JP5312861B2 - Organic EL element and organic EL display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element and an organic EL display excellent in luminous efficiency and film stability. <P>SOLUTION: This organic EL element contains a low molecular weight material represented by a general formula (1): (where, R1 to R16 are substituents which may be the same or independent and are any one of a hydrogen atom, a linear alkyl group, a branched alkyl group and an aryl group), in a luminous layer 4. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an organic EL element and an organic EL display.

Organic electroluminescent elements (hereinafter referred to as organic EL elements) are expected to be applied as next-generation display elements because they can emit light with high luminance and high efficiency at a low voltage.
An organic EL element is a self-luminous light emitting device using an electroluminescence phenomenon (EL) and is similar in principle to an LED (Light Emitting Diode), but uses an organic material as a light emitting material. However, it is different.

The organic EL device is currently required to further lower the voltage and further improve the light emission efficiency from the viewpoint of practical use.
One method for improving the light emission efficiency of the organic EL element is to use triplet excitons. In an organic EL device, holes and electrons are recombined in the light emitting layer to generate singlet excitons and triplet excitons in a ratio of 1: 3, and then radiatively deactivate in the energy deactivation process. It is thought that it emits light. Note that the radiation inactivation from singlet excitons is fluorescence, and the radiation inactivation from triplet excitons is phosphorescence.

  In the conventional organic EL element, in the energy deactivation process of the triplet exciton, since the excitation lifetime of the triplet exciton is long, non-radiative thermal deactivation occurs preferentially over radiation deactivation. Therefore, only radiation deactivation from singlet excitons is used as light emission, and radiation from triplet excitons is not used for light emission.

  On the other hand, as shown in Non-Patent Document 1, a research group at Princeton University investigated an organic EL element using a phosphorescent material as a light emitting layer, and the organic EL element using the phosphorescent material as a light emitting layer emitted a fluorescent material. It was reported that the luminous efficiency was higher than that of the organic EL device used for the layer. It is thought that this is due to the use of triplet excitons that have not been conventionally used. In principle, all of the excitons generated can be used for light emission by using triplet excitons in this way.

  Therefore, in recent years, research on organic EL elements using phosphorescent materials for the light emitting layer has been actively conducted. As a phosphorescent material suitable for the organic EL element, a complex mainly having a heavy metal such as platinum or iridium can be cited. Tris (2-phenylpyridine) iridium has been reported as a typical green phosphorescent material.

  However, organic EL devices using phosphorescent materials in the light-emitting layer have just begun, and unsolved issues such as improvement in light emission efficiency, reduction in drive voltage, improvement in color purity, and optimization of the device structure Many remain. In particular, high light emission efficiency is not stably obtained in a high current / high luminance region.

  In particular, when considering the practical application of an organic EL element as a next-generation display element, an organic EL element that stably exhibits high light emission efficiency from a low current / low luminance region to a high current / high luminance region is required. To achieve this, there is a need for phosphorescent materials with high luminous efficiency and long life that can be driven at low voltage, as well as optimization of organic EL element materials and element structures that use phosphorescent materials in the light-emitting layer. It is being considered.

  Considering the use of an organic EL display composed of organic EL elements as a large screen display and / or a high-definition display, an organic layer, particularly by a wet process using a solution such as a spin coating method, an ink jet method, or a printing method. When the light emitting layer can be formed, it is preferable in terms of the manufacturing process.

As light-emitting materials applicable to the wet process, various low-molecular materials and polymer materials have been widely studied.
In general, since low molecular weight materials are easier to synthesize and purify than high molecular weight materials, many low molecular weight materials have been published as excellent light emitting materials for organic EL devices. The organic EL element used has excellent luminous efficiency and lifetime characteristics. However, there is a problem that low molecular weight materials are easily crystallized when deposited by a wet process. Therefore, the development of a low-molecular material that does not crystallize that can be formed by a wet process is also an important issue.
International Publication No. 01/072927 Pamphlet M.M. A. Bardo et al., Applied. Physics. Letters (Appl. Phys. Lett.), 75, 4 (1999)

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an organic EL element exhibiting high luminous efficiency from a low current / low luminance region to a high current / high luminance region and having excellent film stability. To do.

When the light emitting layer of the organic EL element is composed of a mixture in which a phosphorescent guest material is added to the host material, when a voltage is applied to the organic EL element, the triplet exciton of the guest material is It is thought that radiation deactivation (phosphorescence) occurs.
(1) Injection of holes and electrons into the light emitting layer.
(2) Generation of host excitons by hole-electron recombination (single- and triplet-exciton generation of host material).
(3) Transfer of excitation energy from host material to guest material (singlet and triplet exciton transfer to guest material).
(4) Triplet exciton generation of guest material.
(5) Radiation deactivation (phosphorescence emission) of triplet excitons in the guest material.

  As the energy deactivation process other than the above, a process in which hole or electron trapping and recombination occur in the guest material is also conceivable. Each stage of energy transfer and emission is in a state of competition with various other energy deactivation processes that interfere with the above energy deactivation processes, such as non-radiative thermal deactivation from triplet excitons. Made.

In order to increase the luminous efficiency of the organic EL element, it is preferable to remove other energy deactivation processes such as non-radiative heat deactivation from triplet excitons.
As the method, for example, by using a light emitting material having a high emission quantum yield as a guest material, the emission efficiency of the organic EL element can be improved by quickly deactivating the excitons. In addition, by optimizing the host material surrounding the guest material in the light emitting layer of the organic EL element, the efficiency of excitation energy transfer from the host material to the guest material is improved, and the light emission efficiency of the organic EL element is improved. Can be made. Furthermore, by improving the carrier transportability of the host material, the efficiency of hole / electron injection into the light-emitting layer and the generation of host excitons by recombination of holes / electrons can be increased. Efficiency can be improved.
Thus, in order to improve the light emission efficiency of the organic EL element, the selection of the host material and guest material for the light emitting layer of the organic EL element is extremely important.

  Further, from the viewpoint of durability of the organic EL element, a host material having high film stability is required. Furthermore, from the viewpoint of forming an organic EL element by a wet process, the host material has high film-formability, which has high solubility in an organic solvent and can form a uniform film by applying this solution. Is required.

As a host material in an organic EL element using a phosphorescent material as a guest, N, N′-dicarbazolylbiphenyl (CBP) described in Non-Patent Document 1 and a low-molecular material having a carbazole skeleton described in Patent Document 1 Etc. are known.
However, the organic EL element using these materials has a problem that the light emission efficiency is lowered in a high luminance and high current region. Further, when a film is formed using a solution in which a general low molecular material is dissolved by a wet process, there is a problem that the formed film is crystallized.

As a result of intensive studies, the present inventors have clarified that the above object can be achieved by using a compound in which two carbazole derivatives are linked to spirobifluorene as a material for the light emitting layer.
A compound in which two carbazole derivatives are linked to spirobifluorene has a spirobifluorene that is rigid and has a twisted structure, and thus has high heat resistance and high film stability.
In addition, since this compound has a molecular structure excellent in two carrier transport properties, spirobifluorene and carbazole, the carrier transport property indispensable for driving the organic EL device can be improved.
By using this compound as a host material and adding (doping) a fluorescent material or phosphorescent material as a guest material, it exhibits high luminous efficiency from low current / low luminance region to high current / high luminance region, and film stability It was clarified that an organic EL element excellent in the above can be realized.

In addition, by using this compound as a host material and using a solution in which a fluorescent material or phosphorescent material is mixed as a guest material and dissolved in a solvent, a uniform and excellent thin film can be formed by a solution coating method. It was. As a result, even in an organic EL element prepared by a solution coating method using this solution, an organic EL element exhibiting high luminous efficiency from a low current / low luminance region to a high current / high luminance region and having excellent film stability. Clarified that it can be realized.
Based on the above results, the present invention has been completed.

In order to achieve the above object, the present invention employs the following configuration. That is, the organic EL device of the present invention has a pair of opposing electrodes and a single-layer or multilayer organic thin film layer disposed between the electrodes, and at least one of the organic thin film layers is a light emitting layer. In one organic EL device, the light emitting layer includes a low molecular material represented by the following general formula ( 2) in which two substituted or unsubstituted carbazoles are bonded to a predetermined position of spirobifluorene. It is characterized by being.

In the general formula (2), R _{1 to} R ₁₆ are substituents which may be the same or independent, and are any one of a hydrogen atom, a linear alkyl group, a branched alkyl group and an aryl group. It is.

In the organic EL device of the present invention, the light emitting layer is formed by adding a guest material made of a light emitting material that emits fluorescence or phosphorescence to a host material made of a low molecular compound represented by the general formula ( 2). Features.

  The organic EL device of the present invention is characterized in that the guest material is a phosphorescent metal complex comprising a platinum or iridium atom and a ligand containing an aromatic hydrocarbon.

  The organic EL device of the present invention is characterized in that the phosphorescent metal complex is an iridium complex represented by the following general formula (3) composed of iridium and a ligand phenylpyridine.

In said general formula (3), R < ₁₇ > -R < ₂₄ > is the substituent which may be the same or independent, Comprising: A hydrogen atom, a linear alkyl group, a branched alkyl group, an aryl group, phenyl pyridine Either an aromatic ring fused to a benzene ring or a pyridine ring. L is a ligand other than phenylpyridine. n is an integer of 1 to 3, and m is an integer of 0 to 4.

  The organic EL element of the present invention is characterized in that the pair of electrodes and the organic thin film layer are formed on a flexible substrate.

  The organic EL device of the present invention is characterized in that the organic thin film layer is formed by a solution coating method.

  An organic EL display according to the present invention is an organic EL display in which a plurality of organic EL elements that emit red, green, and blue light are arranged in a lattice to form a plurality of pixels, and the plurality of red, green, and blue At least one of the organic EL elements that emit light is the organic EL element described above.

  The organic EL display according to the present invention is characterized in that each of the plurality of pixels has two organic thin film transistors.

  According to the above configuration, it is possible to provide an organic EL element that exhibits high light emission efficiency from a low current / low luminance region to a high current / high luminance region and is excellent in film stability.

  The organic EL element of the present invention has a pair of opposing electrodes and a single-layer or multilayer organic thin-film layer disposed between the electrodes, and at least one of the organic thin-film layers is a light-emitting layer The light emitting layer includes a low molecular material represented by the above general formula (1) in which two substituted or unsubstituted carbazoles are bonded to any position of spirobifluorene. Organic with improved heat transport and film stability due to having spirobifluorene having a twisted structure, and having two molecular transport structures, spirobifluorene and carbazole. By using this material as a host material and adding (doping) a fluorescent material or phosphorescent material as a guest material, low current and low brightness Showed high luminous efficiency over high current and high luminance region from the pass, we can realize an organic EL device excellent in film stability.

  In the organic EL device of the present invention, a guest material made of a light emitting material that emits fluorescence or phosphorescence is added to a host material made of a low molecular compound whose light emitting layer is represented by the general formula (1) or (2). Therefore, it is possible to realize an organic EL element that exhibits high light emission efficiency from a low current / low luminance region to a high current / high luminance region and has excellent film stability.

  In the organic EL device of the present invention, since the phosphorescent metal complex is an iridium complex represented by the above general formula (3) composed of iridium and the ligand phenylpyridine, it is possible to obtain a high current from a low current / low luminance region. An organic EL element that exhibits high luminous efficiency over a high luminance region and excellent film stability can be realized.

(Embodiment 1)
Hereinafter, the organic EL element which is embodiment of this invention is demonstrated.
FIG. 1 is a schematic view showing an example of an organic EL element according to an embodiment of the present invention.
An organic EL element 10 according to an embodiment of the present invention includes an anode 2, a hole transport layer 3, a light emitting layer 4, a hole blocking layer 5, an electron transport layer 6, and a cathode 7 stacked in this order on a substrate 1. Has been. The hole transport layer 3, the light emitting layer 4, the hole blocking layer 5, and the electron transport layer 6 are organic thin film layers and are configured to be sandwiched between a pair of opposing electrodes 2 and 7. Further, a sealing glass 9 is disposed so as to cover them, and the peripheral edge of the sealing glass 9 and the peripheral edge of the substrate 1 on which the anode 2 is arranged are bonded and sealed to each other by an ultraviolet curable resin 8.

  Although not shown in the drawing, the anode 2 is formed in a plurality of lines when viewed in plan, and the cathode 7 is formed in a plurality of lines orthogonal to the anode 2. Thus, by applying a voltage to the anode 2 and the cathode 7, holes are injected from the anode 2 into the hole transport layer 3 at the intersection of the anode 2 and the cathode 7. The holes are injected into the light emitting layer 4 after moving through the hole transport layer 3. On the other hand, electrons are injected from the cathode 7 into the light emitting layer 4 through the electron transport layer 6 and the hole blocking layer 5. In the light emitting layer 4, the holes and the electrons are recombined to emit light.

<Board>
The substrate 1 is preferably a transparent material. Examples thereof include glass, quartz, and other plastic films.
For example, when a flexible substrate such as a plastic film is used as the substrate 1 and the pair of electrodes 2 and 7 and the organic thin film layers 3, 4, 5 and 6 are formed thereon, the image display unit can be easily formed. It can be set as the flexible organic EL element which can deform | transform.

<Anode>
The anode 2 is preferably a transparent and highly conductive material. For example, a conductive transparent oxide such as indium-tin-oxide (hereinafter, ITO) or indium-zinc-oxide (hereinafter, IZO) can be used.
The anode 2 is formed in a plurality of lines. When forming the anode 2, the anode 2 is formed using a mask, or after the anode 2 is formed on the entire surface, a resist is applied, and a line pattern is formed by an exposure process using a glass mask.

<Hole transport layer>
As a material of the hole transport layer 3, an organic material made of a low-molecular material or a polymer material having a hole transport property can be used.
Examples of the low molecular weight material include benzidine derivatives such as α-NPD, and the film can be formed by a dry process such as a vacuum evaporation method.
For example, when forming a film by a vacuum deposition method, the hole transport layer material is placed in a crucible and set inside the vacuum deposition apparatus so as to face the substrate, and after the pressure inside the vacuum deposition apparatus is reduced, the crucible is By heating, a hole transport layer material is formed on the substrate, and this is used as the hole transport layer.
When element fabrication is performed by a wet process, a hole injection layer may be used instead of the hole transport layer 3. Examples of the hole-injecting polymer material include PEDOT: PSS.

<Light emitting layer>
The light emitting layer 4 has a host-guest structure in which a fluorescent or phosphorescent light emitting low molecular material (host material) is dispersed in a fluorescent or phosphorescent light emitting low molecular material (host material). It is preferable. Thereby, luminous efficiency can be improved. Also, the emission wavelength can be changed.

<Host material>
As the host material, a low molecular material represented by the above general formula (1) in which two substituted or unsubstituted carbazoles are bonded to any position of spirobifluorene is preferable.
In the general formula (1), R _{1 to} R ₁₆ are the same or independent substituents, and are any one of a hydrogen atom, a linear alkyl group, a branched alkyl group, and an aryl group. It is.

A compound in which two carbazole derivatives are linked to spirobifluorene has a spirobifluorene that is rigid and has a twisted structure, and thus has high heat resistance and high film stability.
In addition, since this compound has a molecular structure excellent in two carrier transport properties, spirobifluorene and carbazole, the carrier transport property indispensable for driving the organic EL device can be improved.
Therefore, by using this compound as a host material and adding (doping) a fluorescent material or phosphorescent material as a guest material, the organic EL exhibits high luminous efficiency in a high luminance and high current region and has excellent film stability. An element can be realized.

  Specifically, the low molecular material represented by the general formula (1) is a low molecular material represented by the following chemical structural formulas (1) -1 to (1) -12.

The host material is a low molecular material represented by the above general formula (1), and two substituted or unsubstituted carbazoles are bonded to a predetermined position of spirobifluorene. The low molecular weight material represented by these is preferable.
In the general formula (2), R _{1 to} R ₁₆ are substituents which may be the same or independent, and are any one of a hydrogen atom, a linear alkyl group, a branched alkyl group and an aryl group. It is.
Since carbazole is bonded to the position shown in the general formula (2), the improvement of the stability of the film and the improvement of the charge transport property are more effectively realized.

  Specifically, the low molecular material represented by the general formula (2) is a low molecular material represented by the following chemical structural formulas (2) -1 to (2) -14.

<Guest materials>
As the guest material, a phosphorescent metal complex composed of a platinum or iridium atom and a ligand containing an aromatic hydrocarbon is preferable.
This is because a complex including a platinum or iridium atom and a ligand containing an aromatic hydrocarbon exhibits phosphorescence with high quantum yield.

It is preferable that the phosphorescent metal complex is an iridium complex represented by the following general formula (3) composed of iridium and a ligand phenylpyridine.
In said general formula (3), R < ₁₇ > -R < ₂₄ > is the substituent which may be the same or independent, Comprising: A hydrogen atom, a linear alkyl group, a branched alkyl group, an aryl group, phenyl pyridine Either an aromatic ring fused to a benzene ring or a pyridine ring. L is a ligand other than phenylpyridine. n is an integer of 1 to 3, and m is an integer of 0 to 4.
Among iridium complexes, the iridium complex represented by the general formula (3) exhibits phosphorescence with extremely high quantum efficiency.

Specifically, the low molecular material represented by the general formula (3) is a low molecular material represented by the following chemical structural formulas (3) -1 to (3) -36. In particular, Ir (ppy) ₃ represented by the following chemical structural formula (3) -2 is preferable.

<Light emitting layer forming method by dry process>
For example, when a film is formed by vacuum deposition, a crucible containing a host material consisting of chemical structural formula (2) -1 and a guest material consisting of Ir (ppy) _{3 of} chemical structural formula (3) -2 are added. A crucible is set inside the vacuum vapor deposition apparatus so as to face the substrate, and after the pressure inside the vacuum vapor deposition apparatus is reduced, the two crucibles are heated to form the chemical structural formula (2) -1 on the substrate. A host material composed of Ir and a guest material composed of Ir (ppy) _{3 represented by the} chemical structural formula (3) -2 is co-evaporated to a mass ratio of 94: 6 to form a light-emitting layer 4 having a host-guest structure.

<Light emitting layer forming method by wet process>
For example, in the case of forming a film by a spin coat method, after the substrate on which the hole transport layer 3 is formed is arranged at a predetermined position of the spin coater, the host material represented by the chemical structural formula (2) -1 and the chemical A toluene solution prepared by mixing a guest material composed of Ir (ppy) _{3 represented} by the structural formula (3) -2 with a mass ratio of 94: 6 was applied onto the substrate, and a predetermined rotational speed was applied. Rotate with By drying this, a light emitting layer having a thickness of 40 nm is obtained.

  The thickness of the light emitting layer 4 is preferably 1 nm to 5 μm, more preferably 10 nm to 1 μm, and still more preferably 20 to 200 nm. By setting the film thickness of the light emitting layer 4 within the above range, an optimum voltage can be applied to the light emitting layer 4, and high luminous efficiency can be exhibited in a high luminance / high current region. When the film thickness is too thick, a sufficient voltage cannot be applied and light emission with high luminance cannot be obtained. Conversely, when the film thickness is too thin, the film is easily broken.

<Hole blocking layer>
The hole blocking layer 5 is preferably an organic material that can move electrons easily but can block the movement of holes. Examples thereof include BCP represented by the following chemical structural formula (4).
By providing such a hole blocking layer 5, the density of electrons and holes in the light emitting layer can be improved, and the light emission characteristics of the organic EL element can be improved.

<Electron transport layer>
The electron transport layer 6 is preferably an electron transporting organic material, and examples thereof include Alq represented by the following chemical structural formula (5).
By providing such an electron transport layer 6, the density of electrons and holes in the light emitting layer can be improved, and the light emitting characteristics of the organic EL element can be improved.

<Cathode>
As a material of the cathode 7, a metal having a low work function is preferable. This is because by using a metal having a low work function, an electron injection barrier from the cathode 7 to the organic layer can be lowered, and electrons can be easily injected from the cathode 7. Examples of the metal having a low work function include alkali metals such as Li and Cs, and alkaline earth metals such as Ca, Ba, and Mg.
However, since the metal having a low work function easily reacts with oxygen or moisture in the air, it is formed as an alloy containing the metal such as MgAg or a compound containing the metal such as LiF, LiO ₂ , or CsF. It is preferable. Alternatively, it is desirable to stack a metal having a high work function such as Al or Au on the alkali metal or alkaline earth metal.

  The substrate on which each organic thin film layer is formed is attached to a predetermined position in the chamber of the vacuum evaporator, and a metal mask provided with a plurality of line-shaped openings is arranged on the surface of the substrate to reduce the pressure in the chamber. Then, a metal material is vacuum-deposited to form a plurality of line-shaped cathodes 7 made of the metal material on the substrate.

(Embodiment 2)
Instead of the hole transport layer 3, an element structure using a hole injection layer may be used. As a material for the hole injection layer, an organic material made of a low-molecular material or a high-molecular material having a hole-injecting property can be used.
Examples of the hole-injecting polymer material include PEDOT: PSS, and can be formed by a wet process such as a spin coating method or an inkjet method. PEDOT represents poly (3,4-ethylenedioxythiophene), and PSS represents polysulfostyrene.

  For example, in the case of forming a film by an ink jet method, a hole injection layer material such as a conductive polymer material such as PEDOT: PSS, polyaniline, polythiophene, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl is used. Prepare a hole injection layer solution by mixing it with a solvent such as sulfoxide, N-methyl-2-pyrrolidone, ethylene glycol, diethylene glycol, glycerin, etc., discharge it onto the substrate, dry it and inject holes. Layer.

Furthermore, each layer of the organic thin film layer may be arbitrarily selected to form an element. For example, the organic thin film layer may be an element structure having only a light emitting layer.
Moreover, the formation method of an organic thin film layer is not specifically limited, Methods, such as a vacuum evaporation method, an electron beam method, sputtering, a molecular lamination method, a spin coat method, an inkjet method, a printing method, can be used. From the viewpoint of device characteristics and production, vacuum deposition, spin coating, ink jet, and printing are particularly preferable. In particular, considering the application of organic EL elements to future large screens and high-definition displays, a wet process using a solution such as a spin coating method, an inkjet method, or a printing method is preferable.

(Embodiment 3)
First, one side of a rectangular glass substrate is partitioned into a grid pattern to form metal wiring for signal lines and the like, and a plurality of pixel regions with transparent electrodes for organic EL elements are formed in a grid pattern To do. In addition, organic thin film transistors are formed so as to be arranged in two in each pixel region by a known method.
FIG. 2 is a diagram illustrating a configuration example of one pixel cell in an active drive organic EL display, and FIG. 2A is a conceptual diagram illustrating a circuit of one pixel cell of a display using one organic EL element. FIG. 2B is a layout diagram in plan view of the circuit of FIG.
As shown in FIG. 2, the organic EL elements arranged as pixels in a matrix form are driven at the intersections of the plurality of scanning lines and the plurality of signal lines, so that the organic EL elements are required to emit light. Organic TFTs are used for a drive TFT (Dr) switch that causes a large current to flow from a power supply line, and a switch TFT that accumulates and discharges charge with respect to a storage capacitor that holds a voltage for turning on the drive switch.

Next, using a vacuum deposition method, organic EL elements that emit red light, green light, and blue light were formed in each pixel region, and these were used as pixels. Specifically, the compound represented by the chemical structural formula (2) -1 is used as the host material of the red light emitting pixel, and the iridium complex represented by the chemical structural formula (3) -14 is used as the guest material. A host material represented by a chemical structural formula (2) -1 is used as a host material of a pixel emitting green light, and a guest material composed of Ir (ppy) ₃ represented by a chemical structural formula (3) -2 is used as the guest material. The compound represented by the chemical structural formula (2) -1 is used as a host material of a blue light emitting pixel, and the iridium complex represented by the chemical structural formula (3) -36 is used as the guest material. A full-color organic EL display is manufactured by forming organic EL elements on the substrate so that the pixels are arranged in a grid pattern. Here, the organic EL element that emits green light is the organic EL element of the first embodiment.
By sending a predetermined video signal to the organic EL display, it is possible to check a full color moving image.

  An organic EL element 10 according to an embodiment of the present invention includes a pair of opposed electrodes 2 and 7 and single or multilayer organic thin film layers 3, 4, 5, and 6 disposed between the electrodes 2 and 7. An organic EL device in which at least one of the organic thin film layers 3, 4, 5, and 6 is the light emitting layer 4, and the light emitting layer 4 has 2 substituted or unsubstituted carbazoles at any position of spirobifluorene. The low molecular weight material represented by the general formula (1) that is bonded to each other is included, so that the spirobifluorene having a rigid and twisted structure has high heat resistance and high film stability. Bifluorene and carbazole have two molecular structures with excellent carrier transport properties, so that an organic EL element with improved carrier transport properties can be obtained. Using this material as a host material, a fluorescent material or a phosphorescent material can be used. By adding thereto (dope) as the material, for high current and high luminance region from the low current, low luminance region shows high luminous efficiency, can realize an organic EL device excellent in film stability.

  An organic EL device 10 according to an embodiment of the present invention is a low molecular material represented by the above general formula (1) in the light emitting layer 4, and 2 substituted or unsubstituted carbazoles are present at predetermined positions of spirobifluorene. The low molecular weight material represented by the above general formula (2) is included, so that high luminous efficiency is exhibited from the low current / low luminance region to the high current / high luminance region, and the film stability is improved. An excellent organic EL element can be realized.

  In the organic EL device 10 according to an embodiment of the present invention, the light emitting layer 4 is made of a light emitting material that emits fluorescence or phosphorescence to a host material made of the low molecular compound represented by the general formula (1) or (2). Since the structure is formed by adding a guest material, an organic EL element exhibiting high luminous efficiency from a low current / low luminance region to a high current / high luminance region and having excellent film stability can be realized.

  The organic EL device 10 according to the embodiment of the present invention has a structure in which the guest material is a phosphorescent metal complex composed of platinum or an iridium atom and a ligand containing an aromatic hydrocarbon. An organic EL element exhibiting high luminous efficiency over a high current / high luminance region and excellent in film stability can be realized.

  The organic EL device 10 according to the embodiment of the present invention has a configuration in which the phosphorescent metal complex is an iridium complex represented by the above general formula (3) composed of iridium and a ligand phenylpyridine. An organic EL element exhibiting high luminous efficiency from the luminance region to the high current / high luminance region and having excellent film stability can be realized.

  Since the organic EL element 10 according to the embodiment of the present invention has a configuration in which a pair of electrodes 2 and 7 and an organic thin film layer are formed on a flexible substrate, a low current / low luminance region to a high current / high luminance region It is possible to realize a flexible organic EL element that exhibits high luminous efficiency over a wide range and excellent in film stability.

  The organic EL element 10 according to the embodiment of the present invention has a configuration in which the organic thin film layers 3, 4, 5, and 6 are formed by a solution coating method. A large-screen display having an organic EL element exhibiting luminous efficiency and excellent film stability can be easily realized.

  An organic EL display according to an embodiment of the present invention is an organic EL display in which a plurality of organic EL elements that emit red, green, and blue light are arranged in a lattice to form a plurality of pixels. Since at least one of the organic EL elements exhibiting green and blue light emission is the organic EL element described above, the film exhibits high light emission efficiency from the low current / low luminance region to the high current / high luminance region, and the film This can be realized in an organic EL display including an organic EL element having excellent stability.

The organic EL display which is an embodiment of the present invention has a structure in which each of the plurality of pixels has two organic thin film transistors, and thus exhibits high luminous efficiency from a low current / low luminance region to a high current / high luminance region, and is stable in film This can be realized as an organic EL display including an organic EL element having excellent properties.
Hereinafter, the present invention will be specifically described based on examples. However, the present invention is not limited only to these examples.

Example 1
(Production of organic EL element)
The organic EL device of the present invention having the structure shown in FIG. 1 was produced as follows. First, an anode made of ITO was formed on a 25 × 35 mm square glass substrate, and this was patterned into a plurality of lines. Next, a hole transport material made of α-NPD was formed on the anode by a vacuum deposition method to form a hole transport layer.
Next, a guest material composed of a host material represented by the chemical structural formula (2) -1 and an Ir (ppy) ₃ represented by the chemical structural formula (3) -2 is formed on the hole transport layer in a mass ratio. The light-emitting layer having a host-guest structure was formed by co-evaporation to be 94: 6. Next, a hole blocking material made of BCP was formed on the light emitting layer by a vacuum deposition method to form a 10 nm thick hole blocking layer.
Next, an electron transport material made of Alq was deposited on the hole blocking layer by a vacuum deposition method to form an electron transport layer having a thickness of 30 nm. Next, using a metal mask, a LiF film having a thickness of 0.5 nm was formed on the electron transport layer, and then an Al film having a thickness of 100 nm was formed to form a plurality of line-shaped cathodes.
Finally, in a glove box filled with nitrogen gas, an ultraviolet curable resin is applied to the peripheral edge of the sealing glass, and then the organic layer is bonded to the peripheral edge of the substrate for sealing. It was.

<Evaluation of element characteristics of organic EL element>
A voltage was applied so as to be positive on the ITO anode side of the organic EL element and negative on the aluminum cathode side, current-voltage-luminance characteristics were measured, and an emission spectrum was observed. From the emission spectrum, green light emission from the guest compound having an emission peak of 516 nm was obtained. When the luminance was 100 cd / m ² , the voltage was 5.2 V, the external quantum efficiency was 7.4%, and the power efficiency was 16 lm / W. When the luminance was 10,000 cd / m ² , the voltage was 9.9 V, the external quantum efficiency was 7.6%, and the power efficiency was 8.8 lm / W.

(Example 2)
(Production of organic EL element)
The organic EL of Example 2 was the same as Example 1 except that the following hole injection layer was used instead of the hole transport layer and that the light emitting layer was formed by a wet process as follows. An element was produced.
The hole injection layer was formed by spin coating PEDOT: PSS (HC Starck, HC Starck, Baytron P CH8000, solid content 3%, hereinafter, PEDOT / PSS mixed aqueous solution). And dried at 180 ° C. to form a film thickness of 35 nm. Next, in the light emitting layer, the mass ratio of the host material represented by the chemical structural formula (2) -1 and the guest material composed of Ir (ppy) ₃ represented by the chemical structural formula (3) -2 is 94: The film thickness was adjusted to be 6 and a film thickness of 40 nm was formed by spin coating using a mixed toluene solution.

<Evaluation of element characteristics of organic EL element>
A voltage was applied so as to be positive on the ITO anode side of the organic EL element and negative on the aluminum cathode side, current-voltage-luminance characteristics were measured, and an emission spectrum was observed. From the emission spectrum, green light emission from the guest material having an emission peak of 516 nm was obtained. When the luminance was 100 cd / m ² , the voltage was 6.5 V, the external quantum efficiency was 4.2%, and the power efficiency was 7.5 lm / W. When the luminance was 10,000 cd / m ² , the voltage was 12.0 V, the external quantum efficiency was 4.9%, and the power efficiency was 4.6 lm / W.

(Comparative Example 1)
(Production of organic EL element)
The organic EL of Comparative Example 1 is the same as Example 1 except that N, N′-dicarbazolylbiphenyl (CBP) represented by the following chemical structural formula (6) is used as the host material of the light emitting layer. An element was produced.

<Evaluation of element characteristics of organic EL element>
A voltage was applied so as to be positive on the ITO anode side of the organic EL element and negative on the aluminum cathode side, current-voltage-luminance characteristics were measured, and an emission spectrum was observed. From the emission spectrum, green light emission from the guest compound having an emission peak of 516 nm was obtained. When the luminance was 100 cd / m ² , the voltage was 4.6 V, the external quantum efficiency was 11%, and the power efficiency was 28 lm / W. When the luminance was 10,000 cd / m ² , the voltage was 9.1 V, the external quantum efficiency was 6.5%, and the power efficiency was 7.9 lm / W.

Comparing Example 1 and Comparative Example 1, the device of Example 1 is slightly less efficient than the device of Comparative Example at a luminance of 100 cd / m ² , but in the state of high luminance of 10000 cd / m ² , The external light emission quantum efficiency and power efficiency improved compared with the device. This is considered due to the high stability of the host material used in Example 1.
From the results of Example 2, it was found that the host material used in Example 2 can obtain high-efficiency light emission even by a coating method from a solution.

(Example 3)
(Production of organic EL element)
Before forming a film of a hole transport layer, it was formed a hole injection layer, as well as the Ir _{(piq) 3} represented by Ir _(ppy) instead chemical structural formula of ₃ (3) -14 guests An organic EL device of Example 3 was produced in the same manner as Example 1 except that it was used as a material.

<Evaluation of organic EL element characteristics>
A voltage was applied so as to be positive on the ITO anode side of the organic EL element and negative on the aluminum cathode side, current-voltage-luminance characteristics were measured, and an emission spectrum was observed. From the emission spectrum, red emission from the guest material having an emission peak of 627 nm was obtained. When the luminance was 100 cd / m ² , the voltage was 6.4 V, the external quantum efficiency was 11%, and the power efficiency was 4.0 lm / W. When the luminance was 10,000 cd / m ² , the voltage was 12.5 V, the external quantum efficiency was 6.8%, and the power efficiency was 1.3 lm / W.

(Comparative Example 2)
An organic EL device of Comparative Example 2 was produced in the same manner as in Example 3 except that CBP was used as the host material for the light emitting layer.

<Evaluation of organic EL element characteristics>
A voltage was applied so as to be positive on the ITO anode side of the organic EL element and negative on the aluminum cathode side, current-voltage-luminance characteristics were measured, and an emission spectrum was observed. From the emission spectrum, red emission from the guest material having an emission peak of 627 nm was obtained. When the luminance was 100 cd / m ² , the voltage was 5.9 V, the external quantum efficiency was 8.1%, and the power efficiency was 3.1 lm / W. When the luminance was 10,000 cd / m ² , the voltage was 13.8 V, the external quantum efficiency was 5.2%, and the power efficiency was 0.88 lm / W.

Comparing Comparative Example 2 and Example 3, the device of Example ^3, 100 cd / m 2, 10000 cd / ^{m 2,} in any of the luminance, external quantum efficiency and power efficiency was improved than the element of Comparative Example 2 . This is presumably because the host material used in Example 3 has a large triplet excitation energy confinement effect and high stability with respect to the red material.
The above conditions and results are summarized in Tables 1 and 2.

  The present invention relates to an organic EL element, and may be used in a light emitting element, an illumination device, and a display industry using the organic EL element. This organic EL element can be applied to various devices and products that require light emission with high brightness and high efficiency. Display elements, displays, backlights, electrophotography, illumination light sources, exposure light sources, signs, It can be suitably used in fields such as signboards and interiors. In particular, it can be suitably used for a flat panel display with high energy saving and high visibility.

It is a figure explaining an example of the organic EL element which is embodiment of this invention. It is a figure which shows the structural example of 1 pixel cell in the organic EL display of active drive.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Anode, 3 ... Hole transport layer, 4 ... Light emitting layer, 5 ... Hole blocking layer, 6 ... Electron transport layer, 7 ... Cathode, 8 ... UV curable resin, 9 ... Sealing glass substrate, 10: Organic EL element.

Claims (8)

An organic EL element having a pair of opposing electrodes and a single-layer or multilayer organic thin film layer disposed between the electrodes, wherein at least one of the organic thin film layers is a light-emitting layer,
The organic EL, wherein the light emitting layer contains a low molecular material represented by the following general formula ( 2 ) in which two substituted or unsubstituted carbazoles are bonded to a predetermined position of spirobifluorene. element.

In the general formula (2), R _{1 to} R ₁₆ are substituents which may be the same or independent, and are any one of a hydrogen atom, a linear alkyl group, a branched alkyl group and an aryl group. It is. The light-emitting layer, the host material made of a low molecular material represented by the above general formula (2), according to claim 1, characterized by comprising adding a guest material a light emitting material that emits fluorescence or phosphorescence Organic EL element. The organic EL device according to claim 2 , wherein the guest material is a phosphorescent metal complex composed of a platinum or iridium atom and a ligand containing an aromatic hydrocarbon. 4. The organic EL device according to claim 3 , wherein the phosphorescent metal complex is an iridium complex represented by the following general formula (3) composed of iridium and a ligand phenylpyridine.

In said general formula (3), R < ₁₇ > -R < ₂₄ > is the substituent which may be the same or independent, Comprising: A hydrogen atom, a linear alkyl group, a branched alkyl group, an aryl group, phenyl pyridine Either an aromatic ring fused to a benzene ring or a pyridine ring. L is a ligand other than phenylpyridine. n is an integer of 1 to 3, and m is an integer of 0 to 4. The organic EL element according to any one of claims 1 to 4 , wherein the pair of electrodes and the organic thin film layer are formed on a flexible substrate. The organic EL device according to any one of claims 1 to 5, characterized in that the organic thin film layer is formed by a solution coating method. An organic EL display in which a plurality of organic EL elements that emit red, green, and blue light are arranged in a lattice to form a plurality of pixels,
Wherein the plurality of red, at least any one of an organic EL element which emits green and blue light emitting organic EL display, which is a organic EL device according to any one of claims 1-6. The organic EL display according to claim 7 , wherein each of the plurality of pixels includes two organic thin film transistors.

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