JP2009295306A - Light-emitting device, display, and electronic equipment - Google Patents

Abstract

A light-emitting element having excellent light emission efficiency and a highly reliable display device and electronic device including the light-emitting element are provided.
A light-emitting element 1 is provided between a cathode 12, an anode 3, a cathode 12 and an anode 3, and emits red light between a red light-emitting layer 6, and between a red light-emitting layer 6 and the cathode 12. A blue light-emitting layer 8 that emits blue light, and a layer between the red light-emitting layer 6 and the blue light-emitting layer 8 so as to be in contact therewith, and has a hole mobility higher than that of the first material and the first material. The red light emitting layer 6 includes a first light emitting material and a first host material, and includes a first material, a second material, a second material, When the energy level of HOMO of the host material of 1 is HL _A [eV], HL _B [eV], HL _C [eV], the following expressions (1) and (2) are satisfied: To do.
| HL _B -HL _C | <| HL _A -HL _C | (1)
| HL _A -HL _C | ≧ 0.3 [eV] (2)
[Selection] Figure 1

Description

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

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

  As such a light emitting element, for example, a light emitting element in which two light emitting layers corresponding to two colors of R (red) and B (blue) are stacked between a cathode and an anode to emit white light is known. (For example, refer to Patent Document 1). Such a light-emitting element that emits white light can display a full-color image when used in combination with a color filter in which two colors of R (red) and B (blue) are separately applied to each pixel.

Moreover, in the light emitting element concerning patent document 1, the movement of the carrier (electron and success) between light emitting layers can be restrict | limited by providing an intermediate | middle layer between light emitting layers, The hole in each light emitting layer can be restrict | limited. The amount of recombination between electrons and electrons is adjusted. As a result, performances such as light emission efficiency and light emission lifetime of the light emitting element are improved.
However, in the light emitting device according to Patent Document 1, since a general hole transport material or electron transport material is simply applied to the intermediate layer, the light emission efficiency is not sufficient.

JP 2007-286991 A

  An object of the present invention is to provide a light-emitting element that is excellent in luminous efficiency, a highly reliable display device and an electronic apparatus including the light-emitting element.

Such an object is achieved by the present invention described below.
The light emitting device of the present invention comprises a cathode,
The anode,
A first light-emitting layer provided between the cathode and the anode and emitting light in a first color;
A second light-emitting layer provided between the first light-emitting layer and the cathode and emitting light in a second color different from the first color;
A first material and a second material having a hole mobility higher than that of the first material, provided between the first light emitting layer and the second light emitting layer so as to be in contact therewith; And an intermediate layer composed of
The first light-emitting layer includes a first light-emitting material that emits light in the first color, and a first host material that supports the first light-emitting material as a guest material,
The energy level of the highest occupied molecular orbital of the first material is HL _A [eV], the energy level of the highest occupied molecular orbital of the second material is HL _B [eV], and the highest energy level of the first host material is When the energy level of the occupied molecular orbital is HL _C [eV], the following expressions (1) and (2) are satisfied.
| HL _B -HL _C | <| HL _A -HL _C | (1)
| HL _A -HL _C | ≧ 0.3 [eV] (2)
Thereby, the light emitting element excellent in luminous efficiency can be provided.

In the light-emitting element of the present invention, it is preferable that the second material and the first host material satisfy the relationship of the following formula (3).
| HL _B -HL _C | ≦ 0.2 [eV] (3)
Accordingly, holes are more likely to move preferentially from the first host material of the first light emitting layer to the second material in the intermediate layer, and the light emitting element is particularly excellent in light emission efficiency.

In the light-emitting element of the present invention, it is preferable that the first material has a higher electron mobility than the second material.
Thereby, the electrons transported from the second light emitting layer to the first light emitting layer through the intermediate layer are more easily transported preferentially by the first material. In addition, the light emitting element is particularly excellent in luminous efficiency.
In the light emitting device of the present invention, it is preferable that the light of the second color has a shorter wavelength than the light of the first color.
Thereby, each light emitting layer can emit light in a balanced manner, and the light emitting element has particularly excellent light emission efficiency.

In the light emitting device of the present invention, the energy level of the lowest unoccupied molecular orbital of the first material is LL _A [eV], and the energy level of the lowest unoccupied molecular orbital of the second material is LL _B [eV]. It is preferable that the following expression (4) is satisfied.
LL _A −LL _B ≧ 0.4 [eV] (4)
As described above, since the difference in the energy level of the lowest idle activation is sufficiently large between the first material and the second material, the first material and the second material are transported from the second light emitting layer to the first light emitting layer through the intermediate layer. The electrons that are likely to be transported by the first material.

In the light-emitting element of the present invention, the second light-emitting layer includes a second light-emitting material that emits light in the second color, and a second host material that supports the second light-emitting material,
When the energy level of the lowest unoccupied molecular orbital of the first material is LL _A [eV] and the energy level of the lowest unoccupied molecular orbital of the second host material is LL _D [eV], It is preferable to satisfy (5).
| LL _A −LL _D | ≦ 0.2 [eV] (5)
As a result, the second host material is more likely to transfer electrons preferentially to the first material.

In the light emitting device of the present invention, when the content of the first material in the intermediate layer is A [wt%] and the content of the second material in the intermediate layer is B [wt%] B / (A + B) is preferably 0.1 to 0.9.
Accordingly, carriers (electrons and holes) can be more preferably transported between the first light-emitting layer and the second light-emitting layer via the intermediate layer, and the first light-emitting layer and the second light-emitting layer can be transported. A sufficient amount of electrons and holes can be injected into each to emit light.

In the light emitting device of the present invention, the first material is preferably an acene-based material.
Accordingly, electrons can be smoothly transferred from the second light emitting layer to the first light emitting layer through the intermediate layer, and the light emitting element is particularly excellent in light emission efficiency.
In the light emitting device of the present invention, the second material is preferably an amine material.
Accordingly, holes can be smoothly transferred from the first light emitting layer to the second light emitting layer through the intermediate layer, and the light emitting element is particularly excellent in light emission efficiency.

In the light emitting device of the present invention, the average thickness of the intermediate layer is preferably 1 to 100 nm.
Accordingly, it is possible to more smoothly transfer holes and electrons through the intermediate layer between the first light emitting layer and the second light emitting layer while suppressing the driving voltage, and the light emitting element has sufficient luminance. Can emit light.
In the light emitting device of the present invention, it is preferable that the first light emitting layer is a red light emitting layer that emits red light as the first color.
Thereby, each light emitting layer can be light-emitted in a more balanced manner.
In the light emitting device of the present invention, the second light emitting layer is preferably a blue light emitting layer that emits blue light as the second color.
Thereby, each light emitting layer can be light-emitted in a more balanced manner.

In the light emitting device of the present invention, the first color and the second color are provided between the first light emitting layer and the anode or between the second light emitting layer and the cathode. Preferably has a third light-emitting layer that emits light of a different third color.
Thereby, each light emitting layer can be made to emit light with good balance, and the light of the target color can be emitted comparatively easily.
The display device of the present invention includes the light emitting element of the present invention.
Thereby, a display device having 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 having excellent reliability can be provided.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the light-emitting element, the display device, and the electronic apparatus of the invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram schematically showing a longitudinal section of a preferred embodiment of the light emitting device of the present invention. In the following description, for convenience of explanation, the upper side in FIG. 1 will be described as “upper” and the lower side as “lower”.
A light-emitting element (electroluminescence element) 1 shown in FIG. 1 emits white light by emitting R (red), G (green), and B (blue).

Such a light emitting device 1 includes an anode 3, a hole injection layer 4, a hole transport layer 5, a red light emitting layer (first light emitting layer) 6, an intermediate layer 7, and a blue light emitting layer (second light emitting layer) 8. The green light emitting layer (third light emitting layer) 9, the electron transport layer 10, the electron injection layer 11, and the cathode 12 are laminated in this order.
In other words, the light emitting device 1 includes the hole injection layer 4, the hole transport layer 5, the red light emission layer 6, the intermediate layer 7, the blue light emission layer 8, the green light emission layer 9, the electron transport layer 10, and the electron injection layer 11. A laminated body 15 in which the cathode 12 is laminated in this order is interposed between two electrodes (between the anode 3 and the cathode 12).

The entire light emitting element 1 is provided on the substrate 2 and is sealed with a sealing member 13.
In such a light emitting element 1, electrons are supplied (injected) from the cathode 12 side to the light emitting layers of the red light emitting layer 6, the blue light emitting layer 8, and the green light emitting layer 9, and the anode 3 side. Holes are supplied (injected). In each light emitting layer, holes and electrons recombine, and excitons (excitons) are generated by the energy released during the recombination, and energy (fluorescence or phosphorescence) is generated when the excitons return to the ground state. Is emitted (emitted). Thereby, the light emitting element 1 emits white light.

The substrate 2 supports the anode 3. Since the light-emitting element 1 of the present embodiment is configured to extract light from the substrate 2 side (bottom emission type), the substrate 2 and the anode 3 are substantially transparent (colorless transparent, colored transparent, or translucent), respectively. Has been.
Examples of the constituent material of the substrate 2 include resin materials such as polyethylene terephthalate, polyethylene naphthalate, polypropylene, cycloolefin polymer, polyamide, polyethersulfone, polymethyl methacrylate, polycarbonate, and polyarylate, quartz glass, and soda glass. Such glass materials can be used, and one or more of these can be used in combination.

Although the average thickness of such a board | substrate 2 is not specifically limited, It is preferable that it is about 0.1-30 mm, and it is more preferable that it is about 0.1-10 mm.
In the case where the light emitting element 1 is configured to extract light from the side opposite to the substrate 2 (top emission type), the substrate 2 can be either a transparent substrate or an opaque substrate.
Examples of the opaque substrate include a substrate made of a ceramic material such as alumina, an oxide film (insulating film) formed on the surface of a metal substrate such as stainless steel, and a substrate made of a resin material. It is done.
Hereinafter, each part which comprises the light emitting element 1 is demonstrated sequentially.

(anode)
The anode 3 is an electrode that injects holes into the hole transport layer 5 through a hole injection layer 4 described later. As a constituent material of the anode 3, it is preferable to use a material having a large work function and excellent conductivity.
Examples of the constituent material of the anode 3 include oxides such as ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), In ₃ O ₃ , SnO ₂ , Sb-containing SnO ₂ , and Al-containing ZnO, Au, Pt, and Ag. Cu, alloys containing these, and the like can be used, and one or more of these can be used in combination.
The average thickness of the anode 3 is not particularly limited, but is preferably about 10 to 200 nm, and more preferably about 50 to 150 nm.

(cathode)
On the other hand, the cathode 12 is an electrode that injects electrons into the electron transport layer 10 via an electron injection layer 11 described later. As a constituent material of the cathode 12, it is preferable to use a material having a small work function.
Examples of the constituent material of the cathode 12 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 12, 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 12, the electron injection efficiency and stability of the cathode 12 can be improved.
Although the average thickness of such a cathode 12 is not specifically limited, It is preferable that it is about 100-10000 nm, and it is more preferable that it is about 200-500 nm.
In addition, since the light emitting element 1 of this embodiment is a bottom emission type, the cathode 12 is not particularly required to have light transmittance.

(Hole injection layer)
The hole injection layer 4 has a function of improving the hole injection efficiency from the anode 3.
The constituent material (hole injection material) of the hole injection layer 4 is not particularly limited. For example, copper phthalocyanine or 4,4 ′, 4 ″ -tris (N, N-phenyl-3-methylphenyl) Amino) triphenylamine (m-MTDATA) and the like.
The average thickness of the hole injection layer 4 is not particularly limited, but is preferably about 5 to 150 nm, and more preferably about 10 to 100 nm.
The hole injection layer 4 can be omitted.

(Hole transport layer)
The hole transport layer 5 has a function of transporting holes injected from the anode 3 through the hole injection layer 4 to the red light emitting layer 6.
As the constituent material of the hole transport layer 5, various p-type polymer materials and various p-type low-molecular materials can be used alone or in combination.
The average thickness of the hole transport layer 5 is not particularly limited, but is preferably about 10 to 150 nm, and more preferably about 10 to 100 nm.
The hole transport layer 5 can be omitted.

(Red light emitting layer)
The red light-emitting layer (first light-emitting layer) 6 includes a first light-emitting material that emits red light (first color) and a host material (first host material) that carries the light-emitting material. Has been.
As described above, by using light having a relatively long wavelength as the first color, light emission with a relatively small energy level difference (band gap) between the lowest unoccupied molecular orbital (HOMO) and the highest occupied molecular orbital (LUMO) is obtained. Materials can be used. Thus, a light emitting material having a relatively small band gap easily captures holes and electrons and easily emits light. Therefore, by providing the red light emitting layer 6 on the anode 3 side, the blue light emitting layer 8 and the green light emitting layer 9 which have a large band gap and are difficult to emit light can be set to the cathode 12 side, and each light emitting layer can emit light in a balanced manner.

In addition, when the first light-emitting material is a material having a relatively small band gap as described above, even when the density of electrons and holes in the first light-emitting layer 6 is low, light can be suitably emitted. it can.
Such a red light emitting material is not particularly limited, and various red fluorescent materials and red phosphorescent materials can be used singly or in combination.

  The red fluorescent material is not particularly limited as long as it emits red fluorescence. For example, perylene derivatives such as tetraaryldiindenoperylene derivatives shown in the following chemical formula 1, europium complexes, benzopyran derivatives, rhodamine derivatives, benzothios. Xanthene 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)- And 4H-pyran (DCM).

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

  The content (dope amount) of the red light emitting material in the red light emitting layer 6 is preferably 0.01 to 10 wt%, and more preferably 0.1 to 5 wt%. By setting the content of the red light emitting material within such a range, the light emission efficiency can be optimized, and the red light emitting layer is balanced with the light emitting amount of the blue light emitting layer 8 and the green light emitting layer 9 described later. 6 can emit light.

As a constituent material of the red light emitting layer 6, in addition to the red light emitting material as described above, a first host material using the red light emitting material as a guest material is used. The first host material recombines holes and electrons to generate excitons, and moves the exciton energy to the red light-emitting material (Ferster movement or Dexter movement) to thereby generate a red light-emitting material. It has a function to excite. Such a first host material can be used, for example, by doping the first host material with a red light emitting material, which is a guest material, as a dopant.
The first host material satisfies predetermined conditions with each material in the intermediate layer 7 described later.

Such a first host material is not particularly limited as long as it exhibits the above-described function with respect to the red light emitting material to be used. When the red light emitting material includes a red fluorescent material, for example, Styrylarylene derivatives, naphthacene derivatives, anthracene derivatives such as 2-t-butyl-9,10-di (2-naphthyl) anthracene (TBADN), perylene derivatives, distyrylbenzene derivatives, distyrylamine derivatives, tris (8-quinolinolato) ) Quinolinolato metal complexes such as aluminum complexes (Alq ₃ ), triarylamine derivatives such as tetramers of triphenylamine, oxadiazole derivatives, rubrene and derivatives thereof, silole derivatives, dicarbazole derivatives, oligothiophene derivatives, benzopyrans Derivatives, triazole derivatives Examples include benzoxazole derivatives, benzothiazole derivatives, quinoline derivatives, 4,4′-bis (2,2′-diphenylvinyl) biphenyl (DPVBi), and one of these is used alone or in combination of two or more. It can also be used.
Further, when the red light emitting material includes a red phosphorescent material, examples of the first host material include 3-phenyl-4- (1′-naphthyl) -5-phenylcarbazole, 4,4′-N, N ′. -Carbazole derivatives, such as dicarbazole biphenyl (CBP), etc. are mentioned, Among these, it can also be used individually by 1 type or in combination of 2 or more types.

(Middle layer)
The intermediate layer 7 is provided between the red light emitting layer 6 and the blue light emitting layer 8 described later so as to be in contact therewith. The intermediate layer 7 has a function of adjusting the amount of electrons transported from the blue light emitting layer 8 to the red light emitting layer 6. The intermediate layer 7 has a function of adjusting the amount of holes transported from the red light emitting layer 6 to the blue light emitting layer 8. With this function, the red light emitting layer 6 and the blue light emitting layer 8 can each emit light efficiently.

In particular, in the present invention, the intermediate layer 7 includes a first material and a second material having a hole mobility higher than that of the first material. The energy level of the highest occupied molecular orbital (HOMO) of the first material is HL _A [eV], the energy level of the highest occupied molecular orbital (HOMO) of the second material is HL _B [eV], and the first When the energy level of the highest occupied molecular orbital (HOMO) of the host material is HL _C [eV], the following expressions (1) and (2) are satisfied.
| HL _B -HL _C | <| HL _A -HL _C | (1)
| HL _A -HL _C | ≧ 0.3 [eV] (2)
By satisfying the above formulas (1) and (2), the amount of holes transported from the red light emitting layer 6 to the blue light emitting layer 8 can be controlled. As a result, the light emitting device 1 is excellent in luminous efficiency.

  More specifically, the HOMO energy level of the first host material is closer to the second HOMO energy level than the HOMO energy level of the first material, and the HOMO energy level of the first host material. Is sufficiently separated from the energy level of the second HOMO. For this reason, holes easily move preferentially from the first host material of the red light emitting layer 6 to the second material in the intermediate layer 7. Further, holes are difficult to move from the first host material to the first material. That is, the amount of holes transported from the red light emitting layer 6 to the blue light emitting layer 8 can be adjusted by changing the content ratio of the first material and the second material in the intermediate layer 7. .

The second material has a higher hole mobility than the first material. For this reason, the holes once moved to the second material are efficiently transported to the blue light emitting layer 8.
As described above, since the light emitting element 1 has such an intermediate layer 7, the density of holes in each light emitting layer can be controlled, and each light emitting layer of the light emitting element 1 can emit light in a balanced manner. . For this reason, the luminous efficiency of the light emitting element 1 can be made excellent.

Further, it is preferable that the second material and the first host material satisfy the relationship of the following formula (3). As described above, the difference in the HOMO energy levels between the second material and the first host material is sufficiently small, so that holes are transferred from the first host material of the red light emitting layer 6 to the second layer in the intermediate layer 7. It becomes easy to move to the material of 2 more preferentially.
| HL _B -HL _C | ≦ 0.2 [eV] (3)
Note that it is more preferable to satisfy | HL _B −HL _C | ≦ 0.1 [eV].

In addition, the first material and the second material have the energy level of the lowest unoccupied molecular orbital (LUMO) of the first material as LL _A [eV] and the lowest unoccupied molecular orbital (LUMO) of the second material. When the energy level of) is LL _B [eV], it is preferable that the following expression (4) is satisfied.
LL _A −LL _B ≧ 0.4 [eV] (4)
In addition, it is more preferable to satisfy LL _A −LL _B ≧ 0.5 [eV].
As described above, the difference in the LUMO energy level between the first material and the second material is sufficiently large, so that the electrons transported from the blue light emitting layer 8 to the red light emitting layer 6 through the intermediate layer 7 are Thus, the light-emitting element 1 is easily transported by the first material, and the light-emitting element 1 is particularly excellent in luminous efficiency.

  More specifically, when the first material receives electrons from a second host material, which will be described later, of the blue light emitting layer 8, the electrons transferred to the first material have a sufficient LUMO energy level. It is difficult to move to a high second material and is transported via the first material. The electrons once transferred to the first material are not easily transferred to the second material having a higher LUMO energy level, and are transported through the first material. As described above, the electrons transported from the blue light emitting layer 8 to the red light emitting layer 6 through the intermediate layer 7 are easily transported by the first material. As a result, the amount of electrons transported from the blue light emitting layer 8 to the red light emitting layer 6 through the intermediate layer 7 can be adjusted by adjusting the contents of the first material and the second material. . From the above, it is considered that in the light-emitting element 1, each light-emitting layer emits light in a well-balanced manner and the light emission efficiency is particularly excellent.

Further, when the energy level of the lowest unoccupied molecular orbital of the second host material described later is LL _D [eV], the second host material and the first material satisfy the following formula (5). It is preferable. As described above, since the LUMO energy level difference between the second host material and the first material is sufficiently small, the second host material can easily pass electrons preferentially to the first material. Become. For this reason, the electrons transported from the blue light emitting layer 8 to the red light emitting layer 6 via the intermediate layer 7 are more easily transported preferentially by the first material.

| LL _A −LL _D | ≦ 0.2 [eV] (5)
It is more preferable to satisfy | LL _A −LL _D | ≦ 0.1 [eV].
Moreover, it is preferable that the light emitting element 1 satisfies following formula (6). As described above, since the LUMO energy level of the second material is sufficiently higher than the LUMO energy level of the second host material, electrons injected from the blue light emitting layer 8 into the intermediate layer 7 are It becomes difficult to move to the second material. In other words, the second host material is likely to transfer electrons preferentially by the first material, and the electrons transported from the blue light emitting layer 8 to the red light emitting layer 6 via the intermediate layer 7 are the first host material. Depending on the material, it will be more preferentially transported.

LL _D −LL _B ≧ 0.3 [eV] (6)
In the expression (6), it is more preferable to satisfy LL _D −LL _B ≧ 0.5 [eV], and the effects as described above can be obtained more remarkably.
Moreover, it is preferable that the first material has a higher electron mobility than the second material. Thereby, the electrons transported from the blue light emitting layer 8 to the red light emitting layer 6 through the intermediate layer 7 are more easily transported preferentially by the first material.

Further, the first material and the second material are not particularly limited as long as the relations of the above formulas (1) and (2) are satisfied, and various types having a function of transporting holes. Various materials having a function of transporting materials and electrons can be used. For example, an acene-based material (that is, a material having an acene skeleton) is used as the first material, and an amine-based material (that is, an amine skeleton is used as the second material). Can be used.
The light emitting element 1 can satisfy the above-described formulas (1) and (2) easily by using such compounds as the first material and the second material.

The amine-based material has a hole transport property and a relatively high hole mobility. Further, the acene-based material has an electron transport property and a hole transport property, and has a relatively high electron mobility. Thereby, the intermediate layer 7 has an electron transport property and a hole transport property. That is, the intermediate layer 7 has a bipolar property. Thus, when the intermediate layer 7 has bipolar properties, holes are smoothly transferred from the red light emitting layer 6 to the blue light emitting layer 8 through the intermediate layer 7, and the red light is transmitted from the blue light emitting layer 8 through the intermediate layer 7. Electrons can be smoothly transferred to the light emitting layer 6. As a result, electrons and holes can be efficiently injected into the red light emitting layer 6 and the blue light emitting layer 8 to emit light.
In addition, since such an intermediate layer 7 is excellent in carrier (electron, hole) transportability, electrons and holes are hardly recombined in the intermediate layer 7 and excitons are not easily generated. ing. Thereby, the deterioration by the exciton of the intermediate layer 7 can be prevented or suppressed, and as a result, the durability of the light emitting element 1 can be made excellent.

The acene-based material that can be used as the first material is not particularly limited as long as it can satisfy the formulas (1) and (2) as described above and has an acene skeleton. , Naphthalene derivatives, anthracene derivatives, tetracene derivatives, pentacene derivatives, hexacene derivatives, heptacene derivatives, and the like. Among these, one kind or a combination of two or more kinds can be used, but anthracene derivatives are preferably used.
Anthracene derivatives can be easily formed by a vapor deposition method while having excellent electron transport properties. Therefore, by using an anthracene derivative as the acene-based material, it is possible to easily form the homogeneous intermediate layer 7 while improving the electron transport property of the first material (and thus the intermediate layer 7). .

  In particular, among the anthracene derivatives, the acene-based material used for the intermediate layer 7 is preferably one in which a naphthyl group is introduced at each of the 9th and 10th positions of the anthracene skeleton. Thereby, the effect mentioned above becomes remarkable. Examples of such anthracene derivatives include 9,10-di (2-naphthyl) anthracene (ADN) represented by the following chemical formula 2 and 2-t-butyl- represented by the chemical formula 3 shown below. 9,10-di (2-naphthyl) anthracene (TBADN), 2-methyl-9,10-di (2-naphthyl) anthracene (MADN) as represented by the following chemical formula 4, as represented by the chemical formula 5 below. 2-methyl-9,10-di (1-naphthyl) anthracene (α, α-MADN) and the like.

Such acene-based materials are generally excellent in electron transport properties, and the electron mobility of acene-based materials is higher than the electron mobility of amine-based materials described later. Therefore, electrons can be smoothly transferred from the blue light emitting layer 8 to the red light emitting layer 6 through the intermediate layer 7.
The content of the acene-based material in the intermediate layer 7 is not particularly limited, but is preferably 10 to 90 wt%, more preferably 30 to 70 wt%, and 40 to 60 wt%. Further preferred.

The amine-based material that can be used as the second material is not particularly limited as long as it satisfies the above-described formula (1) and has an amine skeleton. Of the materials, materials having an amine skeleton can be used, but benzidine-based amine derivatives are preferably used.
In particular, among the benzidine-based amine derivatives, the amine-based material used for the intermediate layer 7 is preferably one in which two or more naphthyl groups are introduced. Examples of such benzidine-based amine derivatives include N, N′-bis (1-naphthyl) -N, N′-diphenyl [1,1′-biphenyl] -4, Examples thereof include 4′-diamine (α-NPD) and N, N, N ′, N′-tetranaphthyl-benzidine (TNB) represented by the following chemical formula 7.

Such an amine material generally has excellent hole transport properties, and the hole mobility of the amine material is higher than the hole mobility of the acene material described above. Therefore, holes can be smoothly transferred from the red light emitting layer 6 to the blue light emitting layer 8 through the intermediate layer 7.
The content of the amine-based material in the intermediate layer 7 is not particularly limited, but is preferably 10 to 90 wt%, more preferably 30 to 70 wt%, and 40 to 60 wt%. Further preferred.

  Further, when the content of the first material in the intermediate layer 7 is A [wt%] and the content of the second material in the intermediate layer 7 is B [wt%], B / (A + B) Is preferably from 0.1 to 0.9, more preferably from 0.3 to 0.7, and even more preferably from 0.4 to 0.6. Accordingly, carriers (electrons and holes) can be more preferably transported between the red light emitting layer 6 and the blue light emitting layer 8 via the intermediate layer 7, and the red light emitting layer 6 and the blue light emitting layer 8 are respectively provided. A sufficient amount of electrons and holes can be injected to emit light.

  Moreover, although the average thickness of the intermediate | middle layer 7 is not specifically limited, It is preferable that it is 1-100 nm, It is more preferable that it is 3-50 nm, It is further more preferable that it is 5-30 nm. Thereby, it is possible to more smoothly transfer holes and electrons between the red light emitting layer 6 and the blue light emitting layer 8 through the intermediate layer 7 while suppressing the driving voltage. Bright light can be emitted.

(Blue light emitting layer)
The blue light emitting layer (second light emitting layer) 8 includes a blue light emitting material (second light emitting material) that emits blue light (second color), and a second host material that supports the blue light emitting material as a guest material. It is comprised including.
Such a blue light emitting material is not particularly limited, and various blue fluorescent materials and blue phosphorescent materials can be used alone or in combination of two or more.

  The blue fluorescent material is not particularly limited as long as it emits blue fluorescence. For example, distyryl derivatives, fluoranthene derivatives, pyrene derivatives, perylene and perylene derivatives, anthracene derivatives, benzoxazole derivatives, benzothiazole derivatives, benzimidazoles Derivatives, chrysene derivatives, phenanthrene derivatives, distyrylbenzene derivatives, tetraphenylbutadiene, 4,4′-bis (9-ethyl-3-carbazovinylene) -1,1′-biphenyl (BCzVBi), poly [(9.9- Dioctylfluorene-2,7-diyl) -co- (2,5-dimethoxybenzene-1,4-diyl)], poly [(9,9-dihexyloxyfluorene-2,7-diyl) -ortho-co- (2-methoxy-5- {2-ethoxyhexylo Si} phenylene-1,4-diyl)]], poly [(9,9-dioctylfluorene-2,7-diyl) -co- (ethylnylbenzene)] and the like, and one of these may be used alone. Alternatively, two or more kinds can be used in combination.

The blue phosphorescent material is not particularly limited as long as it emits blue phosphorescence, and examples thereof include metal complexes such as iridium, ruthenium, platinum, osmium, rhenium, and palladium. More specifically, bis [4,6-difluorophenyl pyridinium sulfonate -N, ^{C 2} '] - picolinate - iridium, tris [2- (2,4-difluorophenyl) pyridinate -N, ^{C 2']} iridium , bis [2- (3,5-trifluoromethyl) pyridinate -N, ^{C 2} '] - picolinate - iridium, bis (4,6-difluorophenyl pyridinium sulfonate -N, ^{C 2')} iridium (acetylacetonate ).
In addition, as the second host material that can be used for the blue light-emitting layer 8, the same host material as the first host material described above can be used.

(Green light emitting layer)
The green light emitting layer (third light emitting layer) 9 includes a green light emitting material (third light emitting material) that emits green light (third color) and a third host material that uses the green light emitting material as a guest material. It is configured to include.
Such a green light emitting material is not particularly limited, and various green fluorescent materials and green phosphorescent materials can be used singly or in combination.

  The green fluorescent material is not particularly limited as long as it emits green fluorescence. For example, coumarin derivatives, quinacridone and derivatives thereof, 9,10-bis [(9-ethyl-3-carbazole) -vinylenyl] -anthracene , Poly (9,9-dihexyl-2,7-vinylenefluorenylene), poly [(9,9-dioctylfluorene-2,7-diyl) -co- (1,4-diphenylene-vinylene-2-methoxy -5- {2-ethylhexyloxy} benzene)], poly [(9,9-dioctyl-2,7-divinylenefluorenylene) -ortho-co- (2-methoxy-5- (2-ethoxylhexyloxy) ) -1,4-phenylene)] and the like, and one of these may be used alone or two or more of them may be used in combination.

The green phosphorescent material is not particularly limited as long as it emits green phosphorescence, and examples thereof include metal complexes such as iridium, ruthenium, platinum, osmium, rhenium, and palladium. Among these, at least one of the ligands of these metal complexes preferably has a phenylpyridine skeleton, a bipyridyl skeleton, a porphyrin skeleton, or the like. More specifically, fac - tris (2-phenylpyridine) iridium (Ir (ppy) 3), bis (2-phenyl-pyridinium sulfonate -N, ^{C 2} ') iridium (acetylacetonate), fac - tris [ 5-fluoro-2- (5-trifluoromethyl-2-pyridine) phenyl-C, N] iridium.
Further, as the third host material that can be used for the green light emitting layer 9, the same host material as the first host material described above can be used.

(Electron transport layer)
The electron transport layer 10 has a function of transporting electrons injected from the cathode 12 through the electron injection layer 11 to the green light emitting layer 9.
As a constituent material (electron transport material) of the electron transport layer 10, for example, a quinoline derivative such as an organometallic complex having an 8-quinolinol or its derivative such as tris (8-quinolinolato) aluminum (Alq ₃ ) as a ligand. Oxadiazole derivatives, perylene derivatives, pyridine derivatives, pyrimidine derivatives, quinoxaline derivatives, diphenylquinone derivatives, nitro-substituted fluorene derivatives, and the like, and one or more of these can be used in combination.
Although the average thickness of the electron carrying layer 10 is not specifically limited, It is preferable that it is about 0.5-100 nm, and it is more preferable that it is about 1-50 nm.

(Electron injection layer)
The electron injection layer 11 has a function of improving the efficiency of electron injection from the cathode 12.
Examples of the constituent material (electron injection material) of the electron injection layer 11 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 have high luminance by forming the electron injection layer 11 using the work function. Become.

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

Examples of the alkaline earth metal halide include CaF ₂ , BaF ₂ , SrF ₂ , MgF ₂ , and BeF ₂ .
In addition, as the inorganic semiconductor material, for example, an oxide including at least one element of Li, Na, Ba, Ca, Sr, Yb, Al, Ga, In, Cd, Mg, Si, Ta, Sb, and Zn , Nitrides, oxynitrides, and the like, and one or more of these can be used in combination.
The average thickness of the electron injection layer 11 is not particularly limited, but is preferably about 0.1 to 1000 nm, more preferably about 0.2 to 100 nm, and about 0.2 to 50 nm. Further preferred.

(Sealing member)
The sealing member 13 is provided so as to cover the anode 3, the laminate 15, and the cathode 12, and has a function of hermetically sealing them and blocking oxygen and moisture. By providing the sealing member 13, effects such as improvement in reliability of the light emitting element 1, prevention of deterioration / deterioration (improvement in durability), and the like can be obtained.
Examples of the constituent material of the sealing member 13 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 13, in order to prevent a short circuit, it is required between the sealing member 13 and the anode 3, the laminated body 15, and the cathode 12. Accordingly, it is preferable to provide an insulating film.

Further, the sealing member 13 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 device 1 configured as described above, the intermediate layer 7 configured to include the first material and the second material has electrons between the red light emitting layer 6 and the blue light emitting layer 8. Since the transport of holes can be balanced, the red light emitting layer 6 and the blue light emitting layer 8 can each emit light efficiently. For this reason, the light emitting element 1 has excellent luminous efficiency.

In particular, in this embodiment, the light of the second color has a shorter wavelength than the light of the first color. In such a case, a general light emitting device has a drawback that light having a short wavelength is not easily emitted from the light emitting layer, and it is difficult to balance the light emission of each light emitting layer. However, in the present invention, the intermediate layer 7 as described above can concentrate electrons and holes in the layer that emits light with a short wavelength (in this embodiment, the blue light emitting layer). For this reason, each light emitting layer can emit light in a well-balanced manner, and the light emitting element 1 has excellent luminous efficiency.
In this embodiment, the red light emitting layer 6, the intermediate layer 7, the blue light emitting layer 8, and the green light emitting layer 9 are provided in this order from the anode 3 side to the cathode 12 side, so that R (red), G (green) and B (blue) can be emitted in a well-balanced manner to emit white light.
The above light emitting element 1 can be manufactured as follows, for example.

[1] First, the substrate 2 is prepared, and the anode 3 is formed on the substrate 2.
The anode 3 is, for example, a chemical vapor deposition method (CVD) such as plasma CVD or thermal CVD, a dry plating method such as vacuum deposition, a wet plating method such as electrolytic plating, a thermal spraying method, a sol-gel method, a MOD method, or a metal foil. It can be formed by using, for example, bonding.
[2] Next, the hole injection layer 4 is formed on the anode 3.
The hole injection layer 4 can be formed by, for example, a vapor phase process using a CVD method, a dry plating method such as vacuum deposition or sputtering, or the like.

In addition, the hole injection layer 4 is dried (desolvent or desolvent) after supplying the hole injection layer forming material obtained by, for example, dissolving the hole injection material in a solvent or dispersing in a dispersion medium onto the anode 3. It can also be formed by using a dispersion medium.
As a method for supplying the hole injection layer forming material, for example, various coating methods such as a spin coating method, a roll coating method, and an ink jet printing method can be used. By using such a coating method, the hole injection layer 4 can be formed relatively easily.

Examples of the solvent or dispersion medium used for the preparation of the hole injection layer forming material include various inorganic solvents, various organic solvents, or mixed solvents containing these.
The drying can be performed, for example, by standing in an atmospheric pressure or a reduced pressure atmosphere, heat treatment, or blowing an inert gas.
Prior to this step, the upper surface of the anode 3 may be subjected to oxygen plasma treatment. Thereby, it is possible to impart lyophilicity to the upper surface of the anode 3, remove (clean) organic substances adhering to the upper surface of the anode 3, adjust the work function near the upper surface of the anode 3, and the like. .
Here, the oxygen plasma treatment conditions include, for example, a plasma power of about 100 to 800 W, an oxygen gas flow rate of about 50 to 100 mL / min, a conveyance speed of the member to be treated (anode 3) of about 0.5 to 10 mm / sec, and a substrate. The temperature of 2 is preferably about 70 to 90 ° C.

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

[4] Next, the red light emitting layer 6 is formed on the hole transport layer 5.
The red light emitting layer 6 can be formed by a vapor phase process using, for example, a CVD method, a dry plating method such as vacuum deposition or sputtering, or the like.
[5] Next, the intermediate layer 7 is formed on the red light emitting layer 6.
The intermediate layer 7 can be formed by, for example, a vapor phase process using a CVD method, a dry plating method such as vacuum deposition, sputtering, or the like.

[6] Next, the blue light emitting layer 8 is formed on the intermediate layer 7.
The blue light emitting layer 8 can be formed by, for example, a vapor phase process using a CVD method, a dry plating method such as vacuum deposition or sputtering.
[7] Next, the green light emitting layer 9 is formed on the blue light emitting layer 8.
The green light emitting layer 9 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.

[8] Next, the electron transport layer 10 is formed on the green light emitting layer 9.
The electron transport layer 10 can be formed by a vapor phase process using, for example, a CVD method, a dry plating method such as vacuum deposition, sputtering, or the like.
Further, the electron transport layer 10 is dried (desolvent or dedispersed) after supplying an electron transport layer forming material obtained by, for example, dissolving an electron transport material in a solvent or dispersing in a dispersion medium onto the green light emitting layer 9. It can also be formed by the medium.
[9] Next, the electron injection layer 11 is formed on the electron transport layer 10.
When an inorganic material is used as the constituent material of the electron injection layer 11, the electron injection layer 11 is formed by, for example, a vapor phase process using a CVD method, a dry plating method such as vacuum deposition or sputtering, or coating and baking of inorganic fine particle ink. Etc. can be used.

[10] Next, the cathode 12 is formed on the electron injection layer 11.
The cathode 12 can be formed using, for example, a vacuum evaporation method, a sputtering method, bonding of metal foil, application and baking of metal fine particle ink, and the like.
The light emitting element 1 is obtained through the steps as described above.
Finally, the sealing member 13 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.

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 19B 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 prevention film 33, an anode 3, a laminate (organic EL light emitting unit) 15, a cathode 12, and a cathode cover 34 are laminated in this order on a planarization layer 22. In the present embodiment, the anode 3 of each light emitting element 1R, 1G, 1B constitutes a pixel electrode and is electrically connected to the drain electrode 245 of each driving transistor 24 by a conductive portion (wiring) 27. Moreover, the cathode 12 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 is for converting 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 input / output terminal 1314 for data communication as necessary. Further, the imaging signal stored in the memory of the circuit board 1308 is output to the television monitor 1430 or the personal computer 1440 by a predetermined operation.

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

The light emitting element, the display device, and the electronic device of the present invention have been described based on the illustrated embodiments, but the present invention is not limited to these.
For example, in the above-described embodiment, the light emitting element has three light emitting layers. However, the light emitting layer may be two layers or four or more layers. Further, the emission color of the light emitting layer is not limited to R, G, and B in the above-described embodiment. Even when there are two or more light emitting layers, white light can be emitted by appropriately setting the emission spectrum of each light emitting layer.
Moreover, the intermediate | middle layer should just be provided between the at least 1 interlayer of light emitting layers, and may have an intermediate | middle layer of two or more layers.

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, LG101 (manufactured by LG Chemical Co., Ltd.) was deposited on the ITO electrode by a vacuum deposition method to form a hole injection layer having an average thickness of 30 nm.
<3> Next, N, N′-bis (1-naphthyl) -N, N′-diphenyl [1,1′-biphenyl] -4,4 ′ represented by Chemical Formula 1 is formed on the hole injection layer. -Diamine ((alpha) -NPD) was vapor-deposited by the vacuum evaporation method, and the positive hole transport layer with an average thickness of 20 nm was formed.

  <4> Next, the constituent material of the red light-emitting layer was deposited on the hole transport layer by a vacuum vapor deposition method to form a red light-emitting layer (first light-emitting layer) having an average thickness of 10 nm. As a constituent material of the red light emitting layer, a tetraaryldiindenoperylene derivative (RD-1) represented by Chemical Formula 1 was used as a red light emitting material (guest material), and rubrene (RB) was used as a host material. The content (dope concentration) of the light emitting material (dopant) in the red light emitting layer was 1.5 wt%.

  <5> Next, the constituent material of the intermediate layer was vapor-deposited on the red light emitting layer by a vacuum vapor deposition method to form an intermediate layer having an average thickness of 15 nm. As the constituent material of the intermediate layer, α, α-MADN (acene-based material) represented by the chemical formula 5 is used as the first material, and α-NPD (amine) represented by the chemical formula 6 described above as the second material. System material) was used. The content of the first material in the intermediate layer was 50 wt%, and the content of the second material in the intermediate layer was 50 wt%.

  <6> Next, the constituent material of the blue light-emitting layer was deposited on the intermediate layer by a vacuum vapor deposition method to form a blue light-emitting layer (second light-emitting layer) having an average thickness of 10 nm. As a constituent material of the blue light emitting layer, BD102 (manufactured by Idemitsu Kosan Co., Ltd.) was used as the blue light emitting material, and 2-t-butyl-9,10-di (2-naphthyl) anthracene (TBADN) was used as the host material. Further, the content (dope concentration) of the blue light emitting material (dopant) in the blue light emitting layer was 9.0 wt%.

<7> Next, the constituent material of the green light emitting layer was deposited on the blue light emitting layer by a vacuum deposition method, thereby forming a green light emitting layer (third light emitting layer) having an average thickness of 30 nm. As a constituent material of the green light emitting layer, quinacridone was used as a green light emitting material (guest material), and tris (8-quinolinolato) aluminum (Alq ₃ ) was used as a host material. Further, the content (dope concentration) of the green light emitting material (dopant) in the green light emitting layer was 3.0 wt%.
<8> Next, tris (8-quinolinolato) aluminum (Alq ₃ ) was formed on the green light-emitting layer by a vacuum deposition method, thereby forming an electron transport layer having an average thickness of 20 nm.

<9> Next, on the electron transport layer, lithium fluoride (LiF) was formed by a vacuum vapor deposition method, thereby forming an electron injection layer having an average thickness of 1 nm.
<10> Next, Al was formed into a film by the vacuum evaporation method on the electron injection layer. Thereby, a cathode having an average thickness of 200 nm made of Al was formed.
<11> Next, a glass protective cover (sealing member) was placed over the formed layers, and fixed and sealed with an epoxy resin.
Through the above steps, a light emitting device as shown in FIG. 1 was manufactured.

(Example 2)
A light emitting device was manufactured in the same manner as in Example 1 except that the intermediate layer was formed using TBADN (acene-based material) represented by Chemical Formula 4 as the first material.
(Comparative example)
Except that the intermediate layer was formed using 2-methyl-9,10-di (2-naphthyl) anthracene (MADN) represented by Chemical Formula 4 as the first material, the same as in Example 1 described above. Thus, a light emitting device was manufactured.

2. Evaluation of Radiance (Luminescence Efficiency) For each example and comparative example, a constant current of 18 mA / cm ² was passed through the light emitting element using a DC power source, and the radiance (initial radiance) was measured using a luminance meter. . In each example and comparative example, radiance was measured for five light emitting elements. The radiance is used to evaluate the emission intensity regardless of the shape of the emission spectrum.
Table 1 shows the structure of the red light emitting layer, the blue light emitting layer, the intermediate layer, the energy levels of HOMO and LUMO, and the evaluation results of the radiance described above. However, X1 to X3 and Y1 and Y2 in the table are values obtained by the following formulas, respectively.

X1 = | HL _A -HL _C |-| HL _B -HL _C |
X2 = | HL _A -HL _C |
X3 = | HL _B −HL _C |
Y1 = LL _A -LL _B
Y2 = | LL _A −LL _D |

  As is clear from Table 1, the light emitting elements of the respective examples had higher radiance under a constant current than the light emitting elements of the comparative example serving as a reference. That is, the light emitting device of each example was excellent in luminous efficiency.

It is a figure which shows typically the longitudinal cross-section of suitable embodiment of the light emitting element of this invention. It is a longitudinal cross-sectional view which shows embodiment of the display apparatus to which the display apparatus of this invention is applied. 1 is a perspective view 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.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 1B, 1G, 1R ... Light emitting element 2 ... Substrate 3 ... Anode 4 ... Hole injection layer 5 ... Hole transport layer 6 ... Red light emitting layer (1st light emitting layer) 7 ... Middle Layer 8: Blue light emitting layer (second light emitting layer) 9 ... Green light emitting layer (third light emitting layer) 10 ... Electron transport layer 11 ... Electron injection layer 12 ... Cathode 13 ... Sealing member 15 ...... Stacked body 19B, 19G, 19R ... Color filter 100 ... Display device 100B, 100G, 100R ... Subpixel 20 ... Sealing substrate 21 ... Substrate 22 ... Planarization layer 24 ... Driving transistor 241 ... Semiconductor layer 242 ... Gate insulating layer 243 ... Gate electrode 244 ... Source electrode 245 ... Drain electrode 27 ... Wiring 31 ... Partition 32 ... Reflective film 33 ... Corrosion prevention film 34 ... Cathode cover 3 …… 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 …… I / O terminal for data communication 1430 …… TV monitor 1440 ……Personal computer

Claims (15)

A cathode,
The anode,
A first light-emitting layer provided between the cathode and the anode and emitting light in a first color;
A second light-emitting layer provided between the first light-emitting layer and the cathode and emitting light in a second color different from the first color;
A first material and a second material having a hole mobility higher than that of the first material, provided between the first light emitting layer and the second light emitting layer so as to be in contact therewith; And an intermediate layer composed of
The first light-emitting layer includes a first light-emitting material that emits light in the first color, and a first host material that supports the first light-emitting material as a guest material,
The energy level of the highest occupied molecular orbital of the first material is HL _A [eV], the energy level of the highest occupied molecular orbital of the second material is HL _B [eV], and the highest energy level of the first host material is A light emitting element characterized by satisfying the following expressions (1) and (2) when the energy level of the occupied molecular orbital is HL _C [eV].
| HL _B -HL _C | <| HL _A -HL _C | (1)
| HL _A -HL _C | ≧ 0.3 [eV] (2) 2. The light-emitting element according to claim 1, wherein the second material and the first host material satisfy a relationship of the following formula (3).
| HL _B -HL _C | ≦ 0.2 [eV] (3)   The light-emitting element according to claim 1, wherein the first material has a higher electron mobility than the second material.   4. The light emitting device according to claim 1, wherein the light of the second color has a shorter wavelength than the light of the first color. 5. When the energy level of the lowest unoccupied molecular orbital of the first material is LL _A [eV] and the energy level of the lowest unoccupied molecular orbital of the second material is LL _B [eV], the following formula ( The light emitting device according to any one of claims 1 to 4, which satisfies 4).
LL _A −LL _B ≧ 0.4 [eV] (4) The second light-emitting layer includes a second light-emitting material that emits light in the second color, and a second host material that carries the second light-emitting material,
When the energy level of the lowest unoccupied molecular orbital of the first material is LL _A [eV] and the energy level of the lowest unoccupied molecular orbital of the second host material is LL _D [eV], The light emitting device according to any one of claims 1 to 5, which satisfies (5).
| LL _A −LL _D | ≦ 0.2 [eV] (5)   When the content of the first material in the intermediate layer is A [wt%] and the content of the second material in the intermediate layer is B [wt%], B / (A + B) is The light emitting device according to any one of claims 1 to 6, which is 0.1 to 0.9.   The light emitting device according to claim 1, wherein the first material is an acene-based material.   The light emitting device according to claim 1, wherein the second material is an amine material.   The light emitting device according to claim 1, wherein the intermediate layer has an average thickness of 1 to 100 nm.   The light emitting device according to any one of claims 1 to 10, wherein the first light emitting layer is a red light emitting layer that emits red light as the first color.   The light emitting device according to claim 1, wherein the second light emitting layer is a blue light emitting layer that emits blue light as the second color.   A third color different from the first color and the second color is provided between the first light emitting layer and the anode or between the second light emitting layer and the cathode. The light-emitting element according to claim 1, further comprising a third light-emitting layer that emits light.   A display device comprising the light-emitting element according to claim 1.   An electronic apparatus comprising the display device according to claim 14.

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