JP2005093425A - Light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting element having high luminous efficiency and excellent durability, which can be utilized in the field such as a display element, flat panel display, backlight, lighting, interior, identification marks, signboard, electronic camera, and optical signal generator or the like. <P>SOLUTION: The light emitting element has at least a luminous layer and an electron transporting layer between a positive electrode and a negative electrode and emits light by electric energy. The electron transporting layer is composed of a first electron transporting layer that contacts the luminous layer and a second electron transporting layer that exists between the negative electrode and the first electron transporting layer. The second electron transporting layer contains a heteroaromatic ring derivative having electron accepting nitrogen and the heteroaromatic ring derivative is a compound formed by covalent bond only. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is a light emitting element capable of converting electrical energy into light, and can be used in the fields of display elements, flat panel displays, backlights, lighting, interiors, signs, signboards, electrophotographic machines, optical signal generators, and the like. The present invention relates to a light emitting element.

  In recent years, research on organic thin-film light emitting devices that emit light when electrons injected from a cathode and holes injected from an anode are recombined in an organic phosphor sandwiched between both electrodes has been actively conducted. This light emitting element is characterized by thin light emission with high luminance under a low driving voltage and multicolor light emission by selecting a fluorescent material.

This study was conducted by C.D. W. Since Tang et al. Have shown that organic thin film devices emit light with high brightness, many research institutions have studied. The representative structure of the organic thin film light emitting device presented by the Kodak research group is a hole transporting diamine compound on the ITO glass substrate, 8-hydroxyquinoline aluminum as the light emitting layer, and Mg: Ag as the cathode in sequence. It was provided, and green light emission of 1,000 cd / m ² was possible with a driving voltage of about 10 V (see Non-Patent Document 1).

  In addition, organic thin-film light-emitting elements can be obtained in various emission colors by using various fluorescent materials for the light-emitting layer, and therefore, researches for practical application to displays and the like are actively conducted. Among the three primary color luminescent materials, research on the green luminescent material is the most advanced, and at present, intensive research is being conducted to improve the characteristics of the red and blue luminescent materials.

  In recent years, it has been proposed to use a phosphorescent material in addition to a fluorescent material for the light emitting layer of an organic thin film light emitting element (see Non-Patent Document 2). Phosphorescence in an organic compound refers to light emission accompanying a transition from a triplet excited state to a singlet ground state. When holes and electrons recombine in the light emitting layer, it is considered that singlets and triplets are generated at a ratio of 1: 3 due to the difference in spin multiplicity, and phosphorescent devices are devices that use fluorescence. It is considered that there is a possibility that a luminous efficiency of 3 to 4 times that of the above can be achieved.

On the other hand, in order to improve the light emission efficiency and durability of the organic thin film light emitting element and to reduce the driving voltage, a device configuration has been studied. For example, the electron transport portion between the light emitting layer and the cathode is laminated on a hole blocking layer (first electron transport layer) that restricts the movement of holes from the light emitting layer and a second electron transport layer that is responsible for electron transport. As a result, the recombination probability of holes and electrons in the light emitting layer can be improved, and an improvement in light emission efficiency can be achieved. As the hole blocking material, phenanthroline derivatives and triazole derivatives have been reported to be effective (see Patent Document 1, Patent Document 2, and Patent Document 3).
“Applied Physics Letters”, (USA), 1987, 51, 12, p. 913-915 “Applied Physics Letters”, (USA), 1999, Vol. 74, No. 3, p. 442-444 JP-A-8-109373 JP-A-10-233284 JP 2001-267080 A

  However, in the conventional organic thin film light emitting device, the driving stability of the light emitting device is low, and sufficient durability has not been obtained. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve such problems of the prior art and to provide a light emitting element having high luminous efficiency and excellent durability.

  The present invention aims to achieve the above object, and the light emitting device of the present invention is a device that has at least a light emitting layer and an electron transport layer between an anode and a cathode, and emits light by electric energy, The electron transport layer comprises a first electron transport layer in contact with the light emitting layer and a second electron transport layer present between the cathode and the first electron transport layer, and the second electron transport layer is a complex having electron-accepting nitrogen. A light-emitting element comprising a compound comprising an aromatic ring, wherein the compound comprising a heteroaromatic ring is a compound formed only by a covalent bond.

  According to the present invention, a light emitting device having high luminous efficiency and excellent durability can be obtained by laminating two or more electron transport layers and using a specific material. Therefore, the light-emitting element of the present invention can be applied to fields such as display elements, flat panel displays, backlights, lighting, interiors, signs, signboards, electrophotographic machines, and optical signal generators, and has great technical value. Is.

  Embodiments of the light-emitting element of the present invention will be described in detail. The light emitting device of the present invention is basically composed of an anode and a cathode, and an organic layer made of a light emitting device material interposed between the anode and the cathode.

  In order to extract light, the anode used in the present invention is made of a conductive metal oxide such as tin oxide, indium oxide and indium tin oxide (ITO), or a metal such as gold, silver and chromium, or iodide if transparent. Inorganic conductive materials such as copper and copper sulfide, and conductive polymers such as polythiophene, polypyrrole and polyaniline are not particularly limited, but it is particularly desirable to use ITO glass or Nesa glass.

  The resistance of the transparent electrode is not limited as long as it can supply a sufficient current for light emission of the light emitting element, but is preferably low resistance from the viewpoint of power consumption of the light emitting element. For example, an ITO substrate of 300Ω / □ or less functions as an element electrode, but since it is now possible to supply a substrate of about 10Ω / □, it is particularly desirable to use a low resistance product. The thickness of ITO can be arbitrarily selected according to the resistance value, but is usually used in a range of 100 to 300 nm.

Further, soda lime glass or non-alkali glass is used for the glass substrate, and it is sufficient that the thickness is sufficient to maintain the mechanical strength, so 0.5 mm or more is sufficient. The glass material is preferably alkali-free glass because it is better to have less ions eluted from the glass. However, soda lime glass with a barrier coat such as SiO ₂ is also commercially available, so it can be used. it can. Furthermore, if the anode functions stably, the substrate does not have to be glass. For example, the anode may be formed on a plastic substrate. The ITO film forming method is not particularly limited, such as an electron beam method, a sputtering method, and a chemical reaction method.

  The cathode used in the present invention is not particularly limited as long as it can efficiently inject electrons into the organic layer, but is generally platinum, gold, silver, copper, iron, tin, zinc, aluminum, indium, chromium, lithium, sodium. , Potassium, cesium, calcium and magnesium. Lithium, sodium, potassium, cesium, calcium, magnesium, or alloys containing these low work function metals are effective for increasing the electron injection efficiency and improving device characteristics. However, these low work function metals are generally unstable in the atmosphere. For example, the organic layer is doped with a small amount of lithium, cesium, or magnesium (1 nm or less in vacuum vapor deposition thickness gauge display). Although a method using a highly stable electrode can be given as a preferred example, it is particularly limited to these because inorganic salts such as lithium fluoride, cesium fluoride, lithium oxide and cesium oxide can also be used. It is not something. Furthermore, for electrode protection, metals such as platinum, gold, silver, copper, iron, tin, aluminum and indium, or alloys using these metals, and inorganic substances such as silica, titania and silicon nitride, polyvinyl alcohol, vinyl chloride Lamination of hydrocarbon polymer compounds and the like is a preferred example. The method for producing these electrodes is not particularly limited as long as conduction can be achieved, such as resistance heating, electron beam, sputtering, ion plating, and coating.

  As for the light emitting element of this invention, the organic layer is comprised from light emitting element material. The light emitting device material corresponds to either a compound that emits light by itself or a substance that assists light emission, and refers to a compound that participates in light emission. Specifically, a hole transport material, a light emitting material, and an electron This includes transportation materials.

  In the light-emitting device of the present invention, the organic layer is formed of a layer made of a light-emitting device material, and at least a light-emitting layer and an electron transport layer made of the light-emitting device material exist between the anode and the cathode. The electron transport layer includes a first electron transport layer in contact with the light emitting layer and a second electron transport layer present between the cathode and the first electron transport layer. Examples of the configuration of the organic layer include 1) hole transport layer / light emitting layer / first electron transport layer / second electron transport layer, and 2) light emitting layer / first electron transport layer / second electron transport layer, etc. A laminated structure is mentioned. Moreover, each said layer may consist of a single layer, respectively, and may consist of multiple layers.

  The hole transport layer is formed by laminating and mixing one or more hole transport materials or a mixture of the hole transport material and the polymer binder. Alternatively, an inorganic salt such as iron (III) chloride may be added to the hole transport material to form a layer. Examples of the hole transport material include N, N′-diphenyl-N, N′-di (3-methylphenyl) -4,4′-diphenyl-1,1′-diamine, N, N′-dinaphthyl- Triphenylamine derivatives such as N, N′-diphenyl-4,4′-diphenyl-1,1′-diamine, 4,4 ′, 4 ″ -tris (3-methylphenyl (phenyl) amino) triphenylamine, Biscarbazole derivatives such as bis (N-allylcarbazole) or bis (N-alkylcarbazole), pyrazoline derivatives, stilbene compounds, hydrazone compounds, benzofuran derivatives, thiophene derivatives, oxadiazole derivatives, phthalocyanine derivatives, porphyrin derivatives, etc. For heterocyclic compounds and polymers, polycarbonates and Derivatives, polyvinylcarbazole, polysilane, and the like are preferable, but the compound is not particularly limited as long as it is a compound that forms a thin film necessary for manufacturing a light-emitting element, can inject holes from the anode, and can further transport holes. .

  In the present invention, the light emitting layer may be either a single layer or a plurality of layers, each formed of a light emitting material (host material, dopant material), which may be a mixture of a host material and a dopant material, Either the material alone or the material may be used. That is, in the light emitting element of the present invention, only the host material or the dopant material may emit light in each layer of the light emitting layer, or both the host material and the dopant material may emit light. Each of the host material and the dopant material may be one kind or a plurality of combinations. The dopant material may be included in the host material as a whole, or may be included partially. The dopant material may be either laminated or dispersed. When the amount of the dopant material is too large, a concentration quenching phenomenon occurs, so that it is preferably used at 10 wt% or less, more preferably 5 wt% or less with respect to the host material. As a doping method, it can be formed by a co-evaporation method with a host material, but it may be pre-mixed with the host material and then simultaneously deposited.

  Further, the luminescent material of the present invention may be either fluorescent or phosphorescent. In particular, when the light emitting layer includes a fluorescent light emitting material, the light emitting layer exhibits blue light emission having a peak wavelength at 420 to 490 nm, and the light emitting layer includes a phosphorescent light emitting material, and the light emitting layer exhibits phosphorescent light emission. In this case, since the band gap of the light emitting layer is large and the amount of energy involved in light emission becomes large, the effect of improving the durability according to the present invention becomes remarkable. In the present invention, fluorescence emission refers to light emission due to transition between states having the same spin multiplicity, and phosphorescence emission refers to light emission due to transition between states having different spin multiplicity. For example, light emission associated with a transition from a singlet excited state to a ground state (in general, the ground state of an organic compound is a singlet) is fluorescence, and light emission associated with a transition from a triplet excited state to a ground state is phosphorous. Light emission.

  The dopant material used in the present invention is not particularly limited, and a known compound can be used, and can be selected from various materials according to a desired emission color.

  Specifically, although not limited to this, as a blue to blue-green dopant material, aromatic hydrocarbon compounds such as naphthalene, anthracene, phenanthrene, pyrene, triphenylene, perylene, fluorene, indene and derivatives thereof, Furan, pyrrole, thiophene, silole, 9-silafluorene, 9,9'-spirobisilafluorene, benzothiophene, benzofuran, indole, dibenzothiophene, dibenzofuran, imidazopyridine, phenanthroline, pyrazine, naphthyridine, quinoxaline, pyrrolopyridine, thio Aromatic heterocyclic compounds such as xanthene and derivatives thereof, distyrylbenzene derivatives, tetraphenylbutadiene derivatives, stilbene derivatives, aldazine derivatives, coumarin derivatives, imidazole, thiazole, Azole derivatives such as asiazole, carbazole, oxazole, oxadiazole, triazole and metal complexes thereof, and N, N′-diphenyl-N, N′-di (3-methylphenyl) -4,4′-diphenyl-1, An aromatic amine derivative represented by 1′-diamine and the like can be mentioned.

  Examples of the green to yellow dopant material include coumarin derivatives, phthalimide derivatives, naphthalimide derivatives, perinone derivatives, pyrrolopyrrole derivatives, cyclopentadiene derivatives, acridone derivatives, quinacridone derivatives, and naphthacene derivatives such as rubrene, and the above blue A compound in which a substituent capable of increasing the wavelength such as an aryl group, a heteroaryl group, an arylvinyl group, an amino group, or a cyano group is introduced into the compound exemplified as a blue-green dopant material is also a suitable example.

  Further, examples of the orange to red dopant material include naphthalimide derivatives such as bis (diisopropylphenyl) perylenetetracarboxylic imide, perinone derivatives, rare earth complexes such as Eu complexes having acetylacetone, benzoylacetone and phenanthroline as ligands, 4 -(Dicyanomethylene) -2-methyl-6- (p-dimethylaminostyryl) -4H-pyran and its analogs, metal phthalocyanine derivatives such as magnesium phthalocyanine and aluminum chlorophthalocyanine, rhodamine compounds, deazaflavin derivatives, coumarin derivatives, quinacridone Derivatives, phenoxazine derivatives, oxazine derivatives, quinazoline derivatives, pyrrolopyridine derivatives, squarylium derivatives, violanthrone derivatives, phenazine derivatives, phenoxazones Conductors and thiadiazolopyrene derivatives, etc. can be used. In addition, the compounds exemplified above as blue to blue-green and green to yellow dopant materials can increase the wavelength of aryl groups, heteroaryl groups, arylvinyl groups, amino groups, cyano groups, etc. A compound into which a substituent is introduced is also a suitable example. Furthermore, a phosphorescent metal complex having iridium or platinum represented by tris (2-phenylpyridine) iridium (III) as a central metal is also a suitable example.

  The host material used in the present invention is not particularly limited, but metal chelates such as fused ring derivatives such as anthracene and pyrene, tris (8-quinolinolato) aluminum, which have been known as light emitters. Oxinoid compounds, bisstyryl derivatives such as bisstyrylanthracene derivatives and distyrylbenzene derivatives, tetraphenylbutadiene derivatives, coumarin derivatives, oxadiazole derivatives, pyrrolopyridine derivatives, perinone derivatives, cyclopentadiene derivatives, oxadiazole derivatives, thiadiazolo For pyridine derivatives, pyrrolopyrrole derivatives, and polymer systems, polyphenylene vinylene derivatives, polyparaphenylene derivatives, and polythiophene derivatives are preferably used.

  The host material of the light emitting layer exhibiting phosphorescence emission is not particularly limited, but 4,4′-bis (carbazolyl-N-yl) biphenyl or N, N′-diphenyl-3,3 ′ Carbazole derivatives such as biscarbazole, N, N′-diphenyl-N, N′-di (3-methylphenyl) -4,4′-diphenyl-1,1′-diamine, N, N′-dinaphthyl-N , N′-diphenyl-4,4′-diphenyl-1,1′-diamine and other triphenylamine derivatives, indole derivatives, azole derivatives such as triazole, oxadiazole and imidazole, phenanthroline derivatives, quinoline derivatives, quinoxaline derivatives, Examples thereof include naphthyridine derivatives, oligopyridine derivatives such as bipyridine and terpyridine.

  In the present invention, the electron transport layer is a layer that administers electrons injected from the cathode and further transports electrons. It is desirable that the electron transport efficiency is high and the injected electrons are transported efficiently. For this purpose, it is required that the material has a high electron affinity, a high electron mobility, excellent stability, and a substance that does not easily generate trapping impurities during manufacturing and use. However, considering the transport balance between holes and electrons, if the role of effectively preventing the holes from the anode from flowing to the cathode side without recombination is mainly played, the electron transport capability is much higher. Even if it is not high, the effect of improving the luminous efficiency is equivalent to that of a material having a high electron transport capability. Therefore, the electron transport layer in the present invention includes a hole blocking layer that can efficiently block the movement of holes as the same meaning.

  The electron transport layer in the present invention comprises a first electron transport layer in contact with the light emitting layer, and a second electron transport layer present between the first electron transport layer and the cathode. The first and second electron transport layers are each formed by laminating and mixing one kind or two or more kinds, or a mixture of an electron transport material and a polymer adhesive. Alternatively, a layer may be formed by adding a metal such as lithium or cesium or an inorganic salt such as lithium fluoride or cesium fluoride to the electron transport material.

  It is important that the second electron transport layer of the present invention contains a compound composed of a heteroaromatic ring having electron-accepting nitrogen, and the compound composed of the heteroaromatic ring is a compound formed only by a covalent bond.

  On the other hand, the first electron transport layer is composed of an aromatic ring or heteroaromatic ring composed of one or more atoms selected from carbon, hydrogen, oxygen, sulfur, silicon and phosphorus, a pyrrole derivative and a condensed ring derivative thereof. And at least one selected from metal complexes having electron-accepting nitrogen.

  The electron-accepting nitrogen in the present invention represents a nitrogen atom that forms a multiple bond with an adjacent atom. Since the nitrogen atom has a high electronegativity, the multiple bond has an electron accepting property. Therefore, a heteroaromatic ring having an electron-accepting nitrogen has a high electron affinity. Examples of heteroaromatic rings having electron-accepting nitrogen include, for example, pyridine ring, pyrazine ring, pyrimidine ring, quinoline ring, quinoxaline ring, naphthyridine ring, pyrimidopyrimidine ring, benzoquinoline ring, phenanthroline ring, imidazole ring, oxazole ring, Examples thereof include an oxadiazole ring, a triazole ring, a thiazole ring, a thiadiazole ring, a benzoxazole ring, a benzothiazole ring, a benzimidazole ring and a phenanthrimidazole ring.

  The aromatic ring or heteroaromatic ring composed of one or more atoms selected from carbon, hydrogen, oxygen, sulfur, silicon and phosphorus includes hydrocarbons such as benzene ring, naphthalene ring, phenanthrene ring and anthracene ring. Examples include, but are not limited to, heteroaromatic rings such as aromatic ring, furan ring, thiophene ring and silole ring, and condensed rings thereof.

The ionization potential of the second electron transport layer is not particularly limited, but is preferably 5.8 eV or more and 8.0 eV or less, and more preferably 6.0 eV or more and 7.5 eV or less. Further, it is preferable ionization potential Eg ₁ of the first electron-transporting layer is smaller than the ionization potential Eg ₂ of the second electron-transport layer, the difference _Eg 2 -Eg ₁ ionization potential preferably 0.05eV or more, more preferably 0 .1 eV or more.

  Furthermore, in the light emitting device of the present invention, it is preferable that the film thickness of the first electron transport layer is smaller than the film thickness of the second electron transport layer from the viewpoint of electron transport. Although it has been reported that the absolute value of the ionization potential varies depending on the measurement method, the ionization potential of the present invention is measured using an atmospheric-type ultraviolet photoelectron analyzer (AC-1, manufactured by Riken Kikai Co., Ltd.) This is a value obtained by measuring a thin film deposited on an ITO glass substrate to a thickness of 30 nm to 100 nm.

  The material used for the second electron transport layer is a compound that contains a compound consisting of a heteroaromatic ring having electron-accepting nitrogen, and the compound consisting of the heteroaromatic ring is formed only by a covalent bond. Imidazole derivatives, benzoxazole derivatives, benzthiazole derivatives, oxadiazole derivatives, thiadiazole derivatives, triazole derivatives, pyrazine derivatives, phenanthroline derivatives, quinoxaline derivatives, quinoline derivatives, benzoquinoline derivatives, oligopyridine derivatives such as bipyridine and terpyridine, quinoxaline derivatives and A naphthyridine derivative is exemplified as a preferred compound. Among them, imidazole derivatives such as tris (N-phenylbenzimidazol-2-yl) benzene, oxadiazole derivatives such as 1,3-bis [(4-tert-butylphenyl) 1,3,4-oxadiazolyl] phenylene, Triazole derivatives such as N-naphthyl-2,5-diphenyl-1,3,4-triazole, phenanthroline derivatives such as bathocuproine and 1,3-bis (2-phenyl-1,10-phenanthroline-9-yl) benzene, Benzoquinoline derivatives such as 2,2′-bis (benzo [h] quinolin-2-yl) -9,9′-spirobifluorene, 1,3-bis (4 ′-(2,2 ′: 6′2 ”-Terpyridinyl)) terpyridine derivatives such as benzene, bis (1-naphthyl) -4- (1,8-naphthyridine-2- Le) naphthyridine derivatives such as phenyl phosphine oxide are preferably used from the viewpoint of electron transporting capability.

  On the other hand, the material used for the first electron transport layer is a compound comprising an aromatic ring or a heteroaromatic ring composed of one or more atoms selected from carbon, hydrogen, oxygen, sulfur, silicon and phosphorus, and a pyrrole derivative. And at least one selected from the condensed ring derivatives thereof and metal complexes having electron-accepting nitrogen. Specifically, condensed ring aromatic ring derivatives such as naphthalene and anthracene, styryl aromatic ring derivatives represented by 4,4′-bis (diphenylethenyl) biphenyl, perylene derivatives, perinone derivatives, coumarin derivatives, naphthalimides Derivatives, quinone derivatives such as anthraquinone and diphenoquinone, phosphorus oxide derivatives, carbazole derivatives and indole derivatives. Examples of the metal complex having electron-accepting nitrogen include quinolinol complexes such as tris (8-quinolinolato) aluminum, hydroxyazole complexes such as hydroxyphenyloxazole complexes, azomethine complexes, tropolone metal complexes, and flavonol metal complexes. These electron transport materials are used alone, but may be used in combination with different electron transport materials. Among them, quinolinol complexes such as tris (8-quinolinolato) aluminum, anthracene derivatives such as 9,10-bis (2-naphthyl) anthracene, styryl aromatic ring derivatives such as 4,4′-bis (diphenylethenyl) biphenyl, Carbazole derivatives such as 4,4′-bis (N-carbazolyl) biphenyl and 1,3,5-tris (N-carbazolyl) benzene are preferably used from the viewpoint of durability.

  The method for forming each layer constituting the light-emitting element is not particularly limited, such as resistance heating vapor deposition, electron beam vapor deposition, sputtering, molecular lamination method, coating method, etc., but resistance heating vapor deposition or electron beam vapor deposition is usually a characteristic. In terms of surface.

  The thickness of the layer cannot be limited because it depends on the resistance value of the luminescent material, but is selected from 1 to 1,000 nm. The film thickness of the light emitting layer, the second electron transport layer, and the hole transport layer is preferably 1 nm to 200 nm, and more preferably 5 nm to 100 nm. The film thickness of the first electron transport layer is preferably smaller than the film thickness of the second electron transport layer, but the film thickness range is the same as that of the light emitting layer and the like. The film thickness can usually be measured with a crystal oscillation type film thickness measuring device or the like.

  The light-emitting element of the present invention is a light-emitting element that can convert electrical energy into light. Here, the electric energy mainly indicates a direct current, but a pulse current or an alternating current can also be used. The current value and voltage value are not particularly limited, but in consideration of the power consumption and life of the element, the maximum luminance should be obtained with as low energy as possible.

  The light emitting device of the present invention is suitably used as a display for displaying in a matrix and / or segment system, for example.

  The matrix in the present invention refers to a pixel in which pixels for display are two-dimensionally arranged such as a lattice shape or a mosaic shape, and displays a character or an image by a set of pixels. The shape and size of the pixel are determined by the application. For example, a square pixel with a side of 300 μm or less is usually used for displaying images and characters on a personal computer, monitor, TV, and a pixel with a side of mm order for a large display such as a display panel. become. In monochrome display, pixels of the same color may be arranged. However, in color display, red, green, and blue pixels are displayed side by side. In this case, there are typically a delta type and a stripe type. The matrix driving method may be either a line sequential driving method or an active matrix. The line-sequential driving has an advantage that the structure is simple. However, the active matrix may be superior in consideration of the operation characteristics, so that it is necessary to properly use it depending on the application.

  In the segment system (type) in the present invention, a pattern is formed so as to display predetermined information, and a predetermined region is caused to emit light. For example, the time and temperature display in a digital clock or a thermometer, the operation state display of an audio device or an electromagnetic cooker, the panel display of an automobile, and the like can be mentioned. The matrix display and the segment display may coexist in the same panel.

  The light emitting device of the present invention is also preferably used as a backlight for various devices. The backlight is used mainly for the purpose of improving the visibility of a display device that does not emit light, and is used for a liquid crystal display device, a clock, an audio device, an automobile panel, a display panel, a sign, and the like. In particular, as a backlight for liquid crystal display devices, especially personal computers for which thinning is an issue, considering that conventional methods are made of fluorescent lamps and light guide plates, it is difficult to reduce the thickness. The backlight using the light emitting element in the invention is thin and lightweight.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not limited by these Examples. The ionization potential is a value obtained by measuring a thin film deposited to a thickness of 50 nm on an ITO glass substrate using an atmospheric-type ultraviolet photoelectron analyzer (AC-1, manufactured by Riken Kikai Co., Ltd.).

(Example 1)
A glass substrate on which an ITO transparent conductive film was deposited to a thickness of 150 nm (Asahi Glass Co., Ltd., 15Ω / □, electron beam evaporated product) was cut into 30 × 40 mm and etched. The obtained substrate was ultrasonically washed with acetone and “Semicocrine (registered trademark) 56” (manufactured by Furuuchi Chemical Co., Ltd.) for 15 minutes, respectively, and then washed with ultrapure water. Subsequently, it was ultrasonically cleaned with isopropyl alcohol for 15 minutes and then immersed in hot methanol for 15 minutes and dried. This substrate was subjected to UV-ozone treatment for 1 hour immediately before producing the device, placed in a vacuum deposition apparatus, and evacuated until the degree of vacuum in the apparatus became 5 × 10 ⁻⁵ Pa or less. By the resistance heating method, first, copper phthalocyanine was deposited as a hole injecting material at 10 nm, and 4,4′-bis (N- (1-naphthyl) -N-phenylamino) biphenyl was deposited as a hole transporting material at 50 nm. Next, 1,4-diketo-2,5-bis (3,5-dimethylphenyl) -3,6-diphenylpyrrolo [3,4-c] pyrrole as a light emitting material, a host material, and a dopant material 4,4-difluoro-8-phenyl-1,3,5,7-tetra (4-butylphenyl) -4-bora-3a, 4a-diaza-s-indacene so that the doping concentration is 1% Vapor deposited to a thickness of 25 nm. Next, 10-nm of 1,4-diketo-2,5-bis (3,5-dimethylbenzyl) -3,6-bis (4-methylphenyl) pyrrolo [3,4-c] pyrrole was used as the electron transport material. Then, 1,3-bis (1,10-phenanthrolin-2-yl) benzene was laminated to a thickness of 40 nm to form a second electron transport layer. Next, after doping lithium with a 0.5 nm organic layer, 1,000 nm of aluminum was vapor-deposited to form a cathode, and a 5 × 5 mm square device was fabricated. The film thickness referred to here is a crystal oscillation type film thickness monitor display value. Ionization potential Eg ₁ of the first electron-transport layer is 5.86EV, ionization potential Eg ₂ of the second electron-transport layer is _6.31EV, it was Eg 2> Eg _1. From this light-emitting element, high-efficiency red light emission with a light emission efficiency of 2.5 lm / W was obtained. This light emitting device was direct current driven at 40 mA / cm ² , and did not reach half the luminance even after 1,000 hours.

(Comparative Example 1)
The light emitting device was fabricated in the same manner as in Example 1 except that 1,3-bis (1,10-phenanthrolin-2-yl) benzene was laminated as a 50 nm layer as the electron transport material (one layer of electron transport layer). Produced. From this light-emitting element, high-efficiency red light emission with a light emission efficiency of 2.2 lm / W was obtained. When direct current was driven at 40 mA / cm ² , the luminance was reduced by half in 700 hours.

(Comparative Example 2)
A light emitting device in the same manner as in Example 1 except that 4,4′-bis (2,2-diphenylethenyl) biphenyl containing no heteroaromatic ring having electron-accepting nitrogen was used as the second electron transporting layer. Was made. Ionization potential Eg ₁ of the first electron-transport layer is 5.86EV, ionization potential Eg ₂ of the second electron-transport layer is _6.12EV, it was Eg 2> Eg _1. From this light-emitting element, high-efficiency red light emission with a light emission efficiency of 2.4 lm / W was obtained. When direct current was driven at 40 mA / cm ² , the luminance was reduced by half in 200 hours.

(Example 2)
After vapor deposition up to the hole transport material in the same manner as in Example 1, 2-tert-butyl-9,10-bis (2-naphthyl) anthracene as the light emitting material, and 2,5 as the dopant material. 8,11-tetra-tert-butylperylene was deposited to a thickness of 25 nm so that the doping concentration was 0.5%. Next, as an electron transport material, 2-tert-butyl-9,10-bis (2-naphthyl) anthracene was laminated to a thickness of 5 nm to form a first electron transport layer, and then 1,3-bis (1 , 10-phenanthrolin-2-yl) benzene was laminated to a thickness of 20 nm to form a second electron transport layer. Next, after doping lithium with a 0.5 nm organic layer, 1,000 nm of aluminum was vapor-deposited to form a cathode, and a 5 × 5 mm square device was fabricated. Ionization potential Eg ₁ of the first electron-transport layer is 5.65 eV, the ionization potential Eg ₂ of the second electron-transport layer is _6.31EV, was Eg 2> Eg _1. From this light-emitting element, high-efficiency blue light emission with a luminous efficiency of 1.6 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Comparative Example 3)
The light emitting device was fabricated in the same manner as in Example 2 except that only 1,3-bis (1,10-phenanthrolin-2-yl) benzene was used as the electron transport material and laminated to 25 nm (the electron transport layer was one layer). Produced. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.5 lm / W was obtained. When this light emitting device was DC-driven at 10 mA / cm ² , the luminance was reduced by half in 200 hours.

(Example 3)
A light emitting device was produced in the same manner as in Example 2 except that tris (8-quinolinolato) aluminum (III) was used as the first electron transport layer. Ionization potential Eg ₁ of the first electron-transport layer is 5.62EV, ionization potential Eg ₂ of the second electron-transport layer is _6.31EV, it was Eg 2> Eg _1. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.5 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Comparative Example 4)
A light-emitting element was fabricated in the same manner as in Example 3 except that only tris (8-quinolinolato) aluminum (III) was used as the electron transport material and the film was laminated to 25 nm (one electron transport layer). From this light emitting element, blue light emission with a luminous efficiency of 0.8 lm / W was obtained. When this light emitting device was DC-driven at 10 mA / cm ² , the luminance was reduced by half in 600 hours.

(Comparative Example 5)
1. 1,3-bis (1,10-phenanthrolin-2-yl) benzene was used as the first electron transport layer and tris (8-quinolinolato) aluminum (III) was used as the second electron transport layer as the electron transport material. A light emitting device was fabricated in the same manner as in Example 2 except for the above. Ionization potential Eg ₁ of the first electron-transport layer is 6.31EV, ionization potential Eg ₂ of the second electron-transport layer is _5.62EV, it was Eg 2 <Eg _1. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.2 lm / W was obtained. When this light emitting device was DC-driven at 10 mA / cm ² , the luminance was reduced by half in 300 hours.

(Comparative Example 6)
A light emitting device was produced in the same manner as in Example 3 except that phenylbis (1-pyrenyl) phosphine oxide containing no heteroaromatic ring having electron-accepting nitrogen was used as the second electron transporting layer. Ionization potential Eg ₁ of the first electron-transport layer is 5.62EV, ionization potential Eg ₂ of the second electron-transport layer is _5.84EV, it was Eg 2> Eg _1. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.4 lm / W was obtained. When direct current was driven at 10 mA / cm ² , the luminance was reduced by half in 200 hours.

Example 4
A light emitting device was fabricated in the same manner as in Example 3 except that the thicknesses of the first electron transport layer and the second electron transport layer were 15 nm and 10 nm, respectively. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.2 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Example 5)
A light emitting device was produced in the same manner as in Example 2 except that 2,7-bis (1,10-phenanthrolin-2-yl) naphthalene was used for the second electron transport layer. Ionization potential Eg ₁ of the first electron-transport layer is 5.65 eV, the ionization potential Eg ₂ of the second electron-transport layer is _6.12EV, was Eg 2> Eg _1. From this light-emitting element, high-efficiency blue light emission with a luminous efficiency of 1.6 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Example 6)
A light emitting device was produced in the same manner as in Example 2 except that 1,3-bis (2-phenyl-1,10-phenanthroline-9-yl) benzene was used for the second electron transport layer. Ionization potential Eg ₁ of the first electron-transport layer is 5.65 eV, the ionization potential Eg ₂ of the second electron-transport layer is _6.05EV, was Eg 2> Eg _1. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.5 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Example 7)
A light emitting device was produced in the same manner as in Example 3 except that 1,3-bis (2-phenyl-1,10-phenanthroline-9-yl) benzene was used for the second electron transport layer. Ionization potential Eg ₁ of the first electron-transport layer is 5.62EV, ionization potential Eg ₂ of the second electron-transport layer is _6.05EV, it was Eg 2> Eg _1. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.5 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Example 8)
A light emitting device was produced in the same manner as in Example 2 except that bis (2-methyl-8-quinolinolato) -4-phenylphenolate aluminum (III) was used for the first electron transporting layer. Ionization potential Eg ₁ of the first electron-transport layer is 5.90EV, ionization potential Eg ₂ of the second electron-transport layer is _6.31EV, it was Eg 2> Eg _1. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.4 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

Example 9
A light emitting device was produced in the same manner as in Example 2 except that phenylbis (1-pyrenyl) phosphine oxide was used for the first electron transporting layer. Ionization potential Eg ₁ of the first electron-transport layer is 5.84EV, ionization potential Eg ₂ of the second electron-transport layer is _6.31EV, it was Eg 2> Eg _1. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.7 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Example 10)
A light emitting device was produced in the same manner as in Example 3 except that 1,3-bis (4 ′-(2,2 ′: 6′2 ″ -terpyridinyl)) benzene was used for the second electron transporting layer. The ionization potential Eg ₁ of the first electron transport layer was 5.62 eV, the ionization potential Eg ₂ of the second electron transport layer was 6.05 eV, and Eg ₂ > Eg _1. The light emitting element emitted light. High-efficiency blue light emission with an efficiency of 1.5 lm / W was obtained, and this light-emitting element was driven by direct current at 10 mA / cm ² , and did not reach half the luminance even after 1,000 hours.

(Example 11)
A light-emitting device was produced in the same manner as in Example 3, except that 2,2′-bis (benzo [h] quinolin-2-yl) -9,9′-spirobifluorene was used for the second electron transport layer. did. Ionization potential Eg ₁ of the first electron-transport layer is 5.62EV, ionization potential Eg ₂ of the second electron-transport layer is _6.09EV, it was Eg 2> Eg _1. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.4 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Example 12)
A light emitting device was produced in the same manner as in Example 3 except that bis (1-naphthyl) -4- (1,8-naphthyridin-2-yl) phenylphosphine oxide was used for the second electron transport layer. Ionization potential Eg ₁ of the first electron-transport layer is 5.62EV, ionization potential Eg ₂ of the second electron-transport layer is _5.79EV, it was Eg 2> Eg _1. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.3 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Example 13)
A light emitting device was fabricated in the same manner as in Example 3 except that bis (1-naphthyl) -4- (quinoxalin-2-yl) phenylphosphine oxide was used for the second electron transporting layer. Ionization potential Eg ₁ of the first electron-transport layer is 5.62EV, ionization potential Eg ₂ of the second electron-transport layer is _5.77EV, it was Eg 2> Eg _1. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.3 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Example 14)
A light emitting device in the same manner as in Example 3, except that bis (1-naphthyl) -4- (4-phenyl-2,2′-bipyridin-6-yl) phenylphosphine oxide was used for the second electron transport layer. Was made. Ionization potential Eg ₁ of the first electron-transport layer is 5.62EV, ionization potential Eg ₂ of the second electron-transport layer is 5.64 _eV, it was Eg 2> Eg _1. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.2 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Example 15)
The same as Example 3 except that bis (1-naphthyl) -4- (2-phenyl-1,3,4-oxadiazol-5-yl) phenylphosphine oxide was used for the second electron transport layer. Thus, a light emitting element was manufactured. Ionization potential Eg ₁ of the first electron-transport layer is 5.62EV, ionization potential Eg ₂ of the second electron-transport layer is _5.77EV, it was Eg 2> Eg _1. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.2 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Example 16)
A light emitting device was produced in the same manner as in Example 3 except that bis (1-naphthyl) -4- (quinolin-2-yl) phenylphosphine oxide was used for the second electron transporting layer. Ionization potential Eg ₁ of the first electron-transport layer is 5.62EV, ionization potential Eg ₂ of the second electron-transport layer is _5.79EV, it was Eg 2> Eg _1. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.1 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Example 17)
A light emitting device was produced in the same manner as in Example 3 except that tris (N-phenylbenzimidazol-2-yl) benzene was used for the second electron transport layer. Ionization potential Eg ₁ of the first electron-transport layer is 5.62EV, ionization potential Eg ₂ of the second electron-transport layer is _5.78EV, it was Eg 2> Eg _1. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.2 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Example 18)
Except for using bis (1-naphthyl) -4- (N- (1-naphthyl) -2-phenyl-1,3,4-triazol-5-yl) phenylphosphine oxide in the second electron transport layer, A light emitting element was manufactured in the same manner as in Example 3. Ionization potential Eg ₁ of the first electron-transport layer is 5.62EV, ionization potential Eg ₂ of the second electron-transport layer is _5.76EV, it was Eg 2> Eg _1. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.2 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Example 19)
After vapor deposition up to the hole injection material in the same manner as in Example 1, 4,4′-bis (N- (1-naphthyl) -N-phenylamino) biphenyl as the host material as the light emitting material, and as the dopant material Rubrene was deposited to a thickness of 50 nm so that the dope concentration was 3.5%. Next, as an electron transport material, tris (8-quinolinolato) aluminum (III) was laminated to a thickness of 10 nm to form a first electron transport layer, and then 1,3-bis (1,10-phenanthroline-2- I) Benzene was laminated to a thickness of 40 nm to form a second electron transport layer. Next, after doping the organic layer with 0.5 nm of lithium, 1000 nm of aluminum was vapor-deposited to form a cathode, and a 5 × 5 mm square device was fabricated. Ionization potential Eg ₁ of the first electron-transport layer is 5.62EV, ionization potential Eg ₂ of the second electron-transport layer is _6.31EV, it was Eg 2> Eg _1. From this light emitting element, high efficiency yellow light emission with a light emission efficiency of 1.8 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Comparative Example 7)
The light emitting device was fabricated in the same manner as in Example 19 except that 1,3-bis (1,10-phenanthrolin-2-yl) benzene was used as the electron transport material and the film was laminated to 50 nm (one layer of electron transport layer). Produced. From this light-emitting element, high-efficiency yellow light emission with a light emission efficiency of 2.0 lm / W was obtained. When direct current was driven at 10 mA / cm ² , the luminance was reduced by half in 100 hours.

(Example 20)
The light emitting material is 9,10-bis (2-naphthyl) anthracene as the host material, and 4,4′-bis (2- (4-diphenylaminophenyl) ethenyl) biphenyl and rubrene as the dopant material, each having a doping concentration of 5 A light-emitting element was manufactured in the same manner as in Example 2 except that it was used so as to be 1% and 1%. From this light emitting element, high efficiency white light emission with a luminous efficiency of 3.0 lm / W was obtained. When the light emitting device was DC-driven at 4 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Comparative Example 8)
The light emitting device was fabricated in the same manner as in Example 20 except that only 1,3-bis (1,10-phenanthrolin-2-yl) benzene was used as the electron transport material and laminated to 25 nm (the electron transport layer was one layer). Produced. From this light-emitting element, high-efficiency white light emission with a light emission efficiency of 3.1 lm / W was obtained. When direct current was driven at 4 mA / cm ² , the luminance was reduced by half in 400 hours.

(Example 21)
After vapor deposition up to the hole transport material in the same manner as in Example 1, 4,4′-bis (2,2-diphenylethenyl) biphenyl is used as the host material and 4,4′- as the dopant material. Bis (2- (4-diphenylaminophenyl) ethenyl) biphenyl was vapor-deposited to a thickness of 15 nm so that the doping concentration was 2%, and was used as the first light emitting layer. Next, 1,4-diketo-2,5-bis (3,5-dimethylphenyl) -3,6-diphenylpyrrolo [3,4-c] pyrrole is used as the light emitting material, and 4 is used as the dopant material. , 4-Difluoro-8-phenyl-1,3,5,7-tetra (4-butylphenyl) -4-bora-3a, 4a-diaza-s-indacene at 10 nm so that the doping concentration is 1%. It vapor-deposited to thickness and was set as the 2nd light emitting layer. Next, 1,4-diketo-2,5-bis (3,5-dimethylphenyl) -3,6-diphenylpyrrolo [3,4-c] pyrrole was laminated to a thickness of 5 nm as an electron transporting material. After forming the first electron transport layer, 1,3-bis (1,10-phenanthrolin-2-yl) benzene was laminated to a thickness of 20 nm to form a second electron transport layer. Next, after doping lithium with a 0.5 nm organic layer, 1000 nm of aluminum was vapor-deposited to form a cathode, and a 5 × 5 mm square device was fabricated. Ionization potential Eg ₁ of the first electron-transport layer is 5.86EV, ionization potential Eg ₂ of the second electron-transport layer is _6.31EV, it was Eg 2> Eg _1. From this light-emitting element, high-efficiency white light emission with a light emission efficiency of 2.8 lm / W was obtained. This light emitting device was DC driven at 4 mA / cm ² , and did not reach half the luminance even after 1000 hours.

(Example 22)
After vapor deposition up to the hole injection material in the same manner as in Example 1, 25 nm of 4,4′-bis (N- (1-naphthyl) -N-phenylamino) biphenyl was vapor-deposited as the hole transport material. Next, as the light emitting material, 4,4′-bis (N-carbazolyl) biphenyl is used as the host material, and tris (2-phenylpyridine) iridium (III) is used as the dopant material, so that the doping concentration becomes 6%. Vapor deposited to a thickness of Next, as an electron transport material, bis (2-methyl-8-quinolinolato) -4-phenylphenolate aluminum (III) was laminated to a thickness of 10 nm to form a first electron transport layer, and then 1,3- Bis (1,10-phenanthrolin-2-yl) benzene was laminated to a thickness of 40 nm to form a second electron transport layer. Next, after doping lithium with a 0.5 nm organic layer, 1000 nm of aluminum was vapor-deposited to form a cathode, and a 5 × 5 mm square device was fabricated. Ionization potential Eg ₁ of the first electron-transport layer is 5.90EV, ionization potential Eg ₂ of the second electron-transport layer is _6.31EV, it was Eg 2> Eg _1. From this light-emitting element, high-efficiency green light emission with a luminous efficiency of 14.3 lm / W was obtained. This light emitting device was DC driven at 4 mA / cm ² , and did not reach half the luminance even after 1000 hours.

(Comparative Example 9)
A light emitting device was fabricated in the same manner as in Example 22 except that 1,3-bis (1,10-phenanthrolin-2-yl) benzene was used as the electron transporting material and laminated to 50 nm (the electron transporting layer was one layer). Produced. From this light-emitting element, high-efficiency green light emission with a light emission efficiency of 15.6 lm / W was obtained. When direct current was driven at 4 mA / cm ² , the luminance was reduced by half in 700 hours.

(Example 23)
A light-emitting element was fabricated in the same manner as in Example 2 except that 2- (benzothiazol-2-yl) -9,10-diphenylanthracene was used as the dopant material. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.3 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Example 24)
A light emitting device was produced in the same manner as in Example 2 except that 9-phenyl- (10-phenylethynyl) anthracene was used as the dopant material. From this light-emitting element, high-efficiency blue light emission with a light emission efficiency of 1.5 lm / W was obtained. When the light emitting device was DC-driven at 10 mA / cm ² , the luminance was not halved even after 1,000 hours.

(Example 25)
A glass substrate (manufactured by Asahi Glass Co., Ltd., 15Ω / □, electron beam evaporated product) on which an ITO transparent conductive film is deposited to 150 nm is cut into 30 × 40 mm, and 300 μm pitch (remaining width 270 μm) × 32 stripes by photolithography. Patterned into a shape. One side of the ITO stripe in the long side direction is expanded to a pitch of 1.27 mm (opening width 800 μm) in order to facilitate electrical connection with the outside. The obtained substrate was ultrasonically cleaned with acetone and “Semicocrine (registered trademark) 56” (manufactured by Furuuchi Chemical Co., Ltd.) for 15 minutes, respectively, and then with ultrapure water. Subsequently, it was ultrasonically cleaned with isopropyl alcohol for 15 minutes and then immersed in hot methanol for 15 minutes and dried. This substrate was subjected to UV-ozone treatment for 1 hour immediately before producing the device, placed in a vacuum deposition apparatus, and evacuated until the degree of vacuum in the apparatus became 5 × 10 ⁻⁴ Pa or less. First, 4,4′-bis (N- (m-tolyl) -N-phenylamino) biphenyl was deposited as a hole transport material by a resistance heating method to a thickness of 150 nm. Next, 1,4-diketo-2,5-bis (3,5-dimethylphenyl) -3,6-diphenylpyrrolo [3,4-c] pyrrole as a light emitting material, a host material, and a dopant material 4,4-difluoro-8-phenyl-1,3,5,7-tetra (4-butylphenyl) -4-bora-3a, 4a-diaza-s-indacene so that the doping concentration is 1% Vapor deposited to a thickness of 25 nm. Next, 10-nm of 1,4-diketo-2,5-bis (3,5-dimethylbenzyl) -3,6-bis (4-methylphenyl) pyrrolo [3,4-c] pyrrole was used as the electron transport material. Then, 1,3-bis (1,10-phenanthrolin-2-yl) benzene was laminated to a thickness of 40 nm to form a second electron transport layer. The film thickness referred to here is a crystal oscillation type film thickness monitor display value. Next, the mask provided with 16 250 μm openings (corresponding to the remaining width of 50 μm and 300 μm pitch) by wet etching on a 50 μm thick Kovar plate was replaced with a mask so as to be orthogonal to the ITO stripe in vacuum, It fixed with the magnet from the back surface so that a mask and an ITO board | substrate might closely_contact | adhere. And after doping lithium with a 0.5 nm organic layer, aluminum was vapor-deposited 200 nm, and the 32x16 dot matrix element was produced. When this element was driven in matrix, characters could be displayed without crosstalk.

Claims (6)

A light emitting device having at least a light emitting layer and an electron transport layer between an anode and a cathode and emitting light by electric energy, wherein the electron transport layer is in contact with the light emitting layer, and the cathode and the first electron transport layer. The second electron transport layer contains a compound composed of a heteroaromatic ring having electron-accepting nitrogen, and the compound composed of the heteroaromatic ring is formed only by a covalent bond. A light emitting element characterized by being a compound to be obtained. The light emitting device according to claim 1, wherein the ionization potential of the first electron transport layer is smaller than the ionization potential of the second electron transport layer. The light emitting device according to claim 1, wherein the film thickness of the first electron transport layer is smaller than the film thickness of the second electron transport layer. A compound comprising an aromatic ring or a heteroaromatic ring, wherein the first electron transporting layer is composed of one or more atoms selected from carbon, hydrogen, oxygen, sulfur, silicon and phosphorus, a pyrrole derivative and a condensed ring derivative thereof, and an electron The light emitting device according to claim 1, comprising at least one selected from metal complexes having receptive nitrogen. The light emitting element according to claim 1, wherein the light emitting layer includes at least a fluorescent light emitting material, and the light emitting layer exhibits blue light emission having a peak wavelength at 420 nm to 490 nm. The light-emitting element according to claim 1, wherein the light-emitting layer includes at least a phosphorescent light-emitting material, and the light-emitting layer exhibits phosphorescence.