JPH03137186A - Organic electric field luminescent element - Google Patents

Abstract

PURPOSE:To obtain the subject element, having a positive hole injecting transportation layer composed of a substance consisting essentially of a (co)polymer of an ethylenic monomer, capable of providing efficient light emission even at a low voltage, having sufficient brightness and using an organic electroluminescent element in any of the cathode layer, a light emitting layer, the positive hole injecting transportation layer and the anode. CONSTITUTION:The objective element successively having the cathode layer, a light emitting layer (positive hole blocking layer) and a positive hole injecting transportation layer on the anode, at least one of such electrodes being transparent, the positive hole injecting transportation layer composed of a substance consisting essentially of a polymer prepared by (co)polymerizing an ethylenic monomer, having an aromatic substituent group and expressed by, e.g. formula I to IV (R<1> is H or 1-8C alkyl; R<2> is aromatic residue; X is an integer of 0-6).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an organic electroluminescent device, and more particularly to a device that emits light in response to an electrical signal.

In particular, the present invention relates to an electroluminescent device using an organic compound that can efficiently emit light even at low voltage and has sufficient brightness.

[Conventional technology]

An organic electroluminescent device is constructed by sandwiching an organic light emitter between opposing electrodes, with electrons being injected from one electrode and holes being injected from the other electrode. Light is emitted when the injected electrons and holes recombine within the light emitting layer.

In such devices, a single crystal material such as single crystal anthracene has been used as a light emitter, but single crystal materials are expensive to manufacture and have many problems in terms of mechanical strength. It is not easy to further reduce the thickness to 1 mm.
A single crystal of about 100 volts emits weak light, and a driving voltage of 100 volts or more is often required, making it impractical.

Therefore, an attempt was made to obtain a film of anthracene with a thickness of 1 μm or less, using the vapor deposition method [Thin Solid Films (T
htn 5olid Films) Volume 94, Page 171 1
published in 1982].

However, in order to obtain sufficient performance, it is necessary to form a thin film of several thousand angstroms under strictly controlled film-forming conditions, and even though the light-emitting layer is formed as a thin film with high precision, the carrier Because the density of holes or electrons is very low, and the probability of excitation of functional molecules due to carrier movement or recombination is low, efficient light emission cannot be obtained, and in particular, it is difficult to achieve satisfactory results in terms of power consumption and brightness. The current situation is that this is not the case.

Furthermore, by providing a hole injection layer between the anode and the light-emitting layer, high luminous efficiency can be obtained by increasing the density of holes, which are carriers, as disclosed in JP-A-57-51781 and JP-A-59-194393. It is known from the publication no. However, these methods use a vapor-deposited film of a porphyrin compound or a triphenylamine derivative as a hole injection transport layer, and have the disadvantage of poor productivity.

Furthermore, Japanese Patent Application Laid-Open No. 63-295695 discloses that a porphyrin-based compound as a hole injection layer and a vapor-deposited film of an aromatic tertiary amine as a hole transport layer are laminated and are excellent as a hole injection transport layer. It has been disclosed that poly(N
-vinylcarbazole) are exemplified. However, these methods also have the disadvantage that the porphyrin compound must be provided by vapor deposition, and the productivity is still poor.

[Problem to be solved by the invention]

The present invention solves these problems and provides a highly efficient electroluminescent device.

That is, it is an object of the present invention to provide an organic electroluminescent device that has good luminous efficiency and sufficiently high luminance even at low voltage and low current density, is inexpensive, and is easy to manufacture.

[Means to solve the problem]

As a result of intensive study of polymer compounds as the hole injection transport layer, the present inventors found that high luminous efficiency can be obtained when a specific polymer compound is used, and the present invention has been completed.

That is, the present invention provides an organic electroluminescent device that has a hole injection transport layer, a light emitting layer, and a cathode in this order on an anode, and at least one of these electrodes is transparent. This is an organic electroluminescent device characterized in that the main component is a polymer obtained by polymerizing or copolymerizing an ethylenic monomer having a substituent. In an organic electroluminescent device having a light-emitting layer, a hole-blocking layer, and a cathode, at least one of which is transparent, the hole-injecting and transporting layer polymerizes an ethylenic monomer having an aromatic substituent. Alternatively, it is an organic electroluminescent device characterized in that the main component is a polymer obtained by copolymerization.

The present invention will be explained in detail below.

The present invention relates to an organic electroluminescent device having a hole injection transport layer, a light emitting layer, and a cathode sequentially on an anode, or an organic electroluminescent device having a hole injection transport layer, a light emitting layer, a hole blocking layer, and a cathode sequentially on an anode. In luminescent devices, when a polymer obtained by polymerizing or copolymerizing an ethylenic monomer having an aromatic substituent is used as the main component in the hole injection transport layer, high luminous efficiency and sufficient brightness can be obtained. It is based on the discovery that

The hole injection transport layer is a layer that efficiently injects and transports holes from the anode to the light emitting layer. It is surprising that it exhibits such functions with high efficiency when used as a main component.

The polymer obtained by polymerizing or copolymerizing the ethylenic monomer having an aromatic substituent used in the present invention can be synthesized by a common and well-known method, and if necessary, it can be purified before use. be able to.

The polymer obtained by polymerizing or copolymerizing the ethylenic monomers having an aromatic substituent used in the present invention may be a copolymerization between the monomers used in the present invention, or Copolymerization of the polymer and other components may also be used.

Examples of the ethylenic monomer having an aromatic substituent used in the present invention include the following compounds.

2 CH,=　C C=O CCHt)- 2 (n) CO3-C C=0 (CI(2).

2 (III) R' CH2=　C O (■) (CHri.

2 (In formulas (r), (If), (III), (IV), R1 means hydrogen or a C5 to C1 alkyl group, R2 means an aromatic residue, and X is an integer of 0 to 6. Here, examples of the aromatic residue R2 include compounds represented by the following structural formulas.

(R' is a C3-C6 alkyl group) (Y is H,
Br or Ca) (V is H, Br or CZ) A polymer obtained by polymerizing or copolymerizing the ethylenic monomer having an aromatic substituent of the present invention as a hole injection transport layer For use, it is provided between the anode and the light emitting layer, but the anode,
The hole injection transport layer, the light emitting layer, the hole blocking layer, and the cathode may be provided in this order, or the cathode, the hole blocking layer, the light emitting layer, the hole injection and transport layer, and the anode may be provided in this order. .

As the anode used in the present invention, a transparent or opaque conductive material formed on a transparent insulating support is used, but when the cathode is opaque, the anode needs to be transparent. Preferred examples include conductive oxides such as tin oxide, indium oxide, and indium tin oxide (ITO); gold, tin,
Examples include metals such as chromium; inorganic conductive substances such as iodized steel; and conductive polymers such as polythiophene, polypyrrole, and polyaniline.

Preferred cathodes for use in the present invention include translucent or opaque electrodes made of indium, silver, tin, aluminum, lead, magnesium, or the like.

In order to use the polymer obtained by polymerizing or copolymerizing the ethylenic monomer having an aromatic substituent used in the present invention as a hole injection transport layer, it can be dissolved in an appropriate solvent and applied by dip coating or spin coating. It can be applied and formed by a generally well-known method such as a method. Furthermore, if necessary, various additives may be added for the purpose of improving adhesiveness, flexibility, etc.

The hole injection transport layer does not necessarily have to be a single layer, and may be laminated into two or more layers if necessary. The thickness is preferably as thin as not to cause pinholes, and is usually used at a thickness of 1 micron or less.

The light emitting layer in the present invention is provided between the hole injection transport layer and the cathode or between the hole injection transport layer and the hole blocking layer.

The light-emitting layer is a layer that emits light when holes injected and transported from the anode through the hole injection transport layer and electrons injected and transported from the cathode recombine, and has a high luminescence quantum efficiency for the compound used. Luminescent substances can be used alone or in the form of dissolved or dispersed luminescent substances in a binder resin.

Preferred examples include aromatic compounds such as anthracene, naphthalene, phenanthrene, pyrene, chrysene, perylene derivatives, pigments such as polymethine, oxazine, xanthine, coumarin, and cyanine, aromatic amines, aromatic imines, butadiene, acridine, stilbene derivatives, excimer or excibrex-emitting compounds such as 1,3-dipyrenylpropane, optical brighteners such as oxazole, oxadiazole, benzimidazole, thiazole derivatives, 8-hydroxyquinoline and Examples include metal complexes, ruthenium complexes, rare earth complexes, and derivatives thereof. As the binder, common polymers can be used, such as polystyrene, polymethyl methacrylate, polyacrylonitrile, polyester, polycarbonate, polysulfone, polyphenylene oxide, polyamide, and the like. In this case, the amount of the binder used is not particularly limited, but it is 100% by weight per 1 part by weight of the luminescent agent.
Parts by weight or less are preferred. The thickness of the light emitting layer at this time is desirably 50 Å or more and 1 μm or less.

A hole blocking layer is provided between the light emitting layer and the cathode. When no hole blocking layer is provided, holes that do not contribute to light emission pass through the light emitting layer and reach the cathode. By providing a hole blocking layer,
Holes that pass through the light emitting layer without contributing to light emission can be trapped in the light emitting layer and can be made to contribute to light emission. In this way, the hole blocking layer is a layer provided to obtain higher luminous efficiency. Any electron transporting compound can be used as the compound that can be used for the hole blocking layer, but the first oxidation potential of the compound used for the hole blocking layer is higher than the first oxidation potential of the substance used for the light emitting layer. The effect is particularly remarkable when the voltage is greater than 0.1 V.

As the electron transfer compound used in the hole blocking layer, any electron transfer compound such as organic, inorganic, or metal complex can be used. Preferred examples of the compounds used in dispersed form include the following compounds.

Inorganic compounds include CdS, Cd-3e, Cd
Te, ZnO.

ZnS, Zn5e, ZnTe (n type), n
type single crystal silicon or amorphous silicon, and organic compounds having an amino group or its derivatives such as triphenylmethane, diphenylmethane, xanthine, acridine, azine, thiazine, thiazole,
Various dyes and pigments such as oxazine and azo, indanthrene dyes such as flavanthrone, perinone pigments, perylene pigments, cyanine dyes, 2,4,7-dolinitrofluorenone, tetracyanoquinodimethane, tetracyanoethylene, etc. Further, metal complexes include metal or metal-free phthalocyanines having an electron-withdrawing substituent on the ring, porphyrins having a pyridyl group, quinolyl group, quinoxalyl group, etc. on the ring,
Examples include metal complexes of 8-hydroxyquinoline and its derivatives. The hole blocking layer may be formed by vapor deposition or electrolytic reaction of an electron transporting compound, or may be formed by coating with or without a binder as required. As the binder, ordinary polymers can be used. For example, polystyrene, polymethyl methacrylate, polyacrylonitrile, polyester, polycarbonate,
Examples include polysulfone and polyphenylene oxide. The amount of the binder used in this case is not particularly limited, but is preferably 100 parts by weight or less per 1 part by weight of the electron transfer compound. The hole blocking layer does not necessarily have to be a negative layer and may be laminated in two or more layers if necessary, but its thickness is preferably 50 Å or more and 1 μm or less.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example I ITO glass [manufactured by HOYA@)] was ultrasonically cleaned in acetone, air-dried, and then washed for 5 minutes with an ultraviolet cleaning device [manufactured by Sen Engineering ■, PL-10-110]. A solution prepared by dissolving 0.5 parts by weight of poly [N-vinylcarbazole] [manufactured by Tokyo Kasei Corporation] in 100 parts by weight of 1,2-dichloroethane was dip coated onto this ITO glass.
000 hole injection transport layers were formed.

Next, tris(8-hydroxyquinolino)aluminum was added as a light-emitting layer at a vacuum level of 2.3×10-@Torr.
It was heated to 0.8°C and deposited to a thickness of 800 mm. Further, metal magnesium was deposited as a cathode on the light emitting layer through a shadow mask in an area of 0.1 crl to define the area of the device. When a DC voltage was applied using the ITO glass of the device thus produced as an anode, it emitted green light of 520 nm. Its brightness is 200cd/rr at 7V, 3.5mA/crl? Met.

Comparative Example 1 One layer of copper phthalocyanine (manufactured by Toyo Ink (Kikisha)) was added as a hole injection layer on ITO glass treated in the same manner as in Example 1.
．． A thickness of 350 mm was deposited at a vacuum level of 2 x 10-' Torr. Next, poly-N-carbazole was used as a hole transport layer and tris(8-hydroxyquinolino) was used as a light emitting layer.
Aluminum was used as a cathode, and metal magnesium was provided in the same manner as in Example 1. In order to cause this element to emit light with a brightness of 200 cd/n, a condition of 10 V 17 mA/c/ was required.

Example 2 A device was produced in the same manner as in Example 1, except that poly(3,6-dipromo-N-vinylcarbazole) was dip-coated to a thickness of 300 mm as a hole injection transport layer.

This element is l OO at 8 V, 2 mA/c+I
The brightness was CD/I.

Example 3 A hole injection and transport layer was applied to a thickness of 400 mm by dip coating from a chloroethane solution containing poly(vinylpyrene), and then perylene-3,4,9,1
Example 1 except that a light-emitting layer consisting of 85 parts by weight of 0-tetracarboxylic acid-bis-(2'6-diisoprobylanilide) and 15 parts by weight of polycarbonate was provided by dip coating to a thickness of 800 mm. A device was created in the same manner.

This device emitted 620 nm orange light with a brightness of 120 cd/rd at lOV, 10 mA/crl.

Example 4 Poly(4-diphenylaminophenylmethyl methacrylate) was applied as a hole injection transport layer to a thickness of 500 nm by spin coating, and 2,5-bis[5'-tert-butylbenzoxa Cyril (2'
)) A device was produced in the same manner as in Example 1, except that a light-emitting layer consisting of 80 parts by weight of thiophene and 20 parts by weight of polystyrene was provided to a thickness of 800 mm. This element is 9v, 8
Brightness is 480 at 180cd/i at mA/crl
It exhibited luminescence of nm.

Example 5 Poly(N-acryloyl indole) was provided as a hole injecting and transporting layer to a thickness of 300 nm by spin coding, and on top of that, 2,5 di(4°4'diethylaminone phenyl-diazole) was applied as a light emitting layer. A device was produced in the same manner as in Example 1, except that the film was deposited to a thickness of 800 mm by vapor deposition.

This device emitted blue light with a brightness of 50 cd/rrr under driving conditions of 1 1 V and 1 2 mA/crl.

Example 6 Poly(4-pyrenyl methyl vinyl ether) was applied as a hole injection transport layer by spin coating to a thickness of 500 nm, and 3-(2-benzimidazolyl) was applied thereon.
A device was prepared in the same manner as in Example 1, except that a light-emitting layer consisting of 85 parts by weight of -7-diethylaminocoumarin and 15 parts by weight of polymethyl methacrylate was provided to a thickness of 800 mm.

This device emitted green light with a brightness of 170 cd/rrr at 8 V and 6 mA/crl.

Example 7 A hole injecting and transporting layer was provided to a thickness of 400 mm by dip coating, and on top of it,
A device was produced in the same manner as in Example 1, except that 1,3-bis(l-pyrenyl)propane was deposited as a light-emitting layer to a thickness of 800 mm. This element has l 5 V,
106 cd/r under driving conditions of 15 mA/crl
It emitted blue light of 485 nm with a brightness of d.

Example 8 Poly(2-(N-ethylutatolylamino)ethyl methacrylate) was provided as a hole injection transport layer by spin coating to a thickness of 500 mm, and on top of that, 85 parts by weight of Rhodamine 6G and alcohol-soluble polyamide resin [
A device was prepared in the same manner as in Example 1, except that a light emitting layer consisting of 15 parts by weight of CM-8000 1 manufactured by Toshishima Co., Ltd. was provided to a thickness of 800 mm.

This device exhibited luminance of 70 cd/rrr and emission of 590 nm at 1 2 V and 1 1 mA/cf.

Example 9 Poly[2-(N-carbazolyl) as hole injection transport layer
ethyl vinyl ether] to a thickness of 400 mm by dip coating from a dichloroethane solution, and then
Perylene-3 as a light emitting layer.

4, 9. A vapor-deposited film of 10-tetracarboxylic acid-bis-isobutylimide was provided to a thickness of 800 nm, and a hole-blocking layer of tris(5,7-dichloro-8
- 300% vapor-deposited film of aluminum (hydroxyquinolino)
A device was produced in the same manner as in Example 1 except that it was provided at a human thickness.

This device emitted orange light with a brightness of 80 cd/rrr at 20 V and 20 mA/car.

〔Effect of the invention〕

The organic electroluminescent device of the present invention comprising an anode, a hole injection transport layer, a light emitting layer, and a cathode, or the organic electroluminescence device comprising an anode, a hole injection transport layer, a light emitting layer, a hole blocking layer, and a cathode, Since it consists of a hole injection transport layer mainly composed of a polymer obtained by polymerizing or copolymerizing an ethylenic monomer having an aromatic substituent, it has good luminous efficiency, provides sufficient brightness, and is inexpensive. This is an organic electroluminescent device that is easy to manufacture.

Claims (2)

[Claims] 1. In an organic electroluminescent device that has a hole injection transport layer, a light emitting layer, and a cathode sequentially on an anode, and at least one of these electrodes is transparent, the hole injection transport layer is an ethylenic material having an aromatic substituent. An organic electroluminescent device characterized in that its main component is a polymer obtained by polymerizing or copolymerizing monomers. 2. In an organic electroluminescent device that has a hole injection transport layer, a light emitting layer, a hole blocking layer, and a cathode in order on an anode, and at least one of these electrodes is transparent, the hole injection transport layer is an aromatic An organic electroluminescent device characterized in that the main component is a polymer obtained by polymerizing or copolymerizing an ethylenic monomer having a substituent.