JP2005011804A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element which is suitable for the use for a panel in full color or in multi-color, in which a light emitting efficiency is higher than the organic EL element using light emission from a singlet state, and in which driving stability is improved. <P>SOLUTION: This is an organic electric field light emitting element in which a positive electrode 2, an organic layer and a negative electrode 9 are laminated on a substrate 1, and at least one organic layer is an light emitting layer 5 containing a host agent and a dope agent, and as this host agent, a compound having 2 to 4 of pyrazole structures expressed by a formula 1 in one molecule is used. Here, Ar<SB>4</SB>to Ar<SB>6</SB>represents respectively an aromatic hydrocarbon cyclic group having hydrogen or a substituted group, or an aromatic heterocyclic group independently. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an organic electroluminescent element, and more particularly to a thin film type device that emits light by applying an electric field to a light emitting layer made of an organic compound.

  The development of electroluminescent devices using organic materials (hereinafter referred to as “organic EL devices”) is aimed at improving the efficiency of charge injection from the electrodes, optimizing the types of electrodes, hole transport layers composed of aromatic diamines and 8-hydroxys. With the development of a device (Appl. Phys. Lett., 51, 913, 1987) with a light-emitting layer composed of a quinoline aluminum complex as a thin film between electrodes, a conventional device using a single crystal such as anthracene Compared to the significant improvement in luminous efficiency, it has been promoted with the aim of putting it into practical use for high-performance flat panels with features such as self-emission and high-speed response.

  In order to further improve the efficiency of such an organic EL device, the structure of the above-mentioned anode / hole transport layer / light emitting layer / cathode is basically used, and a hole injection layer, an electron injection layer, and an electron transport layer are provided as appropriate. For example, anode / hole injection layer / hole transport layer / light emitting layer / cathode, anode / hole injection layer / light emitting layer / electron transport layer / cathode, anode / hole injection layer / light emitting layer / electron transport A layer / electron injection layer / cathode structure is known. This hole transport layer has a function of transmitting holes injected from the hole injection layer to the light emitting layer, and the electron transport layer has a function of transmitting electrons injected from the cathode to the light emitting layer. ing.

And by interposing this hole transport layer between the light emitting layer and the hole injection layer, many holes are injected into the light emitting layer with a lower electric field, and further electrons injected into the light emitting layer from the cathode or the electron transport layer. Is known to accumulate at the interface between the hole transport layer and the light-emitting layer and increase the light emission efficiency because the hole transport layer hardly transports electrons.
Similarly, by interposing the electron transport layer between the light emitting layer and the electron injecting layer, many electrons are injected into the light emitting layer with a lower electric field, and holes injected into the light emitting layer from the anode or the hole transport layer are Since the electron transport layer hardly transports holes, it is known that the electron transport layer is accumulated at the interface between the electron transport layer and the light emitting layer, and the light emission efficiency is increased.
Many organic materials have been developed so far in accordance with the functions of these constituent layers.

And by interposing this hole transport layer between the light emitting layer and the hole injection layer, many holes are injected into the light emitting layer with a lower electric field, and further electrons injected into the light emitting layer from the cathode or the electron transport layer. Is known to accumulate at the interface between the hole transport layer and the light-emitting layer and increase the light emission efficiency because the hole transport layer hardly transports electrons.
Similarly, by interposing the electron transport layer between the light emitting layer and the electron injecting layer, many electrons are injected into the light emitting layer with a lower electric field, and holes injected into the light emitting layer from the anode or the hole transport layer are Since the electron transport layer hardly transports holes, it is known that the electron transport layer is accumulated at the interface between the electron transport layer and the light emitting layer, and the light emission efficiency is increased.
Many organic materials have been developed so far in accordance with the functions of these constituent layers.

  On the other hand, many devices including a device provided with a hole transport layer made of aromatic diamine and a light emitting layer made of aluminum complex of 8-hydroxyquinoline used fluorescent light emission. If used, that is, if light emission from a triplet excited state is used, an efficiency improvement of about three times is expected as compared with a conventional device using fluorescence (singlet). For this purpose, it has been studied to use a coumarin derivative or a benzophenone derivative as a light emitting layer (the 51st Japan Society of Applied Physics, 28a-PB-7, 1990), but only a very low luminance is obtained. It was. Thereafter, the use of a europium complex has been studied as an attempt to utilize the triplet state, but this also did not lead to highly efficient light emission.

  Recent Non-Patent Document 1 reported that high-efficiency red light emission is possible by using a platinum complex (T-1, PtOEP). Thereafter, in Non-Patent Document 2, the efficiency is greatly improved by green light emission by doping the light emitting layer with an iridium complex (T-2, Ir (Ppy) 3). Furthermore, it has been reported that these iridium complexes show extremely high luminous efficiency even when the device structure is further simplified by optimizing the light emitting layer (Appl. Phys. Lett., 77, 904 pages). the year of 2000).

  In order to apply an organic EL element to a display element such as a flat panel display, it is necessary to improve the light emission efficiency of the element and at the same time to ensure sufficient stability during driving. However, in the high efficiency organic electroluminescence device using the phosphorescent molecule (T-2) described in Non-Patent Document 2, the driving stability is insufficient in practice (Jpn. J. Appl. Phys., 38, L1502, 1999).

  The main cause of the above drive deterioration is substrate / anode / hole transport layer / light emitting layer / hole blocking layer / electron transport layer / cathode or substrate / anode / hole transport layer / light emitting layer / electron transport layer / cathode. It is estimated that this is due to the deterioration of the thin film shape of the light emitting layer in the element structure. This deterioration in the shape of the thin film is attributed to crystallization (or aggregation) of the organic amorphous thin film due to heat generated when the element is driven, and the low heat resistance is due to the low glass transition temperature (Tg) of the material. It is thought to come from.

  In Non-Patent Document 2, a carbazole compound (H-1, CBP) or triazole compound (H-2, TAZ) is used as the light emitting layer, and a phenanthroline derivative (HB-1) is used as the hole blocking layer. Since these compounds have good symmetry and low molecular weight, they easily crystallize and aggregate to deteriorate the shape of the thin film, and Tg is difficult to observe because of its high crystallinity. Such an unstable thin film shape in the light emitting layer has an adverse effect of shortening the driving life of the device and lowering the heat resistance. For the reasons described above, organic electroluminescence devices using phosphorescence have a serious problem in driving stability of the devices.

  By the way, Patent Document 1 discloses that a compound having an oxadiazole group is used as a host agent in an organic EL device including a host agent and a phosphorescent dopant in the light emitting layer. Patent Document 2 discloses an organic EL element having a thiazole structure or a pyrazole structure in an organic layer. Patent Document 3 discloses an organic EL element having a light-emitting layer containing a phosphorescent iridium complex compound and a carbazole compound. Patent Document 4 discloses an organic EL device having a light emitting layer containing a carbazole compound (PVK), a compound having an oxadiazole group (PBD), and an iridium complex compound (Ir (ppy) 3). Patent Document 5 proposes orthometalated metals and porphyrin metal complexes as phosphorescent light-emitting compounds. However, these also have problems as described above. Patent Document 2 does not disclose an organic EL element using phosphorescence.

JP 2002-352957 A JP 2001-230079 JP 2001-313178 A JP 2003-45611 A JP 2002-158091 A Nature, 395, 151, 1998 Appl. Phys. Lett., 75, 4 pages, 1999

  Improvement of driving stability and heat resistance of organic electroluminescent devices using phosphorescence is an essential requirement in considering applications such as display devices such as flat panel displays and lighting, and the present invention is highly efficient and high. An object of the present invention is to provide an organic electroluminescent device having driving stability.

  As a result of intensive studies, the present inventors have found that the above problem can be solved by using a specific compound in the light emitting layer or the hole blocking layer, and have completed the present invention.

（式中、Ar₄〜Ar₆は各々独立に、水素又は置換基を有していてもよい芳香族炭化水素環基若しくは芳香族複素環基を示すが、少なくとも1つは水素以外の基を示す。） That is, the present invention is an organic electroluminescent device in which an anode, an organic layer and a cathode are laminated on a substrate, wherein at least one organic layer is a light emitting layer containing a host agent and a dopant, and the host agent As an organic electroluminescent element, a compound having 2 to 4 pyrazole structures represented by the following formula I in the same molecule is used.

(In the formula, Ar _{4 to} Ar ₆ each independently represent hydrogen or an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, but at least one represents a group other than hydrogen. Show.)

（式中、Ar₄〜Ar₆は各々独立に、水素又は置換基を有していてもよい芳香族炭化水素環基若しくは芳香族複素環基を示すが、少なくとも1つは水素以外の基を示し、X₂は直接結合、−O−、−S−、＞CO、＞SO₂、＞NAr₇、＞SiAr₈Ar₉又は芳香族炭化水素環基を示す。また、Ar₇〜Ar₉は置換基を有していてもよい芳香族炭化水素環基を示す。） Here, as a compound having 2 to 4 pyrazole structures in the same molecule, a compound represented by the following general formula II is preferable.

(In the formula, Ar _{4 to} Ar ₆ each independently represent hydrogen or an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, but at least one represents a group other than hydrogen. X ₂ represents a direct bond, —O—, —S—,>CO,> SO ₂ ,> NAr ₇ ,> SiAr ₈ Ar ₉ or an aromatic hydrocarbon ring group, and Ar _{7 to} Ar ₉ are An aromatic hydrocarbon ring group which may have a substituent is shown.)

  Preferred examples of the dopant include those containing at least one selected from phosphorescent orthometalated metal complexes and porphyrin metal complexes. Moreover, what contains the organometallic complex containing at least 1 metal chosen from the periodic table 7 thru | or 11 groups as a central metal of a metal complex is mentioned preferably. And as a metal of periodic table 7 thru | or 11 group, the metal chosen from ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum, and gold is mentioned preferably.

  In addition, the present invention is the above-described organic electroluminescent element characterized by having a hole blocking layer, an electron transporting layer or both between the light emitting layer and the cathode.

Hereinafter, the organic electroluminescence device (organic EL device) of the present invention will be further described.
The organic EL device of the present invention has at least one organic layer between an anode and a cathode provided on a substrate, and at least one of the organic layers is a light emitting layer. Includes a host agent and a phosphorescent dopant. And it usually contains a host agent as a main component and a dopant as a subcomponent.

  Here, the main component means a material that occupies 50% by weight or more of the material forming the layer, and the subcomponent means other components. The compound serving as the host agent has an excited triplet level in an energy state higher than the excited triplet level of the phosphorescent dopant.

  The host agent contained in the light emitting layer of the present invention must be a compound that gives a stable thin film shape, has a high glass transition temperature (Tg), and can efficiently transport holes and / or electrons. It is. Furthermore, it is required to be a compound that is electrochemically and chemically stable and does not easily generate impurities at the time of manufacture or use that can trap or emit light. As a compound satisfying such a requirement, one or more of compounds having 2 to 4 pyrazole structures in the same molecule represented by the general formula I (hereinafter referred to as pyrazole compounds) are used.

The pyrazole compound used as a host agent has 2 to 4, preferably 2 to 3 pyrazole structures represented by the above general formula I. In General Formula I, Ar _{4 to} Ar ₆ each independently represents an aromatic hydrocarbon ring group or an aromatic heterocyclic group which may have a substituent. Preferred examples of the aromatic hydrocarbon ring group include aryl groups such as a phenyl group and a naphthyl group, and preferred examples of the aromatic heterocyclic group include heteroaryl groups such as a pyridyl group and a quinolyl group. These groups can have a substituent. Examples of the substituent include a lower alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group, and an aryl group having 6 to 12 carbon atoms such as a phenyl group and a methylphenyl group. Is preferred.

As described above, one of the requirements for providing a stable thin film shape as a host material is an appropriate molecular weight. For this purpose, it is desirable to have two or more pyrazole structures. In addition, organic EL devices using this material are generally formed by vacuum deposition. In this case, the organic compound having a molecular weight larger than necessary requires excessive energy, and decomposition takes precedence over vaporization. . For this reason, about four pyrazole structures are preferable.
On the other hand, it is also important to suppress crystallinity as a requirement to provide a stable thin film shape. In organic compounds, crystallinity is governed by the symmetry of the molecular structure (planarity) and the intermolecular interaction of polar groups. It is thought that it is done. In the pyrazole-based compound used in the present invention, having an aromatic group at any of the 3, 4 and 5 positions of the pyrazole ring inhibits the molecular structure from being flat and suppresses crystallinity. In addition, by arranging a bulky aromatic group around a highly polar nitrogen atom, an effect of suppressing intramolecular interaction is derived.

Ar _{4 to} Ar ₆ are preferably hydrogen or 1 to 3 aromatic hydrocarbon ring groups, and may have a substituent. Preferred examples of the substituent include a lower alkyl group having 1 to 5 carbon atoms. The number of substituents is preferably in the range of 0-3. Specifically, the following aromatic hydrocarbon ring groups are preferred. Phenyl group, 2-methylphenyl group, 3-methylphenyl group, 4-methylphenyl group, 2,4-dimethylphenyl group, 3,4-dimethylphenyl group, 2,4,5-trimethylphenyl group, 4-ethyl Phenyl group, 4-tert-butylphenyl group, 1-naphthyl group, 2-naphthyl group, 1-anthracenyl group, 2-anthracenyl group, 9-anthracenyl group, 9-fencerenyl group and the like. Ar _{4 to} Ar ₆ may be the same as or different from each other. Further, at least two of Ar _{4 to} Ar ₆ are preferably groups other than hydrogen, and particularly groups other than Ar ₅ are preferably groups other than hydrogen.

Preferred examples of the pyrazole compound include compounds represented by the above general formula II. In the general formula II, Ar _{4 to} Ar ₆ are the same as described above, but may be changed independently of each other.

In the general formula II, X ₂ is a divalent linking group, and is a direct bond, —O—, —S—,>CO,> SO ₂ ,> NAr ₇ ,> SiAr ₈ Ar ₉ or a divalent fragrance. It consists of a group hydrocarbon ring group. Here, Ar _{7 to} Ar ₉ are aromatic hydrocarbon ring groups which may have a substituent, preferably 1 to 3 aromatic hydrocarbon ring groups, and may have a substituent. it can. Preferred examples of the substituent include a lower alkyl group having 1 to 5 carbon atoms, and it may be a substituent having 1 to 2 pyrazole structures. The number of substituents is preferably in the range of 0-3. Ar _{7 to} Ar ₉ are preferably aryl groups such as a phenyl group, a naphthyl group, a methylphenyl group, and a methylnaphthyl group, and specific examples thereof include the following aromatic hydrocarbon ring groups. Phenyl group, 2-methylphenyl group, 3-methylphenyl group, 4-methylphenyl group, 2-naphthyl group, 1-anthracenyl group, 2-anthracenyl group, 9-anthracenyl group, 9-fencerenyl group and the like.

Preferred divalent linking groups X ₂ include direct bonds,> NAr ₇ , 1,4-phenylene group, 1,4-naphthylene group, 9,10-anthracenylene group, 4,4′-biphenylene group, etc. A divalent aromatic hydrocarbon ring group may be mentioned.

  Although the preferable specific example of a compound represented by Formula II is shown to Tables 1-4, it is not limited to these. In the table, X2, Ar4, Ar5 and Ar6 correspond to the symbols of formula II. Moreover, when X2 is-, it means a direct bond (single bond).

The organic EL device of the present invention contains a subcomponent, that is, a phosphorescent dopant in the light emitting layer. As this dopant, known phosphorescent metal complex compounds described in the above-mentioned patent documents and non-patent documents can be used, and the central metal of these metal complexes is preferably a metal selected from groups 7 to 11 of the periodic table Is a phosphorescent organometallic complex. This metal is preferably a metal selected from ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum and gold. The dopant and the metal may be one type or two or more types.
The phosphorescent dopant is known as described in Patent Document 1 and the like. The phosphorescent dopant is also preferably a phosphorescent orthometalated metal complex or a porphyrin metal complex, and such orthometalated metal complex or polyphyrin metal complex is described in Patent Document 5 and the like. It is well known. Therefore, these known phosphorescent dopants can be widely used.

  Preferred organometallic complexes include Ir (Ppy) 3 complexes (formula A), Ir (bt) 2 · acac3 complexes (formula B), PtOEt3, etc. having a noble metal element such as Ir as a central metal. Complexes (formula C) are mentioned. Specific examples of these complexes are shown below, but are not limited to the following compounds.

  The present invention can be applied to any of an organic electroluminescent element having a single element, an element having a structure arranged in an array, and a structure having an anode and a cathode arranged in an XY matrix. According to the organic electroluminescence device of the present invention, the light emitting layer contains a compound having a specific skeleton and a phosphorescent metal complex, so that the luminous efficiency is higher than that of the conventional device using light emission from a singlet state. A device that is high and greatly improved in driving stability can be obtained, and can exhibit excellent performance in application to full-color or multi-color panels.

  Hereinafter, an example of the organic EL device of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a structural example of a general organic EL device used in the present invention. 1 is a substrate, 2 is an anode, 3 is a hole injection layer, 4 is a hole transport layer, Represents a light emitting layer, 6 represents a hole blocking layer, 7 represents an electron transport layer, and 8 represents a cathode. Usually, the hole injection layer 3 to the electron transport layer 7 are organic layers, and the organic EL device of the present invention has one or more organic layers including the light emitting layer 5. It is advantageous to have three or more organic layers including the light emitting layer 5, preferably five or more organic layers. In addition, the layer structure of FIG. 1 is an example, and in addition to this, one or more other layers may be provided, or one or more layers may be omitted from this.

  The substrate 1 serves as a support for the organic electroluminescent element, and a quartz or glass plate, a metal plate or a metal foil, a plastic film, a sheet, or the like is used. In particular, a glass plate or a transparent synthetic resin plate such as polyester, polymethacrylate, polycarbonate, or polysulfone is preferable. When using a synthetic resin substrate, it is necessary to pay attention to gas barrier properties. If the gas barrier property of the substrate is too small, the organic electroluminescent element may be deteriorated by the outside air that has passed through the substrate, which is not preferable. For this reason, a method of providing a gas barrier property by providing a dense silicon oxide film or the like on at least one surface of the synthetic resin substrate is also a preferable method.

  An anode 2 is provided on the substrate 1, and the anode 2 plays a role of hole injection into the hole transport layer. This anode is usually made of metal such as aluminum, gold, silver, nickel, palladium, platinum, metal oxide such as oxide of indium and / or tin, metal halide such as copper iodide, carbon black, or poly It is composed of conductive polymers such as (3-methylthiophene), polypyrrole and polyaniline. In general, the anode is often formed by a sputtering method, a vacuum deposition method, or the like. Further, in the case of metal fine particles such as silver, fine particles such as copper iodide, carbon black, conductive metal oxide fine particles, and conductive polymer fine powders, they are dispersed in an appropriate binder resin solution and placed on the substrate 1. It is also possible to form the anode 2 by applying to. Further, in the case of a conductive polymer, a thin film can be directly formed on the substrate 1 by electrolytic polymerization, or the anode 2 can be formed by applying a conductive polymer on the substrate 1 (Appl. Phys. Lett. 60, 2711, 1992). The anode can be formed by stacking different materials. The thickness of the anode 2 varies depending on the required transparency. When transparency is required, the visible light transmittance is usually 60% or more, preferably 80% or more. In this case, the thickness is usually 5 to 1000 nm, preferably 10 to It is about 500 nm. If it can be opaque, the anode 2 may be the same as the substrate 1. Furthermore, it is also possible to laminate different conductive materials on the anode 2 described above.

For the purpose of improving the efficiency of hole injection and improving the adhesion of the entire organic layer to the anode, the hole injection layer 3 is also inserted between the hole transport layer 4 and the anode 2. ing. By inserting the hole injection layer 3, the driving voltage of the initial element is lowered, and at the same time, an increase in voltage when the element is continuously driven with a constant current is suppressed.
Conditions required for the material used for the hole injection layer include that the contact with the anode is good and a uniform thin film can be formed, which is thermally stable, that is, the melting point and the glass transition temperature are high, and the melting point is 300 ° C. or higher. The glass transition temperature is required to be 100 ° C. or higher. Furthermore, the ionization potential is low, hole injection from the anode is easy, and the hole mobility is high.

  For this purpose, phthalocyanine compounds such as copper phthalocyanine (JP-A 63-295695), polyaniline (Appl. Phys. Lett., 64, 1245, 1994), polythiophene (Optical Materials, 9, 125, 1998) and other organic compounds, sputtered carbon films (Synth. Met., 91, 73, 1997), metals such as vanadium oxide, ruthenium oxide, molybdenum oxide Oxides (J. Phys. D, 29, 2750, 1996) have been reported. In the case of the anode buffer layer, a thin film can be formed in the same manner as the hole transport layer, but in the case of an inorganic material, a sputtering method, an electron beam evaporation method, or a plasma CVD method is further used. The film thickness of the hole injection layer 3 formed as described above is usually 3 to 100 nm, preferably 5 to 50 nm.

  A hole transport layer 4 is provided on the hole injection layer 3. The conditions required for the material used in the hole transport layer are materials that have high hole injection efficiency from the hole injection layer 3 and can efficiently transport the injected holes. is required. For this purpose, it is required that the ionization potential is low, the transparency to visible light is high, the hole mobility is high, the stability is high, and trapping impurities are not easily generated during production or use. The Further, in order to contact the light emitting layer 5, it is required not to quench the light emitted from the light emitting layer or to form an exciplex with the light emitting layer to reduce the efficiency. In addition to the above general requirements, when the application for in-vehicle display is considered, the element is further required to have heat resistance. Therefore, a material having a Tg of 90 ° C. or higher is desirable.

  Examples of such a hole transporting material include two or more tertiary amines represented by 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl, and two or more Aromatics having a starburst structure, such as aromatic diamines in which condensed aromatic rings are substituted with nitrogen atoms (Japanese Patent Laid-Open No. 5-234681), 4,4 ', 4 "-tris (1-naphthylphenylamino) triphenylamine Group amine compounds (J. Lumin., 72-74, 985, 1997), aromatic amine compounds consisting of tetramers of triphenylamine (Chem. Commun., 2175, 1996), 2,2 Spiro compounds such as', 7,7'-tetrakis- (diphenylamino) -9,9'-spirobifluorene (Synth. Metals, 91, 209, 1997) and the like. They may be used alone or in combination as necessary.

  In addition to the above-mentioned compounds, polyarylene ether sulfone (Polym. Adv. Tech.) Containing polyvinylcarbazole, polyvinyltriphenylamine (Japanese Patent Laid-Open No. 7-53953), and tetraphenylbenzidine as materials for the hole transport layer 4. , Vol. 7, p. 33, 1996). In the case of the coating method, one or more hole transport materials and, if necessary, additives such as a binder resin and a coating property improving agent that do not trap holes are added and dissolved to prepare a coating solution. Then, it is applied on the anode 2 or the hole injection layer 3 by a method such as spin coating, and dried to form the hole transport layer 4. Examples of the binder resin include polycarbonate, polyarylate, and polyester. If the binder resin is added in a large amount, the hole mobility is lowered.

In the case of the vacuum deposition method, the hole transport material is put in a crucible installed in a vacuum vessel, and after the inside of the vacuum vessel is evacuated to about 10 ⁻⁴ Pa with a suitable vacuum pump, the crucible is heated, The hole transport material is evaporated and the hole transport layer 4 is formed on the substrate 1 on which the anode is formed, which is placed facing the crucible. The film thickness of the hole transport layer 4 is usually 5 to 300 nm, preferably 10 to 100 nm. In order to uniformly form such a thin film, a vacuum deposition method is generally used.

  A light emitting layer 5 is provided on the hole transport layer 4. The light emitting layer 5 contains the host agent and a phosphorescent dopant, and between the electrodes to which an electric field is applied, holes that are injected from the anode and move through the hole transport layer, and electrons that are injected from the cathode and transported by electrons. Excited by recombination with electrons moving through the layer 7 (or the hole blocking layer 6), emits strong light. The light emitting layer 5 may contain other components such as a host material other than the host material used as an essential component in the present invention and a fluorescent dye as long as the performance of the present invention is not impaired.

  Conditions required for the material used for the light emitting layer host agent include high hole injection efficiency from the hole transport layer 4 and electron injection efficiency from the electron transport layer 7 (or hole blocking layer 6). Must be high. For this purpose, it is required that the ionization potential shows an appropriate value, the mobility of holes and electrons is large, the electrical stability is excellent, and impurities that become traps are hardly generated at the time of manufacture or use. . In addition, it is required that an exciplex be formed between the adjacent hole transport layer 4 and electron transport layer 7 (or hole blocking layer 6) and efficiency not be lowered. In addition to the above general requirements, when the application for in-vehicle display is considered, the element is further required to have heat resistance. Therefore, a material having a Tg value of 90 ° C. or higher is desirable.

  When the organometallic complex represented by the formulas A to C is used as a dopant, the amount of the organometallic complex contained in the light emitting layer is preferably in the range of 0.1 to 30% by weight. If it is 0.1% by weight or less, it cannot contribute to the improvement of the light emission efficiency of the device, and if it exceeds 30% by weight, concentration quenching such as formation of a dimer between organometallic complexes occurs, leading to a decrease in light emission efficiency. In an element using conventional fluorescence (singlet), there is a tendency that a slightly larger amount than the amount of the fluorescent dye (dopant) contained in the light emitting layer is preferable. The organometallic complex may be partially included in the light emitting layer or may be non-uniformly distributed. The film thickness of the light emitting layer 5 is usually 10 to 200 nm, preferably 20 to 100 nm.

The light emitting layer 5 is preferably formed by vacuum deposition. Both the host agent and the dope agent are put in a crucible installed in a vacuum vessel, the inside of the vacuum vessel is evacuated to about 10 ^-4 Pa with an appropriate vacuum pump, and then the crucible is heated to host, dope agent Both are co-evaporated and formed on the hole transport layer 4. At this time, the content of the dopant in the host agent is controlled while monitoring the deposition rate separately for the host agent and the dopant.

  The hole blocking layer 6 is laminated on the light emitting layer 5 so as to be in contact with the interface on the cathode side of the light emitting layer 5, but blocks holes moving from the hole transport layer from reaching the cathode. It is formed from a compound that can efficiently transport the role and electrons injected from the cathode in the direction of the light emitting layer. The physical properties required for the material constituting the hole blocking layer are required to have high electron mobility and low hole mobility. The hole blocking layer 6 has a function of confining holes and electrons in the light emitting layer and improving luminous efficiency.

  The electron transport layer 7 is formed of a compound that can efficiently transport electrons injected from the cathode between the electrodes to which an electric field is applied in the direction of the hole blocking layer 6. The electron transporting compound used for the electron transporting layer 7 is a compound that has high electron injection efficiency from the cathode 8 and that can efficiently transport injected electrons with high electron mobility. is necessary.

Materials satisfying such conditions include metal complexes such as aluminum complexes of 8-hydroxyquinoline (Japanese Patent Laid-Open No. 59-194393), metal complexes of 10-hydroxybenzo [h] quinoline, oxadiazole derivatives, Styryl biphenyl derivative, silole derivative, 3- or 5-hydroxyflavone metal complex, benzoxazole metal complex, benzothiazole metal complex, trisbenzimidazolylbenzene (US Pat. No. 5,645,948), quinoxaline compound (JP-A-6-207169) Phenanthroline derivatives (JP-A-5-331459), 2-t-butyl-9,10-N, N'-dicyanoanthraquinonediimine, n-type hydrogenated amorphous silicon carbide, n-type zinc sulfide, n-type Examples include zinc selenide. The film thickness of the electron transport layer 6 is usually 5 to 200 nm, preferably 10 to 100 nm.
The electron transport layer 7 is formed by laminating on the hole blocking layer 6 by a coating method or a vacuum deposition method in the same manner as the hole transport layer 4. Usually, a vacuum deposition method is used.

The cathode 8 serves to inject electrons into the light emitting layer 5. The material used for the cathode 8 can be the material used for the anode 2, but a metal having a low work function is preferable for efficient electron injection, such as tin, magnesium, indium, calcium, A suitable metal such as aluminum or silver or an alloy thereof is used. Specific examples include low work function alloy electrodes such as magnesium-silver alloy, magnesium-indium alloy, and aluminum-lithium alloy. It is also an effective method for improving the efficiency of the device for inserting the LiF at the interface of the cathode and the electron transport layer, MgF _2, Li ₂ O, etc. ultrathin insulating film (0.1~5nm) (Appl. Phys Lett., 70, 152, 1997, JP 10-74586, IEEE Trans. ELectron. Devices, 44, 1245, 1997). The film thickness of the cathode 8 is usually the same as that of the anode 2. For the purpose of protecting the cathode made of a low work function metal, further laminating a metal layer having a high work function and stable to the atmosphere on the cathode increases the stability of the device. For this purpose, metals such as aluminum, silver, copper, nickel, chromium, gold, platinum are used.

  1, for example, a cathode 8, a hole blocking layer 6, a light emitting layer 5, a hole transport layer 4, and an anode 2 on the substrate 1, or substrate 1 / cathode 8 / electron transport layer. 7 / hole blocking layer 6 / light emitting layer 5 / hole transporting layer 4 / hole injecting layer 3 / anode 2 can be laminated in this order, at least one of which is highly transparent as described above. It is also possible to provide the organic electroluminescent element of the present invention between the substrates.

Synthesis example 1
A 2000 ml four-necked flask was charged with 13.0 g (0.23 mol) of potassium hydroxide and 1004.5 g of ethanol. After stirring at room temperature and dissolving potassium hydroxide, 25.8 g (0.12 mol) of chalcone and 26.4 g (0.24 mol) of phenylhydrazine were added at room temperature. After the addition, heating and stirring were continued for 3 hours under reflux. After completion of the reaction, the reaction mixture was cooled to room temperature and the solid content was collected by filtration. The obtained crystals were washed with hexane and dried under reduced pressure to obtain 27.8 g of 1,3,5-triphenylpyrazoline white powder.
Next, 156.0 g of acetonitrile was charged into a 500 ml four-necked flask. Thereafter, 60.0 g (0.181 mol) of antimony pentachloride was added dropwise over 20 minutes so as not to generate intense heat. After dropping, the mixture was allowed to cool to room temperature, and a slurry solution of 25.0 g (0.084 mol) of 1,3,5-triphenylpyrazoline obtained above and 130.2 g of acetonitrile was added. After dropping, stirring was continued for 30 minutes at room temperature. After completion of the reaction, the solid content was collected by filtration. After washing with acetonitrile, it was dried under reduced pressure to obtain 40.6 g of a dark green powder. 35.0 g of this dark green powder and 681.3 g (8.18 mol) of pyridine were charged into a 500 ml four-necked flask and stirred at room temperature for 1 hour. After completion of the reaction, the solid content was collected by filtration. The obtained crystals were recrystallized from methylene chloride and benzene to obtain 4.2 g of white purified crystals of 4,4-bis (3,5-diphenyl-1-pyrazole) diphenyl (hereinafter referred to as BPP). The purity was 100% (HPLC area ratio), the mass analysis value was 590, and the melting point was 285.4 ° C.

The reaction formula of Synthesis Example 1 is shown below.

The results of IR analysis of BPP are shown below.
IR (KBr) 3454, 3046, 1608, 1551, 1503, 1461, 1434, 1413, 1398, 1365, 1182, 1083, 1026, 1008, 972, 957, 915, 855, 828, 762, 693, 603, 546 501

Synthesis example 2
A 500 ml four-necked flask was charged with 21.9 g (0.55 mol) of sodium hydroxide, 100.1 g of methanol, and 195.8 g of ion-exchanged water. After stirring at room temperature and dissolving sodium hydroxide, 73.8 g (0.43 mol) of 1-acetonaphthone was added. Thereafter, the mixture was cooled with ice water, and 48.8 g (0.46 mol) of benzaldehyde was added. After the addition, heating and stirring were continued for 3 hours under reflux. After completion of the reaction, the reaction solution was cooled to room temperature, and the reaction solution was transferred to a separatory funnel to separate the organic layer. The solvent was distilled off under reduced pressure from the obtained organic layer to obtain 106.9 g of a yellow solution of 1-naphthalen-1-yl-3-phenyl-propenone.
Next, using the 1-naphthalen-1-yl-3-phenyl-propenone obtained above as a starting material, the same reaction procedure as in Synthesis Example 1 was performed, and 4,4-bis (3- (1- (1- Naphthyl) -5-phenyl-1-pyrazole) diphenyl (hereinafter referred to as α-BNP) was synthesized. The purity of α-BNP was 99.65% (HPLC area ratio), mass analysis value was 690, and melting point was 263.5 ° C.

The reaction formula of Synthesis Example 2 is shown below.

The IR analysis results of α-BNP are shown below.
IR (KBr) 3448, 3044, 1606, 1546, 1500, 1470, 1452, 1414, 1380, 1360, 1324, 1006, 972, 936, 844, 828, 800, 774, 762, 694, 602, 428

Synthesis example 3
30.0 g (0.75 mol) of sodium hydroxide, 104.7 g of methanol, 279.0 g of ion-exchanged water, 85.1 g (0.50 mol) of 2-acetonaphthone and 53.1 g (0.50 mol) of benzaldehyde Except for the above, the same reaction operation as in Synthesis Example 2 was performed to synthesize 4,4-bis (3- (2-naphthyl) -5-phenyl-1-pyrazole) diphenyl (hereinafter referred to as β-BNP). The purity of β-BNP was 99.52% (HPLC area ratio), mass analysis value was 690, and melting point was 287.1 ° C.

The reaction formula of Synthesis Example 3 is shown below.

Results of IR analysis of β-BNP are shown below.
IR (KBr) 3448, 3052, 1630, 1608, 1504, 1476, 1452, 1412, 1374, 1326, 970, 860, 826, 802, 762, 696, 404, 474

Synthesis example 4
A 500 ml four-necked flask was charged with 25.2 g (0.11 mol) of 1,3-diphenylpropanedione, 25.3 g (0.11 mol) of p-bromophenylhydrazine hydrochloride and 234.7 g of toluene. The mixture was stirred at room temperature, and 6.0 g (0.11 mol) of sodium methoxide was added dropwise at room temperature. After the addition, heating and stirring were continued for 3 hours under reflux. After completion of the reaction, the reaction mixture was cooled to room temperature and the solid content was collected by filtration. The obtained filtrate was concentrated to dryness under reduced pressure. To this residue, 350 ml of methanol was added and stirred with heating for 1 hour. Then, it cooled to room temperature and collect | recovered solid content by filtration. The obtained solid content was washed with methanol and then dried under reduced pressure to obtain 28.4 g of 1- (p-bromophenyl) -3,5-diphenylpyrazole.
Next, 1.87 g (0.005 mol) of 1- (p-bromophenyl) -3,5-diphenylpyrazole obtained above and 10.0 ml of THF were charged into a 200 ml four-necked flask under a nitrogen atmosphere. The mixture was stirred at room temperature, and 6.0 ml (0.010 mol) of a 1.7 M tertiary butyl lithium hexane solution was added dropwise at room temperature. After dropping, stirring was continued for 1 hour at room temperature. Further, a solution prepared by dissolving 0.70 g (0.003 mol) of diphenyldichlorosilane in 10.0 ml of THF was added dropwise at room temperature using a dropping funnel. After the dropwise addition, heating and stirring were continued for 8 hours under reflux. After completion of the reaction, the reaction mixture was cooled to room temperature, and water and toluene were added. The reaction solution was transferred to a separatory funnel and the organic layer was separated. After the solvent was distilled off from the organic layer under reduced pressure, column purification was performed to obtain a pale yellow powder of bis [4- (3,5-diphenyl-1H-pyrazole) phenyl] diphenylsilane (hereinafter referred to as BPPS). 40 g was obtained. The purity was 100% (HPLC area ratio), the mass analysis value was 773, and the melting point was 235.7 ° C.

The reaction formula of Synthesis Example 4 is shown below.

The results of IR analysis of BPPS are shown below.
IR (KBr) 3448, 3052, 1588, 1480, 1460, 1438, 1428, 1408, 1358, 1122, 1104, 1074, 970, 956, 760, 742, 694, 656, 602, 540, 532, 510

Synthesis example 5
In a 50 ml four-necked flask, under a nitrogen atmosphere, 5.00 g (0.013 mol) of 1- (p-bromophenyl) -3,5-diphenylpyrazole, which is a reaction intermediate of Synthesis Example 4, and sodium tertiary butoxide 1. 77 g (0.018 mol), 0.60 g (0.006 mol) of aniline and 25.0 ml of xylene were charged. The mixture was stirred at room temperature, and 4.2 mg (0.019 mmol) of palladium acetate and 0.08 ml of tritertiary butylphosphine were added dropwise at room temperature. After dropping, stirring was continued for 45 hours on an oil bath at 180 ° C. After the reaction, the mixture was cooled to room temperature, and xylene and water were added dropwise. The reaction solution was transferred to a separatory funnel and the organic layer was separated. After distilling off the solvent from the organic layer under reduced pressure, column purification was performed, and light brown of bis [4- (3,5-diphenyl-pyrazol-1-yl) -phenyl] -phenylamine (hereinafter referred to as BDPPA). 3.80 g of powder was obtained. The purity was 99.79% (HPLC area ratio), mass analysis value 681, melting point was 119.1 ° C.

The reaction formula of Synthesis Example 5 is shown below.

The results of IR analysis of BDPPA are shown below.
IR (KBr) 3432, 3052, 1604, 1510, 1488, 1460, 1332, 1274, 972, 838, 824, 758, 694, 596, 548, 520

Reference example 1
The glass transition temperature (Tg) was measured by DSC measurement for the heat resistance characteristics of the compound as a light emitting layer main component (host material) candidate. TAZ is 3-phenyl-4- (1'-naphthyl) -5-phenyl-1,2,4-triazole, CBP is 4,4'-N, N'-dicarbazolediphenyl, BCP is 2,9 -Dimethyl-4,7-diphenyl-1,10-phenanthroline, OXD-7 is an abbreviation for 1,3-bis [(4-t-butylphenyl) -1,3,4-oxadiazolyl] phenylene The host material. The results are shown in Table 5.

Reference example 2
The following evaluation was performed about the thin film stability of the host material. Only the host material was deposited on a glass substrate with a thickness of 100 nm. Thereafter, the deposited film was stored in an atmosphere at a temperature of 20 ° C. and a humidity of 30%, and the number of days that the thin film crystallized was visually observed. The results are shown in Table 6.

Example 1
In FIG. 1, an organic EL device having a layer structure in which the hole injection layer 3 and the hole blocking layer 6 are omitted was produced as follows.
On the glass substrate 1, an indium tin oxide (ITO) transparent conductive film (manufactured by San-on Vacuum) is patterned into a 2 mm wide stripe to form an anode. After ultrasonic cleaning in the order of neutral detergent, ultrapure water, acetone, and isopropyl alcohol, they were dried with nitrogen blow, finally subjected to ultraviolet ozone cleaning, and placed in a vacuum deposition apparatus.

After roughly exhausting the apparatus with an oil rotary pump, the apparatus was exhausted using an oil diffusion pump equipped with a liquid nitrogen trap until the degree of vacuum in the apparatus reached 7-9 × 10 ⁻⁴ Pa. 4,4'-bis [N, N '-(3-tolyl) amino] -3,3'-dimethylbiphenyl (hereinafter referred to as HMTPD) placed in a molybdenum boat placed in the above apparatus was heated and evaporated. The hole transport layer 4 was formed with a film thickness of 60 nm. On top of that, a 25 nm film was formed by using BPP as the main component of the light-emitting layer and tris (2-phenylpyridine) iridium complex (Ir (ppy) ₃ ) as the phosphorescent organometallic complex from two different vapor deposition sources. The light emitting layer 5 was formed with a thickness. At this time, the concentration of Ir (ppy) ₃ was 7 wt%. Further, as the electron transport layer 7, tris (8-hydroxyquinoline) aluminum (hereinafter referred to as Alq ₃ ) was formed with a film thickness of 50 nm.

  Here, the element is once taken out from the apparatus into the atmosphere, and a 2 mm wide stripe shadow mask as a mask to be worn on the cathode is brought into close contact with the ITO stripe of the anode 2 to form another vacuum apparatus. Installed inside. Evacuation was performed in the same manner as the organic layer, and lithium fluoride (LiF) was deposited on the electron transport layer 7 as an electron injection layer at 0.5 nm and aluminum as a cathode 8 at 170 nm.

When an external power source was connected to the obtained organic electroluminescence device and a DC voltage was applied, it was confirmed that these organic electroluminescence devices had the light emission characteristics as shown in Table 7. The maximum wavelength of the device emission spectrum was 512 nm, and it was confirmed that light emission from Ir (ppy) ₃ was obtained.

Comparative Example 1
An organic electroluminescent element was produced in the same manner as in Example 1 except that TAZ was used as the main component of the light emitting layer. Table 7 shows the element characteristics.

Examples 2-5
An organic electroluminescent element was produced in the same manner as in Example 1 except that α-BNP, β-BNP, BDPPA or BPPS was used as the main component of the light emitting layer. When an external power source was connected to the obtained organic electroluminescence device and a DC voltage was applied, the following maximum wavelength of the device emission spectrum was observed, and it was confirmed that light emission from Ir (ppy) ₃ was obtained. It was done.
α-BNP: Maximum wavelength 525nm
β-BNP: Maximum wavelength 520nm
BDPPA: Maximum wavelength 515nm
BPPS: Maximum wavelength 514nm

Schematic diagram showing the layer structure of organic EL elements

Explanation of symbols

1: Substrate 2: Anode 3: Hole injection layer 4: Hole transport layer 5: Light emitting layer 6: Hole blocking layer 7: Electron transport layer 8: Cathode

Claims (6)

An organic electroluminescent device in which an anode, an organic layer and a cathode are laminated on a substrate, wherein at least one organic layer is a light emitting layer containing a host agent and a dopant, A compound having 2 to 4 pyrazole structures represented by the following formula I is used:

(In the formula, Ar _{4 to} Ar ₆ each independently represent hydrogen or an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, but at least one represents a group other than hydrogen. Show.) The organic electroluminescence device according to claim 1, wherein the compound having 2 to 4 pyrazole structures in the same molecule is a compound represented by the following general formula II.

(In the formula, Ar _{4 to} Ar ₆ each independently represents hydrogen or an aromatic hydrocarbon ring group or aromatic heterocyclic group which may have a substituent, but at least one is other than hydrogen. X ₂ represents a direct bond, —O—, —S—,>CO,> SO ₂ ,> NAr ₇ ,> SiAr ₈ Ar ₉ or an aromatic hydrocarbon ring group, and Ar ₇ to Ar ₉ represents an aromatic hydrocarbon ring group which may have a substituent.   The organic electroluminescent element according to claim 1 or 2, wherein the dopant contains at least one selected from a phosphorescent orthometalated metal complex and a porphyrin metal complex. The organic electroluminescent element according to claim 3, wherein the central metal of the metal complex is at least one metal selected from ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum and gold. The organic electroluminescent element according to claim 1, further comprising a hole blocking layer between the light emitting layer and the cathode. The organic electroluminescent element according to claim 1, further comprising an electron transport layer between the light emitting layer and the cathode.

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