JP2012049159A - Light emitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic thin-film light emitter excellent in durability.SOLUTION: The light emitter includes at least a luminous layer and an electron transport layer between a positive electrode and a negative electrode, and emits light utilizing electric energy. The electron transport layer contains a pyrene compound represented by the following general formula (1).

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.

  The organic thin film light emitting element needs to satisfy the improvement in luminous efficiency, the reduction in driving voltage, and the improvement in durability. In particular, when the luminous efficiency is low, it is impossible to output an image that requires high luminance, and the amount of power consumption for outputting desired luminance increases. Further, when the durability of the element is not sufficient, it is difficult to obtain a practical life as a light emitting device. In particular, with respect to blue light-emitting elements, there are few blue light-emitting materials that provide highly reliable elements that exhibit high luminous efficiency and excellent durability. For example, in order to improve luminous efficiency, various luminescent materials have been developed (see, for example, Patent Documents 1 to 6). Moreover, the technique which improves luminous efficiency by improvement of the material used as an electron carrying layer, and the technique which dopes an alkali metal to such a material are disclosed (for example, refer patent documents 7-12).

International Publication WO2007 / 29798 Pamphlet International Publication WO2008 / 108256 Pamphlet International Publication WO2008 / 15945 Pamphlet JP 2007-131723 A JP 2008-214308 A JP 2007-169851 A JP 2000-348864 A JP 2004-277377 A JP 2003-347060 A Japanese Patent Laid-Open No. 2002-352961 Japanese Patent Laid-Open No. 2004-2297 International Publication WO2010 / 001817 Pamphlet

“Applied Physics Letters”, (USA), 1987, 51, 12, p. 913-915

  As described above, the organic thin-film light-emitting element needs to satisfy the improvement of the light emission efficiency, the reduction of the driving voltage, and the improvement of the durability. In particular, the blue light-emitting element has excellent durability and high reliability. There are few blue light-emitting materials that provide.

  Moreover, even when improving the compound used for an electron carrying layer, conventionally well-known combinations like patent documents 7-12 were inadequate for coexistence with high luminous efficiency and durability.

  The object of the present invention is to solve the problems of the prior art and to provide an organic thin film light emitting device excellent in durability.

  The present invention is a light emitting device 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, and the electron transport layer contains a pyrene compound represented by the following general formula (1) The light emitting element is characterized in that.

R ^{1 to} R ⁷ may be the same or different and are selected from the group consisting of hydrogen, an alkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group, an alkynyl group, and an aryl group. X is an alkyl group or an aryl group. Ar ¹ and Ar ² may be the same or different, and each is an aromatic hydrocarbon group having 6 to 30 carbon atoms which may be substituted with a hydrocarbon group.

  According to the present invention, an organic electroluminescent device having excellent durability can be provided.

  The pyrene compound represented by the general formula (1) in the present invention will be described in detail.

R ^{1 to} R ⁷ may be the same or different and are selected from the group consisting of hydrogen, an alkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group, an alkynyl group, and an aryl group. X is an alkyl group or an aryl group. Ar ¹ and Ar ² may be the same or different, and each is an aromatic hydrocarbon group having 6 to 30 carbon atoms which may be substituted with a hydrocarbon group.

  Among these substituents, the alkyl group is, for example, a saturated aliphatic hydrocarbon group such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, or a tert-butyl group. This may or may not have a substituent. The additional substituent in the case of being substituted is not particularly limited as long as it is a group composed only of hydrocarbons, and examples thereof include an alkyl group and an aryl group. This point is also described in the following description. Common. The number of carbon atoms in the alkyl group is not particularly limited, but is usually in the range of 1 to 20 and more preferably 1 to 8 in terms of availability and cost.

  The cycloalkyl group represents a saturated alicyclic hydrocarbon group such as cyclopropyl, cyclohexyl, norbornyl, adamantyl, etc., which may or may not have a substituent. The number of carbon atoms in the alkyl group moiety is not particularly limited, but is usually in the range of 3 or more and 20 or less.

  An alkenyl group shows the unsaturated aliphatic hydrocarbon group containing double bonds, such as a vinyl group, an allyl group, and a butadienyl group, and this may or may not have a substituent. The number of carbon atoms in the alkenyl group is not particularly limited, but is usually in the range of 2-20.

  The cycloalkenyl group refers to an unsaturated alicyclic hydrocarbon group containing a double bond such as a cyclopentenyl group, a cyclopentadienyl group, or a cyclohexenyl group, which may have a substituent. You don't have to.

  An alkynyl group shows the unsaturated aliphatic hydrocarbon group containing triple bonds, such as an ethynyl group, for example, and may or may not have a substituent. The number of carbon atoms of the alkynyl group is not particularly limited, but is usually in the range of 2-20.

  The aryl group represents an aromatic hydrocarbon group such as a phenyl group, a naphthyl group, a biphenyl group, a phenanthryl group, a fluorenyl group, or a terphenyl group. The aryl group may or may not have a substituent. The number of carbon atoms of the aryl group is not particularly limited, but is usually in the range of 6-40.

  Aromatic hydrocarbon groups refer to all groups consisting of a combination of benzene rings, including not only condensed rings such as naphthyl and phenanthryl groups, but also those in which rings such as biphenyl and naphthylphenyl groups are linked by a single bond. . Examples thereof include a phenyl group, a biphenyl group, a terphenyl group, a diphenylphenyl group, a naphthyl group, a naphthylphenyl group, a phenanthryl group, and a phenanthrylphenyl group. In the present specification, a fluorenyl group is also included in the aromatic hydrocarbon group. Therefore, a fluorenylphenyl group is also an aromatic hydrocarbon group.

Ar ¹ and Ar ² are each independently an aromatic hydrocarbon group which may be substituted with a hydrocarbon group, specifically a phenyl group, a biphenyl group, a terphenyl group, a diphenylphenyl group, a naphthyl group, a naphthylphenyl Group, fluorenyl group, fluorenylphenyl group and the like. In addition, these groups may be substituted with an aryl group and / or an alkyl group consisting only of hydrocarbons.

More specifically, Ar ¹ and Ar ² are preferably each independently a group represented by the formula (2), a group represented by the formula (3), or a fluorenyl group.

R ^{8 to} R ¹⁹ are each independently hydrogen, an alkyl group consisting only of hydrocarbons, or an aryl group consisting only of hydrocarbons, and Y and Z are used for linking to the pyrene skeleton. Among the formulas (2), it is particularly preferable that R ¹⁰ is an aryl group consisting only of hydrocarbons, or R ⁹ and R ¹¹ are aryl groups consisting only of hydrocarbons.

However, when the molecular weight of the pyrene compound represented by the general formula (1) is too large, film formation by vapor deposition becomes difficult. Therefore, the number of carbon atoms contained in Ar ¹ and Ar ² is included in the substituent. 6 or more and 30 or less are preferable including the number of carbon atoms. For the same reason, the total number of carbon atoms contained in Ar ¹ and Ar ² is preferably 40 or less.

Furthermore, it is preferable that Ar ¹ and Ar ² are different from each other because the thin film stability is improved due to molecular asymmetry.

  X is an alkyl group or an aryl group, preferably a saturated hydrocarbon group having 1 to 4 carbon atoms, or an aromatic hydrocarbon group having 6 to 18 carbon atoms which may or may not be substituted. . More specifically, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, phenyl group, naphthyl group, biphenyl group, terphenyl group and the like can be mentioned. It is done. In particular, it is preferable that X is a tert-butyl group because the interaction between pyrene skeletons can be suppressed and the thin film stability is improved.

  The pyrene compound represented by the general formula (1) is characterized in that it does not contain a heteroatom and has a structure composed only of a hydrocarbon group, and has a substituent at positions 1, 3, and 7 of the pyrene skeleton. There is. For this reason, it is excellent in electrochemical stability and exhibits high durability. Furthermore, since it has an alkyl group or an aryl group at the 7-position (X) of the pyrene skeleton, the interaction between the pyrene skeletons is suppressed, and the light emission efficiency and the thin film stability are improved.

Although it does not specifically limit as a pyrene compound represented by the said General formula (1), The following examples are specifically mentioned. Note that the combination of Ar ¹ , Ar ² and X is not limited to those exemplified, and a compound exhibiting similar characteristics can be obtained by appropriately combining the structures shown therein.

  Next, embodiments of the light emitting device of the present invention will be described in detail. The light emitting device of the present invention has an anode and a cathode, and an organic layer interposed between the anode and the cathode, and the organic layer includes at least a light emitting layer and an electron transport layer, and the light emitting layer emits light by electric energy. To do.

  Examples of the organic layer include laminated structures such as 1) a hole transport layer / light-emitting layer / electron transport layer and 2) a light-emitting layer / 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. The material is included in the hole transport material, and the electron injection material is included in the electron transport material.

  In the light emitting device of the present invention, the anode and the cathode have a role for supplying a sufficient current for light emission of the device, and at least one of them is preferably transparent or translucent in order to extract light. Usually, the anode formed on the substrate is a transparent electrode.

  The material used for the anode is a material that can efficiently inject holes into the organic layer, and is transparent or translucent to extract light. Tin oxide, indium oxide, indium tin oxide (ITO) indium zinc oxide (IZO) Although not particularly limited, such as conductive metal oxides such as, 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 It is particularly desirable to use ITO glass or Nesa glass. These electrode materials may be used alone, or a plurality of materials may be laminated or mixed. The resistance of the transparent electrode is not limited as long as a current sufficient for light emission of the element can be supplied, but it is desirable that the resistance be low from the viewpoint of power consumption of the element. For example, an ITO substrate with a resistance of 300Ω / □ or less will function as a device electrode, but since it is now possible to supply a substrate with a resistance of approximately 10Ω / □, use a substrate with a low resistance of 20Ω / □ 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. As for the glass material, alkali-free glass is preferred because it is better that there are fewer ions eluted from the glass. Alternatively, soda lime glass provided with a barrier coat such as SiO ₂ is also commercially available and can be used. Furthermore, if the first electrode functions stably, the substrate need not be glass, and for example, an 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 is not particularly limited as long as it can efficiently inject electrons into the light emitting layer. Generally, metals such as platinum, gold, silver, copper, iron, tin, aluminum, and indium, or alloys and multilayer stacks of these metals with low work function metals such as lithium, sodium, potassium, calcium, and magnesium Is preferred. Among these, aluminum, silver, and magnesium are preferable as the main component from the viewpoints of electrical resistance, ease of film formation, film stability, luminous efficiency, and the like. In particular, magnesium and silver are preferable because electron injection into the electron transport layer and the electron injection layer in the present invention is facilitated and low voltage driving is possible.

  Furthermore, for cathode protection, metals such as platinum, gold, silver, copper, iron, tin, aluminum and indium, or alloys using these metals, inorganic materials such as silica, titania and silicon nitride, polyvinyl alcohol, polyvinyl chloride As a preferred example, an organic polymer compound such as a hydrocarbon polymer compound is laminated on the cathode as a protective film layer. However, in the case of an element structure (top emission structure) that extracts light from the cathode side, the protective film layer is selected from materials that are light transmissive in the visible light region. The production method of these electrodes is not particularly limited, such as resistance heating, electron beam, sputtering, ion plating and coating.

  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 needs to efficiently transport holes from the positive electrode between electrodes to which an electric field is applied, and has a high hole injection efficiency, and it is desirable to transport the injected holes efficiently. For this purpose, it is required that the material has an appropriate ionization potential, has a high hole mobility, is excellent in stability, and does not easily generate trapping impurities during manufacture and use. Although it does not specifically limit as a substance which satisfy | fills such conditions, 4,4'-bis (N- (3-methylphenyl) -N-phenylamino) biphenyl, 4,4'-bis (N-- Triphenylamine derivatives such as (1-naphthyl) -N-phenylamino) biphenyl, 4,4 ′, 4 ″ -tris (3-methylphenyl (phenyl) amino) triphenylamine, bis (N-allylcarbazole) or Biscarbazole derivatives such as bis (N-alkylcarbazole), pyrazoline derivatives, stilbene compounds, hydrazone compounds, benzofuran derivatives and thiophene derivatives, oxadiazole derivatives, phthalocyanine derivatives, porphyrin derivatives and other heterocyclic compounds, fullerene derivatives, polymers In the system, the polycarbonate having the monomer in the side chain Chromatography with or styrene derivatives, polythiophene, polyaniline, polyfluorene, polyvinylcarbazole and polysilane are preferred.

  Furthermore, inorganic compounds such as p-type Si and p-type SiC can also be used. Further, a compound represented by the following general formula (4), tetrafluorotetracyanoquinodimethane (4F-TCNQ), or molybdenum oxide can also be used.

R ^{20 to} R ²⁵ may be the same or different and are selected from the group consisting of halogen, sulfonyl group, carbonyl group, nitro group, cyano group, and trifluoromethyl group.

  Among these, it is preferable that the compound (5) (1,4,5,8,9,12-hexaazatriphenylenehexacarbonitrile) is contained in the hole transport layer or the hole injection layer because it can be driven at a lower voltage.

  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 or a host material alone. It may be either. That is, in the light emitting element of the present invention, only the host material or the dopant material may emit light in each light emitting layer, or both the host material and the dopant material may emit light. From the viewpoint of efficiently using electric energy and obtaining light emission with high color purity, the light emitting layer is preferably composed of a mixture of a host material and a dopant material. Further, the host material and the dopant material may be either one kind or a plurality of combinations, respectively. The dopant material may be included in the entire host material or may be partially included. The dopant material may be laminated or dispersed. The dopant material can control the emission color. 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 doping method can be formed by a co-evaporation method with a host material, but may be simultaneously deposited after being previously mixed with the host material.

  Specific light-emitting materials include fused ring derivatives such as anthracene and pyrene, which have been known as light emitters, metal chelated oxinoid compounds such as tris (8-quinolinolato) aluminum, bisstyrylanthracene derivatives and distyryl. Bisstyryl derivatives such as benzene derivatives, tetraphenylbutadiene derivatives, indene derivatives, coumarin derivatives, oxadiazole derivatives, pyrrolopyridine derivatives, perinone derivatives, cyclopentadiene derivatives, oxadiazole derivatives, thiadiazolopyridine derivatives, dibenzofuran derivatives, carbazole derivatives In indolocarbazole derivatives and polymer systems, polyphenylene vinylene derivatives, polyparaphenylene derivatives, polythiophene derivatives, etc. can be used but are not particularly limited. Not shall.

  The host material is a compound having a condensed aryl ring such as naphthalene, anthracene, phenanthrene, pyrene, chrysene, naphthacene, triphenylene, perylene, fluoranthene, fluorene, or indene, or a derivative thereof, N, N′-dinaphthyl-N, N′-diphenyl Aromatic amine derivatives such as -4,4'-diphenyl-1,1'-diamine, metal chelated oxinoid compounds such as tris (8-quinolinato) aluminum (III), bisstyryl derivatives such as distyrylbenzene derivatives, Tetraphenylbutadiene derivative, indene derivative, coumarin derivative, oxadiazole derivative, pyrrolopyridine derivative, perinone derivative, cyclopentadiene derivative, carbazole derivative, pyrrolopyrrole derivative, thiadiazolopyridine derivative , Dibenzofuran derivatives, carbazole derivatives, indolocarbazole derivatives, the polymer system, polyphenylene vinylene derivatives, polyparaphenylene derivatives, polyfluorene derivatives, polyvinylcarbazole derivatives, and polythiophene derivatives can be used is not particularly limited.

The dopant material is not particularly limited, but a compound having a condensed aryl ring such as naphthalene, anthracene, phenanthrene, pyrene, chrysene, triphenylene, perylene, fluoranthene, fluorene, indene or a derivative thereof (for example, 2- (benzothiazol-2-yl) ) -9,10-diphenylanthracene or 5,6,11,12-tetraphenylnaphthacene), furan, pyrrole, thiophene, silole, 9-silafluorene, 9,9'-spirobisilafluorene, benzothiophene, Compounds having heteroaryl rings such as benzofuran, indole, dibenzothiophene, dibenzofuran, imidazopyridine, phenanthroline, pyridine, pyrazine, naphthyridine, quinoxaline, pyrrolopyridine, thioxanthene and derivatives thereof Conductor, borane derivative, distyrylbenzene derivative, 4,4′-bis (2- (4-diphenylaminophenyl) ethenyl) biphenyl, 4,4′-bis (N- (stilben-4-yl) -N-phenyl Aminostyryl derivatives such as amino) stilbene, aromatic acetylene derivatives, tetraphenylbutadiene derivatives, stilbene derivatives, aldazine derivatives, pyromethene derivatives, diketopyrrolo [3,4-c] pyrrole derivatives, 2,3,5,6-1H, 4H -Coumarin derivatives such as tetrahydro-9- (2'-benzothiazolyl) quinolidino [9,9a, 1-gh] coumarin, azole derivatives such as imidazole, thiazole, thiadiazole, carbazole, oxazole, oxadiazole, triazole and metal complexes thereof And N, N′-dipheni Aromatic amine derivatives such as ru-N, N′-di (3-methylphenyl) -4,4′-diphenyl-1,1′-diamine, organic transition metal complexes (for example, Ir (ppy) ₃ Organic iridium complex).

  In the present invention, the electron transport layer is a layer in which electrons are injected from the cathode and further transports electrons. The electron transport layer has high electron injection efficiency, and it is desired to efficiently transport injected electrons. For this reason, the electron transport layer is required to be a substance having a high electron affinity, a high electron mobility, excellent stability, and a trapping impurity that is unlikely to be generated during manufacture and use. In particular, in the case of stacking a thick film, a compound having a molecular weight of 400 or more that maintains a stable film quality is preferable because a low molecular weight compound is likely to be crystallized to deteriorate the film quality. On the other hand, when considering the transport balance of holes and electrons, if the electron transport layer mainly plays a role of effectively preventing the holes from the anode from flowing to the cathode side without recombination, Even if it is made of a material whose transport ability is not so high, the effect of improving the luminous efficiency is equivalent to that of a material made of a material having a high electron transport ability. 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.

  Since the pyrene compound represented by the general formula (1) is a compound composed only of a pyrene skeleton and a hydrocarbon group, it is excellent in thermal, electrochemical and photochemical stability. In addition, since a substituent selected from an alkyl group or an aryl group is introduced at the 7-position of the pyrene skeleton, a stable film quality can be obtained.

  The electron transport material used in the present invention need not be limited to each one of the pyrene compounds represented by the general formula (1) of the present invention, and a plurality of the pyrene compounds of the present invention may be mixed and used. One or more kinds of transport materials may be used by mixing with the pyrene compound of the present invention as long as the effects of the present invention are not impaired. The electron transport material that can be mixed is not particularly limited, but is a compound having a condensed aryl ring such as naphthalene, anthracene, or pyrene or a derivative thereof, or a styryl-based fragrance represented by 4,4′-bis (diphenylethenyl) biphenyl. Ring derivatives, arylamine derivatives such as styrylamine, perylene derivatives, perinone derivatives, coumarin derivatives, naphthalimide derivatives, quinone derivatives such as anthraquinone and diphenoquinone, phosphate derivatives, carbazole derivatives and indole derivatives, tris (8-quinolinolato) aluminum ( And quinolinol complexes such as III) and hydroxyazole complexes such as hydroxyphenyloxazole complexes, azomethine complexes, tropolone metal complexes and flavonol metal complexes.

  Next, the donor compound will be described. The donor compound in the present invention is a compound that facilitates electron injection from the cathode or the electron injection layer to the electron transport layer by improving the electron injection barrier, and further improves the electrical conductivity of the electron transport layer. That is, the light emitting device of the present invention is more preferably one in which an electron transport layer is doped with a donor compound in order to improve the electron transport capability in addition to the pyrene compound represented by the general formula (1).

  Preferred examples of the donor compound in the present invention include an alkali metal, an inorganic salt containing an alkali metal, a complex of an alkali metal and an organic substance, an alkaline earth metal, an inorganic salt containing an alkaline earth metal, or an alkaline earth metal. And a complex of organic substance. Preferable types of alkali metals and alkaline earth metals include alkali metals such as lithium, sodium and cesium, which have a low work function and a large effect of improving the electron transport ability, and alkaline earth metals such as magnesium and calcium.

In addition, since it is easy to deposit in vacuum and is excellent in handling, it is preferably in the form of a complex with an inorganic salt or an organic substance rather than a single metal. Furthermore, it is more preferable that it is in the state of a complex with an organic substance in terms of facilitating handling in the air and easy control of the addition concentration. Examples of inorganic salts include oxides such as LiO and Li ₂ O, nitrides, fluorides such as LiF, NaF, and KF, Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , Rb ₂ CO ₃ , Examples thereof include carbonates such as Cs ₂ CO ₃ . A preferable example of the alkali metal or alkaline earth metal is lithium from the viewpoint that the raw materials are inexpensive and easy to synthesize. Preferred examples of the organic substance in the complex with the organic substance include quinolinol, benzoquinolinol, flavonol, hydroxyimidazopyridine, hydroxybenzazole, hydroxytriazole and the like. Among these, a complex of an alkali metal and an organic substance is preferable, a complex of lithium and an organic substance is more preferable, and lithium quinolinol is particularly preferable.

  In addition, when the doping ratio of the donor compound in the electron transport layer is appropriate, the injection ratio of electrons from the cathode or the electron injection layer to the electron transport layer increases, and the cathode and the electron injection layer or the electron injection layer and the electron The energy barrier between the transport layers is reduced and the driving voltage is reduced. The suitable doping concentration varies depending on the material and the thickness of the doping region, but the molar ratio of the organic compound to the donor compound is preferably in the range of 100: 1 to 1: 100, more preferably 10: 1 to 1:10.

  The method of doping the electron transport layer with a donor compound to improve the electron transport capability is particularly effective when the thin film layer is thick. It is particularly preferably used when the total film thickness of the electron transport layer and the light emitting layer is 50 nm or more. For example, there is a method of using the interference effect to improve the light emission efficiency, but this improves the light extraction efficiency by matching the phase of the light directly emitted from the light emitting layer and the light reflected by the cathode. Is. This optimum condition varies depending on the light emission wavelength, but the total film thickness of the electron transport layer and the light-emitting layer is 50 nm or more, and in the case of long-wavelength light emission such as red, it may be a thick film near 100 nm. .

  The thickness of the electron transport layer to be doped may be part or all of the electron transport layer, but the thicker the entire electron transport layer, the higher the doping concentration. In the case of partial doping, it is desirable to provide a doping region at least at the electron transport layer / cathode interface, and the effect of lowering the voltage can be obtained only by doping in the vicinity of the cathode interface. On the other hand, when the light emitting layer is doped with the donor compound, it is desirable to provide a non-doped region at the light emitting layer / electron transport layer interface when it adversely affects the light emission efficiency.

  Moreover, since the pyrene compound represented by General formula (1) is a compound comprised only from a pyrene skeleton and a hydrocarbon group, it is excellent in chemical stability with respect to a hole. Therefore, the pyrene compound (1) can be suitably used as a hole blocking layer. That is, by inserting the pyrene compound (1) as the second electron transport layer (hole blocking layer) between the electron transport layer and the light emitting layer, deterioration of the electron transport layer due to holes can be prevented, The durability of the element is improved.

  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 organic layer is not limited because it depends on the resistance value of the luminescent material, but is preferably 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 electric energy, but a pulse current or an alternating current can also be used. The current value and 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, etc. 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. In addition, the number of the compound in each following Example points out the number of the compound described above.

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. First, 1,4,5,8,9,12-hexaazatriphenylenehexacarbonitrile is used as the hole injecting material by the resistance heating method, and 4,4'-bis (N- (1 -Naphthyl) -N-phenylamino) biphenyl was deposited by 50 nm. Next, a compound (H-1) as a host material and a compound (D-1) as a dopant material were vapor-deposited in a thickness of 40 nm on the light emitting material so that the doping concentration was 5% by weight. Next, a layer in which the compound (E-1) and the donor compound (lithium fluoride) are mixed is used as an electron transport layer with a deposition rate ratio of 1: 1 (= 0.05 nm / s: 0.05 nm / s) to a thickness of 20 nm. Vapor deposited and laminated.

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 , a blue light emitting device having excellent durability with a driving voltage of 5.2 V, an external quantum efficiency of 4.8%, and a luminance half time of 7000 hours was obtained.

Examples 2-9
A light emitting device was fabricated in the same manner as in Example 1 except that the materials described in Table 1 were used as the host material, the dopant material, and the electron transport layer. The results of each example are shown in Table 1. In Table 1, (E-2), (E-3) and (2E-1) are the compounds shown below.

Comparative Examples 1-9
A light emitting device was fabricated in the same manner as in Example 1 except that the materials described in Table 1 were used as the host material, the dopant material, and the electron transport material. The results of each comparative example are shown in Table 1. In Table 1, (E-4) to (E-6) are the compounds shown below.

Examples 10-20
A light emitting device was fabricated in the same manner as in Example 1 except that the materials described in Table 2 were used as the host material, the dopant material, and the electron transport layer. The results of each example are shown in Table 2. In Table 2, (H-2) to (H-8) and (D-2) to (D-10) are the compounds shown below.

Comparative Examples 10-15
A light emitting device was produced in the same manner as in Example 1 except that the materials described in Table 2 were used as the host material, the dopant material, and the electron transport material. The results of each comparative example are shown in Table 2.

Example 21
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. First, 1,4,5,8,9,12-hexaazatriphenylenehexacarbonitrile is used as the hole injecting material by the resistance heating method, and 4,4'-bis (N- (1 -Naphthyl) -N-phenylamino) biphenyl was deposited by 50 nm. Next, a compound (H-1) as a host material and a compound (D-1) as a dopant material were vapor-deposited in a thickness of 40 nm on the light emitting material so that the doping concentration was 5% by weight. Next, a layer in which the compound (E-1) and the donor compound (2E-1: lithium quinolinol) are mixed at a deposition rate ratio of 1: 1 (= 0.05 nm / s: 0.05 nm / s) is used as an electron transport layer. Laminated to a thickness of 20 nm.

Next, after depositing 1 nm of lithium quinolinol, a co-deposited film of magnesium and silver was deposited at a deposition rate ratio of magnesium: silver = 10: 1 (= 0.5 nm / s: 0.05 nm / s) to 100 nm to form a cathode, A 5 × 5 mm square element was produced. 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 , a blue light-emitting device having excellent durability with a driving voltage of 3.9 V, an external quantum efficiency of 6.1%, and a luminance half-life time of 7200 hours was obtained.

Examples 22-23
A light emitting device was produced in the same manner as in Example 21 except that the materials described in Table 3 were used as the electron transport layer. The results of each example are shown in Table 3.

Example 24
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. First, 1,4,5,8,9,12-hexaazatriphenylenehexacarbonitrile is used as the hole injecting material by the resistance heating method, and 4,4'-bis (N- (1 -Naphthyl) -N-phenylamino) biphenyl was deposited by 50 nm. Next, a compound (H-1) as a host material and a compound (D-1) as a dopant material were vapor-deposited in a thickness of 40 nm on the light emitting material so that the doping concentration was 5% by weight. Next, after depositing (E-1) to a thickness of 5 nm as the electron transport layer 1, a layer in which the compound (E-7) and the donor compound (2E-1) are mixed is deposited as the electron transport layer 2. The layers were deposited and deposited at a ratio of 1: 1 (= 0.05 nm / s: 0.05 nm / s) to a thickness of 15 nm.

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 , a blue light-emitting device having excellent durability with a driving voltage of 4.1 V, an external quantum efficiency of 5.8%, and a luminance half-life of 4500 hours was obtained.

Example 25
A light emitting device was produced in the same manner as in Example 24 except that a layer obtained by mixing the compound (E-8) and the donor compound (2E-1) was used as the electron transport layer 2. The results are shown in Table 4.

Comparative Example 16
A light emitting device was produced in the same manner as in Example 24 except that the compound (E-4) was used as the electron transport layer 1. The results are shown in Table 4.

Comparative Example 17
A light emitting device was fabricated in the same manner as in Example 24 except that after the light emitting material was deposited, the electron transport layer 2 was directly laminated without depositing the electron transport layer 1. The results are shown in Table 4.

Claims (7)

A light-emitting element in which at least a light-emitting layer and an electron transport layer are present between an anode and a cathode and emits light by electric energy, and the electron transport layer contains a pyrene compound represented by the following general formula (1) A light emitting device characterized.

(R ^{1 to} R ⁷ may be the same or different and are selected from the group consisting of hydrogen, an alkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group, an alkynyl group, and an aryl group. X is an alkyl group or an aryl group. Ar ¹ and Ar ² may be the same or different and each is an aromatic hydrocarbon group having 6 to 30 carbon atoms which may be substituted with a hydrocarbon group. The light-emitting device according to claim 1, wherein X is a tert-butyl group. The light emitting device according to claim ¹ , wherein Ar ¹ and Ar ² are different. The light-emitting device according to claim 1, wherein the electron transport layer further contains a donor compound. The donor compound is an alkali metal, an inorganic salt containing an alkali metal, a complex of an alkali metal and an organic substance, an alkaline earth metal, an inorganic salt containing an alkaline earth metal, or a complex of an alkaline earth metal and an organic substance Item 5. A light emitting device according to Item 4. The light-emitting element according to claim 5, wherein the donor compound is a complex of an alkali metal and an organic substance or a complex of an alkaline earth metal and an organic substance. The light emitting device according to claim 1, wherein the cathode is composed of magnesium and silver.