JP2010114232A - Organic electroluminescence element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescence (EL) element capable of using a cathode having resistance to oxidation, without the use of an electron injecting material, such as LiF. <P>SOLUTION: The organic electroluminescence element comprises a pair of electrodes, comprising anodes and cathodes and a plurality of organic compound layers comprising at least a light-emitting layer and an electron transport layer between the pair of electrodes. The electron transport layer includes at least one kind of boron compound expressed by expression (1), and the work function of the cathode is not less than 4.0 eV. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an organic electroluminescent element (hereinafter referred to as “organic EL element”). Specifically, the present invention relates to an organic EL using a specific electron transport material and a specific cathode.

  An organic EL device has a structure in which one or more organic compounds including a light-emitting organic compound are sandwiched between an anode and a cathode, and holes injected from the anode and electrons injected from the cathode are recombined. The light-emitting organic compound is excited by utilizing the energy at the time of light emission to obtain light emission. The organic EL element is called a current-driven element, and the light emission intensity is proportional to the injected current. In order to utilize the flowing current more efficiently, various element structures have been improved.

The prototype of the organic EL element is C.I. W. Proposed by Tang et al. (Non-Patent Document 1). This device comprises an anode (ITO) formed on a glass substrate, a hole transport layer (diamine), an electron transporting light emitting layer (Alq ₃ ), and a cathode (Mg: Ag alloy). ₃ layers. Here, by functionally separating the hole transport layer and the electron-transporting light-emitting layer, the recombination probability of the injected holes and electrons was increased, and light emission at a low voltage became possible.

  Adachi et al. Improved this device and proposed a three-layer device (Non-Patent Document 2). This element is composed of an anode (ITO), a hole transport layer (TPD), a light emitting layer (perylene, etc.), an electron transport layer (PV), and a cathode (Mg) formed on a glass substrate. In this element, the light emitting layer and the electron transport layer are functionally separated, and the light emission color can be selected depending on the light emitting material.

On the other hand, C.I. W. Tang et al. Proposed a method of doping a light emitting material (Non-Patent Document 3). In this device, high-efficiency light emission was realized by doping a light-emitting material such as coumarin into Alq ₃ as a host material by several percent. In this system, since the uniformity of the film can be secured by the host material, there is an advantage that various dye materials having high solid quantum efficiency can be used as the luminescent dopant.

  Functional separation of the charge transport layer is also progressing. S. A. Van Slyke et al. Proposed providing a hole injection layer between a conventional hole transport layer and an anode (Non-Patent Document 4). In this method, the organic EL is driven stably for reasons such as reducing the energy barrier for hole injection and smoothing the ITO surface by matching the ionization potential (HOMO) of the hole injection layer and the work function of the anode. It is said that it can be done.

  On the other hand, L. S. Hung et al. Proposed providing an electron injection layer (Non-patent Document 5). In this method, by providing an extremely thin (about 0.5 nm) lithium fluoride (LiF) electron injection layer between the electron transport layer and the cathode metal, aluminum (Al) can be used as the cathode. . When electrons are injected into the electron transport layer, from the molecular point of view, an anion state in which electrons enter the lowest unoccupied orbit (LUMO) is obtained. That is, the smaller the difference (energy barrier) between the work function of the cathode and the LUMO of the electron transport layer, the easier it is for electrons to be injected. In general, the LUMO of organic compounds is high (the number is small), so it is necessary to use a metal with a low work function accordingly. In the Mg: Ag alloy, the work function is determined by the majority Mg and is 3.7 eV. LiF contains Li (2.9 eV), which has a very low work function, which is considered to have enabled the use of Al (4.3 eV), which has a high work function. Since then, the method of using LiF / Al as a cathode has been described in 1987 by C.I. W. Together with the method using the Mg: Ag alloy reported by Tang et al., It became two major standards for organic EL cathodes.

  The method using Mg: Ag alloy for the cathode uses Mg with a low work function, and is easily oxidized by oxygen and moisture. Therefore, there is a drawback that the driving stability is poor unless very tight sealing is performed. is there. On the other hand, in the method using LiF / Al for the cathode, LiF, which is an electron injection layer, is originally an insulator, so it is necessary to form a film as thin as about 0.5 nm. Since it is known that the performance varies depending on the film thickness of LiF, a very precise film forming technique is required, which causes manufacturing difficulties.

In order to overcome such problems, it is required to use a compound having a low LUMO as an electron transport material, or to use a cathode material that has good electron injection properties and is not easily oxidized to oxygen or water.
As an electron transport material having a low LUMO, a silole (silacyclopentadiene) derivative has attracted attention (Patent Document 1). Silole derivatives form a low LUMO due to the interaction between the σ ^* orbit of Si and the π ^* orbit of butadiene. However, an example in which the cathode structure is changed using a silole derivative is not yet known.

  As an examination of the cathode metal, an example using an alloy is known (Patent Document 2). Here, there is provided an organic EL element using two kinds of metals having a work function resistant to oxidation of greater than 4.0 eV. However, devices that have actually been demonstrated to operate with an alloy cathode use LiF as an electron injection layer, and do not specifically present a method for improving the difficulty in manufacturing a conventional LiF / Al cathode. It was.

Applied Physics Letters, 51 (1987) 913. Japan Journal of Applied Physics, 27 (1988) L269. Journal of Applied Physics, 85 (1989) 3610. Applied Physics Letters, 69 (1996) 2160. Applied Physics Letters, 70 (1997) 152. JP-A-9-87616 US Pat. No. 6,765,349

  An object of the present invention is to provide an organic EL device that can use a cathode resistant to oxidation. Furthermore, it is providing the organic EL element which does not need to use electron injection materials, such as LiF.

  As a result of various studies, the present inventors have used a boron compound in which a boron atom is coordinated to an atom that donates an unshared electron pair in a molecule to form a cyclic structure including the boron atom in an electron transport layer, and is used as a cathode. The present invention has been completed by finding that the above-mentioned problems can be solved in an organic EL device using a metal having a large work function such as aluminum or gold.

  The present invention provides an organic EL element in which a plurality of organic compound layers including at least a light-emitting layer and an electron transport layer are sandwiched between a pair of electrodes each including an anode and a cathode, and the electron transport layer is: General formula (1):

[Wherein, R ¹ , R ² and R ³ are the same or different and are an aryl group or a heterocyclic group which may have a substituent, or any of R ¹ , R ² and R ^3] Two are bonded to each other to form a ring; R ⁴ is a hydrogen atom or a substituent; m is an integer of 0 to 2; when m is 2, a plurality of R ⁴ are the same Or different; Q is a linking group, X is a nitrogen atom, oxygen atom, sulfur atom, phosphorus atom or selenium atom; the dotted semicircular arc may be part of a ring in which Q and X are in common The dotted line and the solid line between Q and X represent a single bond or a double bond; the arrow from X to B represents a coordination bond: R ^a is hydrogen or a monovalent to tetravalent organic skeleton by and; n is an integer of from 1 to 4; when n is an integer of 2 to 4, there exist a plurality R ^{, R 2, R 3, R} 4, m, Q, X, dashed semicircular arc, and the dotted line and the solid line between Q and X are each at least 1 a boron compound represented same or different] Provided is an organic EL device which contains various types and the work function of the cathode is 4.0 eV or more.

  Furthermore, in the compound represented by the general formula (1), an organic EL device in which Q and X are preferably part of a common ring.

More preferably, in the organic EL device, the common ring is a pyridine ring or a quinoline ring, and X is a nitrogen atom of the pyridine ring or the quinoline ring.
Furthermore, the compound represented by the general formula (1) is represented by the following general formula (2):

[Wherein R ¹ , R ² , R ³ , R ⁴ , m, Q, X, a dotted semi-arc, a dotted line and a solid line between Q and X, and an arrow from X to B represent the above formula ( The same meaning as 1); when m is 2, a plurality of R ⁴ are the same or different; R ^b is hydrogen or a monovalent organic skeleton] It is preferable that

  The organic EL element includes an electron transport layer containing at least one compound represented by the general formula (1) or the general formula (2), a cathode having a work function of 4.0 eV or more, and other layers. It is preferable that the organic EL elements are arranged directly adjacent to each other without being sandwiched.

  Further, the cathode having a work function of 4.0 eV or more is more preferably a metal.

  According to the present invention, an organic EL device using a cathode resistant to oxidation can be provided. Furthermore, an organic EL device that does not require the use of an electron injection material such as LiF can be provided.

  Hereinafter, the organic EL device of the present invention will be described in detail.

  The organic EL device of the present invention includes a pair of electrodes composed of an anode and a cathode, and an organic EL device in which a plurality of organic compound layers including at least a light emitting layer and an electron transport layer are sandwiched between the pair of electrodes. The transport layer has the following general formula (1):

[Wherein, R ¹ , R ² and R ³ are the same or different and are an aryl group or a heterocyclic group which may have a substituent, or any of R ¹ , R ² and R ^3] Two are bonded to each other to form a ring; R ⁴ is a hydrogen atom or a substituent; m is an integer of 0 to 2; when m is 2, a plurality of R ⁴ are the same Or different; Q is a linking group, X is a nitrogen atom, oxygen atom, sulfur atom, phosphorus atom or selenium atom; the dotted semicircular arc may be part of a ring in which Q and X are in common It indicates that good; dashed and solid lines between Q and X represents a single bond or a double bond; X from toward the arrow B represents a coordinate bond: R ^a represents hydrogen or 1 to 4 monovalent organic framework by and; n is an integer of from 1 to 4; when n is an integer of 2 to 4, there exist a plurality R ^{, R 2, R 3, R} 4, m, Q, X, dashed semicircular arc, and the dotted line and the solid line between Q and X are each at least 1 a boron compound represented same or different] The cathode has a work function of 4.0 eV or more.

  The organic EL device of the present invention has a light emitting layer and an electron transport layer as an organic compound layer, but a hole injection layer, a hole transport layer, and the like may be appropriately disposed as other organic compound layers. Each layer may be composed of a plurality of layers.

  The light emitting layer used in the organic EL device of the present invention may use fluorescence or phosphorescence, but the proportion of excitons that can be used for light emission is 25% for fluorescence and 100% for phosphorescence. From the viewpoint of luminous efficiency, those utilizing phosphorescence are preferred. In addition, these fluorescent or phosphorescent substances may be used alone to form a light emitting layer, or may be formed in a state dispersed in a host compound.

  Examples of the fluorescent material that can be used in the present invention include benzoxazole derivatives, benzimidazole derivatives, benzothiazole derivatives, styrylbenzene derivatives, polyphenyl derivatives, diphenylbutadiene derivatives, tetraphenylbutadiene derivatives, naphthalimide derivatives, coumarin derivatives, condensed fragrances. Group compounds, perinone derivatives, oxadiazole derivatives, oxazine derivatives, aldazine derivatives, pyralidine derivatives, bisstyrylanthracene derivatives, quinacridone derivatives, pyrrolopyridine derivatives, thiadiazolopyridine derivatives, cyclopentadiene derivatives, styrylamine derivatives, diketopyrrolopyrrole Various metal complexes represented by derivatives, aromatic dimethylidine compounds, metal complexes of 8-quinolinol derivatives and metal complexes of pyromethene derivatives, etc. Li thiophene, polyphenylene, polyphenylene vinylene polymer compounds include compounds such as organic silane derivatives.

  Examples of phosphorescent materials that can be used in the present invention include complexes containing transition metal atoms or lanthanoid atoms.

  Although it does not specifically limit as a transition metal atom, Preferably, ruthenium, rhodium, palladium, tungsten, rhenium, osmium, iridium, platinum etc. are mentioned. More preferred are rhenium, iridium, and platinum.

  Examples of lanthanoid atoms include lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. More preferred are neodymium, europium and gadolinium.

  Examples of complex ligands include halogen ligands (eg, chlorine ligands), nitrogen-containing heterocyclic ligands (eg, phenylpyridine, benzoquinoline, quinolinol, bipyridyl, phenanthroline, etc.), diketone ligands (For example, acetylacetone), carboxylic acid ligand (for example, acetic acid ligand, etc.), carbon monoxide ligand, isonitrile ligand, cyano ligand, and the like.

  The complex may have one transition metal atom or lanthanoid atom, or may be a binuclear complex having two or more. Further, this complex may have a plurality of the above-mentioned ligands, and the ligand in that case may be one kind or a combination of a plurality of ligands.

  Examples of host materials that can be used in the present invention include triazole derivatives, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, fluorenone derivatives, anthraquinodimethane derivatives, anthrone derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, carbodiimide derivatives, Olenylidenemethane derivatives, distyrylpyrazine derivatives, aromatic tetracarboxylic anhydrides such as naphthalene and perylene, phthalocyanine derivatives, carbazole derivatives, polyarylalkane derivatives, pyridine derivatives, pyrazine derivatives, triazine derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylene Diamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives Stilbene derivatives, silazane derivatives, aromatic tertiary amine compounds, styrylamine compounds, aromatic dimethylidine compounds, porphyrin compounds, organic silane derivatives, metal complexes of 8-quinolinol derivatives, metal phthalocyanines, benzoxazoles and benzothiazoles Examples include various metal complexes represented by metal complexes as ligands, organosilane derivatives, and the like.

The electron transport layer used in the organic EL device of the present invention contains at least one boron compound represented by the general formula (1). Hereinafter, the general formula (1) will be described.
Examples of the “aryl group” in the aryl group that may have a substituent represented by R ¹ , R ² , and R ³ include, for example, a phenyl group, a biphenyl group (for example, a 4-biphenyl group), and a naphthyl group. (For example, 2-naphthyl group, etc.), tetrahydronaphthyl group (for example, 5,6,7,8-tetrahydronaphthalen-2-yl group, etc.), indenyl group (for example, 1H-inden-5-yl group, etc.), Indanyl groups (for example, indan-5-yl group) and the like can be mentioned, but are not limited to these aryl groups. Of these aryl groups, a phenyl group, a biphenyl group (for example, a 4-biphenyl group), and a naphthyl group (for example, a 2-naphthyl group) are preferable.

Examples of the “heterocyclic group” in the heterocyclic group which may have a substituent represented by R ¹ , R ² or R ³ include a pyrrolyl group (for example, 2-pyrrolyl group), a pyridyl group, and the like. (For example, 2-pyridyl group), quinolyl group (for example, 2-quinolyl group), piperidinyl group (for example, 4-piperidinyl group) piperidino group, furyl group (for example, 2-furyl group), thienyl group (for example) For example, 2-thienyl group and the like are preferable.

  Examples of the “substituent” in the aryl group and heterocyclic group which may have these substituents include, for example, a halogen atom (eg, fluorine atom, chlorine atom, bromine atom, iodine atom), haloalkyl group (eg, Fluoromethyl group, difluoromethyl group, trifluoromethyl group, etc.), linear or branched alkyl group having 1 to 4 carbon atoms (for example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group) , Tert-butyl group, etc.), C5-C7 cyclic alkyl group (e.g., cyclopentyl group, cyclohexyl group, etc.), C1-C8 linear or branched alkoxy group (e.g., methoxy group, ethoxy group, etc.) Group, propoxy group, isopropoxy group, butoxy group, isobutoxy group, tert-butoxy group, pentyloxy group, Xyloxy group, heptyloxy group, octyloxy group, etc.), hydroxy group, nitro group, cyano group, amino group, mono- or dialkylamino group having 1 to 4 carbon atoms (for example, methylamino group, ethylamino group) Group, dimethylamino group, diethylamino group, etc.), acyl group (eg, acetyl group, propionyl group, butyryl group, etc.), alkenyl group having 2 to 6 carbon atoms (eg, vinyl group, 1-propenyl group, allyl group, etc.) , An alkynyl group having 2 to 6 carbon atoms (for example, ethynyl group, 1-propynyl group, propargyl group, etc.), phenyl group, substituted phenyl group (for example, 4-fluorophenyl group, 4-chlorophenyl group, 4-methylphenyl group) (P-tolyl group), 4-methoxyphenyl group, 4-nitrophenyl group, etc.), carbamoy Group, N, N-dialkylcarbamoyl group (for example, N, N-dimethylcarbamoyl group, N, N-diethylcarbamoyl group, N, N-dipropylcarbamoyl group, etc.), etc., but limited to these substituents Is not to be done.

Alternatively, any one of R ¹ , R ² and R ³ may be bonded to each other to form a ring. As such a ring, for example, as a result of bonding of R ¹ and R ² , a borol ring, a benzoborol ring, a dibenzoborol ring, a 1,4-dihydroborinine ring, a 1,4-dihydrobenzo [b] borinine Ring, 5,10-dihydrodibenzo [b, e] borinine ring, 4H-1,4-oxaborinine ring, 4H-benzo [b] [1,4] oxaborinine ring, 10H-dibenzo [b, e] [1, 4] oxaborinine ring, 1,4-dihydro-1,4-azaborinine ring, 1,4-dihydrobenzo [b] [1,4] azaborinine ring, 5,10-dihydrodibenzo [b, e] [1,4 When an azaborinine ring or the like is formed; When R ¹ and R ³ are bonded to each other to form a 5,6-hydrobenzo [b, d] borinine ring or the like; When these rings have a substituent; But The ring is not limited to these rings. In the above formula (1), examples of the substituent represented by R ⁴ include the substituents listed above as “substituents” in the aryl group and heterocyclic group which may have a substituent. Although it mentions, it is not limited to these substituents.

In the above formula (1), m is the number of substituents R ⁴ bonded to X, and whether the valence of X or the bond between X and X is a single bond or a double bond, It is an integer from 0 to 2, depending on whether Q and X are part of a common ring. When m is 2, a plurality of R ⁴ are the same or different.

In the above formula (1), examples of the linking group represented by Q include ═C <, ═CH—, —CH <, —CH ₂ —, —CH ₂ CH ₂ —, —C ₆ H ₄ — ( For example,-(1,2-C ₆ H ₄ )-, etc.), -C ₁₀ H _6- (eg,-(1,2-C ₁₀ H ₆ )-, etc.), -CO-, -CS-,- Although CN <, -CN = etc. are mentioned, It is not limited to these coupling groups. Among these linking groups, ═C <, —CH ₂ —, and —CH ₂ CH ₂ — are preferable.

  In the above formula (1), X is a nitrogen atom, oxygen atom, sulfur atom, phosphorus atom or selenium atom. Of these atoms, a nitrogen atom and an oxygen atom are preferable.

  In the above formula (1), examples of a ring in which Q and X represented by a dotted semicircular arc are common include, for example, a pyrrole ring, a pyridine ring, an indole ring, an isoindole ring, a quinoline ring, an isoquinoline ring, a furan ring, Pyran ring, benzofuran ring, isobenzofuran ring, chromene ring, isochromene ring, phosphine doll ring, isophosphine dol ring, phosphinoline ring, isophosphinoline ring, thiophene ring, thiopyran ring, thiochromene ring, isothiochromene ring, selenophene ring, selenopyran ring Examples thereof include, but are not limited to, a ring, a selenochromene ring, and an isoselenochromene ring. These rings may have a substituent. Of these rings, a pyridine ring and a quinoline ring are preferred.

In the above formula (1), examples of the monovalent organic skeleton represented by ^Ra include a methyl group, an ethyl group, a propyl group, an isopropyl group, a cyclohexyl group, a phenyl group, and a 4-methylphenyl group (p-tolyl). Group), a naphthyl group (for example, 2-naphthyl group, etc.), and the divalent organic skeleton represented by ^Ra includes, for example, a methylene group, an ethylene group, a trimethylene group, a propylene group, a phenylene group ( for example, 1,4-phenylene group), a naphthylene group (e.g., a 2,6-naphthylene group) is like, Examples of the trivalent organic skeleton represented by ^{R a,} for example, methanetriyl group, ethanetriyl group (E.g., ethane-1,1,2-triyl group) propanetriyl group (e.g., propane-1,2,3-triyl group), benzenetriyl (E.g., benzene-1,3,5-triyl group), naphthalenetriyl group (e.g., naphthalene-1,4,6-triyl group) and the like, tetravalent organic represented by ^{R a} Examples of the skeleton include a methanetetrayl group, an ethanetetrayl group (for example, ethane-1,1,2,2-tetrayl group), and a propanetetrayl group (for example, propane-1,1,2,3- Tetrayl group), benzenetetrayl group (for example, benzene-1,2,4,5-tetrayl group), naphthalenetetrayl group (for example, naphthalene-1,4,5,8-tetrayl group) and the like. The organic skeleton is not limited to these examples.

In the above formula (1), n is the number of boron-containing ring moieties (portions surrounded by square brackets) bonded to hydrogen represented by R ^a or a monovalent to tetravalent organic skeleton, and R ^a represents hydrogen , N is 1, and when R ^a is a 1 to 4 valent organic skeleton, n is a 1 to 4 valent integer. Incidentally, when n is an integer of 2 to ^{4, R 1, R 2, R} 3 where there exist a plurality, R 4, m, Q, X, dashed semicircular arc, and the dotted line between Q and X The solid lines are the same or different.

  The electron transport layer used in the organic EL device of the present invention can be used by combining the boron compound represented by the general formula (1) and another electron transport material. Examples of other electron transport materials include, for example, triazole derivatives, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, fluorenone derivatives, anthraquinodimethane derivatives, anthrone derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, carbodiimide derivatives. , Fluorenylidenemethane derivatives, distyrylpyrazine derivatives, aromatic tetracarboxylic anhydrides such as naphthalene and perylene, phthalocyanine derivatives, metal complexes of 8-quinolinol derivatives, metal phthalocyanines, benzoxazoles and benzothiazoles as ligands Examples include various metal complexes typified by metal complexes and organosilane derivatives.

  When the electron transport layer is used in combination with the boron compound represented by the general formula (1) and another electron transport material, the electron transport layer is efficiently injected from the cathode having a large work function. It is preferable that the boron compound and the cathode represented by are arranged directly adjacent to each other without any other electron transporting material.

  Examples of organic compounds that can be used as the hole injection layer and hole transport layer used in the organic EL device of the present invention include carbazole derivatives, triazole derivatives, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, and pyrazolines. Derivatives, pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aromatic tertiary amine compounds, styrylamine compounds, aromatic dimethylolines Examples thereof include compounds, porphyrin compounds, and organic silane derivatives.

The cathode used in the present invention will be described. The cathode used in the present invention is made of a metal, alloy, conductive metal oxide, or a mixture thereof having a work function of 4.0 eV or more. The work function can be obtained by measurement such as ultraviolet photoelectron spectroscopy (UPS).
Detailed data on the work function of metals is described in Journal of Applied Physics, Vol. 48, No. 11, pages 4729-4733 (1977). Examples of the metal having a work function of 4.0 eV or more include aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, ruthenium, rhodium, palladium, silver, cadmium, indium, Examples thereof include tin, iridium, platinum, and gold. These metals may be used alone or as an alloy.

  Examples of the conductive metal oxide include tin oxide (ATO, FTO) doped with antimony or fluorine, tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO), and the like. It is done.

  Among the above, a metal is preferable as the cathode. More preferable are aluminum, chromium, manganese, iron, cobalt, nickel, copper, silver, platinum, gold and the like.

  As the anode used in the present invention, a metal, an alloy, a metal oxide, a conductive compound, or a mixture thereof can be used as appropriate. For example, conductive metal oxide such as tin oxide (ATO, FTO) doped with antimony or fluorine, tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO), gold, silver , Metals such as chromium and nickel, mixtures or laminates of these metals and conductive metal oxides, inorganic conductive materials such as copper iodide and copper sulfide, organic conductive materials such as polyaniline, polythiophene and polypyrrole, And a laminate of these and ITO. The anode is often used as an electrode on the light extraction side. In this case, a highly transparent conductive metal oxide is particularly preferable.

  These film forming methods are not particularly limited, and known methods can be used as appropriate. Examples of known methods include vacuum deposition, sputtering, ion plating, CVD, plasma CVD, printing, and coating. In particular, the vacuum vapor deposition method and the printing method are preferable for the formation of the organic compound layer.

  The film thickness of the organic compound layer in the organic EL device of the present invention is not particularly limited, but is preferably thin in order to lower the driving voltage. Specifically, the total film thickness is 300 nm or less, more preferably 200 nm or less. . When there are a plurality of organic compound layers, the ratio of each film thickness is not limited, but it is desirable to adjust so that holes and electrons injected from the anode and the cathode recombine in the light emitting layer.

  The organic EL element of the present invention may be sealed if necessary. As the sealing step, a known method can be used as appropriate. For example, a method of adhering a sealing container in an inert gas, a method of forming a sealing film directly on the organic EL element, or the like can be given. In addition to these, a method of enclosing a moisture absorbing material may be used in combination.

  The organic EL element of the present invention can emit light by applying a voltage (usually 15 volts or less) between the anode and the cathode. Normally, a DC voltage is applied, but an AC component may be included.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, the scope of the present invention is not limited only to these Examples. The measurement apparatus and measurement conditions used in the following examples are as follows.
^<1 H-NMR>
Measurement was performed with “Gemini 2000” manufactured by Varian, using deuterated chloroform (CDCl ₃ ). The chemical shift was recorded from tetramethylsilane (SiMe ₄ ) as a part per million (ppm; δ scale) on the low magnetic field side, and the hydrogen nucleus of tetramethylsilane contained in the NMR solvent (CDCl ₃ ) (δ: 0 ppm).
<Voltage application device>
A voltage was applied to the device using a “2400 type source meter” manufactured by Keithley.
<Synthesis example>
Synthesis of (E) -2- (2-phenyl-2-diphenylborylethenyl) -4-phenylquinoline by a reaction represented by the following formula

[Wherein Ph represents a phenyl group; dba represents a dibenzylideneacetone ligand; DPEPhos represents bis [2- (diphenylphosphino) phenyl] ether; the arrow from N to B represents a coordination bond. To express]
2-Chloro-4-phenylquinoline was synthesized according to the method described in Chemical & Pharmaceutical Bulletin, Vol. 28, No. 9, pp. 2618-2622 (1980).
Under a nitrogen atmosphere, tetramethylammonium triphenylethynylborate (3.18 g, 9.31 mmol), 2-chloro-4-phenylquinoline (2.10 g, 8.86 mmol), tris (dibenzylideneacetone) ) Divaladium-chloroform complex (Pd ₂ dba ₃ .CHCl ₃ ) (0.18 g, 0.18 mmol) and bis [2- (diphenylphosphino) phenyl] ether (DPEPhos) (0.23 g, 0.43 mmol) was stirred in toluene (44 mL) at 60 ° C. The reaction solution was cooled to room temperature, passed through silica gel short column chromatography (chloroform), and concentrated on a rotary evaporator. The obtained residue was washed with methanol to obtain (E) -2- (2-phenyl-2-diphenylborylethenyl) -4-phenylquinoline in a yield of 27%.

The physical property values were as follows.
_{1H-NMR (CDCl 3):} δ7.10-7.19 (m, 7H), 7.20-7.23 (m, 3H), 7.32-7.44 (m, 8H), 7.58 −7.61 (m, 5H), 7.64 (s, 1H), 7.88 (dd, J = 8.2, 1.6, 1.2 Hz, 1H), 7.96 (d, J = 8.0 Hz, 1 H).
<Element creation example 1>
A substrate (made by Asahi Glass Co., Ltd .; sheet resistance: 10Ω) on which ITO was deposited on an alkali-free glass at a heat of 150 nm was cut into 29 mm × 25 mm. This substrate was ultrasonically cleaned in a neutral detergent for 5 minutes and then washed with ultrapure water. Furthermore, this substrate was subjected to ultrasonic cleaning for 5 minutes in this order in ultrapure water, acetone and isopropanol. Furthermore, this substrate was boiled and washed with ethanol and dried. This substrate was subjected to UV-ozone treatment and used as a transparent conductive support substrate.

The transparent conductive support substrate was fixed to a substrate holder of a vacuum deposition apparatus (manufactured by ULVAC, Inc.) connected to a glove box in an argon atmosphere. As a hole transporting layer, bis [N- (1-naphthyl) -N-phenyl] benzidine (α-NPD) is put in another crucible, and the pressure is reduced to about 1 × 10 ⁻⁴ Pa so that the film thickness becomes 50 nm. Vapor deposited. Then rubrene was placed in another crucible as a light emitting layer, the pressure was reduced to approximately 1 × 10 -4 ^Pa, it was deposited to a film thickness of 35 nm. Next, (E) -2- (2-phenyl-2-diphenylborylethenyl) -4-phenylquinoline synthesized in << Synthesis Example >> as an electron transporting layer was put in another crucible, and about 1 × 10 ^−4. The pressure was reduced to Pa, and vapor deposition was performed to a film thickness of 15 nm. Next, aluminum (work function 4.3 eV) is put into a tungsten boat as a cathode, the pressure is reduced to about 1 × 10 ⁻³ Pa, vapor deposition is performed to a film thickness of 80 nm, and the organic EL element (1) is formed. Created. At this time, a stainless steel vapor deposition mask was used for the substrate so that the cathode had a circular shape with a diameter of 1 mm. That is, the light emitting area of this organic EL element was 0.79 cm ² . This element was not sealed.
<Element creation example 2>
An organic EL device (2) was prepared in the same manner as in <Device creation example 1> except that gold (work function 5.1 eV) was used instead of aluminum as the cathode.
<< Comparative Element Creation Example 1 >>
Except for using (E) -2- (2-phenyl-2-diphenylborylethenyl) -4-phenylquinoline as the electron transport layer, tris (8-quinlinol) aluminum complex (Alq ₃ ) was used instead of << elements An organic EL device (3) was prepared in the same manner as in Preparation Example 1>.
<< Comparative Element Creation Example 2 >>
Except for using (E) -2- (2-phenyl-2-diphenylborylethenyl) -4-phenylquinoline as the electron transport layer, tris (8-quinlinol) aluminum complex (Alq ₃ ) was used instead of << elements An organic EL device (4) was prepared in the same manner as in Preparation Example 2 >>.
<< Element creation example 3 >>
An organic EL device (5) was prepared in the same manner as in <Device creation example 1> except that magnesium (Mg): silver (Ag) alloy (composition ratio 10: 1) (work function 3.7 eV) was used instead of aluminum as the cathode. )created.
<< Evaluation Example 1 >>
In an argon glove box, a direct current voltage of 0 V to 15 V is applied to the organic EL elements (1) to (5) prepared in << Element Preparation Examples 1 and 2 >> and << Comparative Element Preparation Examples 1 to 3 >>. The presence or absence of light emission and the light emission start voltage were examined. The results of the light emission starting voltage are shown in Table 1. The numbers in parentheses represent the corresponding element numbers.

  When the organic EL element (1) of the present invention and the comparative element (3) were compared, it was confirmed that the organic EL element of the present invention emitted light at a lower voltage. On the other hand, it was found that the light emission start voltage of the organic EL device (1) of the present invention was the same as that of the comparative device (5) and had the same initial performance.

  Further, when the organic EL element (2) of the present invention and the comparative element (4) were compared, the organic EL element of the present invention emitted light, whereas the comparative element (4) did not emit light up to 15V.

From these results, it was revealed that when using a cathode having a large work function, the organic EL device of the present invention has higher performance than the organic EL device using the conventional electron transport layer. .
<< Evaluation Example 2 >>
The organic EL element (1) prepared in << Element Preparation Example 1 >> and the comparative element (5) prepared in << Comparative Element Preparation Example 3 >> were taken out of the argon glove box and exposed to the atmosphere for 8 days. Then, it moved again into the argon glove box, and the presence or absence of light emission and the light emission start voltage when a DC voltage of 0V to 15V was applied were examined. The results of the light emission starting voltage are shown in Table 2. The numbers in parentheses represent the corresponding element numbers.

  When the organic EL element (1) of the present invention and the comparative element (5) were compared, the organic EL element of the present invention was suppressed from being deteriorated by exposure to the atmosphere. In <Evaluation Example 1>, both elements had equivalent initial performance, but it was revealed that the element of the present invention was superior in terms of durability against oxygen and moisture.

Claims (6)

In an organic electroluminescent device in which a pair of electrodes including an anode and a cathode and a plurality of organic compound layers including at least a light emitting layer and an electron transport layer are sandwiched between the pair of electrodes, the electron transport layer has the following general formula ( 1):

[Wherein, R ¹ , R ² and R ³ are the same or different, and may be an aryl group or a heterocyclic group which may have a substituent, or any of R ¹ , R ² and R ³ Two are bonded to each other to form a ring; R ⁴ is a hydrogen atom or a substituent; m is an integer of 0 to 2; when m is 2, a plurality of R ⁴ are the same Or different; Q is a linking group, X is a nitrogen atom, oxygen atom, sulfur atom, phosphorus atom or selenium atom; the dotted semicircular arc may be part of a ring in which Q and X are in common The dotted line and the solid line between Q and X represent a single bond or a double bond; the arrow from X to B represents a coordination bond: R ^a is hydrogen or a monovalent to tetravalent organic skeleton by and; n is an integer of from 1 to 4; when n is an integer of 2 to 4, there exist a plurality R ^{, R 2, R 3, R} 4, m, Q, X, dashed semicircular arc, and the dotted line and the solid line between Q and X are each at least 1 a boron compound represented same or different] An organic electroluminescent device comprising a kind, wherein the work function of the cathode is 4.0 eV or more. The organic electroluminescent element according to claim 1, wherein in the compound represented by the general formula (1), Q and X are part of a common ring. The organic electroluminescence device according to claim 1, wherein the common ring is a pyridine ring or a quinoline ring, X is a nitrogen atom of the pyridine ring or the quinoline ring, and m is 0. . The compound represented by the general formula (1) is represented by the following general formula (2):

[Wherein R ¹ , R ² , R ³ , R ⁴ , m, Q, X, a dotted semi-arc, a dotted line and a solid line between Q and X, and an arrow from X to B represent the above formula ( 2) a compound having the same meaning as 1); when m is 2, a plurality of R ⁴ are the same or different; and R ^b is hydrogen or a monovalent organic skeleton. The organic electroluminescent element of any one of -3. An electron transport layer containing at least one compound represented by the general formula (1) or (2) and a cathode having a work function of 4.0 eV or more are arranged directly adjacent to each other without sandwiching other layers. The organic electroluminescent element according to any one of claims 1 to 4. The organic electroluminescent element according to any one of claims 1 to 5, wherein the cathode having a work function of 4.0 eV or more is a metal.