JP2003059670A - Light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting element that is superior in thermal stability and has high utilization efficiency of electrical energy, and is superior in color purity. SOLUTION: In the light-emitting element having a structure in which at least a positive electrode, a luminous layer, an electron carrier layer, and a negative electrode are laminated in order, the electron carrier layer has an ionization potential 0.1 eV or more larger than the ionization potential of the luminous layer, and the material that mainly constitutes the luminous layer and the electron carrier layer is made of an organic compound having sublimation performance, and further, the organic compound that mainly constitutes the electron carrier layer has a molecular weight of 400 or more and a glass transition temperature of 90 deg.C or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device capable of converting electric energy into light, such as a display device, a flat panel display, a backlight, a lighting, an interior, a sign, a signboard, an electrophotographic machine and an optical signal generator. The present invention relates to a light emitting device that can be used in the field of.

[0002]

2. Description of the Related Art In recent years, active research has been carried out on organic laminated thin-film light emitting devices in which electrons injected from a cathode and holes injected from an anode emit light when recombined in an organic phosphor sandwiched between both electrodes. ing. This element has attracted attention because it is thin, has high-luminance light emission under a low driving voltage, and has multicolor light emission by selecting a fluorescent material.

This work was carried out by Kodak Corp. W. Tan
Since g. et al. showed that an organic laminated thin film device emits light with high brightness (Appl. Phys. Lett. 51 (12)
21, p. 913, 1987), many research institutes are investigating. A typical structure of an organic laminated thin film light emitting device presented by a research group of Kodak Company is a hole transporting diamine compound and a light emitting layer on an ITO glass substrate.
Hydroxyquinoline aluminum and M as cathode
g: Ag was sequentially provided, and a green emission of 1000 cd / m ² was possible with a driving voltage of about 10V.

As a constitution of this organic laminated thin film light emitting device, there is known one in which an electron transporting layer is appropriately provided in addition to the above anode / hole transporting layer / light emitting layer / cathode. The hole transport layer has a function of transporting holes injected from the anode to the light emitting layer, and one electron transport layer transports electrons injected from the cathode to the light emitting layer. It is known that by inserting these layers between the light emitting layer and both electrodes, luminous efficiency and durability are improved. Examples of device configurations using these include anode / hole transport layer / light emitting layer / electron transport layer / cathode, anode / light emitting layer / electron transport layer / cathode, and the like.

[0005]

However, conventionally, even if a few existing materials are used as the electron transport material, the desired emission color is generated because of the interaction with the light emitting material or the emission of the electron transport material itself being mixed. Was not obtained, and high efficiency light emission was obtained, but the durability was short.
For example, although a specific phenanthroline derivative emits light with high efficiency, there is a problem in that a thin film becomes white turbid due to crystallization due to long-time current application. In addition, there are quinolinol metal complexes and benzoquinolinol metal complexes that exhibit relatively good characteristics in light emission efficiency and durability. When used as a transport material, the light emission of these materials may be mixed and the color purity may deteriorate. Further, there are examples using a diquinoline derivative or a triquinoline derivative, but although it shows relatively good durability, it is not clear whether it is effective in improving the luminous efficiency because there is no description of the ionization potential value. It is also unknown whether it functions as an electron transport material in long-wavelength side light emission such as red light emission. In addition, JP-A-2-
Although there are 195683 and JP-A 2000-306676, it is unclear whether the electron-transporting material used for these gives a stable amorphous film, and only low emission brightness is obtained, and further durability is obtained. Is not described at all, and it may not emit light stably for a long time.

An object of the present invention is to solve the problems of the prior art, and to provide a light emitting device which is excellent in thermal stability, high in luminous efficiency, high in luminance and excellent in color purity.

[0007]

According to the present invention, in a light emitting device having a structure in which at least an anode, a light emitting layer, an electron transporting layer and a cathode are laminated in this order, the material mainly constituting the light emitting layer and the electron transporting layer is sublimated. Consisting of organic compounds having properties,
The difference in ionization potential between the light emitting layer and the electron transporting layer is 0.
It is a light emitting device characterized by being 1 eV or more, an organic compound having a molecular weight of 400 or more and a glass transition temperature of 90 ° C. or more of a material mainly constituting an electron transport layer.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the anode is a conductive metal oxide such as tin oxide, indium oxide, indium tin oxide (ITO), or a conductive metal oxide such as gold, silver or chromium if it is transparent for extracting light. Inorganic conductive substances such as metals, copper iodide and copper sulfide, and conductive polymers such as polythiophene, polypyrrole and polyaniline are not particularly limited, but ITO glass or Nesa glass is particularly preferable. The resistance of the transparent electrode is not limited as long as it can supply a sufficient current for light emission of the device, but is preferably low resistance from the viewpoint of power consumption of the device. Eg 3
Although an ITO substrate having a resistance of 00 Ω / □ or less functions as an element electrode, it is now possible to supply a substrate having a resistance of about 10 Ω / □, so it is particularly desirable to use a low resistance product. The thickness of ITO can be arbitrarily selected according to the resistance value, but it is usually used in the range of 100 to 300 nm. Further, soda lime glass, non-alkali glass or the like is used for the glass substrate, and the thickness thereof is sufficient if it is sufficient to maintain mechanical strength.
It is sufficient if it is mm or more. For the glass material,
Alkali-free glass is preferable because it is preferable that the amount of ions eluted from the glass is small, but soda lime glass coated with a barrier coat such as SiO ₂ is also available on the market. Furthermore, if the anode functions stably, the substrate does not have to be glass, and the anode may be formed on a plastic substrate, for example. The ITO film forming method is not particularly limited, such as an electron beam method, a sputtering method and a chemical reaction method.

The cathode is not particularly limited as long as it is a substance capable of efficiently injecting electrons into the organic material layer, but in general, platinum,
Examples thereof include gold, silver, copper, iron, tin, zinc, aluminum, indium, chromium, lithium, sodium, potassium, calcium, magnesium, cesium and strontium. In order to improve the electron injection efficiency and improve the device characteristics, lithium, sodium, potassium, calcium, magnesium, cesium, strontium or an alloy containing these low work function metals is effective. But,
Generally, these low work function metals are often unstable in the atmosphere. For example, the organic layer is doped with a small amount of lithium, cesium, or magnesium (1 nm or less in a vacuum vapor deposition film thickness meter display) to be stable. Although a method using an electrode having a high temperature can be mentioned as a preferable example, it is not particularly limited to these because an inorganic salt such as lithium fluoride can be used. Further, for protecting electrodes, metals such as platinum, gold, silver, copper, iron, tin, aluminum and indium, or alloys using these metals, and silica, titania, inorganic substances such as silicon nitride, polyvinyl alcohol, vinyl chloride, A preferred example is stacking of hydrocarbon-based polymers. These electrodes are also manufactured by resistance heating, electron beam, sputtering,
There is no particular limitation as long as conduction such as ion plating and coating can be achieved.

The light emitting layer is a layer in which a light emitting substance is actually formed, and the light emitting material may be composed of only one kind of organic compound, or may be a mixed layer composed of two or more kinds of organic compounds. From the viewpoint of improving luminous efficiency, color purity, and durability, it is preferable to be composed of two or more kinds of organic compounds. As a combination of two or more kinds of organic compounds, a combination of a host material and a dopant material can be mentioned. In this case, the host material is mainly responsible for the thin film forming ability and the charge transporting ability of the light emitting layer, while the dopant material is mainly responsible for the light emitting ability, and the energy transfer type and the carrier trap type are proposed for the light emitting mechanism. . In the energy transfer type, charges injected from both electrodes are recombined in the host layer to excite the host material, energy is transferred from the excited host material to the dopant material, and finally light emission from the dopant material is obtained. Is. On the other hand, in the carrier trap type, carriers that have moved in the host layer are recombined directly on the dopant material, and the excited dopant emits light. In any case, by using a dopant material having a high color purity and a high fluorescence quantum yield in a solution state as a dopant material having a light emitting ability, it is possible to obtain light emission with high color purity and high efficiency. Furthermore, the addition of the dopant material may cause the film quality of the host layer, which is the base material of the film formation, to tend to reduce the crystallinity, and in this case, the durability is also improved.

When such a combination of the host material and the dopant material is used, the dopant material may be contained in the entire host material, partially contained, or any of them. Further, the dopant material may be laminated, dispersed or any. Further, if the doping amount is too large, the concentration quenching phenomenon occurs, so it is preferable to use 10% by weight or less, and more preferably 2% by weight or less with respect to the host substance.

Further, from the viewpoint of improving the durability, a dopant material may be added for the purpose of trapping the change of the film quality or the excessive carriers without bearing the light emitting ability. The doping conditions in this case are the same as above.

Specific examples of the organic compound or the host material in the combination of the host and the dopant material when the light emitting layer is formed alone include the following. Fused ring derivatives such as anthracene, pyrene, and perylene, pyrazine, naphthyridine, quinoxaline,
Heterocyclic derivatives such as pyrrolopyridine, pyrimidine, thiophene and thioxanthene, tris (8-quinolinolato)
Aluminum complex, quinolinol metal complex such as benzoquinolinol metal complex, bipyridine metal complex, rhodamine metal complex, azomethine metal complex, distyrylbenzene derivative, tetraphenylbutadiene derivative, stilbene derivative, aldazine derivative, coumarin derivative, phthalimide derivative, naphthalimide Derivatives, perinone derivatives, pyrrolopyrrole derivatives, cyclopentadiene derivatives, imidazole derivatives and oxazole derivatives, thiazole derivatives, oxadiazole derivatives, thiadiazole derivatives, triazole derivatives and other azole derivatives and their metal complexes, benzoxazole, benzimidazole, benzothiazole, etc. Benzazole derivatives and their metal complexes, triphenylamine derivatives and carbazole derivatives Emissions derivatives, phosphorescent materials such as merocyanine derivative, a porphyrin derivative ,, tris (2-phenylpyridine) iridium complex, a polymeric, polyphenylene vinylene derivatives, polyparaphenylene derivatives, and polythiophene derivatives may be used.

As the dopant material, conventionally known condensed polycyclic aromatic hydrocarbons such as anthracene and perylene, coumarin derivatives such as 7-dimethylamino-4-methylcoumarin, and bis (diisopropylphenyl) perylene. Naphthalimide derivatives such as tetracarboxylic acid imides, perinone derivatives, rare earth complexes such as acetylacetone and Eu complexes having benzoylacetone and phenanthroline as ligands, dicyanomethylenepyran derivatives, dicyanomethylenethiopyran derivatives, magnesium phthalocyanine, aluminum chlorophthalocyanine Metal phthalocyanine derivatives, porphyrin derivatives, rhodamine derivatives, deazaflavin derivatives, coumarin derivatives, oxazine compounds, thioxanthene derivatives, etc.
Cyanine dye derivative, fluorescein derivative, acridine derivative, quinacridone derivative, pyrrolopyrrole derivative, quinazoline derivative, pyrrolopyridine derivative, squarylium derivative, violanthrone derivative, phenazine derivative, acridone derivative, diazaflavin derivative, pyrromethene derivative and its metal complex, phenoxazine derivative, Phenoxazone derivative, thiadiazolopylene derivative, tris (2-phenylpyridine) iridium complex,
Tris (2-phenylpyridyl) iridium complex, tris {2- (2-thiophenyl) pyridyl} iridium complex, tris {2- (2-benzothiophenyl) pyridyl} iridium complex, tris (2-phenylbenzothiazole) iridium complex , Tris (2-phenylbenzoxazole) iridium complex, trisbenzoquinolineiridium complex, bis (2-phenylpyridyl) (acetylacetonato) iridium complex, bis {2- (2-
Thiophenyl) pyridyl} iridium complex, bis {2-
(2-benzothiophenyl) pyridyl} (acetylacetonato) iridium complex, bis (2-phenylbenzothiazole) (acetylacetonato) iridium complex, bis (2-phenylbenzoxazole) (acetylacetonato) iridium complex, bis Phosphorescent materials such as benzoquinoline (acetylacetonato) iridium complex and platinum porphyrin complex are known, but these may be used alone or in combination of a plurality of derivatives.

The electron transport layer is a layer in which electrons are injected from the cathode,
Further, it is a layer that controls the transport of electrons, has a high electron injection efficiency, and it is desirable to transport the injected electrons efficiently. However, when considering the transport balance of holes and electrons, when the role mainly capable of efficiently blocking the holes from the anode from flowing to the cathode side without recombining, the electron transport capability is not so much. Even if it is not high, it has the same effect of improving the luminous efficiency as a material having a high electron transporting ability. Therefore, the electron-transporting layer in the present invention also includes a hole-blocking layer that can efficiently block the movement of holes as a synonym.

The electron transport layer in the present invention has an ionization potential larger than that of the light emitting layer by 0.1 eV or more.
If the ionization potential difference from the light emitting layer is 0.1 eV or more, holes injected from the anode can be efficiently prevented from flowing to the cathode side without recombination in the light emitting layer, but at high temperature. In consideration of the operating environment and the like, it is more preferably 0.15 eV or more, and even more preferably 0.
It is 2 eV or more. It is reported that the absolute value of the ionization potential differs depending on the measurement conditions and the like. However, the ionization potential difference between the two layers in the present invention is that a single layer of each layer is separately formed on an ITO glass substrate by a thin film formed by vacuum vapor deposition. Atmosphere UV photoelectron analyzer (AC-1,
It is calculated from the ionization potential value measured using Riken Keiki Co., Ltd.). Further, the ionization potential value may change depending on the state of the sample. Therefore, when the light emitting layer or the electron transport layer is a mixed layer composed of two or more kinds of materials, it is necessary to measure the ionization potential value of the mixed layer.

The material mainly constituting the electron transport layer of the present invention is an organic compound having a molecular weight of 400 or more. Even if electrons can be efficiently transported unless the molecular weight is 400 or more,
The electron transport layer is thermally unstable and easily crystallized, so that stable light emission cannot be obtained even when electricity is applied for a long time. Molecular weight is 4
If it is 00 or more, stable light emission can be obtained, but it is more preferably 600 or more. Furthermore, the material has a glass transition temperature of 90 ° C. or higher. The glass transition temperature is one index of the thermal stability of organic compounds, and the higher the glass transition temperature, the more thermally stable an amorphous thin film can be provided. When the glass transition temperature is 90 ° C. or higher as in the present invention, thermally stable and stable light emission can be obtained over long-time energization, but more preferably in consideration of an operating environment at high temperature. It is 120 ° C. or higher, and more preferably 150 ° C. or higher. Further, from the viewpoint of providing a film that is hard to crystallize, the higher the cold crystallization temperature is, more preferably 140 ° C. or higher, more preferably 170 ° C. or higher, further preferably 200 ° C.
That is all. Furthermore, it is preferable that no cold crystallization temperature is observed from the viewpoint of giving a film that is extremely hard to crystallize. What is not observed here is the case where the temperature of the sample is raised at a certain constant rate when measuring the glass transition temperature or cold crystallization temperature of the sample, and the sample is kept at a temperature higher than the glass transition temperature. It does not mean whether crystallization is observed when it is held for a long time. In the present invention, a value obtained by measuring a powder sample by a temperature modulation DSC method using a differential scanning calorimeter is adopted.

The chemical structure of the organic compound constituting the electron transport layer is thiophene dioxide, pyrazole, imidazole, triazole, tetrazole,
Electrons such as aromatic heterocycles such as oxazole, oxadiazole, thiazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrimidone, pyrazine and triazine, and aromatic hydrocarbons such as benzene, naphthalene, anthracene, phenanthrene, pyrene, styrene and stilbene. Those that can be a mother skeleton having a transporting ability and these mother skeletons are modified with a functional group having an electron transporting ability such as a vinyl group, a carbonyl group, a carboxyl group, an aldehyde group, a nitro group, a cyano group, a halogen, a sulfone, or a phosphorus oxide. The organic compound may have a plurality of mother skeletons in order to have the above-mentioned thermal stability while maintaining the electron transporting ability, as long as it contains the compound Multiple mother skeletons linked by conjugated bonds, aromatic hydrocarbons, and aromatic heterocycles Rukoto is preferable. The mother skeleton may be substituted or unsubstituted except for the site used for the connection. Similarly, one of the linking groups may be substituted or unsubstituted at a site other than the site used for linking, and one kind or a mixture thereof may be used.

Among such organic compounds, it is preferable that at least one pyridine ring is contained in the mother skeleton because the electron transporting ability and / or the hole blocking ability is high, and the pyridine ring is more preferable. Is quinoline or naphthyridine condensed with benzene or pyridine, and more preferably benzoquinoline or phenanthroline with quinoline condensed with benzene or pyridine. These mother skeletons may be substituted or non-substituted except for the site used for connection. In addition to the pyridine ring, phosphorus oxide can be mentioned as a preferable mother skeleton.

Specific examples of preferable linking groups include those shown below.

[0021]

[Chemical 1]

[0022]

[Chemical 2]

[0023]

[Chemical 3]

These linking groups can be commercially available or can be synthesized according to a conventional method. Specific examples of some skeletons are shown below.

The synthesis of 9,9'-spirobifluorene skeleton is described in J. Am. Chem. Soc., Vol. 52 (1930), page 2881, JP-A-7-278537. Compound
(a) Synthesis of 9,9-spirobifluorene ”and the like. 2-Bromobiphenyl was Grignarded with metallic magnesium in THF, then from room temperature to 50 ° C.
Then, it is reacted with 9-fluorenone and treated by a conventional method. The obtained hydroxy form is heated and dehydrated in acetic acid with a small amount of hydrochloric acid added, and then treated by a conventional method.

Furthermore, instead of 9-fluorenone, 9-
Spiroxanthene fluorene is obtained using xanthone, spirothioxanthene fluorene is obtained using 9-thioxanthone, and spiro-N-butyl-acridinefluorene is obtained using N-butyl-acridone.
Anthrone can be used to obtain spiro dihydroanthracene fluorene, and suberon can be used to obtain spiro dihydrodibenzocycloheptanefluorene.

The synthesis of the 9,9'-spirobi (9H-9-silafluorene) skeleton is described in J. Am. Chem. So as a reference.
c., vol.80 (1958), page 1883 and the like.
The 2,2'-dibromobiphenyl can be reacted with metallic lithium in ether and then with tetrachlorosilane at a given temperature and treated in a conventional manner.

The synthesis of the tetraphenylmethane skeleton is described in Angew. Chem. Int. Ed. Engl. Vol. 25 (1986) No. 12 as a reference.
Pp. 1098, Tetrahedron Letters, vol.38 (1997)
Pp. 1487 and the like. Triphenylmethanol or triphenylmethyl chloride was mixed with aniline or aniline hydrochloride in a solvent-free or acetic acid solvent.
The reaction was carried out at 0 ° C to 220 ° C, the obtained intermediate was treated by a conventional method to be isolated, and then reacted with isoamyl nitrite at -10 ° C in a mixed solvent of ethanol / sulfuric acid, and phosphinic acid was added and heated. Reflux and treat in the usual manner.

The synthesis of the hexabenzopropellane skeleton is described in Libigs Ann. Chem., Vol. 749 (1971) No. 38 by reference.
Page etc. are mentioned. The 9-fluorenone is reacted with triethyl phosphite and treated with methanol to give the spiroketone compound. Next, the spiroketone compound in ether is reacted with the lithio form of 2-bromobiphenyl at a predetermined temperature and treated by a conventional method. The obtained hydroxy form is heated and dehydrated in acetic acid and methanesulfonic acid. Can be treated by law.

The mother skeleton can be introduced into the linking group according to a conventional method depending on the mother skeleton. For example, a benzoquinoline or phenanthroline mother skeleton can be introduced with a reactive substituent such as an acetyl group. After the introduction, a method of forming a benzoquinoline ring or a phenanthroline ring,
After introducing a reactive substituent such as iodo group or bromo group,
Examples thereof include a method of adding a benzoquinoline ring or a phenanthroline ring.

The acetyl group can be introduced by a general and convenient acylation of Friedel-Crafts. As a reference, an example “A. Starting compound (f) 2,2′-diacetyl-9,” disclosed in JP-A-7-278537 can be used.
9,9'-spirobifluorene from 9,9'-spirobifluorene via 9'-spirobifluorene-
2,2'-dicarboxylic acid "and Helvetiva Chimica Acta, v
ol.52 (1969) p.1210 "Experimenteller Tell 2,2 '
-diacetyl-9,9'-spirobifluorene (IV) "and the like. The acetyl group can be introduced by reacting the linking group with acetyl chloride and aluminum chloride in 1,2-dichloroethane at 50 ° C. and treating by a conventional method.

A method for introducing a benzoquinoline skeleton or a phenanthroline skeleton from an acetyl group is described as a reference.
J. Org. Chem. 1996, 61. p. 3021 “1,3-Di (benzo) [h] q.
uinolin-2-yl) benzene] ”, Tetrahedron Letters, vol.4
0 (1999). 7321 page scheme and the like. The acetyl form of the linking group is 1-amino-in dioxane at 60 ° C.
2-naphthalenecarbaldehyde or 8-amino-
This is a method of reacting with a corresponding naphthalene derivative such as 7-quinolinecarbaldehyde or a quinoline derivative and potassium hydroxide, and treating with a conventional method.

The introduction of the iodo group is described in Japanese Chemical Journal, Vol. 92, No. 11 (1971), page 1023, "1.
Iodination of 1,1-methylnaphthalene "and Tetrahedron
Letters, vol. 38 (1997), page 1487. The linking group is reacted with iodine and periodate dihydrate in 80% acetic acid at 80 ° C. and treated in a conventional manner, or in carbon tetrachloride at 50 ° C. to 60 ° C. with iodine and bis (trifluoroacetoxy). ) Iodobenzene can be introduced by reacting with iodobenzene and treating in a conventional manner.

The introduction of the bromo group is described in Reference of JP-A No. 7-278537, "A. Synthesis of starting compound (a) 9,9'-spirobifluorene", Angew.
Chem. Int. Ed. Engl. 25 (1986) No. 12, page 1098, and the like. The linking group can be reacted with bromine at room temperature and treated in a conventional manner to introduce a bromo group.

To introduce a benzoquinoline skeleton or a phenanthroline skeleton from an iodo group or a bromo group, the iodo or bromo form of the linking group is lithiated with metallic lithium and then reacted with the corresponding anhydrous benzoquinoline or anhydrous phenanthroline, There is a method of treating with water and manganese dioxide.

Further, the introduction of the benzoquinoline skeleton or the phenanthroline skeleton into the linking group is not limited to the method of first synthesizing the linking group and then introducing the reactive substituent into the linking group as described above. A linking group having a reactive substituent introduced therein may be directly obtained by using a raw material containing a reactive substituent. For example, regarding the synthesis of a linking group having an acetyl group introduced below, 4-acetylboronic acid is coupled to 2,2′-bromobiphenyl by Suzuki coupling (Reference: Chem. Rev., vol. 95 (1995)). 2457
It can be obtained by reacting under the conditions of page).

[0037]

[Chemical 4]

The electron transport layer in the present invention is not limited to one kind of the above organic compounds, and a layer may be formed by mixing or laminating a plurality of materials. Furthermore, although it does not have an electron-transporting ability by itself, an organic compound, an inorganic compound, or a metal complex can be electron-transported for various purposes such as improving the transporting ability, thermal stability, and electrochemical stability of the entire electron-transporting layer. You may add to a material and form an electron carrying layer.

The above-mentioned organic compounds mainly constituting the light emitting layer and the electron transporting layer have sublimability. The sublimability used here does not mean that a solid is vaporized without passing through a liquid, but is used in a broad sense that it volatilizes without decomposition when heated in a vacuum and a thin film can be formed. ing. Although the light emitting device of the present invention has a laminated structure, it is easy to form the laminated structure by a dry process such as a vacuum deposition method if it is an organic compound having a sublimation property. Also,
Also in the case of forming a doping layer in the light emitting layer, a doping layer excellent in controllability can be formed by using a co-evaporation method with a host material or a method of pre-mixing with a host material and then performing vapor deposition at the same time. Furthermore, it is necessary to obtain desired patterned light emission when forming a display that uses a matrix or segment system, but an organic compound having a sublimation property can be easily patterned by patterning by a dry process. .

The material mainly constituting the light emitting layer and the electron transporting layer in the present invention means that the properties of the thin film state of each layer are determined by the material. For example, in a light emitting layer made of a combination of a host and a dopant material, the material mainly constituting the light emitting layer means a host material.

The light emitting device of the present invention preferably further has a hole transport layer between the anode and the light emitting layer for the purpose of efficiently recombination of holes and electrons in the light emitting layer. The hole transport layer is a layer that is responsible for injecting holes from the anode and further transporting holes, and specifically, as the hole transport material, N, N′-diphenyl-N, N′-bis. (3-methylphenyl) -4,4'-diphenyl-1,
1'-diamine, N, N'-bis (1-naphthyl)-
N, N'-diphenyl-4,4'-diphenyl-1,
Triphenylamines such as 1'-diamine, bis (N
-Allylcarbazole) or bis (N-alkylcarbazole) s, etc., carbazole derivatives, pyrazoline derivatives, stilbene compounds, distyryl derivatives, hydrazone compounds, oxadiazole derivatives, phthalocyanine derivatives, heterocyclic compounds represented by porphyrin derivatives, In the polymer system, polycarbonate having a side chain of the monomer, a styrene derivative, polyvinylcarbazole,
Examples thereof include polysilane, but the compound is not particularly limited as long as it is a compound capable of forming a thin film necessary for manufacturing an element, injecting holes from the anode, and further transporting holes.
These may be used alone, or a plurality of derivatives may be mixed or laminated to form a layer. Furthermore, although it does not have a hole-transporting ability by itself, an organic compound, an inorganic compound, or a metal complex is used for various purposes such as improving the transportability, thermal stability, and electrochemical stability of the entire hole-transporting layer. It may be added to the hole transport material to form a hole transport layer.

The method of forming each layer is not particularly limited, such as resistance heating vapor deposition, electron beam vapor deposition, sputtering, molecular lamination method, coating method, etc., but resistance heating vapor deposition and electron beam vapor deposition are usually preferable in terms of characteristics. . The thickness of the layer cannot be limited because it depends on the resistance value of the light emitting substance, but is selected from the range of 1 to 1000 nm.

The electric energy mainly refers to a direct current, but it is also possible to use a pulse current or an alternating current.
The current value and the voltage value are not particularly limited, but in consideration of the power consumption and life of the element, it is necessary to obtain the maximum brightness with the lowest possible energy.

The matrix in the present invention refers to a matrix in which pixels for display are arranged, and a character or an image is displayed by a set of pixels. The shape and size of the pixel depend on the application. For example, a quadrangular pixel with a side of 300 μm or less is usually used for displaying images and characters on a personal computer, a monitor, a television, and in the case of a large display such as a display panel, a pixel with a side of mm is used. . For monochrome display, pixels of the same color may be arranged, but for color display, red, red,
Display green and blue pixels side by side. In this case, there are typically a delta type and a stripe type. The driving method of this matrix may be either a line-sequential driving method or an active matrix. The line-sequential drive has an advantage that the structure is simpler, but in consideration of the operation characteristics, the active matrix may be superior in some cases. Therefore, it is necessary to properly use the active matrix depending on the application.

The segment type in the present invention means that a pattern is formed so as to display predetermined information,
The light will be emitted in the determined area. Examples include time and temperature display on digital clocks and thermometers, operation status display of audio equipment and electromagnetic cookers, and panel display of automobiles. The matrix display and the segment display may coexist in the same panel.

The light emitting device of the present invention is also preferably used as a backlight. The backlight is mainly used to improve the visibility of a display device that does not emit light by itself, and is used for a liquid crystal display device, a clock, an audio device, an automobile panel, a display board, a sign, and the like. In particular, as a backlight for a liquid crystal display device, in particular, a personal computer for which thinning has been a problem, it is difficult to reduce the thickness because the conventional type is composed of a fluorescent lamp and a light guide plate. The backlight using the light emitting element in 1 is characterized by being thin and lightweight.

[0047]

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

Example 1 A glass substrate (manufactured by Asahi Glass Co., Ltd., 15 Ω / □, electron beam evaporation product) on which an ITO transparent conductive film was deposited to a thickness of 150 nm was cut into 30 × 40 mm and etched. The obtained substrate was ultrasonically cleaned with acetone and "semicoclin 56" for 15 minutes each, and then with ultrapure water. Subsequently, ultrasonic cleaning was performed for 15 minutes with isopropyl alcohol, and then immersion was performed for 15 minutes in hot methanol for drying. This substrate was subjected to UV-ozone treatment for 1 hour immediately before producing an element and placed in a vacuum vapor deposition apparatus so that the degree of vacuum in the apparatus was 1 × 10 ⁻⁵ Pa.
Exhausted until below. By the resistance heating method, copper phthalocyanine (CuP) was used as the first hole injecting and transporting layer.
c) is vapor-deposited to a thickness of 10 nm, and then N, N′-diphenyl-N, N′-bis (1-naphthyl) -1,1′-diphenyl-4,4′-diamine (as a second hole transport layer (α-NPD) was laminated in a thickness of 50 nm. Further, subsequently, using tris (8-quinolinolato) aluminum (III) (Alq3) as a host material and 3- (2-benzothiazolyl) -7-diethylaminocoumarin as a dopant material in the light emitting layer portion, the dopant is 1.0 wt%.
Was co-deposited to a thickness of 25 nm. Then, ETM1 shown below as an electron transport layer was laminated to a thickness of 25 nm. Subsequently, 0.2 nm of lithium was doped, and finally 150 nm of aluminum was vapor-deposited to form a cathode, and a 5 × 5 mm square device was manufactured. The ionization potential of the light emitting layer is 5.78 eV, the ionization potential of the electron transport layer is 5.97 eV, and the ionization potential difference between both layers is 0.19 eV. Further, ETM1 has a molecular weight of 609 and a glass transition temperature of 112 ° C. From this light emitting device, green light emission based on a dopant material having an emission peak wavelength of 513 nm was obtained with an applied voltage of 10 V, and the emission luminance was 5000 cd / m ² . The initial luminance retention rate of this light-emitting element was 70% after 500 hours had passed after energization, and a uniform light-emitting surface was maintained.

[0049]

[Chemical 5]

Comparative Example 1 A light emitting device was produced in exactly the same manner as in Example 1 except that Alq3 was used as the electron transport layer. The ionization potential of the electron transport layer is 5.79 eV, and the ionization potential difference between the light emitting layer and the electron transport layer is 0.01 eV.
The molecular weight of Alq3 is 459. From this light emitting device, the emission peak wavelength was 513 with an applied voltage of 10V.
Green emission was obtained based on the nm dopant material, and the emission luminance was 3000 cd / m ² .

Comparative Example 2 A light emitting device was produced in exactly the same manner as in Example 1 except that 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) was used as the electron transport layer. The ionization potential of the electron transport layer is 6.20 eV, and the ionization potential difference between the light emitting layer and the electron transport layer is 0.42 eV. The molecular weight of BCP is 360. From this light emitting device, green light emission based on a dopant material having an emission peak wavelength of 523 nm was obtained with an applied voltage of 10 V, and the emission luminance was 8000 cd / m ² . However, the initial luminance retention rate of this light-emitting element after 500 hours had passed after energization was 50% or less, and unevenness was observed on the light-emitting surface.

Example 2 Example 1 was repeated except that EM1 shown below was used as the host material and EM2 was also used as the dopant material in the light emitting layer portion.
A light emitting device was manufactured in exactly the same manner as in. The ionization potential of the light emitting layer is 5.65 eV, and the ionization potential difference between the light emitting layer and the electron transport layer is 0.42 eV.
From this light emitting device, blue light emission based on a dopant material having an emission peak wavelength of 477 nm was obtained at an applied voltage of 15 V, and the emission luminance was 3500 cd / m ² .

[0053]

[Chemical 6]

Example 3 1,4-diketo-2,5 using the light emitting layer portion as a host material
-Bis (3,5-di-t-butylbenzyl) -3,6-
Bis (4-biphenyl) pyrrolo [3,4-c] pyrrole, using EM3 shown below as a dopant material,
A light emitting device was produced in exactly the same manner as in Example 1 except that co-evaporation was performed to a thickness of 15 nm so that the dopant was 1.0 wt%. The ionization potential of the light emitting layer is 5.79.
eV, and the difference in ionization potential between the light emitting layer and the electron transport layer is 0.28 eV. From this light emitting device,
With an applied voltage of V, red emission based on the dopant material having an emission peak wavelength of 629 nm was obtained, and the emission luminance was 8000.
It was cd / m ² .

[0055]

[Chemical 7]

Comparative Example 3 A light emitting device was produced in exactly the same manner as in Example 5 except that Alq3 was used as the electron transport layer. The ionization potential difference between the light emitting layer and the electron transport layer is 0 eV. From this light emitting device, red light emission was not obtained with an applied voltage of 10 V.
Orange emission was obtained with a peak emission wavelength of 29 nm and a shoulder peak near 535 nm.

Example 4 A glass substrate (manufactured by Asahi Glass Co., Ltd., 15Ω / □, electron beam evaporation product) on which an ITO transparent conductive film was deposited to a thickness of 150 nm was cut into 30 × 40 mm, and a 300 μm pitch (remaining width of 270 μm was obtained by a photolithography method. ) × 32 stripes were patterned. In order to facilitate electrical connection to the outside, one side of the ITO stripe in the long side direction is 1.
Widened to 27 mm pitch (opening width 800 μm). The obtained substrate was ultrasonically cleaned with acetone and "semicoclin 56" for 15 minutes each, and then with ultrapure water.
Subsequently, ultrasonic cleaning was performed for 15 minutes with isopropyl alcohol, and then immersion was performed for 15 minutes in hot methanol for drying.
This substrate was subjected to UV-ozone treatment for 1 hour immediately before producing an element and placed in a vacuum vapor deposition apparatus, and the degree of vacuum in the apparatus was 5
Evacuation was performed until the pressure became × 10 ^-4 Pa or less. First, CuPc was evaporated to a thickness of 10 nm by the resistance heating method, and then α-
50 nm of NPD was vapor-deposited. Next, the light emitting layer portion was co-evaporated to a thickness of 25 nm using Alq3 as a host material and 3- (2-benzothiazolyl) -7-diethylaminocoumarin as a dopant material so that the dopant might be 1.0 wt%. Then ETM as electron transport layer
1 was laminated to a thickness of 25 nm. Then, the Kovar plate with a thickness of 50 μm was wet-etched with 16 250 pieces.
A mask provided with a μm opening (remaining width of 50 μm, corresponding to a pitch of 300 μm) was exchanged in a vacuum so as to be orthogonal to the ITO stripe, and fixed with a magnet from the back surface so that the mask and the ITO substrate were in close contact. Then, after doping the organic layer with 0.5 nm of lithium, aluminum was vapor-deposited with 200 nm to produce a 32 × 16 dot matrix device. When this device was matrix-driven, characters could be displayed without crosstalk.

[0058]

INDUSTRIAL APPLICABILITY The present invention can provide a red light emitting device having excellent thermal stability, high utilization efficiency of electric energy, and excellent color purity.

Claims (4)

[Claims] 1. In a light emitting device having a structure in which at least an anode, a light emitting layer, an electron transporting layer and a cathode are laminated in this order, the electron transporting layer is more than 0.1 than the ionization potential of the light emitting layer.
The material having a large ionization potential of eV or more, the material mainly constituting the light emitting layer and the electron transport layer is composed of a sublimable organic compound, and the organic compound mainly constituting the electron transport layer has a molecular weight of 400 or more and a glass transition. Temperature is 90
A light-emitting element having a temperature of not less than ° C. 2. The light emitting device according to claim 1, further comprising a hole transport layer between the anode and the light emitting layer. 3. The light emitting device according to claim 1, wherein the light emitting layer is composed of at least two kinds of organic compounds. 4. The light emitting device according to claim 1, wherein the light emitting device constitutes a display for displaying by a matrix and / or segment system.