JP2012186092A - Light-emitting element, light-emitting device, display device, and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting element which can drive at a low voltage and achieves life prolongation, and also to provide a light-emitting device having this light-emitting element, a display device and an electronic apparatus.SOLUTION: A light-emitting element 1 includes: an anode 3; a cathode 7; a first luminescent layer 42 provided between the anode 3 and cathode 7; a second luminescent layer 62 provided between the cathode 7 and the first luminescent layer 42; and a carrier generation layer 5 provided between the first luminescent layer 42 and the second luminescent layer 62. The carrier generation layer 5 includes an n-type electron transport layer 52 and a buffer layer 51 which are in contact with each other. The n-type electron transport layer 52 contains a first electron transport material and an electron donor material and is provided on the side of the second luminescent layer 62. The buffer layer 51 contains a second electron transport material and is provided on the side of the first luminescent layer 42. Thereby, a function is provided which suppresses dispersion of the electron donor material from the n-type electron transport layer 52 to the first luminescent layer 42.

Description

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

An organic electroluminescence element (so-called organic EL element) is a light emitting element having a structure in which at least one light emitting organic layer is interposed between an anode and a cathode. In such a light-emitting 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 element, for example, one having two or more light-emitting layers between a cathode and an anode and a charge generation layer (carrier generation layer) provided between the light-emitting layers is known. (For example, refer to Patent Document 1).

  In such a light emitting element, an electric field is applied between the anode and the cathode, whereby electrons and holes are generated from the charge generation layer and supplied to each light emitting layer. Therefore, in addition to holes and electrons supplied from the anode and the cathode, holes and electrons supplied from the charge generation layer can be used for light emission of each light emitting layer. Such a light-emitting element can emit light with higher luminance than a light-emitting element having a single light-emitting layer, and is excellent in light emission efficiency. In addition, the light emitting layer can emit light with relatively high luminance even when used with a lower current than a light emitting element having one layer.

  However, since the charge generation layer is configured to include an n-type electron transport layer containing an electron transport material and an electron donor material, in a conventional light emitting device including such an n-type electron transport layer, a constant current is provided. When the driving is continuously performed, the electron donor material contained in the n-type electron transport layer diffuses to the adjacent light emitting layer with time, and as a result, the luminance life of the light emitting element is reduced. There was a problem that.

JP 2007-598448 A

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

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 that is provided between the cathode and the first light emitting layer and emits light when energized between the anode and the cathode;
A carrier generating layer provided between the first light emitting layer and the second light emitting layer and generating electrons and holes;
The carrier generation layer includes an n-type electron transport layer and a buffer layer in contact with each other,
The n-type electron transport layer contains a first electron transport material and an electron donor material, and is provided on the second light emitting layer side,
The buffer layer contains a second electron-transporting material and is provided on the first light-emitting layer side, so that the first light-emitting layer is formed from the n-type electron transport layer of the electron-donating material. It is characterized by having a function of suppressing the diffusion to the surface.
According to such a light-emitting element of the present invention, the electron donor material contained in the n-type electron transport layer is accurately suppressed or prevented from diffusing into the first light-emitting layer. A light-emitting element that can be used and has a long lifetime can be obtained.

In the light emitting device of the present invention, the first electron transport material and the second electron are formed so that the electron donor material is less likely to diffuse in the buffer layer than in the n-type electron transport layer. It is preferable that the type of the transportable material is selected.
Thereby, the effect of confining the electron injecting material in the n-type electron transport layer can be obtained more effectively.

In the light emitting device of the present invention, the first electron transporting material and the second electron transporting material are each selected such that their electron mobility is higher in the first electron transporting material. It is preferred that
This makes it possible to set the increase in the driving voltage of the light emitting element relatively low.
In the light-emitting element of the present invention, it is preferable to select an organic compound containing no metal as the first electron transporting material and an organometallic complex as the second electron transporting material.
Thereby, both the diffusion of the electron donor material into the first light emitting layer and the increase in the driving voltage of the light emitting element can be suppressed or prevented accurately.

In the light emitting device of the present invention, the electron donor material is preferably at least one of an alkali metal, an alkaline earth metal, an alkali metal compound, and an alkaline earth metal compound.
Such an electron donor material has an excellent electron injection property. Therefore, electrons generated in the carrier generation layer can be efficiently injected into the first light emitting layer.

In the light emitting device of the present invention, the buffer layer preferably has an average film thickness of 3.0 nm or more and 20.0 nm or less.
Accordingly, diffusion of the electron donor material from the n-type electron transport layer to the first light emitting layer can be reliably suppressed, and an increase in driving voltage of the light emitting element can be reliably suppressed.

In the light emitting device of the present invention, the content of the electron donor material in the n-type electron transport layer is preferably 0.3 wt% or more and 2.0 wt% or less.
By setting the content of the electron injecting material in such a range, the diffusion tendency of the electron injecting material into the first light emitting layer and the second light emitting layer can be set to be relatively low.
In the light-emitting device of the present invention, the carrier generation layer is further provided with an electron-withdrawing property provided between the second light-emitting layer and the n-type electron transport layer in contact with the n-type electron transport layer. It is preferable to provide an electron withdrawing layer having
In a light-emitting element including the carrier generation layer having such a configuration, it is possible to accurately suppress or prevent the electron donor material contained in the n-type electron transport layer from diffusing into the first light-emitting layer.

In the light emitting device of the present invention, the electron withdrawing layer preferably contains an organic cyanide compound having an aromatic ring.
The aromatic ring-containing organic cyan compound has excellent electron withdrawing properties. Therefore, the amount of holes and electrons generated in the carrier generation layer can be increased by configuring the electron withdrawing layer by including an organic cyanide compound having an aromatic ring.

In the light emitting device of the present invention, it is preferable that the electron withdrawing layer further contains the electron donor material.
As a result, it is possible to accurately suppress or prevent the drive voltage from increasing due to the increase in resistance of the light emitting element even when the light emitting element generates heat due to long-time use.
The light-emitting element of the present invention preferably includes a third light-emitting layer that is provided between the second light-emitting layer and the cathode and emits light when energized between the anode and the cathode.
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, 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.

The light-emitting device of the present invention includes the light-emitting element of the present invention.
Accordingly, it is possible to provide a light emitting device that can suppress an increase in driving voltage even during long-time driving with a constant current.
The display device of the present invention includes the light emitting device of the present invention.
Accordingly, a display device that can be driven stably and has excellent reliability can be provided.
An electronic apparatus according to the present invention includes the display device according to the present invention.
Thereby, an electronic device with excellent reliability can be provided.

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. It is a profile which shows a lithium ion when the light emitting element of Example 1, 4 is analyzed by secondary ion mass spectrometry.

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.
(Light emitting element)
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”.

The light emitting element (electroluminescence element) 1 includes an anode 3, a first light emitting unit (first light emitting unit) 4, a carrier generation layer 5, a second light emitting unit (second light emitting unit) 6, The cathode 7 is 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 unit 4 is a laminate in which a hole transport layer 41 and a first light emitting layer 42 are laminated in this order from the anode 3 side to the cathode 7 side, and the second light emitting unit 6 Is a laminate in which a hole transport layer 61, a second light emitting layer 62, a third light emitting layer 63, a hole blocking layer 64, and an electron transport layer 65 are laminated in this order from the anode 3 side to the cathode 7 side. Is the body.
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 first 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 second light emitting layer 62 and the third 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 first light emitting layer 42, the second light emitting layer 62, and the third 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 particular, in the light-emitting element 1, holes and electrons are further generated in the carrier generation layer 5. Among these, electrons are injected into the first light-emitting portion 4 and holes are injected into the second light-emitting portion 6. Since the light-emitting element 1 can emit light with higher luminance, the light-emitting element 1 having excellent light emission efficiency can be obtained.
In such a light-emitting element 1, for example, the light-emitting element 1 that emits white light can be realized by setting the emission colors of the light-emitting layers 42, 62, and 63 to red, green, and blue, respectively. .

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.
The average thickness of the substrate 2 is not particularly limited, but is preferably 0.1 mm or more and 30 mm or less, and more preferably 0.1 mm or more and 10 mm or less.

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.
A light emitting element 1 is formed on the substrate 2. Hereinafter, each part which comprises the light emitting element 1 is demonstrated sequentially.

[Anode 3]
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 nm or more and 200 nm or less, and more preferably 50 nm or more and 150 nm or less.

[First light emitting unit]
As described above, the first light emitting unit 4 includes the hole transport layer 41 and the first light emitting layer 42.
In the first light emitting unit 4 having such a configuration, when holes are supplied (injected) from the hole transport layer 41 side to the first light emitting layer 42 and electrons are supplied from the n-type electron transport layer 52 side, respectively. In the first light-emitting layer 42, holes and electrons recombine, and excitons (excitons) are generated by the energy released during the recombination, and energy (fluorescence or phosphorus) is returned when the excitons return to the ground state. The first light emitting layer 42 emits light.

Hereinafter, each layer which comprises this 1st light emission part 4 is demonstrated sequentially.
The hole transport layer 41 has a function of transporting holes injected from the anode 3 to the first 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 first light emitting layer 42.
The average thickness of the hole transport layer 41 is not particularly limited, but is preferably 10 nm or more and 150 nm or less, and more preferably 10 nm or more and 100 nm or less.

(First light emitting layer)
The first light emitting layer 42 includes a 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 is appropriately selected according to the color of light to be emitted from the first light-emitting layer 42, and various fluorescent materials and various phosphorescent materials are used alone or in combination of two or more. be able to.

  Specifically, 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-dioctylfluorene-2,7-diyl) -co- (ethylnylbenzene)], 4,4′-bis [4- (diphenylamino) styryl] biphenyl (BDAVBi BD102 (product name, manufactured by Idemitsu Kosan Co., Ltd.) and the like.

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), bis [2- (2′-benzo [4,5-α] thienyl) pyridinate represented by the following formula (1) 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.

The first light emitting layer 42 may include a host material to which the light emitting material is added as a guest material in addition to the above-described light emitting material. Such a first light emitting layer 42 can be formed, for example, by 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. However, when the light emitting material includes a fluorescent material, for example, rubrene and derivatives thereof, distyrylarylene derivatives, naphthacene-based materials such as bis p-biphenylnaphthacene, 3-tert- Anthracene materials such as butyl-9,10-di (naphth-2-yl) anthracene (TBADN), perylene derivatives such as bis-orthobiphenylperylene, pyrene derivatives such as tetraphenylpyrene, distyrylbenzene derivatives, stilbene derivatives Quinolinolato metal complexes, such as distyrylamine derivatives, bis (2-methyl-8-quinolinolato) (p-phenylphenolato) aluminum (BAlq), tris (8-quinolinolato) aluminum complex (Alq ₃ ), triphenylamine Triaries such as tetramers Ruamine derivatives, arylamine derivatives, oxadiazole derivatives, silole derivatives, carbazole 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 (product name, manufactured by Idemitsu Kosan Co., Ltd.) and the like can be mentioned, and one or more of these can be used in combination. Preferably, IDE120 (made by Idemitsu Kosan Co., Ltd.), anthracene-based material, and dianthracene-based material are preferable when the luminescent material is blue or green, and rubrene or rubrene derivative, naphthacene-based material when the luminescent 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 first light emitting layer 42 is preferably 0.1 to 30 wt%. More preferably, it is 5 to 20 wt%. Luminous efficiency can be optimized by setting the content of the light emitting material within such a range.
In addition, as the light emitting material of the first light emitting layer 42, it is preferable to use a fluorescent material. That is, the first light emitting layer 42 preferably includes 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. Thus, as the light emitting material of the first light emitting layer 42, a fluorescent material that is less sensitive to changes in light emission characteristics than impurities than the phosphorescent material is used, so that the light emitting element 1 is continuously driven to the first light emitting layer 42. Even if the constituent material (particularly the electron injecting material) of the n-type electron transport layer 52 is diffused beyond the carrier generation layer 5, the light emission caused by the change in the light emission characteristics of the first light emitting layer 42 A decrease in the luminance life of the element 1 can be suppressed.

Moreover, it is preferable that the peak wavelength of light emission of the first light emitting layer 42 is shorter than the peak wavelength of light emission of the second light emitting layer 62 described later. In other words, the light emission peak wavelength of the second light emitting layer 62 is preferably longer than the light emission peak wavelength of the first light emitting layer 42. Thereby, the 1st light emitting layer 42 and the 2nd light emitting layer 62 can be light-emitted with sufficient balance.
The peak wavelength of light emission of the first 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 first 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 first light emitting layer 42 that is not adjacent to another light emitting layer as in this embodiment, the light emitting material emits light. Even when a light emitting material having a short peak wavelength is used, energy is not easily released to other light emitting layers, and light can be emitted efficiently.
The average thickness of the first 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 the constituent material (especially electron injecting material) of the n-type electron transport layer 52 of the carrier generation layer 5 to be described later diffuses into the first light emitting layer 42, the light emitting characteristics of the first light emitting layer 42 are obtained. Can be maintained in a relatively good state. Further, it is possible to prevent the first 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.

  In the present embodiment, the first light-emitting layer 42 is described as an example having a single light-emitting layer, but the first light-emitting layer 42 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 emitting layer 42 has a some light emitting layer, the intermediate | middle layer may be provided between light emitting layers.

[Carrier generation layer]
The carrier generation layer 5 has a function of generating carriers (holes and electrons).
In this embodiment, the carrier generation layer 5 is formed by laminating a buffer layer 51, an n-type electron transport layer 52, and an electron withdrawing layer 53 in this order from the anode 3 side to the cathode 7 side.
In the present invention, the structure of the carrier generation layer 5 has a feature. Hereinafter, each layer constituting the carrier generation layer 5 will be sequentially described in detail.

(N-type electron transport layer)
The n-type electron transport layer 52 is provided between the buffer layer 51 and the electron withdrawing layer 53 and has a function of transporting electrons from the electron withdrawing layer 53 side to the first light emitting layer 42 side.
In the present invention, such an n-type electron transport layer 52 is composed mainly of an electron transport material having electron transport properties (first electron transport material), and in addition to the electron transport material, It is composed of a mixed material including an electron injecting material (electron donor material) having an electron injecting property.

By providing the n-type electron transport layer 52 having such a configuration, that is, by having a configuration containing an electron transport material and an electron injection material, the n-type electron transport layer 52 has particularly excellent electron transport properties and In order to exhibit the electron injection property, even when driven by a low voltage, the electrons attracted by the electron withdrawing layer 53 are efficiently injected into the n-type electron transport layer 52 and the anode through the n-type electron transport layer 52 It can be efficiently transported to the 3 side. As a result, the heat generation of the light emitting element 1 can be suppressed to a relatively low temperature range.
Further, since the n-type electron transport layer 52 is configured by adding (doping) an electron injecting material to the electron transporting material, in the n-type electron transporting layer 52, the electron transporting material is changed from an electron injecting material to an electron. To become a radical anion state. As a result, the amount of carrier generation in the carrier generation layer 5 increases.

Examples of the electron transporting material (first electron transporting material) used for the n-type electron transporting layer 52 include 8-quinolinol and its derivatives (quinoline derivatives) such as tris (8-quinolinolato) aluminum (Alq ₃ ). Or the like, 1,3-bis (N, Nt-butyl-phenyl) -1,3,4-oxadiazole (OXD-7), 2- [1,1 Oxadiazole derivatives such as' -biphenyl] -4-yl-5- [4- (1,1-dimethylethyl) phenyl] -1,3,4-oxadiazole (PBD), perylene derivatives, pyridine derivatives , Pyrimidine derivatives, quinoxaline derivatives, diphenylquinone derivatives, nitro-substituted fluorene derivatives, and other organic compounds that do not contain metal atoms, and one or more of these may be combined Can be used.

Examples of the electron injecting material (electron donor material) used for the n-type electron transporting layer 52 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. Since such an inorganic insulating material has an excellent electron injection property, electrons generated in the carrier generation layer 5 can be efficiently injected into the first light emitting layer 42. As a result, since electrons can be injected at a low voltage, heat generation of the light emitting element 1 can be suppressed to a relatively low temperature range even by continuous driving of the light emitting element 1 with a constant current.

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.
Further, as the electron injecting material (electron donor material) used for the n-type electron transporting layer 52, it is preferable to use one or more of alkali metal compounds and alkaline earth metal compounds in combination. It is more preferable to use Li ₂ O. Thereby, the electron injection property of the n-type electron transport layer 52 can be further improved while making the electron transport property of the n-type electron transport layer 52 excellent. Further, alkali metal compounds (alkali metal chalcogenides, alkali metal halides, etc.) have a very small work function, and the n-type electron transport layer 52 is formed using the alkali metal compound, whereby the light-emitting element 1 has high luminance. It will be. In particular, Li ₂ O facilitates injection of electrons at a low voltage, so that the heat generation of the light-emitting element 1 can be suppressed to a lower temperature range even when the light-emitting element 1 is continuously driven at a constant current. it can.

The n-type electron transport layer 52 having such a configuration also has a function of blocking holes.
The n-type electron transport layer 52 including the electron transport material and the electron injection material is, for example, an electron transport material formed by co-evaporation or the like using the electron transport material as a host material and the electron injection material as a guest material. It can be formed by doping an electron injecting material.
Further, the content (doping amount) of the electron injecting material in the n-type electron transport layer 52 is preferably 0.3 wt% or more and 2.0 wt% or less, and is 0.5 wt% or more and 1.5 wt%. The following is more preferable. 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 52 can be made excellent in a balanced manner. Further, the diffusion tendency of the electron injecting material into the first light emitting layer 42 and the second light emitting layer 62 can be set to be relatively low.

Furthermore, if the concentration of the electron injecting material (electron donor material) in the n-type electron transporting layer 52 is gradually decreased from the cathode 7 side toward the anode 3 side, electrons generated in the carrier generation layer 5 are The light emitting element 1 can be efficiently transported and injected into one light emitting layer 42, and the amount of the electron injecting material in the n-type electron transporting layer 52 can be suppressed to diffuse into the first light emitting layer 42, thereby extending the life of the light emitting element 1. be able to. In this case, the concentration of the electron injecting material may change stepwise or may change continuously.
The average thickness of the n-type electron transport layer 52 is not particularly limited, but is preferably 10 nm or more and 100 nm or less, and more preferably 10 nm or more and 50 nm or less. Accordingly, electrons attracted by the electron withdrawing layer 53 can be efficiently transported to the anode 3 side, and holes that have passed through the first light emitting unit 4 can be blocked.

(Buffer layer)
The buffer layer 51 is provided between the first light-emitting layer 42 and the n-type electron transport layer 52 described above, that is, in the first light-emitting layer 42 rather than the n-type electron transport layer 52 in contact with each other. And has a function of suppressing diffusion of the electron injecting material from the n-type electron transport layer 52 to the first light emitting layer 42.

Thereby, the decrease in the luminance life of the light emitting element 1 due to the diffusion of the electron injecting material into the first light emitting layer 42 and the deterioration of the light emission characteristics of the first light emitting layer 42 is accurately suppressed or prevented. can do.
In the present invention, such a buffer layer 51 is composed mainly of an electron transporting material (second electron transporting material) having an electron transporting property. By making the buffer layer 51 contain an electron transporting material, the above function can be surely exhibited.

The electron transporting material (second electron transporting material) used for the buffer layer 51 is the same as described for the electron transporting material (first electron transporting material) used for the n-type electron transporting layer 52. Can be used.
Further, the first electron transporting material and the second electron transporting material may be the same type (or the same type) or different types, but n in the buffer layer 51. It is preferable to select different types of materials that increase the diffusibility of the electron injecting material in the type electron transport layer 52. As a result, the electron injecting material is less likely to diffuse in the buffer layer 51 than in the n type electron transporting layer 52, so that the effect of confining the electron injecting material in the n type electron transporting layer 52 can be obtained more effectively. Will be.

The ease of diffusion of the electron injecting material in the n-type electron transporting layer 52 and the buffer layer 51, and the difficulty of the electron injecting material when the electron injecting material having the same concentration gradient exists in each layer. Based on the moving speed at which the injectable material moves, the layer with the higher moving speed is likely to diffuse, and the layer with the slower moving speed is less likely to diffuse.
Further, it is preferable to select different materials for the first electron transporting material and the second electron transporting material so that their electron mobility is higher in the first electron transporting material. Here, the configuration in which the buffer layer 51 is interposed tends to increase the driving voltage of the light emitting element 1, and the first electron transporting material that satisfies the above-described relationship of electron mobility and By selecting the second electron transporting material, that is, by selecting a material having a high electron mobility as the constituent material of the n-type electron transporting layer 52, the driving voltage of the light emitting element 1 is relatively increased. It can be set low.

Considering the above, as a combination of the first electron transporting material and the second electron transporting material, among the electron transporting materials described in the description of the n-type electron transporting layer 52, It is preferable to select an organic compound containing no metal as the electron transporting material and an organometallic complex as the second electron transporting material. Thereby, both the diffusion of the electron injecting material into the first light emitting layer 42 and the increase in the driving voltage of the light emitting element 1 can be suppressed or prevented accurately.
The average thickness of the buffer layer 51 is not particularly limited, but is preferably 3 nm or more and 20 nm or less, and more preferably 5 nm or more and 15 nm or less. Accordingly, diffusion of the electron injecting material from the n-type electron transport layer 52 to the first light emitting layer 42 can be reliably suppressed, and an increase in driving voltage of the light emitting element 1 can be reliably suppressed. .

(Electronic suction layer)
The electron withdrawing layer (electron extraction layer) 53 is provided between the n-type electron transport layer 52 and the hole transport layer 61 and is adjacent to the cathode 7 side (in the present embodiment, the second light emitting unit 6). It has a function of attracting (withdrawing) electrons from the hole transport layer 61). Electrons attracted by the electron withdrawing layer 53 are injected into a layer (n-type electron transporting layer 52) adjacent to the anode 3 side.
Such an electron withdrawing layer 53 is composed mainly of an organic compound having an electron withdrawing property (electron withdrawing material).

As the organic compound having an electron withdrawing property used for the electron withdrawing layer 53, 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 53 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 53 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 with an adjacent layer (hole transporting layer 61). Can do. As a result, when the electron withdrawing layer 53 and the hole transporting layer 61 are in contact with each other, electrons are not present on the electron withdrawing layer 53 side in the vicinity of the interface between the electron withdrawing layer 53 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 53 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 second light emitting layer 62 and the third light emitting layer 63). In addition, electrons generated near the interface between the electron withdrawing layer 53 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 first light emission). It contributes to the light emission of the layer 42). The generation of holes and electrons by the electron withdrawing layer 53 as described above is continuously performed while the driving voltage is applied, and these holes and electrons are generated by the first light emitting layer 42. This contributes to the light emission of the second light-emitting layer 62 and the third light-emitting layer 63.

In addition, the aromatic ring-containing organic cyanide compound is a relatively stable compound and can easily form the electron withdrawing layer 53 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. Furthermore, since the charge can be generated in the electron withdrawing layer 53 at a low voltage, the heat generation of the light emitting element 1 can be suppressed to a relatively low temperature range even by continuous driving of the light emitting element 1 with a constant current. .
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 53 configured using such a compound can sufficiently extract electrons from the adjacent layer (hole transport layer 61), and transports the preferably 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 53 formed using such a compound can more efficiently extract 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 53. Thereby, the effect acquired by using the above-described aromatic ring-containing organic cyanide compound can be exhibited more remarkably.
In addition, the average thickness of the electron withdrawing layer 53 is preferably 5 to 40 nm, and more preferably 10 to 30 nm. Thereby, the function (electron attracting property) of the electron withdrawing layer 53 as described above can be sufficiently exhibited while preventing the drive voltage of the light emitting element 1 from increasing.

The electron withdrawing layer 53 is preferably made of a mixed material including the above-described organic compound having an electron withdrawing property and an electron injecting material having an electron injecting property.
As described above, the electron withdrawing layer 53 includes the electron injecting material, so that both the n-type electron transporting layer 52 and the electron withdrawing layer 53 include the electron injecting material (electron donor material). Will be. By adopting such a configuration, that is, by configuring both the n-type electron transport layer 52 and the electron withdrawing layer 53 such that the electron injecting material is diffused in these layers, light emission associated with long-term use can be obtained. Also due to the heat generation of the element 1, it is possible to accurately suppress or prevent the drive voltage from increasing due to the high resistance of the light emitting element 1.

In this case, as the electron injecting material (electron donor material) used for the electron withdrawing layer 53, various inorganic insulating materials and various inorganic semiconductor materials similar to the electron injecting material used for the n-type electron transporting layer 52 described above are used. Can be used.
Further, the content (doping amount) of the electron injecting material in the electron withdrawing layer 53 is preferably 0.5 wt% or more and 10 wt% or less, and is 2.0 wt% or more and 7.0 wt% or less. Is more preferable. By setting the content of the electron injecting material in such a range, the diffusion of the electron injecting material into the first light emitting layer 42 can be accurately suppressed.

  Further, the electron injecting material contained in the n-type electron transporting layer 52 and the electron injecting material contained in the electron withdrawing layer 53 may be different, but are preferably of the same type. More preferably. As a result, charges can be generated in the carrier generation layer 5 at a low voltage, so that the heat generation of the light emitting element 1 can be suppressed to a relatively low temperature range even by continuous driving of the light emitting element 1 with a constant current. it can.

The content of the electron injecting material in the electron withdrawing layer 53 is preferably greater than the content of the electron injecting material in the n-type electron transporting layer 52. By satisfying such a relationship, the movement of charges (particularly electrons) in the carrier generation layer 5 can be performed more smoothly. Further, it is presumed that the diffusion of the electron injecting material from the n-type electron transport layer 52 to the first light emitting layer 42 is more accurately suppressed.
The total average thickness of the n-type electron transport layer and the electron withdrawing layer 53 is preferably 5 nm or more and 80 nm or less, and more preferably 20 nm or more and 70 nm or less. 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.

In the present embodiment, the case where the carrier generation layer 5 includes the electron withdrawing layer 53 having the above-described configuration has been described. However, the present invention is not limited thereto, and the carrier generation layer is replaced with the electron withdrawing layer 53 as a p-type. You may provide a positive hole transport layer.
The n-type electron transport layer 52 is mainly composed of a hole transporting material having a hole transporting property. In addition to the hole transporting material, the n-type electron transporting layer 52 has an electron accepting material (electron acceptor property). Material).
As the hole transporting material, the same materials as those described above as the constituent material of the hole transport layer 41 can be used.

  The electron-accepting material is not particularly limited. For example, inorganic compounds such as ferric chloride, aluminum chloride, gallium chloride, indium chloride, and antimony pentachloride, hexacyanobutadiene, hexacyanobenzene, tetracyanoethylene, tetra Cyanoquinodimethane, tetrafluorotetracyanoquinodimethane, p-fluoranyl, p-chloranil, p-bromanyl, p-benzoquinone, 2,6-dichlorobenzoquinone, 2,5-dichlorobenzoquinone, tetramethylbenzoquinone, 1,2 , 4,5-tetracyanobenzene, o-dicyanobenzene, p-dicyanobenzene, 1,4-dicyanotetrafluorobenzene, 2,3-dichloro-5,6-dicyanobenzoquinone, p-dinitrobenzene, m-dinitrobenzene , O-ginito Benzene, p-cyanonitrobenzene, m-cyanonitrobenzene, o-cyanonitrobenzene, 1,4-naphthoquinone, 2,3-dichloronaphthoquinone, 1-nitronaphthalene, 2-nitronaphthalene, 1,3-dinitronaphthalene, 1,5 -Dinitronaphthalene, 9-cyanoanthracene, 9-nitroanthracene, 9,10-anthraquinone, 1,3,6,8-tetranitrocarbazole, 2,4,7-trinitro-9-fluorenone, 2,3,5 Organic compounds such as 6-tetracyanopyridine, maleic anhydride, phthalic anhydride, and fullerenes C60 and C70 can be used, and one or more of these can be used in combination.

[Second light emitting unit]
As described above, the second light emitting unit 6 includes the hole transport layer 61, the second light emitting layer 62, the third light emitting layer 63, the hole blocking layer (intermediate layer) 64, and the electron transport layer 65. is doing.
In the second light emitting unit 6 having such a configuration, holes are supplied from the hole transport layer 61 side and electrons are supplied from the hole blocking layer 64 side to the second light emitting layer 62 and the third light emitting layer 63, respectively. (Injection) In the second light-emitting layer 62 and the third light-emitting layer 63, holes and electrons recombine, and excitons (excitons) are generated by the energy released upon this recombination, When the exciton returns to the ground state, energy (fluorescence or phosphorescence) is emitted, so that the second light-emitting layer 62 and the third light-emitting layer 63 each emit light.

Hereinafter, each layer which comprises this 2nd light emission part 6 is demonstrated sequentially.
(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 53) to the second light emitting layer 62. The hole transport layer 61 also has a function of preventing electrons from reaching the carrier generation layer 5 and deteriorating the carrier generation layer 5 by blocking electrons that have passed through the second light emitting layer 62. ing.

In particular, the hole transport layer 61 is provided between the second light-emitting layer 62 and the carrier generation layer 5 so as to be in contact with the carrier generation layer 5.
Thereby, as described above, the electron withdrawing layer 53 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 constituent material as that of the hole transport layer 41 described above can be used.
In particular, among the above, the hole transport material constituting the hole transport layer 61 is preferably an amine compound, and N, N′-di (1-naphthyl) -N, N′-diphenyl-1,1 ′. -Diphenyl-4,4'-diamine (NPD) is more preferable. When such a compound comes into contact with the carrier generation layer 5 (electron withdrawing layer 53), 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 nm or more and 150 nm or less, and more preferably 10 nm or more and 100 nm or less. Accordingly, holes can be transported suitably to the second light emitting layer 62, and electrons that have passed through the second light emitting layer 62 can be suitably blocked.

(Second light emitting layer)
The second 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 first light-emitting layer 42 described above can be used. The light emitting material used for the second light emitting layer 62 may be the same as or different from the light emitting material of the first light emitting layer 42. Further, the emission color of the second light emitting layer 62 may be the same as or different from the emission color of the first light emitting layer 42 described above.

Further, the second light emitting layer 62 may include a host material to which the light emitting material is added as a guest material in addition to the light emitting material.
In the case of using the light emitting material (guest material) and the host material as described above, the content (doping amount) of the light emitting material in the second light emitting layer 62 is preferably 0.1 wt% or more and 10 wt% or less. And more preferably 0.5 wt% or more and 5 wt% or less. 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 second light emitting layer 62, it is preferable to use a phosphorescent material. That is, the second light emitting layer 62 preferably includes a light emitting material that emits phosphorescence when energized between the anode 3 and the cathode 7.
By using a phosphorescent material as the light-emitting material of the second light-emitting layer 62 with little or no impurity diffusion due to continuous driving of the light-emitting element 1, the second light-emitting layer 62 can efficiently emit light. The luminous efficiency of the element 1 can be improved.

In addition, the peak wavelength of light emission of the second light emitting layer 62 is preferably longer than the peak wavelength of light emission of the first light emitting layer 42 described above. Thereby, the 1st light emitting layer 42 and the 2nd light emitting layer 62 can be light-emitted with sufficient balance.
The average thickness of the second light emitting layer 62 is not particularly limited, but is preferably 5 nm or more and 50 nm or less, more preferably 5 nm or more and 40 nm or less, and 5 nm or more and 30 nm or less. Is more preferable. Thereby, the driving voltage of the light emitting element 1 can be suppressed and the second light emitting layer 62 can emit light efficiently. In particular, in the case where the second light emitting layer 62 and the third light emitting layer 63 are stacked as in the present embodiment, by reducing the thickness of the second light emitting layer 62 relatively, holes and Both the second light-emitting layer 62 and the third light-emitting layer 63 are present in a recombination region where electron recombination occurs, and these can emit light in a balanced manner.

(Third light emitting layer)
The third light emitting layer 63 includes a light emitting material.
In the present embodiment, the third light emitting layer 63 is in contact with the second light emitting layer 62 described above. Thereby, both the second light emitting layer 62 and the third light emitting layer 63 can be easily present in the hole and electron recombination region in the second light emitting unit 6. Therefore, both the second light emitting layer 62 and the third 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 first light-emitting layer 42 described above can be used. Note that the light emitting material used for the third light emitting layer 63 may be the same as or different from the light emitting material of the first light emitting layer 42. The light emitting material used for the third light emitting layer 63 may be the same as or different from the light emitting material of the second light emitting layer 62. The emission color of the third light emitting layer 63 may be the same as or different from the emission color of the first light emitting layer 42 described above. The emission color of the third light emitting layer 63 may be the same as or different from the emission color of the second light emitting layer 62 described above.

Further, the third light emitting layer 63 may include a host material to which the light emitting material is added as a guest material in addition to the light emitting material.
In the case of using the light emitting material (guest material) and the host material as described above, the content (doping amount) of the light emitting material in the third light emitting layer 63 is preferably 0.1 wt% or more and 30 wt% or less. More preferably, it is 0.5 wt% or more and 20 wt% or less. 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 third light emitting layer 63, it is preferable to use a phosphorescent material. That is, the third light emitting layer 63 preferably contains a light emitting material that emits phosphorescence when energized between the anode 3 and the cathode 7.
As described above, by using a phosphorescent material as the light emitting material of the third light emitting layer 63 with little or no impurity diffusion due to continuous driving of the light emitting element 1, the third light emitting layer 63 can emit light efficiently. As a result, the light emission efficiency of the light emitting element 1 can be improved.

The peak wavelength of light emission of the third light emitting layer 63 is preferably longer than the peak wavelength of light emission of the first light emitting layer 42 described above. Thereby, the 1st light emitting layer 42, the 2nd light emitting layer 62, and the 3rd light emitting layer 63 can be light-emitted with sufficient balance.
Furthermore, the peak wavelength of light emission of the third light emitting layer 63 is preferably shorter than the peak wavelength of light emission of the second light emitting layer 62. Thereby, the 1st light emitting layer 42, the 2nd light emitting layer 62, and the 3rd light emitting layer 63 can be made to light-emit in a more balanced manner.

From this point of view, when the emission color of the first emission layer 42 is blue, the emission color of the second emission layer 62 and the emission color of the third emission layer 63 are preferably red and green, respectively. .
The average thickness of the third light emitting layer 63 is not particularly limited, but is preferably 5 nm or more and 50 nm or less, more preferably 5 nm or more and 40 nm or less, and 5 nm or more and 30 nm or less. Is more preferable. Thereby, the driving voltage of the light emitting element 1 can be suppressed, and the third light emitting layer 63 can emit light efficiently. In particular, in the case where the second light emitting layer 62 and the third light emitting layer 63 are stacked as in the present embodiment, by reducing the thickness of the third light emitting layer 63 relatively, holes and Both the second light-emitting layer 62 and the third light-emitting layer 63 are present in a recombination region where electron recombination occurs, and these can emit light in a balanced manner.

  In the present embodiment, the case where the second light emitting unit 6 includes two light emitting layers (that is, the second light emitting layer 62 and the third light emitting layer 63) is described as an example. The light emitting unit 6 may have a single light emitting layer. That is, in the second light emitting unit 6, one of the second light emitting layer 62 and the third light emitting layer 63 may be omitted. Further, the second light emitting unit 6 may have three or more light emitting layers. That is, the second light emitting unit 6 may include one or more other light emitting layers in addition to the second light emitting layer 62 and the third 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. Moreover, when the 2nd light emission part 6 has a several light emitting layer, the intermediate | middle layer may be provided between light emitting layers.

(Hole blocking layer)
The hole blocking layer 64 has a function of blocking holes. Thereby, it is possible to prevent holes from being transported from the third light emitting layer 63 to the electron transport layer 65 described above. Therefore, it is possible to prevent the electron transport layer 65 from being deteriorated by holes. The hole blocking layer 64 has a function of transporting electrons. Thereby, electrons received from the electron transport layer 65 described later can be transported to the third light emitting layer 63.

  Examples of the constituent material of the hole blocking layer 64 include 3-phenyl-4- (1′-naphthyl) -5-phenylcarbazole, 4,4′-N, N′-dicarbazole biphenyl (CBP). Quinolinolato metal complexes such as carbazole derivatives, phenanthroline derivatives, triazole derivatives, tris (8-quinolinolato) aluminum (Alq), bis- (2-methyl-8-quinolinolato) -4- (phenylphenolato) aluminum -Dicarbazolyl-3,5-benzene, poly (9-vinylcarbazole), 4,4 ', 4 "-tris (9-carbazolyl) triphenylamine, 4,4'-bis (9-carbazolyl) -2, Carbalisol group-containing compounds such as 2′-dimethylbiphenyl, 2,9-dimethyl-4,7-diphenyl-1 10- phenanthroline (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 64 is not particularly limited, but is preferably 1 nm or more and 50 nm or less, more preferably 3 nm or more and 30 nm or less, and more preferably 5 nm or more and 20 nm or less. Further preferred.
The hole blocking layer 64 may be omitted depending on the configuration of the second light emitting layer 62, the third light emitting layer 63, and the electron transport layer 65.

(Electron transport layer)
The electron transport layer 65 has a function of transporting electrons injected from the cathode 7 to the hole blocking layer 64 and the second light emitting layer 62.
As a constituent material (electron transporting material) of the electron transport layer 65, for example, an organic compound having a ligand such as 8-quinolinol or its derivative (quinoline derivative) such as tris (8-quinolinolato) aluminum (Alq ₃ ) or the like. Metal complexes, 1,3-bis (N, Nt-butyl-phenyl) -1,3,4-oxadiazole (OXD-7), 2- [1,1′-biphenyl] -4-yl Oxadiazole derivatives such as -5- [4- (1,1-dimethylethyl) phenyl] -1,3,4-oxadiazole (PBD), perylene derivatives, pyridine derivatives, pyrimidine derivatives, quinoxaline derivatives, diphenyl Examples include organic compounds that do not contain metal atoms, such as quinone derivatives and nitro-substituted fluorene derivatives, and one or more of these can be used in combination. .
The average thickness of the electron transport layer 65 is not particularly limited, but is preferably 10 nm or more and 100 nm or less, and more preferably 10 nm or more and 50 nm or less.

[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 100 nm or more and 400 nm or less, and more preferably 100 nm or more and 200 nm or less.
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.

[Electron injection layer]
An electron injection layer may be provided between the electron transport layer 65 and the cathode 7.
By adopting a configuration including the electron injection layer, the electron injection efficiency from the cathode 7 to the electron transport layer 65 can be improved.
Examples of the constituent material of the electron injection layer (electron injectable material) include various inorganic insulating materials and various inorganic semiconductor materials.

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

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 is not particularly limited, but is preferably 0.1 nm or more and 1000 nm or less, more preferably 0.2 nm or more and 100 nm or less, and 0.2 or more and 50 nm or less. Is more preferable.

[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 first light emitting layer 42 and recombined with holes injected from the anode 3 to contribute to light emission. The generated holes are transported to the second light-emitting layer 62 and the third light-emitting layer 63 and recombine with electrons injected from the cathode 7, thereby contributing to light emission.

Thus, the light emitting element 1 can cause the first light emitting layer 42, the second light emitting layer 62, and the third light emitting layer 63 to emit light, respectively, so that the light emitting element 1 has a light emitting layer of only one layer. The light emission efficiency can be improved and the drive voltage can be reduced.
In particular, the light-emitting element 1 includes the buffer layer 51 having a function of suppressing the diffusion of the electron-injecting material from the n-type electron transport layer 52 to the first light-emitting layer 42, so that the first light emission It is possible to accurately suppress or prevent a decrease in luminance life of the light-emitting element 1 due to a decrease in the light emission characteristics of the layer 42.

(Manufacturing method of light emitting element)
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 first 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 stacking the buffer layer 51, the n-type electron transport layer 52, and the electron withdrawing layer 53 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 as, for example, a light source. Moreover, a display apparatus (display apparatus of this invention) can be comprised by arrange | positioning the several light emitting element 1 in matrix form.
The driving method of the display device is not particularly limited, and may be either an active matrix method or a passive matrix method.

(Display device)
Next, an example of a display device to which the display device of the present invention is applied will be described.
FIG. 2 is a longitudinal sectional view showing an embodiment of a display device to which the display device of the present invention is applied.
The display device 100 shown in FIG. 2 includes a substrate 21, a plurality of light emitting elements 1R, 1G, and 1B and color filters 19R, 19G, and 10B provided corresponding to the sub-pixels 100R, 100G, and 100B, and each light emitting element 1R. And a plurality of driving transistors 24 for driving 1G and 1B, respectively. Here, the display device 100 is a display panel having a top emission structure.

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, 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. An epoxy layer 35 made of an epoxy resin is formed on the light emitting elements 1R, 1G, and 1B so as to cover them.

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

A light shielding layer 36 is formed between the adjacent color filters 19R, 19G, and 19B. Thereby, it is possible to prevent the unintended subpixels 100R, 100G, and 100B from emitting light.
A sealing substrate 20 is provided on the color filters 19R, 19G, 19B and the light shielding layer 36 so as to cover them.
The display device 100 as described above may be a single color display, and color display is also possible by selecting a light emitting material used for each light emitting element 1R, 1G, 1B.
Such a display device 100 (the display device of the present invention) can be incorporated into various electronic devices.

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 data communication input / output terminal 1314 as necessary. Further, the imaging signal stored in the memory of the circuit board 1308 is output to the television monitor 1430 or the personal computer 1440 by a predetermined operation.

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

The light emitting element, the light emitting device, the display device, and the electronic device of the present invention have been described based on the illustrated embodiments, but the present invention is not limited to these.
For example, 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 this case, it is only necessary that at least one light emitting layer is provided on each of the one surface side and the other surface side of the carrier generation layer.
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′-di (1-naphthyl) -N, N′-diphenyl-1,1′-diphenyl-4,4′-diamine (α-NPD) is vacuumed on the ITO electrode. Vapor deposition was performed to form a hole transport layer having an average thickness of 50 nm (hole transport layer of the first light-emitting portion).
<3> Next, a first light-emitting layer having an average thickness of 30 nm was formed on the hole transport layer by using a vacuum deposition method.
Here, a mixed material of BDAVBi, which is a blue light-emitting material (guest material), and TBADN, which is a host material, was used as a constituent material constituting the first light-emitting layer. Further, the content (dope concentration) of the blue light emitting material in the first light emitting layer was 10 wt%.

<4> Next, 1,3-bis (N, Nt-butyl-phenyl) -1,3,4-oxadiazole (OXD-7) is vacuum-deposited on the first light-emitting layer. A buffer layer having an average thickness of 10 nm was formed by vapor deposition.
<5> Next, on the buffer layer, 1,3-bis (N, Nt-butyl-phenyl) -1,3,4-oxadiazole (OXD-7) as an electron transporting material, Li ₂ O as an electron injecting material was deposited by a vacuum deposition method to form an n-type electron transport layer (n-type electron transport layer of a carrier generation layer) having an average thickness of 30 nm. The content of OXD-7 and Li ₂ O in the n-type electron transport layer was 99: 1 by weight.

<6> Next, on the electron transport layer, hexacyanohexaazatriphenylene (LG Chemical Co., “LG101”) as an electron withdrawing material is deposited by vacuum deposition to form an electron withdrawing layer having an average thickness of 30 nm. did.
Through these steps <4>, <5>, and <6>, a carrier generation layer including a buffer layer, an n-type electron transport layer, and an electron withdrawing layer was obtained.

<7> Next, N, N′-di (1-naphthyl) -N, N′-diphenyl-1,1′-diphenyl-4,4′-diamine is formed on the carrier generation layer (on the electron withdrawing layer). (Α-NPD) was deposited by a vacuum deposition method to form a hole transport layer having an average thickness of 20 nm.
<8> Next, a second light-emitting layer having an average thickness of 5 nm was formed on the hole-transporting layer using a vacuum deposition method.

  Here, the constituent materials constituting the second light emitting layer are represented by btp2Ir (acac) represented by the above formula (1) which is a red light emitting material (guest material) and the above formula (3) which is a host material. A mixed material with 4,4′-N, N′-dicarbazole biphenyl (CBP) was used. Further, the content (dope concentration) of the red light emitting material in the second light emitting layer was 9.0 wt%.

<9> Next, on the 2nd light emitting layer, the 3rd light emitting layer with an average thickness of 5 nm was formed using the vacuum evaporation method.
Here, as a constituent material constituting the third light emitting layer, a mixed material of Ir (ppy) 3 represented by the above formula (2) which is a green light emitting material (guest material) and CBP which is a host material is used. It was. Further, the content (dope concentration) of the green light emitting material in the third light emitting layer was 15 wt%.

<10> Next, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), which is a carbazole derivative, is formed on the third light-emitting layer by a vacuum deposition method, and the average thickness is determined. A 20 nm hole blocking layer was formed.
<11> Next, 1,3-bis (N, Nt-butyl-phenyl) -1,3,4-oxadiazole (OXD-7) is deposited on the hole blocking layer by a vacuum deposition method. Thus, an electron transport layer having an average thickness of 40 nm (electron transport layer of the second light-emitting portion) was formed.

<12> 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.
<13> Next, Al was formed into a film by the vacuum evaporation method on the electron injection layer. Thereby, a cathode having an average thickness of 100 nm made of Al was formed.
<14> Next, a glass protective cover (sealing member) was placed over the formed layers, and fixed and sealed with an epoxy resin.
Through the above steps, the anode, the hole transport layer, the first light emitting layer, the carrier generation layer (buffer layer, n-type electron transport layer, electron withdrawing layer), hole transport layer, and second light emitting layer are formed on the substrate. A light emitting device (tandem light emitting device) in which a third light emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer, and a cathode were laminated in this order was manufactured.

(Example 2)
A light emitting device was produced in the same manner as in Example 1 except that the step <4> was changed to the following step <4A> to form a buffer layer.
<4A> On the first light-emitting layer, 2- [1,1′-biphenyl] -4-yl-5- [4- (1,1-dimethylethyl) phenyl] -1,3,4-oxadi Azole (PBD) was deposited by a vacuum deposition method to form a buffer layer having an average thickness of 10 nm.

(Example 3)
The steps <4> and <5> are changed to the following steps <4B> and <5B> to form a buffer layer and an n-type electron transport layer, and are the same as in Example 1 described above. Thus, a light emitting device was manufactured.
<4B> Tris (8-quinolinolato) aluminum (Alq ₃ ) was deposited on the first light-emitting layer by a vacuum deposition method to form a buffer layer having an average thickness of 5 nm.

<5B> 1,3-bis (N, Nt-butyl-phenyl) -1,3,4-oxadiazole (OXD-7) as an electron transporting material on the buffer layer, and electron injection property Li ₂ O as a material was deposited by a vacuum deposition method to form an n-type electron transport layer having an average thickness of 35 nm (an n-type electron transport layer of a carrier generation layer). The content of OXD-7 and Li ₂ O in the n-type electron transport layer was 99: 1 by weight.

Example 4
A light emitting device was manufactured in the same manner as in Example 1 except that the step <4> was changed to the following step <4C> to form a buffer layer.
<4C> Tris (8-quinolinolato) aluminum (Alq ₃ ) was deposited on the first light-emitting layer by a vacuum deposition method to form a buffer layer having an average thickness of 10 nm.

(Example 5)
The steps <4> and <5> are changed to the following steps <4D> and <5D>, respectively, except that a buffer layer and an n-type electron transport layer are formed. Thus, a light emitting device was manufactured.
<4D> Tris (8-quinolinolato) aluminum (Alq ₃ ) was deposited on the first light-emitting layer by a vacuum deposition method to form a buffer layer having an average thickness of 5 nm.

<5D> On the buffer layer, 2- [1,1′-biphenyl] -4-yl-5- [4- (1,1-dimethylethyl) phenyl] -1,3,4 as an electron transporting material - forming a-oxadiazole (PBD), and Li 2 _O as an electron injecting material was deposited using a vacuum deposition method, n-type electron transport layer having an average thickness of 35nm to (n-type electron transport layer of the carrier generating layer) did. The content of PBD and Li ₂ O in the n-type electron transport layer was 99: 1 by weight.

(Example 6)
The steps <4> and <5> are changed to the following steps <4E> and <5E>, respectively, except that a buffer layer and an n-type electron transport layer are formed. Thus, a light emitting device was manufactured.
<4E> Tris (8-quinolinolato) aluminum (Alq ₃ ) was deposited on the first light-emitting layer by a vacuum deposition method to form a buffer layer having an average thickness of 10 nm.

<5E> On the buffer layer, 2- [1,1′-biphenyl] -4-yl-5- [4- (1,1-dimethylethyl) phenyl] -1,3,4 as an electron transporting material - forming a-oxadiazole (PBD), and Li 2 _O as an electron injecting material was deposited using a vacuum deposition method, n-type electron transport layer having an average thickness of 30nm to (n-type electron transport layer of the carrier generating layer) did. The content of PBD and Li ₂ O in the n-type electron transport layer was 99: 1 by weight.

(Example 7)
The steps <4>, <5>, and <6> were changed to the following steps <4F>, <5F>, and <6F> to form a buffer layer, an n-type electron transport layer, and an electron withdrawing layer. Except for this, a light emitting device was manufactured in the same manner as in Example 1 described above.
<4F> Tris (8-quinolinolato) aluminum (Alq ₃ ) was deposited on the first light-emitting layer by a vacuum deposition method to form a buffer layer having an average thickness of 5 nm.

<5F> On the buffer layer, 1,3-bis (N, Nt-butyl-phenyl) -1,3,4-oxadiazole (OXD-7) as an electron transporting material, and electron injection property Li ₂ O as a material was deposited by a vacuum deposition method to form an n-type electron transport layer having an average thickness of 35 nm (an n-type electron transport layer of a carrier generation layer). The content of OXD-7 and Li ₂ O in the n-type electron transport layer was 99: 1 by weight.

<6F> Next, on the n electron transport layer, hexacyanohexaazatriphenylene (LG Chemical Co., “LG101”) as an electron withdrawing material and Li ₂ O as an electron injecting material are vacuum deposited. Evaporation was performed to form an electron withdrawing layer having an average thickness of 30 nm. The content of hexacyanohexaazatriphenylene and Li ₂ O in this electron withdrawing layer was set to 98: 2 by weight.
(Comparative example)
A light emitting device was manufactured in the same manner as in Example 1 except that the formation of the buffer layer in Step <4> was omitted.

2. Evaluation With respect to the light emitting devices of each of the examples and comparative examples, a current of 10 mA / cm ² was passed by a direct current power source between the anode and the cathode, and the driving voltage applied to the light emitting device was emitted from the light emitting device. The current efficiency of the light was measured, and a value normalized based on the drive voltage and current efficiency measured in Example 1 was obtained.
Furthermore, with respect to the light emitting elements of the examples and the comparative examples, a current of 100 mA / cm ² was passed between the anode and the cathode by a direct current power source, and the time required to reach 80% of the initial luminance ( LT80; Luminance life) was measured, and a value normalized based on the time measured in Example 1 was obtained.

In addition, the light emitting elements of Example 1 and Example 4 were caused to emit light until a current density of 100 mA / cm ² was passed between the anode and the cathode by a direct current power source to 80% of the initial luminance. Then, the ion intensity of Li was analyzed from the anode side of the light emitting element toward the cathode side by the secondary ion mass spectrometry (SIMS).
These results are shown in Table 1 and FIG.

First, as is clear from Table 1, in the light-emitting elements of the respective examples, compared with the light-emitting elements of the comparative examples, by providing a buffer layer, the electron-injecting material ( The diffusion of Li ₂ O) from the n-type electron transport layer to the first light-emitting layer was suppressed, and the lifetime of the light-emitting element could be extended.
As is clear from FIG. 6, Example 1 using an organic compound containing no metal atom and an organometallic complex were used as the electron transporting material (second electron transporting material) used for the buffer layer. In Example 4, diffusion of the electron injecting material (Li ₂ O) in the buffer layer and the first light-emitting layer is suppressed in the light-emitting element of Example 4, which results in a long lifetime of the light-emitting element. It turned out that it has been planned.

  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 ... 1st light emission layer 5 ... Carrier generation layer 51 ... ... buffer layer 52 ... n-type electron transport layer 53 ... electron withdrawing layer 6 ... second light emitting part 61 ... hole transport layer 62 ... second light emitting layer 63 ... third light emitting layer 64 ... ... Hole blocking layer 65 ... Electron transport layer 7 ... Cathode 8 ... Sealing member 15 ... Laminated body 19B, 19G, 19R ... Color filter 100 ... Display device 100R, 100G, 100B ... Sub-pixel 20 ... Sealing substrate 21 ... Substrate 22 ... Planarization layer 24 ... Driving transistor 241 ... Semiconductor layer 242 ... Gate insulating layer 243 ... Gate electrode 244 ... Source electrode 245 ... Drain electrode 27 ... Arrangement 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 …… Cellular phone 1202 …… Operation buttons 1204 …… Earpiece 1206 …… Speaker 1300 …… Digital still camera 1302 …… Case (body) 1304 ...... Light receiving unit 1306 …… Shutter button 1308 …… Circuit board 1312 …… ... Video signal output terminal 1314 ... Input / output terminal for data communication 1430 ... TV monitor 1440 ... Personal computer 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 that is provided between the cathode and the first light emitting layer and emits light when energized between the anode and the cathode;
A carrier generating layer provided between the first light emitting layer and the second light emitting layer and generating electrons and holes;
The carrier generation layer includes an n-type electron transport layer and a buffer layer in contact with each other,
The n-type electron transport layer contains a first electron transport material and an electron donor material, and is provided on the second light emitting layer side,
The buffer layer contains a second electron-transporting material and is provided on the first light-emitting layer side, so that the first light-emitting layer is formed from the n-type electron transport layer of the electron-donating material. A light-emitting element having a function of suppressing diffusion into the light-emitting element.   The types of the first electron transporting material and the second electron transporting material are each set so that the electron donor material is less likely to diffuse in the buffer layer than in the n-type electron transport layer. The light emitting device according to claim 1, which is selected.   The first electron transporting material and the second electron transporting material are each selected such that their electron mobility is higher in the first electron transporting material. The light emitting element as described in.   The light emitting device according to claim 2 or 3, wherein an organic compound containing no metal is selected as the first electron transporting material, and an organometallic complex is selected as the second electron transporting material.   5. The light emitting device according to claim 1, wherein the electron donor material is at least one of an alkali metal, an alkaline earth metal, an alkali metal compound, and an alkaline earth metal compound.   The light emitting device according to claim 1, wherein the buffer layer has an average film thickness of 3.0 nm or more and 20.0 nm or less.   7. The light emitting device according to claim 1, wherein a content of the electron donor material in the n-type electron transport layer is 0.3 wt% or more and 2.0 wt% or less.   Furthermore, the carrier generation layer includes an electron-withdrawing layer having an electron-withdrawing property provided in contact with the n-type electron transport layer between the second light-emitting layer and the n-type electron transport layer. The light emitting device according to claim 1.   The light emitting device according to claim 8, wherein the electron withdrawing layer contains an organic cyanide compound having an aromatic ring.   The light emitting device according to claim 8 or 9, wherein the electron withdrawing layer further contains the electron donor material.   The light emitting device according to any one of claims 1 to 10, further comprising a third light emitting layer that is provided between the second light emitting layer and the cathode and emits light when energized between the anode and the cathode. element.   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 display device according to claim 13.

Images