JP2010225689A - Light emitting element, light emitting device, display device, and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting element which can be driven at a relatively low voltage, to provide a reliable light emitting device having the same light emitting element, to provide a display device, and to provide an electronic apparatus. <P>SOLUTION: The light emitting element 1 includes a cathode 9, an anode 3, a light emitting portion 6 arranged between the cathode 9 and anode 3 and emitting light when a drive voltage is applied, a hole injection layer 4 arranged between the anode 3 and light emitting portion 6 and injecting a hole in a layer on a cathode 9 side. The hole injection layer 4 is formed by containing quinoxaline derivative having a cyano group. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a light emitting element, a light emitting device, a display device, and an electronic apparatus.

  An organic electroluminescence element (so-called organic EL element) is a light emitting element having a structure in which at least one light emitting organic layer is interposed between an anode and a cathode. In such a light emitting device, by applying an electric field between the cathode and the anode, electrons are injected into the light emitting layer from the cathode side and holes are injected from the anode side, and electrons and holes are injected into the light emitting layer. Recombination generates excitons, and when the excitons return to the ground state, the energy is emitted as light.

  As such a light-emitting device, for example, a device in which a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, etc. are laminated between a cathode and an anode to emit light is known. (For example, refer to Patent Document 1 and Non-Patent Document 1). Although the light emitting element having such a configuration can obtain high current efficiency (light emission efficiency), there is a problem that the drive voltage tends to be high because the interface between the layers increases.

JP 2007-286991 A

Hitachi Kuma, et. al, SID 07 DIGEST, P1504 (2007)

  An object of the present invention is to provide a light-emitting element that can be driven at a relatively low voltage, a light-emitting device including the light-emitting element, a display device, and an electronic apparatus.

Such an object is achieved by the present invention described below.
The light emitting device of the present invention comprises a cathode,
The anode,
A light emitting portion that is provided between the cathode and the anode and emits light when a driving voltage is applied;
A hole injection layer that is provided between the anode and the light emitting unit and injects holes into the cathode side layer;
The hole injection layer includes a quinoxaline derivative having a cyano group.
Thus, a light emitting element that can be driven at a relatively low voltage can be provided.

In the light emitting device of the present invention, the quinoxaline derivative preferably contains two or more cyano groups in the molecule.
Thereby, the hole injection layer can inject holes into the hole transport layer more efficiently.
In the light-emitting element of the present invention, the quinoxaline derivative preferably has a quinoxaline dimer as a skeleton.
When such a compound is used, it can be preferably used because it can be easily formed into a film.

このような化合物は、電子輸送性および正孔注入性に特に優れており、発光素子の使用時における駆動電圧をより低いものとすることができる。
本発明の発光素子では、前記キノキサリン誘導体は、キノキサリンの単量体を骨格として有することが好ましい。
このような化合物を用いた場合、容易に成膜が可能であるため、好適に用いることができる。 In the light emitting device of the present invention, the quinoxaline derivative is preferably a compound represented by the following formula (1) or the following formula (2).

Such a compound is particularly excellent in the electron transporting property and the hole injecting property, and the driving voltage at the time of using the light emitting element can be made lower.
In the light emitting device of the present invention, the quinoxaline derivative preferably has a quinoxaline monomer as a skeleton.
When such a compound is used, it can be preferably used because it can be easily formed into a film.

このような化合物は、電子輸送性および正孔注入性に特に優れており、発光素子の使用時における駆動電圧をより低いものとすることができる。 In the light emitting device of the present invention, the quinoxaline derivative is preferably a compound represented by the following formula (3).

Such a compound is particularly excellent in the electron transporting property and the hole injecting property, and the driving voltage at the time of using the light emitting element can be made lower.

In the light emitting device of the present invention, a hole transport layer that is provided between the hole injection layer and the light emitting portion and transports holes to the cathode side layer,
The hole transport layer preferably contains an amine material.
The amine-based material is a material in which electrons can be preferably extracted by a cyano group-containing quinoxaline derivative and holes can be easily injected. Therefore, by using an amine-based material as a constituent material of the hole transport layer, holes can be preferably injected from the anode through the hole injection layer, and the light emitting device has a lower voltage. Can also be suitably driven.

このような化合物は、シアノ基含有キノキサリン誘導体により電子をより好適に引き抜かれることができ、特に容易に正孔が注入されることができるため、発光素子は、より低い電圧であっても好適に駆動できるものとなる。 In the light emitting device of the present invention, the amine material is preferably a compound represented by the following formula (4).

Such a compound can extract electrons more suitably by a cyano group-containing quinoxaline derivative, and in particular, since holes can be easily injected, the light-emitting element is preferably used even at a lower voltage. It can be driven.

The light-emitting device of the present invention includes the light-emitting element of the present invention.
Accordingly, a light emitting device that can be driven at a relatively low voltage can be provided.
The display device of the present invention includes the light emitting device of the present invention.
Accordingly, a display device that can be driven at a relatively low voltage can be provided.
An electronic apparatus according to the present invention includes the display device according to the present invention.
Thereby, an electronic device that can be driven at a relatively low voltage can be provided.

It is a figure which shows typically the longitudinal cross-section of the light emitting element which concerns on 1st Embodiment of this invention. It is a figure which shows typically the longitudinal cross-section of the light emitting element which concerns on 2nd Embodiment of this invention. It is a longitudinal cross-sectional view which shows embodiment of the display apparatus to which the display apparatus of this invention is applied. 1 is a perspective view showing a configuration of a mobile (or notebook) personal computer to which an electronic apparatus of the present invention is applied. It is a perspective view which shows the structure of the mobile telephone (PHS is also included) to which the electronic device of this invention is applied. It is a perspective view which shows the structure of the digital still camera to which the electronic device of this invention is applied.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of a light-emitting element, a light-emitting device, a display device, and an electronic device according to the invention will be described with reference to the accompanying drawings.
<First Embodiment>
FIG. 1 is a diagram schematically showing a longitudinal section of a light emitting device according to a first embodiment of the present invention. In the following description, for convenience of explanation, the upper side in FIG.

A light-emitting element (electroluminescence element) 1 shown in FIG. 1 is an organic light-emitting element that emits white light when plural types of organic light-emitting materials emit light in R (red), G (green), and B (blue). .
Such a light emitting device 1 includes an anode 3, a hole injection layer 4, a hole transport layer 5, a light emitting part 6 composed of a plurality of light emitting layers, an electron transport layer 7, an electron injection layer 8, and a cathode 9 in this order. It has been made. In addition, the light emitting unit 6 has a red light emitting layer (first light emitting layer) 61, an intermediate layer 62, a blue light emitting layer (second light emitting layer) 63, and a green light emitting layer (third light emitting layer) from the anode 3 side to the cathode 9 side. The light emitting layer) 64 is a laminated body laminated in this order.
The entire light emitting element 1 is provided on the substrate 2 and is sealed with a sealing member 10.

  In such a light emitting element 1, electrons are applied to the red light emitting layer 61, the blue light emitting layer 63, and the green light emitting layer 64 from the cathode 9 side by applying a driving voltage to the anode 3 and the cathode 9. While being supplied (injected), holes are supplied (injected) from the anode 3 side. In each light emitting layer, holes and electrons recombine, and excitons (excitons) are generated by the energy released during the recombination, and energy (fluorescence or phosphorescence) is generated when the excitons return to the ground state. Is emitted (emitted). Thereby, the light emitting element 1 emits white light.

The substrate 2 supports the anode 3. Since the light-emitting element 1 of the present embodiment is configured to extract light from the substrate 2 side (bottom emission type), the substrate 2 and the anode 3 are substantially transparent (colorless transparent, colored transparent, or translucent), respectively. Has been.
Examples of the constituent material of the substrate 2 include resin materials such as polyethylene terephthalate, polyethylene naphthalate, polypropylene, cycloolefin polymer, polyamide, polyethersulfone, polymethyl methacrylate, polycarbonate, and polyarylate, quartz glass, and soda glass. Such glass materials can be used, and one or more of these can be used in combination.
Although the average thickness of such a board | substrate 2 is not specifically limited, It is preferable that it is about 0.1-30 mm, and it is more preferable that it is about 0.1-10 mm.

In the case where the light emitting element 1 is configured to extract light from the side opposite to the substrate 2 (top emission type), the substrate 2 can be either a transparent substrate or an opaque substrate.
Examples of the opaque substrate include a substrate made of a ceramic material such as alumina, an oxide film (insulating film) formed on the surface of a metal substrate such as stainless steel, and a substrate made of a resin material. It is done.

Hereinafter, each part which comprises the light emitting element 1 is demonstrated sequentially.
[anode]
The anode 3 is an electrode that injects holes into the hole transport layer 5 through a hole injection layer 4 described later. As a constituent material of the anode 3, it is preferable to use a material having a large work function and excellent conductivity.

Examples of the constituent material of the anode 3 include oxides such as ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), In ₃ O ₃ , SnO ₂ , Sb-containing SnO ₂ , and Al-containing ZnO, Au, Pt, and Ag. Cu, alloys containing these, and the like can be used, and one or more of these can be used in combination.
The average thickness of the anode 3 is not particularly limited, but is preferably about 10 to 200 nm, and more preferably about 50 to 150 nm.

[cathode]
On the other hand, the cathode 9 is an electrode that injects electrons into the electron transport layer 7 through an electron injection layer 8 described later. As a constituent material of the cathode 9, it is preferable to use a material having a small work function.
Examples of the constituent material of the cathode 9 include Li, Mg, Ca, Sr, La, Ce, Er, Eu, Sc, Y, Yb, Ag, Cu, Al, Cs, Rb, and alloys containing these. These can be used alone or in combination of two or more thereof (for example, a multi-layer laminate).

In particular, when an alloy is used as the constituent material of the cathode 9, it is preferable to use an alloy containing a stable metal element such as Ag, Al, or Cu, specifically, an alloy such as MgAg, AlLi, or CuLi. By using such an alloy as the constituent material of the cathode 9, the electron injection efficiency and stability of the cathode 9 can be improved.
Although the average thickness of such a cathode 9 is not specifically limited, It is preferable that it is about 100-10000 nm, and it is more preferable that it is about 200-500 nm.
In addition, since the light emitting element 1 of this embodiment is a bottom emission type, the light transmittance of the cathode 9 is not particularly required.

[Hole injection layer]
The hole injection layer 4 has a function of improving the hole injection efficiency from the anode 3.
In the present invention, the hole injection layer 4 includes a quinoxaline derivative having a cyano group (hereinafter, also referred to as “cyano group-containing quinoxaline derivative”) as a constituent material (hole injection material). The present invention is characterized in this respect.

  Since the cyano group-containing quinoxaline derivative has a cyano group, it has a high electron-withdrawing property. On the other hand, a cyano group-containing quinoxaline derivative has an excellent electron transport property because its quinoxaline skeleton has an excellent electron transport property. Such a cyano group-containing quinoxaline derivative having a cyano group excellent in electron withdrawing property and a quinoxaline skeleton excellent in electron transportability is adjacent when holes are injected from the anode 3 into the hole injection layer 4. Electrons are efficiently extracted from the cathode 9 side layer (hole transport layer 5) to inject holes into the adjacent cathode 9 side layer (hole transport layer 5), and the extracted electrons are efficiently supplied to the anode 3. Can be transported. For this reason, even if the voltage is relatively low, holes injected from the anode 3 are likely to reach the light emitting portion 6, and the light emitting element 1 can be driven at a relatively low voltage.

The cyano group-containing quinoxaline derivative that can be used as the hole injection material is not particularly limited as long as it is a quinoxaline derivative having a cyano group, and examples thereof include a quinoxaline monomer, a quinoxaline dimer, and a trimer. Examples include cyanides of compounds having various quinoxaline skeletons such as oligomers and quinoxaline polymers, and one or more of these can be used in combination.
More specifically, examples of the cyano group-containing quinoxaline derivative include compounds represented by the following formulas (5-1) to (5-10).

Among the above, cyano group-containing quinoxaline derivatives having a quinoxaline monomer and a dimer as a skeleton can be easily used because they can be easily formed into a film. When these compounds are used, the hole injection layer 4 can be suitably formed by a vapor deposition method such as vacuum deposition.
Further, in the cyano group-containing quinoxaline derivative having a quinoxaline monomer as a skeleton, it is more preferable to use the cyano group-containing quinoxaline derivative represented by the formula (5-1). Such a compound is particularly excellent in the electron transport property and the hole injection property, and the driving voltage when the light-emitting element 1 is used can be made lower.

  Moreover, in the cyano group-containing quinoxaline derivative having a quinoxaline dimer as a skeleton, it is more preferable to use the cyano group-containing quinoxaline derivative represented by the formula (5-5) and / or the formula (5-6). . Such a compound is particularly excellent in the electron transport property and the hole injection property, and the driving voltage when the light-emitting element 1 is used can be made lower.

The cyano group-containing quinoxaline derivative preferably has 2 or more cyano groups in the molecule, and more preferably 4 or more cyano groups. Thereby, the hole injection layer 4 can inject holes into the hole transport layer 5 more efficiently.
In addition to the cyano group-containing quinoxaline derivative described above, other hole injection materials may be included.
Such a hole injection material is not particularly limited. For example, 4,4 ′, 4 ″ -tris (N, N-phenyl-3-methylphenylamino) triphenylamine (m-MTDATA), N, N′-bis- (4-diphenylamino-phenyl) -N, N′-diphenyl-biphenyl-4-4′-diamine and the like represented by the formula (6) can be mentioned.

Although the average thickness of such a hole injection layer 4 is not specifically limited, It is preferable that it is 1-100 nm, and it is more preferable that it is 1-80 nm. Thereby, the drive voltage of the light emitting element 1 can be made lower.
In particular, when the cyano group-containing quinoxaline derivative has a quinoxaline monomer as a skeleton, the average thickness of the hole injection layer 4 is not particularly limited, but is preferably 1 to 10 nm, preferably 1 to 5 nm. More preferably. Thereby, the effect of the cyano group-containing quinoxaline derivative can be suitably exhibited while preventing the cyano group-containing quinoxaline derivative from crystallizing and increasing the electrical resistance of the hole injection layer 4.

[Hole transport layer]
The hole transport layer 5 is provided in contact with the hole injection layer 4 and has a function of transporting holes injected from the anode 3 through the hole injection layer 4 to the red light emitting layer 61. is there.
As the constituent material of the hole transport layer 5, various p-type polymer materials and various p-type low-molecular materials can be used alone or in combination. For example, an amine-based material having an amine in its chemical structure. Materials can be used.

  The amine-based material is a material in which electrons can be preferably extracted by a cyano group-containing quinoxaline derivative and holes can be easily injected. For this reason, by using an amine-based material as the constituent material of the hole transport layer 5, holes can be suitably injected from the anode 3 through the hole injection layer 4, and the light emitting element 1 is lower. Even a voltage can be suitably driven.

  Examples of the amine-based material include N, N′-di (1-naphthyl) -N, N′-diphenyl-1,1′-diphenyl-4,4′-diamine represented by the following formula (4) (α -NPD), tetraarylbenzidine derivatives such as N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-diphenyl-4,4′-diamine (TPD), tetraaryldiamino A fluorene compound or a derivative thereof can be used, and one or more of these can be used in combination.

In particular, among the above-described amine materials, N, N′-di (1-naphthyl) -N, N′-diphenyl-1,1′-diphenyl-4,4 ′ represented by the above formula (4) is used. It is preferable to use a diamine (α-NPD). Such a compound can draw out electrons more suitably by a cyano group-containing quinoxaline derivative, and in particular, holes can be easily injected. Therefore, the light-emitting element 1 can be operated at a lower voltage. It can be suitably driven.
The average thickness of the hole transport layer 5 is not particularly limited, but is preferably 10 to 150 nm, and more preferably 10 to 100 nm.

[Light emitting part]
As described above, the light emitting unit 6 includes the red light emitting layer (first light emitting layer) 61, the intermediate layer 62, the blue light emitting layer (second light emitting layer) 63, and the green light emitting layer (third light emitting layer) from the anode 3 side. The light emitting layer) 64 is laminated.

(Red light emitting layer)
The red light emitting layer (first light emitting layer) 61 includes a red light emitting material (first light emitting material) that emits red light (first color).
Such a red light emitting material is not particularly limited, and various red fluorescent materials and red phosphorescent materials can be used singly or in combination.

  The red fluorescent material is not particularly limited as long as it emits red fluorescence. For example, a perylene derivative such as a tetraaryldiindenoperylene derivative represented by the following formula (7), a europium complex, a benzopyran derivative, a rhodamine derivative, Benzothioxanthene derivative, porphyrin derivative, Nile red, 2- (1,1-dimethylethyl) -6- (2- (2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H) , 5H-benzo (ij) quinolizin-9-yl) ethenyl) -4H-pyran-4H-ylidene) propanedinitrile (DCJTB), 4- (dicyanomethylene) -2-methyl-6- (p-dimethylaminostyryl) ) -4H-pyran (DCM) and the like.

The red phosphorescent material is not particularly limited as long as it emits red phosphorescence, and examples thereof include metal complexes such as iridium, ruthenium, platinum, osmium, rhenium, and palladium. Among the ligands of these metal complexes, And those having at least one of phenylpyridine skeleton, bipyridyl skeleton, porphyrin skeleton and the like. More specifically, tris (1-phenylisoquinoline) iridium, bis [2- (2′-benzo [4,5-α] thienyl) pyridinate-N, C ³ ′] iridium (acetylacetonate) (btp2Ir ( acac)), 2,3,7,8,12,13,17,18-octaethyl-12H, 23H-porphyrin-platinum (II), bis [2- (2′-benzo [4,5-α] thienyl ) Pyridinate-N, C ³ '] iridium, bis (2-phenylpyridine) iridium (acetylacetonate).

  Further, as a constituent material of the red light emitting layer 61, in addition to the red light emitting material as described above, a host material (first host material) using this red light emitting material as a guest material may be used. This host material recombines holes and electrons to generate excitons, and excites the red light-emitting material by transferring the exciton energy to the red light-emitting material (Felster movement or Dexter movement). It has a function. Such a first host material can be used, for example, by doping the first host material with a red light emitting material, which is a guest material, as a dopant.

Such a first host material is not particularly limited as long as it exhibits the above-described function with respect to the red light emitting material to be used. When the red light emitting material includes a red fluorescent material, for example, Styrylarylene derivatives, anthracene derivatives as shown in the following formula (8), anthracene derivatives such as 2-t-butyl-9,10-di (2-naphthyl) anthracene (TBADN), perylene derivatives, distyrylbenzene derivatives, di A styrylamine derivative, a quinolinolato-based metal complex such as tris (8-quinolinolato) aluminum complex (Alq ₃ ), a triarylamine derivative such as a tetramer of triphenylamine, an oxadiazole derivative, represented by the following formula (9) Naphthacene such as naphthacene derivatives and derivatives thereof, silole derivatives, dicarbazole Conductors, oligothiophene derivatives, benzopyran derivatives, triazole derivatives, benzoxazole derivatives, benzothiazole derivatives, quinoline derivatives, 4,4′-bis (2,2′-diphenylvinyl) biphenyl (DPVBi), and the like. One kind can be used alone, or two or more kinds can be used in combination.
Further, when the red light emitting material includes a red phosphorescent material, examples of the first host material include 3-phenyl-4- (1′-naphthyl) -5-phenylcarbazole, 4,4′-N, N ′. -Carbazole derivatives, such as dicarbazole biphenyl (CBP), etc. are mentioned, Among these, it can also be used individually by 1 type or in combination of 2 or more types.

When the first host material is included in the red light emitting layer 61, the content (dope amount) of the red light emitting material in the red light emitting layer 61 is preferably 0.01 to 10 wt%, and preferably 0.1 to 5 wt%. % Is more preferred. By setting the content of the red light emitting material in such a range, the light emission efficiency can be optimized, and the red light emitting layer is balanced with the light emitting amount of the blue light emitting layer 63 and the green light emitting layer 64 described later. 61 can emit light.
Moreover, although the average thickness of the red light emitting layer 61 is not specifically limited, It is preferable that it is about 1-20 nm, and it is more preferable that it is about 3-5 nm.

(Middle layer)
The intermediate layer 62 is provided between and in contact with the red light emitting layer 61 described above and a blue light emitting layer 63 described later. The intermediate layer 62 has a function of adjusting the amount of electrons transported from the blue light emitting layer 63 to the red light emitting layer 61. The intermediate layer 62 has a function of adjusting the amount of holes transported from the red light emitting layer 61 to the blue light emitting layer 63. The intermediate layer 62 has a function of preventing exciton energy from moving between the red light emitting layer 61 and the blue light emitting layer 63. With this function, the red light emitting layer 61 and the blue light emitting layer 63 can each emit light efficiently. As a result, each light emitting layer can emit light in a well-balanced manner, and the light emitting element 1 can emit the target color (white in the present embodiment), and the light emission efficiency and light emission lifetime of the light emitting element 1. Can be improved.

The constituent material of the intermediate layer 62 is not particularly limited as long as the intermediate layer 62 can exhibit the functions as described above. For example, a material having a function of transporting holes (a positive layer) Hole transport material), a material having a function of transporting electrons (electron transport material), and the like can be used.
The hole transport material used for such an intermediate layer 62 is not particularly limited as long as the intermediate layer 62 exhibits the function as described above. An amine-based material having a skeleton can be used, but a benzidine-based amine derivative is preferably used.

  In particular, among benzidine-based amine derivatives, the amine-based material used for the intermediate layer 62 is preferably a material into which two or more aromatic ring groups are introduced, and a tetraarylbenzidine derivative is more preferable. Examples of such benzidine-based amine derivatives include N, N′-bis (1-naphthyl) -N, N′-diphenyl [1,1′-biphenyl] -4,4 represented by the formula (4). Examples include '-diamine (α-NPD) and N, N, N', N'-tetranaphthyl-benzidine (TNB). Such an amine-based material is generally excellent in hole transportability. Therefore, holes can be smoothly transferred from the red light emitting layer 61 to the blue light emitting layer 63 via the intermediate layer 62.

  The electron transport material that can be used for the intermediate layer 62 is not particularly limited as long as the intermediate layer 62 exhibits the functions described above, and for example, an acene-based material can be used. Since the acene-based material is excellent in electron transport properties, electrons can be smoothly transferred from the blue light emitting layer 63 to the red light emitting layer 61 through the intermediate layer 62. In addition, since the acene-based material has an excellent structure for excitons, deterioration of the intermediate layer 62 due to excitons can be prevented or suppressed, and as a result, the durability of the light-emitting element 1 can be improved.

Examples of such acene-based materials include naphthalene derivatives, anthracene derivatives, tetracene derivatives, pentacene derivatives, hexacene derivatives, heptacene derivatives, and the like, and one or more of these can be used in combination. , Naphthalene derivatives and anthracene derivatives are preferably used, and anthracene derivatives are more preferably used. Examples of the anthracene derivative include an anthracene derivative represented by the formula (8), 2-t-butyl-9,10-di-2-naphthylanthracene (TBADN), and the like.
Further, the average thickness of the intermediate layer 62 is not particularly limited, but is preferably about 5 to 50 nm, and more preferably about 10 to 30 nm.

(Blue light emitting layer)
The blue light emitting layer (second light emitting layer) 63 includes a blue light emitting material (second light emitting material) that emits blue light (second color).
Such a blue light emitting material is not particularly limited, and various blue fluorescent materials and blue phosphorescent materials can be used alone or in combination of two or more.

  The blue fluorescent material is not particularly limited as long as it emits blue fluorescence. For example, a distyrylamine derivative such as a distyryldiamine compound represented by the following formula (10), a fluoranthene derivative, a pyrene derivative, perylene And perylene derivatives, anthracene derivatives, benzoxazole derivatives, benzothiazole derivatives, benzimidazole derivatives, chrysene derivatives, phenanthrene derivatives, distyrylbenzene derivatives, tetraphenylbutadiene, 4,4'-bis (9-ethyl-3-carbazovinylene)- 1,1′-biphenyl (BCzVBi), poly [(9.9-dioctylfluorene-2,7-diyl) -co- (2,5-dimethoxybenzene-1,4-diyl)], poly [(9, 9-dihexyloxyfluorene-2,7-diyl -Ortho-co- (2-methoxy-5- {2-ethoxyhexyloxy} phenylene-1,4-diyl)], poly [(9,9-dioctylfluorene-2,7-diyl) -co- (ethyl Nilbenzene)] and the like, and one of these may be used alone or two or more of them may be used in combination.

The blue phosphorescent material is not particularly limited as long as it emits blue phosphorescence, and examples thereof include metal complexes such as iridium, ruthenium, platinum, osmium, rhenium, and palladium. More specifically, bis [4,6-difluorophenyl pyridinium sulfonate -N, ^{C 2} '] - picolinate - iridium, tris [2- (2,4-difluorophenyl) pyridinate -N, ^{C 2']} iridium , bis [2- (3,5-trifluoromethyl) pyridinate -N, ^{C 2} '] - picolinate - iridium, bis (4,6-difluorophenyl pyridinium sulfonate -N, ^{C 2')} iridium (acetylacetonate ).

Further, as a constituent material of the blue light emitting layer 63, in addition to the blue light emitting material as described above, a host material (second host material) using the blue light emitting material as a guest material may be used. As the second host material that can be used for the blue light-emitting layer 63, the same host material as the first host material of the red light-emitting layer 61 described above can be used.
When the blue light emitting layer 63 includes the second host material, the content (dope amount) of the blue light emitting material in the blue light emitting layer 63 is preferably 0.01 to 20 wt%, and preferably 1 to 15 wt%. Is more preferable. By setting the content of the blue light emitting material within such a range, the light emission efficiency can be optimized, and the blue light emitting layer is balanced with the light emitting amount of the red light emitting layer 61 and the green light emitting layer 64 described later. 63 can emit light.
The average thickness of the blue light-emitting layer 63 is not particularly limited, but is preferably about 5 to 50 nm, and more preferably about 10 to 40 nm.

(Green light emitting layer)
The green light emitting layer (third light emitting layer) 64 includes a green light emitting material (third light emitting material) that emits green light (third color).
Such a green light emitting material is not particularly limited, and various green fluorescent materials and green phosphorescent materials can be used singly or in combination.

  The green fluorescent material is not particularly limited as long as it emits green fluorescence. For example, coumarin derivatives, quinacridones such as quinacridone derivatives represented by the following formula (11) and derivatives thereof, 9,10-bis [(9- Ethyl-3-carbazole) -vinylenyl] -anthracene, poly (9,9-dihexyl-2,7-vinylenefluorenylene), poly [(9,9-dioctylfluorene-2,7-diyl) -co- ( 1,4-diphenylene-vinylene-2-methoxy-5- {2-ethylhexyloxy} benzene)], poly [(9,9-dioctyl-2,7-divinylenefluorenylene) -ortho-co- (2 -Methoxy-5- (2-ethoxylhexyloxy) -1,4-phenylene)], etc., and one of these may be used alone or two or more may be combined. It is also possible to use Te Align.

The green phosphorescent material is not particularly limited as long as it emits green phosphorescence, and examples thereof include metal complexes such as iridium, ruthenium, platinum, osmium, rhenium, and palladium. Among these, at least one of the ligands of these metal complexes preferably has a phenylpyridine skeleton, a bipyridyl skeleton, a porphyrin skeleton, or the like. More specifically, fac - tris (2-phenylpyridine) iridium (Ir (ppy) 3), bis (2-phenyl-pyridinium sulfonate -N, ^{C 2} ') iridium (acetylacetonate), fac - tris [ 5-fluoro-2- (5-trifluoromethyl-2-pyridine) phenyl-C, N] iridium.
Further, the green light emitting layer 64 may contain a host material (third host material). As the third host material of the green light emitting layer 64, the same host material as the host material of the red light emitting layer 61 described above can be used.

When the green light emitting layer 64 includes the third host material, the content (dope amount) of the green light emitting material in the green light emitting layer 64 is preferably 0.01 to 20 wt%, and 0.5 to 15 wt%. It is more preferable that By setting the content of the green light emitting material in such a range, the light emission efficiency can be optimized, and the green light emitting layer 64 can be formed while balancing the light emitting amount of the red light emitting layer 61 and the blue light emitting layer 63. Can emit light.
Moreover, the average thickness of the green light emitting layer 64 is not particularly limited, but is preferably about 5 to 50 nm, and more preferably about 10 to 40 nm.

(Electron transport layer)
The electron transport layer 7 has a function of transporting electrons injected from the cathode 9 through the electron injection layer 8 to the green light emitting layer 64.
As a constituent material (electron transport material) of the electron transport layer 7, for example, 8-quinolinol or a derivative thereof such as tris (8-quinolinolato) aluminum (Alq ₃ ) represented by the following formula (12) is used as a ligand. Examples include quinoline derivatives such as organometallic complexes, oxadiazole derivatives, perylene derivatives, pyridine derivatives, pyrimidine derivatives, quinoxaline derivatives, diphenylquinone derivatives, nitro-substituted fluorene derivatives, compounds represented by the following formula (13), and the like. One or two or more of them can be used in combination.

  Although the average thickness of the electron carrying layer 7 is not specifically limited, It is preferable that it is about 0.5-100 nm, and it is more preferable that it is about 1-50 nm.

(Electron injection layer)
The electron injection layer 8 has a function of improving the electron injection efficiency from the cathode 9.
Examples of the constituent material (electron injection material) of the electron injection layer 8 include various inorganic insulating materials and various inorganic semiconductor materials.

  Examples of such inorganic insulating materials include alkali metal chalcogenides (oxides, sulfides, selenides, tellurides), alkaline earth metal chalcogenides, alkali metal halides, and alkaline earth metal halides. Of these, one or two or more of these can be used in combination. By forming the electron injection layer using these as main materials, the electron injection property can be further improved. In particular, alkali metal compounds (alkali metal chalcogenides, alkali metal halides, and the like) have a very low work function, and the light-emitting element 1 can be obtained with high luminance by forming the electron injection layer 8 using the work function. Become.

Examples of the alkali metal chalcogenide include Li ₂ O, LiO, Na ₂ S, Na ₂ Se, and NaO.
Examples of the alkaline earth metal chalcogenide include CaO, BaO, SrO, BeO, BaS, MgO, and CaSe.
Examples of the alkali metal halide include CsF, LiF, NaF, KF, LiCl, KCl, and NaCl.
Examples of the alkaline earth metal halide include CaF ₂ , BaF ₂ , SrF ₂ , MgF ₂ , and BeF ₂ .

In addition, as the inorganic semiconductor material, for example, an oxide including at least one element of Li, Na, Ba, Ca, Sr, Yb, Al, Ga, In, Cd, Mg, Si, Ta, Sb, and Zn , Nitrides, oxynitrides, and the like, and one or more of these can be used in combination.
The average thickness of the electron injection layer 8 is not particularly limited, but is preferably about 0.1 to 1000 nm, more preferably about 0.2 to 100 nm, and about 0.2 to 50 nm. Further preferred.

(Sealing member)
The sealing member 10 is provided so as to cover the anode 3, the laminate 15, and the cathode 9, and has a function of hermetically sealing them and blocking oxygen and moisture. By providing the sealing member 10, effects such as improvement of the reliability of the light emitting element 1 and prevention of deterioration / deterioration (improvement of durability) can be obtained.
Examples of the constituent material of the sealing member 10 include Al, Au, Cr, Nb, Ta, Ti, alloys containing these, silicon oxide, various resin materials, and the like. In addition, when using the material which has electroconductivity as a constituent material of the sealing member 10, in order to prevent a short circuit, it is required between the sealing member 10 and the anode 3, the laminated body 15, and the cathode 9. Accordingly, it is preferable to provide an insulating film.
Further, the sealing member 10 may be formed in a flat plate shape so as to face the substrate 2 and be sealed with a sealing material such as a thermosetting resin.
According to the light-emitting element 1 configured as described above, the hole injection layer 4 includes the cyano group-containing quinoxaline derivative, so that holes are efficiently injected into the light-emitting portion 6 and the driving voltage of the light-emitting element 1 is increased. It will be low. In addition, since the light can be efficiently emitted at a low voltage, the light emission lifetime of the light emitting element 1 is also long.

The above light emitting element 1 can be manufactured as follows, for example.
[1] First, the substrate 2 is prepared, and the anode 3 is formed on the substrate 2.
The anode 3 is, for example, a chemical vapor deposition method (CVD) such as plasma CVD or thermal CVD, a dry plating method such as vacuum deposition, a wet plating method such as electrolytic plating, a thermal spraying method, a sol-gel method, a MOD method, or a metal foil. It can be formed by using, for example, bonding.

[2] Next, the hole injection layer 4 is formed on the anode 3.
The hole injection layer 4 can be formed by, for example, a vapor phase process using a CVD method, a dry plating method such as vacuum deposition or sputtering, or the like.
In addition, the hole injection layer 4 is dried (desolvent or desolvent) after supplying the hole injection layer forming material obtained by, for example, dissolving the hole injection material in a solvent or dispersing in a dispersion medium onto the anode 3. It can also be formed by using a dispersion medium.

As a method for supplying the hole injection layer forming material, for example, various coating methods such as a spin coating method, a roll coating method, and an ink jet printing method can be used. By using such a coating method, the hole injection layer 4 can be formed relatively easily.
Examples of the solvent or dispersion medium used for the preparation of the hole injection layer forming material include various inorganic solvents, various organic solvents, or mixed solvents containing these.
The drying can be performed, for example, by standing in an atmospheric pressure or a reduced pressure atmosphere, heat treatment, or blowing an inert gas.

Prior to this step, the upper surface of the anode 3 may be subjected to oxygen plasma treatment. Thereby, it is possible to impart lyophilicity to the upper surface of the anode 3, remove (clean) organic substances adhering to the upper surface of the anode 3, adjust the work function near the upper surface of the anode 3, and the like. .
Here, the oxygen plasma treatment conditions include, for example, a plasma power of about 100 to 800 W, an oxygen gas flow rate of about 50 to 100 mL / min, a conveyance speed of the member to be treated (anode 3) of about 0.5 to 10 mm / sec, and a substrate. The temperature of 2 is preferably about 70 to 90 ° C.
When the cyano group-containing quinoxaline derivative has a quinoxaline monomer or dimer as a skeleton, the hole injection layer 4 can be suitably formed using a gas phase process.

[3] Next, the hole transport layer 5 is formed on the hole injection layer 4.
The hole transport layer 5 can be formed, for example, by a vapor phase process using a CVD method, a dry plating method such as vacuum deposition or sputtering.
Further, by supplying a hole transport layer forming material obtained by dissolving a hole transport material in a solvent or dispersing in a dispersion medium onto the hole injection layer 4, drying (desolvation or dedispersion medium) is performed. Can also be formed.

[4] Next, the red light emitting layer 61 is formed on the hole transport layer 5.
The red light emitting layer 61 can be formed by, for example, a vapor phase process using a CVD method, a dry plating method such as vacuum deposition or sputtering, or the like.
[5] Next, the intermediate layer 62 is formed on the red light emitting layer 61.
The intermediate layer 62 can be formed by, for example, a vapor phase process using a CVD method, a dry plating method such as vacuum deposition or sputtering, or the like.

[6] Next, the blue light emitting layer 63 is formed on the intermediate layer 62.
The blue light emitting layer 63 can be formed by, for example, a vapor phase process using a CVD method, a dry plating method such as vacuum deposition or sputtering, or the like.
[7] Next, the green light emitting layer 64 is formed on the blue light emitting layer 63.
The green light emitting layer 64 can be formed by, for example, a vapor phase process using a CVD method, a dry plating method such as vacuum deposition, sputtering, or the like.

[8] Next, the electron transport layer 7 is formed on the green light emitting layer 64.
The electron transport layer 7 can be formed by, for example, a vapor phase process using a CVD method, a dry plating method such as vacuum deposition, sputtering, or the like.
In addition, the electron transport layer 7 is dried (desolvent or dedispersed) after supplying an electron transport layer forming material obtained by, for example, dissolving an electron transport material in a solvent or dispersing in a dispersion medium onto the green light emitting layer 64. It can also be formed by the medium.

[9] Next, the electron injection layer 8 is formed on the electron transport layer 7.
In the case where an inorganic material is used as the constituent material of the electron injection layer 8, the electron injection layer 8 is formed by, for example, a vapor phase process using a CVD method, a dry plating method such as vacuum deposition or sputtering, or the application and baking of inorganic fine particle ink. Etc. can be used.
[10] Next, the cathode 9 is formed on the electron injection layer 8.
The cathode 9 can be formed by using, for example, a vacuum deposition method, a sputtering method, bonding of metal foil, application and firing of metal fine particle ink, or the like.
The light emitting element 1 is obtained through the steps as described above.
Finally, the sealing member 10 is covered so as to cover the obtained light emitting element 1 and bonded to the substrate 2.

<Second Embodiment>
FIG. 2 is a view schematically showing a longitudinal section of a second embodiment of the light emitting device of the present invention. In the following description, for convenience of explanation, the upper side in FIG. 2, that is, the cathode 9 side is described as “up”, and the lower side, that is, the anode 3 side is described as “lower”.
The light emitting element 1A according to the present embodiment is the same as the light emitting element 1 of the first embodiment described above except that the light emitting portion 6A is a single light emitting layer.

The light emitting unit 6A is configured to include a light emitting material.
The light-emitting material that can be used for the light-emitting portion 6A is not particularly limited, and the above-described red light-emitting material, blue light-emitting material, green light-emitting material, and the like can be appropriately used singly or in combination.
In addition, the light emitting portion 6A may include a host material that supports the light emitting material.
As such a host material, the host material which can be used for the red light emitting layer 61 of 1st Embodiment mentioned above is mentioned.
Even with the configuration as described above, the same effects as those of the first embodiment of the present invention can be obtained.

The light-emitting elements 1 and 1A as described above can be used for, for example, a light-emitting device (the light-emitting device of the present invention).
Since such a light-emitting device includes the light-emitting elements 1 and 1A as described above, the light-emitting device can be driven at a relatively low voltage.
Further, such a light emitting device can be used as a light source used for illumination, for example.
Moreover, the light-emitting device used for a display apparatus can be comprised by arrange | positioning the several light emitting element 1 in a light-emitting device in matrix form.

Next, an example of a display device to which the display device of the present invention is applied will be described.
FIG. 2 is a longitudinal sectional view showing an embodiment of a display device to which the display device of the present invention is applied.
The display device 100 illustrated in FIG. 2 includes a light emitting device 101 including a plurality of light emitting elements 1R, 1G, and 1B provided corresponding to the sub-pixels 100R, 100G, and 100B, and color filters 19R, 19G, and 19B. ing. Here, the display device 100 is a display panel having a top emission structure. The driving method of the display device is not particularly limited, and may be either an active matrix method or a passive matrix method.

The light emitting device 101 includes a substrate 21, light emitting elements 1R, 1G, and 1B, and a driving transistor 24.
A plurality of driving transistors 24 are provided on the substrate 21, and a planarizing layer 22 made of an insulating material is formed so as to cover these driving transistors 24.
Each driving transistor 24 includes a semiconductor layer 241 made of silicon, a gate insulating layer 242 formed on the semiconductor layer 241, a gate electrode 243 formed on the gate insulating layer 242, a source electrode 244, and a drain electrode. H.245.
On the planarization layer 22, light emitting elements 1R, 1G, and 1B are provided corresponding to the driving transistors 24, respectively.

  In the light emitting element 1 </ b> R, the reflective film 32, the corrosion prevention film 33, the anode 3, the stacked body 15, the cathode 9, and the cathode cover 34 are stacked in this order on the planarizing layer 22. In the present embodiment, the anode 3 of each light emitting element 1R, 1G, 1B constitutes a pixel electrode and is electrically connected to the drain electrode 245 of each driving transistor 24 by a conductive portion (wiring) 27. The cathodes 9 of the light emitting elements 1R, 1G, and 1B are common electrodes.

The configurations of the light emitting elements 1G and 1B are the same as the configuration of the light emitting element 1R. In FIG. 2, the same reference numerals are assigned to the same configurations as those in FIG. 1. Further, the configuration (characteristics) of the reflective film 32 may be different among the light emitting elements 1R, 1G, and 1B depending on the wavelength of light.
A partition wall 31 is provided between the adjacent light emitting elements 1R, 1G, and 1B.
Further, an epoxy layer 35 made of an epoxy resin is formed on the light emitting device 101 thus configured so as to cover it.

The color filters 19R, 19G, and 19B are provided on the epoxy layer 35 described above corresponding to the light emitting elements 1R, 1G, and 1B.
The color filter 19R converts the white light W from the light emitting element 1R into red. The color filter 19G converts the white light W from the light emitting element 1G into green. The color filter 19B converts the white light W from the light emitting element 1B into blue. By using such color filters 19R, 19G, and 19B in combination with the light emitting elements 1R, 1G, and 1B, a full color image can be displayed.

A light shielding layer 36 is formed between the adjacent color filters 19R, 19G, and 19B. Thereby, it is possible to prevent the unintended subpixels 100R, 100G, and 100B from emitting light.
A sealing substrate 20 is provided on the color filters 19R, 19G, 19B and the light shielding layer 36 so as to cover them.

The display device 100 as described above may be a single color display, and color display is also possible by selecting a light emitting material used for each light emitting element 1R, 1G, 1B.
Such a display device 100 (display device of the present invention) can be driven at a relatively low voltage because it uses the light emitting device as described above. Therefore, a high-quality image can be displayed with low power consumption.

FIG. 3 is a perspective view showing the configuration of a mobile (or notebook) personal computer to which the electronic apparatus of the present invention is applied.
In this figure, a personal computer 1100 includes a main body 1104 provided with a keyboard 1102 and a display unit 1106 provided with a display. The display unit 1106 is rotatable with respect to the main body 1104 via a hinge structure. It is supported by.
In the personal computer 1100, the display unit included in the display unit 1106 is configured by the display device 100 described above.

FIG. 4 is a perspective view showing a configuration of a mobile phone (including PHS) to which the electronic apparatus of the present invention is applied.
In this figure, a cellular phone 1200 includes a plurality of operation buttons 1202, an earpiece 1204 and a mouthpiece 1206, and a display unit.
In the cellular phone 1200, the display unit is configured by the display device 100 described above.

FIG. 5 is a perspective view showing a configuration of a digital still camera to which the electronic apparatus of the present invention is applied. In this figure, connection with an external device is also simply shown.
Here, an ordinary camera sensitizes a silver salt photographic film with a light image of a subject, whereas a digital still camera 1300 photoelectrically converts a light image of a subject with an image sensor such as a CCD (Charge Coupled Device). An imaging signal (image signal) is generated.

A display unit is provided on the back of a case (body) 1302 in the digital still camera 1300, and is configured to display based on an imaging signal from the CCD, and functions as a finder that displays an object as an electronic image.
In the digital still camera 1300, the display unit is configured by the display device 100 described above.

A circuit board 1308 is installed inside the case. The circuit board 1308 is provided with a memory that can store (store) an imaging signal.
A light receiving unit 1304 including an optical lens (imaging optical system), a CCD, and the like is provided on the front side of the case 1302 (on the back side in the illustrated configuration).
When the photographer confirms the subject image displayed on the display unit and presses the shutter button 1306, the CCD image pickup signal at that time is transferred and stored in the memory of the circuit board 1308.

  In the digital still camera 1300, a video signal output terminal 1312 and an input / output terminal 1314 for data communication are provided on the side surface of the case 1302. As shown in the figure, a television monitor 1430 is connected to the video signal output terminal 1312 and a personal computer 1440 is connected to the data communication input / output terminal 1314 as necessary. Further, the imaging signal stored in the memory of the circuit board 1308 is output to the television monitor 1430 or the personal computer 1440 by a predetermined operation.

  The electronic apparatus of the present invention includes, for example, a television, a video camera, a viewfinder type, in addition to the personal computer (mobile personal computer) in FIG. 3, the mobile phone in FIG. 4, and the digital still camera in FIG. Monitor direct-view video tape recorder, laptop personal computer, car navigation system, pager, electronic notebook (including communication function), electronic dictionary, calculator, electronic game device, word processor, workstation, video phone, security TV Monitors, electronic binoculars, POS terminals, devices equipped with touch panels (for example, cash dispensers and automatic ticket vending machines for financial institutions), medical devices (for example, electronic thermometers, blood pressure monitors, blood glucose meters, electrocardiographs, ultrasound diagnostic devices, internal Endoscope display device), fish finder, various measuring instruments, Vessels such (e.g., gages for vehicles, aircraft, and ships), a flight simulator, various monitors, and a projection display such as a projector.

The light emitting element, the light emitting device, the display device, and the electronic device of the present invention have been described based on the illustrated embodiments, but the present invention is not limited to these.
For example, in the above-described embodiment, the light emitting element has one layer or three layers, but the light emitting layer may be two layers or four layers or more. Even in such a case, the effects as described above can be obtained by including a common host material in each light emitting layer. Further, the emission color of the light emitting layer is not limited to R, G, and B in the above-described embodiment.
In addition, for example, in the above-described embodiment, various derivatives such as a cyano group-containing quinoxaline derivative do not necessarily have to be produced from the basic skeleton.

Next, specific examples of the present invention will be described.
1. Production of light emitting device (Example 1)
<1> First, a transparent glass substrate having an average thickness of 0.5 mm was prepared. Next, an ITO electrode (anode) having an average thickness of 50 nm was formed on the substrate by sputtering.
And after immersing a board | substrate in order of acetone and 2-propanol and ultrasonically cleaning, the oxygen plasma process was performed.

<2> Next, a cyano group-containing quinoxaline derivative ([2.2 ′] Biquinoxalinly-6,7,6 ′, 7′-teracarbonitrile) represented by the above formula (5-5) is deposited on the ITO electrode by a vacuum deposition method. Vapor deposition was performed to form a hole injection layer having an average thickness of 40 nm.
<3> Next, on the hole injection layer, N, N′-bis (1-naphthyl) -N, N′-diphenyl [1,1′-biphenyl] -4, represented by the formula (4), 4′-diamine (α-NPD) was deposited by a vacuum deposition method to form a hole transport layer having an average thickness of 10 nm.

  <4> Next, the constituent material of the red light-emitting layer was deposited on the hole transport layer by a vacuum vapor deposition method to form a red light-emitting layer (first light-emitting layer) having an average thickness of 10 nm. As a constituent material of the red light emitting layer, a tetraaryldiindenoperylene derivative represented by the above formula (7) was used as a red light emitting material (guest material), and a naphthacene derivative represented by the above formula (9) was used as a host material. . The content (dope concentration) of the light emitting material (dopant) in the red light emitting layer was 1.0 wt%.

<5> Next, the constituent material of the intermediate layer was vapor-deposited on the red light emitting layer by a vacuum vapor deposition method to form an intermediate layer having an average thickness of 7 nm. As a constituent material of the intermediate layer, N, N′-bis (1-naphthyl) -N, N′-diphenyl [1,1′-biphenyl] -4,4′-diamine represented by the above formula (4) ( α-NPD) was used.
<6> Next, the constituent material of the blue light-emitting layer was deposited on the intermediate layer by a vacuum vapor deposition method to form a blue light-emitting layer (second light-emitting layer) having an average thickness of 10 nm. As a constituent material of the blue light emitting layer, a distyryldiamine compound represented by the above formula (10) was used as a blue light emitting material, and an anthracene derivative represented by the above formula (8) was used. Further, the content (dope concentration) of the blue light emitting material (dopant) in the blue light emitting layer was 6.0 wt%.

  <7> Next, the constituent material of the green light emitting layer was deposited on the blue light emitting layer by a vacuum deposition method, thereby forming a green light emitting layer (third light emitting layer) having an average thickness of 30 nm. As a constituent material of the green light emitting layer, a quinacridone derivative represented by the above formula (11) was used as a green light emitting material (guest material), and an anthracene derivative represented by the above formula (8) was used as a host material. Further, the content (dope concentration) of the green light emitting material (dopant) in the green light emitting layer was 1.0 wt%.

<8> Next, on the green light-emitting layer, tris (8-quinolinolato) aluminum (Alq ₃ ) represented by the above formula (12) is formed by vacuum deposition to form an electron transport layer having an average thickness of 10 nm. did.
<9> Next, on the electron transport layer, lithium fluoride (LiF) was formed by a vacuum vapor deposition method, thereby forming an electron injection layer having an average thickness of 1 nm.

<10> Next, Al was formed into a film by the vacuum evaporation method on the electron injection layer. Thereby, a cathode having an average thickness of 100 nm made of Al was formed.
<11> Next, a glass protective cover (sealing member) was placed over the formed layers, and fixed and sealed with an epoxy resin.
Through the above steps, a light emitting device as shown in FIG. 1 that emits white light was manufactured.

(Example 2)
As a constituent material of the hole injection layer, the cyano group-containing quinoxaline derivative ([2.2 '] Biquinoxalinly-3,6,7,3', 6 ', 7'-hexacarbonitrile) represented by the above formula (5-6) is used. A light emitting device was manufactured in the same manner as in Example 1 except that.
Example 3
As the constituent material of the hole injection layer, a cyano group-containing quinoxaline derivative ([Quinoxaline-2,3,6,7-teracarbonitrile) represented by the above formula (5-1) is used, and the average thickness of the hole injection layer is determined. A light emitting device was manufactured in the same manner as in Example 1 except that the average thickness of the hole transport layer was 2 nm and 2 nm.

(Comparative Example 1)
As the constituent material of the hole injection layer, a quinoxaline derivative not containing a cyano group represented by the following formula (14) was used, the average thickness of the hole injection layer was 40 nm, and the average thickness of the hole transport layer was 20 nm. A light emitting device was manufactured in the same manner as in Example 1 except for the above.

(Comparative Example 2)
As a constituent material of the hole injection layer, N, N′-bis- (4-diphenylamino-phenyl) -N, N′-diphenyl-biphenyl-4-4′-diamine represented by the above formula (6) is used. A light emitting device was manufactured in the same manner as in Example 1 except that the average thickness of the hole injection layer was 40 nm and the average thickness of the hole transport layer was 20 nm.

2. Evaluation 2-1. Evaluation of luminous efficiency and driving voltage For the light emitting devices of Examples 1 to 3 and Comparative Examples 1 and ^2, a constant current of 10 mA / cm ² was passed through the light emitting device using a DC power source, and the luminance was measured using a luminance meter. . Luminous efficiency (cd / A, luminance per current) was determined from the measured luminance. Further, the driving voltage (V) at this time was measured.

2-2. Evaluation of Luminous Life For the light-emitting elements of Examples 1 to 3 and Comparative Examples 1 and 2, the light-emitting element was caused to emit light with a constant initial luminance using a DC power source, and the luminance was measured using a luminance meter. The time to reach 80% of the luminance (LT80) was measured.
Table 1 shows the evaluation results.

  As is apparent from Table 1, the light emitting elements of Examples 1 to 3 had a lower driving voltage than the light emitting elements of Comparative Examples 1 and 2 under use conditions where the current density was constant. In addition, the light emitting elements of Examples 1 to 3 had a longer light emission lifetime than the light emitting elements of Comparative Examples 1 and 2.

3. Production of light emitting device (Example 4)
<1> First, a transparent glass substrate having an average thickness of 0.5 mm was prepared. Next, an ITO electrode (anode) having an average thickness of 50 nm was formed on the substrate by sputtering.
And after immersing a board | substrate in order of acetone and 2-propanol and ultrasonically cleaning, the oxygen plasma process was performed.

<2> Next, a cyano group-containing quinoxaline derivative ([2.2 ′] Biquinoxalinly-6,7,6 ′, 7′-teracarbonitrile) represented by the above formula (5-5) is deposited on the ITO electrode by a vacuum deposition method. Vapor deposition was performed to form a hole injection layer having an average thickness of 40 nm.
<3> Next, on the hole injection layer, N, N′-bis (1-naphthyl) -N, N′-diphenyl [1,1′-biphenyl] -4, represented by the formula (4), 4′-diamine (α-NPD) was deposited by a vacuum deposition method to form a hole transport layer having an average thickness of 10 nm.

  <4> Next, the constituent material of the light emitting layer was vapor-deposited on the hole transport layer by a vacuum vapor deposition method to form a light emitting layer (light emitting portion) having an average thickness of 40 nm. As a constituent material of the light emitting layer, a tetraaryldiindenoperylene derivative represented by the above formula (7) was used as a red light emitting material (guest material), and a naphthacene derivative represented by the above formula (9) was used as a host material. Further, the content (dope concentration) of the light emitting material (dopant) in the red light emitting layer was 1.0 wt%.

<5> Next, the compound represented by the formula (13) was formed on the light-emitting layer by a vacuum deposition method to form an electron transport layer having an average thickness of 20 nm.
<6> Next, on the electron transport layer, lithium fluoride (LiF) was formed by a vacuum deposition method to form an electron injection layer having an average thickness of 1 nm.
<7> Next, Al was formed into a film by the vacuum evaporation method on the electron injection layer. Thereby, a cathode having an average thickness of 100 nm made of Al was formed.
<8> Next, a glass protective cover (sealing member) was placed over the formed layers, and fixed and sealed with an epoxy resin.
Through the above steps, a light emitting device as shown in FIG.

(Example 5)
The cyano group-containing quinoxaline derivative ([2.2 '] Biquinoxalinly-3,6,7,3', 6 ', 7'-hexacarbonitrile) represented by the above formula (5-6) is used as the constituent material of the hole injection layer. A light emitting device was manufactured in the same manner as in Example 4 except that.
(Example 6)
As the constituent material of the hole injection layer, a cyano group-containing quinoxaline derivative ([Quinoxaline-2,3,6,7-teracarbonitrile) represented by the above formula (5-1) is used, and the average thickness of the hole injection layer is determined. A light emitting device was manufactured in the same manner as in Example 4 except that the average thickness of the hole transport layer was set to 2 nm and 2 nm.

(Comparative Example 3)
As the constituent material of the hole injection layer, a quinoxaline derivative not containing a cyano group represented by the formula (14) was used, the average thickness of the hole injection layer was 40 nm, and the average thickness of the hole transport layer was 10 nm. A light emitting device was manufactured in the same manner as in Example 4 except for the above.
(Comparative Example 4)
As a constituent material of the hole injection layer, N, N′-bis- (4-diphenylamino-phenyl) -N, N′-diphenyl-biphenyl-4-4′-diamine represented by the above formula (6) is used. A light emitting device was manufactured in the same manner as in Example 4 except that the average thickness of the hole injection layer was 40 nm and the average thickness of the hole transport layer was 10 nm.

4). Evaluation 4-1. Evaluation of Luminous Efficiency and Driving Voltage For the light emitting devices of Examples 4 to 6 and Comparative Examples 3 and 4, a constant current of 10 mA / cm ² was passed through the light emitting device using a DC power source, and the luminance was measured using a luminance meter. . Luminous efficiency (cd / A, luminance per current) was determined from the measured luminance. Further, the driving voltage (V) at this time was measured.

4-2. Evaluation of Luminous Life For the light-emitting elements of Examples 4 to 6 and Comparative Examples 3 and 4, the light-emitting element was caused to emit light with a constant initial luminance using a DC power supply, and the luminance was measured using a luminance meter. The time to reach 80% of the luminance (LT80) was measured.
Table 2 shows the evaluation results.

  As is clear from Table 2, the light emitting elements of Examples 4 to 6 had a lower driving voltage than the light emitting elements of Comparative Examples 3 and 4 under the use conditions where the current density was constant. In addition, the light emitting elements of Examples 4 to 6 had a longer light emission lifetime than the light emitting elements of Comparative Examples 3 and 4.

  1, 1A, 1B, 1G, 1R ... Light emitting element 2 ... Substrate 3 ... Anode 4 ... Hole injection layer 5 ... Hole transport layer 6, 6A ... Light emitting part 61 ... Red light emitting layer (first 62 ... Intermediate layer 63 ... Blue light-emitting layer (second light-emitting layer) 64 ... Green light-emitting layer (third light-emitting layer) 7 ... Electron transport layer 8 ... Electron injection layer 9 ... ... Cathode 10 ... Sealing member 15 ... Laminate 19B, 19G, 19R ... Color filter 100 ... Display device 101 ... Light emitting device 100R, 100G, 100B ... Sub-pixel 20 ... Sealing substrate 21 ... Substrate 22 ... Planarization layer 24 ... Driving transistor 241 ... Semiconductor layer 242 ... Gate insulating layer 243 ... Gate electrode 244 ... Source electrode 245 ... Drain electrode 27 ... Wiring 31 ... Partition 32 ... Anti Film 33 ... Corrosion prevention film 34 ... Cathode cover 35 ... Epoxy layer 36 ... Shading layer 1100 ... Personal computer 1102 ... Keyboard 1104 ... Body 1106 ... Display unit 1200 ... Mobile phone 1202 ... Operation Button 1204 ...... Earpiece 1206 ...... Mouthpiece 1300 ...... Digital still camera 1302 ...... Case (body) 1304 ...... Light receiving unit 1306 ...... Shutter button 1308 ...... Circuit board 1312 ...... Video signal output terminal 1314 …… Input / output terminal for data communication 1430 …… TV monitor 1440 …… Personal computer

Claims (11)

A cathode,
The anode,
A light emitting portion that is provided between the cathode and the anode and emits light when a driving voltage is applied;
A hole injection layer that is provided between the anode and the light emitting unit and injects holes into the cathode side layer;
The light-emitting element, wherein the hole injection layer includes a quinoxaline derivative having a cyano group.   The light-emitting element according to claim 1, wherein the quinoxaline derivative contains two or more cyano groups in the molecule.   The light-emitting element according to claim 1, wherein the quinoxaline derivative has a quinoxaline dimer as a skeleton. The light-emitting element according to claim 3, wherein the quinoxaline derivative is a compound represented by the following formula (1) or the following formula (2).

  The light-emitting element according to claim 1, wherein the quinoxaline derivative has a quinoxaline monomer as a skeleton. The light-emitting element according to claim 5, wherein the quinoxaline derivative is a compound represented by the following formula (3).

A hole transport layer that is provided between the hole injection layer and the light emitting part and transports holes to the cathode side layer;
The light-emitting element according to claim 1, wherein the hole transport layer includes an amine material. The light emitting device according to claim 7, wherein the amine material is a compound represented by the following formula (4).

  A light-emitting device comprising the light-emitting element according to claim 1.   A display device comprising the light emitting device according to claim 9.   An electronic apparatus comprising the display device according to claim 10.

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