JP5606227B2 - Organic thin film electroluminescent device with self-assembled monolayer - Google Patents

Description

  The present invention relates to an organic thin film electroluminescent device having a self-assembled monomolecular film.

  An organic thin film electroluminescent element (hereinafter referred to as “organic EL element”) having a structure in which at least one light emitting organic compound layer (organic electroluminescence layer) is sandwiched between a cathode and an anode is compared with an inorganic EL element. Thus, the applied voltage can be greatly reduced, and various light emitting elements can be manufactured (see, for example, Non-Patent Documents 1 to 3 and Patent Documents 1 to 3).

  At present, in order to obtain a higher performance organic EL element, various device structures including material development and improvement have been proposed, and active research is being conducted.

Regarding this organic EL element, various light emitting color elements and elements with high luminance and high efficiency have already been developed, and various uses such as use as a pixel of a display device and use as a light source are being studied. However, few have been put to practical use. The reason is that it is difficult to fabricate the device at low cost. Polymer organic EL devices are being studied as the most promising technology for cost reduction, which is a problem. This is because a polymer organic EL device can produce a light-emitting organic compound layer by applying a polymer light-emitting material on the device under a relatively mild condition at normal pressure and near normal temperature. This is because it is easier to form the organic compound layer than a low-molecular organic EL element that requires the production of a light-emitting organic compound layer below. However, even in a polymer organic EL element, a high-luminance element can be produced by forming a layer of lithium fluoride or lithium oxide between a cathode electrode and an organic compound layer in a special environment such as high temperature or high vacuum. There is still a problem in reducing the cost of device fabrication, such as the need to form a film (see Non-Patent Document 4, for example).
On the other hand, the development of organic-inorganic hybrid LEDs (hereinafter referred to as “HOILED”) (see, for example, Non-Patent Document 5 and Patent Document 4) is also in progress as a new method for reducing costs. A HOILED that can use an air-stable metal essentially does not require sealing, and can achieve a significant cost reduction compared to conventional organic EL devices that have required sealing the device. However, even in the case of this HOILED, the current device fabrication method requires repeated formation of a metal oxide layer in a special environment such as high temperature or high vacuum, thereby achieving cost optimization. It is hard to say that it is.

JP-A-10-153967 Japanese Patent Laid-Open No. 10-12377 Japanese Patent Laid-Open No. 11-40358 JP 2007-53286 A

Appl. Phys. Lett. 51 (12), 913, 1987 Appl. Phys. Lett. 71 (1), 34, 1997 Nature 357, 477, 1992 Appl. Phys. Lett. 70 (2), 152, 1997 Appl. Phys. Lett. 89, 183510, 2006

  The present invention has been made in view of the above situation, and its purpose is to produce a high temperature in the production of an organic EL device having a structure opposite to a normal structure in which a cathode exists between a substrate and a light-emitting organic compound layer. An object of the present invention is to provide an organic thin-film electroluminescent element and a lighting device equipped with the light-emitting element at low cost by reducing the film forming process in a special environment such as high vacuum.

As a result of intensive studies on the above problems, the present inventors have achieved the present invention and are achieved by the following present invention.

That is, the present invention
(1) A substrate, a cathode, a self-assembled monolayer, an organic compound layer containing a luminescent material, and an anode are present in this order, and another layer is present between the cathode and the self-assembled monolayer. It is an organic thin film electroluminescent element characterized by having a structure which does not.

  Thereby, the organic thin film electroluminescent element which has a low molecular and high molecular material which can express the outstanding light-emitting luminance is obtained.

Preferably,
(2) An organic thin film electroluminescent device having a structure in which no other layer exists between the organic compound layer containing the light emitting material closest to the cathode and the self-assembled monolayer in addition to the structure.

  Thereby, electrons are efficiently injected from the cathode side into the organic compound layer containing the light emitting material, so that holes and excitons injected from the anode side can be formed satisfactorily, and light emission luminance is improved.

More preferably,
(3) The organic thin film electroluminescent device is characterized in that the work function of the cathode is larger than 4.0 eV.

  As a result, an organic thin film electroluminescent device having high atmospheric stability and essentially not requiring sealing is obtained.

Even more preferably,
(4) An organic thin film electroluminescent device comprising a metal oxide layer between the anode and the organic compound layer.

Thereby, the injection efficiency of holes from the anode side to the organic compound layer is improved, and the effect of the self-assembled monolayer existing on the cathode can be sufficiently exhibited. When the electrode is a metal oxide, a metal oxide layer having a composition different from that of the electrode is introduced.

Even more preferably,
(5) The organic thin film electroluminescent device is characterized in that a precursor of a self-assembled monomolecular film provided in the organic thin film electroluminescent device is obtained from a compound represented by the following general formula (1).

_{R n -Si-A 4-n} ··· (1)

In the above, n is a positive integer represented by 1 to 3. A is a hydroxyl group, a halogen, or an alkoxy group, and when there are a plurality, A may be different from each other. R is an organic substituent, and when there are a plurality of R, they may be different from each other.

When such a precursor is used to form a self-assembled monolayer on the cathode, the self-assembled monolayer can interact strongly with the cathode, resulting in a more stable organic thin film electroluminescent device. it can.

Furthermore, even more preferably,
(6) An organic thin film electroluminescent device characterized in that an average thickness of a self-assembled monolayer prepared using the precursor of the self-assembled monolayer is from 0.1 nm to 3 nm.

  Thereby, the electron injection from the cathode side can be performed efficiently, and the brightness of the organic thin film electroluminescent element is further improved.

Also,
(7) An illumination device including the organic thin film electroluminescent element.

  Thereby, the illuminating device which can express the outstanding light emission luminance at low cost is obtained.

As described above, according to the present invention, an organic EL element having a structure opposite to a normal structure in which a cathode is present between a substrate and an organic compound layer can be produced at low cost, and provided with it. A lighting device can be provided.

It is a figure which shows typically the longitudinal cross-section of the organic EL element which has a structure contrary to the normal in which a cathode exists between the board | substrate and organic compound layer in this invention. It is a graph which shows the result of having evaluated initial brightness | luminance with respect to the light emitting element manufactured in Examples 1-3 and the comparative example 1. FIG. It is a graph which shows the result of having evaluated initial brightness | luminance with respect to the light emitting element manufactured in Examples 4-6 and the comparative example 1. FIG.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of an organic thin film electroluminescent element and an illuminating device of the invention will be described with reference to the drawings. The present invention is not limited to these structures.
(Embodiment 1)
FIG. 1 is a diagram schematically showing a longitudinal section of an organic EL element having a structure opposite to a normal structure in which a cathode is present between a substrate and an organic compound layer.

  1 includes an organic compound between a cathode (one electrode) 3, an anode (the other electrode) 5, and between the cathode 3 and the anode 5 (between a pair of electrodes). A layer 4 is interposed, and a hole injecting layer 7 is provided between the organic compound layer 4 and the anode 5, and a self-assembled monolayer 6 is provided between the organic compound layer 4 and the cathode 3. It is made. The entire light emitting element 1 is provided on the substrate 2. This light emitting element is thus completed. In addition, as long as this element does not prevent the original purpose from being exhibited, a structure other than that described here may be required. For example, to prevent the element from being exposed to oxygen or water or to protect the electrode. In addition, there is no problem even if sealing with a film or the like.

  The substrate 2 serves as a support for the light-emitting element 1 and is also a support for directly producing a conductive cathode here. The light emitting element 1 of the present embodiment is not limited in the light extraction direction, and is configured to extract light from the substrate 2 side (bottom emission type) and from the anode 5 on the side opposite to the substrate 2. There are three possible configurations: a configuration for extracting light (top emission type) and a configuration for extracting light from both (transparent type). In the case of the top emission type, the substrate 2 and the cathode 3 can be freely selected as long as they do not interfere with the original purpose, regardless of whether the substrate 2 and the cathode 3 are transparent materials or opaque materials. Both must be substantially transparent (colorless transparent, colored transparent or translucent).

  Examples of the constituent material of the substrate 2 that is substantially transparent include resins such as polyethylene terephthalate, polyethylene naphthalate, polypropylene, cycloolefin polymer, polyamide, polyethersulfone, polymethyl methacrylate, polycarbonate, and polyarylate. Examples thereof include glass materials such as quartz glass and soda glass, and one or two or more of these can be used in combination.

Non-transparent substrates that can be used in the top emission type include, for example, a substrate made of a ceramic material such as alumina, an oxide film (insulating film) formed on the surface of a metal substrate such as stainless steel, and aluminum. Examples thereof include a substrate in which an oxide film (insulating film) is formed on the surface of a flexible metal film such as a foil, a substrate made of a resin material, and the like.
Note that the substrate itself may be used as an electrode. In that case, the conductive substrate itself such as a metal plate becomes the cathode.

  Although the average thickness of such a board | substrate 2 is not specifically limited, It is preferable that it is about 0.1-30 mm, and it is more preferable that it is about 0.1-10 mm.

  The cathode 3 in this structure is excellent in conductivity, and in the case of the bottom emission type and the transparent type, it is excellent in transmittance in the wavelength region of light necessary for use as a lighting device. Furthermore, the cathode 3 in this structure is preferably a material having a large work function that is stable in the atmosphere. In particular, when the work function is 4 eV or more, stability in the atmosphere can be obtained. The same applies to the anode 5, which has a large work function, excellent conductivity, and in the case of a top emission type and a transparent type, a material having excellent transparency in the wavelength region of light necessary for use as a lighting device. It is desirable to use it. The work function can be measured by a known method such as ultraviolet photoelectron spectroscopy (UPS).

Examples of constituent materials of the cathode 3 and the anode 5 include ITO (indium tin oxide), IZO (indium zinc oxide), FTO (fluorine tin oxide), In ₂ O ₃ , SnO ₂ , Sb-containing SnO ₂ , and Al-containing ZnO. Examples thereof include oxides such as Al, Au, Pt, Ag, and Cu, and alloys containing these, and one or more of these can be used in combination.

  The average thickness of the cathode 3 is not particularly limited, but is preferably about 10 to 200 nm, and more preferably about 30 to 150 nm. Even when an opaque material such as Al, Au, Pt, Ag, or Cu is used, it can be used as a bottom emission type or transparent type cathode, for example, by setting the average thickness to about 10 to 30 nm. .

  On the other hand, the average thickness of the anode 5 is not particularly limited, but is preferably about 10 to 10000 nm, and more preferably about 30 to 150 nm. Even when an impermeable material such as Al, Au, Pt, Ag, or Cu is used, it can be used as a top emission type or transparent type anode by setting the average thickness to about 10 to 30 nm, for example. .

  The organic compound layer 4 is a layer responsible for light emission, and is a layer containing at least a light emitting material. Examples of the light emitting material include a low molecular light emitting material and a high molecular light emitting material. These light emitting materials may be used singly, a plurality of types may be mixed, or a material that does not emit light may be mixed with other substances. In particular, when used in applications that require various emission colors, such as lighting, it is mixed with other light-emitting materials having different emission spectra, or a polymer is prepared by mixing two or more types of monomers. It is preferable. The organic compound layer 4 may be a single layer or a plurality of layers.

  Examples of the polymer light-emitting material include polyacetylene compounds such as trans-type polyacetylene, cis-type polyacetylene, poly (di-phenylacetylene) (PDPA), poly (alkyl, phenylacetylene) (PAPA), and poly (para-para-). Phenylene vinylene) (PPV), poly (2,5-dialkoxy-para-phenylene vinylene) (RO-PPV), cyano-substituted-poly (para-phenylene vinylene) (CN-PPV), poly (2-dimethyloctyl) Polyparaphenylene vinylene compounds such as silyl-para-phenylene vinylene (DMOS-PPV), poly (2-methoxy, 5- (2′-ethylhexoxy) -para-phenylene vinylene) (MEH-PPV), poly ( Polythiol such as 3-alkylthiophene) (PAT) Compounds, poly (9,9-dialkylfluorene) (PDAF), poly (dioctylfluorene-alt-benzothiadiazole) (F8BT), α, ω-bis [N, N′-di (methylphenyl) aminophenyl] -Poly [9,9-bis (2-ethylhexyl) fluorene-2,7-zyl] (PF2 / 6am4), poly (9,9-dioctyl-2,7-divinylenefluorenyl-ortho-co (anthracene) -9,10-diyl) and other polyfluorene compounds, poly (para-phenylene) (PPP), poly (1,5-dialkoxy-para-phenylene) (RO-PPP) Compounds, polycarbazole compounds such as poly (N-vinylcarbazole) (PVK), poly (methylphenylsilane) (PMPS) Poly (naphthyl phenylsilane) (PnPs), polysilane-based compounds such as poly (biphenylyl phenyl silane) (pBPS), further include a boron compound-based polymer materials such as described in Japanese Patent Application No. 2010-28273.

On the other hand, as a low-molecular light-emitting material, for example, a tricoordinate iridium complex having 2,2′-bipyridine-4,4′-dicarboxylic acid, factory (2-phenylpyridine) iridium (Ir (ppy) ₃ ), 8-hydroxyquinoline aluminum (Alq ₃ ), tris (4-methyl-8 quinolinolate) aluminum (III) (Almq ₃ ), 8-hydroxyquinoline zinc (Znq ₂ ), (1,10-phenanthroline) -tris -(4,4,4-trifluoro-1- (2-thienyl) -butane-1,3-dionate) europium (III) (Eu (TTA) ₃ (phen)), 2,3,7,8, Various metal complexes such as 12, 13, 17, 18-octaethyl-21H, 23H-porphine platinum (II), distyrylbenzene (DSB) Benzene compounds such as diamino distyrylbenzene (DADSB), naphthalene compounds such as naphthalene and nile red, phenanthrene compounds such as phenanthrene, chrysene, chrysene compounds such as 6-nitrochrysene, perylene, N, Perylene compounds such as N'-bis (2,5-di-t-butylphenyl) -3,4,9,10-perylene-di-carboximide (BPPC), coronene compounds such as coronene, anthracene , Anthracene compounds such as bisstyrylanthracene, pyrene compounds such as pyrene, and 4- (di-cyanomethylene) -2-methyl-6- (para-dimethylaminostyryl) -4H-pyran (DCM) Pyran compounds, acridine compounds such as acridine, stilbe Stilbene compounds such as 2,5-dibenzoxazole thiophene, thiophene compounds such as benzoxazole, benzoxazole compounds such as benzimidazole, 2,2 ′-(para-pheny Benzothiazole compounds such as rangevinylene) -bisbenzothiazole, bistyryl (1,4-diphenyl-1,3-butadiene), butadiene compounds such as tetraphenylbutadiene, naphthalimide compounds such as naphthalimide, Coumarin compounds such as coumarin, perinone compounds such as perinone, oxadiazole compounds such as oxadiazole, aldazine compounds, 1,2,3,4,5-pentaphenyl-1,3-cyclo Pentadiene (PPCP) Cyclopentadiene compounds, quinacridone compounds such as quinacridone and quinacridone red, pyridine compounds such as pyrrolopyridine and thiadiazolopyridine, 2,2 ′, 7,7′-tetraphenyl-9,9′-spiro Spiro compounds such as bifluorene, phthalocyanine (H ₂ Pc), metal or metal-free phthalocyanine compounds such as copper phthalocyanine, and boron compound materials described in JP-A-2009-155325 and Japanese Patent Application No. 2010-28273 Etc.

When a material other than the light emitting material is mixed in the organic compound layer 4, it is preferable to use a hole transporting organic material. The hole transporting organic material used as the hole injecting / transporting layer promotes the transport of holes in the organic compound layer. As the hole transporting organic material, various p-type polymer materials and various p-type low molecular materials can be used alone or in combination.

  Examples of the p-type polymer material (organic polymer) include polyarylamines, fluorene-arylamine copolymers, fluorene-bithiophene copolymers, poly (N-vinylcarbazole), polyvinylpyrene, polyvinylanthracene, polythiophene, Examples thereof include polyalkylthiophene, polyhexylthiophene, poly (p-phenylene vinylene), polytinylene vinylene, pyrene formaldehyde resin, ethylcarbazole formaldehyde resin, and derivatives thereof.

  Moreover, the said compound can also be used as a mixture with another compound. As an example, the polythiophene-containing mixture includes poly (3,4-ethylenedioxythiophene / styrene sulfonic acid) (PEDOT / PSS).

On the other hand, examples of p-type low molecular weight materials include 1,1-bis (4-di-para-triaminophenyl) cyclohexane and 1,1′-bis (4-di-para-tolylaminophenyl). Arylcycloalkane compounds such as -4-phenyl-cyclohexane, 4,4 ′, 4 ″ -trimethyltriphenylamine, N, N, N ′, N′-tetraphenyl-1,1′-biphenyl-4 , 4′-diamine, N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-biphenyl-4,4′-diamine (TPD1), N, N′-diphenyl- N, N′-bis (4-methoxyphenyl) -1,1′-biphenyl-4,4′-diamine (TPD2), N, N, N ′, N′-tetrakis (4-methoxyphenyl) -1, 1′-biphenyl-4,4′-diamine (TPD3), , N′-di (1-naphthyl) -N, N′-diphenyl-1,1′-biphenyl-4,4′-diamine (α-NPD), arylamine compounds such as TPTE, N, N, N ′, N′-tetraphenyl-para-phenylenediamine, N, N, N ′, N′-tetra (para-tolyl) -para-phenylenediamine, N, N, N ′, N′-tetra (meta-) Phenylenediamine compounds such as (tolyl) -meta-phenylenediamine (PDA), carbazole compounds such as carbazole, N-isopropylcarbazole, N-phenylcarbazole, stilbene, and 4-di-para-tolylaminostilbene stilbene compounds, oxazole-based compounds such as _{O x} Z, triphenylmethane, triphenylmethane compounds such as m-MTDATA, 1- Pyrazoline compounds such as enyl-3- (para-dimethylaminophenyl) pyrazoline, benzine (cyclohexadiene) compounds, triazole compounds such as triazole, imidazole compounds such as imidazole, 1,3,4-oxa Diazole, oxadiazole compounds such as 2,5-di (4-dimethylaminophenyl) -1,3,4, -oxadiazole, anthracene, anthracene such as 9- (4-diethylaminostyryl) anthracene Compound, fluorenone, 2,4,7, -trinitro-9-fluorenone, 2,7-bis (2-hydroxy-3- (2-chlorophenylcarbamoyl) -1-naphthylazo) fluorenone such as fluorenone, polyaniline Aniline compounds like silane Compounds, pyrrole compounds such as 1,4-dithioketo-3,6-diphenyl-pyrrolo- (3,4-c) pyrrolopyrrole, fluorene compounds such as fluorene, porphyrins, porphyrins such as metal tetraphenylporphyrin Compounds, quinacridone compounds such as quinacridone, phthalocyanine, copper phthalocyanine, tetra (t-butyl) copper phthalocyanine, metal or metal-free phthalocyanine compounds such as iron phthalocyanine, copper naphthalocyanine, vanadyl naphthalocyanine, monochlorogallium Metallic or metal-free naphthalocyanine compounds such as phthalocyanine, N, N′-di (naphthalen-1-yl) -N, N′-diphenyl-benzidine, N, N, N ′, N′-tetraphenylbenzidine Benzidine like Compounds, and the like.

  The average thickness of the organic compound layer 4 is not particularly limited, but is preferably about 10 to 150 nm, more preferably about 40 to 100 nm per layer. Moreover, when the organic compound layer 4 is a multilayer, it is preferable that the average thickness of the whole is about 20-200 nm, and it is more preferable that it is 40-150 nm.

  The organic compound layer 4 transports holes injected from the hole injecting layer 7 and receives electrons from the self-assembled monolayer 6. Holes and electrons recombine, and excitons (excitons) are generated by the energy released during the recombination, and energy (fluorescence and phosphorescence) is emitted (emitted) when the excitons return to the ground state. . The constituent material of the organic compound layer 4 is preferably a material mainly composed of a high-molecular light-emitting material or a material obtained by mixing a p-type polymer material and a low-molecular light-emitting material. A polymer material that can be formed by a liquid phase process can make more contact surfaces with the self-assembled monolayer 6. Thereby, it can be made more excellent in luminous efficiency. In particular, as a constituent material of the organic compound layer 4, a polymer mainly composed of polyfluorene or a derivative thereof, a polymer composed of a boron compound described in JP-A No. 2009-155325, or a Japanese Patent Application No. 2010-28273. A light emitting material mainly composed of a polymer described in No. 1 is preferred. Thereby, the said effect can be improved more.

  The self-assembled monolayer 6 injects electrons from the cathode 3 and transports them to the organic compound layer 4.

  The self-assembled monolayer is prepared by forming a precursor that forms a self-assembled monolayer on the cathode and causing interaction with the cathode surface. The precursor that forms the self-assembled monolayer needs to physically and / or chemically interact with the cathode. Further, in the case of a bottom emission type or transparent type organic EL element, it is necessary to have a characteristic that it does not have a large absorption in the wavelength region of the light used. The self-assembled monolayer formed using the precursor preferably has a high ability to prevent holes injected from the anode side into the organic compound layer from flowing out to the cathode side. More preferably, in addition to the above characteristics, it has oxidation resistance, reduction resistance, and atmospheric stability.

  As the precursor of the self-assembled monolayer, any precursor having a functional group that interacts with the cathode surface may be used. Examples of this functional group include a thiol group, a carboxylic acid group, a silanol group, a halosilyl group, an alkoxysilyl group, an amino group, a hydroxyl group, a phosphonic acid group, a pyridyl group, and a sulfo group. Of these, a silanol group, a halosilyl group, an alkoxysilyl group, a carboxylic acid group, a phosphonic acid group, and a sulfo group are preferable. More preferably, it has a silicon-containing group such as a silanol group, a halosilyl group, and an alkoxysilyl group. The specific structure of these three groups is shown in the following general formula (1).

_{R n -Si-A 4-n} ··· (1)

In the above, A is a hydroxyl group in the case of a silanol group, a halogen such as fluorine, chlorine or bromine in the case of a halosilyl group, and an alkoxy group such as a methoxy group or an ethoxy group in the case of an alkoxysilyl group. N is a positive integer represented by 1 to 3. R is an organic substituent.

Specific examples of R include linear saturated alkyl groups having 1 to 18 carbon atoms, branched saturated alkyl groups, alicyclic saturated alkyl groups, aromatic group-containing groups, linear unsaturated alkyl groups, branched unsaturated alkyl groups. Group or alicyclic unsaturated alkyl group, or ester group having 1 to 18 carbon atoms, nitrile group, carboxylic acid group, ether group, hydroxyl group, thiol group, halogen group, isocyano group, cyanate group, isocyanate group, Thiocyanate group, isothiocyanate group, sulfide group, disulfide group, sulfinyl group, sulfonyl group, nitro group, nitroso group, sulfo group, carbonyl group (for example, ketone and aldehyde), amino group, amine oxide group, nitrone group, amide Group, azide group, acetal group, azo group, azoxy group, azine group, imino group, imide group, enamine group, Namido groups, orthoester group, a diazo group, a diazonium group, a ketal group, onium salt, heterocyclic compounds, hetero element-containing group (P, S, Si, B, etc.) atomic group having a like. More preferably, a linear saturated alkyl group having 1 to 12 carbon atoms, a branched saturated alkyl group, an alicyclic saturated alkyl group, an aromatic group-containing group, a linear unsaturated alkyl group, a branched unsaturated alkyl group, or an alicyclic ring Formula unsaturated alkyl group or halogen group having 1 to 12 carbon atoms, ester group, nitrile group, carboxylic acid group, ether group, hydroxyl group, thiol group, sulfo group, carbonyl group, amino group, amide group, onium base Alternatively, it represents an atomic group having a heterocyclic compound. More preferably, a linear saturated alkyl group having 1 to 8 carbon atoms, a branched saturated alkyl group, an alicyclic saturated alkyl group, an aromatic group-containing group, a halogen group having 1 to 8 carbon atoms, a nitrile group, It represents an atomic group having a carboxylic acid group, a thiol group, a sulfo group, a carbonyl group, an amino group, an onium base or a heterocyclic compound. Particularly preferred is an atomic group having an amino group having 1 to 8 carbon atoms and an onium base. The onium salt mentioned here means that a compound having an electron pair that does not participate in a chemical bond such as an ammonium salt, a phosphonium salt, or a sulfonium salt is coordinated with another cationic compound by the electron pair. Refers to the resulting compound. The counter anion of the onium salt may be a monovalent ion such as fluoride ion, chloride ion or nitrate ion, may be a divalent ion such as sulfide ion or sulfate ion, or may be a trivalent ion such as phosphate ion, Further multivalent ions such as silicotungstate ions may be used.

  As a film forming method, a spin coating method, a dipping method, an ultrasonic method, a gas phase method, or the like can be selected. For these, an optimum method capable of forming a monolayer is selected depending on the precursor of the self-assembled monolayer to be produced. By forming the precursor into a film by such a method, a self-assembled monolayer can be produced.

  The average thickness of the self-assembled monolayer formed by the above method is preferably 0.1 nm or more and 3 nm or less. If the average thickness is less than 0.1 nm, holes injected from the anode may pass through the self-assembled monolayer 6 and reach the cathode 3, which may reduce the luminous efficiency. . On the other hand, if the average thickness is larger than 3 nm, the electron injection efficiency from the cathode side is lowered, and there is a possibility that sufficient emission luminance cannot be obtained. More preferably, the average thickness of the self-assembled monolayer is from 0.2 nm to 2 nm. In addition, average thickness can be measured with the existing well-known analysis methods, such as an ellipsometer and a X-ray reflectivity method (XRR).

  The hole injecting layer 7 injects holes from the anode 5 and transports them to the organic compound layer 4. In the present invention, the hole injecting layer 7 is not essential, but is preferably included in the element in order to improve the efficiency of injecting holes from the anode 5 into the organic compound layer 4.

Examples of the substance constituting the hole injecting layer 7 include p-type polymer materials, organic polymer compounds such as PEDOT / PSS, organic low-molecular compounds such as p-type low-molecular materials, inorganic salts, metals Examples thereof include oxides and metal sulfides. Of these, metal oxides are preferable. Among metal oxides, a compound having a large work function is more preferable, and is not particularly limited. Examples thereof include vanadium oxide (V ₂ O ₅ ), molybdenum oxide (MoO ₃ ), and ruthenium oxide (RuO ₂ ). One or two or more of them can be used in combination.

  Among these, those containing vanadium oxide or molybdenum oxide as the main component are particularly suitable. By using vanadium oxide or molybdenum oxide as a main material, the hole injecting layer 7 can be made particularly excellent in the above-described ability.

  In particular, vanadium oxide or molybdenum oxide has a high hole transport property in itself, so that it is possible to suitably prevent a decrease in the efficiency of hole injection from the anode 5 to the organic compound layer 4. is there.

  The film forming method of the hole injecting layer 7 is not particularly limited, and when a polymer compound is used, a polymer material dissolved in a solvent is formed by an appropriate coating method. I can do it. In addition, low molecular weight compounds, inorganic salts, metal oxides, metal sulfides, and the like can be formed by chemical vapor deposition (CVD) such as plasma CVD, thermal CVD, and laser CVD, vacuum deposition, sputtering, and ion plating. Dry plating methods such as coating, thermal spraying, and liquid phase film forming methods such as electrolytic plating, immersion plating, electroless plating, etc., wet plating methods, sol-gel methods, MOD methods, spray pyrolysis methods, fine particle dispersions Printing techniques such as the doctor blade method, spin coating method, ink jet method, and screen printing method used can be used.

  The average thickness of the hole injecting layer 7 is not particularly limited, but is preferably about 1 to 1000 nm, and more preferably about 5 to 50 nm.

  These are suitable structures for organic EL elements having a cathode on the substrate side.

Moreover, when sealing this organic EL element, the sealing material generally used can be used as a constituent material of sealing structure. For example, Al, Au, Cr, Nb, Ta, Ti or alloys containing these, silicon oxide, various resin materials, and the like can be given.

  Such a light emitting element 1 can be manufactured as follows, for example.

  Below, the case where the organic compound layer 4 comprises a high molecular material as a main material is demonstrated as a representative.

  [1] First, the substrate 2 is prepared, and the cathode 3 is formed on the substrate 2.

  The cathode 3 may be, for example, a chemical vapor deposition method (CVD) such as plasma CVD, thermal CVD, or laser CVD, a dry plating method such as vacuum deposition, sputtering, or ion plating, a vapor deposition method such as a thermal spraying method, or an electrolytic plating. It can be formed using a wet plating method such as immersion plating or electroless plating, a liquid phase film forming method such as a sol-gel method or a MOD method, or a metal foil bonding. FTO is difficult to sputtering, and CVD or spray pyrolysis is used.

  [2] Next, after cleaning the cathode 3, a self-assembled monolayer 6 is formed.

  Cleaning methods include water-based solvents using neutral detergents, cleaning in which acids, alkalis and oxides are used alone or mixed, cleaning with alcoholic solvents such as isopropanol, organic solvents such as acetone, heating, and UV ozone. The washing | cleaning used etc. can be used individually or in multiple numbers. Among these, UV ozone cleaning is preferably used in order to satisfactorily form a self-assembled monolayer. For example, as described above, the self-assembled monolayer 6 can be formed by using a precursor of a self-assembled monolayer using a spin coating method, a dipping method, an ultrasonic method, a gas phase method, or the like. . In the spin coating method, the dipping method, and the ultrasonic method, first, the precursor of the self-assembled monolayer is diluted with an organic solvent. In the case of the spin coating method, the solution is spin coated on a substrate to produce a self-assembled monolayer. In the immersion method, the substrate is immersed in the solution. In the ultrasonic method, the substrate is immersed in the solution, and further, ultrasonic waves are applied in an ultrasonic cleaner. After forming into a film by these methods, it rinses with the said organic solvent, and also ultrasonically cleans with the said organic solvent. In order to more reliably fix the self-assembled monolayer on the substrate, heating may be performed at 60 ° C to 180 ° C. In the vapor phase method, a substrate in which the cathode 3 is washed and a precursor of a self-assembled monolayer are placed in a sealed container, and a film is formed using the vapor pressure of the precursor of the self-assembled monolayer. It is a technique. When the vapor pressure of the precursor is low, heat may be applied during film formation. The substrate formed by maintaining for a certain time in the sealing period is rinsed with an organic solvent, and further ultrasonically cleaned with the organic solvent. Even in this case, heating at 60 ° C. to 180 ° C. may be performed in order to more reliably fix the substrate.

  [4] Next, a light-emitting polymer material is formed as the organic compound layer 4 on the upper surface of the self-assembled monolayer 6. Of course, a hole transporting material may be mixed therein, or a light emitting polymer material may be formed first, and a hole transporting material may be laminated thereon. Here, an example of single-layer film formation is shown. When the organic compound layer 4 is laminated, it can be realized by repeating the method used here.

  First, the polymer material constituting the organic compound layer 4 is dissolved in a solvent (liquid medium) to prepare a liquid material.

Examples of the solvent include inorganic solvents such as nitric acid, sulfuric acid, ammonia, hydrogen peroxide, water, carbon disulfide, carbon tetrachloride, ethylene carbonate, methyl ethyl ketone (MEK), acetone, diethyl ketone, methyl isobutyl ketone (MIBK). , Ketone solvents such as methyl isopropyl ketone (MIPK) and cyclohexanone, alcohol solvents such as methanol, ethanol, isopropanol, ethylene glycol, diethylene glycol (DEG) and glycerin, diethyl ether, diisopropyl ether, 1,2-dimethoxyethane (DME) ), 1,4-dioxane, tetrahydrofuran (THF), tetrahydropyran (THP), anisole, diethylene glycol dimethyl ether (diglyme), diethylene glycol ethyl ether Ether solvents such as carbitol), cellosolv solvents such as methyl cellosolve, ethyl cellosolve and phenyl cellosolve, aliphatic hydrocarbon solvents such as hexane, pentane, heptane and cyclohexane, and aromatic hydrocarbons such as toluene, xylene and benzene. Solvent, aromatic heterocyclic compound solvent such as pyridine, pyrazine, furan, pyrrole, thiophene, methylpyrrolidone, amide solvent such as N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMA), Halogen compound solvents such as chlorobenzene, dichloromethane, chloroform, 1,2-dichloroethane, ester solvents such as ethyl acetate, methyl acetate, ethyl formate, sulfur compound solvents such as dimethyl sulfoxide (DMSO), sulfolane, acetonitrile, propio Tolyl, nitriles such as acrylonitrile, formic acid, acetic acid, trichloroacetic acid, various organic solvents such as an organic acid solvents such as trifluoroacetic acid, or mixed solvents containing them.

  Among these, as the solvent, a nonpolar solvent is suitable, for example, an aromatic hydrocarbon solvent such as xylene, toluene, cyclohexylbenzene, dihydrobenzofuran, trimethylbenzene, tetramethylbenzene, pyridine, pyrazine, furan, Examples include aromatic heterocyclic compound solvents such as pyrrole, thiophene, and methylpyrrolidone, and aliphatic hydrocarbon solvents such as hexane, pentane, heptane, and cyclohexane. These can be used alone or in combination.

  Next, this liquid material is supplied onto the self-assembled monolayer 6 to form a liquid film.

  Examples of the method for supplying the liquid material include spin coating, casting, micro gravure coating, gravure coating, bar coating, roll coating, wire bar coating, dip coating, spray coating, and screen printing. Various coating methods such as a printing method, a flexographic printing method, an offset printing method, and an inkjet printing method can be used. According to such a coating method, a liquid film can be formed relatively easily.

  Next, the solvent is removed from the liquid film.

  [5] Next, the hole injecting layer 7 is formed on the organic compound layer 4.

  The hole-injecting layer 7 can be formed using a polymer compound, a low-molecular compound, an inorganic salt, a metal oxide, a metal sulfide, or the like, and can be formed using a film forming method suitable for each. For example, if it is a high molecular compound, it can form by the method similar to the method of producing the organic compound layer 4 mentioned above. In addition, low molecular compounds, inorganic salts, metal oxides, metal sulfides, and the like can be formed using the vapor phase film formation method, the liquid phase film formation method, or the like as described above.

  Among these, the hole injecting layer 7 is more preferably formed by using a vapor phase film forming method. According to the vapor deposition method, the hole injecting layer 7 can be formed cleanly without breaking the surface of the organic compound layer 4, and the contact with the anode 5 is also improved. As a result, the effects as described above become more remarkable.

  [6] Next, the anode 5 is formed on the hole injecting layer 7 as a final step.

  The anode 5 can be formed using, for example, a vacuum deposition method, a sputtering method, a metal foil bonding, or the like.

  This structure is completed, but if it is to be performed, a sealing step may be performed thereafter.

  The light emitting element 1 of the present invention is manufactured through the above steps.

  Such a light emitting element 1 can be used as, for example, a light source.

  Next, specific examples of the present invention will be described.

1. Production of light emitting device (Example 1)
The manufacturing method of the thin film electroluminescent element of Embodiment 1 which has a polymeric material in an organic layer is shown concretely.
[1] A commercially available transparent glass substrate with ITO having an average thickness of 0.7 mm was prepared.
[2] This substrate was washed with isopropanol and acetone, followed by UV ozone cleaning for 20 minutes.
[3] The substrate with ITO washed in [1] is placed in a solution obtained by diluting 3-aminopropyltrimethoxysilane, which is a precursor of a self-assembled monolayer, with ethanol to 1%, and ultrasonic waves are applied for 10 minutes. The film was formed while applying. Immediately after that, rinsing with ethanol was performed, and ultrasonic cleaning with ethanol was further performed for 10 minutes. After rinsing, immobilization was performed at 90 ° C. for 10 minutes using a hot plate. When the average film thickness was measured by XRR, it was 1.4 nm.
[4] A polyfluorene derivative ADS133YE manufactured by ADS was dissolved in xylene at 1%, applied onto the ITO by spin coating (1000 rpm), and then dried. The drying condition of the liquid material was room temperature in the atmosphere. This completes the organic compound layer.
[5] The production of the hole injecting metal oxide layer and the production process of the anode were carried out in a vacuum evaporator. Here, a molybdenum oxide (MoO ₃ ) layer (hole-injecting metal oxide layer) was deposited on the organic compound layer with an average thickness of 10 nm.
[6] In the continuous process of [5], gold (Au) (anode) was vapor-deposited with an average thickness of 30 nm.

(Example 2)
A device was fabricated in the same manner as in Example 1 except that 3-chloropropyltrimethoxysilane was used as the precursor of the self-assembled monolayer of Example 1. The average film thickness of the self-assembled film was 1.3 nm.

(Example 3)
A device was produced in the same manner as in Example 1 except that 3-trimethoxysilylpropyl N, N, N-trimethylammonium chloride was used as the precursor of the self-assembled monolayer of Example 1. The average film thickness of the self-assembled film was 1.5 nm.

Example 4
After fixing the self-assembled monolayer of Example 3, it was placed in hydrochloric acid at pH 2 in which phosphomolybdic acid (H ₃ PMo ₁₂ O ₄₀ ) was dissolved at 0.5 mmol / L, and ultrasonic waves were applied for 10 minutes. The chloride ions in the self-assembled monolayer were exchanged for phosphomolybdate ions. Immediately after that, rinsing was performed with pure water, and ultrasonic cleaning with pure water was further performed for 10 minutes. After rinsing, the substrate was dried by a hot plate at 90 ° C. for 10 minutes. Then, the process after [4] of Example 1 was performed. The average film thickness of the self-assembled film was 1.7 nm.

(Example 5)
A device was fabricated in the same manner as in Example 4 except that phosphotungstic acid (H ₃ PW ₁₂ O ₄₀ ) was used instead of phosphomolybdic acid in Example 4. The average film thickness of the self-assembled film was 1.7 nm.

(Example 6)
A device was fabricated in the same manner as in Example 4 except that silicotungstic acid (H ₄ SiW ₁₂ O ₄₀ ) was used instead of phosphomolybdic acid in Example 4. The average film thickness of the self-assembled film was 1.7 nm.

(Comparative Example 1)
It was produced in the same manner as in Example 1 except that ethanol in which the self-assembled monomolecular material was not dissolved was used in the step [2] in Example 1.

2. Evaluation The initial luminance was evaluated for the light emitting devices manufactured in each of the examples and comparative examples.

  The luminance measurement was performed by applying a voltage from 0 V to 6 V with a DC power source and measuring with a luminance meter.

  The results are shown in FIGS. 2 and 3, respectively.

As is apparent from FIGS. 2 and 3, it can be seen that the initial characteristics of the light-emitting elements of the respective examples have lower emission start voltages and higher luminance by several orders of magnitude than those of the light-emitting elements of the comparative examples. This is because when the self-assembled monolayer is present on the cathode, charge injection is performed well from the cathode side, so that both holes and electrons are injected well into the light emitting layer. Is formed in the light emitting layer. On the other hand, when the self-assembled monolayer does not exist, either holes or electrons are not injected into the light emitting layer, suggesting that excitons are not formed in the light emitting layer. The structure on the anode side of the device manufactured in this example is known to be a hole-driven device in which holes are injected into the light emitting layer in a larger amount than electrons, and is a self-assembled monomolecule. The film layer is thought to prevent holes from flowing out to the cathode side.
Based on the above facts, the driving mechanism of this device is that the holes injected from the anode side are self-assembled monolayer / organic by the action of the self-assembled monolayer that prevents the outflow of holes. Accumulated at the compound layer interface. It is considered that the accumulated holes bend the HOMO level of the organic compound layer to the low energy side, thereby promoting electron injection from the cathode side and emitting light. Interestingly, the self-assembled monolayer used in the organic EL device is an organic compound layer formed by accumulating holes at the interface while preventing the holes from flowing out to the cathode side. It also plays a role of injecting electrons into the light emitting layer by utilizing the change of the level of. In particular, when an amino group or an onium salt is present in the self-assembled monolayer, the HOMO level can be bent more strongly on the low energy side due to the polarity of the molecule, so that electron injection is performed more efficiently. In particular, in the case of an onium salt, electrons are injected more efficiently. This is considered that the counter anion of the onium salt moves to the anode side by applying a charge to the device, and is effective in improving the efficiency of hole injection from the anode side.
Since the present organic EL device is considered to emit light by the mechanism as described above, it is expected that the present technology can further exhibit this effect with a device having a high hole injection efficiency. In other words, the present technology is more effectively exhibited if it is a hole-driven element. Such a structure is one of the preferred forms of the present technology.

1: Organic EL element 2: Substrate 3: Cathode 4: Organic compound layer 5: Anode 6: Self-assembled monolayer 7: Hole injection layer

Claims (6)

A substrate, a cathode, a self-assembled monolayer, an organic compound layer containing a luminescent material, and an anode exist in this order, and there is no other layer between the cathode and the self-assembled monolayer. An organic thin film electroluminescent device characterized by comprising:
The self-assembled monolayer is an organic thin film electroluminescent device formed using a compound represented by the following general formula (1).
_{R n -Si-A 4-n} ··· (1)
In the above, n is a positive integer represented by 1 to 3, A is a hydroxyl group, a halogen, or an alkoxy group, and when there are a plurality thereof, they may be different from each other, and R is a carbon number having an onium base of 1 It is an organic substituent which is an atomic group of 18 or less, and when there are a plurality, they may be different from each other. 2. The organic thin film electroluminescent device according to claim 1, wherein no other layer exists between the organic compound layer containing a light emitting material closest to the cathode and the self-assembled monolayer. The organic thin film electroluminescent device according to claim 1 or 2, wherein a work function of the cathode is larger than 4.0 eV. 4. The organic thin film electroluminescent device according to claim 1, further comprising at least one metal oxide layer between the anode and the organic compound layer containing a light emitting material. The average thickness of the self-assembled monomolecular film provided in the organic thin film electroluminescent element according to any one of claims 1 to 4 is 0.1 nm or more and 3 nm or less . The organic thin film electroluminescent element in any one . Lighting device characterized in that it comprises an organic thin film electroluminescent element according to any one of claims 1 to 5.

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