JP2000068064A - Luminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the durability of an element by comprising a luminescent material between a positive electrode and a negative electrode, and comprising an element generating the light by electric energy and forming a hole transport layer by a mixture of at least two kinds of materials. SOLUTION: The composition for a material may take the constitution of hole transport material/luminescent material, hole transporting material/luminescent material/electron transport material, luminescent material/electron transport material, or a mixture of these combined materials. A hole transport layer is preferably made of a material, superior in various properties but inferior in film forming property and a material superior in film forming property, a material superior in various properties but inferior in heat resistance and a material superior in heat resistance, a material superior in hole transport property and a material superior in hole injection property, or the like. As the mixing method of the hole transporting material, coating after the mixing and dispersing, codeposition, thermal diffusion after lamination, or the like can be applied, in particular, codeposition is preferred on the basis of characteristics. When a ratio of a material not having a hole transport material is high, since the hole transport becomes difficult, more than two kinds of materials preferably are included in the hole transport material.

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 of (1).

[0002]

2. Description of the Related Art In recent years, active research has been conducted on organic thin-film light emitting devices that emit light when electrons injected from a negative electrode and holes injected from a positive electrode recombine in an organic phosphor sandwiched between both electrodes. I have. This element is characterized by thinness, high luminance light emission under a low driving voltage, and multicolor light emission by selecting a fluorescent material.

[0003] It is known from Kodak's C.I. W. Tang et al. (Appl. Phys. Lett. 51 (12)
21, p. 913, 1987). A typical configuration of the organic laminated thin-film light emitting device presented by Kodak Company is a hole transporting diamine compound and a light emitting layer on an ITO glass substrate,
8-Hydroxyquinoline aluminum, which also has an electron transporting property, and Mg: Ag as a negative electrode were sequentially provided, and green light emission of 1000 candela / m 2 was possible at a driving voltage of about 10 V. The current organic laminated thin-film light-emitting device has a different configuration, such as a device provided with an electron transport layer, in addition to the above-described device components, but basically follows the configuration of Kodak. I have.

By the way, in the hole transporting material of an organic laminated thin film light emitting device (hereinafter referred to as a light emitting device), the hole transporting material, which is an essential role, has a work function with other materials that facilitates hole injection. Various attempts have been made until now, such as a balance, a thin film forming property necessary for device formation, heat generation during driving, heat resistance for use outdoors or in a vehicle, and overall durability.

Specifically, hydrazone-based compounds (JP-A-57-101844 and JP-A-58-15936) and stilbene-based compounds (JP-A-57-14875)
No. 0, JP-A-58-197043), triphenylamine-based compounds (JP-B-58-32372, JP-A-5-198377), oxadiazole derivatives (JP-B-34-10966). And phthalocyanine derivatives (JP-A-57-51781, JP-A-2-12795) and biscarbazole derivatives (JP-A-8-3547) are known.

Attempts have also been made to improve performance by laminating different hole transport materials. Specifically, a phthalocyanine derivative, a triphenylamine-based compound (JP-A-63-29569), and different triphenylamine-based compounds (JP-A-4-308688)
Are known.

[0007]

However, in the prior art, if the element is left untreated, crystallization of the organic film occurs or a non-light-emitting portion called a dark spot expands.
The problem was to improve the durability of the element.

[0008]

In order to achieve the above-mentioned object, the present invention provides a device which emits light by electric energy, in which a substance responsible for light emission is present between a positive electrode and a negative electrode. A light-emitting element having a layer, wherein the hole transport layer is formed by mixing two or more materials.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A positive electrode according to the present invention is made of a conductive metal oxide such as tin oxide, indium oxide, indium tin oxide (ITO), or gold, silver, chromium, if it is transparent to extract light. Such metals, copper iodide, inorganic conductive substances such as copper sulfide, and conductive polymers such as polythiophene, polypyrrole, and polyaniline are not particularly limited. However, it is preferable to use ITO glass or Nesa glass. It is desirable to use. 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, 300Ω /
If it is an ITO glass substrate of □ or less, it functions as an element electrode, but it is now possible to supply a substrate of about 10 Ω / □, so it is particularly preferable to use a low-resistance substrate of 20 Ω / □ or less. desirable. The thickness of the ITO can be arbitrarily selected according to the resistance value.
Often used between nm. Further, as the glass substrate, soda lime glass, non-alkali glass or the like is used, and the thickness only needs to be sufficient to maintain the mechanical strength. As for the material of the glass, alkali-free glass is preferred because it is better that ions eluted from the glass are small.
Soda lime glass having a barrier coat such as No. 2 is also commercially available and can be used. Even when a substrate other than glass is used, any substrate may be used as long as it is transparent and has a high sealing effect. The method of forming the ITO film is not particularly limited, such as an electron beam evaporation method, a sputtering method, and a chemical reaction method. It is desirable that the ITO glass substrate be well cleaned and well dried.

The composition of the substance that controls light emission in the present invention is as follows:
1) a hole transporting material / a light emitting material, 2) a hole transporting material / a light emitting material / an electron transporting material, 3) a light emitting material / an electron transporting material, and 4) a form in which a combination of the above substances is mixed.
Any of these may be used. That is, in addition to the multi-layer structure of 1) to 3), a layer containing a luminescent material alone or a luminescent material and a hole transporting material, or a layer containing a luminescent material, a hole transporting material and an electron transporting material as in 4) is further provided. It may just be provided. The light emitting material may be either a host material alone or a combination of a host material and a dopant material.
In addition, the dopant material may be included in the entire host material, partially, or may be included. The dopant material may be stacked, dispersed, or the like.

The hole transport material in the present invention is required to efficiently transport holes from the positive electrode between the electrodes to which an electric field is applied, and has a high hole injection efficiency. Good transport is desirable. For that purpose, it is required that the ionization potential be small, the hole mobility be large, the stability be further improved, and impurities serving as traps be hardly generated during production and use. Further, it must have the property of forming a thin film necessary for device formation, high heat generation during driving and high heat resistance assuming use outdoors or in a vehicle, and excellent overall durability.

[0012] It is difficult to find a substance that satisfies such a condition alone, and the present invention is characterized in that the hole transport layer is composed of a mixture of two or more materials and complements the necessary role. It is. Specifically, materials having excellent properties but poor film forming properties and materials having excellent film forming properties, materials having excellent properties but poor heat resistance and materials having excellent heat resistance, and materials having excellent hole transport properties and positive Materials having excellent hole injecting properties, and the like.

The form of the hole transport layer may be a mixed layer alone, or a single layer or a combination of different mixed layers. The mixing ratio is not particularly limited either, and the mixing may be uniform or the ratio may be changed in the thickness direction. In the present invention, the hole transport layer may include a hole injection layer portion.

The method of mixing the hole transport material is not particularly limited, and examples thereof include coating after mixing and dispersion, co-evaporation, and heat diffusion after lamination, and co-evaporation is preferred in terms of characteristics.

When the proportion of the material having no hole transporting property increases, the hole transporting becomes difficult. Therefore, it is preferable that each of the two or more kinds of materials has the hole transporting property. It is preferable that at least one of the hole transporting materials is a phthalocyanine derivative, a polyaniline derivative, or a polythiophene derivative because of excellent hole injecting property and excellent heat resistance. it can.

[0016] Because of its excellent hole transporting ability, as a suitable combination with the above hole transporting material, at least one of the hole transporting materials is bis (N- (m-methylphenyl) carbazole) or bis (N-ethylcarbazole). ), Screw (N
-Naphthylcarbazole) or a triarylamine derivative such as TPD, α-NPD, MTDATA, or a triphenylamine compound having a spiro structure.

In terms of heat resistance, biscarbazolyl derivatives are preferable, and among the triarylamine derivatives, those in which at least one of the aryl groups is a condensed ring are more preferable.

Other hole transporting materials used in combination are not particularly limited, but include known compounds such as pyrazoline derivatives, stilbene compounds, hydrazone compounds, oxadiazole derivatives and heterocyclic compounds, polyvinylcarbazole and polysilane. Can be used.

Among the luminescent materials in the present invention, the host material is not particularly limited, but tris (8-quinolinolato) aluminum, a condensed ring derivative such as anthracene or pyrene, which has long been known as a luminescent material, may be used. Metal chelated oxinoid compounds, bisstyryl derivatives such as bisstyrylanthracene derivatives and distyrylbenzene derivatives, tetraphenylbutadiene derivatives, coumarin derivatives, oxadiazole derivatives, pyrrolopyridine derivatives, perinone derivatives, cyclopentadiene derivatives, oxadiazole For derivatives, thiadiazolopyridine derivatives, and polymer systems, polyphenylenevinylene derivatives, polyparaphenylene derivatives, and polythiophene derivatives can be used.

The dopant material added to the host material is not particularly limited, but specific examples thereof include conventionally known condensed ring derivatives such as perylene and rubrene, quinacridone derivatives, phenoxazone 660, DC
M1, perinone, coumarin derivatives and the like can be used as they are. These dopant materials may be used alone or in combination with different dopant materials.

As the electron transporting material in the present invention,
It is necessary to efficiently transport electrons from the negative electrode between the electrodes to which an electric field is applied, and it is desirable that the electron injection efficiency is high and the injected electrons are transported efficiently. For this purpose, it is required that the material has a high electron affinity, a high electron mobility, a high stability, and a small amount of impurities serving as traps during production and use. Materials satisfying such conditions include quinolinol derivative metal complexes represented by 8-hydroxyquinoline aluminum, tropolone metal complexes, flavonol metal complexes, perylene derivatives, perinone derivatives, naphthalene,
There are coumarin derivatives, oxadiazole derivatives, aldazine derivatives, bisstyryl derivatives, pyrazine derivatives, phenanthroline derivatives, and the like, but are not particularly limited. Although these electron transport materials are used alone,
They may be laminated or mixed with different electron transport materials.

The above materials used for the hole transporting layer, the light emitting layer and the electron transporting layer can be used alone to form each layer. Examples of the polymer binder include polyvinyl chloride, polycarbonate, polystyrene, and the like. Poly (N-vinyl carbazo-
), Polymethyl methacrylate, polybutyl methacrylate, polyester, polysulfone, polyphenylene oxide, polybutadiene, hydrocarbon resin, ketone resin, phenoxy resin, polyamide, ethyl cellulose
Curing of solvent-soluble resins such as water, vinyl acetate, ABS resin and polyurethane resin, phenol resin, xylene resin, petroleum resin, urea resin, melamine resin, unsaturated polyester resin, alkyd resin, epoxy resin, silicone resin, etc. It is also possible to use it by dispersing it in a conductive resin or the like.

The method of forming the substance which controls light emission in the present invention is not particularly limited, such as resistance heating evaporation, electron beam evaporation, sputtering, dip coating, and spin casting.
Electron beam evaporation is preferred in terms of properties. The thickness of the layer cannot be limited because it depends on the resistance of the substance that controls light emission.
It is selected from between 1000 nm.

The negative electrode of the present invention efficiently converts electrons,
The substance is not particularly limited as long as it can be injected into the substance that controls light emission. Generally, platinum, gold, silver, copper, iron, tin, aluminum, indium, lithium, sodium, potassium,
Examples include calcium and magnesium. In order to increase the electron injection efficiency and improve the device characteristics, a low work function metal such as lithium, sodium, potassium, calcium, and magnesium is effective. However, since these low work function metals are generally unstable, it is desirable to form an alloy or a laminated structure with the stable metal. Alternatively, a method of doping a substance which controls light emission is also effective.
The method for manufacturing the electrode is not particularly limited as long as it can conduct electricity such as a resistance heating evaporation method, an electron beam evaporation method, a sputtering method, and an ion plating method. Is preferred in terms of characteristics.

The light emitting device of the present invention may be sealed. Before that, a protective layer may be provided to protect the light-emitting element. Platinum,
Metals such as gold, silver, copper, iron, tin, lead, aluminum, titanium, nickel, and indium, or alloys using these metals, and silica, titania, alumina, magnesium oxide, yttrium oxide, germanium oxide, and nickel oxide , Barium oxide, calcium oxide, metal oxides such as iron oxide, magnesium fluoride, lithium fluoride, aluminum fluoride, metal fluorides such as calcium fluoride, resins such as fluororesins, and the like. It is not limited.

The sealing method in the present invention is a method of putting a light emitting element in a container made of a sealing material and sealing it with an adhesive, or bonding the light emitting element to a substrate on which the light emitting element is formed by sandwiching it with a thin sealing material. Examples include a method of sealing with an agent, but the method is not particularly limited.

The sealing material is not particularly limited as long as it prevents moisture from entering the light emitting element. Specifically, soda-lime glass, borosilicate glass, silicate glass, silica glass, non-fluorescent glass, quartz, inorganic substances such as ceramics, metals such as stainless steel and aluminum alloy, fluorine resin, acrylic resin, Polycarbonate resin, epoxy resin, polyester resin, polyamide resin, polystyrene resin, polyethylene resin, polypropylene resin, polyolefin resin,
Examples include resins such as silicone resins.

The adhesive used for sealing is not particularly limited as long as it has a sealing effect. In particular,
An epoxy resin-based adhesive, an acrylate resin-based adhesive, or the like can be used. In addition, a photocurable resin adhesive, a thermosetting resin adhesive, an anaerobic resin adhesive, or the like can be used.

An adsorbent may be included between the light emitting element and the sealing material. The adsorbent is not particularly limited as long as it adsorbs moisture that enters from outside after sealing. Specifically, activated alumina, diatomaceous earth, activated carbon, phosphorus pentoxide, magnesium perchlorate, potassium hydroxide, calcium nitrate, calcium bromide, calcium oxide, barium oxide, barium carbonate, zinc chloride, zinc bromide, sulfuric anhydride Examples include inorganic compounds such as copper, metals such as lithium, beryllium, potassium, sodium, magnesium, rubidium, strontium, and calcium and alloys thereof, and acrylic and methacrylic water-absorbing polymers.

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

It is preferable that the light emitting device of the present invention constitutes a display for displaying by a matrix or segment system or a combination of both.

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, for the display of images and characters on personal computers, monitors, televisions, and the like, generally square pixels with a side of 300 μm or less are used, and in the case of a large display such as a display panel, pixels with a side on the order of mm are used. Become. In the case of monochrome display, pixels of the same color may be arranged, but in the case of color display, red, green and blue pixels are displayed side by side. In this case, there are typically a delta type and a stripe type. Note that the light-emitting element of the present invention can emit red, green, and blue light, so that multi-color or full-color display can be performed by using the display method. The matrix may be driven by either a line-sequential driving method or an active matrix. The line-sequential driving has the advantage of a simpler structure, but the active matrix is sometimes superior in consideration of the operating characteristics. Therefore, it is necessary to use this depending on the application.

In the segment type according to the present invention, a pattern is formed so as to display predetermined information, and a predetermined area emits light. 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 in the present invention,
It 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. Is characterized by its thinness and light weight.

[0035]

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 (15 Ω / □, electron beam evaporated product, manufactured by Asahi Glass Co., Ltd.) on which an ITO transparent conductive film was deposited to a thickness of 150 nm
The wafer was cut into a size of 40 mm and etched. The obtained substrate was subjected to ultrasonic cleaning with acetone and semicocrine 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, placed in a vacuum evaporation apparatus, and evacuated until the degree of vacuum in the apparatus became 5 × 10 ⁻⁵ Pa or less. First, copper phthalocyanine and 3,3′-bis (N- (m
-Methyl) phenylcarbazole) in a ratio of 1: 4 to 1
05 nm was co-evaporated, and 3,3′-bis (N- (m-methyl) phenylcarbazole) was independently evaporated at 15 nm. Next, 100 nm of trisquinolinolate aluminum (III) was deposited as a host material. Next, 0.5 nm of lithium and 200 nm of aluminum were vapor-deposited to form a cathode. The film thickness referred to here is a value displayed on a crystal oscillation type film thickness monitor corrected by a value measured by a surface roughness meter. The light emitting device was taken out into the atmosphere and allowed to emit light after being allowed to stand. Light emission was observed even after one month of standing.

COMPARATIVE EXAMPLE 1 Except that copper phthalocyanine was solely deposited as a hole transport material by 20 nm and 3,3′-bis (N- (m-methyl) phenylcarbazole) was solely deposited by 100 nm, and was completely the same as in Example 1. The device produced in the same manner was taken out into the atmosphere and allowed to stand, and then emitted light. The non-light-emitting portion was observed with the naked eye only after standing for one day, and no light emission was observed after leaving for 10 days.

Example 2 Instead of 3,3'-bis (N- (m-methyl) phenylcarbazole), 4,4'-bis (N- (m-tolyl)
A device manufactured in exactly the same manner as in Example 1 except that (-N-phenylamino) biphenyl was used was taken out into the air and left to emit light. Light emission was observed even after one month of standing.

Example 3 4,4'-bis (N- (2-naphthyl) -N-phenylamino) biphenyl was used in place of 3,3'-bis (N- (m-methyl) phenylcarbazole). Except for this point, the device manufactured in exactly the same manner as in Example 1 was taken out into the air and left to emit light. Light emission was observed even after one month of standing.

[0040]

According to the present invention, a light emitting device having improved durability can be provided.

Continued on the front page F term (reference) 3K007 AB00 AB13 BA06 BB05 CA01 CB01 DA00 DB03 EB00 FA01 5C094 AA31 BA27 CA14 CA19 EA05 EB02 FB01 HA01 HA10

Claims (7)

[Claims] 1. An element which emits light by electric energy in which a substance responsible for light emission exists between a positive electrode and a negative electrode, wherein the element has a hole transport layer, and the hole transport layer comprises two or more kinds of holes. A light-emitting element comprising a mixture of materials. 2. The light-emitting device according to claim 1, wherein said hole transport layer is mixed by co-evaporation. 3. The light emitting device according to claim 1, wherein each of the two or more materials of the hole transport layer is a hole transport material. 4. The light emitting device according to claim 3, wherein at least one of said hole transport materials is a phthalocyanine derivative. 5. The light emitting device according to claim 4, wherein at least one of said hole transport materials is a biscarbazolyl derivative and / or a triarylamine derivative. 6. The light emitting device according to claim 1, wherein said light emitting device constitutes a display for displaying in a matrix and / or segment system. 7. The light emitting device according to claim 1, wherein said light emitting device is a backlight.