JP5834872B2 - LIGHT EMITTING ELEMENT, LIGHT EMITTING DEVICE, DISPLAY DEVICE, AND ELECTRONIC DEVICE - Google Patents

Description

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 element, when an electric field is applied between the cathode and the anode, electrons are injected from the cathode side into the light-emitting layer and holes are injected from the anode side. The excitons are generated by the recombination of holes with holes, and when the excitons return to the ground state, the energy is released as light.
As such a light emitting device, for the purpose of improving luminous efficiency and lifetime, a device using a mixture of a hole transport material and an electron transport material as a host material for both the green light emitting layer and the red light emitting layer that are in contact with each other. It is known (see, for example, Patent Document 1).

However, in the light emitting device according to Patent Document 1, the electron transport material in the light emitting layer located on the anode side inhibits hole transport, and the hole transport material in the light emitting layer located on the cathode side inhibits electron transport. There is a problem that the drive voltage becomes high.
Further, in the light emitting element according to Patent Document 1, the amount of electrons passing from the anode side light emitting layer to the anode side and the amount of holes passing from the cathode side light emitting layer to the cathode side are increased. There was also a problem that the deterioration of other layers was caused, and as a result, the lifetime was reduced.

JP 2007-27092 A

  An object of the present invention is to provide a light emitting element capable of suppressing driving voltage and realizing high light emission efficiency and long life, 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 an anode,
A cathode,
A first light emitting layer that is provided between the anode and the cathode, and emits light when energized between the anode and the cathode;
A second light-emitting layer provided between the cathode and the first light-emitting layer in contact with the first light-emitting layer, and emitting light when energized between the anode and the cathode;
The first light emitting layer includes a first light emitting material and a first host material that holds the first light emitting material,
The second light-emitting layer includes a second light-emitting material and a second host material that holds the second light-emitting material,
The first host material and the second host material are each composed of a mixed material including a hole transport material and an electron transport material,
When the content of the hole transporting material in the first host material is A1, and the content of the electron transporting material in the first host material is B1 ,
A1 / B1 is 13/7 or more and 3 or less,
The content of the hole transporting material in the second host material is less than the content of the electron transporting material in the second host material.

According to the light-emitting element configured as described above, the first light-emitting layer and the second light-emitting layer contain the hole transport material and the electron transport material, respectively. Holes and electrons can be smoothly supplied to the light emitting layer. Therefore, the first light-emitting layer and the second light-emitting layer can each emit light with high light emission efficiency.
In particular, by increasing the content of the hole transporting material in the first light emitting layer and the content of the electron transporting material in the second light emitting layer, the second light emission from the first light emitting layer. Transport of holes to the layer and transport of electrons from the second light emitting layer to the first light emitting layer can be performed smoothly. Therefore, the driving voltage of the light emitting element can be suppressed.

  Further, by suppressing the content of the electron transporting material in the first light emitting layer and the content of the hole transporting material in the second light emitting layer, the material escapes from the first light emitting layer to the anode side. The amount of electrons and the amount of holes that escape from the second light-emitting layer to the cathode can be suppressed. Therefore, another layer (for example, a hole transport layer) located on the anode side with respect to the first light emitting layer, and another layer (for example, an electron transport layer) located on the cathode side with respect to the second light emitting layer. As a result, the lifetime of the light emitting element can be extended.

In the light emitting element of the present invention, it is preferable that the hole transporting material contained in the first host material and the hole transporting material contained in the second host material are the same type.
Thereby, the hole transport property from the first light emitting layer to the second light emitting layer can be enhanced. As a result, the driving voltage can be suppressed and the life can be extended.
In the light-emitting element of the present invention, it is preferable that the electron transporting material contained in the first host material and the electron transporting material contained in the second host material are the same type.
Thereby, the electron transport property from a 2nd light emitting layer to a 1st light emitting layer can be improved. As a result, the driving voltage can be suppressed and the life can be extended.

In the light emitting device of the present invention, the positive electrode of the same kind as the hole transporting material included in the first light emitting layer is provided between the anode and the first light emitting layer so as to be in contact with the first light emitting layer. It is preferable to provide a hole transport layer configured to include a hole transport material.
Thereby, the hole transport property from a hole transport layer to a 1st light emitting layer can be improved. As a result, the driving voltage can be suppressed and the life can be extended.

In the light-emitting element of the present invention, the same kind of electron transport as that of the electron-transporting material included in the second light-emitting layer is provided between the cathode and the second light-emitting layer so as to be in contact with the second light-emitting layer. It is preferable to provide an electron transport layer configured to include a conductive material.
Thereby, the electron transport property from an electron carrying layer to a 2nd light emitting layer can be improved. As a result, the driving voltage can be suppressed and the life can be extended.
In the light emitting element of the present invention, it is preferable that the first light emitting material and the second light emitting material each include a phosphorescent light emitting material.
Thereby, the first light-emitting layer and the second light-emitting layer can emit light with a high balance with high light emission efficiency.

In the light emitting element of the present invention, the triplet energy of the hole transporting material and the electron transporting material in the first host material is greater than the triplet energy of the phosphorescent light emitting material in the first light emitting material, respectively. big,
The triplet energies of the hole transporting material and the electron transporting material in the second host material are preferably larger than the triplet energy of the phosphorescent light emitting material in the second light emitting material, respectively.
Thereby, it is possible to accurately suppress or prevent the triplet energy of the phosphorescent material from deactivating without contributing as energy for light emission (phosphorescence). Therefore, the light emission efficiency can be increased.

In the light emitting device of the present invention, it is preferable that a peak wavelength of the light emission of the first light emitting layer is longer than a peak wavelength of the light emission of the second light emitting layer.
Thereby, the light emission generated in the first light-emitting layer and the second light-emitting layer can be efficiently extracted to the outside.
In the light emitting device of the present invention, the total of the average thickness of the first light emitting layer and the average thickness of the second light emitting layer is preferably 30 nm or more and 50 nm or less.
As a result, it is possible to easily and reliably suppress the amount of electrons that escape from the first light emitting layer to the anode side and the amount of holes that escape from the second light emitting layer to the cathode side while suppressing the driving voltage. it can.

In the light emitting device of the present invention, the light emitting element is provided between the anode and the first light emitting layer or between the cathode and the second light emitting layer, and is energized between the anode and the cathode. It is preferable to provide the 3rd light emitting layer which light-emits by.
Thereby, for example, by setting the emission colors of these light emitting layers to red, green, and blue, a white light emitting element can be realized.

In the light emitting device of the present invention, the first light emitting layer and the second light emitting layer are provided between the light emitting layer closer to the third light emitting layer and the third light emitting layer, And a carrier generation layer for generating holes.
Accordingly, the first light emitting layer, the second light emitting layer, and the third light emitting layer can emit light with a good balance. In addition, the luminous efficiency can be increased and the life can be extended.

The light-emitting device of the present invention includes the light-emitting element of the present invention.
According to the light emitting device configured as described above, it is possible to suppress the driving voltage and realize high light emission efficiency and long life.
The display device of the present invention includes the light emitting device of the present invention.
According to the display device configured as described above, since the light emitting element having the low driving voltage, the high light emission efficiency, and the long life is provided, the reliability is excellent.
An electronic apparatus according to the present invention includes the light emitting device according to the present invention.
According to the electronic device configured as described above, since the light-emitting element having a low driving voltage, high light emission efficiency, and long life is provided, it is excellent in reliability.

It is a figure which shows typically the longitudinal cross-section of the light emitting element concerning suitable 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 of the invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram schematically showing a longitudinal section of a light emitting device according to a preferred embodiment 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”.
Such a light emitting element (electroluminescence element) 1 includes an anode 3, a first light emitting part (first light emitting unit) 4, a carrier generation layer 5, a second light emitting part (second light emitting unit) 6, and a cathode. 7 are laminated in this order.

In other words, the light-emitting element 1 includes a stacked body 15 in which the first light-emitting portion 4, the carrier generation layer 5, and the second light-emitting portion 6 are stacked in this order between two electrodes (the anode 3 and the cathode 7). Between the two).
The first light-emitting portion 4 is a laminate in which a hole transport layer 41 and a light-emitting layer 42 are laminated in this order from the anode 3 side to the cathode 7 side. From the 3 side to the cathode 7 side, the hole transport layer 61, the light emitting layer 62 (first light emitting layer), the light emitting layer 63 (second light emitting layer), the electron transport layer 64, and the electron injection layer 65 are arranged in this order. It is the laminated body laminated | stacked.
The entire light emitting element 1 is provided on the substrate 2 and is sealed with a sealing member 8.

  In such a light emitting element 1, carriers (electrons and holes) are generated in the carrier generation layer 5 by applying a driving voltage between the anode 3 and the cathode 7. Then, holes are supplied (injected) from the anode 3 side to the light emitting layer 42, and electrons are supplied from the carrier generation layer 5. In addition, electrons are supplied (injected) from the cathode 7 side to the light emitting layer 62 and the light emitting layer 63, and holes are supplied (injected) from the carrier generation layer 5. As a result, holes and electrons recombine in each light emitting layer, 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).

In this manner, the light emitting layer 42, the light emitting layer 62, and the light emitting layer 63 can each emit light. Therefore, such a light-emitting element 1 can improve the light emission efficiency and reduce the driving voltage as compared with a light-emitting element having only one light-emitting layer. In addition, the life of the light emitting element 1 can be extended.
Moreover, in such a light emitting element 1, the light emitting element of a white light emission is realizable by making the luminescent color of the light emitting layers 42, 62, and 63 into blue, red, and green, for example.

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 first light emitting unit 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 10 to 200 nm, and more preferably 50 to 150 nm.

[First light emitting unit]
As described above, the first light emitting unit 4 includes the hole transport layer 41 and the light emitting layer 42.
(Hole transport layer)
The hole transport layer 41 has a function of transporting holes injected from the anode 3 to the light emitting layer 42.
As the constituent material of the hole transport layer 41, various p-type polymer materials and various p-type low-molecular materials can be used alone or in combination, for example, N, N′-di (1-naphthyl). ) -N, N′-diphenyl-1,1′-diphenyl-4,4′-diamine (NPD), N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1 ′ -A tetraarylbenzidine derivative such as diphenyl-4,4′-diamine (TPD), a tetraaryldiaminofluorene compound or a derivative thereof (amine-based compound), and the like, and one or more of these may be combined. Can be used.

Among the above-mentioned, the hole transport material preferably has a benzidine structure, and more preferably tetraarylbenzidine or a derivative thereof. Thereby, holes are efficiently injected from the anode into the hole transport layer 41, and holes can be efficiently transported to the light emitting layer 42.
The average thickness of such a hole transport layer 41 is not particularly limited, but is preferably 10 to 150 nm, and more preferably 10 to 100 nm.

(Third light emitting layer)
The light emitting layer 42 includes a light emitting material (third light emitting material).
In the luminescent material, electrons are supplied (injected) from the cathode 7 side, and holes are supplied (injected) from the anode 3 side, whereby the holes and electrons are recombined and released upon this recombination. Exciton (exciton) is generated by the generated energy, and energy (fluorescence or phosphorescence) is emitted (emitted) when the exciton returns to the ground state.
Such a light-emitting material is not particularly limited, and various fluorescent materials and various phosphorescent materials can be used alone or in combination of two or more.

  Examples of the red fluorescent material include perylene derivatives such as tetraaryldiindenoperylene derivatives, europium complexes, benzopyran derivatives, rhodamine derivatives, benzothioxanthene derivatives, porphyrin derivatives, 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.

  Examples of blue fluorescent materials include distyryldiamine derivatives, distyryl derivatives, fluoranthene derivatives, pyrene derivatives, perylene and perylene derivatives, anthracene derivatives, benzoxazole derivatives, benzothiazole derivatives, benzimidazole derivatives, chrysene derivatives, phenanthrene derivatives, dianthrene derivatives, Styrylbenzene derivative, 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-dioctyl-2,7-diyl) - co - (ethyl benzene)], BD102 (product name, include Idemitsu Kosan Co., Ltd.).

Examples of green fluorescent materials include coumarin derivatives, quinacridone derivatives, 9,10-bis [(9-ethyl-3-carbazole) -vinylenyl] -anthracene, poly (9,9-dihexyl-2,7-vinylene full) Orenylene), 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)] and the like.
The yellow fluorescent material is, for example, a compound having a naphthacene skeleton such as a rubrene-based material, in which an aryl group (preferably a phenyl group) is substituted at any position (preferably 2 to 6) with an aryl group (preferably a phenyl group). Compounds, monoindenoperylene derivatives and the like can be used.

Examples of the red phosphorescent material include metal complexes such as iridium, ruthenium, platinum, osmium, rhenium, and palladium. At least one of the ligands of these metal complexes includes a phenylpyridine skeleton, a bipyridyl skeleton, and a porphyrin skeleton. And the like. More specifically, tris (1-phenylisoquinoline) iridium (Ir (piq) 3) represented by the following formula (1), 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).

Examples of the blue phosphorescent material 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 ).

  Examples of the green phosphorescent material 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-phenylpyridinate-N, C2 ′) iridium (acetylacetate) represented by the following formula (2): Nate), and fac-tris [5-fluoro-2- (5-trifluoromethyl-2-pyridine) phenyl-C, N] iridium.

In addition to the light emitting material, the light emitting layer 42 may include a host material (third host material) to which the light emitting material is added as a guest material. Such a light emitting layer 42 can be formed by, for example, doping a host material with a light emitting material as a guest material as a dopant.
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 not particularly limited, but when the light emitting material includes a fluorescent material, for example, rubrene and derivatives thereof, distyrylarylene derivatives, naphthacene materials such as bis p-biphenylnaphthacene, anthracene materials, Perylene derivatives such as bis-orthobiphenylyl perylene, pyrene derivatives such as tetraphenylpyrene, distyrylbenzene derivatives, stilbene derivatives, distyrylamine derivatives, bis (2-methyl-8-quinolinolato) (p-phenylphenolato) aluminum (BAlq), tris (8-quinolinolato) aluminum complex (Alq ₃₎ quinolinolato-based metal complex, triarylamine derivatives such as tetrameric triphenylamine such, arylamine derivatives, oxadiazole derivatives, silole derivatives, Cal Sol derivatives, oligothiophene derivatives, benzopyran derivatives, triazole derivatives, benzoxazole derivatives, benzothiazole derivatives, quinoline derivatives, coronene derivatives, amine compounds, 4,4′-bis (2,2′-diphenylvinyl) biphenyl (DPVBi), IDE120 (a product name, Idemitsu Kosan Co., Ltd.) etc. are mentioned, Among these, it can also be used combining 1 type (s) or 2 or more types. Preferably, IDE120 (made by Idemitsu Kosan Co., Ltd.), anthracene-based material, and dianthracene-based material are preferable when the light-emitting material is blue or green, and rubrene or rubrene derivative, naphthacene-based material when the light-emitting material is red, Perylene derivatives are preferred.

  As the host material, when the light emitting material includes a phosphorescent material, for example, 3-phenyl-4- (1′-naphthyl) -5-phenylcarbazole, 4,4′-N represented by the following formula (3) , N′-dicarbazole biphenyl (CBP), carbazole derivatives, phenanthroline derivatives, triazole derivatives, tris (8-quinolinolato) aluminum (Alq), bis- (2-methyl-8-quinolinolato) -4- (phenylphenolato) ) Quinolinolato metal complexes such as aluminum, N-dicarbazolyl-3,5-benzene, poly (9-vinylcarbazole), 4,4 ′, 4 ″ -tris (9-carbazolyl) triphenylamine, 4,4 ′ -Carbarisol group-containing compounds such as bis (9-carbazolyl) -2,2'-dimethylbiphenyl, Methyl-4,7-diphenyl-1,10-phenanthroline (BCP) and the like, it may be used singly or in combination of two or more of them.

When the light emitting material (guest material) and the host material as described above are used, the content (doping amount) of the light emitting material in the light emitting layer 42 is preferably 0.1 to 30 wt%, and preferably 0.5 to 20 wt%. % Is more preferred. Luminous efficiency can be optimized by setting the content of the light emitting material within such a range.
Further, as the light emitting material of the light emitting layer 42, it is preferable to use a fluorescent material. That is, the light emitting layer 42 preferably contains a light emitting material that emits fluorescence when energized between the anode 3 and the cathode 7.

  A light emitting material that emits phosphorescence (phosphorescent material) has a light emission efficiency superior to that of a light emitting material that emits fluorescence (fluorescent material). However, the phosphorescent material is sensitive to changes in light emission characteristics with respect to impurities, and the light emission characteristics fluctuate when the content of impurities changes with continuous driving of the light emitting element. Therefore, as the light emitting material of the light emitting layer 42, by using a fluorescent material that is less sensitive to changes in light emission characteristics than impurities than the phosphorescent material, the n-type electron transport layer 51 is transferred to the light emitting layer 42 as the light emitting element 1 is continuously driven. Even if the constituent material diffuses, the change in the light emission characteristics of the light emitting layer 42 can be suppressed.

Moreover, it is preferable that the peak wavelength of light emission of the light emitting layer 42 is shorter than the peak wavelength of light emission of the light emitting layer 62 described later. In other words, the light emission peak wavelength of the light emitting layer 62 is preferably longer than the light emission peak wavelength of the light emitting layer 42. Thereby, the light emitting layer 42 and the light emitting layer 62 can be made to emit light with good balance.
The peak wavelength of light emission of the light emitting layer 42 is preferably 500 nm or less, more preferably 400 nm or more and 490 nm or less, and further preferably 430 nm or more and 480 nm or less. In other words, the emission color of the light emitting layer 42 is preferably blue.
A light-emitting material having a short emission peak wavelength is less likely to emit light than a light-emitting material having a long emission peak wavelength. However, in the light-emitting layer 42 not adjacent to another light-emitting layer, a light-emitting material having a short emission peak wavelength may be used. It is difficult for energy to escape to other light emitting layers, and light can be emitted efficiently.

  The average thickness of the light emitting layer 42 is preferably 30 nm or more and 100 nm or less, more preferably 30 nm or more and 70 nm or less, and further preferably 30 nm or more and 50 nm or less. Thereby, even if a constituent material (particularly, an electron donor material) of an n-type electron transport layer 51 of the carrier generation layer 5 described later diffuses into the light emitting layer 42, the light emitting characteristics of the light emitting layer 42 are maintained in a good state. be able to. In addition, it is possible to prevent the light emitting layer 42 from becoming too thick, and as a result, it is possible to prevent the initial driving voltage of the light emitting element 1 from increasing. That is, the driving voltage of the light emitting element 1 can be reduced.

  On the other hand, when the average thickness is less than the lower limit, for example, the n-type electron transport layer 51 emits light depending on the concentration of the electron donor material in the vicinity of the interface between the n-type electron transport layer 51 and the light-emitting layer 42. The light emission characteristics of the light emitting layer 42 may be deteriorated due to the influence of the electron donor material diffused into the layer 42. On the other hand, when the average thickness exceeds the upper limit, the driving voltage of the light emitting element 1 tends to increase.

In the present embodiment, the first light emitting unit 4 includes one light emitting layer as an example. However, the first light emitting unit 4 is a stacked body in which a plurality of light emitting layers are stacked. It may be. In this case, the light emission colors of the plurality of light emitting layers may be the same or different. Moreover, when the 1st light emission part 4 has a several light emitting layer, the intermediate | middle layer may be provided between light emitting layers.
In the first light emitting unit 4, an electron transport layer may be provided on the cathode 7 side with respect to the light emitting layer 42. Such an electron transport layer can be configured in the same manner as an electron transport layer 64 of the second light emitting unit 6 described later. Further, an electron injection layer may be provided on the cathode 7 side with respect to the electron transport layer. Such an electron injection layer can be configured in the same manner as an electron injection layer 65 of the second light emitting unit 6 described later.

[Carrier generation layer]
The carrier generation layer 5 has a function of generating carriers (holes and electrons).
The carrier generation layer 5 is formed by laminating an n-type electron transport layer 51 and an electron withdrawing layer 52 in this order from the anode 3 side to the cathode 7 side.
In addition, the average thickness of the carrier generation layer 5 is preferably 5 to 80 nm, and more preferably 20 to 70 nm. Thereby, the function (carrier generation function) of the carrier generation layer 5 can be sufficiently exhibited while preventing the drive voltage of the light emitting element 1 from increasing.

Hereinafter, each layer constituting the carrier generation layer 5 will be sequentially described in detail.
(Electron transport layer)
The n-type electron transport layer 51 is provided between the light emitting layer 42 and the electron withdrawing layer 52 described above, and has a function of transporting electrons from the electron attracting layer 52 side to the light emitting layer 42 side.
Such an n-type electron transport layer 51 may be composed of an electron transport material having an electron transport property as a main material, but in addition to an electron transport material having an electron transport property, an electron having an electron injection property. It is preferable to include an injectable material (electron donor material).

Thereby, electrons attracted by the electron withdrawing layer 52 can be efficiently injected into the n-type electron transport layer 51 and efficiently transported to the anode 3 side through the n-type electron transport layer 51.
In particular, the n-type electron transport layer 51 is preferably composed of a mixed material including an electron transport material and an electron donor material. The n-type electron transport layer 51 thus configured has excellent electron transport properties and electron injection properties. Therefore, electrons generated in the carrier generation layer 5 can be efficiently transported and injected into the light emitting layer 42.
Further, when the n-type electron transport layer 51 is configured by adding (doping) an electron donor material to the electron transport material, in the n-type electron transport layer 51, the electron transport material receives electrons from the electron donor material. Upon receipt, it becomes a radical anion state. Therefore, the amount of carrier generation in the carrier generation layer 5 can be increased.

Examples of the electron transporting material used for the n-type electron transporting layer 51 include quinoline derivatives such as organometallic complexes having 8-quinolinol or its derivatives such as tris (8-quinolinolato) aluminum (Alq ₃ ) as a ligand. Oxadiazole derivatives, perylene derivatives, pyridine derivatives, pyrimidine derivatives, quinoxaline derivatives, diphenylquinone derivatives, nitro-substituted fluorene derivatives, and the like, and one or more of these can be used in combination.

Examples of the electron injecting material (electron donor material) used for the n-type electron transport layer 51 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.

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.
In particular, as the electron injecting material (electron donor material) used for the n-type electron transport layer 51, one or more of alkali metals, alkaline earth metals, alkali metal compounds, and alkaline earth metal compounds are used. It is preferable to use in combination. Thereby, the electron injection property of the n-type electron transport layer 51 can be further improved while making the electron transport property of the n-type electron transport layer 51 excellent. In particular, alkali metal compounds (alkali metal chalcogenides, alkali metal halides, and the like) have a very small work function, and the n-type electron transport layer 51 is used to form the light-emitting element 1 so that high luminance can be obtained. It will be.

The n-type electron transport layer 51 has a function of blocking holes.
When the n-type electron transport layer 51 is formed using an electron transport material and an electron injection material, the electron transport material is used as a host material, the electron injection material is used as a guest material, and the electron transport material is formed by co-evaporation or the like. The n-type electron transport layer 51 can be formed by doping an electron injecting material.

  Further, when the n-type electron transport layer 51 is configured using an electron transport material and an electron injection material, the content (dope amount) of the electron injection material in the n-type electron transport layer 51 is 0.1 to It is preferably 20 wt%, and more preferably 0.5 to 10 wt%. By setting the content of the electron injecting material in such a range, both the electron transporting property and the electron injecting property of the n-type electron transporting layer 51 can be made excellent in a balanced manner.

Further, when the concentration of the electron donor material (electron injecting material) in the n-type electron transport layer 51 is gradually decreased from the cathode 7 side toward the anode 3 side, electrons generated in the carrier generation layer 5 are emitted. While efficiently transporting and injecting into the layer 42, the life of the light emitting element 1 can be extended by suppressing the amount of the electron donor material in the n-type electron transport layer 51 diffusing into the light emitting layer 42. In this case, the concentration of the electron donor material may change stepwise or may change continuously.
Further, the average thickness of the n-type electron transport layer 51 is not particularly limited, but is preferably 10 to 100 nm, and more preferably 10 to 50 nm. Accordingly, electrons attracted by the electron withdrawing layer 52 can be efficiently transported to the anode 3 side, and holes that have passed through the first light emitting unit 4 can be blocked.

(Electronic suction layer)
The electron withdrawing layer (electron extraction layer) 52 is provided between the light emitting layer 42 and the light emitting layer 62, and is adjacent to the cathode 7 side (in this embodiment, the hole transport layer 61 of the second light emitting unit 6). ) Has a function of sucking (pulling out) electrons from The electrons attracted by the electron withdrawing layer 52 are injected into a layer adjacent to the anode 3 side (in this embodiment, the n-type electron transport layer 51).

Such an electron withdrawing layer 52 is composed of an organic compound having an electron withdrawing property as a main material.
As the organic compound having electron withdrawing property, an organic cyanide compound having an aromatic ring (hereinafter also referred to as “aromatic ring-containing organic cyanide compound”) is preferably used.
The aromatic ring-containing organic cyan compound has excellent electron withdrawing properties. Therefore, by forming the electron withdrawing layer 52 including an organic cyanide compound having an aromatic ring, the generation amount of holes and electrons in the carrier generation layer 5 can be increased.

  The electron withdrawing layer 52 mainly composed of an aromatic ring-containing organic cyanide compound draws electrons from the hole transporting material constituting the hole transporting layer 61 by contacting the adjacent layer (hole transporting layer 61). Can do. As a result, when the electron withdrawing layer 52 and the hole transporting layer 61 are in contact with each other, electrons are not present on the electron withdrawing layer 52 side in the vicinity of the interface between the electron withdrawing layer 52 and the hole transporting layer 61 even if no voltage is applied. And holes are generated on the hole transport layer 61 side. When a driving voltage is applied between the anode 3 and the cathode 7 in such a state, holes generated near the interface between the electron withdrawing layer 52 and the hole transporting layer 61 are moved to the cathode 7 side by the driving voltage. It is transported and contributes to the light emission of the second light emitting unit 6 (specifically, the light emitting layer 62 and the light emitting layer 63). Further, electrons generated near the interface between the electron withdrawing layer 52 and the hole transport layer 61 are transported to the anode 3 side by the driving voltage, and the first light emitting unit 4 (specifically, the light emitting layer 42) is transported. Contributes to light emission. The generation of holes and electrons by the electron withdrawing layer 52 as described above is continuously performed while the drive voltage is applied, and these holes and electrons are generated by the light emitting layer 42, the light emitting layer. 62 and the light emitting layer 63 contribute to light emission.

The aromatic ring-containing organic cyanide compound is a relatively stable compound and can easily form the electron withdrawing layer 52 by a vapor deposition method such as vapor deposition. For this reason, it can use suitably for manufacture of the light emitting element 1, the quality of the manufactured light emitting element 1 becomes easy to be stabilized, and the yield of the light emitting element 1 becomes a high thing.
Such an aromatic ring-containing organic cyan compound is not particularly limited as long as it can exhibit the functions as described above, but is preferably a hexaazatriphenylene derivative into which a cyano group is introduced, for example, It is more preferable to use a hexaazatriphenylene derivative represented by the formula (4).

In the above formula (4), R1 to R6 are each independently a cyano group (—CN), a sulfone group (—SO ₂ R ′), a sulfoxide group (—SOR ′), a sulfonamide group (—SO ₂ NR). _'2), sulfonate groups (-SO ₃ R'), nitro group _(-NO 2), or a trifluoromethane (-CF ₃₎ group, at least one of the substituents of the R1~R6 have cyano group. R ′ is an alkyl group having 1 to 60 carbon atoms, an aryl group, or a heterocyclic group that is substituted or unsubstituted with an amine group, an amide group, an ether group, or an ester group.

Such a compound is excellent in electron withdrawing property. Therefore, the electron withdrawing layer 52 formed using such a compound can sufficiently extract electrons from the adjacent layer (hole transporting layer 61), and transport the suitably extracted electrons to the anode 3 side. can do.
In particular, as the aromatic ring-containing organic cyan compound, in the compound represented by the formula (4) as described above, it is preferable that all of R1 to R6 are cyano groups. That is, as the aromatic ring-containing organic cyan compound, it is preferable to use hexacyanohexaazatriphenylene as represented by the following formula (5). Such a compound has a plurality of cyano groups having a high electron-withdrawing property. Therefore, the electron withdrawing layer 52 formed using such a compound can more efficiently draw electrons from the constituent material of the adjacent layer (such as the hole transporting material of the hole transporting layer 61), and the carrier ( The amount of generation of electrons and holes) can be increased.

The aromatic ring-containing organic cyanide compound is preferably present in an amorphous state in the electron withdrawing layer 52. Thereby, the effect of the aromatic ring-containing organic cyanide compound as described above can be obtained more remarkably.
Moreover, the average thickness of the electron withdrawing layer 52 is preferably 5 to 40 nm, and more preferably 10 to 30 nm. Thereby, the function (electron attracting property) of the electron withdrawing layer 52 as described above can be sufficiently exhibited while preventing the drive voltage of the light emitting element 1 from being increased.

  In the carrier generation layer 5 configured as described above, another layer may be interposed between the n-type electron transport layer 51 and the electron withdrawing layer 52. For example, between the n-type electron transport layer 51 and the electron withdrawing layer 52, a diffusion preventing layer for preventing diffusion of the material between these layers, or electrons from the electron withdrawing layer 52 side to the n-type electron transporting layer 51 side. An electron injection layer for injecting may be provided.

[Second light emitting unit]
As described above, the second light emitting unit 6 includes the hole transport layer 61, the light emitting layer 62, the light emitting layer 63, the electron transport layer 64, and the electron injection layer 65.
(Hole transport layer)
The hole transport layer 61 has a function of transporting holes injected from the carrier generation layer 5 (the electron withdrawing layer 52) to the light emitting layer 62. The hole transport layer 61 also has a function of preventing electrons from reaching the carrier generation layer 5 and deterioration of the carrier generation layer 5 by blocking electrons that have passed through the light emitting layer 62.

In particular, the hole transport layer 61 is provided in contact with the carrier generation layer 5 between the light emitting layer 62 and the carrier generation layer 5 described above.
Thereby, as described above, the electron withdrawing layer 52 can efficiently withdraw electrons from the hole transport layer 61. As a result, the amount of holes and electrons generated in the carrier generation layer 5 can be increased.
As the constituent material of the hole transport layer 61, the same material as the constituent material of the hole transport layer 41 or the same material as the hole transport material in the host material of the light emitting layer 62 described later can be used.

The hole transport layer 61 is provided in contact with the light emitting layer 62. Such a hole transport layer 61 is preferably configured to contain the same hole transport material as the hole transport material (hole transport host material) contained in the light emitting layer 62.
Thereby, the hole transport property from the hole transport layer 61 to the light emitting layer 62 can be improved. As a result, the driving voltage of the light emitting element 1 can be suppressed and the life of the light emitting element 1 can be extended.

Further, as the hole transport material constituting the hole transport layer 61, an amine compound is preferable. Such a compound is brought into contact with the carrier generation layer 5 (electron withdrawing layer 52), whereby electrons are quickly extracted and holes are generated and injected.
The average thickness of the hole transport layer 61 is not particularly limited, but is preferably 10 to 150 nm, and more preferably 10 to 100 nm. Thereby, while being able to transport a hole suitably to the light emitting layer 62, the electron which passed the light emitting layer 62 can be blocked suitably.

(First light emitting layer)
The light emitting layer 62 includes a light emitting material.
Such a light emitting material is not particularly limited, and a light emitting material similar to that of the light emitting layer 42 described above can be used. Note that the light emitting material used for the light emitting layer 62 may be the same as or different from the light emitting material of the light emitting layer 42. The light emission color of the light emitting layer 62 may be the same as or different from the light emission color of the light emitting layer 42 described above.

In addition, a phosphorescent material is preferably used as the light emitting material (first light emitting material) included in the light emitting layer 62. That is, the light emitting layer 62 preferably includes a light emitting material that emits phosphorescence when energized between the anode 3 and the cathode 7.
When the light emitting material (first light emitting material) of the light emitting layer 62 contains a phosphorescent light emitting material (particularly, when both the first light emitting material and the second light emitting material contain a phosphorescent light emitting material). The light emitting layer 62 and the light emitting layer 63 can emit light with a high balance with high luminous efficiency.
In addition, by using a phosphorescent material as a light emitting material of the light emitting layer 62 with little or no impurity diffusion due to continuous driving of the light emitting element 1, the light emitting layer 62 can efficiently emit light. As a result, the light emitting element 1 emits light. Efficiency can be improved.

The light emitting layer 62 includes a host material to which the light emitting material is added as a guest material in addition to the light emitting material.
The host material (first host material) included in the light emitting layer 62 holds the first light emitting material.
The first host material is a mixed material including a hole transporting material (hereinafter also referred to as “hole transporting host material”) and an electron transporting material (hereinafter also referred to as “electron transporting host material”). It consists of

  Thereby, the light emitting material is efficiently excited in the light emitting layer 62, and the light emitting layer 62 transports holes from the anode 3 side to the cathode 7 side and transports electrons from the cathode 7 side to the anode 3 side. Can be performed smoothly. In addition, deterioration of the light emitting layer 62 due to carriers can be prevented or suppressed. In addition, since the carrier transportability of the light emitting layer 62 can be prevented from being lowered, the light emission balance between the light emitting layer 62 and the light emitting layer 63 can be maintained over a long period.

In particular, the content of the hole transporting material in the first host material is larger than the content of the electron transporting material in the first host material.
Accordingly, the content of the hole transporting material in the light emitting layer 62 is increased, and electrons can be smoothly transported from the light emitting layer 62 to the light emitting layer 63. Therefore, the driving voltage of the light emitting element 1 can be suppressed.
Further, the content of the electron transporting material in the light emitting layer 62 is suppressed, and the amount of electrons that escape from the light emitting layer 62 to the anode 3 side can be suppressed. Therefore, deterioration of other layers (for example, the hole transport layer 61) located on the anode 3 side with respect to the light emitting layer 62 can be prevented or suppressed, and as a result, the life of the light emitting element 1 can be extended.

  Examples of the hole transporting material contained in the first host material include 4,4 ′, 4 ″ -tris (N-carbazolyl) -triphenylamine (TCTA), 4,4 ′, 4 ″. -Triphenylamine compounds such as tris (N-phenyl-Nm-tolylamino) triphenylamine (m-MTDATA) or derivatives thereof, N, N'-di (1-naphthyl) -N, N'-diphenyl- 1,1′-diphenyl-4,4′-diamine (NPD), N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-diphenyl-4,4′-diamine And tetraarylbenzidine derivatives such as (TPD), tetraaryldiaminofluorene compounds or derivatives thereof (amine compounds), etc., and one or more of these are combined. It can be used Te.

Moreover, as an electron transport material contained in the first host material, for example, an organometallic complex having an 8-quinolinol or its derivative such as tris (8-quinolinolato) aluminum (Alq ₃ ) as a ligand, etc. Quinoline derivatives, oxadiazole derivatives such as 1,3-bis (N, Nt-butyl-phenyl) -1,3,4-oxadiazole (OXD-7), perylene derivatives, pyridine derivatives, pyrimidine derivatives, Examples include quinoxaline derivatives, diphenylquinone derivatives, nitro-substituted fluorene derivatives, 1,3,5-tris (2-N-phenylbenzimidazolyl) benzene (TPBi), and combinations of one or more of these Can be used.
The mixing ratio of the hole transporting material and the electron transporting material in the first host material (hole transporting material: electron transporting material) is preferably 60:40 to 80:20, and 65 : It is more preferable that it is 35-75: 25. Thereby, the effect mentioned above can be exhibited notably.

Moreover, it is preferable that it is 0.1-20 wt%, and, as for content (dope amount) of the luminescent material in the light emitting layer 62, it is more preferable that it is 0.5-15 wt%. Luminous efficiency can be optimized by setting the content of the light emitting material within such a range.
In the case where a phosphorescent material is used as the light-emitting material (first light-emitting material) of the light-emitting layer 62, the triplet energies of the hole-transport material and the electron-transport material in the first host material are It is preferable that it is larger than the triplet energy of the phosphorescent material in the light emitting material.
Thereby, it is possible to accurately suppress or prevent the triplet energy of the phosphorescent material from deactivating without contributing as energy for light emission (phosphorescence). Therefore, the light emission efficiency can be increased.

Moreover, it is preferable that the light emission peak wavelength of the light emitting layer 62 is longer than the light emission peak wavelength of the light emitting layer 63 described later. Thereby, the light emission generated in the light emitting layer 62 and the light emitting layer 63 can be efficiently extracted to the outside.
Moreover, it is preferable that the light emission peak wavelength of the light emitting layer 62 is longer than the light emission peak wavelength of the light emitting layer 42 described above. Thereby, the light emitting layer 42 and the light emitting layer 62 can be made to emit light with good balance.

  Further, the average thickness of the light emitting layer 62 is not particularly limited, but is preferably 5 to 50 nm, more preferably 5 to 40 nm, and further preferably 5 to 30 nm. Thereby, while suppressing the drive voltage of the light emitting element 1, the light emitting layer 62 can be light-emitted efficiently. In particular, in the case where the light emitting layer 62 and the light emitting layer 63 are stacked as in the present embodiment, the recombination region that causes the recombination of holes and electrons by relatively reducing the thickness of the light emitting layer 62. Inside, both the light emitting layer 62 and the light emitting layer 63 exist, and these can be light-emitted with good balance.

(Second light emitting layer)
The light emitting layer 63 includes a light emitting material.
The light emitting layer 63 is in contact with the light emitting layer 62 described above. Thereby, both the light emitting layer 62 and the light emitting layer 63 can be easily present in the recombination region of holes and electrons in the second light emitting unit 6. Therefore, both the light emitting layer 62 and the light emitting layer 63 can easily emit light.

  Such a light emitting material is not particularly limited, and a light emitting material similar to that of the light emitting layer 42 described above can be used. Note that the light emitting material used for the light emitting layer 63 may be the same as or different from the light emitting material of the light emitting layer 42. The light emitting material used for the light emitting layer 63 may be the same as or different from the light emitting material of the light emitting layer 62. Further, the light emission color of the light emitting layer 63 may be the same as or different from the light emission color of the light emitting layer 42 described above. The light emission color of the light emitting layer 63 may be the same as or different from the light emission color of the light emitting layer 62 described above.

Further, as the light emitting material (second light emitting material) included in the light emitting layer 63, it is preferable to use a phosphorescent material. That is, the light emitting layer 63 preferably contains a light emitting material that emits phosphorescence when energized between the anode 3 and the cathode 7.
Since the second light-emitting material includes the phosphorescent light-emitting material (particularly, because both the first light-emitting material and the second light-emitting material include the phosphorescent light-emitting material), the light-emitting layer 62 can be obtained with high light emission efficiency. Further, the light emitting layer 63 can emit light with a good balance.
In addition, by using a phosphorescent material as a light emitting material of the light emitting layer 63 with little or no impurity diffusion due to continuous driving of the light emitting element 1, the light emitting layer 63 can efficiently emit light. As a result, the light emitting element 1 emits light. Efficiency can be improved.

The light emitting layer 63 includes a light emitting material and a host material to which the light emitting material is added as a guest material.
The host material (second host material) contained in the light emitting layer 63 holds the second light emitting material.
Further, the second host material is composed of a mixed material including a hole transporting material and an electron transporting material.
Thereby, the light emitting material in the light emitting layer 63 is efficiently excited, and the light emitting layer 63 transports holes from the anode 3 side to the cathode 7 side and transports electrons from the cathode 7 side to the anode 3 side. Can be performed smoothly. In addition, deterioration of the light emitting layer 63 due to carriers can be prevented or suppressed.

In particular, the content of the hole transporting material in the second host material is smaller than the content of the electron transporting material in the second host material.
Accordingly, the content of the electron transporting material in the light emitting layer 63 is increased, and electrons can be smoothly transported from the light emitting layer 63 to the light emitting layer 62. Therefore, the driving voltage of the light emitting element 1 can be suppressed.

Further, the content of the hole transporting material in the light emitting layer 63 is suppressed, and the amount of holes that escape from the light emitting layer 63 to the cathode 7 side can be suppressed. Therefore, deterioration of other layers (for example, the electron transport layer 64) positioned on the cathode 7 side with respect to the light emitting layer 63 can be prevented or suppressed, and as a result, the life of the light emitting element 1 can be extended.
As the hole transporting material contained in the second host material, the same material as the hole transporting material contained in the first host material described above can be used.

Further, as the electron transporting material contained in the second host material, the same material as the electron transporting material contained in the first host material described above can be used.
The hole transporting material contained in the second host material is preferably the same type as the hole transporting material contained in the first host material described above. Thereby, the hole transport property from the light emitting layer 62 to the light emitting layer 63 can be improved. As a result, the driving voltage can be suppressed and the life can be extended.

The electron transporting material contained in the second host material is preferably the same type as the electron transporting material contained in the first host material described above. Thereby, the electron transport property from the light emitting layer 63 to the light emitting layer 62 can be improved. As a result, the driving voltage can be suppressed and the life can be extended.
The compounding ratio of the hole transporting material and the electron transporting material in the second host material (hole transporting material: electron transporting material) is preferably 40:60 to 20:80, and 35 : 65-25: 75 is more preferable. Thereby, the effect mentioned above can be exhibited notably.

Moreover, it is preferable that it is 0.1-30 wt%, and, as for content (dope amount) of the luminescent material in the light emitting layer 63, it is more preferable that it is 0.5-20 wt%. Luminous efficiency can be optimized by setting the content of the light emitting material within such a range.
In the case where a phosphorescent material is used as the light-emitting material (second light-emitting material) of the light-emitting layer 63, the triplet energies of the hole transport material and the electron transport material in the second host material are the second It is preferable that it is larger than the triplet energy of the phosphorescent material in the light emitting material.
Thereby, it is possible to accurately suppress or prevent the triplet energy of the phosphorescent material from deactivating without contributing as energy for light emission (phosphorescence). Therefore, the light emission efficiency can be increased.
Moreover, it is preferable that the light emission peak wavelength of the light emitting layer 63 is longer than the light emission peak wavelength of the light emitting layer 42. Thereby, the light emitting layer 42, the light emitting layer 62, and the light emitting layer 63 can be light-emitted with good balance.

Further, the average thickness of the light emitting layer 63 is not particularly limited, but is preferably 5 to 50 nm, more preferably 5 to 40 nm, and further preferably 5 to 30 nm. Thereby, while suppressing the drive voltage of the light emitting element 1, the light emitting layer 63 can be light-emitted efficiently. In particular, in the case where the light emitting layer 62 and the light emitting layer 63 are stacked as in the present embodiment, the recombination region that causes recombination of holes and electrons by making the thickness of the light emitting layer 63 relatively thin. Inside, both the light emitting layer 62 and the light emitting layer 63 exist, and these can be light-emitted with good balance.
The total of the average thickness of the light emitting layer 62 and the average thickness of the light emitting layer 63 is preferably 30 nm or more and 50 nm or less. Accordingly, it is possible to easily and reliably suppress the amount of electrons that escape from the light emitting layer 62 to the anode 3 side and the amount of holes that escape from the light emitting layer 63 to the cathode 7 side while suppressing the driving voltage.

  In the present embodiment, the case where the second light emitting unit 6 includes two light emitting layers (that is, the light emitting layer 62 and the light emitting layer 63) is described as an example. You may have a light emitting layer more than a layer. That is, the second light emitting unit 6 may include one or more other light emitting layers in addition to the light emitting layer 62 and the light emitting layer 63 described above. Moreover, when the 2nd light emission part 6 has a several light emitting layer, the light emission color of a some light emitting layer may mutually be the same, or may differ. When the second light emitting unit 6 has three or more light emitting layers, an intermediate layer is provided between the other light emitting layers other than between the first light emitting layer and the second light emitting layer. It may be.

(Electron transport layer)
The electron transport layer 64 has a function of transporting electrons injected from the cathode 7 through the electron injection layer 65 to the light emitting layer 63.
Examples of the constituent material (electron transporting material) of the electron transporting layer 64 include quinolines such as organometallic complexes having 8-quinolinol or a derivative thereof such as tris (8-quinolinolato) aluminum (Alq ₃ ) as a ligand. Derivatives, oxadiazole derivatives, perylene derivatives, pyridine derivatives, pyrimidine derivatives, quinoxaline derivatives, diphenylquinone derivatives, nitro-substituted fluorene derivatives, 1,3,5-tris (2-N-phenylbenzimidazolyl) benzene (TPBi), etc. 1 type or 2 types or more of these can be used in combination.

The electron transport layer 64 is provided in contact with the light emitting layer 63. Such an electron transport layer 64 is preferably configured to include the same kind of electron transport material as the electron transport material (electron transport host material) included in the light emitting layer 63.
Thereby, the electron transport property from the electron carrying layer 64 to the light emitting layer 63 can be improved. As a result, the driving voltage of the light emitting element 1 can be suppressed and the life of the light emitting element 1 can be extended.

Although the average thickness of the electron carrying layer 64 is not specifically limited, It is preferable that it is 10-100 nm, and it is more preferable that it is 10-50 nm.
An intermediate layer may be provided between the electron transport layer 64 and the light emitting layer 63. An example of such an intermediate layer is a hole blocking layer. Hereinafter, the hole blocking layer will be briefly described.

(Hole blocking layer)
The hole blocking layer has a function of blocking holes. Thereby, it is possible to prevent holes from being transported from the light emitting layer 63 to the electron transport layer 64 described above. Therefore, it is possible to prevent the electron transport layer 64 from being deteriorated by holes. The hole blocking layer has a function of transporting electrons. Thereby, electrons received from the electron transport layer 64 described later can be transported to the light emitting layer 63.

Examples of the constituent material of the hole blocking layer include 3-phenyl-4- (1′-naphthyl) -5-phenylcarbazole, 4,4′-N, N′-dicarbazole biphenyl (CBP), and the like. Carbazole derivatives, phenanthroline derivatives, triazole derivatives, quinolinolato metal complexes such as tris (8-quinolinolato) aluminum (Alq), bis- (2-methyl-8-quinolinolato) -4- (phenylphenolato) aluminum, N- Dicarbazolyl-3,5-benzene, poly (9-vinylcarbazole), 4,4 ′, 4 ″ -tris (9-carbazolyl) triphenylamine, 4,4′-bis (9-carbazolyl) -2,2 Carbazolyl group-containing compounds such as' -dimethylbiphenyl, 2,9-dimethyl-4,7-diphenyl-1,10-phena Tororin (BCP) and the like, may be used singly or in combination of two or more of them.
The average thickness of the hole blocking layer is not particularly limited, but is preferably 1 to 50 nm, more preferably 3 to 30 nm, and further preferably 5 to 20 nm.

(Electron injection layer)
The electron injection layer 65 has a function of improving the electron injection efficiency from the cathode 7.
Examples of the constituent material (electron injection material) of the electron injection layer 65 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 configuring the electron injection layer 65 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 small work function, and the light-emitting element 1 can have high luminance by forming the electron injection layer 65 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 65 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.

[cathode]
The cathode 7 is an electrode that injects electrons into the second light emitting unit 6 described above. As a constituent material of the cathode 7, it is preferable to use a material having a small work function.
Examples of the constituent material of the cathode 7 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 7, 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 7, the electron injection efficiency and stability of the cathode 7 can be improved.
The average thickness of the cathode 7 is not particularly limited, but is preferably about 100 to 400 nm, and more preferably about 100 to 200 nm.
In addition, since the light emitting element 1 of this embodiment is a bottom emission type, the light transmittance of the cathode 7 is not particularly required.

[Sealing member]
The sealing member 8 is provided so as to cover the anode 3, the laminated body 15, and the cathode 7, and has a function of hermetically sealing them and blocking oxygen and moisture. By providing the sealing member 8, 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 8 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 8, in order to prevent a short circuit, between the sealing member 8 and the anode 3, the laminated body 15, and the cathode 7, it is required. Accordingly, it is preferable to provide an insulating film.
Further, the sealing member 8 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, holes and electrons are generated in the carrier generation layer 5 by applying a voltage between the anode 3 and the cathode 7. The generated electrons are transported to the light emitting layer 42 and recombined with holes injected from the anode 3, thereby contributing to light emission. The generated holes are transported to the light emitting layer 62 and the light emitting layer 63 and recombine with electrons injected from the cathode 7 to contribute to light emission.
As a result, the light emitting element 1 can emit light from the light emitting layer 42, the light emitting layer 62, and the light emitting layer 63, respectively. Therefore, the light emitting element 1 improves the light emission efficiency and is driven as compared with the light emitting element having only one light emitting layer. The voltage can be reduced.

In particular, the light-emitting element 1 smoothly supplies holes and electrons to the light-emitting layer 62 and the light-emitting layer 63 because the light-emitting layer 62 and the light-emitting layer 63 contain a hole transport material and an electron transport material, respectively. be able to. Therefore, the light emitting layer 62 and the light emitting layer 63 can each emit light with high light emission efficiency. In addition, since the light-emitting layer 62 and the light-emitting layer 63 contain a hole transporting material and an electron transporting material, respectively, deterioration of the light-emitting layer 62 and the light-emitting layer 63 due to carriers can be prevented or suppressed.
In particular, by increasing the content of the hole transporting material in the light emitting layer 62 and the content of the electron transporting material in the light emitting layer 63, respectively, transport of electrons from the light emitting layer 62 to the light emitting layer 63, and In addition, it is possible to smoothly transport holes from the light emitting layer 63 to the light emitting layer 62. Therefore, the driving voltage of the light emitting element 1 can be suppressed.

  Further, by suppressing the content of the electron transporting material in the light emitting layer 62 and the content of the hole transporting material in the light emitting layer 63, the amount of electrons that escape from the light emitting layer 62 to the anode 3 side, and The amount of holes that escape from the light emitting layer 63 to the cathode 7 side can be suppressed. Therefore, another layer (for example, hole transport layer 61) located on the anode 3 side with respect to the light emitting layer 62, and another layer (for example, electron transport layer 64) located on the cathode 7 side with respect to the light emitting layer 63. As a result, the life of the light emitting element 1 can be extended.

The light emitting element 1 configured as described above can be manufactured, for example, as follows.
[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 first light-emitting portion 4 is formed on the anode 3.
The first light emitting unit 4 can be provided by sequentially forming the hole transport layer 41 and the light emitting layer 42 on the anode 3.
Each layer as described above 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.

Alternatively, a liquid material obtained by dissolving the constituent materials of each layer in a solvent or dispersing in a dispersion medium is supplied onto the anode 3 (or a layer above it) and then dried (desolvent or dedispersion medium). Can be formed.
As a method for supplying the liquid 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 layers constituting the first light emitting unit 4 can be formed relatively easily.
Examples of the solvent or dispersion medium used for the preparation of the liquid material include various inorganic solvents, various organic solvents, and 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 carrier generation layer 5 is formed on the first light emitting unit 4.
The carrier generation layer 5 can be formed by sequentially laminating an n-type electron transport layer 51 and an electron withdrawing layer 52 on the first light emitting unit 4.
Each layer constituting the carrier generation layer 5 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, a material formed by dissolving the material of the layer constituting the carrier generation layer 5 in a solvent or dispersing in a dispersion medium is supplied onto the first light emitting unit 4 and then dried (desolvent or dedispersion medium). Can also be formed.

[4] Next, the second light-emitting portion 6 is formed on the carrier generation layer 5.
The second light emitting unit 6 can be formed in the same manner as the first light emitting unit 4.
[5] Next, the cathode 7 is formed on the second light emitting unit 6.
The cathode 7 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 8 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, the light-emitting device is driven at a relatively low voltage, has high light emission efficiency and a long light emission lifetime, and has high reliability.
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, 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, a reflective film 32, a corrosion preventing film 33, an anode 3, a laminate (organic EL light emitting unit) 15, a cathode 7, and a cathode cover 34 are laminated on the planarizing layer 22 in this order. 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. Moreover, the cathode 7 of each light emitting element 1R, 1G, 1B is a common electrode.

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.
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.

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 (R). The color filter 19G converts the white light W from the light emitting element 1G into green (G). The color filter 19B converts the white light W from the light emitting element 1B into blue (B). 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 can be performed without using a color filter by selecting a light emitting material used for each light emitting element 1R, 1G, 1B. .

Since such a display device 100 (the display device of the present invention) uses the light emitting device as described above, it is driven at a relatively low voltage, has excellent durability (long emission life), and excellent light emission efficiency. It is. Therefore, high-quality images can be displayed over a long period of time with low power consumption, and the reliability is excellent.
Such a display device 100 (the display device of the present invention) can be incorporated into various electronic devices. Since such an electronic device uses the display device as described above, it is possible to increase the light emission efficiency and reduce the driving voltage while maintaining excellent durability. Therefore, a high-quality image can be displayed over a long period of time, and the reliability is excellent.

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 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.

  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, the light-emitting element described above has been described as having three light-emitting layers. However, the present invention is not limited to this. For example, the light-emitting element may have two light-emitting layers or four or more layers. The light emitting layer may be included.

In the above-described embodiment, the light emitting element is described as an example in which two light emitting portions are provided with a carrier generation layer sandwiched therebetween (so-called tandem light emitting element). However, the number of light emitting portions is one. Also good. In this case, for example, in the light emitting element of the above-described embodiment, the first light emitting unit and the carrier generation layer may be omitted.
In the above-described embodiment, the case where the third light emitting layer is provided between the anode and the first light emitting layer has been described as an example, but the third light emitting layer is provided between the cathode and the second light emitting layer. A light emitting layer may be provided. In this case, for example, a carrier generation layer may be provided between the second light emitting layer and the third light emitting layer.

In the case where the third light-emitting layer is provided, a carrier between the light-emitting layer closer to the third light-emitting layer of the first light-emitting layer and the second light-emitting layer and the third light-emitting layer is provided. Instead of the generation layer, a layer having no carrier generation function, for example, an intermediate layer including at least one of a hole transport material and an electron transport material may be provided.
In the light-emitting element described above, the light-emitting portion (light-emitting unit) has been described as having a layer other than the light-emitting layer (for example, a hole transport layer, an electron transport layer, and the like). As long as it has the light emitting layer of a layer, it may be comprised only by the light emitting layer, for example.

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, N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-diphenyl-4,4′-diamine (TPD) is vacuum-deposited on the ITO electrode. Vapor deposition was performed by the method to form a hole transport layer having an average thickness of 60 nm.

<3> Next, a first light-emitting layer (red light-emitting layer) having an average thickness of 10 nm was formed on the hole-transporting layer using a vacuum deposition method.
Here, btp2Ir (acac) which is a red phosphorescent material (guest material) was used as a light emitting material (first light emitting material) of the first light emitting layer. Further, as the host material (first host material) of the first light-emitting layer, 4,4 ′, 4 ″ -tris (N-carbazolyl) -tri, which is a hole transporting material (hole transporting host material), is used. Mixed material of phenylamine (TCTA): 70 wt% and 1,3,5-tris (2-N-phenylbenzimidazolyl) benzene (TPBi): 30 wt%, which is an electron transport material (electron transport host material) Was used.
Further, the content (dope concentration) of the red phosphorescent material in the first light emitting layer was 10.0 wt%.

<4> Next, on the 1st light emitting layer, the 2nd light emitting layer (green light emitting layer) with an average thickness of 10 nm was formed using the vacuum evaporation method.
Here, Ir (ppy) 3 which is a green phosphorescent material (guest material) was used as the light emitting material (second light emitting material) of the second light emitting layer. As the host material (second host material) of the second light-emitting layer, 4,4 ′, 4 ″ -tris (N-carbazolyl) -tri, which is a hole transporting material (hole transporting host material), is used. A mixed material of phenylamine (TCTA): 30 wt% and 1,3,5-tris (2-N-phenylbenzimidazolyl) benzene (TPBi): 70 wt%, which is an electron transporting material (electron transporting host material) Was used.
Further, the content (dope concentration) of the green phosphorescent material in the second light emitting layer was 15.0 wt%.

<5> Next, on the second light-emitting layer, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) is deposited by a vacuum deposition method, and an electron transport layer having an average thickness of 65 nm. Formed.
<6> Next, Al was formed into a film by the vacuum evaporation method on the electron carrying layer. Thereby, a cathode having an average thickness of 200 nm made of Al was formed.
<7> 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 element in which an anode, a hole transport layer, a first light-emitting layer, a second light-emitting layer, an electron transport layer, and a cathode were stacked in this order on the substrate was manufactured.

(Example 2)
A light emitting device was manufactured in the same manner as in Example 1 except that the average thickness of the first light emitting layer and the second light emitting layer was 25 nm, respectively, and the average thickness of the electron transport layer was 35 nm.
(Example 3)
The average thickness of the first light-emitting layer and the second light-emitting layer is 25 nm, the average thickness of the electron transport layer is 35 nm, TCTA is used as the constituent material of the hole transport layer, and the constituent material of the electron transport layer is A light emitting device was manufactured in the same manner as in Example 1 except that TPBi was used.
That is, a light emitting device was manufactured in the same manner as in Example 2 except that TCTA was used as the constituent material of the hole transport layer and TPBi was used as the constituent material of the electron transport layer.

Example 4
A tandem light emitting device to which the present invention was applied was manufactured.
The light emitting element of Example 4 has a configuration in which the light emitting part of the light emitting element of Example 3 described above and another light emitting part having a blue light emitting layer are connected via a carrier generation layer.
Hereinafter, the production of the light emitting device of Example 4 will be specifically described.

<1A> First, an ITO electrode (anode) was formed on a substrate in the same manner as in <1> of Example 1 described above.
And after immersing a board | substrate in order of acetone and 2-propanol and ultrasonically cleaning, the oxygen plasma process was performed.
<2A> Next, N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-diphenyl-4,4′-diamine (TPD) is vacuum-deposited on the ITO electrode. It vapor-deposited by the method, and the positive hole transport layer (hole transport layer of the 1st light emission part) with an average thickness of 70 nm was formed.

<3A> Next, a third light-emitting layer (blue light-emitting layer) having an average thickness of 30 nm was formed on the hole transport layer by using a vacuum deposition method.
Here, as a constituent material constituting the third light emitting layer, a mixed material of BD102 (made by Idemitsu Kosan Co., Ltd.) which is a blue light emitting material (guest material) and BH215 (made by Idemitsu Kosan Co., Ltd.) which is a host material is used. It was. In addition, the content (dope concentration) of the blue light emitting material in the first light emitting layer was 10.0 wt%.

<4A> Next, tris (8-quinolinolato) aluminum (Alq ₃ ) was vapor-deposited on the third light-emitting layer by a vacuum evaporation method, and an electron transport layer having an average thickness of 20 nm (electron transport of the first light-emitting portion). Layer).
<5A> Next, on this electron transport layer, tris (8-quinolinolato) aluminum (Alq ₃ ) and Li ₂ O were deposited by a vacuum deposition method, and an n-type electron transport layer (carrier) having an average thickness of 20 nm. The n-type electron transport layer of the generation layer) was formed. The content of (8-quinolato) aluminum (Alq ₃ ) and Li ₂ O in the n-type electron transport layer was set to 99: 1 by volume ratio.

<6A> Next, on the n-type electron transport layer, hexacyanohexaazatriphenylene was deposited by a vacuum deposition method to form an electron withdrawing layer having an average thickness of 20 nm. Thereby, a carrier generation layer composed of an n-type electron transport layer and an electron withdrawing layer was obtained.
<7A> Next, 4,4 ′, 4 ″ -tris (N-carbazolyl) -triphenylamine (TCTA) is deposited on the carrier generation layer (on the electron withdrawing layer) by a vacuum deposition method, and the average thickness is measured. A 20 nm hole transport layer (hole transport layer of the second light-emitting portion) was formed.

<8A> Next, a first light-emitting layer (red light-emitting layer) having an average thickness of 25 nm was formed on the hole transport layer by using a vacuum deposition method.
Here, btp2Ir (acac) which is a red phosphorescent material (guest material) was used as a light emitting material (first light emitting material) of the first light emitting layer. Further, as the host material (first host material) of the first light-emitting layer, 4,4 ′, 4 ″ -tris (N-carbazolyl) -tri, which is a hole transporting material (hole transporting host material), is used. A mixed material of phenylamine (TCTA): 70 wt% and 1,3,5-tris (2-N-phenylbenzimidazolyl) benzene (TPBi): 30 wt%, which is an electron transporting material (electron transporting host material) Was used.
Further, the content (dope concentration) of the red phosphorescent material in the first light emitting layer was 10.0 wt%.

<9A> Next, a second light-emitting layer (green light-emitting layer) having an average thickness of 25 nm was formed on the first light-emitting layer by vacuum evaporation.
Here, Ir (ppy) 3 which is a green phosphorescent material (guest material) was used as the light emitting material (second light emitting material) of the second light emitting layer. As the host material (second host material) of the second light-emitting layer, 4,4 ′, 4 ″ -tris (N-carbazolyl) -tri, which is a hole transporting material (hole transporting host material), is used. A mixed material of phenylamine (TCTA): 30 wt% and 1,3,5-tris (2-N-phenylbenzimidazolyl) benzene (TPBi): 70 wt%, which is an electron transporting material (electron transporting host material) Was used.
Further, the content (dope concentration) of the green phosphorescent material in the second light emitting layer was 15.0 wt%.

<10A> Next, 1,3,5-tris (2-N-phenylbenzimidazolyl) benzene (TPBi) is deposited on the second light-emitting layer by a vacuum deposition method, and an electron transport layer having an average thickness of 35 nm is formed. (Electron transport layer of second light-emitting portion) was formed.
<11A> 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 1.0 nm.

<12A> 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 200 nm made of Al was formed.
<13A> 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, on the substrate, the anode, the hole transport layer, the third light emitting layer, the carrier generation layer (n-type electron transport layer, electron withdrawing layer), the hole transport layer, the first light emitting layer, the second A light emitting device (tandem light emitting device) in which the light emitting layer, the electron transport layer, the electron injection layer, and the cathode were laminated in this order was manufactured.

(Comparative Example 1)
Only TCTA which is a hole transporting material (hole transporting host material) as the host material (first host material) of the first light emitting layer and the host material (second host material) of the second light emitting layer. A light emitting device was manufactured in the same manner as in Example 1 described above except that was used.
(Comparative Example 2)
Only TPBi, which is an electron transporting material (electron transporting host material), is used as the host material (first host material) of the first light emitting layer and the host material (second host material) of the second light emitting layer. A light emitting device was manufactured in the same manner as in Example 1 described above, except that the above was used.
(Comparative Example 3)
The mixing ratio (TCTA: TPDi) of TCTA and TPBi in the host material (first host material) of the first light emitting layer is set to 30:70 (weight ratio), and the host material (second 2), a light emitting device was manufactured in the same manner as in Example 1 except that the mixing ratio of TCTA and TPBi (TCTA: TPDi) was 70:30 (weight ratio).

(Comparative Example 4)
TPD is used as the constituent material of the hole transport layer of the second light emitting part, BCP is used as the constituent material of the electron transport layer of the second light emitting part, and the average thickness of the electron transport layer of the second light emitting part is 65 nm. And the mixing ratio (TCTA: TPDi) of TCTA and TPBi in the host material (first host material) of the first light emitting layer is 30:70 (weight ratio), and the host material of the second light emitting layer A light emitting device was manufactured in the same manner as in Example 4 except that the mixing ratio (TCTA: TPDi) of TCTA and TPBi in (second host material) was set to 70:30 (weight ratio).
Table 1 shows the configurations of the light-emitting elements of the above examples and comparative examples.

2. Evaluation 2-1. Evaluation of luminous efficiency (driving voltage, radiance) About the light emitting element of each Example and each comparative example, a 100 mA / cm < ² > constant current was sent through the light emitting element using DC power supply. At that time, the luminance was measured using a luminance meter and the driving voltage was measured.
2-2. Evaluation of Luminous Life For each of the light emitting devices of each Example and each Comparative Example, a constant current of 100 mA / cm ² was continuously supplied to the light emitting device using a DC power source, while the luminance was measured using a luminance meter. The time (LT80) at which 80% of the initial luminance was reached was measured.

2-3. Evaluation of color balance For each light emitting device of each example and each comparative example, a constant current of 100 mA / cm ² was passed through the light emitting device using a direct current power source, and the luminescent color in the initial state was visually observed, and the chromaticity meter was The chromaticity (x, y) (CIE color system) of light in the initial state was measured. Then, the constant current is kept flowing, while the luminance is measured using a luminance meter, and the chromaticity of light is measured using a chromaticity meter in a state where the luminance is reduced by 20% (80% of the initial luminance). (X, y) (CIE color system) was measured.
Table 2 shows the results of the above evaluations. In Table 2, with respect to driving voltage, radiance, and lifetime, Examples 1 to 3 and Comparative Examples 1 to 3 were evaluated by standardizing Comparative Example 1 as a reference, and Example 4 and Comparative Example 4 were evaluated. Then, the evaluation was standardized and evaluated based on Comparative Example 4.

As is clear from Table 2, all of the light-emitting elements of Examples 1 to 4 were able to suppress driving voltage and achieve high light emission efficiency and long life. In addition, the light-emitting elements of Examples 1 to 4 were able to emit light in a well-balanced manner over a long period of time between the first light-emitting layer and the second light-emitting layer.
On the other hand, in the light emitting element of Comparative Example 1, the light emission of the first light emitting layer is small, the light emission of the second light emitting layer is mainly performed, and the first light emitting layer and the second light emitting layer emit light in a balanced manner. I couldn't.

In the light emitting element of Comparative Example 2, the light emission of the second light emitting layer is small, the light emission of the first light emitting layer is mainly performed, and the first light emitting layer and the second light emitting layer can emit light in a balanced manner. could not.
The light emitting element of Comparative Example 3 was able to emit light in a balanced manner between the first light emitting layer and the second light emitting layer in the initial state, but in the state where the luminance was reduced by 20%, The second light emitting layer could not emit light with a good balance.
In addition, the light-emitting element of Comparative Example 4 had a greater change in color balance from the initial state to the state where the luminance was reduced by 20%, compared with the light-emitting element of Example 4.

  DESCRIPTION OF SYMBOLS 1, 1G, 1R, 1B ... Light emitting element 2 ... Board | substrate 3 ... Anode 4 ... 1st light emission part 41 ... Hole transport layer 42 ... Light emitting layer (3rd light emitting layer) 5 ... Carrier Generation layer 51... N-type electron transport layer 52... Electron withdrawing layer 6... Second light emitting part 61 .. hole transport layer 62 .. light emitting layer (first light emitting layer) 63. 64 ... Electron transport layer 65 ... Electron injection layer 7 ... Cathode 8 ... Sealing member 15 ... Laminate 19B, 19G, 19R ... Color filter 100 ... Display device 101 ... Light emission 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 24 …… Drain electrode 27 …… Wiring 31 …… Partition wall 32 …… Reflection film 33 …… Corrosion prevention film 34 …… Cathode cover 35 …… Epoxy layer 36 ...... Light shielding layer 1100 …… Personal computer 1102 …… Keyboard 1104 …… Main body 1106... Display unit 1200... Mobile phone 1202 .. Operation buttons 1204 .. Earpiece 1206 .. Mouthpiece 1300 .. Digital still camera 1302 .. Case (body) 1304. Button 1308 ... Circuit board 1312 ... Video signal output terminal 1314 ... Input / output terminal for data communication 1430 ... TV monitor 1440 ... Personal computer W ... White light

Claims (14)

The anode,
A cathode,
A first light emitting layer that is provided between the anode and the cathode, and emits light when energized between the anode and the cathode;
A second light-emitting layer provided between the cathode and the first light-emitting layer in contact with the first light-emitting layer, and emitting light when energized between the anode and the cathode;
The first light emitting layer includes a first light emitting material and a first host material that holds the first light emitting material,
The second light-emitting layer includes a second light-emitting material and a second host material that holds the second light-emitting material,
The first host material and the second host material are each composed of a mixed material including a hole transport material and an electron transport material,
When the content of the hole transporting material in the first host material is A1, and the content of the electron transporting material in the first host material is B1 ,
A1 / B1 is 13/7 or more and 3 or less,
The light-emitting element, wherein the content of the hole transporting material in the second host material is less than the content of the electron transporting material in the second host material.   The light-emitting element according to claim 1, wherein the hole transporting material contained in the first host material and the hole transporting material contained in the second host material are the same.   3. The light-emitting element according to claim 1, wherein the electron transporting material contained in the first host material and the electron transporting material contained in the second host material are of the same type.   It is provided between the anode and the first light emitting layer so as to be in contact with the first light emitting layer, and includes a hole transporting material of the same type as the hole transporting material contained in the first light emitting layer. The light emitting device according to any one of claims 1 to 3, further comprising a configured hole transport layer.   It is provided between the cathode and the second light emitting layer in contact with the second light emitting layer, and includes an electron transporting material of the same type as the electron transporting material contained in the second light emitting layer. The light emitting device according to claim 1, further comprising an electron transport layer.   The light emitting element according to claim 1, wherein each of the first light emitting material and the second light emitting material includes a phosphorescent light emitting material. The triplet energy of the hole transporting material and the electron transporting material in the first host material is greater than the triplet energy of the phosphorescent light emitting material in the first light emitting material, respectively.
The triplet energy of the hole transporting material and the electron transporting material in the second host material is greater than the triplet energy of the phosphorescent light emitting material in the second light emitting material, respectively. Light emitting element.   The light emitting element according to any one of claims 1 to 7, wherein a peak wavelength of the light emission of the first light emitting layer is longer than a peak wavelength of the light emission of the second light emitting layer.   The light emitting element according to any one of claims 1 to 8, wherein a sum of an average thickness of the first light emitting layer and an average thickness of the second light emitting layer is 30 nm or more and 50 nm or less.   Third light emission that is provided between the anode and the first light-emitting layer or between the cathode and the second light-emitting layer and emits light when energized between the anode and the cathode. The light emitting device according to claim 1, further comprising a layer.   Carrier provided between the first light emitting layer and the third light emitting layer, of the first light emitting layer and the second light emitting layer, and the third light emitting layer to generate electrons and holes. The light emitting device according to claim 10, further comprising a generation layer.   A light-emitting device comprising the light-emitting element according to claim 1.   A display device comprising the light-emitting device according to claim 12.   An electronic apparatus comprising the light emitting device according to claim 12.

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