JP2003109759A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electroluminescent element of which an organic light emitting layer or at least either of the organic light emitting layer or an organic carrier transport layer contains an organic material of high conductivity and heat resistance. SOLUTION: The organic material is to be a conductive compound expressed in formula (1), in which, n denotes an integer from 4 to 10, k denotes an integer from 1 to n, and Ark and Ark ' denote an aryl group or a heterocyclic group each of which may have a substituent.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an organic electroluminescent device having an organic light emitting layer or an organic light emitting layer and an organic carrier transport layer sandwiched between a cathode and an anode.

[0002]

2. Description of the Related Art Organic electroluminescent elements are expected to be used as display elements of various display devices, illumination light sources such as backlights, etc., because they can emit high-luminance light at low voltage. As shown in FIG. 1, a typical structure of an organic electroluminescence device is, on a substrate, an anode that is a transparent electrode, an organic hole transport layer that efficiently transports holes from the anode, and a fluorescent organic light emission. It has a structure in which a layer, an organic electron transport layer for efficiently transporting electrons from the cathode, and a cathode of a metal electrode are sequentially laminated. Here, the organic hole transport layer, the organic light emitting layer, and the organic electron transport layer are each formed of a suitable organic material. When a DC voltage is applied to both electrodes of such an organic electroluminescent device, electrons are injected from the cathode to the conduction level of the organic light emitting layer through the organic electron transport layer, while holes are emitted from the anode and organic electrons are transmitted through the hole transport layer. Injected to the valence level of the light emitting layer. The fluorescent material forming the organic light-emitting layer is excited to an excited singlet state by the energy emitted when the electrons and holes that move between both levels in the organic light-emitting layer are recombined, and the fluorescent material is excited. Fluorescence is emitted when energy is relaxed.

In the conventional organic electroluminescent device having the structure shown in FIG. 1, many organic material layers such as an organic hole transport layer, an organic light emitting layer, and an organic electron transport layer are thin films made of an insulating material. In order to apply a voltage between both electrodes and inject a current, the injection efficiency of carriers (holes or electrons) that control conductivity at the interface between the electrode-organic material layer and the organic material layer is improved, It was necessary to increase the carrier density and carrier mobility of the material layer thin film itself. Specifically, a metal complex typified by a tris (8-hydroxyquinolinato) aluminum complex (Alq), TPD (bis [N- (3-methylphenyl) -N-phenyl] benzidine), α-NPD ( Bis [N- (1-naphthyl)-
Aryl amines represented by N-phenyl] benzidine) have been used.

[0004]

However, in these conventional organic electroluminescent devices using an organic material, carrier injection characteristics at the interface between the electrode and the organic material layer, carrier density and carrier migration in the thin film of the organic material layer. Due to the low degree of conductivity, the conductivity is insufficient and a high voltage must be applied between the electrodes. Applying a high voltage to the organic electroluminescent device causes a problem of shortening the life of the device.

Further, in the conventional organic electroluminescence device using an organic material, the device is heated to a high temperature due to heat generation due to energization during driving and heat generation due to light emission, resulting in peeling of the interface between the cathode and the organic electron transport layer. There is also a problem that the cathode may be oxidized and the element may be deteriorated.

The present invention has been made in view of the above problems, and provides an organic electroluminescent device in which at least one of the organic light emitting layer or the organic light emitting layer and the organic carrier transport layer contains an organic material having high conductivity and heat resistance. The purpose is to do.
Here, the organic carrier transport layer represents an organic hole transport layer and an organic electron transport layer.

[0007]

The invention according to claim 1 is
In an organic electroluminescent device having an organic light emitting layer or an organic light emitting layer and an organic carrier transport layer sandwiched between a cathode and an anode, at least one of the organic light emitting layer, or the organic light emitting layer and the organic carrier transport layer is generally Formula (1)

[0008]

[Chemical 2] , N is an integer of 4 to 10, and k is 1
Ar is an integer from n to Ar _k, And Ar_k’
An aryl group or a heterocyclic group which may have a substituent,
It is characterized in that it contains a conductive compound.

According to the first aspect of the present invention, it is possible to provide an organic electroluminescent device in which at least one of the organic light emitting layer or the organic light emitting layer and the organic carrier transport layer contains an organic material having high conductivity and heat resistance. .

According to a second aspect of the invention, in the organic electroluminescent element according to the first aspect, n is 4 and Ar is
_k and Ar _k ′ are each a phenyl group.

According to the second aspect of the present invention, there is provided an organic electroluminescent device comprising an organic light emitting layer or at least one of the organic light emitting layer and the organic carrier transport layer, which contains an organic material having high conductivity and heat resistance and capable of being easily formed. Can be provided.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described. In the present invention, an organic light emitting layer or an organic light emitting layer and an organic carrier transporting layer sandwiched between a cathode and an anode are represented by the general formula (1):

[0013]

[Chemical 3] An organic electroluminescent device comprising a cyclic compound of silicon represented by:

Here, the number n of silicon units forming a ring is n.
Is an integer of 4 to 10. In order to form a silicon cyclic compound, n must be an integer of 3 or more. However, when n is 3, steric hindrance is great and synthesis is difficult. When n is an integer of 11 or more, the synthesis is difficult and at the same time, the molecular weight becomes too large, and it is difficult to form a vapor deposition film by vacuum vapor deposition. Preferably n is 4,
5 and 6. k is the number of units of silicon forming a ring, and takes an integer of 1 to n.

Also, Ar _k and Ar _k '(k = 4, ...,
n) each represents an aryl group or a heterocyclic group which may have a substituent. Generally, in an organic conductive compound, in order to improve conductivity, it is necessary to include a π bond having a weak bonding force in the molecule. Therefore, in the conductive compound containing a ring composed of silicon represented by the general formula (1), a bond that does not contribute to the bond between silicon is bonded to an aryl group or a heterocyclic group having a π bond. Is desirable. These aryl groups or heterocyclic groups may have a substituent.

[0016] Aryl group Ar _k, and Ar _k 'is an aryl group of monocyclic or fused polycyclic, and preferably from 5 to 14 carbon atoms, such as phenyl, 1,3-cyclopentadiene-1 Yl, 2-indenyl, 1-naphthyl, 2-naphthyl, 2-anthryl, 2-phenanthryl, 4-biphenylyl and the like.

The heterocyclic group Ar _k, and Ar k _'is the sum of the carbon and the number of hetero atoms is 5 to 14, preferably a nitrogen atom, an oxygen atom, an aromatic heterocyclic ring containing at least one sulfur atom Groups such as pyrrolyl, imidazolyl, pyrazolyl, pyridyl, pyrazinyl, pyrimidinyl, furyl, thienyl, thiazolyl, isothiazolyl, oxazolyl, isoxazolyl, quinolyl, indolyl, carbazolyl, acridinyl and the like.

These aryl group and heterocyclic group may have a substituent, and the substituent preferably has 1 to 10 carbon atoms.
An alkyl group such as methyl, ethyl, n-propyl,
Isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl,
C2-C10 alkenyl groups such as n-heptyl, n-octyl, n-nonyl, n-decyl, etc., such as vinyl, allyl, 1-butenyl, 2-butenyl, 3-pentenyl, etc. 10 alkynyl groups, eg
C2-C10 alkoxy groups such as ethynyl, propargyl, 3-pentynyl, etc., halogen groups such as methoxy, ethoxy, propoxy, butoxy, etc.
Fluoro, chloro, bromo and iodo.

The inventor has found that such a known silicon cyclic compound having a π-electron system aryl group or heterocyclic group has higher carrier transport performance than conventional carrier transport materials. Focusing attention, the present invention newly provides an organic electroluminescent device having excellent conductivity by including this conductive compound in the organic material layer of the organic electroluminescent device. The voltage required for causing a constant current to flow in such an organic electroluminescent device to cause it to emit light is lower than in the prior art, and thus the life of the device can be extended.

Further, such a conductive compound has a large molecular weight and a high melting point. Therefore, even if the organic electroluminescent device has a high heat resistance and a high temperature is generated due to heat generated when the organic electroluminescent device is driven, the thin film containing such a conductive compound has high heat stability as compared with the conventional device.

Therefore, by using a thin film containing a conductive compound represented by the general formula (1) as an organic material layer in an organic electroluminescent device, an organic electroluminescent device having high conductivity and heat resistance is provided. be able to.

Preferably, the chemical formula (2)

[0023]

[Chemical 4] In the general formula (1), n is 4, and Ar
_k and Ar _k '(k = 1 to 4) are phenyl groups, that is, an organic electroluminescent device including at least one thin film containing octaphenyltetrasilane. Since this compound has a π-electron system in the four-membered ring of silicon, it has high conductivity, and since it has a large molecular weight of 729, it has a high melting point and therefore also excellent heat resistance. Further, in the general formula (1), since the number of n is 4 which is the minimum, there is an advantage that the molecular weight does not become too large and the film formation is easy. Therefore, the organic electroluminescent element having the thin film containing the conductive compound represented by the chemical formula (2) can be provided as an element which is excellent in conductivity and heat resistance and is easy to form a film.

In the organic electroluminescent device having the structure shown in FIG. 1, the conductive compound represented by the general formula (1) is
It is preferably used in at least one carrier transport layer, ie an organic hole transport layer and / or an organic electron transport layer.

When the conductive compound represented by the general formula (1) is used only in the organic hole transport layer, the organic electron transport layer contains a conventional triazole derivative, oxazole derivative, oxadiazole derivative, fluorenone. Examples thereof include derivatives, carbodiimide derivatives, distyrylpyrazine derivatives, phthalocyanine derivatives, and metal complexes of 8-quinolinol derivatives.

When the conductive compound represented by the general formula (1) is used only in the organic electron transport layer, the organic hole transport layer contains carbazole derivative, triazole derivative,
Oxazole derivative, oxadiazole derivative, imidazole derivative, stilbene derivative, fluorenone derivative, hydrazone derivative, poly (N-vinylcarbazo-
) Derivatives and the like.

When used in the organic light-emitting layer, the conductive compound represented by the general formula (1) alone does not emit strong fluorescent light, and therefore must be used in combination with another material. For the organic light emitting layer, conventionally used styrylbenzene derivatives, oxadiazole derivatives, benzoxazole derivatives, benzothiazole derivatives, benzimidazole derivatives, cyclopentadiene derivatives, coumarin derivatives, etc. may be used.

The anode is preferably a conductive metal oxide or metal having a work function of 4 ev or less, such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), gold, silver, in order to enhance the injection efficiency of holes. Chromium, nickel, etc. are preferable, especially IT that is transparent and transmits light emitted from the device.
O is desirable.

The cathode is, for example, an alkali metal such as lithium, sodium and potassium or a fluoride thereof, an alkaline earth metal such as magnesium and calcium, or a halide thereof, in consideration of adhesion with an adjacent layer, ionization potential and stability. Fluoride, aluminum, gold, silver, lead and the like are preferable.

Further, glass is usually used for the substrate, and it is desirable to use non-alkali glass in order to suppress the ions eluted from the glass. In addition to this,
A protective layer may be provided to prevent moisture, oxygen, or other substances that deteriorate the element from entering the element, and any material that functions as a protective layer can be used.

Using the above materials, conventional anodes and cathodes (both having a thickness of 10 nm to 5 μm), thin films of organic light emitting layers (thickness of 1 nm to 5 μm) and thin films of hole transport layers and electron transport layers (films) are formed. Thickness of 1 nm to 5 μm) by resistance heating vapor deposition,
The organic electroluminescence device of the present invention can be manufactured by appropriately using an electron beam method, a sputtering method, a coating method, or the like.

An example is octaphenyltetrasilane. Octaphenyltetrasilane is, for example, Al
Product numbers 44,481-2 from Drich can be obtained. The purity of this reagent is 97% (catalog value)
And, a high-purity compound can be obtained. The melting point of this reagent is 320 ° C. (catalog value), and the melting point of TPD, which is a typical hole transporting material of conventional organic electroluminescent devices, is 175 to 177 ° C. and the melting point of α-NPD is 274 to 274 ° C.
Higher than 279 ° C. Therefore, the conductive compound used in the present invention is very excellent in heat resistance, and when used in an organic material layer of an organic electroluminescence device, it can provide an organic electroluminescence device stable against heat generation.

[0033]

According to the present invention, it is possible to provide an organic electroluminescent device in which at least one of the organic light emitting layer or the organic light emitting layer and the organic carrier transport layer contains an organic material having high conductivity and heat resistance.

[0034]

[Brief description of drawings]

FIG. 1 is a diagram showing a basic structure of an organic electroluminescent device.

Continued front page    (72) Inventor Yoichi Itagaki             1601 Sakai, Atsugi, Kanagawa Mitsumi Electric Co., Ltd.             Company Atsugi Office F-term (reference) 3K007 AB06 AB11 DB03 EB00

Claims (2)

[Claims] 1. An organic electroluminescent device having an organic light emitting layer or an organic light emitting layer and an organic carrier transport layer sandwiched between a cathode and an anode, wherein at least the organic light emitting layer, or the organic light emitting layer and the organic carrier transport layer. One is the general formula (1) In expressed, n is an integer from 4 to 10, k is 1 or an integer of n, Ar _k, and Ar k _'is which may have a substituent aryl group or heterocyclic group An organic electroluminescent device comprising a conductive compound which is 2. The n is 4, and Ar _k and Ar
The organic electroluminescent device according to claim 1, wherein each _k ′ is a phenyl group.