JP4743186B2 - Organic electroluminescence element and display device - Google Patents

Description

  The present invention relates to an organic electroluminescence (hereinafter also abbreviated as organic EL) element and a display device. More specifically, the present invention relates to an organic electroluminescence element having excellent emission luminance and a display device having the organic electroluminescence element of the present invention.

  As a light-emitting electronic display device, there is an electroluminescence display (ELD). As a component of ELD, an inorganic electroluminescent element and an organic electroluminescent element are mentioned. Inorganic electroluminescent elements have been used as planar light sources, but an alternating high voltage is required to drive the light emitting elements. An organic electroluminescence element has a structure in which a light emitting layer containing a compound that emits light is sandwiched between a cathode and an anode, and injects electrons and holes into the light emitting layer to recombine excitons. It is an element that emits light by utilizing light emission (fluorescence / phosphorescence) generated when this exciton is deactivated, and can emit light at a voltage of several volts to several tens of volts. Therefore, it has a wide viewing angle, high visibility, and since it is a thin-film type complete solid-state device, it is attracting attention from the viewpoints of space saving and portability.

  However, for organic EL elements for practical use in the future, development of organic EL elements that emit light efficiently and with high luminance with lower power consumption is desired.

  Various organic EL elements have been reported so far. For example, Appl. Phys. Lett. , Vol. 51, 913 or a combination of a hole injection layer described in JP-A-59-194393 and an organic light-emitting layer, a hole injection layer described in JP-A-63-295695, an electron injection transport layer, , Jpn. Journal of Applied Physics, vol. 127, no. 2 A combination of the hole transfer layer, the light emitting layer, and the electron transfer layer described on pages 269 to 271 is disclosed. However, a device with higher luminance is demanded, and further improvement in energy conversion efficiency and light emission quantum efficiency is expected. In addition, a problem that the light emission life is short has been pointed out.

  The cause of this deterioration in luminance over time has not been fully elucidated, but the electroluminescent device that emits light decomposes the organic compound itself that constitutes the thin film by the light emitted by itself and the heat generated at that time. Factors derived from organic compounds, which are organic EL element materials, such as crystallization of organic compounds, have also been pointed out.

  Moreover, at present, electron transport materials have little knowledge, and in combination with the use of antibonding orbitals, no useful high-performance electron transport materials that can withstand practical use have been found. For example, the research group at Kyushu University includes 2- (4-biphenyl) -5- (4-t-butylphenyl) -1,3,4-oxadizole (t-BuPBD), which is an oxadiazole derivative, 1,3-bis (4-t-butylphenyl-1,3,4-oxadizodyl) biphenylene (OXD-1), 1,3-bis (4) which are oxadiazole dimer derivatives with improved thin film stability -T-butylphenyl-1,3,4-oxadizolyl) phenylene (OXD-7) (Jpn. J. Appl. Phys. Vol. 31 (1992), p. 1812). In addition, a research group at Yamagata University has produced a white light emitting device by using a triazole-based electron transport material having excellent electron blocking properties (Science, 3 March 1995, Vol. 267, p. 1332). Further, JP-A-5-331459 describes that phenanthroline derivatives are useful as electron transport materials.

  However, the conventional electron transporting material has a low thin film forming ability and easily crystallizes, so that there is a problem that the light emitting element is destroyed, and the element performance that can withstand practical use cannot be expressed.

  In addition, a technique has been reported in which the luminous efficiency is improved by forming the luminous layer with a host compound and a small amount of phosphor. For example, in Japanese Patent No. 3093796, a small amount of a phosphor is doped into a stilbene derivative, a distyrylarylene derivative or a tristyrylarylene derivative to achieve an improvement in light emission luminance and a longer device lifetime.

  An 8-hydroxyquinoline aluminum complex as a host compound, a device having an organic light-emitting layer doped with a small amount of phosphor (Japanese Patent Laid-Open No. 63-264692), an 8-hydroxyquinoline aluminum complex as a host compound, An element having an organic light emitting layer doped with a quinacridone dye (Japanese Patent Laid-Open No. 3-255190) is known. As described above, the emission luminance is improved by doping a phosphor having a high fluorescence quantum yield as compared with the conventional device.

  However, the light emission from the small amount of the phosphor to be doped is light emission from the excited singlet, and when the light emission from the excited singlet is used, the generation ratio of the singlet exciton and the triplet exciton is 1: 3, the generation probability of the luminescent excited species is 25%, and the light extraction efficiency is about 20%. Therefore, the limit of the external extraction quantum efficiency (ηext) is 5%. However, since an organic EL device using phosphorescence emission from an excited triplet was reported from Princeton University (MA Baldo et al., Nature, 395, 151-154 (1998)), room temperature. In recent years, research on phosphorescent materials has been actively conducted (for example, MA Baldo et al., Nature, 403, 17, 750-753 (2000), US Pat. No. 6,097). , No. 147). When the excited triplet is used, the upper limit of the internal quantum efficiency is 100%. In principle, the luminous efficiency is up to four times that of the excited singlet, and almost the same performance as a cold cathode tube is obtained. It can be applied to and is attracting attention.

  Of course, the host when using the phosphorescent compound as a dopant needs to have an emission maximum wavelength in a region shorter than the emission maximum wavelength of the phosphorescent compound. I know that there is.

  The 10th International Works on Inorganic and Organic Electroluminescence (EL'00, Hamamatsu) reports on several phosphorescent compounds. For example, Ikai et al. Uses a hole transporting compound as a host of a phosphorescent compound. In addition, M.M. E. Thompson et al. Use various electron transport materials as a host of phosphorescent compounds doped with a novel iridium complex. Furthermore, Tsutsui et al. Have obtained high luminous efficiency by introducing a hole blocking layer.

  Japanese Patent Application Laid-Open No. 2001-192651 describes an example in which a benzene derivative containing a condensed arylene group is used as a host of a phosphorescent compound, but in this case as well, the initial characteristics such as emission luminance are relatively good. However, it has been found that there is a problem with the light emission lifetime.

  The hole blocking layer is structurally the same as the electron transport layer used in ordinary organic EL elements, but the function of holes that leak from the light emitting layer to the cathode side rather than the electron transport function. It is named as a hole block layer because it has a powerful function of preventing movement, and can be interpreted as a kind of electron transport layer. Therefore, in the present application, the hole blocking layer is also referred to as an electron transport layer, and a material (hole blocker) used in the layer is also referred to as an electron transport material.

  Examples of the host compound of the phosphorescent compound include C.I. Adachi et al. , Appl. Phys. Lett. 77, page 904 (2000), etc., but a new approach is required for the properties required for the host compound to obtain a high-brightness organic electroluminescence device. .

  However, none of the reports has obtained a configuration that can achieve both improvement in light emission luminance and durability of the device.

  Therefore, the present invention has been made for the purpose of achieving both improvement in light emission luminance and durability of the device using a 1,2,3,4-tetraphenylbenzene compound. By using a 1,3,4-tetraphenylbenzene compound as a host compound for phosphorescence emission and / or by using a 1,2,3,4-tetraphenylbenzene compound as an electron transport material (hole blocker), The present invention provides an organic electroluminescence element that achieves both improvement in emission luminance and durability, and a display device with high emission luminance and long life using the organic electroluminescence element of the present invention.

The above object of the present invention has been achieved by the following.
(1) An organic electroluminescence device having a light emitting layer containing a host compound and a phosphorescent compound, wherein the host compound is a compound represented by the following general formula (2).

_Wherein, Ar 11 _{to Ar 14} each independently represent a substituted or unsubstituted phenyl _{group, R 11,} R ₁₂ represents a cyclohexyl group. ]
(2) The organic electroluminescence device according to (1), further having an electron transport layer and containing the compound represented by the general formula (2) in the electron transport layer.
(3) The organic electroluminescence device according to (1) or (2), wherein the phosphorescent compound is an iridium compound, an osmium compound or a platinum compound.
(4) The organic electroluminescence device according to (3), wherein the phosphorescent compound is an iridium compound.
(5) A display device comprising the organic electroluminescent element according to any one of (1) to (3).

  According to the present invention, an organic electroluminescence element that achieves both improvement in emission luminance and durability, and a display device with high emission luminance and a long lifetime are obtained.

  The present invention will be described in more detail. First, the compound represented by the general formula (2) will be described. The general formula (1) that produces the same effect as the present invention will be described at the same time.

[Wherein, Ar _{1 to} Ar ₃ each independently represents a substituted or unsubstituted phenyl group, and R _{1 to} R ₃ each independently represents a hydrogen atom or a substituent. However, at least one of R _{1 to} R ₃ represents a hydrogen atom, a substituted alkyl group or an unsubstituted alkyl group. Adjacent R _{1 to} R ₃ may be condensed with each other to form a ring. ]
In the general formulas (1) and (2), the substituents represented by R _{1 to} R ₃ and R ₁₁ and R ₁₂ are alkyl groups (methyl group, ethyl group, i-propyl group, hydroxyethyl group). , Methoxymethyl group, trifluoromethyl group, t-butyl group, cyclopentyl group, cyclohexyl group, benzyl group, etc.), alkenyl group (vinyl group, propenyl group, styryl group, etc.), alkynyl group (ethynyl group, etc.), aryl group (Phenyl group, naphthyl group, p-tolyl group, p-chlorophenyl group, etc.), alkyloxy group (methoxy group, ethoxy group, i-propoxy group, butoxy group, etc.), aryloxy group (phenoxy group, etc.), alkylthio group (Methylthio group, ethylthio group, i-propylthio group, etc.), arylthio group (phenylthio group, etc.), halogen atom (fluorine atom, salt) Atom, bromine atom, iodine atom, etc.), amino group (dimethylamino group, methylamino group, diphenylamino group, etc.), cyano group, nitro group, heterocyclic group (pyrrole group, pyrrolidyl group, pyrazolyl group, imidazolyl group, pyridyl group) Group, benzimidazolyl group, benzothiazolyl group, benzoxazolyl group, etc.). Examples of the aromatic group include the above aryl group and heteroaryl group (pyrrole group, pyrazolyl group, imidazolyl group, pyridyl group, benzimidazolyl group, benzothiazolyl group, benzooxazolyl, etc.), and each substituent is further optional. It may be substituted with a substituent. Further, adjacent substituents may be condensed with each other to form a ring.

Of the substituents represented by R _{1 to} R ₃ and R ₁₁ and R ₁₂ , an alkyl group is particularly preferred.

In the general formula (2), among the substituted or unsubstituted phenyl groups represented by Ar _{1 to} Ar ₃ and Ar _{11 to} Ar ₁₄ , the substituent of the substituted phenyl group is the substituent described in the above R _{1 to} R _3. Is applicable.

  The compound of the present invention is a compound having strong fluorescence in a solid state, is excellent in electroluminescence, and can be effectively used as a light emitting material. In addition, since the electron injection property and the electron transport property from the metal electrode are very excellent, the compound of the present invention can be used as an electron transport material in an element using another light emitting material or the compound of the present invention as a light emitting material. When used as a hole blocker), it exhibits excellent luminous efficiency.

  Specific examples of the compound of the present invention are listed below, but the present invention is not limited thereto.

  These compounds are described in Tetrahedron Letters 41 (2000) 4261-4264 and J. Am. Am. Chem. Soc. 1997, 119, 7291-7302 Angew. Chem. , Int. Ed. Engl. 36 (1997) 1740, etc., can be easily synthesized.

  In addition, as a result of intensive studies on the host compound of the phosphorescent compound, the present inventors have used the 1,2,3,4-tetraphenylbenzene compound of the present invention as a host compound to produce an organic electroluminescence device. It has been found that the emission brightness and lifetime of the device are improved when fabricated.

  The host compound of the present invention is a compound having the largest mixing ratio (mass) in the light emitting layer composed of two or more compounds, and the other compounds are referred to as dopant compounds. For example, if the light emitting layer is composed of two types of compound A and compound B and the mixing ratio is A: B = 10: 90, compound A is a dopant compound and compound B is a host compound. Furthermore, if a light emitting layer is comprised from 3 types of compound A, compound B, and compound C, and the mixing ratio is A: B: C = 5: 10: 85, compound A and compound B are dopant compounds, Compound C is a host compound. The phosphorescent compound in the present invention is a kind of dopant compound.

  The phosphorescent compound of the present invention is a compound in which light emission from an excited triplet is observed, and is a compound having a phosphorescence quantum yield of 0.001 or more at 25 ° C. Preferably it is 0.01 or more. More preferably, it is 0.1 or more.

  The phosphorescence quantum yield can be measured by the method described in Spectroscopic II, page 398 (1992 edition, Maruzen) of Experimental Chemistry Course 4 of the 4th edition. Although the phosphorescence quantum yield in a solution can be measured using various solvents, the phosphorescence quantum yield used in the present invention is only required to achieve the phosphorescence quantum yield in any solvent.

  A complex compound containing a Group VIII metal in the periodic table of elements is preferred, and an iridium, osmium, or platinum complex compound is more preferred. More preferred are iridium complex compounds.

  Specific examples of the phosphorescent compound used in the present invention are shown below, but are not limited thereto. These compounds are described, for example, in Inorg. Chem. 40, 1704-1711, and the like.

  In another embodiment, in addition to the host compound and the phosphorescent compound, at least one fluorescent compound having a fluorescence maximum wavelength is contained in a region longer than the maximum wavelength of light emission from the phosphorescent compound. There is also. In this case, electroluminescence as an organic EL element can be emitted from the fluorescent compound by energy transfer from the host compound and the phosphorescent compound. Preferred as the fluorescent compound is one having a high fluorescence quantum yield in a solution state. Here, the fluorescence quantum yield is preferably 0.1 or more, particularly preferably 0.3 or more. Specifically, coumarin dyes, pyran dyes, cyanine dyes, croconium dyes, squalium dyes, oxobenzanthracene dyes, fluorescein dyes, rhodamine dyes, pyrylium dyes, perylene dyes, stilbene dyes , Polythiophene dyes, or rare earth complex phosphors.

  The fluorescence quantum yield here can also be measured by the method described in page 362 (1992 version, Maruzen) of Spectroscopic II of the Fourth Edition Experimental Chemistry Course 7.

  Hereinafter, the electroluminescence element (EL element) will be described.

  In a broad sense, the light emitting layer in an EL element refers to a layer that emits light when a current is passed through an electrode composed of a cathode and an anode. Specifically, it refers to a layer containing a fluorescent compound that emits light when an electric current is passed through an electrode composed of a cathode and an anode. Usually, an electroluminescence element (EL element) has a structure in which a light emitting layer is sandwiched between a pair of electrodes. The organic EL device of the present invention has a hole transport layer, an electron transport layer, an anode buffer layer, a cathode buffer layer, and the like in addition to the light emitting layer as required, and has a structure sandwiched between a cathode and an anode.

In particular,
(I) Anode / light emitting layer / cathode (ii) Anode / hole transport layer / light emitting layer / cathode (iii) Anode / light emitting layer / electron transport layer / cathode (iv) Anode / hole transport layer / light emitting layer / electron There is a structure represented by transport layer / cathode (v) anode / anode buffer layer / hole transport layer / light emitting layer / electron transport layer / cathode buffer layer / cathode.

  As a method of forming a light emitting layer using the above compound, there is a method of forming a thin film by a known method such as a vapor deposition method, a spin coat method, a cast method, an LB method, etc. preferable. Here, the molecular deposition film refers to a thin film formed by deposition from the gas phase state of the compound or a film formed by solidification from the molten state or liquid phase state of the compound. Normally, this molecular deposited film can be distinguished from a thin film (molecular accumulated film) formed by the LB method by a difference in aggregated structure and higher order structure and a functional difference resulting therefrom.

  Further, as described in JP-A-57-51781, this light-emitting layer is prepared by dissolving the above compound as a light-emitting material together with a binder such as a resin in a solvent, and then using this as a spin coating method or the like. It can be obtained by coating with a thin film.

  There is no restriction | limiting in particular about the film thickness of the light emitting layer formed in this way, Although it can select suitably according to a condition, Usually, it is the range of 5 nm-5 micrometers.

  Here, the phosphorescent compound described in the present invention is specifically a heavy metal complex compound as described above, preferably a complex system having a group VIII metal as a central metal in the periodic table of elements. A compound, and more preferably an osmium, iridium, or platinum complex compound.

  As these phosphorescent compounds, the phosphorescence quantum yield as described above is 0.001 or more at 25 ° C., and the phosphorescence emission maximum wavelength is longer than the fluorescence maximum wavelength of the fluorescent compound serving as the host. Thus, for example, the emission maximum of the phosphorescent compound using the phosphorescent compound having a wavelength longer than the emission maximum wavelength of the fluorescent compound serving as the host, that is, utilizing the triplet state, the fluorescence maximum of the host compound. An EL element that emits electroluminescence at a wavelength longer than the wavelength can be obtained. Accordingly, the phosphorescent maximum wavelength of the phosphorescent compound to be used is not particularly limited, and in principle can be obtained by selecting a central metal, a ligand, a ligand substituent, and the like. The emission wavelength can be changed.

  For example, a fluorescent compound having a fluorescence maximum wavelength in the 350 nm to 440 nm region is used as a host compound, and an organic EL element that emits light in the green region is obtained by using, for example, an iridium complex having phosphorescence in the green region. I can do it.

  In another embodiment, as described above, in addition to the fluorescent compound A as the host compound and the phosphorescent compound, the fluorescent maximum wavelength is set in a region longer than the maximum wavelength of light emission from the phosphorescent compound. The fluorescent compound B may contain at least one kind of fluorescent compound B, and electroluminescence as an organic EL element obtains light emission from the fluorescent compound B by energy transfer from the fluorescent compound A and the phosphorescent compound. You can also

  The color emitted by the fluorescent compound of the present specification is shown in FIG. 4.16 on page 108 of “New Color Science Handbook” (edited by the Japan Society for Color Science, University of Tokyo Press, 1985). It is determined by the color when the result measured by Minolta) is applied to the CIE chromaticity coordinates.

  The molecular weight of the host compounds represented by the general formulas (1) to (6) is preferably 600 to 2000. If the molecular weight is in this molecular weight range, Tg (glass transition temperature) is increased, and thermal stability is improved. The device life is improved. More preferably, the molecular weight is 800-2000. Moreover, it is preferable that Tg is 100 degree | times or more. Further, when the molecular weight is within this range, the light emitting layer can be easily produced by a vacuum vapor deposition method, and the production of the organic EL element is facilitated. Furthermore, the thermal stability of the fluorescent compound in the organic EL element is also improved.

  Next, other layers constituting the EL element in combination with a light emitting layer such as a hole injection layer, a hole transport layer, an electron injection layer, and an electron transport layer will be described.

  The hole injection layer and the hole transport layer have a function of transmitting the holes injected from the anode to the light emitting layer, and the hole injection layer and the hole transport layer are interposed between the anode and the light emitting layer. Therefore, a lot of holes are injected into the light emitting layer with a lower electric field, and the electrons injected into the light emitting layer from the cathode, the electron injection layer, or the electron transport layer are converted into the light emitting layer and the hole injection layer or the hole transport layer. Due to the barrier of electrons existing at the interface, the device has excellent light emitting performance, such as being accumulated at the interface in the light emitting layer and improving the light emission efficiency. The material of the hole injection layer and hole transport layer (hereinafter referred to as hole injection material and hole transport material) has a property of transmitting the holes injected from the anode to the light emitting layer. If it is a thing, there will be no restriction | limiting in particular, In the conventionally known thing used for the hole injection layer of an electroluminescent material, and the hole injection layer of a EL element, and a hole transport layer, it is conventionally used as a hole charge injection transport material. Any one can be selected and used.

  The hole injection material and the hole transport material have either hole injection or transport or electron barrier properties, and may be either organic or inorganic. Examples of the hole injection material and hole transport material include triazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, and oxazoles. Derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aniline copolymers, and conductive polymer oligomers, particularly thiophene oligomers. As the hole injecting material and the hole transporting material, those described above can be used, and porphyrin compounds, aromatic tertiary amine compounds, and styrylamine compounds, particularly aromatic tertiary amine compounds can be used. preferable.

  Representative examples of the aromatic tertiary amine compound and styrylamine compound include N, N, N ′, N′-tetraphenyl-4,4′-diaminophenyl; N, N′-diphenyl-N, N ′. -Bis (3-methylphenyl)-[1,1'-biphenyl] -4,4'-diamine (TPD); 2,2-bis (4-di-p-tolylaminophenyl) propane; Bis (4-di-p-tolylaminophenyl) cyclohexane; N, N, N ′, N′-tetra-p-tolyl-4,4′-diaminobiphenyl; 1,1-bis (4-di-p- Tolylaminophenyl) -4-phenylcyclohexane; bis (4-dimethylamino-2-methylphenyl) phenylmethane; bis (4-di-p-tolylaminophenyl) phenylmethane; N, N′-diphenyl-N, N -Di (4-methoxyphenyl) -4,4'-diaminobiphenyl; N, N, N ', N'-tetraphenyl-4,4'-diaminodiphenyl ether; 4,4'-bis (diphenylamino) quadri N; N, N-tri (p-tolyl) amine; 4- (di-p-tolylamino) -4 '-[4- (di-p-tolylamino) styryl] stilbene; 4-N, N-diphenyl Amino- (2-diphenylvinyl) benzene; 3-methoxy-4'-N, N-diphenylaminostilbenzene; N-phenylcarbazole and further described in US Pat. No. 5,061,569 Having two condensed aromatic rings in the molecule, for example, 4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (NPD), JP-A-4-3 4,4 ′, 4 ″ -tris [N- (3-methylphenyl) -N-phenylamino] triphenylamine in which three triphenylamine units described in Japanese Patent No. 8688 are linked in a starburst type ( MTDATA).

  Furthermore, a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain can also be used.

  In addition, inorganic compounds such as p-type-Si and p-type-SiC can also be used as the hole injection material and the hole transport material. The hole injection layer and the hole transport layer are formed by thinning the hole injection material and the hole transport material by a known method such as a vacuum deposition method, a spin coating method, a casting method, or an LB method. Can be formed. Although there is no restriction | limiting in particular about the film thickness of a positive hole injection layer and a positive hole transport layer, Usually, it is about 5 nm-5 micrometers. The hole injection layer and hole transport layer may have a single layer structure composed of one or more of the above materials, or may have a multilayer structure composed of a plurality of layers having the same composition or different compositions.

  Furthermore, the electron transport layer used as necessary only needs to have a function of transmitting electrons injected from the cathode to the light emitting layer, and the material thereof is selected from any conventionally known compounds. Can be used.

  Examples of materials used for this electron transport layer (hereinafter referred to as electron transport materials) include heterocyclic tetracarboxylic acid anhydrides such as nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, naphthalene perylene, carbodiimides, Examples include fluorenylidenemethane derivatives, anthraquinodimethane and anthrone derivatives, and oxadiazole derivatives. Furthermore, in the above oxadiazole derivative, a thiadiazole derivative in which the oxygen atom of the oxadiazole ring is substituted with a sulfur atom, and a quinoxaline derivative having a quinoxaline ring known as an electron withdrawing group can also be used as an electron transport material.

  Furthermore, a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain can also be used.

Further, metal complexes of 8-quinolinol derivatives such as tris (8-quinolinol) aluminum (Alq ₃ ), tris (5,7-dichloro-8-quinolinol) aluminum, tris (5,7-dibromo-8-quinolinol) aluminum. , Tris (2-methyl-8-quinolinol) aluminum, tris (5-methyl-8-quinolinol) aluminum, bis (8-quinolinol) zinc (Znq), and the like, and the central metal of these metal complexes is In, Mg, Metal complexes replaced with Cu, Ca, Sn, Ga, or Pb can also be used as the electron transport material. In addition, metal-free or metal phthalocyanine, or those having terminal ends substituted with an alkyl group or a sulfonic acid group can be preferably used as the electron transport material. In addition, the distyrylpyrazine derivative exemplified as the material of the light emitting layer can also be used as an electron transport material, and similarly to the hole injection layer and the hole transport layer, inorganic such as n-type-Si and n-type-SiC. A semiconductor can also be used as an electron transport material.

  The electron transport layer can be formed by forming the above compound by a known thin film forming method such as a vacuum deposition method, a spin coating method, a casting method, or an LB method. Although the film thickness as an electron carrying layer does not have a restriction | limiting in particular, Usually, it selects in 5 nm-5 micrometers. The electron transport layer may have a single layer structure composed of one or two or more of these electron transport materials, or may have a laminated structure composed of a plurality of layers having the same composition or different compositions.

  Further, in the present invention, the fluorescent compound is not limited to the light emitting layer alone, and the hole transport layer adjacent to the light emitting layer, or the fluorescent compound serving as a host compound of the phosphorescent compound in the electron transport layer; At least one fluorescent compound having a fluorescent maximum wavelength may be contained in the same region, whereby the luminous efficiency of the EL element can be further increased. As the fluorescent compound contained in these hole transport layer and electron transport layer, the fluorescence maximum wavelength is in the range of 350 nm to 440 nm, more preferably in the range of 390 nm to 410 nm, as in the light emitting layer. A compound is used.

  The substrate preferably used for the organic EL device of the present invention is not particularly limited as long as it is transparent, and there are no particular limitations as long as it is transparent. Examples of the substrate preferably used in the electroluminescent device of the present invention include glass, quartz, and a light transmissive plastic film.

  Examples of the light transmissive plastic film include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyetherimide, polyetheretherketone, polyphenylene sulfide, polyarylate, polyimide, and polycarbonate (PC). And a film made of cellulose triacetate (TAC), cellulose acetate propionate (CAP), or the like.

  Next, a suitable example for producing the organic EL element will be described. As an example, a method for manufacturing an EL element composed of the anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / electron injection layer / cathode will be described.

  First, a thin film made of a desired electrode material, for example, an anode material, is formed on a suitable substrate by a method such as vapor deposition or sputtering so as to have a film thickness of 1 μm or less, preferably 10 to 200 nm. An anode is produced. Next, a thin film comprising a hole injection layer, a hole transport layer, a light emitting layer, and an electron transport layer / electron injection layer, which is a device material, is formed thereon.

  Furthermore, a buffer layer (electrode interface layer) may be present between the anode and the light emitting layer or hole injection layer and between the cathode and the light emitting layer or electron injection layer.

  The buffer layer is a layer provided between the electrode and the organic layer in order to lower the driving voltage and improve the luminous efficiency. “The organic EL element and its forefront of industrialization (published by NTS Corporation on November 30, 1998) 2) Chapter 2 “Electrode Materials” (pages 123 to 166) in detail, and includes an anode buffer layer and a cathode buffer layer.

  The details of the anode buffer layer are also described in JP-A-9-45479, 9-260062, and 8-288069. Specific examples thereof include a phthalocyanine buffer layer represented by copper phthalocyanine, vanadium oxide. And an oxide buffer layer, an amorphous carbon buffer layer, and a polymer buffer layer using a conductive polymer such as polyaniline (emeraldine) or polythiophene.

  The details of the cathode buffer layer are also described in JP-A-6-325871, JP-A-9-17574, JP-A-10-74586, and the like. Specifically, a metal buffer layer represented by strontium, aluminum and the like, Examples thereof include an alkali metal compound buffer layer typified by lithium fluoride, an alkaline earth metal compound buffer layer typified by magnesium fluoride, an oxide buffer layer typified by aluminum oxide and lithium oxide, and the like.

  The buffer layer is preferably a very thin film, and depending on the material, the film thickness is preferably in the range of 0.1 to 100 nm.

  Further, in addition to the basic constituent layer, a layer having other functions may be laminated as required. For example, JP-A-11-204258, JP-A-11-204359, and “Organic EL device and its industrialization front line ( It may have a functional layer such as a hole blocking layer described on page 237 of “November 30, 1998, NTS Corporation”.

  The buffer layer may function as a light emitting layer when at least one of the compounds of the present invention is present in at least one of the cathode buffer layer and the anode buffer layer.

  Next, the electrode of the organic EL element will be described. The electrode of the organic EL element consists of a cathode and an anode.

As the anode in the organic EL element, an electrode material made of a metal, an alloy, an electrically conductive compound, or a mixture thereof having a high work function (4 eV or more) is preferably used. Specific examples of such electrode materials include metals such as Au, conductive transparent materials such as CuI, indium tin oxide (ITO), SnO ₂ , and ZnO.

  The anode may be formed by a thin film of these electrode materials by a method such as vapor deposition or sputtering, and a pattern having a desired shape may be formed by a photolithography method, or (100 μm) when pattern accuracy is not so required. As described above, a pattern may be formed through a mask having a desired shape when the electrode material is deposited or sputtered. When light emission is extracted from the anode, it is desirable that the transmittance is greater than 10%, and the sheet resistance as the anode is preferably several hundred Ω / □ or less. Further, although the film thickness depends on the material, it is usually selected in the range of 10 nm to 1 μm, preferably 10 nm to 200 nm.

On the other hand, as the cathode, a material having a low work function (4 eV or less) metal (referred to as an electron injecting metal), an alloy, an electrically conductive compound, and a mixture thereof as an electrode material is used. Specific examples of such electrode materials include sodium, sodium-potassium alloy, magnesium, lithium, magnesium / copper mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al ₂ O ₃ ) Mixtures, indium, lithium / aluminum mixtures, rare earth metals and the like. Among these, a mixture of an electron injecting metal and a second metal which is a stable metal having a larger work function value than this from the viewpoint of durability against electron injecting and oxidation, for example, a magnesium / silver mixture, magnesium / Aluminum mixtures, magnesium / indium mixtures, aluminum / aluminum oxide (Al ₂ O ₃ ) mixtures, lithium / aluminum mixtures and the like are preferred. The cathode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering. Further, the sheet resistance as the cathode is preferably several hundred Ω / □ or less, and the film thickness is usually selected in the range of 10 nm to 1 μm, preferably 50 to 200 nm. In addition, in order to transmit light emission, if either one of the anode or the cathode of the organic EL element is transparent or translucent, the light emission efficiency is improved, which is convenient.

  Next, a method for manufacturing the organic EL element will be described.

As the thinning method, there are a spin coating method, a casting method, a vapor deposition method and the like as described above, but a vacuum vapor deposition method is preferable because a homogeneous film can be easily obtained and pinholes are hardly generated. When a vacuum deposition method is employed for thinning, the deposition conditions vary depending on the type of compound used, the target crystal structure of the molecular deposition film, the association structure, etc., but generally a boat heating temperature of 50 to 450 ° C., vacuum It is desirable to select appropriately within a range of a degree of 10 ⁻⁶ to 10 ⁻³ Pa, a deposition rate of 0.01 to 50 nm / second, a substrate temperature of −50 to 300 ° C., and a film thickness of 5 nm to 5 μm.

  As described above, a method such as vapor deposition or sputtering of a thin film made of a desired electrode material, for example, an anode material, on a suitable substrate so as to have a film thickness of 1 μm or less, preferably 10 to 200 nm. After forming an anode by forming a thin film of each layer comprising a hole injection layer, a hole transport layer, a light emitting layer, and an electron transport layer / electron injection layer as described above on the anode, A desired organic EL device can be obtained by forming a thin film made of a cathode material to a thickness of 1 μm or less, preferably 50 to 200 nm by a method such as vapor deposition or sputtering, and providing a cathode. . The organic EL device is preferably produced from the hole injection layer to the cathode in this manner consistently by a single evacuation. However, the production order is reversed so that the cathode, the electron injection layer, the light emitting layer, It is also possible to produce the hole injection layer and the anode in this order. In the case of applying a DC voltage to the organic EL device thus obtained, light emission can be observed by applying a voltage of about 5 to 40 V with the positive polarity of the anode and the negative polarity of the cathode. Further, even when a voltage is applied with the opposite polarity, no current flows and no light emission occurs. Further, when an AC voltage is applied, light is emitted only when the anode is in the + state and the cathode is in the-state. The alternating current waveform to be applied may be arbitrary.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, the aspect of this invention is not limited to this.

Example 1
After patterning on a substrate (made by NH Techno Glass Co., Ltd .: NA-45) with a 150 nm ITO film on glass as the anode, the transparent support substrate provided with this ITO transparent electrode was ultrasonically cleaned with i-propyl alcohol. Then, it was dried with dry nitrogen gas, and UV ozone cleaning was performed for 5 minutes. This transparent support substrate was fixed to a substrate holder of a commercially available vacuum deposition apparatus, while 200 mg of α-NPD was put in a molybdenum resistance heating boat, and 200 mg of Comparative Compound 1 was put in another molybdenum resistance heating boat. 200 mg of bathocuproin (BCP) was put into a molybdenum resistance heating boat, and 200 mg of Alq ₃ was put into another molybdenum resistance heating boat, which was attached to a vacuum deposition apparatus.

Next, after reducing the vacuum chamber to 4 × 10 ⁻⁴ Pa, the heating boat containing α-NPD was heated by heating, and the film thickness was formed on the transparent support substrate at a deposition rate of 0.1 to 0.3 nm / sec. Vapor deposition was performed at 50 nm to provide a hole transport layer. The substrate temperature during vapor deposition was room temperature.

Next, the heating boat containing the comparative compound 1 was energized and heated to provide a 30 nm light emitting layer at a deposition rate of 0.1 to 0.3 nm / sec. Further, the heating boat containing BCP was heated by energization to provide a hole blocking layer having a thickness of 10 nm. Further, the heating boat containing Alq ₃ was heated by energization to provide an electron transport layer having a thickness of 20 nm at a deposition rate of 0.1 to 0.3 nm / sec.

Next, a vacuum chamber is opened, and a stainless steel rectangular perforated mask is placed on the electron injection layer. On the other hand, 3 g of magnesium is placed in a molybdenum resistance heating boat, and 0.02 of silver is placed in a tungsten vapor deposition basket. After putting 5 g and depressurizing the vacuum tank to 2 × 10 ⁻⁴ Pa again, energizing the boat containing magnesium to deposit magnesium at a deposition rate of 1.5 to 2.0 nm / sec. Was heated, and silver was vapor-deposited at a vapor deposition rate of 0.1 nm / sec to obtain a cathode made of the mixture of magnesium and silver, thereby producing a comparative organic EL element OLED1-1 shown in Table 1.

  Organic EL elements OLED1-2 to 1-7 were produced in the same manner as the organic EL element OLED1-1 except that the comparative compounds of the organic EL element OLED1-1 were changed to the compounds shown in Table 1. The emission color was blue to green.

These devices were continuously lit by applying a DC voltage of 10 V under a dry nitrogen gas atmosphere at a temperature of 23 ° C., and the light emission luminance (cd / m ² ) at the start of lighting and the time for halving the luminance were measured. The light emission luminance is expressed as a relative value when the organic EL element OLED1-1 is 100, and the time when the luminance is halved is expressed as a relative value when the time when the luminance of the organic electroluminescence element OLED1-1 is halved is 100. The results are shown in Table 1. The light emission luminance [cd / m ² ] was measured using Minolta CS-1000.

  From Table 1, the organic EL device using the compounds described in the table has improved emission luminance at the start of lighting, and particularly has a longer time to reduce the luminance by half, compared to the organic EL device using a comparative compound having a similar structure. You can see that it has improved.

Example 2 (Host)
Organic electroluminescent element OLED2-1 was produced by the same method as Example 1 except using the light emitting layer with a film thickness of 30 nm which vapor-deposited compound 6 and DCM-2 with the mass ratio of 100: 1.

  When these devices were applied with a DC voltage of 10 V in a dry nitrogen gas atmosphere at a temperature of 23 degrees, red light emission was obtained.

  Green or blue light emission was obtained by changing DCM-2 of the organic electroluminescent element OLED2-1 to Qd-2 or BCzVBi, respectively.

Example 3 (Electron Transport Material)
After patterning on a substrate (made by NH Techno Glass Co., Ltd .: NA-45) with a 150 nm ITO film on glass as the anode, the transparent support substrate provided with this ITO transparent electrode was ultrasonically cleaned with i-propyl alcohol. Then, it was dried with dry nitrogen gas, and UV ozone cleaning was performed for 5 minutes. This transparent support substrate is fixed to a substrate holder of a commercially available vacuum deposition apparatus. Meanwhile, 200 mg of m-MTDATXA is put into a molybdenum resistance heating boat, and 200 mg of DPVBi is put into another molybdenum resistance heating boat. 200 mg of BCP was put in a resistance heating boat made of molybdenum and attached to a vacuum deposition apparatus.

Next, after the pressure in the vacuum chamber is reduced to 4 × 10 ⁻⁴ Pa, the heating boat containing m-MTDATXA is energized and heated to form a film thickness on the transparent support substrate at a deposition rate of 0.1 to 0.3 nm / sec. Vapor deposition was performed at 25 nm, and the heating boat containing DPVBi was energized and heated, and deposition was performed at a deposition rate of 0.1 to 0.3 nm / sec to a thickness of 20 nm to provide a light emitting layer. The substrate temperature during vapor deposition was room temperature. Then, the heating boat containing BCP was energized and heated to provide a 30 nm electron transport layer at a deposition rate of 0.1 to 0.3 nm / sec.

Next, a vacuum chamber is opened, and a stainless steel rectangular perforated mask is placed on the electron transport layer. On the other hand, 3 g of magnesium is placed in a molybdenum resistance heating boat, and 0.02 of silver is placed in a tungsten vapor deposition basket. After putting 5 g and depressurizing the vacuum tank to 2 × 10 ⁻⁴ Pa again, energizing the boat containing magnesium to deposit magnesium at a deposition rate of 1.5 to 2.0 nm / sec. Was heated, and silver was vapor-deposited at a vapor deposition rate of 0.1 nm / sec to obtain a cathode made of the mixture of magnesium and silver, thereby producing a comparative organic EL element OLED3-1 shown in Table 2.

  Organic electroluminescent elements OLED3-2 to 9 were produced in the same manner as organic electroluminescent element OLED3-1 except that the BCP of organic EL element OLED3-1 was changed to the compounds shown in Table 2.

These elements were continuously lit by applying a DC voltage of 10 V under a dry nitrogen gas atmosphere at a temperature of 23 ° C., and the light emission luminance (cd / m ² ) at the start of lighting and the time during which the luminance was reduced by half were measured. The light emission luminance is expressed as a relative value when the organic electroluminescence element OLED3-1 is 100, and the time when the luminance is halved is expressed as a relative value when the time when the luminance of the organic electroluminescence element OLED3-1 is halved is 100. The results are shown in Table 2. In all elements, the emission color was blue.

  From Table 2, it can be seen that the organic EL device using the compounds described in the table has improved the light emission luminance at the start of lighting, the light emission efficiency, and the time to reduce the luminance by half. In particular, it can be seen that the time for halving the luminance is improved.

Example 4 (cathode buffer layer)
Except that the cathode of the organic electroluminescence element OLED3-4 produced in Example 3 was replaced with Al, and a cathode buffer layer was provided by depositing lithium fluoride with a thickness of 0.5 nm between the electron transport layer and the cathode. Thus, an organic electroluminescence element (OLED4-1) was produced.

As in Example 3, the light emission luminance (cd / m ² ) at the start of lighting and the time during which the luminance was reduced by half were measured. It was time 320 to do. Similarly, organic electroluminescent elements OLED3-3 to 9-9 were more effective when a cathode buffer layer was introduced.

Example 5 (Three colors of light emission)
The organic electroluminescence element used in Example 3 was replaced with a light emitting layer in which Alq ₃ or Alq ₃ and DCM-2 were deposited at a mass ratio of 100: 1 from DPVBi in the same manner. A luminescence element was produced, and the light emission luminance (cd / m ² ) at the start of lighting and the time during which the luminance was reduced by half were measured. As a result, in the same manner as in Example 3, in the organic electroluminescence device using the compound for the electron transport layer, it was confirmed that the light emission luminance (cd / m ² ) at the start of lighting and the time for halving the luminance were improved.

In the case of using the Alq ₃ in the light emitting layer green light it was obtained, Alq ₃ and DCM-2 100: red light was emitted from the light emitting layer were co-deposited at 1.

Example 6
Organic EL elements OLED6-1 to 6-9 were produced as follows.

<Production of organic EL element>
After patterning on a substrate (NA-45 manufactured by NH Techno Glass Co., Ltd.) having a film of 150 nm of ITO (indium tin oxide) formed on a glass substrate of 100 mm × 100 mm × 1.1 mm as an anode, this ITO transparent electrode was provided. The transparent support substrate was ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen gas, and subjected to UV ozone cleaning for 5 minutes.

This transparent support substrate is fixed to a substrate holder of a commercially available vacuum deposition apparatus, while 200 mg of α-NPD is put into a molybdenum resistance heating boat, and 200 mg of CBP is put into another resistance heating boat made of molybdenum. Put 200 mg of bathocuproin (BCP) in a resistance heating boat, 100 mg of Ir-1 (phosphorescent compound) in another resistance heating boat made of molybdenum, and 200 mg of Alq ₃ in another resistance heating boat made of molybdenum. Attached to the vapor deposition equipment. Next, after the pressure in the vacuum chamber was reduced to 4 × 10 ⁻⁴ Pa, the heating boat containing α-NPD was energized and heated, and deposited on the transparent support substrate at a deposition rate of 0.1 nm / sec. The hole transport layer was provided. Further, the heating boat containing CBP and Ir-1 was energized and heated, and co-deposited on the hole transport layer at a deposition rate of 0.1 nm / sec and 0.01 nm / sec, respectively, to have a film thickness of 20 nm. A light emitting layer was provided. In addition, the substrate temperature at the time of vapor deposition was room temperature. Further, an electron transport layer that also serves as a hole blocking function with a film thickness of 10 nm is provided by energizing and heating the heating boat containing BCP and depositing on the light emitting layer at a deposition rate of 0.1 nm / sec. It was. On top of that, the heating boat containing Alq ₃ was further energized and heated, and deposited on the electron transport layer at a deposition rate of 0.1 nm / sec to further provide an electron injection layer having a thickness of 40 nm. . In addition, the substrate temperature at the time of vapor deposition was room temperature.

  Next, LiF 0.5nm and Al110nm were vapor-deposited, the cathode was formed, and the organic EL element OLED6-1 was produced.

  Organic EL elements OLED6-2 to 6-9 were produced in exactly the same manner except that the CBP of the light emitting layer was replaced with the compounds shown in Table 3 above.

<Evaluation of light emission luminance and light emission lifetime of organic EL elements OLED6-1 to 6-9>
In the organic EL element OLED6-1, current started to flow at an initial driving voltage of 3 V, and green light was emitted from the phosphorescent compound that is a dopant of the light emitting layer. The luminance of the organic EL elements OLED6-1 to 6-9 and the time for halving the luminance when a 9 V DC voltage was applied in a dry nitrogen gas atmosphere at 23 ° C. were measured. The light emission luminance is expressed as a relative value when the organic electroluminescence element OLED6-1 is set to 100, and the time during which the luminance is reduced by half is also expressed as a relative value when the organic electroluminescence element OLED6-1 is set as 100. The light emission luminance [cd / m ² ] was measured using Minolta CS-1000.

  As is apparent from Table 3, the electroluminescence device using the compound of the present invention as a host has a high emission luminance and a long emission lifetime, and thus was found to be very useful as an organic EL device.

  The same effect was obtained also in the organic EL device produced in the same manner as the organic EL devices OLED6-1 to 6-9 except that the phosphorescent compound was changed to Ir-12 or Ir-9. Note that blue light was emitted from the element using Ir-12, and red light was emitted from the element using Ir-9.

Example 7
Organic EL elements OLED7-1 to 7-9 were produced in exactly the same manner except that the electron transport layer BCP of the organic EL element OLED6-1 produced in Example 6 was replaced with the compounds shown in Table 4.

<Evaluation of Luminous Luminance and Luminous Life of Organic EL Elements OLED6-1 and OLEDs 7-1 to 7-9>
In the organic EL element OLED6-1, current started to flow at an initial driving voltage of 3 V, and green light was emitted from the phosphorescent compound that is a dopant of the light emitting layer. When the organic EL element OLED6-1 was applied with a 9 V DC voltage in a dry nitrogen gas atmosphere at a temperature of 23 ° C., the light emission luminance and the time to reduce the luminance by half were measured. The light emission luminance is expressed as a relative value when the organic electroluminescence element OLED6-1 is set to 100, and the time during which the luminance is reduced by half is also expressed as a relative value when the organic electroluminescence element OLED6-1 is set as 100. The light emission luminance [cd / m ² ] was measured using Minolta CS-1000.

  As is clear from Table 4, an electroluminescence device using the compound described in the table for the electron transport layer (hole blocking layer) has a high light emission luminance and a long light emission lifetime, and thus is very useful as an organic EL device. I found out that

  The same effect was obtained also in the organic EL device produced in the same manner as the organic EL devices OLED7-1 to 7-9 except that the phosphorescent compound was changed to Ir-12 or Ir-9. Note that blue light was emitted from the element using Ir-12, and red light was emitted from the element using Ir-9.

Example 8
The red, green, and blue light-emitting organic electroluminescence elements produced in Example 6 were juxtaposed on the same substrate, and the active matrix type full-color display device shown in FIG. 1 was produced.

  FIG. 1 shows only a schematic diagram of a display portion of the produced full-color display device. That is, a wiring portion including a plurality of scanning lines 5 and data lines 6 and a plurality of juxtaposed pixels 3 (light emission color is a red region pixel, a green region pixel, a blue region pixel, etc.) on the same substrate. The scanning line 5 and the plurality of data lines 6 in the wiring portion are each made of a conductive material, and the scanning lines 5 and the data lines 6 are orthogonal to each other in a lattice shape and are connected to the pixels 3 at orthogonal positions ( Details are not shown). The plurality of pixels 3 are driven by an active matrix system provided with an organic EL element corresponding to each emission color, a switching transistor as an active element, and a driving transistor, and a scanning signal is applied from a scanning line 5. Then, an image data signal is received from the data line 6 and light is emitted according to the received image data. In this way, full-color display is possible by appropriately juxtaposing the red, green, and blue pixels.

  By driving the full-color display device, a clear full-color moving image display with high luminance was obtained.

The schematic diagram of the display part of the produced full color display apparatus.

Explanation of symbols

A display unit 3 pixels 5 scanning lines 6 data lines

Claims (5)

The organic electroluminescent element which has a light emitting layer containing a host compound and a phosphorescent compound, A host compound is a compound represented by following General formula (2), The organic electroluminescent element characterized by the above-mentioned.

_Wherein, Ar 11 _{to Ar 14} each independently represent a substituted or unsubstituted phenyl _{group, R 11,} R ₁₂ represents a cyclohexyl group. ] The organic electroluminescence device according to claim 1, further comprising an electron transport layer and a compound represented by the general formula (2) contained in the electron transport layer. 3. The organic electroluminescence device according to claim 1, wherein the phosphorescent compound is an iridium compound, an osmium compound or a platinum compound. The organic electroluminescent device according to claim 3, wherein the phosphorescent compound is an iridium compound. A display device comprising the organic electroluminescence element according to claim 1.

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