JP2006089728A - Light-emitting element, light-emitting device and illuminator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-emitting element, a light-emitting device, and an illuminator which have each a broad spectrum near to that of solar light and a high color-rendering property. <P>SOLUTION: This light-emitting element is characterized by containing at least two light-emitting centers between a pair of electrodes, wherein at least one of the light-emitting centers is a quinoxaline derivative represented by the general formula (1) [R1 to R4 are each H or a 6C alkyl (straight chain structure or branched structure)]. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light-emitting element, and more particularly to a light-emitting element, a light-emitting device, and a lighting device that are excellent in color rendering.

  Development of a display using a self-luminous thin-film light-emitting element that emits light when an electric current flows is being actively promoted.

  These light-emitting elements emit light when an electrode is connected to a single-layer or multilayer thin film formed using organic, inorganic, or both, and a current is passed. Such thin-film light emitting devices are expected to have low power consumption, space saving, visibility, and the like, and further expansion of the market is expected in the future.

  Among these, the function of the light-emitting element having a multilayer structure can be manufactured by dividing the function for each layer, so that an element that emits light more efficiently than before can be manufactured (see, for example, Non-Patent Document 1). .

C. W. Tan et al., Applied Physics Letters, Vol. 51, no. 12, 913-915 (1987)

  A light-emitting element having a multilayer structure sandwiches a light-emitting laminate composed of a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and the like between an anode and a cathode. However, among these, the hole injection layer, the hole transport layer, the electron transport layer, and the electron injection layer may include layers that are not used depending on the element configuration. In addition, the hole transport layer and the electron transport layer may also serve as a light emitting layer. In this case, a technique is used in which an electron transport layer or a hole transport layer having a high carrier transport property is doped with a dye having a high light emission efficiency. By using this method, a material having high emission efficiency but low carrier transportability can be used as the light emitting layer (see, for example, Non-Patent Document 2).

C. W. Tan et al., Journal of Applied Physics, Vol. 65, no. 9, 3710-3716 (1989)

  By the way, the thin-film light-emitting element having the above-described features is also expected to be used for lighting devices. When used in these applications, white light emission is desired. Therefore, an attempt has been made to obtain white light emission by providing a plurality of types of light emission centers exhibiting different light emission colors in the same light emitting element (see, for example, Patent Document 1).

JP-A-7-142169

  White light is recognized when all the pyramidal cells of the human eye are stimulated in the same way. In order to manufacture a light emitting element that emits light recognized as white, light emitting materials exhibiting three colors of red, green, and blue are allowed to emit light at the same time, or two types of light emission exhibiting complementary colors. It has been found that it is good to have the materials emit light simultaneously.

  However, most of the white light produced by such a method has a shape in which the spectrum protrudes in each color, and is inferior in color rendering as compared with natural light having almost the same intensity in all wavelength components.

  In other words, the color of an object is recognized by the human eye by absorbing or reflecting light in a specific wavelength band, but the light of a specific wavelength band protrudes and has high intensity, or vice versa. When a light with very low intensity is applied to a specific color, compared to a case where light having almost the same intensity in all wavelength components such as sunlight is applied, a specific color is strengthened, The color changes and looks weak.

  As described above, the light emission spectrum of the light emitting element, the light emitting device, and the lighting device is preferably light having a broad spectrum that is closer to sunlight. In the present invention, such a light emitting element and light emitting device with higher color rendering properties are used. An object is to provide a lighting device.

  1 of the present invention has a layer containing an organic compound between a pair of electrodes, the layer containing an organic compound contains at least two kinds of luminescent center substances, and at least one of the plurality of luminescent center substances has the following general formula A light-emitting element characterized by being a quinoxaline derivative represented by (1).

  In the general formula (1), R1 to R4 are hydrogen or an alkyl group having 6 carbon atoms (straight chain structure or branched structure).

  1 of the present invention has a layer containing an organic compound between a pair of electrodes, the layer containing an organic compound contains at least two kinds of luminescent center substances, and at least one of the plurality of luminescent center substances has the following general formula A light-emitting element characterized by being a quinoxaline derivative represented by (2).

  1 of the present invention has a layer containing an organic compound between a pair of electrodes, the layer containing an organic compound contains at least two kinds of luminescent center substances, and at least one of the plurality of luminescent center substances has the following general formula A light-emitting element characterized by being a quinoxaline derivative represented by (3).

  1 of the present invention has a layer containing an organic compound between a pair of electrodes, the layer containing an organic compound contains at least two kinds of luminescent center substances, and at least one of the plurality of luminescent center substances has the following general formula A light-emitting element characterized by being a quinoxaline derivative represented by (4).

  1 of the present invention has a layer containing an organic compound between a pair of electrodes, the layer containing an organic compound contains at least two kinds of luminescent center substances, and at least one of the plurality of luminescent center substances has the following general formula A light-emitting element characterized by being a quinoxaline derivative represented by (5).

  1 of the present invention has a layer containing an organic compound between a pair of electrodes, the layer containing an organic compound contains at least two kinds of luminescent center substances, and at least one of the plurality of luminescent center substances has the following general formula A light-emitting element characterized by being a quinoxaline derivative represented by (6).

  1 of the present invention has a layer containing an organic compound between a pair of electrodes, the layer containing an organic compound contains at least two kinds of luminescent center substances, and at least one of the plurality of luminescent center substances has the following general formula A light-emitting element characterized by being a quinoxaline derivative represented by (7).

  1 of the present invention is a light-emitting device having the light-emitting element having the above structure between a pair of substrates.

  Since the present invention includes a quinoxaline derivative represented by the following general formula (1) having a very broad spectrum as one of the light-emitting materials in a light-emitting element, the spectrum of light emitted from the light-emitting element can be easily converted to a spectrum of sunlight. You can get closer.

  In addition, a light emitting device and a lighting device with higher color rendering can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention can be implemented in many different modes, and those skilled in the art can easily understand that the modes and details can be variously changed without departing from the spirit and scope of the present invention. Is done. Therefore, the present invention is not construed as being limited to the description of this embodiment mode.

(Embodiment 1)
The general formula of the compound used as one of the emission center substances in the light emitting device of the present invention is represented by the following formula (1).

  In general formula (1), R1 to R4 are hydrogen or an alkyl group having 6 carbon atoms (straight chain structure or branched structure).

  Next, specific examples of the quinoxaline derivative represented by the general formula (1) are given below.

  Subsequently, a method for synthesizing the quinoxaline derivative of the above formula (1) will be described. The quinoxaline derivative represented by the general formula (1) can be synthesized by the following synthesis schemes (9) to (11).

  First, a quinoxaline ring is prepared by dehydrating condensation reaction of phenylenediamine and 2,3-bis (bromophenyl) 1,2-dione (reaction scheme (9)).

  Subsequently, the quinoxaline derivative synthesized in the above reaction scheme (9) is used as a boronic acid (reaction scheme (10)).

  Finally, the quinoxaline derivative represented by the above formula (1) can be synthesized by coupling the boronic acid synthesized in the reaction scheme (10) and the aryl halide with a palladium catalyst.

  The difference between the above general formulas (2), (3) and (4) (or the above general formulas (5), (6) and (7)) is the difference in the substitution position of the pyrenyl group. However, in the synthesis scheme (9), when the quinoxaline derivative of the above general formulas (1) and (5) is obtained as a substance to be reacted with phenylenediamine, 2-bis- (4-bromo-phenyl)- In the case of obtaining ethane-1,2-dione (the following formula (12)) and quinoxaline derivatives of the above general formulas (2) and (6), 2-bis- (3-bromo-phenyl) -ethane-1,2 -Dione (following formula (13)), when obtaining quinoxaline derivatives of the above general formulas (3) and (7), 2-bis- (2-bromo-phenyl) -ethane-1,2-dione (following formula (14)) may be used for synthesis.

  The difference between the general formulas (2) to (4) and (5) to (7) is that a t-butyl group is introduced into R1 to R4 of the pyrenyl group. In the reaction scheme (11), when synthesizing the quinoxaline derivatives represented by the general formulas (2) to (4), R1 to R4 are hydrogen, and the quinoxaline represented by the general formulas (5) to (7) When synthesizing a derivative, R1 to R4 may be t-butyl groups. Further, although not mentioned in the above formula as an example, R1 to R4 may be an n-butyl group.

  In addition, 2,7-di-tert-butyl-1-bromopyrene used for synthesizing a quinoxaline derivative in which a t-butyl group is introduced into R1 to R4 can be synthesized by the following reaction scheme (15). .

  Next, a structure and a manufacturing method of a white light-emitting element using the quinoxaline derivative represented by the general formula (1) will be described with reference to FIGS.

  Note that in this specification, a light emission center refers to a substance that actually emits light when current is passed between a pair of electrodes included in a light emitting element.

  In the white light-emitting element of the present invention, a pair of electrodes including a first electrode 101 and a second electrode 108 is formed over a substrate 100 having an insulating surface, and a first carrier injection layer 102 and a first carrier are interposed therebetween. A layer containing an organic compound in which a transport layer 103), a first light-emitting layer 104, a second light-emitting layer 105, and (a second carrier transport layer 106 and a second carrier injection layer 107) are stacked. Yes.

Either the first light-emitting layer 104 or the second light-emitting layer is a layer made of a quinoxaline derivative single film represented by the above general formula (1), and light emitted from the light emission center of the other light-emitting layer is red. Emitting light having a peak of its spectrum in the range of 580 nm to 700 nm, such as 4-dicyanomethylene-2-methyl-6- (p-dimethylamino-styryl) -4H-pyran (abbreviation: DCM1), 4 -(Dicyanomethylene) -2-methyl-6- [2- (julolidin-9-yl) ethenyl] -4H-pyran (abbreviation: DCM2), 4-dicyanomethylene-2-methyl-6- (1,1, 7,7-tetramethyljulolidyl-9-enyl) -4H-pyran (abbreviation: DCJT) 4-dicyanomethylene-2-t-butyl-6- (1,1,7,7-te La methyl Ju Lori Jill 9-enyl) -4H- pyran, bis [2- (2'-benzothienyl) pyridinato -N, C ³ '] - (acetylacetonato) iridium (abbreviation: Ir (btp) ₂ ( acac)) and the like having a larger energy gap and relatively excellent carrier transportability (for example, 4,4′-bis [N- (1-naphthyl) -N-phenyl-amino] -biphenyl (abbreviation: α -NPD) or a layer dispersed in tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ) or the like. Alternatively, a single film of a light emitting material that emits red light may be used.

  The first electrode 101 and the second electrode 108 are paired, and one of them functions mainly as an anode, and the other functions mainly as a cathode. In addition, the first carrier and the first electrode 101, the second carrier and the second electrode 108 are in a corresponding relationship, and when the corresponding electrode is an anode, the carrier is a hole, and when it is a cathode The carrier becomes an electron. That is, if the first electrode 101 is an anode, the second electrode 108 is a cathode, the first carrier is a hole, and the second carrier is an electron.

  Note that the first carrier injection layer 102, the first carrier transport layer 103, the second carrier transport layer 106, and the second carrier injection layer 107 may or may not be provided, and are selected as appropriate. This is easily done by those skilled in the art. In addition, a layer having an appropriate function such as a hole blocking layer may be added.

  As the substrate 100, glass, quartz, plastic (polyimide, acrylic, polyethylene terephthalate, polycarbonate, polyacrylate, polyethersulfone, or the like) can be used.

  As the anode material, 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 the anode material include ITO (indium tin oxide), ITSO (indium tin silicon oxide), and IZO (indium zinc oxide) in which 2 to 20% zinc oxide (ZnO) is mixed with indium oxide. In addition, gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd ), Or a nitride of metal (TiN) or the like can be used.

As the cathode material, it is preferable to use a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like having a low work function (work function of 3.8 eV or less). Specific examples of the cathode material include elements belonging to Group 1 or Group 2 of the element periodicity, that is, alkali metals such as Li and Cs, and alkaline earth metals such as Mg, Ca, and Sr, and alloys containing them. In addition to (Mg: Ag, Al: Li) and compounds (LiF, CsF, CaF ₂ ), transition metals including rare earth metals can be used, but metals such as Al, Ag, ITO (including alloys) ).

The material that can be used for the hole injection layer is preferably a material that can receive holes from the anode. Further, it is preferable to use a material that is in contact with the hole injection layer and can inject holes into a layer provided on the cathode side of the hole injection layer. For example, phthalocyanine (abbreviation: H ₂ —Pc), copper phthalocyanine (abbreviation: Cu—Pc), 4,4′-bis [N- (4- (N, N-di-m-tolylamino) phenyl ) -N-phenylamino] biphenyl (abbreviation: DNTPD) or 4,4 ′, 4 ″ -tris [N- (3-methylphenyl) -N-phenylamino] triphenylamine (abbreviation: MTDATA) Aromatic amine compounds such as) 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 co-evaporation technique.

  As a material that can be used for the hole transport layer, an aromatic amine-based compound (that is, a compound having a benzene ring-nitrogen bond) is preferably used. 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: α-NPD) And starburst aromatic amine compounds such as MTDATA and 4,4 ′, 4 ″ -tris (N, N-diphenyl-amino) -triphenylamine (abbreviated as TDATA) described above. It is preferable to form by using. 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. This mixture can be formed by a technique such as co-evaporation.

Examples of materials that can be used for the electron injection layer include compounds of alkali metals or alkaline earth metals such as lithium fluoride (LiF), cesium fluoride (CsF), and calcium fluoride (CaF ₂ ). . In addition, a mixture of a substance having a high electron transporting property such as tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ) and an alkaline earth metal such as magnesium (Mg) may be used.

  As a material that can be used for the electron transport layer, 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 is preferably used. In addition, it is preferable to use a material having a higher ionization potential than the material forming the light emitting layer. However, when a hole blocking layer is provided between the light emitting layer and the electron transport layer, the light emitting layer is not necessarily formed. It is not necessary to use a material having a higher ionization potential than the material being used.

Specific examples of such an electron transporting material include Alq ₃ , bis (2-methyl-8-quinolinolato) -4-phenylphenolato-aluminum (abbreviation: BAlq), tris (8-quinolinolato) gallium (abbreviation: Gaq). ₃ ), having a quinoline skeleton or benzoquinoline skeleton such as tris (4-methyl-8-quinolinolato) aluminum (abbreviation: Almq ₃ ), bis (10-hydroxybenzo [h] -quinolinato) beryllium (abbreviation: BeBq ₂ ) And metal complexes. In addition, bis [2- (2-hydroxyphenyl) -benzoxazolate] zinc (abbreviation: Zn (BOX) ₂ ), bis [2- (2-hydroxyphenyl) -benzothiazolate] zinc (abbreviation: Zn) A metal complex having an oxazole-based or thiazole-based ligand such as (shown as (BTZ) ₂ ) can also be used as a material for forming the electron transport layer. 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 In addition to (abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: BPhen), bathocuproin (abbreviation: BCP), inorganic substances such as titanium oxide may be used.

  An example of the light-emitting element of the present invention having such a structure is given below. Note that this structure is an example, and the present invention is not limited to this.

A specific configuration of the white light-emitting element of the present invention in this embodiment mode is shown below. After depositing 110 nm of ITO using the first electrode 101 (anode) as a first electrode 101 (anode) on the glass substrate 100, 50 nm of DNTPD as the first carrier injection layer 102 (hole injection layer) is formed by vapor deposition. Α-NPD is 10 nm as the carrier transport layer 103 (hole transport layer), the red light-emitting layer is 30 nm as the first light-emitting layer 104, and the quinoxaline derivative represented by the general formula (1) is 20 nm as the second light-emitting layer 105. The second carrier transport layer 106 (electron transport layer) is made of 30 nm Alq, the second carrier injection layer 107 (electron injection layer) is made of CaF ₂ 1 nm, and the second electrode 108 (cathode) is made of aluminum 150 nm. Form.

  Note that the first light-emitting layer 104 is 4- (dicyanomethylene) -2-methyl-6- [2- (julolidin-9-yl) ethenyl] -4H-pyran (abbreviation: DCM2) having an emission center in α-NPD. ) May be co-deposited so as to be 1 wt%. Of course, another red light emitting layer may be used, and α-NPD may be another substance. In this case, a material having a band gap larger than that of the light emission center material is selected as a material to be co-evaporated with the light emission center material. Further, the first light-emitting layer 104 may be a layer made of a material that emits red light alone. In the second light-emitting layer 105, the quinoxaline derivative itself represented by the general formula (1) itself serves as the emission center, but may be formed by co-evaporation of another appropriate substance and the quinoxaline derivative.

  In the light-emitting element of the present invention having the above structure, holes are injected from the first electrode 101 into the first carrier injection layer 102 when a voltage is applied. Then, holes injected from the electrode are transported by the first carrier transport layer 103, and holes are injected into the first light emitting layer 104. On the other hand, electrons are injected from the second electrode 108 into the second carrier injection layer 107, and the electrons even injected from the electrode are transported by the second carrier transport layer 106 and injected into the second light emitting layer. . Then, electrons and holes injected in the light emitting layer are recombined, and light emission is obtained when the light emitting material in an excited state returns to the ground state. The light-emitting element of the present invention in this embodiment mode can produce a white light-emitting element that can emit light closer to natural light having a certain degree of light emission intensity in almost all wavelength bands of visible light. In addition, the light-emitting device and the lighting device of the present invention manufactured using the light-emitting element can be a lighting device with high color rendering properties.

(Embodiment 2)
In this embodiment mode, a mode in which the spacing layer 109 is provided between the first light-emitting layer 104 and the second light-emitting layer 105 in Embodiment Mode 1 will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected about the same thing as Embodiment 1, and description is also abbreviate | omitted. Refer to the corresponding description of the first embodiment.

  The present embodiment is different from the first embodiment in that the spacing layer 109 is provided. When light emitting materials having different energy gaps are formed in contact with each other, energy transfer occurs between the light emitting materials, and only one of the light emitting materials emits light strongly, and the other light emitting material emits weak light. There is a possibility that a phenomenon of light emission occurs. In addition, when a substance serving as a base of a light-emitting material is a substance that emits light, the base may also emit light depending on an energy gap. In order to improve the imbalance of the emission color, a spacing layer 109 may be provided between the emission regions. The spacing layer 109 needs to have a light-transmitting property, and may be formed of an electron transporting material or a hole transporting material. Specifically, the electron transporting material and the hole transporting material described in the embodiment mode may be used.

A specific configuration of the white light-emitting element of the present invention in this embodiment mode is shown below. After depositing 110 nm of ITO using the first electrode 101 (anode) as a first electrode 101 (anode) on the glass substrate 100, 50 nm of DNTPD as the first carrier injection layer 102 (hole injection layer) is formed by vapor deposition. As the carrier transport layer 103 (hole transport layer), α-NPD is 10 nm, the red light emitting layer is 30 nm as the first light emitting layer 104, BAlq is 5 nm as the spacing layer 109, and the second light emitting layer 105 is represented by the general formula (1) The quinoxaline derivative represented by the formula (2) is 25 nm, Alq is 30 nm as the second carrier transport layer 106 (electron transport layer), CaF ₂ is 1 nm as the second carrier injection layer 107 (electron injection layer), and the second electrode 108 (cathode) ) Is formed by stacking 150 nm of aluminum.

Note that the first light-emitting layer 104 is formed by co-evaporation of Ir (btp) ₂ (acac) serving as a light emission center in 4,4′-bis (N-carbazolyl) biphenyl (abbreviation: CBP) so as to be 8 wt%. The film may be formed by Of course, another red light emitting layer may be used, and CBP may be another substance. In this case, a material having a band gap larger than that of the light emission center material is selected as a material to be co-evaporated with the light emission center material. Further, the first light-emitting layer 104 may be a layer made of a material that emits red light alone. In the second light-emitting layer 105, the quinoxaline derivative itself represented by the general formula (1) itself serves as the emission center, but may be formed by co-evaporation of another appropriate substance and the quinoxaline derivative.

  The light-emitting element of the present invention in this embodiment mode can produce a white light-emitting element that can emit light closer to natural light having a certain degree of light emission intensity in almost all wavelength bands of visible light. In addition, the light-emitting device and the lighting device of the present invention manufactured using the light-emitting element can have high color rendering properties.

(Embodiment 3)
In this embodiment mode, a structure different from that of Embodiment Mode 6 of the white light emitting element using the phosphorescent material of the present invention will be described with reference to FIG. In addition, the same code | symbol is attached | subjected about the same thing as Embodiment 1, and description may be abbreviate | omitted. Refer to the corresponding description of the first embodiment.

A specific configuration of the white light-emitting element of the present invention in this embodiment mode is shown below. After depositing 110 nm of ITO using the first electrode 101 (anode) as a first electrode 101 (anode) on the glass substrate 100, 50 nm of DNTPD as the first carrier injection layer 102 (hole injection layer) is formed by vapor deposition. Α-NPD is 10 nm as the carrier transport layer 103 (hole transport layer), the red light emitting layer is 30 nm as the first light emitting layer 104, the third carrier transport layer 120, the carrier generating layer 121, and the fourth carrier transport. The layer 122, the second light-emitting layer 105 is 40 nm of the quinoxaline derivative represented by the general formula (1), the second carrier transport layer 106 (electron transport layer) is Alq of 30 nm, and the second carrier injection layer 107 (electron injection) The layer (CaF ₂ ) is 1 nm, and the second electrode 108 (cathode) is aluminum (150 nm) stacked.

  The third carrier and the fourth carrier are carriers having attributes opposite to those of the first carrier and the second carrier, respectively. In this embodiment, the first carrier is a hole and the second carrier is an electron. Therefore, the third carrier is an electron, and the fourth carrier is a hole. The third carrier transport layer 120 and the fourth carrier transport layer 122 may be a single layer or a plurality of layers. In this embodiment, the third carrier transport layer 120 is formed of a plurality of layers of BCP 10 nm and Alq 20 nm. The fourth carrier transport layer 122 is formed by depositing α-NPD to a thickness of 10 nm.

  Further, the layer 121 that generates carriers may be a single layer or a plurality of layers. When the layer 121 is formed by a plurality of layers, the layer that generates the third carriers in the direction in contact with the third carrier transport layer 120 is the fourth carrier transport. A layer that generates fourth carriers is formed in contact with the layer 122. In this embodiment, the carrier-generating layer 121 is formed of two layers, and a film in which Alq and Li are co-deposited at a molar ratio of 1: 1 on the side in contact with the third carrier transport layer 120 is formed. A film in which α-NPD and MoOx are co-deposited so as to have a molar ratio of 1: 1 is stacked on the side in contact with the fourth carrier transport layer 122 to a thickness of 10 nm.

  A transparent conductive film can also be used as a layer for generating carriers, specifically, indium tin oxide (abbreviation: ITO), indium tin oxide containing silicon, or 2 to 20% oxidation. Examples thereof include indium oxide containing zinc. Further, such a transparent conductive film may be provided between the layer that generates the third carrier and the layer that generates the fourth carrier.

Note that the first light-emitting layer 104 is formed by co-evaporation of Ir (btp) ₂ (acac) serving as a light emission center in 4,4′-bis (N-carbazolyl) biphenyl (abbreviation: CBP) so as to be 8 wt%. The film may be formed by Of course, another red light emitting layer may be used, and CBP may be another substance. In this case, a material having a band gap larger than that of the light emission center material is selected as a material to be co-evaporated with the light emission center material. Further, the first light-emitting layer 104 may be a layer made of a material that emits red light alone. In the second light-emitting layer 105, the quinoxaline derivative itself represented by the general formula (1) itself serves as the emission center, but may be formed by co-evaporation of another appropriate substance and the quinoxaline derivative.

  In the light-emitting element of the present invention in this embodiment, when current is supplied, carriers are injected from the first electrode 101 and the second electrode 108, and carriers are generated from the layer 121 that generates carriers. The first carrier and the third carrier are recombined in the first light-emitting layer, the second carrier and the fourth carrier are recombined in the second light-emitting layer, and the light-emitting material in each layer is excited to emit excited light. Light is emitted when the material returns to the ground state.

  Since the light-emitting element of this embodiment has a certain amount of light emission intensity in almost all wavelength bands of visible light, a white light-emitting element that can obtain light emission closer to natural light can be manufactured. In addition, the light-emitting device and the lighting device of the present invention manufactured using the light-emitting element can have high color rendering properties.

(Embodiment 4)
Next, an example of the light emitting device of the present invention will be described with reference to FIG. When a light-emitting device is manufactured, sealing is performed in order to protect the light-emitting element from a substance that promotes deterioration such as water. In FIG. 4, reference numeral 100 denotes a substrate, 101 denotes a first electrode, and 110 denotes a laminate from the first carrier injection layer to the second electrode. A light-emitting element including the first electrode 101 and the stacked body 110 is a light-emitting element having the structure of Embodiments 1 to 3.

  In the case where the counter substrate 113 is used for sealing, an insulating sealant 111 is provided and bonded to the end portion side of the substrate 100 from the light emitting element so that the external connection portion 112 is exposed. The space between the counter substrate 113 and the substrate 100 may be filled with an inert gas such as dry nitrogen, or a sealant may be applied to the entire surface of the pixel portion, thereby bonding the counter substrate. It is preferable to use an ultraviolet curable resin or the like for the sealing material. The sealing material may contain a desiccant or particles for keeping the gap between the substrates constant. Subsequently, a wiring 114 such as a conductive film or a flexible wiring board is attached to the external connection portion, whereby the light emitting device is completed.

  The light emitting device of the present invention having such a configuration can obtain light emission closer to natural light having a certain level of light emission intensity in almost all wavelength bands of visible light, and can be a lighting device with high color rendering properties. Become.

  Note that such a light-emitting device may be used as a backlight of a liquid crystal display device.

  Of course, the configuration of the light emitting device is not limited to the configuration of the present embodiment.

(Embodiment 5)
In this embodiment mode, a lighting device of the present invention will be described with reference to FIG. In the lighting device in this embodiment, the light emitting element as shown in Embodiments 1 to 3 or the light emitting device as shown in Embodiment 4 is mounted.

  FIG. 5A illustrates a light-emitting device of the present invention that is used as indoor lighting 1001. Since the illumination device of the present invention can easily obtain light having sufficient light emission intensity in almost all visible light wavelength ranges, an illumination device with extremely excellent color rendering can be obtained. Moreover, it can also be set as the surface emitting illuminating device, for example, the illuminating device of this invention can also be used for the ceiling whole surface. Further, the lighting device of the present invention can be used not only on the ceiling but also on walls, floors, pillars, and the like. Further, the lighting device of the present invention can be provided with flexibility by being formed on a flexible substrate, and can be installed on a curved surface. Further, it can be used not only indoors but also outdoors, and can be installed on a building wall or the like as an external light.

  FIG. 5B shows the lighting device of the present invention used as the lighting 1002 in the tunnel. Since the lighting device of the present invention is excellent in color rendering, it is possible to see things in the tunnel as in natural light, and to suppress a sense of incongruity in the tunnel.

  FIG. 5C illustrates an example in which the lighting device of the present invention is used as interior lighting 1003. The lighting device of the present invention can be added flexibility by being formed on a flexible substrate and is surface emitting, so that it is processed into a free shape as shown in FIG. Is possible.

  Moreover, since the illuminating device of this invention is excellent in color rendering, it is also very suitable to use as illumination at the time of taking a photograph. Further, when taking a picture, it is possible to take a picture similar to that when the subject is illuminated with natural light by illuminating the subject with a large area of light.

(Embodiment 6)
In this embodiment mode, a light-emitting device that can illuminate at a constant luminance regardless of the variation factor in consideration of the temperature characteristics and luminance change characteristics of the electroluminescence element will be described with reference to FIGS. .

  In the light emitting device shown in FIGS. 6 and 7, the electroluminescent element 404 has the same structure as that of the first embodiment. In addition to the electroluminescent element 404, a monitor element 403 is disposed. One or a plurality of monitor elements 403 can be provided. The monitor element 403 may be provided adjacent to the electroluminescent element 404 or may be provided on another part of the substrate on which the electroluminescent element 404 is formed.

  It is desirable that the monitor element 403 and the electroluminescent element 404 are manufactured in the same manufacturing process. That is, the structure of the element is the same as the constituent material. By making the electroluminescent element 404 and the monitor element 403 the same, temperature characteristics and deterioration characteristics can be made similar. As a result, it is possible to improve the accuracy of correction with respect to the luminance variation of the electroluminescent element 404. The structures of the electroluminescent element 404 and the monitor element 403 are the same as those in the first embodiment, and two or more electroluminescent elements formed on the same plane are connected in series with the adjacent or adjacent electroluminescent elements. This is the structure. However, the monitor element 403 may have a typical laminated structure in which an organic thin film is sandwiched between a pair of electrodes without complicating the electrode structure.

  The monitor element 403 is connected to the current source 401. One terminal of the monitor element 403 connected to the current source 401 is also connected to the input side of the voltage generation circuit 402. The output side of the voltage generation circuit 402 is connected to the electroluminescent element 404.

  The current source 401 supplies a constant current to the monitor element 403. When the environmental temperature changes while the monitor element 403 is driven at a constant current, the resistance value changes. When the resistance value of the monitor element 403 changes, the current value flowing through the monitor element 403 is constant, so that the potential difference between both electrodes of the monitor element 403 changes. By detecting the potential difference of the monitor element 403 at this time, it is possible to detect a change in the environmental temperature. In the monitor element 403, the other electrode potential not connected to the current source 401 is constant. Therefore, it is possible to detect a change in electrode potential on the side connected to the current source 401 of the monitor element 403.

  Also, the resistance value of the monitor element 403 changes when the light emission characteristics of the monitor element 403 driven by constant current change with time. Similarly in this case, the change in the light emission characteristics can be known by detecting the potential difference of the monitor element 403. That is, the degree of deterioration of the light emission luminance can be detected.

  The voltage generation circuit 402 uses one electrode potential of the monitor element 403 as an input potential. The potential output from the voltage generation circuit 402 is the same as the potential detected by the monitor element 403. With this voltage generation circuit 402, one electrode potential of the monitor element 403 can be reflected in the drive voltage of the electroluminescent element 404.

  The voltage generation circuit 402 can be configured by a voltage follower circuit using an operational amplifier, as shown in the inset of FIG. Since the non-inverting input terminal of the voltage follower circuit has a high input impedance and the output terminal has a low output impedance, the input side and the output side are output as the same potential, and the current of the current source 401 is output without flowing into the voltage follower circuit. Current can flow from the terminal. Note that other circuit configurations can be applied as long as the circuit can prevent potential fluctuations, such as the voltage follower circuit illustrated here.

  In the light emitting device, a current source 401, a monitor element 403, and a voltage generation circuit 402 constitute a temperature and deterioration compensation circuit (hereinafter referred to as a compensation circuit). That is, the ratio of the total amount of charge flowing in the electroluminescent element provided in the light emitting unit and the monitor element is operated under different driving conditions for both the electroluminescent element provided in the light emitting part and the monitor element equivalent to the electroluminescent element. However, control is performed so as to satisfy a certain relationship in consideration of luminance degradation.

  The light-emitting device of this embodiment compares the amount of electric charge of the electroluminescent element 404 with the amount of electric charge flowing to the monitor element 403 by considering essential deterioration that occurs in the electroluminescent element. Correction is made so that the brightness is constant. Thereby, constant luminescence driving can be performed to keep the luminance of the electroluminescent element 404 constant. For example, the driving condition of the monitor element 403 is set to be more overloaded than the driving condition of the electroluminescent element 404, and the constant luminescence driving is realized by controlling the luminance so as to keep it constant.

  An example of a light-emitting device that can illuminate at a constant luminance regardless of the variation factor in consideration of the temperature characteristics and luminance aging characteristics of the electroluminescent element will be described with reference to FIG.

  The light emitting device shown in FIG. 7 includes a monitor element 403 and an electroluminescent element 404. The monitor element 403 is driven with a constant current by a current source 401. The constant voltage source 405 has a function of generating a constant voltage, and a constant voltage source having a small temperature coefficient such as a known band gap regulator is used. The voltage generated from the constant voltage source 405 is converted into a constant current having a small temperature coefficient by the operational amplifier 406, the transistor 407, and the resistor 408. The converted current is inverted by a current mirror circuit including the transistor 409, the transistor 410, the resistor 411, and the resistor 412, and is supplied to the electroluminescent element 404. The voltage of the constant voltage source 405 is controlled according to the output of the voltage generation circuit 402 that detects the potential difference of the monitor element 403. In this case, when the output voltage of the voltage generation circuit 402 is increased, the output voltage of the constant voltage source 405 is also increased and the amount of current flowing through the electroluminescence element 404 is increased.

  The light emitting device of FIG. 7 uses the monitor element 403 to correct the voltage generated from the constant voltage source 405 according to the temperature change and the change with time, thereby changing the luminance due to both the temperature change and the change with time. Can be prevented.

  In this way, by combining the means for correcting the luminance of the electroluminescent element according to the temperature change and the change with time, it is possible to prevent the burden on the eyes due to the decrease in illuminance, and always provide the illumination with optimum brightness. be able to.

(Embodiment 7)
In this embodiment, a light-emitting device corresponding to one embodiment of the present invention will be described with reference to FIGS. FIG. 10 is a top view of a panel in which a transistor and a light-emitting element formed over a substrate are sealed with a sealing material formed between a counter substrate 4006 and FIG. 10B is a cross-sectional view of FIG. It corresponds to. The configuration of the light emitting element 4011 of this panel has any of the configurations shown in Embodiment Modes 1 to 3.

  A sealant 4005 is provided so as to surround the pixel portion 4002, the signal line driver circuit 4003, and the scan line driver circuit 4004 which are provided over the substrate 4001. A counter substrate 4006 is provided over the pixel portion 4002, the signal line driver circuit 4003, and the scan line driver circuit 4004. Therefore, the pixel portion 4002, the signal line driver circuit 4003, and the scan line driver circuit 4004 are sealed together with the filler 4007 by the substrate 4001, the sealant 4005, and the counter substrate 4006.

  The pixel portion 4002, the signal line driver circuit 4003, and the scan line driver circuit 4004 provided over the substrate 4001 include a plurality of thin film transistors. In FIG. 10B, the thin film transistor 4008 included in the signal line driver circuit 4003 is provided. And a thin film transistor 4010 included in the pixel portion 4002.

  Further, the light-emitting element 4011 is electrically connected to the thin film transistor 4010, and each thin film transistor 4010 is supplied with a signal from the driver. The light-emitting element 4011 can be turned on and off to output an image to the light-emitting device. .

  Further, full color display can be performed by providing color filters 4020 to 4022 corresponding to red, green, and blue on the counter substrate 4006 and emitting light through the color filters. Since light emitted from the light-emitting element 4011 included in the light-emitting device in this embodiment has a broad spectrum, it can be used regardless of the transmission wavelength of the color filter.

  Note that there is no limitation on a method for manufacturing the thin film transistor, and it may be manufactured by a known method.

  A lead wiring 4014 corresponds to a wiring for supplying a signal or a power supply voltage to the pixel portion 4002, the signal line driver circuit 4003, and the scan line driver circuit 4004. The lead wiring 4014 is connected to the connection terminal 4016 through the lead wiring 4015. The connection terminal 4016 is electrically connected to a terminal included in a flexible printed circuit (FPC) 4018 through an anisotropic conductive film 4019.

  Note that as the filler 4007, in addition to an inert gas such as nitrogen or argon, an ultraviolet curable resin or a thermosetting resin can be used, and polyvinyl chloride, acrylic, polyimide, epoxy resin, silicon resin, polyvinyl butyral, Alternatively, ethylene vinylene acetate can be used.

  Note that the display device of the present invention includes in its category a panel in which a pixel portion having a light-emitting element is formed and a module in which an IC is mounted on the panel.

<Synthesis example>
In this synthesis example, 2- (4- (pyren-1-yl) phenyl) -3- (4- (pyren-3-yl) phenyl) quinoxaline (abbreviation: PPQ) represented by the above structural formula (2) is used. This is a synthesis method.

<Step 1: Synthesis of 2,3-bis (4-bromophenyl) quinoxaline>
First, 6.8 g of 1,2-phenylenediamine and 22.1 g of 1,2-bis- (4-bromo-phenyl) -ethane-1,2-dione were dissolved in 350 ml of chloroform and heated to reflux for 3 hours. . Subsequently, it was washed with 1N hydrochloric acid, water and saturated brine, and dried over magnesium sulfate. Thereafter, the mixture was concentrated under reduced pressure to obtain 24.4 g of a white solid 2,3-bis (4-bromophenyl) quinoxaline. The synthesis scheme and the structural formula are shown in the following formula (16).

<Step 2: Synthesis of 2,3-bis (4-dihydroxyborylphenyl) quinoxaline>
First, in a nitrogen atmosphere, 15.8 g of 2,3-bis (4-bromophenyl) quinoxaline obtained in Step 1 above was dissolved in 180 ml of dry tetrahydrofuran (THF) and then cooled to -78 ° C. Subsequently, 50 ml of a normal butyl lithium hexane solution (1.6 M) was slowly added dropwise at -78 ° C. After dripping all, it stirred at -60 degreeC for 3 hours. The mixture was cooled again to -78 ° C, 20 ml of isopropyl borate was added, and the mixture was stirred at -78 ° C for 1 hour, and then stirred overnight at room temperature. Thereafter, the reaction vessel was cooled in an ice bath, 350 ml of 2N hydrochloric acid was added dropwise, and the mixture was stirred for 1 hour. The precipitated solid was collected by suction filtration and dried under reduced pressure to obtain 12.5 g of an orange solid 2,3-bis (4-dihydroxyborylphenyl) quinoxaline. The synthesis scheme and structural formula are shown in the following formula (17).

<Step 3: Synthesis of 2- (4- (pyren-1-yl) phenyl) -3- (4- (pyren-3-yl) phenyl) quinoxaline (abbreviation: PPQ) used in the present invention>
2,3-bis (4-dihydroxyborylphenyl) quinoxaline 5.0 g, 1-bromopyrene 8.4 g, tri (o-tolyl) phosphine 0.64 g, palladium acetate 67 synthesized by the method of Step 2 above under nitrogen atmosphere 0.0 mg was dissolved in 50 ml of dimethoxyethane. Subsequently, an aqueous potassium carbonate solution (12.4 g, 50 ml of pure water) was added, stirred for 10 minutes at room temperature, and then heated and stirred at 80 ° C. for 12 hours. The reaction solution was extracted with ethyl acetate, washed with water and saturated brine, and dried over magnesium sulfate. The solvent was concentrated under reduced pressure to obtain 4.8 g of a yellow solid. Sublimation purification was performed to obtain PPQ. The synthesis scheme and the structural formula are shown in the following formula (18).

FIG. 8 shows the analysis results of the present quinoxaline derivative and PPQ by nuclear magnetic resonance spectroscopy ( ¹ H-NMR).

  Subsequently, FIG. 9 shows an emission spectrum of a light-emitting element manufactured using only PPQ as the emission center.

  The light emitting element is formed by depositing ITO as an anode on an insulating substrate by sputtering, followed by DNTPD as a hole injecting material at 50 nm, TPD as a hole transporting material at 10 nm, and PPQ as a light emitting layer at 40 nm. Then, Alq was formed as an electron transporting material by 20 nm, CaF as an electron injecting material was formed by 1 nm, and Al as a cathode by 150 nm in order, respectively, by vapor deposition.

  As can be seen from FIG. 9, the emission of PPQ has a broad emission spectrum from 425 nm to 725 nm, which has a maximum at around 500 nm, and is very useful for forming light emitting elements, light emitting devices, and lighting devices with excellent color rendering properties. It turns out to be an advantageous material. As described above, the white light emitting element, the light emitting device, and the lighting device using PPQ as a part of the light emission center can be easily made excellent in color rendering.

FIG. 7 illustrates an example of a light-emitting element of the present invention (Embodiment 1). FIG. 7 illustrates an example of a light-emitting element of the present invention (Embodiment 2). FIG. 7 illustrates an example of a light-emitting element of the present invention (Embodiment 3). FIG. 4 illustrates an example of a light-emitting device of the present invention (Embodiment 4). FIG. 10 illustrates an example of a lighting device of the present invention (Embodiment 5). FIG. 10 illustrates an example of a circuit mounted on a light-emitting device of the present invention (Embodiment 6). FIG. 10 illustrates an example of a circuit mounted on a light-emitting device of the present invention (Embodiment 6). The NMR measurement result of the luminescent material (PPQ) used for the light emitting element of this invention. The emission spectrum of the luminescent material (PPQ) used for the light emitting element of this invention. FIG. 7 illustrates an example of a light-emitting device of the present invention (Embodiment 7).

Explanation of symbols

100 substrate 101 first electrode 102 first carrier injection layer 103 first carrier transport layer 104 first light emitting layer 105 second light emitting layer 106 second carrier transport layer 107 second carrier injection layer 108 second Electrode 109 spacing layer 110 laminate 111 sealing material 112 external connection portion 113 counter substrate 114 wiring 120 third carrier transport layer 121 carrier generation layer 122 fourth carrier transport layer 401 current source 402 voltage generation circuit 403 monitor element 404 Electroluminescent Element 405 Constant Voltage Source 406 Operational Amplifier 407 Transistor 408 Resistor 409 Transistor 410 Transistor 411 Resistor 412 Resistor 1001 Illumination 1002 Illumination 1003 Illumination 4001 Substrate 4002 Pixel Unit 4003 Signal Line Driver Circuit 4004 Scan Line Driver Circuit 4005 Sealing Material 4 06 counter substrate 4007 filler 4008 TFT 4010 TFT 4011 light emitting device 4014 wire 4015 wire 4016 connecting terminals 4018 a flexible printed circuit (FPC)
4019 Anisotropic conductive film 4020 Color filter 4021 Color filter 4022 Color filter

Claims (10)

Between a pair of substrates,
Having a light emitting element,
The light emitting element includes an organic compound layer between a pair of electrodes, and the organic compound layer includes at least two kinds of emission center substances, and at least one of the plurality of emission center substances is represented by the following general formula (1). A light-emitting device which is a quinoxaline derivative represented.

(In the general formula (1), R1 to R4 are hydrogen or an alkyl group having 6 carbon atoms (straight chain structure or branched structure).) Between a pair of substrates,
Having a light emitting element,
The light-emitting element includes an organic compound layer between a pair of electrodes, and the organic compound layer includes at least two kinds of emission center substances, and at least one of the plurality of emission center substances is represented by the following general formula (2). A light-emitting device which is a quinoxaline derivative represented.

Between a pair of substrates,
Having a light emitting element,
The light emitting element includes an organic compound layer between a pair of electrodes, and the organic compound layer includes at least two kinds of emission center substances, and at least one of the plurality of emission center substances is represented by the following general formula (3). A light-emitting device which is a quinoxaline derivative represented.

Between a pair of substrates,
Having a light emitting element,
The light-emitting element includes an organic compound layer between a pair of electrodes, and the organic compound layer includes at least two kinds of emission center substances, and at least one of the plurality of emission center substances is represented by the following general formula (4). A light-emitting device which is a quinoxaline derivative represented.

Between a pair of substrates,
Having a light emitting element,
The light-emitting element includes an organic compound layer between a pair of electrodes, and the organic compound layer includes at least two kinds of emission center substances, and at least one of the plurality of emission center substances is represented by the following general formula (5). A light-emitting device which is a quinoxaline derivative represented.

Between a pair of substrates,
Having a light emitting element,
The light-emitting element includes an organic compound layer between a pair of electrodes, and the organic compound layer includes at least two types of emission center substances, and at least one of the plurality of emission center substances is represented by the following general formula (6). A light-emitting device which is a quinoxaline derivative represented.

Between a pair of substrates,
Having a light emitting element,
The light-emitting element includes an organic compound layer between a pair of electrodes, and the organic compound layer includes at least two kinds of emission center substances, and at least one of the plurality of emission center substances is represented by the following general formula (7). A light-emitting device which is a quinoxaline derivative represented.

  8. The light-emitting device according to claim 1, wherein a substance that emits red light is included as one of the emission center substances. 9.   8. The light-emitting device according to claim 1, wherein a substance having an emission spectrum peak at 580 to 750 nm is included as one of the emission center substances. An illuminating device using the light emitting device according to any one of claims 1 to 9.

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