Patent Application
20140377546
The present invention relates to a transparent electrode, an electronic device and an organic electroluminescent element, in particular a transparent electrode having both conductivity and optical transparency, and an electronic device and an organic electroluminescent element each using the transparent electrode.
An organic-field light-emitting element (i.e. an organic electroluminescent element), which utilizes electroluminescence (hereinafter “EL”) of an organic material, is a thin-film type completely-solid state element capable of light emission at a low voltage of about several volts to several ten volts and having many excellent characteristics; for example, high luminescence, high efficiency of light emission, thin and light, and therefore recently has attracted attention as a surface emitting body for backlights of various displays, display boards such as signboards and emergency lights, and light sources of lights.
The organic EL element is configured in such a way that a luminescent layer composed of an organic material is sandwiched between two electrodes, and emission light generated in the luminescent layer passes through the electrode(s) and is extracted to the outside. For that, at least one of the two electrodes is configured as a transparent electrode.
For the transparent electrode, oxide semiconductor materials, such as indium tin oxide (SnO2—In2O3 or ITO), are used in general, but it has been considered to stack ITO and silver in order to reduce resistance. (Refer to, for example, Patent Documents 1 and 2.) However, because ITO uses a rare metal, indium, material costs are high, and also annealing at about 300° C. is needed after its deposition in order to reduce resistance.
Then, there have been proposed an art to realize compatibility of light transmittance and conductivity by making a thin film with an alloy of silver, which has high electrical conductivity, and Mg and an art to make a thin film with Zn and/or Sn, which are easy to obtain at low costs, as raw materials. (Refer to, for example, Patent Documents 3 and 4.)
However, in the art to make a thin film with an alloy of silver and Mg, there are problems that resistance of the obtained thin film is about 100Ω/□, which is insufficient, and that deterioration over time is significant because Mg is easily oxidized. Further, in the art to make a thin film with Zn and/or Sn as raw materials, there are problems, for example, that sufficient resistance cannot be obtained, that a ZnO thin film containing Zn reacts with water, whereby its properties easily change, and that an SnO2 thin film containing Sn is difficult to etch.
Then, objects of the present invention include providing a transparent electrode having sufficient conductivity and optical transparency, and an electronic device and an organic electroluminescent element each provided with the transparent electrode.
In order to achieve the above objects, according to an aspect of the present invention, there is provided a transparent electrode including: a conductive layer; and an intermediate layer disposed adjacent to the conductive layer, wherein the intermediate layer contains a diazacarbazole derivative represented by the following General Formula (1), and the conductive layer is composed of silver as a main component.
In General Formula (1), E1 to E8 each represent C(R1) or N with one of E1 to E4 being N and one of E5 to E8 being N, and R and R1 each represent a hydrogen atom or a substitute.
According to another aspect of the present invention, there is provided an electronic device including the transparent electrode.
According to another aspect of the present invention, there is provided an organic electroluminescent element including the transparent electrode.
The transparent electrode of the present invention is configured in such a way that the conductive layer composed of silver as a main component is disposed on the upper side of the intermediate layer containing the diazacarbazole derivative represented by General Formula (1). Consequently, when the conductive layer is formed on the upper side of the intermediate layer, the silver atom(s) of the conductive layer and the diazacarbazole derivative of the intermediate layer, the diazacarbazole derivative being represented by General Formula (1), react with each other, and the diffusion distance of the silver atom(s) on the surface of the intermediate layer decreases, whereby cohesion of silver is prevented. Hence, the thin film composed of silver, which is easily isolated in the shape of islands by film growth in the nucleus growth mode (Volumer-Weber (VW) mode) in general, is formed by film growth in the layer growth mode (Frank-van der Merwe (FW) mode). Consequently, although being thin, the conductive layer having a uniform thickness can be obtained. As a result, the transparent electrode can be made as the one which ensures conductivity while keeping light transmittance as a thinner layer.
According to the present invention, there can be provided a transparent electrode having sufficient conductivity and optical transparency, and an electronic device and an organic electroluminescent element each provided with the transparent electrode.
Hereinafter, embodiments of the present invention are described in the following order with reference to the drawings.
1. Transparent Electrode
2. Uses of Transparent Electrode
3. First Embodiment of Organic EL Element
4. Second Embodiment of Organic EL Element
5. Third Embodiment of Organic EL Element
6. Uses of Organic EL Elements
7. Illumination Device—1
8. Illumination Device—2
<<1. Transparent Electrode>>
Next, the structures of the base 11 on which the transparent electrode 1 having this multilayer structure is disposed, and the intermediate layer 1a and the conductive layer 1b, which constitute the transparent electrode 1, are detailed in the order named. The “transparent” of the transparent electrode 1 of the present invention means that the light transmittance at a wavelength of 550 nm is 50% or more.
<Base 11>
The base 11 on which the transparent electrode 1 of the present invention is formed is, for example, glass or plastic, but not limited thereto. The base 11 may be transparent or nontransparent. In the case where the transparent electrode 1 of the present invention is used for an electronic device which extracts light from the base 11 side, it is preferable that the base 11 be transparent. Examples of the transparent base 11 used by preference include glass, quartz and a transparent resin film.
Examples of the glass include silica glass, soda-lime silica glass, lead glass, borosilicate glass and alkali-free glass. On the surface of any of these glass materials, as needed, a physical treatment, such as polishing, may be carried out, or a coating composed of an inorganic matter or an organic matter or a hybrid coating composed of these may be formed, in view of adhesion to the intermediate layer 1a, durability and evenness.
Examples of the resin film include polyesters, such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); polyethylene; polypropylene; cellulose esters and their derivatives, such as cellophane, cellulose diacetate, cellulose triacetate, cellulose acetate butyrate, cellulose acetate propionate (CAP), cellulose acetate phthalate (TAC) and cellulose nitrate; polyvinylidene chloride; polyvinyl alcohol; polyethylene vinyl alcohol; syndiotactic polystyrene; polycarbonate; norbornene resin; polymethyl pentene; polyether ketone; polyimide; polyether sulfone (PES); polyphenylene sulfide; polysulfones; polyether imide; polyether ketone imide; polyamide; fluororesin; nylon; polymethyl methacrylate; acrylic; polyarylates; and cycloolefin resins, such as ARTON™ (produced by JSR Corporation) and APEL™ (produced by MITSUI CHEMICALS, INC.).
On the surface of the resin film, a coating composed of an inorganic matter or an organic matter or a hybrid coating composed of these may be formed. It is preferable that this coating or hybrid coating be a barrier film (also called a barrier layer or the like) having a water vapor permeability (at 25±0.5° C. and a relative humidity of 90±2% RH) of 0.01 g/(m2·24 h) or less determined by a method in conformity with JIS-K-7129-1992. It is preferable that the coating or hybrid coating be a high-barrier film having an oxygen permeability of 10−3 ml/(m2·24 h·atm) or less determined by a method in conformity with JIS-K-7126-1987 and a water vapor permeability of 10−5 g/(m2·24 h) or less.
As a material which forms the above-described barrier film, any material can be used as long as it is impermeable to, for example, moisture or oxygen which causes deterioration of an element. Examples thereof include silicon oxide, silicon dioxide and silicon nitride. In order to reduce fragility of the barrier film, it is far preferable that the barrier film have a multilayer structure of an inorganic layer and a layer (organic layer) composed of an organic material. Although the stacking order of the inorganic layer and the organic layer is not particularly limited, it is preferable that these layers be alternately stacked multiple times.
A method for forming the barrier film is not particularly limited. For example, vacuum deposition, sputtering, reactive sputtering, molecular beam epitaxy, cluster ion beam, ion plating, plasma polymerization, atmospheric pressure plasma polymerization, plasma CVD, laser CVD, thermal CVD and coating can be used therefor. However, atmospheric pressure plasma polymerization described in Japanese Patent Application Laid-Open Publication No. 2004-68143 is particularly preferable.
On the other hand, in the case where the base 11 is nontransparent, a metal substrate or film composed of aluminum or stainless steel, a nontransparent resin substrate, a ceramic substrate or the like can be used.
<Intermediate Layer 1a>
The intermediate layer 1a is a layer made with a diazacarbazole derivative represented by the following General Formula (1). In the case where the intermediate layer 1a is formed on the base 11, examples of its forming method include wet processes, such as application, the ink-jet method, coating and dipping, and dry processes, such as vapor deposition (resistance heating, the EB method, etc.), sputtering and CVD. In particular, vapor deposition is used by preference.
[Diazacarbazole Derivative Represented by General Formula (1)]
The diazacarbazole derivative contained in the intermediate layer of the transparent electrode of the present invention is represented by the following General Formula (1).
In General Formula (1), E1 to E8 each represent C(R1) or N, one of E1 to E4 is N, and one of E5 to E8 is N. This R1 is synonymous with the below-described R in General Formula (1).
In General Formula (1), R represents a hydrogen atom or a substituent.
Examples of the substituent represented by R in General Formula (1) include: an alkyl group (for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, a tert-butyl group, a pentyl group, a hexyl group, an octyl group, a dodecyl group, a tridecyl group, a tetradecyl group and a pentadecyl group); a cycloalkyl group (for example, a cyclopentyl group and a cyclohexyl group); an alkenyl group (for example, a vinyl group and an allyl group); an alkynyl group (for example, an ethynyl group and a propargyl group); an aromatic hydrocarbon group (also called an aromatic carbon ring group, an aryl group or the like, for example; a phenyl group, a p-chlorophenyl group, a mesityl group, a tolyl group, a xylyl group, a naphthyl group, an anthryl group, an azulenyl group, an acenaphthenyl group, a fluorenyl group, a phenanthryl group, an indenyl group, a pyrenyl group and a biphenyryl group); an aromatic heterocyclic group (for example, a furyl group, a thienyl group, a pyridyl group, a pyridazinyl group, a pyrimidinyl group, a pyrazinyl group, a triazinyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, a quinazolinyl group, a carbazolyl group, a carbolinyl group, a diazacarbazolyl group (indicating a group formed in such a way that one of carbon atoms constituting a carboline ring of a carbolinyl group is substituted by a nitrogen atom) and a phtharazinyl group); a heterocyclic group (for example, a pyrrolidyl group, an imidazolidyl group, a morpholyl group and an oxazolidyl group); an alkoxy group (for example, a methoxy group, an ethoxy group, a propyloxy group, a pentyloxy group, an hexyloxy group, an octyloxy group and a dodecyloxy group); a cycloalkoxy group (for example, a cyclopentyloxy group and a cyclohexyloxy group); an aryloxy group (for example, a phenoxy group and a naphthyloxy group); an alkylthio group (for example, a methylthio group, an ethylthio group, a propylthio group, a pentylthio group, a hexylthio group, an octylthio group and a dodecylthio group); a cycloalkylthio group (for example, a cyclopentylthio group and a cyclohexylthio group); an arylthio group (for example, a phenylthio group and a naphthylthio group); an alkoxycarbonyl group (for example, a methyloxycarbonyl group, an ethyloxycarbonyl group, a butyloxycarbonyl group, an octyloxycarbonyl group and a dodecyloxycarbonyl group); an aryloxycarbonyl group (for example, a phenyloxycarbonyl group and a naphthyloxycarbonyl group); a sulfamoyl group (for example, an aminosulfonyl group, a methylaminosulfonyl group, a dimethylaminosulfonyl group, a butylaminosulfonyl group, a hexylaminosulfonyl group, a cyclohexylaminosulfonyl group, an octylaminosulfonyl group, a dodecylaminosulfonyl group, a phenylaminosulfonyl group, a naphthylaminosulfonyl group and a 2-pyridylaminosulfonyl group); an acyl group (for example, an acetyl group, an ethylcarbonyl group, a propylcarbonyl group, a pentylcarbonyl group, a cyclohexylcarbonyl group, an octylcarbonyl group, a 2-ethylhexylcarbonyl group, a dodecylcarbonyl group, a phenylcarbonyl group, a naphthylcarbonyl group and a pyridylcarbonyl group); an acyloxy group (for example, an acetyloxy group, an ethylcarbonyloxy group, a butylcarbonyloxy group, an octylcarbonyloxy group, a dodecylcarbonyloxy group and a phenylcarbonyloxy group); an amido group (for example, a methylcarbonylamino group, an ethylcarbonylamino group, a dimethylcarbonylamino group, a propylcarbonylamino group, a pentylcarbonylamino group, a cyclohexylcarbonylamino group, a 2-ethylhexylcarbonylamino group, an octylcarbonylamino group, a dodecylcarbonylamino group, a phenylcarbonylamino group and a naphthylcarbonylamino group); a carbamoyl group (for example, an aminocarbonyl group, a methylaminocarbonyl group, a dimethylaminocarbonyl group, a propylaminocarbonyl group, a pentylaminocarbonyl group, a cyclohexylaminocarbonyl group, an octylaminocarbonyl group, a 2-ethylhexylaminocarbonyl group, a dodecylaminocarbonyl group, a phenylaminocarbonyl group, a naphthylaminocarbonyl group and a 2-pyridylaminocarbonyl group); an ureido group (for example, a methylureido group, an ethylureido group, a pentylureido group, a cyclohexylureido group, an octylureido group, a dodecylureido group, a phenylureido group, a naphthylureido group and a 2-pyridylaminoureido group); a sulfinyl group (for example, a methylsulfinyl group, an ethylsulfinyl group, a butylsulfinyl group, a cyclohexylsulfinyl group, a 2-ethylhexylsulfinyl group, a dodecylsulfinyl group, a phenylsulfinyl group, a naphthylsulfinyl group and a 2-pyridylsulfinyl group); an alkylsulfonyl group (for example, a methylsulfonyl group, an ethylsulfonyl group, a butylsulfonyl group, a cyclohexylsulfonyl group, a 2-ethylhexylsulfonyl group and a dodecylsulfonyl group); an arylsulfonyl group or a heteroarylsulfonyl group (for example, a phenylsulfonyl group, a naphthylsulfonyl group and a 2-pyridylsulfonyl group); an amino group (for example, an amino group, an ethylamino group, a dimethylamino group, a butylamino group, a cyclopentylamino group, a 2-ethylhexylamino group, a dodecylamino group, an anilino group, a naphthylamino group, a 2-pyridylamino group, a piperidyl group (also called a piperidinyl group) and a 2,2,6,6-tetramethyl piperidinyl group); a halogen atom (for example, a fluorine atom, a chlorine atom and a bromine atom); a fluorohydrocarbon group (for example, a fluoromethyl group, a trifluoromethyl group, a pentafluoroethyl group and a pentafluorophenyl group); a cyano group; a nitro group; a hydroxyl group; a mercapto group; a silyl group (for example, a trimethylsilyl group, a triisopropylsilyl group, a triphenylsilyl group and a phenyldiethylsilyl group); a phosphate group (for example, dihexylphosphoryl group); a phosphite group (for example, diphenylphosphinyl group); and a phosphono group.
[Diazacarbazole Derivative Represented by General Formula (2)]
It is preferable that the diazacarbazole derivative represented by General Formula (1) be further represented by the following General Formula (2).
In General Formula (1), E21 to E26 each represent C(R4). This R4 is synonymous with the below-described R3 in General Formula (2).
In General Formula (2), R3 represents a hydrogen atom or a substituent.
Examples of the substituent represented by R3 in General Formula (2) can be the same as those of the substituent represented by R in the above General Formula (1).
[Diazacarbazole Derivative Represented by General Formula (3)]
It is preferable that the diazacarbazole derivative represented by General Formula (1) be further represented by the following General Formula (3).
In General Formula (3), E31 to E42 each represent C(R5). This R5 represents a hydrogen atom or a substituent. Examples of the substituent represented by R5 in General Formula (3) can be the same as those of the substituent represented by R in the above General Formula (1).
In General Formula (3), Y1 represents a divalent linking group composed of an arylene group, a heteroarylene group or a combination thereof.
Examples of the arylene group of the divalent linking group represented by Y1 in General Formula (3) include an o-phenylene group, a p-phenylene group, a naphthalenediyl group, an anthracenediyl group, a naphthacenediyl group, a pyrenediyl group, a naphthylnaphthalenediyl group, a biphenyldiyl group (for example, a [1,1′-biphenyl]-4,4′-diyl group, a 3,3′-biphenyldiyl group and a 3,6-biphenyldiyl group), a terphenyldiyl group, a quaterphenyldiyl group, a quinquephenyldiyl group, a sexiphenyldiyl group, a septiphenyldiyl group, an octiphenyldiyl group, a nobiphenyldiyl group and a deciphenyldiyl group.
Examples of the heteroarylene group of the divalent linking group represented by Y1 in General Formula (3) include divalent groups derived from a group consisting of a carbazole ring, a carboline ring, a diazacarbazole ring (also called a monoazacarboline ring, indicating a ring formed in such a way that one of carbon atoms constituting a carboline ring is substituted by a nitrogen atom), a triazole ring, a pyrrole ring, a pyridine ring, a pyrazine ring, a quinoxaline ring, a thiophene ring, an oxadiazole ring, a dibenzofuran ring, a dibenzothiophene ring and an indole ring.
As the divalent linking group composed of an arylene group, a heteroarylene group or a combination thereof represented by Y1, the heteroarylene group containing a group derived from a condensed aromatic heterocycle formed in such away that three or more rings are condensed is preferable. As the group derived from a condensed aromatic heterocycle formed in such a way that three or more rings are condensed, a group derived from a dibenzofuran ring or a group derived from a dibenzothiophene ring is preferable.
[Specific Examples of Compound]
Specific examples of the compound represented by General Formula (1), (2) or (3) of the present invention are shown below, but the compound is not limited thereto.
<Conductive Layer 1b>
The conductive layer 1b is a layer composed of silver as a main component and is formed on the intermediate layer 1a.
Examples of a method for forming the conductive layer 1b include wet processes, such as application, the ink-jet method, coating and dipping, and dry processes, such as vapor deposition (resistance heating, the EB method, etc.), sputtering and CVD. In particular, vapor deposition is used by preference. By being formed on the intermediate layer 1a, the conductive layer 1b has sufficient conductivity without annealing at high temperature (for example, a heating process at 150° C. or more) after its formation, but, as needed, may be subjected to annealing at high temperature or the like after its formation.
The conductive layer 1b may be composed of an alloy containing silver (Ag). Examples of the alloy include silver magnesium (AgMg), silver copper (AgCu), silver palladium (AgPd), silver palladium copper (AgPdCu) and silver indium (AgIn).
The conductive layer 1b may be configured, as needed, in such a way that a layer containing silver as a main component is divided into a plurality of layers and the layers are stacked.
It is preferable that the thickness of the conductive layer 1b be within a range from 5 to 8 nm. If the thickness is more than 8 nm, an absorbing component or a reflection component of the layer increases and transmittance of the transparent electrode decreases, which is undesirable. On the other hand, if the thickness is less than 5 nm, conductivity of the layer is insufficient, which is undesirable.
The transparent electrode 1 having a multilayer structure of the intermediate layer 1a and the conductive layer 1b formed on the upper side of the intermediate layer 1a may be configured in such a way that the conductive layer 1b has the upper side which is covered with a protective layer or on which another conductive layer is disposed. In this case, in order not to reduce optical transparency of the transparent electrode 1, it is preferable that the protective layer and the above-mentioned another conductive layer have optical transparency. On the lower side of the intermediate layer 1a, namely, between the intermediate layer 1a and the base 11, a layer may also be disposed as needed.
<Effects of Transparent Electrode 1>
The transparent electrode 1 is configured in such a way that the conductive layer 1b composed of silver as a main component is disposed on the intermediate layer 1a made with the diazacarbazole derivative represented by General Formula (1). Consequently, when the conductive layer 1b is formed on the upper side of the intermediate layer 1a, the silver atom(s) of the conductive layer 1b and the diazacarbazole derivative of the intermediate layer 1a, the diazacarbazole derivative being represented by General Formula (1), react with each other, and the diffusion distance of the silver atom(s) on the surface of the intermediate layer 1a decreases, whereby cohesion of silver is prevented.
In general, in forming the conductive layer 1b composed of silver as a main component, thin-film growth is carried out in the nucleus growth mode (Volumer-Weber (VW) mode). Hence, silver particles are easily isolated in the shape of islands, and when the layer is thin, conductivity is difficult to obtain, and sheet resistance increases. Therefore, in order to ensure conductivity, the layer needs to be thick. However, when the layer is thick, the light transmittance decreases, which is improper as a transparent electrode.
However, according to the transparent electrode 1 of the present invention, as described above, cohesion of silver on the intermediate layer 1a is prevented. Hence, in forming the conductive layer 1b composed of silver as a main component, thin-film growth is carried out in the layer growth mode (Frank-van der Merwe (FW) mode).
The “transparent” of the transparent electrode 1 of the present invention means that the light transmittance at a wavelength of 550 nm is 50% or more. Each of the above-mentioned materials used for the intermediate layer 1a has sufficiently excellent optical transparency as compared with the conductive layer 1b composed of silver as a main component. On the other hand, conductivity of the transparent electrode 1 is mainly ensured by the conductive layer 1b. Therefore, as described above, the conductive layer 1b composed of silver as a main component being thinner and ensuring conductivity can increase both conductivity and optical transparency of the transparent electrode 1.
<<2. Uses of Transparent Electrode>>
The transparent electrode 1 thus configured can be used for various electronic devices. Examples of the electronic devices include an organic EL element, an LED (Light Emitting Diode), a liquid crystal element, a solar battery and a touch panel. As an electrode member which requires optical transparency in each of these electronic devices, the transparent electrode 1 can be used.
Hereinafter, as an example of the uses, embodiments of organic EL elements each using the transparent electrode are described.
<<3. First Embodiment of Organic EL Element>>
<Structure of Organic EL Element 100>
An organic EL element 100 shown in
The layer structure of the organic EL element 100 is not limited to the below-described examples and may be a general layer structure. In the embodiment, the transparent electrode 1 functions as an anode (i.e. a positive pole), and the counter electrode 5a functions as a cathode (i.e. a negative pole). For this case, the light-emitting functional layer 3 having a layer structure of a positive hole injection layer 3a, a positive hole transport layer 3b, a luminescent layer 3c, an electron transport layer 3d and an electron injection layer 3e stacked on the transparent electrode 1 as an anode in the order named is shown as an example. It is essential for the light-emitting functional layer 3 to have, among them, at least the luminescent layer 3c made with an organic material. The positive hole injection layer 3a and the positive hole transport layer 3b may be provided as a positive hole transport/injection layer. The electron transport layer 3d and the electron injection layer 3e may be provided as an electron transport/injection layer. Further, of the light-emitting functional layer 3, for example, the electron injection layer 3e may be composed of an inorganic material.
In the light-emitting functional layer 3, in addition to these layers, a positive hole block layer, an electron block layer and the like may be disposed at their needed positions as needed. Further, the luminescent layer 3c may have a plurality of luminescent layers for different colors, the luminescent layers emitting emission light of respective wavelength ranges, and may have a multilayer structure of these luminescent layers stacked with a non-luminescent intermediate layer(s) therebetween. The intermediate layer(s) may double as a positive hole block layer and an electron block layer. Further, the counter electrode 5a as a cathode may also have a multilayer structure as needed. In the structure described above, only the portion where the light-emitting functional layer 3 is sandwiched between the transparent electrode 1 and the counter electrode 5a is a luminescent region in the organic EL element 100.
In the above-described layer structure, in order to reduce resistance of the transparent electrode 1, an auxiliary electrode 15 may be disposed in contact with the conductive layer 1b of the transparent electrode 1.
The organic EL element 100 thus configured is sealed with a sealing member 17, which is described below, on the transparent substrate 13 in order to prevent deterioration of the light-emitting functional layer 3 made with an organic material and the like. The sealing member 17 is fixed to the transparent substrate 13 side with an adhesive 19. Terminal portions of the transparent electrode 1 and the counter electrode 5a are disposed in such a way as to be exposed from the sealing member 17 while being insulated from each other by the light-emitting functional layer 3 on the transparent substrate 13.
Hereinafter, the main layers of the above-described organic EL element 100 are detailed in the following order; the transparent substrate 13, the transparent electrode 1, the counter electrode 5a, the luminescent layer 3c of the light-emitting functional layer 3, other layers of the light-emitting functional layer 3, the auxiliary electrode 15 and the sealing member 17. After that, a production method of the organic EL element 100 is described.
[Transparent Substrate 13]
The transparent substrate 13 is the above-described base 11 on which the transparent electrode 1 of the present invention is disposed, and of the above-described base 11, the base 11 which is transparent and has optical transparency is used therefor.
[Transparent Electrode 1 (Anode)]
The transparent electrode 1 is the above-described transparent electrode 1 of the present invention and configured in such a way that the intermediate layer 1a and the conductive layer 1b are formed on the transparent substrate 13 in the order named. Especially in the embodiment, the transparent electrode 1 functions as an anode, and the conductive layer 1b is the substantial anode.
[Counter Electrode 5a (Cathode)]
The counter electrode 5a is an electrode layer which functions as a cathode for supplying electrons to the light-emitting functional layer 3 and is composed of, for example, a metal, an alloy, an organic or inorganic conductive compound, or a mixture thereof. Examples thereof include: aluminum; silver; magnesium; lithium; magnesium/copper mixture; magnesium/silver mixture; magnesium/aluminum mixture; magnesium/indium mixture; indium; lithium/aluminum mixture; rare-earth metal; and oxide semiconductors, such as ITO, ZnO, TiO2 and SnO2.
The counter electrode 5a can be produced by forming a thin film of any of the above-mentioned conductive materials by vapor deposition, sputtering or another method. It is preferable that the sheet resistance of the counter electrode 5a be several hundred Ω/□ or less. The thickness is selected from normally a range from 5 nm to 5 μm, preferably a range from 5 nm to 200 nm.
In the case where the organic EL element 100 is configured to extract emission light h from the counter electrode 5a side too, the counter electrode 5a should be composed of a conductive material having excellent optical transparency selected from the above-mentioned conductive materials.
[Luminescent Layer 3c]
The luminescent layer 3c used in the present invention contains a phosphorescent compound as a luminescent material.
The luminescent layer 3c is a layer which emits light through recombination of electrons injected from the electrode or the electron transport layer 3d and positive holes injected from the positive hole transport layer 3b. A portion to emit light may be either inside of the luminescent layer 3c or an interface between the luminescent layer 3c and its adjacent layer.
The structure of the luminescent layer 3c is not particularly limited as long as the luminescent material contained therein satisfies a light emission requirement. Further, the luminescent layer 3c may be composed of a plurality of layers having the same emission spectrum and/or maximum emission wavelength. In this case, it is preferable that non-luminescent intermediate layers (not shown) be present in respective spaces between the luminescent layers 3c.
The total thickness of the luminescent layer(s) 3c is preferably within a range from 1 to 100 nm and, in view of obtaining a lower driving voltage, far preferably within a range from 1 to 30 nm. The total thickness of the luminescent layer(s) 3c is, if the non-luminescent intermediate layers are present between the luminescent layers 3c, the thickness including the thickness of the intermediate layers.
In the case where the luminescent layer 3c has a multilayer structure of a plurality of layers stacked, it is preferable to adjust the thickness of each luminescent layer to be within a range from 1 to 50 nm and far preferable to adjust the thickness thereof to be within a range from 1 to 20 nm. In the case where the stacked luminescent layers are for respective luminescent colors of blue, green and red, a relationship between the thickness of the luminescent layer for blue, the thickness of the luminescent layer for green and the thickness of the luminescent layer for red is not particularly limited.
The luminescent layer 3c thus configured can be formed by forming a thin film of a luminescent material with/without a host compound, which are described below, by a well-known thin-film forming method such as vacuum deposition, spin coating, casting, the LB method or the ink-jet method.
The luminescent layer 3c may be composed of a plurality of luminescent materials mixed or a phosphorescent material and a fluorescent material (also called a fluorescent dopant or a fluorescent compound) mixed.
It is preferable that the luminescent layer 3c contain a host compound (also called a luminescent host or the like) and a luminescent material (also called a luminescent dopant compound) and emit light from the luminescent material.
(Host Compound)
The host compound contained in the luminescent layer 3c is a compound exhibiting, in phosphorescence emission at room temperature (25° C.), preferably a phosphorescence quantum yield of less than 0.1 and far preferably a phosphorescence quantum yield of less than 0.01. Further, of the compounds contained in the luminescent layer 3c, a volume percentage of the host compound in the layer being 50% or more is preferable.
As the host compound, one type of well-known host compounds may be used solo, or a plurality of types thereof may be used together. Use of a plurality of types of host compounds enables adjustment of transfer of charges, thereby increasing efficiency of the organic EL element. Further, use of a plurality of types of luminescent materials described below enables mixture of emission light of different colors, thereby producing any luminescent color.
The host compound to be used may be a well-known low molecular weight compound, a high polymer having a repeating unit or a low molecular weight compound (a vapor deposition polymerizable luminescent host) having a polymerizable group such as a vinyl group or an epoxy group.
Of the well-known host compounds, a compound which has a positive hole transport property and an electron transport property, prevents red shift and has a high Tg (glass transition temperature) is preferable. The glass transition temperature Tg here is a value obtained using DSC (Differential Scanning Colorimetry) by a method in conformity with JIS-K-7121.
Specific examples (H1 to H79) of the host compound usable in the present invention are shown below, but the host compound is not limited thereto. In the host compounds H68 to H79, x and y represent a ratio in a random copolymer. The ratio can be x:y=1:10, for example.
As the specific examples of the well-known host compounds, compounds mentioned in the following documents can also be used; for example, Japanese Patent Application Laid-Open Publication Nos. 2001-257076, 2002-308855, 2001-313179, 2002-319491, 2001-357977, 2002-334786, 2002-8860, 2002-334787, 2002-15871, 2002-334788, 2002-43056, 2002-334789, 2002-75645, 2002-338579, 2002-105445, 2002-343568, 2002-141173, 2002-352957, 2002-203683, 2002-363227, 2002-231453, 2003-3165, 2002-234888, 2003-27048, 2002-255934, 2002-260861, 2002-280183, 2002-299060, 2002-302516, 2002-305083, 2002-305084 and 2002-308837.
(Luminescent Material)
Examples of the luminescent material usable in the present invention include a phosphorescent compound (also called a phosphorescent material or the like).
The phosphorescent compound is a compound in which light emission from an excited triplet state is observed, and, to be more specific, a compound which emits phosphorescence at room temperature (25° C.) and exhibits at 25° C. a phosphorescence quantum yield of 0.01 or more, preferably a phosphorescence quantum yield of 0.1 or more.
The phosphorescence quantum yield can be measured by a method mentioned on page 398 of Bunko II of Dai 4 Han Jikken Kagaku Koza 7 (Spectroscopy II of Lecture of Experimental Chemistry vol. 7, 4th edition) (1992, published by Maruzen Co., Ltd.). The phosphorescence quantum yield in a solution can be measured by using various solvents. With respect to the phosphorescent compound used in the present invention, it is only necessary to achieve the above-mentioned phosphorescence quantum yield (0.01 or more) with one of appropriate solvents.
Two types of principles regarding light emission of the phosphorescent compound are cited. One is an energy transfer type, wherein carriers recombine on a host compound to which the carriers are transferred so as to produce an excited state of the host compound, this energy is transferred to a phosphorescent compound, and hence light emission from the phosphorescent compound is carried out. The other is a carrier trap type, wherein a phosphorescent compound serves as a carrier trap, carriers recombine on the phosphorescent compound, and hence light emission from the phosphorescent compound is carried out. In either case, the excited state energy of the phosphorescent compound is required to be lower than that of the host compound.
The phosphorescent compound to be used can be suitably selected from well-known phosphorescent compounds used for luminescent layers of general organic EL elements, preferably a complex compound containing a metal of Groups 8 to 10 in the element periodic table; far preferably an iridium compound, an osmium compound, a platinum compound (a platinum complex compound) or a rare-earth complex; and most preferably an iridium compound.
In the present invention, at least one luminescent layer 3c may contain two or more types of phosphorescent compounds, and a concentration ratio of the phosphorescent compounds in the luminescent layer 3c may vary in a direction of the thickness of the luminescent layer 3c.
It is preferable that the phosphorescent compound(s) in the total amount of the luminescent layer(s) 3c be 0.1 vol % or more and less than 30 vol %.
(Compound Represented by General Formula (4))
The compound (phosphorescent compound) contained in the luminescent layer 3c is preferably a compound represented by the following General Formula (4).
It is preferable that the phosphorescent compound (also called a phosphorescent metal complex) represented by General Formula (4) be contained in the luminescent layer 3c of the organic EL element 100 as a luminescent dopant, but the compound may be contained in a layer of the light-emitting functional layer other than the luminescent layer 3c.
In the above General Formula (4), P and Q each represent a carbon atom or a nitrogen atom; A1 represents an atomic group which forms an aromatic hydrocarbon ring or an aromatic heterocycle with P—C; A2 represents an atomic group which forms an aromatic heterocycle with Q-N; P1-L1-P2 represents a bidentate ligand, P1 and P2 each independently represent a carbon atom, a nitrogen atom or an oxygen atom, and L1 represents an atomic group which forms the bidentate ligand with P1 and P2; j1 represents an integer of one to three, and j2 represents an integer of zero to two, provided that the sum of j1 and j2 is two or three; and M1 represents a transition metal element of Groups 8 to 10 in the element periodic table.
In General Formula (4), P and Q each represent a carbon atom or a nitrogen atom.
Examples of the aromatic hydrocarbon ring which is formed by A1 with P—C in General Formula (4) include a benzene ring, a biphenyl ring, a naphthalene ring, an azulene ring, an anthracene ring, a phenanthrene ring, a pyrene ring, a chrysene ring, a naphthacene ring, a triphenylene ring, an o-terphenyl ring, an m-terphenyl ring, a p-terphenyl ring, an acenaphthene ring, a coronene ring, a fluorene ring, a fluoranthrene ring, a naphthacene ring, a pentacene ring, a perylene ring, a pentaphene ring, a picene ring, a pyrene ring, a pyranthrene ring and an anthranthrene ring.
These rings may each have a substituent represented by R in General Formula (1) too.
Examples of the aromatic heterocycle which is formed by A1 with P—C in General Formula (4) include a furan ring, a thiophene ring, an oxazole ring, a pyrrole ring, a pyridine ring, a pyridazine ring, a pyrimidine ring, a pyrazine ring, a triazine ring, a benzimidazole ring, an oxadiazole ring, a triazole ring, an imidazole ring, a pyrazole ring, a triazole ring, an indole ring, a benzimidazole ring, a benzothiazole ring, a benzoxazole ring, a quinoxaline ring, a quinazoline ring, a phthalazine ring, a carbazole ring and an azacarbazole ring.
The azacarbazole ring indicates a ring formed in such a way that at least one of carbon atoms of a benzene ring constituting a carbazole ring is substituted by a nitrogen atom.
These rings may each have a substituent represented by R in General Formula (1) too.
Examples of the aromatic heterocycle which is formed by A2 with Q-N in General Formula (4) include an oxazole ring, an oxadiazole ring, an oxatriazole ring, an isoxazole ring, a tetrazole ring, a thiadiazole ring, a thiatriazole ring, an isothiazole ring, a pyrrole ring, a pyridine ring, a pyridazine ring, a pyrimidine ring, a pyrazine ring, a triazine ring, an imidazole ring, a pyrazole ring and a triazole ring.
These rings may each have a substituent represented by R in General Formula (1) too.
In General Formula (4), P1-L1-P2 represents a bidentate ligand, P1 and P2 each independently represent a carbon atom, a nitrogen atom or an oxygen atom, and L1 represents an atomic group which forms the bidentate ligand with P1 and P2.
Examples of the bidentate ligand represented by P1-L1-P2 include phenylpyridine, phenylpyrazole, phenylimidazole, phenyltriazole, phenyltetrazole, pyrazabole, acetylacetone and picolinic acid.
In General Formula (4), j1 represents an integer of one to three, and j2 represents an integer of zero to two, provided that the sum of j1 and j2 is two or three. In particular, j2 being zero is preferable.
In General Formula (4), M1 represents a transition metal element (simply called a transition metal) of Groups 8 to 10 in the element periodic table. In particular, M1 being iridium is preferable.
(Compound Represented by General Formula (5))
Of the compounds represented by General Formula (4), a compound represented by the following General Formula (5) is far preferable.
In the above General Formula (5), Z represents a hydrocarbon ring group or a heterocyclic group; P and Q each represent a carbon atom or a nitrogen atom; A1 represents an atomic group which forms an aromatic hydrocarbon ring or an aromatic heterocycle with P—C; A3 represents —C(R01)=C(R02)-, —N═C(R02)-, —C(R01)=N— or —N═N—, and R01 and R02 each represent a hydrogen atom or a substituent; P1-L1-P2 represents a bidentate ligand, P1 and P2 each independently represent a carbon atom, a nitrogen atom or an oxygen atom, and L1 represents an atomic group which forms the bidentate ligand with P1 and P2; j1 represents an integer of one to three, and j2 represents an integer of zero to two, provided that the sum of j1 and j2 is two or three; M1 represents a transition metal element of Groups 8 to 10 in the element periodic table.
Examples of the hydrocarbon ring group represented by Z in General Formula (5) include a non-aromatic hydrocarbon ring group and an aromatic hydrocarbon ring group. Examples of the non-aromatic hydrocarbon ring group include a cyclopropyl group, a cyclopentyl group and a cyclohexyl group. These groups may be each a non-substituted group or may each have a substituent described below.
Examples of the aromatic hydrocarbon ring group (also called an aromatic hydrocarbon group, an aryl group or the like) include a phenyl group, a p-chlorophenyl group, a mesityl group, a tolyl group, a xylyl group, a naphthyl group, an anthryl group, an azulenyl group, an acenaphthenyl group, a fluorenyl group, a phenanthryl group, an indenyl group, a pyrenyl group and a biphenyl group.
These groups may be each a non-substituted group or may each have a substituent represented by R in General Formula (1).
Examples of the heterocyclic group represented by Z in General Formula (5) include a non-aromatic heterocyclic group and an aromatic heterocyclic group. Examples of the non-aromatic heterocyclic group include groups derived from, for example, an epoxy ring, an aziridine ring, a thiirane ring, an oxetane ring, an azetidine ring, a thietane ring, a tetrahydrofuran ring, a dioxorane ring, a pyrrolidine ring, a pyrazolidine ring, an imidazolidine ring, an oxazolidine ring, a tetrahydrothiophene ring, a sulforane ring, a thiazolidine ring, an ε-caprolactone ring, an ε-caprolactam ring, a piperidine ring, a hexahydropyridazine ring, a hexahydropyrimidine ring, a piperazine ring, a morpholine ring, a tetrahydropyrane ring, a 1,3-dioxane ring, a 1,4-dioxane ring, a trioxane ring, a tetrahydrothiopyrane ring, a thiomorpholine ring, a thiomorpholine-1,1-dioxide ring, a pyranose ring and a diazabicyclo[2,2,2]-octane ring.
These groups may be each a non-substituted group or may each have a substituent represented by R in General Formula (1).
Examples of the aromatic heterocyclic group include a pyridyl group, a pyrimidinyl group, a furyl group, a pyrrolyl group, an imidazolyl group, a benzimidazolyl group, a pyrrazolyl group, a pyradinyl group, a triazolyl group (for example, a 1,2,4-triazole-1-yl group and a 1,2,3-triazole-1-yl group), an oxazolyl group, a benzoxazolyl group, a triazolyl group, an isoxazolyl group, an isothiazolyl group, a furazanyl group, a thienyl group, a quinolyl group, a benzofuryl group, a dibenzofuryl group, a benzothienyl group, a dibenzothienyl group, an indolyl group, a carbazolyl group, a carbolinyl group, a diazacarbazolyl group (indicating a group formed in such a way that one of carbon atoms constituting a carboline ring of a carbolinyl group is substituted by a nitrogen atom), a quinoxalinyl group, a pyridazinyl group, a triazinyl group, a quinazolinyl group and a phthalazinyl group.
These groups may be each a non-substituted group or may each have a substituent represented by R in General Formula (1).
The group represented by Z is preferably an aromatic hydrocarbon ring group or an aromatic heterocyclic group.
Examples of the aromatic hydrocarbon ring which is formed by A1 with P—C in General Formula (5) include a benzene ring, a biphenyl ring, a naphthalene ring, an azulene ring, an anthracene ring, a phenanthrene ring, a pyrene ring, a chrysene ring, a naphthacene ring, a triphenylene ring, an o-terphenyl ring, an m-terphenyl ring, a p-terphenyl ring, an acenaphthene ring, a coronene ring, a fluorene ring, a fluoranthrene ring, a naphthacene ring, a pentacene ring, a perylene ring, a pentaphene ring, a picene ring, a pyrene ring, a pyranthrene ring and an anthranthrene ring.
These rings may each have a substituent represented by R in General Formula (1) too.
Examples of the aromatic heterocycle which is formed by A1 with P—C in General Formula (5) include a furan ring, a thiophene ring, an oxazole ring, a pyrrole ring, a pyridine ring, a pyridazine ring, a pyrimidine ring, a pyrazine ring, a triazine ring, a benzimidazole ring, an oxadiazole ring, a triazole ring, an imidazole ring, a pyrazole ring, a triazole ring, an indole ring, a benzimidazole ring, a benzothiazole ring, a benzoxazole ring, a quinoxaline ring, a quinazoline ring, a phthalazine ring, a carbazole ring, a carboline ring and an azacarbazole ring.
The azacarbazole ring indicates a ring formed in such a way that at least one of carbon atoms of a benzene ring constituting a carbazole ring is substituted by a nitrogen atom.
These rings may each have a substituent represented by R in General Formula (1) too.
The substituent represented by each of R01 and R02 in each of —C(R01)=C(R02)-, —N═C(R02)- and —C(R01)=N— represented by A3 in General Formula (5) is synonymous with the substituent represented by R in General Formula (1).
Examples of the bidentate ligand represented by P1-L1-P2 in General Formula (5) include phenylpyridine, phenylpyrazole, phenylimidazole, phenyltriazole, phenyltetrazole, pyrazabole, acetylacetone and picolinic acid.
j1 represents an integer of one to three, and j2 represents an integer of zero to two, provided that the sum of j1 and j2 is two or three. In particular, j2 being zero is preferable.
The transition metal element (simply called a transition metal) of Groups 8 to 10 in the element periodic table represented by M1 in General Formula (5) is synonymous with the transition metal element of Groups 8 to 10 in the element periodic table represented by M1 in General Formula (4).
(Compound Represented by General Formula (6))
Of the compounds represented by the above General Formula (4), a compound represented by the following General Formula (6) is preferable.
In the above General Formula (6), R03 represents a substituent; R04 represents a hydrogen atom or a substituent, and a plurality of R04 may be combined with each other to form a ring; n01 represents an integer of one to four; R05 represents a hydrogen atom or a substituent, and a plurality of R05 may be combined with each other to form a ring; n02 represents an integer of one to two; R06 represents a hydrogen atom or a substituent, and a plurality of R06 may be combined with each other to form a ring; n03 represents an integer of one to four; Z1 represents an atomic group required to form a six-membered aromatic hydrocarbon ring or a five-membered or six-membered aromatic heterocycle with C—C; Z2 represents an atomic group required to form a hydrocarbon ring group or a heterocyclic group; P1-L1-P2 represents a bidentate ligand, P1 and P2 each independently represent a carbon atom, a nitrogen atom or an oxygen atom, and L1 represents an atomic group which forms the bidentate ligand with P1 and P2; j1 represents an integer of one to three, and j2 represents an integer of zero to two, provided that the sum of j1 and j2 is two or three; M1 represents a transition metal element of Groups 8 to 10 in the element periodic table; and R03 and R06, R04 and R06, and R05 and R06 may be each combined with each other to form a ring.
The substituent represented by each of R03, R04, R05 and R06 in General Formula (6) is synonymous with the substituent represented by Y1 in General Formula (1).
Examples of the six-membered aromatic hydrocarbon ring which is formed by Z1 with C—C in General Formula (6) include a benzene ring.
These rings may each have a substituent represented by R in General Formula (1) too.
Examples of the five-membered or six-membered aromatic heterocycle which is formed by Z1 with C—C in General Formula (6) include an oxazole ring, an oxadiazole ring, an oxatriazole ring, an isoxazole ring, a tetrazole ring, a thiadiazole ring, a thiatriazole ring, an isothiazole ring, a thiophene ring, a furan ring, a pyrrole ring, a pyridine ring, a pyridazine ring, a pyrimidine ring, a pyrazine ring, a triazine ring, an imidazole ring, a pyrazole ring and a triazole ring.
These rings may each have a substituent represented by R in General Formula (1) too.
Examples of the hydrocarbon ring group represented by Z2 in General Formula (6) include a non-aromatic hydrocarbon ring group and an aromatic hydrocarbon ring group. Examples of the non-aromatic hydrocarbon ring group include a cyclopropyl group, a cyclopentyl group and a cyclohexyl group. These groups may be each a non-substituted group or may each have a substituent described below.
Examples of the aromatic hydrocarbon ring group (also called an aromatic hydrocarbon group, an aryl group or the like) include a phenyl group, a p-chlorophenyl group, a mesityl group, a tolyl group, a xylyl group, a naphthyl group, an anthryl group, an azulenyl group, an acenaphthenyl group, a fluorenyl group, a phenanthryl group, an indenyl group, a pyrenyl group and a biphenyl group. These groups may be each a non-substituted group or may each have a substituent represented by R in General Formula (1).
Examples of the heterocyclic group represented by Z2 in General Formula (6) include a non-aromatic heterocyclic group and an aromatic heterocyclic group. Examples of the non-aromatic heterocyclic group include groups derived from, for example, an epoxy ring, an aziridine ring, a thiirane ring, an oxetane ring, an azetidine ring, a thietane ring, a tetrahydrofuran ring, a dioxorane ring, a pyrrolidine ring, a pyrazolidine ring, an imidazolidine ring, an oxazolidine ring, a tetrahydrothiophene ring, a sulforane ring, a thiazolidine ring, an ε-caprolactone ring, an ε-caprolactam ring, a piperidine ring, a hexahydropyridazine ring, a hexahydropyrimidine ring, a piperazine ring, a morpholine ring, a tetrahydropyrane ring, a 1,3-dioxane ring, a 1,4-dioxane ring, a trioxane ring, a tetrahydrothiopyrane ring, a thiomorpholine ring, a thiomorpholine-1,1-dioxide ring, a pyranose ring and a diazabicyclo[2,2,2]-octane ring. These groups may be each a non-substituted group or may each have a substituent represented by R in General Formula (1).
Examples of the aromatic heterocyclic group include a pyridyl group, a pyrimidinyl group, a furyl group, a pyrrolyl group, an imidazolyl group, a benzimidazolyl group, a pyrrazolyl group, a pyradinyl group, a triazolyl group (for example, a 1,2,4-triazole-1-yl group and a 1,2,3-triazole-1-yl group), an oxazolyl group, a benzoxazolyl group, a triazolyl group, an isoxazolyl group, an isothiazolyl group, a furazanyl group, a thienyl group, a quinolyl group, a benzofuryl group, a dibenzofuryl group, a benzothienyl group, a dibenzothienyl group, an indolyl group, a carbazolyl group, a carbolinyl group, a diazacarbazolyl group (indicating a group formed in such a way that one of carbon atoms constituting a carboline ring of a carbolinyl group is substituted by a nitrogen atom), a quinoxalinyl group, a pyridazinyl group, a triazinyl group, a quinazolinyl group and a phthalazinyl group.
These rings may be each a non-substituted ring or may each have a substituent represented by R in General Formula (1).
The group which is formed by each of Z1 and Z2 in General Formula (6) is preferably a benzene ring.
The bidentate ligand represented by P1-L1-P2 in General Formula (6) is synonymous with the bidentate ligand represented by P1-L1-P2 in General Formula (4).
The transition metal element of Groups 8 to 10 in the element periodic table represented by M1 in General Formula (6) is synonymous with the transition metal element of Groups 8 to 10 in the element periodic table represented by M1 in General Formula (4).
The phosphorescent compound to be used can be suitably selected from the well-known phosphorescent compounds, which are usable for the luminescent layer 3c of the organic EL element 100.
The phosphorescent compound of the present invention is preferably a complex compound containing a metal of Groups 8 to 10 in the element periodic table; far preferably an iridium compound, an osmium compound, a platinum compound (a platinum complex compound) or a rare-earth complex; and most preferably an iridium compound.
Specific examples (Pt-1 to Pt-3, A-1, and Ir-1 to Ir-45) of the phosphorescent compound of the present invention are shown below, but the present invention is not limited thereto. In these compounds, m and n each represent the number of cycles.
The above-mentioned phosphorescent compounds (also called phosphorescent metal complexes or the like) can be synthesized by employing methods mentioned in documents such as Organic Letter, vol. 3, No. 16, pp. 2579-2581 (2001); Inorganic Chemistry, vol. 30, No. 8, pp. 1685-1687 (1991); J. Am. Chem. Soc., vol. 123, p. 4304 (2001); Inorganic Chemistry, vol. 40, No. 7, pp. 1704-1711 (2001); Inorganic Chemistry, vol. 41, No. 12, pp. 3055-3066 (2002); New Journal of Chemistry, vol. 26, p. 1171 (2002); and European Journal of Organic Chemistry, vol. 4, pp. 695-709 (2004); and reference documents and the like mentioned in these documents.
(Fluorescent Material)
Examples of the fluorescent material include a coumarin dye, a pyran dye, a cyanine dye, a croconium dye, a squarium dye, an oxobenzanthracene dye, a fluorescein dye, a rhodamine dye, a pyrylium dye, a perylene dye, a stilbene dye, a polythiophene dye and a rare-earth complex phosphor.
[Injection Layer: Positive Hole Injection Layer 3a and Electron Injection Layer 3e]
The injection layer is a layer disposed between an electrode and the luminescent layer 3c for reduction of the driving voltage and increase of luminance of light emitted, which is detailed in Part 2, Chapter 2 “Denkyoku Zairyo (Electrode Material)” (pp. 123-166) of “Yuki EL Soshi To Sono Kogyoka Saizensen (Organic EL Element and Front of Industrialization thereof) (Nov. 30, 1998, published by N.T.S Co., Ltd.)”, and examples thereof include the positive hole injection layer 3a and the electron injection layer 3e.
The injection layer can be provided as needed. In the case of the positive hole injection layer 3a, it may be present between the anode and the luminescent layer 3c or the positive hole transport layer 3b. In the case of the electron injection layer 3e, it may be present between the cathode and the luminescent layer 3c or the electron transport layer 3d.
The positive hole injection layer 3a is also detailed in documents such as Japanese Patent Application Laid-Open Publication Nos. 9-45479, 9-260062 and 8-288069, and examples thereof include: a phthalocyanine layer of, for example, copper phthalocyanine; an oxide layer of, for example, vanadium oxide; an amorphous carbon layer; and a high polymer layer using a conductive high polymer such as polyaniline (emeraldine) or polythiophene.
The electron injection layer 3e is also detailed in documents such as Japanese Patent Application Laid-Open Publication Nos. 6-325871, 9-17574 and 10-74586, and examples thereof include: a metal layer of, for example, strontium or aluminum; an alkali metal halide layer of, for example, potassium fluoride; an alkali earth metal compound layer of, for example, magnesium fluoride; and an oxide layer of, for example, molybdenum oxide. It is preferable that the electron injection layer 3e of the present invention be a very thin film, and the thickness thereof be within a range from 1 nm to 10 μm although it depends on the material thereof.
[Positive Hole Transport Layer 3b]
The positive hole transport layer 3b is composed of a positive hole transport material having a function to transport positive holes, and, in a broad sense, the positive hole injection layer 3a and the electron block layer are of the positive hole transport layer 3b. The positive hole transport layer 3b may be composed of a single layer or a plurality of layers.
The positive hole transport material is a material having either the property to inject or transport positive holes or a barrier property against electrons and is either an organic matter or an inorganic matter. Examples thereof include a triazole derivative, an oxadiazole derivative, an imidazole derivative, a polyarylalkane derivative, a pyrazoline derivative, a pyrazolone derivative, a phenylenediamine derivative, an arylamine derivative, an amino-substituted chalcone derivative, an oxazole derivative, a styrylanthracene derivative, a fluorenone derivative, a hydrazone derivative, a stilbene derivative, a silazane derivative, an aniline copolymer and an oligomer of a conductive high polymer such as a thiophene oligomer.
As the positive hole transport material, those mentioned above can be used. However, it is preferable to use a porphyrin compound, an aromatic tertiary amine compound or a styrylamine compound, in particular an aromatic tertiary amine compound.
Representative examples of the aromatic tertiary amine compound and the styrylamine compound include: N,N,N′,N′-tetraphenyl-4,4′-diaminophenyl; N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine (TDP); 2,2-bis(4-di-p-tolylaminophenyl)propane;
High polymer materials in each of which any of these materials is introduced into a high polymer chain or constitutes a main chain of a high polymer can also be used. Inorganic compounds such as a p type-Si and a p type-SiC can also be used as the positive hole injection material and the positive hole transport material.
It is also possible to use so-called p type positive hole transport materials mentioned in documents such as Japanese Patent Application Laid-Open Publication No. 11-251067 and Applied Physics Letters, 80 (2002), p. 139 by J. Huang et. al. In the present invention, it is preferable to use these materials in view of producing a light emitting element having higher efficiency.
The positive hole transport layer 3b can be formed by forming a thin film of any of the above-mentioned positive hole transport materials by a well-known method such as vacuum deposition, spin coating, casting, printing including the ink-jet method, or the LB method. The thickness of the positive hole transport layer 3b is not particularly limited, but it is generally about 5 nm to 5 μm, preferably 5 to 200 nm. The positive hole transport layer 3b may have a single-layer structure composed of one type or two or more types of the above-mentioned materials.
The material of the positive hole transport layer 3b can be doped with impurities so that p property increases. Examples thereof include those mentioned in documents such as Japanese Patent Application Laid-Open Publication Nos. 4-297076, 2000-196140 and 2001-102175 and J. Appl. Phys., 95, 5773 (2004).
Increase of p property of the positive hole transport layer 3b is preferable as it enables production of an element which consumes lower electric power.
[Electron Transport Layer 3d]
The electron transport layer 3d is composed of a material having a function to transport electrons, and, in a broad sense, the electron injection layer 3e and the positive hole block layer (not shown) are of the electron transport layer 3d. The electron transport layer 3d may have a single-layer structure or a multilayer structure of a plurality of layers.
The electron transport material (which doubles as a positive hole block material) which constitutes a layer portion adjacent to the luminescent layer 3c in the electron transport layer 3d having a single-layer structure or in the electron transport layer 3d having a multilayer structure should have a function to transport electrons injected from the cathode to the luminescent layer 3c. The material to be used can be suitably selected from well-known compounds. Examples thereof include a nitro-substituted fluorene derivative, a diphenylquinone derivative, a thiopyrandioxide derivative, carbodiimide, a fluorenylidenemethane derivative, anthraquinodimethane, an anthrone derivative and an oxadiazole derivative. A thiadiazole derivative formed in such a way that an oxygen atom of an oxadiazole ring of an oxadiazole derivative is substituted by a sulfur atom and a quinoxaline derivative having a quinoxaline ring which is well-known as an electron withdrawing group can also be used as the material of the electron transport layer 3d. Further, high polymer materials in each of which any of these materials is introduced into a high polymer chain or constitutes a main chain of a high polymer can also be used.
Still further, metal complexes of 8-quinolinol derivatives such as: tris(8-quinolinol)aluminum (Alq3), tris(5,7-dichloro-8-quinolinol)aluminum, tris(5,7-dibromo-8-quinolinol)aluminum, tris(2-methyl-8-quinolinol)aluminum, tris(5-methyl-8-quinolinol)aluminum and bis(8-quinolinol)zinc (Znq); and metal complexes formed in such a way that central metal of each of the above-mentioned metal complexes is substituted by In, Mg, Cu, Ca, Sn, Ga or Pb can also be used as the material of the electron transport layer 3d.
Yet further, metal-free and metal phthalocyanine and those formed in such a way that an end of each of the above-mentioned materials is substituted by an alkyl group, a sulfonic acid group or the like can also be used as the material of the electron transport layer 3d by preference. Still further, the distyrylpyrazine derivative mentioned as an example of the material of the luminescent layer 3c can also be used as the material of the electron transport layer 3d. Yet further, inorganic semiconductors such as an n type-Si and an n type-SiC can also be used as the material of the electron transport layer 3d, as with the positive hole injection layer 3a and the positive hole transport layer 3b.
The electron transport layer 3d can be formed by forming a thin film of any of the above-mentioned materials by a well-known method such as vacuum deposition, spin coating, casting, printing including the ink-jet method, or the LB method. The thickness of the electron transport layer 3d is not particularly limited, but it is generally about 5 nm to 5 μm, preferably 5 to 200 nm. The electron transport layer 3d may have a single-layer structure composed of one type or two or more types of the above-mentioned materials.
The electron transport layer 3d can be doped with impurities so that n property increases. Examples thereof include those mentioned in documents such as Japanese Patent Application Laid-Open Publication Nos. 4-297076, 10-270172, 2000-196140 and 2001-102175 and J. Appl. Phys., 95, 5773 (2004). It is preferable that the electron transport layer 3d contain potassium, a potassium compound or the like. As the potassium compound, for example, potassium fluoride can be used. Increase of n property of the electron transport layer 3d enables production of an element which consumes lower electric power.
As the material (electron transportable compound) of the electron transport layer 3d, materials which are the same as the above-mentioned materials for the intermediate layer 1a may be used. The same applies to the electron transport layer 3d which doubles as the electron injection layer 3e. Accordingly, materials which are the same as the above-mentioned materials for the intermediate layer 1a may be used therefor.
[Block Layer: Positive Hole Block Layer and Electron Block Layer]
The block layer is provided as needed in addition to the basic constituent layers of the thin film composed of an organic compound(s) as described above. Examples thereof include positive hole block layers mentioned in documents such as Japanese Patent Application Laid-Open Publication Nos. 11-204258 and 11-204359 and p. 273 of “Yuki EL Soshi To Sono Kogyoka Saizensen (Organic EL Element and Front of Industrialization thereof) (Nov. 30, 1998, published by N.T.S Co., Ltd.)”.
The positive hole block layer has a function of the electron transport layer 3d in a broad sense. The positive hole block layer is composed of a positive hole block material having a function to transport electrons with a significantly low property to transport positive holes and can increase recombination probability of electrons and positive holes by blocking positive holes while transporting electrons. The structure of the electron transport layer 3d described below can be used as the positive hole block layer of the present invention as needed. It is preferable that the positive hole block layer be disposed adjacent to the luminescent layer 3c.
On the other hand, the electron block layer has a function of the positive hole transport layer 3b in a broad sense. The electron block layer is composed of a material having a function to transport positive holes with a significantly low property to transport electrons and can increase recombination probability of electrons and positive holes by blocking electrons while transporting positive holes. The structure of the positive hole transport layer 3b described below can be used as the electron block layer as needed. The thickness of the positive hole block layer of the present invention is preferably 3 to 100 nm and far preferably 5 to 30 nm.
[Auxiliary Electrode 15]
The auxiliary electrode 15 is provided in order to reduce resistance of the transparent electrode 1 and disposed in contact with the conductive layer 1b of the transparent electrode 1. As a material which forms the auxiliary electrode 15, a metal having low resistance is preferable. Examples thereof include gold, platinum, silver, copper and aluminum. Because these metals have low optical transparency, the auxiliary electrode 15 is formed by patterning within an extent not to be affected by extraction of emission light h from a light extraction face 13a. Examples of a method for forming the auxiliary electrode 15 include vapor deposition, sputtering, printing, the ink-jet method and the aerosol-jet method. It is preferable that the line width of the auxiliary electrode 15 be 50 μm or less in view of an open area ratio to extract light, and the thickness of the auxiliary electrode 15 be 1 μm or more in view of conductivity.
[Sealing Member 17]
The sealing member 17 covers the organic EL element 100, and may be a plate-type (film-type) sealing member and fixed to the transparent substrate 13 side with the adhesive 19 or may be a sealing layer. The sealing member 17 is disposed in such a way as to cover at least the luminescent layer 3c while exposing the terminal portions of the transparent electrode 1 and the counter electrode 5a of the organic EL element 100. The sealing member 17 may be provided with an electrode, and the terminal portions of the transparent electrode 1 and the counter electrode 5a of the organic EL element 100 may be conductive with this electrode.
Examples of the plate-type (film-type) sealing member 17 include a glass substrate, a polymer substrate and a metal substrate. These substrate materials may be made to be thinner films to use. Examples of the glass substrate include, in particular, soda-lime glass, glass containing barium and strontium, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass and quartz. Examples of the polymer substrate include polycarbonate, acrylic, polyethylene terephthalate, polyether sulfide and polysulfone. Examples of the metal substrate include ones composed of at least one type of metals or alloys selected from the group consisting of stainless steel, iron, copper, aluminum, magnesium, nickel, zinc, chromium, titanium, molybdenum, silicon, germanium and tantalum.
In particular, a polymer substrate or a metal substrate in the shape of a thin film can be used by preference as the sealing member in view of making an element thin.
It is preferable that the film-type polymer substrate have an oxygen permeability of 1×10−3 ml/(m2·24 h·atm) or less determined by a method in conformity with JIS K 7126-1987 and a water vapor permeability (at 25±0.5° C. and a relative humidity of 90±2% RH) of 1×10−3 g/(m2·24 h) or less determined by a method in conformity with JIS K 7129-1992.
The above-mentioned substrate materials may be each processed to be in the shape of a concave plate to be used as the sealing member 17. In this case, the above-mentioned substrate materials are processed by sandblasting, chemical etching or the like to be concave.
The adhesive 19 for fixing the plate-type sealing member 17 to the transparent substrate 13 side is used as a sealing agent for sealing the organic EL element 100 which is sandwiched between the sealing member 17 and the transparent substrate 13. Examples of the adhesive 19 include: photo-curable and thermosetting adhesives having a reactive vinyl group of an acrylic acid oligomer or a methacrylic acid oligomer; and moisture-curable adhesives such as 2-cyanoacrylate.
Examples of the adhesive 19 further include thermosetting and chemical curing (two-liquid-mixed) ones such as an epoxy-based one, still further include hot-melt ones such as polyamide, polyester and polyolefin and yet further include cationic curing ones such as a UV-curable epoxy resin adhesive.
The organic material of the organic EL element 100 is occasionally deteriorated by heat treatment. Therefore, the adhesive 19 is preferably one which is capable of adhesion and curing at from room temperature to 80° C. In addition, a desiccating agent may be dispersed into the adhesive 19.
The adhesive 19 may be applied to an adhesion portion of the sealing member 17 and the transparent substrate 13 with a commercial dispenser or may be printed in the same way as screen printing.
In the case where spaces are formed between the plate-type sealing member 17, the transparent substrate 13 and the adhesive 19, it is preferable, in a gas phase and a liquid phase, to inject an inert gas, such as nitrogen or argon, and an inert liquid, such as fluorohydrocarbon or silicone oil, respectively, into the spaces. The spaces may be made to be vacuum, or a hygroscopic compound may be enclosed therein.
Examples of the hygroscopic compound include: metal oxide (for example, sodium oxide, potassium oxide, calcium oxide, barium oxide, magnesium oxide and aluminum oxide); sulfate (for example, sodium sulfate, calcium sulfate, magnesium sulfate and cobalt sulfate); metal halide (for example, calcium chloride, magnesium chloride, cesium fluoride, tantalum fluoride, cerium bromide, magnesium bromide, barium iodide and magnesium iodide); and perchlorate (for example, barium perchlorate and magnesium perchlorate). With respect to sulfate, metal halide and perchlorate, anhydrous ones are used by preference.
On the other hand, in the case where the sealing layer is used as the sealing member 17, the sealing layer is disposed on the transparent substrate 13 in such a way as to completely cover the light-emitting functional layer 3 of the organic EL element 100 and also expose the terminal portions of the transparent electrode 1 and the counter electrode 5a of the organic EL element 100.
The sealing layer is made with an inorganic material or an organic material, in particular a material impermeable to matters such as moisture and oxygen which cause deterioration of the light-emitting functional layer 3 of the organic EL element 100. Examples of the material to be used include inorganic materials such as silicon oxide, silicon dioxide and silicon nitride. In order to reduce fragility of the sealing layer, the sealing layer may have a multilayer structure of a layer composed of any of these inorganic materials and a layer composed of an organic material.
A method for forming these layers is not particularly limited, and usable methods include vacuum deposition, sputtering, reactive sputtering, molecular beam epitaxy, cluster ion beam, ion plating, plasma polymerization, atmospheric pressure plasma polymerization, plasma CVD, laser CVD, thermal CVD and coating.
[Protective Layer/Protective Plate]
Although not shown in the drawings, a protective layer or protective plate may be disposed in such a way that the organic EL element 100 and the sealing member 17 are sandwiched between the protective layer or protective plate and the transparent substrate 13. The protective layer or protective plate is for mechanical protection of the organic EL element 100. In the case where the sealing member 17 is a sealing layer in particular, it is preferable to provide the protective layer or protective plate because mechanical protection of the organic EL element 100 is not enough.
Usable materials for the protective layer or protective plate include: a glass plate; a polymer plate and a polymer film thinner than that; a metal plate and a metal film thinner than that; a polymer material layer; and a metal material layer. In particular, it is preferable to use a polymer film as it is light and thin.
[Production Method of Organic EL Element 100]
A production method of the organic EL element 100, which is shown in
First, an intermediate layer 1a composed of a compound containing nitrogen atoms is formed on a transparent substrate 13 by a suitable method such as vapor deposition in such a way as to have a thickness of 1 μm or less, preferably 10 nm to 100 nm. Next, a conductive layer 1b composed of silver (or an alloy containing silver as a main component) is formed on the intermediate layer 1a by a suitable method such as vapor deposition in such a way as to have a thickness of 12 nm or less, preferably 4 nm to 9 nm. Thus, a transparent electrode 1 as an anode is produced.
Next, a positive hole injection layer 3a, a positive hole transport layer 3b, a luminescent layer 3c and an electron transport layer 3d are formed on the transparent electrode 1 in the order named, thereby forming a light-emitting functional layer 3. These layers may be formed by spin coating, casting, the ink-jet method, vapor deposition, printing or the like. However, vacuum deposition and spin coating are particularly preferable because, for example, they tend to produce homogeneous layers and hardly generate pinholes. Further, different forming methods may be used to form the respective layers. In the case where vapor deposition is employed to form these layers, although vapor deposition conditions differ depending on, for example, the type of compounds to use, it is generally preferable that the conditions be suitably selected from their respective ranges of: 50° C. to 450° C. for a boat heating temperature; 10−6 Pa to 10−2 Pa for degree of vacuum; 0.01 nm/sec to 50 nm/sec for a deposition rate; −50° C. to 300° C. for a substrate temperature; and 0.1 μm to 5 μm for thickness.
After the light-emitting functional layer 3 is formed in the above-described manner, a counter electrode 5a as a cathode is formed on the upper side thereof by a suitable forming method such as vapor deposition or sputtering. At the time, the counter electrode 5a is formed by patterning to be a shape of being lead from the upper side of the light-emitting functional layer 3 to the periphery of the transparent substrate 13, the terminal portion of the counter electrode 5a being on the periphery of the transparent substrate 13, while being insulated from the transparent electrode 1 by the light-emitting functional layer 3. Thus, the organic EL element 100 is obtained. After that, a sealing member 17 is disposed in such a way as to cover at least the light-emitting functional layer 3 while exposing the terminal portions of the transparent electrode 1 and the counter electrode 5a of the organic EL element 100.
Thus, a desired organic EL element is formed on a transparent substrate 13. In production of an organic EL element 100, it is preferable to produce layers from a light-emitting functional layer 3 to a counter electrode 5a altogether by one vacuum drawing. However, the transparent substrate 13 may be taken out from the vacuum atmosphere halfway and another forming method may be carried out. In this case, consideration should be given, for example, to doing works under a dry inert gas atmosphere.
When a DC voltage is applied to the organic EL element 100 thus obtained, light emission is observed by application of a voltage of about 2 V or more and 40 V or less with the transparent electrode 1 as an anode being the positive polarity and the counter electrode 5a as a cathode being the negative polarity. Alternatively, an AC voltage may be applied thereto. The waveform of the AC voltage to be applied is arbitrary.
<Effects of Organic EL Element 100>
The above-described organic EL element 100 uses the transparent electrode 1 of the present invention having both conductivity and optical transparency as an anode and is provided with the light-emitting functional layer 3 and the counter electrode 5a as a cathode on the upper side of the transparent electrode 1. Hence, the organic EL element 100 can emit light with high luminance by application of a sufficient voltage to between the transparent electrode 1 and the counter electrode 5a, can further increase the luminance by increase of extraction efficiency of emission light h from the transparent electrode 1 side and can extend emission lifetime by reduction of the driving voltage for obtaining desired luminance.
<<4. Second Embodiment of Organic EL Element>>
<Structure of Organic EL Element>
The organic EL element 200 shown in
The layer structure of the organic EL element 200 thus configured is not limited to the below-described examples and hence may be a general layer structure, which is the same as the first embodiment. As an example thereof for the second embodiment, there is shown a layer structure of an electron injection layer 3e, an electron transport layer 3d, a luminescent layer 3c, a positive hole transport layer 3b and a positive hole injection layer 3a staked on the upper side of the transparent electrode 1, which functions as a cathode, in the order named. It is essential to have, among them, at least the luminescent layer 3c composed of an organic material.
In addition to these layers, as described in the first embodiment, the light-emitting functional layer 3 employs various components as needed. In the structure described above, only the portion where the light-emitting functional layer 3 is sandwiched between the transparent electrode 1 and the counter electrode 5b is a luminescent region in the organic EL element 200, which is also the same as the first embodiment.
Further, in the above-described layer structure, in order to reduce resistance of the transparent electrode 1, an auxiliary electrode 15 may be disposed in contact with the conductive layer 1b of the transparent electrode 1, which is also the same as the first embodiment.
The counter electrode 5b used as an anode is composed of, for example, a metal, an alloy, an organic or inorganic conductive compound, or a mixture thereof. Examples thereof include: metals, such as gold (Au); copper iodide (CuI); and oxide semiconductors, such as ITO, ZnO, TiO2 and SnO2.
The counter electrode 5b thus configured can be produced by forming a thin film of any of the above-mentioned conductive materials by vapor deposition, sputtering or another method. It is preferable that the sheet resistance of the counter electrode 5b be several hundred Ω/□ or less. The thickness is selected from normally a range from 5 nm to 5 μm, preferably a range from 5 nm to 200 nm.
In the case where the organic EL element 200 is configured to extract emission light h from the counter electrode 5b side too, as the material of the counter electrode 5b, a conductive material having excellent optical transparency to be used is selected from the above-mentioned conductive materials.
The organic EL element 200 thus configured is, as with the first embodiment, sealed with a sealing member 17 in order to prevent deterioration of the light-emitting functional layer 3.
Detailed structures of the main layers constituting the above-described organic EL element 200 except for the counter electrode 5b used as an anode and a production method of the organic EL element 200 are the same as those of the first embodiment. Hence, detailed description thereof is omitted.
<Effects of Organic EL Element 200>
The above-described organic EL element 200 uses the transparent electrode 1 of the present invention having both conductivity and optical transparency as a cathode and is provided with the light-emitting functional layer 3 and the counter electrode 5b as an anode on the upper side of the transparent electrode 1. Hence, the organic EL element 200 can emit light with high luminance by application of a sufficient voltage to between the transparent electrode 1 and the counter electrode 5a, can further increase the luminance by increase of extraction efficiency of emission light h from the transparent electrode 1 side and can extend emission lifetime by reduction of the driving voltage for obtaining desired luminance.
<<5. Third Embodiment of Organic EL Element>>
<Structure of Organic EL Element>
The organic EL element 300 shown in
The layer structure of the organic EL element 300 thus configured is not limited to the below-described examples and hence may be a general layer structure, which is the same as the first embodiment. As an example thereof for the third embodiment, there is shown a layer structure of a positive hole injection layer 3a, a positive hole transport layer 3b, a luminescent layer 3c and an electron transport layer 3d stacked on the upper side of the counter electrode 5c, which functions as an anode, in the order named. It is essential to have, among them, at least the luminescent layer 3c made with an organic material. The electron transport layer 3d doubles as an electron injection layer 3e and accordingly is provided as an electron transport layer 3d having an electron injection property.
A component specific to the organic EL element 300 of the third embodiment is the electron transport layer 3d having the electron injection property being provided as an intermediate layer 1a of the transparent electrode 1. That is, in the third embodiment, the transparent electrode 1 used as a cathode is composed of the intermediate layer 1a, which doubles as the electron transport layer 3d having the electron injection property, and a conductive layer 1b disposed on the upper side thereof.
This electron transport layer 3d is made with any of the above-mentioned materials for the intermediate layer 1a of the transparent electrode 1.
In addition to these layers, as described in the first embodiment, the light-emitting functional layer 3 employs various components as needed. However, there is no occasion where an electron injection layer or a positive hole block layer is disposed between the electron transport layer 3d, which doubles as the intermediate layer 1a of the transparent electrode 1, and the conductive layer 1b of the transparent electrode 1. In the structure described above, only the portion where the light-emitting functional layer 3 is sandwiched between the transparent electrode 1 and the counter electrode 5c is a luminescent region in the organic EL element 300, which is also the same as the first embodiment.
Further, in the above-described layer structure, in order to reduce resistance of the transparent electrode 1, an auxiliary electrode 15 may be disposed in contact with the conductive layer 1b of the transparent electrode 1, which is also the same as the first embodiment.
The counter electrode 5c used as an anode is composed of, for example, a metal, an alloy, an organic or inorganic conductive compound, or a mixture thereof. Examples thereof include: metals, such as gold (Au); copper iodide (CuI); and oxide semiconductors, such as ITO, ZnO, TiO2 and SnO2.
The counter electrode 5c thus configured can be produced by forming a thin film of any of the above-mentioned conductive materials by vapor deposition, sputtering or another method. It is preferable that the sheet resistance of the counter electrode 5c be several hundred Ω/□ or less. The thickness is selected from normally a range from 5 nm to 5 μm, preferably a range from 5 nm to 200 nm.
In the case where the organic EL element 300 is configured to extract emission light h from the counter electrode 5c side too, as the material of the counter electrode 5c, a conductive material having excellent optical transparency to be used is selected from the above-mentioned conductive materials. In this case, as the substrate 131, one which is the same as the transparent substrate 13 described in the first embodiment is used, and a face of the substrate 131 facing outside is a light extraction face 131a.
<Effects of Organic EL Element 300>
The above-described organic EL element 300 is provided with: as the intermediate layer 1a, the electron transport layer 3d having the electron injection property and constituting the top portion of the light-emitting functional layer 3; and the conductive layer 1b on the upper side thereof, thereby being provided with, as a cathode, the transparent electrode 1 composed of the intermediate layer 1a and the conductive layer 1b on the upper side thereof. Hence, as with the first and second embodiments, the organic EL element 300 can emit light with high luminance by application of a sufficient voltage to between the transparent electrode 1 and the counter electrode 5c, can further increase the luminance by increase of extraction efficiency of emission light h from the transparent electrode 1 side and can extend emission lifetime by reduction of the driving voltage for obtaining desired luminance. In the case where the counter electrode 5c has optical transparency, emission light h can be extracted from the counter electrode 5c side too.
In the third embodiment, the intermediate layer 1a of the transparent electrode 1 doubles as the electron transport layer 3d having the electron injection property. However, the embodiment is not limited thereto, and hence the intermediate layer 1a may double as an electron transport layer 3d not having the electron injection property or double not as an electron transport layer but as an electron injection layer. The intermediate layer 1a may be formed as a very thin film to an extent of not affecting the light emission function of an organic EL element. In this case, the intermediate layer 1a has neither the electron transport property nor the electron injection property.
In the case where the intermediate layer 1a of the transparent electrode 1 is formed as a very thin film to an extent of not affecting the light emission function of an organic EL element, a counter electrode on the substrate 131 and the transparent electrode 1 on the light-emitting functional layer 3 may be a cathode and a anode, respectively. In this case, the light-emitting functional layer 3 is composed of, for example, an electron injection layer 3e, an electron transport layer 3d, a luminescent layer 3c, a positive hole transport layer 3b and a positive hole injection layer 3a stacked on the counter electrode (cathode) on the substrate 131 in the order named. Then, on the upper side thereof, the transparent electrode 1 having a multilayer structure of the very thin intermediate layer 1a and the conductive layer 1b is disposed as an anode.
<<6. Uses of Organic EL Elements>>
Each of the organic EL elements having the above-described structures is a surface emitting body as described above and hence can be used for various light sources. Examples thereof are not limited to but include illumination devices such as a household light and an interior light, backlights of a timepiece and a liquid crystal device, a light of a signboard, a light source of a signal, a light source of an optical storage medium, a light source of an electrophotographic copier, a light source of a device for processing in optical communications and a light source of an optical sensor. The organic EL element can be effectively used for, in particular, a backlight of a crystal liquid display device which is combined with a color filter or a light source of a light.
The organic EL element of the present invention may be used for a sort of lamp, such as a light source of a light or a light source for exposure, or may be used for a projection device which projects images or a direct-view display device of still images and moving images. In this case, with recent increase in size of illumination devices and displays, a luminescent face may be enlarged by two-dimensionally connecting, namely, tiling, luminescent panels provided with organic EL elements thereof.
A driving system thereof used for a display device for moving image playback may be a simple matrix (passive matrix) system or an active matrix system. Further, use of two or more types of organic EL elements of the present invention having different luminescent colors enables production of a color or full-color display device.
Hereinafter, as examples of the uses, an illumination device and an illumination device having a luminescent face enlarged by tiling are described.
<<7. Illumination Device—1>>
An illumination device of the present invention has the above-described organic EL element.
The organic EL element used for an illumination device of the present invention may be designed as an organic EL element having any one of the above-described structures and a resonator structure. Although not limited thereto, the organic EL element configured to have a resonator structure is intended to be used for a light source of an optical storage medium, a light source of an electrophotographic copier, a light source of a device for processing in optical communications and a light source of an optical sensor. The organic EL element may be used for the above-mentioned uses by being configured to carry out laser oscillation.
The materials used for the organic EL element of the present invention are applicable to an organic EL element which emits substantially white light (also called a white organic EL element). For example, white light can be obtained by simultaneously emitting light of different luminescent colors with luminescent materials and mixing the luminescent colors. A combination of luminescent colors may be one containing three maximum emission wavelengths of three primary colors of red, green and blue or one containing two maximum emission wavelengths utilizing a relationship of complementary colors, such as blue and yellow or blue-green and orange.
A combination of luminescent materials to obtain a plurality of luminescent colors may be a combination of a plurality of phosphorescent or fluorescent materials or a combination of a phosphorescent or fluorescent material and a pigment material which emits light with light from the phosphorescent or fluorescent material as excitation light. In a white organic EL element, a plurality of luminescent dopants may be combined and mixed.
Unlike a structure to obtain white light by apposing organic EL elements which emit light of different colors in an array form, this kind of white organic EL element itself emits white light. Hence, most of all the layers constituting the element do not require masks when formed. Consequently, for example, an electrode layer can be formed on the entire surface by vapor deposition, casting, spin coating, the ink-jet method, printing or the like, and accordingly productivity increases.
The luminescent materials used for a luminescent layer (s) of this kind of white organic EL element is not particularly limited. For example, in the case of a backlight of a liquid crystal display element, materials therefor are suitably selected from the metal complexes of the present invention and the well-known luminescent materials to match a wavelength range corresponding to CF (color filter) characteristics and combined, thereby emitting white light.
Use of the above-described white organic EL element enables production of an illumination device which emits substantially white light.
<<8. Illumination Device—2>>
In the illumination device thus configured, the center of each of the luminescent panels 21 is a luminescent region A, and a non-luminescent region B is generated between the luminescent panels 21. Hence, a light extraction member for increasing a light extraction amount from the non-luminescent region B may be disposed in the non-luminescent region B of a light extraction face 13a. As the light extraction member, a light condensing sheet or a light diffusing sheet can be used.
As described below, transparent electrodes of Samples No. 1 to No. 17 were each produced in such a way that the area of a conductive region was 5 cm×5 cm. As each of Samples No. 1 to No. 4, a transparent electrode having a single-layer structure was produced, and as each of Samples No. 5 to No. 17, a transparent electrode having a multilayer structure of an intermediate layer and a conductive layer was produced.
<Production of Transparent Electrodes of Samples No. 1 to No. 4>
The transparent electrode having a single-layer structure of each of Samples No. 1 to No. 4 was produced as described below. First, a base composed of transparent alkali-free glass was fixed to a base holder of a commercial vacuum deposition device, and the base holder was mounted in a vacuum tank of the vacuum deposition device. In addition, silver (Ag) was placed in a tungsten resistive heating board, and the heating board was mounted in the vacuum tank. Next, after the pressure of the vacuum tank was reduced to 4×10−4 Pa, the resistive heating board was electrically heated. Thus, the transparent electrode having a single-layer structure composed of silver was formed on the base at a deposition rate of 0.1 nm/sec to 0.2 nm/sec. Values of the thickness of the transparent electrodes of Samples No. 1 to No. 4 were 5 nm, 8 nm, 10 nm and 15 nm, respectively, which are shown in TABLE 1 below.
<Production of Transparent Electrode of Sample No. 5>
On a base composed of transparent alkali-free glass, Alq3 represented by the following structural formula was deposited by sputtering in advance to form an intermediate layer having a thickness of 25 nm, and on the upper side thereof, a conductive layer composed of silver (Ag) having a thickness of 8 nm was formed by vapor deposition. Thus, the transparent electrode was obtained. The conductive layer was formed by vapor deposition in the same way as that of each of Samples No. 1 to No. 4.
<Production of Transparent Electrode of Sample No. 6>
A base composed of transparent alkali-free glass was fixed to a base holder of the commercial vacuum deposition device, ET-1 represented by the following structural formula was placed in a tantalum resistive heating board, and the base holder and the heating board were mounted in a first vacuum tank of the vacuum deposition device. In addition, silver (Ag) was placed in a tungsten resistive heating board, and the heating board was mounted in a second vacuum tank.
In this state, first, after the pressure of the first vacuum tank was reduced to 4×10−4 Pa, the heating board having ET-1 therein was electrically heated. Thus, an intermediate layer composed of ET-1 having a thickness of 25 nm was formed on the base at a deposition rate of 0.1 nm/sec to 0.2 nm/sec.
Next, the base on which the intermediate layer had been formed was transferred to the second vacuum tank, keeping its vacuum state. After the pressure of the second vacuum tank was reduced to 4×10−4 Pa, the heating board having silver therein was electrically heated. Thus, a conductive layer composed of silver having a thickness of 8 nm was formed at a deposition rate of 0.1 nm/sec to 0.2 nm/sec, and the transparent electrode having a multilayer structure of the intermediate layer and the conductive layer on the upper side thereof was obtained.
<Production of Transparent Electrodes of Samples No. 7 to No. 14>
The transparent electrodes of Samples No. 7 to No. 14 were each produced in the same way as the transparent electrode of Sample No. 6, except that the material of the intermediate layer and the thickness of the conductive layer were changed to those shown in TABLE 1 below.
<Production of Transparent Electrodes of Samples No. 15 to No. 17>
The transparent electrodes of Samples No. 15 to No. 17 were each produced in the same way as the transparent electrode of Sample No. 6, except that the base was changed to PET and the material of the intermediate layer was changed to those shown in TABLE 1 below.
<Evaluation of Transparent Electrodes of Samples No. 1 to No. 17-1>
With respect to each of the produced transparent electrodes of Samples No. 1 to No. 17, light transmittance was measured. The light transmittance was measured with a spectrophotometer (U-3300 manufactured by Hitachi, Ltd.) with a base which was the same as that of each of the samples as a baseline. The result is shown in TABLE 1 below.
<Evaluation of Transparent Electrodes of Samples No. 1 to No. 17-2>
With respect to each of the produced transparent electrodes of Samples No. 1 to No. 17, sheet resistance was measured. The sheet resistance was measured with a resistivity meter (MCP-T610 manufactured by Mitsubishi Chemical Corporation) by the 4-terminal method, 4-pin probe method and constant-current method. The result is shown in TABLE 1 below.
<Evaluation Result of Transparent Electrodes of Samples No. 1 to No. 17>
As it is obvious from TABLE 1, all the transparent electrodes of Samples No. 7 to No. 17 each having the structure of the present invention, in which a conductive layer composed of silver (Ag) as a main component was disposed on an intermediate layer made with a diazacarbazole derivative represented by General Formula (1), had a light transmittance of 58% or more and a sheet resistance of 40Ω/□ or less. On the other hand, all the transparent electrodes of Samples No. 1 to No. 6 each not having the structure of the present invention had a light transmittance of less than 58%, and some of them had a sheet resistance of more than 40Ω/□.
Thus, it was confirmed that the transparent electrodes each having the structure of the present invention had both high light transmittance and high conductivity.
Top-and-bottom emission type organic EL elements respectively using, as anodes, the transparent electrodes of Samples No. 1 to No. 17 produced in First Example were produced. The procedure for producing them is described with reference to
First, a transparent substrate 13 on which the transparent electrode 1 of each of Samples No. 1 to No. 17 produced in First Example has been formed was fixed to a substrate holder of a commercial vacuum deposition device, and a vapor deposition mask was disposed in such a way as to face a formation face of the transparent electrode 1. Further, heating boards in the vacuum deposition device were filled with materials of respective layers constituting a light-emitting functional layer 3 at their respective amounts optimal to form the layers. The heating boards used were composed of a tungsten material for resistance heating.
Next, the pressure of a vapor deposition room of the vacuum deposition device was reduced to 4×10−4 Pa, and the heating boards having the respective materials therein were electrically heated successively so that the layers were formed as described below.
First, the heating board having therein α-NPD as a positive hole transport/injection material represented by the following structural formula was electrically heated. Thus, a positive hole transport/injection layer 31 composed of α-NPD and functioning as both a positive hole injection layer and a positive hole transport layer was formed on the conductive layer 1b of the transparent electrode 1. At the time, the deposition rate was 0.1 nm/sec to 0.2 nm/sec, and the thickness was 20 nm.
Next, the heating board having therein a host material H4 represented by the above structural formula and the heating board having therein a phosphorescent compound Ir-4 represented by the above structural formula were independently electrified. Thus, a luminescent layer 32 composed of the host material H4 and the phosphorescent compound Ir-4 was formed on the positive hole transport/injection layer 31. At the time, the electrification of the heating boards was adjusted in such a way that the deposition rate of the host material H4: the deposition rate of the phosphorescent compound Ir-4=100:6. In addition, the thickness was 30 nm.
Next, the heating board having therein BAlq as a positive hole block material represented by the following structural formula was electrically heated. Thus, a positive hole block layer 33 composed of BAlq was formed on the luminescent layer 32. At the time, the deposition rate was 0.1 nm/sec to 0.2 nm/sec, and the thickness was 10 nm.
After that, the heating boards having therein ET-2 represented by the following structural formula and potassium fluoride, respectively, as electron transport materials were independently electrified. Thus, an electron transport layer 34 composed of ET-2 and potassium fluoride was formed on the positive hole block layer 33. At the time, the electrification of the heating boards was adjusted in such a way that the deposition rate of ET-2: the deposition rate of potassium fluoride=75:25. In addition, the thickness was 30 nm.
Next, the heating board having therein potassium fluoride as an electron injection material was electrically heated. Thus, an electron injection layer 35 composed of potassium fluoride was formed on the electron transport layer 34. At the time, the deposition rate was 0.01 nm/sec to 0.02 nm/sec, and the thickness was 1 nm.
After that, the transparent substrate 13 on which the layers up to the electron injection layer 35 had been formed was transferred from the vapor deposition room of the vacuum deposition device into a treatment room of a sputtering device, the treatment room in which an ITO target as a counter electrode material had been placed, keeping its vacuum state. Next, in the treatment room, an optically transparent counter electrode 5a composed of ITO having a thickness of 150 nm was formed at a deposition rate of 0.3 nm/sec to 0.5 nm/sec as a cathode. Thus, an organic EL element 400 was formed on the transparent substrate 13.
After that, the organic EL element 400 was covered with a sealing member 17 composed of a glass substrate having a thickness of 300 μm, and the space between the sealing member 17 and the transparent substrate 13 was filled with an adhesive 19 (a sealing material) in a state in which the sealing member 17 and the transparent substrate 13 enclosed the organic EL element 400. As the adhesive 19, an epoxy-based photo-curable adhesive (LUXTRAK LC0629B produced by Toagosei Co., Ltd.) was used. The adhesive 19, with which the space between the sealing member 17 and the transparent substrate 13 was filled, was irradiated with UV light from the glass substrate (sealing member 17) side, thereby being cured, so that the organic EL element 400 was sealed.
In forming the organic EL element 400, a vapor deposition mask was used for forming each layer so that the center having an area of 4.5 cm×4.5 cm of the transparent substrate 13 having an area of 5 cm×5 cm became a luminescent region A, and a non-luminescent region B having a width of 0.25 cm was provided all around the luminescent region A. Further, the transparent electrode 1 as an anode and the counter electrode 5a as a cathode were formed in shapes of being lead to the periphery of the transparent substrate 13, their terminal portions being on the periphery of the transparent substrate 13, while being insulated from each other by the light-emitting functional layer 3 composed of the layers from the positive hole transport/injection layer 31 to the electron injection layer 35.
Thus, luminescent panels of Samples No. 1 to No. 17, in each of which the organic EL element 400 was disposed on the transparent substrate 13 and sealed with the sealing member 17 and the adhesive 19, were obtained. In each of these luminescent panels, emission light h of colors generated in the luminescent layer 32 was extracted from both the transparent electrode 1 side, namely, the transparent substrate 13 side, and the counter electrode 5a side, namely, the sealing member 17 side.
<Evaluation of Luminescent Panels of Samples No. 1 to No. 17-1>
With respect to each of the produced luminescent panels of Samples No. 1 to No. 17, light transmittance was measured. The light transmittance was measured with a spectrophotometer (U-3300 manufactured by Hitachi, Ltd.) with a base which was the same as that of each of the samples as a baseline. The result is shown in TABLE 2 below.
<Evaluation of Luminescent Panels of Samples No. 1 to No. 17-2>
With respect to each of the produced luminescent panels of Samples No. 1 to No. 17, a driving voltage was measured. In the driving voltage measurement, front luminance was measured on both the transparent electrode 1 side (i.e. transparent substrate 13 side) and the counter electrode 5a side (i.e. sealing member 17 side) of the luminescent panel, and a voltage of the time when the sum thereof was 1000 cd/m2 was determined as the driving voltage. The luminance was measured with a spectroradiometer CS-1000 (manufactured by Konica Minolta Sensing Inc.). The smaller the obtained value of the driving voltage is, the more favorable result it means.
The result is shown in TABLE 2 below.
<Evaluation Result of Luminescent Panels of Samples No. 1 to No. 17>
As it is obvious from TABLE 2, all the luminescent panels of Samples No. 7 to No. 17 each using the transparent electrode 1 having the structure of the present invention as an anode of the organic EL element had a light transmittance of 54% or more and a driving voltage of 4.0 V or less. On the other hand, all the luminescent panels of Samples No. 1 to No. 6 each using the transparent electrode not having the structure of the present invention as an anode of the organic EL element had a light transmittance of less than 54%, and some of them did not emit light even when a voltage was applied or emitted light with a driving voltage of more than 4.0 V.
Thus, it was confirmed that the organic EL elements each using the transparent electrode having the structure of the present invention were able to emit light with high luminescence at a low driving voltage. Accordingly, it was confirmed that reduction of the driving voltage for obtaining predetermined luminescence and extension of the emission life were expected.
As described above, the present invention is suitable to provide a transparent electrode having sufficient conductivity and optical transparency, and an electronic device and an organic electroluminescent element each provided with the transparent electrode.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-001858 | Jan 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2013/050167 | 1/9/2013 | WO | 00 | 7/10/2014 |
