JPH08264279A - Organic thin film luminescent element - Google Patents

Abstract

PURPOSE: To use metal of a small work function for electron injection by providing a luminescent layer, a protective layer, an electric charge transportation layer so as to be sandwiched between electrodes, and forming the electrodes of a conductive carbon intercalation complex containing metal of the work function of 3.0ev or less. CONSTITUTION: An organic thin film luminescent element EL element 1 is composed of a metal electrode 6 as a cathode electrode on a substrate 2 and a transparent electrode 3, one layer of electric charge transportation layer 4 and a luminescent layer 5 sandwiched between the electrodes 6, 3, and a protective coat 7 provided on the top layer. Where, the metal electrode 6 is a metal of work function of 3.0ev or less, for instance, a conductive carbon intercalation complex containing Li, the transparent electrode 3 is an anode. When the carbon intercalation complex is used as the electrode material of the metal electrode 6 for electron implantation, the same can be formed into a thin film and the electron injection efficiency becomes high. When a metal such as Li exists between the layers, stability can be obtained, and metallic luster can be eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge injection type organic thin film light emitting device which can be used as a flat panel display or a planar light emitting body as a light source.

[0002]

2. Description of the Related Art A stacked organic thin film light emitting device using a thin film for facilitating charge injection and transport adjacent to an organic thin film as a light emitting layer is actively developed because it can obtain high brightness at low voltage. It is being advanced. Such an organic thin film light emitting device is realized as a structure in which a plurality of organic thin film layers are sandwiched by a transparent electrode for injecting holes and for taking out emitted light and a vapor deposition film of a metal electrode having a small work function for electron injection. It

As described above, it is advantageous that the metal electrode is made of a metal material having a small work function. The smaller the work function of the metal electrode material, the higher the electron injection efficiency and the lower voltage driving becomes possible. It is expected that the life will be long when a constant brightness is obtained. However, an alkali metal having a small work function is extremely difficult to use because it reacts violently with water and it is difficult to form a thin film by vapor deposition. Generally, Mg, In, Al, or the like, which is relatively stable and easy to handle and is co-evaporated with silver, is mainly used. Compared with alkali metals, these metals have a large work function and low electron injection efficiency, and therefore have many disadvantages such as high driving voltage. Further, although it is stabilized, Mg cannot be said to be sufficiently stable and is gradually oxidized and deteriorated. For this reason, the emission lifetime was not sufficient (see Matsumura et al., Proceedings of the 41st Joint Lecture on Applied Physics (1994) P1072).

On the other hand, in the organic thin film light emitting device having the above structure,
From the transparent electrode side, the metal electrode acts as a mirror that reflects light incident from the outside. Therefore, it is known that the amount of light emitted from the light emitting pixel increases including the reflected light from the metal electrode. In particular, research into a microresonator utilizing the optical resonance phenomenon by adjusting the film thickness is also underway.
However, it is also known that the reflected light from such a metal electrode poses a practical difficulty. That is, in the display in a dark place, there is no problem at all, and as described above, the phenomenon that the emission intensity is increased is advantageous. External light may be strongly reflected from the electrodes, and the display may not be seen at all. Also, even in the case of not so strong light, in a bright place, the difference in intensity between the emitted light and the reflected light is small, and it is often difficult to see the display by light emission. It is possible to obtain light emission superior to external light by using a higher voltage and a larger current, but this is a problem in terms of power consumption and it is not an effective method because it shortens the element life. .

Therefore, it is desired to obtain a new type of metal electrode which has a higher electron injection efficiency and does not cause the problem of external light reflection.

[0006]

An object of the present invention is, firstly, that a metal such as Li having a small work function can be stably used for a metal electrode for electron injection, and an organic material having a high electron injection efficiency can be obtained. It is to provide a thin film light emitting device. Secondly, in addition to the above-mentioned object, it is to provide an organic thin film light emitting device in which reflection of external light from a metal electrode for electron injection is small and a display by light emission from the device is easy to see.

[0007]

The above objects are achieved by the present invention described in (1) to (6) below. (1) A substrate, a first electrode, a second transparent electrode, at least one charge transport layer and a light emitting layer each sandwiched between these electrodes, and a protective layer, An organic thin film light emitting device in which the first electrode is composed of a conductive carbon intercalation compound containing a metal having a work function of 3.0 eV or less. (2) The organic thin film light emitting device according to (1) above, wherein the carbon intercalation compound is a carbonaceous material containing an alkali metal. (3) The above (2), wherein the carbonaceous material is non-graphitizable carbon
Organic thin film light emitting device. (4) The above (1), wherein the alkali metal is lithium.
The organic thin film light emitting device according to any one of (3). (5) The organic thin film light emitting device according to any one of (1) to (4), wherein the surface light reflectance of the first electrode is 40% or less. (6) The organic thin film light emitting device of any one of the above (1) to (5), wherein the first electrode is formed on an insulating substrate having a surface light reflectance of 40% or less.

[0008]

In the present invention, a conductive carbon intercalation compound containing a metal having a work function of 3.0 eV or less is used as the electrode material of the first electrode as a metal electrode for electron injection, and this thin film is used as a metal for electron injection. It is used as an electrode. Therefore, a metal electrode having a high electron injection efficiency can be obtained, and the drive voltage can be reduced. Further, such a metal such as Li is present between the layers, so that sufficient stability can be obtained as compared with a pure metal. Furthermore, so-called metallic luster can be eliminated, and reflection of external light, which makes it difficult to see the light emitted from the pixels, can be prevented or reduced. When the film thickness is small, the film becomes nearly transparent, and therefore the same effect can be obtained by using a material having a low light reflectance for the base. That is, the range of selection of materials and structures can be widened, and in the case of an element, the display is easy to see and the life is greatly improved.

Incidentally, a carbon intercalation compound in which Li is inserted or doped has been put to practical use as an electrode material for a Li battery. However, the intercalation compound in this case is used in a bulk state and is not used in a thin film state as in the present invention.

[0010]

Specific Structure The specific structure of the present invention will be described in detail below.

In the present invention, the work function is 3.0 eV as the electrode material of the first electrode as the metal electrode for electron injection.
A conductive carbon intercalation compound containing the following metals is used. The carbon intercalation compound is composed of a carbonaceous material, at least a part of which is layered, and the metal, and the metal is doped or inserted between the layers of the carbonaceous material to form an atomic or ionic form. Exists in. The carbonaceous material to be used is not particularly limited, but non-graphitizable carbon (hard carbon) that does not become graphite even if heat-treated at a temperature of about 3000 ° C. because of incomplete surface orientation is preferable. As hard carbon, there is a polyacene type obtained by heat-treating a phenol type resin or a furfuryl alcohol type resin,
The H / C is about 0.01 to 0.5. Also, hard carbon can be obtained by film formation by a vapor phase method.
In these, the carbonaceous material may be any as long as it has sufficient gaps between the molecular fragments so that the metal can bury, and a sheet composed of molecular fragments (for example, a hexagonal network structure sheet in graphite) is used. It may have a structure of stacking with a predetermined regularity, or may have a so-called amorphous structure in which molecular fragments are randomly arranged with a sufficient gap, but at least It is preferable that a part of the structure is randomly arranged. As a result, the metal can be stored not only in the layers but also in the microscopic holes formed by the random arrangement, and the ratio of the metal present is increased.

On the other hand, as a metal having a work function of 3.0 eV or less, preferably 1.5 to 3.0 eV, Li, Na, K and C are used.
Examples thereof include alkali metals such as s, Eu, and Sm, and lanthanoid elements. Among them, Li, Na, K, and particularly Li
Etc. are preferred. If the work functions of these metals are shown, Li (2.93eV), Na (2.36eV), K
(2.28eV), Cs (1.95eV), Eu (2.5e)
V) and Sm (2.1 eV). These values are described in Chemistry Handbook Basic Edition 2-493 (Edited by The Chemical Society of Japan, 1984).

By using such an intercalation compound as an electrode material, it is possible to prevent a metal such as Li from reacting with water. Therefore, it is possible to use the metal electrode with excellent electron injection efficiency, because it can be used stably, and the advantage of these metals that the work function is small can be utilized as it is.

In the intercalation compound used in the present invention, L
The proportion of the metal such as i is preferably about 0.3 to 5 per ₆ carbon atoms (that is, C ₆ ) constituting the carbonaceous material, and more preferably about 0.5 to 5. With such a ratio of the metal, the electron injection electrode can sufficiently function. More preferably, in the non-graphitizable material, it is preferable that the metal such as Li is incorporated not only in the interlayer but also in the micropores in the non-graphitized portion, and in particular, at least one metal such as Li is present per C _6. It is preferable. As a result, the action as the electron injection electrode is further improved.

Although the intercalation compound has conductivity, its conductivity is about 10 ^-4 to 10 ² Scm ^-1 . And
The carbonaceous material itself also exhibits conductivity, and its conductivity is 10 ^-12.
It is about 10 ^-5 Scm ^-1 .

The metal electrode in the organic thin film light emitting device of the present invention is in the form of a thin film, and a thin film of an intercalation compound containing a metal having a work function of 3.0 eV or less is formed as follows.

First, a thin film of carbonaceous material is formed. The thin film at this time may be formed by a vacuum film forming method or a coating method. As the vacuum film forming method, a vacuum vapor deposition method, an ion plating method, a sputtering method, a CVD (chemical vapor deposition) method,
There is a plasma decomposition method and the like, and the CVD method is preferable.

For example, when the carbonaceous material is obtained by the CVD method, benzene, toluene, decalin or the like may be used as a source and the method may be carried out according to a known method.

Among the carbonaceous materials, in the case of polyacene type, it is preferable to form a polyacene thin film by the method described in US Pat. No. 4,601,849. In particular,
Form a coating of phenolic resin or furfuryl alcohol (furan) resin to a specified thickness on a substrate such as a glass substrate.
A polyacene thin film is obtained by a thermal condensation reaction in an inert gas atmosphere. This reaction is carried out by using an electric furnace or the like to raise the temperature from room temperature (about 15 to 30 ° C.) to about 500 to 800 ° C. at a heating rate of 30 ° C./hr to 50 ° C./hr. Alternatively, it may be irradiated with excimer laser light (Nishio et al., Proceedings of the 55th Autumn Meeting of Applied Physics (1994) Autumn Meeting 20a-H.
-1, etc.).

After forming a thin film of carbonaceous material by any method as described above, the film is doped with a metal having a work function of 3.0 eV or less. Doping of a metal having a work function of 3.0 eV or less may be performed according to a general method known as a method for synthesizing an intercalation compound (for example, Two-bulb method, mixing method, electrochemical method, etc.) (Inagaki et al., Carbon material). See Advanced Carbon Series 2, "Graphite Intercalation Compounds" (1990), Realize Publishing Co., Ltd.).

These include methods from the gas phase and methods from the liquid phase. In the vapor phase method, doping can be performed by bringing a metal vapor into contact with a thin film of carbonaceous material. In this case, if it is Li, it is necessary to heat it to about 400 ° C., but it is also possible to perform it at a lower temperature by performing it under reduced pressure.

Although a film may be formed after a driving system is installed in the manufacture of the device, heating (temperature of 200 ° C. or higher) is generally not preferable when such a manufacturing method is adopted.

In order to dope in the liquid phase, oxidative doping may be performed using an oxidizing agent in an aqueous solution of a metal salt such as Li salt (halide, ClO ₄ salt, etc.) or an organic solvent solution. Alternatively, a metal having a work function of 3.0 eV or less, such as metal Li, may be used as a counter electrode while being electrochemically oxidized and doped. Furthermore, a method is also preferred in which an aqueous solution of a metal salt such as a Li salt or an organic solvent solution is energized with carbon as a counter electrode to dope. The energization condition at this time may be a low current of 0.01 to 5 mA, and 0.01 to 5
After energizing at 0.5 mA for 10 to 20 minutes, it may be energized at 2 to 5 mA for about 1 to 2 hours.

In addition, a metal such as Li may be melted and applied. Also, in some cases, L may be obtained by ion implantation
A metal such as i may be introduced.

Further, as a method for directly forming a thin film of an intercalation compound, there are an ion plating method, a method of alternately sputtering a carbonaceous material and a metal such as Li as a target, or a method of simultaneous sputtering.

In any of these methods, almost the same intercalation compound can be obtained and used as an electron injecting electrode.

Formation of an intercalation compound containing a metal such as Li
It can be confirmed by expanding the interlayer distance by X-ray diffraction. For example, the carbonaceous material is non-graphitizable carbon,
If the case of doping Li is shown, it is 0.34 before doping.
0.36 nm, but 0.371 due to Li doping
nm. It should be noted that the metal is usually said to be present in an ionic state, but as described above, for example, when introduced into the fine pores of the non-graphitizable carbon, there are some that are present in an atomic state, and 100% ionized. I'm not. In the present invention, it is preferable that the atomic ratio is large.

The thickness of such a thin film of the intercalation compound may be a certain thickness or more at which electrons can be sufficiently injected.
nm or more, preferably 100 nm or more. Also,
The upper limit value is not particularly limited, but may be 1000 μm or less, preferably 100 μm or less, because if it is too thick, peeling may occur.

It is preferable that the metal electrode in the present invention absorbs a large amount of light and does not reflect external light in order to obtain a luminescent display that is easy to see. The surface reflectance of the thin film of the intercalation compound in this case varies depending on the wavelength, but is 40% or less as an average value in the wavelength region of visible light, and further 0 to 30%.
It is preferred that In order to obtain such surface reflectance, the film thickness is preferably 300 nm or more, and more preferably 500 nm or more.

On the other hand, when importance is attached to flexibility, it is better to reduce the film thickness, and the film thickness is preferably about 50 to 200 nm. Since the thin film of the intercalation compound in this case becomes transparent, it is preferable to form the thin film on an insulating substrate having a low light reflectance. The underlying insulating substrate preferably has a surface reflectance of 40% or less, more preferably 0 to 30%. Usually, such a substrate material is preferably Si, SiC, SiN, or glass whose surface is oxidized, and is not particularly limited. The thickness of the substrate generally used is about 0.01 to 1 mm.

The organic thin film light emitting device of the present invention (hereinafter also referred to as "EL device") has a metal electrode as a first electrode and a second transparent electrode on a substrate, and is sandwiched between these electrodes. Each has at least one charge transport layer and at least one light emitting layer, and further has a protective layer as the uppermost layer. And
As described above, the metal electrode is composed of an intercalation compound containing an alkali metal.

FIG. 1 shows an example of the structure of such an EL element. The EL element 1 of FIG. 1 has a transparent electrode 3, which is an anode, a charge transport layer 4, a light emitting layer 5, a metal electrode 6, which is a cathode, and a protective layer 7, in this order on a transparent substrate 2.

The EL element 11 of FIG. 2 may have the structure of FIG. 2, and the EL element 11 of FIG.
3, a light emitting layer 14, a charge transport layer 15, a transparent electrode 16 as an anode, and a transparent protective layer 17 are sequentially provided.

The EL device of the present invention is not limited to the illustrated example, but may have various structures, for example, an electron injecting and transporting layer interposed between the light emitting layer and the metal electrode.

The metal electrode can be formed as described above, the organic material layer such as the light emitting layer can be formed by vacuum vapor deposition, and the anode can be formed by vapor deposition or sputtering. Each of these films is required. Depending on the method, it is possible to perform patterning by a method such as mask vapor deposition or film formation and then etching, thereby obtaining a desired light emitting pattern. Further, the substrate is a thin film transistor (TFT), and by forming each film according to the pattern, the display and drive pattern can be used as it is. Finally, SiO
_A protective layer made of an inorganic material such as ₂ , SiC, SiN ₂ , Al ₂ O ₃ , and SIALON may be formed.

Although the protective layer may be transparent or opaque in the configuration of FIG. 1 in view of display, it needs to be transparent in the configuration of FIG. To make it transparent, select a transparent material (eg SiO ₂ , SIALON, etc.) or use
Alternatively, the thickness may be controlled to be transparent (preferably, the transmittance of emitted light is 80% or more).

Generally, the thickness of the protective layer is 50 to 1200 nm.
The degree. The protective layer may be formed by sputtering or the like.

Next, the organic material layer provided in the EL device of the present invention will be described.

The light emitting layer has a function of injecting holes and electrons, a function of transporting them, and a function of generating excitons by recombination of holes and electrons. It is preferable to use a relatively electronically neutral compound in the light emitting layer.

The charge transport layer has a function of facilitating the injection of holes from the anode, a function of transporting holes and a function of hindering electrons, and is also called a hole injection / transport layer.

In addition, if necessary, it is easy to inject electrons from the cathode between the light emitting layer and the cathode as described above, for example, when the electron injecting and transporting function of the compound used for the light emitting layer is not so high. An electron injecting and transporting layer having a function of, a function of transporting electrons, and a function of blocking holes may be provided.

The hole injecting and transporting layer and the electron injecting and transporting layer are
Increase and confine holes and electrons injected into the light emitting layer,
The recombination region is optimized to improve the luminous efficiency.

The hole injecting and transporting layer and the electron injecting and transporting layer may be separately provided in the layer having the injecting function and the layer having the transporting function.

The thickness of the light emitting layer, the thickness of the hole injecting and transporting layer, and the thickness of the electron injecting and transporting layer are not particularly limited and may vary depending on the forming method, but usually about 5 to 1000 nm, particularly 1 nm.
It is preferably 0 to 200 nm.

The thickness of the hole injecting / transporting layer and the thickness of the electron injecting / transporting layer may be the same as the thickness of the light emitting layer or about 1/10 to 10 times, although it depends on the design of the recombination / light emitting region. . When the electron injection layer and the electron injection layer are separated from the transport layer, it is preferable that the injection layer has a thickness of 1 nm or more and the transport layer has a thickness of 20 nm or more. At this time, the upper limit of the thickness of the injection layer and the transport layer is usually about 100 nm in the injection layer and 100 in the transport layer.
It is about 0 nm. Such a film thickness is the same when two injecting and transporting layers are provided.

Further, recombination can be achieved by controlling the film thickness while considering the carrier mobility and carrier density (determined by the ionization potential and electron affinity) of the light emitting layer, electron injecting and transporting layer and hole injecting and transporting layer to be combined. It is possible to freely design the area and the light emitting area, and it is possible to design the light emitting color, control the light emitting luminance and the light emitting spectrum by the interference effect of both electrodes, and control the spatial distribution of light emission.

The light emitting layer of the EL device of the present invention contains a fluorescent substance which is a compound having a light emitting function. Examples of the fluorescent substance include at least one selected from compounds such as those disclosed in JP-A-63-264692, such as quinacridone, rubrene, and styryl dyes. Other examples include metal complex dyes such as tris (8-quinolinolato) aluminum, tetraphenylbutadiene, anthracene, perylene, coronene, and 12-phthaloperinone derivatives. The light emitting layer may also serve as the electron injecting and transporting layer, and in such a case, tris (8-quinolinolato) aluminum or the like is preferably used. These fluorescent substances are vapor-deposited or dispersed in a resin binder and coated to form a light emitting layer with a predetermined thickness.

The electron injecting and transporting layer, which is provided as necessary, includes an organometallic complex such as tris (8-quinolinolato) aluminum, an oxadiazole derivative, a perylene derivative, a pyridine derivative, a pyrimidine derivative, a quinoline derivative, and a quinoxaline derivative. , A diphenylquinone derivative,
A nitro-substituted fluorene derivative or the like can be used.
As described above, the electron injecting and transporting layer may also serve as the light emitting layer, and in such a case, it is also preferable to use tris (8-quinolinolato) aluminum or the like. The electron injecting and transporting layer may be formed by vapor deposition or the like like the light emitting layer.

When the electron injecting and transporting layer is separately formed into the electron injecting layer and the electron transporting layer, preferred combinations can be selected and used from the compounds for the electron injecting and transporting layer. At this time, it is preferable to stack the compound layers having a large electron affinity value in this order from the cathode side. The stacking order is the same when two or more electron injecting and transporting layers are provided.

Further, the hole injecting and transporting layer is formed, for example, in JP-A-63-295695 and JP-A-2-191694.
Various organic compounds described in JP-A No. 3-792, JP-A No. 3-792, etc. can be used. Examples thereof include aromatic tertiary amines, hydrazone derivatives, carbazole derivatives, triazole derivatives, imidazole derivatives, oxadiazole derivatives having an amino group, and polythiophene. Two or more of these compounds may be used in combination, and when they are used in combination, they may be laminated in different layers or mixed.

When the hole injecting and transporting layer is separately formed into the hole injecting layer and the hole transporting layer, preferable combinations can be selected and used from the compounds for the hole injecting and transporting layer. At this time, it is preferable to stack layers of a compound having a small ionization potential in order from the anode (ITO or the like) side. Further, it is preferable to use a compound having a good thin film property on the surface of the anode. This stacking order is the same when two or more hole injecting and transporting layers are provided. By adopting such a stacking order, the driving voltage is lowered, and it is possible to prevent the occurrence of current leakage and the generation / growth of dark spots. In addition, since vapor deposition is used to form a device, a thin film of about 1 to 10 nm can be made uniform and pinhole-free, so that the hole injection layer has a small ionization potential and absorption in the visible region. Even if such a compound is used, it is possible to prevent a decrease in efficiency due to a change in the color tone of the emission color or reabsorption.

Among them, it is preferable to use the aromatic tertiary amine in combination with polythiophene. After depositing polythiophene as the hole injecting layer or the first hole injecting and transporting layer having a good thin film property on the anode, the aromatic tertiary amine is used. Stacking amine as the hole transport layer or the second hole injecting and transporting layer is more preferable from the viewpoint of the ionization potential.

The polythiophene preferably used in the present invention is a polymer having a structural unit shown in Chemical formula 1 (hereinafter, also referred to as "polymer A"), a structural unit shown in Chemical formula 1 and a chemical formula 2. And a polymer having a structural unit (hereinafter, also referred to as “copolymer B”) and a polymer represented by Chemical Formula 3 (hereinafter, “polymer C”).

[0054]

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[0055]

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[0056]

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First, the polymer A will be described. The polymer A has a structural unit represented by Chemical Formula 1, and is represented by, for example, Chemical Formula 4.

[0058]

[Chemical 4]

Regarding Chemical Formulas 1 and 4, R ₃₁ and R 4
Each of ₃₂ represents a hydrogen atom, an aromatic hydrocarbon group or an aliphatic hydrocarbon group, which may be the same or different.

The aromatic hydrocarbon group represented by R ₃₁ and R ₃₂ may be unsubstituted or may have a substituent, and preferably has 6 to 15 carbon atoms. When it has a substituent, examples of the substituent include an alkyl group, an alkoxy group, an amino group and a cyano group. Specific examples of the aromatic hydrocarbon group include a phenyl group, a tolyl group, a methoxyphenyl group, a biphenyl group and a naphthyl group.

Examples of the aliphatic hydrocarbon group represented by R ₃₁ and R ₃₂ include an alkyl group and a cycloalkyl group, which may be unsubstituted or may have a substituent. Of these, those having 1 to 6 carbon atoms are preferable, and specific examples thereof include a methyl group, an ethyl group, an i-propyl group, and a t-butyl group.

As R ₃₁ and R ₃₂ , a hydrogen atom and an aromatic hydrocarbon group are preferable, and a hydrogen atom is particularly preferable.

Average degree of polymerization of polymer A in the layer
M) is 4 to 100, preferably 5 to 40, and more preferably 5 to 20. In this case, even if the repeating unit shown in Chemical formula 1 is a completely identical polymer (homopolymer), it is a copolymer composed of structural units in which the combination of R ₃₁ and R ₃₂ in Chemical formula 1 is different. It may be. The copolymer may be a random copolymer, an alternating copolymer, a block copolymer, or the like.

The weight average molecular weight of the polymer A in the layer is about 300 to 10,000.

The end groups of polymer A (X ₁ and X
₂ ) is a hydrogen atom or a halogen atom such as chlorine, bromine or iodine. This end group is generally introduced depending on the starting material in the synthesis of polymer A. Furthermore, other substituents can be introduced at the final stage of the polymerization reaction.

The polymer A is preferably composed only of the structural unit of Chemical formula 1, but it may contain other monomer components as long as it is 10 mol% or less.

A specific example of the polymer A is shown in Chemical formula 5. In Chemical formula 5, a combination of R ₃₁ and R _{32 in} Chemical formulas 1 to 4 is shown.

[0068]

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Next, the copolymer B will be described. The copolymer B has a structural unit of chemical formula 1 and a structural unit of chemical formula 2, and is represented by, for example, chemical formula 6.

[0070]

[Chemical 6]

The chemical formula 1 is the same as that of the polymer A. Therefore, R ₃₁ and R ₃₂ in Chemical formula 6 are the same as those in Chemical formula 1.

With respect to the chemical formula 2, R ₃₃ and R ₃₄
Each represent a hydrogen atom, an aromatic hydrocarbon group or an aliphatic hydrocarbon group, which may be the same or different.

An aromatic hydrocarbon group represented by R ₃₃ and R ₃₄ ,
Specific examples of the aliphatic hydrocarbon group are the same as those listed for R ₃₁ and R _{32 in} Chemical formula 1. Further, the preferable ones of R ₃₃ and R ₃₄ are the same as those of R ₃₁ and R ₃₂ . Further, R ₃₃ and R ₃₄ may be bonded to each other to form a ring and condensed with a thiophene ring. Examples of the condensed ring in this case include a benzene ring. This R ₃₃ , R ₃₄
The same applies to Chemical Formula 6.

The average degree of polymerization of copolymer B in the layer (v + w in Chemical formula 6) is 4 to 10 as in the case of polymer A.
0, preferably 5 to 40, more preferably 5 to 20. Further, the ratio of the structural unit of Chemical formula 1 to the structural unit of Chemical formula 2 is 10 in terms of the molar ratio of the structural unit of Chemical formula 1 / the structural unit of Chemical formula 2.
It is about / 1 to 1/10.

The weight average molecular weight of the copolymer B in the layer is about 300 to 10,000.

The terminal groups of the copolymer B (X ₁ and X ₂ in the chemical formula 6) are the same as those of the polymer A, and in general, the starting materials used in the synthesis of the copolymer B or the ratio thereof are different from each other. Dependent.

The copolymer B, like the polymer A,
It is preferably composed of the structural unit of Chemical formula 1 and the structural unit of Chemical formula 2, but other monomer components may be contained as long as they are 10 mol% or less. Further, the copolymer B may be any of a random copolymer, an alternating copolymer, a block copolymer and the like, and the structural formula of Chemical formula 6 includes such a structure. Furthermore, the structural units of Chemical formulas 1 and 2 may be the same or different.

A specific example of the copolymer B is shown in Chemical formula 7. In chemical formula 7, a combination of R ₃₁ and R ₃₂ in chemical formula 1, a combination of R ₃₃ and R ₃₄ in chemical formula 2, that is, a combination of R ₃₁ , R ₃₂ , R ₃₃ and R ₃₄ in chemical formula 6 is shown.

[0079]

[Chemical 7]

Further, the polymer C of Chemical formula 3 will be described. Regarding Chemical Formula 3, R ₃₃ and R ₃₄ have the same meanings as those of Chemical Formula 2, and preferred ones are also the same.

X ₁ and X _{2, which} may be the same or different, each is a hydrogen atom or a halogen atom such as chlorine, bromine or iodine, like the end groups of the polymer A and the copolymer B. . X ₁ and X ₂ depend on the starting materials in the synthesis of polymer C.

N represents an average degree of polymerization, and is 4 to 100, preferably 5 to 4 in the same layer as the polymer A and the copolymer B.
It is 0, more preferably 5 to 20. In this case, R ₃₃
The combination of R ₃₄ and R ₃₄ may be the same polymer (homopolymer), or the combination of R ₃₃ and R ₃₄ may be different copolymers. The copolymer may be a random copolymer, an alternating copolymer, a block copolymer, or the like.

The weight average molecular weight of the polymer C in the layer is about 300 to 10,000.

The polymer C preferably has a structure shown in Chemical formula 3, but like the polymers A and B, if it is 10 mol% or less, it contains other monomer components. May be.

Specific examples of the polymer C are shown in Chemical formulas 8 and 9. The chemical formula 8 is the same as the chemical formula 3, and the chemical formula 9 shows the combination of R ₃₃ and R ₃₄ of the chemical formula 8.

[0086]

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[0087]

[Chemical 9]

In the present invention, as the polythiophene, it is particularly preferable to use the polymer C among the above polymers.

The polythiophene may be used alone or in combination of two or more.

The polythiophene used in the present invention has a melting point of 3
It has a temperature of not lower than 00 ° C. or has no melting point, and a high-quality film in an amorphous state or a microcrystalline state can be obtained by vacuum vapor deposition.

The hole injecting and transporting layer may be formed by vapor-depositing the above compounds or coating them by dispersing them in a resin binder as in the light emitting layer. Particularly, good vapor deposition can be obtained by vapor deposition.

The organic layer may contain a singlet oxygen quencher. Examples of such a quencher include rubrene, nickel complex, diphenylisobenzofuran, and tertiary amine.

In the present invention, for the transparent electrode used as the anode, the material and thickness of the anode are preferably determined so that the transmittance of emitted light is preferably 80% or more. Specifically, for example, ITO, SnO ₂ , Ni, A
It is preferable to use u, Pt, Pd, polypyrrole doped with a dopant, or the like for the anode. The thickness of the anode is preferably about 10-500 nm. In addition, it is necessary that the driving voltage is low in order to improve the reliability of the device, but a preferable value is 10 to 30 Ω / cm ² I
TO is mentioned.

As the substrate material, in the case of the structure shown in FIG. 1, a transparent or translucent material such as glass or resin is used in order to take out emitted light from the substrate side. Further, the substrate may be provided with a color filter film, a color conversion film containing a fluorescent substance, or a dielectric reflection film to control the emission color. In addition, in the configuration of FIG. 2, an opaque substrate may be used. In this case, in addition to glass or the like, ceramics such as alumina, a metal sheet such as stainless steel that has been subjected to an insulation treatment such as surface oxidation, or a heat such as a phenol resin. A curable resin, a thermoplastic resin such as polycarbonate, or the like can be used.

Next, a method for manufacturing the EL element of the present invention will be described.

The cathode is preferably formed as described above, and the anode is preferably formed by a vapor phase growth method such as a vapor deposition method or a sputtering method.

For forming the hole injecting / transporting layer, the light emitting layer and the electron injecting / transporting layer, it is preferable to use the vacuum deposition method because a uniform thin film can be formed. When the vacuum deposition method is used, a homogeneous thin film having an amorphous state or a crystal grain size of 0.1 μm or less (usually, the lower limit is about 0.001 μm) can be obtained. If the crystal grain size exceeds 0.1 μm, non-uniform light emission occurs, the drive voltage of the device must be increased, and the charge injection efficiency is significantly reduced.

The conditions of vacuum vapor deposition are not particularly limited, but 1
The degree of vacuum is 0 ^-3 Pa or less, and the deposition rate is 0.1 to 1 nm / se.
It is preferably about c. Moreover, it is preferable to form each layer continuously in a vacuum. If they are continuously formed in a vacuum, it is possible to prevent impurities from adsorbing to the interface of each layer, so that high characteristics can be obtained. In addition, the drive voltage of the element can be lowered.

When a vacuum vapor deposition method is used to form each of these layers, when a plurality of compounds are contained in one layer, it is preferable that the boats containing the compounds are individually temperature-controlled for co-evaporation, but they are mixed in advance. You may vapor-deposit after that.
In addition to this, a solution coating method (spin coating, dipping, casting, etc.), Langmuir-Blodgett (LB) method, or the like can also be used. In the solution coating method, a predetermined compound may be dispersed in a matrix substance such as a polymer.

The EL device of the present invention is usually used as a DC drive type EL device, but it can also be AC drive or pulse drive. The applied voltage is usually about 2 to 20V.

[0101]

EXAMPLES Hereinafter, the present invention will be described in more detail by showing specific examples of the present invention together with comparative examples.

<Example 1> 200 nm thick on a glass substrate
The transparent electrode on which ITO was formed was patterned, ultrasonically cleaned with a neutral detergent, acetone, and ethanol, and then pulled out from boiling ethanol and dried. After the surface of this transparent electrode was washed with UV / O _3, it was fixed to a substrate holder of a vacuum evaporation apparatus, and the pressure inside the tank was reduced to 1 × 10 ⁻⁴ Pa or less.

First, poly (thiophene-2,5-diyl) was vapor deposited at a vapor deposition rate of 0.1 nm / sec to a thickness of 20 nm.
The first hole injecting and transporting layer was used.

Next, while maintaining the reduced pressure state, N, N'-
Deposition rate of diphenyl-N, N'-m-tolyl-4,4'-diamino-1,1'-biphenyl (TPD) was 0.2.
It was vapor-deposited at a thickness of 55 nm at nm / sec to form a second hole injecting and transporting layer.

Further, while maintaining the reduced pressure, Tris (8-
(Quinolinolato) aluminum was vapor-deposited at a vapor deposition rate of 0.2 nm / sec. To a thickness of 50 nm to form an electron injection / transport / light-emitting layer.

Further, while maintaining the reduced pressure, a graphite-like carbon layered compound was formed into a film with a thickness of 200 nm by the CVD method. The CVD was performed using benzene as a source and Ar as a carrier gas under a pressure of 1 × 10 ⁻⁴ Pa and a temperature of 100 ° C.

Then, take it out from the vacuum device and quickly
Dry ethylene carbonate (LClO ₄ dissolved in L
(1 mol / l solution of iClO ₄ )
i was used as a counter electrode, and graphite was used as a negative electrode. By conducting electricity, Li was doped while being electrochemically oxidized to form a cathode. The energization at this time was carried out at 0.02 mA for 15 minutes and then at 3 mA for 2 hours. This was washed 3 times with acetone and dried under reduced pressure at room temperature.

Finally, SiO ₂ was sputtered to a thickness of 1000 nm to form an organic thin film light emitting device (EL device) as a protective layer.
I got

A DC voltage was applied to this organic thin film light emitting device, and it was continuously driven at a constant current density of 10 mA / cm ² . In the initial stage, yellow-green (light emission maximum wavelength λmax = 500 nm) light emission of 5.6 V and 380 cd / cm ² was confirmed. The half-life time of luminance is 2500 hours, during which the driving voltage rises by 1.3.
It was V. Moreover, the appearance and growth of dark spots were not observed at all. Furthermore, after that, current leakage does not occur,
Stable light emission was continued.

The work function of Li is 2.93 eV (reference value).

The surface of the above device was dark blue, the surface reflectance was in the range of 0 to 30% (visible region), and the luminescence display was easier to see than the mirror-like silvery white of MgAg.

The formation of the carbonaceous material doped with Li was confirmed by the spread of the interlayer distance by X-ray diffraction.
The number of Li per 6 carbons in this product was about 1.8.

Example 2 An EL element was obtained in the same manner as in the EL element of Example 1, except that a thin film of a carbonaceous material doped with Li was formed as follows.

A furfuryl alcohol-based resin (furan-based resin) was fired at 1200 ° C. in a nitrogen stream and ground, and a 10% toluene solution of a polycarbonate resin was mixed so that the dry weight ratio of the resin was 90:10. Made into a paste. This was coated on a glass substrate. After thoroughly drying the solvent, propylene carbonate (PC):
1,2-dimethoxyethane (DME) = 1: 1 (volume ratio) in which LiClO ₄ was dissolved to be a 1M solution was used as an electrolytic solution, and a current density of 0.5 mA / cm ² was applied at a constant current. It was used as an electrode. The conductivity of the thin film is 10 ⁻⁴ to 10
It was ^-1 Scm ^-1 .

When the characteristics of this EL device were evaluated in the same manner as in Example 1, the same good results as in Example 1 were obtained.

The surface color of this product was almost black, the reflectance was low at any wavelength, the surface reflectance was 0 to 30% (visible region), and there was no metallic reflection. The luminescent display was easy to see. The production of the Li-doped carbonaceous material was confirmed in the same manner as in Example 1, and the number of Li per 6 carbons was about the same as in Example 1.

Example 3 1) Formation of Li-Doped Polyacene Film A solution of a novolac-type phenolic resin, methanol and formalin (37% aqueous solution) in a weight ratio of 3: 3: 1 was applied onto a glass substrate. Coated with water and dried in air for 30 minutes to distill off the methanol. The glass substrate was placed in 5N hydrochloric acid as it was, and then cured at 70 ° C. for 90 minutes.

The cured film was thoroughly washed with warm water and dried in air for about 1 day to obtain a phenol resin film having a thickness of about 20 μm.

This film was placed in an electric furnace which was flushed with nitrogen.
Heat treatment was performed from room temperature to 700 ° C at a rate of 40 ° C / hr to obtain a film. The conductivity was about 10 ^-6 Scm ^-1 .

Next, when a film prepared in a 1 mol / liter propylene carbonate solution of LiClO ₄ was used as an anode and a carbon plate was immersed as a cathode and a voltage was applied, the current value immediately became about 0.01 mA. It was The current is 0.2mA for 15 minutes, then about 3mA
Was energized for 2 hours. Immediately after reaching 3 mA, the film was removed from the electrolyte, washed 3 times with acetone and then dried under vacuum at room temperature to give a dark blue film (30 μm
Thick). It showed a conductivity of 10 ^-3 Scm ^-1 .

2) Preparation of EL element After patterning the Li-doped polyacene-based film obtained above by dry etching if necessary, this was fixed to a substrate holder of a vacuum vapor deposition apparatus, and a bath was prepared. The pressure inside was reduced to 1 × 10 ⁻⁴ Pa or less.

Tris (8-quinolinolato) aluminum was vapor-deposited at a vapor deposition rate of 0.2 nm / sec. To a thickness of 50 nm to form an electron injecting / transporting / light-emitting layer.

Then, while maintaining the reduced pressure state, N, N'-
Deposition rate of diphenyl-N, N'-m-tolyl-4,4'-diamino-1,1'-biphenyl (TPD) was 0.2.
It was vapor-deposited at a thickness of 55 nm at nm / sec to form a second hole injecting and transporting layer.

Further, poly (thiophene-2,5-diyl) was vapor-deposited at a rate of 0.1 nm / sec while maintaining the reduced pressure.
It was vapor-deposited to a thickness of nm to form a first hole injecting and transporting layer.

Next, ITO was formed into a film with a thickness of 200 nm by sputtering. Finally, sputter SiO ₂ as a whole to 80
An EL device was obtained by forming a 0 nm thick transparent protective layer.

The characteristics of this EL device were evaluated in the same manner as in Example 1. Initially, it was 30 at 5V.
A light emission of 0 cd / m ² was confirmed. In addition, the stability of light emission was sufficient.

Further, when the surface reflectance of the surface of the polyacene film doped with Li was examined, it was 8% (visible region), and the light emission display was easy to see.

The formation of the polyacene film doped with Li could be confirmed in the same manner as in Example 1. The number of Li per 6 carbons in this product was 4.9.

Example 4 An EL device was obtained in the same manner as in the EL device of Example 3, except that a Li-doped polyacene film was formed as follows.

Of a polyacene-based film doped with Li
Formed xylene modified phenol-formaldehyde resin (phenol: xylene = 1: 1, Mitsubishi Gas Chemical PR-1
440M) was applied to the glass substrate with an applicator.
After drying at room temperature for 2 hours, it was further treated at 150 ° C. for 2 hours. Then, heat treatment was applied from room temperature to 610 ° C. at a temperature rising rate of 40 ° C./hr in an electric furnace in a nitrogen atmosphere.

This film was electrochemically doped with Li in the same manner as in Example 3 to finally obtain a black film showing a conductivity of 10 ^-2 Scm ^-1 .

The characteristics of this EL element were evaluated in the same manner as in Example 1. Initially, 320 cd / m at 5 V was obtained.
Light emission of ² was confirmed. In addition, the stability of light emission was sufficient.

Further, when the surface reflectance of the surface of the polyacene film doped with Li was examined, it was 9%, and the luminescence display was easy to see.

The formation of the Li-doped polyacene film was confirmed by X-ray diffraction as in Example 1. The number of Li per 6 carbons in this product was about 2.

Example 5 An EL device was obtained in the same manner as in the EL device of Example 3, except that a Li-doped polyacene film was formed as follows.

Of a polyacene-based film doped with Li
Formed furan resin (Hitafuran 302 manufactured by Hitachi Chemical) was applied to a glass substrate with an applicator. After drying for 2 hours,
Pretreatment was carried out at 100 ° C. for 2 hours. Then from room temperature to 640
The heat treatment was performed up to 40 ° C. at a temperature rising rate of 40 ° C./hr.

This film was electrochemically doped with Li in the same manner as in Example 3 to obtain a blue-black conductive film of 10 ^-2 Scm ^-1 .

When the characteristics of this EL element were evaluated in the same manner as in Example 1, good results substantially equivalent to those in Examples 3 and 4 were obtained.

Furthermore, the surface reflectance of the surface of the polyacene film doped with Li was examined and found to be 6%, showing that the luminescence display was easy to see.

The formation of the Li-doped polyacene film was confirmed by X-ray diffraction as in Example 1. The number of Li per 6 carbons in this product is 4.
It was about 6.

In Example 3, the doping metal was Li.
When each of Na, K, Cs, Eu, and Sm was changed to luminescence, luminescence was observed.

Comparative Example 1 In the EL element of Example 1, instead of using the intercalation compound as the cathode material, MgAg (weight ratio 10: 1) was deposited at a deposition rate of 0.2 nm / sec while maintaining a reduced pressure. An EL device was obtained in the same manner except that the cathode was formed by vapor deposition to a thickness of about 200 nm.

The characteristics of this EL device were evaluated in the same manner as in Example 1. Initially, it was 10 cd / m ^{2 at} 5V.
Only the light emission of was confirmed. Also, the stability of light emission is
It was inferior to Examples 1 to 5.

The work function of Mg is 3.66 eV (reference value).

[0145]

According to the present invention, the work function of Li or the like 3.
A metal of 0 eV or less can be stably used for a metal electrode for electron injection, and stable light emission with high brightness can be obtained. Further, the light emission display is easy to see without reflection of external light from the metal electrode.

[Brief description of drawings]

FIG. 1 is a side view showing a configuration example of an EL element of the present invention.

FIG. 2 is a side view showing another configuration example of the EL element of the present invention.

[Explanation of symbols]

 1, 11 EL element 2, 12 substrate 3, 16 transparent electrode 4, 15 charge transport layer 5, 14 light emitting layer 6, 13 metal electrode 7, 17 protective layer

Claims (6)

[Claims] 1. A substrate, a first electrode, a second transparent electrode, at least one charge-transporting layer and a light-emitting layer each sandwiched between these electrodes, and a protective layer. An organic thin film light emitting device in which the first electrode is composed of a conductive carbon intercalation compound containing a metal having a work function of 3.0 eV or less. 2. The organic thin film light emitting device according to claim 1, wherein the carbon intercalation compound is a carbonaceous material containing an alkali metal. 3. The organic thin film light emitting device according to claim 2, wherein the carbonaceous material is non-graphitizable carbon. 4. The organic thin film light emitting device according to claim 1, wherein the alkali metal is lithium. 5. The surface light reflectance of the first electrode is 40%.
The organic thin film light emitting device according to claim 1, which is as follows. 6. The organic thin film light emitting device according to claim 1, wherein the first electrode is formed on an insulating substrate having a surface light reflectance of 40% or less.