JP2010027761A - Light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic thin-film light emitting element whose durability lifetime is improved without making a drive voltage worse. <P>SOLUTION: The light emitting element is an organic light emitting device which includes, on a first electrode formed on a substrate, a thin film layer including at least a light emitting layer and an electron transporting layer, and a second electrode formed on the thin film layer, the electron transporting layer containing an organic compound represented by formula (1) and an organometallic complex. Here, A is a group having a substituted or unsubstituted phenanthroline skeleton or substituted or unsubstituted benzoquinoline skeleton. Further, B is a direct bond, a double bond, a triple bond, a substituted or unsubstituted n-valent aromatic hydrocarbon residue, a substituted or unsubstituted n-valent heterocyclic ring residue, or an n-valent residue generated by mixing them, where n is a natural number equal to or greater than 2. <P>COPYRIGHT: (C)2010,JPO&INPIT

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. A typical 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, 8-hydroxyquinoline aluminum as a light emitting layer, and Mg: Ag as a cathode sequentially. 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 and the improvement in durability. In order to improve the light emission efficiency, there is a method of using the interference effect with the reflected light from the cathode. However, under the optimum conditions, the thin film layer is thickened, so that the driving voltage is increased. When the drive voltage increases, there is a problem that the amount of power consumption for outputting desired luminance increases. On the other hand, in order to improve durability, it is preferable to use a compound having a high glass transition point. However, in general, many compounds having a high glass transition point have a three-dimensionally bulky structure, and molecular orbital overlap is small. As a result, the charge mobility is reduced, and as a result, the drive voltage is increased. Further, when the film thickness of the thin film layer is increased in order to enhance the durability against leakage due to foreign matter contamination and continuous driving, the driving voltage increases accordingly.

As a device for reducing the driving voltage for such a problem, a method of doping the electron transport layer with a metal such as an alkali metal, an alkaline earth metal, or a transition metal, or a metal salt or metal oxide thereof (Patent Document 1). 2), and a method of doping an electron transport layer with an organometallic complex such as a lithium quinolinol complex (see Non-Patent Document 2 and Patent Document 3) has been proposed.
“Applied Physics Letters”, (USA), 1987, 51, 12, p. 913-915 “Journal of Physics D: Applied Physics”, (USA) 2007, 40, p. 6535-6540 JP-A-10-270171 JP-A-10-270172 JP 2004-319424 A

  However, when a technique such as Patent Document 1, Patent Document 2 or Non-Patent Document 2 is used, although the effect of reducing the drive voltage and improving the light emission efficiency can be seen, it is sufficient in terms of the element durability life. Was not obtained. Moreover, when the technique of patent document 3 was used, although the durable life improvement was also seen, the effect was not enough and the room for the further improvement was left.

  The object of the present invention is to provide an organic thin film light emitting device that solves the problems of the prior art and has an improved durability life without deteriorating the driving voltage.

  The present invention achieves the above object, and includes a thin film layer including at least a light emitting layer and an electron transport layer on a first electrode formed on a substrate, and a second film formed on the thin film layer. An organic electroluminescence device including an electrode, wherein the electron transport layer includes an organic compound represented by the following general formula (1) and an organometallic complex.

(Here, A is a group having a substituted or unsubstituted phenanthroline skeleton or a substituted or unsubstituted benzoquinoline skeleton. B is a direct bond, or a double bond, triple bond, substituted or unsubstituted n-valent aromatic group. (It is a hydrocarbon residue, a substituted or unsubstituted n-valent aromatic heterocyclic residue, or an n-valent residue obtained by mixing them. N is a natural number of 2 or more.)

  According to the present invention, it is possible to provide an organic electroluminescence device having excellent luminous efficiency without deterioration in driving voltage and improved durability life.

  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 a thin film layer interposed between the anode and the cathode. The thin film layer includes at least a light emitting layer and an electron transport layer.

  Examples of the configuration of such a thin film layer are 1) hole transport layer / light emitting layer / electron transport layer, 2) hole injection layer / hole transport layer / light emitting layer / electron transport layer, and 3) hole transport layer. / Light emitting layer / electron transport layer / electron injection layer, or 4) a stacked structure such as hole injection layer / hole transport layer / light emitting layer / electron transport layer / electron injection layer. A hole blocking layer may be further included between the light emitting layer and the electron transport layer. Moreover, each said layer may consist of a single layer, respectively, and may consist of multiple layers.

  The electron transport layer in the present invention contains a compound represented by the following general formula (1).

  Here, A is a group having a substituted or unsubstituted phenanthroline skeleton or a substituted or unsubstituted benzoquinoline skeleton. B is a single bond, or a linking group that connects a plurality of phenanthroline skeletons or benzoquinoline skeletons. Specifically, a double bond, a triple bond, a substituted or unsubstituted n-valent aromatic hydrocarbon residue, a substituted or unsubstituted n-valent aromatic heterocyclic residue, or a mixed n-valent aromatic residue Residue. n is a natural number of 2 or more.

  A may or may not have a substituent. Examples of the substituent in the case of having a substituent include an alkyl group, a cycloalkyl group, a heterocyclic group, an alkenyl group, a cycloalkenyl group, Examples include alkynyl groups, alkoxy groups, alkylthio groups, aryl ether groups, aryl thioether groups, aryl groups, heteroaryl groups, cyano groups, amino groups, silyl groups, and the like.

  Among these substituents, the alkyl group represents, for example, a saturated aliphatic hydrocarbon group such as a methyl group, an ethyl group, a propyl group, or a butyl group, which may be unsubstituted or substituted. The substituent in the case of being substituted is not particularly limited, and examples thereof include an alkyl group, an aryl group, a heteroaryl group, and the like, and this point is common to the following description. Further, the number of carbon atoms of the alkyl group is not particularly limited, but is usually in the range of 1 to 20 from the viewpoint of availability and cost.

  The cycloalkyl group refers to a saturated alicyclic hydrocarbon group such as a cyclopropyl group, a cyclohexyl group, a norbornyl group, an adamantyl group, and the like, which may be unsubstituted or substituted. Although carbon number of an alkyl group part is not specifically limited, Usually, it is the range of 3-20.

  The heterocyclic group refers to a group consisting of an aliphatic ring having atoms other than carbon, such as a pyran ring, piperidine ring and cyclic amide, in the ring, which may be unsubstituted or substituted. . Although carbon number of a heterocyclic group is not specifically limited, Usually, it is the range of 2-20.

  Moreover, an alkenyl group shows the unsaturated aliphatic hydrocarbon group containing double bonds, such as a vinyl group, an allyl group, and a butadienyl group, for example, and this may be unsubstituted or substituted. Although carbon number of an alkenyl group is not specifically limited, Usually, it is 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 is unsubstituted or substituted. It doesn't matter.

  The alkynyl group refers to an unsaturated aliphatic hydrocarbon group containing a triple bond such as an ethynyl group, which may be unsubstituted or substituted. Although carbon number of an alkynyl group is not specifically limited, Usually, it is the range of 2-20.

  The alkoxy group refers to, for example, an aliphatic hydrocarbon group via an ether bond such as a methoxy group, and the aliphatic hydrocarbon group may be unsubstituted or substituted. Although carbon number of an alkoxy group is not specifically limited, Usually, it is the range of 1-20.

  The alkylthio group is a group in which an oxygen atom of an ether bond of an alkoxy group is substituted with a sulfur atom.

  The aryl ether group refers to, for example, an aromatic hydrocarbon group via an ether bond such as a phenoxy group, and the aromatic hydrocarbon group may be unsubstituted or substituted. Although carbon number of an aryl ether group is not specifically limited, Usually, it is the range of 6-40.

  The arylthioether group is a group in which the oxygen atom of the ether bond of the arylether group is substituted with a sulfur atom.

  Moreover, an aryl group shows aromatic hydrocarbon groups, such as a phenyl group, a naphthyl group, a biphenyl group, a phenanthryl group, a terphenyl group, a pyrenyl group, for example. The aryl group may be unsubstituted or substituted. Although carbon number of an aryl group is not specifically limited, Usually, it is the range of 6-40.

  The heteroaryl group refers to an aromatic group having an atom other than carbon, such as a furanyl group, a thiophenyl group, an oxazolyl group, a pyridyl group, or a quinolinyl group, which is unsubstituted or substituted. It doesn't matter. Although carbon number of a heteroaryl group is not specifically limited, Usually, it is the range of 2-30.

  The amino group may be unsubstituted or substituted, and examples of the substituent include an alkyl group, a cycloalkyl group, an aryl group, a heteroaryl group, and the like, and these substituents may be further substituted. .

  A silyl group refers to, for example, a functional group having a bond to a silicon atom, such as a trimethylsilyl group, which may or may not have a substituent. Although carbon number of a silyl group is not specifically limited, Usually, it is the range of 3-20. The number of silicon is usually in the range of 1-6. Among these, preferred substituents from the viewpoint of thermal stability include aryl groups and heteroaryl groups.

  The n-valent aromatic hydrocarbon residue in B is the remaining part of the aromatic hydrocarbon such as benzene, naphthalene, anthracene, pyrene, biphenyl, terphenyl, fluorene, spirofluorene, etc., excluding n hydrogen atoms These may or may not have a substituent. Examples of the substituent in the case of being substituted include those similar to the above-mentioned substituent of A. Among these, preferred substituents from the viewpoint of thermal stability include aryl groups and heteroaryl groups.

  The n-valent aromatic heterocyclic residue in B is other than carbon such as pyridine, pyrimidine, pyrazine, triazine, quinoline, quinoxaline, phenanthroline, phenazine, furan, thiophene, benzofuran, benzothiophene, dibenzofuran, dibenzothiophene, etc. This is the remaining part obtained by removing n hydrogen atoms from an aromatic compound having the following atoms in the ring. These may or may not have a substituent. Examples of the substituent in the case of being substituted include those similar to the above-mentioned substituent of A. Among these, preferred substituents from the viewpoint of thermal stability include aryl groups and heteroaryl groups.

  Among B, for example, an aromatic hydrocarbon and an n-valent residue mixed with an aromatic heterocycle include, for example, 2,6-diphenylpyridine, 2,5-diphenylthiophene, 2,4,6-triphenyl. This is the remaining part obtained by removing n hydrogen atoms from a compound in which an aromatic hydrocarbon such as triazine and an aromatic heterocycle are mixed. In these rings, each ring may or may not have a substituent. Examples of the substituent in the case of being substituted include those similar to the above-mentioned substituent of A. Among these, preferred substituents from the viewpoint of thermal stability include aryl groups and heteroaryl groups.

  Examples of B are not particularly limited, but specific examples include the following.

  The compound represented by the general formula (1) functions as an electron transport material in the present invention. In general, the electron transport material is preferably a material in which electrons are efficiently injected from the cathode and efficiently transports electrons to the light emitting layer, that is, a material having a high electron affinity and a high electron mobility. Furthermore, it is required that the film has excellent thin film stability, and the impurities that become traps are less likely to be generated during manufacture and use. Since a low molecular weight compound is likely to be deteriorated due to crystallization or the like, a compound having a molecular weight of 400 or more that maintains a stable film quality is preferable.

  The organic compound represented by the general formula (1) is a compound satisfying such conditions, and has a high electron affinity because it contains a phenanthroline or benzoquinoline skeleton, and is an excellent material for injecting electrons from the cathode. . Moreover, since it has a multimeric structure and has a moderately bulky three-dimensional structure, crystallization is suppressed and it has excellent thin film stability.

  A in the general formula (1) may have either a phenanthroline skeleton or a benzoquinoline skeleton, but has a substituted or unsubstituted phenanthroline skeleton having a larger electron affinity or a larger ionization potential. It is preferable. Among these, a 1,10-phenanthroline skeleton is particularly preferable from the viewpoint of easily forming a bidentate coordination complex with a metal atom.

  Although it does not specifically limit as an organic compound represented by General formula (1), Specifically, the following examples are given.

  In addition, the electron transport layer in this invention may contain the organic compound which has electron transport property besides the organic compound represented by General formula (1). Examples of such organic compounds include silole derivatives, benzimidazole derivatives, oxadiazole derivatives, triazole derivatives, phosphine oxide derivatives, triazine derivatives, pyridine derivatives, pyrimidine derivatives, and triarylborane derivatives. These may be contained in the same layer, or may be contained separately in different layers with a plurality of electron transport layers.

  Moreover, the electron carrying layer in this invention has an organometallic complex with the organic compound represented by General formula (1). By containing the organic compound represented by the general formula (1) and the organometallic complex, the thin film stability is further improved. Usually, the impurity mobility of the organic thin film doped with impurities is generally such that the impurity becomes a charge trap, the original charge mobility of the organic thin film is impaired, and as a result, the drive voltage is increased. However, in the combination of the organic compound and organometallic complex used in the present invention, the metal atom contained in the doped organometallic complex and the organic compound represented by the general formula (1) form a charge transfer complex, The electrical conductivity of the thin film is improved (n-doping effect). Therefore, light can be emitted without impairing the driving voltage of the element. As a result, the carrier balance of the element is not disturbed, and the light emission efficiency is not lowered.

  The organic compound represented by the general formula (1) has a phenanthroline skeleton or a benzoquinoline skeleton. By combining a compound having a plurality of such skeletons with an organometallic complex, the device can be operated at a lower voltage. It can be driven, and the durability life of the element can be improved. On the other hand, when a compound having only one phenanthroline skeleton or benzoquinoline skeleton and an organometallic complex are combined, such an effect is insufficient. Although the detailed mechanism is unknown, when a compound having a plurality of phenanthroline skeletons or benzoquinoline skeletons and an organometallic complex is combined with a compound having only one phenanthroline skeleton or benzoquinoline skeleton and an organometallic complex In comparison, it is considered that the n-doping effect is stronger.

  Further, the organometallic complex generally has an ionization potential (AC-2 (made by Riken Keiki Co., Ltd.) and other atmospheric photoelectron spectrometers) smaller than the organic compound represented by the general formula (1). There are many things. When such an organometallic complex is used, the organic compound represented by the general formula (1) is preferentially trapped in holes entering the electron transport layer without being recombined in the light emitting layer. It is considered that there is an effect of preventing deterioration of the device, and as a result, the device durability life is improved. From the above, it is preferable that the organometallic complex used in the present invention has a smaller ionization potential than the organic compound represented by the general formula (1). In addition, it is preferable that the complex itself has an electron transporting property. Examples of such organometallic complexes include porphyrin metal complexes, phthalocyanine metal complexes, naphthalocyanine metal complexes, rare earth metal complexes such as organic europium complexes, organic iridium complexes, heavy transition metal complexes such as organic platinum complexes, terbium, nickel Acetylacetonate complexes such as magnesium, lithium and calcium, and metal chelated oxinoid compounds represented by tris (8-quinolinolato) aluminum which itself functions as an electron transport layer. These organometallic complexes may be binuclear complexes.

  The central metal of the organometallic complex is preferably an alkali metal or alkaline earth metal that has a small work function and can be expected to have an n-doping effect. Alkali metal simple substance and alkaline earth metal simple substance reacts violently with moisture in the atmosphere, so it is difficult to handle, but even if such a metal forms a complex with an organic ligand, it is stable in the atmosphere. There is an advantage of easy handling. Furthermore, when the electron transport layer doped with a single metal is in direct contact with the light emitting layer, there is a problem in that the exciton involved in the light emission is deactivated by the metal atom and the light emission efficiency is lowered. However, such a problem does not occur even if the electron transport layer doped with the organometallic complex is in direct contact with the light emitting layer.

  Furthermore, it is more preferable that the central metal is lithium from the viewpoint of low cost and easy synthesis and thermal stability during vapor deposition.

  The organometallic complex as described above is not particularly limited, but specific examples include the following.

  The content of the organometallic complex in the electron transport layer varies depending on the type of electron transport material used and its film thickness, but is usually 0.1% by weight or more and 80% by weight or less based on the total amount of the compounds contained in the electron transport layer. Is preferred. More preferably, it is 10 weight% or more, More preferably, it is 20 weight% or more, More preferably, it is 50 weight% or less. When the concentration is higher than 80% by weight, the driving voltage may be increased. The organometallic complex may be uniformly contained in the entire region of the electron transport layer, but may be contained with a concentration gradient. In this case, for example, a mode in which the electron transport layer is contained at a high concentration on the light emitting layer side and at a low concentration on the electrode side is preferable. Furthermore, even if it is partially contained, for example, at the interface of the electron transport layer in contact with the light emitting layer, an improvement in durability life can be expected. In this case, the region containing the organometallic complex is preferably a region from the interface between the light emitting layer and the electron transport layer to 50% of the thickness of the electron transport layer. Also in this case, a concentration gradient may be provided so as to be contained at a higher concentration on the light emitting layer side.

  In addition, when the organometallic complex is partially contained in the interface portion in contact with the light emitting layer of the electron transport layer, another material may be further contained in the remaining portion of the electron transport layer. Examples of the material contained here include organometallic complexes of a type different from the organometallic complex, and alkali metals, alkaline earth metals, rare earth metals, transition metals, metal salts or metal oxides thereof, and the like. .

  Furthermore, when the electron transport layer is composed of a plurality of layers, the organometallic complex may be contained only in the layer containing the organic compound represented by the general formula (1) or represented by the general formula (1). It may also be contained in a layer that does not contain the organic compound.

  Usually, in order to smoothly inject electrons from the cathode to the electron transport layer, an alkali metal, alkaline earth metal, alkali metal salt, alkaline earth metal salt, organic alkali metal complex is interposed between the electron transport layer and the cathode. It is possible to insert an electron injection layer such as an organic alkaline earth metal complex thinly, or to provide an electron injection layer doped with an alkali metal, an alkaline earth metal, an alkali metal salt, an alkaline earth gold salt or the like in an electron transport material. It is common. However, in the present invention, if the electron transport layer containing the organometallic complex as described above is in direct contact with the cathode, this layer also functions as an electron injection layer. Therefore, it can be driven at a sufficiently low voltage without inserting an electron injection layer between the electron transport layer and the cathode. Of course, there is no problem even if an electron injection layer is further provided.

  The first electrode and the second electrode have a role of supplying a sufficient current for light emission of the element, and at least one of the first electrode and the second electrode is preferably transparent or translucent in order to extract light. Usually, the first electrode formed on the substrate is a transparent electrode, which is an anode, and the second electrode is a cathode.

  If the material used for the first electrode is transparent or semi-transparent to extract light, a conductive metal oxide such as tin oxide, indium oxide, indium tin oxide (ITO), zinc indium oxide (IZO), or gold Metals such as silver and chromium, inorganic conductive materials such as copper iodide and copper sulfide, 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 a current sufficient for light emission of the element can be supplied. 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. The ITO film forming method is not particularly limited, such as an electron beam evaporation method, a sputtering method, or a chemical reaction method.

As the glass substrate, soda lime glass, non-alkali glass, or the like is used, and it is sufficient that the thickness is sufficient to maintain the mechanical strength, so 0.5 mm or more is sufficient. As for the glass material, alkali-free glass is preferred because it is better that ions eluted from the glass are less, but soda-lime glass with a barrier coat such as SiO ₂ is also commercially available and can be used.

  The material used for the second electrode 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. In particular, aluminum, silver, and magnesium are preferable as the main components from the viewpoints of electrical resistance, ease of film formation, film stability, luminous efficiency, and the like.

  The method for forming the thin film layer includes resistance heating vapor deposition, electron beam vapor deposition, sputtering, molecular lamination method, coating method, etc., and is not particularly limited. Is preferable.

  As a hole transport material used for the hole transport layer, it is necessary to efficiently transport holes from the positive electrode between electrodes to which an electric field is applied, and the hole injection efficiency is high. It is desirable to transport 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, Triphenylamine derivatives, such as TPD, m-MTDATA, (alpha) -NPD, biscarbazolyl derivative, a pyrazoline derivative, a stilbene type compound, a hydrazone type compound, and a phthalocyanine derivative A known hole transporting material such as a heterocyclic compound represented by the formula (1), polyvinylcarbazole, or polysilane can be used. These hole transport materials may be used alone, but may be used by being laminated or mixed with different hole transport materials.

  The light emitting material used for the light emitting layer may be only the host material or a combination of the host material and the guest material. In addition, the guest material may be included in the entire host material, or may be included partially. The guest material may be either laminated or dispersed.

  Specifically, the light-emitting material includes 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 diesters. Bisstyryl derivatives such as styrylbenzene derivatives, tetraphenylbutadiene derivatives, coumarin derivatives, oxadiazole derivatives, pyrrolopyridine derivatives, perinone derivatives, cyclopentadiene derivatives, oxadiazole derivatives, thiadiazolopyridine derivatives, polyphenylene vinylene derivatives in polymer systems Polyparaphenylene derivatives, polythiophene derivatives, and the like can be used, but are not particularly limited.

  When a host material and a dopant material are used in combination, these materials are not particularly limited, and known materials can be used. Specifically, as host materials, metal chelated oxinoid compounds such as condensed polycyclic aromatic derivatives such as fluorene derivatives, spirofluorene derivatives, anthracene derivatives, pyrene derivatives, styrylarylene derivatives, and tris (8-quinolinolato) aluminum. , Carbazole derivatives and the like can be used. As dopant materials, condensed ring derivatives such as perylene and rubrene, arylamine derivatives, azole derivatives, benzoazole derivatives, quinacridone derivatives, phenoxazone 660, DCM1, perinone, coumarin derivatives, pyromethene (diazaindacene) derivatives, cyanine dyes and the like are used as they are. Can be used. Moreover, the organic iridium complex, the organic platinum complex, etc. which have phosphorescence currently examined actively can also be used. These are, for example, JP 2000-7604 A, JP 2000-53676 A, JP 2000-191560 A, JP 2001-284050 A, JP 2001-335516 A, and International Publication WO 2004/018587. Pamphlet, Japanese Patent Application Laid-Open No. 5-17765, International Publication WO 2002/02059, International Publication WO 2004/083162, International Publication WO 2004/044088, Japanese Patent Application Laid-Open No. 2007-230960, Japanese Patent Application Laid-Open No. 2006-38930, Although it is a material currently disclosed by Unexamined-Japanese-Patent No. 2007-77185, Unexamined-Japanese-Patent No. 2007-63501, etc., it is not restricted to these, A well-known thing can be used.

  As a combination of a host material and a dopant material, the dopant material has a LUMO (lowest orbital orbital) energy level that is the same or smaller than that of the host material, that is, the dopant traps electrons moving on the host. The combination that is easy to do is preferable because the effect of improving the durability life is greatly exhibited.

  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.

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, a compound (H-1) as a host material and a compound (D-1) as a dopant material were vapor-deposited on the light-emitting material to a thickness of 40 nm so that the doping concentration was 2% by weight. Next, a layer in which the organic compound (E-1) and the lithium quinolinol complex (LiQ) were mixed at a weight ratio of 4: 1 was laminated to a thickness of 20 nm as an electron transport layer. Next, 0.5 nm of LiQ was laminated as an electron injection layer.

Next, magnesium and silver were co-deposited at a weight ratio of 9: 1 to 100 nm to form a cathode, thereby producing a 5 × 5 mm square device. The film thickness referred to here is a crystal oscillation type film thickness monitor display value. When this light-emitting element was DC-driven at 10 mA / cm ² , high-efficiency blue light emission with a driving voltage of 4.0 V, an external quantum efficiency (EQE) of 4.3%, and an emission peak wavelength of 453 nm was obtained. When this element was set to an initial luminance of 1000 cd / m ² and continuously driven with a direct current, the time for the luminance to attenuate by 20% was 30 hours.

Examples 2-7
A light emitting device was produced in the same manner as in Example 1 except that the conditions described in Table 1 were used as the electron transport layer. The results of each example are shown in Table 1.

Comparative Example 1
Emission was carried out in the same manner as in Example 1 except that the compound (E-5) was used for the electron transport layer, and an electron transport layer co-deposited so that the weight ratio of (E-5) and LiQ was 2: 1 was used. An element was produced. When this light emitting element was DC-driven at 10 mA / cm ² , blue light emission with a driving voltage of 6.0 V and an external quantum efficiency of 3.1% was obtained. When this element was set to an initial luminance of 1000 cd / m ² and continuously driven with a direct current, the time for the luminance to attenuate by 20% was 12 hours.

Comparative Examples 2-6
A light emitting device was produced in the same manner as in Example 1 except that the conditions described in Table 1 were used as the electron transport layer. The results of each comparative example are shown in Table 1.

Examples 8-14
A light-emitting element was fabricated in the same manner as in Example 1 except that the conditions described in Table 2 were used as the electron transport layer and the LiQ layer as the electron injection layer was not stacked. The results of each example are shown in Table 2.

Comparative Examples 7-12
A light emitting device was fabricated in the same manner as in Example 1 except that the conditions described in Table 2 were used as the electron transport layer and the LiQ layer as the electron injection layer was not laminated. The results of each comparative example are shown in Table 2.

Examples 15-22
The light emitting device was manufactured in the same manner as in Example 1 except that the conditions described in Table 3 were used for the electron transport layer, and the compound (H-2) was used as the host material and the compound (D-2) was used as the dopant material. Produced. The results of each example are shown in Table 3. In the endurance life measurement of Examples 15 to 22, the initial luminance was set to 2000 cd / m ² .

Comparative Examples 13-18
The light emitting device was manufactured in the same manner as in Example 1 except that the conditions described in Table 3 were used for the electron transport layer, and the compound (H-2) was used as the host material and the compound (D-2) was used as the dopant material. Produced. The results of each example are shown in Table 3. In the endurance life measurement of Comparative Examples 13 to 18, all were set to an initial luminance of 2000 cd / m ² .

  The compounds used in each example and comparative example are shown below.

Claims (4)

An organic electroluminescent device comprising a thin film layer including at least a light emitting layer and an electron transport layer on a first electrode formed on a substrate, and a second electrode formed on the thin film layer, wherein the electron transport layer Contains an organic compound represented by the following general formula (1) and an organometallic complex.

(Here, A is a group having a substituted or unsubstituted phenanthroline skeleton or a substituted or unsubstituted benzoquinoline skeleton. B is a direct bond, or a double bond, triple bond, substituted or unsubstituted n-valent aromatic group. (It is a hydrocarbon residue, a substituted or unsubstituted n-valent aromatic heterocyclic residue, or an n-valent residue obtained by mixing them. N is a natural number of 2 or more.) The light emitting device according to claim 1, wherein A in the general formula (1) is a group having a substituted or unsubstituted 1,10-phenanthroline skeleton. 3. The light emitting device according to claim 1, wherein the organometallic complex is a compound containing an alkali metal or an alkaline earth metal. The light-emitting element according to claim 1, wherein the organometallic complex is a lithium-containing compound.