JP6781534B2 - Organic electroluminescence elements, display devices and lighting devices - Google Patents

Description

The present invention, organic electroluminescent element, a display device and a lighting device organic electroluminescent device is provided for it. More specifically, the present invention relates to an organic electroluminescence device having improved luminous efficiency and the like.

Organic EL devices (also referred to as "organic electroluminescent devices") that utilize the electroluminescence of organic materials (hereinafter abbreviated as "EL") have already been put into practical use as a new light emitting system that enables planar light emission. It is a technology that has been used. Organic EL elements have recently been applied not only to electronic displays but also to lighting equipment, and their development is expected.

There are two types of light emission methods for organic EL: "phosphorescence emission" that emits light when returning from the excited triplet state to the ground state, and "fluorescence emission" that emits light when returning from the excited singlet state to the ground state. There is.

When an electric field is applied to the organic EL element, holes and electrons are injected from the anode and the cathode, respectively, and recombine in the light emitting layer to generate excitons. At this time, singlet excitons and triplet excitons are generated at a ratio of 25%: 75%, so phosphorescence emission using triplet excitons has a theoretically higher internal quantum than fluorescence emission. It is known that efficiency can be obtained.

However, in order to actually obtain high quantum efficiency in the phosphorescence method, it is necessary to use a complex using a rare metal such as iridium or platinum as the central metal, and in the future it is necessary to use a rare metal reserve or the metal itself. There is concern that price will be a major industrial issue.

On the other hand, various developments have been made to improve the luminous efficiency of the fluorescent light emitting type, and new movements have emerged in recent years.

For example, in Patent Document 1, a phenomenon in which singlet excitons are generated by collision of two triplet excitons (Triplet-Triplet Animation: hereinafter, abbreviated as “TTA” as appropriate. Further, Triplet-Triplet Fusion: “TTF”. (Also referred to as)), a technique for efficiently causing TTA to improve the efficiency of the fluorescent element is disclosed. Although the luminous efficiency of the fluorescent light emitting material is improved to 2 to 3 times that of the conventional fluorescent light emitting material by this technology, the theoretical singlet excitation element generation efficiency in TTA is only about 40%, so that the phosphorescent light emission is still performed. It has a problem of high luminous efficiency.

Further, in recent years, a phenomenon utilizing a phenomenon in which reverse intersystem crossing (Reverse Intersystem Crossing: hereinafter abbreviated as "RISC" as appropriate) occurs from a triplet exciton to a singlet exciton (thermoactive delayed fluorescence ("" Also referred to as "thermally excited delayed fluorescence": Thermally Activated Fluorescence: Hereinafter, abbreviated as "TADF" as appropriate), and the possibility of using it for an organic EL element has been reported (for example). (See Patent Document 2, Non-Patent Document 1, and Non-Patent Document 2.). When the delayed fluorescence by this TADF mechanism is used, 100% internal quantum, which is theoretically equivalent to phosphorus light emission, is obtained even in fluorescence emission by electric field excitation. Efficiency is possible.

In order for the TADF phenomenon to occur, it is necessary that 75% triplet excitons generated by electric field excitation at room temperature or the temperature of the light emitting layer in the light emitting element undergo reverse intersystem crossing to singlet excitons. Furthermore, 100% internal quantum efficiency is theoretically possible because the singlet excitons generated by the inverse intersystem crossing fluoresce like the 25% singlet excitons generated by the direct excitation. In order for this inverse intersystem crossing to occur, the absolute value of the difference between the lowest excited singlet energy level (S ₁ ) and the lowest excited triplet energy level (T ₁ ) (hereinafter referred to as ΔEst) is extremely small. Is essential.

Further, it is known that when a compound exhibiting TADF property is included in the light emitting layer as a third component (assist dopant) in the light emitting layer composed of a host compound and a light emitting compound, it is effective in exhibiting high luminous efficiency ( See Non-Patent Document 3). By generating 25% singlet excitons and 75% triplet excitons on the assist dopant by field excitation, the triplet excitons generate singlet excitons with inverse intersystem crossing (RISC). be able to. The energy of the singlet exciton is transferred to the luminescent compound, and the luminescent compound can emit light. Therefore, it is theoretically possible to make the luminescent compound emit light by using 100% exciton energy, and high luminous efficiency is exhibited.

In an organic EL device using phosphorescence, TTA, or TADF as a light emitting layer, deterioration suppression from triplet excitons is suppressed not only in the light emitting layer but also in a charge transfer layer other than the light emitting layer (hereinafter, abbreviated as peripheral layer). Is known to be important for the development of high luminescence efficiency. For suppressing deterioration of triplet excitons, it is necessary to design a T ₁ level position near layer material to a higher energy level than the T ₁ level of the light emitting material.

However, even if a material having a high T ₁ level is used in the peripheral layer, it is difficult to completely confine triplet excitons in the light emitting layer, which is one of the factors that reduce the luminous efficiency. For example, FIG. 1A is a schematic diagram showing an energy diagram of a peripheral layer material and a light emitting material. As shown in FIG. 1A, it includes the process of deactivation after excitons T ₁ level position near layer material from the S ₁ level of the light emitting material is moved, the cause of reducing the luminous efficiency of the fluorescent or phosphorescent It has become. Therefore, a new method for suppressing triplet exciton deterioration is eagerly desired.

International Publication No. 2010/134350 Japanese Unexamined Patent Publication No. 2013-116975

H. Uoyama, et al. , Nature, 2012, 492, 234-238 Q. Zhang et al. , Nature, Photonics, 2014, 8, 326-332 H. Nakanоtani, et al. , Nature Communication, 2014, 5, 4016-4022

The present invention has been made in view of the above problems and situations, and a solution to the present invention is to provide a new organic electroluminescence device having high luminous efficiency. Another object is to provide a display device and an illumination apparatus equivalent organic electroluminescent device is provided.

As a result of investigating the causes of the above problems in order to solve the above problems, the present inventor has found that the absolute value of the difference between the lowest excited singlet energy level and the lowest excited triplet energy level in the charge transfer layer is 0. We have found that the light emission efficiency can be improved by containing a compound having a specific structure of 5 eV or less, and have arrived at the present invention.

That is, the above problem according to the present invention is solved by the following means.

1. 1. As at least a charge transport layer between an anode and a cathode an organic electroluminescence device having an electron-transporting layer, the electron transporting layer contains a π-conjugated compound having a structure represented by the following general formula (1) An organic electroluminescence element, wherein the absolute value (ΔEst) of the difference between the lowest excited singlet energy level and the lowest excited triplet energy level of the π-conjugated compound is 0.5 eV or less.

２．前記Ｂ及びＣは、各々独立に、それぞれ置換されていてもよい、ベンゼン環、ナフタレン環、インデン環、ベンゾシロール環、インドール環、ベンゾフラン環、ベンゾチオフェン環、チエノチオフェン環、フェナントレン環、フルオレン環、ジベンゾシロール環、ジベンゾボロール環、カルバゾール環、ジベンゾフラン環又はジベンゾチオフェン環を表すことを特徴とする第１項に記載の有機エレクトロルミネッセンス素子。 (In the formula, A represents a group having a ring structure, A represents an aryl group substituted with an electron-withdrawing group, or a heteroaryl group optionally substituted. B and C represent a monocyclic group or a heteroaryl group. Represents an aryl ring or a heteroaryl ring, each of which is composed of a fused ring structure of up to 3 rings and may be substituted independently of each. X is O, S, N-R ¹ , C-R ² (R). ³ ), Si-R ⁴ (R ⁵ ), B-R ⁶ or single bond. R ^{1 to} R ⁶ each independently have a hydrogen atom, which may be substituted alkyl group, aryl group or Represents a heteroaryl group , except for the compounds represented by T-9 and T-19 below. )

2. The B and C may be independently substituted, respectively. The organic electroluminescence element according to item 1, wherein the organic electroluminescence element represents a dibenzosilol ring, a dibenzoborol ring, a carbazole ring, a dibenzofuran ring or a dibenzothiophene ring.

3. 3. The π-conjugated compound having a structure represented by the general formula (1) is a π-conjugated compound having a structure represented by any of the following general formulas (2) to (15). The organic electroluminescence device according to the first or second paragraph.

(In the formula, A and X are synonymous with A and X in the general formula (1). Y is O, S, N-R ⁷ , C-R ⁸ (R ⁹ ), Si-R ¹⁰ (R). ¹¹ ), B-R ¹² or CH = CH. R ^{7 to} R ¹² each independently represent a hydrogen atom, which may be substituted, an alkyl group, an aryl group or a heteroaryl group.)
4. The ring structure A according to the general formulas (2) to (15) is substituted with an aryl ring having 6 to 20 carbon atoms and 1 to 5 fluorine atoms substituted with 1 to 5 cyano groups. Aryl rings having 6 to 20 carbon atoms, aryl rings having 6 to 20 carbon atoms substituted with 1 to 5 fluoroalkyl groups, benzene rings substituted with optionally substituted nitrogen-containing aromatic rings, or The organic electroluminescence element according to item 3, wherein the nitrogen-containing aromatic ring may be substituted.

5. The organic electroluminescence device has a light emitting layer, and a π-conjugated compound having a structure represented by the general formula (1) is contained in the electron transport layer adjacent to the light emitting layer. The organic electroluminescence device according to any one of items 1 to 4.

6 . A display device comprising the organic electroluminescence device according to any one of items 1 to 5.

7 . A lighting device comprising the organic electroluminescence device according to any one of items 1 to 5.

By the above means of the present invention, it is possible to provide a new organic electroluminescence device that has realized high luminous efficiency. Further, it is possible to provide a display device and an illumination apparatus equivalent organic electroluminescent device is provided.

Although the mechanism of expression or mechanism of action of the effects of the present invention has not been clarified, it is inferred as follows.

In the present invention, the structure is represented by the general formula (1), and the absolute value (ΔEst) of the difference between the lowest excited singlet energy level and the lowest excited triplet energy level is 0.5 eV or less. This is effective in the case of an organic electroluminescence device containing a conjugated compound in the charge transfer layer.

For example, a case where the π-conjugated compound according to the present invention is used in the peripheral layer adjacent to the light emitting layer will be described. In the prior art, the triplet excitons leaked from the light emitting layer to the peripheral layer were dominated by deactivation in the non-radiative deactivation process (see FIG. 1A). On the other hand, singlet excitons can be generated by causing reverse intersystem crossing (RISC) in the peripheral layer containing the π-conjugated compound used in the present invention as the peripheral layer material (see FIG. 1B). Furthermore, the generated singlet excitons return to the light emitting layer by energy transfer, so that they can contribute to light emission again. In the present invention, by regenerating triplet excitons in the peripheral layer into singlet excitons in the light emitting layer, which was not possible with the prior art, higher luminous efficiency is achieved as compared with the conventional organic electroluminescence element. It is thought that it can be realized.

The layer in which the π-conjugated compound according to the present invention is used is not limited to the peripheral layer adjacent to the light emitting layer, and can be used for all layers in which charges move.

Schematic diagram showing energy diagrams of peripheral layer material and luminescent material Schematic diagram showing energy diagrams of peripheral layer materials and luminescent materials using π-conjugated compounds Schematic diagram showing an energy diagram when a π-conjugated compound functions as an assist dopant in the light emitting layer. Schematic diagram showing an energy diagram when the π-conjugated compound in the light emitting layer functions as a host compound. Schematic diagram showing an example of a display device composed of an organic EL element Schematic diagram of a display device using the active matrix method Schematic diagram showing a pixel circuit Schematic diagram of a display device using the passive matrix method Schematic diagram of the lighting device Cross-sectional view of the lighting device

The organic electroluminescence device of the present invention is an organic electroluminescent device having an electron-transporting layer as at least a charge transport layer between an anode and a cathode, the electron transport layer is represented by the above general formula (1) Structure It is characterized in that it contains a π-conjugated compound having a π-conjugated system compound, and the absolute value of the difference between the lowest excited singlet energy level and the lowest excited triplet energy level of the π-conjugated system compound is 0.5 eV or less. To do. This feature is a technical feature common to the inventions according to each claim.

In an embodiment of the present invention, from the viewpoint of exhibiting the effect of the present invention, the B and C may be independently substituted, respectively, a benzene ring, a naphthalene ring, an inden ring, a benzocilol ring, an indole ring, and the like. It preferably represents a benzofuran ring, a benzothiophene ring, a thienothiophene ring, a phenanthrene ring, a fluorene ring, a dibenzosilol ring, a dibenzoborol ring, a carbazole ring, a dibenzofuran ring or a dibenzothiophene ring.

Further, the π-conjugated compound having the structure represented by the general formula (1) is a π-conjugated compound having the structure represented by any of the general formulas (2) to (15). It is preferable from the viewpoint of the occurrence of the inverse intersystem crossing phenomenon.

Further, in the present invention, the ring structure A described in the general formulas (1) to (15) is an aryl ring having 6 to 20 carbon atoms in which 1 to 5 cyano groups are substituted, and 1 to 5 aryl rings. Aryl ring having 6 to 20 carbon atoms substituted with a fluorine atom, an aryl ring having 6 to 20 carbon atoms substituted with 1 to 5 fluoroalkyl groups, and a nitrogen-containing aromatic ring optionally substituted. It is preferable to represent a substituted benzene ring or a optionally substituted nitrogen-containing aromatic ring from the viewpoint of exhibiting the effect of the present invention.

In an embodiment of the present invention, the organic electroluminescence device has a light emitting layer, and a π-conjugated compound having a structure represented by the general formula (1) is applied to the charge transfer layer adjacent to the light emitting layer. It is preferable that it is contained from the viewpoint of high luminous efficiency.

Further, in the present invention, the organic electroluminescence element has a light emitting layer, and the light emitting layer has a π-conjugated compound having a structure represented by the general formula (1), a fluorescent light emitting compound, and phosphorescence. It preferably contains at least one of the luminescent compounds. As a result, the effect of increasing the luminous efficiency can be obtained. Further, the light emitting layer may contain a π-conjugated compound having a structure represented by the general formula (1), at least one of a fluorescent compound and a phosphorescent compound, and a host compound. preferable.

Further, it can be used as an organic electroluminescence device material containing a π-conjugated compound having a structure represented by the general formula (1) and a charge-transfer thin film containing the π-conjugated compound. Further, the organic EL element of the present invention can be suitably provided in a lighting device and a display device.

Hereinafter, the present invention, its constituent elements, and modes and modes for carrying out the present invention will be described in detail. In the present application, "~" is used to mean that the numerical values described before and after the value are included as the lower limit value and the upper limit value.

Before going into this paper, the light emitting method and light emitting material of the organic EL related to the technical idea of the present invention will be described.

<Light emission method of organic EL>
There are two types of light emission methods for organic EL: "phosphorescence emission" that emits light when returning from the excited triplet state to the ground state, and "fluorescence emission" that emits light when returning from the excited singlet state to the ground state. is there.

When excited by an electric field such as an organic EL, triplet excitators are generated with a 75% probability and singlet excitors are generated with a 25% probability, so phosphorescence emission is more efficient than fluorescence emission. It is an excellent method to realize low power consumption.

On the other hand, even in fluorescence emission, triplet exciters, which are normally generated with a 75% probability and whose energy of the exciter is normally only heat due to non-radiation deactivation, are present at high density. A method using a TTA (Triplet-Triplet Annihilation, or Triplet-Triplet Fusion: abbreviated as "TTF") mechanism that generates one singlet-excited element from two triplet-excited states to improve light emission efficiency It has been found.

Furthermore, in recent years, by reducing the energy gap between the excited singlet state and the excited triplet state by the discovery of Adachi et al., Excitation with a low energy level due to Joule heat during light emission and / or the ambient temperature at which the light emitting element is placed. A phenomenon in which an inverse cross between the triplet state and the excited singlet state occurs, and as a result, fluorescence emission close to 100% is possible (also referred to as thermal excitation type delayed fluorescence or thermal excitation type delayed fluorescence: "TADF"). Fluorescent substances that make this possible have been found (see, for example, Non-Patent Document 1 and the like).

<Phosphorescent compound>
As mentioned above, phosphorus light emission is theoretically three times more advantageous than fluorescence emission in terms of emission efficiency, but energy deactivation (= phosphorus light emission) from the excited triplet state to the singlet base state is prohibited. Since it is a transition and the intersystem crossing from the excited singlet state to the excited triplet state is also a forbidden transition, its velocity constant is usually small. That is, since the transition is unlikely to occur, the exciton lifetime becomes long on the order of milliseconds to seconds, and it is difficult to obtain desired light emission.

However, when a complex using a heavy metal such as iridium or platinum emits light, the rate constant of the forbidden transition increases by 3 orders of magnitude or more due to the heavy atom effect of the central metal, and depending on the selection of the ligand, 100 It is also possible to obtain a phosphorus photon yield of%.

However, in order to obtain such ideal luminescence, it is necessary to use precious metals such as iridium, palladium, and platinum, which are rare metals, so-called white metals, and when they are used in large quantities, their reserves and their reserves The price of the metal itself becomes a major industrial problem.

<Fluorescent compound>
A general fluorescent compound does not particularly need to be a heavy metal complex like a phosphorescent compound, and is a so-called organic compound composed of a combination of general elements such as carbon, oxygen, nitrogen and hydrogen. In addition, other non-metal elements such as phosphorus, sulfur, and silicon can be used, and complexes of typical metals such as aluminum and zinc can also be used, so that the variety can be said to be almost infinite.

However, since only 25% of excitons can be applied to light emission with a conventional fluorescent compound as described above, high-efficiency light emission such as phosphorescence light emission cannot be expected.

<Delayed fluorescent compound>
[Excited triplet-triplet annihilation (TTA) delayed fluorescent compound]
A light emitting method using delayed fluorescence has been introduced to solve the problems of fluorescent compounds. The TTA method originating from collisions between triplet excitons can be described by the following general formula. That is, there is an advantage that a part of triplet excitons, in which the exciton energy is conventionally converted only into heat by non-radiation deactivation, can cross the singlet excitons that can contribute to light emission. Even in an actual organic EL element, it is possible to obtain an external extraction quantum efficiency about twice that of a conventional fluorescent light emitting element.

General formula: T ^* + T ^* → S ^* + S
(In the equation, T ^* represents a triple term exciter, S ^* represents a single term exciter, and S represents a base state molecule.)
However, as can be seen from the above equation, since only one singlet exciton that can be used for light emission is generated from the two triplet excitons, it is not possible in principle to obtain 100% internal quantum efficiency by this method.

[Thermal activated delayed fluorescence (TADF) compound]
The TADF method, which is another high-efficiency fluorescence emission method, is a method that can solve the problems of TTA.

Fluorescent compounds have the advantage of being able to design an infinite number of molecules as described above. That is, among the molecularly designed compounds, there are compounds in which the energy level differences between the excited triplet state and the excited singlet state are extremely close to each other.

Although such a compound does not have a heavy atom in the molecule, an intersystem crossing from an excited triplet state to an excited singlet state, which cannot normally occur due to a small ΔEst, occurs. Furthermore, since the rate constant of deactivation (= fluorescence emission) from the excited singlet state to the ground state is extremely large, the triplet exciter itself is thermally deactivated to the ground state (non-radiation deactivation). It is more rhythmically advantageous to return to the ground state while emitting fluorescence via the excited singlet state. Therefore, TADF can theoretically emit 100% fluorescence.

<Molecular design concept for ΔEst>
The molecular design for reducing the above ΔEst will be described.

In principle, in order to reduce ΔEst, it is most effective to reduce the spatial overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) in the molecule. Is.

It is generally known that HOMO is distributed in an electron donating site and LUMO is distributed in an electron attracting site in the electron orbit of a molecule. By introducing an electron donating and electron attracting skeleton into the molecule, HOMO is distributed. And the position where LUMO exists can be moved away.

For example, in Applied Physics Vol. 82, No. 6, 2013 of "Organic Optoelectronics Reaching the Practical Use Stage", electron-withdrawing skeletons such as cyano groups and triazines and electron donations such as carbazole and diphenylamino groups are provided. LUMO and HOMO are localized by introducing a sexual skeleton.

It is also effective to reduce the change in molecular structure between the base state and the excited triple term state of the compound. As a method for reducing the structural change, for example, making the compound rigid is effective. Rigidity described here means that there are few parts in the molecule that can move freely, such as suppressing free rotation in the bond between rings in the molecule and introducing a fused ring with a large π-conjugated surface. means. In particular, it is possible to reduce the structural change in the excited state by making the portion involved in light emission rigid.

<General problems with TADF compounds>
The TADF compound has various problems in terms of its light emitting mechanism and molecular structure. The following describes some of the problems that TADF compounds generally have.

In the TADF compound, it is necessary to separate the sites where HOMO and LUMO are present as much as possible in order to reduce ΔEst. Therefore, the electronic state of the molecule is a donor / acceptor type molecule in which the HOMO site and LUMO site are separated. It becomes a state close to the inner CT (intramolecular charge transfer state).

When a plurality of such molecules are present, stabilization is achieved when the donor portion of one molecule and the acceptor portion of the other molecule are brought close to each other. Such a stabilized state is not limited to the formation between two molecules, but can be formed between a plurality of molecules such as between three molecules or five molecules, and as a result, various stabilized states having a wide distribution can be obtained. It will be present and the shapes of the absorption and emission spectra will be broad. In addition, even when a multi-molecule aggregate of more than two molecules is not formed, various existence states can be taken depending on the difference in the direction and angle of interaction between the two molecules, so basically the absorption spectrum and The shape of the emission spectrum is broad.

Broad emission spectrum poses two major problems. One is the problem that the color purity of the emitted color becomes low. When applied to lighting applications, it does not pose a big problem, but when used for electronic displays, the color reproduction range becomes smaller and the color reproducibility of pure colors becomes lower, so it is actually applied as a product. Will be difficult.

Another problem is the rising wavelength on the short wavelength side of the emission spectrum (referred to as "fluorescent 0-0 band".) To reduce the wavelength, i.e. higher S ₁ (higher energy of the lowest excited singlet energy level) It is to do.

Naturally, when the fluorescence 0-0 band has a shorter wavelength, the phosphorescence 0-0 band derived from T _{1, which} has a lower energy than S ₁ , also has a shorter wavelength (higher T ₁ ). Therefore, the compound used in the host compound in order not to cause reverse energy transfer from the dopant, arises the need to ₁ reduction and high T ₁ of high S.

This is a very big problem. A host compound basically composed of an organic compound takes a state of a plurality of active and unstable chemical species such as a cationic radical state, an anionic radical state and an excited state in an organic EL element, and these chemical species are intramolecular. It can be made to exist relatively stably by expanding the π-conjugated system of.

However, in order to achieve high S ₁ and high T ₁ , it is necessary to reduce or cut off the π-conjugated system in the molecule, which makes it difficult to achieve both stability and, as a result. This will shorten the life of the light emitting element.

Further, in the TADF compound containing no heavy metal, the transition from the excited triplet state to the ground state is a forbidden transition, so the existence time (exciton lifetime) in the excited triplet state is from several hundred μs to milliseconds. Very long, on the order of seconds. Therefore, even if the T ₁ energy level of the host compound is a higher energy level than that of the fluorescent compound, and the excited triplet state of the fluorescent compound from the length of the dwell time to the host compound The probability of reverse energy transfer increases. As a result, the inverse intersystem crossing from the excited triplet state to the excited singlet state of the TADF compound, which was originally intended, does not sufficiently occur, and the unfavorable reverse energy transfer to the host compound becomes the mainstream, resulting in sufficient emission efficiency. Will not be obtained.

In order to solve the above problems, it is necessary to sharpen the emission spectrum shape of the TADF compound and reduce the difference between the emission maximum wavelength and the rising wavelength of the emission spectrum. This can be basically achieved by reducing the change in the molecular structure of the excited singlet state and the excited triplet state.

Further, in order to suppress the reverse energy transfer to the host compound, it is effective to shorten the existence time (exciton lifetime) of the excited triplet state of the TADF compound. To achieve this, we need to take measures such as reducing the change in the molecular structure between the ground state and the excited triplet state and introducing substituents and elements suitable for unwinding the forbidden transition. Can be solved.

Hereinafter, various measuring methods for the π-conjugated compound according to the present invention will be described.

[Electron density distribution]
In the π-conjugated compound according to the present invention, it is preferable that HOMO and LUMO are substantially separated in the molecule from the viewpoint of reducing ΔEst. The distribution state of these HOMO and LUMO can be obtained from the electron density distribution when the structure is optimized obtained by the molecular orbital calculation.

For the structural optimization and the calculation of the electron density distribution by the molecular orbital calculation of the π-conjugated compound in the present invention, the molecular orbital calculation software using B3LYP as a functional and 6-31G (d) as a basis function is used as the calculation method. It can be calculated by using, and the software is not particularly limited, and any of them can be used in the same manner.

In the present invention, Gaussian 09 (Revision C.01, MJ Frisch, et al, Gaussian, Inc., 2010.) manufactured by Gaussian, USA was used as the software for calculating the molecular orbital.

Further, "HOMO and LUMO are substantially separated" means that the central parts of the HOMO orbital distribution and the LUMO orbital distribution calculated by the above molecular calculation are separated, and more preferably, the HOMO orbital distribution and the LUMO orbital are separated. It means that the distributions of are almost non-overlapping.

Regarding the separated state of HOMO and LUMO, the time-dependent density functional theory (Time-Dependent DFT) is applied from the structural optimization calculation using B3LYP as the functional and 6-31G (d) as the base function. Excited state calculation is performed to obtain the energy levels of S ₁ and T ₁ (E (S ₁ ) and E (T ₁ ), respectively) and calculated as ΔEst = | E (S ₁ ) -E (T ₁ ) |. It is also possible to do. The smaller the calculated ΔEst, the more separated HOMO and LUMO are. In the present invention, ΔEst calculated by using the same calculation method as described above is 0.5 eV or less, preferably 0.2 eV or less, and more preferably 0.1 eV or less.

[Lowest excited singlet energy level S ₁ ]
For the lowest excited singlet energy level S ₁ of π-conjugated compound in the present invention is defined by what is calculated in the same manner as the conventional method in the present invention. That is, a compound to be measured is vapor-deposited on a quartz substrate to prepare a sample, and the absorption spectrum (vertical axis: absorbance, horizontal axis: wavelength) of this sample is measured at room temperature (300 K). A tangent line is drawn with respect to the rising edge of the absorption spectrum on the long wavelength side, and the calculation is performed from a predetermined conversion formula based on the wavelength value at the intersection of the tangent line and the horizontal axis.

However, if the molecule itself of the π-conjugated compound used in the present invention has a relatively high cohesiveness, an error due to cohesiveness may occur in the measurement of the thin film. Π-conjugated compound in the present invention that the Stokes shift is relatively small, considering that further structural changes in the excited state and the ground state is small, the lowest excited singlet energy level S ₁ in the present invention, room temperature (25 ° C. ), The peak value of the maximum emission wavelength in the solution state of the π-conjugated compound was used as an approximate value.

Here, as the solvent used, a solvent that does not affect the aggregated state of the π-conjugated compound, that is, a solvent that is less affected by the solvent effect, for example, a non-polar solvent such as cyclohexane or toluene can be used.

[Lowest excited triplet energy level T ₁ ]
The lowest excited triplet energy level (T ₁ ) of the π-conjugated compound used in the present invention was calculated from the photoluminescence (PL) characteristics of the solution or thin film. For example, as a calculation method for a thin film, a dispersion of a dilute π-conjugated compound is made into a thin film, and then a streak camera is used to measure the transient PL characteristics to separate the fluorescent component and the phosphorescent component. The lowest excited triplet energy level can be obtained from the lowest excited singlet energy level with the absolute value of the energy difference as ΔEst.

In the measurement and evaluation, the absolute PL quantum yield measuring device C9920-02 (manufactured by Hamamatsu Photonics Co., Ltd.) was used for the measurement of the absolute PL quantum yield. The emission lifetime was measured using a streak camera C4334 (manufactured by Hamamatsu Photonics Co., Ltd.) while exciting the sample with laser light.

<< Constituent layer of organic EL element >>
The organic EL element of the present invention has at least a charge transfer layer between the anode and the cathode, and at least one of the charge transfer layers has a structure represented by the general formula (1) and at least. It contains a π-conjugated compound in which the absolute value of the difference between the excited singlet energy level and the lowest excited triplet energy level is 0.5 eV or less.

In the present invention, the charge transfer layer refers to a layer in which charges such as holes and electrons move. Specific examples thereof include a hole injection layer, a hole transport layer, an electron blocking layer, a light emitting layer, a hole blocking layer, an electron transport layer, and an electron injection layer.

Typical element configurations in the organic EL device of the present invention include, but are not limited to, the following configurations.
(1) anode / light emitting layer // cathode (2) anode / light emitting layer / electron transport layer / cathode (3) anode / hole transport layer / light emitting layer / cathode (4) anode / hole transport layer / light emitting layer / Electron transport layer / cathode (5) Electron / hole transport layer / light emitting layer / electron transport layer / electron injection layer / cathode (6) anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / cathode (7) Electron / hole injection layer / hole transport layer / (electron blocking layer /) light emitting layer / (hole blocking layer /) electron transport layer / electron injection layer / cathode Among the above, the configuration of (7) is It is preferably used, but is not limited thereto.

The light emitting layer used in the present invention is composed of a single layer or a plurality of layers, and when there are a plurality of light emitting layers, a non-light emitting intermediate layer may be provided between the light emitting layers.

If necessary, a hole blocking layer (also referred to as a hole barrier layer) or an electron injection layer (also referred to as a cathode buffer layer) may be provided between the light emitting layer and the cathode, and the light emitting layer and the anode may be provided. An electron blocking layer (also referred to as an electron barrier layer) or a hole injection layer (also referred to as an anode buffer layer) may be provided between them.

The electron transport layer used in the present invention is a layer having a function of transporting electrons, and in a broad sense, an electron injection layer and a hole blocking layer are also included in the electron transport layer. Further, it may be composed of a plurality of layers.

The hole transport layer used in the present invention is a layer having a function of transporting holes, and in a broad sense, a hole injection layer and an electron blocking layer are also included in the hole transport layer. Further, it may be composed of a plurality of layers.

In the above typical device configuration, the layer excluding the anode and the cathode is also referred to as an "organic layer".

(Tandem structure)
Further, the organic EL element of the present invention may be an element having a so-called tandem structure in which a plurality of light emitting units including at least one light emitting layer are laminated. As a typical element configuration of the tandem structure, for example, the following configuration can be mentioned.

Anode / first light emitting unit / intermediate layer / second light emitting unit / intermediate layer / third light emitting unit / cathode Here, even if the first light emitting unit, the second light emitting unit and the third light emitting unit are all the same, It may be different. Further, the two light emitting units may be the same, and the remaining one may be different.

A plurality of light emitting units may be directly laminated or laminated via an intermediate layer, and the intermediate layer is generally an intermediate electrode, an intermediate conductive layer, a charge generation layer, an electron extraction layer, a connection layer, or an intermediate layer. A known material structure can be used as long as it is also called an insulating layer and has a function of supplying electrons to the adjacent layer on the anode side and holes to the adjacent layer on the cathode side.

Examples of the material used for the intermediate layer include ITO (inorganic tin oxide), IZO (inorganic zinc oxide), ZnO ₂ , TiN, ZrN, HfN, TiOx, VOx, CuI, InN, GaN, CuAlO ₂ , and CuGaO. ₂ , SrCu ₂ O ₂ , LaB ₆ , RuO ₂ , Al and other conductive inorganic compound layers, Au / Bi ₂ O _{3 and} other bilayer films, SnO ₂ / Ag / SnO ₂ , ZnO / Ag / ZnO, _{Bi 2 O 3 / Au / Bi} 2 O 3, TiO 2 / TiN / TiO 2, TiO 2 / ZrN / TiO 2 or the like multilayer film, also fullerenes such as _{C 60,} conductive organic material layer such as oligothiophene, metal Examples thereof include conductive organic compound layers such as phthalocyanines, metal-free phthalocyanines, metal porphyrins, and metal-free porphyrins, but the present invention is not limited thereto.

Preferred configurations in the light emitting unit include, for example, configurations in which the anode and the cathode are removed from the configurations (1) to (7) mentioned in the above typical element configurations, and the present invention includes these. Not limited.

Specific examples of the tandem organic EL element include, for example, US Pat. No. 6,337,492, US Pat. No. 7,420,203, US Pat. No. 7,473,923, US Patent No. 6872472, US Pat. No. 6,107,734, US Pat. No. 6,337,492, International Publication No. 2005/09087, Japanese Patent Application Laid-Open No. 2006-228712, Japanese Patent Application Laid-Open No. 2006-24791, Japanese Patent Application Laid-Open No. 2006-49393, Japanese Patent Application Laid-Open No. 2006-49394, Japanese Patent Application Laid-Open No. 2006-49396, Japanese Patent Application Laid-Open No. 2011 -96679, Japanese Patent Application Laid-Open No. 2005-340187, Japanese Patent No. 4711424, Japanese Patent No. 3496681, Japanese Patent No. 3884564, Japanese Patent No. 421369, Japanese Patent Application Laid-Open No. 2010-192719, Japanese Patent Application Laid-Open No. 2009-07629 The element configurations and configurations described in Japanese Patent Application Laid-Open No. 2008-0784414, Japanese Patent Application Laid-Open No. 2007-059848, Japanese Patent Application Laid-Open No. 2003-272860, Japanese Patent Application Laid-Open No. 2003-045676, International Publication No. 2005/094130, etc. Materials and the like can be mentioned, but the present invention is not limited thereto.

Hereinafter, each layer constituting the organic EL device of the present invention will be described.

《Light emitting layer》
The light emitting layer used in the present invention is a layer that provides a place where electrons and holes injected from an electrode or an adjacent layer are recombined and emit light via excitons, and the light emitting portion is a light emitting layer. It may be in the layer or at the interface between the light emitting layer and the adjacent layer. The structure of the light emitting layer used in the present invention is not particularly limited as long as it satisfies the requirements specified in the present invention.

The total thickness of the light emitting layer is not particularly limited, but the homogeneity of the formed film, prevention of applying an unnecessary high voltage at the time of light emission, and improvement of the stability of the emission color with respect to the drive current are improved. From the viewpoint, it is preferably adjusted to the range of 2 nm to 5 μm, more preferably to the range of 2 to 500 nm, and further preferably to the range of 5 to 200 nm.

The thickness of the individual light emitting layers used in the present invention is preferably adjusted to the range of 2 nm to 1 μm, more preferably to the range of 2 to 200 nm, and further preferably to the range of 3 to 150 nm. Be adjusted.

The light emitting layer used in the present invention contains a light emitting dopant (a light emitting compound, a light emitting dopant, also simply referred to as a dopant), and further contains the above-mentioned host compound (a matrix material, a light emitting host compound, also simply referred to as a host). Is preferably contained.

(1) Light-emitting dopant Examples of the light-emitting dopant include a fluorescence-emitting dopant (also referred to as a fluorescence-emitting compound or a fluorescence dopant), a delayed fluorescence dopant, or a phosphorescence-emitting dopant (also referred to as a phosphorescence-emitting compound or a phosphorescence dopant). ) Is preferably used. In the present invention, it is preferable that at least one light emitting layer contains a light emitting compound described later.

In the present invention, the light emitting layer preferably contains the luminescent compound in the range of 0.1 to 50% by mass, and particularly preferably in the range of 1 to 30% by mass.

The concentration of the luminescent compound in the light emitting layer can be arbitrarily determined based on the specific luminescent compound used and the requirements of the device, and the concentration is uniform with respect to the layer thickness direction of the light emitting layer. It may be contained or may have an arbitrary concentration distribution.

Further, the luminescent compound used in the present invention may be used in combination of a plurality of types, and may be used in combination of fluorescent compounds having different structures or in combination of a fluorescent compound and a phosphorescent compound. You may. Thereby, an arbitrary emission color can be obtained.

The π-conjugated compound, the luminescent compound, and the host compound according to the present invention in which the absolute value (ΔEst) of the difference between the lowest excited singlet energy level and the lowest excited triplet energy level is 0.5 eV or less. When contained in the light emitting layer, the π-conjugated compound according to the present invention acts as an assist dopant. On the other hand, when the light emitting layer contains the π-conjugated compound and the luminescent compound according to the present invention and does not contain the host compound, the π-conjugated compound according to the present invention acts as the host compound.

The mechanism for exhibiting the effect is the same in all cases, and the point of converting triplet excitons generated on the π-conjugated compound according to the present invention into singlet excitons by an intersystem crossing (RISC). It is in.

As a result, theoretically all exciton energies generated on the π-conjugated compound according to the present invention can be transferred to the luminescent compound, and high luminous efficiency can be achieved.

Therefore, when the light emitting layer contains the three components of the π-conjugated compound, the luminescent compound, and the host compound according to the present invention, the energy levels of S ₁ and T ₁ of the π-conjugated compound are the S of the host compound. ₁ and T ₁ of the lower than the energy level, it is preferably higher than the energy level of the S ₁ and T ₁ of the light-emitting compound.

Similarly, light emitting layer, the energy level of the S ₁ and T ₁ of the case containing the two components of the light emitting compound and [pi conjugated compound according to the present invention, [pi-conjugated compounds, S ₁ luminescent compound And T ₁ are preferably higher than the energy level.

1C and 1D show schematic views of the case where the π-conjugated compound of the present invention acts as an assist dopant and a host compound, respectively. 1C and 1D are examples, and the process of generating triplet excitons generated on the π-conjugated compound according to the present invention is not limited to electric field excitation, and energy transfer within the light emitting layer or from the interface of the peripheral layer. And electron transfer are also included.

Further, in FIGS. 1C and 1D, a fluorescent compound is used as the light emitting material, but the present invention is not limited to this, and a phosphorescent compound may be used, or a fluorescent compound and phosphorescent light emission. Both sex compounds may be used.

When the π-conjugated compound according to the present invention is used as an assist dopant, the light emitting layer contains a host compound having a mass ratio of 100% or more with respect to the π-conjugated compound, and is a fluorescent compound and / or a phosphorescent compound. Is preferably contained within a mass ratio of 0.1 to 50% with respect to the π-conjugated compound.

When the π-conjugated compound according to the present invention is used as the host compound, the light emitting layer contains a fluorescent compound and / or a phosphorescent compound within a mass ratio of 0.1 to 50% with respect to the π-conjugated compound. It is preferable to contain in.

When the π-conjugated compound according to the present invention is used as an assist dopant or a host compound, it is preferable that the emission spectrum of the π-conjugated compound according to the present invention and the absorption spectrum of the luminescent compound overlap.

The emission colors of the organic EL element of the present invention and the compound used in the present invention are shown in FIG. 3.16 on page 108 of the "New Color Science Handbook" (edited by the Japan Color Society, Tokyo University Press, 1985). It is determined by the color when the result measured by the luminometer CS-1000 (manufactured by Konica Minolta Co., Ltd.) is applied to the CIE chromaticity coordinates.

In the present invention, it is also preferable that the light emitting layer of one layer or a plurality of layers contains a plurality of light emitting dopants having different light emitting colors and exhibits white light emission.

The combination of light emitting dopants showing white color is not particularly limited, and examples thereof include a combination of blue and orange, a combination of blue and green and red, and the like.

The white color in the organic EL device of the present invention means that the chromaticity in the CIE 1931 color system at 1000 cd / m ² is x = 0.39 ± 0.09 when the 2 degree viewing angle front luminance is measured by the above method. , Y = 0.38 ± 0.08, preferably within the region.

(1.1) π-conjugated compound The π-conjugated compound according to the present invention has a structure represented by the following general formula (1), and has the lowest excited singlet energy level and the lowest of the π-conjugated compound. The absolute value of the difference from the excited triplet energy level is 0.5 eV or less.

In the charge transfer layer, the π-conjugated compound according to the present invention converts triplet excitons generated on the π-conjugated compound into singlet excitons by intersystem crossing (RISC) without deactivating them. , A compound having a function of improving light emission efficiency by suppressing exciton deactivation, and can be preferably used as an organic EL element material.

Specifically, the hole injection layer, hole transport layer, electron blocking layer, light emitting layer, hole blocking layer, electron transport layer, electron injection layer and the like of the organic EL device contain the π-conjugated compound according to the present invention. The light emission efficiency can be improved by making the light emission efficiency.

The compound having the structure represented by the general formula (1) will be described below.

In the formula, A represents a group having a ring structure, and A represents an aryl group substituted with an electron-withdrawing group or a heteroaryl group optionally substituted. B and C represent an aryl ring or a heteroaryl ring which is composed of a condensed ring structure of up to a single ring or three rings and may be substituted independently of each other. X represents O, S, N-R ¹ , CR ² (R ³ ), Si-R ⁴ (R ⁵ ), BR ⁶ or a single bond. R ^{1 to} R ⁶ each independently represent a hydrogen atom, which may be substituted, an alkyl group, an aryl group or a heteroaryl group.

A represents a group having a ring structure, and A represents an aryl group substituted with an electron-withdrawing group or a heteroaryl group which may be substituted.

As the aryl group constituting the ring structure A, an aryl ring having 6 to 20 carbon atoms is preferable. Specifically, benzene ring, inden ring, naphthalene ring, azulene ring, fluoranthene ring, phenanthrene ring, anthracene ring, acenaphthylene ring, biphenylene ring, chrysene ring, naphthalene ring, pyrene ring, pentalene ring, acetylene ring, heptalene. Examples thereof include a ring, a triphenylene ring, an as-indacene ring, a chrysene ring, an s-indacene ring, a preadene ring, a phenalene ring, a fluoranthene ring, a perylene ring, and an acephenylene ring. More preferably, a benzene ring, a naphthalene ring, a fluorene ring, a phenanthrene ring, an anthracene ring, a biphenylene ring, a chrysene ring, a pyrene ring, a triphenylene ring, a chrysene ring, a fluoranthene ring, and a perylene ring. A benzene ring is particularly preferable.

This aryl ring is substituted with an electron-attracting substituent. The electron-attracting property means a property of reducing the electron density at a specific position of a molecule, and the electron-attracting group means a substituent having such a property. Specific electron-attracting substituents include, for example, heteroaryl groups, halogen atoms, acyl groups, arylcarbonyl groups, alkoxycarbonyl groups, aryloxycarbonyl groups, cyano groups, alkylsulfinyl groups, arylsulfinyl groups, and alkyls. It can be selected from a sulfonyl group, an arylsulfonyl group, a nitro group or an alkyl group or an aryl group substituted with these groups. Preferably, it is an aryl ring having 6 to 20 carbon atoms substituted with 1 to 5 fluorine atoms, 1 to 5 fluoroalkyl groups, a fluorine atom, a cyano group, and a nitrogen-containing aromatic ring.

Examples of the heteroaryl group constituting the ring structure A include a 5-membered ring or a 6-membered nitrogen-containing heteroaryl ring, an oxygen-containing heteroaryl ring, or a sulfur-containing heteroaryl ring. Preferably, it is a nitrogen-containing heteroaryl ring, and is a pyridine ring, a pyridazine ring, a pyrimidine ring, a pyrazine ring, a triazine ring, a quinoline ring, an isoquinoline ring, a quinazoline ring, a synnoline ring, a quinoxaline ring, a phthalazine ring, a pteridine ring, an acrydin ring, A phenanthridine ring or a phenanthrolin ring is more preferable. Particularly preferred are a pyridine ring, a pyridazine ring, a pyrimidine ring, a pyrazine ring, a triazine ring, a quinoline ring, an isoquinoline ring, a phenanthridine ring, or a phenanthroline ring.

As the group to be substituted with the heteroaryl group, an aryl group or a heteroaryl group is preferable. Examples of the aryl group and the heteroaryl group include the same aryl group and heteroaryl group constituting the ring structure A.

The alkyl group may be linear, branched, or cyclic, and examples thereof include linear, branched, or cyclic alkyl groups having 1 to 20 carbon atoms, and specifically, methyl group, ethyl group, and n-. Propyl group, isopropyl group, n-butyl group, s-butyl group, t-butyl group, n-pentyl group, neopentyl group, n-hexyl group, cyclohexyl group, 2-ethylhexyl group, n-heptyl group, n-octyl Group, 2-hexyloctyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n- Examples thereof include heptadecyl group, n-octadecyl group, n-nonadecil group and n-icosyl group, and methyl group, ethyl group, isopropyl group, t-butyl group, cyclohexyl group, 2-ethylhexyl group and 2-hexyloctyl group are preferable. ..

The alkoxy group may be either a linear group or a branched chain, and examples thereof include a linear or branched alkoxy group having 1 to 20 carbon atoms, and specific examples thereof include a methoxy group, an ethoxy group, and an n-. Propoxy group, isopropoxy group, n-butoxy group, isobutoxy group, t-butoxy group, n-pentyloxy group, neopentyloxy group, n-hexyloxy group, cyclohexyloxy group, n-heptyloxy group, n-octyl Oxy group, 2-ethylhexyloxy group, nonyloxy group, decyloxy group, 3,7-dimethyloctyloxy group, n-undecyloxy group, n-dodecyloxy group, n-tridecyloxy group, n-tetradecyloxy group , 2-n-hexyl-n-octyloxy group, n-pentadecyloxy group, n-hexadecyloxy group, n-heptadecyloxy group, n-octadecyloxy group, n-nonadesyloxy group, n-icosyloxy group Examples thereof include a methoxy group, an ethoxy group, an isopropoxy group, a t-butoxy group, a cyclohexyloxy group, a 2-ethylhexyloxy group and a 2-hexyloctyloxy group.

Among these, A is an aryl ring having 6 to 20 carbon atoms substituted with 1 to 5 cyano groups, an aryl ring having 6 to 20 carbon atoms substituted with 1 to 5 fluorine atoms, and the like. Aryl rings with 6 to 20 carbon atoms substituted with 1 to 5 fluoroalkyl groups, benzene rings substituted with optionally substituted nitrogen-containing heteroaryl rings or optionally substituted nitrogen-containing aromatics. It is preferably a ring.

B and C represent an aryl ring or a heteroaryl ring which is composed of a condensed ring structure of up to a single ring or three rings and may be substituted independently of each other.

B and C may be independently substituted, respectively, benzene ring, naphthalene ring, indene ring, benzosilol ring, indole ring, benzofuran ring, benzothiophene ring, thienothiophene ring, phenanthrene ring, fluorene ring, dibenzo. It preferably represents a silol ring, a dibenzoborol ring, a carbazole ring, a dibenzofuran ring or a dibenzothiophene ring.

X represents O, S, N-R ¹ , CR ² (R ³ ), Si-R ⁴ (R ⁵ ), BR ⁶ or a single bond. Here, for example, C-R ² (R ³ ) represents a divalent group in which two groups R ² and R ³ are substituted on a carbon atom. R ^{1 to} R ⁶ each independently represent a hydrogen atom, which may be substituted, an alkyl group, an aryl group or a heteroaryl group. Examples of the alkyl group include the same ones as described above, and the same ones are preferable. Examples of the aryl group and the heteroaryl group include the same aryl group and heteroaryl group constituting the ring structure A.

The π-conjugated compound having a structure represented by the general formula (1) is preferably a π-conjugated compound having a structure represented by any of the following general formulas (2) to (15).

(In the formula, A and X are synonymous with A and X in the general formula (1). Y is O, S, N-R ⁷ , C-R ⁸ (R ⁹ ), Si-R ¹⁰ (R). ¹¹ ), BR ¹² or CH = CH. R ^{7 to} R ¹² each independently represent a hydrogen atom, which may be substituted, an alkyl group, an aryl group or a heteroaryl group. R ^{7 to} R ¹² are the same groups as R ^{1 to} R ⁶ described in X in the general formula (1).

Hereinafter, preferred specific examples of the π-conjugated compound according to the present invention will be given, but these compounds may be further substituted with a substituent, structural isomers and the like may be present, and the present invention is not limited to this description. ..

<Synthesis method>
The above-mentioned π-conjugated compound is described in, for example, the method described in International Publication No. 2011/055933, International Publication No. 2011/132866 and International Publication No. 2012/035853, or the references described in these documents. It can be synthesized by referring to the method.

(1.2) Fluorescent Luminescent Dopant As the fluorescent luminescent dopant (fluorescent dopant), the π-conjugated compound of the present invention may be used, or a known fluorescent dopant or delayed fluorescence used in the light emitting layer of an organic EL element. You may appropriately select and use from sex dopants.

Specific examples of known fluorescent dopants that can be used in the present invention include, for example, anthracene derivatives, pyrene derivatives, chrysene derivatives, fluorantene derivatives, perylene derivatives, fluorene derivatives, arylacetylene derivatives, styrylarylene derivatives, styrylamine derivatives, and arylamine derivatives. , Boron complex, coumarin derivative, pyran derivative, cyanine derivative, croconium derivative, squalium derivative, oxobenzanthracene derivative, fluorescein derivative, rhodamine derivative, pyrylium derivative, perylene derivative, polythiophene derivative, rare earth complex compound and the like. Further, in recent years, light emitting dopants using delayed fluorescence have also been developed, and these may be used. Specific examples of the light emitting dopant using delayed fluorescence include the compounds described in International Publication No. 2011/156793, Japanese Patent Application Laid-Open No. 2011-213643, Japanese Patent Application Laid-Open No. 2010-93181, and the like. Is not limited to these.

(1.3) Phosphorescent Dopant The phosphorescent dopant used in the present invention will be described.

The phosphorescent dopant used in the present invention is a compound in which light emission from an excited triplet is observed, specifically, a compound that emits phosphorescence at room temperature (25 ° C.), and a phosphorescent quantum yield. Is defined as a compound of 0.01 or more at 25 ° C., with a preferred phosphorescent quantum yield of 0.1 or more.

The phosphorus photon yield can be measured by the method described on page 398 (1992 edition, Maruzen) of Spectroscopy II of the 4th edition Experimental Chemistry Course 7. The phosphorescence quantum yield in a solution can be measured using various solvents, but the phosphorescence dopant used in the present invention achieves the above phosphorescence quantum yield (0.01 or more) in any of any solvents. Just do it.

The phosphorescent dopant can be appropriately selected from known ones used for the light emitting layer of the organic EL element. Specific examples of known phosphorescent dopants that can be used in the present invention include compounds described in the following documents.

Nature 395, 151 (1998), Apple. Phys. Lett. 78, 1622 (2001), Adv. Mater. 19,739 (2007), Chem. Mater. 17, 3532 (2005), Adv. Mater. 17,1059 (2005), International Publication No. 2009/10991, International Publication No. 2008/101842, International Publication No. 2003/040257, US Patent Application Publication No. 2006/835469, US Patent Application Publication No. 2006 / 0202194, US Patent Application Publication No. 2007/0087321, US Patent Application Publication No. 2005/0244673, Inorg. Chem. 40,1704 (2001), Chem. Mater. 16,2480 (2004), Adv. Mater. 16, 2003 (2004), Angew. Chem. lnt. Ed. 2006, 45, 7800, Apple. Phys. Lett. 86,153505 (2005), Chem. Lett. 34,592 (2005), Chem. Common. 2906 (2005), Inorg. Chem. 42,1248 (2003), International Publication No. 2009/050290, International Publication No. 2002/015645, International Publication No. 2009/000673, US Patent Application Publication No. 2002/0034656, US Pat. No. 7,332,232, USA Publication of Patent Application No. 2009/01087737, Publication of US Patent Application No. 2009/00397776, US Patent No. 6921915, US Patent No. 6687266, US Patent Application Publication No. 2007/0190359, US Patent Application Publication No. 2006/0008670, US Patent Application Publication No. 2009/0158464, US Patent Application Publication No. 2008/0015355, US Patent No. 7250226, US Patent No. 7396598, US Patent Application Publication No. 2006/0263635, US Patent Application Publication No. 2003/0138657, US Patent Application Publication No. 2003/0152802, US Patent No. 70090928, Angew. Chem. lnt. Ed. 47, 1 (2008), Chem. Mater. 18,5119 (2006), Inorg. Chem. 46,4308 (2007), Organometallics 23,3745 (2004), Apple. Phys. Lett. 74,1361 (1999), International Publication No. 2002/002714, International Publication No. 2006/090024, International Publication No. 2006/056418, International Publication No. 2005/019373, International Publication No. 2005/123873, International Publication No. 2005/123873, International Publication No. 2007/004380, International Publication No. 2006/082742, US Patent Application Publication No. 2006/0251923, US Patent Application Publication No. 2005/02060441, US Patent No. 73935999 , US Patent No. 7534505, US Patent No. 7445855, US Patent Application Publication No. 2007/0190359, US Patent Application Publication No. 2008/0297033, US Patent No. 7338722, US Patent Application Publication No. 2002 / 0134984, US Patent No. 7279704, US Patent Application Publication No. 2006/098120, US Patent Application Publication No. 2006/103874, International Publication No. 2005/076380, International Publication No. 2010/032663 , International Publication No. 2008140115, International Publication No. 2007/052431, International Publication No. 2011/134013, International Publication No. 2011/157339, International Publication No. 2010/086089, International Publication No. 2009/1163646, International Publication No. 2012/20327, International Publication No. 2011/051404, International Publication No. 2011/004639, International Publication No. 2011/073149, US Patent Application Publication No. 2012/228583, US Patent Application Publication No. 2012/212126 Japanese Patent Application Laid-Open No. 2012-069737, Japanese Patent Application Laid-Open No. 2012-195554, Japanese Patent Application Laid-Open No. 2009-114086, Japanese Patent Application Laid-Open No. 2003-81988, Japanese Patent Application Laid-Open No. 2002-302671 and JP-A-2002-363552 And so on.

Among them, preferred phosphorescent dopants include organometallic complexes having Ir as the central metal. More preferably, a complex containing at least one coordination mode of a metal-carbon bond, a metal-nitrogen bond, a metal-oxygen bond, and a metal-sulfur bond is preferable.

(2) Host Compound The host compound used in the present invention is a compound mainly responsible for charge injection and transport in the light emitting layer, and its own light emission is not substantially observed in the organic EL device.

Among the compounds contained in the light emitting layer, the host compound preferably has a mass ratio of 20% or more in the layer. The host compound may be used alone or in combination of two or more. By using a plurality of types of host compounds, it is possible to adjust the charge transfer, and it is possible to improve the efficiency of the organic EL device.

The host compounds preferably used in the present invention will be described below.

As the host compound, the π-conjugated compound used in the present invention may be used as described above, but there is no particular limitation. From the viewpoint of reverse energy transfer, those having an excitation energy higher than the excitation single-term energy level of the dopant are preferable, and those having an excitation triple-term energy higher than the excitation triple-term energy level of the dopant are more preferable.

The host compound is responsible for carrier transport and exciton production within the light emitting layer. Therefore, it can exist stably in all active species in the cation radical state, the anion radical state, and the excited state, does not cause chemical changes such as decomposition and addition reaction, and further, the host molecule is present in the layer over time of energization. It is preferable not to move at the angstrom level.

Further, when the light emitting dopant to particular combination showing the TADF emission, since long dwell time of the excited triplet state of TADF compound, the T ₁ energy level of the host compound itself is high, further host compound each other association that in a state not to create a low T ₁ state, that the TADF compound and the host compound does not form a exciplex, such that the host compound does not form a electro-mer by the electric field, molecules such as the host compound does not lower T ₁ of Appropriate design of the structure is required.

In order to satisfy such requirements, it is necessary that the host compound itself has high electron hopping mobility, high hole hopping mobility, and a small structural change in the excited triple term state. Is. Carbazole skeleton as representative of the host compounds satisfying such requirements, azacarbazole skeleton, dibenzofuran skeleton, such as dibenzothiophene skeleton or aza dibenzofuran skeleton, it may preferably be mentioned those having a high The T ₁ energy level.

Further, the host compound has a hole transporting ability or an electron transporting ability, prevents the wavelength of light emission from being lengthened, and is stable against heat generation when the organic EL device is driven at a high temperature or during the device driving. From the viewpoint of operation, it is preferable to have a high glass transition temperature (Tg). Tg is preferably 90 ° C. or higher, and more preferably 120 ° C. or higher.

Here, the glass transition point (Tg) is a value obtained by a method based on JIS K 7121-2012 using DSC (Differential Scanning Colorimetry).

Further, as the host compound used in the present invention, it is also preferable to use the π-conjugated compound according to the present invention as described above. This is because the π-conjugated compound according to the present invention has a condensed ring structure, so that the π-electron cloud is widened, the carrier transport property is high, and the glass transition temperature (Tg) is high. Further, the π-conjugated compound according to the present invention has a high T ₁ , and can be suitably used for a light emitting material having a short emission wavelength (that is, a large T ₁ and S ₁ ).

When a known host compound is used for the organic EL device of the present invention, specific examples thereof include the compounds described in the following documents, but the present invention is not limited thereto.

JP 2001-257076, 2002-308855, 2001-313179, 2002-319491, 2001-357977, 2002-334786, 2002-8860, 2002-334787A, 2002-15871, 2002-334788, 2002-43056, 2002-334789, 2002-75645, 2002-338579, 2002. 2002-105445, 2002-343568, 2002-141173, 2002-352957, 2002-203683, 2002-363227, 2002-231453, 2003 No. 3165, No. 2002-234888, No. 2003-27048, No. 2002-255934, No. 2002-260861, No. 2002-280183, No. 2002-299060, No. 2002- 302516, 2002-305083, 2002-305084, 2002-308837, US Patent Application Publication No. 2003/0175553, US Patent Application Publication No. 2006/0280965, USA Publication of Patent Application Publication No. 2005/0112407, Publication of US Patent Application Publication No. 2009/0017330, Publication of US Patent Application Publication No. 2009/0030202, Publication of US Patent Application Publication No. 2005/0238919, International Publication No. 200109234, International Publication No. 2009021126, International Publication No. 2008056746, International Publication No. 2004093207, International Publication No. 2005089025, International Publication No. 2007063796, International Publication No. 2007063754, International Publication No. 2004107822, International Publication No. 2005030900 , International Publication No. 20061149666, International Publication No. 2009086028, International Publication No. 2009003898, International Publication No. 2012023947, Japanese Patent Application Laid-Open No. 2008-074939, Japanese Patent Application Laid-Open No. 2007-254297, EP2034538, International Publication No. 2011055933, International Publication No. It is published No. 2012035853, etc.

Hereinafter, specific examples of the compound as the host compound used in the present invention include the compounds represented by H-1 to H231 described in paragraphs [0255] to [0293] of JP-A-2015-38941. And the compounds represented by the following chemical formulas H-232 to H-236 are included, but the host compound is not limited thereto.

The preferred host compound used in the present invention may be a low molecular weight compound having a molecular weight capable of sublimation purification, or a polymer having a repeating unit.

In the case of a low molecular weight compound, since sublimation purification is possible, purification is easy, and there is an advantage that a high-purity material can be easily obtained. The molecular weight is not particularly limited as long as it can be sublimated and purified, but the molecular weight is preferably 3000 or less, more preferably 2000 or less.

In the case of a polymer or oligomer having a repeating unit, there is an advantage that a film is easily formed by a wet process, and in general, a polymer has a high Tg, which is preferable in terms of heat resistance.

<< Charge transfer layer other than light emitting layer >>
In the organic EL element of the present invention, at least one of the charge transfer layers has a structure represented by the general formula (1), and has the lowest excited singlet energy level and the lowest excited triplet energy level. Contains a π-conjugated compound having an absolute difference of 0.5 eV or less.

The π-conjugated compound having the structure represented by the general formula (1) may be contained in a charge transfer layer (peripheral layer) other than the above-mentioned light emitting layer.

This is because singlet excitons can be generated without deactivating the triplet excitons leaked from the light emitting layer to the peripheral layer. Therefore, it is preferable that the π-conjugated compound according to the present invention is contained in the charge transfer layer adjacent to the light emitting layer in order to improve the luminous efficiency. Specifically, it is preferably contained in the electron transport layer or the hole transport layer, and more preferably contained in the electron transport layer.

Further, since the π-conjugated compound according to the present invention is a charge-transfer compound, it is also preferable to provide an intermediate layer adjacent to the light emitting layer and to contain the π-conjugated compound according to the present invention in this intermediate layer. .. In this case, the thickness of the intermediate layer is not particularly limited, but is preferably in the range of 0.1 to 100 nm.

When the peripheral layer contains the π-conjugated compound according to the present invention, it may be used alone or in combination of two or more. Furthermore, it may be mixed with other charge transport materials. The charge transfer layers other than the light emitting layer will be described below.

《Electron transport layer》
In the present invention, the electron transport layer may be made of a material having a function of transporting electrons and may have a function of transmitting electrons injected from the cathode to the light emitting layer.

The total thickness of the electron transport layer according to the present invention is not particularly limited, but is usually in the range of 2 nm to 5 μm, more preferably 2 to 500 nm, and further preferably 5 to 200 nm.

Further, in the organic EL element, when the light generated in the light emitting layer is taken out from the electrode, the light taken out directly from the light emitting layer and the light taken out after being reflected by the electrode located at the opposite electrode to the electrode that takes out the light interfere with each other. It is known to wake up. When light is reflected by the cathode, this interference effect can be efficiently utilized by appropriately adjusting the total thickness of the electron transport layer between several nm and several μm.

On the other hand, if the layer thickness of the electron transport layer is increased, the voltage tends to increase. Therefore, especially when the layer thickness is thick, the electron mobility of the electron transport layer is preferably ^10-5 cm ² / Vs or more. ..

The material used for the electron transport layer (hereinafter referred to as an electron transport material) may have any of electron injection property, transport property, and hole barrier property, and is related to the present invention as described above. A π-conjugated compound may be used, or any of conventionally known compounds can be selected and used.

Conventionally known compounds include, for example, nitrogen-containing aromatic heterocyclic derivatives (carbazole derivatives, azacarbazole derivatives (one or more carbon atoms constituting the carbazole ring substituted with nitrogen atoms), pyridine derivatives, pyrimidine derivatives. , Pyrazine derivative, pyridazine derivative, triazine derivative, quinoline derivative, quinoxalin derivative, phenanthroline derivative, azatriphenylene derivative, oxazole derivative, thiazole derivative, oxaziazole derivative, thiadiazol derivative, triazole derivative, benzimidazole derivative, benzoxazole derivative, benzthiazole derivative Derivatives, etc.), dibenzofuran derivatives, dibenzothiophene derivatives, silol derivatives, aromatic hydrocarbon ring derivatives (naphthalene derivatives, anthracene derivatives, triphenylene derivatives, etc.) and the like.

Further, metal complexes having a quinolinol skeleton or dibenzoquinolinol skeleton as ligands, for example, tris (8-quinolinol) aluminum (Alq), 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), etc., and metal complexes thereof. A metal complex in which the central metal is replaced with In, Mg, Cu, Ca, Sn, Ga or Pb can also be used as an electron transport material.

In addition, metal-free or metal phthalocyanine, or those whose terminals are substituted with an alkyl group, a sulfonic acid group, or the like can also be preferably used as an electron transport material. Further, the distyrylpyrazine derivative exemplified as the material of the light emitting layer can also be used as an electron transport material, and an inorganic semiconductor such as n-type-Si or n-type-SiC is used like the hole injection layer and the hole transport layer. Can also be used as an electron transport material.

Further, it is also possible to use a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain.

In the electron transport layer according to the present invention, the electron transport layer may be doped with a doping material as a guest material to form an electron transport layer having a high n property (electron rich). Examples of the doping material include n-type dopants such as metal compounds and metal compounds such as metal halides. Specific examples of the electron transport layer having such a structure include, for example, JP-A-4-2970776, JP-A-10-270172, JP-A-2000-196140, JP-A-2001-102175, J. Mol. Apple. Phys. , 95, 5773 (2004) and the like.

Specific examples of known and preferable electron transporting materials used in the organic EL device of the present invention include, but are not limited to, the compounds described in the following documents.

US Patent No. 6528187, US Patent No. 7230107, US Patent Application Publication No. 2005/0025993, US Patent Application Publication No. 2004/0036077, US Patent Application Publication No. 2009/0115316, US Patent Publication No. 2009/0101870, US Patent Application Publication No. 2009/0179554, International Publication No. 2003/060956, International Publication No. 2008/132805, Appl. Phys. Lett. 75, 4 (1999), Apple. Phys. Lett. 79,449 (2001), Apple. Phys. Lett. 81, 162 (2002), Apple. Phys. Lett. 81, 162 (2002), Apple. Phys. Lett. 79,156 (2001), US Patent No. 7964293, US Patent Application Publication No. 2009/030202, International Publication No. 2004/080975, International Publication No. 2004/063159, International Publication No. 2005/085387, International Publication No. 2006/067931, International Publication No. 2007/086552, International Publication No. 2008/114690, International Publication No. 2009/0694242, International Publication No. 2009/0667779, International Publication No. 2009/054253, International Publication No. 2011/086935, International Publication No. 2010/150593, International Publication No. 2010/047707, EP23111826, JP-A-2010-251675, JP-A-2009-209133, JP-A-2009-124114, JP-A. 2008-277810, 2006-156445, 2005-340122, 2003-45662, 2003-31367, 2003-282270, International Publication 2012 / 115534 etc.

More preferred known electron transport materials in the present invention include aromatic heterocyclic compounds containing at least one nitrogen atom, such as pyridine derivatives, pyrimidine derivatives, pyrazine derivatives, triazine derivatives, dibenzofuran derivatives, dibenzothiophene derivatives, aza. Examples thereof include dibenzofuran derivatives, azadibenzothiophene derivatives, carbazole derivatives, azacarbazole derivatives, and benzimidazole derivatives.

The electron transport material may be used alone or in combination of two or more.

《Hole blocking layer》
The hole blocking layer is a layer having a function of an electron transporting layer in a broad sense, and is preferably made of a material having a function of transporting electrons and a small ability to transport holes, and holes while transporting electrons. It is possible to improve the recombination probability of electrons and holes by blocking the above.

In addition, the structure of the electron transport layer described above can be used as the hole blocking layer according to the present invention, if necessary.

The hole blocking layer provided in the organic EL device of the present invention is preferably provided adjacent to the cathode side of the light emitting layer.

The layer thickness of the hole blocking layer according to the present invention is preferably in the range of 3 to 100 nm, and more preferably in the range of 5 to 30 nm.

As the material used for the hole blocking layer, the material used for the above-mentioned electron transport layer containing the π-conjugated compound according to the present invention is preferably used, and the above-mentioned host containing the π-conjugated compound according to the present invention. Materials used as compounds are also preferably used for the hole blocking layer.

《Electron injection layer》
The electron injection layer (also referred to as “cathode buffer layer”) according to the present invention is a layer provided between the cathode and the light emitting layer in order to reduce the driving voltage and improve the emission brightness. It is described in detail in Volume 2, Chapter 2, "Electrode Materials" (pages 123-166) of "Forefront of Industrialization (published by NTS Co., Ltd. on November 30, 1998)".

In the present invention, the electron injection layer may be provided as needed and may be present between the cathode and the light emitting layer or between the cathode and the electron transport layer as described above.

The electron injection layer is preferably a very thin film, and the layer thickness is preferably in the range of 0.1 to 5 nm, although it depends on the material. Further, it may be a non-uniform layer (film) in which the constituent material is intermittently present.

The details of the electron-injected layer are also described in JP-A-6-325871, JP-A-9-17574, JP-A-10-74586, and the like, and specific examples of materials preferably used for the electron-injected layer include , Metals such as strontium and aluminum, alkali metal compounds such as lithium fluoride, sodium fluoride and potassium fluoride, alkaline earth metal compounds such as magnesium fluoride and calcium fluoride, oxidation Examples thereof include metal oxides typified by aluminum, metal complexes typified by 8-hydroxyquinolinate lithium (Liq), and the like. It is also possible to use the above-mentioned electron transport material containing the π-conjugated compound according to the present invention.

Further, the material used for the above-mentioned electron injection layer may be used alone or in combination of two or more.

《Hole transport layer》
In the present invention, the hole transport layer may be made of a material having a function of transporting holes and may have a function of transmitting holes injected from the anode to the light emitting layer.

The total thickness of the hole transport layer according to the present invention is not particularly limited, but is usually in the range of 5 nm to 5 μm, more preferably 5 to 500 nm, and further preferably 5 to 200 nm.

The material used for the hole transport layer (hereinafter referred to as the hole transport material) may have any of hole injection property, transport property, and electron barrier property, and is π-conjugated according to the present invention. A system compound may be used, or any of conventionally known compounds can be selected and used.

For example, porphyrin derivative, phthalocyanine derivative, oxazole derivative, oxadiazole derivative, triazole derivative, imidazole derivative, pyrazoline derivative, pyrazolone derivative, phenylenediamine derivative, hydrazone derivative, stilben derivative, polyarylalkane derivative, triarylamine derivative, carbazole derivative. , Indolocarbazole derivative, isoindole derivative, acene derivative such as anthracene and naphthalene, fluorene derivative, fluorenone derivative, polyvinylcarbazole, polymer material or oligomer in which aromatic amine is introduced into the main chain or side chain, polysilane, conductivity Examples thereof include sex polymers or oligomers (eg, PEDOT / PSS, aniline-based copolymers, polyaniline, polythiophene, etc.).

Examples of the triarylamine derivative include a benzidine type represented by α-NPD (4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl) and a starburst type represented by MTDATA. Examples thereof include compounds having fluorene or anthracene in the triarylamine linking core portion.

Hexaazatriphenylene derivatives as described in JP-A-2003-591432 and JP-A-2006-135145 can also be used as the hole transport material in the same manner.

Further, a hole transport layer having a high p property doped with impurities can also be used. Examples thereof include JP-A-4-297076, JP-A-2000-196140, and JP-A-2001-102175. Apple. Phys. , 95, 5773 (2004) and the like.

In addition, JP-A-11-251667, J. Am. Hung et. al. So-called p-type hole transporting materials and inorganic compounds such as p-type-Si and p-type-SiC as described in the authored literature (Applied Physics Letters 80 (2002), p.139) can also be used. Further, an orthometalated organometallic complex having Ir or Pt in the central metal as represented by Ir (ppy) 3 is also preferably used.

As the hole transport material, the above-mentioned materials can be used, but a triarylamine derivative, a carbazole derivative, an indolocarbazole derivative, an azatriphenylene derivative, an organic metal complex, and an aromatic amine are introduced into the main chain or the side chain. High molecular weight materials or oligomers are preferably used.

Specific examples of known and preferable hole transporting materials used in the organic EL device of the present invention include the compounds described in the following documents in addition to the above-mentioned documents, but the present invention is limited thereto. Not done.

For example, Apple. Phys. Lett. 69,2160 (1996), J. Mol. Lumin. 72-74,985 (1997), Apple. Phys. Lett. 78,673 (2001), Apple. Phys. Lett. 90,183503 (2007), Apple. Phys. Lett. 90,183503 (2007), Apple. Phys. Lett. 51,913 (1987), Synth. Met. 87,171 (1997), Synth. Met. 91,209 (1997), Synth. Met. 111,421 (2000), SID Symposium Digital, 37,923 (2006), J. Mol. Mater. Chem. 3,319 (1993), Adv. Mater. 6,677 (1994), Chem. Mater. 15, 3148 (2003), US Patent Application Publication No. 2003/0162053, US Patent Application Publication No. 2002/0158242, US Patent Application Publication No. 2006/0240279, US Patent Application Publication No. 2008 / 0220265, US Patent No. 5061569, International Publication No. 2007/002683, International Publication No. 2009/01809, EP650955, US Patent Application Publication No. 2008/01245772, US Patent Application Publication No. 2007/0278938 Specification, US Patent Application Publication No. 2008/0106190, US Patent Application Publication No. 2008/0018221, International Publication No. 2012/115342, Japanese Patent Application Laid-Open No. 2003-591432, JP-A-2006-135145. , US Patent Application No. 13/585981, etc.

The hole transporting material may be used alone or in combination of two or more.

《Electronic blocking layer》
The electron blocking layer is a layer having a function of a hole transporting layer in a broad sense, and is preferably made of a material having a function of transporting holes and a small ability to transport electrons, while transporting holes. By blocking the electrons, the recombination probability of the electrons and holes can be improved.

Further, the structure of the hole transport layer described above can be used as an electron blocking layer according to the present invention, if necessary.

The electron blocking layer provided in the organic EL element of the present invention is preferably provided adjacent to the anode side of the light emitting layer.

The layer thickness of the electron blocking layer according to the present invention is preferably in the range of 3 to 100 nm, and more preferably in the range of 5 to 30 nm.

As the material used for the electron blocking layer, the material used for the hole transport layer described above containing the π-conjugated compound according to the present invention is preferably used, and the host compound described above is also preferably used for the electron blocking layer.

《Hole injection layer》
The hole injection layer (also referred to as “anode buffer layer”) according to the present invention is a layer provided between the anode and the light emitting layer in order to reduce the driving voltage and improve the emission brightness, and is an “organic EL element”. It is described in detail in Volume 2, Chapter 2, "Electrode Materials" (pages 123-166) of "The Forefront of Industrialization (published by NTS Co., Ltd. on November 30, 1998)".

In the present invention, the hole injection layer may be provided as needed and may be present between the anode and the light emitting layer or between the anode and the hole transport layer as described above.

The details of the hole injection layer are also described in JP-A-9-45479, 9-2660062, 8-288609, etc., and examples of the material used for the hole injection layer include , Materials used for the hole transport layer described above containing the π-conjugated compound according to the present invention.

Among them, phthalocyanine derivatives typified by copper phthalocyanine, hexaazatriphenylene derivatives as described in JP-A-2003-591432 and JP-A-2006-135145, metal oxides typified by vanadium oxide, amorphous carbon. , Polyaniline (emeraldine), polythiophene and other conductive polymers, tris (2-phenylpyridine) iridium complexes and the like, orthometallated complexes, triarylamine derivatives and the like are preferable.

The material used for the hole injection layer described above may be used alone or in combination of two or more.

"Additive"
The organic layer in the present invention described above may further contain other additives.

Examples of the additive include halogen elements such as bromine, iodine and chlorine, halogenated compounds, alkali metals and alkaline earth metals such as Pd, Ca and Na, compounds and complexes of transition metals, salts and the like.

The content of the additive can be arbitrarily determined, but is preferably 1000 ppm or less, more preferably 500 ppm or less, still more preferably 50 ppm or less, based on the total mass% of the contained layer. ..

However, it is not within this range depending on the purpose of improving the transportability of electrons and holes and the purpose of favoring the energy transfer of excitons.

<< Method of forming organic layer >>
A method for forming an organic layer (hole injection layer, hole transport layer, light emitting layer, hole blocking layer, electron transport layer, electron injection layer, intermediate layer, etc.) according to the present invention will be described.

The method for forming the organic layer according to the present invention is not particularly limited, and conventionally known methods such as a vacuum vapor deposition method and a wet method (also referred to as a wet process) can be used.

The wet method includes a spin coating method, a casting method, an inkjet method, a printing method, a die coating method, a blade coating method, a roll coating method, a spray coating method, a curtain coating method, an LB method (Langmuir-Blogget method), and the like. From the viewpoint of easy obtaining a homogeneous thin film and high productivity, a method having high suitability for the roll-to-roll method such as a die coating method, a roll coating method, an inkjet method, and a spray coating method is preferable.

Examples of the liquid medium for dissolving or dispersing the organic EL material used in the present invention include ketones such as methyl ethyl ketone and cyclohexanone, fatty acid esters such as ethyl acetate, halogenated hydrocarbons such as dichlorobenzene, toluene and xylene. Aromatic hydrocarbons such as mesitylene and cyclohexylbenzene, aliphatic hydrocarbons such as cyclohexane, decalin and dodecane, and organic solvents such as DMF and DMSO can be used.

Further, as a dispersion method, dispersion can be performed by a dispersion method such as ultrasonic waves, high shear force dispersion, or media dispersion.

Further, a different film forming method may be applied to each layer. The case of employing an evaporation method in the deposition, the deposition conditions may vary due to kinds of materials used, generally boat temperature 50 to 450 ° C., vacuum of ¹⁰ -6 ^{to 10} -2 Pa, deposition rate 0.01 It is desirable to appropriately select within the range of 50 nm / sec, substrate temperature -50 to 300 ° C., layer (film) thickness 0.1 nm to 5 μm, preferably 5 to 200 nm.

The formation of the organic layer according to the present invention is preferably carried out consistently from the hole injection layer to the cathode by one vacuuming, but it may be taken out in the middle and a different film forming method may be applied. In that case, it is preferable to carry out the work in a dry inert gas atmosphere.

"anode"
As the anode in the organic EL element, a metal, an alloy, an electrically conductive compound having a large work function (4 eV or more, preferably 4.5 eV or more) and a mixture thereof as an electrode material are preferably used. Specific examples of such an electrode material include metals such as Au and conductive transparent materials such as CuI, indium tin oxide (ITO), SnO ₂ , and ZnO. Further, a material such as IDIXO (In ₂ O _3- ZnO) which is amorphous and can produce a transparent conductive film may be used.

For the anode, a thin film may be formed by forming 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 when pattern accuracy is not required so much (about 100 μm or more). The pattern may be formed through a mask having a desired shape during vapor deposition or sputtering of the electrode material.

Alternatively, when a coatable substance such as an organic conductive compound is used, a wet film forming method such as a printing method or a coating method can also be used. When light emission is taken out from this anode, it is desirable to increase the transmittance to more than 10%, and the sheet resistance as the anode is preferably several hundred Ω / □ or less.

The film thickness of the anode depends on the material, but is usually selected within the range of 10 nm to 1 μm, preferably 10 to 200 nm.

"cathode"
As the cathode, a metal having a small work function (4 eV or less) (referred to as an electron-injectable metal), an alloy, an electrically conductive compound, or 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 ) Examples thereof include a mixture, indium, a lithium / aluminum mixture, aluminum, and a rare earth metal. Among these, from the viewpoint of electron injectability and durability against oxidation and the like, a mixture of an electron injectable metal and a second metal which is a stable metal having a larger work function value than this, for example, a magnesium / silver mixture. Magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al ₂ O ₃ ) mixture, lithium / aluminum mixture, aluminum and the like are suitable.

The cathode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering. The sheet resistance of the cathode is preferably several hundred Ω / □ or less, and the film thickness is usually selected in the range of 10 nm to 5 μm, preferably 50 to 200 nm.

In order to transmit the emitted light, it is convenient that the emission brightness is improved if either the anode or the cathode of the organic EL element is transparent or translucent.

Further, a transparent or translucent cathode can be produced by producing the above metal on the cathode having a film thickness of 1 to 20 nm and then producing the conductive transparent material mentioned in the description of the anode on the cathode. By applying the above, it is possible to manufacture an element in which both the anode and the cathode are transparent.

[Support board]
The type of support substrate (hereinafter, also referred to as substrate, substrate, etc.) that can be used for the organic EL element of the present invention is not particularly limited, and even if it is transparent, it is opaque. You may. When light is taken out from the support substrate side, the support substrate is preferably transparent. Examples of the transparent support substrate preferably used include glass, quartz, and a transparent resin film. A particularly preferable support substrate is a resin film capable of imparting flexibility to the organic EL element.

Examples of the resin film include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyethylene, polypropylene, cellophane, cellulose diacetate, cellulose triacetate (TAC), cellulose acetate butyrate, and cellulose acetate propionate. CAP), cellulose acetate phthalate, cellulose esters such as cellulose nitrate or derivatives thereof, polyvinylidene chloride, polyvinyl alcohol, polyethylene vinyl alcohol, syndiotactic polystyrene, polycarbonate, norbornene resin, polymethylpentene, polyether ketone, polyimide , Polyether sulfone (PES), polyphenylene sulfide, polysulfones, polyetherimide, polyetherketoneimide, polyamide, fluororesin, nylon, polymethylmethacrylate, acrylic or polyarylates, Arton (trade name: JSR) or Appel Cycloolefin resins such as (trade name: manufactured by Mitsui Kagaku Co., Ltd.) can be mentioned.

A film of an inorganic substance, an organic substance, or a hybrid film of both of them may be formed on the surface of the resin film, and the water vapor permeability (25 ± 0.5 ° C.) measured by a method according to JIS K 7129-1992. it is preferable that the relative humidity of (90 ± 2)% RH) is less of a barrier film 0.01g ^/ m 2 · 24h, more, oxygen permeability measured by the method based on JIS K 7126-1987 ^{There, 1 × 10 -3 cm 3 /} m 2 · 24h · atm or less, the water vapor permeability is preferably ^{1 × 10 -5 g / m 2} · 24h or less of the high barrier film.

As the material for forming the barrier film, any material that causes deterioration of the element such as water and oxygen but has a function of suppressing infiltration may be used, and for example, silicon oxide, silicon dioxide, silicon nitride and the like can be used. Further, in order to improve the brittleness of the film, it is more preferable to have a laminated structure of these inorganic layers and layers made of an organic material. The stacking order of the inorganic layer and the organic layer is not particularly limited, but it is preferable to stack the inorganic layer and the organic layer alternately a plurality of times.

The method for forming the barrier film is not particularly limited, and for example, vacuum deposition method, sputtering method, reactive sputtering method, molecular beam epitaxy method, cluster ion beam method, ion plating method, plasma polymerization method, atmospheric pressure plasma polymerization method. , Plasma CVD method, laser CVD method, thermal CVD method, coating method and the like can be used, but the atmospheric pressure plasma polymerization method as described in JP-A-2004-68143 is particularly preferable.

Examples of the opaque support substrate include a metal plate such as aluminum and stainless steel, a film or opaque resin substrate, and a ceramic substrate.

The external extraction quantum efficiency of the light emission of the organic EL device of the present invention at room temperature (25 ° C.) is preferably 1% or more, more preferably 5% or more.

Here, the external extraction quantum efficiency (%) = the number of photons emitted to the outside of the organic EL element / the number of electrons passed through the organic EL element × 100.

Further, a hue improving filter such as a color filter may be used in combination, or a color conversion filter that converts the emission color from the organic EL element into multiple colors using a phosphor may be used in combination.

[Sealing]
Examples of the sealing means used for sealing the organic EL element of the present invention include a method of adhering a sealing member, an electrode, and a support substrate with an adhesive. The sealing member may be arranged so as to cover the display area of the organic EL element, and may be intaglio-shaped or flat-plate-shaped. Further, transparency and electrical insulation are not particularly limited.

Specific examples thereof include a glass plate, a polymer plate / film, and a metal plate / film. Examples of the glass plate include soda lime glass, barium / strontium-containing glass, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, and quartz. Examples of the polymer plate include polycarbonate, acrylic, polyethylene terephthalate, polyether sulfide, and polysulfone. Examples of the metal plate include those made of one or more metals or alloys selected from the group consisting of stainless steel, iron, copper, aluminum, magnesium, nickel, zinc, chromium, titanium, molybdenum, silicon, germanium and tantalum.

In the present invention, a polymer film or a metal film can be preferably used because the organic EL element can be thinned. Furthermore, the polymer film is JIS K.
7126-1987 oxygen permeability measured in compliance with the method provided in the ^{1 × 10 -3 cm 3 / m} 2 · 24h · atm or less, as measured by the method based on JIS K 7129-1992, the water vapor transmission rate (25 ± 0.5 ° C., a relative humidity of 90 ± 2%) is preferably one of the following ^{1 × 10 -3 g / m 2} · 24h.

Sandblasting, chemical etching, etc. are used to process the sealing member into a concave shape.

Specific examples of the adhesive include a photocurable and thermosetting adhesive having a reactive vinyl group of an acrylic acid-based oligomer, a moisture-curable adhesive such as 2-cyanoacrylic acid ester, and the like. be able to. In addition, heat and chemical curing type (two-component mixture) such as epoxy type can be mentioned. Further, hot melt type polyamide, polyester and polyolefin can be mentioned. In addition, a cation-curable type ultraviolet-curable epoxy resin adhesive can be mentioned.

Since the organic EL element may be deteriorated by heat treatment, it is preferable that the organic EL element can be adhesively cured from room temperature to 80 ° C. Further, the desiccant may be dispersed in the adhesive. A commercially available dispenser may be used to apply the adhesive to the sealing portion, or printing may be performed as in screen printing.

Further, it is also preferable that the electrode and the organic layer are coated on the outside of the electrode on the side facing the support substrate with the organic layer sandwiched therein, and an inorganic or organic layer is formed in contact with the support substrate to form a sealing film. .. In this case, the material for forming the film may be any material having a function of suppressing infiltration of a material that causes deterioration of the element such as moisture and oxygen, and for example, silicon oxide, silicon dioxide, silicon nitride or the like may be used. it can.

Further, in order to improve the brittleness of the film, it is preferable to have a laminated structure of these inorganic layers and layers made of an organic material. The method for forming these films is not particularly limited, and for example, vacuum deposition method, sputtering method, reactive sputtering method, molecular beam epitaxy method, cluster ion beam method, ion plating method, plasma polymerization method, atmospheric pressure plasma weight. Legal, plasma CVD method, laser CVD method, thermal CVD method, coating method and the like can be used.

In the gas phase and liquid phase, an inert gas such as nitrogen or argon or an inert liquid such as fluorinated hydrocarbon or silicon oil may be injected into the gap between the sealing member and the display region of the organic EL element. preferable. It is also possible to create a vacuum. It is also possible to enclose a hygroscopic compound inside.

Examples of the hygroscopic compound include metal oxides (eg, sodium oxide, potassium oxide, calcium oxide, barium oxide, magnesium oxide, aluminum oxide, etc.) and sulfates (eg, sodium sulfate, calcium sulfate, magnesium sulfate, cobalt sulfate, etc.). Etc.), metal halides (eg calcium chloride, magnesium chloride, cesium fluoride, tantalum fluoride, cerium bromide, magnesium bromide, barium iodide, magnesium iodide, etc.), perchlorates (eg, perchlorate) Barium, magnesium perchlorate, etc.) and the like, and anhydrous salts are preferably used for sulfates, metal halides and perchlorates.

[Protective film, protective plate]
A protective film or a protective plate may be provided on the outside of the sealing film or the sealing film on the side facing the support substrate with the organic layer sandwiched in order to increase the mechanical strength of the element. In particular, when the sealing is performed by the sealing film, its mechanical strength is not necessarily high, so it is preferable to provide such a protective film and a protective plate. As a material that can be used for this, a glass plate, a polymer plate / film, a metal plate / film, etc. similar to those used for the sealing can be used, but the polymer film is lightweight and thin. It is preferable to use.

[Light extraction improvement technology]
The organic EL element emits light inside a layer having a refractive index higher than that of air (within a refractive index of about 1.6 to 2.1), and about 15% to 20% of the light generated in the light emitting layer is emitted. It is generally said that only can be taken out. This is because light incident on the interface (intersection between the transparent substrate and air) at an angle θ equal to or greater than the critical angle causes total internal reflection and cannot be taken out of the element, and the transparent electrode or light emitting layer and the transparent substrate This is because the light is totally reflected between them, the light is waveguideed through the transparent electrode or the light emitting layer, and as a result, the light escapes toward the side surface of the element.

As a method for improving the efficiency of light extraction, for example, a method of forming irregularities on the surface of a transparent substrate to prevent total reflection at the interface between the transparent substrate and the air (for example, US Pat. No. 4,774,435), the substrate A method of improving efficiency by providing light-collecting property (for example, Japanese Patent Application Laid-Open No. 63-314795), a method of forming a reflective surface on a side surface of an element (for example, Japanese Patent Application Laid-Open No. 1-220394), a substrate A method of forming an antireflection film by introducing a flat layer having an intermediate refractive index between the light emitting body and the light emitting body (for example, Japanese Patent Application Laid-Open No. 62-172691), which has a lower refractive index than the substrate between the substrate and the light emitting body. A method of introducing a flat layer having a refractive index (for example, Japanese Patent Application Laid-Open No. 2001-202827), a method of forming a diffraction grating between layers of a substrate, a transparent electrode layer or a light emitting layer (including between the substrate and the outside world) ( JP-A-11-283751) and the like.

In the present invention, these methods can be used in combination with the organic EL element of the present invention, but a method of introducing a flat layer having a lower refractive index than the substrate between the substrate and the light emitter, or the substrate, transparent. A method of forming a diffraction grating between layers (including between the substrate and the outside world) of either the electrode layer or the light emitting layer can be preferably used.

According to the present invention, by combining these means, an element having higher brightness or excellent durability can be obtained.

When a medium having a low refractive index is formed between the transparent electrode and the transparent substrate with a thickness longer than the wavelength of light, the light emitted from the transparent electrode has a higher efficiency of being taken out to the outside as the refractive index of the medium is lower. Become.

Examples of the low refractive index layer include airgel, porous silica, magnesium fluoride, and a fluorine-based polymer. Since the refractive index of the transparent substrate is generally in the range of about 1.5 to 1.7, it is preferable that the low refractive index layer has a refractive index of about 1.5 or less. Further, it is preferably 1.35 or less.

Further, it is desirable that the thickness of the low refractive index medium is at least twice the wavelength in the medium. This is because the effect of the low refractive index layer diminishes when the thickness of the low refractive index medium becomes about the wavelength of light and the film thickness of the electromagnetic wave exuded by evanescent enters the substrate.

The method of introducing the diffraction grating into the interface where total reflection occurs or any medium is characterized in that the effect of improving the light extraction efficiency is high. This method is generated from the light emitting layer by utilizing the property that the diffraction grating can change the direction of light to a specific direction different from refraction by so-called Bragg diffraction such as first-order diffraction or second-order diffraction. Of the generated light, the light that cannot go out due to total reflection between the layers is diffracted by introducing a diffraction grating between either layer or in the medium (inside the transparent substrate or in the transparent electrode). , Trying to get the light out.

It is desirable that the diffraction grating to be introduced has a two-dimensional periodic refractive index. This is because the light emitted by the light emitting layer is randomly generated in all directions, so a general one-dimensional diffraction grating that has a periodic refractive index distribution only in one direction diffracts only the light that travels in a specific direction. The light extraction efficiency does not increase so much.

However, by making the refractive index distribution a two-dimensional distribution, light traveling in all directions is diffracted, and the light extraction efficiency is improved.

The position where the diffraction lattice is introduced may be in any of the layers or in the medium (inside the transparent substrate or in the transparent electrode), but it is desirable that the position is near the organic light emitting layer where light is generated. At this time, the period of the diffraction grating is preferably in the range of about 1/2 to 3 times the wavelength of the light in the medium. It is preferable that the arrangement of the diffraction grating is two-dimensionally repeated, such as a square lattice shape, a triangular lattice shape, and a honeycomb lattice shape.

[Condensing sheet]
The organic EL element of the present invention is processed to provide a structure on a microlens array on the light extraction side of a support substrate (substrate), or by combining with a so-called condensing sheet, in a specific direction, for example, with respect to an element light emitting surface. By condensing light in the front direction, the brightness in a specific direction can be increased.

As an example of a microlens array, a quadrangular pyramid having a side of 30 μm and an apex angle of 90 degrees is arranged two-dimensionally on the light extraction side of the substrate. One side is preferably in the range of 10 to 100 μm. If it is smaller than this, the effect of diffraction occurs and it is colored, and if it is too large, the thickness becomes thick, which is not preferable.

As the condensing sheet, for example, a sheet that has been put into practical use in an LED backlight of a liquid crystal display device can be used. As such a sheet, for example, a brightness increasing film (BEF) manufactured by Sumitomo 3M Ltd. can be used. The shape of the prism sheet may be, for example, a base material having a Δ-shaped stripe having an apex angle of 90 degrees and a pitch of 50 μm, or a shape having a rounded apex angle and a randomly changing pitch. It may have a formed shape or another shape.

Further, the light diffusing plate / film may be used in combination with the condensing sheet in order to control the light emission angle from the organic EL element. For example, a diffusion film (light-up) manufactured by Kimoto Co., Ltd. can be used.

[Use]
The organic EL element of the present invention can be used as an electronic device, for example, a display device, a display, and various light emitting devices.

As the light emitting device, for example, a lighting device (household lighting, in-car lighting), a backlight for a clock or a liquid crystal, a signboard advertisement, a traffic light, a light source of an optical storage medium, a light source of an electrophotographic copying machine, a light source of an optical communication processor, light Examples thereof include, but are not limited to, a light source for a sensor, but the light source can be effectively used as a backlight for a liquid crystal display device and a light source for lighting.

If necessary, the organic EL device of the present invention may be patterned by a metal mask, an inkjet printing method, or the like at the time of film formation. In the case of patterning, only the electrodes may be patterned, the electrodes and the light emitting layer may be patterned, or all the layers of the device may be patterned. In the fabrication of the device, a conventionally known method is used. Can be done.

<Display device>
The display device provided with the organic EL element of the present invention may be monochromatic or multicolored, but here, a multicolor display device will be described.

In the case of a multicolor display device, a shadow mask is provided only when the light emitting layer is formed, and a film can be formed on one surface by a vapor deposition method, a casting method, a spin coating method, an inkjet method, a printing method, or the like.

When patterning only the light emitting layer, the method is not limited, but a vapor deposition method, an inkjet method, a spin coating method, and a printing method are preferable.

The configuration of the organic EL element provided in the display device is selected from the above-mentioned configuration examples of the organic EL element, if necessary.

The method for manufacturing the organic EL device is as shown in the above-described aspect of manufacturing the organic EL device of the present invention.

When a DC voltage is applied to the multicolor display device thus obtained, light emission can be observed by applying a voltage of about 2 to 40 V with the positive polarity of the anode and the negative polarity of the cathode. Further, even if a voltage is applied with the opposite polarity, no current flows and no light emission occurs. When an AC voltage is further applied, light is emitted only when the anode is in the + state and the cathode is in the-state. The waveform of the applied alternating current may be arbitrary.

The multicolor display device can be used as a display device, a display, or various light emitting light sources. Full-color display is possible by using three types of organic EL elements that emit blue, red, and green in a display device or display.

Examples of the display device or display include televisions, personal computers, mobile devices, AV devices, teletext displays, information displays in automobiles, and the like. In particular, it may be used as a display device for reproducing a still image or a moving image, and the driving method when used as a display device for reproducing a moving image may be either a simple matrix (passive matrix) method or an active matrix method.

Light emitting devices include household lighting, interior lighting, backlights for clocks and liquid crystals, signboard advertisements, traffic lights, light sources for optical storage media, light sources for electrophotographic copying machines, light sources for optical communication processors, light sources for optical sensors, etc. However, the present invention is not limited thereto.

Hereinafter, an example of a display device having the organic EL element of the present invention will be described with reference to the drawings.

FIG. 2 is a schematic view showing an example of a display device composed of an organic EL element. It is a schematic diagram of the display of a mobile phone or the like that displays image information by emitting light of an organic EL element.

The display 1 has a display unit A having a plurality of pixels, a control unit B that scans an image of the display unit A based on image information, a wiring unit C that electrically connects the display unit A and the control unit B, and the like.

The control unit B is electrically connected via the display unit A and the wiring unit C, sends a scanning signal and an image data signal to each of a plurality of pixels based on image information from the outside, and the scanning signal is used to send a pixel for each scanning line. Lights up sequentially according to the image data signal, scans the image, and displays the image information on the display unit A.

FIG. 3 is a schematic view of a display device based on the active matrix method.

The display unit A has a wiring unit C including a plurality of scanning lines 5 and data lines 6 and a plurality of pixels 3 and the like on the substrate. The main members of the display unit A will be described below.

FIG. 3 shows a case where the light emitted from the pixel 3 is taken out in the direction of the white arrow (downward).

The scanning line 5 and the plurality of data lines 6 of the wiring portion are each made of a conductive material, and the scanning line 5 and the data line 6 are orthogonal to each other in a grid pattern and are connected to the pixel 3 at orthogonal positions (details are shown in the figure). Not).

When a scanning signal is applied from the scanning line 5, the pixel 3 receives an image data signal from the data line 6 and emits light according to the received image data.

Full-color display is possible by appropriately arranging pixels in the red region, pixels in the green region, and pixels in the blue region of the emission color on the same substrate.

Next, the light emitting process of the pixel will be described. FIG. 4 is a schematic view showing a pixel circuit.

The pixel includes an organic EL element 10, a switching transistor 11, a drive transistor 12, a capacitor 13, and the like. Full-color display can be performed by using organic EL elements that emit red, green, and blue light as the organic EL elements 10 for a plurality of pixels and arranging them side by side on the same substrate.

In FIG. 4, an image data signal is applied from the control unit B to the drain of the switching transistor 11 via the data line 6. Then, when a scanning signal is applied from the control unit B to the gate of the switching transistor 11 via the scanning line 5, the driving of the switching transistor 11 is turned on, and the image data signal applied to the drain is the capacitor 13 and the driving transistor 12. It is transmitted to the gate of.

By transmitting the image data signal, the capacitor 13 is charged according to the potential of the image data signal, and the drive transistor 12 is driven on. In the drive transistor 12, the drain is connected to the power supply line 7, the source is connected to the electrode of the organic EL element 10, and the power supply line 7 is connected to the organic EL element 10 according to the potential of the image data signal applied to the gate. Current is supplied.

When the scanning signal is transferred to the next scanning line 5 by the sequential scanning of the control unit B, the driving of the switching transistor 11 is turned off. However, since the capacitor 13 holds the potential of the charged image data signal even when the drive of the switching transistor 11 is turned off, the drive of the drive transistor 12 is kept on and the next scan signal is applied. The light emission of the organic EL element 10 continues until. When the next scanning signal is applied by the sequential scanning, the driving transistor 12 is driven according to the potential of the next image data signal synchronized with the scanning signal, and the organic EL element 10 emits light.

That is, for the light emission of the organic EL element 10, the switching transistor 11 and the drive transistor 12, which are active elements, are provided for the organic EL element 10 of each of the plurality of pixels, and the organic EL element 10 of each of the plurality of pixels 3 emits light. It is carried out. Such a light emitting method is called an active matrix method.

Here, the light emission of the organic EL element 10 may be light emission of a plurality of gradations by a multi-valued image data signal having a plurality of gradation potentials, or may be on or off of a predetermined amount of light emission by a binary image data signal. Good. Further, the potential of the capacitor 13 may be continuously maintained until the next scanning signal is applied, or may be discharged immediately before the next scanning signal is applied.

The present invention is not limited to the active matrix method described above, and may be a passive matrix type light emission drive in which the organic EL element emits light in response to the data signal only when the scanning signal is scanned.

FIG. 5 is a schematic view of a display device based on the passive matrix method. In FIG. 5, a plurality of scanning lines 5 and a plurality of image data lines 6 are provided in a grid pattern so as to face each other with the pixel 3 interposed therebetween.

When the scanning signal of the scanning line 5 is applied by the sequential scanning, the pixel 3 connected to the applied scanning line 5 emits light according to the image data signal.

In the passive matrix method, the pixel 3 has no active element, and the manufacturing cost can be reduced.

By using the organic EL element of the present invention, a display device having improved luminous efficiency was obtained.

<Lighting device>
The organic EL element of the present invention can also be used in a lighting device.

The organic EL element of the present invention may be used as an organic EL element having a resonator structure. The purpose of using the organic EL element having such a resonator structure includes a light source of an optical storage medium, a light source of an electrophotographic copying machine, a light source of an optical communication processor, a light source of an optical sensor, and the like. Not limited. Further, it may be used for the above purpose by oscillating a laser.

Further, the organic EL element of the present invention may be used as a kind of lamp such as for lighting or an exposure light source, a projection device of a type for projecting an image, or a type for directly visually recognizing a still image or a moving image. It may be used as a display device (display).

When used as a display device for moving image playback, the drive system may be either a passive matrix system or an active matrix system. Alternatively, a full-color display device can be manufactured by using two or more kinds of organic EL elements of the present invention having different emission colors.

Further, the π-conjugated compound used in the present invention can be applied to a lighting device including an organic EL element that emits substantially white light. For example, when a plurality of light emitting materials are used, white light emission can be obtained by simultaneously emitting a plurality of light emitting colors and mixing the colors. The combination of a plurality of emission colors may include three emission maximum wavelengths of the three primary colors of red, green and blue, or two using the relationship of complementary colors such as blue and yellow and blue-green and orange. It may contain the maximum emission wavelength.

Further, in the method for forming the organic EL element of the present invention, a mask may be provided only when the light emitting layer, the hole transport layer, the electron transport layer, or the like is formed, and the mask may be applied separately. Since the other layers are common, patterning such as a mask is not required, and an electrode film can be formed on one surface by a vapor deposition method, a casting method, a spin coating method, an inkjet method, a printing method, or the like, and productivity is also improved.

According to this method, unlike a white organic EL device in which light emitting elements of a plurality of colors are arranged in parallel in an array, the elements themselves emit white light.

[One aspect of the lighting device of the present invention]
An aspect of the lighting device of the present invention provided with the organic EL element of the present invention will be described.

The non-light emitting surface of the organic EL element of the present invention is covered with a glass case, a glass substrate having a thickness of 300 μm is used as a sealing substrate, and an epoxy-based photocurable adhesive (Lux manufactured by Toa Synthetic Co., Ltd.) is used as a sealing material around the glass substrate. Track LC0629B) is applied, which is placed on the cathode and brought into close contact with the transparent support substrate, irradiated with UV light from the glass substrate side, cured, sealed, and illuminated as shown in FIGS. 6 and 7. The device can be formed.

FIG. 6 shows a schematic view of the lighting device, and the organic EL element (organic EL element 101 in the lighting device) of the present invention is covered with a glass cover 102 (note that the sealing work with the glass cover is lighting. The organic EL element 101 in the apparatus was carried out in a glove box in a nitrogen atmosphere (in an atmosphere of high-purity nitrogen gas having a purity of 99.999% or more) without being brought into contact with the atmosphere).

FIG. 7 shows a cross-sectional view of the lighting device, where 105 is a cathode, 106 is an organic layer, and 107 is a glass substrate with a transparent electrode. The glass cover 102 is filled with nitrogen gas 108, and a water catching agent 109 is provided.

By using the organic EL element of the present invention, a lighting device having improved luminous efficiency was obtained.

<Organic EL element material>
As the organic EL element material, the electron transporting material according to the present invention is an electron transporting material containing a π-conjugated compound having a structure represented by the general formula (1), and is the π-conjugated compound. The compound is characterized in that the absolute value of the difference between the lowest excited singlet energy level and the lowest excited triplet energy level is 0.5 eV or less.

By using this π-conjugated compound in the charge transfer layer of the organic EL element, triplet excitons generated on the π-conjugated compound are not deactivated, but become singlet excitons by inverse intersystem crossing (RISC). By converting to and suppressing the deactivation of excitons, the light emission efficiency of the organic EL element can be improved.

Further, the π-conjugated compound according to the present invention as an electron transporting material can also be used for an electron transporting thin film .

<Charge transfer thin film>
As the charge transfer thin film, the electron transporting thin film according to the present invention contains a π-conjugated compound having a structure represented by the general formula (1) and has the lowest excited singlet energy of the π-conjugated compound. The absolute value of the difference between the level and the lowest excited triplet energy level is 0.5 eV or less.

The charge-transfer thin film of the present invention can be produced in the same manner as in the method for forming the organic layer.

The method for forming the charge-transfer thin film of the present invention is not particularly limited, and conventionally known methods such as a vacuum vapor deposition method and a wet method (also referred to as a wet process) can be used.

The wet method includes a spin coating method, a casting method, an inkjet method, a printing method, a die coating method, a blade coating method, a roll coating method, a spray coating method, a curtain coating method, an LB method (Langmuir-Blogget method), and the like. From the viewpoint of easy obtaining a homogeneous thin film and high productivity, a method having high suitability for the roll-to-roll method such as a die coating method, a roll coating method, an inkjet method, and a spray coating method is preferable.

Examples of the liquid medium for dissolving or dispersing the charge-transfer thin film used in the present invention include ketones such as methyl ethyl ketone and cyclohexanone, fatty acid esters such as ethyl acetate, halogenated hydrocarbons such as dichlorobenzene, toluene and xylene. , Aromatic hydrocarbons such as mesitylene and cyclohexylbenzene, aliphatic hydrocarbons such as cyclohexane, decalin and dodecane, and organic solvents such as DMF and DMSO can be used.

Further, as a dispersion method, dispersion can be performed by a dispersion method such as ultrasonic waves, high shear force dispersion, or media dispersion.

Further, a different film forming method may be applied to each layer. The case of employing an evaporation method in the deposition, the deposition conditions may vary due to kinds of materials used, generally in the range boat heating temperature of 50 to 450 ° C., a vacuum degree of 10 -6 ^{to 10} -2 ^Pa range The vapor deposition rate should be appropriately selected within the range of 0.01 to 50 nm / sec, the substrate temperature within the range of -50 to 300 ° C., the layer thickness within the range of 0.1 nm to 5 μm, and preferably within the range of 5 to 200 nm. desirable.

When the spin coating method is adopted for film formation, it is preferable to carry out the spin coater within the range of 100 to 1000 rpm and within the range of 10 to 120 seconds in a dry inert gas atmosphere.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In the examples, the indication of "parts" or "%" is used, but unless otherwise specified, it indicates "parts by mass" or "% by mass".

The compounds used in the examples are shown below.

[Example 1]
<< Fabrication of organic EL element 1-1 >>
After patterning on a substrate (NA45 manufactured by NH Technoglass Co., Ltd.) in which ITO (indium tin oxide) was formed to a thickness of 100 nm on a glass substrate of 100 mm × 100 mm × 1.1 mm as an anode, this ITO transparent electrode was used. The transparent support substrate provided with the above was ultrasonically washed with isopropyl alcohol, dried with dry nitrogen gas, and UV ozone washed for 5 minutes.

On this transparent support substrate, poly (3,4-ethylenedioxythiophene) -polystyrene sulfonate (PEDOT / PSS, Bayer, Baytron P Al 4083) was diluted to 70% with pure water at 3000 rpm. After forming a thin film by a spin coating method under the condition of 30 seconds, it was dried at 200 ° C. for 1 hour to provide a hole injection layer having a layer thickness of 20 nm. This transparent support substrate was fixed to a substrate holder of a commercially available vacuum vapor deposition apparatus, and each of the vapor deposition crucibles in the vacuum vapor deposition apparatus was filled with the constituent materials of each layer in an optimum amount for manufacturing an element. As the crucible for vapor deposition, a crucible made of molybdenum or tungsten made of a resistance heating material was used.

After depressurizing to a vacuum degree of 1 × 10 ^-4 Pa, α-NPD as a hole transport material is vapor-deposited on the hole injection layer at a vapor deposition rate of 0.1 nm / sec to form a hole transport layer having a layer thickness of 40 nm. did. CDBP and luminescent compound 1 were co-deposited as host compounds at a vapor deposition rate of 0.1 nm / sec so as to be 95% and 5% by volume, respectively, to form a light emitting layer having a layer thickness of 30 nm.

Then, TPBi was vapor-deposited as an electron-transporting material at a vapor deposition rate of 0.1 nm / sec to form an electron-transporting layer having a layer thickness of 30 nm.

Further, after forming sodium fluoride with a thickness of 1 nm, 100 nm of aluminum was vapor-deposited to form a cathode.

The non-light emitting surface side of the element is covered with the can-shaped glass case shown in FIGS. 6 and 7 in an atmosphere of high-purity nitrogen gas having a purity of 99.999% or more, and an electrode take-out wiring is installed to install an organic EL element. 1-1 was prepared.

<< Fabrication of Organic EL Elements 1-2-1-10 >>
In the production of the organic EL device 1-1, the electron transport layer is used as the second component of the TPBi and the electron transport material, and the compounds shown in Table 1 are co-deposited at a volume ratio of 70:30 and a vapor deposition rate of 0.1 nm / sec. The organic EL elements 1-2 to 1-10 were produced in the same manner as in the production of the organic EL element 1-1, except that the electron transport layer having a layer thickness of 30 nm was formed.

<< Fabrication of organic EL element 1-11 >>
In the production of the organic EL element 1-6, the organic EL element 1-11 was produced in the same manner as the organic EL element 1-6 except that the host compound in the light emitting layer was changed from CDBP to the exemplary compound T-20.

《Evaluation》
(Measurement of luminous efficiency)
Each of the above-produced organic EL elements is made to emit light at room temperature (about 25 ° C.) under a constant current condition of ^2.5 mA / cm ² , and the luminous brightness immediately after the start of light emission is measured by the spectral radiance meter CS-2000 (Konica Minolta). The luminous efficiency was calculated by measuring using (manufactured by Konica Minolta). The obtained results showed relative values with the organic EL element 1-1 as 100.

(Measurement of ΔEst)
The absolute value (ΔEst) of the difference between the lowest excited singlet energy level and the lowest excited triplet energy level is determined by the molecular orbital calculation software Gaussian09 (Revision C.01, MJ Frisch, et al, Gaussian, Inc.). , 2010.), Using the optimized structure calculated by the density general function method using the general function B3LYP and the base function 6-31G (d), the time-dependent density using the same general function and base function as above. It was calculated by calculating the excited state by the general function method (Time-Dependent DFT).

The results obtained are shown in Table 1.

From Table 1, in the organic EL elements 1-2 and 1-3 in which a compound having ΔEst greater than 0.5 eV was used for the electron transport layer, the light emission efficiency was not significantly improved as compared with the organic EL element 1-1. The improvement in light emission efficiency is more remarkable in the organic EL elements 1-4 to 1-11 of the present invention using the π-electron conjugated compound having ΔEst of 0.5 eV or less, and the π-electron conjugated compound according to the present invention is used as an electron. It can be seen that inclusion in the transport layer is effective in improving the light emission efficiency. Moreover, this tendency was more remarkable as the ΔEst was smaller. Further, when a π-electron conjugated compound is used in the light emitting layer together with the electron transport layer, a larger effect can be obtained.

[ Reference example 2 ]
<< Fabrication of organic EL element 2-1 >>
After patterning on a substrate (NA45 manufactured by NH Technoglass Co., Ltd.) in which ITO (indium tin oxide) was formed to a thickness of 100 nm on a glass substrate of 100 mm × 100 mm × 1.1 mm as an anode, this ITO transparent electrode was used. The transparent support substrate provided with the above was ultrasonically washed with isopropyl alcohol, dried with dry nitrogen gas, and UV ozone washed for 5 minutes.

On this transparent support substrate, poly (3,4-ethylenedioxythiophene) -polystyrene sulfonate (PEDOT / PSS, Bayer, Baytron P Al 4083) was diluted to 70% with pure water at 3000 rpm. After forming a thin film by a spin coating method under the condition of 30 seconds, it was dried at 200 ° C. for 1 hour to provide a hole injection layer having a layer thickness of 20 nm. This transparent support substrate was fixed to a substrate holder of a commercially available vacuum vapor deposition apparatus, and each of the vapor deposition crucibles in the vacuum vapor deposition apparatus was filled with the constituent materials of each layer in an optimum amount for manufacturing an element. As the crucible for vapor deposition, a crucible made of molybdenum or tungsten made of a resistance heating material was used.

After depressurizing to a degree of vacuum of 1 × 10 ^-4 Pa, α-NPD was deposited on the hole injection layer at a vapor deposition rate of 0.1 nm / sec to form a hole transport layer having a layer thickness of 40 nm. CBP and luminescent compound 1 were co-deposited as host compounds at a vapor deposition rate of 0.1 nm / sec so as to be 95% and 5% by volume, respectively, to form a light emitting layer having a layer thickness of 30 nm.

Then, TPBi was vapor-deposited at a vapor deposition rate of 0.1 nm / sec to form an electron transport layer having a layer thickness of 30 nm.

Further, after forming sodium fluoride with a thickness of 1 nm, 100 nm of aluminum was vapor-deposited to form a cathode.

The non-light emitting surface side of the element is covered with the can-shaped glass case shown in FIGS. 6 and 7 in an atmosphere of high-purity nitrogen gas having a purity of 99.999% or more, and an electrode take-out wiring is installed to install an organic EL element. 2-1 was prepared.

<< Fabrication of organic EL elements 2-2-2-10 >>
In the production of the organic EL element 2-1, the layer thicknesses of the light emitting layer and the electron transport layer were set to 25 nm, respectively, and the materials shown in Table 2 were deposited between the light emitting layer and the electron transport layer at a vapor deposition rate of 0.1 nm / sec. The organic EL element 2-2-2-10 was produced in the same manner as in the production of the organic EL element 2-1 except that the intermediate layer having a thickness of 10 nm was formed.

<< Fabrication of organic EL element 2-11 >>
In the production of the organic EL element 2-8, the organic EL element 2-11 is produced in the same manner as the organic EL element 2-8 except that the light emitting material in the light emitting layer is changed from the luminescent compound 1 to the exemplary compound T-38. did.

《Evaluation》
Luminous efficiency was measured in the same manner as in Example 1. The results are shown in Table 2. The obtained results showed relative values with the organic EL element 2-1 as 100.

From Table 2, in the comparative organic EL elements 2-2 and 2-3 using compounds having an absolute value of ΔEst larger than 0.5 eV, the light emission efficiency is not significantly improved as compared with the organic EL element 2-1. The improvement in light emission efficiency is more remarkable in the organic EL elements 2-4 to 2-11 of the reference example using the π-electron conjugated compound having a ΔEst value of 0.5 eV or less, and the intermediate layer according to the present invention. It can be seen that the inclusion of the π-conjugated compound is effective in improving the light emission efficiency. Moreover, this tendency was more remarkable as the ΔEst was smaller. Furthermore, it can be seen that a greater effect can be obtained when a π-conjugated compound is used in the light emitting layer together with the intermediate layer.

[ Reference example 3 ]
<< Fabrication of organic EL element 3-1 >>
A transparent substrate provided with this ITO transparent electrode after patterning on a substrate (NA45 manufactured by NH Technoglass Co., Ltd.) in which ITO (indium tin oxide) was deposited at 100 nm on a glass substrate of 100 mm × 100 mm × 1.1 mm as an anode. The support substrate was ultrasonically washed with isopropyl alcohol, dried with dry nitrogen gas, and UV ozone washed for 5 minutes.

On this transparent support substrate, poly (3,4-ethylenedioxythiophene) -polystyrene sulfonate (PEDOT / PSS, Bayer, Baytron P Al 4083) was diluted to 70% with pure water at 3000 rpm. After forming a thin film by a spin coating method under the condition of 30 seconds, it was dried at 200 ° C. for 1 hour to provide a hole injection layer having a layer thickness of 20 nm. This transparent support substrate was fixed to a substrate holder of a commercially available vacuum vapor deposition apparatus, and each of the vapor deposition crucibles in the vacuum vapor deposition apparatus was filled with the constituent materials of each layer in an optimum amount for manufacturing an element. As the crucible for vapor deposition, a crucible made of molybdenum or tungsten made of a resistance heating material was used.

After depressurizing to a degree of vacuum of 1 × 10 ^-4 Pa, α-NPD was deposited on the hole injection layer at a vapor deposition rate of 0.1 nm / sec to form a hole transport layer having a layer thickness of 40 nm. The mCP and the luminescent compound 2 were co-deposited at a vapor deposition rate of 0.1 nm / sec so as to be 91% and 9% by volume, respectively, to form a light emitting layer having a layer thickness of 30 nm.

Then, TPBi was vapor-deposited at a vapor deposition rate of 0.1 nm / sec to form an electron transport layer having a layer thickness of 30 nm.

Further, after forming sodium fluoride with a film thickness of 1 nm, aluminum 100 nm was vapor-deposited to form a cathode.

The non-light emitting surface side of the element is covered with the can-shaped glass case shown in FIGS. 6 and 7 in an atmosphere of high-purity nitrogen gas having a purity of 99.999% or more, and an electrode take-out wiring is installed to install an organic EL element. 3-1 was prepared.

<< Fabrication of organic EL element 3-2 >>
Except that mCP was used as the host compound, luminescent compound 2 was used as the luminescent compound, and comparative compound 1 was used as the third component, and the light emitting layer was formed so that the respective ratios were 80%, 5%, and 15% by volume. The organic EL element 3-2 was produced in the same manner as in the production of the organic EL element 3-1.

<< Fabrication of organic EL elements 3-3 to 3-10 >>
As shown in Table 2, organic EL elements 3-3 to 3-10 were produced in the same manner as the organic EL element 3-2 except that the third component (assist dopant) was changed.

《Evaluation》
Luminous efficiency was measured in the same manner as in Example 1. The results are shown in Table 3. The obtained results showed relative values with the organic EL element 3-1 as 100.

From Table 3, in the organic EL devices 3-2 and 3-3 using compounds having ΔEst greater than 0.5 eV, the results were obtained that the light emission efficiency was lower than that of the organic EL device 3-1. The improvement in light emission efficiency is more remarkable in the organic EL devices 3-4 to 3-10 of the reference example using the π-conjugated compound according to the present invention having ΔEst of 0.5 eV or less, and the assist dopant of the third component It can be seen that the inclusion in the light emitting layer is effective in improving the light emitting efficiency. Further, it can be seen that this tendency is more remarkable as the ΔEst is smaller.

[ Reference example 4 ]
<< Fabrication of organic EL element 4-1 >>
ITO (indium tin oxide) as an anode is formed on a glass substrate having a thickness of 50 mm × 50 mm and a thickness of 0.7 mm to a thickness of 150 nm, and after patterning, a transparent substrate to which the ITO transparent electrode is attached. Was ultrasonically washed with isopropyl alcohol, dried with dry nitrogen gas, and UV ozone washed for 5 minutes, and then this transparent substrate was fixed to a substrate holder of a commercially available vacuum vapor deposition apparatus.

Each of the vapor deposition crucibles in the vacuum vapor deposition apparatus was filled with the constituent materials of each layer in the optimum amount for manufacturing the device. As the crucible for vapor deposition, a crucible made of molybdenum or tungsten made of a resistance heating material was used.

After depressurizing to a vacuum degree of 1 × 10 ^-4 Pa, the crucible for vapor deposition containing HAT-CN is energized and heated, and thin-film deposition is performed on an ITO transparent electrode at a vapor deposition rate of 0.1 nm / sec. A hole injection transport layer was formed.

Next, α-NPD was deposited on the hole injection layer at a vapor deposition rate of 0.1 nm / sec to form a hole transport layer having a layer thickness of 40 nm. The host compound mCP and the comparative compound 1 were co-deposited at a vapor deposition rate of 0.1 nm / sec so as to be 93% and 7% by volume, respectively, to form a light emitting layer having a layer thickness of 30 nm.

Then, BCP was vapor-deposited at a vapor deposition rate of 0.1 nm / sec to form an electron transport layer having a layer thickness of 30 nm.

Further, after forming lithium fluoride with a film thickness of 0.5 nm, aluminum 100 nm was vapor-deposited to form a cathode.

The non-light emitting surface side of the element is covered with the can-shaped glass case shown in FIGS. 6 and 7 in an atmosphere of high-purity nitrogen gas having a purity of 99.999% or more, and an electrode take-out wiring is installed to install an organic EL element. 4-1 was prepared.

<< Fabrication of organic EL elements 4-2-4-9 >>
Organic EL devices 4-2 to 4-9 were produced in the same manner as the organic EL device 4-1 except that the luminescent compound was changed from Comparative Compound 1 as shown in Table 4.

《Evaluation》
Luminous efficiency was measured in the same manner as in Example 1. The results are shown in Table 4. The obtained results showed relative values with the organic EL element 4-1 as 100.

From Table 4, from the organic EL element 4-3 of the reference example using the π-conjugated compound having ΔEst of 0.5 eV or less, rather than the organic EL elements 4-1 and 2 using the compound having ΔEst greater than 0.5 eV. In 4-9, the improvement in light emission efficiency is more remarkable, and it can be seen that the π-conjugated compound according to the present invention is useful as a fluorescent light emitting compound. Further, it can be seen that this tendency is more remarkable as the ΔEst is smaller.

[ Reference example 5 ]
<< Fabrication of organic EL element 5-1 >>
After forming an ITO (indium tin oxide) film with a thickness of 150 nm on a glass substrate having a thickness of 50 mm × 50 mm × 0.7 mm, patterning was performed to form an ITO transparent electrode as an anode. The transparent substrate provided with the ITO transparent electrode was ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen gas, and then UV ozone washed for 5 minutes. The obtained transparent substrate was fixed to a substrate holder of a commercially available vacuum vapor deposition apparatus.

Each of the resistance heating boats for vapor deposition in the vacuum vapor deposition apparatus was filled with the constituent materials of each layer in the optimum amount for manufacturing the device. The resistance heating boat was made of molybdenum or tungsten.

After depressurizing the inside of the vacuum vapor deposition apparatus to a vacuum degree of 1 × 10 ^-4 Pa, the resistance heating boat containing HAT-CN is energized and heated, and vapor deposition is performed on the ITO transparent electrode at a vapor deposition rate of 0.1 nm / sec. A hole injection layer having a thickness of 15 nm was formed.

Next, α-NPD was deposited at a vapor deposition rate of 0.1 nm / sec to form a hole transport layer having a thickness of 30 nm.

Next, a resistance heating boat containing Comparative Compound 1 as the host compound and Tris (2-phenylpyridinato) iridium (III) as the luminescent compound was energized and heated, and the deposition rate was 0.1 nm / sec, respectively. Co-deposited on the hole transport layer at 0.010 nm / sec to form a light emitting layer with a thickness of 40 nm.

Next, HB-1 was vapor-deposited at a vapor deposition rate of 0.1 nm / sec to form a first electron transport layer having a thickness of 5 nm.

Further, ET-1 was vapor-deposited on it at a vapor deposition rate of 0.1 nm / sec to form a second electron transport layer having a thickness of 45 nm.

Then, lithium fluoride was vapor-deposited to a thickness of 0.5 nm, and then 100 nm of aluminum was vapor-deposited to form a cathode, thereby producing an organic EL element 5-1.

<< Fabrication of Organic EL Elements 5-2-5-15 >>
A light emitting layer was formed in the same manner as the organic EL element 5-1 except that the host compound was changed as shown in Table 3, to prepare an organic EL element 5-2 to 5-15.

Luminous efficiency was measured in the same manner as in Example 1. The results are shown in Table 5. The obtained results showed relative values with the organic EL element 5-1 as 100.

From Table 5, the organic EL device 5- of the reference example using the π-conjugated compound having ΔEst of 0.5 eV or less rather than the organic EL devices 5-1 and 5-2 using compounds having ΔEst greater than 0.5 eV. From 3 to 5-15, the improvement in light emission efficiency is more remarkable. Further, it can be seen that this tendency is more remarkable as the ΔEst is smaller. It can be seen that the π-conjugated compound according to the present invention is useful as the host compound.

1 Display 3 pixels 5 Scanning line 6 Data line 7 Power supply line 10 Organic EL element 11 Switching transistor 12 Drive transistor 13 Condenser 101 Organic EL element in lighting device 102 Glass cover 105 Cathode 106 Organic layer 107 Glass substrate with transparent electrode 108 Nitrogen gas 109 Water trapping agent A Display unit B Control unit C Wiring unit

Claims (7)

An organic electroluminescence element having at least an electron transport layer as a charge transfer layer between an anode and a cathode, and the electron transport layer contains a π-conjugated compound having a structure represented by the following general formula (1). Moreover, the organic electroluminescence element is characterized in that the absolute value (ΔEst) of the difference between the lowest excited singlet energy level and the lowest excited triplet energy level of the π-conjugated compound is 0.5 eV or less.

(In the formula, A represents a group having a ring structure, A represents an aryl group substituted with an electron-withdrawing group, or a heteroaryl group optionally substituted. B and C represent a monocyclic group or a heteroaryl group. Represents an aryl ring or a heteroaryl ring, each of which is composed of a fused ring structure of up to 3 rings and may be substituted independently of each. X is O, S, N-R ¹ , C-R ² (R). ³ ), Si-R ⁴ (R ⁵ ), B-R ⁶ or single bond. R ^{1 to} R ⁶ each independently have a hydrogen atom, which may be substituted alkyl group, aryl group or Represents a heteroaryl group, except for the compounds represented by T-9 and T-19 below.)

The B and C may be independently substituted, respectively, benzene ring, naphthalene ring, indene ring, benzosilol ring, indol ring, benzofuran ring, benzothiophene ring, thienothiophene ring, phenanthrene ring, fluorene ring, The organic electroluminescence element according to claim 1, wherein it represents a dibenzosilol ring, a dibenzoborol ring, a carbazole ring, a dibenzofuran ring or a dibenzothiophene ring. The π-conjugated compound having a structure represented by the general formula (1) is a π-conjugated compound having a structure represented by any of the following general formulas (2) to (15). The organic electroluminescence element according to claim 1 or 2.

(In the formula, A and X are synonymous with A and X in the general formula (1). Y is O, S, N-R ⁷ , C-R ⁸ (R ⁹ ), Si-R ¹⁰ (R). ¹¹ ), B-R ¹² or CH = CH. R ^{7 to} R ¹² each independently represent a hydrogen atom, which may be substituted, an alkyl group, an aryl group or a heteroaryl group.) The ring structure A according to the general formulas (2) to (15) is substituted with an aryl ring having 6 to 20 carbon atoms and 1 to 5 fluorine atoms substituted with 1 to 5 cyano groups. Aryl rings having 6 to 20 carbon atoms, aryl rings having 6 to 20 carbon atoms substituted with 1 to 5 fluoroalkyl groups, benzene rings substituted with optionally substituted nitrogen-containing aromatic rings, or The organic electroluminescence element according to claim 3, wherein the nitrogen-containing aromatic ring may be substituted. A claim characterized in that the organic electroluminescence device has a light emitting layer, and a π-conjugated compound having a structure represented by the general formula (1) is contained in the electron transport layer adjacent to the light emitting layer. The organic electroluminescence device according to any one of items 1 to 4. A display device comprising the organic electroluminescence device according to any one of claims 1 to 5. A lighting device comprising the organic electroluminescence device according to any one of claims 1 to 5.

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