JP2002367786A - Luminous element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a luminous element with good thermal stability, good electric energy utilization efficiency and with good color purity. SOLUTION: With the luminous element having a sequentially laminated structure of at least a positive electrode, a luminous layer, a hole transport layer, an electron transport layer and a negative electrode, the relation between the luminous layer and the electron transport layer is (Ip (ETL)-Ip (EML))>(Ea (ETL)-Ea (EML)). The main material composing the luminous layer and the electron transport layer is made of an organic compound with sublimatic nature, and the main material composing the electron transport layer is an organic compound with molecular mass of not less than 400. [Ea : electron affinity (eV), Ip : ionization potential (eV), EML: luminous layer, and ETL: electron transport layer].

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

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

[0003] This study was carried out by Kodak Corporation. W. Tan
g. et al. showed that the organic laminated thin film element emits light with high luminance (Appl. Phys. Lett. 51 (12)
21, p. 913, 1987), and many research institutions are conducting studies. A typical configuration of an organic laminated thin film light emitting device presented by a research group of Kodak Company is a diamine compound having a hole transporting property and a light emitting layer on an ITO glass substrate.
Aluminum hydroxyquinoline and M as cathode
g: Ag was sequentially provided, and green light emission of 1000 cd / m ² was possible at a driving voltage of about 10 V.

With respect to the structure of this organic layered thin film light emitting device, there is known a structure in which an electron transport layer is appropriately provided in addition to the anode / hole transport layer / light emitting layer / cathode. The hole transporting layer has a function of transporting holes injected from the anode to the light emitting layer, and one electron transporting layer transports electrons injected from the cathode to the light emitting layer. It is known that luminous efficiency and durability are improved by inserting these layers between the light emitting layer and both electrodes. 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 small number of existing electron transporting materials are used, a desired emission color is required because of the interaction with the light emitting material or the mixed emission of the electron transporting material. However, there have been problems such as the inability to obtain light emission and the high efficiency of light emission but short durability.
For example, although a specific phenanthroline derivative shows high-efficiency light emission, there is a problem that the thin film becomes cloudy due to crystallization due to long-term energization. In addition, quinolinol metal complexes and benzoquinolinol metal complexes exhibit relatively good properties in terms of luminous efficiency and durability. When used as a transport material, the luminescence of these materials themselves may be mixed and the color purity may be degraded. Japanese Patent Application Laid-Open No. H10-74584 reports a preferable relationship between the electron affinity and / or the ionization potential between the light emitting layer and the electron transporting layer. What level of luminous efficiency and color purity were obtained? Unknown.

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

[0007]

Means for Solving the Problems The present invention, at least an anode, an emission layer, an electron transport layer, the light-emitting element having a cathode are sequentially stacked, light-emitting layer, the electron transport layer (I _{p
(ETL) -I p (EML)} )> (E a (ETL) -E a
(EML)), wherein the material mainly constituting the light emitting layer and the electron transport layer is composed of an organic compound having sublimability, and the material mainly constituting the electron transport layer has a molecular weight of 40.
A light-emitting element, which is a compound having 0 or more organic compounds. (Where E _a : electron affinity (eV), I _p : ionization potential (eV), EML: light-emitting layer, ETL:
Electron transport layer)

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the anode is made of a conductive metal oxide such as tin oxide, indium oxide, indium tin oxide (ITO) or a metal such as gold, silver or chromium if it is transparent to extract light. Although not particularly limited, such as metals, inorganic conductive substances such as copper iodide and copper sulfide, and conductive polymers such as polythiophene, polypyrrole, and polyaniline, it is particularly preferable to use ITO glass or Nesa glass. The resistance of the transparent electrode is not limited as long as a current sufficient for light emission of the element can be supplied, but is preferably low from the viewpoint of power consumption of the element. For example, 3
Although an ITO substrate having a resistance of 00 Ω / □ or less functions as an element electrode, a substrate having a resistance of about 10 Ω / □ can be supplied at present. The thickness of the ITO can be arbitrarily selected according to the resistance value, but is usually used in a range of usually 100 to 300 nm. Further, the glass substrate is made of soda lime glass, non-alkali glass, or the like, and the thickness only needs to be sufficient to maintain the mechanical strength.
mm or more is sufficient. For the glass material,
Alkali-free glass is preferred because less ions elute from the glass is preferred, but soda-lime glass with a barrier coat such as SiO ₂ is also commercially available and can be used. Furthermore, if the anode functions stably, the substrate does not need to be glass, and for example, the anode may be formed on a plastic substrate. The method of forming the ITO film 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 can efficiently inject electrons into the present organic material layer.
Gold, silver, copper, iron, tin, zinc, aluminum, indium, chromium, lithium, sodium, potassium, calcium, magnesium, cesium, strontium and the like. Lithium, sodium, potassium, calcium, magnesium, cesium, strontium, or an alloy containing these low work function metals is effective for improving the device characteristics by increasing the electron injection efficiency. But,
In general, these low work function metals are generally unstable in the air. For example, an organic layer is doped with a small amount of lithium, cesium, or magnesium (1 nm or less as indicated by a film thickness gauge by vacuum evaporation) to obtain stability. Although a method using an electrode having a high density can be cited as a preferable example, the method is not particularly limited to these, since an inorganic salt such as lithium fluoride can be used. Furthermore, for electrode protection, metals such as platinum, gold, silver, copper, iron, tin, aluminum and indium, or alloys using these metals, and inorganic substances such as silica, titania and silicon nitride, polyvinyl alcohol, vinyl chloride, It is preferable to laminate a hydrocarbon polymer or the like. These electrodes are manufactured by resistance heating, electron beam, sputtering,
There is no particular limitation as long as conduction such as ion plating and coating can be obtained.

The light emitting layer is a layer on which a light emitting substance is actually formed. 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 organic compounds. As a combination composed of two or more organic compounds, a combination of a host material and a dopant material can be given. In this case, the host material mainly plays a role of forming a thin film and a charge transporting ability of the light emitting layer, while the dopant material mainly plays a role of the light emitting ability, and an energy transfer type and a carrier trap type have been proposed for the light emitting mechanism. . In the energy transfer type, charges injected from both electrodes recombine 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. It is. On the other hand, in the carrier trap type, carriers moving in the host layer recombine 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, light emission with high color purity and high efficiency can be obtained. Further, the film quality of the host layer, which forms the base for film formation, sometimes acts in the direction of decreasing the crystallinity by the addition of the dopant material, 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, or may be contained partially. Further, the dopant material may be laminated, dispersed, or the like. When the doping amount is too large, the concentration quenching phenomenon occurs. Therefore, the doping amount is preferably 10% by weight or less, more preferably 2% by weight or less based on the host material.

Further, there is a case where a dopant material is added for the purpose of changing the film quality or trapping excessive carriers without taking on the luminous ability from the viewpoint of improving the durability. 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 forming the light emitting layer alone include the following. Fused ring derivatives such as anthracene, pyrene and perylene, pyrazine, naphthyridine, quinoxaline,
Heterocyclic derivatives such as pyrrolopyridine, pyrimidine, thiophene, thioxanthene, tris (8-quinolinolato)
Quinolinol metal complexes such as aluminum complexes, benzoquinolinol metal complexes, bipyridine metal complexes, rhodamine metal complexes, azomethine metal complexes, distyrylbenzene derivatives, tetraphenylbutadiene derivatives, stilbene derivatives, aldazine derivatives, coumarin derivatives, phthalimide derivatives, naphthalimide Derivatives, perinone derivatives, pyrrolopyrrole derivatives, cyclopentadiene derivatives, imidazole derivatives, oxazole derivatives, thiazole derivatives, azole derivatives such as oxadiazole derivatives, thiadiazole derivatives, triazole derivatives and their metal complexes, benzoxazole, benzimidazole, benzothiazole, etc. Benzazole derivatives and metal complexes thereof, and 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 Eu complexes having acetylacetone, benzoylacetone and phenanthroline as ligands, dicyanomethylenepyran derivatives, dicyanomethylenethiopyran derivatives, magnesium phthalocyanine, aluminum chlorophthalocyanine Such as metal phthalocyanine derivatives, porphyrin derivatives, rhodamine derivatives, deazaflavin derivatives, coumarin derivatives, oxazine compounds, thioxanthene derivatives,
Cyanine dye derivative, fluorescein derivative, acridine derivative, quinacridone derivative, pyrrolopyrrole derivative, quinazoline derivative, pyrrolopyridine derivative, squarylium derivative, biolanthrone derivative, phenazine derivative, acridone derivative, diazaflavin derivative, pyromethene derivative and its metal complex, phenoxazine derivative, Phosphorescent materials such as a phenoxazone derivative, a thiadiazolopyrene derivative, and a tris (2-phenylpyridine) iridium complex are known, but these may be used alone or as a mixture of a plurality of derivatives.

Electrons are injected from the cathode into the electron transport layer.
Further, the layer is responsible for transporting electrons, has a high electron injection efficiency, and desirably transports the injected electrons efficiently. However, considering the transport balance between holes and electrons, if the role of mainly preventing the holes from the anode from flowing to the cathode side without recombination is to play an important role, the electron transport capability is not so high. Even if it is not high, the effect of improving the luminous efficiency is equivalent to a material having a high electron transporting ability. Therefore, the electron transport layer in the present invention includes a hole blocking layer capable of efficiently blocking the movement of holes as the same thing.

The material mainly constituting the electron transport layer of the present invention comprises an organic compound having a molecular weight of 400 or more. Molecular weight 4
If it is less than 00, even if electrons can be transported efficiently, the electron transport layer is thermally unstable and tends to be crystallized, and stable light emission cannot be obtained for a long-time energization. If the molecular weight is 400 or more, stable light emission can be obtained, but more preferably 600 or more.

Further, as an index of the thermal stability of the organic compound, a glass transition temperature is cited, and a higher glass transition temperature can provide a thermally stable amorphous thin film. The material mainly constituting the electron transporting layer of the present invention preferably has a glass transition temperature of 90 ° C. or higher, more preferably 120 ° C. or higher, and still more preferably 150 ° C.
That is all. Further, from the viewpoint of providing a film that is difficult to crystallize, it is preferable that the cold crystallization temperature is higher, specifically, it is preferably 140 ° C. or higher, more preferably 1 ° C. or higher.
70 ° C. or higher, more preferably 200 ° C. or higher. Furthermore, it is preferable that a cold crystallization temperature is not observed from the viewpoint of giving a film which is extremely difficult to crystallize. What is not observed here is the case where the sample is heated at a certain rate when measuring the glass transition temperature or the cold crystallization temperature of the sample. It does not mean whether or not crystallization is observed when held for a 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 such an electron transporting layer includes thiophenedoxide, 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. Modification of functional groups having electron transport ability such as vinyl group, carbonyl group, carboxyl group, aldehyde group, nitro group, cyano group, halogen, sulfone, and phosphorus oxide which can be a parent skeleton having transport ability The organic compound may have any chemical structure as long as the organic compound contains a plurality of mother skeletons, while maintaining the electron transporting ability and having the above-mentioned thermal stability. Multiple mother skeletons are linked by conjugated bonds, aromatic hydrocarbons and aromatic heterocycles Rukoto is preferable. The mother skeleton may be substituted or unsubstituted at positions other than those used for connection. Similarly, one of the linking groups may be substituted or unsubstituted at a portion other than the portion used for linking, and may be a single type or a mixture thereof. Among such organic compounds, since the electron transporting ability and the hole blocking ability are high, it is preferable that the mother skeleton contains at least one pyridine ring, and more preferably, the pyridine ring has benzene or pyridine. Condensed quinoline or naphthyridine, more preferably benzoquinoline or phenanthroline in which quinoline is condensed with benzene or pyridine. These mother skeletons may be substituted or unsubstituted at positions other than those used for connection. In addition, other than the pyridine ring, phosphorus oxide can also be mentioned as a preferable mother skeleton.

The electron transporting layer in the present invention is not limited to one kind of the above-mentioned organic compound, but may be formed by mixing or laminating a plurality of materials. In addition, although it does not have electron transport capability itself, it transports organic compounds, inorganic compounds, and metal complexes for various purposes such as improving the transport capability, thermal stability, and electrochemical stability of the entire electron transport layer. The electron transport layer may be formed by adding to the material.

The organic compounds mainly constituting the light emitting layer and the electron transporting layer have sublimability. Sublimation here is not strictly meaning that a solid evaporates without passing through a liquid, but is used in a broad sense that it evaporates without decomposing when heated in a vacuum and a thin film can be formed. ing. Although the light-emitting element of the present invention has a laminated structure, it is easy to form a laminated structure by a dry process such as a vacuum deposition method as long as it is an organic compound having a sublimation property. Also,
In the case where a doping layer is formed in a light emitting layer, a doping layer with excellent controllability can be formed by using a co-evaporation method with a host material or a method in which the doping layer is mixed with a host material in advance and then simultaneously evaporated. Furthermore, it is necessary to obtain a desired patterned light emission when constructing a display for displaying in a matrix or segment system, etc., but if it is an organic compound having sublimability, it can be easily patterned by patterning in a dry process. .

The material mainly constituting the light emitting layer and the electron transport layer in the present invention means that the properties of each layer in a thin film state are determined by the material. For example, in a light emitting layer composed 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 layer and the electron transporting layer of the present invention comprise (I_p
(ETL) -I_p(EML))> (E _a(ETL) -E_a
(EML)), the materials that mainly constitute each layer,
Additives etc. of the above compound group
It must be properly selected from among them. here,
E_a: Electron affinity (eV), I_p： Ionization potential
(EV), EML: light emitting layer, ETL: electron transport layer
You.

(I _p (ETL) −I _p (EML))> (E
_a (ETL) −E _a (EML)) indicates that the hole injection barrier from the light emitting layer to the electron transport layer is more injecting electrons from the electron transport layer to the light emitting layer between the light emitting layer and the electron transport layer. Means larger than the barrier. Therefore, it is possible to efficiently prevent the holes injected from the anode from flowing to the cathode side without being recombined with the electrons from the cathode side in the light emitting layer, thereby improving the luminous efficiency. Further, since the electron transport layer itself does not emit light, high color purity light emission can be obtained only from the light emitting layer. If the above relationship is satisfied, a sufficient effect can be obtained. However, in consideration of the operating environment at a high temperature, (I _{p
(ETL) -I p (EML)} )> (E a (ETL) -E a
(EML)) is 0.1 eV or more, and more preferably 0.2 eV or more.

Although it has been reported that the absolute values of the electron affinity and the ionization potential vary depending on the measurement conditions and the like, the values obtained as follows are used in the present invention. A single layer of each layer is separately formed by vacuum evaporation on an ITO glass substrate and a quartz glass substrate, and an air atmosphere type ultraviolet photoelectron analyzer (AC-1, manufactured by Riken Keiki Co., Ltd.) is used by using the thin film on the ITO glass substrate. The ionization potential was measured. At this time, it is considered that the ionization potential value changes depending on the state of the sample. Therefore, when any one of the hole transport layer, the light-emitting layer, and the electron transport layer is a mixed layer composed of two or more materials, the mixed layer itself is not a single layer of the main constituent materials forming the layer. It is necessary to measure the ionization potential value. On the other hand, the electron affinity was calculated from an energy gap value and an ionization potential value estimated from an ultraviolet / visible absorption spectrum measured using a thin film on a quartz glass substrate.

The light emitting device of the present invention preferably has a hole transport layer between the anode and the light emitting layer for the purpose of efficiently recombining holes and electrons in the light emitting layer. The hole transporting layer is a layer in which holes are injected from the anode and transports the holes, and as a hole transporting material, specifically, 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
-Arylcarbazole) or bis (N-alkylcarbazole) s, pyrazoline derivatives, stilbene compounds, distyryl derivatives, hydrazone compounds, oxadiazole derivatives, phthalocyanine derivatives, heterocyclic compounds represented by porphyrin derivatives, Polycarbonate having a monomer in a side chain, a styrene derivative, polyvinyl carbazole, polysilane, etc. are listed. If there is, it is not particularly limited. These may be used alone, or a plurality of derivatives may be mixed or laminated to form a layer. Furthermore, although it does not itself have a hole transporting ability, organic compounds, inorganic compounds, and metal complexes are used for various purposes such as improving the transporting ability, thermal stability, and electrochemical stability of the entire hole transporting layer. A hole transporting layer may be formed by adding to a hole transporting material.

Furthermore the hole-transporting layer of the invention between the light-emitting layer _{(E a (EML) -E a} (HTL))> (I p (EM
L) -I _p (HTL)),
Materials and additives mainly constituting each layer are appropriately selected from the above group of compounds so as to satisfy this relationship. Here, E _a : electron affinity (eV), I _p : ionization potential (eV), EML: light emitting layer, HTL: hole transport layer.

(E _a (EML) −E _a (HTL))> (I
_p (EML) relationship -I _p (HTL)) of between the light emitting layer and the hole transport layer, towards the light-emitting layer of an electron injecting barrier to the hole transport layer from the hole transport layer to the light-emitting layer It means larger than the hole injection barrier. Therefore, it is possible to efficiently prevent the electrons injected from the cathode from flowing to the anode side without being recombined with holes from the anode side in the light emitting layer, thereby improving the luminous efficiency. Further, since the hole transport layer itself does not emit light, high color purity light emission can be obtained only from the light emitting layer. If the above relationship is satisfied, a sufficient effect can be obtained. However, considering the operating environment under a high temperature, it is more preferable that E is satisfied.
_{a (EML) -E a (HTL} ))> (I p (EML) -I p
(HTL)) is 0.1 eV or more, and more preferably 0.2 eV or more.

The method for forming each layer is not particularly limited, such as resistance heating evaporation, electron beam evaporation, sputtering, molecular lamination, and coating. However, resistance heating evaporation and electron beam evaporation are usually preferable in terms of characteristics. . The thickness of the layer depends on the resistance of the luminescent material and cannot be limited, but is selected from the range of 1 to 1000 nm.

Although the electric energy mainly indicates a direct current, a pulse current or an alternating current can also be used.
The current value and the voltage value are not particularly limited. However, in consideration of the power consumption and life of the device, it is necessary to obtain the maximum luminance with the lowest possible energy.

The matrix in the present invention refers to a matrix in which pixels for display are arranged in a lattice, and displays a character or an image by a set of pixels. The shape and size of the pixel depend on the application. For example, a square pixel having a side of 300 μm or less is usually used for displaying images and characters on a personal computer, a monitor, and a television. In the case of a large display such as a display panel, a pixel having a side of mm order is used. . For monochrome display, pixels of the same color may be arranged, but for color display, red, red,
Green and blue pixels are displayed side by side. In this case, there are typically a delta type and a stripe type. The matrix may be driven by either a line-sequential driving method or an active matrix. The line-sequential driving has the advantage that the structure is simpler, but the active matrix is sometimes superior when the operating characteristics are taken into consideration.

In the present invention, the segment type is a pattern in which predetermined information is displayed and a pattern is formed.
Light is emitted from the determined area. For example, there are a time display and a temperature display on a digital clock or a thermometer, an operation state display of an audio device, an electromagnetic cooker, or the like, and a panel display of an automobile. 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 for improving the visibility of a display device that does not emit light, and is used for a liquid crystal display device, a clock, an audio device, an automobile panel, a display panel, a sign, and the like. In particular, as for the backlight for liquid crystal display devices, particularly for personal computer applications where thinning is an issue, the present invention is considered to be difficult because the conventional type is made of a fluorescent lamp or a light guide plate, and it is difficult to make it thin. The backlight using the light emitting element in the above is characterized by being thin and lightweight.

[0033]

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples. Note that ΔI _p (ET-EM), Δ
E _a (ET-EM), ΔI _p (EM-HT), ΔE _a (E
M-HT) represents the following formula, respectively.

ΔI _p (ET-EM) = I _p (ETL) −I _p (EML) ΔE _a (ET-EM) = E _a (ETL) −E _a (EML) ΔI _p (EM-HT) = I _p (EML) −I _p (HTL) ΔE _a (EM-HT) = E _a (EML) −E _a (HTL) (where E _a : electron affinity (eV), I _p : ionization potential (eV) , EML: light-emitting layer, ETL: electron transport layer, HTL: hole transport layer).

Example 1 A glass substrate on which an ITO transparent conductive film was deposited to a thickness of 150 nm (product of Asahi Glass Co., Ltd., 15 Ω / □, electron beam deposited) was cut into 30 × 40 mm and etched. The obtained substrate was subjected to ultrasonic cleaning with acetone and "Semicocline 56" for 15 minutes each, and then with ultrapure water. Subsequently, the substrate was subjected to ultrasonic cleaning with isopropyl alcohol for 15 minutes, immersed in hot methanol for 15 minutes, and dried. This substrate was subjected to UV-ozone treatment for 1 hour immediately before producing the element, and was placed in a vacuum evaporation apparatus, and the degree of vacuum in the apparatus was 1 × 10 ⁻⁵ Pa
Evacuation was performed until the following. First, copper phthalocyanine (CuP) is used as a first hole injection / transport layer by a resistance heating method.
c) was deposited to a thickness of 10 nm and subsequently used as a second hole transport layer as N, N′-diphenyl-N, N′-bis (1-naphthyl) -1,1′-diphenyl-4,4′-diamine ( α-NPD) was laminated to a thickness of 50 nm. Subsequently, EM1 shown below was deposited as a light emitting layer to a thickness of 25 nm. Next, ETM1 shown below was laminated to a thickness of 25 nm as an electron transport layer. Subsequently, lithium was added to 0.
Doping 2nm, and finally aluminum 150nm
A 5 × 5 mm square device was prepared by vapor deposition to form a cathode.

The hole transport layer has an ionization potential and an electron affinity of 5.44 eV and 2.44 eV, respectively, and the light-emitting layer has an ionization potential and an electron affinity of 5.4, respectively.
3, 2.51 eV, the ionization potential and the electron affinity of the electron transport layer were 6.03 and 3.08 eV, respectively, and ΔI _p (ET-EM) = 0.6 eV> ΔE _a (ET-E
M) = 0.57 eV ΔE _a (EM-HT) = 0.07 eV> ΔI _p (EM-H
T) =-0.01 eV. The molecular weight of ETM1 is 890. The light-emitting element emitted blue light based on EM1 having a light-emitting peak wavelength of 462 nm at an applied voltage of 15 V, and the light-emitting luminance was 2500 cd / m ² . Also,
The initial luminance retention rate of this light-emitting element 100 hours after the passage of electricity was 80%, and a uniform light-emitting surface was maintained.

[0037]

Embedded image

Example 2 A light emitting device was manufactured in the same manner as in Example 1 except that ETM2 shown below was used as the electron transporting layer. The ionization potential and electron affinity of the electron transport layer are each 6.
09 eV, 2.95 eV, and ΔI _p (ET-EM) = 0.66 eV> ΔE _a (ET-E
M) = 0.44 eV. The molecular weight of ETM2 is 670,
The glass transition temperature was 165 ° C., and no cold crystallization temperature was observed. The light-emitting element emitted blue light based on EM1 having a light-emitting peak wavelength of 462 nm and an emission luminance of 3000 cd / m ² at an applied voltage of 15 V. The light-emitting element had an initial luminance retention ratio of 80% after 100 hours had passed from energization, and maintained a uniform light-emitting surface.

[0039]

Embedded image

Comparative Example 1 A light emitting device was manufactured in exactly the same manner as in Example 1 except that Alq3 was used as the electron transport layer. The ion transport potential and the electron affinity of the electron transport layer are 5.79 eV, respectively.
3.03 eV, ΔI _p (ET-EM) = 0.36 eV <ΔE _a (ET-E
M) = 0.52 eV. The molecular weight of Alq3 is 459. At a voltage of 15 V, the light-emitting element emits light based on EM1 having an emission peak wavelength of 462 nm and 53
It had a shoulder peak near 5 nm, did not emit blue light, and emitted light blue light.

Comparative Example 2 A light emitting device was produced in the same manner as in Example 1 except that 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) was used as the electron transporting layer. . The ion transport potential and the electron affinity of the electron transport layer are 6.20 eV and 2.64 eV, respectively, and ΔI _p (ET-EM) = 0.77 eV> ΔE _a (ET-E
M) = 0.13 eV. The molecular weight of BCP is 360.
This light-emitting element emits blue light based on EM1 having an emission peak wavelength of 462 nm at an applied voltage of 15 V,
The emission luminance was 2500 cd / m ² . However, the initial luminance retention rate of this light emitting element 100 hours after energization was 50% or less, and unevenness was observed on the light emitting surface.

Example 3 1,4-diketo-2,5 using the light emitting layer as a host material
Using -bis (3,5-di-tert-butylbenzyl) -3,6-bis (3-methoxyphenyl) pyrrolo [3,4-c] pyrrole and EM2 shown below as a dopant material, the dopant was 0.1%. A light emitting device was manufactured in exactly the same manner as in Example 2 except that co-evaporation was performed to a thickness of 15 nm so as to be 5 wt%. The ionization potential and the electron affinity of the light-emitting layer are 5.62 and 3.32 eV, respectively, and ΔI _p (ET-EM) = 0.47 eV> ΔE _a (ET-E
M) = − 0.37 eV ΔE _a (EM-HT) = 0.88 eV> ΔI _p (EM-H
T) = 0.18 eV. The light-emitting element emits red light based on a dopant material having a light emission peak wavelength of 640 nm at an applied voltage of 14 V, and has a light emission luminance of 4000 cd / m 2.
^{Was 2} .

[0043]

Embedded image

Example 4 A light emitting device was produced in the same manner as in Example 3 except that HTM1 shown below was used as the second hole transport layer. The ionization potential and the electron affinity of the hole transport layer are 5.63 eV and 2.25 eV, respectively, and ΔE _a (EM-HT) = 1.07 eV> ΔI _p (EM-H
T) =-0.01 eV. The light-emitting element emits red light based on a dopant material having a light emission peak wavelength of 640 nm at an applied voltage of 14 V, and has a light emission luminance of 4500 cd / m 2.
^{Was 2} .

[0045]

Embedded image

Example 5 A glass substrate (available from Asahi Glass Co., Ltd., 15 Ω / □, electron beam vapor-deposited) 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 270 μm) was obtained by photolithography. ) X 32 stripes were patterned. One side of the long side of the ITO stripe is used to facilitate electrical connection with the outside.
It is expanded to a pitch of 27 mm (opening width 800 μm). The obtained substrate was subjected to ultrasonic cleaning with acetone and "Semicocline 56" for 15 minutes each, and then with ultrapure water.
Subsequently, the substrate was subjected to ultrasonic cleaning with isopropyl alcohol for 15 minutes, immersed in hot methanol for 15 minutes, and dried.
This substrate was subjected to UV-ozone treatment for 1 hour immediately before the device was manufactured, and was placed in a vacuum evaporation apparatus.
Evacuation was performed until the pressure became × 10 ⁻⁴ Pa or less. First, CuPc was deposited to a thickness of 10 nm by a resistance heating method, and then α-
NPD was deposited to a thickness of 50 nm. Next, 1,4-diketo-2,5-bis (3,5-di-t
-Butylbenzyl) -3,6-bis (3-methoxyphenyl) pyrrolo [3,4-c] pyrrole, using EM2 as a dopant material, and having a thickness of 15 nm so that the dopant is 0.5 wt%. Evaporated. Subsequently, ETM2 was laminated to a thickness of 25 nm as an electron transport layer. Next, 16 openings of 250 μm (remaining width 50 μm, 3
(Equivalent to a pitch of 00 μm).
The mask was replaced so as to be orthogonal to the TO stripe, and the mask and the ITO substrate were fixed with a magnet from the back so that the ITO substrate was in close contact with the mask. Then, after doping the organic layer with 0.5 nm of lithium, 200 nm of aluminum was vapor-deposited to produce a 32 × 16 dot matrix element. When this device was driven in a matrix, characters could be displayed without crosstalk.

[0047]

According to the present invention, it is possible to provide a red light emitting device having excellent thermal stability, high utilization efficiency of electric energy, and excellent color purity.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3K007 AB02 AB03 AB04 AB11 BA06 CA01 CB01 DA01 DB03 EB00

Claims (6)

[Claims] 1. A light-emitting element having a structure in which at least an anode, a light-emitting layer, an electron transport layer, and a cathode are sequentially stacked, wherein the light-emitting layer and the electron transport layer are I _p (ETL) −I _p (EML))>
(With the relationship between _{E a (ETL) -E a (} EML), materials that the material mainly constituting the light emitting layer and an electron transport layer is made of an organic compound having a sublimation property, further mainly constituting the electron transporting layer is A light-emitting element characterized by being an organic compound having a molecular weight of 400 or more (here, E _a : electron affinity (e
V), I _p : ionization potential (eV), EML:
Light-emitting layer, ETL: electron transport layer) 2. The light emitting device according to claim 1, wherein a glass transition temperature of an organic compound mainly constituting the electron transport layer is 90 ° C. or higher. 3. The method according to claim 1, further comprising a hole transporting layer between the anode and the light emitting layer, wherein the light emitting layer and the hole transporting layer are (E _a (EML) −E _a (H
2. The light-emitting device according to claim 1, wherein a relationship of (TL))> (I _p (EML) -I _p (HTL) is satisfied, wherein E _a : electron affinity (eV), I _p : ionization. Potential (eV), EML: light emitting layer, HTL: hole transport layer) 4. The light emitting device according to claim 1, wherein the light emitting layer is composed of at least two kinds of organic compounds. 5. The organic compound mainly constituting the electron transport layer includes a plurality of mother skeletons, and the plurality of mother skeletons are conjugated, substituted or unsubstituted aromatic hydrocarbon, substituted or unsubstituted aromatic heterocyclic. 2. The light emitting device according to claim 1, comprising an organic compound having a structure linked by either a ring or a group obtained by mixing them. 6. The light emitting device according to claim 1, wherein the light emitting device constitutes a display for displaying in a matrix and / or segment system.