JPH05320633A - Organic electroluminescent device - Google Patents

Abstract

(57) [Summary] An organic electroluminescent device having a light emitting layer containing a light emitting material between a pair of electrodes, at least one of which is transparent or semitransparent, wherein the light emitting layer is based on 100 parts by weight of the light emitting material. The following chemical formula 1 [In the formula, R ₁ and R ₂ are each independently hydrogen and a carbon number of 1 to 1.
A group selected from a 12-alkyl group or an aryl group having 6 to 14 carbon atoms, Ar ₁ and Ar ₂ are each independently selected from an aryl group having 6 to 14 carbon atoms or a heterocyclic compound group having 4 to 12 carbon atoms. Group, X represents O, S or Se. 0.005 to 1 of at least one pyrrolo [3,4-c] pyrrole compound selected from the compounds represented by
An organic electroluminescence device comprising 5 parts by weight. [Effect] It is possible to provide a high-luminance organic EL having improved luminous efficiency, and the organic EL can be suitably used for a planar light source as a backlight, a display device such as a flat panel display and the like.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an organic electroluminescence device (hereinafter referred to as an organic EL device). For more information,
The present invention relates to an organic EL device having a light emitting layer containing a light emitting material doped with a pyrrolo [3,4-c] pyrrole compound.

[0002]

2. Description of the Related Art Inorganic electroluminescence device (hereinafter, inorganic EL device) using an inorganic phosphor as a light emitting material
Is used for a surface light source as a backlight or a display device such as a flat panel display, for example, but a high-voltage alternating current was required to emit light.

Recently, C.I. W. Tang et al. Produced an organic EL device having a two-layer structure in which an organic fluorescent dye was used as a light emitting layer and an organic hole transport compound used in a photoconductor for electrophotography and the like were laminated, and it was driven at a low voltage and a high voltage. An organic EL device having high efficiency and high brightness has been realized (Japanese Patent Laid-Open No. 59-194393).
Publication). Compared with inorganic EL elements, organic EL elements have the advantages of low voltage drive, high brightness, and the ability to easily emit light of multiple colors.
Many attempts have been reported on organic charge transport compounds [Japanese Journal of Applied Physics (Jpn. Appl. Phys.) No. 27).
Vol., L269 (1988)], [Journal of Applied Physics (J. Appl. Phy.
s. ), 65, 3610 (1989)]. Also,
Japanese Patent Application Laid-Open No. 1-118418 discloses pyrrolo [3,4
It was shown that an organic EL device using a -c] pyrrole compound as a light emitting material was used to form a light emitting layer using the pyrrolo [3,4-c] pyrrole compound alone, and orange light emission was observed. As a result of a study by the inventors, as can be seen from the comparative example described below, no luminescence was observed by itself.

[0004]

The organic EL elements reported so far have a relatively high brightness, but have a problem that the luminous efficiency is insufficient. For this reason, there has been a demand for a light emitting material having high luminous efficiency and high brightness with a small current.

[0005]

As a result of various studies, the present inventors have found that when a specific amount of a pyrrolo [3,4-c] pyrrole compound is mixed with a luminescent material, the luminescent material is not the pyrrolo [3,4] It was found that an organic EL device with higher brightness can be obtained by emitting light from the -c] pyrrole compound or by improving the light emission efficiency as compared with the case where the light emitting material is used alone.

That is, the present invention relates to an organic electroluminescence device having a light emitting layer containing a light emitting material between a pair of electrodes, at least one of which is transparent or semitransparent, wherein the light emitting layer is as follows with respect to 100 parts by weight of the light emitting material. Chemical 1

[0007]

[Chemical 2] [In the formula, R ₁ and R ₂ are each independently hydrogen and a carbon number of 1 to 1.
A group selected from a 12-alkyl group or an aryl group having 6 to 14 carbon atoms, Ar ₁ and Ar ₂ are each independently selected from an aryl group having 6 to 14 carbon atoms or a heterocyclic compound group having 4 to 12 carbon atoms. Group, X represents O, S or Se. 0.005 to 1 of at least one pyrrolo [3,4-c] pyrrole compound selected from the compounds represented by
It is to provide an organic electroluminescence device characterized by containing 5 parts by weight. Hereinafter, the organic EL device of the present invention will be described in detail.

The pyrrolo [3,4-c] pyrrole compound used in the present invention together with the light emitting material is a compound represented by the chemical formula 2, wherein R ₁ and R ₂ are independently hydrogen or carbon as described above. C1-C12 alkyl group or C6
A group selected from an aryl group having 14 to 14 and Ar ₁ and Ar ₂ are each independently a group selected from an aryl group having 6 to 14 carbon atoms or a heterocyclic compound group having 4 to 12 carbon atoms.
Here, examples of the alkyl group having 1 to 12 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, and an octyl group, and a carbon number of 6
As the aryl group of to 14, a phenyl group, a 4-chlorophenyl group, a 4-cyanophenyl group, a 4-methylphenyl group, a 4-ethylphenyl group, a 4-propylphenyl group,
4-butylphenyl group, 4-pentylphenyl group, 4-
Hexylphenyl group, 1-naphthalene group, 2-naphthalene group and the like. Examples of the heterocyclic compound group having 4 to 12 carbon atoms include thienyl group, 2-pyridyl group, 3-pyridyl group, and 4
-Pyridyl group is exemplified. Of these, R ₁ and R ₂ are preferably hydrogen, a methyl group or an ethyl group, and most preferably hydrogen. As Ar ₁ and Ar ₂ , a phenyl group, a 4-chlorophenyl group, a 4-cyanophenyl group,
A 4-methylphenyl group is preferred.

As a specific compound, Japanese Patent Application Laid-Open No. 58-21 is available.
The compounds described in JP-A No. 0084 and JP-A No. 59-24758 are exemplified, and more specifically, the following structural formula (1)
The compounds represented by (11) to (11) are mentioned.

[0010]

[Chemical 3]

[0011]

[Chemical 4]

[0012]

[Chemical 5]

The mixing ratio of the pyrrolo [3,4-c] pyrrole compound and the light emitting material is such that the film structure of the light emitting material is modified or the compound molecule of the light emitting material is changed to pyrrolo [3,4].
The concentration is not lower than the concentration at which the energy transfer to the -c] pyrrole molecule efficiently occurs. On the other hand, if the concentration is too high, the concentration quenching of the pyrrolo [3,4-c] pyrrole molecule reduces the emission efficiency, which is not preferable. Specifically, the mixing ratio is preferably 0.005 to 15 parts by weight of the pyrrolo [3,4-c] pyrrole compound with respect to 100 parts by weight of the light emitting material, and more preferably from the viewpoint of reducing the effect of concentration quenching. 0.01 to 10 parts by weight, more preferably 0.0
1 to 5 parts by weight. Since the purity of these compounds affects the emission characteristics, it is desirable to purify them by reprecipitation purification, sublimation purification, etc. after synthesis.

The light emitting material as the base material of the light emitting layer has a film structure modified with a pyrrolo [3,4-c] pyrrole compound or a light emitting material produced by recombination of holes and electrons injected from an electrode. From the excited singlet state of the molecule, the pyrrolo [3,4
A light-emitting material that causes energy transfer to the -c] pyrrole compound is effective for improving the light emission efficiency and for emitting light of the pyrrolo [3,4-c] pyrrole compound. For this purpose, the light-emitting material is preferably a compound having a fluorescence spectrum with a large overlap with the fluorescence spectrum of the pyrrolo [3,4-c] pyrrole compound, and particularly the maximum of the fluorescence spectrum of the pyrrolo [3,4-c] pyrrole compound used. A compound having a maximum peak wavelength of a fluorescence spectrum which is the same as or shorter than the peak wavelength is preferable, more preferably a compound having a wavelength difference of 150 nm or less, more preferably 100 nm or less. Good. For example, when X is O in Chemical formula 2, the maximum peak wavelength of the fluorescence spectrum is 40 among the fluorescent compounds used as the light emitting material.
A compound in the range of 0 to 560 nm can be selected. Specifically, an aluminum quinolinol complex is preferably used. When X is S in Chemical formula 2, a compound having a maximum peak wavelength of the fluorescence spectrum in the range of 500 to 650 nm can be selected and used.

Pyrrolo [3,4-c] represented by the above chemical formula 2
The light emitting layer containing a pyrrole compound is formed by a vacuum co-evaporation method with a light emitting material as a base material or a mixed solution of the pyrrolo [3,4-c] pyrrole compound and the light emitting material by a spin coating method, a casting method, a dipping method, or a bar. It can be formed by a known method such as a coating method such as a coating method and a roll coating method. In the vacuum co-evaporation method, the light-emitting material and the pyrrolo [3,4-c] pyrrole compound are evaporated from different evaporation sources and vapor-deposited on the same substrate, or the light-emitting material and the pyrrolo-containing compound are contained in the same evaporation source. There is a one-source vapor deposition method in which a [3,4-c] pyrrole compound is mixed, charged, evaporated and vapor-deposited on a substrate. As for the mixing ratio of the pyrrolo [3,4-c] pyrrole compound and the light emitting material, in the two-source deposition method, the deposition rate of the light emitting material and the pyrrolo [3,4-c] pyrrole compound are individually detected to control the mixing ratio. The method is generally used.
On the other hand, in the one-source vapor deposition method, the mixing ratio in the film is controlled by the mixing charging ratio of the pyrrolo [3,4-c] pyrrole compound and the light emitting material. In addition, when a thin film is formed by a coating method, in order to remove the solvent, the pressure is reduced or under an inert atmosphere at 30 to 200 ° C., preferably 60 to 100.
Heat treatment at a temperature of ° C is desirable. The vacuum vapor deposition method is preferably used from the viewpoint of finely controlling the film thickness.

The present invention also includes the use of a layer in which the above-mentioned pyrrolo [3,4-c] pyrrole compound and the luminescent material as the base material and a known polymer compound are mixed as the luminescent layer. In this case, the amount of the pyrrolo [3,4-c] pyrrole compound is in the same range as described above for the light emitting material used. The polymer compound to be used is not particularly limited, but those which do not extremely disturb the charge transporting property and the light emitting property are preferable, and examples thereof include poly (N-vinylcarbazole), polyaniline and its derivatives, polythiophene and its derivatives, and poly (p- Examples thereof include phenylene vinylene) and its derivatives, poly (2,5-thienylene vinylene) and its derivatives, polycarbonate, polysiloxane, and vinyl polymers such as polymethyl acrylate, polymethyl methacrylate, polystyrene and polyvinyl chloride. It The poly (N-vinylcarbazole), polyaniline and its derivatives, polythiophene and its derivatives, poly (p-phenylene vinylene) and its derivatives, poly (2,5-thienylene vinylene) and its derivatives are mentioned below. It also functions as a hole transporting compound.

The formation of the mixed layer of the above-mentioned pyrrolo [3,4-c] pyrrole compound and the luminescent material as the base material and the polymer compound is performed by forming the polymer compound and the pyrrolo [3,4-c] pyrrole compound and the polymer compound. The coating method described above can be employed after mixing the luminescent material in a solution state or a molten state and dispersing the pyrrolo [3,4-c] pyrrole compound and the luminescent material as a base material.

When a precursor polymer such as poly (p-phenylene vinylene) and its derivative and poly (2,5-thienylene vinylene) and its derivative is used, the pyrrolo [3,4-c] pyrrole is in solution. After mixing with the compound,
30 to 300 ° C., preferably 60 to 2 in an inert atmosphere
Heat treatment is performed at a temperature of 00 ° C. to convert the polymer into a target polymer.

In the present invention, a charge transport layer is provided between the light emitting layer and any of the electrodes (the charge transport layer in the present invention is a generic term for a hole transport layer and an electron transport layer unless otherwise specified). It may be provided. The charge transporting material (general term for hole transporting material and electron transporting material) used at that time is not particularly limited and known materials can be used, for example, triphenyldiamine derivative, oxadiazole derivative, pyrazoline derivative, arylamine. A derivative, a stilbene derivative, an anthraquinodimethane derivative, or the like can be used. Specifically, for example, those described in JP-A-2-209988 and JP-A-3-37992 can be used. Of these, either the electron-transporting compound or the hole-transporting compound, or both, may be used at the same time. The thickness of the charge transport layer varies depending on the type of compound used and the like, and therefore may be appropriately determined within a range that does not impair sufficient film formability and light emission characteristics.

These charge-transporting materials can be compounded by known methods such as vacuum deposition, or coating methods such as spin-coating, casting, dipping, bar-coating and roll-coating methods of the solution of the charge-transporting material. The charge transport layer can be formed by appropriately adopting it. When the charge transport material is not a polymer compound, it is preferable to use the vacuum vapor deposition method from the viewpoint of finely controlling the film thickness.

In the present invention, as the light emitting layer,
It is also possible to use a mixture of the pyrrolo [3,4-c] pyrrole compound, a light emitting material as a base material, and the charge transport material, or a mixture of these with a known polymer compound as a medium. It can also be used as a dispersed layer. In this case, the amount of the pyrrolo [3,4-c] pyrrole compound based on the light emitting material as the base material is in the same range as described above. The mixing ratio of the light emitting material and the charge transport material is not particularly limited, but is preferably in the range of 0.1: 100 to 1: 1 (weight), and the ratio of the sum of the polymer compound and these materials is not particularly limited. However, preferably 100: 0.0
It is in the range of 1 to 1: 3 (weight). In this case, the polymer compound used is preferably the above-mentioned polymer compound which does not strongly absorb visible light. Specifically, poly (N-vinylcarbazole), polythiophene and its derivatives,
Poly (p-phenylene vinylene) and its derivatives, poly (2,5-thienylene vinylene) and its derivatives, polymethyl acrylate, polymethyl methacrylate, polystyrene, vinyl polymers such as polyvinyl chloride, polycarbonate, polysiloxane, etc. Is exemplified. The same method as described above can be used to form the mixed layer. Further, although these layers can be used in only one layer, another layer of a charge transport material or the like may be provided if necessary.

A typical structure of the organic EL device of the present invention will be described below. The structure itself of the element can be a known structure. For example, the above-mentioned anode / hole transport layer / light-emitting layer / cathode (/ indicates that layers are laminated), or anode / hole or electron transport / light-emitting (mixture of charge-transport material and light-emitting material) layer In addition to the structure of / cathode, a structure having a conductive polymer layer between the anode and the hole transport layer may be adopted, or a structure having an electron transport layer between the light emitting layer and the cathode. You can also take
Further, the structure of anode / conductive polymer / hole transport layer / light emitting layer / electron transport layer / cathode can be adopted.

Hereinafter, regarding the production of the organic EL element, the anode /
The production method will be described below by taking a structure having a hole transport layer / light emitting layer / cathode as an example. As the transparent or semitransparent electrode of the pair of electrodes, the transparent or semitransparent electrode is formed on a transparent substrate such as glass or transparent plastic. This is the anode. A conductive metal oxide film as the material of the electrode,
A semitransparent metal thin film or the like is used. Specifically, indium tin oxide (ITO), tin oxide (NES
A), Au, Pt, Ag, Cu or the like is used. As a manufacturing method, a vacuum deposition method, a sputtering method, a plating method, or the like is used.

Next, a hole transport layer is provided, and the film thickness is 0.5 nm to 10 μm, preferably 1 nm to 1 μm. 2 to increase the current density and emission brightness
The range of 500 nm is preferred.

Next, a light emitting layer is provided on the hole transport layer.
The film thickness of the light emitting layer needs to be at least such that pinholes are not generated, but if it is too thick, the resistance of the device increases and a high driving voltage is required, which is not preferable. Therefore, the thickness of the light emitting layer is 0.5 nm to 10 μm, preferably 1 nm to 1 μm, and more preferably 5 to 200 nm. Note that this range is also preferable in the case of a mixed layer of a hole transport material and a light emitting material. The light-emitting layer is composed of at least one kind of pyrrolo [3,4-c] pyrrole compound and one or more kinds of light-emitting materials as a base material, and the method for mixing these is as described above from different vapor deposition sources. Can be appropriately selected from the co-evaporation method, the method of depositing a mixture, the method of applying a mixed solution and drying, and the like.

Next, an electrode is provided on the light emitting layer. This electrode becomes the electron injection cathode. The material is not particularly limited, but a material having low ionization energy is preferable. For example, Al, In, Mg, Mg-Ag alloy, M
A g-In alloy, a graphite thin film, etc. are used. As a method for producing the cathode, a known vacuum deposition method, sputtering method or the like is used.

Although the organic EL device of the present invention can be manufactured as described above, it is possible to manufacture the organic EL device having another structure by the same method.

[0028]

In the present invention, the pyrrolo [3,4-c] of the formula 2 is
Although the pyrrole compound has strong concentration quenching, it emits very strong fluorescence in a state where it is not aggregated, so that the pyrrolo [3,4-c] pyrrole compound is added to the light emitting material in an amount of 0.0
It is considered that the organic EL device using the mixture containing 05 to 15% by weight has improved luminous efficiency.

[0029]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.

Example 1 An ITO film having a thickness of 40 nm was attached by sputtering.
4,4'-bilayer as a charge (hole) transport layer on a glass substrate.
Deposition of su (3-methyl-diphenylamino) biphenyl
To form a film with a thickness of 40 nm. Then Tris (8
-Quinolinol) aluminum (hereinafter Alq₃) And JP
It was synthesized by the method described in JP-A-58-210084.
A compound represented by the structural formula (2) (hereinafter referred to as compound A)
Is Alq ₃Compound A is 1.0 weight to 100 weight parts
Evaporate by mixing so that it becomes a part by volume and by single source evaporation method.
A 40 nm light emitting layer was produced by. Cathode on it
As a magnesium-silver alloy [magnesium: silver = 1
0: 1 (weight)] is vapor-deposited to 200 nm to form an organic EL device.
It was made. The degree of vacuum during vapor deposition is 3 x 10^-6To
It was rr or less. 100mA / cm for this device²Electric power
Brightness is 2093 cd / m ²The green uniform
A uniform EL emission was observed. Brightness is proportional to current density
I was there. Emission spectrum when driving light emission spectrofluorometer
When measured using (Model 850 manufactured by Hitachi, Ltd.),
The large peak wavelength is 534 nm and the shoulder at 570 nm
It was seen. This is about 1 × 10^-6mol / l dimethylpho
Of the fluorescence spectrum of compound A measured with the lumamide solution
The maximum peak wavelength is 524 nm and the shoulder is 564 nm.
It is confirmed that they are in agreement with each other and the light emission is from the compound A.
did. In addition, in the obtained emission spectrum, Alq₃From
The peak that seems to be (shoulder at 500 nm) is extremely
It was weak. Alq₃Of the fluorescence spectrum of
The maximum peak wavelength was 520 nm.

Example 2 An organic EL device was prepared in the same manner as in Example 1 except that the compound A was mixed in an amount of 0.36 parts by weight with respect to 100 parts by weight of Alq ₃ . 100mA /
When an electric current of cm ² was applied, the luminance was 2002 cd / m ^2.
A uniform EL emission of green was observed. The brightness was proportional to the current density. The fluorescence spectrum was almost the same as in Example 1.

Example 3 An organic EL device was prepared in the same manner as in Example 1 except that the compound A was mixed in an amount of 0.012 parts by weight with respect to 100 parts by weight of Alq ₃ . 100mA / cm for this device
^When a current of ² was applied, a green uniform EL emission having a brightness of 3066 cd / m ² was observed. The brightness was proportional to the current density.

Comparative Example 1 The same method as in Example 1 was repeated except that the compound A was mixed in an amount of 23.6 parts by weight with respect to 100 parts by weight of Alq ₃ .
An organic EL device was produced. 100mA / cm for this device
^When a current of ² was passed, a green uniform EL emission with a brightness of 59.2 cd / m ² was observed. The brightness was proportional to the current density.

Comparative Example 2 An organic EL device was prepared in the same manner as in Example 1 except that Compound A was vapor-deposited alone as a light emitting layer. When a voltage of 30.0 V was applied to this element, the current density was 18.4 m.
A current of A / cm ² flowed, but no EL emission was observed. When a higher voltage was applied, the element was destroyed by heat generation.

Comparative Example 3 An organic EL device was produced in the same manner as in Example 1 except that Alq ₃ was vapor-deposited alone as a light emitting layer. When a current of 100 mA / cm ² was passed through this element, a brightness of 161 was obtained.
A uniform green EL emission of 8 cd / m ² was observed. The brightness was proportional to the current density.

[0036]

INDUSTRIAL APPLICABILITY In the present invention, by adding a pyrrolo [3,4-c] pyrrole compound to a light emitting material as a light emitting layer, it is possible to provide a high-brightness organic EL having improved luminous efficiency. The organic EL can be suitably used for a planar light source as a backlight and a display device such as a flat panel display.

Claims (2)

[Claims] 1. An organic electroluminescent device having a light emitting layer containing a light emitting material between a pair of electrodes, at least one of which is transparent or semi-transparent, wherein the light emitting layer is represented by the following chemical formula 1. Chemical 1] [In the formula, R ₁ and R ₂ are each independently hydrogen and a carbon number of 1 to 1.
A group selected from a 12-alkyl group or an aryl group having 6 to 14 carbon atoms, Ar ₁ and Ar ₂ are each independently selected from an aryl group having 6 to 14 carbon atoms or a heterocyclic compound group having 4 to 12 carbon atoms. Group, X represents O, S or Se. 0.005 to 1 of at least one pyrrolo [3,4-c] pyrrole compound selected from the compounds represented by
An organic electroluminescence device comprising 5 parts by weight. 2. The organic electroluminescence device according to claim 1, wherein the light emitting material is a compound having a maximum peak wavelength of a fluorescence spectrum which is the same as or shorter than the maximum peak wavelength of the fluorescence spectrum of the pyrrolo [3,4-c] pyrrole compound. ..