the same manner as in Comparative Example 1 except that a mixed film of Liq and Al (molar ratio; Al: Liq = 1: 0.5) was formed to 5 nm, and subsequently MoO ₃ was formed to 5 nm. An organic electroluminescence device was obtained.

The intermediate layer was formed in the same manner as in Comparative Example 1 except that a mixed film of Liq and Al (molar ratio; Al: Liq = 1: 0.5) was formed to 5 nm, and subsequently WO ₃ was formed to 5 nm. An organic electroluminescence device was obtained.
[Comparative Example 2]

An organic electroluminescence device was obtained in the same manner as in Comparative Example 1 except that the intermediate layer was formed by depositing 5 nm of Liq and then depositing 5 nm of V ₂ O ₅ .
[Comparative Example 3]

The intermediate layer was formed into a film having a thickness of 5nm to Liq, and 1nm deposited Al, followed except that 5nm film of _V 2 _{O 5} and is in the same manner as in Comparative Example 1, the organic electroluminescence element Obtained.

As the intermediate layer, a mixed film of Liq and Al (molar ratio; Al: Liq = 1: 0.5) was formed to a thickness of 5 nm, Al was formed to a thickness of 1 nm, and then V ₂ O ₅ was deposited to a thickness of 5 nm. In the same manner as in Comparative Example 1, an organic electroluminescence element was obtained.

As an intermediate layer, a mixed film of Liq and Pt (molar ratio; Pt: Liq = 1: 0.5) was formed to a thickness of 5 nm, and subsequently V ₂ O ₅ was formed to a thickness of 5 nm. Thus, an organic electroluminescence element was obtained.

The intermediate layer was formed in the same manner as in Comparative Example 1 except that a mixed film of Liq and Al (molar ratio; Al: Liq = 1: 1.5) was formed to 5 nm, and subsequently MoO ₃ was formed to 5 nm. An organic electroluminescence device was obtained.

The intermediate layer was formed in the same manner as in Comparative Example 1 except that a mixed film of Liq and Al (molar ratio; Al: Liq = 1: 2) was formed to 5 nm, and subsequently V ₂ O ₅ was formed to 5 nm. An organic electroluminescence device was obtained.

As the intermediate layer, a mixed film of Liq and Al (molar ratio; Al: Liq = 1: 0.5) was formed to a thickness of 5 nm, and the mixed film (molar ratio; Al: Li = 1: 1) was formed by a co-evaporation method of Al and Li. An organic electroluminescent device was obtained in the same manner as in Comparative Example 1 except that 1) was formed to 1 nm and subsequently V ₂ O ₅ was formed to 5 nm. Although it is formed by co-evaporation here, it may be formed by sputtering.

As the intermediate layer, a mixed film of Liq and Al (molar ratio; Al: Liq = 1: 0.5) was formed to 5 nm, V ₂ O ₅ was formed to 5 nm, and subsequently IZO was formed to 5 nm. In the same manner as in Comparative Example 1, an organic electroluminescence element was obtained.

For the intermediate layer, a mixed film of Liq and Al (molar ratio; Al: Liq = 1: 0.5) was formed to 5 nm, IZO was formed to 5 nm, and then V ₂ O ₅ was formed to 5 nm. In the same manner as in Comparative Example 1, an organic electroluminescence element was obtained.

As the intermediate layer, a mixed film of dibenzo-18-crown-6 (chemical formula 5) and Al clad with Li (molar ratio; Al: dibenzo-18-crown-6 = 1: 0.5) was formed to a thickness of 5 nm. Organic electroluminescence in the same manner as in Comparative Example 1 except that a mixed film of Al and Li (molar ratio; Al: Li = 1: 1) was formed to 1 nm and subsequently V ₂ O ₅ was formed to 5 nm. An element was obtained.

As the intermediate layer, a mixed film of Liq and Al (molar ratio; Al: Liq = 1: 1.5) was formed to 5 nm, V ₂ O ₅ was formed to 5 nm, and then IZO was formed to 5 nm. In the same manner as in Comparative Example 1, an organic electroluminescence element was obtained.

The intermediate layer was formed except that a mixed film of Cs ₂ CO ₃ and Al (molar ratio; Al: Cs ₂ CO ₃ = 1: 0.5) was formed to 5 nm, and then V ₂ O ₅ was formed to 5 nm. In the same manner as in Comparative Example 1, an organic electroluminescence element was obtained.

As described above, the organic electroluminescence elements obtained in the conventional examples, Examples 1 to 13 and Comparative Examples 1 to 3 are connected to a power source (KEYTHLEY 2400), and the current efficiency and the initial light emission luminance when 10 mA / cm ² is applied. The relative value of the light emission luminance half-life when 1000 (cd / m ² ) was set was evaluated. In addition, “BM-9” manufactured by Topcon Corporation was used for luminance evaluation. The results are shown in Table 1.

  As can be seen in Table 1, the organic electroluminescence elements of the respective examples had high current efficiency and at the same time long luminance half life.

  On the other hand, the reference example with one light emitting layer had low current efficiency and short luminance half life. In Comparative Example 1 and Comparative Example 3, high current efficiency was obtained, but the luminance half-life was shorter than that of this example. In Comparative Example 2, both current efficiency and luminance half life were lower than those of the reference example.

  As described above, since the organic electroluminescence element of the present invention has a long life and high efficiency, it can be applied to an illumination light source, a backlight for a liquid crystal display, a flat panel display, and the like.

It is the schematic which shows an example of the layer structure of the organic electroluminescent element of this invention. It is a schematic plan view which shows the organic electroluminescent element produced in the Example. Sectional view of the A-A 'plane in FIG. It is the schematic which shows an example of the laminated constitution of the organic electroluminescent element of conventional invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Anode 2 Cathode 3 Intermediate layer 4a Light emitting layer 4b Light emitting layer 5 Substrate 10 Conductive layer

Claims (7)

  An organic electroluminescence device comprising a plurality of light emitting layers laminated via an intermediate layer between an anode and a cathode, wherein the intermediate layer is an organometallic complex of an electron donating metal having a work function of 3.7 eV or less Alternatively, an organic electroluminescence device comprising a laminate in which a mixed layer of a metal carbonate and a reducing metal and a metal oxide layer are stacked. The organic electroluminescence device according to claim 1,
The organic electroluminescence device, wherein the mixed layer is a co-evaporated layer. The organic electroluminescence device according to claim 1 or 2,
An organic electroluminescence device comprising a metal layer sandwiched between a mixed layer and a metal oxide layer constituting the intermediate layer. The organic electroluminescence device according to claim 3,
The organic electroluminescent element, wherein the metal layer is an alloy composed of two or more kinds of metals. An organic electroluminescence device according to any one of claims 1 to 4,
The organic electroluminescence device, wherein the metal oxide layer is a laminate of an ambipolar conductive metal oxide and a conductive metal oxide. It is an organic electroluminescent element in any one of Claims 1 thru | or 5, Comprising:
The organic electroluminescence device, wherein the reducing metal is a metal selected from the group consisting of aluminum, titanium, tungsten, platinum, palladium, zirconium, and hafnium. The organic electroluminescence device according to claim 5, wherein
An organic electroluminescence device, wherein the ambipolar conductive metal oxide is an oxide made of a metal selected from vanadium, molybdenum, rhenium, tungsten, nickel, zinc, copper, indium, strontium, tin, niobium, and tantalum.

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