JP2015201279A - Light-emitting element, light-emitting device, display device and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting element having excellent light-emitting characteristics and life characteristics maintaining the light-emitting characteristics for a long period of time, and further to provide a light-emitting device being provided with the light-emitting element and being excellent in reliability, a display device and an electronic apparatus.SOLUTION: A light-emitting element 1 includes: a negative electrode 9; a positive electrode 3; a light-emitting section 6 provided between the negative electrode 9 and the positive electrode 3; and an electron transport layer 7 provided between the negative electrode 9 and the light-emitting section 6. The light-emitting section 6 is provided with a first light-emitting layer 61 and a second light-emitting layer 62 laminated from a positive electrode 3 side to a negative electrode 9 side. The electron transport layer 7 is provided so as to be brought into contact with the second light-emitting layer 62. The first light-emitting layer 61 is configured so as to contain a light-emitting material, a host material and an assist dopant material. One of the host material and the assist dopant material is a material having high electronic transport properties, and the other is a material having high hole transport properties. The second light-emitting layer 62 does not contain the assist dopant material and is configured so as to contain the light-emitting material and the host material.

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. Are recombined, that is, carriers are recombined to generate excitons, and when the excitons return to the ground state, the energy is emitted as light.

  Thus, the light emitting layer which emits light is normally formed including a light emitting material (light emitting dopant) and a host material.

  Here, the host material is generally contained in the highest proportion among the constituent components in the light emitting layer, and has a role of supporting the film of the light emitting layer, and when a voltage is applied between the electrodes. Carrier recombination occurs in the molecule of the host material, and excitation energy generated thereby is transferred to the light emitting material to cause the light emitting material to emit light. On the other hand, the light-emitting material is a compound having fluorescence or phosphorescence and plays a role of substantially emitting light when excited by receiving excitation energy from the host material.

  In the organic EL element having such a configuration, the carrier recombination position is determined by the carrier transportability of the host material used in the light emitting layer. In addition, when a fluorescent material is used as a light-emitting material, many materials used as host materials including anthracene compounds such as anthracene and naphthacene, which are widely used as host materials, have hole and electron carrier transport properties. The bias is large. Therefore, the recombination positions of carriers are concentrated near the interface of the light emitting layer. As a result, only the light emitting material near the interface, that is, a part of the light emitting material in the light emitting layer contributes to light emission. Therefore, in the light emitting material located in the vicinity of the interface, there is a problem that the deterioration is locally promoted and the luminance deterioration of the light emitting layer is accelerated.

  On the other hand, in recent years, the light-emitting layer includes an assist dopant material for controlling carrier transportability as a constituent material other than the light-emitting material and the host material, thereby controlling the carrier transportability in the light-emitting layer. It has been reported that organic EL elements have higher efficiency and longer life (for example, see Patent Document 1).

  However, in this Patent Document 1, the characteristics of the organic EL element are improved by controlling the relationship between the HOMO and LUMO of the host material and the assist dopant material. However, only the relationship between the HOMO and LUMO is controlled. However, the carrier transportability of holes and electrons could not be sufficiently controlled, and it could not be said that the recombination position of carriers in the light emitting layer could be set to a good position.

JP 2005-108727 A

  An object of the present invention is to provide a light-emitting element having excellent light-emitting characteristics and a lifetime characteristic that maintains such light-emitting characteristics over a long period of time, and a light-emitting device, a display device, and an electronic device that are provided with the light-emitting elements and have excellent reliability. There is.

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;
An electron transport layer that is provided between the cathode and the light emitting unit and transports electrons to the light emitting unit;
The light emitting unit includes a first light emitting layer and a second light emitting layer laminated from the anode side to the cathode side,
The electron transport layer is provided in contact with the second light emitting layer,
The first light-emitting layer includes a light-emitting material, a host material that holds the light-emitting material, and an assist dopant material.
One of the host material and the assist dopant material is a material having a high electron transporting property, and the other is a material having a high hole transporting property,
The second light emitting layer includes the light emitting material and the host material without including the assist dopant material.

  As a result, a light-emitting element having excellent light-emitting characteristics and life characteristics that maintain such light-emitting characteristics over a long period of time can be obtained.

  In the light emitting device of the present invention, the assist dopant material in the first light emitting layer preferably has a content of 20 wt% or more and 70 wt% or less.

  Thereby, holes and electrons can be flowed in a more balanced manner in the first light emitting layer. Therefore, the recombination site where carriers recombine can be sufficiently separated from the vicinity of the interface on the anode side of the first light-emitting layer, and the recombination site can be further spread over the first and second light-emitting layers. Can be spread over a wide range.

In the light emitting device of the present invention, the host material is preferably an acene compound.
Since the acene-based compound is a host material having a high electron transporting property, the electrons can smoothly flow through the first and second light-emitting layers.

  In the light emitting device of the present invention, the assist dopant material is preferably an amine compound.

  Thereby, holes and electrons can be flowed in a more balanced manner in the first light emitting layer. Therefore, the recombination site where carriers recombine can be sufficiently separated from the vicinity of the interface on the anode side of the first light-emitting layer, and the recombination site can be further spread over the first and second light-emitting layers. Can be spread over a wide range.

In the light emitting device of the present invention, the amine compound is preferably a compound represented by the following formula (4).

  As a result, holes and electrons can flow in a more balanced manner in the first light emitting layer. Therefore, the recombination site where carriers recombine can be sufficiently separated from the vicinity of the interface on the anode side of the first light emitting layer, and the recombination site can be further extended across the first and second light emitting layers. Can be spread over a wide range.

  In the light emitting device of the present invention, it is preferable that the light emitting materials contained in the first light emitting layer and the second light emitting layer are the same.

  Thereby, it can be set as the light emitting element from which the 1st light emitting layer and the 2nd light emitting layer light-emit the same color.

  In the light emitting device of the present invention, it is preferable that the light emitting materials contained in the first light emitting layer and the second light emitting layer are different from each other.

  Thus, a light emitting element in which the first light emitting layer and the second light emitting layer emit different colors can be obtained.

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 which shows embodiment of the light emitting element 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 illustrating 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 of the invention will be described with reference to the accompanying drawings.

First, the light emitting device (organic electroluminescence device) 1 of the present invention will be described.
FIG. 1 is a diagram schematically showing a longitudinal section showing an embodiment of a light emitting device of the present invention. In the following description, for convenience of explanation, the upper side in FIG. 1 will be described as “upper” and the lower side as “lower”.

  A light-emitting element (electroluminescence element) 1 shown in FIG. 1 is an organic light-emitting element (white light-emitting element) in which a plurality of types of organic light-emitting materials emit light of a specific color.

  Such a light-emitting element 1 includes an anode 3, a hole injection layer 4, a hole transport layer 5, a light-emitting portion 6 composed of a plurality of light-emitting layers, an electron transport layer 7, an electron injection layer 8, and a cathode. 9 are laminated in this order. In other words, between the anode 3 and the cathode 9, the hole injection layer 4, the hole transport layer 5, the light emitting unit 6, the electron transport layer 7, and the electron injection layer 8 are arranged from the anode 3 side. The laminated body 15 laminated | stacked in order is provided. The light emitting unit 6 is a laminate in which a first light emitting layer 61 and a second light emitting layer 62 are laminated in this order from the anode 3 side to the cathode 9 side.

  The entire light emitting element 1 is provided on the substrate 2 and is sealed with a sealing member 10.

  In the light emitting element 1, when a driving voltage is applied to the anode 3 and the cathode 9, electrons are supplied (injected) from the cathode 9 side to the first light emitting layer 61 and the second light emitting layer 62. At the same time, holes are supplied (injected) from the anode 3 side. In each of the light emitting layers 61 and 62, holes and electrons recombine, and excitons (excitons) are generated by the energy released upon the recombination, and when excitons return to the ground state, energy (fluorescence exchange) is generated. The light emitting layers 61 and 62 emit 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 100-500 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 (that is, has a hole injection property).

  The hole injection layer 4 includes a material having a hole injection property (that is, a hole injection material).

  The hole injecting material is not particularly limited. For example, copper phthalocyanine, 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 represented by the following formula (1).

  Among these, as the hole injecting material, it is preferable to use an amine compound from the viewpoint of excellent hole injecting property.

  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.

  The hole injection layer 4 may be omitted depending on the combination of constituent materials included in the anode 3 and the hole transport layer 5.

[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 first light emitting layer 61. Is.
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. Compounds can be used.

  An amine-based compound is a material that can suitably draw out electrons by a hole injection material and can easily inject holes. For this reason, by using an amine compound as a 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.

  As an amine compound, for example, N, N′-di (1-naphthyl) -N, N′-diphenyl-1,1′-diphenyl-4,4′-diamine represented by the following formula (2) (α -NPD), N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1'-diphenyl-4,4'-diamine (TPD), a compound represented by the following formula (3) And tetraarylbenzidine derivatives such as compounds represented by the following formula (4), tetraaryldiaminofluorene compounds or derivatives thereof, and the like, and one or more of them can be used in combination.

  In particular, among the above-described amine compounds, N, N′-di (1-naphthyl) -N, N′-diphenyl-1,1′-diphenyl-4,4 ′ represented by the above formula (2) is used. It is preferable to use a diamine (α-NPD). Such a compound can extract electrons more preferably by a hole injection material, and can easily inject holes, so that the light-emitting element 1 is suitable even at a lower voltage. Can be driven.

  Although the average thickness of such a hole transport layer 5 is not specifically limited, It is preferable that it is 10-150 nm, and it is more preferable that it is 10-100 nm.

  The hole transport layer 5 can be omitted depending on the combination of constituent materials included in the hole injection layer 4 and the first light emitting layer 61.

[Light emitting part]
As described above, the light emitting unit 6 is a stacked body in which the first light emitting layer 61 and the second light emitting layer 62 are stacked from the anode 3 side.

Hereinafter, each of these layers will be described sequentially.
(First light emitting layer)
The first light-emitting layer 61 has a light-emitting material that emits light of a specific color (first light-emitting material), a host material that holds the light-emitting material (first host material), and a movement opposite to the host material And an assist dopant material having a degree (first assist dopant material).

  The light emitting material (first light emitting material) is appropriately selected according to the color of the light emitted from the first light emitting layer 61. For example, when the first light emitting layer 61 emits red light, When the red light emitting material is used as the light emitting material and the first light emitting layer 61 emits blue light, the blue light emitting material is used as the light emitting material, and the first light emitting layer 61 is further green. When emitting the above light, a green light emitting material is used as the light emitting material.

  The red light emitting material is not particularly limited, and various red fluorescent materials and red phosphorescent materials can be used alone or in combination of two or more.

  The red fluorescent material is not particularly limited as long as it emits red fluorescence. For example, perylene derivatives such as tetraaryldiindenoperylene derivatives represented by the following formula (5), europium complexes, benzopyran derivatives, rhodamine derivatives , 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-dimethylamino) Styryl) -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).

  Moreover, it does not specifically limit as a blue luminescent material, Various blue fluorescent material and blue phosphorescent material can be used 1 type or in combination of 2 or more types.

  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 (8), 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-dii ) -Ortho-co- (2-methoxy-5- {2-ethoxyhexyloxy} phenylene-1,4-diyl)], poly [(9,9-dioctylfluorene-2,7-diyl) -co- ( Ethylenylbenzene)] and the like. Among these, one can be used alone or two or more can 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 ).

  Furthermore, it does not specifically limit as a green luminescent material, Various green fluorescent material and green phosphorescent material can be used 1 type or in combination of 2 or more types.

  The green fluorescent material is not particularly limited as long as it emits green fluorescence. For example, quinacridone such as a coumarin derivative, a quinacridone derivative represented by the following formula (9), 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 can also be used in conjunction.

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.

  In addition to the light emitting material (first light emitting material), the constituent material of the first light emitting layer 61 includes a host material (first host material) that uses this light emitting material as a guest material. This host material recombines holes and electrons to generate excitons and to transfer the exciton energy to the luminescent material (Felster movement or Dexter movement) to excite the luminescent material. Have. Such a host material is used by, for example, doping a host material with a light-emitting material that is a guest material as a light-emitting dopant.

Such a host material is not particularly limited as long as it exhibits the functions described above with respect to the light emitting material to be used. However, when the light emitting material contains a fluorescent material, for example, the following formula (6) is shown. Anthracene derivatives such as, anthracene derivatives such as 2-t-butyl-9,10-di (2-naphthyl) anthracene (TBADN), and naphthacene derivatives represented by the following formula (7) (acene compounds) , Distyrylarylene derivatives, perylene derivatives, distyrylbenzene derivatives, distyrylamine derivatives, quinolinolato metal complexes such as tris (8-quinolinolato) aluminum complex (Alq ₃ ), and triarylamines such as tetramers of triphenylamine Derivatives, oxadiazole derivatives, silole derivatives, dicarbazole derivatives Examples include oligothiophene derivatives, benzopyran derivatives, triazole derivatives, benzoxazole derivatives, benzothiazole derivatives, quinoline derivatives, 4,4′-bis (2,2′-diphenylvinyl) biphenyl (DPVBi), and one of these Can be used alone or in combination of two or more. Among these, an acene compound is preferable. Since the acene-based compound is a host material having a high electron transporting property, this allows the electrons to smoothly flow through the first light-emitting layer 61.

  When the light-emitting material includes a phosphorescent material, examples of the host material include 3-phenyl-4- (1′-naphthyl) -5-phenylcarbazole, 4,4′-N, N′-dicarbazole biphenyl ( Carbazole derivatives such as CBP) and the like, and one of these may be used alone or two or more of them may be used in combination.

  The content (doping amount) of the light emitting material in the first light emitting layer 61 is slightly different depending on the kind of the light emitting material to be used, but is preferably 0.01 to 10 wt%, for example, 0.1 to 5 wt%. More preferably. By setting the content of the light emitting material within such a range, the light emission efficiency can be optimized, and the first light emitting layer 61 is made to balance with the light emitting amount of the second light emitting layer 62 described later. Can emit light.

  In addition to the light emitting material (first light emitting material) and the host material (first host material), the constituent material of the first light emitting layer 61 includes an assist dopant material (first assist dopant material). It is.

  This assist dopant material has a reverse mobility with respect to the host material, that is, when the host material has a high electron transport property, it is a material with a high hole transport property, and the host material is a positive material. When the material has a high hole transporting property, it is a material having a high electron transporting property. As described above, the assist dopant material has a mobility opposite to that of the host material, so that holes and electrons can flow in the first light-emitting layer 61 in a balanced manner. It functions to adjust the position in the thickness direction where electrons recombine to generate excitons. Such an assist dopant material is used by mixing with a host material, for example.

  Since the first light-emitting layer 61 having such a configuration is normally capable of transporting electrons smoothly, a material having a high electron transporting property is used as a host material. A material having high hole transportability is preferably selected.

  The assist dopant material (first assist dopant material) is not particularly limited as long as it has a reverse mobility with respect to the host material. For example, N, N′-di-acid represented by the following formula (2) is used. (1-naphthyl) -N, N′-diphenyl-1,1′-diphenyl-4,4′-diamine (α-NPD), N, N′-diphenyl-N, N′-bis (3-methylphenyl) ) -1,1′-diphenyl-4,4′-diamine (TPD), a compound represented by the following formula (3), a tetraarylbenzidine derivative such as a compound represented by the following formula (4), a tetraaryldiaminofluorene compound Or its derivatives (amine compounds), oxadiazole derivatives, perylene derivatives, pyridine derivatives, pyrimidine derivatives, quinoxaline derivatives and diphenylquino Derivatives and the like, may be used alone among these alone or in combination two or more.

  The average thickness of the first light emitting layer 61 is not particularly limited, but is preferably about 5 to 50 nm, and more preferably about 10 to 40 nm.

(Second light emitting layer)
The second light-emitting layer 62 does not include the assist dopant material included in the first light-emitting layer 61, and a light-emitting material that emits light in a specific color (second light-emitting material) and a host material that holds the light-emitting material (first light-emitting material). 2 host materials).

  The light emitting material (second light emitting material) is appropriately selected according to the color of light emitted from the second light emitting layer 62, similarly to the first light emitting layer 61. For example, the second light emitting layer 62 is made red. Red light emitting material is used as the light emitting material, and when the second light emitting layer 62 emits blue light, a blue light emitting material is used as the light emitting material. Further, when the second light emitting layer 62 emits green light, a green light emitting material is used as the light emitting material.

  Therefore, when the first light emitting layer 61 and the second light emitting layer 62 emit light of the same color, the first light emitting material and the second light emitting material included in each of them are the same. Things are used. In the case where the first light-emitting layer 61 and the second light-emitting layer 62 emit light of different colors, the first light-emitting material and the second light-emitting material included in each of them are different (dissimilar). ) Is used. The “same luminescent material” referred to here is the same luminescent material if it emits the same color, and the “different luminescent material” means that it emits a different color. This is referred to as a different kind of light emitting material.

  As the red light emitting material, the blue light emitting material, and the green light emitting material, for example, the same materials as those described as the red light emitting material, the blue light emitting material, and the green light emitting material of the first light emitting layer 61 can be used.

  In addition to the light emitting material (second light emitting material), the constituent material of the second light emitting layer 62 includes a host material (second host material) that uses this light emitting material as a guest material. This host material recombines holes and electrons to generate excitons and to transfer the exciton energy to the luminescent material (Felster movement or Dexter movement) to excite the luminescent material. Have. Such a host material is used by, for example, doping a host material with a light-emitting material that is a guest material as a light-emitting dopant.

  As such a host material, for example, the same materials as described as the host material of the first light emitting layer 61 can be used.

  The content (doping amount) of the light emitting material in the second light emitting layer 62 is slightly different depending on the type of the light emitting material used, but is preferably 0.01 to 10 wt%, for example, 0.1 to 5 wt%. More preferably. By setting the content of the light emitting material within such a range, the light emission efficiency can be optimized, and the second light emitting layer 62 emits light while balancing the light emitting amount of the first light emitting layer 61. be able to.

  Further, the average thickness of the second light emitting layer 62 is not particularly limited, but is preferably about 5 to 50 nm, and more preferably about 10 to 40 nm.

  As described above, in a light-emitting element having a light-emitting layer between an anode and a cathode, it is usually necessary to smoothly flow electrons to the light-emitting layer. Therefore, a material having a high electron transport property is used as the host material. It is done. For this reason, the bias in the electron carrier transport property is increased, and the recombination positions of carriers are concentrated in the vicinity of the interface between the hole transport layer and the light emitting layer. As a result, the light emitting element having such a configuration usually has a problem that the luminance degradation of the light emitting layer tends to occur locally in the vicinity of the interface.

  In order to solve such problems, for example, in addition to the light emitting material and the host material, the light emitting layer further has an opposite mobility (high hole transportability) to the host material. It is conceivable that the material is included as a constituent material.

  Thus, the carrier transport property in a light emitting layer is controllable by making a light emitting layer contain assist dopant material. As a result, the position in the thickness direction where excitons are generated by recombination of holes and electrons is adjusted, so that the light emitting element can be highly efficient and have a long lifetime. However, the carrier transportability of holes and electrons cannot be sufficiently controlled simply by including an assist dopant material or controlling the relationship between the host material and the assist dopant material HOMO, LUMO, The recombination position of carriers in the light emitting layer could not be set to a good position.

  More specifically, by including the assist dopant material, holes are smoothly transported in the light emitting layer, and as a result, holes are supplied to the cathode side from the light emitting layer, and electron transport is performed. The constituent material contained in the layer is altered and deteriorated, resulting in a new problem that the light emitting characteristics of the light emitting element are lowered.

  In order to solve this problem, the present invention includes a first light emitting layer 61 and a second light emitting layer 62 in which the light emitting element 1 (light emitting unit 6) is laminated from the anode 3 side to the cathode 9 side. Further, the first light emitting layer 61 is moved in a direction opposite to the light emitting material (first light emitting material), the host material holding the light emitting material (first host material), and the host material. And the second light emitting layer 62 does not include the assist dopant material, and includes the light emitting material (second light emitting material) and the host material (second material). Host material).

  As described above, in the present invention, the light-emitting layer (light-emitting portion 6) is a laminate in which the first light-emitting layer 61 and the second light-emitting layer 62 are stacked, and the first light-emitting layer 61 is further assisted. It is assumed that the dopant material is contained, and the second light-emitting layer 62 does not contain the assist dopant material. Thereby, holes are transported smoothly in the first light-emitting layer 61, but hole transport is inhibited in the second light-emitting layer 62 compared to the first light-emitting layer 61. . As a result, the holes that have passed through the first light emitting layer 61 pass through the second light emitting layer 62 and reach the electron transport layer 7 adjacent to the second light emitting layer 62 accurately. Suppressed or prevented. That is, the second light emitting layer 62 functions as a block layer that suppresses or prevents the passage of holes to the electron transport layer 7. Therefore, the alteration / deterioration of the constituent material contained in the electron transport layer 7 can be accurately suppressed or prevented.

  From the above, the position where carriers recombine can be sufficiently separated from the vicinity of the interface between the hole transport layer 5 and the first light emitting layer 61, and this recombination site can be connected to the light emitting layers 61 and 62. Therefore, it is possible to suppress the local deterioration of the light emitting material (dopant material) in the vicinity of the interface. As a result, the light emitting element 1 has excellent light emission characteristics and life characteristics that maintain such light emission characteristics over a long period of time.

Further, when the mobility of holes in the first light emitting layer 61 is μh [cm ² / Vs] and the mobility of electrons is μe [cm ² / Vs], the mobility ratio μe / μh, that is, It is preferable that the relationship between the hole mobility and the electron mobility in the first light emitting layer 61 satisfies the relationship of the following formula (1).
0.01 ≦ μe / μh ≦ 100 (1)

  By satisfying the relational expression (1), it can be said that holes and electrons flow in a balanced manner in the first light emitting layer 61. Therefore, the position where the carriers recombine (recombination site) can be sufficiently separated from the vicinity of the interface between the first light emitting layer 61 and the hole transport layer 5, and the recombination site can be separated from the light emitting layer 61, Since it can be spread over a wider range over 62, the above-described effect can be exhibited more reliably.

  Note that the value of the mobility ratio μe / μh can be obtained by measuring the hole mobility and the electron mobility by impedance spectroscopy and obtaining these ratios.

  The μe / μh value is preferably 0.01 or more and 100 or less, more preferably 0.1 or more and 10 or less, as shown in the formula (1). Thereby, the recombination site in the light emitting layers 61 and 62 can be expanded more reliably.

  Moreover, as an assist dopant material (1st assist dopant material), when an acene type compound is used among the things mentioned above as a host material, it is preferable that each is an amine type compound. As a result, holes and electrons can flow in the first light emitting layer 61 in a more balanced manner. Therefore, the relational expression (1) can be easily satisfied.

  Furthermore, the acene compound is preferably a compound represented by the formula (4). Thereby, the said effect can be exhibited more notably.

  Further, the content of the assist dopant material in the first light emitting layer 61 is preferably 20 wt% or more and 70 wt% or less, and more preferably 20 wt% or more and 50 wt% or less. By setting the content of the assist dopant material within such a range, it becomes possible to flow holes and electrons in the first light emitting layer 61 in a more balanced manner. Therefore, it can be easily set to satisfy the relational expression (1).

  Further, the film thicknesses of the first light-emitting layer 61 and the second light-emitting layer 62 are not particularly limited as long as they are in the ranges as described above, but the respective film thicknesses are set to T (EML1) and T When (EML2) is satisfied, it is preferable that the relationship of T (EML1) ≦ T (EML2) is satisfied. As described above, the second light-emitting layer 62 has the same thickness as the first light-emitting layer 61 or thicker than that, so that the second light-emitting layer 62 has an electron transport layer. The function as a block layer for suppressing or preventing the passage of holes to 7 can be more reliably exhibited.

(Electron transport layer)
The electron transport layer 7 is provided in contact with the second light emitting layer 62 between the cathode 9 and the light emitting portion 6, and electrons injected from the cathode 9 through the electron injection layer 8 are second emitted. It has a function of transporting to the layer 62 (light emitting portion 6).

Examples of the constituent material (electron transport material) of the electron transport layer 7 include phenanthroline derivatives such as 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), and tris represented by the following formula (10). (8-quinolinolato) quinoline derivatives such as organometallic complexes having 8-quinolinol or a derivative thereof such as aluminum (Alq ₃ ) as a ligand, azaindolizine derivatives such as a compound represented by the following formula (11), An oxadiazole derivative, a perylene derivative, a pyridine derivative, a pyrimidine derivative, a quinoxaline derivative, a diphenylquinone derivative, a nitro-substituted fluorene derivative, and the like can be given, and one or more of these 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.

  The electron injection layer 8 may be omitted depending on the combination of constituent materials included in the cathode 9 and the electron transport layer 7.

(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.

  Moreover, the sealing member 10 can be made to oppose the board | substrate 2 as flat form, and can seal between these, for example with sealing materials, such as a thermosetting resin.

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.

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

[5] Next, the second light emitting layer 62 is formed on the first light emitting layer 61.
The second light emitting layer 62 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.

[6] Next, the electron transport layer 7 is formed on the second light emitting layer 62.
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 supplied with a material for forming an electron transport layer obtained by, for example, dissolving an electron transport material in a solvent or dispersed in a dispersion medium on the second light emitting layer 62, and then drying (desolving or removing the material). It can also be formed by dedispersing medium).

[7] 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.

[8] 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 of metal fine particle ink, and baking.
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.
The light emitting element 1 as described above can be used, for example, in a light emitting device (the light emitting device of the present invention).

  Since such a light emitting device includes the light emitting element 1 as described above, it 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.

  A 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. 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.

The configurations of the light emitting elements 1G and 1B are the same as the configuration of the light emitting element 1R except that the colors of light emitted from the light emitting elements 1G and 1B are different. 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.

  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 laminate 15 includes a hole injection layer 4, a hole transport layer 5, a light emitting unit 6, an electron transport layer 7, and an electron injection layer 8 stacked in this order from the anode 3 side. The injection layer 4, the hole transport layer 5, and the light emitting unit 6 are provided separately for each of the light emitting elements 1 R, 1 G, and 1 B by being separated by the partition wall 31. The injection layer 8 is provided in common to the light emitting elements 1R, 1G, and 1B.

  The light-emitting elements 1R, 1G, and 1B are configured as described above, and the light-emitting element 1R, the light-emitting element 1G, and the light-emitting element 1B are each red by appropriately selecting the type of light-emitting material included in each light-emitting portion 6. , Green and blue can be emitted, thereby realizing a full-color image display.

  In addition, an epoxy layer 35 made of an epoxy resin is formed on the light emitting device 101 thus configured so as to cover it.

On the epoxy layer 35, the light shielding layer 36 provided with the opening part 19 corresponding to light emitting element 1R, 1G, 1B is provided. Thereby, it is possible to prevent the unintended subpixels 100R, 100G, and 100B from emitting light.
On the light shielding layer 36, the sealing substrate 20 is provided 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 a 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 halide 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 imaging device 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 input / output terminal 1314 for data communication 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.

  In addition to the personal computer (mobile personal computer) of FIG. 3, the mobile phone of FIG. 4, and the digital still camera of FIG. 5, the electronic apparatus of the present invention includes, for example, a television, a video camera, a viewfinder type, 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 with touch panels (for example, cash dispensers of financial institutions, automatic ticket vending machines), medical devices (for example, electronic thermometers, blood pressure monitors, blood glucose meters, electrocardiographs, ultrasound diagnostic devices, internal Endoscope display device), fish finder, Seed measuring instruments, gauges (e.g., gages for vehicles, aircraft, and ships), a flight simulator, other various monitors such, can be applied to the projection type display device 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 been described as having the two light emitting layers of the first light emitting layer and the second light emitting layer. However, the present invention is not limited to this. One having one or more other light emitting layers between one light emitting layer and the second light emitting layer, that is, one having three or more light emitting layers may be used.

  In the above embodiment, the light emitting material contained in the first and second light emitting layers has been described as emitting light of red, blue or green, but is not limited to the material emitting such light. For example, a light emitting material that emits light of other colors such as yellow or orange can also be used.

Next, specific examples of the present invention will be described.
1. Manufacturing of light-emitting elements

Example 1A
<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, on the ITO electrode, N, N′-bis (1-naphthyl) -N, N′-diphenyl [1,1′-biphenyl] -4,4 ′ represented by the above formula (2) -Diamine ((alpha) -NPD) was vapor-deposited by the vacuum evaporation method, and the positive hole transport layer with an average thickness of 60 nm was formed.

  <3> Next, on the hole transport layer, the constituent material of the blue light-emitting layer was deposited by a vacuum evaporation method to form a first blue light-emitting layer (first light-emitting layer) having an average thickness of 30 nm. As a constituent material of the first blue light emitting layer, a distyryldiamine compound represented by the above formula (8) is used as a blue light emitting material, and an anthracene derivative represented by the above formula (6) is used as a host material. The amine derivative represented by the formula (4) was used as the material. Further, the content (doping concentration) of the blue light emitting material (dopant) in the blue light emitting layer is 8.0 wt%, and the anthracene derivative represented by the formula (6) and the amine derivative represented by the formula (4) The mixing ratio was 70:30.

  <4> Next, a constituent material of the second blue light-emitting layer is deposited on the first blue light-emitting layer by a vacuum evaporation method, and a second blue light-emitting layer (second light-emitting layer) having an average thickness of 10 nm is obtained. Formed. As a constituent material of the second blue light emitting layer, a distyryldiamine compound represented by the above formula (8) was used as a blue light emitting material, and an anthracene derivative represented by the above formula (6) was used as a host material. In addition, the content (dope concentration) of the blue light emitting material (dopant) in the blue light emitting layer was 8.0 wt%.

  <5> Next, an azaindolizine derivative represented by the above formula (11) was formed on the second blue light-emitting layer by a vacuum evaporation 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 vapor deposition method, thereby forming 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, the light emitting device of Example 1A as shown in FIG. 1 in which the first and second light emitting layers emit the same color (blue) was manufactured.

(Comparative Example 1A)
A light emitting device of Comparative Example 1A was manufactured in the same manner as in Example 1A, except that the addition of the blue light emitting material in Step <3> was omitted and that Step <4> was omitted.

(Comparative Example 2A)
A light emitting device of Comparative Example 2A was manufactured in the same manner as Example 1A, except that Step <4> was omitted.

2. Evaluation of Luminous Life For the light-emitting elements of Example 1A and Comparative Examples 1A and 2A, the light-emitting element was allowed 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% (LT80) was measured, and for the light emitting elements of Example 1A and Comparative Example 2A, the relative value when LT80 measured with the light emitting element of Comparative Example 1A was taken as 100 was determined.
Table 1 shows the evaluation results.

  As is clear from Table 1, in the light-emitting element of Example 1A, the first light-emitting layer containing the assist dopant material and the second light-emitting layer not containing the assist dopant material were laminated in this order from the anode side. As a result, the light emission lifetime was longer than that of Comparative Examples 1A and 2A that do not have the light emitting portion having such a configuration.

3. Production of light emitting device (Example 1B)
<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, on the ITO electrode, N, N′-bis (1-naphthyl) -N, N′-diphenyl [1,1′-biphenyl] -4,4 ′ represented by the above formula (2) -Diamine ((alpha) -NPD) was vapor-deposited by the vacuum evaporation method, and the positive hole transport layer with an average thickness of 60 nm was formed.

  <3> Next, the constituent material of the blue light emitting layer was vapor-deposited on the hole transport layer by a vacuum vapor deposition method to form a blue light emitting layer (first light emitting layer) having an average thickness of 20 nm. As a constituent material of the blue light emitting layer, a distyryldiamine compound represented by the above formula (8) is used as a blue light emitting material, an anthracene derivative represented by the above formula (6) is used as a host material, and the above as an assist dopant material. An amine derivative represented by the formula (4) was used. Further, the content (doping concentration) of the blue light emitting material (dopant) in the blue light emitting layer is 8.0 wt%, and the anthracene derivative represented by the formula (6) and the amine derivative represented by the formula (4) The mixing ratio was 70:30.

  <4> Next, on the blue light emitting layer, the constituent material of the green light emitting layer was vapor-deposited by a vacuum evaporation method to form a green light emitting layer (second light emitting layer) having an average thickness of 20 nm. As a constituent material of the green light emitting layer, a quinacridone derivative represented by the above formula (9) was used as a green light emitting material (guest material), and an anthracene derivative represented by the above formula (6) 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%.

  <5> Next, an azaindolizine derivative represented by the formula (11) was formed on the green 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 vapor deposition method, thereby forming 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, the light emitting device of Example 1B as shown in FIG. 1 in which the first and second light emitting layers emit different colors (blue and green) was manufactured.

(Comparative Example 1B)
A light emitting device of Comparative Example 1B was manufactured in the same manner as in Example 1B except that the constituent materials of the blue light emitting layer used in Step <3> were as follows.

  That is, as a constituent material of the blue light emitting layer, a distyryldiamine compound represented by the above formula (8) is used as a blue light emitting material, an anthracene derivative represented by the above formula (6) is used as a host material, and an assist is further provided. What added the dopant material was omitted. In addition, the content (dope concentration) of the blue light emitting material (dopant) in the blue light emitting layer was 8.0 wt%.

(Comparative Example 2B)
A light emitting device of Comparative Example 2B was manufactured in the same manner as in Example 1B except that the constituent materials of the green light emitting layer used in Step <4> were as follows.

  That is, as a constituent material of the green light emitting layer, a quinacridone derivative represented by the above formula (9) is used as a green light emitting material (guest material), and an anthracene derivative represented by the above formula (6) is used as a host material. The amine derivative represented by the formula (4) was used as the material. Further, the content (dope concentration) of the green light emitting material (dopant) in the green light emitting layer is 1.0 wt%, and the anthracene derivative represented by the formula (6) and the amine derivative represented by the formula (4) The mixing ratio was 70:30.

4). Evaluation of Luminescence Life For the light-emitting elements of Example 1B and Comparative Examples 1B and 2B, 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% (LT80) was measured, and for the light emitting elements of Example 1B and Comparative Example 2B, the relative value when LT80 measured with the light emitting element of Comparative Example 1B was taken as 100 was determined.
Table 2 shows the evaluation results.

  As is clear from Table 2, in the light emitting device of Example 1B, the first light emitting layer containing the assist dopant material and the second light emitting layer not containing the assist dopant material were laminated in this order from the anode side. As a result, the light emission lifetime was longer than that of Comparative Examples 1B and 2B that did not have the light emitting portion having such a configuration.

DESCRIPTION OF SYMBOLS 1, 1B, 1G, 1R ... Light emitting element 2 ... Substrate 3 ... Anode 4 ... Hole injection layer 5 ... Hole transport layer 6 ... Light emitting part 61 ... First light emitting layer 62 ... First 2 light emitting layer 7 ... electron transport layer 8 ... electron injection layer 9 ... cathode 10 ... sealing member 15 ... laminate 19 ... opening 100 ... display device 101 ... light emitting devices 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 wall 32 ... Reflective film 33 ... Corrosion prevention film 34 ... Cathode cover 35 ... Epoxy layer 36 ... Light shielding layer 1100 ... Personal computer 1102 ... Keyboard 1104 ... Main body Part 11 6 ...... Display unit 1200 ...... mobile phone 1202 ...... operation buttons 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 …… Data input / output terminal 1430 …… TV monitor 1440 …… Personal computer

Claims (10)

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;
An electron transport layer that is provided between the cathode and the light emitting unit and transports electrons to the light emitting unit;
The light emitting unit includes a first light emitting layer and a second light emitting layer laminated from the anode side to the cathode side,
The electron transport layer is provided in contact with the second light emitting layer,
The first light-emitting layer includes a light-emitting material, a host material that holds the light-emitting material, and an assist dopant material.
One of the host material and the assist dopant material is a material having a high electron transporting property, and the other is a material having a high hole transporting property,
The second light-emitting layer does not include the assist dopant material, and includes the light-emitting material and the host material.   2. The light emitting device according to claim 1, wherein the content of the assist dopant material in the first light emitting layer is 20 wt% or more and 70 wt% or less.   The light emitting device according to claim 1, wherein the host material is an acene compound.   The light emitting device according to any one of claims 1 to 3, wherein the assist dopant material is an amine compound. The light emitting device according to claim 4, wherein the amine compound is a compound represented by the following formula (4).

  The light emitting device according to claim 1, wherein the light emitting material contained in each of the first light emitting layer and the second light emitting layer is the same.   6. The light emitting element according to claim 1, wherein the light emitting material contained in each of the first light emitting layer and the second light emitting layer is different. 6.   A light-emitting device comprising the light-emitting element according to claim 1.   A display device comprising the light-emitting device according to claim 8.   An electronic apparatus comprising the display device according to claim 9.

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