JPH1126164A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EL element having high luminous efficiency and keeping stable luminescent characteristics over a long period of time by arranging a mixture layer of an organic luminescent material and/or an organic electron carrying material, and an aluminum alloy having the specific composition between an organic luminescent layer and a cathode. SOLUTION: A mixture layer 5 arranged between an organic luminescent layer 4 and a cathode 6 contains an organic luminescent material and 1 or an organic electron carrying material, and a aluminum alloy. The aluminum alloy contains 0.01-50 pts.wt. at least one kind of metal selected from the group comprising alkali metals, alkali earth metals, and rare earth metals as an alloy metal based on 100 pts.wt. aluminum. Since the aluminum alloy in the mixture layer 5 has low work function, the electron injection barrier of an organic EL element is lowered, and driving voltage can be lowered, and in addition oxidation of the cathode 6 can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence device used for a flat display, a flat light source and the like.

[0002]

2. Description of the Related Art With the rapid progress of technological development in the field of information communication in recent years, great expectations have been placed on flat displays instead of CRTs. Among them, electroluminescent elements (hereinafter referred to as EL elements) have been actively studied since they are excellent in high-speed response, visibility, luminance and the like.

At present, a practically used ZnS / Mn-based inorganic EL device has a problem that the driving voltage is as high as about 100 V and sufficient luminance cannot be obtained. Meanwhile, 19
The organic EL device, which was announced by Tang et al. Of Kodak Company in 1987, can drive a DC low voltage of 10 V or less, obtain a high luminance of 1000 cd / m ^2, and have a luminous efficiency of 1.5 lm / W. Excellent (Appl. Phys. Lett., 5
1 , 913 (1987)).

[0004] With this announcement, advantages such as low-voltage driving and multi-coloring by designing organic molecules compared with inorganic EL devices were shown, and many organic EL devices such as new organic materials and new cathode materials were shown. Research on devices has begun.

[0005]

The Mg-Ag alloy cathode (atomic ratio: 10: 1, work function: about 3.8 eV) developed by Tang et al. Has a low work function of Mg (work function: 3.6 eV). Silver is added for the purpose of improving the adhesion to the thin film. However, in the atmosphere, there is a problem that oxidation inside the metal cannot be suppressed. Therefore, it has been desired to lower the electron injection barrier of the organic EL element and suppress the oxidation of the cathode.

An object of the present invention has been made in view of the above circumstances of the prior art, and has as its object to lower the electron injection barrier and suppress the oxidation of the cathode, and to further improve the luminous efficiency. Another object of the present invention is to provide an organic EL device capable of maintaining stable light-emitting characteristics for a long period of time.

[0007]

SUMMARY OF THE INVENTION The present invention relates to an organic electroluminescence device having at least an anode, a hole transport layer, an organic light emitting layer containing an organic light emitting substance, and a cathode. , Organic luminescent materials and / or
Alternatively, a mixed layer containing an organic electron transporting substance and an aluminum alloy is provided, and the aluminum alloy is made of aluminum 10
Organic electroluminescence characterized by being an alloy containing 0.01 to 50 parts by weight of at least one metal selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals as alloy metal with respect to 0 parts by weight. An element is provided.

The cathode is made of an aluminum alloy, and the aluminum alloy contains at least one metal selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals as an alloy metal per 100 parts by weight of aluminum. Provided is an organic electroluminescent device, which is an alloy containing 0.01 to 50 parts by weight.

Further, the present invention provides an organic electroluminescent device which is an alloy containing at least one metal selected from the group consisting of lithium, magnesium, calcium, yttrium, europium and gadolinium as an alloy metal.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The organic EL device of the present invention has at least an anode, a hole transport layer, an organic light emitting layer containing an organic light emitting substance, a mixed layer, and a cathode. The mixed layer located between the organic light emitting layer and the cathode comprises an organic light emitting substance and / or
Or, it contains an organic electron transporting substance and an aluminum alloy.
The aluminum alloy of this mixed layer is aluminum 100
The alloy contains 0.01 to 50 parts by weight of at least one metal selected from the group consisting of an alkali metal, an alkaline earth metal and a rare earth metal as an alloy metal with respect to parts by weight.

Since the work function of the aluminum alloy of the mixed layer is low, the electron injection barrier of the organic EL can be reduced and the driving voltage can be reduced. Further, it has an effect of suppressing oxidation of the cathode. This makes it possible to obtain a long-life organic EL element with good luminous efficiency.

Hereinafter, the organic EL device of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows the organic E in the present invention.
It is sectional drawing of the typical example of an L element. In FIG. 1, 1
Is a substrate, 2 is an anode, 3 is a hole transport layer, 4 is an organic light emitting layer,
Reference numeral 5 denotes a mixed layer containing an organic light emitting substance and / or an organic electron transporting substance and an aluminum alloy, and reference numeral 6 denotes a cathode.

The substrate 1 in the present invention is a support for the organic EL device, and is made of glass, plastic, or the like.
As the plastic, a transparent substrate such as polycarbonate, polymethacrylate, and polysulfone can be preferably used.

On a substrate 1, a transparent electrode as an anode 2 is provided. As the transparent electrode, an indium tin oxide (ITO) thin film or a tin oxide film can be usually used. Further, it may be made of a metal having a large work function, such as aluminum or gold, an inorganic conductive substance such as copper iodide, or a conductive polymer such as poly (3-methylthiophene), polypyrrole, or polyaniline.

The method of producing the anode is generally carried out by a vacuum deposition method, a sputtering method, or the like. In the case of a conductive polymer, a solution with an appropriate binder is applied to the substrate. Alternatively, a thin film can be formed directly on a substrate by electrolytic polymerization. The thickness of the anode depends on the required transparency, but the visible light transmittance is 60% or more, preferably 80% or more.
It is 5 to 1000 nm, preferably 10 to 500 nm.

A hole transporting layer 3 is provided on the anode 2. As the hole transporting material, a material having a low injection barrier from the anode 2 and a high hole mobility can be used.
As such a hole transport material, a known hole transport material can be used. For example, N, N'-diphenyl-N,
N′-di (3-methylphenyl) -1,1′-biphenyl-4,4′-diamine (hereinafter referred to as TPD),
Aromatic diamine compounds such as 1'-bis (4-di-p-tolylaminophenyl) cyclohexane;
The hydrazone compounds disclosed in JP-A-11591 can be used.

Further, a polymer material such as poly-N-vinylcarbazole or polysilane can also be preferably used (Appl. Phys. Lett., 59, 27).
60 (1991)).

As a method for producing the organic hole transporting material thin film, a vacuum evaporation method, a dipping method, a spin coating method, an L
Various methods such as the method B can be applied. In order to produce a uniform thin film of submicron order without defects such as pinholes, a vacuum evaporation method and a spin coating method are particularly preferable.

In the case of spin coating, a binder resin which does not trap holes can be used by dissolving it in a coating solution. Examples of such a binder resin include polyether sulfone, polycarbonate, and polyester. The content of the binder resin is preferably from 10 to 50% by weight which does not decrease the hole mobility.

The material of the hole transport layer 3 includes not only the above-mentioned organic substances but also p-metals such as metal chalcogenides, metal halides, metal carbides, nickel oxides, lead oxides, copper iodides, and lead sulfides. A type compound semiconductor, p-type hydrogenated amorphous silicon, p-type hydrogenated amorphous silicon carbide, or the like can also be used.

The hole transporting layer made of such an inorganic substance can be formed by a commonly known method such as a vacuum evaporation method, a sputtering method, and a CVD method. Regardless of whether an organic substance or an inorganic substance is used, the thickness of the hole transport layer 3 is usually 10 to 200 nm, preferably 20 to 80 nm.
nm.

In the present invention, the anode 2 and the hole transport layer 3
Between them, an interface layer may be provided to prevent leakage current, reduce hole injection failure, improve adhesion, and the like. As such an interface layer material, a derivative of triphenylamine as disclosed in JP-A-4-308688,
4 ', 4 "-tris {N- (3-methylphenyl) -N
-Phenylamino @ triphenylamine (hereinafter MTDA)
TA), 4,4 ', 4 "-tris {N, N-diphenylamino} triphenylamine (hereinafter, referred to as TDATA), copper phthalocyanine, etc. can be preferably used. , 5 to 30 nm.

On the hole transport layer 3, an organic light emitting layer 4 is provided. As the organic light emitting substance of this organic light emitting layer,
A compound having a high fluorescence quantum yield, a high electron injection efficiency from the cathode 6, and a high electron mobility is effective.

As the organic luminescent substance used in the present invention, known organic luminescent substances can be used. For example, tris (8-quinolinolato) aluminum (hereinafter A)
LQ) is famous. In addition, a metal complex of 8-quinolinol such as lithium, beryllium, magnesium, calcium, zinc, aluminum, and scandium can be preferably used.

The thickness of the organic light emitting layer 4 is usually 1
It is 0 to 200 nm, preferably 20 to 80 nm. As a method for improving the luminous efficiency of the device and at the same time enabling multicoloring, the organic light emitting layer may be doped with another dye material having a high fluorescence quantum yield.

As such a doped dye material, known materials can be used, for example, stilbene dyes, oxazole dyes, cyanine dyes, xanthene dyes, oxazine dyes, perylene dyes, coumarin dyes. Dyes, laser dyes such as acridine dyes, anthracene derivatives, naphthacene derivatives, pentacene derivatives,
Aromatic hydrocarbons such as pyrene derivatives and perylene derivatives, quinacridone derivatives, tetraphenylbutadiene,
-Dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) and the like can be widely used.

In the present invention, between the organic light emitting layer 4 and the cathode 6, a mixed layer 5 containing an organic light emitting substance and / or an organic electron transporting substance and an aluminum alloy is provided. The aluminum alloy of this mixed layer is aluminum 1
At least one metal selected from the group consisting of an alkali metal, an alkaline earth metal and a rare earth metal as an alloy metal is contained in an amount of 0.01 to 50 parts by weight with respect to 00 parts by weight.

The concentration of the alloy metal contained in the mixed layer is 0.0
If the amount is less than 1 part by weight, the barrier against electron injection from the cathode increases, and the driving voltage of the device increases. On the other hand, if it exceeds 50 parts by weight, the alloy metal is easily oxidized, so that it is difficult to obtain stable performance over a long period of time.

The work function of the aluminum alloy in the mixed layer is preferably lower than that of a cathode material described later. Thereby, the electron injection barrier of the organic EL can be reduced. Further, it has an effect of suppressing oxidation of the material of the cathode. Thus, an organic EL element that can be driven with low power consumption, has high luminous efficiency, and has a long life can be obtained. Further, it has an effect of suppressing the reaction between the organic light emitting layer and the cathode during or after the formation of the cathode, because it has affinity with the organic light emitting layer, adhesion to the cathode, and is chemically stable.

An alkali metal used as an alloy metal,
Alkaline earth metals and rare earth metals have the effect of lowering the work function of aluminum alloys. This alloy metal is
Although a very small amount is effective, the amount is 0.01 parts by weight or more based on 100 parts by weight of aluminum. In particular, 0.1
The effect is preferably large to 20 parts by weight because the effect is large. Among these alloy metals, lithium, magnesium, calcium, yttrium, europium and gadolinium are preferred.

As the organic luminescent substance in the mixed layer, the known organic luminescent substance used in the above-mentioned organic luminescent layer can be used. Further, as the organic electron transporting substance, a substance having a high electron affinity and a high electron mobility is required, and a known organic electron transporting substance can be used. A substance satisfying such conditions is a cyclopentadiene derivative ( JP-A-2-289675), oxadiazole derivatives (JP-A-2-216791), bisstyrylbenzene derivatives (JP-A-1-245087), p-phenylene compounds (JP-A-3-33183), and phenanthroline derivatives (JP-A-5-205) 331459), and triazole derivatives (JP-A-7-90260).

The organic light-emitting substance and the organic electron-transporting substance in the mixed layer are used alone or as a mixture. In the mixture of the mixed layer, they are used in a total amount (even if only one substance is present) of 10 to 9%.
9% by weight and about 1 to 90% by weight of the aluminum alloy. This is because if the aluminum alloy is less than 1% by weight, the effect of reducing the voltage and suppressing the cathode oxidation is small, and if it exceeds 90% by weight, it is close to a case where the cathode is an aluminum alloy and no mixed layer is provided.

Further, in the mixed layer, the contents of the aluminum alloy and the organic material can be changed. Specifically, a mixed layer having a high alloy concentration is provided on the side close to the cathode, and a mixed layer having a high organic material concentration is provided on the side close to the organic light emitting layer. From the organic light emitting layer side.

The thickness of the mixed layer 5 is 0.5 to 50 nm, preferably 20 nm or less. This is 0.5
If it is less than nm, it is difficult to obtain the affinity and adhesion between the cathode and the organic light-emitting layer, and if it exceeds 50 nm, the driving voltage of the device becomes high, so that it is 0.5 to 50 nm.

As a method for producing this mixed layer, various thin film forming methods can be used. However, an aluminum alloy formed in a predetermined ratio and an organic luminescent substance or an organic electron transporting substance are deposited in different ways. A uniform mixed layer thin film can be easily prepared by putting the film in a boat and performing co-evaporation therefrom.

As the cathode of the present invention, various kinds of cathodes including known cathodes for organic EL can be used. For example, there are a magnesium-aluminum alloy, a magnesium-silver alloy, a magnesium-indium alloy, an aluminum-lithium alloy, and aluminum.

Particularly, in the case of this cathode, an aluminum alloy is preferable because the work function of the cathode itself can be reduced. Alkali metals, alkaline earth metals and rare earth metals are also preferred as alloy metals of this aluminum alloy.

Although this alloy metal is effective even in a very small amount, it is used in an amount of 0.01 part by weight or more based on 100 parts by weight of aluminum. In particular, it is preferably 0.1 to 20 parts by weight. Among these alloy metals, lithium, magnesium, calcium, yttrium, europium, and gadolinium are particularly preferable in terms of low work function, adhesion to the organic light emitting layer, and easy handling. The thickness of the cathode 6 is not particularly limited, but may be usually 10 to 500 nm.

The aluminum alloy in the mixed layer and the aluminum alloy used for the cathode may have the same metal composition or different metal compositions without any problem. By using such a mixed layer and a cathode together, the luminous efficiency is further improved, and stable luminescent characteristics can be maintained for a long period of time.

In the organic EL device of the present invention, in order to secure storage stability and driving stability in the atmosphere, the device is shielded from oxygen and moisture in the atmosphere by coating a polymer film or sealing with glass. You may.

The organic EL device of the present invention is used as a full-surface light emitter, used as a backlight or a wall illumination device of a liquid crystal display device, or formed by patterning pixels.
It can be used as a display.

[0042]

EXAMPLES Hereinafter, specific embodiments of the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not necessarily limited to these.

Example 1 (Example) An anode (sheet resistance 7Ω / □) was formed on a glass substrate by depositing ITO to a thickness of 200 nm. On this anode, MTDATA was deposited to a thickness of 10 nm by a vacuum deposition method to form a boundary layer. Next, TPD was deposited to a thickness of 50 nm to form a hole transport layer. Then, ALQ is applied to a film thickness of 5
An organic light emitting layer was formed by vapor deposition at 0 nm.

Next, an Al--Li alloy (aluminum 1
(Including 0.5 parts by weight of lithium with respect to 00 parts by weight) and ALQ were simultaneously co-evaporated using different evaporation boats to form a 10 nm-thick mixed layer containing 20% by weight of ALQ. Finally, the above Al-Li alloy was deposited to a thickness of 200 nm using a deposition boat to form a cathode,
An L element was produced.

Example 2 (Comparative Example) No mixed layer comprising the Al-Li alloy of Example 1 and ALQ was provided, and the cathode was replaced with Mg- instead of Al-Li alloy.
Ag alloy (silver is 37 parts for 100 parts by weight of magnesium)
An organic EL device was produced in the same manner as in Example 1 except that the organic EL element was used.

Example 3 (Comparative Example) An organic EL device was manufactured in the same manner as in Example 1 except that the mixed layer composed of the Al-Li alloy and ALQ was not provided.

Example 4 (Example) Same as Example 1 except that the cathode of Example 1 was replaced by an Mg-Ag alloy (containing 37 parts by weight of silver with respect to 100 parts by weight of magnesium) instead of the Al-Li alloy. Thus, an organic EL device was produced.

Examples 5 to 9 (Examples) In place of the Al-Li alloy of Example 1, Al-Mg (Example 5, magnesium was added in an amount of 0.5 with respect to 100 parts by weight of aluminum)
Parts by weight), Al-Ca (Example 6, aluminum 100
1 part by weight of calcium to 1 part by weight), Al-Y
(Example 7, 100 parts by weight of aluminum containing 10 parts by weight of yttrium), Al-Eu (Example 8, 100 parts by weight of aluminum containing 10 parts by weight of europium), Al-Gd (Example 9, 100 parts by weight of aluminum) An organic EL device was produced in the same manner as in Example 1, except that gadolinium was used in an amount of 10 parts by weight with respect to parts by weight.

Example 10 (Example) On the same ITO anode as that used in Example 1, TPD was deposited to a film thickness of 50 nm by a vacuum deposition method to form a hole transport layer. Then, bis (2-methyl-8-quinolinolato)
(Phenolate) Aluminum (III) and quinacridone were co-evaporated from different evaporation boats to a thickness of 40 nm to form an organic light emitting layer. At this time, the concentration of quinacridone was 0.5 mol%. Then, ALQ is applied to a thickness of 20 n
m to form a second organic light emitting layer.

Next, an Al—Ca alloy (aluminum 1
00 parts by weight and 2 parts by weight of calcium) and A
LQ is co-evaporated from a different evaporation boat and ALQ is 4
A 5 nm-thick mixed layer containing 0% by weight was formed. Further thereon, a second mixed layer having a thickness of 5 nm and containing 20% by weight of ALQ in the mixed layer was formed. Finally, the above Al
A cathode was formed by evaporating a -Ca alloy to a thickness of 200 nm.

Example 11 (Example) On the same anode as that used in Example 1, T was deposited by vacuum evaporation.
PD was deposited to a thickness of 50 nm to form a hole transport layer.
Next, bis (2-methyl-8-quinolinolato) aluminum (III) -μ-oxo-bis (2-methyl-8-quinolinolato) aluminum (III) was co-evaporated to a thickness of 50 nm to form an organic light emitting layer. .

Next, perylenetetracarboxylic diimide (PTCDI) and an Al-Gd alloy (aluminum 10
0 parts by weight and 15 parts by weight of gadolinium) were co-evaporated from different evaporation boats to give PTCDI of 30 parts by weight.
A mixed layer containing 10% by weight and having a thickness of 10 nm was formed. Finally, the above-mentioned Al-Gd alloy was deposited as a cathode to a thickness of 200 nm to form a cathode.

Example 12 (Example) The mixed layer containing the Al-Li alloy of Example 1 and ALQ was
An organic EL device was produced in the same manner as in Example 1 except that a mixed layer containing 1% by weight of a Li alloy and 99% by weight of ALQ was used.

Example 13 (Example) A mixed layer containing the Al—Li alloy of Example 1 and ALQ was
An organic EL device was produced in the same manner as in Example 1, except that a mixed layer containing 90% by weight of a Li alloy and 10% by weight of ALQ was used.

The luminous efficiency (the value (lm / W) at a current density of 20 mA / cm ² ) and the driving stability (10 mA / min. In nitrogen) of the organic EL devices produced in the above examples (Examples and Comparative Examples)
The time (hour) required for the initial luminance to drop to half of the original when driven at a constant current of ² cm ² ) and 10 m in nitrogen
Table 1 shows the measurement results of the dark spot area ratio (%) after driving at a constant current of A / cm ² for 100 hours.

[0056]

[Table 1]

[0057]

As described above, according to the present invention,
A mixed layer containing an organic light emitting substance and / or an organic electron transporting substance and an aluminum alloy is provided between the organic light emitting layer and the cathode. As a result, the barrier against electron injection from the cathode to the organic light emitting layer can be reduced, so that a device having excellent luminous efficiency can be obtained. In addition, since the adhesiveness to the cathode and the aluminum alloy have excellent chemical stability, it is possible to obtain an organic EL device having excellent light-emitting characteristics over a long period of time.

Further, since the mixed layer contains an organic light emitting substance and / or an organic electron transporting substance and an aluminum alloy, the adhesion between the organic light emitting layer and the cathode can be improved. Further, since the aluminum alloy has excellent chemical stability, the organic EL having excellent luminescence characteristics over a long period of time.
An element can be obtained. The present invention can be applied to various applications within a range that does not impair the effects of the present invention.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a typical example of an organic EL device of the present invention.

[Explanation of symbols]

 1: substrate 2: anode 3: hole transport layer 4: organic light emitting layer 5: mixed layer 6: cathode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Ryo Takahashi 1150 Hazawa-cho, Kanagawa-ku, Yokohama

Claims (3)

[Claims] 1. An organic electroluminescent device having at least an anode, a hole transport layer, an organic light emitting layer containing an organic light emitting substance, and a cathode, wherein an organic light emitting substance and / or between the organic light emitting layer and the cathode is provided. A mixed layer containing an organic electron transporting substance and an aluminum alloy is provided, and the aluminum alloy is at least one selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals as alloy metals with respect to 100 parts by weight of aluminum. 0.01 metal
An organic electroluminescent device comprising an alloy containing up to 50 parts by weight. 2. The cathode is made of an aluminum alloy. The aluminum alloy contains at least one metal selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals as an alloy metal per 100 parts by weight of aluminum. The organic electroluminescence device according to claim 1, wherein the organic electroluminescence device is an alloy containing from 01 to 50 parts by weight. 3. The organic electroluminescent device according to claim 1, wherein the aluminum alloy is an alloy containing at least one metal selected from the group consisting of lithium, magnesium, calcium, yttrium, europium and gadolinium as alloy metals. .