JP2008071993A - Light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-emitting element which is usable in the fields of display elements, flat panel displays, backlights, illuminations, interior, signs, signboards, electronic cameras, optical signal generators, etc., requires low drive voltage, and has a long life. <P>SOLUTION: The light-emitting element includes a light-emitting layer which contains a light-emitting material and an aromatic amine having hole transportability, and an electron transporting layer which is made of an element selected from elements of carbon, hydrogen, nitrogen, oxygen, silicon, and phosphorus and contains a compound composed of a heteroaryl ring structure containing an electron-accepting nitrogen. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light emitting device using an aromatic amine useful as a fluorescent dye or a hole transport agent, and includes a display device, a flat panel display, a backlight, illumination, an interior, a sign, a signboard, an electrophotographic machine, and an optical signal. The present invention relates to a light-emitting element that can be used in fields such as a generator.

  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 light-emitting body 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 light-emitting material.

This study was conducted by Eastman Kodak's C.I. W. Since Tang et al. Have shown that organic thin-film light-emitting elements 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 an ITO glass substrate, tris (8-quinolinolato) aluminum (III) as a light emitting layer, and a cathode. Mg: Ag (alloy) was sequentially 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.

  As a method for improving the light emission characteristics in the organic thin film light emitting element, promotion of recombination of electrons and holes performed in the light emitting layer can be mentioned. For this purpose, it is important to increase the transport ability of electrons and holes in the device, and to maintain the balance of holes and electrons in the light emitting layer, which is representative of luminous efficiency, driving voltage, lifetime, etc. It is expected that the emission characteristics will be improved.

From such a viewpoint, for example, a technique using an assist dopant that complements carrier movement in the light-emitting layer (see Patent Document 1) is known, but tris (8-quinolinolato) aluminum having a low electron transporting ability is used in the electron transport layer. (III) is used, and the driving voltage is high, and a sufficient effect cannot be obtained. On the other hand, examples of using an oxadiazole derivative (see Patent Document 2), a silacyclopentadiene derivative (see Patent Document 3), and a phenanthroline derivative (see Patent Document 4) as an electron transport layer having a high electron transport capability are known. However, although it has an effect of reducing the driving voltage, the life tends to be shortened. This is because it is difficult to maintain a balance between holes and electrons in the light emitting layer when using an electron transporting material having a high electron transporting ability. By simply using a conventionally known light emitting material for the light emitting layer, It is impossible to achieve both low driving voltage and long life.
JP 2005-108726 A JP-A-8-193075 JP-A-9-87616 JP 2004-281390 A Applied Physics Letters (USA) 1987, 51, 12, 913-915

  Accordingly, an object of the present invention is to solve such problems of the prior art and to provide a light emitting element having a low driving voltage and a long lifetime.

  The present invention is a light-emitting element in which at least a light-emitting layer and an electron transport layer exist between an anode and a cathode and emits light by electric energy, the light-emitting layer contains a light-emitting material and a hole-transporting aromatic amine, And an electron transport layer containing a compound composed of an element selected from carbon, hydrogen, nitrogen, oxygen, silicon, and phosphorus and having a heteroaryl ring structure containing electron-accepting nitrogen. It is an element.

  According to the present invention, a light emitting device having a low driving voltage and a long lifetime can be obtained.

  Embodiments of the light emitting device according to the present invention will be described with examples. The light emitting device of the present invention is composed of at least an anode and a cathode, and an organic layer containing a light emitting device material interposed between the anode and the cathode.

  The anode used in the present invention is not particularly limited as long as it can efficiently inject holes into the organic layer, but it is preferable to use a material having a relatively large work function. For example, tin oxide, indium oxide, zinc oxide Conductive metal oxides such as indium and indium tin oxide (ITO), metals such as gold, silver and chromium, inorganic conductive materials such as copper iodide and copper sulfide, conductive polymers such as polythiophene, polypyrrole and polyaniline, etc. Is mentioned. These electrode materials may be used alone, or a plurality of materials may be laminated or mixed.

  The resistance of the anode is not limited as long as a current sufficient for light emission of the light emitting element can be supplied. 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 / □, use a low-resistance product of 100Ω / □ or less. Is particularly desirable. 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.

In order to maintain the mechanical strength of the light emitting element, the light emitting element is preferably formed over a substrate. As the substrate, a glass substrate such as soda glass or non-alkali glass is preferably used. As the thickness of the glass substrate, it is sufficient that the thickness is sufficient to maintain the mechanical strength. The glass material is preferably alkali-free glass because it is better to have less ions eluted from the glass, but soda lime glass with a barrier coat such as SiO ₂ is also available on the market. 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 material used for the cathode used in the present invention is not particularly limited as long as it is a substance that 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, and alloys thereof. 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, since these low work function metals are generally unstable in the atmosphere, they are stable by doping or laminating a small amount of lithium or magnesium in the organic layer (1 nm or less in the vacuum vapor deposition thickness gauge display). A preferred example is a method for obtaining a highly conductive electrode. Also, an inorganic salt such as lithium fluoride can be used. Furthermore, for electrode protection, metals such as platinum, gold, silver, copper, iron, tin, aluminum and indium, or alloys using these metals, inorganic substances such as silica, titania and silicon nitride, polyvinyl alcohol, polyvinyl chloride Lamination of organic polymer compounds such as hydrocarbon polymer compounds 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.

  The organic layer constituting the light emitting device of the present invention comprises at least a light emitting layer and an electron transport layer made of a light emitting device material. Examples of the configuration of the organic layer include a stacked configuration such as a hole transport layer / a light-emitting layer / an electron transport layer in addition to a configuration including a light-emitting layer and an electron transport layer. Each of the layers may be a single layer or a plurality of layers. When the hole transport layer and the electron transport layer have a plurality of layers, the layers in contact with the electrodes may be referred to as a hole injection layer and an electron injection layer, respectively. In the material, the electron injection material is included in the electron transport material.

  The hole transport layer is formed by a method of laminating or mixing one or more hole transport materials or a method using a mixture of a hole transport material and a polymer binder. Alternatively, the hole transport layer may be formed by adding an inorganic salt such as iron (III) chloride to the hole transport material. The hole transport material 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. For example, 4,4′-bis (N- (3-methylphenyl) -N-phenylamino) biphenyl, 4,4′-bis (N- (1-naphthyl) -N-phenylamino) biphenyl, 4,4 Triphenylamine derivatives such as', 4 "-tris (3-methylphenyl (phenyl) amino) triphenylamine, biscarbazole derivatives such as bis (N-allylcarbazole) or bis (N-alkylcarbazole), pyrazoline derivatives, Heterocyclic compounds such as stilbene compounds, hydrazone compounds, benzofuran derivatives, thiophene derivatives, oxadiazole derivatives, phthalocyanine derivatives, porphyrin derivatives, and polymers, polycarbonates, styrene derivatives, polythiophene, polyaniline having the above monomers in the side chain , Polyfluorene, poly Such alkenyl carbazole and polysilane are preferred.

  In the present invention, the light emitting layer is formed of a light emitting material and an aromatic amine having a hole transporting property. By using an aromatic amine having a hole transporting property together with a light emitting material, the hole transporting ability in the light emitting layer can be improved as compared with the case of the light emitting material alone. As a result, by combining with an electron transport layer made of an electron transport material having a high electron transport capability, the balance of holes and electrons in the light-emitting layer can be maintained, and long-life light emission becomes possible. In addition, since the balance is realized while maintaining a high hole / electron transport capability, it is possible to achieve both a low driving voltage and a long life.

  The light-emitting material may be a single material or a mixture of multiple materials (host material, dopant material), but separates the functions of film formation, hole / electron transport, and light emission from the viewpoints of efficiency, color purity, and lifetime. Preferred is a mixture of a host material and a dopant material that can be formed. That is, in the light emitting device of the present invention, only one of the host material and the dopant material may emit light, 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 entire light emitting layer, or may be partially included. If the amount of the dopant material is too large, a concentration quenching phenomenon occurs, so that it is preferably used at 20% by weight or less, more preferably 10% by weight or less with respect to the host material. The dopant material can be formed by a co-evaporation method with the host material, but it may be pre-mixed with the host material and then simultaneously deposited.

  Further, the light emitting layer may be either a single layer or a plurality of layers, and the light emitting material of each layer may be a mixture of a host material and a dopant material, or a host material alone.

  A single light-emitting material or host material has a high light-emitting ability, and it is necessary to efficiently recombine holes received from the hole transport layer or the direct anode and electrons received from the electron transport layer.

  Materials satisfying such conditions include fused ring derivatives such as anthracene, phenanthrene, pyrene, perylene, chrysene, metal chelated oxinoid compounds such as tris (8-quinolinolato) aluminum (III), benzoxazole derivatives, benzthiazole Derivatives, thiadiazole derivatives, thiophene derivatives, tetraphenylbutadiene derivatives, cyclopentadiene derivatives, oxadiazole derivatives, bisstyryl derivatives such as bisstyrylanthracene derivatives and distyrylbenzene derivatives, coumarin derivatives, pyrrolopyridine derivatives, pyrrolopyrrole derivatives, silole derivatives, For perinone derivatives and carbazole derivative polymers, polyphenylene vinylene derivatives, polyparaphenylene derivatives, polyfluorene derivatives, Carbazole derivatives and polythiophene derivatives.

  When a dopant material is included, it is desirable that the dopant material added to the light emitting material has a high quantum yield and does not easily cause concentration quenching. Furthermore, it is required to be a substance that is excellent in stability and is unlikely to generate trapping impurities during manufacturing and use.

  As substances satisfying such conditions, compounds having an aryl ring such as naphthalene, anthracene, phenanthrene, pyrene, triphenylene, perylene, fluorene, indene and derivatives thereof, which are conventionally known as fluorescent materials, furan, pyrrole, thiophene, Heteroaryl rings such as silole, 9-silafluorene, 9,9'-spirobisilafluorene, benzothiophene, benzofuran, indole, dibenzothiophene, dibenzofuran, imidazopyridine, phenanthroline, pyrazine, naphthyridine, quinoxaline, pyrrolopyridine, thioxanthene Compounds and derivatives thereof, distyrylbenzene derivatives, aminostyryl derivatives, aromatic acetylene derivatives, tetraphenylbutadiene derivatives, stilbene derivatives, aldadi Derivatives, coumarin derivatives, pyromethene derivatives and metal complexes thereof, azole derivatives such as imidazole, thiazole, thiadiazole, carbazole, oxazole, oxadiazole, triazole and metal complexes thereof, and 4,4′-bis (N- (3-methylphenyl) An aromatic amine derivative typified by (-)-N-phenylamino) biphenyl, and the like, but is not limited thereto.

  As the dopant material, not only the fluorescent material but also a phosphorescent material is preferably used. Specifically, porphyrin platinum complex, tris (2-phenylpyridyl) iridium complex, tris {2- (2-thiophenyl) pyridyl} iridium complex, tris {2- (2-benzothiophenyl) pyridyl} iridium complex, tris (2-phenylbenzothiazole) iridium complex, tris (2-phenylbenzoxazole) iridium complex, trisbenzoquinoline iridium complex, bis (2-phenylpyridyl) (acetylacetonato) iridium complex, bis {2- (2-thiophenyl) ) Pyridyl} iridium complex, bis {2- (2-benzothiophenyl) pyridyl} (acetylacetonato) iridium complex, bis (2-phenylbenzothiazole) (acetylacetonato) iridium complex, bis (2-phenylbenzooxa) Z Le) (acetylacetonato) iridium complex, bis benzoquinoline (acetylacetonate) iridium, etc. complex.

  The aromatic amine used in the present invention is used for the purpose of improving hole transportability in the light emitting layer, and is selected from those having excellent hole transportability and small interaction with the light emitting material. Although there is an ionization potential as an index of the hole transport property of an aromatic amine, in the present invention, it is preferable to use an aromatic amine in which the ionization potential of the aromatic amine is smaller than the ionization potential of the light emitting material. When the light emitting material is composed of a host and a dopant, the ionization potential of the aromatic amine is preferably smaller than the ionization potential of the host material responsible for carrier transport.

  The absolute value of the ionization potential varies depending on the measurement conditions and the like, but in the present invention, the value obtained as follows was used. A thin film of each material was produced on an ITO glass substrate by vacuum deposition, and the ionization potential was measured with an atmospheric type ultraviolet photoelectron analyzer (AC-1, manufactured by Riken Keiki Co., Ltd.).

  The aromatic amine used in the present invention is added to such an extent that it does not affect the light emitting ability of the light emitting material. Specifically, it is preferably 50% by weight or less, more preferably 25% by weight or less based on a single light emitting material or host material. The addition method of the aromatic amine is the same as that of the dopant material in the above light emitting material. Further, when the light emitting layer is composed of a plurality of layers, the aromatic amine is for improving the hole transport property of the light emitting layer, and therefore it should be contained in at least one layer.

  Examples of such aromatic amines include 4,4'-bis (N- (3-methylphenyl) -N-phenylamino) biphenyl, 4,4'-bis (N- (1-naphthyl) -N- Phenylamino) biphenyl, triphenylamine derivatives such as 4,4 ′, 4 ″ -tris (3-methylphenyl (phenyl) amino) triphenylamine, and the like. Suitable derivatives having less interaction depending on the light-emitting material to be combined The aromatic amine of the present invention may have fluorescence in the visible light region, and in that case, it may contribute to light emission together with the light emitting material.

  The electron transport layer in the present invention contains a compound composed of an element selected from carbon, hydrogen, nitrogen, oxygen, silicon, and phosphorus and having a heteroaryl ring structure containing 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 heteroaryl ring containing electron-accepting nitrogen has high electron affinity, excellent electron transport ability, and can be used for an electron transport layer to reduce the driving voltage of a light-emitting element. Examples of the heteroaryl ring containing an electron-accepting nitrogen include, for example, a pyridine ring, a pyrazine ring, a pyrimidine ring, a quinoline ring, a quinoxaline ring, a naphthyridine ring, a pyrimidopyrimidine ring, a benzoquinoline ring, a phenanthroline ring, an imidazole ring, an 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.
Examples of these compounds having a heteroaryl ring include benzimidazole derivatives, benzoxazole derivatives, benzthiazole derivatives, oxadiazole derivatives, thiadiazole derivatives, triazole derivatives, pyrazine derivatives, phenanthroline derivatives, quinoxaline derivatives, quinoline derivatives, benzoquinolines. Preferred examples include derivatives, oligopyridine derivatives such as bipyridine and terpyridine, quinoxaline derivatives, and naphthyridine derivatives. Among them, benzimidazole 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 bathocuproin and 1,3-bis (1,10-phenanthroline-9-yl) benzene, 2,2 Benzoquinoline derivatives such as' -bis (benzo [h] quinolin-2-yl) -9,9'-spirobifluorene, 2,5-bis (6 '-(2', 2 "-bipyridyl))-1 Bipyridine derivatives such as 1,1-dimethyl-3,4-diphenylsilole, 1,3-bis (4 ′-(2,2 ′: 6′2 ″ -terpi A terpyridine derivative such as lysinyl)) benzene and a naphthyridine derivative such as bis (1-naphthyl) -4- (1,8-naphthyridin-2-yl) phenylphosphine oxide are preferably used from the viewpoint of electron transport ability.

  The electron transport material may be used alone, but two or more of the electron transport materials may be mixed and used, or one or more of the other electron transport materials may be mixed and used in the electron transport material. It is also possible to use a mixture with a metal such as an alkali metal or an alkaline earth metal. The ionization potential of the 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.

  The method of 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 used in terms of element characteristics. preferable.

  The thickness of the layer cannot be limited because it depends on the resistance value of the light emitting element material, but is selected from 1 to 1000 nm. The film thicknesses of the light emitting layer, the electron transport layer, and the hole transport layer are each preferably 1 nm to 200 nm, and more preferably 5 nm to 100 nm.

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

  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.

  In the matrix method, pixels for display are two-dimensionally arranged such as a lattice shape or a mosaic shape, and a character or an image is displayed 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. Although the structure of the line sequential drive is simple, the active matrix may be superior in consideration of the operation characteristics, and it is necessary to use it depending on the application.

  The segment system in the present invention is a system in which a pattern is formed so as to display predetermined information and an area determined by the arrangement of the pattern 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, the light-emitting element of the present invention is preferably used for a backlight for a liquid crystal display device, particularly a personal computer for which a reduction in thickness is being considered, and a backlight that is thinner and lighter than conventional ones can be provided.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not limited by these Examples.

Example 1
A glass substrate (manufactured by Geomat Co., Ltd., 11Ω / □, sputtered product) having an ITO transparent conductive film deposited to 150 nm was cut into 38 × 46 mm and etched. The obtained substrate was ultrasonically cleaned with “Semico Clean 56” (trade name, manufactured by Furuuchi Chemical Co., Ltd.) for 15 minutes and then with ultrapure water. 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. 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, the compound (H-1, ionization potential: 5.5 eV) as the host material and the compound (D-1) as the dopant material are added to the light emitting material so that the doping concentration is 2%, and the fragrance to be added A compound (A-1, ionization potential 5.4 eV) was deposited as a group amine to a thickness of 40 nm so that the dope concentration was 10%. Next, the compound (E-1) was laminated to a thickness of 35 nm as an electron transporting material. Next, after depositing 0.5 nm of lithium fluoride, 1000 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. When this light emitting device was DC-driven at 10 mA / cm ² , high-efficiency blue light emission with a driving voltage of 4.8 V and a light emission efficiency of 3.2 cd / A was obtained. When this light emitting device was continuously driven at a direct current of 40 mA / cm ² , the luminance half time was 300 hours.

Example 2
A light emitting device was produced in the same manner as in Example 1 except that the compound (A-2, ionization potential 5.3 eV) was used as the aromatic amine to be added. When this light emitting device was DC-driven at 10 mA / cm ² , high-efficiency blue light emission with a driving voltage of 4.7 V and a light emission efficiency of 3.4 cd / A was obtained. When this light emitting device was continuously driven at a direct current of 40 mA / cm ² , the luminance half time was 320 hours.

Example 3
A light emitting device was produced in the same manner as in Example 1 except that the compound (A-3, ionization potential 5.2 eV) was used as the aromatic amine to be added. When this light-emitting element was DC-driven at 10 mA / cm ² , high-efficiency blue light emission with a drive voltage of 4.5 V and a light emission efficiency of 3.3 cd / A was obtained. When this light emitting device was continuously driven at a direct current of 40 mA / cm ² , the luminance half time was 290 hours.

Example 4
A light emitting device was produced in the same manner as in Example 1 except that the compound (D-2) was used as the dopant material. When this light-emitting element was DC-driven at 10 mA / cm ² , high-efficiency blue light emission with a driving voltage of 4.8 V and a light emission efficiency of 3.3 cd / A was obtained. When this light emitting device was continuously driven at a direct current of 40 mA / cm ² , the luminance half time was 350 hours.

Example 5
A light emitting device was produced in the same manner as in Example 1 except that (E-2) was used as the electron transport material. When this light emitting device was DC-driven at 10 mA / cm ² , high-efficiency blue light emission with a driving voltage of 4.6 V and a light emission efficiency of 3.1 cd / A was obtained. When this light emitting device was continuously driven at a direct current of 40 mA / cm ² , the luminance half time was 330 hours.

Example 6
A light emitting device was produced in the same manner as in Example 1 except that (E-3) was used as the dopant material. When this light-emitting element was DC-driven at 10 mA / cm ² , high-efficiency blue light emission with a drive voltage of 4.5 V and a light emission efficiency of 3.3 cd / A was obtained. When this light emitting device was continuously driven at a direct current of 40 mA / cm ² , the luminance half time was 350 hours.

Example 7
A light emitting device was produced in the same manner as in Example 1 except that (E-4) was used as the dopant material. When this light-emitting element was DC-driven at 10 mA / cm ² , high-efficiency blue light emission with a driving voltage of 4.8 V and a light emission efficiency of 3.4 cd / A was obtained. When this light emitting device was continuously driven at a direct current of 40 mA / cm ² , the luminance half time was 340 hours.

Example 8
A light emitting device was produced in the same manner as in Example 1 except that (E-5) was used as the dopant material. When this light-emitting element was DC-driven at 10 mA / cm ² , high-efficiency blue light emission with a driving voltage of 4.7 V and a light emission efficiency of 3.1 cd / A was obtained. When this light emitting device was continuously driven at a direct current of 40 mA / cm ² , the luminance half time was 340 hours.

Comparative Example 1
A light emitting device was produced in the same manner as in Example 1 except that the aromatic amine to be added was not used. When this light emitting device was DC-driven at 10 mA / cm ² , high-efficiency blue light emission with a driving voltage of 5 V and a light emission efficiency of 3 cd / A was obtained. When this light emitting device was continuously driven at a direct current of 40 mA / cm ² , the luminance half time was 200 hours.

Comparative Example 2
A light emitting device was fabricated in the same manner as in Example 4 except that the aromatic amine to be added was not used. When this light emitting device was DC-driven at 10 mA / cm ² , high-efficiency blue light emission with a driving voltage of 5.2 V and a light emission efficiency of 3.2 cd / A was obtained. When this light emitting device was continuously driven at a direct current of 40 mA / cm ² , the luminance half time was 220 hours.

Comparative Example 3
A light emitting device was produced in the same manner as in Example 1 except that (E-6) was used as the electron transport material. When this light emitting device was DC-driven at 10 mA / cm ² , high-efficiency blue light emission with a driving voltage of 6.4 V and a light emission efficiency of 3.2 cd / A was obtained. When this light emitting device was continuously driven at a direct current of 40 mA / cm ² , the luminance half time was 500 hours.

Example 9
A light emitting device was fabricated in the same manner as in Example 1 except that the compound (H-2, ionization potential 5.8 eV) was used as the host material, and (D-3) was used as the dopant material. When this light-emitting element was DC-driven at 10 mA / cm ² , high-efficiency green light emission with a driving voltage of 5.5 V and a light emission efficiency of 10.5 cd / A was obtained. When this light emitting device was continuously driven at a direct current of 40 mA / cm ² , the luminance half time was 350 hours.

Comparative Example 4
A light emitting device was produced in the same manner as in Example 9 except that the aromatic amine to be added was not used. When this light emitting device was DC-driven at 10 mA / cm ² , high-efficiency green light emission with a driving voltage of 6 V and a light emission efficiency of 10 cd / A was obtained. When this light emitting device was continuously driven at a direct current of 40 mA / cm ² , the luminance half time was 200 hours.

Comparative Example 5
A light emitting device was produced in the same manner as in Example 9 except that (E-6) was used as the electron transport material. When this light-emitting element was DC-driven at 10 mA / cm ² , high-efficiency green light emission with a driving voltage of 7.2 V and a light emission efficiency of 9 cd / A was obtained. When this light emitting device was continuously driven at a direct current of 40 mA / cm ² , the luminance half time was 600 hours.

Example 10
A light emitting device was produced in the same manner as in Example 9 except that (D-4) was used as the dopant material. When this light-emitting element was DC-driven at 10 mA / cm ² , high-efficiency red light emission with a driving voltage of 6.3 V and a light emission efficiency of 5.2 cd / A was obtained. When this light emitting device was continuously driven at a direct current of 40 mA / cm ² , the luminance half time was 1300 hours.

Comparative Example 6
A light emitting device was produced in the same manner as in Example 10 except that the aromatic amine to be added was not used. When this light-emitting element was DC-driven at 10 mA / cm ² , high-efficiency red light emission with a driving voltage of 8 V and a light emission efficiency of 5 cd / A was obtained. When this light emitting device was continuously driven at a direct current of 40 mA / cm ² , the luminance half time was 700 hours.

Comparative Example 7
A light emitting device was produced in the same manner as in Example 10 except that (E-6) was used as the electron transporting material. When this light emitting device was DC-driven at 10 mA / cm ² , high-efficiency red light emission with a driving voltage of 10 V and a light emission efficiency of 4.4 cd / A was obtained. When this light emitting device was continuously driven at a direct current of 40 mA / cm ² , the luminance half time was 1500 hours.

Claims (2)

A light-emitting element in which at least a light-emitting layer and an electron transport layer exist between an anode and a cathode and emits light by electric energy, the light-emitting layer includes a light-emitting material and a hole-transporting aromatic amine, and the electron transport layer A light-emitting element comprising a compound composed of an element selected from carbon, hydrogen, nitrogen, oxygen, silicon, and phosphorus and having a heteroaryl ring structure containing electron-accepting nitrogen. The light emitting device according to claim 1, wherein the light emitting material comprises a host material and a dopant material.