JP4912745B2 - Light emitting element and light emitting device - Google Patents

Description

  The present invention relates to an organometallic complex capable of converting an excited triplet state into light emission, a light-emitting element using the organometallic complex, and a light-emitting device using the light-emitting element.

  A light-emitting element using an organic compound is an element in which a layer containing an organic compound or an organic compound film emits light when an electric field is applied. The light emission mechanism is such that when an organic compound film is sandwiched between electrodes and a voltage is applied, electrons injected from the cathode and holes injected from the anode recombine in the organic compound film to form molecular excitons. It is said that when the molecular exciton returns to the ground state, it emits energy and emits light.

In such a light emitting device, the organic compound film is usually formed as a thin film having a thickness of less than 1 μm. In addition, such a light emitting element is a self-luminous element in which the organic compound film itself emits light, and thus a backlight as used in a conventional liquid crystal display is not necessary. Accordingly, it is a great advantage that such a light-emitting element can be manufactured to be extremely thin and lightweight. For example, in an organic compound film of about 100 to 200 nm, the time from carrier injection to recombination is about several tens of nanoseconds considering the carrier mobility of the organic compound film. Even if the process from light emission to light emission is included, light emission occurs within approximately microseconds. Therefore, one of the features is that the response speed is very fast. Further, since such a light-emitting element is a carrier-injection type light-emitting element, it can be driven with a DC voltage, and noise is hardly generated. Regarding the driving voltage, first, an organic compound film having a uniform ultra-thin thickness of about 100 nm is selected, and an electrode material that reduces a carrier injection barrier with respect to the organic compound film is selected. By introducing the structure, sufficient luminance of 100 cd / m ² is achieved at 5.5 V (see Non-Patent Document 1, for example).

  As described above, a light-emitting element using an organic compound is one of the great advantages that it has a wide variety of emission colors in addition to element characteristics such as thinness, light weight, high-speed response, and direct-current low-voltage driving. The factor is the diversity of the organic compound itself. That is, the flexibility of being able to develop materials of various emission colors by molecular design (for example, introduction of substituents) and the like gives rise to rich colors. It can be said that the largest application field of light-emitting elements utilizing the richness of color is a full-color flat panel display. This is because there are many organic compounds that can emit light of the three primary colors of red, green, and blue, so that full colorization can be easily achieved by patterning them.

The above-described element characteristics such as thinness, light weight, high-speed response, and direct-current low-voltage driving can be said to be suitable characteristics for a flat panel display. However, in recent years, as an attempt to further increase the luminous efficiency, use of a phosphorescent material instead of a fluorescent material has been cited. In a light-emitting element using an organic compound, light is emitted when the molecular exciton returns to the ground state, and the light emission includes light emission (fluorescence) from the excited singlet state (S ^* ) and an excited triplet state (T ^* ) ^. ) (Phosphorescence) is possible, and when a fluorescent material is used, only light emission (fluorescence) from S * contributes.

However, the statistical generation ratio of S ^* and T ^* in the light-emitting element is considered to be S ^* : T ^* = 1: 3 (for example, see Non-Patent Document 2). Therefore, the theoretical limit of the internal quantum efficiency (ratio of photons generated with respect to injected carriers) in a light emitting device using a fluorescent material is 25% on the basis of S ^* : T ^* = 1: 3. Has been. In other words, in the case of a light emitting element using a fluorescent material, at least 75% of the injected carriers are wasted.

In other words, if it is possible to use light emission from T ^* , that is, phosphorescence, the light emission efficiency is considered to improve (simply 3 to 4 times). However, general organic compounds emit light from T ^* at room temperature ( (Phosphorescence) is not observed, and usually only emission (fluorescence) from S ^* is observed. However, in recent years, light-emitting elements that can convert energy emitted when returning from T ^* to the ground state (hereinafter referred to as “triplet excitation energy”) into light emission have been announced one after another, and the light emission efficiency is high. It is attracting attention (see, for example, Non-Patent Document 3).
C. W. Tan, 1 other person, Applied Physics Letters, vol. 51, no. 12, 913-915 (1987) Tetsuo Tsutsui, “Applied Physics Society Organic Molecules / Bioelectronics Subcommittee, 3rd Workshop Text”, P.M. 31 (1993) J. et al. Duane, two others, Advance Materials (2003), 15, 3, FEB5, p. 224-228

  In Document 3, an iridium complex using a dibenzo [f, h] quinoxaline derivative as a ligand is synthesized and used as a light-emitting substance in a light-emitting element. Although the obtained light emitting element has high luminous efficiency, the emission color shows orange-red, and red emission with good color purity is not realized.

  An object of the present invention is to provide a red light-emitting element exhibiting high light emission efficiency and excellent color purity in a light-emitting element using an organometallic complex capable of converting an excited triplet state into light emission. It is another object of the present invention to provide a color-rich light-emitting device that can emit more colors by using a red light-emitting element with excellent color purity.

  In order to achieve the above object, the present invention takes the following measures.

One form of the light-emitting element of the present invention includes a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a second electrode, which are sequentially stacked on the first electrode, and the light-emitting element. The layer has an organometallic complex having a structure represented by the following general formula (1), and the electron injection layer has an organic compound and a substance exhibiting an electron donating property to the organic compound. To do.

In formula (1), R ^{1 to} R ⁵ each represent any one of hydrogen, a halogen element, an acyl group, an alkyl group, an alkoxyl group, an aryl group, a cyano group, and a heterocyclic group. Ar represents an aryl group or a heterocyclic group. M represents a Group 9 element or a Group 10 element. Ar is preferably an aryl group having an electron-withdrawing substituent or a heterocyclic group having an electron-withdrawing substituent. When Ar is an aryl group having an electron-withdrawing substituent or a heterocyclic group having an electron-withdrawing substituent, phosphorescence having higher emission intensity can be emitted.

One form of the light-emitting element of the present invention includes a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a second electrode, which are sequentially stacked on the first electrode, and the light-emitting element. The layer has an organometallic complex having a structure represented by the following general formula (2), and the electron injection layer has an organic compound and a substance exhibiting an electron donating property to the organic compound. To do.

In formula (2), R ^{1 to} R ⁹ each represent any one of hydrogen, a halogen element, an acyl group, an alkyl group, an alkoxyl group, an aryl group, a cyano group, and a heterocyclic group. However, any one of R ^{6 to} R ⁹ represents an electron-withdrawing substituent. M represents a Group 9 element or a Group 10 element. When any of R ^{6 to} R ⁹ is a group having an electron-withdrawing substituent, phosphorescence having a larger emission intensity can be emitted.

One form of the light-emitting element of the present invention includes a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a second electrode, which are sequentially stacked on the first electrode, and the light-emitting element. The layer has an organometallic complex having a structure represented by the following general formula (3), and the electron injection layer has an organic compound and a substance exhibiting an electron donating property to the organic compound. To do.

In formula (3), R ^{2 to} R ¹⁴ each represent any one of hydrogen, a halogen element, an acyl group, an alkyl group, an alkoxyl group, an aryl group, a cyano group, a heterocyclic group, and an electron-withdrawing substituent. M represents a Group 9 element or a Group 10 element. At least one of R ^{6 to} R ⁹ is preferably an electron-withdrawing substituent. Thereby, phosphorescence having a larger emission intensity can be emitted.

One form of the light-emitting element of the present invention includes a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a second electrode, which are sequentially stacked on the first electrode, and the light-emitting element. The layer has an organometallic complex having a structure represented by the following general formula (4), and the electron injection layer has an organic compound and a substance exhibiting an electron donating property to the organic compound. To do.

In formula (4), R ¹⁵ and R ¹⁶ each represent hydrogen, a halogen element, an acyl group, an alkyl group, an alkoxyl group, an aryl group, a cyano group, a heterocyclic group, or an electron-withdrawing substituent. M represents a Group 9 element or a Group 10 element. R ¹⁶ is preferably an electron-withdrawing substituent. Thereby, phosphorescence having a larger emission intensity can be emitted.

One form of the light-emitting element of the present invention includes a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a second electrode, which are sequentially stacked on the first electrode, and the light-emitting element. The layer has an organometallic complex represented by the following general formula (5), and the electron injection layer has an organic compound and a substance exhibiting an electron donating property to the organic compound.

In Formula (5), R ^{1 to} R ⁵ each represent any one of hydrogen, a halogen element, an acyl group, an alkyl group, an alkoxyl group, an aryl group, a cyano group, and a heterocyclic group. Ar represents an aryl group having an electron-withdrawing substituent or a heterocyclic group having an electron-withdrawing substituent. M represents a Group 9 element or a Group 10 element. When M is a Group 9 element, n = 2, and when M is a Group 10 element, n = 1. L represents a monoanionic ligand. When Ar is an electron-withdrawing substituent, phosphorescence with higher emission intensity can be emitted.

One form of the light-emitting element of the present invention includes a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a second electrode, which are sequentially stacked on the first electrode, and the light-emitting element. The layer has an organometallic complex represented by the following general formula (6), and the electron injection layer has an organic compound and a substance exhibiting an electron donating property to the organic compound.

In Formula (6), R ^{1 to} R ⁵ each represent any one of hydrogen, a halogen element, an acyl group, an alkyl group, an alkoxyl group, an aryl group, a cyano group, and a heterocyclic group. R ^{6 to} R ⁹ each represent hydrogen, an acyl group, an alkyl group, an alkoxyl group, an aryl group, a heterocyclic group, or an electron-withdrawing substituent, and at least one is an electron-withdrawing substituent. Preferably there is. M represents a Group 9 element or a Group 10 element. When M is a Group 9 element, n = 2, and when M is a Group 10 element, n = 1. L is a monoanionic ligand having a beta diketone structure, a monoanionic bidentate chelate ligand having a carboxyl group, or a monoanionic bidentate chelate ligand having a phenolic hydroxyl group, Represents one of the following. When at least one of R ^{6 to} R ⁹ is an electron-withdrawing substituent, phosphorescence with higher emission intensity can be emitted.
However, among the organometallic complexes represented by the general formula (6), when R ^{1 to} R ⁹ are hydrogen and the anionic ligand L is an acetylacetone anion, or at least one of R ^{6 to} R ⁹ Unless one has an electron withdrawing substituent.

One form of the light-emitting element of the present invention includes a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a second electrode, which are sequentially stacked on the first electrode, and the light-emitting element. The layer has an organometallic complex represented by the following general formula (7), and the electron injection layer has an organic compound and a substance exhibiting an electron donating property to the organic compound.

In Formula (7), R ^{2 to} R ¹⁴ represent any one of hydrogen, a halogen element, an acyl group, an alkyl group, an alkoxyl group, an aryl group, a cyano group, a heterocyclic group, and an electron-withdrawing substituent. M represents a Group 9 element or a Group 10 element. When M is a Group 9 element, n = 2, and when M is a Group 10 element, n = 1. L represents an anionic ligand. Here, it is preferable that at least one of R ^{6 to} R ⁹ is an electron-withdrawing substituent. Thereby, phosphorescence having a larger emission intensity can be emitted.

One form of the light-emitting element of the present invention includes a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a second electrode, which are sequentially stacked on the first electrode, and the light-emitting element. The layer has an organometallic complex represented by the following general formula (8), and the electron injection layer has an organic compound and a substance exhibiting an electron donating property to the organic compound.

In the formula (8), R ¹⁵ and R ¹⁶ represent any one of hydrogen, a halogen element, an acyl group, an alkyl group, an alkoxyl group, an aryl group, a cyano group, a heterocyclic group, and an electron-withdrawing substituent. M represents a Group 9 element or a Group 10 element. When M is a Group 9 element, n = 2, and when M is a Group 10 element, n = 1. L represents an anionic ligand. Here, R ¹⁶ is preferably an electron-withdrawing substituent. Thereby, phosphorescence having a larger emission intensity can be emitted.

Further, the anionic ligand L may be a ligand represented by any one of the following formulas (9) to (15).

  The anionic ligand L is an anionic ligand having a beta diketone structure, an anionic bidentate ligand having a carboxyl group, or an anionic bidentate ligand having a phenolic hydroxyl group. It is good also as a feature.

  The electron-donating substance may be a metal having a small work function.

  The metal may be any one of Li, Mg, and Cs.

  The light-emitting element may have a current efficiency of 2.0 cd / A or more and CIE chromaticity coordinates X ≧ 0.7 and Y ≦ 0.3.

  The light emitting device may be characterized in that an external quantum efficiency of 5% or more and CIE chromaticity coordinates X ≧ 0.7 and Y ≦ 0.3.

  The electron transport layer may have a triplet excitation energy higher than a triplet excitation energy of the organometallic complex.

  The hole transport layer may have triplet excitation energy higher than triplet excitation energy of the organometallic complex.

  The light emitting layer may include a host material having a triplet excitation energy higher than a triplet excitation energy of the organometallic complex.

  According to the present invention, a light emitting element having high luminous efficiency and excellent color purity can be obtained. In addition, by using a light-emitting element with excellent color purity, a light-emitting device with rich colors that can emit more colors can be manufactured.

  Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the following description, and it is easily understood by those skilled in the art that modes and details can be variously changed without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the description of the embodiments below. Note that in the structures of the present invention described below, the same reference numerals may be used in common in different drawings.

(Embodiment 1)
One mode of a light-emitting element of the present invention will be described with reference to FIG. As shown in FIG. 1, a structure in which a first electrode 101 is formed over a substrate 100, a layer 102 containing a light-emitting substance is formed over the first electrode 101, and a second electrode 103 is formed thereover. Have Note that the layer 102 containing a light-emitting substance is formed by stacking a plurality of layers. In Embodiment 1, a hole injection layer 111, a hole transport layer 112, a light-emitting layer 113, an electron transport layer 114, and an electron injection are used. Layer 115 is provided. These layers can be formed by a vapor deposition method or a coating method.

  As a material used for the substrate 100, for example, quartz, glass, plastic, a flexible substrate, or the like can be used. Note that other materials may be used as long as they function as a support in the manufacturing process of the light-emitting element. Note that the first electrode 101 in Embodiment Mode 1 functions as an anode, and the second electrode 103 functions as a cathode.

  As an anode material for forming the first electrode 101, it is preferable to use a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like having a high work function (work function of 4.0 eV or more). Specific examples of such an anode material include indium tin oxide (ITO), ITSO (indium tin silicon oxide) containing silicon oxide in ITO, and 2 to 20 wt% in indium oxide. In addition to IZO (indium zinc oxide) formed using a target mixed with zinc oxide (ZnO), gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), or a nitride (TiN) of a metal material can be given.

  On the other hand, as a material for forming the second electrode 103, a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like having a low work function (a work function of 3.8 eV or less) can be used. Specific examples of such a cathode material include elements belonging to Group 1 or Group 2 of the periodic table, that is, alkali metals such as lithium (Li) and cesium (Cs), magnesium (Mg), calcium (Ca), strontium ( Alkaline earth metals such as Sr) and alloys containing them (Mg: Ag, Al: Li). However, by providing a layer having an excellent function of injecting electrons between the second electrode 103 and the light-emitting layer 113 by stacking with the second electrode, regardless of the work function, Al, Various conductive materials including the materials mentioned as the material of the first electrode 101 such as Ag, ITO, and ITSO can be used as the second electrode 103.

  The first electrode 101 and the second electrode 103 are formed by depositing the above-described anode material or cathode material by a vapor deposition method, a sputtering method, or the like. The film thickness is preferably 10 to 500 nm.

  In the light-emitting element of the present invention, light generated by recombination of carriers in the light-emitting layer is emitted to the outside from one or both of the first electrode 101 and the second electrode 103. For example, when light is emitted from the first electrode 101, the first electrode 101 is formed of a light-transmitting material, and when light is emitted from the second electrode 103 side, the second electrode 101 is formed. The electrode 103 is formed of a light-transmitting material.

  In Embodiment 1, the layer 102 containing a light-emitting substance is formed by sequentially stacking a hole injection layer 111, a hole transport layer 112, a light-emitting layer 113, an electron transport layer 114, and an electron injection layer 115.

The hole injection layer 111 is provided in contact with the first electrode 101. Note that the hole injection layer 111 is formed using a material that can receive holes from the first electrode 101 and can inject holes into the hole transport layer 112. For example, phthalocyanine compounds such as phthalocyanine (abbreviation: H ₂ —Pc), copper phthalocyanine (abbreviation: Cu—Pc), and 4,4′-bis [N- (4- (N, N-di-m- Tolylamino) phenyl) -N-phenylamino] biphenyl (abbreviation: DNTPD) and 4,4 ′, 4 ″ -tris [N- (3-methylphenyl) -N-phenylamino] triphenylamine (abbreviation: MTDATA) An aromatic amine-based compound (that is, having a benzene ring-nitrogen bond) or the like can be used. Alternatively, a conductive inorganic compound (including a semiconductor) such as molybdenum oxide (MoOx) or vanadium oxide (VOx) can be used. Furthermore, a mixture of the conductive inorganic compound and the aromatic amine compound as described above or below can be used. This mixture can be formed by a technique such as co-evaporation. Note that the co-evaporation method is an evaporation method in which evaporation is performed simultaneously from a plurality of evaporation sources in one processing chamber.

  The hole transport layer 112 is formed using a material that can transport holes. Specifically, it is preferably formed using an aromatic amine compound, for example, 4,4′-bis [N- (3-methylphenyl) -N-phenyl-amino] -biphenyl (abbreviation: TPD). ), 4,4′-bis [N- (1-naphthyl) -N-phenyl-amino] -biphenyl (abbreviation: NPB), and 4,4 ′, 4 ″ -tris (N-carbazolyl) triphenyl Starburst aromatic amine compounds such as amine (abbreviation: TCTA), 4,4 ′, 4 ″ -tris (N, N-diphenyl-amino) -triphenylamine (abbreviation: TDATA) and MTDATA described above Can be formed. Alternatively, a mixture of a conductive inorganic compound (including a semiconductor) such as molybdenum oxide (MoOx) or vanadium oxide (VOx) and an aromatic amine-based compound as described above can be used.

  The light-emitting layer 113 includes at least one organic compound selected from the organometallic complexes having the structures represented by the general formulas (1) to (4) and the organometallic complexes represented by the general formulas (5) to (8). A metal complex and a host material are formed by co-evaporation.

Specific examples of the substituents R ^{1 to} R ¹⁶ described in the general formulas (1) to (8) are as follows. Examples of the acyl group include an acetyl group, a propionyl group, an isobutyryl group, and a methacryloyl group. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, a tert-butyl group, and an octyl group. Examples of the alkoxyl group include a methoxy group, an ethoxy group, and a propoxy group. Examples of the aryl group include a phenyl group, a 4-methylphenyl group, and a 4-ethylphenyl group. Examples of the heterocyclic group include a pyridyl group, a bipyridyl group, and a methylpyridyl group. Examples of the electron-withdrawing substituent include a fluoro group, a trifluoromethyl group, and a cyano group.

  Specific examples of the Group 9 element or the Group 10 element include iridium and platinum. However, it is not limited to these exemplified elements.

  Ligand L is either a monoanionic ligand having a beta diketone structure, a monoanionic bidentate ligand having a carboxyl group, or a monoanionic bidentate ligand having a phenolic hydroxyl group is there. Specific examples thereof include anions represented by the formulas (9) to (15). These ligands are effective because they have high coordination ability and can be obtained at low cost.

  The organometallic complexes having the structures represented by the general formulas (1) to (4) and the organometallic complexes represented by the general formulas (5) to (8) are likely to receive holes by an organic-metal bond. In addition to this, the quinoxaline skeleton makes it easier to receive electrons, so that there is an advantage that carriers can be trapped effectively.

  Furthermore, the electron-withdrawing substituent is preferably any one of a halogen group, a haloalkyl group, and a cyano group. Thereby, the chromaticity and quantum efficiency of these organometallic complexes are improved. Further, among the halogen groups, a fluoro group is particularly preferable, and among the haloalkyl groups, a trifluoromethyl group is particularly preferable. This further improves the electron trapping property.

  The host material is selected from the organometallic complexes having the structures represented by the general formulas (1) to (4) and the organometallic complexes represented by the general formulas (5) to (8). It is preferable to use a substance having an energy gap larger than that of at least one organometallic complex. Note that the energy gap is an energy difference between the lowest unoccupied molecular orbital (LUMO) level and the highest occupied molecular orbital (HOMO) level.

Specific examples of substances that can be used as the host material include 4,4′-bis (N-carbazolyl) biphenyl (abbreviation: CBP), 4,4 ′, 4 ″ -tris (N-carbazolyl) triphenylamine (Abbreviation: TCTA), aromatic amine compounds such as NPB and TPD described above, tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), tris (8-quinolinolato) gallium (abbreviation: Gaq ₃ ), tris (4 A metal complex such as -methyl-8-quinolinolato) aluminum (abbreviation: Almq ₃ ) can also be given. These Alq ₃ , Gaq ₃ , and Almq ₃ are listed as specific examples of electron transporting metal complexes.

The electron transport layer 114 is preferably formed using a material that can transport electrons injected from the electrode functioning as a cathode into the layer containing a light-emitting substance to the light-emitting layer. Specific examples of such a material include metal complexes having a quinoline skeleton or a benzoquinoline skeleton such as Alq ₃ , Gaq ₃ , Almq ₃ , and bis (10-hydroxybenzo [h] -quinolinato) beryllium (abbreviation: BeBq ₂ ). And bis (2-methyl-8-quinolinolato) -4-phenylphenolato-aluminum (abbreviation: BAlq). In addition, bis [2- (2-hydroxyphenyl) -benzoxazolate] zinc (abbreviation: Zn (BOX) ₂ ), bis [2- (2-hydroxyphenyl) -benzothiazolate] zinc (abbreviation: Zn (BTZ) ₂ ) and other metal complexes having an oxazole-based or thiazole-based ligand can also be used as a material for forming the electron transport layer 114. In addition, 2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole (abbreviation: PBD) and 1,3-bis [5- (p-tert- Butylphenyl) -1,3,4-oxadiazol-2-yl] benzene (abbreviation: OXD-7), 3- (4-tert-butylphenyl) -4-phenyl-5- (4-biphenylyl)- 1,2,4-triazole (abbreviation: TAZ), 3- (4-tert-butylphenyl) -4- (4-ethylphenyl) -5- (4-biphenylyl) -1,2,4-triazole (abbreviation) : P-EtTAZ), bathophenanthroline (abbreviation: BPhen), bathocuproin (abbreviation: BCP), and inorganic substances such as titanium oxide may be used.

  The electron-injection layer 115 is formed using a layer in which any of the above-described electron-transport materials is mixed with a substance that exhibits an electron-donating property with respect to any of the electron-transport materials. As a substance exhibiting an electron donating property, for example, a metal having a small work function can be given. Specifically, alkali metals and alkaline earth metals are preferable, and Li, Mg, and Cs are particularly preferable. Note that such an electron injection layer 115 can be formed by a technique such as co-evaporation.

  In the light-emitting element of the present invention, as a result of improving the amount of electrons injected into the light-emitting layer by mixing an organic compound and a substance exhibiting an electron donating property with respect to the organic compound in the electron-injecting layer, the electron-transporting layer And the organometallic complex used as the light-emitting substance can emit light more efficiently.

  Note that the layer structure of the light-emitting element of the present invention is not limited to the above-described layer structure, and the light-emitting element may be sequentially formed from an electrode functioning as a cathode.

(Embodiment 2)
One mode of a light-emitting element of the present invention is described with reference to FIG. As shown in FIG. 2, a structure in which a first electrode 101 is formed over a substrate 100, a layer 202 containing a light-emitting substance is formed over the first electrode 101, and a second electrode 103 is formed thereon. Have Note that the difference from Embodiment 1 is that a material having triplet excitation energy larger than the triplet excitation energy of the organometallic complex which is a light-emitting substance is used for the hole transport layer, the host included in the light-emitting layer, and the electron transport layer. Is a point. Components similar to those in Embodiment 1 are denoted by common reference numerals, and detailed description thereof is omitted. In addition, the first electrode 101 in this embodiment functions as an anode, and the second electrode 103 functions as a cathode.

  Although the layer 202 containing a light-emitting substance is formed by stacking a plurality of layers, in this embodiment, a hole injection layer 111, a hole transport layer 212, a light-emitting layer 213, an electron transport layer 214, and an electron injection layer 215 are formed. Are sequentially laminated. These layers can be formed by a vapor deposition method or a coating method.

  For the materials and manufacturing methods of the first electrode 101, the second electrode 103, and the hole injection layer 111, the description of the first electrode, the second electrode, and the hole injection layer in Embodiment 1 can be referred to. In addition, also in the luminescent substance, as in Embodiment 1, any of the organometallic complexes having the structures represented by the general formulas (1) to (4) and the general formulas (5) to (8) described above. These organometallic complexes are used.

  The hole transport layer 212 is formed using a material that can transport holes and has triplet excitation energy higher than that of the organometallic complex that is a light-emitting substance. There is no particular limitation as long as the above conditions are satisfied, and it can be formed using a starburst type aromatic amine compound in addition to the aromatic amine compound as in the first embodiment. Alternatively, a mixture of a conductive inorganic compound (including a semiconductor) such as molybdenum oxide (MoOx) or vanadium oxide (VOx) and an aromatic amine-based compound as described above can be used. For example, when Alq or CBP is used as the host material of the light emitting layer, NPB or TCTA having higher triplet excitation energy is preferable.

The light-emitting layer 213 includes at least one organic compound selected from the organometallic complexes having the structures represented by the general formulas (1) to (4) and the organometallic complexes represented by the general formulas (5) to (8). A metal complex and a host material are formed by co-evaporation. As the host material, at least one organic compound selected from an organometallic complex having a structure represented by general formulas (1) to (4) and an organometallic complex represented by general formulas (5) to (8). A material having a triplet excitation energy larger than that of the metal complex is used. There is no particular limitation as long as the above conditions are satisfied, and an aromatic amine compound such as NPB or TPD or a metal complex such as Alq ₃ , Gaq ₃ , or Almq ₃ may be used as the host material as in the first embodiment. it can.

The electron-transport layer 214 can transport electrons injected from the electrode functioning as a cathode into the layer containing a light-emitting substance toward the light-emitting layer and has triplet excitation larger than the triplet excitation energy of the organometallic complex that is the light-emitting substance. A material having energy is used. As long as the above conditions are satisfied, there is no particular limitation, and as in Embodiment 1, a metal complex having a quinoline skeleton such as Alq ₃ , Gaq ₃ , Almq ₃ , or BeBq ₂ or a benzoquinoline skeleton or BAlq can be given. In addition, a metal complex having an oxazole-based or thiazole-based ligand such as Zn (BOX) ₂ or Zn (BTZ) ₂ can also be used as a material for forming the electron transport layer 214. In addition to PBD, OXD-7, TAZ, p-EtTAZ, BPhen, and BCP, inorganic materials such as titanium oxide may be used.

As the electron injecting layer 215, as in the electron injecting layer 115 described in Embodiment 1, a layer in which an organic compound and a substance that exhibits an electron donating property with respect to the organic compound are mixed is preferably used. Alternatively, the same material as that of the electron-transport layer 114 described in Embodiment 1 can be used. In addition, an alkali metal halide such as LiF or CsF, an alkaline earth halide such as CaF ₂ , or an ultrathin film of an alkali metal oxide such as Li ₂ O may be used. Alkali metal complexes such as lithium acetylacetonate (abbreviation: Li (acac)) and 8-quinolinolato-lithium (abbreviation: Liq) are also effective.

  In the light-emitting element of the present invention, the material used for the hole transport layer, the host included in the light-emitting layer, and the electron transport layer has triplet excitation energy greater than the triplet excitation energy of the organometallic complex that is a light-emitting substance. Thus, current efficiency and external quantum efficiency can be improved. Specifically, a current efficiency of 2.0 cd / A or higher or an external quantum efficiency of 5% or higher is possible. Further, the color purity is also good, and CIE chromaticity coordinates X ≧ 0.7 and Y ≦ 0.3, which can exceed the NTSC (National Television System Committee) standard.

  Note that in this embodiment, a material having triplet excitation energy higher than that of the organometallic complex which is a light-emitting substance is used for the hole transport layer 212, the host included in the light-emitting layer 213, and the electron transport layer 214. As shown in the case, the effect similar to the above can be obtained with any one or two of the three layers.

In this example, an organometallic complex represented by the general formula (7) described above as a light-emitting substance, bis {2,3-bis (4-fluorophenyl) quinoxalinato} acetylacetonatoiridium (III) [abbreviation: Ir ( Fdpq) ₂ (acac)] will be described with reference to FIGS. 1A to 1E for a light-emitting element using a mixed layer of Alq and Li as an electron injection layer and a manufacturing method thereof. Ir (Fdpq) ₂ (acac) is shown in Formula (16).

  An ITSO film was formed over the substrate 100 by a sputtering method to form the first electrode 101.

  Next, the substrate 100 on which the first electrode 101 was formed was fixed to a substrate holder provided in the vacuum evaporation apparatus so that the surface on which the first electrode 101 was formed faced down.

  Next, a DNTPD film was formed to a thickness of 50 nm on the first electrode 101 by a resistance heating evaporation method, so that a hole injection layer 111 was formed.

  Next, NPB was formed to a thickness of 10 nm on the hole injection layer 111 by a resistance heating vapor deposition method to form a hole transport layer 112.

Next, Ir (Fdpq) ₂ (acac) and Alq ₃ were deposited on the hole transport layer 112 to a thickness of 30 nm by co-evaporation, whereby the light-emitting layer 113 was formed. Here, the mass ratio between Alq ₃ and Ir (Fdpq) ₂ (acac) was 1: 0.08 (= Alq ₃ : Ir (Fdpq) ₂ (acac)). Thus, Ir (Fdpq) ₂ (acac) is dispersed in the layer made of Alq ₃ .

Next, Alq ₃ was formed to a thickness of 10 nm on the light-emitting layer 113 by an evaporation method using resistance heating, so that an electron transport layer 114 was formed.

Next, on the electron transport layer 114, the electron injection layer 115 was formed into a film with a thickness of 50 nm by co-evaporating Alq ₃ and Li. Here, the mass ratio between Alq ₃ and Li was set to 1: 0.01 (= Alq ₃ : Li).

  Next, the second electrode 103 was formed over the electron injection layer 115 by using an evaporation method using resistance heating of aluminum. The light-emitting element manufactured as described above was sealed in a nitrogen atmosphere.

(Comparative Example 1)
As a comparative example of the light-emitting element in this example, a light-emitting element having an electron injection layer into which Li was not introduced was manufactured. In this comparative example, the electron injection layer 115 is made of only Alq _3, and a layer having an excellent function of injecting electrons between the electron injection layer 115 and the second electrode 103 is provided with a thickness of 1 nm. In addition, it produced using the substance and method similar to Example 1 other than that.

Specifically, DNTPD which is the hole injection layer 111 is formed to a thickness of 50 nm on the first electrode 101, and NPB is formed as the hole transport layer 112 to a thickness of 10 nm. Then, Ir (Fdpq) ₂ (acac) and Alq ₃ were formed as the light emitting layer 113 by co-evaporation so as to have a thickness of 30 nm. On the light-emitting layer 113, Alq ₃ was deposited as an electron transport layer 114 and an electron injection layer 115 by using a resistance heating vapor deposition method so that both layers had a thickness of 60 nm. Further, CaF ₂ having an excellent function of injecting electrons was formed on the electron injection layer 115 so as to have a film thickness of 1 nm using a vapor deposition method using resistance heating. Note that the difference in film thickness of the light-emitting elements in this example and Comparative Example 1 is 1 nm.

The emission spectra of the light-emitting elements in this example and comparative example 1 are shown in FIG. In the light emitting device of the comparative example, a broad peak was observed in the vicinity of 525 nm, whereas it was found that the light emitting device of this example can be suppressed. Note that the peak near 525 nm shows green and is considered to be due to Alq ₃ .

Since the organometallic complex used in the present invention has a strong electron trapping property, the light emitting region is in the vicinity of the interface between the light emitting layer and the electron transport layer. Therefore, when the amount of electrons injected into the device is small, holes reach the electron transport layer, and Alq _{3 of the} electron transport layer emits light as in Comparative Example 1. In this example, by introducing Li into the electron injection layer, the amount of electron injection into the light emitting layer was improved, and as a result, the green light emission of Alq ₃ due to the penetration of holes into the electron transport layer was suppressed, and the light emitting material It is considered that Ir (Fdpq) ₂ (acac) used as 1 was able to emit light more efficiently.

  From the above, it can be said that the light-emitting element of the present invention is a good element exhibiting high luminous efficiency.

In this embodiment, the Ir _(Fdpq) 2 (acac) in the light-emitting substance, a light-emitting element using TAZ having triplet excitation energy greater than the triplet excitation energy of Ir _(Fdpq) 2 (acac) in the electron transport layer This will be described with reference to FIG.

  An ITSO film was formed over the substrate 100 by a sputtering method, so that the first electrode 101 was formed.

  Next, the substrate 100 on which the first electrode 101 was formed was fixed to a substrate holder provided in the vacuum evaporation apparatus so that the surface on which the first electrode 101 was formed faced down.

  Next, a DNTPD film was formed to a thickness of 40 nm on the first electrode 101 by a vapor deposition method using resistance heating, so that a hole injection layer 111 was formed.

  Next, NPB was formed to a thickness of 20 nm on the hole injection layer 111 by a resistance heating vapor deposition method to form a hole transport layer 212.

Next, Ir (Fdpq) ₂ (acac) and Alq ₃ were deposited on the hole transport layer 212 to a thickness of 30 nm by co-evaporation, whereby the light-emitting layer 213 was formed. Here, the mass ratio between Alq ₃ and Ir (Fdpq) ₂ (acac) was 1: 0.08 (= Alq ₃ : Ir (Fdpq) ₂ (acac)). Thus, Ir (Fdpq) ₂ (acac) is dispersed in the layer made of Alq ₃ .

  Next, TAZ was formed to a thickness of 20 nm on the light-emitting layer 213 by a vapor deposition method using resistance heating, so that an electron transport layer 214 was formed.

  Next, on the electron transport layer 214, the electron injection layer 215 was formed to have a film thickness of 40 nm by co-evaporating TAZ and Li. Here, the mass ratio between TAZ and Li was set to 1: 0.01 (= TAZ: Li).

  Next, the second electrode 103 was formed over the electron injection layer 215 by using an aluminum evaporation method using resistance heating. The light-emitting element manufactured as described above was sealed in a nitrogen atmosphere.

(Comparative Example 2)
While the electron transport layer 214 and the electron injection layer 215 in this example are TAZ and TAZ: Li, respectively, in Comparative Example 2, Alq ₃ having a triplet excitation energy lower than TAZ is used instead of TAZ, and the electron transport layer is formed. 214 and the electron injection layer 215 were made of Alq ₃ and Alq ₃ : Li, respectively. Other structures were manufactured using the same materials and techniques as in Example 2. Table 1 shows a summary of the element structures of this example and comparative example 2.

A voltage was applied to the light-emitting elements in this example and Comparative Example 2 so that the potential of the first electrode 101 was higher than the potential of the second electrode 103, and the operating characteristics of the light-emitting elements were examined. The measurement was performed in a state kept at room temperature (25 ° C.). The results are shown in FIG. 4A shows the result of examining the current density-luminance characteristic, FIG. 4B shows the result of examining the voltage-luminance characteristic, and FIG. 4C shows the result of examining the luminance-current efficiency characteristic. In FIG. 4A, the horizontal axis represents current density (mA / cm ² ), and the vertical axis represents luminance (cd / m ² ). In FIG. 4B, the horizontal axis represents voltage (V), and the vertical axis represents luminance (cd / m ² ). In FIG. 4C, the horizontal axis represents luminance (cd / m ² ), and the vertical axis represents current efficiency (cd / A).

From these results, it was found that the light-emitting element in Comparative Example 2 emitted light with a luminance of 500 cd / m ² when a voltage of 8.0 V was applied, whereas the light-emitting element in this example was 7.4 V. . In addition, the light-emitting element of this example is superior in current efficiency and external quantum efficiency to the light-emitting element of Comparative Example 2. The current efficiency at 500 cd / m ² is 2.3 cd / A and the external quantum efficiency is 6.7. %Met. Note that the external quantum efficiency is a ratio of the number of photons emitted outside the device to the number of electrons injected into the light emitting device. Therefore, when the number of photons per unit area is Np and the number of electrons per unit area is Ne, it can be expressed by the following equation (17).

Np is L (luminance (cd / m ² )), λ is wavelength (nm), I (λ) is normalized emission spectrum (normalized emission intensity at each wavelength), and K (λ) is a standard relative luminous efficiency curve. , C is the speed of light, and h is the Planck constant, it can be expressed by the following equation (18).

Ne can be expressed by the following formula (19), where J is current density (A / m ² ) and e is the elementary charge amount (C).

The following equation (20) can be derived from equations (17) to (19).

  Therefore, the external quantum efficiency was calculated to be 6.7% from the current efficiency obtained from the above measurement and the emission spectrum shown in FIG.

  From the above, by selecting a material having a triplet excitation energy larger than the triplet excitation energy of the organometallic complex that is the light-emitting substance as the material for the electron transport layer and having a larger triplet excitation energy, the current can be further increased. It has been found that efficiency and external quantum efficiency can be improved.

  In addition, the light-emitting element in this example has a CIE chromaticity coordinate of (X, Y) = (0.71, 0.29), and is found to be a red light-emitting element with excellent color purity. As shown in FIG. 14, the CIE chromaticity coordinates exceed the NTSC standard, and the display device having the light emitting element of the present invention can express a rich color.

In this example, the same material and method as in Example 2 were used except that the host material in the light emitting layer was changed as follows. In this embodiment, the host material in the light emitting layer 213 has a triplet excitation energy larger than the triplet excitation energy of Ir (Fdpq) ₂ (acac) which is a light emitting substance, and has a triplet excitation energy larger than that of Alq _3. CBP was used.

The light-emitting layer 213 was formed by forming Ir (Fdpq) ₂ (acac) and CBP to a thickness of 30 nm by co-evaporation. Here, the mass ratio between CBP and Ir (Fdpq) ₂ (acac) was 1: 0.08 (= CBP: Ir (Fdpq) ₂ (acac)). Thus, Ir (Fdpq) ₂ (acac) is dispersed in the layer made of CBP.

The light-emitting element manufactured as described above was sealed in a nitrogen atmosphere. After that, voltage was applied so that the potential of the first electrode 101 was higher than the potential of the second electrode 103, and the operating characteristics of the light-emitting element were examined. The measurement was performed in a state kept at room temperature (25 ° C.). The results are shown in FIG. In addition, in order to see the effect by the difference in host material in a present Example, the measurement result in Example 2 is also shown in FIG. 6A shows the result of examining the current density-luminance characteristics, FIG. 6B shows the result of examining the voltage-luminance characteristics, and FIG. 6C shows the results of examining the brightness-current efficiency characteristics. In addition, FIG. 7 shows an emission spectrum of the light-emitting element in this example, and Table 2 shows a summary of the element structures of this example and Example 2.

The light emitting element in this example requires a voltage of 8.2 V when emitting light with a luminance of 500 cd / m ² , and the voltage is somewhat higher than that of the light emitting element of Example 2. However, the light-emitting element of this example has higher current efficiency and external quantum efficiency than the light-emitting element of Example 2, and the current efficiency at 500 cd / m ² is 4.9 cd / A and the external quantum efficiency is 10. It was 9%.

  Based on the above, by selecting a material having a larger triplet excitation energy and a larger triplet excitation energy of the organometallic complex that is the light-emitting substance as the host material of the light-emitting layer, the current efficiency and the external quantum can be further increased. It has been found that efficiency can be improved.

  In addition, the light-emitting element in this example has a CIE chromaticity coordinate of (X, Y) = (0.71, 0.29), and is found to be a red light-emitting element with excellent color purity. As shown in FIG. 14, the CIE chromaticity coordinates exceed the NTSC standard, and the display device having the light emitting element of the present invention can express a rich color.

In this example, the same material and method as in Example 3 were used except that the electron transport layer and the electron injection layer were changed as follows. In this example, the electron transport layer and the electron injection layer have BCP larger than the triplet excitation energy of Ir (Fdpq) ₂ (acac) which is a light-emitting substance.

  The electron transport layer 214 was formed by depositing BCP to a thickness of 20 nm using a resistance heating vapor deposition method. In addition, the electron injection layer 215 was formed to have a film thickness of 40 nm by co-evaporating BCP and Li. Here, the mass ratio of BCP and Li was set to 1: 0.01 (= BCP: Li).

The light-emitting element manufactured as described above was sealed in a nitrogen atmosphere. After that, voltage was applied so that the potential of the first electrode 101 was higher than the potential of the second electrode 103, and the operating characteristics of the light-emitting element were examined. The measurement was performed in a state kept at room temperature (25 ° C.). The results are shown in FIG. 8A shows the result of examining the current density-luminance characteristic, FIG. 8B shows the result of examining the voltage-luminance characteristic, and FIG. 8C shows the result of examining the luminance-current efficiency characteristic. In addition, in a present Example, the measurement result in Example 3 is also shown in FIG. Further, FIG. 9 shows an emission spectrum of the light-emitting element in this example, and Table 3 shows a summary of the element structures of this example and Example 3.

The light-emitting element in this example emitted light with a luminance of 500 cd / m ² when a voltage of 8.8 V was applied. The light-emitting element of this example has excellent current efficiency and external quantum efficiency as in Example 3. The current efficiency at 500 cd / m ² is 4.1 cd / A, and the external quantum efficiency is 9.0%. It was.

  From the above, current efficiency and external quantum efficiency can be improved by using a material larger than the triplet excitation energy of the organometallic complex which is a light-emitting substance for the electron transport layer and the electron injection layer.

  In addition, the light-emitting element in this example has a CIE chromaticity coordinate of (X, Y) = (0.71, 0.29), and is found to be a red light-emitting element with excellent color purity.

  In addition, when compared with the results of Example 3, the light emitting device in this example also exhibits higher current efficiency and external quantum efficiency, but the light emitting device in Example 3 exhibits higher current efficiency and external quantum efficiency. I understood. This is presumably because TAZ having a triplet excitation energy higher than that of the BCP used in this example is used for the electron transport layer of the light emitting element in Example 3. Therefore, it can be said that the electron transport layer is preferably a material having a larger triplet excitation energy of the organometallic complex which is a light-emitting substance and a larger triplet excitation energy.

The CIE chromaticity coordinates described above exceed the NTSC standard as shown in FIG. 14, and the display device having the light emitting element of the present invention can express a rich color.

In this example, the hole transport layer was manufactured using the same material and method as in Example 3 except that the hole transport layer was changed as follows. In this example, TCTA having a triplet excitation energy larger than the triplet excitation energy of Ir (Fdpq) ₂ (acac) which is a light-emitting substance was used for the hole transport layer.

  The hole transport layer 212 was formed by depositing TCTA so as to have a thickness of 20 nm using a resistance heating vapor deposition method.

The light-emitting element manufactured as described above was sealed in a nitrogen atmosphere. After that, voltage was applied so that the potential of the first electrode 101 was higher than the potential of the second electrode 103, and the operating characteristics of the light-emitting element were examined. The measurement was performed in a state kept at room temperature (25 ° C.). The results are shown in FIG. In addition, in order to see the effect by the difference in hole transportable material in a present Example, the measurement result in Example 3 is also shown in FIG. 10A shows the results of examining the current density-luminance characteristics, FIG. 10B shows the results of examining the voltage-luminance characteristics, and FIG. 10C shows the results of examining the luminance-current efficiency characteristics. In addition, FIG. 11 shows an emission spectrum of the light-emitting element in this example, and Table 4 shows a summary of the element structures of this example and Example 3.

When the light emitting element in this example emits light with a luminance of 500 cd / m ² , a voltage of 9.6 V is required and the voltage is somewhat higher than that of the light emitting element of Example 3. However, the light-emitting element of this example has better current efficiency and external quantum efficiency than the light-emitting element of Example 3, the current efficiency at 500 cd / m ² is 5.5 cd / A, and the external quantum efficiency is 12. 2%.

This is because the HOMO level of the hole transport layer 212 of the light-emitting element in this example is closer to the HOMO level of Ir (Fdpq) ₂ (acac), which is a light-emitting substance, compared to NPB used in Example 3. This is thought to be due to the use of.

  Therefore, it is possible to further improve the current efficiency and the external quantum efficiency by using a hole transporting material having a HOMO level closer to the HOMO level of the organometallic complex that is a light-emitting substance in the hole transport layer. all right.

  In addition, the light-emitting element in this example has a CIE chromaticity coordinate of (X, Y) = (0.71, 0.29), and is found to be a red light-emitting element with excellent color purity. As shown in FIG. 14, the CIE chromaticity coordinates exceed the NTSC standard, and the display device having the light emitting element of the present invention can express a rich color.

  The light-emitting element of the present invention is not limited to the structure of this example, and can be freely combined with other embodiments or examples.

In this example, (acetylacetonato) bis [2- (4-fluorophenyl) -3-methylquinoxalinato] iridium which is a kind of organometallic complex represented by the general formula (6) described above as a light-emitting substance is used. (III) _{[abbreviation: Ir (MFpq) 2 (acac} ) and shows] a, a BCP having triplet excitation energy greater than the triplet excitation energy of Ir _(MFpq) 2 _(acac) as the electron transport layer, an electron injection layer A light-emitting element using a mixed layer made of Alq and Li and a manufacturing method thereof will be described with reference to FIGS. Ir (MFpq) ₂ (acac) is shown in Formula (21).

  An ITSO film was formed over the substrate 100 by a sputtering method to form the first electrode 101.

  Next, the substrate 100 on which the first electrode 101 was formed was fixed to a substrate holder provided in the vacuum evaporation apparatus so that the surface on which the first electrode 101 was formed faced down.

  Next, NPB and molybdenum oxide (VI) were co-evaporated on the first electrode 101, whereby the hole injection layer 111 with a thickness of 50 nm was formed. The deposition rate ratio between NPB and molybdenum oxide (VI) was adjusted to be NPB: molybdenum oxide (VI) = 4: 1.

  Next, NPB was formed to a thickness of 10 nm on the hole injection layer 111 by a resistance heating vapor deposition method to form a hole transport layer 212.

Next, Ir (MFpq) ₂ (acac) and Alq ₃ were deposited on the hole transport layer 212 to a thickness of 30 nm by co-evaporation, whereby the light-emitting layer 213 was formed. Here, the mass ratio of Alq ₃ to Ir (MFpq) ₂ (acac) was set to 1: 0.08 (= Alq ₃ : Ir (MFpq) ₂ (acac)). As a result, Ir (MFpq) ₂ (acac) is dispersed in the Alq ₃ layer.

  Next, BCP was formed to a thickness of 10 nm on the light-emitting layer 213 by a vapor deposition method using resistance heating, so that an electron transport layer 214 was formed.

Next, on the electron transport layer 214, the electron injection layer 215 was formed to have a film thickness of 50 nm by co-evaporating Alq ₃ and Li. Here, the mass ratio between Alq ₃ and Li was set to 1: 0.01 (= Alq ₃ : Li).

  Next, the second electrode 103 was formed over the electron injection layer 215 by using an aluminum evaporation method using resistance heating. The light-emitting element manufactured as described above was sealed in a nitrogen atmosphere.

A voltage was applied to the light-emitting element in this example so that the potential of the first electrode 101 was higher than the potential of the second electrode 103, and the operating characteristics of the light-emitting element were examined. The measurement was performed in a state kept at room temperature (25 ° C.). The results are shown in FIG. 15A shows the result of examining the current density-luminance characteristics, FIG. 15B shows the result of examining the voltage-luminance characteristics, and FIG. 15C shows the results of examining the luminance-current efficiency characteristics. In FIG. 15A, the horizontal axis represents current density (mA / cm ² ), and the vertical axis represents luminance (cd / m ² ). In FIG. 15B, the horizontal axis represents voltage (V), and the vertical axis represents luminance (cd / m ² ). In FIG. 15C, the horizontal axis represents luminance (cd / m ² ), and the vertical axis represents current efficiency (cd / A). Further, FIG. 16 shows an emission spectrum of the light-emitting element in this example.

From these results, it was found that the light-emitting element in this example emitted light with a luminance of 500 cd / m ² when a voltage of 7.2 V was applied. The light-emitting element of this example was excellent in current efficiency and external quantum efficiency. The current efficiency at 500 cd / m ² was 3.1 cd / A and the external quantum efficiency was 7.4%.

  From the above, the amount of electrons injected into the light emitting layer is improved by introducing Li into the electron injecting layer, and the triplet greater than the triplet excitation energy of the organometallic complex that is the light emitting substance as the material of the electron transporting layer. It was found that a light emitting device having excellent current efficiency and external quantum efficiency can be obtained by selecting a material having excitation energy.

  In addition, the light-emitting element in this example has a CIE chromaticity coordinate of (X, Y) = (0.71, 0.29), and is found to be a red light-emitting element with excellent color purity. Note that the CIE chromaticity coordinates exceed the NTSC standard, and the display device having the light emitting element of the present invention can express a rich color.

In this example, the same material and method as in Example 6 were used except that the host material in the light emitting layer was changed as follows. In this embodiment, the host material in the light-emitting layer 213 has triplet excitation energy larger than the triplet excitation energy of Ir (MFpq) ₂ (acac) that is a light-emitting substance, and has triplet excitation energy larger than that of Alq _3. CBP was used.

The light-emitting layer 213 was formed by forming Ir (MFpq) ₂ (acac) and CBP to a thickness of 30 nm by co-evaporation. Here, the mass ratio between CBP and Ir (MFpq) ₂ (acac) was 1: 0.08 (= CBP: Ir (MFpq) ₂ (acac)). As a result, Ir (MFpq) ₂ (acac) is dispersed in the layer made of CBP.

The light-emitting element manufactured as described above was sealed in a nitrogen atmosphere. After that, voltage was applied so that the potential of the first electrode 101 was higher than the potential of the second electrode 103, and the operating characteristics of the light-emitting element were examined. The measurement was performed in a state kept at room temperature (25 ° C.). The results are shown in FIG. In addition, in order to see the effect by the difference in host material in a present Example, the result of a present Example is shown in FIG. 15 in addition to the measurement result in Example 6. FIG. In addition, FIG. 17 shows an emission spectrum of the light-emitting element in this example, and Table 5 shows a summary of the element structures of this example and Example 6.

The light emitting element in this example requires a voltage of 8.0 V when emitting light with a luminance of 500 cd / m ² , and the voltage is somewhat higher than that of the light emitting element of Example 6. However, the light-emitting element of this example is more excellent in current efficiency and external quantum efficiency than the light-emitting element of Example 6, the current efficiency at 500 cd / m ² is 6.7 cd / A, and the external quantum efficiency is 12%. Met.

  From the above, it is possible to further improve the current efficiency and the external quantum efficiency by selecting a material having a triplet excitation energy larger than that of the organometallic complex that is the light-emitting substance as the host material of the light-emitting layer. all right.

  In addition, the light-emitting element in this example has a CIE chromaticity coordinate of (X, Y) = (0.70, 0.30), and is found to be a red light-emitting element with excellent color purity. The CIE chromaticity coordinates exceed the NTSC standard, and the display device having the light emitting element of the present invention can express a rich color.

In this example, (acetylacetonato) bis [2,3-bis (4-trifluoromethylphenyl) quinoxalinato] iridium (a kind of organometallic complex represented by the general formula (7) described above as a light-emitting substance) III) A light-emitting element was fabricated using the same material and method as in Example 7 except that [abbreviation: Ir (CF ₃ dpq) ₂ (acac)] was used. Ir (CF ₃ dpq) ₂ (acac) is shown in Formula (22).

A voltage was applied to the light-emitting element in this example so that the potential of the first electrode 101 was higher than the potential of the second electrode 103, and the operating characteristics of the light-emitting element were examined. The measurement was performed in a state kept at room temperature (25 ° C.). The results are shown in FIG. FIG. 18A shows the results of the current density-luminance characteristics, FIG. 18B shows the voltage-luminance characteristics, and FIG. 18C shows the brightness-current efficiency characteristics. In FIG. 18A, the horizontal axis represents current density (mA / cm ² ), and the vertical axis represents luminance (cd / m ² ). In FIG. 18B, the horizontal axis represents voltage (V), and the vertical axis represents luminance (cd / m ² ). In FIG. 18C, the horizontal axis represents luminance (cd / m ² ), and the vertical axis represents current efficiency (cd / A). FIG. 19 shows an emission spectrum of the light-emitting element in this example.

From these results, it was found that the light-emitting element in this example emitted light with a luminance of 500 cd / m ² when a voltage of 10.4 V was applied. In addition, the light-emitting element of this example was excellent in current efficiency and external quantum efficiency. The current efficiency at 500 cd / m ² was 5.3 cd / A and the external quantum efficiency was 10%.

  From the above, the amount of electrons injected into the light emitting layer is improved by introducing Li into the electron injecting layer, and the triplet greater than the triplet excitation energy of the organometallic complex that is the light emitting substance as the material of the electron transporting layer. By selecting a material having an excitation energy as a host material of the light emitting layer and having a triplet excitation energy larger than that of the organometallic complex as a light emitting substance, a light emitting device having excellent current efficiency and external quantum efficiency can be obtained. I understood.

  In addition, the light-emitting element in this example has a CIE chromaticity coordinate of (X, Y) = (0.70, 0.30), and is found to be a red light-emitting element with excellent color purity. Note that the CIE chromaticity coordinates exceed the NTSC standard, and the display device having the light emitting element of the present invention can express a rich color.

  In this example, a light-emitting device having the light-emitting element of the present invention will be described with reference to FIG. 12A is a top view of the light-emitting device, and FIG. 12B is a cross-sectional view taken along the line A-A ′ in FIG. 12A (a cross-sectional view cut along A-A ′). Reference numeral 300 denotes a substrate, 301 a drive circuit portion (source side drive circuit) indicated by a dotted line, 302 a pixel portion, and 303 a drive circuit portion (gate side drive circuit). Reference numeral 304 denotes a sealing substrate, 305 denotes a sealing material, and the inside surrounded by the sealing material 305 is a space 306.

  Note that reference numeral 307 denotes wiring for transmitting signals input to the source side driver circuit 301 and the gate side driver circuit 303, and a video signal, a clock signal, and a start signal from an FPC (flexible printed circuit) 308 serving as an external input terminal. Receive signals, reset signals, etc. Although only the FPC is shown here, a printed wiring board (PWB) may be attached to the FPC. The light emitting device of the present invention includes not only the light emitting device main body but also a state in which an FPC or PWB is attached thereto.

  Next, a cross-sectional structure will be described with reference to FIG. A driver circuit portion and a pixel portion are formed over the substrate 300. Here, a source side driver circuit 301 which is one of the driver circuit portions and a pixel portion 302 are shown.

  Note that the source side driver circuit 301 is formed with a CMOS circuit in which an n-channel TFT 323 and a p-channel TFT 324 are combined. Further, the driving circuit constituted by TFTs may be formed by a known CMOS circuit, PMOS circuit or NMOS circuit. In this embodiment, a driver integrated type in which a drive circuit is formed on a substrate is shown. However, this is not always necessary, and the driver circuit may be formed outside the substrate.

  The pixel portion 302 is formed of a plurality of pixels including a switching TFT 311, a current control TFT 312, and a first electrode 313 electrically connected to the drain thereof. Note that an insulator 314 is formed so as to cover an end portion of the first electrode 313. Here, a positive photosensitive acrylic resin film is used.

  In order to improve the formation of the layer 316 containing a light-emitting substance to be formed later, the insulator 314 is preferably formed so that an upper end portion or a lower end portion thereof has a curved surface having a curvature. For example, in the case where positive photosensitive acrylic is used as the material of the insulator 314, it is preferable that only the upper end portion of the insulator 314 has a curved surface having a curvature radius (0.2 μm to 3 μm). As the insulator 314, either a negative type that becomes insoluble in an etchant by photosensitive light or a positive type that becomes soluble in an etchant by light can be used. Furthermore, the material of the insulator 314 is not limited to an organic material, and an inorganic material can be used. For example, silicon oxide, silicon oxynitride, or the like can be used.

  Further, a layer 316 containing a light-emitting substance and a second electrode 317 are formed over the first electrode 313.

  The layer 316 containing a light-emitting substance is formed by an evaporation method, a coating method, or the like. The layer 316 containing a light-emitting substance is formed using at least the organometallic complex having the structure represented by the general formulas (1) to (4) and the general formula (5) to the general formula (5) to the above-described embodiment or example. A light emitting layer having at least one of the organometallic complexes represented by (8), an electron injection layer having an organic compound and a substance exhibiting an electron donating property to the compound, or a triple higher than the organometallic complex As long as it has an electron transport layer having a term excitation energy, a host material, or a hole transport layer, the laminated structure of other layers is not particularly limited and can be appropriately selected.

  For the first electrode 313 functioning as an anode, the layer 316 containing a light-emitting substance, and the second electrode 317 functioning as a cathode, each material described in Embodiment 1 can be selected as appropriate. .

  Further, the sealing substrate 304 is attached to the substrate 300 with the sealant 305, whereby the first electrode 313 and the layer 316 containing a light-emitting substance in the space 306 surrounded by the substrate 300, the sealing substrate 304, and the sealant 305. The light emitting element 318 having the second electrode 317 and the second electrode 317 is provided. Note that the space 306 includes a structure filled with a sealant 305 in addition to a case where the space 306 is filled with an inert gas (such as nitrogen or argon).

  Note that an epoxy-based resin is preferably used for the sealant 305. Moreover, it is desirable that these materials are materials that do not transmit moisture and oxygen as much as possible. In addition to a glass substrate or a quartz substrate, a plastic substrate made of FRP (Fiberglass-Reinforced Plastics), PVF (polyvinyl fluoride), Mylar, polyester, acrylic, or the like can be used as a material used for the sealing substrate 304.

  By using the light-emitting element of the present invention that exhibits high luminous efficiency and excellent color purity, a colorful display device that can emit more colors can be obtained.

  This embodiment can be appropriately combined with any of Embodiment Modes 1 and 2 and Examples 1 to 8.

  Further, the present invention is not limited to the above-described embodiments.

  In this example, various electric appliances completed using a light-emitting device having the light-emitting element of the present invention will be described. Since the light-emitting device to which the present invention is applied uses a red light-emitting element that exhibits high light emission efficiency and excellent color purity, light emission with rich colors can be achieved.

  As an electric appliance manufactured using a light-emitting device formed using the present invention, a camera such as a television, a video camera, or a digital camera, a goggle-type display (head-mounted display), a navigation system, a sound reproduction device (car audio) , Audio components, etc.), notebook personal computers, game machines, portable information terminals (mobile computers, cellular phones, portable game machines, electronic books, etc.), and image playback devices (specifically digital And a device equipped with a display device capable of reproducing a recording medium such as a use disc (DVD) and displaying the image thereof. Some specific examples of the electric appliance will be described with reference to FIG. The electric appliance using the light emitting device of the present invention is not limited to these specific examples.

  FIG. 13A illustrates a display device, which includes a housing 400, a support base 401, a display portion 402, a speaker portion 403, a video input terminal 404, and the like. The display device 402 is manufactured using a light-emitting device formed using the present invention. The display device includes all information display devices such as a personal computer, a TV broadcast reception, and an advertisement display.

  The display portion 402 is provided with the light emitting element of the present invention. The layer containing a light-emitting substance included in the light-emitting element includes at least an organometallic complex having a structure represented by the general formulas (1) to (4) and an organometallic represented by the general formulas (5) to (8). An electron-injecting layer having a light-emitting layer having at least one of complexes, an organic compound and a substance exhibiting an electron donating property to the compound, or an electron-transporting layer having higher triplet excitation energy than the organometallic complex; Host material or hole transport layer. By using the light-emitting element of the present invention, a colorful display device can be obtained.

  FIG. 13B illustrates a laptop personal computer, which includes a main body 500, a housing 501, a display portion 502, a keyboard 503, an external connection port 504, a pointing mouse 505, and the like.

The display portion 502 is provided with the light-emitting element of the present invention. The layer containing a light-emitting substance included in the light-emitting element includes at least an organometallic complex having a structure represented by the general formulas (1) to (4) and an organometallic represented by the general formulas (5) to (8). An electron-injecting layer having a light-emitting layer having at least one of complexes, an organic compound and a substance exhibiting an electron donating property to the compound, or an electron-transporting layer having higher triplet excitation energy than the organometallic complex; Host material or hole transport layer. By using the light-emitting element of the present invention, a personal computer that can display rich colors can be obtained.

  FIG. 13C illustrates a video camera, which includes a main body 600, a display portion 601, a housing 602, an external connection port 603, a remote control receiving portion 604, an image receiving portion 605, a battery 606, an audio input portion 607, operation keys 608, an eyepiece. Part 609 and the like.

The display portion 601 is provided with the light-emitting element of the present invention. The layer containing a light-emitting substance included in the light-emitting element includes at least an organometallic complex having a structure represented by the general formulas (1) to (4) and an organometallic represented by the general formulas (5) to (8). An electron-injecting layer having a light-emitting layer having at least one of complexes, an organic compound and a substance exhibiting an electron donating property to the compound, or an electron-transporting layer having higher triplet excitation energy than the organometallic complex; Host material or hole transport layer. By using the light-emitting element of the present invention, a video camera having a colorful display portion can be obtained.

  FIG. 13D shows a cellular phone, which includes a main body 700, a housing 701, a display portion 702, a voice input portion 703, a voice output portion 704, operation keys 705, an external connection port 706, an antenna 707, and the like.

The display portion 702 is provided with the light-emitting element of the present invention. The layer containing a light-emitting substance included in the light-emitting element includes at least an organometallic complex having a structure represented by the general formulas (1) to (4) and an organometallic represented by the general formulas (5) to (8). An electron-injecting layer having a light-emitting layer having at least one of complexes, an organic compound and a substance exhibiting an electron donating property to the compound, or an electron-transporting layer having higher triplet excitation energy than the organometallic complex; Host material or hole transport layer. By using the light-emitting element of the present invention, a mobile phone having a colorful display portion can be obtained.

  As described above, the applicable range of the present invention is extremely wide and can be used for display devices in various fields. In addition, the electronic device of this example can be appropriately combined with any one of Embodiments 1 and 2 and Examples 1 to 9.

6A and 6B illustrate an element structure of a light-emitting element of the present invention. 6A and 6B illustrate an element structure of a light-emitting element of the present invention. FIG. 11 shows an emission spectrum of the light-emitting element manufactured in Example 1. FIG. 6 shows operating characteristics of the light-emitting element manufactured in Example 2 FIG. 9 shows an emission spectrum of the light-emitting element manufactured in Example 2. FIG. 10 shows operating characteristics of the light-emitting element manufactured in Example 3 FIG. 11 shows an emission spectrum of the light-emitting element manufactured in Example 3. FIG. 9 shows operating characteristics of the light-emitting element manufactured in Example 4 FIG. 9 shows an emission spectrum of the light-emitting element manufactured in Example 4. FIG. 10 shows operating characteristics of the light-emitting element manufactured in Example 5 FIG. 9 shows an emission spectrum of the light-emitting element manufactured in Example 5. FIG. 7 is a diagram of a display device using the light emitting element of the present invention. Illustration of electronic device using light emitting element of the present invention The figure which compared the light emitting element of this invention and the NTSC standard The figure which shows the operating characteristic of the light emitting element produced in Example 6 and 7 FIG. 11 shows an emission spectrum of the light-emitting element manufactured in Example 6. FIG. 11 shows an emission spectrum of the light-emitting element manufactured in Example 7. FIG. 10 shows operating characteristics of the light-emitting element manufactured in Example 8 FIG. 11 shows an emission spectrum of the light-emitting element manufactured in Example 8.

Explanation of symbols

100 substrate 101 first electrode 102 layer 103 containing luminescent material second electrode 111 hole injection layer 112 hole transport layer 113 light emitting layer 114 electron transport layer 115 electron injection layer 202 layer 212 containing luminescent material hole transport layer 213 light emitting layer 214 Electron transport layer 215 Electron injection layer 300 Substrate 301 Source side driver circuit portion 302 Pixel portion 303 Gate side driver circuit portion 304 Sealing substrate 305 Sealant 306 Space 307 Wiring 308 FPC
311 TFT for switching
312 Current control TFT
313 First electrode 314 Insulator 316 Layer containing light-emitting substance 317 Second electrode 318 Light-emitting element 323 n-channel TFT
324 p-channel TFT
400 Housing 401 Support base 402 Display unit 403 Speaker unit 404 Video input terminal 500 Main body 501 Housing 502 Display unit 503 Keyboard 504 External connection port 505 Pointing mouse 600 Main body 601 Display unit 602 Housing 603 External connection port 604 Remote control receiving unit 605 Image receiving unit 606 Battery 607 Audio input unit 608 Operation key 609 Eyepiece 700 Main body 701 Case 702 Display unit 703 Audio input unit 704 Audio output unit 705 Operation key 706 External connection port 707 Antenna

Claims (10)

A hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and a second electrode, which are sequentially stacked on the first electrode;
The light emitting layer has an organometallic complex represented by the following general formula (2),
The electron injection layer includes an organic compound and any one of an alkali metal, an alkaline earth metal, an alkali metal halide, an alkaline earth halide, an alkali metal oxide, and an alkali metal complex. Light emitting element.

(In the formula, R ^{1 to} R ⁵ represent hydrogen, a halogen element, an acyl group, an alkyl group, an alkoxyl group, an aryl group, a cyano group, or a heterocyclic group. Ar represents a halogen group, a haloalkyl group, or a cyano group. Represents an aryl group having any one of the above substituents or a heterocyclic group having any one of a halogen group, a haloalkyl group, and a cyano group , and M represents a Group 9 element or a Group 10 element. When M is a group 9 element, n = 2, and when it is a group 10 element, n = 1. L represents an anionic ligand.) In claim 1,
The light-emitting element, wherein the anionic ligand L is a ligand represented by any of the following formulas (3) to (9).
In claim 1,
The anionic ligand L is an anionic ligand having a beta diketone structure, an anionic bidentate ligand having a carboxyl group, or an anionic bidentate ligand having a phenolic hydroxyl group. A light emitting element characterized by the above. In any one of Claims 1 thru | or 3 ,
A light emitting device having an external quantum efficiency of 5% or more and CIE chromaticity coordinates X ≧ 0.7 and Y ≦ 0.3. In any one of Claims 1 thru | or 3 ,
A light-emitting element having a current efficiency of 2.0 cd / A or more and CIE chromaticity coordinates X ≧ 0.7 and Y ≦ 0.3. In any one of Claims 1 thru | or 5,
The light-emitting element, wherein the electron injection layer includes an organic compound and any one of Li, Mg, and Cs. In any one of Claims 1 thru | or 6 ,
The light-emitting element, wherein the electron transport layer has triplet excitation energy higher than triplet excitation energy of the organometallic complex. In any one of Claims 1 thru | or 7 ,
The light-emitting element, wherein the hole transport layer has triplet excitation energy higher than triplet excitation energy of the organometallic complex. In any one of Claims 1 thru | or 8 ,
The light emitting layer includes a host material having a triplet excitation energy higher than a triplet excitation energy of the organometallic complex. A light-emitting device comprising the light-emitting element according to claim 1 .