WO2014057971A1 - Electroluminescence element - Google Patents

Abstract

Disclosed is an electroluminescence element wherein a first electrode (2) (cathode), a first light-emitting layer (22), a second light-emitting layer (24), and a second electrode (8) (anode) are laminated on a substrate (1) in said order. In said element, the first light-emitting layer (22) contains quantum dots (30), the second light-emitting layer (24) contains a phosphorescence emission dopant, and an electron transport layer (21) is formed between the first electrode (2) and the first light-emitting layer (22).

Description

Electroluminescence element

The present invention relates to an electroluminescence element (EL element), and more particularly to an electroluminescence element excellent in luminous efficiency, luminous lifetime and color rendering.

In recent years, an organic electroluminescence element using an organic substance (hereinafter, abbreviated as “organic EL element” or “OLED; Organic light-Emitting Diode” as appropriate) is a solid light-emitting type that is lightweight, thin, and high. The use as an efficient and inexpensive large-area full-color display element and light source array is regarded as promising, and research and development is actively promoted.
In particular, in mobile bodies (cell phones, automobiles, aircraft), illumination that is thinner and lighter than conventional ones and that does not break (illumination made of a flexible substrate) is expected. In addition, while these new values are expected, the performance is low with respect to existing fluorescent lamps and white LEDs, and there is a need for technologies for further increasing efficiency and extending the life.

An organic EL element is composed of an organic functional layer (single layer portion or multilayer portion) having a thickness of only about 0.1 μm containing an organic light emitting substance between a pair of anode and cathode formed on a film. It is a thin film type all solid state device. When a relatively low voltage of about 2 to 20 V is applied to such an organic EL element, electrons are injected from the cathode and holes are injected from the anode into the organic compound layer. It is known that emission is obtained by releasing energy as light when the electrons and holes recombine in the light emitting layer and the energy level returns from the conduction band to the valence band. This technology is expected as a flat display and lighting.
In addition, recently discovered organic EL devices that use phosphorescence can realize a luminous efficiency that is approximately four times that of previous methods that use fluorescence. Research and development of organic functional layer layers and electrodes are conducted all over the world. In particular, as one of the measures to prevent global warming, application to lighting fixtures that occupy much of human energy consumption has begun to be studied. There are many attempts to reduce costs.

On the other hand, one of the major drawbacks of organic light-emitting diodes (OLEDs) is the wide spectral width of the light emitted by those OLEDs. Many of the spectra have such a wavelength band. In such an emission spectrum, the color rendering property cannot be improved, and there is a limit to increasing the light emission efficiency.

One solution to this problem is to use a hybrid diode that includes an organic light emitting layer (which emits fluorescence and phosphorescence) and quantum dots.
A quantum dot is a nanoparticle made of an inorganic semiconductor material having dimensions that are small enough to allow excitons to be confined within a three-dimensional space.
Typically, a quantum dot is composed of a core surrounded by a shell made of a semiconductor material having a forbidden band wider than that of the core. In order to change the chemical and physicochemical properties of the quantum dots, such as the ability of the quantum dots to remain suspended in the solvent, molecules may be deposited on the shell. Quantum dots emit light and have a relatively narrow emission band compared to organic light emitters, so that when properly incorporated as a light emitting element in an optoelectronic component, the quantum dots are , Making it possible to obtain extremely vivid colors. That is, it is expected that the color rendering property and light emission efficiency of OLED illumination can be further enhanced by combining quantum dots with OLEDs.

However, there is a large mismatch between the valence and conduction bands of quantum dots and the highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) of adjacent organic semiconductors.
Although LEDs including such an organic light emitting material and a quantum dot compound in the same layer have been proposed so far (a light emitting device that defines the wavelength relationship between quantum dots and phosphorescent light emitting materials as in Patent Document 1, (See, for example, composite light-emitting elements in which phosphorescent light-emitting molecules are incorporated into the ligands of quantum dots as in Patent Document 2), and high efficiency LEDs have not been obtained so far due to this mismatch. .
Therefore, for example, an attempt to separate a layer containing quantum dots and a layer containing phosphorescent material into separate layers (forbidden band of phosphorescent material between the phosphorescent light emitting layer and the quantum dot light emitting layer as in Patent Document 3) Although a light-emitting element having a buffer layer having a larger forbidden band has been proposed), a good efficiency has not been obtained yet.

However, all of these light emitting elements are so-called “normal layer type” elements in which a transparent electrode is used as an anode, that is, a hole injection layer / hole transport layer is formed on the transparent electrode. Since the quantum dot layer is generally formed by a coating method, the light emitting layer is preferably the first light emitting layer (the light emitting layer closer to the substrate). However, when a quantum dot layer is formed on the hole transport layer as a forward layer type device, the quantum dot layer functions as a hole blocking layer because the energy level of the quantum dot itself is very deep. In addition, it is assumed that it is difficult to obtain a highly efficient device because it is difficult to inject holes into the tip of the quantum dot layer.

International Publication No. 2011/147522 JP 2007-513478 A JP 2011-238590 A

The present invention has been made in view of the above problems and situations, and a problem to be solved is to provide an electroluminescence element having high luminous efficiency and long life.

In order to solve the above-mentioned problems, the present inventor has examined the cause of the above-mentioned problems. When the transparent electrode side is applied as a cathode (“cathode”) (“reverse layer type”), Since the electron transport layer and then the quantum dot layer are formed, it is sufficient that electrons can be injected into the quantum dot layer, and the electrons can actually flow well into the quantum dot layer having a deep LUMO level. It has been found that a good white light emitting device can be obtained by providing a charge generation layer, and the present invention has been completed.

That is, the said subject concerning this invention is solved by the following means.
1. An electroluminescent element in which a first electrode, a first light emitting layer, a second light emitting layer, and a second electrode are stacked in this order on a substrate,
The first light emitting layer contains quantum dots,
The second light emitting layer contains a phosphorescent light emitting dopant,
An electroluminescence element, wherein an electron transport layer is formed between the first electrode and the first light emitting layer.
2. Preferably, the light emitting layer containing the quantum dots has a light emission maximum wavelength in a wavelength region of 450 to 470 nm.
3. Preferably, the quantum dots are composed of Si, Ge, GaN, GaP, CdS, CdSe, CdTe, InP, InN, ZnS, In ₂ S ₃ , ZnO, CdO, CuInS, CuInSe, CuInGaSe, or a mixture thereof. .
4). Preferably, the film thickness of the light emitting layer containing the quantum dots is in the range of 10 to 30 nm.

5. Preferably, the light emitting layer containing the phosphorescent light emitting dopant has a maximum emission wavelength in a wavelength region of at least 520 to 560 nm and 600 to 640 nm.
6). Preferably, the light emitting layer containing the phosphorescent light emitting dopant has a light emission maximum wavelength in a wavelength region of at least 470 to 490 nm, 520 to 560 nm, and 600 to 640 nm.

7). Preferably, the light emitting layer containing the quantum dots contains a host compound.
8). More preferably, the emission maximum wavelength attributed to the 0-0 transition band in the phosphorescence spectrum of the host compound is in the wavelength region of 414 to 459 nm.

9. More preferably, the host compound is represented by the general formula (1).

 

[Wherein, X represents NR ′, oxygen atom, sulfur atom, CR′R ″ or SiR′R ″.
y ₁ and y ₂ each represent CR ′ or a nitrogen atom.
R ′ and R ″ each represent a hydrogen atom or a substituent.
Ar ₁ and Ar ₂ each represent an aromatic ring and may be the same or different from each other.
m and n each represents an integer of 0 to 4. ]
10. More preferably, in the general formula (1), X is an oxygen atom.
11. More preferably, in the general formula (1), at least one of Ar1 and Ar2 is represented by the general formula (2).

 

[Wherein, y ₁ and y ₂ each represent CR ′ or a nitrogen atom.
R ′ represents a hydrogen atom or a substituent.
Ar ₁ and Ar ₂ each represent an aromatic ring and may be the same or different from each other.
m and n each represents an integer of 0 to 4. ]
12 Preferably, the phosphorescent dopant is represented by the general formula (3).

 

[Wherein R 1 represents a substituent.
Z represents a nonmetallic atom group necessary for forming a 5- to 7-membered ring.
n1 represents an integer of 0 to 5.
B1 to B5 each represent a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom, and at least one represents a nitrogen atom.
M1 represents a group 8-10 metal in the periodic table.
X1 and X2 represent a carbon atom, a nitrogen atom or an oxygen atom.
L1 represents an atomic group forming a bidentate ligand together with X1 and X2.
m1 represents an integer of 1, 2 or 3, m2 represents an integer of 0, 1 or 2, and m1 + m2 is 2 or 3. ]
13. Preferably, it has a tandem structure in which a charge generation layer is formed between the first light emitting layer and the second light emitting layer.
14 More preferably, the charge generation layer contains a compound represented by the general formula (4).

 

[In the formula (4), each R is independently hydrogen, halogen group, alkyl group having 1 to 12 carbon atoms, alkoxy group, alkylamino group, alkylsilyl group, aryl group, arylamino group, heterocyclic group, The substituent is selected from the group consisting of an ester group, an amide group, a nitro group and a nitrile group.
Adjacent Rs may be bonded to each other to form a cyclic structure. ]

According to the present invention, it is possible to obtain a light emitting element having high color rendering properties and a high color temperature by combining an OLED exhibiting highly efficient light emission and a quantum dot having a sharp light emission spectrum. Further, according to the reverse layer structure of the present invention, a long-life light-emitting element can be obtained because it is not necessary to use a compound that is susceptible to moisture and oxygen such as KF. In particular, it is possible to provide a light-emitting element that emits white light, which has a high color temperature and high color rendering, which has been difficult with known combinations.

It is sectional drawing which shows schematic structure of an EL element.

Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In the present invention, “˜” is used to mean that the numerical values described before and after it are included as the lower limit value and the upper limit value.

<< Configuration of EL element >>
As shown in FIG. 1, an EL element 100 according to a preferred embodiment of the present invention has a support substrate 1. A first electrode 2 is formed on the support substrate 1, an organic functional layer 20 is formed on the first electrode 2, and a second electrode 8 is formed on the organic functional layer 20.

The organic functional layer 20 refers to each layer constituting the EL element 100 provided between the first electrode 2 and the second electrode 8.

The organic functional layer 20 includes, for example, an electron transport layer 21, a first light emitting layer 22, a charge generation layer 23 (intermediate layer), a second light emitting layer 24, and a hole transport layer 25. A hole injection layer or the like may be included.

The first electrode 2, the organic functional layer 20, and the second electrode 8 on the support substrate 1 are sealed with a flexible sealing member 10 through a sealing adhesive 9.

It should be noted that these reverse layer type structures (see FIG. 1) of the EL element 100 are merely preferred specific examples, and the present invention is not limited to the configuration illustrated in FIG. As a typical configuration of the EL element 100, for example, layer structures as exemplified in the following (i) to (xii) can be given.

(I) Support substrate / first electrode / electron transport layer / first light emitting layer / second light emitting layer / second electrode / sealing adhesive / sealing member (ii) support substrate / first Electrode / electron transport layer / first light emitting layer / intermediate layer / second light emitting layer / second electrode / sealing adhesive / sealing member (iii) support substrate / first electrode / electron transport layer / First light emitting layer / charge generation layer / second light emitting layer / second electrode / sealing adhesive / sealing member (iv) support substrate / first electrode / electron injection layer / electron transport layer / first 1 light emitting layer / second light emitting layer / second electrode / sealing adhesive / sealing member (v) support substrate / first electrode / electron injection layer / electron transport layer / first light emitting layer / Intermediate layer / second light emitting layer / second electrode / sealing adhesive / sealing member (vi) support substrate / first electrode / electron injection layer / electron transport layer / first light emitting layer / charge generation Layer / second light emitting layer / second electrode Sealing adhesive / sealing member

(Vii) Support substrate / first electrode / electron transport layer / first light emitting layer / second light emitting layer / hole transport layer / second electrode / sealing adhesive / sealing member (viii) support Substrate / first electrode / electron transport layer / first light emitting layer / intermediate layer / second light emitting layer / hole transport layer / second electrode / sealing adhesive / sealing member (ix) support substrate / First electrode / electron transport layer / first light emitting layer / charge generation layer / second light emitting layer / hole transport layer / second electrode / sealing adhesive / sealing member (x) support substrate / First electrode / electron injection layer / electron transport layer / first light emitting layer / second light emitting layer / hole transport layer / second electrode / sealing adhesive / sealing member (xi) support substrate / First electrode / electron injection layer / electron transport layer / first light emitting layer / intermediate layer / second light emitting layer / hole transport layer / second electrode / adhesive for sealing / sealing member (xii) ) Support substrate / first electrode / electron injection layer Electron transporting layer / first emitting layer / charge generation layer / second emitting layer / hole transport layer / second electrode / encapsulation adhesive / sealing member

(Xiii) Support substrate / first electrode / electron transport layer / first light emitting layer / second light emitting layer / hole transport layer / hole injection layer / second electrode / adhesive for sealing / sealing Member (xiv) Support substrate / first electrode / electron transport layer / first light emitting layer / intermediate layer / second light emitting layer / hole transport layer / hole injection layer / second electrode / adhesive for sealing Agent / sealing member (XV) support substrate / first electrode / electron transport layer / first light emitting layer / charge generation layer / second light emitting layer / hole transport layer / hole injection layer / second electrode / Sealing adhesive / sealing member (xvi) support substrate / first electrode / electron injection layer / electron transport layer / first light emitting layer / second light emitting layer / hole transport layer / hole injection layer / Second electrode / sealing adhesive / sealing member (xvii) support substrate / first electrode / electron injection layer / electron transport layer / first light emitting layer / intermediate layer / second light emitting layer / positive Hole transport layer / hole injection layer / second electrode / Fixing adhesive / sealing member (xviii) support substrate / first electrode / electron injection layer / electron transport layer / first light emitting layer / charge generating layer / second light emitting layer / hole transport layer / hole Injection layer / second electrode / adhesive for sealing / sealing member

<< Organic functional layer of EL element >>
Next, details of the organic functional layer constituting the EL element will be described.

[1] Injection layer: hole injection layer, electron injection layer In an EL device, an injection layer can be provided as necessary.
The injection layer includes an electron injection layer and a hole injection layer. The electron injection layer is between the first electrode and the first light emitting layer or the electron transport layer as described above, and the hole injection layer is the second electrode. You may exist between a 2nd light emitting layer or a positive hole transport layer.

The injection layer referred to in the present invention is a layer provided between the electrode and the organic functional layer in order to lower the driving voltage and improve the light emission luminance. “The organic EL element and its industrialization front line (November 30, 1998, NT. 2) Chapter 2 “Electrode Materials” (pages 123 to 166) of “Part 2” of S. Co., Ltd.) and includes a hole injection layer and an electron injection layer.

The details of the hole injection layer are described, for example, in JP-A-9-45479, JP-A-9-260062, and JP-A-8-288069. Injection materials include triazole derivatives, oxadiazole derivatives, imidazole derivatives, pyrazoline derivatives and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives. , Polymers containing silazane derivatives, aniline copolymers, polyarylalkane derivatives, or conductive polymers, preferably polythiophene derivatives, polyaniline derivatives, polypyrrole derivatives, more preferably Thiophene derivatives. In addition, as described in Chem. Rev. 107, 1233 (2007), Phys. You may be comprised with the composition which improved the electroconductivity combining the derivative | guide_body preferable as a material, or the positive hole transport material mentioned later.

The details of the electron injection layer are described in, for example, JP-A-6-325871, JP-A-9-17574, and JP-A-10-74586, and specific examples thereof include strontium and aluminum. A metal buffer layer, an alkali metal compound buffer layer typified by lithium fluoride, an alkaline earth metal compound buffer layer typified by magnesium fluoride, and an oxide buffer layer typified by aluminum oxide. In addition, a composition in which conductivity is improved by doping the above-described alkali metal compound, alkali metal, an electron transport material described later with an n-type dopant as described in WO2005 / 86251, WO2007 / 107306, or the like is also preferably used. (For example, an electron injection layer in which an alkali metal and an electron transport layer are combined can be formed with reference to Appl. Phys. Lett. 94, 083303 (2009)).

However, as described above, these materials are often unstable to oxygen and moisture and contribute to lowering the efficiency of the device. Therefore, it is preferable not to use these materials, particularly alkali metals or alkali metal compounds. . However, when it is necessary to use, it is desirable that the buffer layer (injection layer) is a very thin film, and potassium fluoride and sodium fluoride are preferable. The film thickness is about 0.1 nm to 5 μm, preferably 0.1 to 100 nm, more preferably 0.5 to 10 nm, and most preferably 0.5 to 4 nm.

[2] Hole transport layer In the present invention, the hole transport layer is 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 of the present invention is not particularly limited, but is usually in the range of 5 nm to 5 μm, more preferably 2 nm to 500 nm, and further preferably 5 nm to 200 nm.
The material used for the hole transport layer (hereinafter referred to as a hole transport material) may have any of the hole injection property or the transport property and the electron barrier property. Any one can be selected and used.
For example, porphyrin derivatives, phthalocyanine derivatives, oxazole derivatives, oxadiazole derivatives, triazole derivatives, imidazole derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylenediamine derivatives, hydrazone derivatives, stilbene derivatives, polyarylalkane derivatives, triarylamine derivatives, carbazole derivatives , Indolocarbazole derivatives, isoindole derivatives, acene derivatives such as anthracene and naphthalene, fluorene derivatives, fluorenone derivatives, and polymer materials or oligomers in which an aromatic amine is introduced into the main chain or side chain, polysilane , Conductive polymers or oligomers (for example, PEDOT: PSS, aniline copolymers, polyaniline, polythiophene, etc.) and the like.
Examples of the triarylamine derivative include a benzidine type typified by αNPD, a starburst type typified by MTDATA, and a compound having fluorene or anthracene in the triarylamine-linked core such as Spiro-TPD.

In addition, hexaazatriphenylene derivatives such as those described in JP-T-2003-519432 and JP-A-2006-135145 can also be used as hole transport materials.
Furthermore, 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, JP-A-2001-102175, J. Pat. Appl. Phys. 95, 5773 (2004), and the like.
JP-A-11-251067, J. Org. Huang et. al. It is also possible to use so-called p-type hole transport materials, inorganic compounds such as p-type-Si and p-type-SiC, as described in the literature (Applied Physics Letters 80 (2002), p. 139). Further, ortho-metalated organometallic complexes having Ir or Pt as the central metal represented by Ir (ppy) 3 are also preferably used.
Although the above-mentioned materials can be used as the hole transport material, a triarylamine derivative, carbazole derivative, indolocarbazole derivative, azatriphenylene derivative, organometallic complex, aromatic amine is introduced into the main chain or side chain. The polymer materials or oligomers used are preferably used.

Specific examples of known preferred hole transport materials used in the organic EL device of the present invention include the compounds described in the following documents in addition to the documents listed above, but the present invention is not limited thereto. Not.
For example, Appl. Phys. Lett. 69, 2160 (1996), J.A. Lumin. 72-74, 985 (1997), Appl. Phys. Lett. 78, 673 (2001), Appl. Phys. Lett. 90, 183503 (2007), Appl. Phys. Lett. 90, 183503 (2007), Appl. Phys. Lett. 51, 913 (1987), Synth. Met. 87, 171 (1997), Synth. Met. 91, 209 (1997), Synth. Met. 111, 421 (2000), SID Symposium Digest, 37, 923 (2006), J. Am. Mater. Chern. 3, 319 (1993), Adv. Mater. 6, 677 (1994), Chern. Mater. 15,3148 (2003), U.S. Patent Publication No. 20030162053, U.S. Patent Publication No. 200201558242, U.S. Patent Publication No. 20060240279, U.S. Patent Publication No. 20080220265, U.S. Patent No. 5061569, International Publication No. 2007002683, and International Publication No. 2007002683. 2008018009, EP650955, U.S. Patent Publication No. 20080124572, U.S. Patent Publication No. 200707078938, U.S. Patent Publication No. 200880106190, U.S. Pat. Publication No. 20080018221, International Publication No. -135145, US Patent Application No. 13/585981, and the like.
The hole transport material may be used alone or in combination of two or more.

[3] Electron transport layer The electron transport layer constituting the organic functional layer of the EL element is made of a material 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. . The electron transport layer can be provided as a single layer or a plurality of layers.

Conventionally, when a single electron transport layer and a plurality of electron transport layers are used, as an electron transport material (also serving as a hole blocking material) used for an electron transport layer adjacent to the light emitting layer on the first electrode side. Is only required to have a function of transmitting electrons injected from the first electrode to the light emitting layer, and as the material, any one of conventionally known compounds can be selected and used. , Fluorene derivatives, carbazole derivatives, azacarbazole derivatives, oxadiazole derivatives, triazole derivatives, silole derivatives, pyridine derivatives, pyrimidine derivatives, 8-quinolinol derivatives, and the like.

In addition, metal-free or metal phthalocyanine, or those having terminal ends substituted with an alkyl group or a sulfonic acid group can be preferably used as the electron transporting material.

Among these, carbazole derivatives, azacarbazole derivatives, pyridine derivatives and the like are preferable in the present invention, and more preferably an azacarbazole derivative.

The electron transport layer can be formed by thinning the electron transport material by a known method such as a spin coating method, a casting method, a printing method including an ink jet method, an LB method, and the like, preferably It can be formed by a wet process using a coating solution containing an electron transport material and a fluorinated alcohol solvent.

The thickness of the electron transport layer is not particularly limited, but is usually about 5 nm to 5 μm, preferably 5 to 200 nm. The electron transport layer may have a single layer structure composed of one or more of the above materials.

It is also possible to use an n-type electron transport layer doped with impurities as a guest material. Examples thereof include JP-A-4-297076, JP-A-10-270172, JP-A-2000-196140, 2001-102175, J.A. Appl. Phys. 95, 5773 (2004), and the like.

The electron transport layer according to the present invention preferably contains an organic alkali metal salt. The type of organic substance is not particularly limited, but for example, formate, acetate, propionic acid, butyrate, valerate, caprate, enanthate, caprylate, oxalate, malonate, Succinate, benzoate, phthalate, isophthalate, terephthalate, salicylate, pyruvate, lactate, malate, adipate, mesylate, tosylate, benzenesulfonate Preferably, formate, acetate, propionate, butyrate, valerate, caprate, enanthate, caprylate, oxalate, malonate, succinate, benzoate Etc. More preferably, it is an alkali metal salt of an aliphatic carboxylic acid such as formate, acetate, propionate, butyrate, etc., and the aliphatic carboxylic acid preferably has 4 or less carbon atoms, most preferably acetate. It is.

The kind of alkali metal of the organic alkali metal salt is not particularly limited, and examples thereof include Na, K, and Cs, preferably K, Cs, and more preferably Cs. Examples of the alkali metal salt of the organic substance include a combination of the organic substance and the alkali metal, preferably, formic acid Li, formic acid K, Na formic acid, formic acid Cs, Li acetate, K acetate, Na acetate, Cs acetate, Lipropionate, Propionic acid Na, propionic acid K, propionic acid Cs, oxalic acid Li, oxalic acid Na, oxalic acid K, oxalic acid Cs, malonic acid Li, malonic acid Na, malonic acid K, malonic acid Cs, succinic acid Li, succinic acid Na, succinic acid K, succinic acid Cs, benzoic acid Li, benzoic acid Na, benzoic acid K, benzoic acid Cs, more preferably Li acetate, K acetate, Na acetate, Cs acetate, most preferably Cs acetate.

The content of the alkali metal salt of these organic substances is preferably in the range of 1.5 to 35% by mass, more preferably in the range of 3 to 25% by mass with respect to 100% by mass of the electron transport layer to be added. Most preferably, it is in the range of 5 to 15% by mass.

[4] Light emitting layer The light emitting layer constituting the EL element is divided into a first light emitting layer and a second light emitting layer.
The first light emitting layer contains quantum dots, and the second light emitting layer contains a phosphorescent dopant.

The structure of the light emitting layer is not particularly limited as long as the contained light emitting material satisfies the above requirements.

There may be a plurality of layers having the same emission spectrum or emission maximum wavelength.
It is preferable that a non-light emitting intermediate layer or a charge generation layer is provided between the first light emitting layer and the second light emitting layer. This is because it is possible to avoid contact between two light emitting materials having different energy levels, that is, quantum dots and a phosphorescent dopant, and to prevent a decrease in light emission efficiency due to carrier trapping or the like. In particular, when a charge generation layer is provided, the amount of injected carriers for the two light emitting layers can be halved and the life can be improved.

The thickness of the light emitting layer is preferably in the range of 1 to 100 nm, and more preferably 50 nm or less because a lower driving voltage can be obtained.
Note that the thickness of the light emitting layer is the total thickness of the first light emitting layer and the second light emitting layer, and an intermediate layer made of only a non-light emitting host compound exists between the light emitting layers. The film thickness includes the intermediate layer.

It is preferable to adjust the film thickness of each light emitting layer to a range of 1 to 50 nm.

The individual light emitting layers may emit blue, green, and red colors, and there is no particular limitation on the film thickness relationship of each light emitting layer.

For the formation of the light-emitting layer, a light-emitting material or a host compound, which will be described later, is formed into a known thin film such as, for example, a vacuum evaporation method, a spin coating method, a casting method, an LB method (Langmuir Brodgett method), an inkjet method, or the like. The film can be formed by the method.

A plurality of light emitting materials may be mixed in each light emitting layer, and a phosphorescent light emitting material and a fluorescent light emitting material may be mixed and used in the same light emitting layer.

As a configuration of the light emitting layer, the first light emitting layer contains a host compound and quantum dots, and the second light emitting layer contains a host compound and a light emitting material (also referred to as a light emitting dopant compound).

(4.1) Host compound The host compound is a compound having a short emission wavelength in which the emission wavelength attributed to the 0-0 transition band in the phosphorescence spectrum is in the range of 414 to 459 nm (2.7 to 3.0 eV). That is, it is a compound having a high triplet energy.

In this way, even in the triplet energy level, by using a host compound having a wider band gap than the quantum dot compound, carrier injection into the quantum dot compound and exciton confinement become efficient. Increased lifetime due to efficient light emission and reduced thermal deactivation process can be obtained.

The host compound according to the present invention is not particularly limited as long as it satisfies the above conditions.

The emission wavelength attributed to the 0-0 transition band in the phosphorescence spectrum of the host compound according to the present invention can be determined by the following method.

First, the host compound to be measured is dissolved in a well-deoxygenated ethanol / methanol = 4/1 (vol / vol) mixed solvent, put into a phosphorescence measurement cell, and then excited with liquid nitrogen temperature of 77K. After irradiating with excitation light, an emission spectrum at 100 ms is measured. Since phosphorescence has a longer emission lifetime than fluorescence, it can be considered that light remaining after 100 ms is almost phosphorescence. For compounds with a phosphorescence lifetime shorter than 100 ms, measurement may be performed with a shorter delay time, but phosphorescence and fluorescence cannot be separated if the delay time is shortened so that it cannot be distinguished from fluorescence. Since this is a problem, it is necessary to select a delay time that can be separated.

For the host compound that cannot be dissolved in the solvent system, any solvent that can dissolve the host compound may be used. In practice, the above-described measurement method is considered to have no problem because the solvent effect of the phosphorescence wavelength is negligible.

Next, the 0-0 transition band is determined. In the present invention, the 0-0 transition band having the maximum emission wavelength that appears on the shortest wavelength side in the phosphorescence spectrum chart obtained by the above measurement method is Define.

Since the phosphorescence spectrum is usually weak in intensity, it may become difficult to distinguish between noise and peak when enlarged. In such a case, the emission spectrum during excitation light irradiation (for convenience, this is referred to as a steady light spectrum) is expanded, and after the excitation light is irradiated, the emission spectrum after 100 ms (for convenience, this is referred to as a phosphorescence spectrum). It can be determined by reading the peak wavelength of the phosphorescence spectrum from the stationary light spectrum portion derived from the phosphorescence spectrum.

Also, by smoothing the phosphorescence spectrum, noise and peak can be separated and peak wavelength can be read. As the smoothing process, a smoothing method of Savitzky & Golay can be applied.

As a measuring apparatus that can be used in the above measurement, a fluorometer F4500 manufactured by Hitachi High-Technology Corporation can be exemplified.

As the host compound, a compound having a phosphorescence quantum yield of phosphorescence emission at room temperature (25 ° C.) of less than 0.1 is preferable. More preferably, the phosphorescence quantum yield is less than 0.01. Moreover, it is preferable that the volume ratio in the layer is 50% or more among the compounds contained in a light emitting layer.

The host compound is not particularly limited as long as it is a compound having the above conditions defined in the present invention, and a known 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 movement of charges, and the EL element can be highly efficient. Moreover, it becomes possible to mix different light emission by using multiple types of luminescent material mentioned later, and can thereby obtain arbitrary luminescent colors.

The host compound used in the present invention is not particularly limited as long as it is a compound having the above-mentioned conditions defined in the present invention, and may be a conventionally known low molecular compound or a high molecular compound having a repeating unit, and may be a vinyl group. Or a low molecular compound (polymerizable light-emitting host) having a polymerizable group such as an epoxy group, but when a high molecular weight material is used, the compound may take up the solvent and swell or gelate, and the solvent is unlikely to escape. In order to prevent this phenomenon, it is preferable that the molecular weight is not high. Specifically, it is preferable to use a material having a molecular weight of 2,000 or less during coating, and a molecular weight of 1,000 or less during coating. It is more preferable to use a material, and in particular, a host compound having a molecular weight in the range of 500 to 1000 is preferable.

As the known host compound, a compound that has a hole transporting ability and an electron transporting ability, prevents the emission of light from being increased in wavelength, and has a high Tg (glass transition temperature) is preferable. Here, the glass transition point (Tg) is a value determined by a method based on JIS-K-7121 using DSC (Differential Scanning Colorimetry).

Specific examples of known host compounds include compounds described in the following documents. For example, Japanese Patent Laid-Open Nos. 2001-257076, 2002-308855, 2001-313179, 2002-319491, 2001-357777, 2002-334786, 2002-8860 Gazette, 2002-334787, 2002-15871, 2002-334788, 2002-43056, 2002-334789, 2002-75645, 2002-338579 No. 2002-105445, No. 2002-343568, No. 2002-141173, No. 2002-352957, No. 2002-203683, No. 2002-363227, No. 2002-231453. No. 2003-3165, No. 2002-234888, No. 2003-27048, No. 2002-255934, No. 2002-286061, No. 2002-280183, No. 2002-299060. 2002-302516, 2002-305083, 2002-305084, 2002-308837, etc., and a compound having the above-mentioned conditions defined in the present invention can be selected and used. it can.

Furthermore, the host compound according to the present invention is preferably a compound represented by the following general formula (1). This is because the compound represented by the following formula (1) has a condensed ring structure and therefore has a high carrier transport property, and also has the above-described broad triplet energy (0-0 band of phosphorescence).

 

In the general formula (1), “X” represents NR ′, oxygen atom, sulfur atom, CR′R ″ or SiR′R ″.
“Y ₁ and y ₂ ” each represent CR ′ or a nitrogen atom.
“R ′ and R ″” each represents a hydrogen atom or a substituent.
“Ar ₁ and Ar ₂ ” each represent an aromatic ring and may be the same or different from each other.
“M, n” represents an integer of 0-4.

In X, y ₁ and y ₂ in the general formula (1), examples of the substituent represented by R ′ and R ″ include an alkyl group (for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, t -Butyl group, pentyl group, hexyl group, octyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, etc.), cycloalkyl group (eg, cyclopentyl group, cyclohexyl group, etc.), alkenyl group (eg, vinyl group, allyl group) Group), alkynyl group (for example, ethynyl group, propargyl group, etc.), aromatic hydrocarbon ring group (aromatic carbocyclic group, aryl group, etc.), for example, phenyl group, p-chlorophenyl group, mesityl group, tolyl Group, xylyl group, naphthyl group, anthryl group, azulenyl group, acenaphthenyl group, fluorenyl group, phenanthryl , Indenyl group, pyrenyl group, biphenylyl group, etc.), aromatic heterocyclic group (for example, pyridyl group, pyrimidinyl group, furyl group, pyrrolyl group, imidazolyl group, benzoimidazolyl group, pyrazolyl group, pyrazinyl group, triazolyl group (for example, 1 , 2,4-triazol-1-yl group, 1,2,3-triazol-1-yl group, etc.), oxazolyl group, benzoxazolyl group, thiazolyl group, isoxazolyl group, isothiazolyl group, furazanyl group, thienyl group Quinolyl group, benzofuryl group, dibenzofuryl group, benzothienyl group, dibenzothienyl group, indolyl group, carbazolyl group, carbolinyl group, diazacarbazolyl group (one of the carbon atoms constituting the carboline ring of the carbolinyl group is nitrogen (Represented by atoms replaced), quinoxalini Group, pyridazinyl group, triazinyl group, quinazolinyl group, phthalazinyl group, etc.), heterocyclic group (eg, pyrrolidyl group, imidazolidyl group, morpholyl group, oxazolidyl group, etc.), alkoxy group (eg, methoxy group, ethoxy group, propyloxy) Group, pentyloxy group, hexyloxy group, octyloxy group, dodecyloxy group, etc.), cycloalkoxy group (eg, cyclopentyloxy group, cyclohexyloxy group, etc.), aryloxy group (eg, phenoxy group, naphthyloxy group, etc.) Alkylthio groups (for example, methylthio group, ethylthio group, propylthio group, pentylthio group, hexylthio group, octylthio group, dodecylthio group, etc.), cycloalkylthio groups (for example, cyclopentylthio group, cyclohexylthio group, etc.), arylthio Group (for example, phenylthio group, naphthylthio group, etc.), alkoxycarbonyl group (for example, methyloxycarbonyl group, ethyloxycarbonyl group, butyloxycarbonyl group, octyloxycarbonyl group, dodecyloxycarbonyl group, etc.), aryloxycarbonyl group ( For example, phenyloxycarbonyl group, naphthyloxycarbonyl group, etc.), sulfamoyl group (for example, aminosulfonyl group, methylaminosulfonyl group, dimethylaminosulfonyl group, butylaminosulfonyl group, hexylaminosulfonyl group, cyclohexylaminosulfonyl group, octylamino) Sulfonyl groups, dodecylaminosulfonyl groups, phenylaminosulfonyl groups, naphthylaminosulfonyl groups, 2-pyridylaminosulfonyl groups, etc.), acyl groups (eg Acetyl group, ethylcarbonyl group, propylcarbonyl group, pentylcarbonyl group, cyclohexylcarbonyl group, octylcarbonyl group, 2-ethylhexylcarbonyl group, dodecylcarbonyl group, phenylcarbonyl group, naphthylcarbonyl group, pyridylcarbonyl group, etc.), acyloxy group (For example, acetyloxy group, ethylcarbonyloxy group, butylcarbonyloxy group, octylcarbonyloxy group, dodecylcarbonyloxy group, phenylcarbonyloxy group, etc.), amide group (for example, methylcarbonylamino group, ethylcarbonylamino group, dimethyl group) Carbonylamino group, propylcarbonylamino group, pentylcarbonylamino group, cyclohexylcarbonylamino group, 2-ethylhexylcarbonylamino group, octyl Rucarbonylamino group, dodecylcarbonylamino group, phenylcarbonylamino group, naphthylcarbonylamino group, etc.), carbamoyl group (for example, aminocarbonyl group, methylaminocarbonyl group, dimethylaminocarbonyl group, propylaminocarbonyl group, pentylaminocarbonyl group) Cyclohexylaminocarbonyl group, octylaminocarbonyl group, 2-ethylhexylaminocarbonyl group, dodecylaminocarbonyl group, phenylaminocarbonyl group, naphthylaminocarbonyl group, 2-pyridylaminocarbonyl group, etc.), ureido group (for example, methylureido group, Ethylureido group, pentylureido group, cyclohexylureido group, octylureido group, dodecylureido group, phenylureido group, naphthylureido group, 2 Pyridylaminoureido group, etc.), sulfinyl groups (for example, methylsulfinyl group, ethylsulfinyl group, butylsulfinyl group, cyclohexylsulfinyl group, 2-ethylhexylsulfinyl group, dodecylsulfinyl group, phenylsulfinyl group, naphthylsulfinyl group, 2-pyridylsulfinyl group) Etc.), alkylsulfonyl group (eg, methylsulfonyl group, ethylsulfonyl group, butylsulfonyl group, cyclohexylsulfonyl group, 2-ethylhexylsulfonyl group, dodecylsulfonyl group, etc.), arylsulfonyl group or heteroarylsulfonyl group (eg, phenylsulfonyl) Group, naphthylsulfonyl group, 2-pyridylsulfonyl group, etc.), amino group (eg, amino group, ethylamino group, dimethylamino group, buty Amino group, cyclopentylamino group, 2-ethylhexylamino group, dodecylamino group, anilino group, naphthylamino group, 2-pyridylamino group, etc.), halogen atom (eg, fluorine atom, chlorine atom, bromine atom etc.), fluorinated carbonization Hydrogen group (for example, fluoromethyl group, trifluoromethyl group, pentafluoroethyl group, pentafluorophenyl group, etc.), cyano group, nitro group, hydroxy group, mercapto group, silyl group (for example, trimethylsilyl group, triisopropylsilyl group) , Triphenylsilyl group, phenyldiethylsilyl group, etc.). These substituents may be further substituted with the above substituents. A plurality of these substituents may be bonded to each other to form a ring.

Among them, as a structure having excellent electron transport properties, a compound in which X is NR ′ or an oxygen atom in the general formula (1) is preferable. That is, a compound having a (aza) carbazole ring or a (aza) dibenzofuran ring is preferable. Here, R ′ is an aromatic hydrocarbon group (also called an aromatic carbocyclic group, aryl group, etc., for example, phenyl group, p-chlorophenyl group, mesityl group, tolyl group, xylyl group, naphthyl group, anthryl group, Azulenyl, acenaphthenyl, fluorenyl, phenanthryl, indenyl, pyrenyl, biphenylyl) or aromatic heterocyclic groups (eg furyl, thienyl, pyridyl, pyridazinyl, pyrimidinyl, pyrazinyl, triazinyl) Group, imidazolyl group, pyrazolyl group, thiazolyl group, quinazolinyl group, phthalazinyl group, etc.) are particularly preferred.

The above aromatic hydrocarbon group and aromatic heterocyclic group may each have a substituent represented by R ′ and R ″ in X of the general formula (1).

In the general formula (1), examples of the atom represented by y ₁ and y ₂ include CR ′ and a nitrogen atom, and CR ′ is more preferable. Such a compound is also excellent in hole transportability, and can efficiently recombine and emit electrons and holes injected from the first electrode and the second electrode in the light emitting layer.

In the general formula (1), examples of the aromatic ring represented by Ar ₁ and Ar ₂ include an aromatic hydrocarbon ring and an aromatic heterocyclic ring. The aromatic ring may be a single ring or a condensed ring, and may be unsubstituted or may have a substituent represented by R ′ and R ″ in X of the general formula (1).

In the general formula (1), examples of the aromatic hydrocarbon ring represented by Ar ₁ and Ar ₂ include a benzene ring, biphenyl ring, naphthalene ring, azulene ring, anthracene ring, phenanthrene ring, pyrene ring, chrysene ring, Naphthacene ring, triphenylene ring, o-terphenyl ring, m-terphenyl ring, p-terphenyl ring, acenaphthene ring, coronene ring, fluorene ring, fluoranthrene ring, naphthacene ring, pentacene ring, perylene ring, pentaphen ring, Examples include a picene ring, a pyrene ring, a pyranthrene ring, and an anthraanthrene ring.

In the partial structure represented by the general formula (1), examples of the aromatic heterocycle represented by Ar ₁ and Ar ₂ include a furan ring, a dibenzofuran ring, a thiophene ring, an oxazole ring, a pyrrole ring, a pyridine ring, and a pyridazine. Ring, pyrimidine ring, pyrazine ring, triazine ring, benzimidazole ring, oxadiazole ring, triazole ring, imidazole ring, pyrazole ring, thiazole ring, indole ring, indazole ring, benzimidazole ring, benzothiazole ring, benzoxazole ring, Quinoxaline ring, quinazoline ring, cinnoline ring, quinoline ring, isoquinoline ring, phthalazine ring, naphthyridine ring, carbazole ring, carboline ring, diazacarbazole ring (one of the carbon atoms of the hydrocarbon ring constituting the carboline ring is a nitrogen atom) Has been replaced Shown) and the like.

These rings may further have a substituent represented by R ′ and R ″ in the general formula (1).

Among the above, in the general formula (1), the aromatic ring represented by Ar ₁ and Ar ₂ is preferably a carbazole ring, carboline ring, dibenzofuran ring, or benzene ring, and more preferably used. , A carbazole ring, a carboline ring, and a benzene ring, more preferably a benzene ring having a substituent, and particularly preferably a benzene ring having a carbazolyl group.

In the general formula (1), the aromatic rings represented by Ar ₁ and Ar ₂ are each preferably a condensed ring of three or more rings, and as an aromatic hydrocarbon condensed ring in which three or more rings are condensed. Specifically, naphthacene ring, anthracene ring, tetracene ring, pentacene ring, hexacene ring, phenanthrene ring, pyrene ring, benzopyrene ring, benzoazulene ring, chrysene ring, benzochrysene ring, acenaphthene ring, acenaphthylene ring, triphenylene ring, Coronene ring, benzocoronene ring, hexabenzocoronene ring, fluorene ring, benzofluorene ring, fluoranthene ring, perylene ring, naphthperylene ring, pentabenzoperylene ring, benzoperylene ring, pentaphen ring, picene ring, pyranthrene ring, coronene ring, naphthocoronene ring , Ovalene ring, Ansula Ntoren ring and the like. In addition, these rings may further have the above substituent.

Specific examples of the aromatic heterocycle condensed with three or more rings include an acridine ring, a benzoquinoline ring, a carbazole ring, a carboline ring, a phenazine ring, a phenanthridine ring, a phenanthroline ring, a carboline ring, a cyclazine ring, Kindin ring, tepenidine ring, quinindrin ring, triphenodithiazine ring, triphenodioxazine ring, phenanthrazine ring, anthrazine ring, perimidine ring, diazacarbazole ring (any one of the carbon atoms constituting the carboline ring is a nitrogen atom Phenanthroline ring, dibenzofuran ring, dibenzothiophene ring, naphthofuran ring, naphthothiophene ring, benzodifuran ring, benzodithiophene ring, naphthodifuran ring, naphthodithiophene ring, anthrafuran ring, anthradifuran ring, Emissions tiger thiophene ring, anthradithiophene ring, thianthrene ring, phenoxathiin ring, such as thio fan train ring (naphthothiophene ring). In addition, these rings may further have a substituent.

In the general formula (1), m and n represent an integer of 0 to 4, preferably 0 to 2, and in particular, when X is an oxygen atom or a sulfur atom, 1 to 2 It is preferable that
m and n may be the same as or different from each other.

In the present invention, a host compound having both a dibenzofuran ring and a carbazole ring is particularly preferable.

In general formula (1), at least one of Ar1 and Ar2 is preferably represented by general formula (2).

 

In general formula (2), “y ₁ and y ₂ ” each represent CR ′ or a nitrogen atom.
“R ′” each represents a hydrogen atom or a substituent.
“Ar ₁ and Ar ₂ ” each represent an aromatic ring and may be the same or different from each other.
“M, n” represents an integer of 0 to 4, and may be the same or different from each other.

Examples of the substituent for y _1, y ₂ and R ′ are the same as those described in the general formula (1).
Aromatic ring represented by Ar ₁ and Ar ₂ may be the same as the aromatic ring represented by Ar ₁ and Ar ₂ in the general formula (1).

Hereinafter, the emission wavelength attributed to the 0-0 transition band in the phosphorescence spectrum is preferably at least shorter than 459 nm. If the wave length is longer than this, the efficiency of energy transfer to the quantum dot compound decreases. Further, if it is less than 414 nm, the drive voltage becomes high, and there is a concern that the light emission efficiency is lowered. That is, the range of 414 to 459 nm (2.7 to 3.0 eV) is preferable. Examples of the host compound according to the present invention in the range of less than 459 nm (2.7 eV) include compounds represented by the general formula (1) and other structures, but are not limited thereto.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(4.2) Luminescent Material As the luminescent material according to the present invention, generally, a fluorescent compound or a phosphorescent material (also referred to as a phosphorescent compound or a phosphorescent compound) can be used. In the present invention, at least a phosphorescent compound is used.

In the present invention, a phosphorescent compound 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 has a phosphorescence quantum yield of 25. Although it is defined as a compound of 0.01 or more at ° C., a preferable phosphorescence quantum yield is 0.1 or more.

The above phosphorescence quantum yield can be measured by the method described in Spectra II, page 398 (1992 edition, Maruzen) of the Fourth Edition Experimental Chemistry Course 7. The phosphorescence quantum yield in a solution can be measured using various solvents, but when using a phosphorescent material in the present invention, the above phosphorescence quantum yield (0.01 or more) is achieved in any solvent. It only has to be done.

There are two types of light emission principles of phosphorescent materials. One is the recombination of carriers on the host compound to which carriers are transported to generate an excited state of the host compound, and this energy is converted into the phosphorescent material. The energy transfer type that obtains light emission from the phosphorescent light emitting material by moving it, and the other is that the phosphorescent light emitting material becomes a carrier trap, and carrier recombination occurs on the phosphorescent light emitting material, and light emission from the phosphorescent light emitting material In any case, the excited state energy of the phosphorescent material is lower than the excited state energy of the host compound.

The phosphorescent light-emitting material can be appropriately selected from known materials used for the light-emitting layer of the organic EL element, but is preferably a complex compound containing a group 8-10 metal in the periodic table of elements. More preferred are iridium compounds, osmium compounds, platinum compounds (platinum complex compounds), and rare earth complexes, and most preferred are iridium compounds.

The phosphorescent dopant according to the present invention includes a phosphorescent dopant having an emission wavelength belonging to the 0-0 transition band in the phosphorescence spectrum in the range of 460 to 827 nm (2.7 to 1.5 eV). It is preferable that
Among them, it is preferable to include a phosphorescent dopant having an emission maximum wavelength in a wavelength region of at least 520 to 560 nm and 600 to 640 nm, and further including a phosphorescence dopant having an emission maximum wavelength in a wavelength region of 460 to 490 nm. preferable.

The emission wavelength attributed to the 0-0 transition band of the phosphorescent dopant according to the present invention can be determined by the same method used for the measurement of the emission wavelength attributed to the 0-0 transition band of the host compound. .

The phosphorescent compound according to the present invention is preferably a combination that produces white light in combination with light emission from the quantum dots. For example, there are combinations such as blue light emitted from quantum dots, green light emitted from phosphorescent compounds, and red, and blue light emitted from quantum dots and light blue light emitted from phosphorescent compounds. . As the phosphorescent compound that emits light blue, a phosphorescent dopant represented by the following general formula (3) is preferable.

 

In the general formula (3), R ₁ represents a substituent. Z represents a nonmetallic atom group necessary for forming a 5- to 7-membered ring. n1 represents an integer of 0 to 5. B ₁ to B _{5 each} represent a carbon atom, a nitrogen atom, an oxygen atom, or a sulfur atom, and at least one represents a nitrogen atom. M ₁ represents a group 8 to group 10 metal in the periodic table. X ₁ and X ₂ represent a carbon atom, a nitrogen atom, or an oxygen atom, and L ₁ represents an atomic group that forms a bidentate ligand together with X ₁ and X ₂ . m1 represents an integer of 1, 2, or 3, m2 represents an integer of 0, 1, or 2, and m1 + m2 is 2 or 3.

The phosphorescent compound represented by the general formula (3) according to the present invention has a HOMO of −5.15 to −3.50 eV, a LUMO of −1.25 to +1.00 eV, and preferably a HOMO of − 4.80 to −3.50 eV, and LUMO is −0.80 to +1.00 eV.

In the phosphorescent compound represented by the general formula (3), examples of the substituent represented by R ₁ include an alkyl group (eg, methyl group, ethyl group, propyl group, isopropyl group, tert-butyl group). Pentyl group, hexyl group, octyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, etc.), cycloalkyl group (for example, cyclopentyl group, cyclohexyl group, etc.), alkenyl group (for example, vinyl group, allyl group, etc.) Alkynyl group (eg, ethynyl group, propargyl group, etc.), aromatic hydrocarbon ring group (also called aromatic carbocyclic group, aryl group, etc.), for example, phenyl group, p-chlorophenyl group, mesityl group, tolyl group, xylyl Group, naphthyl group, anthryl group, azulenyl group, acenaphthenyl group, fluorenyl group, phenanthryl group, Indenyl group, pyrenyl group, biphenylyl group, etc.), aromatic heterocyclic group (for example, pyridyl group, pyrimidinyl group, furyl group, pyrrolyl group, imidazolyl group, benzoimidazolyl group, pyrazolyl group, pyrazinyl group, triazolyl group (for example, 1, 2,4-triazol-1-yl group, 1,2,3-triazol-1-yl group, etc.), oxazolyl group, benzoxazolyl group, thiazolyl group, isoxazolyl group, isothiazolyl group, furazanyl group, thienyl group, A quinolyl group, a benzofuryl group, a dibenzofuryl group, a benzothienyl group, a dibenzothienyl group, an indolyl group, a carbazolyl group, a carbolinyl group, a diazacarbazolyl group (one of the carbon atoms constituting the carboline ring of the carbolinyl group is a nitrogen atom) Quinoxalinyl) , Pyridazinyl group, triazinyl group, quinazolinyl group, phthalazinyl group, etc.), heterocyclic group (eg, pyrrolidyl group, imidazolidyl group, morpholyl group, oxazolidyl group, etc.), alkoxy group (eg, methoxy group, ethoxy group, propyloxy group, Pentyloxy group, hexyloxy group, octyloxy group, dodecyloxy group, etc.), cycloalkoxy group (eg, cyclopentyloxy group, cyclohexyloxy group, etc.), aryloxy group (eg, phenoxy group, naphthyloxy group, etc.), alkylthio Groups (for example, methylthio group, ethylthio group, propylthio group, pentylthio group, hexylthio group, octylthio group, dodecylthio group, etc.), cycloalkylthio groups (for example, cyclopentylthio group, cyclohexylthio group, etc.), arylthio (Eg, phenylthio group, naphthylthio group, etc.), alkoxycarbonyl group (eg, methyloxycarbonyl group, ethyloxycarbonyl group, butyloxycarbonyl group, octyloxycarbonyl group, dodecyloxycarbonyl group, etc.), aryloxycarbonyl group (eg, , Phenyloxycarbonyl group, naphthyloxycarbonyl group, etc.), sulfamoyl group (for example, aminosulfonyl group, methylaminosulfonyl group, dimethylaminosulfonyl group, butylaminosulfonyl group, hexylaminosulfonyl group, cyclohexylaminosulfonyl group, octylaminosulfonyl group) Group, dodecylaminosulfonyl group, phenylaminosulfonyl group, naphthylaminosulfonyl group, 2-pyridylaminosulfonyl group, etc.), acyl group (for example, Acetyl group, ethylcarbonyl group, propylcarbonyl group, pentylcarbonyl group, cyclohexylcarbonyl group, octylcarbonyl group, 2-ethylhexylcarbonyl group, dodecylcarbonyl group, phenylcarbonyl group, naphthylcarbonyl group, pyridylcarbonyl group, etc.), acyloxy group ( For example, acetyloxy group, ethylcarbonyloxy group, butylcarbonyloxy group, octylcarbonyloxy group, dodecylcarbonyloxy group, phenylcarbonyloxy group, etc.), amide group (for example, methylcarbonylamino group, ethylcarbonylamino group, dimethylcarbonyl) Amino group, propylcarbonylamino group, pentylcarbonylamino group, cyclohexylcarbonylamino group, 2-ethylhexylcarbonylamino group, octyl Sulfonylamino group, dodecylcarbonylamino group, phenylcarbonylamino group, naphthylcarbonylamino group, etc.), carbamoyl group (for example, aminocarbonyl group, methylaminocarbonyl group, dimethylaminocarbonyl group, propylaminocarbonyl group, pentylaminocarbonyl group, Cyclohexylaminocarbonyl group, octylaminocarbonyl group, 2-ethylhexylaminocarbonyl group, dodecylaminocarbonyl group, phenylaminocarbonyl group, naphthylaminocarbonyl group, 2-pyridylaminocarbonyl group, etc.), ureido group (for example, methylureido group, ethyl) Ureido group, pentylureido group, cyclohexylureido group, octylureido group, dodecylureido group, phenylureido group, naphthylureido group, 2- Lysylaminoureido group, etc.), sulfinyl groups (for example, methylsulfinyl group, ethylsulfinyl group, butylsulfinyl group, cyclohexylsulfinyl group, 2-ethylhexylsulfinyl group, dodecylsulfinyl group, phenylsulfinyl group, naphthylsulfinyl group, 2-pyridylsulfinyl group) Group), alkylsulfonyl group (eg methylsulfonyl group, ethylsulfonyl group, butylsulfonyl group, cyclohexylsulfonyl group, 2-ethylhexylsulfonyl group, dodecylsulfonyl group etc.), arylsulfonyl group or heteroarylsulfonyl group (eg phenyl Sulfonyl group, naphthylsulfonyl group, 2-pyridylsulfonyl group, etc.), amino group (for example, amino group, ethylamino group, dimethylamino group, butyryl) Mino group, cyclopentylamino group, 2-ethylhexylamino group, dodecylamino group, anilino group, naphthylamino group, 2-pyridylamino group, etc.), cyano group, nitro group, hydroxy group, mercapto group, silyl group (for example, trimethylsilyl group) , Triisopropylsilyl group, triphenylsilyl group, phenyldiethylsilyl group, etc.). Of these substituents, preferred are an alkyl group and an aryl group.

Z represents a nonmetallic atom group necessary for forming a 5- to 7-membered ring. Examples of the 5- to 7-membered ring formed by Z include a benzene ring, naphthalene ring, pyridine ring, pyrimidine ring, pyrrole ring, thiophene ring, pyrazole ring, imidazole ring, oxazole ring and thiazole ring. Of these, a benzene ring is preferred.

B ₁ to B ₅ represent a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom, and at least one represents a nitrogen atom. The aromatic nitrogen-containing heterocycle formed by these five atoms is preferably a monocycle. Examples include pyrrole ring, pyrazole ring, imidazole ring, triazole ring, tetrazole ring, oxazole ring, isoxazole ring, thiazole ring, isothiazole ring, oxadiazole ring, and thiadiazole ring. Among these, a pyrazole ring and an imidazole ring are preferable, and an imidazole ring in which B2 and B5 are nitrogen atoms is particularly preferable. These rings may be further substituted with the above substituents. Preferred as the substituent are an alkyl group and an aryl group, and more preferably an aryl group.

L ₁ represents an atomic group that forms a bidentate ligand together with X ₁ and X ₂ . Specific examples of the bidentate ligand represented by X ₁ -L ₁ -X ₂ include, for example, substituted or unsubstituted phenylpyridine, phenylpyrazole, phenylimidazole, phenyltriazole, phenyltetrazole, pyrazabol, picolinic acid And acetylacetone. These groups may be further substituted with the above substituents.

m1 represents an integer of 1, 2 or 3, m2 represents an integer of 0, 1 or 2, and m1 + m2 is 2 or 3. Especially, the case where m2 is 0 is preferable. As the metal represented by M ₁ , a transition metal element belonging to Group 8 to 10 of the periodic table (also simply referred to as a transition metal) is used, among which iridium and platinum are preferable, and iridium is more preferable.

Specific examples of the phosphorescent compound (D-1 to D-93) represented by the general formula (3) are shown below. Among these examples, the 0-0 transition band in the phosphorescence spectrum is exemplified. A phosphorescent compound having an emission wavelength belonging to is in the range of 460 to 827 nm (2.7 to 1.5 eV) is more preferable.

 

 

 

 

 

 

 

 

 

 

 

(4.3) Quantum Dots The present invention is characterized in that the light emitting layer contains quantum dots having an emission wavelength in the range of 413 to 477 nm.

That is, as shown in FIG. 1, the quantum dots 30 are contained in the first light emitting layer 22. The quantum dots 30 may exist at the interface between the first light emitting layer 22 and a layer adjacent to the light emitting layer (for example, the electron transport layer 21 and the charge generation layer 23).
In the present invention, it is particularly preferable that the quantum dots are contained in at least the first light emitting layer.

The quantum dot according to the present invention refers to a particle having a predetermined size, which is composed of a crystal of a semiconductor material and has a quantum confinement effect, and is a fine particle having a particle diameter of about several nanometers to several tens of nanometers. This means that the quantum dot effect can be obtained.

The particle diameter of the quantum dots (fine particles) according to the present invention is specifically preferably in the range of 1 to 20 nm, more preferably in the range of 1 to 10 nm.

The energy level E of such a quantum dot is generally expressed by the following formula (I) when the Planck constant is “h”, the effective mass of the electron is “m”, and the radius of the fine particle is “R”. Is done.

Formula (I)
E∝h ² / mR ²
As shown by the formula (I), the band gap of the quantum dot increases in proportion to “R ⁻² ”, and a so-called quantum dot effect is obtained. Thus, the band gap value of a quantum dot can be controlled by controlling and defining the particle diameter of the quantum dot. That is, by controlling and defining the particle diameter of the fine particles, it is possible to provide diversity not found in ordinary atoms. For this reason, it is possible to convert electrical energy into light of a desired wavelength by exciting it with light or applying a voltage to an EL element including a quantum dot to confine electrons and holes in the quantum dot and recombine them. Can be emitted. In the present invention, such a light-emitting quantum dot material is defined as a quantum dot.

As described above, the average particle diameter of the quantum dots is about several nanometers to several tens of nanometers. However, when used as one of the light emitting materials for white light emission, the average particle diameter is set to the target light emission color. . For example, when it is desired to obtain red light emission, the average particle diameter of the quantum dots is preferably set within a range of 3.0 to 20 nm. When green light emission is desired to be obtained, the average particle diameter of the quantum dots is set to It is preferable to set within the range of 1.5 to 10 nm, and when it is desired to obtain blue light emission, it is preferable to set the average particle diameter of the quantum dots within the range of 1.0 to 3.0 nm. However, the average particle diameter of the blue-emitting quantum dots varies depending on the material constituting the quantum dots.

As a method for measuring the average particle diameter, a known method can be used. For example, a quantum dot particle observation is performed with a transmission electron microscope (TEM), and a method for obtaining the number average particle size of the particle size distribution therefrom, or a method for obtaining an average particle size using an electron force microscope (AFM), A particle size measuring apparatus using a dynamic light scattering method, for example, “ZETASIZER Nano-Series—Nano-ZS, manufactured by Malvern, Inc. can be measured using a spectrum obtained by a small-angle X-ray scattering method. A method of deriving a particle size distribution using particle size distribution simulation calculation and the like can be mentioned. In the present invention, a method of obtaining an average particle size using an electron force microscope (AFM) is preferable.

In the quantum dot according to the present invention, the aspect ratio (major axis diameter / minor axis diameter) is preferably in the range of 1.0 to 2.0, more preferably 1.1 to 1. .7 range. The aspect ratio (major axis diameter / minor axis diameter) related to the quantum dots according to the present invention can also be determined by measuring the major axis diameter and the minor axis diameter using, for example, an electron force microscope (AFM). . The number of individuals to be measured is preferably 300 or more.

The addition amount of the quantum dots is preferably in the range of 0.01 to 50% by mass, and in the range of 0.05 to 25% by mass, when the total constituent materials of the layer to be added are 100% by mass. More preferably, it is most preferably in the range of 0.1 to 20% by mass. If the addition amount is 0.01% by mass or more, white light emission with sufficient luminance efficiency and good color rendering can be obtained, and if it is 50% by mass or less, an appropriate distance between quantum dot particles can be maintained. The size effect can be exhibited sufficiently.

In addition, since the phosphorescent compound described above has a relatively long excitation lifetime on the order of millimeters or microseconds, so-called concentration quenching, in which the exciton energy is relaxed and lost when the concentration in the layer is too high. There is a problem. However, by adding these quantum dots to the light-emitting layer or its adjacent layer, not only the light emission of the quantum dots and the phosphorescent compound itself is obtained, but the details are unknown, but the shape of the entire layer by the quantum dots is not known. The effect of improving the luminous efficiency of the phosphorescent compound, which is presumed to be due to the change or the dispersibility of the phosphorescent compound due to the surface energy of the quantum dots, is obtained.

Examples of the constituent material of the quantum dot include a simple substance of a periodic table group 14 element such as carbon, silicon, germanium, and tin, a simple substance of a periodic table group 15 element such as phosphorus (black phosphorus), and a periodicity of selenium, tellurium, and the like. Table 16 group element simple substance, compound consisting of a plurality of periodic table group 14 elements such as silicon carbide (SiC), tin oxide (IV) (SnO ₂ ), tin sulfide (II, IV) (Sn (II) Sn (IV) S ₃ ), tin sulfide (IV) (SnS ₂ ), tin (II) sulfide (SnS), tin (II) selenide (SnSe), tin telluride (II) (SnTe), lead sulfide (II) ) (PbS), lead selenide (II) (PbSe), lead telluride (II) (PbTe) periodic table group 14 element and periodic table group 16 element compound, boron nitride (BN), phosphorus Boron halide (BP), Boron arsenide (BAs), Aluminum nitride (AlN), Al phosphide Ni (AlP), aluminum arsenide (AlAs), aluminum antimonide (AlSb), gallium nitride (GaN), gallium phosphide (GaP), gallium arsenide (GaAs), gallium antimonide (GaSb), indium nitride (InN), Compounds of Group 13 elements of the periodic table and Group 15 elements of the periodic table such as indium phosphide (InP), indium arsenide (InAs), indium antimonide (InSb), etc. (or III-V group compound semiconductors), aluminum sulfide ( Al ₂ S ₃ ), aluminum selenide (Al ₂ Se ₃ ), gallium sulfide (Ga ₂ S ₃ ), gallium selenide (Ga ₂ Se ₃ ), gallium telluride (Ga ₂ Te ₃ ), indium oxide (In ₂₎ O _3), indium sulfide _{(In 2 S} 3), indium selenide (I ₂ Se _3), compounds of tellurium indium _(In 2 Te ₃₎ periodic table group 13 elements and the periodic table group 16 element such as, thallium chloride (I) (TlCl), thallium bromide (I) (TlBr ), Compounds of group 13 elements of the periodic table and elements of group 17 of the periodic table such as thallium (I) iodide (TlI), zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe), tellurium Zinc iodide (ZnTe), cadmium oxide (CdO), cadmium sulfide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe), mercury sulfide (HgS), mercury selenide (HgSe), mercury telluride (HgTe) ) periodic table group 12 element and the periodic table compound of group 16 element such as (or II-VI compound semiconductor), arsenic sulfide (III) (as 2 S _3), selenium arsenic (III _(As 2 _Se 3), telluride arsenic _{(III) (As 2 Te 3} ), antimony sulfide _{(III) (Sb 2 S 3} ), selenium antimony _{(III) (Sb 2 Se 3} ), antimony telluride (III ) (Sb ₂ Te ₃ ), bismuth sulfide (III) (Bi ₂ S ₃ ), bismuth selenide (III) (Bi ₂ Se ₃ ), bismuth telluride (III) (Bi ₂ Te ₃ ), etc. Compounds of Group 15 elements and Group 16 elements of the periodic table, Group 11 elements of the periodic table and Group 16 of the periodic table such as copper (I) (Cu ₂ O), copper selenide (Cu ₂ Se), etc. Periodic tables of compounds with elements, copper chloride (I) (CuCl), copper bromide (I) (CuBr), copper iodide (I) (CuI), silver chloride (AgCl), silver bromide (AgBr), etc. Compounds of Group 11 elements and Periodic Table Group 17 elements, nickel oxide (II) (N compounds of periodic table group 10 elements such as iO) and periodic table group 16 elements, periodic table group 9 elements such as cobalt (II) oxide (CoO), cobalt sulfide (II) (CoS) and periodic table Compounds with Group 16 elements, compounds of Group 8 elements of the periodic table such as triiron tetroxide (Fe ₃ O ₄ ), iron (II) sulfide (FeS), and Group 16 elements of the periodic table, manganese (II) oxide A compound of a periodic table group 7 element such as (MnO) and a periodic table group 16 element, a periodic table group 6 element such as molybdenum sulfide (IV) (MoS ₂ ), tungsten oxide (IV) (WO ₂ ), etc. Compounds with Group 16 elements of the Periodic Table, Periodic Table Group 5 elements such as vanadium (II) oxide (VO), vanadium oxide (IV) (VO ₂ ), tantalum oxide (V) (Ta ₂ O ₅ ) and the period Table compound of group 16 element, a titanium oxide _{(TiO 2, Ti 2 O 5} , Ti 2 O , A compound of Group 4 of the periodic table element and Periodic Table Group 16 element of _Ti 5 _{O 9,} etc.) and the like, magnesium sulfide (MgS), the second group elements and the periodic table periodic table such as magnesium selenide (MgSe) Compounds with group 16 elements, cadmium (II) chromium (III) (CdCr ₂ O ₄ ), cadmium selenide (II) chromium (III) (CdCr ₂ Se ₄ ), copper sulfide (II) chromium (III) ( Examples thereof include chalcogen spinels such as CuCr ₂ S ₄ ), mercury (II) selenide, chromium (III) (HgCr ₂ Se ₄ ), barium titanate (BaTiO ₃ ), etc., but SnS ₂ , SnS, SnSe, SnTe, PbS , PbSe, PbTe, etc. compounds of periodic table group 14 elements and periodic table group 16 elements, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, etc. III-V group compound semiconductors such as Ga ₂ O ₃ , Ga ₂ S ₃ , Ga ₂ Se ₃ , Ga ₂ Te ₃ , In ₂ O ₃ , In ₂ S ₃ , In ₂ Se ₃ , In ₂ Te _3, etc. Compounds of Group 13 elements and Group 16 elements of the periodic table, ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, HgO, HgS, HgSe, HgTe and other II-VI group compound semiconductors, As ₂ O ₃ , As ₂ S ₃ , As ₂ Se ₃ , As ₂ Te ₃ , Sb ₂ O ₃ , Sb ₂ S ₃ , Sb ₂ Se ₃ , Sb ₂ Te ₃ , Bi ₂ O ₃ , Bi ₂ S ₃ , Bi ₂ A compound of a periodic table group 15 element such as Se ₃ or Bi ₂ Te ₃ and a group 16 element of the periodic table, a compound of periodic table group 2 element such as MgS or MgSe, and a group 16 element of the periodic table are preferable, Among them, Si, Ge GaN, GaP, InN, InP, Ga ₂ O ₃ , Ga ₂ S ₃ , In ₂ O ₃ , In ₂ S ₃ , ZnO, ZnS, CdO, and CdS are more preferable. Since these substances do not contain highly toxic negative elements, they are excellent in environmental pollution resistance and safety to living organisms, and since a pure spectrum can be stably obtained in the visible light region, light emitting devices Is advantageous for the formation of Of these materials, CdSe, ZnSe, and CdS are preferable in terms of light emission stability. From the viewpoints of luminous efficiency, high refractive index, and safety, ZnO and ZnS quantum dots are preferable. The quantum dots may be CuInS, CuInSe, or CuInGaSe.
Said material may be used by 1 type and may be used in combination of 2 or more type.

Note that the above-described quantum dots can be doped with a small amount of various elements as impurities as necessary. By adding such a doping substance, the emission characteristics can be greatly improved.

In the quantum dot according to the present invention, the emission wavelength is preferably in the range of 413 to 477 nm (2.6 to 3.6 eV). This is because the quantum dot of this emission wavelength, that is, the blue quantum dot, has the widest band gap and is the quantum dot with the deepest HOMO and the shallow LUMO. As a result, when it is installed as the first light emitting layer of the OLED having the reverse layer configuration, it is possible to obtain a quantum dot layer having the highest electron transporting property and the highest hole blocking property. Further, since it is also a light emitting region that is very difficult to emit with the phosphorescent dopant, the first light emitting layer that shines in this region can impart high color temperature, high color rendering, and the like.

The emission wavelength (band gap) as used in the present invention is the band gap (eV) in a quantum dot, and the emission wavelength (nm) = 1240 in the case of an inorganic quantum dot. / Band gap (eV).

The band gap (eV) of a quantum dot can be measured using a Tauc plot.

The Tauc plot, which is one of the optical scientific measurement methods of the band gap (eV), will be described.

The measurement principle of the band gap (E ₀ ) using the Tauc plot is shown below.

In the region of relatively large absorption near the optical absorption edge on the long wavelength side of the semiconductor material, the light absorption coefficient α, the light energy hν (where h is the Planck constant, ν is the frequency), and the band cap energy E ₀ In the meantime, the following equation (A) is considered to hold.

Formula (A)
αhν = B (hν−E ₀ ) ²
Therefore, an absorption spectrum is measured, and hν is plotted (so-called Tauc plot) with respect to (αhν) raised to the 0.5th power, and the value of hν at α = 0 with extrapolation of the straight section is sought. It becomes the band gap energy E ₀ of the quantum dot.

In the case of quantum dots, the difference between absorption and emission spectra (Stokes shift) is small and the waveform is sharp, so the maximum wavelength of the emission spectrum can be used as an index of the band gap.

In addition, as another method for estimating the energy levels of these organic and inorganic functional materials, energy levels required by scanning tunneling spectroscopy, ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, Auger electron spectroscopy, and the like. And a method for optically estimating the band gap.

In addition, these quantum dots were generated not only in light emission due to direct recombination of holes and electrons in the quantum dots, but also in an organic electron block hole transport layer, an organic light emission layer, or a hole block electron transport layer. The energy of excitons may be absorbed by the quantum dots to obtain light emission from the quantum dot core. Since these quantum dots are lightly doped, other phosphorescent compounds can also absorb the exciton energy to obtain light emission.

The surface of the quantum dot is preferably coated with an inert inorganic coating layer or a coating composed of an organic ligand. That is, the surface of the quantum dot has a core / shell structure having a core region made of a quantum dot material and a shell region made of an inert inorganic coating layer or an organic ligand. Is preferred.

This core / shell structure is preferably formed of at least two kinds of compounds, and a gradient structure (gradient structure) may be formed of two or more kinds of compounds. This effectively prevents aggregation of the quantum dots in the coating liquid, improves the dispersibility of the quantum dots, improves the luminance efficiency, and prevents color shifts that occur when driven continuously. Can be suppressed. Further, the light emission characteristics can be stably obtained due to the presence of the coating layer.

In addition, when the surface of the quantum dot is covered with a coating (shell part), a surface modifier as described later can be reliably supported in the vicinity of the surface of the quantum dot.

The thickness of the coating (shell part) is not particularly limited, but is preferably in the range of 0.1 to 10 nm, and more preferably in the range of 0.1 to 5 nm.

In general, the emission color can be controlled by the average particle diameter of the quantum dots, and if the thickness of the coating is within the above range, the thickness of the coating can be determined from the thickness corresponding to several atoms. The thickness is less than one, the quantum dots can be filled with high density, and a sufficient amount of light emission can be obtained. In addition, the presence of the coating can suppress non-luminous electron energy transfer due to defects existing on the particle surfaces of the core particles and electron traps on the dangling bonds, thereby suppressing a decrease in quantum efficiency.

(4.4) Functional surface modifier When forming an organic functional layer containing quantum dots by a wet coating method, a surface modifier is attached in the vicinity of the surface of the quantum dots in the coating solution used therefor. It is preferable. Thereby, especially the dispersion stability of the quantum dot in a coating liquid can be made excellent. In addition, when a quantum dot is manufactured, by attaching a surface modifier to the surface of the quantum dot, the shape of the formed quantum dot becomes highly spherical, and the particle size distribution of the quantum dot can be kept narrow. Therefore, it can be made particularly excellent.

Functional surface modifiers applicable in the present invention may be those directly attached to the surface of the quantum dots, or those attached via a shell (the surface modifier is directly attached to the shell. In other words, it may not be in contact with the core of the quantum dot.

Examples of the surface modifier include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, and polyoxyethylene oleyl ether; tripropylphosphine, tributylphosphine, trihexylphosphine, trioctylphosphine, and the like. Trialkylphosphines; polyoxyethylene alkylphenyl ethers such as polyoxyethylene n-octylphenyl ether and polyoxyethylene n-nonylphenyl ether; tri (n-hexyl) amine, tri (n-octyl) amine, tri ( tertiary amines such as n-decyl) amine; tripropylphosphine oxide, tributylphosphine oxide, trihexylphosphine oxide, trioctylphosphineoxy Organic phosphorus compounds such as tridecylphosphine oxide; polyethylene glycol diesters such as polyethylene glycol dilaurate and polyethylene glycol distearate; organic nitrogen compounds such as nitrogen-containing aromatic compounds such as pyridine, lutidine, collidine and quinolines; hexylamine; Aminoalkanes such as octylamine, decylamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine; dialkyl sulfides such as dibutyl sulfide; dialkyl sulfoxides such as dimethyl sulfoxide and dibutyl sulfoxide; sulfur-containing aromatics such as thiophene Organic sulfur compounds such as compounds; higher fatty acids such as palmitic acid, stearic acid and oleic acid; alcohols; sorbitan fatty acid esters; fatty acid-modified poly Stealtes; tertiary amine-modified polyurethanes; polyethyleneimines and the like. When the quantum dots are prepared by the method described later, the surface modifier may be a fine particle of quantum dots in a high-temperature liquid phase. It is preferable that the substance is coordinated to be stabilized, specifically, trialkylphosphines, organic phosphorus compounds, aminoalkanes, tertiary amines, organic nitrogen compounds, dialkyl sulfides, dialkyl sulfoxides. , Organic sulfur compounds, higher fatty acids and alcohols are preferred. By using such a surface modifier, the dispersibility of the quantum dots in the coating solution can be made particularly excellent. Moreover, the shape of the quantum dot formed at the time of manufacture of a quantum dot can be made into a higher sphericity, and the particle size distribution of a quantum dot can be made sharper.

In the present invention, as described above, the size (average particle diameter) of the quantum dots is preferably in the range of 1 to 20 nm. In the present invention, the size of the quantum dots means the total area composed of a core region composed of a quantum dot material, a shell region composed of an inert inorganic coating layer or an organic ligand, and a surface modifier. Represents size. If the surface modifier or shell is not included, the size does not include it.

(4.5) Manufacturing method of quantum dot As a manufacturing method of a quantum dot, the manufacturing method of the following quantum dots etc. which are performed conventionally are mentioned, However, It is not limited to these, Well-known arbitrary The method can be used. Moreover, it can also be purchased as a commercial product from Aldrich, CrystalPlex, NNLab, etc.

For example, as a process under high vacuum, molecular beam epitaxy method, CVD method, etc .; as a liquid phase production method, raw material aqueous solution, for example, alkanes such as n-heptane, n-octane, isooctane, or benzene, toluene Inverted micelles, which exist as reverse micelles in non-polar organic solvents such as aromatic hydrocarbons such as xylene, and crystal growth in this reverse micelle phase, inject a thermally decomposable raw material into a high-temperature liquid-phase organic medium Examples thereof include a hot soap method for crystal growth and a solution reaction method involving crystal growth at a relatively low temperature using an acid-base reaction as a driving force, as in the hot soap method. Any method can be used from these production methods, and among these, the liquid phase production method is preferred.

In the liquid phase production method, the organic surface modifier present on the surface when the quantum dots are synthesized is referred to as an initial surface modifier. For example, examples of the initial surface modifier in the hot soap method include trialkylphosphines, trialkylphosphine oxides, alkylamines, dialkyl sulfoxides, alkanephosphonic acid and the like. These initial surface modifiers are preferably exchanged for the above-described functional surface modifiers by an exchange reaction.

Specifically, for example, the initial surface modifier such as trioctyl phosphine oxide obtained by the hot soap method described above is obtained by performing the functional surface modification described above by an exchange reaction performed in a liquid phase containing the functional surface modifier. It is possible to replace it with an agent.

The following shows an example of a method for producing quantum dots.

<1> Production example 1 of quantum dots
First, CdO powder (1.6 mmol, 0.206 g; Aldrich, + 99.99%) and oleic acid (6.4 mmol, 1.8 g; Aldrich, 95%) were mixed with 40 ml of trioctylamine (TOA, Aldrich, 95 %). The mixed solution was heat-treated at 150 ° C. while stirring at high speed, and the temperature was increased to 300 ° C. while N ₂ was allowed to flow. Then, at 300 ° C., 0.2 ml of 2.0 mol / L Se (Alfa Aesar) added to trioctylphosphine (TOP, Strem, 97%) is injected into the Cd-containing mixture at high speed.

After 90 seconds, 1.2 mmol of n-octanethiol added to TOA (210 μl in 6 ml) is injected at a rate of 1 ml / min using a syringe pump and allowed to react for 40 minutes.

Next, 0.92 g of zinc acetate and 2.8 g of oleic acid are dissolved in 20 ml of TOA at 200 ° C. in an N ₂ atmosphere to prepare a 0.25 mol / L Zn precursor solution.

Next, a 16 ml aliquot of Zn-oleic acid solution (heated at 100 ° C.) is injected into the Cd-containing reaction medium at a rate of 2 ml / min. Thereafter, 6.4 mmol of n-octanethiol in TOA (1.12 ml in 6 ml) is injected at a rate of 1 ml / min using a syringe pump.

The entire reaction takes 2 hours. After the reaction is complete, the product is cooled to about 50-60 ° C. and the organic sludge is removed by centrifugation (5,600 rpm). Add ethanol (Fisher, HPLC grade) until there is no opaque mass. Next, the precipitate obtained by centrifugation is dissolved in toluene (Sigma-Aldrich, Anhydrous 99.8%) to obtain a CdSe / CdS / ZnS core-shell quantum dot colloidal solution.

<2> Production example 2 of quantum dots
When a quantum dot having a core / shell structure of CdSe / ZnS is to be obtained, (CH ₃ ) ₂ Cd (dimethyl cadmium), TOPSe (trioctylphosphine selenine selene) is used as an organic solvent using TOPO (trioctylphosphine oxide) as a surfactant. A precursor material corresponding to the core (CdSe) is injected to generate a crystal, and is maintained at a high temperature for a certain period of time so that the crystal grows at a certain size, and then corresponds to the shell (ZnS). CdSe / ZnS quantum dots capped with TOPO can be obtained by injecting the precursor material so that a shell is formed on the surface of the core already formed.

<3> Production example 3 of quantum dots
Under an argon stream, 7.5 g of tri-n-octylphosphine oxide (TOPO) (manufactured by Kanto Chemical Co., Ltd.), 2.9 g of stearic acid (manufactured by Kanto Chemical Co., Ltd.), 620 mg of n-tetradecylphosphonic acid (manufactured by AVOCADO), And 250 mg of cadmium oxide (made by Wako Pure Chemical Industries Ltd.) was added, and it heat-mixed at 370 degreeC. After naturally cooling this to 270 ° C., a solution prepared by dissolving 200 mg of selenium (manufactured by STREM CHEMICAL) in 2.5 mL of tributylphosphine (manufactured by Kanto Chemical Co., Inc.) in advance, dried under reduced pressure, and CdSe coated with TOPO Get fine particles.

Next, 15 g of TOPO was added to the obtained CdSe fine particles and heated, and subsequently a solution of 1.1 g of zinc diethyldithiocarbamate (manufactured by Tokyo Chemical Industry Co., Ltd.) dissolved in 10 mL of trioctylphosphine (manufactured by Sigma Aldrich) at 270 ° C. was added. Then, nanoparticles with CdSe nanocrystals with TOPO fixed on the surface and ZnS as the core (hereinafter also referred to as TOPO fixed quantum dots) were obtained. In addition, the quantum dot of this state is soluble in organic solvents, such as toluene and tetrahydrofuran (THF).

Thereafter, the prepared TOPO fixed quantum dots were dissolved in THF, heated to 85 ° C., and N-[(S) -3-mercapto-2-methylpropionyl] -L-proline (Sigma) dissolved in ethanol there. (Aldrich) 100 mg was added dropwise and refluxed for about 12 hours. After refluxing for 12 hours, an aqueous NaOH solution was added, and the mixture was heated at 90 ° C. for 2 hours to evaporate THF. The obtained unpurified quantum dots are purified and concentrated using ultrafiltration (Millipore, “Microcon”) and Sephadex column (Amersham Biosciences, “MicroSpin G-25 Columns”). A hydrophilic quantum dot in which N-[(S) -3-mercapto-2-methylpropionyl] -L-proline is immobilized on the surface of the quantum dot can be produced.

(4.6) Quantum Dot Film Formation Method The quantum dot film formation method is preferably a wet process. For example, spin coating method, casting method, die coating method, blade coating method, roll coating method, ink jet method, printing method, spray coating method, curtain coating method, LB method (Langmuir Brodgett method), etc. Can do.

Furthermore, a film forming method using a transfer method (film, stamp, etc.) that transfers after forming a monomolecular film of quantum dots on another medium is also useful.

In this case, the solvent used preferably includes a solvent having a boiling point of 100 to 150 ° C. By using the solvent in such a range, an appropriate drying speed is obtained, the quantum dot compound contained in the coating film can be properly oriented, and higher luminous efficiency and durability can be obtained.

As such a solvent, toluene, xylene, chlorobenzene, n-butanol and the like can be raised. Moreover, a mixed solvent containing these solvents may be used, and the ratio is preferably in the range of 9: 1 to 0:10.

[5] Charge generation layer The charge generation layer is a layer that generates holes and electrons when an electric field is formed. The generation interface may be in the charge generation layer. It may be at or near the layer interface. For example, when the charge generation layer is a single layer, the charge generation of electrons and holes may be within the charge generation layer, or may be at the interface between the adjacent layer and the charge generation layer.

In the present invention, it is more preferable that the charge generation layer is composed of two or more layers and includes one or both of a p-type semiconductor layer and an n-type semiconductor layer.

The charge generation layer may function as a hole injection layer, a hole transport layer, an electron transport layer, or an electron injection layer and can be used as the same layer, but the charge generation layer generates holes and electrons. It is defined as a layer having an interface or a layer having an interface.

The configuration of the charge generation layer in the present invention (reverse layer configuration) is as follows.

1. 1. Light emitting unit / bipolar layer (one layer) / light emitting unit 2. Light emitting unit / p-type layer / n-type layer / light emitting unit Light emitting unit / p-type layer / intermediate layer / n-type layer / light emitting unit The bipolar layer is a layer capable of generating and transporting holes and electrons inside the layer by an external electric field. The n-type layer is a charge transport layer in which majority carriers are electrons, and preferably has conductivity higher than that of a semiconductor. The p-type layer is a charge transport layer in which majority carriers are holes, and preferably has conductivity higher than that of a semiconductor. The intermediate layer may be provided if necessary in order to improve the charge generation capability and long-term stability, for example, an n-type layer and a p-type diffusion prevention layer, a pn reaction suppression layer, Examples include a level adjusting layer that adjusts the charge level of the p-type layer and the n-type layer.

In the present invention, a bipolar layer, a p-type layer, and an n-type layer may be further provided between the light emitting unit and the charge generation layer. In the present invention, these layers are included in the light emitting unit and are not regarded as charge generating layers, although they may be provided if necessary when the generated charge is quickly injected into the light emitting unit.

In the present invention, the charge generation layer is preferably formed of at least two layers, and is a layer having a function of injecting holes in the cathode direction of the device and electrons in the anode direction when a voltage is applied. preferable.

The layer interface between two or more charge generation layers may have a clear interface (heterointerface, homointerface), and a multidimensional interface such as a bulk heterostructure, islands, or phase separation. It may be formed.

The thickness of each of the two layers is preferably in the range of 1 to 100 nm, and more preferably in the range of 10 to 50 nm.

The light transmittance of the charge generation layer according to the present invention preferably has a high transmittance for the light emitted from the light emitting layer. In order to sufficiently extract light and obtain sufficient luminance, the transmittance at a wavelength of 550 nm is preferably 50% or more, and more preferably 80% or more.

Among the charge generation layers formed from the two or more layers, one layer has an inorganic compound or organic compound having a work function of 3.0 eV or less, and the other layer has a work function of 4.0 eV. The above inorganic compounds or organic compounds can be preferably used. More preferably, one layer of the charge generation layer is a metal having a work function of 3.0 eV or less, or an inorganic oxide, an inorganic salt, an organometallic complex, or an organic salt, and the other layer is a work layer. A metal having a function of 4.0 eV or more, or an inorganic oxide, an inorganic salt, an organometallic complex, or an organic salt.

An example of a preferred charge generation layer configuration is shown below.

i) A structure using a molybdenum layer as a part of a charge generation layer between light emitting units, such as ITO / EL-unit / Li / Al / MoO3 / EL-unit / Al, which is conventionally known can also be used. .

Here, EL-unit represents a light emitting unit, and the layer structure of the light emitting unit itself is not particularly limited, but includes at least one light emitting layer. A layer structure including a transport layer and an electron transport layer can be used, and a known layer structure including a hole injection layer, a hole transport light emitting layer, an electron injection layer, an electron transport light emitting layer, and the like can also be used. . For example, one light emitting unit can have a layer configuration such as a hole injection transport layer / light emission layer / electron injection transport layer.

ii) Further, when there are two light emitting units as described in JP 2010-192719 A, there are three ITO / EL-unit / LiF / Al / HAT / EL-unit / Al and three light emitting units. In the case of more than one, a layer structure such as ITO / EL-unit / LiF / Al / HAT / EL-unit /... / LiF / Al / HAT / EL-unit / Al can be mentioned. Each description of the light emitting unit is synonymous with the above description (HAT represents a hexaazatriphenylene compound).

Furthermore, in the organic EL device of the present invention, the organic material described in paragraphs 0079 to 0180 of WO2011-46166, the inorganic material described in paragraphs 0181 to 0203, and the like are used as the constituent material of the charge generation layer. However, the present invention is not limited to these.
Among these, it is preferable that the compound which has a hexaazatriphenylene structure represented by following formula (4) is included as a p-type layer.

 

In the general formula (4), each R independently represents hydrogen, a halogen group, an alkyl group having 1 to 12 carbon atoms, an alkoxy group, an alkylamino group, an alkylsilyl group, an aryl group, an arylamino group, a heterocyclic group, The substituent is selected from the group consisting of an ester group, an amide group, a nitro group and a nitrile group. Adjacent Rs may be bonded to each other to form a cyclic structure.

The compound having a structure represented by the general formula (4) is preferably a p-type material having a structure represented by the general formula (5).

 

Since such a material has a very deep LUMO level, when it comes into contact with an n-type material layer with or without an intermediate layer, charges can be efficiently generated. It can be preferably used for the generation layer.
On the other hand, as an n-type layer, an n-type layer in which an electron transport layer is n-doped with an alkali metal or the like (US Pat. No. 7,719,180, etc.), and an n-type layer combining an n-type dopant and an n-type host of Novaled, Inc. Etc. can be preferably used. Usually, n-type dopants such as alkali metals are highly prone to deterioration due to their high activity, but an n-type layer combining NET18 and NDN26, NDN77, NDN87, etc. of Novaled can be preferably used (Reference: Display International) The Society Information Display (SID) 2012 DIGEST, 21-1).

<< First electrode (cathode, cathode) >>
As the first electrode, a material having a small work function (5 eV or less) metal (referred to as an electron injecting metal), an alloy, an electrically conductive compound, and a mixture thereof as an electrode material is used. Specific examples of such electrode materials include sodium, sodium-potassium alloy, magnesium, lithium, magnesium / copper mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al ₂ O ₃ ) Mixtures, indium, lithium / aluminum mixtures, rare earth metals and the like.
Among these, from the viewpoint of durability against oxidation or the like, the second electrode includes, for example, a magnesium / silver mixture, a magnesium / aluminum mixture, a magnesium / indium mixture, an aluminum / aluminum oxide (Al ₂ O ₃ ) mixture, lithium, and the like. / Aluminum mixtures, aluminum etc. are preferred.
Note that in order to transmit the emitted light, if either the first electrode or the second electrode of the EL element is transparent or translucent, it is convenient to improve the light emission luminance. The first electrode is preferably a transparent electrode because the light generated in the light emitting layer can be taken out by making the electrode transparent. That is, an electrode made of a metal oxide such as ITO, IZO, AZO, or FTO may be used.
The first electrode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering. The sheet resistance as the first electrode 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.

<< second electrode (anode, anode) >>
As the first electrode, an electrode material made of a metal, an alloy, an electrically conductive compound and a mixture thereof having a high work function (4 eV or more) is preferably used. Specific examples of such an electrode substance include a conductive transparent material such as a metal such as Au, CuI, indium-tin composite oxide (hereinafter abbreviated as ITO), SnO ₂ , and ZnO. Alternatively, an amorphous material such as IDIXO (In ₂ O ₃ —ZnO) capable of forming a transparent conductive film may be used.
In the first electrode, a thin film may be formed by depositing these electrode materials by a method such as vapor deposition or sputtering, and a desired shape pattern may be formed by a photolithography method, or when pattern accuracy is not required (100 μm or more) The degree) may form a pattern through a mask having a desired shape at the time of vapor deposition or sputtering of the electrode material. Or when using the substance which can be apply | coated like an organic electroconductivity compound, wet film-forming methods, such as a printing system and a coating system, can also be used.
When light emission is extracted from the first electrode, it is desirable that the transmittance be greater than 10%, and the sheet resistance as the first electrode is preferably several hundred Ω / □ or less. Further, although the film thickness depends on the material, it is usually in the range of 10 to 1000 nm, preferably in the range of 10 to 200 nm.

Further, after the metal is formed on the second electrode with a thickness of 1 to 20 nm, the metal oxide-based conductive transparent material mentioned in the description of the first electrode is formed thereon, so that the transparent or A semitransparent second electrode can be manufactured, and by applying this, an EL element in which both the first electrode and the second electrode are transmissive can be manufactured.
Whether the first electrode / second electrode functions as an anode / cathode (forward layer) or a cathode / anode (reverse layer) depends on the work functions of the first electrode and the second electrode. However, it is often determined by whether there is a hole transporting layer or an electron transporting layer between these electrodes and the light emitting layer. That is, if there is a hole transport layer between the first electrode and the light emitting layer, it functions as a normal layer structure, and conversely, if there is an electron transport layer between the first electrode and the light emitting layer, it functions as a reverse layer structure.

《Support substrate》
There are no particular limitations on the material of the support substrate (hereinafter also referred to as a substrate, substrate, substrate, support, etc.), such as glass or plastic, and it may be transparent or opaque. When extracting light 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. Since a substrate that is more flexible than a rigid substrate exerts the effect of suppressing high-temperature storage stability and chromaticity variation, a particularly preferable support substrate has flexibility that can give flexibility to an EL element. Resin film.

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, cellulose acetate propionate ( CAP), cellulose esters such as cellulose acetate phthalate, cellulose nitrate or derivatives thereof, polyvinylidene chloride, polyvinyl alcohol, polyethylene vinyl alcohol, syndiotactic polystyrene, polycarbonate, norbornene resin, polymethylpentene, polyether ketone, polyimide , Polyethersulfone (PES), polyphenylene sulfide, polysulfone , Polyetherimide, polyetherketoneimide, polyamide, fluororesin, nylon, polymethylmethacrylate, acrylic or polyarylates, cyclone resins such as Arton (trade name, manufactured by JSR) or Appel (trade name, manufactured by Mitsui Chemicals) Etc.

On the surface of the resin film, an inorganic film, an organic film or a hybrid film of both may be formed. The water vapor permeability (25 ± 0.5 ° C.) measured by a method according to JIS K 7129-1992. , Relative humidity (90 ± 2)% RH) is preferably 0.01 g / (m ² · 24 h · atm) or less, and further measured by a method according to JIS K 7126-1987. It is a high barrier film having an oxygen permeability of 1 × 10 ⁻³ cm ³ / (m ² · 24 h · atm) or less and a water vapor permeability of 1 × 10 ⁻³ g / (m ² · 24 h · atm) or less. The water vapor permeability is more preferably 1 × 10 ⁻⁵ g / (m ² · 24 h · atm) or less.

The material for forming the barrier film may be any material that has a function of suppressing entry of factors that cause deterioration of the EL element such as moisture and oxygen. 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 more preferable to have a laminated structure of these inorganic layers and organic material layers. Although there is no restriction | limiting in particular about the lamination order of an inorganic layer and an organic functional layer, It is preferable to laminate | stack both alternately several times.

The method for forming the barrier film is not particularly limited. For example, the 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 A polymerization method, a plasma CVD method (CVD: Chemical Vapor Deposition), a laser CVD method, a thermal CVD method, a coating method, and the like can be used, but atmospheric pressure plasma weight as described in JP-A-2004-68143 is used. A legal method is particularly preferred.

Examples of the opaque support substrate include metal plates such as aluminum and stainless steel, films, opaque resin substrates, ceramic substrates, and the like.

In the EL element, the external extraction efficiency of light emission at room temperature 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 EL element / the number of electrons sent to the EL element × 100.

<Sealing>
As a sealing means applicable to the EL element, for example, a method of adhering a sealing member, an electrode, and a support substrate with a sealing adhesive can be exemplified.

The sealing member may be disposed so as to cover the display area of the EL element, and may be concave or flat. Further, transparency and electrical insulation are not particularly limited.

Specific examples 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, silicone, germanium, and tantalum.

In the present invention, as the sealing member, a polymer film or a metal film can be preferably used because the EL element can be thinned. Furthermore, the polymer film has an oxygen permeability measured by a method according to JIS K 7126-1987 of 1 × 10 ⁻³ cm ³ / (m ² · 24 h · atm) or less, and conforms to JIS K 7129-1992. The water vapor permeability (25 ± 0.5 ° C., relative humidity (90 ± 2)% RH) measured by the above method is preferably 1 × 10 ⁻³ g / (m ² · 24 h) or less.

For processing the sealing member into a concave shape, sandblasting, chemical etching, or the like is used.

Specific examples of the sealing adhesive include photo-curing and thermosetting adhesives having a reactive vinyl group of acrylic acid-based oligomers and methacrylic acid-based oligomers, and moisture-curing types such as 2-cyanoacrylic acid esters. Mention may be made of adhesives. Moreover, heat | fever and chemical curing types (two-component mixing), such as an epoxy type, can be mentioned. Moreover, hot-melt type polyamide, polyester, and polyolefin can be mentioned. Moreover, a cationic curing type ultraviolet curing epoxy resin adhesive can be mentioned.

In addition, since an EL element may be deteriorated by heat treatment, a material that can be adhesively cured from room temperature to 80 ° C. is preferable. Further, a desiccant may be dispersed in the adhesive. Application | coating of the adhesive agent to a sealing part may use commercially available dispenser, and may print like screen printing.

It is also preferable that the electrode and the organic functional layer are coated on the outside of the electrode facing the support substrate with the organic functional layer interposed therebetween, and an inorganic or organic layer is formed in contact with the support substrate to form a sealing film. Can be. In this case, the material for forming the film may be any material that has a function of suppressing intrusion of elements that cause deterioration of elements such as moisture and oxygen. 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 organic materials. The method for forming these films is not particularly limited. For example, vacuum deposition, sputtering, reactive sputtering, molecular beam epitaxy, cluster ion beam method, ion plating method, plasma polymerization method, atmospheric pressure plasma A polymerization method, a plasma CVD method, a laser CVD method, a thermal CVD method, a coating method, or the like can be used.

In order to form a gas phase and a liquid phase in the gap between the sealing member and the display area of the EL element, an inert gas such as nitrogen or argon, or an inert liquid such as fluorinated hydrocarbon or silicon oil. Is preferably injected. A vacuum is also possible. Moreover, a hygroscopic compound can also be enclosed inside.

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

Sealing includes casing type sealing (can sealing) and close contact type sealing (solid sealing), but solid sealing is preferable from the viewpoint of thinning. When a flexible EL element is manufactured, solid sealing is preferable because the sealing member is also required to be flexible.

In the following, a preferred embodiment when performing solid sealing will be described.

As the sealing adhesive according to the present invention, a thermosetting adhesive, an ultraviolet curable resin, or the like can be used, but preferably a thermosetting adhesive such as an epoxy resin, an acrylic resin, or a silicone resin, more preferably moisture resistant. It is an epoxy thermosetting adhesive resin that is excellent in water resistance and water resistance and has little shrinkage during curing.

The water content of the sealing adhesive according to the present invention is preferably 300 ppm or less, more preferably 0.01 to 200 ppm, and most preferably 0.01 to 100 ppm.

The moisture content in the present invention may be measured by any method. For example, a volumetric moisture meter (Karl Fischer), an infrared moisture meter, a microwave transmission moisture meter, a heat-dry weight method, a GC / MS, IR, DSC (Differential Scanning Calorimeter), TDS (Temperature Desorption Analysis). Further, using a precision moisture meter AVM-3000 (Omnitech) or the like, moisture can be measured from a pressure increase caused by evaporation of moisture, and moisture content of a film or a solid film can be measured.

In the present invention, the moisture content of the sealing adhesive can be adjusted by, for example, placing it in a nitrogen atmosphere with a dew point temperature of −80 ° C. or lower and an oxygen concentration of 0.8 ppm, and changing the time. Further, it can be dried in a vacuum state of 100 Pa or less while changing the time. Further, the sealing adhesive can be dried only with an adhesive, but can also be placed in advance on the sealing member and dried.

When close sealing (solid sealing) is performed, as the sealing member, for example, a 50 μm thick PET (polyethylene terephthalate) laminated with an aluminum foil (30 μm thick) can be used. Using this as a sealing member, it was uniformly applied to the aluminum surface using a dispenser, a sealing adhesive was placed in advance, the resin substrate and the sealing member were aligned, and both were crimped (0 0.1-3 MPa) and at a temperature of 80-180 ° C., it can be tightly bonded (bonded) to achieve close sealing (solid sealing).

Heating or pressure bonding time varies depending on the type, amount, and area of the adhesive, but temporary bonding is performed at a pressure of 0.1 to 3 MPa, and heat curing time is in the range of 5 seconds to 10 minutes at a temperature of 80 to 180 ° C. Just choose.

It is preferable to use a heated pressure-bonding roll because pressure bonding (temporary bonding) and heating can be performed simultaneously, and internal voids can be eliminated simultaneously.

Further, as a method for forming the adhesive layer, a coating method such as roll coating, spin coating, screen printing, spray coating, or the like can be used using a dispenser depending on the material.

As described above, solid sealing is a form in which there is no space between the sealing member and the EL element substrate and the resin is covered with a cured resin.

Examples of the sealing member include metals such as stainless steel, aluminum and magnesium alloys, polyethylene terephthalate, polycarbonate, polystyrene, nylon, plastics such as polyvinyl chloride, and composites thereof, glass, and the like. In the case of a resin film, a laminate of gas barrier layers such as aluminum, aluminum oxide, silicon oxide, and silicon nitride can be used as in the case of a resin substrate.

The gas barrier layer can be formed by sputtering, vapor deposition or the like on both surfaces or one surface of the sealing member before molding the sealing member, or may be formed on both surfaces or one surface of the sealing member after sealing by a similar method. . Also in this case, the oxygen permeability is 1 × 10 ⁻³ ml / (m ² · 24 h · atm) or less, the water vapor permeability (25 ± 0.5 ° C., relative humidity (90 ± 2)% RH) is 1 × It is preferably 10 ⁻³ g / (m ² · 24 h) or less.

The sealing member may be a film laminated with a metal foil such as aluminum. As a method for laminating the polymer film on one side of the metal foil, a generally used laminating machine can be used. As the adhesive, polyurethane-based, polyester-based, epoxy-based, acrylic-based adhesives and the like can be used. You may use a hardening | curing agent together as needed. A hot melt lamination method, an extrusion lamination method and a coextrusion lamination method can also be used, but a dry lamination method is preferred.

In addition, when the metal foil is formed by sputtering or vapor deposition and is formed from a fluid electrode material such as a conductive paste, it may be created by a method of forming a metal foil on a polymer film as a base. Good.

《Protective film, protective plate》
In order to increase the mechanical strength of the EL element, a protective film or a protective plate may be provided outside the sealing film or the sealing film on the side facing the support substrate with the organic functional layer interposed therebetween. In particular, when sealing is performed with a sealing film, the mechanical strength is not necessarily high, and thus it is preferable to provide such a protective film and a protective plate. As a material that can be used for this, the same glass plate, polymer plate / film, metal plate / film, etc. used for the sealing can be used, but the polymer film is light and thin. Is preferably used.

In the present invention, it is preferable to have a light extraction member between the flexible support substrate and the first electrode or at any position on the light emission side from the flexible support substrate.

Examples of the light extraction member include a prism sheet, a lens sheet, and a diffusion sheet. Further, a diffraction grating or a diffusion structure introduced into an interface or any medium that causes total reflection can be used.

Usually, in an EL element that emits light from a substrate, a part of the light emitted from the light emitting layer causes total reflection at the interface between the substrate and air, causing a problem of light loss. In order to solve this problem, prismatic or lens-like processing is applied to the surface of the substrate, or prism sheets, lens sheets, and diffusion sheets are affixed to the surface of the substrate, thereby suppressing total reflection and light extraction efficiency. To improve.

Also, in order to increase the light extraction efficiency, a method of introducing a diffraction grating or a method of introducing a diffusion structure in an interface or any medium that causes total reflection is known.

<< Method for Manufacturing EL Element >>
As an example of a method for manufacturing an EL element, a method for manufacturing an EL element including a first electrode / electron transport layer / first light emitting layer / charge generation layer / hole transport layer / hole injection layer / second electrode is used. explain.

First, a desired electrode material, for example, a thin film made of a first electrode material is formed on a suitable substrate by a thin film forming method such as vapor deposition or sputtering so as to have a thickness of 1 μm or less, preferably 10 to 200 nm. Thus, the first electrode is manufactured.

Next, an organic functional layer (organic compound thin film) including an electron transport layer, a first light emitting layer, a charge generation layer, a second light emitting layer, a hole transport layer, and a hole injection layer is formed thereon.

The step of forming the organic functional layer mainly includes: (i) a step of applying and laminating the coating liquid constituting the organic functional layer on the first electrode of the support substrate; and (ii) after the application and lamination. And a step of drying the coating liquid.

In the step (i), as a method for forming each layer, as described above, a vapor deposition method, a wet process (for example, spin coating method, casting method, die coating method, blade coating method, roll coating method, ink jet method, printing method, spray coating). Method, curtain coating method, LB method (Langmuir-Blodgett method and the like can be used).
In the method for producing an EL device of the present invention, a light emitting layer containing at least quantum dots (first light emitting layer) is formed by a coating method, and the coating liquid for forming the light emitting layer has a boiling point of 100 to 150 ° C. A form containing a solvent within the range is preferred.

In the formation of the organic functional layer other than the first light emitting layer, a wet process is preferable in the present invention because a homogeneous film is easily obtained and pinholes are hardly generated. Film formation by a coating method such as a casting method, a die coating method, a blade coating method, a roll coating method, or an ink jet method is preferable.

Examples of the liquid medium for dissolving or dispersing the EL material include ketones such as methyl ethyl ketone and cyclohexanone, fatty acid esters such as ethyl acetate, halogenated hydrocarbons such as dichlorobenzene, toluene, xylene, mesitylene, cyclohexylbenzene and the like. Aromatic hydrocarbons, aliphatic hydrocarbons such as cyclohexane, decalin and dodecane, and organic solvents such as dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) can be used. Among them, the boiling point is in the range of 100 to 150 ° C. It is preferable to use the solvent in the inside. Moreover, as a dispersion method, it can disperse | distribute by dispersion methods, such as an ultrasonic wave, high shear force dispersion | distribution, and media dispersion | distribution.

In addition, it is preferable that the preparation process for dissolving or dispersing the EL material and the application process until the EL material is applied on the base material are in an inert gas atmosphere. Since film formation can be performed without deteriorating device performance, it may not always be performed in an inert gas atmosphere. In this case, the manufacturing cost can be suppressed, which is more preferable.

In addition, when forming each layer (for example, a charge generation layer, a 2nd light emitting layer, etc.) of organic functional layers other than a 1st light emitting layer, the layer can also be formed by a well-known vapor deposition method.

(Ii) In the step (ii), the coated and laminated organic functional layer is dried.

“Drying” as used herein refers to reduction to 0.2% or less when the solvent content of the film immediately after coating is 100%.

As the means for drying, those generally used can be used, and examples thereof include reduced pressure or pressure drying, heat drying, air drying, IR drying, and electromagnetic wave drying. Of these, heat drying is preferable, the temperature is equal to or higher than the boiling point of the solvent having the lowest boiling point in the organic functional layer coating solvent, and the temperature is lower than (Tg + 20) ° C. of the material having the lowest Tg among the Tg of the organic functional layer material. Most preferably, it is held at In the present invention, more specifically, it is preferable to hold and dry at 80 ° C. or higher and 150 ° C. or lower, and more preferable to hold and dry at 100 ° C. or higher and 130 ° C. or lower.

The atmosphere when drying the coating liquid after coating / lamination is preferably an atmosphere having a volume concentration of a gas other than the inert gas of 200 ppm or less, but it is not necessarily in an inert gas atmosphere as in the liquid preparation coating process. It may not be necessary. In this case, the manufacturing cost can be suppressed, which is more preferable.

The inert gas is preferably a rare gas such as nitrogen gas or argon gas, and most preferably nitrogen gas in terms of production cost.

The coating / laminating and drying steps of these layers may be single wafer manufacturing or line manufacturing. Further, the drying process may be performed while being conveyed on the line, but from the viewpoint of productivity, it may be deposited or rolled in a non-contact manner in a roll form.

After these layers are dried, a thin film made of the second electrode material is formed thereon by a method such as vapor deposition or sputtering so as to have a film thickness of 1 μm or less, preferably in the range of 50 nm to 200 nm. By providing the second electrode, a desired EL element can be obtained.

An EL element can be manufactured by adhering the contact sealing or sealing member to the electrode and the support substrate with an adhesive after the heat treatment.

<Application>
The EL element of the present invention can be used as various light sources such as a display device, a display, and illumination.

Examples of light sources include home lighting, interior lighting, clock and liquid crystal backlights, billboard advertisements, traffic lights, light sources for optical storage media, light sources for electrophotographic copying machines, light sources for optical communication processors, and light sources for optical sensors. Furthermore, it can be used in a wide range of applications such as general household appliances that require a display device, but it can be used effectively as a backlight for a liquid crystal display device combined with a color filter, and as a light source for illumination. it can.

In the EL element of the present invention, patterning may be performed by a metal mask, an ink jet printing method, or the like as needed during film formation. In the case of patterning, only the electrode may be patterned, the electrode and the light emitting layer may be patterned, or the entire layer of the element may be patterned. In the fabrication of the element, a conventionally known method is used. Can do.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

<< Preparation of sample (EL element) >>
(1) Production of Comparative Example Sample 1 Production was carried out with reference to Patent Document 3.
(1.1) Formation of first electrode A 120 nm thick ITO (Indium Tin Oxide) film is formed on a prepared white plate glass substrate having a thickness of 0.5 mm by sputtering, and patterned by photolithography. A first electrode layer (anode) was formed. The pattern was such that the light emission area was 50 mm square.

(1.2) Formation of hole injection layer The patterned ITO substrate was subjected to ultrasonic cleaning with isopropyl alcohol, dried with dry nitrogen gas, and subjected to UV ozone cleaning for 5 minutes. On this substrate, poly (3,4-ethylenedioxythiophene) -polystyrene sulfonate (abbreviated as PEDOT / PSS, manufactured by Bayer, Baytron P Al 4083) diluted to 70% with pure water at 3000 rpm for 30 seconds After forming the film by spin coating, the film was dried at 200 ° C. for 1 hour to provide a hole injection layer having a thickness of 30 nm.

(1.3) Formation of hole transport layer This substrate was transferred to a nitrogen atmosphere using nitrogen gas (grade G1), and the following compound (PolyTPD) (Mw = 80,000) as the hole transport material was added. A solution of 0.5% dissolved in chlorobenzene was formed by spin coating at 1500 rpm for 30 seconds, and then kept at 160 ° C. for 30 minutes to form a 30 nm-thick hole transport layer.

 

(1.4) Formation of First Light-Emitting Layer Next, a light-emitting layer composition having the following composition was formed as a light-emitting layer by spin coating at 1500 rpm for 30 seconds, dried at 120 ° C. for 5 minutes, and then AFM. The coating film thickness was confirmed using
<Quantum dot light emitting layer composition>
Quantum dots (Trilite (registered trademark) 450 manufactured by Cytodiagnostics) 20 parts by weight Hexane 1,000 parts by weight

(1.5) Formation of intermediate layer Subsequently, the substrate was attached to a vacuum deposition apparatus without being exposed to the atmosphere. Further, H-121 (TCTA) and TMM060 (Merck) were set on a resistance heating boat made of molybdenum, and an intermediate layer made of TMM060 doped with 25% by weight of H-121 was formed to a thickness of 20 nm.

(1.6) Formation of Second Light-Emitting Layer Next, a second light-emitting layer made of a phosphorescent light-emitting material was vapor-deposited at the following vapor deposition rate ratio to form a composition composed of these.
<Light emitting layer composition>
Iridium complex G: 4.0 parts by mass Iridium complex R: 1.0 parts by mass TMM04 (manufactured by Merck): 92 parts by mass

Iridium complex G;

Iridium complex R;

(1.7) Formation of Electron Transport Layer / Electron Injection Layer and Second Electrode A BPhen layer having a thickness of 20 nm was formed as an electron transport layer, and Ca was doped into BPhen having a thickness of 5 nm as an electron injection layer. A layer was formed.
Further, a normal layer type EL element 1 was obtained by vapor-depositing aluminum having a thickness of 100 nm as a second electrode (cathode).

 

(1.8) Sealing and production of white electroluminescent device Subsequently, the substrate was taken out from the vacuum deposition apparatus without being exposed to the atmosphere, and an epoxy adhesive was used as a glass cap and a thermosetting adhesive in the glove box. Sealed to produce Comparative Example Sample 1 (white electroluminescent device).
As the thermosetting adhesive, an epoxy adhesive mixed with the following (A) to (C) was used.
(A) Bisphenol A diglycidyl ether (DGEBA)
(B) Dicyandiamide (DICY)
(C) Epoxy adduct curing accelerator

(2) Production of Comparative Example Sample 2 In Comparative Example Sample 1 “(1.5) Formation of Intermediate Layer and (1.6) Formation of Second Light-Emitting Layer”, the composition was changed to the following. Similarly, Sample 2 of Comparative Example was produced.
<Intermediate layer>
H-121: 100 parts by mass
<Second light emitting layer>
Iridium complex D-90 (B): 7.6 parts by mass,
Iridium complex R: 0.1 part by mass Iridium complex G: 0.3 part by mass H-121: 92 parts by mass

(3) Production of Comparative Example Sample 3 In Comparative Example Sample 1 “(1.5) Formation of Intermediate Layer and (1.6) Formation of Second Light-Emitting Layer”, the composition was changed to the following. Similarly, Sample 3 of Comparative Example was produced.
<Intermediate layer>
H-121: 100 parts by mass
<Second light emitting layer>
Iridium complex D-90 (B): 7.6 parts by mass,
Iridium complex R: 0.1 part by mass Iridium complex G: 0.3 part by mass H-73: 92 parts by mass

(4) Production of Example Sample 4 (4.1) Formation of First Electrode A first electrode (cathode, cathode) was formed in the same manner as in Comparative Example Sample 1.

(4.2) Formation of Electron Transport Layer The patterned ITO substrate was ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen gas, and subjected to UV ozone cleaning for 5 minutes. On this substrate, a sol-gel ZnO forming solution prepared by the following method was formed by spin coating at 2000 rpm for 30 seconds, and then baked at 300 ° C. for 5 minutes to form a 30 nm thick electron composed of ZnO. A transport layer was provided.

<Preparation of sol-gel ZnO forming liquid>
Anhydrous zinc acetate (Sigma-Aldrich 99.999% grade) 157 parts by mass 2-methoxyethanol 960 parts by mass ethanolamine 40 parts by mass

(4.3) Formation of First Light-Emitting Layer Next, a light-emitting layer composition having the following composition and a composition double-diluted with the same solvent were respectively formed by spin coating at 1500 rpm for 30 seconds, and then 30 ° C. at 30 ° C. Each of the light emitting layers having a film thickness of 40 nm was formed by holding for 30 minutes.
<Quantum dot light emitting layer composition>
Quantum dots (Site Diagnostics Trilite (registered trademark) 450, 450 nm emission) 20 parts by weight Hexane 1,000 parts by weight

(4.4) Formation of intermediate layer Subsequently, the substrate was attached to a vacuum deposition apparatus without being exposed to the atmosphere. A molybdenum resistance heating boat containing H-73 is attached to a vacuum deposition apparatus, and the vacuum chamber is depressurized to 4 × 10 ⁻⁵ Pa, and then the boat is energized and heated to form H-73. An intermediate layer having a thickness of 20 nm was formed.

(4.5) Formation of Second Light-Emitting Layer Subsequently, the second light-emitting layer was formed to a thickness of 30 nm so that the evaporation rate was adjusted and the following ratio was obtained.
Iridium complex G: 4.0 parts by mass Iridium complex R: 1.0 parts by mass Host compound H-73: 92 parts by mass

(4.6) Formation of Hole Transport Layer / Hole Injection Layer with Second Electrode Subsequently, the substrate was attached to a vacuum deposition apparatus without being exposed to the atmosphere. A molybdenum resistance heating boat containing Spiro-TPD, H-121 and F4-TCNQ is attached to a vacuum evaporation system, and after the vacuum chamber is depressurized to 4 × 10 ⁻⁵ Pa, the boat is energized. By heating, a hole transporting layer having a film thickness of 60 nm is formed on the light emitting layer at a Spiro-TPD of 0.02 nm / second, and subsequently, H-121 and F4-TCNQ are similarly formed at 0.02 nm / second and 0.02 nm, respectively. A hole injection layer having a thickness of 10 nm was formed on the hole transport layer at 005 nm / second.
Subsequently, 100 nm of aluminum was deposited to form an anode.

 

Thereafter, sealing was performed in the same manner as in Comparative Example Sample 1 to obtain an inverted layer type Example Sample 4.

(5) Production of Example Sample 5 Example Sample 5 was produced in the same manner as Example Sample 4 except that the first light-emitting layer was changed as follows in the production of Example Sample 4.
<First light emitting layer>
Quantum dots (Site Diagnostics Trilite (registered trademark) 450, 450 nm emission) 10 parts by weight Host compound H-73 10 parts by weight Hexane 500 parts by weight Toluene 500 parts by weight

(6) Production of Example Sample 6 Example Sample 6 was produced in the same manner as Example Sample 5, except that the second light-emitting layer was changed as follows in the production of Example Sample 4.
<Second light emitting layer>
Iridium complex D-90 (B): 7.6 parts by mass,
Iridium complex G: 0.3 part by mass Iridium complex R: 0.1 part by mass Host compound H-210: 92 parts by mass

(7) Production of Example Sample 7 Example Sample 7 was produced in the same manner as Example Sample 5, except that the second light-emitting layer was changed as follows in the production of Example Sample 5.
<Second light emitting layer>
Iridium complex D-90 (B): 7.6 parts by mass,
Iridium complex G: 0.3 part by mass,
Iridium complex R: 0.1 part by mass Host compound H-73: 92 parts by mass

(8) Production of Example Samples 8 to 11 Example Sample 7 and Example 11 were produced in the same manner as in Example Sample 7, except that the conditions for forming the first light-emitting layer (spin coating conditions) were changed as follows. Example samples 8 to 11 were produced in the same manner.
<First light emitting layer>
Example Sample 8 4000 rpm
Example Sample 9 2500 rpm
Example Sample 10 1000 rpm
Example Sample 11 700 rpm

(9) Production of Example Samples 12 to 17 Example Samples 12 to 17 were produced in the same manner as Example Sample 7, except that the first light emitting layer was changed as follows in the production of Example 7. did.
In Example Samples 15 to 17, the intermediate layer was formed of the same compound as the host compound of the first light emitting layer.

<First Light-Emitting Layer of Example 12>
Quantum dot (Trilite (registered trademark) 480, 480 nm light emission manufactured by Cytodiagnostics) 10 parts by mass Host compound H-73 10 parts by mass Hexane 500 parts by mass Toluene 500 parts by mass <First emission layer of Example 13>
Quantum dot (Site Diagnostics Co., Ltd. Trilite (registered trademark) 490, 490 nm emission) 10 parts by mass Host compound CBP 10 parts by mass Hexane 500 parts by mass Toluene 500 parts by mass <First emission layer of Example 14>
Quantum dot (Site Diagnostics, Trilite (registered trademark) 450, 450 nm emission) 10 parts by weight Host compound H-212 10 parts by weight Hexane 500 parts by weight Toluene 500 parts by weight

 

<First Light-Emitting Layer of Example 15>
Quantum dot (TRILITE (registered trademark) 450, 450 nm emission manufactured by Cytodiagnostics) 10 parts by mass Host compound H-210 10 parts by mass Hexane 500 parts by mass Toluene 500 parts by mass <First emission layer of Example 16>
Quantum dots (TRILITE (registered trademark) 450 manufactured by Cytodiagnostics, 450 nm emission) 10 parts by mass Host compound H-115 10 parts by mass Hexane 500 parts by mass Toluene 500 parts by mass <First emission layer of Example 17>
Quantum dot (TRILITE (registered trademark) 450, 450 nm light emission manufactured by Cytodiagnostics) 10 parts by mass Host compound H-60 10 parts by mass Hexane 500 parts by mass Toluene 500 parts by mass

(10) Production of Example Sample 18 In production of Example Sample 4, Example 1 was carried out in the same manner as Example Sample 4 except that the first light emitting layer and the second light emitting layer were changed as follows. Sample 18 was produced.
<First light emitting layer (quantum dot light emitting layer composition)>
Trilite (registered trademark) 540 manufactured by Sight Diagnostics Co., Ltd. Emission wavelength 540 nm, 8 parts by mass Trilite (registered trademark) 630 manufactured by Sight Diagnostics Co., Ltd. Emission wavelength 630 nm, 2 parts by mass Host compound H-73 10 parts by mass Hexane 1,000 Part by mass <second light emitting layer>
Iridium complex D-93 (Ir (dbfmi)) 8 parts by mass,
92 parts by mass of host compound H-73

<Evaluation of sample>
The following evaluations were performed on Comparative Samples 1 to 3 and Example Samples 4 to 18.

(1) Measurement of color temperature and color rendering properties For each sample, the emission luminance of each sample is measured using a spectral radiance meter CS-2000 (manufactured by Konica Minolta Sensing) at room temperature (about 23-25 ° C). Then, the color temperature and color rendering properties at an emission luminance of 1000 cd / m ² were evaluated. The criteria for evaluation are as follows.
<Color temperature>
A: More than 5000K B: Less than 5000K Δ: Less than 4000K ×: Less than 3000K <Color rendering property>
◎: 85 or more ○: Less than 85 △: Less than 80 ×: Less than 75

(2) Measurement of luminous efficiency Each sample was allowed to emit light at room temperature (about 23 ° C.) under a constant current condition of ^2.5 mA / cm ² , and the luminance L immediately after the start of emission was measured using a spectral radiance meter CS-2000. (Measured using Konica Minolta Optics).
Next, a relative light emission luminance was obtained with the light emission luminance of Comparative Example Sample 1 being 1.0, and this was used as a measure of the initial light emission efficiency (external extraction quantum efficiency). It represents that it is excellent in luminous efficiency, so that a numerical value is large.

(3) Evaluation of continuous drive stability (lifetime) Each sample was continuously driven, the luminance was measured using the above-mentioned spectral radiance meter CS-2000, and the time for which the measured luminance was 70% (LT70) was obtained. . The driving condition was set to a current value of 4000 cd / m ² at the start of continuous driving.
The relative value which set LT70 of the comparative example sample 1 to 1.00 was calculated | required, and this was made into the scale of continuous drive stability. The larger the value, the better the continuous driving stability (long life).

 

 

 

 

(4) Summary As shown in Table 4, in the example samples 4 to 18, the color temperature and the color rendering properties are high, the luminous efficiency is high, and the lifetime is also improved. This is presumably because the carrier transportability is improved by the reverse layer structure, and the light emission balance is improved.
In particular, it can be seen that this effect is prominent when a specific host having an emission wavelength belonging to the 0-0 transition band in the phosphorescence spectrum in the range of 414 to 459 nm is used for the first light emitting layer.

In Example 2, a tandem EL element having a charge generation layer was manufactured, and the durability was compared with that of the single-type Example Sample 16 manufactured in Example 1.
The composition of the tandem-type intermediate layer was prepared with reference to US Pat. No. 7,719,180 and International Society for Display The Society Information Display (SID) 09 DIGEST, p499.
In practice, the intermediate layer formed as a layer of only the host compound containing no dopant in the “(4.4) Formation of the intermediate layer” is converted into the following charge generation layer (hole transport layer / p-type). The effect of the tandem element was confirmed by substituting 5 layers of layer / intermediate layer / n-type layer / electron transport layer).

(1) Example Sample 21
First, Spiro-TPD was deposited as a hole transport layer to a thickness of 20 nm.
Next, as a p-type layer, NDP9 manufactured by Novaled was deposited on Spiro-TPD in an amount of 10: 1 (weight ratio) to a thickness of 5 nm.
Next, aluminum was deposited to a thickness of 1 nm to form an intermediate electrode layer.
Next, NET18 and NDN26 manufactured by Novaled were deposited as an n-type layer at a ratio of 10: 1 to a thickness of 5 nm (the n-type layer has a function of an electron transport layer).
Subsequent formation of the second light-emitting layer and the like were performed in the same manner as in the preparation of the example sample 16, thereby producing an inverted layer tandem example sample 21.

(2) Example Sample 22
An example sample 22 was produced in the same manner as in the example sample 21, except that the p-type layer was a layer obtained by doping Spiro-TPD with F4-TCNQ at a ratio of 10: 1.

(3) Example Sample 23
Prepared in the same manner as in Example Sample 21, except that HATCN (1,4,5,8,9,12-hexaazatriphenylenehexacarbonitrile, see general formula (5)) was used as the p-type layer. Example sample 23 was produced.

 

 

(4) Summary Initial efficiency and LT70 were similarly evaluated for the obtained Example Samples 16 and 21 to 23.
As shown in Table 6, it can be seen that the tandem example samples 21 to 23 are advantageous in terms of the LT 70 as compared to the single type example sample 16. This is because the applied electric field only needs to be shared by the two units, and the electric field applied per unit cell is reduced.
As these charge generation layers, it was confirmed that, in particular, Example Sample 23 using HATCN had a long lifetime and was good.

The present invention can be particularly suitably used to provide an electroluminescent device with high luminous efficiency and long life.

DESCRIPTION OF SYMBOLS 1 Support substrate 2 1st electrode 8 2nd electrode 9 Sealing adhesive 10 Flexible sealing member 20 Organic functional layer 21 Electron transport layer 22 1st light emitting layer 23 Charge generation layer 24 2nd light emitting layer 25 Hole transport layer 30 Quantum dot 100 Electroluminescence device

Claims (14)

1. An electroluminescent element in which a first electrode, a first light emitting layer, a second light emitting layer, and a second electrode are stacked in this order on a substrate,
   The first light emitting layer contains quantum dots,
   The second light emitting layer contains a phosphorescent light emitting dopant,
   An electroluminescence element, wherein an electron transport layer is formed between the first electrode and the first light emitting layer.
2. The electroluminescent device according to claim 1,
   The electroluminescent device, wherein the light emitting layer containing the quantum dots has a light emission maximum wavelength in a wavelength region of 450 to 470 nm.
3. The electroluminescent device according to claim 1,
   The quantum dots are composed of Si, Ge, GaN, GaP, CdS, CdSe, CdTe, InP, InN, ZnS, In ₂ S ₃ , ZnO, CdO, CuInS, CuInSe, CuInGaSe or a mixture thereof. An electroluminescence element.
4. The electroluminescent device according to claim 1,
   An electroluminescent element, wherein the light emitting layer containing the quantum dots has a thickness in a range of 10 to 30 nm.
5. The electroluminescent device according to claim 1,
   The electroluminescent device, wherein the light emitting layer containing the phosphorescent light emitting dopant has a light emission maximum wavelength in a wavelength region of at least 520 to 560 nm and 600 to 640 nm.
6. The electroluminescent device according to claim 1,
   The electroluminescent device, wherein the light emitting layer containing the phosphorescent light emitting dopant has a maximum emission wavelength in a wavelength region of at least 460 to 490 nm, 520 to 560 nm, and 600 to 640 nm.
7. The electroluminescent device according to claim 1,
   The light emitting layer containing the quantum dots contains a host compound.
8. The electroluminescent device according to claim 7, wherein
   An electroluminescent device, wherein an emission maximum wavelength attributed to a 0-0 transition band in a phosphorescence spectrum of the host compound is in a wavelength region of 414 to 459 nm.
9. The electroluminescent device according to claim 7, wherein
   The host compound is represented by the general formula (1).
   

   

   
   [Wherein, X represents NR ′, oxygen atom, sulfur atom, CR′R ″ or SiR′R ″.
   y ₁ and y ₂ each represent CR ′ or a nitrogen atom.
   R ′ and R ″ each represent a hydrogen atom or a substituent.
   Ar ₁ and Ar ₂ each represent an aromatic ring and may be the same or different from each other.
   m and n each represents an integer of 0 to 4. ]
10. The electroluminescent device according to claim 9,
    X is an oxygen atom in the said General formula (1), The electroluminescent element characterized by the above-mentioned.
11. The electroluminescent device according to claim 9,
    In said general formula (1), at least one of Ar1 and Ar2 is represented by General formula (2), The electroluminescent element characterized by the above-mentioned.
    

    

    
    [Wherein, y ₁ and y ₂ each represent CR ′ or a nitrogen atom.
    R ′ represents a hydrogen atom or a substituent.
    Ar ₁ and Ar ₂ each represent an aromatic ring and may be the same or different from each other.
    m and n each represents an integer of 0 to 4. ]
12. The electroluminescent device according to claim 1,
    The phosphorescent light emitting dopant is represented by the general formula (3).
    

    

    
    [Wherein R 1 represents a substituent.
    Z represents a nonmetallic atom group necessary for forming a 5- to 7-membered ring.
    n1 represents an integer of 0 to 5.
    B1 to B5 each represent a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom, and at least one represents a nitrogen atom.
    M1 represents a group 8-10 metal in the periodic table.
    X1 and X2 represent a carbon atom, a nitrogen atom or an oxygen atom.
    L1 represents an atomic group forming a bidentate ligand together with X1 and X2.
    m1 represents an integer of 1, 2 or 3, m2 represents an integer of 0, 1 or 2, and m1 + m2 is 2 or 3. ]
13. The electroluminescent device according to claim 1,
    An electroluminescence element having a tandem structure in which a charge generation layer is formed between the first light emitting layer and the second light emitting layer.
14. The electroluminescent device according to claim 13, wherein
    The electroluminescent element characterized in that the charge generation layer contains a compound represented by the general formula (4).
    

    

    
    [In the formula (4), each R is independently hydrogen, halogen group, alkyl group having 1 to 12 carbon atoms, alkoxy group, alkylamino group, alkylsilyl group, aryl group, arylamino group, heterocyclic group, The substituent is selected from the group consisting of an ester group, an amide group, a nitro group and a nitrile group.
    Adjacent Rs may be bonded to each other to form a cyclic structure. ]

Images