JPWO1998008360A1 - organic EL element - Google Patents

Abstract

(57) [Abstract] A specific coumarin derivative is incorporated into the light-emitting layer of an organic EL device, and a specific tetraaryldiamine derivative is incorporated into the hole-injecting and/or transporting layer. Furthermore, a specific coumarin derivative, a specific quinacridone compound, or a specific styryl compound is incorporated into the mixed-layer-type light-emitting layer. Two or more light-emitting layers, including a mixed-layer-type light-emitting layer, are provided, and two or more dopants are incorporated to emit two or more light-emitting species. This results in a highly reliable organic EL device that emits light with high brightness and continuous emission. Multicolor emission is also possible.

Description

[Detailed Description of the Invention] Organic EL Device Technical Field The present invention relates to an organic EL (electroluminescent) device, and more specifically to a device that emits light when an electric field is applied to a thin film made of an organic compound.

BACKGROUND ART Organic electroluminescent (EL) devices are devices that have a structure in which a thin film containing a fluorescent organic compound is sandwiched between a cathode and an anode. Electrons and holes are injected into the thin film and recombined to generate excitons. Light is emitted (fluorescence or phosphorescence) when these excitons deactivate.

The organic EL element is characterized by its ability to emit high-brightness surface light of approximately 100 to 100,000 cd/m ² at a low voltage of approximately 10 V, and by selecting the type of fluorescent material, it is possible to emit light ranging from blue to red.

On the other hand, organic EL devices suffer from short emission lifetimes, poor storage durability, and low reliability. This is due to physical changes in the organic compounds. (The growth of crystalline domains and other factors can cause uneven interfaces, leading to poor charge injection, short circuits, and dielectric breakdown. The use of low-molecular-weight compounds with molecular weights of 500 or less can lead to the appearance and growth of crystal grains, significantly reducing film properties. Furthermore, even if the interface is rough, such as with ITO, significant crystal grain appearance and growth can occur, resulting in reduced luminous efficiency, current leakage, and loss of light emission. This can also lead to dark spots, which are areas that do not emit light.) Cathode oxidation and peeling (Metals with low work functions, such as Na, Mg, Li, Ca, K, and Al, have been used to facilitate electron injection. However, these metals react with moisture and oxygen in the air, causing peeling between the organic layer and the cathode, preventing charge injection. In particular, when polymer compounds are used and films are formed using spin coating, residual solvents and decomposition products from film formation accelerate the oxidation reaction of the electrode, causing electrode peeling and resulting in non-luminescent areas.) Low luminous efficiency and high heat generation (Since current is passed through the organic compound, the organic compound must be placed under a high electric field, which inevitably generates heat. This heat causes the organic compound to melt, crystallize, or thermally decompose, resulting in device degradation and destruction.) Photochemical and electrochemical changes in the organic compound layer

Coumarin compounds have been proposed as fluorescent materials for organic EL devices (e.g., JP-A-63-264692, JP-A-2-191694, JP-A-3-792, JP-A-5-202356, JP-A-6-9952, JP-A-6-240243, etc.). Coumarin compounds are used alone in the emissive layer, or as guest compounds or dopants in conjunction with host compounds such as tris(8-quinolinolato)aluminum. In such organic EL devices, the hole injection layer, hole transport layer, or hole injection/transport layer combined with the light-emitting layer uses a tetraphenyldiamine derivative having a 1,1'-biphenyl-4,4'-diamine skeleton and phenyl or substituted phenyl groups on the two nitrogen atoms of the diamine, such as N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine. However, such organic EL devices have insufficient reliability in terms of emission lifetime and heat resistance, and when used as a host compound, high brightness devices have not been obtained.

Meanwhile, a stacked white-light-emitting organic EL element has been proposed to address the multicolor emission of organic EL elements [Yoshiharu Sato, IEICE Technical Report, OME94-78 (1995-03)]. In this case, the emitting layers are a blue emitting layer using a zinc oxazole complex, a green emitting layer using tris(8-quinolinolato)aluminum, and a red emitting layer in which tris(8-quinolinolato)aluminum is doped with a red fluorescent dye (P-660, DCM1).

In this way, the red-emitting layer is doped with an emitting species to enable red emission. The other layers are undoped. The green and blue-emitting layers are selected to emit light only from the host material, which significantly limits the flexibility in material selection and tuning of the emission color.

Typically, the emission color of an organic EL device is changed by adding trace amounts of emissive species, i.e., doping. One advantage is that the emissive species can be easily changed by changing the type of doping. Therefore, while multicolor emission is theoretically possible by doping several emissive species, if all of these emissive species are uniformly doped into a single host, there are cases where only one of the doped emissive species emits light, or where some species do not emit light. In other words, even if all of the emissive species are mixed and doped into a single host, it is difficult to get all of them to emit light. This is because energy is transferred only to certain emissive species.

For these reasons, there have been no examples to date of stable emission by doping two or more luminescent species.

Generally, the half-life of an organic EL device is in a trade-off relationship with its luminance. It has been reported that doping tris(8-quinolinolato)aluminum or N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine with rubrene extends the device's life, achieving an initial luminance of ^{approximately} 500 cd/m² and a half-life of approximately 3,500 hours [Tsutsui, Tetsuo, Applied Physics, Vol. 66, No. 2 (1997)]. However, the emission color of this device is limited to yellow (around 560 nm). Further improvements in life are desirable.

Disclosure of the Invention The objective of this invention is to realize an organic EL device with high reliability and luminous efficiency, capable of emitting a variety of luminescent colors, using photo- and electronically functional materials that exhibit minimal physical, photochemical, or electrochemical changes. In particular, the invention utilizes organic thin films formed by vapor deposition of high-molecular-weight compounds to achieve highly reliable, high-brightness light-emitting devices that minimize drive voltage increases, brightness losses, current leakage, and the appearance and growth of non-emissive regions. Furthermore, the invention aims to provide an organic EL device capable of emitting multicolor light and with a tunable emission spectrum, as well as high brightness and long life.

These objects can be achieved by the present inventions (1) to (18) below.

(1) An organic electroluminescent device having an emissive layer containing a coumarin derivative represented by the following formula (I) and a hole-injecting and/or hole-transporting layer containing a tetraaryldiamine derivative represented by the following formula (II):

[In formula (I), R₁, R₂and R₃R each represent a hydrogen atom, a cyano group, a carboxyl group, an alkyl group, an aryl group, an acyl group, an ester group, or a heterocyclic group, and may be the same or different.₁~R₃may be bonded to each other to form a ring.₄and R₇each represents a hydrogen atom, an alkyl group, or an aryl group, R₅and R₆each represents an alkyl group or an aryl group, R₄and R₅, R₅and R₆and R₆and R₇may be bonded to each other to form a ring.] [In formula (II), Ar₁, Ar₂, Ar₃and Ar₄each represents an aryl group, Ar₁ ~Ar₄At least one of R is a polycyclic aryl group derived from a fused ring or ring assembly having two or more benzene rings.₁₁and R₁₂R each represents an alkyl group, and p and q each represent 0 or an integer from 1 to 4.₁₃and R₁₄each represents an aryl group, and r and s each represent 0 or an integer of 1 to 5.] (2) The organic EL device of (1), wherein the emissive layer containing the coumarin derivative is formed by doping the coumarin derivative as a dopant into a host material.

(3) The organic EL device according to (2), wherein the host material is a quinolinonato metal complex.

(4) An organic EL device having an emissive layer in which a mixed layer containing a hole injecting/transporting compound and an electron injecting/transporting compound is further doped with a coumarin derivative represented by formula (I), a quinacridone compound represented by formula (III), or a styrylamine compound represented by formula (IV) as a dopant.

[In formula (I), _R1 , _R2 , and _R3 each represent a hydrogen atom, a cyano group, a carboxyl group, an alkyl group, an aryl group, an acyl group, an ester group, or a heterocyclic group, which may be the same or different, and _R1 to _R3 may each be bonded to each other to form a ring. _R4 and _R7 each represent a hydrogen atom, an alkyl group, or an aryl group. _R5 and _R6 each represent an alkyl group or an aryl group, and _R4 and _R5 , _R5 and _R6 , and _R6 and _R7 may each be bonded to each other to form a ring.] [In formula (III), _R21 and _R22 each represent a hydrogen atom, an alkyl group, or an aryl group, and may be the same or different. _R23 and _R24 each represent an alkyl group or an aryl group, and t and u each represent 0 or an integer of 1 to 4. When t or u is 2 or greater, adjacent _R23s or adjacent _R24s may be bonded to each other to form a ring.] [In formula (IV), _R31 represents a hydrogen atom or an aryl group. _R32 and _R33 represent a hydrogen atom, an aryl group, or an alkenyl group, which may be the same or different. _R34 represents an arylamino group or an arylaminoaryl group, and v is 0 or an integer of 1 to 5.] (5) The organic EL device of (4), wherein the hole injection transport compound is an aromatic tertiary amine, and the electron injection transport compound is a quinolinonato metal complex.

(6) The organic electroluminescent device according to (5), wherein the aromatic tertiary amine is a tetraaryldiamine derivative represented by the following formula (II):

[In formula (II), Ar₁, Ar₂, Ar₃and Ar₄each represents an aryl group, Ar₁ ~Ar₄At least one of R is a polycyclic aryl group derived from a fused ring or ring assembly having two or more benzene rings.₁₁and R₁₂R each represents an alkyl group, and p and q each represent 0 or an integer from 1 to 4.₁₃and R₁₄each represents an aryl group, and r and s each represent 0 or an integer of 1 to 5.] (7) The organic EL device of any one of (1) to (6), wherein the light-emitting layer is sandwiched between at least one hole-injecting and/or hole-transporting layer and at least one electron-injecting and/or electron-transporting layer.

(8) The organic EL device according to (1), (2), (3), or (7), wherein the hole injection and/or transport layer is further doped with rubrene as a dopant.

(9) The organic EL element according to any one of (1) to (8), wherein a color filter and/or a fluorescent conversion filter is disposed on the light extraction side, and the light is extracted through the color filter and/or the fluorescent conversion filter.

(10) An organic EL device having two or more light-emitting layers including a bipolar light-emitting layer, a hole-injecting and/or transporting layer on the anode side of the light-emitting layer, and an electron-injecting and/or transporting layer on the cathode side, wherein the two or more light-emitting layers are a combination of bipolar light-emitting layers, or a combination of a bipolar light-emitting layer and a hole-transporting light-emitting layer on the anode side of the bipolar light-emitting layer and/or an electron-transporting light-emitting layer on the cathode side.

(11) The organic EL element of (10), wherein the bipolar light-emitting layer is a mixed layer containing a hole injection transport compound and an electron injection transport compound.

(12) The organic EL element of (11), wherein the two or more light-emitting layers are all mixed layers.

(13) The organic EL element according to any one of (10) to (12), wherein at least one of the two or more light-emitting layers is doped with a dopant.

(14) The organic EL device according to any one of (10) to (13), wherein all of the two or more light-emitting layers are doped with a dopant.

(15) The organic EL element of any one of (10) to (14), wherein the two or more light-emitting layers have different light-emitting characteristics, and the light-emitting layer with the longer maximum emission wavelength is located closer to the anode.

(16) The organic EL element according to any one of (13) to (15), wherein the dopant is a compound having a naphthacene skeleton.

(17) The organic EL element of any one of (13) to (16), wherein the dopant is a coumarin derivative represented by the following formula (I):

[In formula (I), _R1 , _R2 , and _R3 each represent a hydrogen atom, a cyano group, a carboxyl group, an alkyl group, an aryl group, an acyl group, an ester group, or a heterocyclic group, which may be the same or different, and _R1 to _R3 may each be bonded to each other to form a ring. _R4 and _R7 each represent a hydrogen atom, an alkyl group, or an aryl group. _R5 and _R6 each represent an alkyl group or an aryl group, and _R4 and _R5 , _R5 and _R6 , and _R6 and _R7 may each be bonded to each other to form a ring.] (18) The organic EL device of any of (11) to (17), wherein the hole injection transport compound is an aromatic tertiary amine, and the electron injection transport compound is a quinolinonato metal complex.

The organic EL device of the present invention uses a coumarin derivative represented by formula (I) in the light-emitting layer and a tetraaryldiamine derivative represented by formula (II) in the hole-injecting and/or transporting layer, and the light-emitting layer is formed by doping a coumarin derivative represented by formula (I), a quinacridone compound represented by formula (II), and a styrylamine compound represented by formula (III) into a mixed layer of a hole-injecting and transporting compound. Therefore, a high luminance of about 100,000 cd/ ^m2 or more can be stably obtained. Furthermore, by selecting a host material that is highly durable relative to the coumarin derivative represented by formula (I), long-term stable operation is possible even at a device current density of about 30 mA/ ^cm2 .

The vapor-deposited films of the above compounds are in a stable amorphous state, resulting in excellent thin-film properties and uniform, even light emission. They are also stable in air for over a year and do not crystallize.

Furthermore, the organic EL device of the present invention emits light efficiently at low driving voltages and low driving currents. The maximum emission wavelength of the organic EL device of the present invention is approximately 480 to 640 nm. For example, Japanese Patent Application Laid-Open No. 6-240243 discloses an organic EL device having an emissive layer in which tris(8-quinolinolato)aluminum is used as the host material and a compound encompassed by the coumarin derivatives represented by formula (I) of the present invention is used as the guest material. However, the hole transport layer uses N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine, which is different from the compound represented by formula (II) of the present invention. Furthermore, there are no known examples of doping a mixed-layer type emissive layer with a coumarin derivative of formula (I), a quinacridone compound of formula (II), or a styrylamine compound of formula (III).

Furthermore, in the present invention, in order to change the carrier transport ability of each light-emitting layer and enable two or more types of light emission, two or more light-emitting layers are used, at least one of which is a bipolar type, preferably a mixed layer type, and a combination of two bipolar type light-emitting layers, preferably two mixed layers, or a combination of a bipolar type light-emitting layer, preferably a mixed layer, with a hole-transporting light-emitting layer provided on the anode side of the bipolar type light-emitting layer, preferably the mixed layer, and/or an electron-transporting light-emitting layer provided on the cathode side, is used, and more preferably, each light-emitting layer is doped with a dopant.

Among these, the particularly preferred embodiment of providing a mixed layer and doping the mixed layer expands the recombination region throughout the mixed layer and near the interface between the mixed layer and the hole-transporting emissive layer or near the interface between the mixed layer and the electron-transporting emissive layer, generating excitons, which transfer energy from the respective hosts in each emissive layer to the nearest emissive species, enabling emission of two or more emissive species (dopants). Furthermore, when using a mixed layer, the electron resistance and hole resistance of the mixed layer itself can be dramatically improved by selecting a compound stable against hole and electron injection. In contrast, combining a hole-transporting emissive layer and an electron-transporting emissive layer without a bipolar emissive layer also enables emission of two or more emissive species, but the control of the emissive layers is difficult, the intensity ratio between the two species changes rapidly, and the resistance to both holes and electrons is low, resulting in a short lifespan and being unsuitable for practical use. Furthermore, by adjusting the combination of host materials in the emissive layer, the combination and quantitative ratio of host materials in the mixed layer, which is a bipolar emissive layer, or the film thickness ratio, it is possible to adjust the electron and hole carrier supply capacity. This allows for the tuning of the emission spectrum. This, in turn, enables the creation of multicolor emitting organic EL devices. Furthermore, by providing an emissive layer (especially a mixed layer) doped with a compound having a naphthacene skeleton, such as rubrene, the doped layer, such as rubrene, functions as a carrier trap layer, reducing carrier injection into adjacent layers (e.g., electron transport layer and hole transport layer), thereby suppressing deterioration of these layers, resulting in high brightness (approximately 1000 cd/ ^m² ) and a long life (luminance half-life of approximately 50,000 hours). Furthermore, by providing an emissive layer with a long-wavelength emission maximum wavelength in the emission spectrum on the anode side, optical interference effects can be utilized, improving the light extraction efficiency of each emitted light, and enabling higher brightness.

Incidentally, IEICE Technical Report, OME94-78 (1995-03) proposes a white-light-emitting organic EL device, but unlike the present invention, there is no mention whatsoever of doping a bipolar-type emissive layer, particularly two or more emissive layers including a mixed layer.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an example of an organic EL element of the present invention. FIG. 2 is a graph showing the emission spectrum of the organic EL element. FIG. 3 is a graph showing the emission spectrum of the organic EL element. FIG. 4 is a graph showing the emission spectrum of the organic EL element. FIG. 5 is a graph showing the emission spectrum of the organic EL element. FIG. 6 is a graph showing the emission spectrum of the organic EL element. FIG. 7 is a graph showing the emission spectrum of the organic EL element. FIG. 8 is a graph showing the emission spectrum of the organic EL element. FIG. 9 is a graph showing the emission spectrum of the organic EL element. FIG. 10 is a graph showing the emission spectrum of the organic EL element. FIG. 11 is a graph showing the emission spectrum of the organic EL element. FIG. 12 is a graph showing the emission spectrum of the organic EL element. FIG. 13 is a graph showing the emission spectrum of the organic EL element. FIG. 14 is a graph showing the emission spectrum of the organic EL element.

Best Mode for Carrying Out the Invention The following describes in detail the preferred embodiment of the present invention.

The organic EL device of the present invention has an emissive layer containing a coumarin derivative represented by formula (I) and a hole-injecting and/or hole-transporting layer containing a tetraaryldiamine derivative represented by formula (II).

Regarding formula (I), in formula (I), R ₁ to R ₃ each represent a hydrogen atom, a cyano group, a carboxyl group, an alkyl group, an aryl group, an acyl group, an ester group or a heterocyclic group, and these may be the same or different.

The alkyl group represented by _R1 to _R3 preferably has 1 to 5 carbon atoms, may be linear or branched, and may have a substituent (such as a halogen atom). Specific examples of the alkyl group include a methyl group, an ethyl group, a (n-, i-)propyl group, a (n-, i-, s-, t-)butyl group, a n-pentyl group, an isopentyl group, a t-pentyl group, and a trifluoromethyl group.

The aryl group represented by _R1 to _R3 is preferably a monocyclic group, preferably has 6 to 24 carbon atoms, and may have a substituent (such as a halogen atom or an alkyl group). Specific examples include a phenyl group.

The acyl groups represented by R ₁ to R ₃ preferably have 2 to 10 carbon atoms, and specific examples thereof include an acetyl group, a propionyl group, and a butyryl group.

The ester groups represented by R ₁ to R ₃ preferably have 2 to 10 carbon atoms, and specific examples thereof include a methoxycarbonyl group, an ethoxycarbonyl group, and a butoxycarbonyl group.

The heterocyclic group represented by _R1 to _R3 preferably has a nitrogen atom (N), an oxygen atom (O), or a sulfur atom (S) as a heteroatom, and is preferably a group derived from a 5-membered heterocycle fused to a benzene ring or a naphthalene ring. Also preferred is a group derived from a nitrogen-containing 6-membered heterocycle having a benzene ring as a fused ring. Specifically, preferred are 2-yl, benzothiazolyl, benzoxazolyl, benzimidazolyl, naphthothiazolyl, 2-pyridyl, 3-pyridyl, 4-pyridyl, 2-pyrazinyl, 2-quinolyl, 7-quinolyl, etc., and these may have a substituent, and in this case, the substituent may be an alkyl group, an aryl group, an alkoxy group, an aryloxy group, etc.

Preferred examples of the heterocyclic groups represented by R ₁ to R ₃ are shown below.

In formula (I), R ₁ to R ₃ may be bonded to each other to form a ring, and examples of the ring formed include a carbon ring such as cyclopentene.

It is preferred that R ₁ to R ₃ are not simultaneously hydrogen atoms, and it is particularly preferred that R ₁ is a heterocyclic group as described above.

In formula (I), _R4 and _R7 each represent a hydrogen atom, an alkyl group (e.g., a methyl group), or an aryl group (e.g., a phenyl group, a naphthyl group), and _R5 and _R6 each represent an alkyl group or an aryl group, which may be the same or different but are usually the same, and are particularly preferably alkyl groups.

Examples of the alkyl groups represented by R ₄ to R ₇ include the same as those represented by R ₁ to _{R 3} .

_R4 and _R5 , _R5 and _R6 , and _R6 and _R7 may each be bonded to each other to form a ring, and it is particularly preferred that _R4 and _R5 , and _R6 and _R7 are each bonded to each other to simultaneously form a 6-membered ring together with a carbon atom (C) and a nitrogen atom (N). When a partially hydrogenated quinolizine ring is formed in this way, the structural formula shown in the following formula (Ia) is preferred. In particular, this prevents fluorescence quenching due to interactions between coumarin compounds, improving the fluorescence quantum yield.

In formula (Ia), _R1 to _R3 have the same meanings as in formula (I). _R41 , _R42 , _R71 and _R72 each represent a hydrogen atom or an alkyl group, and examples of the alkyl group include the same as those for _R1 to _R3 .

Specific examples of coumarin derivatives represented by formula (I) are listed below, but the present invention is not limited to these. Below, they are represented by combinations of _R1 and the like in formula (I) and formula (Ia). In the following, Ph represents a phenyl group.

These compounds can be synthesized by the methods described in JP-A-6-9952, Ger. Offen. 109812-5, and the like.

The coumarin derivatives of formula (I) may be used alone or in combination of two or more.

Next, the tetraaryldiamine derivative of formula (II) used in the hole injection and/or transport layer will be described.

In formula (II), Ar₁, Ar₂, Ar₃and Ar₄each represents an aryl group, Ar₁ ~Ar₄At least one of the aryl groups is a polycyclic aryl group derived from a fused ring or ring assembly having two or more benzene rings.

The aryl groups represented by Ar ₁ to Ar ₄ may have a substituent and preferably have a total carbon number of 6 to 24. Examples of monocyclic aryl groups include a phenyl group and a tolyl group, and examples of polycyclic aryl groups include a 2-biphenylyl group, a 3-biphenylyl group, a 4-biphenylyl group, a 1-naphthyl group, a 2-naphthyl group, an anthryl group, a phenanthryl group, a pyrenyl group, and a perylenyl group.

In formula (II), it is preferred that the amino group moiety obtained by combining Ar ₁ and Ar ₂ is the same as the amino group moiety obtained by combining Ar ₃ and Ar ₄ .

In formula (II), R ₁₁ and R ₁₂ each represent an alkyl group, and p and q each represent 0 or an integer of 1 to 4.

Examples of the alkyl group represented by _R11 and _R12 include the same as those for _R1 to _R3 in formula (I), with methyl group being preferred. p and q are preferably 0 or 1.

In formula (II), R ₁₃ and R ₁₄ each represent an aryl group, and r and s each represent 0 or an integer of 1 to 5.

Examples of the aryl group represented by _R13 and _R14 include the same groups as those represented by _R1 to _R3 in formula (I), with a phenyl group being preferred. r and s are preferably 0 or 1.

Specific examples of tetraaryldiamine derivatives represented by formula (II) are shown below, but the present invention is not limited to these. Below, they are shown using combinations of _Ar1 and the like in formula (IIa). Furthermore, for _R51 to _R58 and _R59 to _R68 , when all of them are H, they are represented by H, and when there is a substituent, only the substituent is represented.

These compounds can be synthesized by the method described in EP 0650955 A1 (corresponding Japanese Patent Application No. 7-43564) or the like.

These compounds have molecular weights of approximately 1000 to 2000, melting points of approximately 200 to 400°C, and glass transition temperatures of approximately 130 to 200°C. Therefore, by conventional vacuum deposition or other methods, they form a transparent, amorphous state that is stable even at room temperature or above, resulting in a smooth, high-quality film that can be maintained for an extended period of time. Furthermore, they can be formed into thin films by themselves without the use of a binder resin.

The tetraaryldiamine derivatives of formula (II) may be used alone or in combination of two or more.

The organic EL device of the present invention uses a coumarin derivative of formula (I) in an emissive layer and a tetraaryldiamine derivative of formula (II) in a hole injection and/or transport layer, such as a hole injection transport layer.

An example of the configuration of an organic EL element of the present invention is shown in Figure 1. The organic EL element 1 shown in this figure has an anode 3, a hole injection transport layer 4, an emissive layer 5, an electron injection transport layer 6, and a cathode 7, arranged in this order on a substrate 2, with emitted light extracted from the substrate 2 side. A color filter film 8 and a fluorescence conversion filter film 9 are provided between the substrate 2 and the anode 3, from the substrate 2 side, to control the emitted color. The organic EL element 1 also has a sealing layer 10 that covers these layers 4 to 6, 8, and 9 and the electrodes 3 and 7, and the entire device is disposed within a casing 11 integrated with the glass substrate 2. A gas or liquid 12 is filled between the sealing layer 10 and the casing 11. The sealing layer 10 is made of a resin such as Teflon, and the casing 11 may be made of glass, aluminum, or the like, and can be bonded to the substrate 2 or the like with a photocurable resin adhesive or the like. The gas or liquid 12 may be dry air, an inert gas such as N ₂ or Ar, an inert liquid such as a fluorocarbon compound, or a moisture absorbent.

The light-emitting layer functions to inject holes and electrons, transport them, and generate excitons through the recombination of holes and electrons. It is preferable to use bipole (electron and hole) stable compounds with high fluorescence intensity for the light-emitting layer. The hole injection/transport layer facilitates hole injection from the anode, stably transports holes, and reduces electron transport. The electron injection/transport layer facilitates electron injection from the cathode, stably transports electrons, and reduces hole transport. These layers confine holes and electrons injected into the light-emitting layer, increasing their density and improving recombination rates, optimizing the recombination region, and improving luminous efficiency. The hole injection/transport layer and electron injection/transport layer are provided as needed, taking into account the level of the hole injection, hole transport, electron injection, and electron transport functions of the compounds used in the light-emitting layer. For example, if the compound used in the light-emitting layer has a high hole injection/transport function or electron injection/transport function, the light-emitting layer may function as both the hole injection/transport layer and the electron injection/transport layer without providing a hole injection/transport layer or an electron injection/transport layer. In some cases, neither the hole injection/transport layer nor the electron injection/transport layer may be provided. Furthermore, the hole injection/transport layer and the electron injection/transport layer may each be provided as separate layers having an injection function and a transport function.

The thicknesses of the light-emitting layer, hole injecting and transporting layer, and electron injecting and transporting layer are not particularly limited and will vary depending on the formation method, but are generally about 5 to 1,000 nm, and preferably 10 to 200 nm.

The thickness of the hole injection/transport layer and the electron injection/transport layer depends on the design of the recombination/light-emitting region, but may be approximately the same as the thickness of the light-emitting layer or approximately 1/10 to 10 times that. When separate injection and transport layers for electrons and holes are used, the injection layer is preferably 1 nm or thicker, and the transport layer is preferably 20 nm or thicker. In this case, the upper limit of the injection and transport layer thickness is typically approximately 1000 nm for the injection layer and approximately 100 nm for the transport layer. This thickness also applies when two injection/transport layers are used.

Furthermore, by controlling the film thickness and taking into account the carrier mobility and carrier density (determined by the ionization potential and electron affinity) of the combined light-emitting layer, electron injection/transport layer, and hole injection/transport layer, it is possible to freely design the recombination and emission regions. This allows for the design of emission color, control of emission brightness and spectrum through the optical interference effect between the two electrodes, and control of the spatial distribution of emission, thereby achieving the desired color purity and achieving high-efficiency devices.

The coumarin derivative of formula (I) is a compound that has high fluorescence intensity and is therefore preferably used in the light-emitting layer. Its content in the light-emitting layer is preferably 0.01 wt% or more, and more preferably 1.0 wt% or more.

In the present invention, the light-emitting layer can contain fluorescent substances other than the coumarin derivative of formula (I). Examples of such fluorescent substances include at least one selected from compounds such as those disclosed in JP-A-63-264692, e.g., quinacridone, rubrene, and styryl dyes. Other examples include quinoline derivatives such as metal complex dyes containing 8-quinolinol or its derivatives as a ligand, such as tris(8-quinolinolato)aluminum, tetraphenylbutadiene, anthracene, perylene, coronene, and 12-phthaloperinone derivatives.

Further examples include phenylanthracene derivatives disclosed in JP-A-8-12600 and tetraarylethene derivatives disclosed in JP-A-8-12969.

In particular, the coumarin derivative of Formula (I) is preferably used in combination with a host material, particularly a host material capable of emitting light by itself, and is preferably used as a dopant. In such cases, the content of the coumarin derivative in the emissive layer is preferably 0.01 to 10 wt %, more preferably 0.1 to 5 wt %. By using the coumarin derivative in combination with a host material, the emission wavelength characteristics of the host material can be changed, enabling emission to be shifted to a longer wavelength, and improving the luminous efficiency and stability of the device.

In practice, the doping concentration can be determined based on the required brightness, lifetime, and driving voltage. A concentration of 1 wt% or more produces a high-brightness device, while a concentration of 1.5 wt% to 6 wt% produces a high-brightness device with a small increase in driving voltage and a long emission lifetime.

As a host material for doping the coumarin derivative of formula (I), a quinoline derivative is preferred. Furthermore, a quinolinonato metal complex, particularly an aluminum complex, having 8-quinolinol or a derivative thereof as a ligand is preferred. In this case, the 8-quinolinol derivative is 8-quinolinol substituted with a halogen atom or an alkyl group, or fused with a benzene ring. Examples of such aluminum complexes include those disclosed in JP-A-63-264692, JP-A-3-255190, JP-A-5-70733, JP-A-5-258859, and JP-A-6-215874. These compounds are electron-transporting host materials.

Specific examples include tris(8-quinolinolato)aluminum, bis(8-quinolinolato)magnesium, bis(benzo{f}-8-quinolinolato)zinc, bis(2-methyl-8-quinolinolato)aluminum oxide, tris(8-quinolinolato)indium, tris(5-methyl-8-quinolinolato)aluminum, 8-quinolinolatolithium, tris(5-chloro-8-quinolinolato)gallium, bis(5-chloro-8-quinolinolato)calcium, 5,7-dichloro-8-quinolinolatoaluminum, tris(5,7-dibromo-8-hydroxyquinolinolato)aluminum, and poly[zinc(II)-bis(8-hydroxy-5-quinolinyl)methane].

Aluminum complexes having other ligands in addition to 8-quinolinol or a derivative thereof may also be used. Examples of such complexes include bis(2-methyl-8-quinolinolato)(phenolato)aluminum(III), bis(2-methyl-8-quinolinolato)(ortho-cresolato)aluminum(III), bis(2-methyl-8-quinolinolato)(meta-cresolato)aluminum(III), bis(2-methyl-8-quinolinolato)(para-cresolato)aluminum(III), bis(2-methyl-8-quinolinolato)(ortho-phenylphenolato)aluminum(III), bis(2-methyl-8-quinolinolato)(meta-phenylphenolato)aluminum(III), and bis(2-methyl-8-quinolinolato). ) (para-phenylphenolato) aluminum(III), bis(2-methyl-8-quinolinolato) (2,3-dimethylphenolato) aluminum(III), bis(2-methyl-8-quinolinolato) (2,6-dimethylphenolato) aluminum(III), bis(2-methyl-8-quinolinolato) (3,4-dimethylphenolato) aluminum(III), bis(2-methyl-8-quinolinolato) (3,5-dimethylphenolato) aluminum(III), bis(2-methyl-8-quinolinolato) (3,5-di-tert-butylphenolato) aluminum(III), bis(2-methyl-8-quinolinolato) (2,6-diphenylphenolato) aluminum(III), bis(2-methyl-8-quinolinolato) (2 ,4,6-triphenylphenolato)aluminum(III), bis(2-methyl-8-quinolinolato)(2,3,6-trimethylphenolato)aluminum(III), bis(2-methyl-8-quinolinolato)(2,3,5,6-tetramethylphenolato)aluminum(II), bis(2-methyl-8-quinolinolato)(1-naphtholato)aluminum(III), bis(2-methyl-8-quinolinolato)(2-naphtholato)aluminum(III), bis(2,4-dimethyl-8-quinolinolato)(ortho-phenylphenolato)aluminum(III), bis(2,4-dimethyl-8-quinolinolato)(para-phenylphenolato)aluminum(III), bis(2,4-dimethyl-8-quinolinolato)(methyl Examples include bis(2,4-dimethyl-8-quinolinolato)(3,5-dimethylphenolato)aluminum(III), bis(2,4-dimethyl-8-quinolinolato)(3,5-di-tert-butylphenolato)aluminum(III), bis(2-methyl-4-ethyl-8-quinolinolato)(para-cresolato)aluminum(III), bis(2-methyl-4-methoxy-8-quinolinolato)(para-phenylphenolato)aluminum(II), bis(2-methyl-5-cyano-8-quinolinolato)(ortho-cresolato)aluminum(III), and bis(2-methyl-6-trifluoromethyl-8-quinolinolato)(2-naphtholato)aluminum(III).

Other examples include bis(2-methyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(2-methyl-8-quinolinolato)aluminum(III), bis(2,4-dimethyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(2,4-dimethyl-8-quinolinolato)aluminum(III), bis(4-ethyl-2-methyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(4-ethyl-2-methyl-8-quinolinolato)aluminum(III), and bis(2-methyl-4-methoxy bis(2-methyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(2-methyl-4-methoxyquinolinolato)aluminum(III), bis(5-cyano-2-methyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(5-cyano-2-methyl-8-quinolinolato)aluminum(III), bis(2-methyl-5-trifluoromethyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(2-methyl-5-trifluoromethyl-8-quinolinolato)aluminum(III), and the like may also be used.

Among these, tris(8-quinolinolato)aluminum is particularly preferred in the present invention.

Other preferred host materials include phenylanthracene derivatives described in JP-A-8-12600 and tetraarylethene derivatives described in JP-A-8-12969.

The phenylanthracene derivative is represented by the following formula (V).

Formula (V) A ¹ -L ¹ -A ² (V) In formula (V), A ¹ and A ² each represent a monophenylanthryl group or a diphenylanthryl group, and they may be the same or different.

The monophenylanthryl group or diphenylanthryl group represented by ^A1 or ^A2 may be unsubstituted or substituted. If substituted, examples of the substituent include an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an amino group, etc., and these substituents may be further substituted. In addition, the substitution position of such a substituent is not particularly limited, but it is preferably a phenyl group bonded to the anthracene ring, not to the anthracene ring. In addition, the bonding position of the phenyl group on the anthracene ring is preferably the 9th or 10th position of the anthracene ring.

In formula (V), ^L1 represents a single bond or an arylene group. The arylene group represented by ^L1 is preferably unsubstituted, and specific examples thereof include ordinary arylene groups such as phenylene groups, biphenylene groups, and anthrylene groups, as well as groups in which two or more arylene groups are directly linked. ^L1 is preferably a single bond, p-phenylene group, 4,4'-biphenylene group, etc.

The arylene group represented by ^L1 may be one in which two or more arylene groups are linked via an alkylene group, -O-, -S-, or -NR-. Here, R represents an alkyl group or an aryl group. Examples of the alkyl group include a methyl group and an ethyl group, and examples of the aryl group include a phenyl group. Among these, an aryl group is preferred, and in addition to the above-mentioned phenyl group, it may be ^A1 or ^A2 , or it may even be a phenyl group substituted with ^A1 or ^A2 . Examples of the alkylene group include a methylene group, an ethylene group, and the like.

The tetraarylethene derivative is represented by the following formula (VI).

In formula (VI), Ar ¹ , Ar ² and Ar ³ each represent an aromatic residue, and may be the same or different.

Examples of the aromatic residues represented by ^Ar1 to ^Ar3 include aromatic hydrocarbon groups (aryl groups) and aromatic heterocyclic groups. The aromatic hydrocarbon groups may be monocyclic or polycyclic aromatic hydrocarbon groups, including fused rings and ring assemblies. The aromatic hydrocarbon groups preferably have a total of 6 to 30 carbon atoms and may have a substituent. When substituted, examples of the substituent include alkyl groups, aryl groups, alkoxy groups, aryloxy groups, and amino groups. Examples of the aromatic hydrocarbon groups include phenyl groups, alkylphenyl groups, alkoxyphenyl groups, arylphenyl groups, aryloxyphenyl groups, aminophenyl groups, biphenyl groups, naphthyl groups, anthryl groups, pyrenyl groups, and perylenyl groups.

The aromatic heterocyclic group preferably contains O, N, or S as a heteroatom and may be a 5-membered or 6-membered ring. Specific examples include a thienyl group, a furyl group, a pyrrolyl group, and a pyridyl group.

As the aromatic group represented by Ar ¹ to Ar ³ , a phenyl group is particularly preferred.

n is an integer of 2 to 6, and particularly preferably an integer of 2 to 4.

^L2 represents an n-valent aromatic residue, preferably a divalent to hexavalent, more preferably a divalent to tetravalent, residue derived from an aromatic hydrocarbon, aromatic heterocycle, aromatic ether, or aromatic amine. These aromatic residues may further have a substituent, but are preferably unsubstituted.

The compounds of formulas (V) and (VI) can be electron-transporting or hole-transporting host materials depending on the combination of groups.

The coumarin derivative of Formula (I) is preferably used in a light-emitting layer in combination with the host material described above. Alternatively, it may be used as a mixed layer containing at least one hole-injecting/transporting compound and at least one electron-injecting/transporting compound. The compound of Formula (I) is preferably incorporated into this mixed layer as a dopant. The content of the coumarin derivative of Formula (I) in this mixed layer is preferably 0.01 to 20 wt %, more preferably 0.1 to 15 wt %.

In the mixed layer, hopping conduction paths for both carriers are created, allowing each carrier to move through the material with the dominant polarity, making it difficult for carrier injection of the opposite polarity to occur. Therefore, by ensuring that each compound mixed is stable with respect to carriers, the organic compound is less susceptible to damage, which has the advantage of extending the device's lifespan. Furthermore, by incorporating a coumarin derivative of formula (I) into such a mixed layer, the emission wavelength of the mixed layer itself can be altered while remaining stable with respect to carriers. This shifts the emission wavelength primarily to longer wavelengths, increasing the emission intensity and improving the device's stability.

The hole injection transport compound and electron injection transport compound used in the mixed layer may be selected from the compounds for hole injection transport layers, etc. and the compounds for electron injection transport layers, etc., described below, respectively. Among these, aromatic tertiary amines are preferably used as the hole injection transport compound. Specific examples include tetraaryldiamine derivatives of formula (II), N,N'-bis(-3-methylphenyl)-N,N'-diphenyl-4,4'-diaminobiphenyl, N,N'-bis(-3-biphenyl)-N,N'-diphenyl-4,4'-diaminobiphenyl, N,N'-bis(-4-t-butylphenyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine, Examples of suitable electron injection/transport compounds include those described in JP-A-63-295695, JP-A-5-234681, and EP 0650955 A1 (corresponding Japanese Patent Application No. 7-43564), such as N,N,N',N'-tetrakis(-3-biphenyl)-1,1'-biphenyl-4,4'-diamine and N,N'-diphenyl-N,N'-bis-(-4'-(N-3(methylphenyl)-N-phenyl)aminobiphenyl-4-yl)benzidine. Among these, tetraaryldiamine derivatives of formula (II) are preferred. Furthermore, preferred electron injection/transport compounds include quinoline derivatives, and metal complexes containing 8-quinolinol or its derivatives as ligands, particularly tris(8-quinolinolato)aluminum.

In this case, the mixing ratio is preferably determined based on the carrier density and carrier mobility. The weight ratio of the hole injection transport compound to the electron injection transport compound is preferably about 1/99 to 99/1, more preferably about 20/80 to 80/20, and particularly preferably about 30/70 to 70/30. However, this limitation may not be imposed depending on the combination of materials in the device.

Here, a hole injection/transport compound is one in which, when the hole and electron current densities are measured using a single-layer film element in which a single-layer film of this compound approximately 1 μm thick is disposed between a cathode and an anode, the hole current density is more than twice, preferably six times or more, and more preferably ten times or more, of the electron current density. On the other hand, an electron injection/transport compound is one in which, when the hole and electron current densities are measured using a similarly configured single-layer film element, the electron current density is more than twice, preferably six times or more, and more preferably ten times or more, of the hole current density. The cathode and anode used above are the same as those actually used.

The thickness of the mixed layer is preferably from a thickness corresponding to one molecular layer to less than the thickness of the organic compound layer, and more preferably from 1 to 85 nm, more preferably from 5 to 60 nm, and even more preferably from 5 to 50 nm.

In the mixed layer described above, in addition to the coumarin derivative of formula (I), a quinacridone compound of formula (III) or a styrylamine compound of formula (IV) can be used as a dopant. In this case, the doping amount is the same as that of the coumarin derivative of formula (I).

Regarding formula (III), in formula (III), _R21 and _R22 represent a hydrogen atom, an alkyl group, or an aryl group, which may be the same or different. The alkyl group represented by _R21 and _R22 preferably has 1 to 5 carbon atoms and may have a substituent. Specific examples include a methyl group, an ethyl group, a propyl group, and a butyl group.

The aryl group represented by _R21 and _R22 may have a substituent and preferably has a total of 1 to 30 carbon atoms, and specific examples thereof include a phenyl group, a tolyl group, and a diphenylaminophenyl group.

_R23 and _R24 each represent an alkyl group or an aryl group, and specific examples thereof include the same as those for _R21 and _R22 . t and u each represent 0 or an integer of 1 to 4, preferably 0. When t and u are 2 or greater, adjacent _R23s and adjacent _R24s may be bonded to each other to form a ring, and examples of such a ring include carbon rings such as a benzene ring and a naphthalene ring.

Specific examples of quinacridone compounds of formula (III) are shown below. Specific examples are shown by combinations of _R21, etc. in formula (IIIa) below. The fused benzene rings at both ends are also shown with the 1- to 5-positions, so that the positions of any further fused benzene rings attached thereto can be seen.

These compounds can be synthesized by known methods, for example, those described in US Pat. Nos. 2,821,529, 2,821,530, 2,844,484 and 2,844,485, and commercially available products can also be used.

Regarding formula (IV), in formula (IV), _R31 represents a hydrogen atom or an aryl group. The aryl group represented by _R31 may have a substituent, and preferably has a total of 6 to 30 carbon atoms, such as a phenyl group.

R ₃₂ and R ₃₃ each represent a hydrogen atom, an aryl group or an alkenyl group, and may be the same or different.

The aryl group represented by _R32 and _R33 may have a substituent, and preferably has a total of 6 to 70 carbon atoms. Specific examples include a phenyl group, a naphthyl group, and an anthryl group, and preferred substituents include an arylamino group and an arylaminoaryl group. It is also preferred that the substituent includes a styryl group. In such a case, it is also preferred that the monovalent groups derived from the compound represented by formula (IV) are bonded to each other either by themselves or via a linking group.

The alkenyl group represented by _R32 and _R34 may have a substituent, and preferably has a total of 2 to 50 carbon atoms, such as a vinyl group. Preferably, it forms a styryl group together with the vinyl group. In such a case, it is also preferable that monovalent groups derived from the compound represented by formula (IV) are bonded to each other either by themselves or via a linking group.

R ₃₄ represents an arylamino group or an arylaminoaryl group, which may contain a styryl group. In such a case, it is also preferable that, as described above, monovalent groups derived from the compound represented by formula (IV) are bonded to each other by themselves or via a linking group.

Specific examples of the styryl amine compound of formula (IV) are shown below.

These compounds can be synthesized by known methods, for example, by subjecting triphenylamine derivatives to a Wittig reaction or by (homo- or hetero-)coupling of halogenated triphenylamine derivatives using a Ni(O) complex, and commercially available products can also be used.

The mixed layer may contain one dopant or two or more dopants in combination.

The mixed layer is preferably formed by co-evaporation, in which compounds are evaporated from different evaporation sources. However, if the vapor pressures (evaporation temperatures) are similar or very close, they can be mixed in advance on the same evaporation board and then evaporated. A homogeneous mixture of compounds is preferred for the mixed layer, but in some cases, the compounds may exist in an island-like configuration. The emissive layer is generally formed to a desired thickness by evaporating an organic fluorescent material, spin-coating it directly as a solution, or dispersing it in a resin binder and coating it.

In the present invention, at least one hole injection and/or transport layer, i.e., at least one layer selected from the group consisting of a hole injection and transport layer, a hole injection layer, and a hole transport layer, is provided. In particular, when the light-emitting layer is not a mixed layer type, at least one layer contains a tetraaryldiamine derivative of formula (II). The content of the tetraaryldiamine derivative of formula (II) in such a layer is preferably 10 wt % or more. Compounds for the hole injection and/or transport layer that can be used in combination with the tetraaryldiamine derivative of formula (II) in the same layer or in a separate layer include various organic compounds described in JP-A Nos. 63-295695, 2-191694, and 3-792, such as aromatic tertiary amines, hydrazone derivatives, carbazole derivatives, triazole derivatives, imidazole derivatives, oxadiazole derivatives having an amino group, and polythiophenes. These compounds may be used in combination of two or more types, or may be laminated. When combined with a mixed-layer-type emissive layer, a wide range of compounds can be used, not necessarily limited to the tetraaryldiamine derivative of formula (II). However, depending on the device design, it may be preferable to use the hole injection/transport compound used in the mixed layer in the hole injection/transport layer or hole transport layer adjacent to the emissive layer.

When the hole injection transport layer is formed by dividing it into a hole injection layer and a hole transport layer, a preferred combination can be selected from compounds for use in the hole injection transport layer.

In this case, it is preferable to stack layers of compounds with low ionization potential in order from the anode (e.g., tin-doped indium oxide: ITO) side. It is preferable to provide a hole injection layer in contact with the anode and a hole transport layer in contact with the light-emitting layer. It is also preferable to use a compound with good thin-film properties on the anode surface. This relationship between ionization potential and stacking order applies even when two or more hole injection and transport layers are provided. This stacking order reduces the driving voltage and prevents current leakage and the occurrence and growth of dark spots. Furthermore, when fabricating devices, vapor deposition can be used, allowing even thin films of approximately 1 to 10 nm to be uniform and pinhole-free. Therefore, even if a compound with low ionization potential and visible absorption is used in the hole injection layer, changes in the emitted color and a decrease in efficiency due to reabsorption can be prevented.

The tetraaryldiamine derivative of formula (II) is generally preferably used in a layer on the light-emitting layer side.

In the present invention, an electron injecting and/or transporting layer may be provided as an electron injecting and/or transporting layer. For the electron injecting and transporting layer, quinoline derivatives, oxadiazole derivatives, perylene derivatives, pyridine derivatives, pyrimidine derivatives, quinoxaline derivatives, diphenylquinone derivatives, nitro-substituted fluorene derivatives, and the like, such as organometallic complexes having 8-quinolinol or its derivatives as a ligand, such as tris(8-quinolinolato)aluminum, can be used. The electron injecting and transporting layer may also serve as the light-emitting layer, and in such cases, tris(8-quinolinolato)aluminum or the like is preferably used. The electron injecting and transporting layer may be formed by vapor deposition or the like, similar to the light-emitting layer.

When the electron injecting and transporting layer is formed by dividing it into an electron injecting layer and an electron transporting layer, a preferred combination can be selected from compounds for use in the electron injecting and transporting layer.

In this case, it is preferable to stack the layers of compounds having the largest electron affinity from the cathode side, and it is preferable to provide an electron injection layer in contact with the cathode and an electron transport layer in contact with the light-emitting layer. The relationship between electron affinity and stacking order is also the same when two or more electron injection and transport layers are provided.

In the present invention, a compound known as a singlet oxygen quencher may be contained in the organic compound layer such as the light-emitting layer, hole injecting and transporting layer, or electron injecting and transporting layer. Examples of such a quencher include rubrene, nickel complexes, diphenylisobenzofuran, and tertiary amines.

In particular, in the hole injection/transport layer, hole injection layer, or hole transport layer, rubrene is preferably used in combination with an aromatic tertiary amine such as a tetraaryldiamine derivative of Formula (II). In this case, the amount of rubrene used is preferably 0.1 to 20 wt % of the aromatic tertiary amine such as a tetraaryldiamine derivative of Formula (II). For details of such rubrene, see EP 065095 A1 (corresponding Japanese Patent Application No. 7-43564). By incorporating rubrene into a hole transport layer or the like, compounds in the hole transport layer or the like can be protected from electron injection. Furthermore, by shifting the recombination region from near the interface in a layer containing an electron injection/transport compound such as tris(8-quinolinolato)aluminum to near the interface in a layer containing a hole injection/transport compound such as an aromatic tertiary amine, tris(8-quinolinolato)aluminum or the like can be protected from hole injection. It should be noted that the present invention is not limited to rubrene, and any compound having a lower electron affinity than the hole-injecting/transporting compound and being stable with respect to electron injection and hole injection can be similarly used.

In the present invention, the cathode is preferably made of a material with a low work function, such as Li, Na, Mg, Al, Ag, or In, or an alloy containing one or more of these. Furthermore, the cathode preferably has fine crystal grains, and is particularly preferably in an amorphous state. The cathode thickness is preferably approximately 10 to 1,000 nm. Furthermore, the sealing effect can be improved by vapor-depositing or sputtering Al or a fluorine compound at the end of the electrode formation process.

In order for an organic EL element to emit light from a surface, at least one electrode must be transparent or semi-transparent. Since there are limitations on the cathode material as mentioned above, it is preferable to determine the material and thickness of the anode so that the transmittance of the emitted light is 80% or more. Specifically, for example, ITO (tin-doped indium oxide), IZO (zinc-doped indium oxide), SnO ₂ , Ni, Au, Pt, Pd, or dopant-doped polypyrrole is preferably used for the anode. The thickness of the anode is preferably approximately 10 to 500 nm. Furthermore, a low driving voltage is required to improve the reliability of the element. A preferred example is ITO (thickness 10 to 300 nm) with a resistance of 10 to 30 Ω/cm ² or less than 10 Ω/cm ² (usually 0.1 to 10 Ω/cm ² ). In practice, the ITO film thickness and optical constants should be designed so that the optical interference effect caused by the multiple reflections of light at both ITO interfaces and the cathode surface can achieve high light extraction efficiency and high color purity. In addition, in large devices such as displays, the resistance of ITO becomes high, so wiring made of Al or the like may be used.

There are no particular limitations on the substrate material, but in the illustrated example, a transparent or translucent material such as glass or resin is used to extract emitted light from the substrate side. Furthermore, as shown in the illustration, the substrate may be fitted with a color filter film, a fluorescent conversion filter film containing a fluorescent material, or a dielectric reflective film to control the emitted color.

If an opaque material is used for the substrate, the stacking order shown in FIG. 1 may be reversed.

In the present invention, by using various coumarin derivatives of formula (I) in the light-emitting layer, emission of, for example, green (λmax 490 to 550 nm), blue (λmax 440 to 490 nm), or red (λmax 580 to 660 nm) can be obtained, and emission of λmax 480 to 640 nm can be particularly preferably obtained.

In this case, the CIE chromaticity coordinates of green, blue, and red should preferably be equal to or greater than the color purity of current CRTs or equal to the color purity of the NTSC standard.

The above chromaticity coordinates can be measured using a general colorimeter. In the present invention, measurements are performed using measuring instruments such as the BM-7 and SR-1 manufactured by Topcon Corporation.

In the present invention, the preferred λmax and light emission with x and y values of the CIE chromaticity coordinates may be obtained by providing a color filter film, a fluorescence conversion filter film, or the like.

The color filter film may be a color filter similar to those used in LCD displays, but the characteristics of the color filter can be adjusted to match the light emitted by the OLED device to optimize extraction efficiency and color purity. It is also preferable to use a color filter that can block short-wavelength light that is absorbed by the EL device material and the fluorescence conversion layer, thereby improving the device's light resistance and display contrast. The light to be blocked is green light with wavelengths above 560 nm and below 480 nm, blue light with wavelengths above 490 nm, and red light with wavelengths below 580 nm. Using such color filters allows for the desired x and y values on the CIE chromaticity coordinates to be obtained. The color filter film thickness should be approximately 0.5 to 20 μm.

Alternatively, an optical thin film such as a dielectric multilayer film may be used in place of the color filter.

The fluorescence conversion filter film absorbs EL light and converts the emitted color by emitting light from the phosphors in the fluorescence conversion film. It is made up of three materials: a binder, a fluorescent material, and a light-absorbing material.

Fluorescent materials generally need only have a high fluorescence quantum yield, and it is desirable for them to have strong absorption in the EL emission wavelength range. Specifically, fluorescent materials with a maximum emission wavelength (λmax) of 490-550 nm for green, 440-480 nm for blue, and 580-640 nm for red, and with a half-width of 10-100 nm around λmax, are preferred. Laser dyes are typically suitable, including rhodamine compounds, perylene compounds, cyanine compounds, phthalocyanine compounds (including subphthalocyanines), naphthalimide compounds, fused-ring hydrocarbon compounds, fused heterocyclic compounds, and styryl compounds.

The binder should basically be a material that does not quench the fluorescence, and is preferably one that can be finely patterned by photolithography, printing, etc. Also, a material that will not be damaged during ITO film formation is preferable.

The light-absorbing material is used when the light absorption of the fluorescent material is insufficient, but it does not have to be used if it is not necessary. Also, the light-absorbing material should be selected so as not to quench the fluorescence of the fluorescent material.

By using such a fluorescent conversion filter, desirable x and y values in the CIE chromaticity coordinates can be obtained. The thickness of the fluorescent conversion filter film should be approximately 0.5 to 20 μm.

In the present invention, a color filter film and a fluorescence conversion filter film may be used in combination as in the illustrated example, and preferably, a color filter film that cuts off light of a specific wavelength is disposed on the side from which emitted light is extracted.

It is also preferable to provide a protective film on the color filter film or the fluorescence conversion filter film. The protective film may be made of glass, resin, or other materials, and should be selected so as to prevent damage to the filter film and prevent problems in subsequent processes. The thickness of the protective film is approximately 1 to 10 μm. The provision of the protective film prevents damage to the filter film, flattens the surface, adjusts the refractive index and film thickness, and improves light extraction efficiency.

Commercially available materials can be used as they are for the color filter film, fluorescence conversion filter film, and protective film, and these films can be formed by coating methods, electrolytic polymerization methods, vapor deposition methods (evaporation, sputtering, CVD), etc.

Next, a method for producing the organic EL element of the present invention will be described.

The cathode and anode are preferably formed by a vapor deposition method such as evaporation or sputtering.

Vacuum deposition is preferred for forming the hole injection/transport layer, light-emitting layer, and electron injection/transport layer, as it allows for the formation of homogeneous thin films. Vacuum deposition produces homogeneous thin films in an amorphous state or with a crystal grain size of 0.1 μm or less (typically, the lower limit is around 0.001 μm). Crystal grain sizes exceeding 0.1 μm result in non-uniform light emission, necessitating a higher device drive voltage, and significantly reducing charge injection efficiency.

The conditions for vacuum deposition are not particularly limited, but a vacuum of ^10-3 Pa ( ^10-5 Torr) or less and a deposition rate of approximately 0.001 to 1 nm/sec are preferred. It is also preferable to form each layer successively in a vacuum. Forming each layer successively in a vacuum prevents impurities from being adsorbed at the interface between the layers, resulting in high performance. Furthermore, the driving voltage of the device can be reduced.

When using vacuum deposition to form these layers, if multiple compounds are to be contained in a single layer, it is preferable to individually control the temperature of each boat containing the compounds and perform co-deposition. However, the compounds may also be mixed in advance and then vapor-deposited. Other methods, such as solution coating (spin coating, dipping, casting, etc.) and the Langmuir-Blodgett (LB) method, can also be used. In solution coating, the compounds may be dispersed in a matrix material such as a polymer.

While the above has described organic EL elements that emit a single color, the present invention can also construct organic EL elements capable of emitting two or more light-emitting species. Such organic EL elements have two or more light-emitting layers, including a bipolar light-emitting layer, and the two or more light-emitting layers are either a combination of bipolar light-emitting layers, a combination of a bipolar light-emitting layer and a hole-transporting light-emitting layer located closer to the anode, or a combination of a bipolar light-emitting layer and an electron-transporting light-emitting layer located closer to the cathode.

Here, a bipolar light-emitting layer is a light-emitting layer in which electron injection/transport and hole injection/transport are equal in magnitude within the light-emitting layer, and the electrons and holes are distributed throughout the light-emitting layer, so that recombination points and light-emitting points are spread throughout the light-emitting layer.

More specifically, the current density due to electrons injected from the electron transport layer and the current density due to holes injected from the hole transport layer are on the same order of magnitude, i.e., the ratio of the current densities of the two carriers is 1/10 to 10/1, preferably 1/6 to 6/1, and more preferably 1/2 to 2/1.

In this case, the ratio of the current densities of the two carriers can be determined by using the same electrodes as those actually used, depositing a single-layer light-emitting layer to a thickness of approximately 1 μm, and measuring the current density.

On the other hand, a hole-transporting light-emitting layer has a higher hole current density than a bipolar-type light-emitting layer, and an electron-transporting light-emitting layer has a higher electron current density than a bipolar-type light-emitting layer.

Furthermore, the bipolar type light emitting layer will be mainly described.

Generally, the current density is determined by the product of the carrier concentration and the carrier mobility.

In other words, the carrier density in the light-emitting layer is determined by the barriers at each interface. For example, the electron density is determined by the size of the electron barrier (difference in electron affinity) at the light-emitting layer interface where the electrons are injected, and the hole density is determined by the size of the hole barrier (difference in ionization potential) at the light-emitting layer interface where the holes are injected. In addition, the carrier mobility is determined by the type of material used in the light-emitting layer.

These values determine the distribution of electrons and holes in the light-emitting layer and hence the light-emitting region.

In reality, if the carrier concentration and carrier mobility in the electrode, electron transport layer, and hole transport layer are sufficiently high, the problem can be solved simply by the interfacial barrier, as described above. However, when organic compounds are used in the electron transport layer and hole transport layer, the transport capacity of the carrier transport layer becomes insufficient relative to the light-emitting layer. Therefore, the carrier concentration in the light-emitting layer also depends on the energy level of the carrier injection electrode and the carrier transport properties (carrier mobility and energy level) of the carrier transport layer. Therefore, the current density of each carrier in the light-emitting layer depends heavily on the properties of the organic compounds used in each layer.

Here we will explain further using a relatively simple case.

For example, consider a configuration of anode/hole transport layer/light-emitting layer/electron transport layer/cathode, where the carrier density in each carrier transport layer at the interface with the light-emitting layer is constant.

In this case, if the barrier for holes from the hole-transporting layer to the emissive layer and the barrier for electrons from the electron-transporting layer to the emissive layer are equal or very close (<0.2 V), the amount of carriers injected into the emissive layer will be similar, and the electron and hole concentrations near each interface will be equal or very close. If the mobilities of each carrier in the emissive layer are equal, recombination will occur efficiently within the emissive layer (assuming no carrier penetration), resulting in a high-brightness, high-efficiency device. However, if the collision probability between electrons and holes is high and recombination occurs in a localized region, or if there is a large carrier barrier (>0.2 eV) within the emissive layer, the emission region will not expand and simultaneous emission of multiple emissive molecules with different emission wavelengths will be impossible, making this unsuitable for a bipolar emissive layer. For a bipolar emissive layer, it is necessary to create an emissive layer without a large carrier barrier, which would narrow the recombination region while maintaining an appropriate electron-hole collision probability.

In addition, the electron-blocking function of the hole-transporting layer and the hole-blocking function of the electron-transporting layer are also effective in improving efficiency by preventing carrier penetration from the light-emitting layer. Furthermore, in a configuration with multiple light-emitting layers, these functions are important for designing a bipolar light-emitting layer in which each blocking layer serves as a recombination point and a light-emitting point, driving multiple light-emitting layers to emit light.

Next, if the carrier mobilities within the light-emitting layer are different, adjusting the carrier density in each carrier-transporting layer at the light-emitting layer interface can create a bipolar light-emitting layer similar to the simple case described above. Naturally, the carrier concentration at the interface of the carrier-injecting layer with the lower carrier mobility in the light-emitting layer must be increased.

Furthermore, if the carrier density in each carrier transport layer at the interface with the light-emitting layer is different, by adjusting the carrier mobility within the light-emitting layer, a state similar to that of a bipolar light-emitting layer can be formed, similar to the simple case described above.

However, there is a limit to how much adjustment can be made, and ideally, it is desirable that the carrier mobilities and carrier concentrations in the light-emitting layer are equal or nearly equal.

By providing a bipolar light-emitting layer as described above, a light-emitting device with multiple light-emitting layers can be obtained. However, to ensure the luminescence stability of each light-emitting layer, the light-emitting layer must be physically, chemically, electrochemically, and photochemically stabilized.

In particular, the light-emitting layer is required to perform functions such as electron injection/transport, hole injection/transport, recombination, and light emission. The electron/hole injection/transport state corresponds to an anion radical/cation radical or a similar state, and organic solid thin film materials must be stable in this electrochemical state.

Furthermore, the principle of organic electroluminescence (EL) is that it is electrically excited and deactivated by light emission, which causes fluorescence. Therefore, even a trace amount of degradation products that deactivate the fluorescence in the solid thin film can fatally shorten the luminescence lifetime, making it unsuitable for practical use.

To achieve stable emission from a device, it is necessary to have a compound and device structure that are stable as described above, particularly an electrochemically stable compound and device structure.

While it would be possible to form an emissive layer using a compound that satisfies all of the above requirements, it is difficult to form a bipolar emissive layer using a single compound. A simpler method is to create a stable bipolar emissive layer by blending a hole-transporting compound and an electron-transporting compound, both of which are stable for each carrier. Furthermore, the blended layer can be doped with a highly fluorescent dopant to enhance the fluorescence and thereby increase brightness.

Therefore, the bipolar light-emitting layer in the present invention is preferably a mixed layer type, and preferably, all two or more light-emitting layers are mixed layers. Furthermore, it is preferable that at least one of the two or more light-emitting layers is doped with a dopant, and more preferably, all light-emitting layers are doped with a dopant.

A preferred device configuration of the present invention is one in which a dopant-doped mixed-layer type emissive layer is provided with an additional dopant-doped emissive layer, resulting in two or more doped emissive layers. Combinations of doped emissive layers include two mixed layers, a mixed layer and a hole-transporting emissive layer provided on the anode side of the mixed layer, and/or an electron-transporting emissive layer provided on the cathode side of the mixed layer. Combinations of mixed layers are particularly preferred for achieving a long life.

In this case, the mixed layer is a layer containing a hole injection transport compound and an electron injection transport compound, as described above, and the mixture is used as a host material. The hole-transporting light-emitting layer uses a hole injection transport compound, and the electron-transporting light-emitting layer uses an electron injection transport compound as a host material.

Next, the light-emitting process in such a particularly preferred organic EL element will be described.

i) First, we will explain the combination of mixed layers, for example, the case where there are two mixed layers. The mixed layer next to the hole injection and/or transport layer (abbreviated as "hole layer") is called the first mixed layer, and the mixed layer next to the electron injection and/or transport layer (abbreviated as "electron layer") is called the second mixed layer. Holes injected from the hole layer can pass through the first mixed layer to the second mixed layer, and electrons injected from the electron layer can pass through the second mixed layer to the first mixed layer. The recombination probability is determined by the electron concentration, hole concentration, and electron-hole collision probability. However, the recombination region is widely dispersed because there are no barriers such as the first and second mixed layers or interfaces. Therefore, excitons are generated in the first and second mixed layers, and energy transfer occurs from their respective hosts to the nearest emitting species. Excitons generated in the first mixed layer transfer energy to the emissive species (dopants) in this layer, and then transfer energy to the emissive species (dopants) in the second mixed layer, enabling the two emissive species to emit light.

This phenomenon also occurs when the mixed layer has three or more layers.

However, when dopants act as carrier traps, the trap depth must be taken into consideration.

ii) Next, we will explain the combination of a hole-transporting emissive layer and a mixed emissive layer, for example, by providing two layers, in this order from the hole layer side: a hole-transporting emissive layer and a mixed emissive layer. Holes injected from the hole layer pass through the hole-transporting emissive layer, while electrons injected from the electron layer travel through the mixed emissive layer, spreading and recombining near the interface between the hole-transporting emissive layer and the mixed emissive layer, and throughout the mixed emissive layer. Excitons are generated near the interface of the hole-transporting emissive layer and in the mixed emissive layer, respectively, and energy transfer occurs from the respective hosts to the emissive species with the smallest energy gap within the exciton migration range. In this process, excitons generated near the interface of the hole-transporting layer transfer energy to the emissive species (dopants) in that layer, and in the mixed layer transfer energy to the emissive species (dopants) in that layer, enabling the two emissive species to emit light. In addition, electrons are transported at the dopant LUMO level of the hole-transporting layer, recombine in the hole-transporting emissive layer, and emit light, enabling two types of light emission.

iii) Furthermore, regarding the combination of an electron-transporting emitting layer and a mixed emitting layer, for example, two layers are provided in this order from the electron layer side: an electron-transporting emitting layer and a mixed emitting layer. Electrons injected from the electron layer pass through the electron-transporting emitting layer and proceed to the mixed layer, while holes injected from the hole layer enter the mixed layer. They spread and recombine near the interface between the mixed layer and the electron-transporting emitting layer, and throughout the mixed emitting layer. Excitons are generated near the interface of the electron-transporting emitting layer and within the mixed emitting layer, respectively, and energy transfer occurs from the respective hosts to the emitting species with the smallest exciton migration gap. In this process, excitons generated at the interface of the electron-transporting emitting layer transfer energy to the emitting species (dopant) in this layer, and in the mixed emitting layer, energy transfer occurs to the emitting species (dopant) in this layer. Alternatively, holes are transported at the HOMO level of the dopant in the electron-transporting layer and recombine in the electron-transporting emitting layer, enabling two emitting species to emit light.

Regarding ii) and iii), the same phenomenon occurs when these combinations are used or when the number of light-emitting layers is three or more.

The mixing ratio of the hole injection/transport compound and electron injection/transport compound as host materials in the mixed layer can be varied depending on the desired carrier transport properties of the host, and is typically selected from a volume ratio ranging from 5/95 to 95/5. A high ratio of the hole injection/transport compound results in a large hole transport amount, shifting the recombination region toward the anode. A high ratio of the electron injection/transport compound results in a large electron transport amount, shifting the recombination region toward the cathode. This changes the balance of the emission intensities of the mixed layer. Thus, the emission intensities of each emitting layer can be altered by changing the carrier transport properties of the mixed-layer host.

In addition, in the present invention, the carrier transport properties can be changed by changing the type of host material.

In this way, the present invention makes it possible to adjust the light-emitting characteristics of two or more light-emitting layers for each layer. Therefore, the carrier transport properties and structure of the light-emitting layers can be optimized. In this case, two or more light-emitting species may be present in one layer.

The thickness of each of the light-emitting layers corresponding to such multicolor emission is preferably 5 to 100 nm, more preferably 10 to 80 nm, and the total thickness of the light-emitting layers is preferably 60 to 400 nm. The thickness of each of the mixed layers is preferably 5 to 100 nm, more preferably 10 to 60 nm.

When multiple light-emitting layers with different emission characteristics are provided, it is preferable to provide the light-emitting layer with the longest maximum emission wavelength closer to the anode. Furthermore, in order to achieve a long lifetime, it is preferable to dope the light-emitting layer (particularly the mixed layer) with a compound having a naphthacene skeleton, such as rubrene, as a dopant.

Next, we will explain the host materials and dopants used in organic EL devices capable of producing such multicolor emission. As dopants, the coumarin derivatives represented by formula (I), quinacridone compounds represented by formula (III), styrylamine compounds represented by formula (VI), and compounds having a naphthacene skeleton, such as rubrene, which have already been described, can be used. In addition, compounds that can serve as light-emitting materials, as described above, can also be used. Furthermore, fused polycyclic compounds represented by formula (VII) can also be used. Formula (VII) will now be described. Formula (VII) also includes the aforementioned rubrene.

(Ar) _m -L (VII) In formula (VII), Ar represents an aromatic residue, m is an integer of 2 to 8, and each Ar may be the same or different.

Examples of the aromatic residue include aromatic hydrocarbon residues and aromatic heterocyclic residues.

The aromatic hydrocarbon residue may be any hydrocarbon group containing a benzene ring, such as a monocyclic or polycyclic aromatic hydrocarbon residue, including fused rings and ring aggregates.

The aromatic hydrocarbon residue preferably has a total of 6 to 30 carbon atoms and may have a substituent. When the aromatic hydrocarbon residue has a substituent, examples of the substituent include an alkyl group, an alkoxy group, an aryl group, an aryloxy group, an amino group, and a heterocyclic group. Examples of the aromatic hydrocarbon residue include a phenyl group, an alkylphenyl group, an alkoxyphenyl group, an arylphenyl group, an aryloxyphenyl group, an alkenylphenyl group, an aminophenyl group, a naphthyl group, an anthryl group, a pyrenyl group, and a perylenyl group. The aromatic hydrocarbon residue may also be an arylalkynyl group derived from an alkynylarene (arylalkyne).

The aromatic heterocyclic residue preferably contains an O, N, or S heteroatom and may be a five- or six-membered ring. Specific examples include a thienyl group, a furyl group, a pyrrolyl group, and a pyridyl group.

Ar is preferably an aromatic hydrocarbon residue, and particularly preferably a phenyl group, an alkylphenyl group, an arylphenyl group, an alkenylphenyl group, an aminophenyl group, a naphthyl group, an arylalkynyl group, or the like.

The alkylphenyl group preferably has 1 to 10 carbon atoms in the alkyl portion. The alkyl group may be linear or branched, and examples thereof include methyl, ethyl, (n,i)-propyl, (n,i,sec,tert)-butyl, (n,i,neo,tert)-pentyl, and (n,i,neo)-hexyl. These alkyl groups may be substituted at any of the o-, m-, and p-positions on the phenyl group. Specific examples of such alkylphenyl groups include (o,m,p)-tolyl, 4-n-butylphenyl, and 4-t-butylphenyl.

The arylphenyl group preferably has a phenyl group in the aryl moiety. Such a phenyl group may be substituted, and the substituent is preferably an alkyl group, specifically the alkyl groups exemplified above for the alkylphenyl group. Furthermore, the aryl moiety may be a phenyl group substituted with an aryl group such as a phenyl group. Specific examples of such arylphenyl groups include (o, m, p)-biphenylyl, 4-tolylphenyl, 3-tolylphenyl, and terephenylyl.

The alkenylphenyl group preferably has a total of 2 to 20 carbon atoms in the alkenyl portion, and the alkenyl group is preferably a triarylalkenyl group, such as a triphenylvinyl group, a tritolylvinyl group, or a tribiphenylvinyl group. Specific examples of such alkenylphenyl groups include a triphenylvinylphenyl group.

The aminophenyl group preferably has an amino moiety that is a diarylamino group. Examples of the arylamino group include a diphenylamino group and a phenyltolylamino group. Specific examples of such aminophenyl groups include a diphenylaminophenyl group and a phenyltolylaminophenyl group.

The naphthyl group may be a 1-naphthyl group, a 2-naphthyl group, or the like.

The arylalkynyl group preferably has a total of 8 to 20 carbon atoms, and examples thereof include a phenylethynyl group, a tolylethynyl group, a biphenylylethynyl group, a naphthylethynyl group, a diphenylaminophenylethynyl group, an N-phenyltolylaminophenylethynyl group, and a phenylpropynyl group.

Furthermore, L in formula (VII) represents an m (2-8)-valent residue of a fused polycyclic aromatic ring having 3 to 10 rings, preferably 3 to 6 rings. A fused ring refers to a cyclic structure formed by a carbocyclic ring or a heterocyclic ring in which two or more of the constituent atoms of the ring are covalently bonded to other rings. Examples of fused polycyclic aromatic rings include fused polycyclic aromatic hydrocarbons and fused polycyclic aromatic heterocyclic rings.

Examples of condensed polycyclic aromatic hydrocarbons include anthracene, phenanthrene, naphthacene, pyrene, chrysene, triphenylene, benzo[c]phenanthrene, benzo[a]anthracene, pentacene, perylene, dibenzo[a,j]anthracene, dibenzo[a,h]anthracene, benzo[a]naphthacene, hexacene, and anthanthrene.

Examples of fused polycyclic aromatic heterocycles include naphtho[2,1-f]isoquinoline, α-naphthaphenanthridine, phenanthroxazole, quinolino[6,5-f]quinoline, benzo[b]thiophanthrene, benzo[g]thiophanthrene, benzo[i]thiophanthrene, and benzo[b]thiophanthraquinone.

In particular, condensed polycyclic aromatic hydrocarbons are preferred, and L is preferably a divalent to octavalent, or even divalent to hexavalent, residue derived from such a condensed polycyclic aromatic hydrocarbon.

Specific examples of such divalent to octavalent fused polycyclic aromatic residues L are shown below.

The divalent to octavalent residue of the fused polycyclic aromatic ring represented by L may further have a substituent.

In particular, L is preferably a divalent to octavalent, and more preferably a divalent to hexavalent, residue derived from naphthacene, pentacene, or hexacene, in which benzene rings are linearly condensed. In particular, those derived from naphthacene, i.e., those constituting a compound having a naphthacene skeleton, are preferred.

Furthermore, L is preferably a divalent to hexavalent, and more preferably a divalent to tetravalent, residue derived from anthracene. However, when L is a divalent or trivalent residue derived from anthracene, at least one of the two or three Ars is a residue derived from an alkynyl arene (aryl alkyne). It is even more preferable that two or more of the Ars be such residues. L is particularly preferably a trivalent residue derived from anthracene. Compounds of formula (VII) with such an L, where two Ars are arylalkynyl groups and one Ar is a bis(arylalkynyl)anthryl group, are preferred, and compounds represented by formula (VII-A) are particularly preferred.

( _Ar11 ) ₂ - _L1 - _L2- ( _Ar12 ) ₂ (VII-A) In the formula, _L1 and _L2 each represent a trivalent residue derived from anthracene, and are usually the same but may be different. _Ar11 and _Ar12 each represent an arylalkynyl group, and are usually the same but may be different. The bonding positions of the arylalkynyl group on the anthracene are preferably the 9th and 10th positions of the anthracene, and the anthracenes are preferably bonded to each other at the 1st or 2nd positions. Specific examples of the arylalkynyl group include those described above.

Specific examples of compounds represented by formula (VIII) are shown below, but the present invention is not limited to these. Here, formulas (VII-1) to (VII-8) are used to show combinations of R ₀₁ and the like. Note that when R ₀₁ to R ₀₄ are shown collectively, they represent H unless otherwise specified, and when all are H, they are represented by H.

The amount of the dopant is preferably 0.01 to 10% by volume of the light-emitting layer.

On the other hand, the host material used in the light-emitting layer can be selected from the host materials, hole injecting and transporting compounds, and electron injecting and transporting compounds listed above.

Preferred examples of the hole-transporting host material, which is a hole-injecting and transporting compound, include aromatic tertiary amines including tetraaryldiamine derivatives represented by formula (II).

Below, hole-transporting host materials are listed, although some are included in or overlap with the compounds described above. Here, they are shown as combinations of Φ ₁ and the like according to formulas (H-1) to (H-12). Note that formulas (H-6a) to (H-6c) and formulas (H-7a) to (H-7e) have the same combinations, so they are collectively shown as H-6 and H-7.

On the other hand, as the electron-transporting host material, which is an electron-injecting and transporting compound, the above-mentioned quinolinolato metal complex is preferred.

The electron-transporting host materials are listed below, although some of them are included in or overlap with the above-mentioned compounds. Here, they are shown as combinations of Φ ₁₀₁ and the like according to formulas (E-1) to (E-14).

The hole-transporting host material and the electron-transporting host material in the light-emitting layer may each be used alone or in combination of two or more kinds.

In such an organic EL device, a hole injection and transport layer is provided on the anode side and an electron injection and/or transport layer is provided on the cathode side, sandwiching the light-emitting layer. In this case, the hole injection and/or transport layer, electron injection and/or transport layer, anode, cathode, etc. are the same as those described above.

The method for manufacturing an organic EL element, such as the method for forming an organic compound layer including a mixed layer, is also the same as described above.

The organic EL element of the present invention is typically used as a DC-driven EL element, but it can also be AC-driven or pulse-driven. The applied voltage is typically about 2 to 20 V.

Examples The following examples of the present invention will be used to further explain the present invention.

Example 1 A glass substrate having a 100 nm thick ITO transparent electrode (anode) was subjected to ultrasonic cleaning using a neutral detergent, acetone, and ethanol, then removed from the boiling ethanol, dried, and cleaned with UV ozone. The substrate was then fixed to a substrate holder in a vapor deposition system and the pressure was reduced to 1×10 ⁻⁶ torr.

Next, 4,4',4"-tris(-N-(-3-methylphenyl)-N-phenylamino)triphenylamine (MTDATA) was evaporated at a deposition rate of 2 nm/sec to a thickness of 50 nm to form a hole injection layer.

Exemplary compound II-102, N,N'-diphenyl-N,N'-bis-(-4'-(N-(m-biphenyl)-N-phenyl)aminobiphenyl-4-yl)benzidine, was evaporated at a deposition rate of 2 nm/sec to a thickness of 20 nm to form a hole transport layer.

Next, exemplary compound I-201 and tris(8-quinolinolato)aluminum (A1Q3) were vapor-deposited in a weight ratio of 2:100 to a thickness of 50 nm to form an emitting layer.

Next, while maintaining the reduced pressure, tris(8-quinolinolato)aluminum was deposited at a deposition rate of 0.2 nm/sec to a thickness of 10 nm as an electron injecting and transporting layer.

Furthermore, while maintaining the reduced pressure, MgAg (weight ratio 10:1) was evaporated at a deposition rate of 0.2 nm/sec to a thickness of 200 nm to form a cathode, and Al was evaporated to a thickness of 100 nm as a protective layer, completing an EL device.

When a voltage was applied to this EL element and a current was passed through it, the voltage was 14 V and 800 mA/cm.² 103,800 cd/m²Green light emission (maximum emission wavelength λmax = 525 nm, chromaticity coordinates x = 0.28, y = 0.68) was confirmed, and this emission was stable for over 10,000 hours in a dry argon atmosphere. There was no appearance or growth of non-luminescent areas. The brightness half-life was 10 mA/cm.²890 hours (initial brightness 1288 cd/m², drive voltage increase 1.5V), initial brightness 300cd/m²So it was 4,500 hours.

Example 2 A device was fabricated in the same manner as in Example 1. However, in the hole transport layer, Example Compound II-101, N,N'-diphenyl-N,N'-bis-(4'-(N,N-bis(m-biphenyl)aminobiphenyl-4-yl)benzidine, was used instead of Example Compound II-102.

When a voltage was applied to this EL element and a current was passed through it, the voltage was 14 V and 753 mA/cm.² 100480cd/m²Green light emission (maximum emission wavelength λmax = 525 nm, chromaticity coordinates x = 0.31, y = 0.66) was observed, and this emission was stable for over 10,000 hours in a dry nitrogen atmosphere. No partial non-luminous areas appeared or grew. The half-life of the luminance was 10 mA/cm.²680 hours (1433 cd/m², drive voltage increase 1.5V) Initial brightness 300cd/m²So it was 4000 hours.

Example 3 A device was fabricated in the same manner as in Example 1. However, Example Compound I-203 was used in place of Example Compound I-201 in the light-emitting layer.

When a voltage was applied to this EL element and a current was passed, it was 13 V and 553 mA/cm.² 69,500 cd/m²Green light emission (maximum emission wavelength λmax = 515 nm, chromaticity coordinates x = 0.26y = 0.66) was observed, and this emission was stable for more than 10,000 hours in a dry nitrogen atmosphere. No non-luminescent areas appeared or grew. The brightness half-life was 10 mA/cm.²600 hours (1078 cd/m², drive voltage increase 1.5V) Initial brightness 300 cd/m²So it was 4000 hours.

Example 4 A device was fabricated in the same manner as in Example 1. However, Example Compound I-202 was used in place of Example Compound I-201 in the light-emitting layer.

When a voltage was applied to this EL element and a current was passed, it was 14 V and 753 mA/cm.² 71,700 cd/m²Green light emission (maximum emission wavelength λmax = 515 nm, chromaticity coordinates x = 0.2, y = 0.64) was observed, and this emission was stable for over 10,000 hours in a dry nitrogen atmosphere. There was no appearance or growth of non-luminescent areas. The brightness half-life was 10 mA/cm.²800 hours (998 cd/m², drive voltage increase 1.5V) Initial brightness 300 cd/m²So it was 5000 hours.

Example 5 A device was fabricated in the same manner as in Example 1. However, Example Compound I-103 was used in place of Example Compound I-201 in the light-emitting layer.

When a voltage was applied to this EL element and a current was passed through it, the voltage was 16 V and 980 mA/cm.² 61,400 cd/m²Green light emission (maximum emission wavelength λmax = 510 nm, chromaticity coordinates x = 0.2, y = 0.63) was observed, and this emission was stable for over 10,000 hours in a dry nitrogen atmosphere. There was no appearance or growth of non-luminescent areas. The brightness half-life was 10 mA/cm.²3000 hours (730 cd/m², drive voltage increase 8.0V) Initial brightness 300 cd/m²So it was 10,000 hours.

Example 6 A device was fabricated in the same manner as in Example 1. However, Example Compound I-104 was used in place of Example Compound I-201 in the light-emitting layer.

When a voltage was applied to this EL element and a current was passed through it, the voltage was 12 V and 625 mA/cm² 40300cd/m²Green light emission (maximum emission wavelength λmax = 500 nm, chromaticity coordinates x = 0.2, y = 0.58) was observed, and this emission was stable for over 10,000 hours in a dry nitrogen atmosphere. There was no appearance or growth of non-luminescent areas. The brightness half-life was 10 mA/cm.²800 hours (680 cd/m², driving voltage increase 2.5V) Initial brightness 300 cd/m²So there were 4,000 hours.

Comparative Example 1 A device was fabricated in the same manner as in Example 1. However, N,N'-bis(-3-methylphenyl)-N,N'-diphenyl-4,4'-diaminobiphenyl (TPD001) was used in the hole transport layer instead of Example Compound II-102.

When a voltage was applied to this EL element and a current was passed, it was 13 V and 518 mA/cm.² 71,700 cd/m²Green light emission (maximum emission wavelength λmax = 525 nm, chromaticity coordinates x = 0.2, y = 0.66) was confirmed, and this emission was stable for more than 10,000 hours in a dry nitrogen atmosphere. The half-life of the luminance was 10 mA/cm.²65 hours (1281 cd/m) at constant current drive², drive voltage increase 1.5V) Initial brightness 300cd/m²So it was 800 hours.

Comparative Example 2 A device was fabricated in the same manner as in Example 1. However, N,N'-bis(-3-biphenyl)-N,N'-diphenyl-4,4'-diaminobiphenyl (TPD006) was used in the hole transport layer instead of Example Compound II-102.

When a voltage was applied to this EL element and a current was passed through it, the voltage was 14 V and 532 mA/cm.² 81,000 cd/m²Green light emission (maximum emission wavelength λmax = 525 nm, chromaticity coordinates x = 0.3 2y = 0.65) was confirmed, and this emission was stable for more than 10,000 hours in a dry nitrogen atmosphere. The half-life of the luminance was 10 mA/cm.²68 hours (1730 cd/m) at constant current drive², drive voltage increase 2.0V) Initial brightness 300cd/m²So it was 800 hours.

Comparative Example 3 A device was fabricated in the same manner as in Example 1. However, N,N'-bis(-3-t-butylphenyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (TPD008) was used in the hole transport layer instead of Example Compound II-102.

When a voltage was applied to this EL element and a current was passed, the voltage was 13 V and 508 mA/cm.² 79,300 cd/m²Green light emission (maximum emission wavelength λmax = 525 nm, chromaticity coordinates x = 0.3, y = 0.66) was confirmed, and this emission was stable for more than 10,000 hours in a dry nitrogen atmosphere. The half-life of the luminance was 10 mA/cm.²29 hours (1749 cd/m) at constant current drive², drive voltage increase 1.4V) Initial brightness 300cd/m²So it was 500 hours.

Comparative Example 4 A device was fabricated in the same manner as in Example 1. However, N,N,N',N'-tetrakis(-m-biphenyl)-1,1'-biphenyl-4,4'-diamine (TPD005) was used in the hole transport layer instead of Example Compound II-102.

When a voltage was applied to this EL element and a current was passed through it, the voltage was 14 V and 643 mA/cm.² 102,700 cd/m²The green light emission (maximum emission wavelength λmax = 525 nm, chromaticity coordinates x = 0.28, y = 0.68) was confirmed, and this emission was stable for more than 10,000 hours in a dry nitrogen atmosphere. The half-life of the luminance was 10 mA/cm.²115 hours with constant current drive (1842 cd/m², drive voltage increase 1.8V) Initial brightness 300cd/m²So it was 1600 hours.

Comparative Example 5 A device was fabricated in the same manner as in Example 1. However, in the hole injection layer, N,N'-diphenyl-N,N'-bis-(-4'-(N-(3-methylphenyl)-N-phenyl)aminobiphenyl-4-yl)benzidine (TPD017) was used instead of Example Compound II-102.

When a voltage was applied to this EL element and a current was passed, it was 14 V and 715 mA/cm.² 75,600 cd/m²Green light emission (maximum emission wavelength λmax = 525 nm, chromaticity coordinates x = 0.3 2y = 0.66) was observed, and this emission was stable for more than 10,000 hours in a dry nitrogen atmosphere. The half-life of the luminance was 10 mA/cm.²197 hours (1156 cd/m², drive voltage increase 2.3V) Initial brightness 300cd/m²So it was 2000 hours.

Comparative Example 6 A device was fabricated in the same manner as in Example 1. However, the following quinacridone (Example Compound III-1) was used in place of Example Compound I-201 in the light-emitting layer, and was incorporated at 0.75 wt%.

When a voltage was applied to this EL element and a current was passed, it was 16 V and 840 mA/cm.² 60,000 cd/m²The light emitted was yellow-green (maximum emission wavelength λmax = 540 nm, chromaticity coordinates x = 0.37, y = 0.60), and this light emission was stable for more than 10,000 hours in a dry nitrogen atmosphere. The half-life of the luminance was 10 mA/cm.²100 hours at constant current drive (800 cd/m², drive voltage increase 3.2V) Initial brightness 300cd/m²So it was 500 hours.

The characteristics of the organic EL elements of Examples 1 to 6 and Comparative Examples 1 to 6 are summarized in Tables 1 and 2.

From the above results, it is clear that the EL device of the present invention, which combines the coumarin derivative of formula (I) and the tetraaryldiamine derivative of formula (II), has a long luminescence life.

Example 7 A 1 μm-thick color filter film was formed on a glass substrate by coating using a Fuji Hunt CR-2000. A 5 μm-thick red fluorescent conversion film was then formed on top of this using a Fuji Hunt CT-1 with a 2 wt% solution of BASF Lumogen F Red 300 and baked. An overcoat was then formed on top of this using a Fuji Hunt CT-1 and baked to a thickness of 1 μm. A 100 nm-thick ITO film was sputtered on top of this to create a red element substrate with an anode. A device was fabricated using this substrate in the same manner as in Example 1.

The color filter material cuts off light with wavelengths of 580 nm or less, and the red fluorescent conversion material had a maximum emission wavelength λmax of 630 nm and a half-width of the spectrum around λmax of 50 nm.

When a voltage was applied to this EL element and a current was passed, it was 15 V and 615 mA/cm.² 9000 cd/m²Red light emission (maximum emission wavelength λmax = 600 nm, chromaticity coordinates x = 0.60, y = 0.38) was confirmed, and this light emission was stable for more than 10,000 hours in a dry nitrogen atmosphere. No partial non-luminescent areas appeared or grew.

Example 8 A device was fabricated in the same manner as in Example 1, except that the hole transport layer was formed by co-evaporation using Exemplified Compound II-102 and rubrene in a 10:1 (weight ratio).

When a voltage was applied to this EL element and a current was passed through it, the voltage was 14 V and 750 mA/cm.² 79,800 cd/m²Green light emission (maximum emission wavelength λmax = 525 nm, 555 nm, chromaticity coordinates x = 0.38, y = 0.57) was confirmed, and this emission was stable for more than 10,000 hours in a dry nitrogen atmosphere. The brightness half-life was 10 mA/cm.²700 hours (1173 cd/m) at constant current drive², drive voltage increase 2.5V), initial brightness 300cd/m²So it was 4500 hours.

Example 9 In Example 1, the light-emitting layer was formed using N,N,N',N'-tetrakis(-m-biphenyl)-1,1'-biphenyl-4,4'-diamine (TPD005) as the hole injection/transport compound and tris(8-quinolinolato)aluminum (AlQ3) as the electron injection/transport compound, deposited at approximately the same deposition rate of 0.5 nm/sec. Simultaneously, Example Compound I-103 was also deposited at a deposition rate of approximately 0.007 nm/sec to form a 40 nm-thick mixed layer. The ratio of TPD005:AlQ3:Example Compound I-103 in the mixed layer was 50:50:0.7 (film thickness ratio). Otherwise, the device was fabricated in the same manner as in Example 1. However, the hole injection/transport layer using MTDATA was 50 nm thick, the hole transport layer using TPD005 was 10 nm thick, and the electron injection/transport layer using AlQ3 was 40 nm thick.

When a voltage was applied to this EL element and a current was passed through it, the voltage was 18 V and 600 mA/cm.² 54,000 cd/m²Green light emission (maximum emission wavelength λmax = 510 nm, chromaticity coordinates x = 0.3, y = 0.60) was confirmed, and this emission was stable for more than 10,000 hours in a dry nitrogen atmosphere. The half-life of the luminance was 10 mA/cm.²6000 hours with constant current drive (1030 cd/m², drive voltage increase 2.0V), initial brightness 300cd/m²So it was 20,000 hours.

It was found that the characteristics were significantly improved compared to the device without the mixed layer of Comparative Example 4.

Example 10 In Example 1, a hole injection layer was formed to a thickness of 40 nm, a hole transport layer was formed to a thickness of 20 nm using TPD005 and rubrene (7 wt%), and an emissive layer was formed on top of this using TPD005, AlQ3, and exemplary compound I-103, as in Example 9. A device was fabricated in the same manner as in Example 1, except that:

When a voltage was applied to this EL element and a current was passed through it, the voltage was 12 V and 650 mA/cm.² 67,600 cd/m²Green light emission (maximum emission wavelength λmax = 510 nm, 550 nm, chromaticity coordinates x = 0.38, y = 0.56) was confirmed, and this emission was stable for more than 10,000 hours in a dry nitrogen atmosphere. The brightness half-life was 10 mA/cm.²6,500 hours (900 cd/m) at constant current drive², drive voltage increase 2.0V), initial brightness 300cd/m²So it was 25,000 hours.

Example 11 In Example 1, the light-emitting layer was formed by depositing exemplary compound II-102 as the hole injection/transport compound and tris(8-quinolinolato)aluminum (A1Q3) as the electron injection/transport compound at approximately the same deposition rate of 0.5 nm/sec. Simultaneously, exemplary compound I-201 was also deposited at a deposition rate of approximately 0.015 nm/sec to form a 40 nm-thick mixed layer. The ratio of exemplary compound II-102:AlQ3:exemplary compound I-201 in the mixed layer was 50:50:1.5 (film thickness ratio). A device was otherwise fabricated in the same manner as in Example 1. However, the hole injection/transport layer using MTDATA was 50 nm thick, the hole transport layer using II-102 was 10 nm thick, and the electron injection/transport layer using AlQ3 was 20 nm thick.

When a voltage was applied to this EL element and a current was passed through it, it was 13 V and 750 mA/cm² 98,000 cd/m²Green light emission (maximum emission wavelength λmax = 525 nm, chromaticity coordinates x = 0.29y = 0.67) was confirmed, and this emission was stable for more than 10,000 hours in a dry nitrogen atmosphere. The half-life of the luminance was 10 mA/cm.²4000 hours with constant current drive (1100 cd/m², drive voltage increase 2.0V), initial brightness 300cd/m²The result was 18,000 hours.

Example 12 In Example 1, a hole injection layer was formed to a thickness of 40 nm, a hole transport layer was formed to a thickness of 20 nm using exemplary compound II-102 and rubrene, and an emissive layer was formed on top of this using exemplary compound II-102, AlQ3, and exemplary compound I-201, as in Example 9. A device was fabricated in the same manner.

When a voltage was applied to this EL element and a current was passed, 13 V and 900 mA/cm² 80,000 cd/m²The emission was yellow-green (maximum emission wavelength λmax = 525 nm, 560 nm, chromaticity coordinate x = 0.40, y = 0.55), and this emission was stable for more than 10,000 hours in a dry nitrogen atmosphere. The half-life of the luminance was 10 mA/cm.²6000 hours (1050 cd/m) with constant current drive², drive voltage increase 1.5V), initial brightness 300cd/m² The result was 25,000 hours.

Example 13 In Examples 9 and 10, an element was fabricated using Example Compound III-1 (quinacridone) instead of Example Compound I-103, and its characteristics were examined. Excellent characteristics were obtained.

Example 14 In Examples 9 and 10, a device was fabricated using Example Compound IV-1 (a styrylamine compound) instead of Example Compound I-103, and its characteristics were examined. Good characteristics were obtained.

Example 15 In Examples 11 and 12, an element was fabricated using Example Compound II-1 (quinacridone) instead of Example Compound I-201, and its characteristics were examined. Good characteristics were obtained.

Example 16 In Examples 11 and 12, a device was fabricated using Example Compound IV-1 (a styrylamine compound) instead of Example Compound I-201, and its characteristics were examined. Excellent characteristics were obtained.

Examples of organic EL devices capable of emitting multicolor light are shown below. The compound HIM for the hole injection layer, the compound for the hole transport layer, and TPD005 used as the hole transporting host material in these examples are shown below.

Next, the emission spectra of a coumarin derivative (exemplified compound I-103), rubrene (exemplified compound I-22) and tris(8-quinolinolato)aluminum (AlQ3) are shown as reference examples.

<Reference Example 1> The emission spectrum of a coumarin derivative is shown in Figure 2. This emission spectrum was measured using an organic EL device with the following configuration.

Preparation of Organic EL Device A glass substrate (1.1 mm thick) having a 100 nm thick ITO transparent electrode (anode) was ultrasonically cleaned using a neutral detergent, acetone, and ethanol, removed from the boiling ethanol, dried, and cleaned with UV ozone. The substrate was then fixed to a substrate holder in a deposition apparatus and the pressure was reduced to 1 × ^10-6 Torr.

Next, N,N'-diphenyl-N,N'-bis[N-phenyl-N-4-tolyl(4-aminophenyl)]benzidine (HIM) was evaporated at a deposition rate of 2 nm/sec to a thickness of 50 nm to form a hole injection layer.

N,N,N',N'-tetrakis(-3-biphenyl-1-yl)benzidine (TPD005) was evaporated at a deposition rate of 2 nm/sec to a thickness of 10 nm to form a hole transport layer.

Furthermore, tris(8-quinolinolato)aluminum (AlQ3) and a coumarin derivative were co-deposited at deposition rates of 2 nm/sec and 0.02 nm/sec to form an electron-transporting light-emitting layer with a thickness of 70 nm and containing 1.0 vol% of the coumarin derivative.

Furthermore, while maintaining the reduced pressure, MgAg (weight ratio 10:1) was evaporated at a deposition rate of 0.2 nm/sec to a thickness of 200 nm to form a cathode, and Al was evaporated to a thickness of 100 nm as a protective layer, completing an organic EL device.

As can be seen from Figure 2, the coumarin derivative has a maximum emission wavelength around 510 nm. The half-width of the emission spectrum (the width at half the peak intensity) was 70 nm.

<Reference Example 2> The emission spectrum of rubrene is shown in Figure 3. This emission spectrum was measured using an organic EL device with the following configuration.

Preparation of Organic EL Device A glass substrate (1.1 mm thick) having a 100 nm thick ITO transparent electrode (anode) was ultrasonically cleaned using a neutral detergent, acetone, and ethanol, removed from the boiling ethanol, dried, and cleaned with UV ozone. The substrate was then fixed to a substrate holder in a deposition apparatus and the pressure was reduced to 1 × ^10-6 Torr.

Next, N,N'-diphenyl-N,N'-bis[N-phenyl-N-4-tolyl(4-aminophenyl)]benzidine (HIM) was evaporated at a deposition rate of 2 nm/sec to a thickness of 15 nm to form a hole injection layer.

N,N,N',N'-tetrakis-(-3-biphenyl-1-yl)benzidine (TPD005) was evaporated at a deposition rate of 2 nm/sec to a thickness of 15 nm to form a hole transport layer.

Furthermore, TPD005 and tris(8-quinolinolato)aluminum (AlQ3) were co-deposited at a volume ratio of 1:1, with 2.5 vol% of rubrene (Example Compound 1-20) added, to a thickness of 40 nm to form a mixed layer-type first emissive layer. The deposition rates were 0.05 nm/sec, 0.05 nm/sec, and 0.00025 nm/sec, respectively.

Next, while maintaining the reduced pressure, tris(8-quinolinolato)aluminum (AlQ3) was evaporated at a deposition rate of 0.2 nm/sec to a thickness of 55 nm as an electron injecting, transporting, and emitting layer.

Furthermore, while maintaining the reduced pressure, MgAg (weight ratio 10:1) was evaporated at a deposition rate of 0.2 nm/sec to a thickness of 200 nm to form a cathode, and Al was evaporated to a thickness of 100 nm as a protective layer, completing an organic EL device.

As can be seen from Figure 3, rubrene has an emission maximum wavelength at about 560 nm. The half-width of the emission spectrum was 75 nm.

<Reference Example 3> The emission spectrum of a coumarin derivative is shown in Figure 2. This emission spectrum was measured using an organic EL device with the following configuration.

Fabrication of Organic EL Devices The emission spectrum of tris(8-quinolinolato)aluminum (AlQ3) is shown in Figure 4. This emission spectrum was measured using an organic EL device with the following configuration:

Preparation of Organic EL Device A glass substrate (1.1 mm thick) having a 100 nm thick ITO transparent electrode (anode) was ultrasonically cleaned using a neutral detergent, acetone, and ethanol, removed from the boiling ethanol, dried, and then cleaned with UV ozone. The substrate was then fixed to a substrate holder in a deposition device and the pressure was reduced to 1 × ^10-6 torr.

Next, 4,4',4"-tris(-N-(-3-methylphenyl)-N-phenylamino)triphenylamine (MTDATA) was evaporated at a deposition rate of 2 nm/sec to a thickness of 40 nm to form a hole injection layer.

N,N,N'N'-tetrakis(-3-biphenyl-1-yl)benzidine (TPD005) was evaporated at a deposition rate of 2 nm/sec to a thickness of 15 nm to form a hole-transporting layer.

Next, while maintaining the reduced pressure, tris(8-quinolinolato)aluminum was deposited at a deposition rate of 0.2 nm/sec to a thickness of 70 nm as an electron injecting/transporting light-emitting layer.

Furthermore, while maintaining the reduced pressure, MgAg (weight ratio 10:1) was evaporated at a deposition rate of 0.2 nm/sec to a thickness of 200 nm to form a cathode, and Al was evaporated to a thickness of 100 nm as a protective layer, completing an EL device.

As can be seen from Figure 4, tris(8-quinolinolato)aluminum (AlQ3) has an emission maximum wavelength near 540 nm. The half-width of the emission spectrum was 110 nm.

Example 17 A glass substrate (1.1 mm thick) having a 100 nm thick ITO transparent electrode (anode) was subjected to ultrasonic cleaning using a neutral detergent, acetone, and ethanol, then removed from the boiling ethanol, dried, and cleaned with UV ozone. The substrate was then fixed to a substrate holder in a deposition apparatus and the pressure was reduced to 1 × ¹⁰ Torr.

Next, N,N'-diphenyl-N,N'-bis[N-phenyl-N-4-tolyl(4-aminophenyl)]benzidine (HIM) was evaporated at a deposition rate of 2 nm/sec to a thickness of 50 nm to form a hole injection layer.

N,N,N',N'-tetrakis-(-3-biphenyl-1-yl)benzidine (TPD005) was evaporated at a deposition rate of 2 nm/sec to a thickness of 15 nm to form a hole transport layer.

Furthermore, TPD005 and tris(8-quinolinolato)aluminum (AlQ3) were co-deposited at a volume ratio of 1:1, with 2.5 vol% of rubrene (Example Compound 1-22) added, to a thickness of 20 nm to form a mixed layer-type first emissive layer. The deposition rates were 0.05 nm/sec, 0.05 nm/sec, and 0.0025 nm/sec, respectively.

A mixed layer-type second emissive layer was formed by co-depositing TPD005 and AlQ3 at a volume ratio of 1:1, with 1.0 vol% of the exemplary coumarin derivative compound I-103, to a thickness of 20 nm. The deposition rates were 0.05 nm/sec, 0.05 nm/sec, and 0.001 nm/sec, respectively.

Next, while maintaining the reduced pressure, tris(8-quinolinolato)aluminum (AlQ3) was deposited at a deposition rate of 0.2 nm/sec to a thickness of 50 nm as an electron injecting, transporting, and emitting layer.

Furthermore, while maintaining the reduced pressure, MgAg (weight ratio 10:1) was evaporated at a deposition rate of 0.2 nm/sec to a thickness of 200 nm to form a cathode, and Al was evaporated to a thickness of 100 nm as a protective layer, completing an organic EL device.

When a voltage was applied to this organic EL element and a current was passed through it, 10 V, 50 mA/cm² 5000 cd/m²The light emitted was yellow-green (emission maximum wavelength λmax = 560 nm, 500 nm, chromaticity coordinates x = 0.39, y = 0.55), and this light emission was stable for over 1,000 hours in a dry argon atmosphere. There was no appearance or growth of non-luminescent areas. The brightness half-life was 10 mA/cm.²40,000 hours (initial brightness 1,000 cd/m) with constant current drive², initial drive voltage 7.2 V, drive voltage increase 3.0 V).

Figure 5 shows the emission spectrum. Figure 5 shows that both the coumarin derivative and rubrene emit light. The emission spectrum ratio C/R, coumarin derivative (510 nm)/rubrene (560 nm), was 0.65. The half-width of the emission spectrum (the width at half the maximum peak intensity) was 120 nm, indicating that both the coumarin derivative and rubrene emit light. Furthermore, the lifetime was significantly longer than in Example 9. Therefore, it is clear that the mixed layer containing rubrene contributes to the long lifetime.

Comparative Example 7 In Example 17, after forming a hole-transporting layer of TPD005, AlQ3, rubrene, and coumarin were co-evaporated at deposition rates of 0.1 nm/sec, 0.0025 nm/sec, and 0.001 nm/sec, respectively, to form a 40 nm-thick electron-transporting light-emitting layer containing 2.5 vol% rubrene and 1.0 vol% coumarin derivative, followed by the formation of a 50 nm-thick electron-injecting/transporting layer of AlQ3. An organic EL device was obtained in the same manner as in Example 17.

The resulting emission spectrum is shown in Figure 6. Figure 6 shows that only rubrene emitted light. The C/R ratio was 0, and the half-width of the emission spectrum was 70 nm.

Comparative Example 8 An organic EL device was obtained in the same manner as in Comparative Example 7, except that a hole-transporting emissive layer was formed using TPD005 instead of AlQ3 as the host material for the emissive layer.

The emission spectrum is shown in Figure 7. From Figure 7, it can be seen that only rubrene is emitting light. The C/R ratio was 0, and the half-width of the emission spectrum was 70 nm.

Comparative Example 9 In Example 17, after forming a hole-transporting layer of TPD005, AlQ3 and rubrene were co-deposited at deposition rates of 0.1 nm/sec and 0.0025 nm/sec, respectively, to form a 20 nm-thick electron-transporting emissive layer containing 2.5 vol% rubrene. AlQ3 and a coumarin derivative were then co-deposited at deposition rates of 0.1 nm/sec and 0.001 nm/sec, respectively, to form a 20 nm-thick electron-transporting emissive layer containing 1.0 vol% coumarin derivative. Subsequently, a 50 nm-thick electron-injecting/transporting layer of AlQ3 was formed. An organic EL device was obtained in the same manner as in Example 17.

The resulting emission spectrum is shown in Figure 8. Figure 8 indicates that the emission was solely from rubrene. The C/R ratio was 0, and the half-width of the emission spectrum was 70 nm.

Comparative Example 10 An organic EL device was obtained in the same manner as in Comparative Example 9, except that two hole-transporting emissive layers were formed, both of which used TPD005 as the host material for the two-layer emissive layer.

The emission spectrum is shown in Figure 9. From Figure 9, it can be seen that the emission is from the coumarin derivative and AlQ3. The half-width of the spectrum was 90 nm.

Comparative Example 11 In Example 17, after forming a hole-transporting layer of TPD005, TPD005 and rubrene were co-deposited at deposition rates of 0.1 nm/sec and 0.0025 nm/sec, respectively, to form a hole-transporting emissive layer containing 2.5 vol% rubrene to a thickness of 20 nm. Next, AlQ3 and a coumarin derivative were co-deposited at deposition rates of 0.1 nm/sec and 0.001 nm/sec, respectively, to form a 20 nm-thick electron-transporting emissive layer containing 1.0 vol% coumarin derivative. Subsequently, a 50 nm-thick electron-injecting/transporting layer of AlQ3 was formed. An organic EL device was obtained in the same manner as in Example 17.

When a voltage was applied to this organic EL element and a current was passed, the voltage was 12 V and 50 mA/cm.² 4500 cd/m²The yellow-green light emission (maximum emission wavelength λmax = 560 nm, 510 nm, chromaticity coordinates x = 0.42, y = 0.54) was observed, and this emission was stable for more than 10 hours in a dry argon atmosphere. There was no appearance or growth of non-luminescent areas. The brightness half-life was 10 mA/cm.²100 hours (initial brightness 1000 cd/m) with constant current drive², initial driving voltage 6.5 V, driving voltage increase 3.0 V).

The emission spectra are shown in Figure 10. It can be seen that both the coumarin derivative and rubrene emit light. The emission spectral ratio C/R in this case was 0.5. The half-width was 80 nm.

Although this material exhibits luminescence from coumarin derivatives and rubrene, the luminescence lifetime is short and it is not practical.

Example 18 In Example 17, after forming a hole-transporting layer of TPD005, TPD005, AlQ3, and rubrene were co-deposited at deposition rates of 0.05 nm/sec, 0.05 nm/sec, and 0.0025 nm/sec, respectively, to form a 20 nm-thick mixed-layer light-emitting layer with a TPD005:AlQ3 ratio of 1:1 and 2.5 vol% rubrene. Next, AlQ3 and a coumarin derivative were co-deposited at deposition rates of 0.1 nm/sec and 0.001 nm/sec, respectively, to form a 20 nm-thick electron-transporting light-emitting layer containing 1.0 vol% coumarin derivative. Then, an organic EL device was obtained in the same manner as in Example 17, except that a 50 nm-thick electron-injecting/transporting layer of AlQ3 was formed.

When a voltage was applied to this organic EL element and a current was passed, the voltage was 12 V and 50 mA/cm.² 4000 cd/m²The yellow-green light emitted from the sample (maximum emission wavelength λmax = 510 nm, 560 nm, chromaticity coordinates x = 0.42, y = 0.54) was stable for over 1,000 hours in a dry argon atmosphere. There was no evidence of the appearance or growth of non-luminescent areas. The brightness half-life was 10 mA/cm.²40,000 hours (initial brightness 1,000 cd/m) with constant current drive², initial drive voltage 6.9 V, drive voltage increase 3.0 V).

The emission spectra are shown in Figure 11. It can be seen that both the coumarin derivative and rubrene emit light. The emission spectral ratio C/R in this case was 0.42. The half-width was 130 nm.

Example 19 An organic EL device was obtained in the same manner as in Example 17, except that the volume ratio of the TPD005 and AlQ3 host materials in the first and second mixed-layer-type emitting layers was TPD005/AlQ3 = 75/25.

When a voltage was applied to this organic EL element and a current was passed, the voltage was 12 V and 50 mA/cm.² 4100 cd/m²The light emitted was yellow-green (maximum emission wavelength λmax = 510 nm, 560 nm, chromaticity coordinates x = 0.32, y = 0.58), and this light emission was stable for over 1,000 hours in a dry argon atmosphere. There was no appearance or growth of non-luminescent areas. The brightness half-life was 10 mA/cm.²30,000 hours (initial brightness 900 cd/m) with constant current drive², initial driving voltage 7.2 V, driving voltage increase 2.5 V).

The emission spectrum is shown in Figure 12. It can be seen from Figure 12 that both the coumarin derivative and rubrene emit light. The emission spectrum ratio C/R in this case was 1.4. The half-width was 120 nm. This shows that by changing the ratio of the host materials in the mixed layer, a different C/R ratio from that in Example 17 can be obtained.

Example 20 An organic EL device was obtained in the same manner as in Example 17, except that the volume ratio of the TPD005 and AlQ3 host materials in the first and second mixed-layer-type emitting layers was TPD005/AlQ3 = 66/33.

When a voltage was applied to this organic EL element and a current was passed, the voltage was 12 V and 50 mA/cm.² 3500 cd/m²The light emitted was yellow-green (emission maximum wavelength λmax = 510 nm, 560 nm, chromaticity coordinates x = 0.34, y = 0.57), and this light emission was stable for over 1,000 hours in a dry argon atmosphere. There was no appearance or growth of non-luminescent areas. The brightness half-life was 10 mA/cm.²20,000 hours (initial brightness 900 cd/m) with constant current drive²The initial driving voltage was 7.3 V, and the driving voltage increase was 2.5 V.

The emission spectrum is shown in Figure 13. It can be seen from Figure 13 that both the coumarin derivative and rubrene emit light. The emission spectrum ratio C/R in this case was 1.4. The half-width was 130 nm. This shows that by changing the ratio of the host materials in the mixed layer, a different C/R ratio from that in Example 17 can be obtained.

Example 21 An organic EL device was obtained in the same manner as in Example 17, except that the volume ratio of the TPD005 and AlQ3 host materials in the first and second mixed-layer-type emitting layers was TPD005/AlQ3 = 25/75.

When a voltage was applied to this organic EL element and a current was passed, the voltage was 12 V and 50 mA/cm.² 4200 cd/m²The light emitted was yellow-green (emission maximum wavelength λmax = 510 nm, 560 nm, chromaticity coordinates x = 0.47, y = 0.51), and this light emission was stable for over 1,000 hours in a dry argon atmosphere. There was no appearance or growth of non-luminescent areas. The brightness half-life was 10 mA/cm.²15,000 hours (initial brightness 900 cd/m) with constant current drive², initial driving voltage 7.5 V, driving voltage increase 2.5 V).

The emission spectrum is shown in Figure 14. It can be seen that both the coumarin derivative and rubrene emit light. The emission spectrum ratio C/R in this case was 0.25. The half-width was 80 nm. Thus, it can be seen that a different C/R ratio from that in Example 17 can be obtained by changing the ratio of the host materials in the mixed layer.

The results of Examples 17 to 21 show that the emission characteristics change when the host material of the emitting layer is changed.

Furthermore, when the results of Comparative Examples 7 to 11 are also considered, it is clear that a method for producing multicolor light emission is achieved by adjusting the carrier transport properties of the host in the light-emitting layer to fall within the range of the present invention.

From the above, it was found that by selecting the carrier transport properties of the stacked light-emitting layers as in the present invention (preferably by providing two or more light-emitting layers, including a mixed-layer type light-emitting layer, as a bipolar light-emitting layer), it is possible to obtain practical levels of light emission from two or more light-emitting species. Therefore, it was confirmed that multicolor emission is possible.

Furthermore, it can be seen that by changing the mixture ratio of the host material in the bipolar mixed layer, it is possible to change the contribution from each of the two or more emissive layers. Furthermore, the mixture ratio can be changed independently for each layer, which can also lead to changes in the light emission. Such bipolar host materials can be not only mixed types, but also single bipolar materials. The key to this invention is to select the carrier transport properties of the stacked emissive layers, and changing the carrier transport properties requires changing the materials.

INDUSTRIAL APPLICABILITY From the above, it is clear that organic EL devices using the compounds of the present invention are capable of high-brightness emission and are highly reliable, with minimal decrease in brightness and increase in driving voltage during continuous emission. Furthermore, they can stably emit light from multiple fluorescent substances, achieving light emission across a wide spectral range, enabling multicolor emission. Furthermore, the multicolor emission spectrum can be freely designed.

───────────────────────────────────────────────────── Continued from the front page (72) Inventor: Tetsuji Inoue TDK Corporation, 1-13-1 Nihonbashi, Chuo-ku, Tokyo (Note) This publication is based on the publication published internationally by the International Bureau of Patents (WIPO). The effect of the international publication of the Japanese patent application (Japanese utility model registration application) related to this publication arises pursuant to Article 184-10, Paragraph 1 of the Patent Act (Article 48-13, Paragraph 2 of the Utility Model Act) and is unrelated to this publication.

Claims (18)

[Claims] 1. An organic EL device having an emitting layer containing a coumarin derivative represented by the following formula (I) and a hole-injecting and/or hole-transporting layer containing a tetraaryldiamine derivative represented by the following formula (II):[In formula (I), R₁, R₂and R₃R each represent a hydrogen atom, a cyano group, a carboxyl group, an alkyl group, an aryl group, an acyl group, an ester group, or a heterocyclic group, and may be the same or different.₁~R₃may be bonded to each other to form a ring.₄and R₇each represents a hydrogen atom, an alkyl group, or an aryl group, R₅and R₆each represents an alkyl group or an aryl group, R₄and R₅, R₅and R₆and R₆and R₇may be bonded to each other to form a ring.] [In formula (II), Ar₁, Ar₂, Ar₃and Ar₄each represents an aryl group, Ar₁ ~Ar₄At least one of R is a polycyclic aryl group derived from a fused ring or ring assembly having two or more benzene rings.₁₁and R₁₂R each represents an alkyl group, and p and q each represent 0 or an integer from 1 to 4.₁₃and R₁₄each represents an aryl group, and r and s each represent 0 or an integer from 1 to 5. 2. The organic EL device of claim 1, wherein the light-emitting layer containing the coumarin derivative is formed by doping the coumarin derivative as a dopant into a host material. 3. The organic EL device of claim 2, wherein the host material is a quinolinonato metal complex. 4. An organic EL device having a light-emitting layer in which a mixed layer containing a hole injecting and transporting compound and an electron injecting and transporting compound is further doped with a coumarin derivative represented by the following formula (I), a quinacridone compound represented by the following formula (III), or a styrylamine compound represented by the following formula (IV) as a dopant. [In formula (I), _R1 , _R2 , and _R3 each represent a hydrogen atom, a cyano group, a carboxyl group, an alkyl group, an aryl group, an acyl group, an ester group, or a heterocyclic group, which may be the same or different, and _R1 to _R3 may each be bonded to each other to form a ring. _R4 and _R7 each represent a hydrogen atom, an alkyl group, or an aryl group. _R5 and _R6 each represent an alkyl group or an aryl group, and _R4 and _R5 , _R5 and _R6 , and _R6 and _R7 may each be bonded to each other to form a ring.] [In formula (III), _R21 and _R22 each represent a hydrogen atom, an alkyl group, or an aryl group, and may be the same or different. _R23 and _R24 each represent an alkyl group or an aryl group, and t and u each represent 0 or an integer of 1 to 4. When t or u is 2 or greater, adjacent _R23s or adjacent _R24s may be bonded to each other to form a ring.] [In formula (IV), _R31 represents a hydrogen atom or an aryl group. _R32 and _R33 represent a hydrogen atom, an aryl group, or an alkenyl group, and may be the same or different. _R34 represents an arylamino group or an arylaminoaryl group. v is 0 or an integer of 1 to 5.] 5. The organic EL device of claim 4, wherein the hole injecting and transporting compound is an aromatic tertiary amine, and the electron injecting and transporting compound is a quinolinonato metal complex. 6. The organic EL device of claim 5, wherein the aromatic tertiary amine is a tetraaryldiamine derivative represented by the following formula (II):[In formula (II), Ar₁, Ar₂, Ar₃and Ar₄each represents an aryl group, Ar₁ ~Ar₄At least one of R is a polycyclic aryl group derived from a fused ring or ring assembly having two or more benzene rings.₁₁and R₁₂R each represents an alkyl group, and p and q each represent 0 or an integer from 1 to 4.₁₃and R₁₄each represents an aryl group, and r and s each represent 0 or an integer from 1 to 5. 7. The organic EL device of any one of claims 1 to 6, wherein the light-emitting layer is sandwiched between at least one hole-injecting and/or hole-transporting layer and at least one electron-injecting and/or electron-transporting layer. 8. The organic EL device of claim 1, 2, 3, or 7, wherein the hole injection and/or transport layer is further doped with rubrene as a dopant. 9. The organic EL element of any one of claims 1 to 8, wherein a color filter and/or a fluorescence conversion filter is disposed on the light extraction side, and the light is extracted through the color filter and/or the fluorescence conversion filter. 10. An organic EL device having two or more light-emitting layers including a bipolar light-emitting layer, a hole-injecting and/or transporting layer on the anode side of the light-emitting layer, and an electron-injecting and/or transporting layer on the cathode side, wherein the two or more light-emitting layers are a combination of bipolar light-emitting layers, or a combination of a bipolar light-emitting layer and a hole-transporting light-emitting layer on the anode side of the bipolar light-emitting layer and/or an electron-transporting light-emitting layer on the cathode side. 11. The organic EL device of claim 10, wherein the bipolar light-emitting layer is a mixed layer containing a hole injecting and transporting compound and an electron injecting and transporting compound. 12. The organic EL element of claim 11, wherein the two or more light-emitting layers are all mixed layers. 13. The organic EL device of any one of claims 10 to 12, wherein at least one of the two or more light-emitting layers is doped with a dopant. 14. The organic EL device of any one of claims 10 to 13, wherein all of the two or more light-emitting layers are doped with a dopant. 15. The organic EL element of any one of claims 10 to 14, wherein the two or more light-emitting layers have different light-emitting characteristics, and the light-emitting layer having the longer maximum emission wavelength is disposed closer to the anode. 16. The organic EL device of any one of claims 13 to 15, wherein the dopant is a compound having a naphthacene skeleton. 17. The organic EL device according to any one of claims 13 to 16, wherein the dopant is a coumarin represented by the following formula (I): [In formula (I), _R1 , _R2 , and _R3 each represent a hydrogen atom, a cyano group, a carboxyl group, an alkyl group, an aryl group, an acyl group, an ester group, or a heterocyclic group, which may be the same or different, and _R1 to _R3 may each be bonded to each other to form a ring. _R4 and _R7 each represent a hydrogen atom, an alkyl group, or an aryl group. _R5 and _R6 each represent an alkyl group or an aryl group, and _R4 and _R5 , _R5 and _R6 , and _R6 and _R7 may each be bonded to each other to form a ring.] 18. The organic EL device according to any one of claims 11 to 17, wherein the hole injecting and transporting compound is an aromatic tertiary amine, and the electron injecting and transporting compound is a quinolinonato metal complex.