JP5303726B2 - Organic electroluminescence device - Google Patents

Description

  The present invention relates to an organic electroluminescence device having high current efficiency and a method for manufacturing the same.

In recent years, Tang et al. Have an organic electroluminescent element (hereinafter referred to as an organic EL element) having a two-layer structure in which an organic fluorescent dye is used as a light emitting layer and an organic charge transport compound used in an electrophotographic photoreceptor or the like is laminated. (Patent Document 1: Japanese Patent Laid-Open No. 59-194393). Furthermore, it has been reported that when a small amount of a fluorescent dye is doped in the electron transport light-emitting layer, light emission from the fluorescent dye occurs, and an element with high efficiency and long life can be obtained. Compared with competing devices, organic EL devices are characterized by the fact that they can easily emit light of many colors in addition to low voltage drive and high brightness. Many attempts have been reported for compounds (Non-Patent Document 1: Japanese Journal of Applied Physics Vol. 27, L269 (1988)). 2: Journal of Applied Physics (J. Appl. Phys.), 65, 3610 (1989)).
In addition to an organic EL element that mainly uses a low-molecular organic compound, a polymer light-emitting element that uses a polymer light-emitting material (hereinafter referred to as a polymer phosphor) is disclosed in Patent Document 2 (WO90113148 specification). ), Patent Document 3 (JP-A-3-244630), Non-Patent Document 3 (Appl. Phys. Lett. 58, 1982 (1991)), etc. . In an example of the specification of WO90113148, poly (p-phenylene vinylene) (hereinafter referred to as PPV) converted into a conjugated polymer by forming a film of a soluble precursor on an electrode and performing heat treatment. )) Using a thin film is disclosed.
Such conventional organic EL elements have been improved in luminance and life due to improvements in materials and element configurations, but have not yet reached a practical level required for display for display and illumination applications.
Such a conventional organic EL element has one light emitting unit including a light emitting layer between opposed electrodes. For the purpose of improving the performance, a light emitting layer is provided between opposed electrodes. There has been proposed an organic EL element (sometimes referred to as a stacked element) having a plurality of light emitting units including each light emitting unit partitioned by a charge generation layer (Patent Document 4: Japanese Patent Application Laid-Open No. 2003-272860). Publication).
JP 59-194393 A WO90113148 published specification JP-A-3-244630 JP 2003-272860 A Japanese Journal of Applied Physics (Jpn. J. Appl. Phys.) Vol. 27, L269 (1988) Journal of Applied Physics (J. Appl. Phys.), 65, 3610 (1989) Applied Physics Letters (Appl. Phys. Lett.), 58, 1982 (1991).

  However, since the above-mentioned multilayer elements are limited to those using low molecular weight materials, a method for realizing a multilayer element using a polymer material that can use a coating method and a printing method suitable for mass production is desired. It was.

The inventors of the present invention have solved the above-mentioned problems and intensively studied to make it possible to produce a laminated organic EL element even in a polymer system. As a result, the charge generation layer is produced by laminating or mixing materials having different work functions. As a result, it has been found that even in a polymer material system capable of forming a film from a solution, the stacked organic EL element operates effectively, and electrons and holes are effectively injected into the organic material, and the present invention has been made. .
The present invention is as follows.
(1) two opposing electrodes connected to an external circuit that provides electrical energy, at least one of which is transparent or translucent, and one or more organic layers between the electrodes, One of the layers is a light emitting layer, and an organic light emitting device comprising a plurality of light emitting units that emit light by recombination of holes and electrons, and a charge generation layer sandwiched between two of the plurality of light emitting units. In the electroluminescence element,
Two adjacent ones of the plurality of light emitting units are separated by the charge generation layer,
The charge generation layer comprises one or more types of a metal having a work function of 3.0 eV or less or a compound thereof (A) and one or more types of a compound (B) having a work function of 4.0 eV or more,
In at least one of the plurality of light-emitting units, the light-emitting layer contains a polymer light-emitting material.
(2) The charge generation layer includes a first layer containing at least one kind of the metal or a compound thereof (A) and a second layer containing at least one kind of the compound (B). The organic electroluminescence device according to (1), wherein the first layer is on the side facing the electrode for injecting holes.
(3) The organic material according to (1), wherein the charge generation layer is a mixed layer containing one or more of the metal or the compound (A) and one or more of the compound (B) in one layer. Electroluminescence element.
(4) The organic electroluminescence device according to any one of (1) to (3), wherein the transmittance of the charge generation layer with respect to a wavelength at 550 nm is 30% or more.
(5) The organic electroluminescence device according to any one of (1) to (4), wherein the metal having a work function of 3.0 eV or less is selected from the group consisting of an alkali metal and an alkaline earth metal.
(6) The organic electroluminescence device according to any one of (1) to (5), wherein the compound having a work function of 4.0 eV or more is a transition metal oxide.
(7) The above transition metal oxide according to (6), wherein the transition metal oxide is an oxide of one or more metals selected from the group consisting of V, Nb, Ta, Cr, Mo, W, Mn, Tc, and Re. Organic electroluminescence device.
(8) The metal according to any one of (1) to (4), wherein the metal having a work function of 3.0 eV or less is Li, and the compound having a work function of 4.0 eV or more is V ₂ O ₅ . Organic electroluminescence device.
(9) The organic electroluminescence device according to any one of (1) to (5), wherein the compound having a work function of 4.0 eV or more is at least one organic compound.
(10) The organic electroluminescence device according to any one of (1) to (9), wherein the polymer light-emitting material has a weight average molecular weight of 10,000 to 10,000,000 and is soluble in an organic solvent.
(11) The organic electroluminescent element according to any one of (1) to (10), wherein the light emitting layers of two light emitting units separated by one charge generating layer are not identical in emission color.
(12) The thickness of the layer including one light-emitting unit and one charge generation layer between the two opposing electrodes determines the wavelength of light generated from the light-emitting unit between the light-emitting unit and the charge generation layer. The organic electroluminescence device according to any one of the above (1) to (11), which is within ± 20% of an integral multiple of ¼ of the value divided by the average refractive index.
(13) The method for producing an organic electroluminescent element according to any one of (1) to (12) above, wherein at least one of the layers constituting the light emitting unit is formed by film formation from a solution. .
(14) A light emitting device having the organic electroluminescence element according to any one of (1) to (12).
According to the present invention, since a light emitting layer containing a polymer light emitting material can be formed by a coating method, the manufacturing time of the stacked EL device is greatly increased compared to the low molecular stacked device in which the entire layer of the device is manufactured by vapor deposition. Can be shortened.

  The organic electroluminescence device of the present invention can be made into a tandem organic EL device with a polymer material by using the charge generation layer unique to the present invention.

The charge generation layer in the present invention is a layer having a function of injecting holes in the cathode direction and injecting electrons in the anode direction when a voltage is applied.
In the organic electroluminescence device of the present invention, this charge generation layer is sandwiched between two light emitting units. Here, in the present invention, the “light emitting unit” refers to a laminated structure including one or more organic layers, one of which is a light emitting layer, which emits light by recombination of holes and electrons. The organic EL device of the present invention has a structure in which a plurality of light emitting units are stacked with a charge generation layer interposed therebetween. Further, in at least one light emitting unit among the plurality of light emitting units, one of the one or more organic layers constituting the light emitting unit includes a light emitting layer containing a polymer light emitting material.
The “light emitting unit” in the present invention corresponds to a portion obtained by removing the opposing electrodes (anode and cathode) from the components of a conventional organic EL element having only one light emitting layer. Therefore, the organic EL device of the present invention has a structure in which a structure in which a plurality of light emitting units including an organic layer having a polymer light emitting material are partitioned by a charge generation layer unique to the present invention is sandwiched between two opposing electrodes. It can be said that. Here, at least one of the two opposing electrodes is transparent or translucent, and the light generated in the light emitting layer can be effectively extracted outside.

The charge generation layer in the present invention comprises one or more kinds of metals having a work function of 3.0 eV or less or a compound thereof (A) and one or more kinds of compounds (B) having a work function of 4.0 eV or more. It is characterized by that. A metal compound having a work function of 3.0 eV or less refers to a compound having a work function of 3.0 eV or less and a work function of the compound itself of 3.0 eV or less. If the work function is out of the above range, effective charge injection is unlikely to occur, and the effects of the present invention cannot be obtained sufficiently.
The metal having a work function of 3.0 eV or less constituting the charge generation layer can be selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals. Of these, alkali metals and alkaline earth metals are preferred. Examples of the alkali metal include lithium (Li) (2.93 eV), sodium (Na) (2.36 eV), potassium (K) (2.28 eV), rubidium (Rb) (2.16 eV), and cesium (Ce) ( 1.95 eV) and alkaline earth metals are preferably calcium (Ca) (2.9 eV) and barium (Ba) (2.52 eV) (the work function is shown in parentheses). Li is more preferable.
In addition, the metal compound having a work function of 3.0 eV or less constituting the charge generation layer is an oxide, halide, fluoride, boride, nitride, carbide, or the like of the above metal.
In order to sufficiently obtain the effects of the present invention, the thickness of the first layer is preferably 10 nm or less, more preferably 6 nm or less.

The charge generation layer in the present invention is used in combination with one or more of the above compounds (B) rather than using one or more of the metals having the work function of 3.0 eV or less or the compound (A) alone. By doing so, it exhibits a significantly superior effect.
There are the following two types of charge generation layers using a combination of the metal or its compound (A) and the compound (B).
(I) The charge generation layer comprises a first layer containing at least one kind of the metal or a compound thereof (A) and a second layer containing at least one kind of the compound (B) (laminated structure). .
(Ii) The charge generation layer is a mixed layer containing one or more of the metal or its compound (A) and one or more of the compound (B) in one layer (mixed layer).
In the case of a laminated structure, it is preferable to laminate the first layer on the anode side (the side facing the hole-injecting electrode) and the second layer on the cathode side. In the case of a mixed layer, a continuous film is formed by forming a layer in which two kinds of materials are mixed at a time by a method such as co-evaporation, or by forming the material constituting the first layer extremely thin. A mixed layer can be formed by using a method of forming a previous island-like discrete structure and forming a second layer on this structure to form a mixed layer.
As the material constituting the second layer, an inorganic or organic compound having a work function of 4.0 eV or more is selected. As the inorganic compound having a work function of 4.0 eV or more, a transition metal oxide is desirable. Among the transition metal oxides, vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo ), Tungsten (W), manganese (Mn), technetium (Tc), rhenium (Re), and other oxides are preferable. V ₂ O ₅ and MoO ₃ are more preferable.
In addition, as an organic compound having a work function of 4.0 eV or more used for the second layer, it is difficult to dissolve in a coating solution used in a later step and easily accepts electrons from the material of the first layer. Material is preferred. More preferably, a charge transfer complex is formed with the material of the first layer. An example of such a material is tetrafluoro-tetracyanoquinodimethane (4F-TCNQ).
The thickness of the second layer is preferably 2 nm or more and 100 nm or less, and more preferably 4 nm or more and 80 nm or less.

  The charge generation layer of the present invention may further include a transparent conductive thin film as the third layer. As the transparent conductive thin film, indium oxide, zinc oxide, tin oxide, indium tin oxide (ITO) that is a composite thereof, or the like can be used.

  As a method for forming the charge generation layer of the present invention, a vacuum deposition method, a sputtering method, a coating method, or the like can be used.

  As for the light transmittance of the charge generation layer of the present invention, it is desirable to have a high transmittance for the light emitted from the light emitting layer. In order to sufficiently extract light and obtain sufficient luminance, the transmittance at a wavelength of 550 nm is desirably 30% or more, and more preferably 50% or more.

(Mixed color, white)
Since the organic EL element of the present invention is a stacked element and includes a plurality of light emitting units that emit light at the same time, the light emission wavelengths of the respective light emitting units can be made different from each other to be different colors by color mixing. is there. In particular, it can be made white by combining two colors having a complementary color relationship, mixing three colors such as RGB, or mixing four or more colors.

(Cavity effect)
In the organic EL device of the present invention, the thickness of the layer including the light emitting unit and the charge generation layer sandwiched between two opposing electrodes determines the wavelength of light generated from the light emitting unit and the average refraction of the light emitting unit and the charge generation layer. It is preferably an integral multiple of 1/4 of the value divided by the rate. This is because the maximum light extraction efficiency can be obtained by the light interference effect in the configuration satisfying such a relationship. When this relationship is strictly established, the effect is maximum, but even if there is an error, the effect is recognized, and the film thickness is generally an integral multiple of 1/4 of the value obtained by dividing the emission wavelength by the average refractive index. It may be within 20%. Furthermore, it is preferable because the light interference effect is maximized when the position of the substantially emitting region is at a position where the distance from the light-reflecting electrode is an integral multiple of 1/4 of the emission wavelength.
When the organic EL element is composed of a plurality of light emitting units having different emission colors, it is preferable to control the film thickness so that the above relationship is established with respect to any one wavelength. Alternatively, the layer thickness may be controlled so that the relationship of the above layer thicknesses holds simultaneously for the two wavelengths.

A conventionally known structure can be used as the structure of the light emitting unit in the present invention. That is,
(Anode) / light emitting layer / (cathode),
(Anode) / hole transport layer / light emitting layer / (cathode),
(Anode) / Hole transport layer / Light emitting layer / Electron transport layer / (Cathode)
Etc. In addition to these, a charge injection layer may be used for the purpose of facilitating charge injection between the electrode and the organic layer. The charge injection layer includes an electron injection layer on the cathode side and a hole injection layer on the anode side. Further, an interlayer may be inserted between the hole transport layer and the light emitting layer or between the electron injection layer and the light emitting layer for the purpose of increasing the light emission efficiency.

In the present invention, the transparent electrode or the semitransparent electrode which is the first electrode can be a metal oxide, metal sulfide or metal thin film having high electrical conductivity, and a material having a high transmittance can be suitably used. Are appropriately selected depending on the organic layer to be used. Specifically, indium oxide, zinc oxide, tin oxide, and a composite film made of conductive glass made of indium / tin / oxide (ITO), indium / zinc / oxide, etc. (NESA) Etc.), gold, platinum, silver, copper and the like are used, and ITO, indium / zinc / oxide, and tin oxide are preferable. Examples of the production method include a vacuum deposition method, a sputtering method, an ion plating method, a plating method, and the like. Further, as the anode, an organic transparent conductive film such as polyaniline or a derivative thereof, polythiophene or a derivative thereof may be used.
The film thickness of the anode can be appropriately selected in consideration of light transmittance and electrical conductivity, and is, for example, 10 nm to 10 μm, preferably 20 nm to 1 μm, more preferably 50 nm to 500 nm. is there.

Further, a hole injection layer may be formed between the anode and the light emitting unit in order to facilitate hole injection. As a material for the hole injection layer, a material having an ionization potential intermediate between the anode material and the hole transport material is preferable. For example, conductive polymers such as phthalocyanine derivatives and polythiolene derivatives, Mo oxide, amorphous carbon, carbon fluoride, polyamine compounds and other layers having a thickness of 1 to 200 nm, or metal oxides, metal fluorides, organic insulating materials, etc. A layer having a thickness of 2 nm or less is desirable.
Conductive polymer materials include polyaniline and derivatives thereof, polythiophene and derivatives thereof, polypyrrole and derivatives thereof, polyphenylene vinylene and derivatives thereof, polythienylene vinylene and derivatives thereof, polyquinoline and derivatives thereof, polyquinoxaline and derivatives thereof, aromatic Examples thereof include polymers containing an amine structure in the main chain or side chain.
The electrical conductivity of the conductive polymer is preferably 10 ⁻⁷ S / cm or more and 10 ³ S / cm or less. In order to reduce the leakage current between the light emitting pixels, 10 ⁻⁵ S / cm or more. 10 ² S / cm or less is more preferable, and 10 ⁻⁵ S / cm or more and 10 ¹ S / cm or less is more preferable. Usually, in order to increase the hole injection property by setting the electric conductivity of the conductive polymer to 10 ⁻⁵ S / cm or more and 10 ³ S / cm or less, the conductive polymer is doped with an appropriate amount of anion. As examples of anions, polystyrene sulfonate ions, alkylbenzene sulfonate ions, camphor sulfonate ions, and the like are preferably used.

  As the second electrode of the present invention, a material having a small work function is preferable. For example, alkali metals such as lithium, sodium, potassium, rubidium and cesium, alkaline earth metals such as beryllium, magnesium, calcium, strontium and barium, metals such as aluminum, scandium, vanadium and zinc, yttrium, indium, cerium and samarium Rare earth metals such as europium, terbium, ytterbium, or two or more alloys thereof, or one or more thereof, and gold, silver, platinum, copper, manganese, titanium, cobalt, nickel, tungsten, tin Among them, an alloy with one or more, graphite, a graphite intercalation compound, or the like is used. Examples of the alloy include magnesium-silver alloy, magnesium-indium alloy, magnesium-aluminum alloy, indium-silver alloy, lithium-aluminum alloy, lithium-magnesium alloy, lithium-indium alloy, calcium-aluminum alloy, and the like. The cathode may have a laminated structure of two or more layers.

  The film thickness of the cathode can be appropriately selected in consideration of electric conductivity and durability, but is, for example, 10 nm to 10 μm, preferably 20 nm to 1 μm, and more preferably 50 nm to 500 nm.

In order to facilitate electron injection between the cathode and the light emitting unit, an electron injection layer may be formed. As a material for the electron injection layer, a material having an intermediate electron affinity between the cathode material and the electron transport material is desirable. For example, a metal fluoride, a metal oxide, an organic insulating material, or the like can be given. Among them, a metal fluoride or a metal oxide such as an alkali metal or an alkaline earth metal is preferable. Conductive polymer materials are also used.
As the material of the conductive polymer, the polymer material having the electrical conductivity described in the hole injection material may be used, but in order to improve the electron injection property, an appropriate amount of cation is doped. Examples of cations include lithium ions, sodium ions, potassium ions, tetrabutylammonium ions, and the like.
The film thickness of the electron injection layer is, for example, 1 nm to 150 nm, and preferably 2 nm to 100 nm.

As a method for producing the first electrode (anode) or the second electrode (cathode), a vacuum deposition method, a sputtering method, a laminating method for thermocompression bonding a metal thin film, or the like is used.
The order in which the first electrode and the second electrode are formed on the substrate is not particularly limited, and can be appropriately selected according to the top emission type and bottom emission type element structures.

  Furthermore, in the organic EL element of the present invention, a plurality of light emitting units are used, and the light emitting units include one or more organic layers. One of the one or more organic layers is a light emitting layer, and light emission occurs when holes and electrons recombine there. For the organic layer, a charge transport material or a light emitting material used for a low molecular organic EL element, or a polymer light emitting material used for a polymer organic EL element is used. Examples of light emission colors include light emission of an intermediate color and white other than light emission of three primary colors of red, blue, and green. The full color element preferably emits light of three primary colors, and the planar light source emits light of white or intermediate color.

Examples of the charge transport material and the light emitting material used for the low molecular organic EL element include known low molecular compounds and triplet light emitting complexes. Examples of low molecular weight compounds include naphthalene derivatives, anthracene or derivatives thereof, perylene or derivatives thereof, polymethine-based, xanthene-based, coumarin-based, cyanine-based pigments, 8-hydroxyquinoline or metal complexes of derivatives thereof, aromatic amines, and the like. , Tetraphenylcyclopentadiene or a derivative thereof, or tetraphenylbutadiene or a derivative thereof can be used.
Further examples of triplet light emitting complexes include, for example, Ir (ppy) ₃ , Btp ₂ Ir (acac) having iridium as a central metal, PtOEP having platinum as a central metal, and Eu (TTA) ₃ having europium as a central metal. phen and the like. .

The thickness of each of these layers is appropriately selected so that the light emission efficiency and the driving voltage are as desired, but is generally 5 nm to 200 nm. As a positive hole transport layer, 10-100 nm is illustrated, Preferably it is 20-80 nm. As a light emitting layer, 10-100 nm is illustrated and 20-80 nm is preferable. In the hole blocking layer, 5 to 50 nm is exemplified, and 10 to 30 nm is preferable. As an electron injection layer, 10-100 nm is illustrated and 20-80 nm is preferable.
Examples of the method for forming these layers include vacuum processes such as vacuum deposition, cluster deposition, and molecular beam deposition. In addition, in the case of materials capable of forming solubility and emulsion, the coating method and printing described later are used. A method for forming a film by the method is exemplified.

Polymer light-emitting materials used for polymer organic EL devices include polyfluorene, derivatives and copolymers thereof, polyarylene, derivatives and copolymers thereof, polyarylene vinylene, derivatives and copolymers thereof, aromatic amines And (co) polymers of derivatives thereof. The light-emitting material and the charge transport material may be mixed with the above-described light-emitting material or charge transport material for a low molecular organic EL element.
In the organic EL device of the present invention, the light emitting layer in at least one of the plurality of light emitting units contains a polymer light emitting material.
The polymer light emitting material preferably has a weight average molecular weight of 10,000 to 10,000,000, more preferably 20,000 to 5,000,000. The polymer light emitting material is preferably soluble in an organic solvent.
Examples of the thickness of the polymer light emitting layer include 5 nm to 300 nm, preferably 30 to 200 nm, and more preferably 40 to 15 nm.

The light emitting layer containing a polymer material, the charge transport layer and the charge injection layer, the light emitting layer not containing the polymer material, and the film forming method of the charge transport layer and the charge injection layer described so far include a coating method from a solution, The printing method can be mentioned. The solvent can be easily removed from this solution by drying after coating. In addition, the same technique can be applied even when a charge transport material or a light emitting material is mixed, which is very advantageous in production. As a film forming method from a solution, a spin coating method, a casting method, a micro gravure coating method, a gravure coating method, a bar coating method, a roll coating method, a wire bar coating method, a dip coating method, a spray coating method, a screen printing method, Application methods such as a flexographic printing method, an offset printing method, and an ink jet printing method can be used. A charge injection material that is in the form of an emulsion and dispersed in water or alcohol can be formed into a film by the same method as that for a solution.
Although there is no restriction | limiting in particular as a solvent used for a polymeric material by a coating method or a printing method, The thing which can melt | dissolve or disperse | distribute materials other than the solvent which comprises a coating liquid is preferable. When the material constituting the coating solution is soluble in a non-polar solvent, the solvent is a chlorine solvent such as chloroform, methylene chloride or dichloroethane, an ether solvent such as tetrahydrofuran, toluene, xylene, tetralin or anisole. , Aromatic hydrocarbon solvents such as n-hexylbenzene and cyclohexylbenzene, aliphatic hydrocarbon solvents such as decalin and bicyclohexyl, ketone solvents such as acetone, methyl ethyl ketone, 2-heptanone, ethyl acetate, butyl acetate, Ester solvents such as ethyl cellosolve acetate and propylene glycol monomethyl ether acetate can be suitably used.

  The substrate on which the organic EL device of the present invention is formed may be any substrate that does not change when forming the electrodes and each layer of the device, and examples thereof include glass, plastic, polymer film, and silicon substrate. In the case of an opaque substrate, the opposite electrode is preferably transparent or translucent.

Hereinafter, examples and comparative examples will be shown to describe the present invention in more detail, but the present invention is not limited to these examples.
Example _{1 (ITO / PEDOT / MEH-} PPV / Li / V 2 O 5 / MEH-PPV / LiAl)
A production example of the organic EL element of the present invention will be described with reference to FIG. An ITO film used as the anode 2 is formed on a glass substrate 1 having a thickness of 150 nm by a sputtering method, and a PEDOT: PSS solution made by BYTRON is formed to a thickness of 40 nm by a spin coating method. Heat treatment was performed to form a hole injection layer 3-1. Subsequently, MEH-PPV (poly (2-methoxy-5- (2′-ethyl-hexyloxy) -para-phenylenevinylene) manufactured by Aldrich, 1 wt% toluene having a weight average molecular weight of about 200,000 as a light emitting material was used. A solution was prepared, and this was spin-coated on a substrate on which PEDOT: PSS was previously formed to form a first light-emitting layer 3-2 with a thickness of 90 nm. One light emitting layer 3-2 is collectively referred to as a first light emitting unit 3.
On top of this, Li (work function: 2.93 eV) and V ₂ O ₅ (work function: 4 eV or more) are sequentially formed with a thickness of 2 nm and 20 nm, respectively, as the charge generation layer 4 by vacuum deposition. The layer 4-1 and the second layer 4-2 were used. Here, the deposition of Li is performed by using an Al-Li alloy (Li content 0.05%) by depositing only Li that flies first for several tens of seconds before Al begins to fly, and immediately after that, V ₂ O ₅ was deposited.
Further, a 1 wt% toluene solution of MEH-PPV was spin-coated on the V ₂ O ₅ film to form a second light emitting layer (second light emitting unit) 5 with a film thickness of 90 nm. Further, an Al—Li alloy having a thickness of 100 nm was formed thereon as a cathode 6 by vacuum evaporation. Thus, an organic EL element having a structure in which two light emitting units were separated by one charge generation layer was produced.
When a DC voltage was applied to the obtained device, the light emission starting voltage was 12 V and the maximum luminance was 80 cd / m ² .
The current efficiency was 0.072 cd / A, which was increased 1.95 times compared to the element of Comparative Example 1 (0.037 cd / A) described below.

Comparative Example 1
For comparison, an element having only one light emitting unit as shown in FIG. 2 was produced in the same manner as in Example 1 except that the charge generation layer and the second light emitting layer were not provided in Example 1. The reference numerals in FIG. 2 are the same as those in FIG.
When a DC voltage was applied to the comparative element, the light emission starting voltage was 5.5 V and the maximum luminance was 52 cd / m ² . The current efficiency was 0.037 cd / A.

Comparative Example 2
An organic EL device was produced in the same manner as in Example 1 except that the charge generation layer was composed of only one layer of V ₂ O _{5 having} a thickness of 30 nm. The obtained device did not emit light even when the light emission starting voltage was 40V.

高分子材料２

Example 2 (color mixing element composed of a stack of light emitting units of different colors)
Instead of MEH-PPV, which is the light emitting layer in Example 1, first light emission including a polymer light emitting layer made of a polymer light emitting material 1 (abbreviated as F8-TPA-BT) represented by Structural Formula 1 that emits green light. After the unit and the charge generation layer 4 are formed, a PEDOT / PSS layer is formed, and then a polymer light-emitting material composed of the polymer light-emitting material 2 (abbreviated as F8-TPA-PDA) represented by Structural Formula 2 that emits blue light. After forming the second light-emitting unit including the layers, a cathode was formed in the same manner as in Example 1 to produce light-emitting elements having different emission wavelengths from the two light-emitting units.
Polymer material 1

Polymer material 2

Comparative Examples 3 and 4 (Comparison with Example 2, single element consisting only of green and blue light-emitting layers)
For comparison with Example 2, an element composed of one light-emitting unit having a structure of ITO / PEDOT / light-emitting layer / cathode (Li / Al) was used as a green light-emitting layer material F8-TPA-BT (Comparative Example 1), blue Two of the light emitting materials F8-TPA-PDA (Comparative Example 2) were produced.

  The driving voltages in Comparative Examples 1 and 2 were 3.6 V and 5.4 V, respectively, whereas in Example 2, the driving voltage was 8.0 V, which was close to the expected voltage of an element in which two units were stacked. In the element of Example 2, the spectrum was broadened due to color mixture from the two layers, and whited green light emission was obtained.

  The organic electroluminescence device of the present invention can be used for the production of a tandem organic EL device made of a polymer material by using the charge generation layer unique to the present invention.

The figure which shows the cross-sectional layer structure of the organic EL element of Example 1 of this invention. The figure which shows the cross-sectional layer structure of the conventional organic EL element.

Explanation of symbols

1 Substrate 2 Anode (hole injection electrode)
DESCRIPTION OF SYMBOLS 3 1st light emission unit 3-1 Hole injection layer 3-2 1st light emission layer 4 Charge generation layer 4-1 1st layer 4-2 2nd layer 5 2nd light emission layer (2nd light emission layer) unit)
6 Cathode (electron injection electrode)

Claims (13)

Two opposing electrodes connected to an external circuit for providing electrical energy, at least one of which is transparent or translucent, and one or more organic layers between the electrodes, Is a light emitting layer, and includes a plurality of light emitting units that emit light by recombination of holes and electrons, and an organic electroluminescent device comprising a charge generation layer sandwiched between two of the plurality of light emitting units In
Two adjacent ones of the plurality of light emitting units are separated by the charge generation layer,
The charge generation layer includes a first layer made of an alkali metal or alkaline earth metal having a work function of 3.0 eV or less, and a second layer made of the compound (B) having a work function of 4.0 eV or more . all SANYO stacked in this order from the anode side,
The organic electroluminescent device, at least one emitting layer, characterized by containing a polymer luminescent material of the plurality of light emitting units. The organic electroluminescence device according to claim 1 Symbol placement transmittance versus wavelength is 30% or more at 550nm of the charge generating layer. The organic electroluminescence device according to claim 1 or 2, wherein the compound having a work function of 4.0 eV or more is a transition metal oxide. The organic electroluminescence device according to claim 3, wherein the transition metal oxide is an oxide of one or more metals selected from the group consisting of V, Nb, Ta, Cr, Mo, W, Mn, Tc, and Re. . The organic electroluminescence device according to claim 1 or 2 , wherein the metal having a work function of 3.0 eV or less is Li, and the compound having a work function of 4.0 eV or more is V ₂ O ₅ . The organic electroluminescence device according to claim 1 or 2, wherein the compound having a work function of 4.0 eV or more is at least one organic compound. The organic electroluminescence device according to any one of claims 1 to 6 , wherein the polymer light emitting material has a weight average molecular weight of 10,000 to 10,000,000 and is soluble in an organic solvent. The organic electroluminescent device of any one of claims 1-7 emission color of the light emitting layer of the two light-emitting units are separated by one of the charge generation layer is not the same. The thickness of the layer including one light emitting unit and one charge generation layer between the two opposing electrodes determines the wavelength of light generated from the light emitting unit and the average refractive index of the light emitting unit and the charge generation layer. the organic electroluminescent device of any one of claims 1-8 is within ± 20% of 1/4 of the integral multiple of a value obtained by dividing by. The charge generation layer is one formed by a vacuum deposition method, an organic electroluminescent device of any one of claims 1-9. And forming a film from a solution of at least one layer of the layers constituting the light emitting unit, a method of manufacturing an organic electroluminescent device of any one of claims 1-10. How a charge generating layer, and forming by the vacuum deposition method, for manufacturing an organic electroluminescent device of any one of claims 1-10. The light-emitting device which has an organic electroluminescent element as described in any one of Claims 1-10 .

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