JP2000068057A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electroluminescent(EL) element securing superior color stability and having long service life and high luminous efficiency. SOLUTION: In an organic EL element 7, constituted by sandwiching plural organic luminous layers 83, 84 with a positive electrode 71 and a negative electrode 72, the organic luminous layers 83, 84 are laminated such that their ionization potential grows larger from the positive electrode 71 in the direction towards the negative electrode 72. The electron affinity for organic luminous material of at least one of the luminous layers 83, 84 is set at more 2.6 eV, and plural kinds of fluorescent materials having different colors are doped into the organic luminous layers 83, 84. Thereby, electrons and positive holes can be recombined in the organic luminous layers 83, 84, which improves color stability and luminous efficiency, and prolongs the service life of the element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an organic electroluminescence device, and more particularly, to an organic electroluminescence device having a structure in which a plurality of organic light emitting layers are sandwiched between an anode and a cathode.

[0002]

BACKGROUND ART Electroluminescence devices utilizing electroluminescence (hereinafter referred to as "EL" for electroluminescence)
Abbreviated. ) Is self-luminous, has high visibility, and is a completely solid element, and thus has features such as excellent impact resistance. Therefore, its use as a light emitting element in various display devices has attracted attention.

[0003] This EL element includes an inorganic EL element using an inorganic compound as a light emitting material and an organic EL element using an organic compound. Among them, the organic EL element, in particular, requires a large applied voltage. Research and development have been conducted as next-generation light-emitting elements because they can be reduced in size, can be easily miniaturized, consume low power, and can emit surface light.
The configuration of the organic EL device is based on the configuration of anode / organic light emitting layer / cathode and provided with a hole injection / transport layer or an electron injection layer as appropriate, for example, anode / hole injection / transport layer / organic. Known structures include a light emitting layer / cathode and an anode / hole injection / transport layer / organic light emitting layer / electron injection / transport layer / cathode. Here, the hole injecting / transporting layer has a function of injecting holes from the anode and transporting them to the organic light emitting layer, and the electron injecting / transporting layer injecting electrons from the cathode and transporting them to the organic light emitting layer. Has the function of transport. The organic light emitting layer has a function of receiving injection of holes and electrons and a function of emitting fluorescence by recombination of holes and electrons.

[0004] As a method of multicoloring the light emission of such an organic EL element, white light emitted from the organic EL element is converted into light of three colors by using three kinds of color filters of red, green and blue. There is a method of separating and extracting, a method of providing a fluorescent layer on the light extracting side of the blue organic light emitting layer, and converting the color of blue light to multicolor. In particular, the method has attracted attention because it is more efficient than the method because it uses blue light emission after color conversion. However, in any of the methods, since reduction in light extraction efficiency due to multicoloring is unavoidable, an organic EL device having high luminance and long life is required. In particular, in the method (1), an organic EL device which emits blue-green broadband light, specifically, an organic EL device having an initial luminance of 200 cd (candela) / m ² and a lifetime of 15,000 hr or more has been desired.

[0005] In response to such demands, various element configurations have been studied in order to improve the luminous efficiency and extend the life, and as one method, the luminous efficiency is improved by increasing the number of organic luminescent layers. Methods have been proposed. Specifically, (1) the organic light emitting layer has a two-layer structure, the first light emitting layer on the anode side is a blue light emitting layer made of an aluminum complex compound, and the second light emitting layer on the cathode side is a red fluorescent layer. A method of extracting white light as a red light-emitting layer comprising an aluminum complex compound containing a substance (EP0644349), (2) forming an organic light-emitting layer in a two-layer structure, and forming the first light-emitting layer on the anode side as a distyryl arylene-based A method of extracting white light (US Pat. No. 5,503,910) has been proposed in which a blue light-emitting layer composed of a compound is used, and a second light-emitting layer on the cathode side is a light-emitting layer obtained by adding a red fluorescent substance to an aluminum complex compound that emits green light.

Another method for extending the life of the organic EL device is to (3) provide both a single organic light emitting layer made of an aluminum complex and a hole transporting layer made of a diamine compound as orange. (4) a method of doping fluorescent rubrene (JP-A-7-65958), (4) a light-emitting layer comprising a mixture of an electron-transport compound comprising an aluminum complex and a hole-transport compound comprising a diamine compound; A method for obtaining luminescence having a green component and an orange component by incorporating coumarin and rubrene as dopants (WO 9
8/08360) is known.

[0007]

However, (1)
The organic EL device obtained by the method (2) has a problem that the emission is unstable and the emission color is easily changed. In particular,
In the method (1), since the aluminum complex used for the first light emitting layer and emits blue light has a short life, specifically, the half life at an initial luminance of 200 cd / m ² is shorter than 5000 hr. One light-emitting layer deteriorates quickly,
The life of the device itself was shortened, and the emission color changed drastically due to the deterioration of the first emission layer, so that practically usable performance was not obtained. Further, in the method (3), although orange light emission can be obtained from the hole transport layer, sufficient light emission cannot be obtained with other colors, so that multicoloring could not be achieved.
In the method (4), since four kinds of compounds are mixed to form a light-emitting layer, it is difficult to uniformly prepare the light-emitting layer. In any of the methods (1) to (4), blue-green light emission cannot be obtained, so that the above-described method cannot be employed, and thus, it is not possible to efficiently achieve multicolor.

[0008] It is an object of the present invention to provide an organic EL device which can realize multiple colors, can secure excellent color stability, and has a long life and high luminous efficiency.

[0009]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors to solve the above-mentioned problems, the organic light-emitting layer is multilayered and doped with a plurality of kinds of fluorescent substances, and the electron affinity and The present inventors have found that the object can be achieved by selecting an organic light emitting material constituting each organic light emitting layer based on the ionization potential and recombining holes and electrons in the organic light emitting layer. That is, in the above-described methods (1) and (2), holes easily pass from the organic light emitting layer to the cathode side, and recombination of holes and electrons in the organic light emitting layer is not sufficiently performed. In the method (3), the hole transport layer has a configuration in which electrons are difficult to be injected, and light emission in the hole transport layer is insufficient. Is low. The present invention has been completed based on such findings.

Specifically, the present invention relates to an organic EL device comprising an anode and a cathode, and a plurality of organic light-emitting layers sandwiched between the anode and the cathode, wherein each of the organic light-emitting layers comprises The organic light-emitting material is composed of an organic light-emitting material, and at least one layer is composed of an organic light-emitting material having an electron affinity of 2.6 eV or more, and the ionization potential of the organic light-emitting material increases from the anode side to the cathode side. The stacked organic light emitting layers are characterized by being doped with two or more kinds of fluorescent substances having different color systems as a whole.

Here, the electron affinity corresponds to the energy difference between the vacuum level and the conduction level of the organic host material, which is an organic luminescent material. The ionization potential is determined by the difference between the vacuum level and the organic host material. This corresponds to the energy difference from the valence electron level. In the present invention, since the plurality of organic light-emitting layers are stacked such that the ionization potential increases from the anode side toward the cathode side, holes can be prevented from passing from the organic light-emitting layer to the cathode side,
Since electrons and holes can be recombined in the organic light emitting layer, the device can emit light with high efficiency and excellent color stability can be obtained.

When an electron injection layer or the like is provided as another organic compound layer between the organic light emitting layer and the cathode, holes rarely pass through the electron injection layer or the like. Degradation can be prevented, and the quantitative balance between electrons and holes can be maintained, so that the loss of this balance does not promote the passage of holes.
Therefore, the deterioration of the electron injection layer due to the passage of holes can be prevented, and the life of the element can be extended. further,
The excited state generated by recombination of holes and electrons does not become light because energy is easily transferred to the cathode when generated in an electron injection layer or the like. However, in the present invention, holes and electrons are regenerated in an organic light emitting layer. Since they can be combined, it is possible to realize improvements in luminous efficiency and color stability.

Since the electron affinity of the organic light-emitting material constituting at least one organic light-emitting layer is specified to be 2.6 eV or more, an electron injection barrier (electron injection) that inhibits injection of electrons into the organic light-emitting layer. (The energy level difference between the level and the conduction level of the organic light emitting layer) can be reduced, so that injection of electrons into the organic light emitting layer can be facilitated and the luminous efficiency can be increased. In this case, all the organic light emitting layers may be made of organic light emitting materials each having an electron affinity of 2.6 eV or more.

Further, since a plurality of types of fluorescent substances are doped into the whole of the organic light-emitting layers laminated in a plurality of layers, light emission of a desired color can be obtained by appropriately selecting fluorescent substances having different color systems. Is obtained. Further, when a fluorescent substance is doped in the organic light emitting layer, energy transfer from the excited state of the organic host substance (organic light emitting material) generated by recombination of electrons and holes from the excited state of the fluorescent substance. This causes the fluorescent substance to emit light. Therefore, by configuring the organic light emitting layer with an organic host material and a fluorescent material, the balance between holes and electrons injected into the organic light emitting layer is improved, and as a result, the luminous efficiency and life of the device are improved. it can.

In this case, the plurality of organic light emitting layers include:
Three kinds of fluorescent substances of a first primary color system, a second primary color system, and a third primary color system may be doped. Here, the first main color system, the second main color system, and the third main color system are any of a red system, a green system, and a blue system. By appropriately adding the fluorescent substances of these three color systems to the organic light emitting layer,
Since stable white light emission can be obtained from the plurality of organic light emitting layers, multicoloring using a color filter can be easily performed.

In the above, the plurality of organic light emitting layers comprise a first light emitting layer on the anode side and a second light emitting layer laminated on the cathode side of the first light emitting layer. It is preferable that the fluorescent material of one primary color is doped, and the second light emitting layer is doped with the fluorescent material of the second primary color.

As described above, by doping the first and second light emitting layers, which will be the organic light emitting layers, with the respective fluorescent substances,
Since all organic light-emitting layers are doped with a fluorescent substance, the light-emitting efficiency of the entire device does not decrease due to the decrease in the light-emitting efficiency of the undoped organic light-emitting layer, and the light-emitting efficiency of the device is reliably increased. be able to. In addition, the organic light-emitting layer that is not doped may be rapidly deteriorated in driving, and the deterioration of the organic EL element may be accelerated by the deterioration of this layer. By doping, the progress of deterioration of the entire device can be delayed, so that a longer life can be realized.

In this case, the first light emitting layer may be doped with a blue fluorescent material, and the second light emitting layer may be doped with a green fluorescent material. By doing so, light emission of any of blue-green, greenish-blue, and bluish-green can be obtained. Light of a desired color can be efficiently produced.

In the above description, it is desirable that the difference in the ionization potential between the organic light emitting materials constituting each organic light emitting layer be 0.2 eV or more in the adjacent organic light emitting layers. By doing so, holes can be efficiently retained in the organic light emitting layer on the anode side, so that the luminous efficiency can be further improved. Further, it is preferable that all the organic light emitting materials are not metal complexes. This is because some of the metal complexes have a short life and are preferably avoided.

In the adjacent organic light emitting layers, the difference in electron affinity between the organic light emitting materials constituting each organic light emitting layer is 0.2%.
It is desirable to be eV or less. By doing so, the difference in electron affinity between the organic light emitting layers can be reduced,
Since the barrier for electron injection from the organic light emitting layer on the cathode side to the organic light emitting layer on the anode side can be reduced, the injection of electrons into the organic light emitting layer on the anode side, where electrons are difficult to inject, is facilitated. Can be.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [1] Organic Light-Emitting Layer (A) Organic Light-Emitting Material (Organic Host Material) In the organic EL device of the present invention, an organic light-emitting layer made of an organic light-emitting material is laminated to form a multilayer. These organic light emitting layers are doped with fluorescent substances of two or more kinds of color systems in total. That is, fluorescent substances of a plurality of color systems are appropriately added to the organic light emitting layer. As an organic host material that is one of the constituent components of the organic light emitting layer, holes and electrons can be injected, and holes and electrons are transported and have a function of emitting fluorescence by recombination, There is no particular limitation as long as the electron affinity is 2.6 eV or more, and various organic compounds can be used. That is, generally, the work function of the metal constituting the cathode is 3.0 eV or more,
Also, the conduction level of the electron injection / transport layer is often about 3.0 eV. Therefore, by setting the electron affinity of the host material in the organic light emitting layer to 2.6 eV or more, the electron injection barrier is reduced, thereby facilitating the injection of electrons into the organic light emitting layer and increasing the light emission efficiency. be able to. The electron affinity of the organic host material is 2.6 eV to 3.2 eV.
eV is particularly preferable, and the electron affinity of the host material of the organic light emitting layer closest to the cathode is 2.8 to 3.
It is preferable to be in the range of 1 eV from the viewpoint of extending the life.

When the ionization potential of the organic host material is in the range of 5.4 to 6.0 eV, holes can be easily injected into the organic light emitting layer, and an unreasonable voltage is not applied. It is preferable in terms of conversion.

Such an organic host substance can be selected from, for example, distyrylarylene derivatives represented by the general formula (I).

[0024]

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Here, in the general formula (I), k, m and n are each 0 or 1, and (k + m +
n) ≧ 1. In the formula, X and Y each independently represent a substituted or unsubstituted aryl group having 6 to 20 carbon atoms.
In the formula, R ^{1 to} R ¹² , R ^{3 ′} , R ^{4 ′} , R ^{9 ′} , R ^{10 ′} _,
R ³ ″, R ⁴ ″, R ⁹ ″ and R ¹⁰ ″ are each independently an alkyl group having 1 to 6 hydrogen atoms, an alkoxy group having 1 to 6 carbon atoms, an aryloxy group having 6 to 18 carbon atoms, 6-2
0 aryl group, amino group, alkylamino group, arylamino group, cyano group, nitro group, hydroxyl group, halogen atom, or

[0026]

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FIG. Here, the aryl group having 6 to 20 carbon atoms represented by X and Y includes a phenyl group, a naphthyl group, a biphenyl group, a terphenyl group, an anthranyl group,
Examples include a phenanthryl group, a pyrenyl group, and a perylenyl group. Examples of the substituent include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a sec-butyl group, a t-butyl group,
i-pentyl group, t-pentyl group, neopentyl group, n
-Hexyl group, alkyl group having 1 to 6 carbon atoms such as i-hexyl group, methoxy group, ethoxy group, n-propoxy group,
An alkoxy group having 1 to 6 carbon atoms such as an i-propoxy group, an n-butyloxy group, an i-butyloxy group, a sec-butyloxy group, an i-pentyloxy group, a t-pentyloxy group, an n-hexyloxy group, and a phenoxy group. An aryloxy group having 6 to 18 carbon atoms such as a naphthyloxy group, a phenyl group, an amino group, an alkylamino group, an arylamino group, a cyano group, a nitro group, a hydroxyl group or fluorine, chlorine,
Examples thereof include halogen atoms such as bromine and iodine atoms. These substituents may be single or plurally substituted.

Here, R ^{1 to} R ¹² , R ^{3 ′} , R ^{4 ′} , R ^{9 ′} ,
R ^{10 ′} _, R ³ ″, R ⁴ ″, R ⁹ ″, R ¹⁰ ″
As the alkyl group of 6, a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a sec-butyl group, a t-butyl group, an i-pentyl group, a t- Examples include a pentyl group, a neopentyl group, an n-hexyl group, and an i-hexyl group. Examples of the alkoxy group having 1 to 6 carbon atoms include a methoxy group, an ethoxy group, an n-propoxy group, an i-propoxy group, an n-butyloxy group,
Examples thereof include an i-butyloxy group, a sec-butyloxy group, an i-pentyloxy group, a t-pentyloxy group, and an n-hexyloxy group. Examples of the aryloxy group having 6 to 18 carbon atoms include a phenoxy group and a naphthyloxy group, and examples of the aryl group having 6 to 20 carbon atoms include a phenyl group and a naphthyl group. Further, an amino group, showed a -NH _2, alkylamino groups, -NHR,
-NR ₂ (R is an alkyl group having 1 to 6 carbon atoms) indicates, arylamino group, -NHAr, -NAr ₂ (Ar is an aryl group having 6 to 20 carbon atoms).

Examples of the halogen atom include fluorine, chlorine, bromine and iodine atoms. Further, in the general formula (I), when k = 1 and m = n = 0, R ¹
And R ² , R ³ and R ⁴ , R ⁵ and R ⁶ , R ⁷ and R ⁸ , R ⁹ and R ¹⁰ , and R ¹¹ and R ¹² are combined with each other to be saturated or unsaturated. May form a 5- or 6-membered ring. In this case, a ring may be formed via a hetero atom (N, O, S). As a specific example of this, R ¹
And R ² , R ⁹ and R ¹⁰ , R ⁵ and R ⁶ each form an unsaturated 6-membered ring,

[0030]

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And the like. R ⁷ and R ⁸ form a saturated 5-membered ring via a heteroatom O, R ¹¹ and R ¹² form a saturated 5-membered ring via a heteroatom N, and R ³ and R ⁴ , R ⁹ and R ^{9 When 10} forms a saturated 6-membered ring,

[0032]

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And the like. Further, in the general formula (I), when k = m = 1 and n = 0, the general formula is represented as follows.

[0034]

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(Where R ^{1 to} R ¹² , R ^{3 ′} , R ^{4 ′} ,
R ^{9 ′} and R ^{10 ′} are the same as described above. ) R ¹ and R ² , R ³
And R ⁴ , R ^{3 ′} and R ^{4 ′} , R ⁵ and R ⁶ , R ⁷ and R ⁸ , R ⁹ and R ¹⁰ , R ^{9 ′} and R ^{10 ′} , R ¹¹ and R ¹² are mutually bonded and saturated. Alternatively, it may or may not form an unsaturated 5-membered or 6-membered ring. In that case, a ring may be formed via a hetero atom (N, O, S).

R ² and R ³ , R ⁴ and R ^{3 '} , R ^4' and R 3
⁵ , R ⁸ and R ⁹ , R ¹⁰ and R ^{9 ′} , and R ^{10 ′} and R ¹¹ are bonded to each other to form or form a saturated or unsaturated 5- or 6-membered ring. It is not necessary. In that case, a ring may be formed via a hetero atom (N, O, S). Specific examples of these include R ² and R ³ , R ¹⁰
And R ^{9 ′} and R ^{4 ′} and R ⁵ each form a saturated 5-membered ring,

[0037]

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And the like. R ⁴ and R ³ ', R ¹⁰ and R ^9'
Forms a saturated 6-membered ring,

[0039]

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And the like. R ¹⁰

[0041]

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In the case where R ^{9 ′} is hydrogen and forms a 5-membered ring,

[0043]

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And the like. Further, in the general formula (I), when k = m = n = 1, the general formula is represented as follows.

[0045]

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(Where R¹~ R¹², R^{3 '}, R^Four',
R^{9 '}, R^Ten', R^Three″, R^Four″, R⁹″, R^Ten″ Is the same as above
The same. ) R¹And R^Two, R^ThreeAnd R^Four, R^{3 '}And R^Four', R^Three″ And R^Four″,
R^FiveAnd R⁶, R⁷And R ⁸, R⁹And R^Ten, R^{9 '}And R^Ten', R
⁹″ And R^Ten″, R¹¹And R¹²Are saturated with each other
May form an unsaturated 5- or 6-membered ring,
May not be formed. In that case, a heteroatom
A ring may be formed via (N, O, S).

Further, R^TwoAnd R^Three, R^FourAnd R^{3 '}, R^Four'And R
^Three″, R^Four″ And R^Five, R⁸And R⁹, R ^TenAnd R^{9 '}, R^Ten'When
R⁹″, R^Ten″ And R¹¹Are saturated or unsaturated
Even if it forms a saturated 5- or 6-membered ring, or
It may not be formed. In that case, the hetero atom (N,
A ring may be formed via O, S). These specific
A good example is R⁸, R⁹, R^Ten″, R¹¹But,

[0048]

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Wherein each unsaturated 6-membered ring is formed,
When R ^{3 ′} and R ^{4 ′} form a saturated 5-membered ring via the hetero atom N,

[0050]

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And the like. X and Y may be bonded to a substituent to form a substituted or unsubstituted saturated 5-membered ring or saturated 6-membered ring. As a specific styryl compound having a saturated 5-membered ring or 6-membered ring, when X and Y form a saturated 5-membered ring, the case where k = m = 1 and n = 0 is shown as an example.

[0052]

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When X and Y form a saturated 6-membered ring,

[0054]

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And the like. In the present invention, the glass transition temperature of the organic light emitting layer is preferably 75 ° C. or higher. As such an organic host compound, a compound represented by the general formula (I
I)

[0056]

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(Wherein, R ^{1 to} R ¹² , R ^{3 ′} , R ^{4 ′} , R ^{9 ′} ,
^{R 10 ', R 3 ",} R 4", R 9 ", R 10", X, Y, k, m
And n are the same as above. It is desirable to select from the compounds represented by ()). The styryl compound represented by the general formula (I) can be produced by various known methods. Specifically, there are the following three methods. [Method 1] General formula (a)

[0058]

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(Where k, m and n are each 0 or 1, and (k + m + n) ≧ 1.
R ^{1 to} R ¹² , R ^{3 ′} , R ^{4 ′} , R ^{9 ′} , R ^{10 ′} , R ³ ″,
R ⁴ ″, R ⁹ ″ and R ¹⁰ ″ are the same as described above, and R represents an alkyl group having 1 to 4 carbon atoms or a phenyl group.) And a general formula (b)

[0060]

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(Wherein X and Y are the same as described above) by condensing a carbonyl compound represented by the formula (Wittig reaction or Wittig-Horner) in the presence of a base.
Reaction). [Method 2] General formula (c)

[0062]

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(Where k, m and n are each 0 or 1, and (k + m + n) ≧ 1.
R ^{1 to} R ¹² , R ^{3 ′} , R ^{4 ′} , R ^{9 ′} , R ^{10 ′} , R ³ ″,
R ⁴ ″, R ⁹ ″ and R ¹⁰ ″ are the same as described above) and a dialdehyde compound represented by the general formula (d)

[0064]

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(Wherein X and Y are the same as described above, and R is the same as in the case of the general formula (a)).
g reaction or Wittig-Horner reaction). As a reaction solvent used in this synthesis, hydrocarbons, alcohols, and ethers are preferable. Specifically, methanol; ethanol; isopropanol; butanol; 2-methoxyethanol;
-Dimethoxyethane; bis (2-methoxyethyl) ether; dioxane; tetrahydrofuran; toluene; Dimethyl sulfoxide;
N, N-dimethylformamide; N-methylpyrrolidone; 1,3-dimethyl-2-imidazolidinone and the like are also preferably used. Particularly, tetrahydrofuran and dimethyl sulfoxide are preferred.

Examples of the condensing agent include sodium hydroxide, potassium hydroxide, sodium amide, sodium hydride, n-butyllithium, and sodium methylate, potassium
Alcoholates such as t-butoxide are preferred;
-Butyllithium, potassium-t-butoxide are preferred. The reaction temperature varies depending on the type of the reaction raw materials used and cannot be unambiguously determined, but can be generally specified in a wide range from 0 ° C to about 100 ° C. Particularly preferably 0
C. to room temperature. [Method 3] General formula (e)

[0067]

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(Where X, Y, R ¹ , R ² , R ⁷ , R ⁸
Or, R ⁵ , R ⁶ , R ¹¹ and R ¹² are the same as described above. )
A Grignard reagent prepared by reacting a bromo compound represented by the formula with Mg, and a general formula (f)

[0069]

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(Where k, m and n are each 0 or 1, and (k + m + n) ≧ 1. Also, R ³ , R ⁴ , R ⁹ , R ¹⁰ , R ^{3 ′} , R ^{3 4 '} , R9 ^' , R
^{10 ', R 3 ", R} 4", R 9 ", R 10" are as defined above. Can be synthesized by a Grignard reaction in which the dibromoarylene derivative represented by the formula (1) is coupled under a metal catalyst.

As the transition metal complex catalyst used for the coupling, a nickel catalyst and a palladium catalyst are preferable.
NiCl ₂ (dppp) (Tokyo Kasei), [NiCl
₂ (PPh ₃ ) ₂ ], PdcL ₂ (dppf), Pd
(PPh ₃ ) ₄ or the like is used. As a reaction solvent, dehydrated diethyl ether, THF, di-n-propyl ether, di-n-butyl ether, di-i-propyl ether, diethylene glycol dimethyl ether (diglyme), dioxane, dimethoxyethane (DME) and the like can be used. it can.

Preferably, diethyl ether or TH
F is good. Hereinafter, specific examples (1) to (62) of the styryl compound used in the present invention will be described, but the present invention is not limited thereto.

[0073]

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[0074]

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[0075]

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[0076]

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[0077]

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[0078]

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[0079]

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[0080]

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[0081]

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In the present invention, as long as it has the above-mentioned functions, it is not limited to the distyrylarylene derivative, and other organic host substances may be used. For example, bisanthracene derivative, styrylamine derivative, distyrylamine derivative, diamine derivative, triamine derivative,
An oligomer amine may be used. However, from the viewpoint of luminous efficiency, it is preferable to use a distyrylarylene derivative. Each organic light emitting layer may be composed of one kind of organic host substance, or may be composed of a combination of two or more kinds of organic host substances.

Such an organic host material (organic light emitting material) has a long half-life, specifically, 5000
It is preferable to use a material having a value of hr or more. In other words, when an organic host material having a short half-life is used, the life of the organic light emitting layer itself containing the organic host material is shortened, so that the emission of the fluorescent material in the organic light emitting layer decreases (deteriorates). The emission color may change, the lifetime of the entire device may be shortened, or the balance between holes and electrons may be lost, leading to accelerated deterioration. When confirming the half-life of each organic light emitting layer, the initial luminance of the organic EL element provided with only a predetermined organic light emitting layer to be measured, excluding the organic light emitting layer other than the object to be measured, is 200 cd / m 2. ^The life test may be performed in 2. This life test is generally
The measurement is performed by continuous constant current driving under a dry inert gas, and the time until the luminance is reduced to half is measured. The glass transition temperature of the organic light emitting material is preferably Tg> 100 ° C. There are conventionally used materials having a Tg <100 ° C., but they may change color under driving and may change color even under high-temperature storage.

(B) Layer Structure of Organic Light-Emitting Layer In the organic EL device of the present invention, as described above, the electron affinity of the organic host material constituting at least one organic light-emitting layer is set to 2.6 eV or more. In order to further improve the injectability of electrons into each organic light emitting layer and increase the luminous efficiency, it is preferable to stack and arrange the organic light emitting layers such that the electron affinity of the host material increases from the anode to the cathode. .

Specifically, for example, as a host material of the light emitting layer adjacent to the anode, 9,10-di [4- (2,2′-) having an electron affinity of 2.7 eV is used.
Diphenylvinyl-1-yl) phenyl] anthracene (hereinafter may be abbreviated as DPVDPAN. The structural formula (2) is used, and electron affinity is used as a host material of the light emitting layer adjacent to the light emitting layer on the cathode side. Is 2.82 eV
4,4'-bis (2,2-diphenylvinyl)-
2 ', 7'-diphenyl-4', 5 ', 9', 10'-
Tetrahydropyrene (hereinafter may be abbreviated as DPVDPTHHPy. The structural formula is the above (40)) or 4,4′-bis (2,2-diphenylvinyl) -terphenylene (hereinafter, referred to as having an electron affinity of 2.80 eV). DPVTP in some cases.).

In the arrangement in which the electron affinity of the host material increases from the anode to the cathode in this manner, in order to further improve the injectability of electrons into the organic light emitting layer and increase the luminous efficiency, the adjacent host material must be The difference in electron affinity is set to 0.
It is preferably set to 2 eV or less. Specific examples of such an arrangement include the examples described above.

Next, the relationship between the ionization potentials of the respective organic host materials constituting the organic light emitting layer will be described. In general, in organic substances, holes have higher mobilities than electrons, so holes that have not been recombined with electrons in the organic light-emitting layer are directly transmitted to the cathode and do not contribute to light emission. For this reason, in order to increase the luminous efficiency, it is necessary to keep the holes in the organic light emitting layer as much as possible and to increase the recombination probability of electrons and holes. To this end, it is effective to create an energy barrier when holes move from the anode to the cathode.

In the present invention, the organic light emitting layer is arranged such that the ionization potential of the organic host substance in the organic light emitting layer increases from the layer near the anode toward the cathode. For such an arrangement, an organic host material having a different ionization potential may be used. For example, DPVDPAN having an ionization potential of 5.60 eV is used as the organic host material of the light emitting layer adjacent to the anode. As a host material of an adjacent light emitting layer (second light emitting layer),
DPVDPTH with an ionization potential of 5.86 eV
Py or DPV with an ionization potential of 5.96 eV
There is a configuration using TP.

In order to increase the luminous efficiency of the organic EL element, the ionization potential of the host substance may be arranged as described above. In such an arrangement, the difference between the ionization potentials of the adjacent host substances is 0.1 mm. 2e
V or more is more preferable. With such an arrangement, the probability of holes remaining in the organic light emitting layer is further increased, and the luminous efficiency is further improved. As an arrangement in which the difference in ionization potential is 0.2 eV or more, for example, the above-described arrangement of the organic host substance can be given.

Next, the relationship between the energy levels of the organic host materials constituting each organic light emitting layer will be described with reference to the drawings. Generally, an organic EL element emits light through a series of processes of injection, transport, recombination, and generation of fluorescence into carriers (holes and electrons) into an organic light emitting layer. FIG. 1 shows the positional relationship of the energy level of a conventional organic EL device having one organic light emitting layer. In FIG. 1 (FIGS. 2 and 3
Similarly, the electron injection level 1 means the conduction level of the electron transport layer when the layer adjacent to the organic light emitting layer is the electron transport layer, and the metal constituting the cathode when the cathode is in direct contact with the organic light emitting layer. Corresponds to the Fermi level. On the other hand, the hole injection level 2 means the valence level of the hole transport layer when the layer adjacent to the organic light emitting layer is a hole transport layer, and the metal constituting the anode when the anode is in direct contact with the organic light emitting layer. Corresponds to the Fermi level.

When a voltage is applied between an anode and a cathode (not shown), electrons are injected from the electron injection level 1 to the conduction level 3 of the organic light emitting layer, while from the hole injection level 2, the valence electrons of the organic light emitting layer are changed. Holes are injected into level 4. The electrons and holes injected into the organic light emitting layer recombine in the organic light emitting layer, and the host material emits light from the generated excited state. At this time, if the fluorescent material is doped in the organic light emitting layer, energy transfer from the excited state of the host material generated by the recombination of electrons and holes to the excited state of the dopant occurs, and the dopant emits light.

FIG. 2 and FIG. 3 show one embodiment of the preferable positional relationship of the energy level in the organic light emitting layer of the organic EL device of the present invention. Here, the first light emitting layer as an organic light emitting layer adjacent to the anode and the hole transport layer,
A second light emitting layer is provided as an organic light emitting layer adjacent to a cathode, an electron transport layer, and the like. 2 and 3, the difference between the energy level between the vacuum level and the conduction level 31 (the conduction level of the first light emitting layer), or the difference between the vacuum level and the conduction level 32 (the conduction level of the second light emitting layer). The energy level difference corresponds to the electron affinity. As shown in FIG. 2, by using a host material having a high electron affinity, the electron injection barrier 52 into the organic light emitting layer is reduced, and the injection of electrons into the organic light emitting layer is facilitated, thereby improving the light emission efficiency. . Further, from FIG. 2, by adopting a configuration in which the electron affinity of the first light emitting layer is smaller than the electron affinity of the second light emitting layer, the injection of electrons into the second light emitting layer can be performed smoothly. Conceivable.

Further, by reducing the difference in electron affinity between the first light emitting layer and the second light emitting layer, the electron injection barrier 51 from the second light emitting layer to the first light emitting layer is reduced, and the first light emitting layer is reduced. Injection of electrons into the layer is facilitated, and luminous efficiency is improved.
For this reason, the host material constituting at least one organic light emitting layer has an electron affinity of 2.6 eV or more, and the organic light emitting layer has an electron affinity of each host material that increases from the anode side to the cathode side. And the difference in electron affinity between each host material is 0.2 e
V or less was defined as a preferred embodiment.

On the other hand, in the present invention, it is preferable that the ionization potential between the host materials constituting each organic light-emitting layer is arranged such that the ionization potential of the host material increases from the anode side to the cathode side. And That is, as shown in FIG. 2, the energy level is reduced (increased ionization potential) in the order of the hole injection level 2, the valence level 41 of the first light emitting layer, and the valence level 42 of the second light emitting layer. This is because holes can be kept in the light emitting layer and recombine with electrons in the light emitting layer so that the holes injected into each light emitting layer do not pass directly to the cathode. In particular, the difference in ionization potential corresponding to the hole injection barrier 62 is set to 0.2 eV
With the above, holes can be efficiently retained in the first light emitting layer, and luminous efficiency can be improved.

FIG. 3 also shows one aspect of a preferable positional relationship of the energy level in the organic light emitting layer of the organic EL device of the present invention. 2 and 3, the first and second light emitting layers have the same relationship with respect to the ionization potential, but differ in the relationship of electron affinity. That is, FIG.
In this case, the electron affinity of the second light emitting layer is lower than that of the first light emitting layer. For this reason, it is difficult to significantly increase the electron affinity of the organic host material constituting the second light emitting layer beyond 2.6 eV, and it is highly possible that the electron injection barrier 52 becomes larger than in the case of FIG. In this case, the electron injection property is not improved as much as in the case of FIG. Therefore, in the present invention, the configuration of FIG. 2 is more preferable than that of FIG.

(C) Fluorescent Substance On the other hand, a fluorescent substance, which is another component constituting the organic light emitting layer, is added (doped) to the organic light emitting layer in order to improve the efficiency and life of the organic EL device. Things. The fluorescent substance emits light in the organic light emitting layer by transferring energy from the excited state of the host substance generated by the recombination of electrons and holes to the excited state of the fluorescent substance.

The fluorescent substance is not particularly limited as long as it can emit light in response to recombination of holes and electrons. For example, known fluorescent dyes and the like can be used. It is important to select a material whose energy difference between the energy level and the conduction level) is smaller than the energy gap of the organic host material. This is because energy is efficiently transferred from the excited state of the organic host material to the excited state of the fluorescent substance (dopant).

As such a fluorescent substance, for example,
Perylene derivatives, rubrene derivatives, coumarin derivatives, stilbene derivatives, tristyrylarylene derivatives, distyrylarylene derivatives and the like can be mentioned. Among them, a distyrylarylene derivative can be preferably used, and an example of the derivative is diphenylaminovinylarylene.

In the present invention, two or more kinds of different color systems are selected from such fluorescent substances, and the selected fluorescent substance is doped into at least one of the plurality of organic light emitting layers. . For example, an organic light-emitting layer is composed of two layers, a first light-emitting layer on the anode side and a second light-emitting layer on the cathode side, and as a fluorescent substance, a first main color system, a second main color system, and a third main color. When appropriately selected from the three types of fluorescent substances of the system and used, preferred combinations of the fluorescent substance and the organic light emitting layer include the combinations shown in Table 1 below.

[0100]

[Table 1]

Of the combinations shown in Table 1, No. 1 in which a fluorescent substance was added to both the first and second light emitting layers. 1,3,3
The combination of 4, 5, and 6 is particularly preferable because it can achieve a longer life and higher efficiency.

Here, the first main color system, the second main color system and the third main color system are any of the red system, the green system and the blue system as described above. That is, when these three-color fluorescent substances are added, white light is emitted,
When blue and green fluorescent substances are added,
One of blue-green, greenish blue, and bluish green. When a red or green fluorescent substance is used, the color becomes one of orange, yellow, and yellowish orange, and when a red and blue fluorescent substance is used, the color becomes purple. And a luminescent color such as pink. Note that blue-green (blue) and orange (red) fluorescent substances may be added to obtain white light emission. Further, the color tone of the emission color can be set to a desired color tone by adjusting the amount of the fluorescent substance added, or adjusting the film thickness of the first and second light emitting layers.

The composition ratio of the organic host substance and the fluorescent substance in each organic light emitting layer may be appropriately selected in consideration of the luminous efficiency and the life of the device. It is preferable to add so as to be 1: 1 to 10: 1. It is preferable that such a fluorescent substance is uniformly dispersed in the organic light emitting layer. For example, the organic light emitting layer may be composed of a mixture of a fluorescent substance and an organic host substance, The organic light emitting layer may be constituted by copolymerizing a substance with a predetermined ratio and using the copolymer.

[2] Configuration of Organic EL Device (A) Device Configuration The layer configuration of the organic EL device of the present invention is not particularly limited, and may have various modes. A structure in which two or more organic light emitting layers are sandwiched between the cathodes), and a hole injection transport layer or an electron injection layer may be interposed as an organic compound layer as necessary. Examples of the layer configuration of the organic EL element formed on the transparent substrate include the following. Anode / organic light emitting layer (two or more layers) / cathode anode / hole injection layer / organic light emitting layer (two or more layers) / cathode anode / organic light emitting layer (two or more layers) / electron injection layer / cathode anode / hole injection Layer / organic light emitting layer (two or more layers) / electron injection layer / cathode anode / hole injection layer / hole transport layer / organic light emitting layer (two or more layers) / electron injection layer / cathode

In these structures (1) to (12), the organic compound layers such as the hole injection layer, the hole transport layer, and the electron injection layer are not particularly limited as long as they have the functions described later. In addition, between the adjacent organic light emitting layers, a layer made of a mixture of organic light emitting materials constituting these two organic light emitting layers may be interposed. Further, between the organic light emitting layer and another layer adjacent to the organic light emitting layer, a layer in which a material forming the other layer and an organic light emitting material forming the organic light emitting layer are mixed is interposed. Is also good. Further, a layer having another function, for example, a layer serving as an electron barrier or a layer serving as a hole barrier may be provided between the organic light emitting layers. In the above configuration, an element can be manufactured by laminating an anode to a cathode in order on a transparent substrate, or
The element can also be manufactured by laminating in order from the cathode side.
Such an organic EL element is preferably supported on a substrate, and there is no particular limitation on the substrate, and those conventionally used in organic EL elements, for example, those made of glass or plastic can be employed. In this case, by using a transparent substrate having transparency, light can be extracted through the transparent substrate. Further, light may be extracted from the opposite side of the transparent substrate by using a transparent material for the anode and / or the cathode.

(B) Hole Injection / Transport Layer The hole injection / transport layer (hole injection layer, hole transport layer) has a function of injecting holes from the anode and transmitting the holes to the light emitting layer. Since the injection of electrons into the layer is not considered, electrons are hardly injected. Therefore, even if the hole injection transport layer is doped with a fluorescent substance, the luminous efficiency is extremely low, and the contribution to the luminous efficiency of the device is extremely small.

The function of transmitting holes is 10 ⁴ to 1
0 when an electric field is applied in ⁶ V / cm those having 10 ^-6 cm ² / V · s or more hole mobility is preferable. If necessary, the hole injection layer and the hole transport layer can be overlapped. As a material used for such a hole injection transport layer, for example, a compound represented by the general formula (III)

[0108]

Embedded image

Compounds represented by the following formulas can be mentioned.
In the general formula (III), Q ¹ and Q ² each represent a group having a nitrogen atom and at least three carbon rings (at least one of which is an aromatic ring such as a phenyl group); G may be the same or different, and G represents a cycloalkylene group, an arylene group or a linking group comprising a carbon-carbon bond.

In the present invention, as the material of the hole injection transport layer, a compound represented by the above general formula (III) may be selected from oligomer amines in which three or more arylamines are connected in a linear or branched manner. It is preferable to choose from. Such compounds include, for example, those represented by the general formula (IV)

[0111]

Embedded image

(In the formula, R ^{13 to} R ¹⁷ each represent an alkyl group, an alkoxy group or a phenyl group, which may be the same or different. When the substituent is a phenyl group, May be condensed with a group to be formed to form a naphthyl group.), And specific examples thereof include the following.

[0113]

Embedded image

These hole injecting and transporting materials may be used alone or in combination of two or more.

(C) Electron injection layer The electron injection layer (electron injection transport layer) has a function of transmitting electrons injected from the cathode to the organic light emitting layer.
The material can be arbitrarily selected from conventionally known electron transfer compounds. Specifically, a metal complex of 8-hydroxyquinoline or a derivative thereof, or an oxadiazole derivative is preferably used. Examples of metal complexes of 8-hydroxyquinoline or derivatives thereof include:
Metal chelate oxanoid compounds including a chelate of oxine (generally 8-quinolinol or 8-hydroxyquinoline) and the like. These compounds may be used alone or in combination of two or more.

(D) Anode The anode is an electrode for injecting holes into the device. As the anode, a metal, an alloy, an electrically conductive compound or a mixture thereof having a large work function (4 eV or more) is used. An electrode material is preferably used. Specific examples of such an electrode material include metals such as Au, CuI, and IT.
Conductive transparent materials such as O (indium tin oxide), SnO ₂ , and ZnO are exemplified. The anode can be formed by using these electrode substances to form a thin film by a method such as vacuum deposition or sputtering. When light emission is extracted from the electrode serving as the anode, the transmittance for light emission is 1
It is desirable to make it larger than 0%, and the sheet resistance as an electrode is preferably several hundred Ω / □ or less. Further, the film thickness is selected in the range of usually 10 nm to 1 μm, preferably 50 to 200 nm, though it depends on the material.

(E) Cathode The cathode is an electrode for injecting electrons into the device. As the cathode, a metal, an alloy, an electrically conductive compound and a mixture thereof having a small work function (4 eV or less) are used. What is used as a substance is used. Specific examples of such an electrode material include sodium, sodium-potassium alloy, magnesium, lithium, magnesium / copper mixture, magnesium / silver alloy, aluminum-lithium alloy, Al / Al ₂ O ₃ laminate, indium, rare earth metal And the like.

The cathode can be produced by using these electrode substances to form a thin film by a method such as vacuum evaporation or sputtering. When light is extracted from the electrode serving as the cathode, it is desirable that the transmittance for the light emission be greater than 10%, and the sheet resistance as the electrode is 10%.
0 Ω / port or less is preferred. Further, although the film thickness depends on the material, it is usually 10 nm to 1 μm, preferably 50 to 200 n.
m.

[3] Production of Organic EL Device Next, a preferred method for producing an organic EL device will be described. First, a thin film made of a desired electrode material, for example, a material for an anode, is formed on an appropriate substrate by 10 nm to 1 μm, preferably 5 nm.
An anode is formed by a method such as vapor deposition or sputtering so as to have a thickness in the range of 0 to 200 nm.
Next, a thin film made of each material of a hole injection layer, a hole transport layer, two or more organic light emitting layers, and an electron injection layer, which are element materials, is formed on the anode.

As a method for producing these thin films, there are a spin coating method, a casting method, a vapor deposition method and the like, and a vacuum vapor deposition method is preferred because a uniform film is easily obtained and a pinhole is hardly formed. preferable. When a vapor deposition method is adopted as the film forming method, the vapor deposition conditions vary depending on the type of the compound to be used, the target crystal structure of the molecular deposition film, the association structure, and the like, but generally, the boat heating temperature of the vapor deposition source is 50 to 400 ° C. ,
Vacuum degree 10 ^-6 to 10 ^-3 Pa, deposition rate 0.01 to 50 n
m / sec, substrate temperature -50 to 300 ° C, film thickness 5 nm to 5μ
It is desirable to select an appropriate value within the range of m.

As a method of doping the organic light emitting layer with a fluorescent substance, for example, a co-evaporation method with an organic host substance can be mentioned. Specifically, 2
Prepare two resistance heating boats, put the organic host material in one, put the fluorescent material as a dopant in the other,
By simultaneously heating the two boats and simultaneously depositing these materials, a fluorescent material can be doped into the organic light emitting layer.

After forming these organic compound layers, a thin film made of a cathode material is formed thereon to a thickness of 10 nm to 1 μm, preferably 50 to 200 nm, for example, by vapor deposition or sputtering. A cathode is formed by forming a film by the method described above, and a desired organic EL device is obtained. In addition,
In the production of this organic EL device, it is also possible to produce the organic EL device by reversing the production order, providing the cathode on the substrate, and then laminating the above layers in the reverse order.

The thus obtained organic EL device has:
When a DC voltage is applied, light emission can be observed by applying a voltage of about 3 to 40 V with the anode having a positive polarity and the cathode having a negative polarity. Also, even if a voltage is applied with the opposite polarity, no current flows and no light emission occurs. Further, when an AC voltage is applied, light is emitted only when the positive electrode becomes + and the negative electrode becomes-. The waveform of the applied alternating current may be arbitrary.

[0124]

[Example 1]

(1) Element Configuration of Organic EL Element FIG. 4 shows an organic EL element 7 of this example.
The organic EL element 7 has an element configuration in which an organic compound layer 73 is sandwiched between an anode 71 and a cathode 72, and is formed on a transparent glass substrate 79. The anode 71 is formed on a glass substrate 79, and the organic compound layer 7 is formed on the anode 71.
3 are stacked, and a cathode 72 is provided thereon. The organic compound layer 73 includes a hole injection layer 81 formed on the anode 71, a hole transport layer 82 stacked thereon, and an organic light emitting layer stacked on the hole transport layer 82. The first light-emitting layer 83 and the second light-emitting layer 84 as the first layer, and the electron injection layer 85 laminated on the second light-emitting layer 84 on the cathode 72 side, and the cathode 72 is formed on the electron injection layer 85. Have been.

(2) Production of Organic EL Device The organic EL device of Example 1 was produced in the following procedure. That is, 25 mm x 75 mm x 1.1 m
A transparent support substrate was formed by forming an ITO electrode with a thickness of 120 nm on an m-size glass substrate. The substrate was ultrasonically cleaned with isopropyl alcohol for 5 minutes, then with pure water for 5 minutes, and finally again with isopropyl alcohol for 5 minutes. After that, isopropyl alcohol was removed from the surface of the substrate by spraying dry nitrogen, and then ultraviolet / ozone cleaning was performed.

The washed transparent support substrate was fixed to a substrate holder of a commercially available vacuum evaporation apparatus (manufactured by Nippon Vacuum Engineering Co., Ltd.), and seven molybdenum resistance heating boats were prepared. Each of these boats has 4,4′-bis [N, N-di- (m-tolyl) amino] -4 ″ -phenyl-triphenylamine (hereinafter referred to as “hole injection material”).
500 mg, 4,4′-bis [N-phenyl-N- (1-naphthyl) as a hole transport material
-4-aminophenyl] triphenylamine (hereinafter referred to as T
500 mg, 9,10-di [4- (2,9) as a light emitting material (organic host material) of the first light emitting layer
2'-diphenylvinyl-1-yl) phenyl] anthracene (DPVDPAN; structural formula is (2)) 100
mg, 4,4′-bis [2- (4- (N, N-diphenylamino) phenyl) as a fluorescent substance of the first light emitting layer
Vinyl] biphenyl (hereinafter abbreviated as DPAVBi) 10
0 mg, 4,4 ″ ′-bis (2,2-diphenylvinyl) as a light emitting material (organic host substance) of the second light emitting layer
-(2 ', 2''-diphenylquarterphenylene)
(Hereinafter, abbreviated as DPVDPQP, and the structural formula is (3
1)) 100 mg, 3 as a fluorescent substance of the second light emitting layer
100 mg of-(2'-benzothiazolyl) -7-diethylaminocoumarin (hereinafter abbreviated as coumarin 6) and tris (8-hydroxyquinoline) aluminum (hereinafter abbreviated as Alq) as an electron injecting material were added.

Then, the inside of the vacuum chamber is set to 1 × 10 ⁻⁴ P
After reducing the pressure to a, first, the boat containing the TPD 74 was heated to deposit the TPD 74 on the transparent support substrate (on the ITO electrode) to form a 60-nm-thick hole injection layer. Next, the boat containing the TPD 78 was heated to evaporate the TPD 78, and a hole transport layer having a thickness of 20 nm was formed on the hole injection layer. Next, the boat with DPVDPAN and DPA
DPVDPA by simultaneously heating the boat containing VBi
N and DPAVBi were simultaneously evaporated, and a 20 nm-thick first light emitting layer was deposited on the hole transporting layer. In addition,
The weight ratio between DPVDPAN and DPAVBi in the first light emitting layer was 40: 1.

Subsequently, the boat containing DPVDPQP and the boat containing coumarin 6 are simultaneously heated to obtain DPVDP.
The QP and coumarin 6 were evaporated, and a second light-emitting layer having a thickness of 20 nm was deposited on the first light-emitting layer. The weight ratio between DPVDPQP and coumarin 6 in the second light emitting layer was 40: 1. After that, the boat containing Alq is heated to deposit Alq on the second light emitting layer, and the thickness is 20 nm.
Was formed.

Next, the substrate on which the film was formed was taken out of the vacuum chamber, a stainless steel mask was placed on the electron injection layer, and the substrate was fixed to the substrate holder again. continue,
Lithium concentration of 5 atom% consisting of aluminum and lithium
Is used as a vapor deposition material for forming a cathode, the degree of vacuum at the time of vapor deposition is 1 × 10 ⁻⁴ Pa, and the vapor deposition rate is 0.5 to 1.0 nm.
/ Second to form a cathode having a thickness of 150 nm.

In this manner, the first light emitting layer in which DPVDPAN is doped with DPAVBi as a blue fluorescent substance in DPVDPAN and the second light emitting layer in which DPVDPQP is doped with coumarin 6 as a fluorescent substance are formed by hole transport. An organic EL device sandwiched between an anode and a cathode via a layer, a hole injection layer, and an electron injection layer was produced.

(3) Luminescence Test of Organic EL Device The organic EL device of Example 1 obtained in (2) was
The light emission state, initial performance, and half-life (half-life) were examined. That is, the organic EL element has a positive ITO electrode,
When the l-Li alloy electrode was made negative and a DC voltage of 6 V was applied, uniform blue-green light emission was obtained. Initial performance was as follows: applied voltage 6 V, current density 2.0 mA / cm ² , luminance 210
cd / m ² , and the luminous efficiency was as high as 10.05 cd / A. Further, as far as the visual observation and the observation with a luminance meter (manufactured by Minolta Co., Ltd., CS-100) were observed, no light emitting point was recognized in the light emitting surface, and the uniformity of light emission was excellent. When the device was driven at a constant current with an initial luminance of 100 cd / m ² under a nitrogen stream, the luminance was 50 cd / m ^2.
The half-life before becoming was 8200 hours. Also,
It was confirmed that there was no change in the emission color.

[Embodiment 2] In this embodiment 2, the same procedure as in the above-mentioned embodiment 1 except that DP
Instead of VDPQP, 4,4′-bis (2,2-diphenylphenyl) -2 ′, 7′-diphenyl-4 ′,
5 ', 9', 10'-tetrahydropyrene (DPVDP
THPy. The structural formula is the same as that of (40)),
An organic EL device was manufactured in the same manner as in Example 1. When a light emission test was performed on the obtained organic EL device in the same manner as in Example 1, uniform blue-green light emission was obtained.
In addition, no light-emitting point was found in the light-emitting surface, and there was no change in the light-emitting color even after the life test. Table 2 shows the results regarding the luminous efficiency and the lifetime.

Example 3 Example 3 is an experiment in which the first light emitting layer is doped with a blue fluorescent substance and the second light emitting layer is doped with an orange (red) fluorescent substance. That is, in the third embodiment, 4,4′-bis (2,2-diphenylvinyl) is used as the host material of the second light emitting layer in the first embodiment instead of DPVDPQP.
Coumarin 6 using terphenylene (DPVTP)
Except that rubrene, an orange fluorescent substance, was used instead of
An organic EL device was manufactured in the same manner as in Example 1.
When a light emission test was performed on the obtained organic EL device in the same manner as in Example 1, uniform white light emission was obtained.
In addition, no light-emitting point was found in the light-emitting surface, and there was no change in the light-emitting color even after the life test. Table 2 shows the results regarding the luminous efficiency and the lifetime.

[Comparative Example 1] In Comparative Example 1, a fluorescent substance DPAVBi and coumarin 6 were omitted when the first and second light emitting layers were prepared in Example 1 described above.
An organic EL device was manufactured in the same manner as in Example 1, and a luminescence test was performed in the same manner. Table 2 shows the results.

[Comparative Example 2] In Example 1, the DPVD
An organic EL device was prepared in the same manner as in Example 1 except that the first light emitting layer was formed using TPD78 instead of PAN, and a light emission test was performed in the same manner. The weight ratio between TPD78 and DPAVBi in the first light emitting layer was 40: 1 as in Example 1. Table 2 shows the results of the luminescence test.
Shown in

[Comparative Example 3] In Example 1, the DPVD
An organic EL device was manufactured in the same manner as in Example 1 except that the first light emitting layer was formed using DPVDPQP instead of PAN, and the second light emitting layer was formed using DPBDPAN instead of DPVDPQP. A luminescence test was performed in the same manner. Table 2 shows the results of the luminescence test.

[0137]

[Table 2]

Table 3 shows the electron affinity and ionization potential of the organic host substance used in each of the examples and comparative examples.

[0139]

[Table 3]

From Tables 2 and 3, it was confirmed that, in comparison with Comparative Examples 2 and 3, in Examples 1 to 3, luminous efficiency equal to or higher than that was achieved, and the life was significantly extended. Was done. Comparing Comparative Example 1 in which the fluorescent substance of the first and second light emitting layers is omitted with Example 1, Comparative Example 1 has lower luminous efficiency and shorter lifetime. From this, it was confirmed that the doping of the fluorescent substance contributes to both the improvement of the luminous efficiency and the extension of the lifetime. Further, comparing Comparative Example 2 and Example 1, it is possible to obtain a more efficient and longer life organic EL device by setting the electron affinity of the organic light emitting material constituting the organic light emitting layer to 2.6 eV or more. You can see that. However, it has been shown that a device having a good life can be obtained even if the first light emitting layer having an electron affinity of 2.6 eV or less is used. Furthermore, comparing Comparative Example 3 with Example 1, it is necessary to make the ionization potential of the second light emitting layer larger than the ionization potential of the first light emitting layer in order to achieve higher efficiency and longer life. It can be seen that it is.

As described above, the performances of the organic EL devices of Examples 1 to 3 are superior to those of Comparative Examples 1 to 3. However, when Examples 1 to 3 are compared, the performance is higher than that of Example 1. Examples 2 and 3 are even better. The reason for this is that, in Examples 2 and 3, the organic host substance forming the second light emitting layer has a higher electron affinity than the first light emitting layer, whereas in Example 1, the first light emitting layer is formed. It is considered that the organic host substance has a higher electron affinity. Therefore, in Examples 2 and 3, it is considered that the injection property of electrons into the organic light emitting layer was further improved, and the luminous efficiency was improved.
In addition, since the injection property of electrons into the organic light emitting layer is further improved, the abundance of holes and electrons in the organic light emitting layer is more balanced, and a smoother energy transfer is performed, so that a longer life is achieved. It is thought that the realization was realized.

[Embodiment 4] The present embodiment 4 is an experiment in which the first light emitting layer is doped with a blue fluorescent substance and an orange fluorescent substance, and the second light emitting layer is doped with a green fluorescent substance. In the fourth embodiment, in the first embodiment,
An organic EL device was obtained in the same manner as in Example 1, except for the following changes.

That is, eight resistance heating boats were prepared, and in the same manner as in Example 1, each of the seven types of materials was put into the boat, and rubrene as an orange fluorescent substance was put into the boat alone. After the hole injection layer and the hole transport layer were formed in the same manner as in Example 1, the boat containing DPVPPAN, the boat containing DPAVBi, and the boat containing rubrene were heated to obtain a DP.
VDPAN, DPAVBi and rubrene were simultaneously evaporated, and a 20 nm-thick first light emitting layer was deposited and deposited on the hole transport layer. Note that DPVDPAN in the first light emitting layer
The weight ratio between DPAVBi and rubrene was 40: 1: 1. Thereafter, the second light emitting layer, the electron injection layer, and the cathode were laminated in the same manner as in Example 1 to obtain an organic EL device of Example 4.

The light emitting state, initial performance, and half-life (half-life) of the obtained organic EL device were examined.
That is, the organic EL element has a positive ITO electrode,
When the i-alloy electrode was made negative and a DC voltage of 6 V was applied, uniform white light emission was obtained. Initial performance was as follows: applied voltage 6 V, current density 2.0 mA / cm ² , luminance 170 cd /
m ² , and the luminous efficiency was 8.5 cd / A, which was a high efficiency. In addition, a visual and luminance meter (manufactured by Minolta, CS-1)
As observed in 00), no light-emitting point was observed in the light-emitting surface, and the light emission was excellent in uniformity. Then, when this element was driven at a constant current under a nitrogen stream at an initial luminance of 100 cd / m ² , the half-life until the luminance reached 50 cd / m ² was 7,300 hours. It was also confirmed that there was no change in the emission color.

[Embodiment 5] In the present embodiment 5, the same procedure as in the above embodiment 4 was carried out except that DP was used as the organic host material of the second light emitting layer.
Instead of VDPQP, DPVDP used in Embodiment 2
Except for using THPy (the structural formula is the above (40)),
An organic EL device was produced in the same manner as in Example 4. When a light emission test was performed on the obtained organic EL device in the same manner as in Example 4, uniform white light emission was obtained. In addition, no light-emitting point was found in the light-emitting surface, and there was no change in the light-emitting color even after the life test. Table 4 shows the results regarding the luminous efficiency and the lifetime.

[Embodiment 6] In this embodiment 6, according to the above embodiment 4, DPVD is used as the host material of the second light emitting layer.
An organic EL device was manufactured in the same manner as in Example 1 except that DPVTP used in Example 3 was used instead of PQP. When a light emission test was performed on the obtained organic EL device in the same manner as in Example 1, uniform white light emission was obtained. In addition, no light emitting point is seen in the light emitting surface,
There was no change in the emission color even after the life test. Table 4 shows the results regarding the luminous efficiency and the lifetime.

Comparative Example 4 An organic EL was prepared in the same manner as in Example 4 except that the following points were changed.
An element was obtained. That is, the fluorescent substance in the first light emitting layer was omitted, and this was used as the second light emitting layer. TP which is a hole transport material
The rubrene was evaporated together with D78 to dope the hole transport layer with rubrene, and this was used as a first light emitting layer. A light emission test was performed in the same manner as in Example 4. Table 4 shows the results.

[0148]

[Table 4]

Table 4 shows that when Examples 4 to 6 are compared with Comparative Example 4, the white light emitting devices of Examples 4 to 6 have a long life and high efficiency. The light emitting layer has a TPD7 having an electron affinity of 2.4 eV and less than 2.6 eV.
8 and rubrene is added only to this layer, so that it is difficult to inject electrons, deterioration is likely to occur, and the device has a short life. Also, from Table 4, as the first light emitting layer, the electron affinity is 2.4 eV and 2.6.
It has been found that using TPD78 lower than eV and adding a fluorescent substance to both the first and second light-emitting layers increases the life.

[Embodiment 7] In Embodiment 7, in Embodiment 4, the material of the first light emitting layer was TPD78, and the material of the second light emitting layer was DPVDPAN. The electron affinity of TPD78 was 2.4 eV, the ionization potential was 5.4 eV, the first layer had an electron affinity of 2.6 eV or less, and the second layer had an electron affinity of 2.6 eV or more. Then, rubrene was used instead of coumarin 6 as a fluorescent substance added to the second light emitting layer. From Example 7, it can be seen that when at least one light emitting layer has an electron affinity of 2.6 eV or more, considerable efficiency and life can be realized.

[0151]

According to the present invention, in an organic electroluminescence device having a plurality of organic light emitting layers sandwiched between an anode and a cathode, the ionization potential of the plurality of organic light emitting layers is increased from the anode side to the cathode side. By stacking the layers so as to increase the size, electrons and holes can be surely recombined in the organic light emitting layer, so that the device can emit light with high efficiency and have excellent color stability. Further, since holes can be prevented from passing to the cathode side, the life of the element can be prolonged.

By setting the electron affinity of the organic light-emitting material constituting at least one organic light-emitting layer to 2.6 eV or more, the electron injection barrier that hinders the injection of electrons into the organic light-emitting layer can be reduced, and Since electrons can be easily injected into the layer, luminous efficiency can be increased. Further, by doping the entire organic light emitting layer with a fluorescent substance having a plurality of different color systems, light emission of a desired color can be obtained, and the balance between holes and electrons injected into the organic light emitting layer is improved. Therefore, the luminous efficiency and life of the device can be improved.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a positional relationship between energy levels near a light emitting layer of an organic EL element.

FIG. 2 is a conceptual diagram showing a particularly preferred embodiment of a positional relationship between energy levels in the vicinity of a light emitting layer of the organic EL device of the present invention.

FIG. 3 is a conceptual diagram showing a preferred embodiment of a positional relationship of energy levels in the vicinity of a light emitting layer of the organic EL device of the present invention.

FIG. 4 is a view showing an element configuration of an organic EL element of Example 1 of the present invention.

[Explanation of symbols]

Reference Signs List 1 electron injection level 2 hole injection level 3 conduction level 4 valence electron level 7 organic EL element 31 conduction level of first light emitting layer 32 conduction level of second light emitting layer 41 valence level of first light emitting layer 42 second light emitting layer 51 Difference in electron affinity between the first light emitting layer and the second light emitting layer 52 Difference between electron affinity and electron injection level in the second light emitting layer 61 Difference between ionization potential and hole injection level in the first light emitting layer 62 Difference in ionization potential between one light emitting layer and second light emitting layer 71 Anode 72 Cathode 73 Organic compound layer 79 Transparent substrate 81 Hole injection layer 82 Hole transport layer 83 First light emitting layer (organic light emitting layer) 84 Second light emitting layer ( Organic light emitting layer) 85 Electron injection layer

Claims (8)

[Claims] 1. An organic electroluminescence device comprising an anode and a cathode, and a plurality of organic light-emitting layers sandwiched between the anode and the cathode, wherein each of the organic light-emitting layers is made of an organic light-emitting material. And at least one layer is made of an organic light emitting material having an electron affinity of 2.6 eV or more, and is stacked in the order of increasing the ionization potential of the organic light emitting material from the anode side toward the cathode side, An organic electroluminescent device, wherein the plurality of organic light emitting layers are doped with two or more kinds of fluorescent substances having different color systems in total. 2. An organic electroluminescence device comprising an anode and a cathode, and a plurality of organic light-emitting layers sandwiched between the anode and the cathode, wherein each of the organic light-emitting layers has an electron affinity of 2. 6 eV or more of organic light emitting materials, and the organic light emitting materials are stacked in the order of increasing ionization potential from the anode side to the cathode side. An organic electroluminescent device characterized by being doped with fluorescent substances having different color systems as described above. 3. The organic electroluminescence device according to claim 1, wherein the plurality of organic light-emitting layers include a first main color system, a second main color system, and a third main color system. An organic electroluminescent device, wherein the organic electroluminescent device is doped with various kinds of fluorescent substances. 4. The organic electroluminescence device according to claim 1, wherein the plurality of organic light emitting layers are a first light emitting layer on an anode side and a cathode on the first light emitting layer. A first light emitting layer is doped with a fluorescent material of a first main color system, and the second light emitting layer is doped with a fluorescent material of a second main color system. An organic electroluminescent device, comprising: 5. The organic electroluminescence device according to claim 4, wherein the first light emitting layer is doped with a blue fluorescent material, and the second light emitting layer is doped with a green fluorescent material. An organic electroluminescent device, comprising: 6. The organic electroluminescent device according to claim 1, wherein the difference in ionization potential between the organic light emitting materials constituting each organic light emitting layer is 0 in the adjacent organic light emitting layers. An organic electroluminescence device characterized by being at least 2 eV. 7. The organic electroluminescence device according to claim 1, wherein a difference in electron affinity between the organic light emitting materials constituting each organic light emitting layer is 0 in adjacent organic light emitting layers. An organic electroluminescence device, which is not more than 2 eV. 8. The organic electroluminescence device according to claim 1, wherein the organic light emitting material does not contain a metal complex.