WO2009081918A1 - Organic/inorganic hybrid electroluminescent element - Google Patents

Abstract

Disclosed is an organic/inorganic hybrid electroluminescent element (1) that includes at least an anode (10), a hole transport zone (11), a luminescent zone (13), and a cathode (15), in that order, wherein the hole transport zone and the luminescent zone are adjacent, and there are nanocrystalline luminescent microparticles (12) in the vicinity of the interface between the hole transport zone and the luminescent zone, and an organic/inorganic hybrid electroluminescent element wherein the luminescence band frequency of an organic electroluminescent element with the same structure as the aforementioned electroluminescent element, except for having no nanocrystalline luminescent microparticles, is blue light with a peak luminescence wavelength of 490 nm or less.

Description

Organic / inorganic hybrid electroluminescent device

The present invention relates to an organic / inorganic hybrid electroluminescent element (QD-LED) element comprising a combination of a laminated structure of organic electroluminescent elements (organic EL elements) and an inorganic nanocrystal luminescent material.

An organic EL element is a self-luminous element utilizing the principle that a fluorescent substance emits light by recombination energy of holes injected from an anode and electrons injected from a cathode by applying an electric field.
In the conventional organic EL device, it was necessary to develop new light emitting material molecules in order to obtain a device having a new emission color. In addition, there is a problem that the emission spectrum is relatively wide and it is difficult to improve color purity.

By the way, an organic / inorganic hybrid electroluminescent device (hereinafter referred to as “QD-LED”) in which a laminated structure of an organic EL device and an inorganic nanocrystal phosphor are combined has been studied. In a narrow sense, a semiconductor nanocrystal using a crystal is referred to as “QD-LED”. In the present application, a wide variety of inorganic nanocrystals are included in the QD-LED.
An inorganic nanocrystal luminescent material is characterized in that the luminescent color can be arbitrarily controlled by changing the composition and particle size of the nanocrystal. In addition, monodisperse nanocrystals are characterized by a small half-value width of the emission spectrum, good color purity of light emission, and, since they are inorganic materials, they are resistant to deterioration and have high reliability.

Regarding QD-LED, for example, Non-Patent Document 1 discloses an element having a film formed by dispersing polyvinyl carbazole (PVK) or an oxadiazole derivative as an organic material and dispersing CdSe nanocrystals in a mixture thereof. It has been reported.

Non-Patent Document 2 discloses N, N′-bis (3-methylphenyl)-(1,1′-biphenyl) -4,4′-diamine (TPD) as a hole transport layer and a metal complex (TPD) as a light-emitting layer. There is disclosed a QD-LED element using Alq3) and having quantum dots (QD) made of semiconductor nanocrystals arranged at the interface.

Non-Patent Documents 3 and 4 disclose QD-LED elements in which TPD is used as a hole transport layer, triazole derivative (TAZ) is used as a light emitting layer, and quantum dots made of semiconductor nanocrystals are arranged at the interface. In this device, a chloroform mixed solution of quantum dots and TPD is spin-coated in a nitrogen atmosphere, the solvent is dried to separate the organic substance and the quantum dots, and a monolayer film of nanocrystal luminescent particles on the TPD surface (monolayer) Is forming.
Non-Patent Document 5 discloses a QD-LED element in which poly-TPD is used as a hole transport layer, Alq3 is used as a light emitting layer, and a cadmium semiconductor nanocrystal is arranged at the interface. In this element, the semiconductor nanocrystal layer is a plurality of monolayers.

Patent Document 1 discloses an electroluminescent device in which a light emitting layer is sandwiched between opposing electrodes, and the light emitting layer is made of a polymer compound in which semiconductor ultrafine particles are dispersed. This element has an electron transport layer between the cathode and the light-emitting layer, a hole blocking layer between the light-emitting layer and the electron transport layer, and an electron between the light-emitting layer and the hole transport layer. It has a blocking layer.

Patent Document 2 discloses an electroluminescent device using semiconductor ultrafine particles composed of a semiconductor crystal and a ligand coordinated on the surface thereof.
Patent Document 3 discloses an electroluminescent device including an independent nanocrystalline light emitting layer in contact with the polymer hole transport layer between the polymer hole transport layer and the organic electron transport layer.

Patent Document 4 discloses a current injection type light emitting element in which a light emitting layer is made of a medium in which inorganic fluorescent matrix nanoparticles doped with one or more kinds of elements as light emission centers are dispersed. In this element, multi-wavelength light emission using a plurality of dopants is realized.

Patent Document 5 discloses a QD-LED element in which a matrix layer is sandwiched between opposing electrodes, and a semiconductor nanocrystal is contained in the matrix layer. It is described that this element can have a hole blocking layer or an electron blocking layer in addition to an electrode, a hole transport layer, an electron transport layer and a semiconductor nanocrystal.
JP 2004-172102 A JP 2004-315661 A JP 2005-353595 A JP 2005-38634 A International Publication No. 2003/084292 Pamphlet B. O. Dabbousi and M.D. G. Bawendi, Appl. Phys. Lett. 66 (1995) 1316-1318 S. Coe et al. , Nature, 420 (2002) 800-803. S. Coe-Sullivan et al, Organic Electronics, 4 (2003) pp. 123-130. V. Bullovic and M.M. Bawendi, SID 06 Digest 35.1 (2006) 1368-1371 Q. Sun et al. , Nature Photonics, 18 November 2007; doi: 10.1038; nphoton. 2007.226

The elements described in the non-patent document or the patent document described above have the following problems, for example.
The element of Non-Patent Document 1 has low efficiency because it does not employ an organic laminated structure that is functionally separated.
In the structure of the element of Non-Patent Document 2, the light emission of the organic EL element not containing QD is green (derived from Alq3, and the emission peak wavelength is 530 nm). Therefore, the energy transfer from the light emitting layer to the QD was inefficient, and the external quantum efficiency was as low as 0.5%.
The elements of Non-Patent Documents 3 and 4 also have a low external quantum efficiency of 1%. This is because the hole transport layer (TPD) has a HOMO level of 5.4 eV and the light-emitting layer (TAZ) has a HOMO level of 6.5 eV, a large difference of 1.1 eV, and holes are effective in the light-emitting layer. This is probably because sufficient light emission efficiency was not obtained.
The element of Non-Patent Document 5 has a high operating voltage. This is considered to be because nanocrystal light-emitting fine particles are used as a plurality of monolayers.

The element of Patent Document 4 realizes multi-wavelength light emission using a plurality of dopants, but the light emission start voltage is 7 V, the luminance at 10 V is 100 cd / m ^2, and a high voltage is necessary for light emission. It was.

Patent Document 5 reports device performance of 1% external quantum efficiency, 1.5 cd / A luminous efficiency, and about 6V turn-on voltage, but the efficiency is still low. This is probably because the energy levels of the materials forming the hole transport layer and the electron transport layer are not properly matched.

The present invention has been made in view of the above problems, and an object thereof is to provide a QD-LED element that can be driven at a low voltage and has high efficiency.

According to the present invention, the following QD-LED elements are provided.
1. It includes at least an anode, a hole transport zone, a light emission zone, and a cathode in this order. The hole transport zone and the light emission zone are adjacent to each other, and there are nanocrystal light emitting fine particles near the interface between the hole transport zone and the light emission zone. An organic / inorganic hybrid electroluminescent device,
An organic / inorganic hybrid electroluminescent device that emits blue light having an emission peak wavelength in a light emission band of 490 nm or less of an organic electroluminescent device having the same configuration as the electroluminescent device except that the nanocrystal luminescent fine particles are not present.
2. 2. The organic / inorganic hybrid electroluminescent device according to 1, wherein the nanocrystal luminescent fine particles are semiconductor nanocrystals.
3. 3. The organic / inorganic hybrid electroluminescent device according to 1 or 2, wherein a difference between a HOMO energy level of the main material in the hole transport band and a HOMO energy level of the main material in the emission band is less than 1 eV.
4). The organic / inorganic hybrid electroluminescence according to 1 or 2, wherein a difference between a HOMO energy level of the main material in the hole transport band and a HOMO energy level of the main material in the emission band is less than 0.5 eV. element.
5). 5. The organic / inorganic hybrid electroluminescent device according to 3 or 4, wherein an emission peak wavelength of light emitted from the emission band is 470 nm or less.
6). 6. The organic / inorganic hybrid electroluminescent device according to 5, wherein a main material of the light emission band is a material having an anthracene skeleton.
7). 7. The organic / inorganic hybrid electroluminescent device according to 5 or 6, wherein the main material of the hole transport zone is an aromatic amine derivative.

According to the present invention, it is possible to provide a high-efficiency QD-LED element driven at a low voltage.
This element is suitable for illumination and information display.

It is a schematic sectional drawing which shows one Embodiment of the QD-LED element of this invention. 2 is an energy diagram of a QD-LED element 1. It is an example of the energy diagram of a QD-LED element, (a) is an example of the conventional element, (b) is an example of the element of this invention. It is a schematic sectional drawing which shows other embodiment of the QD-LED element of this invention. 2 is a transmission electron micrograph of the hole transport layer and QD formed in Example 1. FIG.

The QD-LED element of the present invention includes at least an anode, a hole transport zone, a light emission zone, and a cathode in this order. The hole transport zone and the light emission zone are adjacent to each other, and there are nanocrystal light emitting fine particles in the vicinity of the interface between the hole transport zone and the light emission zone. Incidentally, the vicinity of the interface means the interface between the hole transport zone and the light emission zone and its peripheral part. The QD-LED element will be described with reference to the drawings.

FIG. 1 is a schematic sectional view showing a first embodiment of the QD-LED element of the present invention.
In the QD-LED element 1, an anode 10, a hole transport zone 11, a light emission zone 13, an electron injection zone 14, and a cathode 15 are laminated in this order on a substrate (not shown). The hole transport zone 11 and the emission zone 13 are adjacent to each other, and a nanocrystal emission fine particle 12 (hereinafter referred to as “QD” as a nanocrystal emission fine particle, and a state in which it forms a layer is referred to as a “QD layer”). Is inserted).

In the device 1, holes supplied from the hole transport zone 11 and electrons supplied from the electron transport zone 14 are combined in the light emission zone 13, and the QD 12 existing in the vicinity emits light. Although the mechanism by which QD12 emits light is not fully understood, an electron-hole pair is generated as an excited state of an organic molecule in the emission band, and excitation energy is transferred from the excited state to QD, so that QD's electronic excitation is achieved. It is believed that light is emitted when a state is generated and the excited state of the QD is deactivated.

The “hole transport zone” refers to a thin film-like component mainly responsible for hole transport as a function, and if it has that function, it may be a layer that may not be clearly distinguished as a layer. The hole transport zone is mainly composed of a material responsible for hole transport, but may contain components having other functions or may have mixed boundaries as necessary. Hereinafter, in this broad sense, the “hole transport zone” may be referred to as a “hole transport layer”. Similarly, “hole injection zone, light emission zone, electron transport zone, electron injection zone” may also be referred to as “hole injection layer, light emitting layer, electron transport layer, electron injection layer” in a broad sense.

In the present invention, the hole transport layer 11 and the light emitting layer 13 are adjacent to each other, and the QD layer 12 is disposed in the vicinity of the interface. As will be described later, since QD is in the form of particles having a diameter of several nanometers to several tens of nanometers, the hole transport layer 11 and the light emitting layer 13 are completely separated as a complete thin film even if they are arranged in layers. is not. In that sense, the hole transport layer 11 and the light emitting layer 13 are adjacent to each other.
Since QD12 is an inorganic substance as will be described later, it has an advantage that it is less likely to deteriorate than an organic substance. In addition, QD has an advantage that the degree of freedom in designing the emission color is large because the emission wavelength can be selected depending on the material used and its size.

In the element of the present invention, the light emitted from the light emitting layer 13 is blue light having an emission peak wavelength of 490 nm or less. Thereby, since the efficiency of energy transfer from the light emitting layer to the QD is improved, the external quantum efficiency can be increased. The absorption coefficient of QD has a feature that becomes larger as light of a shorter wavelength is used. To make use of this feature, it is desirable that the material forming the light emitting layer is a highly efficient blue light emitting material. Therefore, the emission peak wavelength of the light emitted from the light emitting layer 13 is preferably blue light having a wavelength of 470 nm or less. The lower limit wavelength of blue light is preferably 390 nm or more.

For example, Non-Patent Document 2 discloses a configuration in which Alq3 that is a light emitting layer is adjacent to a hole transport layer (TPD), and the light emitting layer Alq3 is a green EL light emitting material. With this element without QD, green emission is observed at an emission peak of 520 to 530 nm. In this case, the overlap between the emission wavelength region of the light emitting layer and the light absorption wavelength region of the QD becomes small, and the efficiency of energy transfer from the organic excited state to the QD is poor.

Here, “light emitted from the light emitting layer” is different from light emitted from the QD-LED element. The light emitted from the light emitting layer means light generated from the material used for the light emitting layer. On the other hand, the light emitted by the QD-LED element means the sum of the light emitted by the QD and the light emitted by the constituent members such as the light emitting layer.
The light emitted from the light emitting layer can be measured by preparing an element (specific EL element) having a configuration excluding QD from the configuration of the QD-LED element and examining the emission spectrum. In the QD-LED element of the present invention, the light emission of the intrinsic EL element is preferably mainly derived from the emission band (light emitting layer). Whether or not the light emitting layer emits light can be judged from a comparison between the light emission spectrum of the element and the PL spectrum of the thin film of each material. Specifically, the emission spectrum of the element and the thin film PL spectrum of each material are plotted with the peak value of the emission intensity, the difference in wavelength of the emission peak is ± 10 mm or less, and the difference in emission half width is Based on the coincident peak at ± 50 mm or less, it is determined which layer the light emission of the element is due to.

In the element of the present invention, the difference between the highest occupied molecular orbital (HOMO) energy level of the main material of the hole transport layer 11 and the HOMO energy level of the main material of the light-emitting layer is preferably less than 1 eV, particularly It is preferably less than 0.5 eV. This will be described with reference to FIG.
FIG. 2 is an energy diagram of the QD-LED element 1.
In the present invention, the difference (ΔE _H ) between the HOMO level of the hole transport layer 11 and the HOMO level of the light emitting layer 13 is preferably less than 1 eV. With such a configuration, holes reach the light emitting layer 13 without feeling a barrier, and excitons can be efficiently generated there.
In the present invention, the HOMO and LUMO levels of the QD are not particularly defined and can be applied to various QDs.
Further, the “main material” of the light emitting layer and the hole transport layer means a material contained in each layer in the highest weight ratio.

FIG. 3 is an example of an energy diagram of a QD-LED element. (A) shows an example of a conventional QD-LED element, and (b) shows an example of the element of the present invention.
The configuration of the conventional element is the configuration disclosed in Non-Patent Documents 2 to 4 and Patent Document 5 described above. N, N′-diphenyl-N, N′-bis (3-methylphenyl)-(1,1′-biphenyl) -4,4′-diamine (TPD) as the hole transport layer and 3- ( 4-biphenylyl) -4-phenyl-5-terbutylphenyl-1,2,4-triazole (TAZ) is used, and a QD layer exists at the interface. In addition, ITO is an anode, Alq3 is an electron injection layer, and MgAg alloy is a cathode.
QD is a core-shell type semiconductor nanocrystal having CdSe as a core and ZnS as a shell. The HOMO and LUMO levels of QD are examples and are cited from Non-Patent Document 3.

In the conventional device configuration, the HOMO level of the hole transport layer is 5.4 eV, the HOMO level of the light emitting layer is 6.5 eV, and the difference is as large as 1.1 eV. For this reason, holes injected from the anode (ITO) cannot exceed this gap. Therefore, an excited state is generated in the hole transport layer. In fact, in this element, in the organic EL element in which QD is omitted, light emission derived from TPD as the hole transport layer is observed in addition to light emission derived from Alq3 as the electron transport layer.

On the other hand, FIG. 3B shows an energy diagram of the element of Example 1 described later. The HOMO level of the material HT1 forming the hole transport layer of this element is 5.5 eV, the HOMO level of the material EM1 forming the light emitting layer is 5.7 eV, and the difference is as small as 0.2 eV. Thereby, the holes reach the light emitting layer without feeling a barrier, and excitons can be efficiently generated there. The material EM1 for forming the light emitting layer is a blue light emitting material having a sufficient energy band gap of 3.0 eV. In fact, an organic EL element having a configuration in which QD is omitted from this configuration emits blue light derived from EM1. This means that the large absorption in the short wavelength region of QD and the emission wavelength region of EM1 are well overlapped, thereby causing energy transfer from the excitons in the light emitting layer to QD efficiently. Efficient electroluminescence can be achieved. In addition, the close proximity of the HOMO levels of the hole transport layer and the light emitting layer leads to a reduction in the voltage of the device, thereby realizing a power saving device. PEDOT: PSS forms a hole injection zone (layer).

The element shown in FIG. 1 is an example of the element of the present invention, and the present invention is not limited to this. For example, the element configuration shown in FIG. 4 may be used.
FIG. 4 is a schematic sectional view showing a second embodiment of the QD-LED element of the present invention. This QD-LED element 2 is the same as the element configuration of FIG. 1 except that a hole injection zone 21 is formed between the anode 10 and the hole transport zone 11.
In addition, as long as the effects of the present invention are not impaired, an electron injection layer may be inserted between the electron transport layer and the cathode, or the electron transport layer may be omitted. In the present invention, the configuration of the hole transport layer / light-emitting layer is essential, but a hole block layer or an electron block layer may be provided outside the hole transport layer as necessary. The QD is arranged near the interface between the hole transport layer and the light emitting layer. As can be seen from the above light emission mechanism, the QD does not have to be strictly layered at the boundary, and has a distribution in the light emitting layer. It may be distributed.

The light emitting device of the present invention may have, for example, the following structures (1) to (10) or a partial structure having the following structure.
(1) Anode / hole transport layer / light emitting layer / electron transport layer / cathode (FIG. 1)
(2) Anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / cathode (FIG. 4)
(3) Anode / hole transport layer / light emitting layer / electron transport layer / electron injection layer / cathode (4) Anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / electron injection layer / cathode ( 5) Anode / insulating layer / hole transporting layer / light emitting layer / electron transporting layer / cathode (6) Anode / hole transporting layer / light emitting layer / electron transporting layer / insulating layer / cathode (7) Anode / insulating layer / positive Hole transport layer / light emitting layer / electron transport layer / insulating layer / cathode (8) anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / insulating layer / cathode (9) anode / insulating layer / positive Hole injection layer / hole transport layer / light emitting layer / electron transport layer / electron injection layer / cathode (10) anode / insulating layer / hole injection layer / hole transport layer / light emitting layer / electron transport layer / electron injection layer / Insulating layer / cathode

Of these, the configurations of (1), (2), (3), (4), (7), (8) and (10) are preferably used.
The element of the present invention may be a top emission type or a bottom emission type. Either type can be realized by making the electrode on the light extraction side light-transmissive.
Hereinafter, each component of the light emitting device of the present invention and materials used therefor will be described.

[Hole injection layer and hole transport layer]
The hole injection layer and the hole transport layer (hereinafter collectively referred to as a hole injection / transport layer) are layers that assist hole injection into the light emitting layer and transport to the light emitting region, and have a hole mobility. Large and ionization energy is usually as small as 5.5 eV or less. As such a hole injecting / transporting layer, a material that transports holes to the light emitting medium layer with a lower electric field strength is preferable, and an electric field application with a hole mobility of, for example, 10 ⁴ to 10 ⁶ V / cm is preferable. Sometimes it is preferably at least 10 ⁻⁴ cm ² / V · sec.
The material for forming the hole injecting / transporting layer is not particularly limited as long as it has the above-mentioned preferable properties, and conventionally used as a charge transporting material for holes in an optical transmission material or organic EL. Any known material used for the hole injection / transport layer of the device can be selected and used.

Specific examples include triazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, Examples include hydrazone derivatives, stilbene derivatives, silazane derivatives, polysilanes, aniline copolymers, and conductive polymer oligomers (particularly thiophene oligomers).
As the material for the hole injection / transport layer, the above-mentioned materials can be used, but it is preferable to use porphyrin compounds, aromatic tertiary amine compounds and styrylamine compounds, particularly aromatic tertiary amine compounds.

In addition, there are two condensed aromatic rings in the molecule, for example, 4,4′-bis (N- (1-naphthyl) -N-phenylamino) biphenyl (NPD), and three triphenylamine units. And 4,4 ′, 4 ″ -tris (N- (3-methylphenyl) -N-phenylamino) triphenylamine (MTDATA) linked in a starburst type.

As the material for the hole injection / transport layer, an aromatic amine derivative represented by the following formula (1) is particularly desirable.

[Wherein L ₁ is a divalent group consisting of a substituted or unsubstituted arylene group or heterocyclic group having 5 to 60 carbon atoms, and Ar ¹⁰¹ to Ar ¹⁰⁴ are each a substituted or unsubstituted nuclear atom number of 5 to 50 substituents or substituents represented by the following formula. Here, the number of nuclear atoms is the number of atoms that form a ring.

(In the formula, L ₂ is a substituted or unsubstituted divalent group having 5 to 60 carbon atoms, an arylene group or a heterocyclic group, and Ar ¹⁰⁵ to Ar ¹⁰⁶ are each a substituted or unsubstituted nuclear atom having 5 to 5 carbon atoms. 50 substituents.)]

Examples of L ₁ and L ₂ include biphenylene, terphenylene, phenanthrene, and fluorenylene, preferably biphenylene and terphenylene, and more preferably biphenylene.

Examples of Ar ¹⁰¹ to Ar ¹⁰⁶ include a biphenyl group, a terphenyl group, a phenanthrenyl group, a fluorenyl group, a 1-naphthyl group, a 2-naphthyl group, and a phenyl group, preferably a biphenyl group, a terphenyl group, a 1-naphthyl group, or It is a phenyl group.

In the compound represented by the formula (1), Ar ¹⁰¹ to Ar ¹⁰⁴ are preferably the same substituent. In this case, Ar ¹⁰¹ to Ar ¹⁰⁴ are preferably a biphenyl group or a terphenyl group, and more preferably a biphenyl group.

The compound represented by formula (1) ^is preferably ^Ar 102 ^{~ Ar 104} of the substituents of Ar 101 ^{~ Ar 104} are the same substituents. In this case, Ar ¹⁰² to Ar ¹⁰⁴ are preferably a biphenyl group or a terphenyl group, more preferably a biphenyl group, and Ar ¹⁰¹ is preferably a biphenyl group, a terphenyl group, a phenanthrenyl group, a fluorenyl group, or a 1-naphthyl group. 2-naphthyl group or phenyl group, more preferably biphenyl group, terphenyl group, 1-naphthyl group or phenyl group. More preferably, Ar ¹⁰² to Ar ¹⁰⁴ are biphenyl, and Ar ¹⁰¹ is a terphenyl group or a 1-naphthyl group.

In the compound represented by the formula (1), it is preferable that three or more of the substituents of Ar ¹⁰¹ to Ar ¹⁰⁴ are different substituents. Ar ¹⁰¹ to Ar ¹⁰⁶ are preferably a biphenyl group, a terphenyl group, a phenanthrenyl group, a fluorenyl group, a 1-naphthyl group, a 2-naphthyl group, or a phenyl group, and more preferably a biphenyl group, a terphenyl group, or a 1-naphthyl group. Group or phenyl group. More preferably, Ar ¹⁰³ to Ar ¹⁰⁴ are biphenyl, Ar ¹⁰¹ is a terphenyl group and 1-naphthyl group, and Ar ¹⁰² is a phenyl group. A compound in which Ar ¹⁰¹ and Ar ¹⁰⁶ are 1-naphthyl groups and Ar ¹⁰² , Ar ¹⁰³ and Ar ¹⁰⁵ are phenyl groups is also preferable.

Specific examples of the aromatic amine derivative are shown below.

In addition, a nitrogen-containing heterocyclic derivative represented by the following formula disclosed in Japanese Patent No. 3571977 can also be used.

(Wherein R ¹⁰¹ to R ¹⁰⁶ each represent a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, or a substituted or unsubstituted heterocyclic group. R ¹⁰¹ to R ¹⁰⁶ may be the same or different, and R ¹⁰¹ and R ¹⁰² , R ¹⁰³ and R ¹⁰⁴ , R ¹⁰⁵ and R ¹⁰⁶ , R ¹⁰¹ and R ¹⁰⁶ , R ¹⁰² and R ¹⁰³ , R ¹⁰⁴ And R ¹⁰⁵ may form a condensed ring.)

Furthermore, the compound of the following formula described in US Publication 2004/0113547 can also be used.

(Wherein R ¹³¹ to R ¹³⁶ are substituents, preferably an electron-withdrawing group such as a cyano group, a nitro group, a sulfonyl group, a carbonyl group, a trifluoromethyl group, or a halogen.)

It should be noted that inorganic compounds such as p-type Si and p-type SiC can also be used as the material for the hole injection / transport layer.

An acceptor material is also suitable as the hole injection material for forming the hole injection / transport layer. The acceptor is an easily reducible organic compound.
The ease of reduction of a compound can be measured by a reduction potential. For example, in the reduction potential using a saturated calomel (SCE) electrode as a reference electrode, the reduction potential of the acceptor is preferably −0.3 V or more, more preferably −0.8 V or more, and particularly preferably tetracyanoquinodimethane ( A compound having a value larger than the reduction potential (about 0 V) of TCNQ) is preferred.

The acceptor is preferably an organic compound having an electron-withdrawing substituent or an electron-deficient ring.
Examples of the electron-withdrawing substituent include halogen, CN-, carbonyl group, arylboron group and the like.
Examples of electron-deficient rings include 2-pyridyl, 3-pyridyl, 4-pyridyl, 2-quinolyl, 3-quinolyl, 4-quinolyl, 2-imidazole, 4-imidazole, 3-pyrazole, 4-pyrazole, pyridazine, and pyrimidine , Pyrazine, cinnoline, phthalazine, quinazoline, quinoxaline, 3- (1,2,4-N) -triazolyl, 5- (1,2,4-N) -triazolyl, 5-tetrazolyl, 4- (1-O, 3-N) -oxazole, 5- (1-O, 3-N) -oxazole, 4- (1-S, 3-N) -thiazole, 5- (1-S, 3-N) -thiazole, 2 A compound selected from the group consisting of -benzoxazole, 2-benzothiazole, 4- (1,2,3-N) -benzotriazole, and benzimidazole. Not be limited to these.

The acceptor is preferably an imide derivative such as a quinoid derivative, an arylborane derivative, a thiopyran dioxide derivative, or a naphthalimide derivative.

As the quinoid derivative, the following compounds are preferable.

(Wherein R ¹ to R ⁴⁸ are each hydrogen, halogen, fluoroalkyl group, cyano group, alkoxy group, alkyl group or aryl group, provided that R ¹ to R ⁴⁸ are all hydrogen or Except for fluorine, X is an electron-withdrawing group, and has one of the structures of the following formulas (j) to (p), preferably the structures of (j), (k), and (l). .

(Wherein R ⁴⁹ to R ⁵² are each a hydrogen atom, a fluoroalkyl group, an alkyl group, an aryl group or a heterocyclic group, and R ⁵⁰ and R ⁵¹ may form a ring.)
Y is —N═ or —CH═. )

Specific examples of the quinoid derivative include the following compounds.

As the arylborane derivative, a compound having the following structure is preferable.

(Wherein Ar ¹ to Ar ⁷ are each an aryl group having an electron withdrawing group (including a heterocycle), Ar ⁸ is an arylene group having an electron withdrawing group, and S is 1 or 2. )

Specific examples of the arylborane derivative include the following compounds.

Particularly preferred is a compound having at least one fluorine as a substituent for aryl, and examples thereof include tris β- (pentafluoronaphthyl) borane (PNB).

As the imide derivative, naphthalenetetracarboxylic acid diimide compound and pyromellitic acid diimide compound are preferable.

Examples of the thiopyran dioxide derivative include a compound represented by the following formula (3a), and examples of the thioxanthene dioxide derivative include a compound represented by the following formula (3b).

In the formula (3a) and the formula (3b), R ⁵³ to R ⁶⁴ are each hydrogen, halogen, a fluoroalkyl group, a cyano group, an alkyl group, or an aryl group. Preferably, they are hydrogen and a cyano group.
In the formulas (3a) and (3b), X represents an electron withdrawing group and is the same as X in the formulas (1a) to (1i). A structure of (j), (k), (l) is preferable.

The halogen, fluoroalkyl group, alkyl group and aryl group represented by R ⁵³ to R ⁶⁴ are the same as R ¹ to R ⁴⁸ .

Specific examples of the thiopyran dioxide derivative represented by the formula (3a) and the thioxanthene dioxide derivative represented by the formula (3b) are shown below.

(In the formula, tBu is a t-butyl group.)

Further, in the above formulas (1a) to (1i) and (3a) to (3b), the electron withdrawing group X may be a substituent (x) or (y) represented by the following formula.

In the formula, Ar ⁹ and Ar ¹⁰ are a substituted or unsubstituted heterocyclic ring, a substituted or unsubstituted aryloxycarbonyl or an aldehyde, preferably pyridine, pyrazine, or quinoxaline. Ar ⁹ and Ar ¹⁰ may be linked to each other to form a 5-membered or 6-membered cyclic structure.

When an acceptor material is used, it may be used alone or in combination with other materials.
In this case, the content of the acceptor contained in the hole injecting / transporting layer is preferably 1 to 100 mol%, more preferably 50 to 100 mol%, based on the entire layer.
In addition to the acceptor, the hole injecting / transporting layer can contain a hole transporting and light transmitting material, but is not necessarily limited thereto.

The hole injection / transport layer can be formed by thinning the above compound by a known method such as a vacuum deposition method, a spin coating method, a casting method, or an LB method. The thickness of the hole injection / transport layer is not particularly limited, but is usually 1 nm to 100 nm. As long as the hole injection / transport layer contains the above compound in the hole injection / transport layer, the hole injection / transport layer may be composed of one or more of the above-described materials. May be a laminate of hole injection / transport layers made of different types of compounds.

In the light emitting device of the present invention, as described above, the hole injection layer and the hole transport layer may be provided separately, or the hole injection layer may be omitted and only the hole transport layer may be used. Good. Here, the difference between the HOMO energy level of the material mainly forming the hole transport layer and the HOMO energy level of the material mainly forming the light emitting layer is preferably less than 1 eV. A combination satisfying this relationship can be selected from the light emitting layer materials exemplified later.

[QD layer]
The nanocrystal light-emitting fine particles used for the QD layer are composed of inorganic nanocrystals in which inorganic crystals are made ultrafine to the nanometer order. As the inorganic nanocrystal, one that absorbs visible and / or near-ultraviolet light and emits visible fluorescence is used. Since the transparency is high and the scattering loss is small, an inorganic nanocrystal having an ultrafine particle size of preferably 20 nm or less, more preferably 10 nm or less is used.

The surface of the inorganic nanocrystal is preferably subjected to a compatibilizing treatment. Examples of the compatibilization treatment include treatment such as modifying or coating the surface with a long-chain alkyl group, phosphoric acid, resin, or the like.

Specific examples of the inorganic nanocrystal used in the present invention include the following.
(1-a) Nanocrystal phosphor in which metal oxide is doped with transition metal ions Nanocrystal phosphors in which metal oxide is doped with transition metal ions include Y ₂ O ₃ , Gd ₂ O ₃ , ZnO, Y ₃ Examples include a metal oxide such as Al ₅ O ₁₂ and Zn ₂ SiO ₄ doped with transition metal ions that absorb visible light, such as Eu ²⁺ , Eu ³⁺ , Ce ³⁺ , and Tb ³⁺ .

(1-b) Nanocrystal phosphor in which metal chalcogenide is doped with transition metal ions Nanocrystal phosphor in which metal chalcogenide is doped with transition metal ions includes metal chalcogenides such as ZnS, CdS, and CdSe, Eu ²⁺ , Eu ³⁺ , Ce ³⁺ , Tb ^{3+ and the} like doped with transition metal ions that absorb visible light. In order to prevent S, Se, and the like from being pulled out by reaction components of the matrix resin described later, the surface may be modified with a metal oxide such as silica, an organic substance, or the like.

(1-c) Nanocrystal phosphor that absorbs and emits visible light using semiconductor band gap (semiconductor nanocrystal)
As the material of the semiconductor nano-kustal, group IV element, group IIa element-VIb group element compound, group IIIa element-Vb group compound, group IIIb element-Vb group compound, chalcopyrite compound The crystal | crystallization consisting of can be mentioned.

Specifically, Si, Ge, MgS, MgSe, ZnS, ZnSe, ZnTe, AlP, AlAs, AlSb, GaP, GaAs, GaSb, CdS, CdSe, CdTe, InP, InAs, InSb, AgAlAs ₂ , AgAlSe ₂ , AgAlTe _{2, AgGaS 2, AgGaSe 2,} AgGaTe 2, AgInS 2, AgInSe 2, AgInTe 2, ZnSiP 2, ZnSiAs 2, ZnGeP 2, ZnGeAs 2, ZnSnP 2, ZnSnAs 2, ZnSnSb 2, CdSiP 2, CdSiAs 2, CdGeP 2, Examples thereof include crystals such as CdGeAs ₂ , CdSnP ₂ , and CdSnAs ₂ and mixed crystal composed of these elements or compounds.

Preferably, Si, AlP, AlAs, AlSb, GaP, GaAs, InP, ZnSe, ZnTe, CdS, CdSe, CdTe, CuGaSe ₂ , CuGaTe ₂ , CuInS ₂ , CuInSe ₂ , CuInTe ₂ are direct transition type semiconductors. ZnSe, ZnTe, GaAs, CdS, CdTe, InP, CuInS ₂ , and CuInSe ₂ are more preferable in terms of high luminous efficiency.

Among the above-mentioned inorganic nanocrystals, the emission wavelength can be easily controlled by the particle size, it has a large absorption in the blue wavelength range and the near ultraviolet wavelength range, and the degree of overlap between the absorption and emission in the emission range is large, and therefore preferably a semiconductor Use nanocrystals.

Hereinafter, the function of the semiconductor nanocrystal will be described.
As known in the literature such as JP-T-2002-510866, these semiconductor materials have a band gap of about 0.5 to 4.0 eV at room temperature in bulk materials (meaning non-particulate materials). Have By forming microparticles with these materials and making the particle size nanosized, electrons in the semiconductor are confined in the nanocrystal. As a result, the band gap in the nanocrystal increases.

Theoretically, the width of the band gap is known to be inversely proportional to the square of the particle diameter of the semiconductor fine particles. Therefore, the band gap can be controlled by controlling the particle size of the semiconductor particles. These semiconductors absorb light having a wavelength smaller than the wavelength corresponding to the band gap, and emit fluorescence having a wavelength corresponding to the band gap.

The band gap of the bulk semiconductor is preferably 1.0 eV to 3.0 eV at 20 ° C. Below 1.0 eV, when nanocrystallized, the fluorescence wavelength is too sensitively shifted with respect to the change in particle size, which is not preferable in terms of difficulty in production management. On the other hand, if it exceeds 3.0 eV, only fluorescence having a shorter wavelength than the near-ultraviolet region is emitted, which is not preferable in that it is difficult to apply as a light emitting element.

The semiconductor nanocrystal can be produced by a known method, for example, a method described in US Pat. No. 6,501,091. As a production example described in this publication, a precursor solution in which trioctylphosphine (TOP) is mixed with trioctylphosphine selenide and dimethylcadmium is added to trioctylphosphine oxide (TOPO) heated to 350 ° C. There is a way to do it.

The semiconductor nanocrystal is preferably a core-shell type semiconductor nanoparticle comprising core particles made of semiconductor nanocrystals and at least one shell layer made of a semiconductor material having a larger band gap than the semiconductor material used for the core particles. It is a crystal. This has a structure in which the surface of a core fine particle made of, for example, CdSe (band gap: 1.74 eV) is covered with a shell of a semiconductor material having a large band gap, such as ZnS (band gap: 3.8 eV). Thereby, it becomes easy to express the confinement effect of excitons generated in the core fine particles. In the specific example of the semiconductor nanocrystal described above, S, Se, and the like are extracted by an active component (unreacted monomer, moisture, etc.) in the transparent medium described later, the crystal structure of the nanocrystal is broken, and the fluorescence disappears. This phenomenon is easy to occur. In order to prevent this, the surface may be modified with a metal oxide such as silica or an organic substance.

The core-shell type semiconductor nanocrystal can be produced by a known method, for example, the method described in US Pat. No. 6,501,091. For example, in the case of a CdSe core / ZnS shell structure, it can be produced by introducing a precursor solution in which diethyl zinc and trimethylsilyl sulfide are mixed with TOP into a TOPO liquid in which CdSe core particles are dispersed and heated to 140 ° C.

In addition, a so-called Type II nanocrystal (J. Am. Chem. Soc., Vol. 125, No. 38, 2003, p11466-11467) in which carriers forming excitons are separated between a core and a shell is used. It can also be used.
Furthermore, nanocrystals (Angewandte Chemie, Vol. 115, 2003, p5189-5193), etc., in which two or more layer structures are laminated on the core to form a multi-shell structure and stability, emission efficiency, and emission wavelength adjustment are improved. May be used.

In addition, the said light emission fine particle may be used individually by 1 type, and may be used in combination of 2 or more type.

In the light emitting device of the present invention, the nanocrystal light emitting fine particles are preferably semiconductor nanocrystals, and more preferably a semiconductor containing at least one compound selected from the group consisting of CdSe, CdTe, CdS, InP, GaAs, ZnSe and ZnTe. Nanocrystal.

The QD layer of the light-emitting device of the present invention is prepared by spin-coating a liquid mixture prepared by dispersing a hole injection material, a hole transport material, or an electron transport material and nanocrystal light-emitting fine particles in a solvent, and then drying to obtain a phase. It can be manufactured by separating. Alternatively, the nanocrystal light-emitting fine particles can be directly dispersed in a solvent, and the dispersion can be coated by a known method such as spin coating, casting, dipping, or spray coating.

[Light emitting layer]
The light emitting layer combines the holes injected from the hole transport layer with the electrons injected from the cathode side through the electron transport layer and the like, thereby generating an excited state and transferring energy to the QD layer. .
As a method for forming the light emitting layer, for example, a known method such as a vapor deposition method, a spin coating method, or an LB method can be applied. The light emitting layer is particularly preferably a molecular deposited film. Here, the molecular deposition film is a thin film formed by deposition from a material compound in a gas phase state or a film formed by solidification from a material compound in a solution state or a liquid phase state. Can be classified from a thin film (accumulated film) formed by the LB method according to a difference in an agglomerated structure and a higher-order structure and a functional difference resulting therefrom.
Further, as disclosed in JP-A-57-51781, a binder such as a resin and a material compound are dissolved in a solvent to form a solution, which is then thinned by a spin coating method or the like. In addition, a light emitting layer can be formed.
In the present invention, one type of material may be used from among the light emitting materials exemplified below, and a plurality of types may be mixed and used as long as the purpose is not impaired, or other known light emitting materials may be contained. Alternatively, a plurality of types of light emitting layers may be stacked and used.

Light emitting materials that can be used for the light emitting layer include, for example, anthracene, naphthalene, phenanthrene, pyrene, tetracene, coronene, chrysene, fluorescein, perylene, phthaloperylene, naphthaloperylene, perinone, phthaloperinone, naphthaloperinone, diphenylbutadiene, tetraphenylbutadiene, coumarin, and oxadiene. Azole, aldazine, bisbenzoxazoline, bisstyryl, pyrazine, cyclopentadiene, quinoline metal complex, aminoquinoline metal complex, benzoquinoline metal complex, imine, diphenylethylene, vinylanthracene, diaminocarbazole, pyran, thiopyran, polymethine, merocyanine, imidazole Chelating oxinoid compounds, quinacridone, rubrene, and fluorescent dyes, but are not limited to these. Not intended to be.

Specific examples of the host material that can be used for the light emitting layer include compounds represented by the following (i) to (ix).
Asymmetric anthracene represented by the following formula (i).

(In the formula, Ar ⁰⁰¹ is a substituted or unsubstituted condensed aromatic group having 10 to 50 nuclear carbon atoms. Ar ⁰⁰² is a substituted or unsubstituted aromatic group having 6 to 50 nuclear carbon atoms. X ⁰⁰¹ to X ⁰⁰³ independently represents a substituted or unsubstituted aromatic group having 6 to 50 nuclear carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 5 to 50 nuclear atoms, a substituted or unsubstituted carbon group having 1 to 50 alkyl groups, substituted or unsubstituted alkoxy groups having 1 to 50 carbon atoms, substituted or unsubstituted aralkyl groups having 6 to 50 carbon atoms, substituted or unsubstituted aryloxy groups having 5 to 50 carbon atoms, substituted Or an unsubstituted arylthio group having 5 to 50 nucleus atoms, a substituted or unsubstituted alkoxycarbonyl group having 1 to 50 carbon atoms, a carboxyl group, a halogen atom, a cyano group, a nitro group, a hydroxy group A, b and c are each an integer of 0 to 4. n is an integer of 1 to 3. When n is 2 or more, [] is the same or different. Good, where the number of nuclear carbons is the number of carbons forming the aromatic ring.)

An asymmetric monoanthracene derivative represented by the following formula (ii).

(In the formula, Ar ⁰⁰³ and Ar ⁰⁰⁴ are each independently a substituted or unsubstituted aromatic ring group having 6 to 50 nuclear carbon atoms, and m and n are each an integer of 1 to 4, provided that When m = n = 1 and the bonding position of Ar ⁰⁰³ and Ar ^{004 to} the benzene ring is symmetrical, Ar ⁰⁰³ and Ar ⁰⁰⁴ are not the same, and m or n is an integer of 2 to 4 M and n are different integers.
R ⁰⁰¹ to R ⁰¹⁰ are each independently a hydrogen atom, a substituted or unsubstituted aromatic ring group having 6 to 50 nuclear carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 5 to 50 nuclear atoms, substituted Or an unsubstituted alkyl group having 1 to 50 carbon atoms, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group having 1 to 50 carbon atoms, a substituted or unsubstituted aralkyl group having 6 to 50 carbon atoms, Substituted or unsubstituted aryloxy group having 5 to 50 nucleus atoms, substituted or unsubstituted arylthio group having 5 to 50 nucleus atoms, substituted or unsubstituted alkoxycarbonyl group having 1 to 50 carbon atoms, substituted or unsubstituted A silyl group, a carboxyl group, a halogen atom, a cyano group, a nitro group, and a hydroxy group. )

An asymmetric pyrene derivative represented by the following formula (iii).

[ ^Wherein Ar ⁰⁰⁵ and Ar ⁰⁰⁶ are each a substituted or unsubstituted aromatic group having 6 to 50 nuclear carbon atoms. L ⁰⁰¹ and L ⁰⁰² are a substituted or unsubstituted phenylene group, a substituted or unsubstituted naphthalenylene group, a substituted or unsubstituted fluorenylene group, or a substituted or unsubstituted dibenzosilolylene group, respectively.
m is an integer from 0 to 2, n is an integer from 1 to 4, s is an integer from 0 to 2, and t is an integer from 0 to 4.
L ⁰⁰¹ or Ar ⁰⁰⁵ binds to any of the 1-5 positions of pyrene, and L ⁰⁰² or Ar ⁰⁰⁶ binds to any of the 6-10 positions of pyrene. However, when n + t is an even number, Ar ⁰⁰⁵ , Ar ⁰⁰⁶ , L ⁰⁰¹ , and L ⁰⁰² satisfy the following (1) or (2).
(1) Ar ⁰⁰⁵ ≠ Ar ⁰⁰⁶ and / or L ⁰⁰¹ ≠ L ⁰⁰² (where ≠ indicates a group having a different structure)
(2) When Ar ⁰⁰⁵ = Ar ⁰⁰⁶ and L ⁰⁰¹ = L ⁰⁰² (2-1) m ≠ s and / or n ≠ t, or (2-2) When m = s and n = t,
(2-2-1) L ⁰⁰¹ and L ⁰⁰² or pyrene are bonded to different bonding positions on Ar ⁰⁰⁵ and Ar ⁰⁰⁶ , respectively (2-2-2) L ⁰⁰¹ and L ⁰⁰² , or pyrene is , Ar ⁰⁰⁵ and Ar ⁰⁰⁶ are bonded at the same bonding position, and L ⁰⁰¹ and L ⁰⁰² or Ar ⁰⁰⁵ and Ar ⁰⁰⁶ are substituted at positions 1 and 6 or 2 and 7 in pyrene There is no. ]

An asymmetric anthracene derivative represented by the following formula (iv).

(In the formula, A ⁰⁰¹ and A ⁰⁰² are each independently a substituted or unsubstituted condensed aromatic ring group having 10 to 20 nuclear carbon atoms.
Ar ⁰⁰⁷ and Ar ⁰⁰⁸ are each independently a hydrogen atom or a substituted or unsubstituted aromatic ring group having 6 to 50 nuclear carbon atoms.
R ⁰¹¹ to R ⁰²⁰ are each independently a hydrogen atom, a substituted or unsubstituted aromatic ring group having 6 to 50 nuclear carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 5 to 50 nuclear atoms, a substituted group Or an unsubstituted alkyl group having 1 to 50 carbon atoms, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group having 1 to 50 carbon atoms, a substituted or unsubstituted aralkyl group having 6 to 50 carbon atoms, Substituted or unsubstituted aryloxy group having 5 to 50 nucleus atoms, substituted or unsubstituted arylthio group having 5 to 50 nucleus atoms, substituted or unsubstituted alkoxycarbonyl group having 1 to 50 carbon atoms, substituted or unsubstituted A silyl group, a carboxyl group, a halogen atom, a cyano group, a nitro group or a hydroxy group.
Ar ⁰⁰⁷ , Ar ⁰⁰⁸ , R ⁰¹⁹ and R ⁰²⁰ may each be plural, and adjacent ones may form a saturated or unsaturated cyclic structure.
However, in the formula (iv), a symmetric group with respect to the XY axis shown on the anthracene is not bonded to the 9th and 10th positions of the central anthracene. )

An anthracene derivative represented by the following formula (v).

(Wherein R ⁰²¹ to R ⁰³⁰ are each independently a hydrogen atom, alkyl group, cycloalkyl group, optionally substituted aryl group, alkoxyl group, aryloxy group, alkylamino group, alkenyl group, arylamino group, or substituted. A and b each represent an integer of 1 to 5, and when they are 2 or more, R ^021s or R ^022s may be the same or different from each other In addition, R ⁰²¹ or R ⁰²² may be bonded to each other to form a ring, or R ⁰²³ and R ⁰²⁴ , R ⁰²⁵ and R ⁰²⁶ , R ⁰²⁷ and R ⁰²⁸ , R ⁰²⁹ and R ⁰³⁰ are L ⁰⁰³ may be a single bond, —O—, —S—, —N (R) — (R is an alkyl group or an optionally substituted aryl group). Represents an alkylene group or an arylene group.)

An anthracene derivative represented by the following formula (vi).

(Wherein R ⁰³¹ to R ⁰⁴⁰ each independently represents a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, an alkoxyl group, an aryloxy group, an alkylamino group, an arylamino group, or an optionally substituted multicyclic group) C, d, e and f each represent an integer of 1 to 5, and when they are 2 or more, R ^031s , R ^032s , R ^036s or R ^037s may be the same. R ⁰³¹ may be different from each other, R ⁰³² may be bonded to each other, R ⁰³³ may be bonded to each other, or R ⁰³⁷ may be bonded to each other to form a ring, and R ⁰³³ and R ⁰³⁴ , R ⁰³⁹ and R ⁰⁴⁰ are based on each other. bonded to ring the optionally formed .L ⁰⁰⁴ is a single bond, -O -, - S -, - N (R) - (R is an aryl group which may be alkyl or substituted), Al Shows the alkylene group or an arylene group.)

A spirofluorene derivative represented by the following formula (vii).

( ^Wherein A ⁰⁰⁵ to A ⁰⁰⁸ are each independently a substituted or unsubstituted biphenylyl group or a substituted or unsubstituted naphthyl group.)

A condensed ring-containing compound represented by the following formula (viii).

(Wherein A ⁰¹¹ to A ⁰¹³ represent a divalent group similar to L _{1 in the} above formula (1), and A ⁰¹⁴ to A ⁰¹⁶ are a hydrogen atom or an aryl group having 6 to 50 nuclear carbon atoms, respectively. R ⁰⁴¹ to R ⁰⁴³ each independently represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, an alkoxyl group having 1 to 6 carbon atoms, or an aryl having 5 to 18 carbon atoms. An oxy group, an aralkyloxy group having 7 to 18 carbon atoms, an arylamino group having 5 to 16 carbon atoms, a nitro group, a cyano group, an ester group having 1 to 6 carbon atoms, or a halogen atom, of A ⁰¹¹ to A ⁰¹⁶ At least one is a group having three or more condensed aromatic rings.)

Fluorene compound represented by the following formula (ix).

Wherein R ⁰⁵¹ and R ⁰⁵² are a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, or a substituted amino group. Represents a cyano group or a halogen atom, R ⁰⁵¹ bonded to different fluorene groups and R ⁰⁵² may be the same or different, and R ⁰⁵¹ and R ⁰⁵² bonded to the same fluorene group are the same. R ⁰⁵³ and R ⁰⁵⁴ may be a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heterocyclic ring. R ⁰⁵³ and R ⁰⁵⁴ representing a group and bonded to different fluorene groups may be the same or different. R ⁰⁵³ and R ⁰⁵⁴ bonded to the same fluorene group may be the same or different, and Ar ⁰¹¹ and Ar ⁰¹² are substituted or unsubstituted condensed polycyclic aromatics having a total of 3 or more benzene rings. Represents a condensed polycyclic heterocyclic group in which the total of a group or a benzene ring and a heterocyclic ring is bonded to a fluorene group by 3 or more substituted or unsubstituted carbons, and Ar ⁰¹¹ and Ar ⁰¹² are the same or different N represents an integer of 1 to 10.)

Among these materials, an anthracene derivative is preferable, a monoanthracene derivative or a bianthracene derivative is more preferable, an asymmetric anthracene is particularly preferable, or an anthracene compound used in Examples described later.

The thickness of the light emitting layer of the element of the present invention is, for example, 1 to 100 nm, preferably 5 to 60 nm. When the thickness of the light emitting layer is more than 100 nm, the voltage necessary for operating the light emitting element is increased, which may increase power consumption. On the other hand, when the thickness of the light emitting layer is less than 1 nm, it is difficult to increase the density of excitons generated in the layer, and there is a possibility that the light emitting layer does not function sufficiently.

[Electron injection layer and electron transport layer]
An electron injection layer and an electron transport layer (hereinafter collectively referred to as an electron injection layer and a transport layer) are layers that assist injection of electrons into the light emitting layer and transport them to the light emitting region, and have a high electron mobility. In addition, the adhesion improving layer is a layer made of a material that has a particularly good adhesion to the cathode in the electron injection layer.
The electron transport layer is appropriately selected with a film thickness of several nm to several μm, but when the film thickness is particularly large, the electron mobility is at least 10 when an electric field of 10 ⁴ to 10 ⁶ V / cm is applied in order to avoid an increase in voltage. It is preferably ⁻⁵ cm ² / Vs or higher.

As a material used for the electron injection layer and the electron transport layer, 8-hydroxyquinoline or a metal complex of its derivative or an oxadiazole derivative is preferable. Specific examples of metal complexes of 8-hydroxyquinoline or its derivatives include metal chelate oxinoid compounds containing a chelate of oxine (generally 8-quinolinol or 8-hydroxyquinoline), such as tris (8-quinolinolato) aluminum. it can.

Examples of the oxadiazole derivatives include electron transfer compounds represented by the following formula.

(In the formula, Ar ³⁰¹ , Ar ³⁰² , Ar ³⁰³ , Ar ³⁰⁵ , Ar ³⁰⁶ , and Ar ³⁰⁹ each represent a substituted or unsubstituted aryl group. Ar ³⁰⁴ , Ar ³⁰⁷ , and Ar ³⁰⁸ are each substituted or unsubstituted. Represents an arylene group.)

Here, examples of the aryl group include a phenyl group, a biphenyl group, an anthranyl group, a perylenyl group, and a pyrenyl group. Examples of the arylene group include a phenylene group, a naphthylene group, a biphenylene group, an anthranylene group, a peryleneylene group, and a pyrenylene group. Examples of the substituent include an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, and a cyano group. This electron transfer compound is preferably a thin film-forming compound.

Specific examples of the electron transfer compound include the following.

(Me represents a methyl group, and tBu represents a tbutyl group.)

Furthermore, materials represented by the following formulas (A) to (F) can also be used as materials used for the electron injection layer and the electron transport layer.

(In the formulas (A) and (B), A ³¹¹ to A ³¹³ each represent a nitrogen atom or a carbon atom.
Ar ³¹¹ is a substituted or unsubstituted aryl group having 6 to 60 nuclear carbon atoms or a substituted or unsubstituted heteroaryl group having 3 to 60 nuclear atoms, and Ar ³¹¹ ′ is a substituted or unsubstituted nuclear carbon atom. An arylene group of 6 to 60 or a substituted or unsubstituted heteroarylene group of 3 to 60 nuclear atoms, and Ar ³¹² represents a hydrogen atom, a substituted or unsubstituted aryl group of 6 to 60 nuclear carbon atoms, a substituted or unsubstituted An unsubstituted heteroaryl group having 3 to 60 nucleus atoms, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, or a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms. However, any one of Ar ³¹¹ and Ar ³¹² is a substituted or unsubstituted condensed ring group having 10 to 60 nuclear carbon atoms, or a substituted or unsubstituted monoheterocondensed ring group having 3 to 60 nucleus atoms.
L ³¹¹ , L ³¹² and L ³¹³ are each a single bond, a substituted or unsubstituted arylene group having 6 to 60 nuclear carbon atoms, a substituted or unsubstituted heteroarylene group having 3 to 60 nuclear atoms, or a substituted or unsubstituted group. Substituted fluorenylene group.
R and R ³¹¹ are each a hydrogen atom, a substituted or unsubstituted aryl group having 6 to 60 nuclear carbon atoms, a substituted or unsubstituted heteroaryl group having 3 to 60 nuclear atoms, a substituted or unsubstituted carbon atom having 1 to 20 alkyl groups, or substituted or unsubstituted alkoxy groups having 1 to 20 carbon atoms, n is an integer of 0 to 5, and when n is 2 or more, a plurality of Rs may be the same or different. In addition, adjacent R groups may be bonded to each other to form a carbocyclic aliphatic ring or a carbocyclic aromatic ring. The nitrogen-containing heterocyclic derivative represented by this.

HAr-L ³¹⁴ -Ar ³²¹ -Ar ³²² (C)
(In the formula, HAr is a nitrogen-containing heterocyclic ring having 3 to 40 carbon atoms which may have a substituent, and L ³¹⁴ has a carbon number of 6 to 60 optionally having a single bond or a substituent. An arylene group, a heteroarylene group having 3 to 60 atoms which may have a substituent, or a fluorenylene group which may have a substituent, and Ar ³²¹ may have a substituent A divalent aromatic hydrocarbon group having 6 to 60 carbon atoms, and Ar ³²² is an aryl group having 6 to 60 carbon atoms which may have a substituent or an atomic number which may have a substituent A nitrogen-containing heterocyclic derivative represented by 3 to 60 heteroaryl groups).

^Wherein X ³⁰¹ and Y ³⁰¹ are each a saturated or unsaturated hydrocarbon group having 1 to 6 carbon atoms, an alkoxy group, an alkenyloxy group, an alkynyloxy group, a hydroxy group, a substituted or unsubstituted aryl group, a substituted group Or an unsubstituted heterocycle or a structure in which X and Y are combined to form a saturated or unsaturated ring, and R ³⁰¹ to R ³⁰⁴ are each a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an aryloxy group Perfluoroalkyl group, perfluoroalkoxy group, amino group, alkylcarbonyl group, arylcarbonyl group, alkoxycarbonyl group, aryloxycarbonyl group, azo group, alkylcarbonyloxy group, arylcarbonyloxy group, alkoxycarbonyloxy group, aryl Oxycarbonyloxy group, sulfi Group, sulfonyl group, sulfanyl group, silyl group, carbamoyl group, aryl group, heterocyclic group, alkenyl group, alkynyl group, nitro group, formyl group, nitroso group, formyloxy group, isocyano group, cyanate group, isocyanate group, A thiocyanate group, an isothiocyanate group, or a cyano group, which may be substituted, or adjacent groups may form a substituted or unsubstituted condensed ring. Pentadiene derivative.

(Wherein R ³²¹ to R ³²⁸ and Z ³²² are each a hydrogen atom, a saturated or unsaturated hydrocarbon group, an aromatic hydrocarbon group, a heterocyclic group, a substituted amino group, a substituted boryl group, an alkoxy group or an aryl group. X ³⁰² , Y ³⁰² and Z ³²¹ each represents a saturated or unsaturated hydrocarbon group, aromatic hydrocarbon group, heterocyclic group, substituted amino group, alkoxy group or aryloxy group; ³²¹ and Z ³²² may be bonded to each other to form a condensed ring. N represents an integer of 1 to 3, and when n or (3-n) is 2 or more, R ³²¹ to R ³²⁸ , X ³⁰² , Y ³⁰² , Z ³²² and Z ³²¹ may be the same or different, provided that n is 1, X, Y and R ³²² are methyl groups and R ³²⁸ is a hydrogen atom or a substituted boryl group, and n is 3. Z ³²¹ does not include a compound having a methyl group.)

[ ^Wherein Q ³⁰¹ and Q ³⁰² each represent a ligand represented by the following formula (K), and L ³¹⁵ represents a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group , Substituted or unsubstituted aryl group, substituted or unsubstituted heterocyclic group, —OR (where R is a hydrogen atom, substituted or unsubstituted alkyl group, substituted or unsubstituted cycloalkyl group, substituted or unsubstituted aryl Group, a substituted or unsubstituted heterocyclic group) or a ligand represented by —O—Ga—Q ³⁰³ (Q ³⁰⁴ ) (Q ³⁰³ and Q ³⁰⁴ are the same as Q ³⁰¹ and Q ³⁰² ). . ] The gallium complex represented by this.

[Wherein, ring A ³⁰¹ and A ³⁰² are each a 6-membered aryl ring structure condensed with each other, which may have a substituent. ]

This metal complex has strong properties as an n-type semiconductor and has a large electron injection capability. Furthermore, since the generation energy at the time of complex formation is also low, the bondability between the metal and the ligand of the formed metal complex is strengthened, and the fluorescence quantum efficiency as a light emitting material is large.
Specific examples of the substituents of the rings A ³⁰¹ and A ³⁰² that form the ligand of the formula (K) include chlorine, bromine, iodine, halogen atoms of fluorine, methyl group, ethyl group, propyl group, butyl Group, s-butyl group, t-butyl group, pentyl group, hexyl group, heptyl group, octyl group, stearyl group, trichloromethyl group and other substituted or unsubstituted alkyl groups, phenyl group, naphthyl group, biphenyl group, anthranyl Group, phenanthryl group, fluorenyl group, pyrenyl group, 3-methylphenyl group, 3-methoxyphenyl group, 3-fluorophenyl group, 3-trichloromethylphenyl group, 3-trifluoromethylphenyl group, 3-nitrophenyl group, etc. Substituted or unsubstituted aryl group, methoxy group, n-butoxy group, t-butoxy group, trichloromethoxy group Trifluoroethoxy group, pentafluoropropoxy group, 2,2,3,3-tetrafluoropropoxy group, 1,1,1,3,3,3-hexafluoro-2-propoxy group, 6- (perfluoroethyl) Substituted or unsubstituted alkoxy group such as hexyloxy group, phenoxy group, p-nitrophenoxy group, pt-butylphenoxy group, 3-fluorophenoxy group, pentafluorophenoxy group, 3-trifluoromethylphenoxy group, etc. A substituted or unsubstituted aryloxy group, a methylthio group, an ethylthio group, a t-butylthio group, a hexylthio group, an octylthio group, a trifluoromethylthio group, or a substituted or unsubstituted alkylthio group, a phenylthio group, a p-nitrophenylthio group, pt-butylphenylthio group, 3-fluorophenylthio O group, pentafluorophenylthio group, substituted or unsubstituted arylthio group such as 3-trifluoromethylphenylthio group, cyano group, nitro group, amino group, methylamino group, ethylamino group, diethylamino group, dipropylamino Group, mono- or di-substituted amino group such as dibutylamino group, diphenylamino group, bis (acetoxymethyl) amino group, bis (acetoxyethyl) amino group, bis (acetoxypropyl) amino group, bis (acetoxybutyl) amino group, etc. Substituted or unsubstituted acylamino group, hydroxyl group, siloxy group, acyl group, carbamoyl group, methylcarbamoyl group, dimethylcarbamoyl group, ethylcarbamoyl group, diethylcarbamoyl group, propylcarbamoyl group, butylcarbamoyl group, phenylcarbamoyl group, etc. Mosquito Cycloalkyl groups such as vamoyl group, carboxylic acid group, sulfonic acid group, imide group, cyclopentane group, cyclohexyl group, pyridinyl group, pyrazinyl group, pyrimidinyl group, pyridazinyl group, triazinyl group, indolinyl group, quinolinyl group, acridinyl group, Pyrrolidinyl, dioxanyl, piperidinyl, morpholinyl, piperazinyl, carbazolyl, furanyl, thiophenyl, oxazolyl, oxadiazolyl, benzoxazolyl, thiazolyl, thiadiazolyl, benzothiazolyl, triazolyl, imidazolyl And heterocyclic groups such as benzimidazolyl group. Moreover, the above substituents may combine to form a further 6-membered aryl ring or heterocyclic ring.

In a preferred form of the organic EL element, a reducing dopant is contained in a region for transporting electrons or an interface region between the cathode and the organic layer. Here, the reducing dopant is defined as a substance capable of reducing the electron transporting compound. Accordingly, various materials can be used as long as they have a certain reducibility, such as alkali metals, alkaline earth metals, rare earth metals, alkali metal oxides, alkali metal halides, alkaline earth metals. Oxides, alkaline earth metal halides, rare earth metal oxides or rare earth metal halides, alkali metal carbonates, alkaline earth metal carbonates, rare earth metal carbonates, alkali metal organic complexes, alkalis At least one substance selected from the group consisting of organic complexes of earth metals and organic complexes of rare earth metals can be preferably used.

More specifically, preferable reducing dopants include Li (work function: 2.9 eV), Na (work function: 2.36 eV), K (work function: 2.28 eV), Rb (work function: 2). .16 eV) and Cs (work function: 1.95 eV), at least one alkali metal selected from the group consisting of Ca (work function: 2.9 eV), Sr (work function: 2.0 to 2.5 eV) , And at least one alkaline earth metal selected from the group consisting of Ba (work function: 2.52 eV), and those having a work function of 2.9 eV or less are particularly preferred.
Among these, a more preferable reducing dopant is at least one alkali metal selected from the group consisting of K, Rb, and Cs, more preferably Rb or Cs, and most preferably Cs.

These alkali metals have particularly high reducing ability, and the addition of a relatively small amount to the electron injection region can improve the light emission luminance and extend the life of the organic EL element. Further, as a reducing dopant having a work function of 2.9 eV or less, a combination of two or more alkali metals is also preferable. Particularly, a combination containing Cs, such as Cs and Na, Cs and K, Cs and Rb, or Cs. And a combination of Na and K.
By including Cs in combination, the reducing ability can be efficiently exhibited, and by adding to the electron injection region, the emission luminance and the life of the organic EL element can be improved.

In the present invention, an electron injection layer composed of an insulator or a semiconductor may be further provided between the cathode and the organic layer. At this time, current leakage can be effectively prevented and the electron injection property can be improved.
As such an insulator, it is preferable to use at least one metal compound selected from the group consisting of alkali metal chalcogenides, alkaline earth metal chalcogenides, alkali metal halides and alkaline earth metal halides. If the electron injection layer is composed of these alkali metal chalcogenides or the like, it is preferable in that the electron injection property can be further improved.

Specifically, preferable alkali metal chalcogenides include, for example, Li ₂ O, LiO, Na ₂ S, Na ₂ Se, and NaO, and preferable alkaline earth metal chalcogenides include, for example, CaO, BaO, SrO, and BeO. , BaS, and CaSe. Further, preferable alkali metal halides include, for example, LiF, NaF, KF, CsF, LiCl, KCl, and NaCl. Examples of preferable alkaline earth metal halides include fluorides such as CaF ₂ , BaF ₂ , SrF ₂ , MgF ₂ and BeF ₂ , and halides other than fluorides.

Further, as a semiconductor constituting the electron transport layer, an oxide containing at least one element of Ba, Ca, Sr, Yb, Al, Ga, In, Li, Na, Cd, Mg, Si, Ta, Sb, and Zn. , Nitrides or oxynitrides, or a combination of two or more.
Moreover, it is preferable that the inorganic compound which comprises an electron carrying layer is a microcrystal or an amorphous insulating thin film. If the electron transport layer is composed of these insulating thin films, a more uniform thin film is formed, and pixel defects such as dark spots can be reduced.
Examples of such inorganic compounds include the alkali metal chalcogenides, alkaline earth metal chalcogenides, alkali metal halides, and alkaline earth metal halides described above.

[substrate]
The light emitting element of the present invention is manufactured on a substrate. The substrate here is a substrate that supports the light-emitting element, and is preferably a smooth substrate having a light transmittance in the visible region of 400 to 700 nm of 50% or more.

Specifically, a glass plate, a polymer plate, etc. are mentioned. 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.
In addition, translucency is unnecessary when a support substrate is located on the opposite side to the light extraction direction.

[anode]
The anode of the light emitting element plays a role of injecting holes into the hole transport layer or the light emitting layer. When transparency is required on the anode side, indium tin oxide alloy (ITO), tin oxide (NESA) ), Indium zinc oxide alloy, gold, silver, platinum, copper and the like can be applied. In addition, when a reflective electrode that does not require transparency is used, a metal or an alloy such as aluminum, molybdenum, chromium, or nickel can be used in addition to these metals.
These materials can be used alone, but an alloy of these materials or a material to which other elements are added can be appropriately selected and used.

When light emitted from the light emitting layer is taken out from the anode, the transmittance of the anode for light emission is preferably greater than 10%. The sheet resistance of the anode is preferably several hundred Ω / □ or less. Although the film thickness of the anode depends on the material, it is usually selected in the range of 10 nm to 1 μm, preferably 10 to 200 nm.

[cathode]
As the cathode, a metal, an alloy, an electrically conductive compound, or a mixture thereof having a low work function (4 eV or less) can be used as an electrode material. Specific examples of such electrode materials include sodium, sodium-potassium alloy, magnesium, lithium, magnesium / silver alloy, aluminum / aluminum oxide, aluminum / lithium alloy, indium, and rare earth metals.
The cathode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering.

Here, when light emitted from the light emitting layer is taken out from the cathode, it is preferable that the transmittance with respect to the light emitted from the cathode is larger than 10%.
The sheet resistance as the cathode is preferably several hundred Ω / □ or less, and the film thickness is usually 10 nm to 1 μm, preferably 50 to 200 nm.

[Insulation layer]
Since a light emitting element applies an electric field to an ultrathin film, pixel defects are likely to occur due to leakage or short circuit. In order to prevent this, it is preferable to insert an insulating thin film layer between the pair of electrodes.

Examples of materials used for the insulating layer include aluminum oxide, lithium fluoride, lithium oxide, cesium oxide, magnesium oxide, magnesium fluoride, calcium oxide, calcium fluoride, cesium fluoride, cesium carbonate, aluminum nitride, titanium oxide, and oxide. Examples thereof include silicon, germanium oxide, silicon nitride, boron nitride, molybdenum oxide, ruthenium oxide, and vanadium oxide.
A mixture or laminate of these may be used.

In the light-emitting element of the present invention, the formation method of each layer is not particularly described, and is a vacuum evaporation method, an LB method, a resistance heating evaporation method, an electron beam method, a sputtering method, a molecular lamination method, a coating method (spin coating method, Various methods such as a casting method, a dip coating method, an ink jet method, and a printing method can be used.

In addition, as for the film thickness of each layer of the light emitting device of the present invention, unless otherwise specified, generally, if the film thickness is too thin, defects such as pinholes are likely to occur. In general, the range of several nm to 1 μm is preferable.
[Example]

EXAMPLES Next, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to these Examples.
In addition, the structure of the material used by the Example or the comparative example is shown below. Table 1 shows the HOMO level and LUMO level of each material.

The HOMO level is a value measured for the deposited film of each raw material using a work function measuring apparatus AC3 (manufactured by Riken Keiki Co., Ltd.).
The LUMO level was calculated by estimating the energy gap Eg from the absorption edge of the deposited film and taking into account the actual value of the HOMO level.

Example 1
A glass substrate (manufactured by Geomatic Co., Ltd.) with an ITO transparent electrode (thickness 120 nm) having a thickness of 25 mm × 75 mm × 1.1 mm was subjected to ultrasonic cleaning in isopropyl alcohol for 5 minutes, and then UV ozone cleaning was performed for 30 minutes. On the substrate, poly (ethylenedioxy) thiophene: polystyrene sulfonic acid (hereinafter referred to as PEDOT: PSS) used as a hole injection layer by spin coating (1500 rpm, 30 seconds) was formed to a thickness of 40 nm, Drying was performed at 200 ° C. for 30 minutes.
1.69 ml of a HT1 toluene solution (concentration 2 wt%) and 1.2 ml of a CdSe / ZnS core-shell quantum dot toluene dispersion (ED-C11-TOL-0620 manufactured by Evident Technology, Inc., concentration 10 mg / ml) are mixed. Further, 0.51 ml of toluene was added to prepare an HT1 / QD mixed solution. This solution was formed into a film by spin coating (1500 rpm, 30 seconds) on the PEDOT: PSS coated substrate in a glove box substituted with dry nitrogen.

In FIG. 5, the cross-sectional photograph which observed the layer structure with the transmission electron microscope (TEM) is shown.
From this photograph, it was observed that the entire surface of the hole transport layer (HT1 layer) having a film thickness of about 40 nm was covered with the QD single particle film in the form of a layer.

This substrate was fixed to a substrate holder of a commercially available vapor deposition apparatus (manufactured by Nippon Vacuum Technology Co., Ltd.), and the pressure in the vacuum chamber was reduced to 1 × 10 ⁻⁴ Pa. Using a normal vacuum deposition method, a light emitting material EM1 is deposited as a light emitting layer, an electron injection material Alq3 is deposited as an electron injection layer to a thickness of 40 nm and 20 nm, respectively, and finally LiF and Al are deposited as a cathode at 1 nm and 150 nm, respectively. It evaporated until it became the thickness of.
Thereafter, the inside of the vacuum chamber was returned to atmospheric pressure, and the obtained laminate was taken out from the vapor deposition apparatus.

A DC voltage was applied to the obtained device, and the light emission characteristics were evaluated with a spectral radiance meter (Minolta CS1000). As a result, with an applied voltage of 9 V, good device characteristics such as emission luminance of 115 cd / m ² , efficiency of 4.7 cd / A, and external quantum efficiency of 2.5% were obtained. The chromaticity was (0.591, 0.334), and good red light emission derived from QD. Here, the HOMO level of HT1 was 5.5 eV, that of EM1 was 5.7 eV, and the absolute value of the difference was 0.2 eV. The external quantum efficiency was calculated with reference to the following literature.
“Organic EL Display” Shizuka Tokito et al .; Ohmsha, August 20, 2004, p42-43

In addition, the blue light emission derived from the light emitting layer (EM1) was obtained from the element produced similarly to Example 1 except not using QD, and the light emission peak wavelength at that time was 442 nm.
Table 2 shows the materials used and the evaluation results of the devices manufactured in Example 1 and Examples and Comparative Examples described later.

Example 2
A device was prepared in the same manner as in Example 1 except that a toluene dispersion of CdSe / ZnS core-shell quantum dots (ED-C11-TOL-0520 manufactured by Evident Technology, Inc., concentration 10 mg / ml) was used as the nanocrystal. Preparation and evaluation.
As a result, with an applied voltage of 6.5 V, good device characteristics were obtained, such as emission luminance of 192 cd / m ² , efficiency of 4.9 cd / A, and external quantum efficiency of 2.3%. The chromaticity was (0.193, 0.693), and good green light emission derived from QD was obtained. Here, the HOMO level of HT1 was 5.5 eV, that of EM1 was 5.7 eV, and the difference was 0.2 eV (see Table 2). From the element obtained by removing QD, blue light emission derived from EM1 was obtained, and the emission peak wavelength at that time was 442 nm.

Comparative Example 1
A glass substrate (manufactured by Geomatic Co., Ltd.) with an ITO transparent electrode (thickness 120 nm) having a thickness of 25 mm × 75 mm × 1.1 mm was subjected to ultrasonic cleaning in isopropyl alcohol for 5 minutes, and then UV ozone cleaning was performed for 30 minutes.
1.69 ml of the above TPD toluene solution (concentration 2 wt%) and 1.2 ml of a CdSe / ZnS core-shell quantum dot toluene dispersion (ED-C11-TOL-0620 manufactured by Evident Technology, Inc., concentration 10 mg / ml) After mixing, 0.51 ml of toluene was further added to prepare a TPD / QD mixed solution. This solution was spin-coated (1500 rpm, 30 seconds) on the previous substrate in a glove box substituted with dry nitrogen. When the cross section of this substrate was observed with a TEM, it was observed that the entire surface of the hole transport layer (TPD layer) was covered with a QD monolayer film in a layered manner. And the pressure inside the vacuum chamber was reduced to 1 × 10 ⁻⁴ Pa. Using a normal vacuum deposition method, a light emitting material TAZ is deposited as a light emitting layer, an electron injection material Alq3 is deposited as an electron injection layer to a thickness of 40 nm and 20 nm, respectively, and finally LiF and Al are respectively deposited as a cathode at 1 nm and 150 nm. It evaporated until it became the thickness of.
Thereafter, the inside of the vacuum chamber was returned to atmospheric pressure, and the obtained laminate was taken out from the vapor deposition apparatus.

A DC voltage was applied to the obtained device, and the light emission characteristics were evaluated using a spectral radiance meter (Minolta CS1000). As a result, when the applied voltage was 30 V, the emission luminance was 5.4 cd / m ² , the efficiency was 0.043 cd / A, and the external quantum efficiency was 0.016%, which was extremely low efficiency. The chromaticity was (0.474, 0.462), and in addition to light emission derived from QD, green light emission (emission peak wavelength 520 nm) derived from Alq3 was superimposed. Here, the HOMO level of TPD constituting the hole transport layer was 5.4 eV, that of TAZ constituting the light emitting layer was 6.5 eV, and the difference was 1.1 eV.
Note that the light emission of the device excluding QD from this device is not derived from the light emitting layer, but is derived from green light emitted from Alq3 that forms the electron injection layer (emission peak wavelength 520 nm) and blue light emitted from TPD (peak wavelength is 425 nm). However, the main light emission was green light emission derived from Alq3. Note that which layer emits light was determined by comparison with the PL spectrum of the thin film of each material.

Comparative Example 2
A glass substrate (manufactured by Geomatic Co., Ltd.) with an ITO transparent electrode (thickness 120 nm) having a thickness of 25 mm × 75 mm × 1.1 mm was subjected to ultrasonic cleaning in isopropyl alcohol for 5 minutes, and then UV ozone cleaning was performed for 30 minutes. On the substrate, poly (ethylenedioxy) thiophene: polystyrene sulfonic acid (hereinafter referred to as PEDOT: PSS) used as a hole injection layer by spin coating (1500 rpm, 30 seconds) was formed to a thickness of 40 nm, Drying was performed at 200 ° C. for 30 minutes.
1.69 ml of a HT1 toluene solution (concentration 2 wt%) described later and 1.2 ml of a CdSe / ZnS core-shell quantum dot toluene dispersion (ED-C11-TOL-0620 manufactured by Evident Technology, Inc., concentration 10 mg / ml) After mixing, 0.51 ml of toluene was further added to prepare an HT1 / QD mixed solution. This solution was spin-coated (1500 rpm, 30 seconds) on the PEDOT: PSS-coated substrate in a glove box substituted with dry nitrogen.
This substrate was fixed to a substrate holder of a commercially available vapor deposition apparatus (manufactured by Nippon Vacuum Technology Co., Ltd.), and the pressure in the vacuum chamber was reduced to 1 × 10 ⁻⁴ Pa. Using a normal vacuum deposition method, a light emitting material TAZ is deposited as a light emitting layer, an electron injection material Alq3 is deposited as an electron injection layer to a thickness of 40 nm and 20 nm, respectively, and finally LiF and Al are respectively deposited as a cathode at 1 nm and 150 nm. It evaporated until it became the thickness of.
Thereafter, the inside of the vacuum chamber was returned to atmospheric pressure, and the obtained laminate was taken out from the vapor deposition apparatus.

A DC voltage was applied to the obtained device, and the light emission characteristics were evaluated using a spectral radiance meter (Minolta CS1000). As a result, at an applied voltage of 7 V, the emission luminance was 172 cd / m 2, the efficiency was 0.13 cd / A, and the external quantum efficiency was 0.043%. The chromaticity was (0.447, 0.424), and in addition to the light emission derived from QD, green light emission derived from Alq3 (emission peak wavelength 520 nm) and blue light emission derived from HT1 (peak wavelength 420 nm) were superimposed. . Here, the HOMO level of HT1 was 5.5 eV, that of TAZ was 6.5 eV, and the difference was 1.0 eV.
Blue light emission derived from the hole transport layer (HT1) was obtained from the device excluding QD from this device, and the emission peak wavelength at that time was 420 nm.

The QD-LED element of the present invention can be suitably used for a flat display for TV or the like. Further, it can be suitably used for light sources such as flat light emitters and display backlights, display units such as mobile phones, PDAs, car navigation systems, vehicle instrument panels, and lighting.
The entire contents of the documents described in this specification are incorporated herein by reference.

Claims (7)

1. Including at least an anode, a hole transport zone, a light emission zone and a cathode in this order,
   The hole transport band and the light emission band are adjacent to each other, and an organic / inorganic hybrid electroluminescent device having nanocrystal light emitting fine particles near the interface between the hole transport band and the light emission band,
   An organic / inorganic hybrid electroluminescent device that emits blue light having an emission peak wavelength in a light emission band of 490 nm or less of an organic electroluminescent device having the same configuration as the electroluminescent device except that the nanocrystal luminescent fine particles are not present.
2. The organic / inorganic hybrid electroluminescent device according to claim 1, wherein the nanocrystal luminescent fine particles are semiconductor nanocrystals.
3. The organic / inorganic hybrid electroluminescence according to claim 1 or 2, wherein a difference between a HOMO energy level of the main material in the hole transport zone and a HOMO energy level of the main material in the emission zone is less than 1 eV. element.
4. The organic / inorganic hybrid type according to claim 1 or 2, wherein a difference between a HOMO energy level of the main material in the hole transport band and a HOMO energy level of the main material in the emission band is less than 0.5 eV. Electroluminescent device.
5. The organic / inorganic hybrid electroluminescent device according to claim 3 or 4, wherein an emission peak wavelength of light emitted from the emission band is 470 nm or less.
6. The organic / inorganic hybrid electroluminescent device according to claim 5, wherein a main material of the light emission band is a material having an anthracene skeleton.
7. The organic / inorganic hybrid electroluminescent device according to claim 5 or 6, wherein the main material of the hole transport zone is an aromatic amine derivative.

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