JP2005216677A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent element with a long life in which deterioration of luminance, generation and growth of a dark spot, and rising of voltage due to element drive are suppressed by improving adhesion between an electrode and an organic membrane and stable light emitting characteristics are sustained for a long period of time. <P>SOLUTION: The organic electroluminescent element comprises a substrate, a first electrode 15 laminated on this substrate, and an organic membrane 17 having a luminous layer and a second electrode laminated in order on this first electrode 14 side, and furthermore a self-organized polymer film 16 which acts adhesively to the first electrode 15 and the organic membrane 17 is installed between the first electrode 15 and the organic membrane 17. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an organic electroluminescence element (hereinafter referred to as “organic EL element”), and more particularly to an organic EL element that is suitably used mainly for various displays and light-emitting elements for information industry equipment.

Electroluminescence has long been known as a phenomenon that emits light when an alternating high voltage is applied to a zinc sulfide (ZnS) phosphor. The organic EL element realizes this light emission phenomenon using a fluorescent organic compound as a light emitting substance.
Research on organic EL devices has been conducted for a long time, and the basic structure starts from a two-layer single heterostructure reported by Tang et al. In 1987. The structure is such that a hole transport layer, an electron transport layer serving also as a light emitting layer, and a metal cathode are sequentially laminated on a transparent electrode (ITO). By adopting such a structure, carrier recombination efficiency is increased, and characteristics of luminance of 1000 cd / m ² or more, external quantum efficiency of 1.3%, and luminous luminous efficiency of 1.51 m / W are obtained at a low voltage of 10 V or less. Therefore, this organic EL element has opened the way to practical use of organic EL elements up to now.

  Later, in research on organic EL devices, improvement of the electron injection balance by introducing an electron transport layer, doping of an electron transport material, etc., and improvement of the device structure such as the confinement effect of excitons were proposed. The organic EL element used there has a structure in which the functions of hole transport, electron transport and light emission are separated and materials suitable for each function are used. As a result, the performance as an organic EL element is drastically improved, and some elements having this structure have already been put into practical use.

  Research on high-molecular organic EL devices using high-molecular organic compounds has been conducted on the basis of conducting polymer poly (paraphenylene vinylene) (PPV) thin films published by Burroughhes et al. The layer element is the first. In order to improve the performance of the polymer organic EL element, for example, doping of a sensitizing dye into the light emitting layer has been proposed. Soon after, a two-layer element emitting red light using CN-PPV in which PPV was used for the hole transport layer and a cyano group having a high electron-withdrawing property was introduced into the light-emitting and electron transport layer was reported. After that, based on these basic materials, material development aimed at improving characteristics such as emission wavelength, emission efficiency, heat resistance, and emission lifetime has been activated and has now reached.

  On the other hand, even in an organic EL element having high luminance and light emission efficiency in the initial stage of driving and low driving voltage, the luminance is lowered, dark spots are generated and grown by continuous driving, the driving voltage is increased, and electrical short-circuiting is performed. There is a problem that deterioration with time occurs. There are several causes for such deterioration, which are roughly classified into those related to the interfacial phenomenon of the laminate, those caused by thermal changes, and those caused by electrochemical instability. In addition, although there are factors specific to the material used, it is considered that many causes of deterioration are common to low molecules and polymers.

One of the causes of deterioration involving the interfacial phenomenon of lamination is a decrease in adhesion between the electrode and the organic film. Generally, the surface of an electrode used in an organic EL element is hydrophilic, and the organic material forming the organic film is hydrophobic, so that the adhesion at these interfaces is low. The decrease in the adhesion between the electrode and the organic film, such as the peeling of the organic film from the electrode, was (1) electrode surface defects, (2) pinholes due to fine particles, aggregates, etc. This is caused by deterioration of the film portion due to oxygen or moisture or deterioration due to softening. These problems have been addressed by reducing defects on the electrode surface, fine particles and aggregates, forming a protective film, and improving sealing technology (see Non-Patent Document 1).
However, the above countermeasures have not yet led to a fundamental solution, and are still unsatisfactory for constructing a high-performance organic EL element. This is because the adhesion between the electrode and the organic film is inherently low due to the structure of the material. For example, the presence of a slight amount of oxygen or moisture contained in the electrode material or organic material greatly affects the decrease in adhesion. is there.
“Forefront of practical application of organic EL element display”, Toray Research Center, Inc., June 15, 2002, p. 272-289 (8.2 Life extension of organic EL device)

  In the present invention, by improving the adhesion between the electrode and the organic film, luminance reduction due to element driving, generation and growth of dark spots, and voltage increase are suppressed, and stable light emission characteristics are maintained over a long period of time. It is an object to provide a long-life organic EL element.

  Thus, according to the present invention, there is provided a substrate, a first electrode laminated on the substrate, an organic film and a second electrode having a light emitting layer sequentially laminated on the first electrode side, and the first electrode. There is provided an organic electroluminescence device in which a self-assembled polymer thin film that is in close contact with the first electrode and the organic film is provided between the electrode and the organic film.

  According to the present invention, the self-assembled polymer thin film that is in close contact with the first electrode and the organic film is formed between the first electrode and the organic film. Long-life organic EL that improves adhesion between the first electrode and the organic film, suppresses a decrease in brightness due to element driving, generation and growth of dark spots, and an increase in voltage, and maintains stable light emission characteristics over a long period of time. An element can be provided.

  Hereinafter, embodiments of the organic EL element of the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments, and various embodiments can be implemented within the scope of the present invention.

  FIG. 1 is a schematic cross-sectional view of a main part showing the layer structure of an organic EL element of the present invention (Embodiment 1), and FIG. 2 is a schematic cross-sectional view of the main part showing the layer structure of another organic EL element of the present invention. FIG. 3 is a schematic cross-sectional view of a self-assembled polymer thin film in an organic EL element of the present invention (Embodiment 2), and FIG. 4 is another diagram in the organic EL element of the present invention. FIG. 6 is a schematic cross-sectional view of a self-assembled polymer thin film (Embodiment 4). In FIGS. 1 and 2, the same elements are denoted by the same reference numerals.

The organic EL device of the present invention includes a substrate 1, a first electrode 2 stacked on the substrate 1, and an organic film 4 and a second electrode 5 each having a light emitting layer sequentially stacked on the first electrode 2 side, And a structure including at least a self-assembled polymer thin film 3 which is provided between the first electrode 2 and the organic film 4 and acts on the first electrode 2 and the organic film 4 in close contact. Moreover, in the organic EL element of Embodiment 1 shown in FIG. 1 and the organic EL element of Embodiment 2 shown in FIG. 2, each organic film 4 is composed of a hole transport layer 6 and an electron transport light emitting layer 7, In the first embodiment, the hole transport layer 6 and the electron transporting light emitting layer 7 are laminated in this order from the self-assembled polymer thin film 3 side. In the second embodiment, the electron transporting light emitting layer 7 is stacked from the self assembled polymer thin film 3 side. And the hole transport layer 6 are laminated in this order.
In the present invention, the adhesion action means that at least the self-assembled polymer thin film is directly chemisorbed on the first electrode, and the organic film is intermolecular force with the self-assembled polymer thin film (Van der Faels force, electrostatic force). It is defined as including adsorption. Here, the chemical adsorption means chemical adsorption occurring between the forming polymer constituting the self-assembled polymer thin film and the surface of the first electrode or special adsorption with energy comparable to the chemical bond. Further, the intermolecular force (Vandelphals force, electrostatic force) is larger between the hydrophobic group on the surface of the self-assembled polymer thin film and the organic film than between the hydrophilic group on the first electrode and the organic film.

The substrate used in the present invention is not particularly limited as long as the laminated surface is made of an insulating material. However, when light is extracted from the substrate side, the substrate is made of a material having a high light transmittance. There is a need. Specifically, inorganic materials such as glass and quartz; plastics such as polyethylene terephthalate (PET), polycarbazole and polyimide; insulating substrates such as ceramics such as alumina; SiO ₂ and organic insulation on metal substrates such as aluminum and iron Examples thereof include a substrate coated with an insulator such as a material; a substrate obtained by subjecting the surface of a metal substrate such as aluminum to an insulation treatment by a method such as anodization.

A pair of the first electrode 2 and the second electrode 5 used in the present invention functions as a hole injection electrode (anode) or an electron injection electrode (cathode). That is, the first electrode 2 and the second electrode 5 are a hole injection electrode and an electron injection electrode, respectively, or an electron injection electrode and a hole injection electrode, respectively.
Further, when the first electrode 2 is subjected to a hydrophilization treatment such as an alkali solution treatment, an ozone treatment, an ultraviolet light irradiation treatment in the presence of oxygen or under vacuum, or a plasma irradiation treatment, the self-organization height formed thereon is increased. This is preferable because the film forming property of the molecular thin film 3 is improved.

  As a material constituting the hole injection electrode, a material having a large work function is preferable. Specific examples include metals (gold, platinum, nickel, etc.) and transparent electrode materials [oxides made of indium and tin (ITO), oxides made of indium and zinc (IDIXO), tin oxide, etc.), polyaniline, and the like. It is done. In the case where light is extracted from the hole injection electrode side, it is necessary to be made of a material having a high light transmittance, and is preferably made of a material selected from ITO, IDIXO, tin oxide, gold and polyaniline. .

As a material constituting the electron injection electrode, a material having a small work function is preferable. Specifically, K, Li, Na, Mg, La, Ce, Ca, Sr, Ba, Al, Ag, In, Sn, Zn, and Zr or the like, or two components or three containing the metal element The alloy of a component is mentioned, It is preferable to use these. By using an alloy, the stability as an electrode is improved. Examples of the alloy include Ag · Mg (Ag: 0.1 to 50 atm%), Al·Li (Li: 0.01 to 14 atm%), In · Mg (Mg: 50 to 80 atm%), Al · Ca (Ca : 0.01 to 20 atm%). In addition, as an electron injection electrode, alkali metal fluorides (LiF, NaF, KF, RbF, CsF) or oxides (Li ₂ O, Na ₂ O, K ₂ O, Li, Na, K, Rb, Cs, etc.) Rb ₂ O, Cs ₂ O) may be used. Furthermore, alkali metal peroxides, composite oxides, halides other than fluorides, alkali metal nitrides, salts, and the like can also be used.
As the electron injection electrode, a single layer thin film made of the above material or a multilayer thin film made of two or more kinds of materials is used.

The organic EL device of the present invention is characterized in that a self-assembled polymer thin film is formed on the first electrode on the organic film side.
A self-assembled monolayer is already known as a thin film similar to this self-assembled polymer thin film.
A self-assembled monolayer is a film obtained by selective chemical adsorption of a functional group at one end of a molecule with atoms constituting the substrate. Due to the nature of the adsorption mechanism, only the monolayer is self-assembled. It is called a self-assembled monolayer because it is formed in an integrated state.

  Self-assembled monolayers do not suffer from the weak interaction between the substrate and the monolayer, unlike LB films (Langmuir Blodgett films), but use chemical adsorption between the substrate and molecular functional groups. Therefore, there are restrictions on the combination. A number of molecules for forming self-assembled monolayers have been developed so far, such as organic alkoxysilanes, organic halosilanes, organic disilazanes, carboxylic acids, hydroxamic acids, phosphonic acids, thiols, sulfides. And the like.

In addition, by selecting the type of terminal group opposite to the functional group that chemisorbs to the base material in the molecule for forming the self-assembled monolayer, the hydrophilicity and hydrophobicity of the monolayer surface, optical characteristics, electrical properties, Physicochemical properties such as characteristics can be changed, and a laminated film can be formed.
On the other hand, a self-assembled polymer thin film is a polymer thin film formed on a substrate in a self-assembled manner, and utilizes chemical adsorption (adhesion action) between the substrate and the molecular functional group. It can be obtained by the same formation method as that of the self-assembled monolayer except that the film-forming molecule is not a monomolecule but a polymer. In addition, after forming a self-assembled monolayer using a forming molecule having a polymerizable group, radical polymerization by heat or light irradiation, anionic polymerization or cationic polymerization using a polymerization initiator, or condensation polymerization using a condensing agent It is also possible to form a self-assembled polymer thin film by polymerizing molecules by depolymerization using a reducing agent.
In addition, since self-assembled polymer thin films are formed by chemical bonds between molecules, self-assembled monolayers that form two-dimensional molecular assemblies by van der Waals forces between molecules Compared with this, it is a dense high-quality film in which the bonds between molecules are stronger and defects such as pinholes are less likely to occur.
This method can be used to create a regular array of molecular packings, ie, a two-dimensional crystal. Various electronic devices, optical devices, and the like can be constructed by utilizing such characteristics.

  Next, the self-assembled polymer thin film (Embodiments 3 and 4) in the organic EL device of the present invention will be described with reference to FIGS. 3 and 4, 15 and 22 are first electrodes, 16 and 23 are self-assembled polymer thin films, and 17 and 24 are organic films. In FIG. 3, reference numeral 18 denotes a self-assembled polymer thin film comprising a side chain 20 having a functional group 19 that is chemically adsorbed directly on the surface of the first electrode 15 and a hydrophobic main chain 21. It is a polymer. In FIG. 4, reference numeral 25 denotes a side chain 27 having a functional group 26 directly chemisorbed on the surface of the first electrode 22 at one end, a main chain 28 showing hydrophilicity, and a functional group 29 showing hydrophobicity. Is a polymer for forming a self-assembled polymer thin film comprising a side chain 30 having at the other end.

  Specifically, in the self-assembled polymer thin film used in Embodiment 3, the structure of the main chain 21 of the forming polymer 18 is not particularly limited as long as it exhibits hydrophobicity, and is a copolymer or homopolymer. The repeating unit may be an ethylene structure, an oxyethylene structure, a phenylene structure, an iminoethylene structure, a peptide structure, an inorganic polymer structure, or the like, but is not limited to this exemplified repeating unit.

In the self-assembled polymer thin film used in Embodiment 4, the structure of the main chain 28 of the forming polymer 25 has a side chain 30 having a hydrophobic functional group 29 bonded to the end, for example, Examples include structures represented by the general formulas (1) and (2), whereby the surface of the self-assembled polymer thin film can be made hydrophobic.
_{(1) - (CH 2)} p -Z- (CH 2) q -CH 3
_{(2) - (CH 2)} p -Z- (CH 2) q -CF 3
The main chain 28 in the fourth embodiment may be hydrophobic as in the first embodiment, and a structure in which a side chain 30 having a hydrophobic functional group 29 at the end is bonded to the hydrophobic main chain 28. It is also possible.

In the third and fourth embodiments, the structures of the side chains 20 and 27 having functional groups 19 and 26 bonded to the first electrodes 15 and 22 (chemical adsorption) at the terminals are represented by the following general formulas (3) to (8), for example. ).
_{(3) - (CH 2)} p -Z- (CH 2) q -SiCl n X 3-n
_{(4) - (CH 2)} p -Z- (CH 2) q -Si (OR) n X 3-n
_{(5) - (CH 2)} p -Z- (CH 2) q -PO 3 H 2
_{(6) - (CH 2)} p -Z- (CH 2) q -COOH
_{(7) - (CH 2)} p -Z- (CH 2) q -NO 2 H 2
_{(8) - (CH 2)} p -Z- (CH 2) q -SH

The substituents and variables in the general formulas (1) to (8) will be described.
Z represents —CH ₂ —, alkenylene, alkynylene, phenylene, aminophenylene, alkylphenylene, phenylene vinylene, phenyleneethynylene, pyridinylene, pyridylvinylene, pyridylethynyl, thienylene, pyronylene, acene (ie, condensed polycyclic) skeleton, And pyridinopyridinylene. Among them, —CH ₂ — and alkenylene are preferable, and —CH ₂ — is particularly preferable.
X is a lower alkyl group, and —CH ₃ or —C ₂ H ₅ is particularly preferred.
R is a lower alkyl group, and examples thereof include —CH ₃ and —C ₂ H ₅ .
n is an integer of 1 to 3.
p and q are integers that do not include a negative value, and p + q = 2 to 30 is most easy to handle and is preferable.
The polymerization degree of the polymers 18 and 25 for forming a self-assembled polymer thin film is not particularly limited, but is preferably in the range of 10 to 20000, and particularly preferably in the range of 50 to 3000.

In the present invention, as described above, the polymers 18 and 25 for forming a self-assembled polymer thin film have functional groups 19 and 26 that are directly chemisorbed to the surfaces of the first electrodes 15 and 22 at the ends of the side chains 20 and 27. The functional groups 19 and 26 are preferably chlorosilyl group, lower alkoxysilyl group, carboxyl group, phosphonic acid group, hydroxamic acid group and thiol group (general formula (3)). To (8)). Among these, a particularly preferred functional group is a phosphonic acid group.
As described above, the self-assembled polymer thin film forming polymers 18 and 25 are directly chemically adsorbed on the surfaces of the first electrodes 15 and 22, whereby the self-assembled polymer thin film and the first electrode are firmly adhered to each other. .

In the present invention, as described above, the polymers 18 and 25 for forming the self-assembled polymer thin film have a hydrophobic main chain 21 structure or a hydrophobic functional group 29 at the end of the other side chain 30. Preferably, the functional group 29 includes a methyl group, a fluoro group (see general formulas (1) and (2)), and a methyl group is particularly preferable.
As described above, when the surface of the self-assembled polymer thin film exhibits high hydrophobicity, the adhesion of the organic films 17 and 24 formed thereon is directly applied to the highly hydrophilic first electrodes 15 and 22. Compared with the case of forming 17 and 24, it is much improved.

[Method of forming self-assembled polymer thin film]
As a method of forming a self-assembled polymer thin film on the first electrode on the organic film side using the above-mentioned polymer for forming a self-assembled polymer thin film, for example, for forming a self-assembled polymer thin film The polymer is dissolved in a solvent, the first electrode is immersed in the obtained solution, the polymer for forming the self-assembled polymer thin film is reacted on the first electrode, and then the first electrode is separated from the solution. Then, a method of washing with a solution for dissolving the molecules for forming the self-assembled polymer thin film to remove the unreacted polymer for forming the self-assembled polymer thin film and drying by heating can be mentioned. The “reaction” referred to herein is a chemical bond that occurs between the polymer for forming the self-assembled polymer thin film and the surface of the first electrode or a special adsorption with an energy comparable to the chemical bond (chemical adsorption). ).

The solvent for dissolving the polymer for forming the self-assembled polymer thin film is preferably selected from the followings depending on the functional group of the polymer for forming.
In the case of a forming polymer having a lower alkoxysilyl group, water, alcohol, ketone and the like can be mentioned.
In the case of a forming polymer having a chlorosilyl group, examples thereof include aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, ether compounds, and the like. Specifically, water, methanol, ethanol, propanol, 2-propanol, acetone, 2-butanone and mixtures thereof, hexane, decane, hexadecane, benzene, toluene, xylene, carbon tetrachloride, chloroform, methylene chloride, 1, Examples thereof include 1,2-trichloroethane, diethyl ether, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, and mixtures thereof, but are not particularly limited as long as they are compounds having no carbonyl group.
In the case of a forming polymer having a carboxyl group, a phosphonic acid group, a hydroxamic acid, and a thiol group, there is no particular limitation as long as the forming polymer is dissolved and does not react with these. Specific examples include the above-mentioned solvents.

  The concentration of the polymer for forming the self-assembled polymer thin film in the solution is not particularly limited, but a low concentration is not preferable because it takes time to form the self-assembled polymer thin film. Accordingly, the range in which the concentration of the functional group that binds to the first electrode of the polymer for forming the self-assembled polymer thin film is preferably about 0.002 to 10 mmol / L, but is not limited to this range.

The temperature in the treatment of immersing the first electrode in the polymer solution for forming the self-assembled polymer thin film and reacting the polymer for forming on the first electrode is not particularly limited, but is in the range of −10 to 100 ° C. Is preferable, and the range of 0 to 50 ° C. is particularly preferable.
In addition, the treatment time is not particularly limited. However, since the treatment takes a long time when the temperature is low, and the treatment is completed in a short time when the temperature is high, the range of 1 minute to 1 day is generally preferable. A range of ˜5 hours is particularly preferred.

  The film thickness of the self-assembled polymer thin film depends on the side chain length of the forming polymer, but is usually preferably 0.2 to 10 nm, particularly preferably 0.5 to 5 nm.

In the present invention, the organic film may have a single layer structure or a multilayer structure, and has at least a light emitting layer. For example, the following configurations (a) to (f) may be mentioned, but the present invention is not limited to these. In the configurations (b) to (f) of the multilayer structure, the left side may be the first electrode side and the right side may be the first electrode side.
(A) light emitting layer (b) hole transport layer / light emitting layer (c) light emitting layer / electron transport layer (d) hole transport layer / light emitting layer / electron transport layer (e) hole injection layer / hole transport layer / light emitting layer / Electron transport layer (f) hole injection layer / hole transport layer / light emitting layer / hole block layer / electron transport layer

In the present invention, the light emitting layer may contain a material other than the light emitting material. For example, an electron transporting light emitting layer containing an electron transport material (corresponding to reference numeral 7 in FIG. 1 and reference numeral 13 in FIG. 2), hole It is good also as a hole transportable light emitting layer containing a transport material.
Each of the light emitting layer, the hole injection layer, the hole transport layer, the hole block layer, and the electron transport layer may have a single layer structure or a multilayer structure, and a buffer layer may be further provided on the organic film. Moreover, these layers can be comprised with a well-known material in the said field | area, and can be formed by a well-known method.
The thickness of each layer of the organic film is usually about 1 to 1000 nm.

The hole transport material constituting the hole transport layer includes low molecular weight compounds such as benzidine derivatives, styrylamine derivatives, triphenylmethane derivatives, triphenyl (or aryl) amine derivatives, and hydrazone derivatives, polyaniline, polythiophene, polyvinylcarbazole, poly And a polymer compound such as a mixture of (3,4-ethylenedioxythiophene) and polystyrenesulfonic acid. Among these, α-NPD (α-naphthylphenyldiamine) is a frequently used compound and is particularly preferable.
The hole transport layer can be formed by a known method, and a wet method is preferred.

  As the fluorescent substance having a light emitting function constituting the light emitting layer, at least one selected from compounds such as quinacridone, rubrene and styryl dyes; 8-quinolinol such as tris (8-quinolinolato) aluminum (Alq3) and the like Quinoline derivatives such as metal complex dyes with derivatives as ligands, low molecules such as tetraphenylbutadiene, anthracene, perylene, coronene, 12-phthaloperinone derivatives, phenylanthracene derivatives, tetraarylethene derivatives; coumarins, perylenes, pyrans , Anthrone, porphyrene, quinacridone, N, N′-dialkyl substituted quinacridone, naphthalimide, N, N′-diaryl substituted pyrrolopyrrole, etc. Which is dissolved in a polymer such as alkenyl carbazole and a polymer fluorescent substance, such as polyaryl vinylene or polyfluorene, and the like.

  Moreover, it is also preferable to use it in combination with a host substance that can emit light by itself, and it is also preferable to use it as a dopant. In such a case, the content of the compound in the light emitting layer is preferably 0.02 to 10 wt%, and particularly preferably 0.2 to 4 wt%. By using in combination with the host material, the emission wavelength characteristic of the host material can be changed, for example, to the longer wavelength side, and the light emission efficiency and stability of the device are improved.

  Examples of the electron transport material constituting the electron transport layer include quinoline derivatives such as organometallic complexes having 8-quinolinol and its derivatives such as tris (8-quinolinolato) aluminum (Alq3) and derivatives thereof, oxadiazole derivatives, and perylene. Derivatives, pyridine derivatives, pyrimidine derivatives, quinoxaline derivatives, diphenylquinone derivatives, nitro-substituted fluorene derivatives, and the like.

  The organic EL element of the present invention may be provided with a known polarizing plate in order to improve the contrast of the organic EL element, and also prevents the entry of oxygen and moisture into the element from the outside. In order to improve the lifetime, a known sealing film such as glass or a sealing substrate may be provided.

  The present invention will be described more specifically based on examples and comparative examples, but the materials used in the examples and their amounts, numerical conditions such as processing temperature and processing time are only examples, and these examples However, the present invention is not limited thereto.

[Example 1]
As the organic EL device of the present invention, a two-layer device was produced as follows.
First, ITO serving as a hole injection electrode was formed on a 2 × 4 cm glass substrate by sputtering to have a film thickness of 200 nm. The sheet resistance of the obtained ITO film was 10Ω / □ or less. Next, photolithography and etching treatment were performed on the ITO film to form a 2 mm wide strip-shaped hole injection electrode. The glass substrate on which the hole injection electrode was formed was ultrasonically washed with acetone and IPA (2-propanol) for 10 minutes each and then dried.

Next, the glass substrate on which the hole injection electrode was formed was immersed in a poly (10 acryloyloxydecylphosphonic acid) ethanol solution having a phosphonic acid group concentration of 1 mM and held for about 2 hours. Thereafter, the glass substrate is washed with ethanol to remove excess poly (10 acryloyloxydecylphosphonic acid) adhering to the surface, and then heated and dried in an oven at 110 ° C. for 2 hours to form a surface of the hole injection electrode. A self-assembled polymer thin film was formed. The formation of a thin film of poly (10 acryloyloxydecylphosphonic acid) was confirmed by AFM measurement and FT-IR measurement, and the film thickness was 1.2 nm.
Poly (10 acryloyloxydecylphosphonic acid) is prepared by dissolving 700 μmol of 10 acryloyloxydecylphosphonic acid (see Japanese Patent Application Laid-Open No. 2000-7687) in an aqueous solution of 1500 μl, and a 1.0% aqueous ammonium peroxide solution as a polymerization initiator. In addition, 75 μl (microliter) of 1.0% N, N, N ′, N′-tetramethylethylenediamine aqueous solution was added and radical polymerization was performed for synthesis.

Next, a glass substrate having a self-assembled polymer thin film formed on the hole injection electrode was placed in a vacuum deposition apparatus for forming an organic film, and a hole was formed on the self-assembled polymer thin film using a vacuum deposition method. Α-NPD was formed as a transport layer so that the film thickness was 40 nm at a deposition rate of 0.5 nm / second.
Subsequently, Alq3 was formed as an electron-transporting light-emitting layer on the hole transport layer using a vacuum deposition method so that the film thickness was 70 nm at a deposition rate of 0.5 nm / second.

Thereafter, a glass substrate on which a hole injection electrode, a self-assembled polymer thin film, a hole transport layer, and an electron transporting light emitting layer were formed was placed in a vacuum deposition apparatus for forming an electrode. In a vacuum deposition method using a metal mask made of LiF, LiF is formed as an electron injection electrode so that the film thickness becomes 1 nm at a deposition rate of 0.02 nm / second, and subsequently Al is deposited at a deposition rate of 1.0 nm / second. The film was formed to have a thickness of 150 nm. In this way, an electron injection electrode composed of a strip-shaped LiF / Al layer having a width of 2 mm perpendicular to the hole injection electrode was formed.
Finally, the whole was glass-sealed to obtain an organic EL element.

[Example 2]
Instead of poly (10 acryloyloxydecylphosphonic acid) used in Example 1 above, Example 2 was carried out except that poly (10 methacryloyloxydecylphosphonic acid) was used to form a self-assembled polymer thin film. An organic EL device was produced in the same manner as in Example 1. When the film thickness of the self-assembled polymer thin film of Example 2 was measured by the same method as in Example 1, the film thickness was 1.3 nm.
In addition, poly (10 methacryloyloxydecylphosphonic acid) is prepared by dissolving 700 μmol of 10 methacryloyloxydecylphosphonic acid (see Japanese Patent Application Laid-Open No. 2000-7687) in 1500 μl of an aqueous solution, and a 1.0% ammonium peroxide aqueous solution as a polymerization initiator. In addition, 75 μl each of 1.0% N, N, N ′, N′-tetramethylethylenediamine aqueous solution was added and radical polymerization was performed for synthesis.

[Comparative Example 1]
An organic EL device was produced in the same manner as in Example 1 except that the self-assembled polymer thin film was not formed.

[Example 3]
As the organic EL element of Example 3 of the present invention, a two-layer element was produced as follows.
First, a 2 × 4 cm glass substrate is placed in a vacuum vapor deposition apparatus for forming an electrode film, and Al is deposited on the glass substrate as an electron injection electrode by a vacuum vapor deposition method using a stainless steel metal mask. The film was formed to a thickness of 150 nm at 0.0 nm / second, and then LiF was formed to a thickness of 1 nm at a deposition rate of 0.02 nm / second. In this manner, an electron injection electrode composed of a strip-like Al / LiF layer having a width of 2 mm was formed. Next, the glass substrate on which the electron injection electrode was formed was ultrasonically washed with acetone and IPA (2-propanol) for 10 minutes each and then dried.

  Next, the glass substrate on which the electron injection electrode was formed was immersed in a poly (10 acryloyloxydecylphosphonic acid) ethanol solution having a phosphonic acid group concentration of 1 mM and held for about 2 hours. Thereafter, the glass substrate is washed with ethanol to remove excess poly (10 acryloyloxydecylphosphonic acid) adhering to the surface, and then heated and dried in an oven at 110 ° C. for 2 hours to form the surface of the hole injection electrode. A self-assembled polymer thin film was formed. In addition, when formation of the thin film of poly (10 acryloyl oxydecyl phosphonic acid) was confirmed by AFM measurement and FT-IR measurement, the film thickness was 1.3 nm.

Next, a glass substrate having a self-assembled polymer thin film formed on the electron injection electrode is placed in a vacuum deposition apparatus for forming an organic film, and the electron is deposited on the self-assembled polymer thin film using a vacuum deposition method. Alq3 was formed as a transporting light-emitting layer so that the film thickness was 70 nm at a deposition rate of 0.5 nm / second.
Subsequently, α-NPD was formed as a hole transport layer on the electron transporting light-emitting layer so as to have a film thickness of 40 nm at a deposition rate of 0.5 nm / second by using a vacuum deposition method.

Thereafter, a glass substrate on which an electron injection electrode, a self-assembled polymer thin film, an electron transporting light emitting layer and a hole transport layer were formed was placed in a vacuum deposition apparatus for electrode formation, and a stainless steel plate was formed on the hole transport layer. By sputtering using a metal mask, ITO was formed as a hole injection electrode so as to have a film thickness of 200 nm. In this way, a hole injection electrode made of strip-like ITO having a width of 2 mm perpendicular to the electron injection electrode was formed.
Finally, the whole was glass-sealed to obtain an organic EL element.

[Example 4]
Instead of poly (10 acryloyloxydecylphosphonic acid) used in Example 3 above, Example 4 was carried out except that poly (10 methacryloyloxydecylphosphonic acid) was used to form a self-assembled polymer thin film. An organic EL device was produced in the same manner as in Example 3 (confirmation). When the film thickness of the self-assembled polymer thin film of Example 4 was measured in the same manner as in Example 3, the film thickness was 1.5 nm.

[Comparative Example 2]
An organic EL device was produced in the same manner as in Example 3 except that the self-assembled polymer thin film was not formed.

A direct current voltage was applied to each of the organic EL elements of Examples 1 to 4 and Comparative Examples 1 and 2 produced by the above procedure, and the organic EL elements were continuously driven at a constant current density of 10 mA / cm ² to evaluate the characteristics.
Table 1 shows the initial luminance of each organic EL element, its driving voltage, the luminance half-time, the voltage increased by the luminance half-time, and the number of dark spots exceeding 100 μm in terms of a circle equivalent diameter. The number of dark spots was measured visually.

  From the results in Table 1, the organic EL elements of Example 1 and Example 2 are lower in luminance than those of Comparative Example 1, and the organic EL elements of Example 3 and Example 4 are lower in luminance due to element driving than in Comparative Example 2. It was found that the generation and growth of dark spots and the voltage increase were suppressed.

  Thus, the organic EL device of the present invention has a self-assembled polymer thin film on the first electrode on the organic film side, for example, a lower alkoxysilyl group, a chlorosilyl group, a carboxyl group, a phosphonic acid group, a hydroxamant at the end of the side chain. A functional group that directly chemisorbs on the surface of the first electrode, such as an acid group and a thiol group, and a hydrophobic main chain structure or a hydrophobic functional group such as a methyl group or a fluoro group at the end of the other side chain Since a self-assembled polymer thin film made of an organic polymer having a group is formed, the adhesion between the first electrode and the organic film is improved, the luminance is lowered by driving the device, the generation and growth of dark spots, and the voltage rise. It is possible to provide a long-life organic EL element in which the light emission is suppressed and stable light emission characteristics are maintained over a long period of time.

  It can be used for various displays for information industry equipment, backlights for liquid crystal displays and lighting equipment.

It is a schematic sectional drawing of the principal part which shows the layer structure of the organic EL element of this invention (Embodiment 1). It is a schematic sectional drawing of the principal part which shows the layer structure of the other organic EL element of this invention (Embodiment 2). It is a schematic cross section of the self-assembled polymer thin film in the organic EL device of the present invention (Embodiment 3). It is a schematic cross section of another self-assembled polymer thin film in the organic EL device of the present invention (Embodiment 4).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2, 15, 22 1st electrode 3, 16, 23 Self-assembled polymer thin film 4, 17, 24 Organic film 5 Second electrode 6 Hole transport layer 7 Electron transport light emitting layer 18, 25 Self-assembled polymer Molecule for forming thin film 19, 26 Functional group directly chemisorbed on the surface of the first electrode 21 Main chain showing hydrophobicity 20, 27, 30 Side chain 28 Main chain showing hydrophilicity 29 Functional group showing hydrophobicity

Claims (10)

  A substrate, a first electrode laminated on the substrate, an organic film having a light emitting layer sequentially laminated on the first electrode side, and a second electrode, and further comprising a gap between the first electrode and the organic film An organic electroluminescence device comprising a self-assembled polymer thin film that has an adhesive action on the first electrode and the organic film.   The organic electroluminescence device according to claim 1, wherein the self-assembled polymer thin film is formed of an organic polymer having a functional group directly chemisorbed on the surface of the first electrode at the end of the side chain.   The functional group possessed at the end of the side chain of the self-assembled polymer thin film is selected from a lower alkoxysilyl group, a chlorosilyl group, a carboxyl group, a phosphonic acid group, a hydroxamic acid group, and a thiol group. Organic electroluminescence device.   The organic electroluminescent element according to any one of claims 1 to 3, wherein the self-assembled polymer thin film is formed of an organic polymer having a hydrophobic main chain structure.   The organic electroluminescence device according to any one of claims 1 to 3, wherein the self-assembled polymer thin film is formed of an organic polymer having a hydrophobic functional group at the end of the other side chain.   The organic electroluminescence device according to claim 5, wherein the hydrophobic functional group is a methyl group or a fluoro group.   The organic electroluminescence device according to any one of claims 1 to 6, wherein the self-assembled polymer thin film has a thickness of 0.2 to 10 nm.   The organic electroluminescence device according to claim 1, wherein the first electrode and the second electrode are each a hole injection electrode or an electron injection electrode, or are each an electron injection electrode or a hole injection electrode.   The organic electroluminescence device according to claim 8, wherein the hole injection electrode is formed of a material selected from ITO, IDIXO, tin oxide, gold, and polyaniline.   The electron injection electrode includes a single element of a metal element selected from K, Li, Na, Mg, La, Ce, Ca, Sr, Ba, Al, Ag, In, Sn, Zn, and Zr, or the metal element The organic electroluminescence device according to claim 8 or 9, wherein the organic electroluminescence device is formed of a two-component or three-component alloy.

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