JPWO2008035595A1 - Organic electroluminescence device - Google Patents

Abstract

The organic electroluminescence device having an excellent emission lifetime is an organic electroluminescence device having at least a light emitting layer containing a host material and a dopant material between a cathode and an anode facing each other. The dopant material is represented by the following general formula (1). The concentration of the dopant material is reduced from the anode side to the cathode side in the thickness direction of the light emitting layer. In the formula, R1 represents a substituent. Z represents a group of nonmetallic atoms necessary to form a 5- to 7-membered ring. N1 represents an integer of 0 to 5. B1 to B5 represent Represents a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom, at least one represents a nitrogen atom, M1 represents a group 8-10 metal in the periodic table, and X1 and X2 represent a carbon atom, a nitrogen atom or an oxygen atom. L1 represents an atomic group forming a bidentate ligand together with X1 and X2.)

Description

  The present invention relates to an organic electroluminescence element.

  Conventionally, as a light-emitting electronic display device, there is an electroluminescence display (hereinafter referred to as ELD). Examples of the constituent elements of ELD include inorganic electroluminescent elements and organic electroluminescent elements (hereinafter also referred to as organic EL elements). Inorganic electroluminescent elements have been used as planar light sources, but an alternating high voltage is required to drive the light emitting elements. An organic EL device has a structure in which a light emitting layer containing a compound that emits light is sandwiched between a cathode and an anode, injects electrons and holes into the light emitting layer, and recombines them to generate excitons (exciton). It is an element that emits light by using light emission (fluorescence / phosphorescence) when this exciton is deactivated, and can emit light at a voltage of several volts to several tens of volts, and is also self-luminous. In addition, it is attracting attention from the viewpoints of space saving, portability and the like because it is a thin film type complete solid element with a wide viewing angle and high visibility.

  However, in organic EL elements for practical use in the future, development of organic EL elements that emit light efficiently and with high luminance with lower power consumption is desired.

  In Japanese Patent No. 3093796, a small amount of a phosphor is doped into a stilbene derivative, a distyrylarylene derivative or a tristyrylarylene derivative to achieve an improvement in light emission luminance and a longer device lifetime. Further, an element having an organic light-emitting layer in which an 8-hydroxyquinoline aluminum complex is used as a host compound and a small amount of phosphor is doped thereto (for example, JP-A 63-264692), and an 8-hydroxyquinoline aluminum complex is used as a host compound. For example, an element having an organic light emitting layer doped with a quinacridone dye (for example, JP-A-3-255190) is known.

  As described above, when light emission from excited singlet is used, the generation ratio of singlet excitons and triplet excitons is 1: 3, and thus the generation probability of luminescent excited species is 25%. Since the efficiency is about 20%, the limit of the external extraction quantum efficiency (ηext) is set to 5%.

  However, since Princeton University reported on an organic EL device using phosphorescence emission from an excited triplet (MA Baldo et al., Nature, 395, 151-154 (1998)), Research on materials that exhibit phosphorescence has become active.

  For example, M.M. A. Baldo et al. , Nature, 403, 17, 750-753 (2000), US Pat. No. 6,097,147, and the like.

  When the excited triplet is used, the upper limit of the internal quantum efficiency is 100%. In principle, the luminous efficiency is four times that of the excited singlet, and there is a possibility that almost the same performance as a cold cathode tube can be obtained. Therefore, it is attracting attention as a lighting application.

  For example, S.M. Lamansky et al. , J .; Am. Chem. Soc. , 123, 4304 (2001), etc., many compounds are being studied for synthesis centering on heavy metal complexes such as iridium complexes.

  In addition, the aforementioned M.I. A. Baldo et al. , Nature, 403, 17, 750-753 (2000), studies have been made using tris (2-phenylpyridine) iridium as a dopant.

In addition, M.M. E. Thompson et al. In The 10th International Works on Inorganic and Organic Electroluminescence (EL'00, Hamamatsu) used L ₂ Ir (acac), for example, (ppy) ₂ Ir (acac), e 0 g, Tetsuo Tsutsui, etc. Again The 10th International Workshop on Inorganic and Organic Electroluminescence (EL'00, Hamamatsu), the dopant as tris (2-(p-tolyl) pyridine) iridium (Ir (ptpy) _3), tris (benzo [H] Quinoline) Iridium (Ir (bzq) ₃ ) and the like have been studied (these metal complexes are generally called ortho-metalated iridium complexes).

  In addition, the S. Lamansky et al. , J .; Am. Chem. Soc. , 123, 4304 (2001) and Japanese Patent Application Laid-Open No. 2001-247859, etc., attempts have been made to form devices using various iridium complexes.

  In order to obtain high luminous efficiency, in the 10th International Workshop on Inorganic and Organic Electroluminescence (EL'00, Hamamatsu), Ikai et al. Uses a hole transporting compound as a host of a phosphorescent compound. In addition, M.M. E. Thompson et al. Use various electron transporting materials as a host of phosphorescent compounds, doped with a novel iridium complex.

  Orthometalated complexes in which the central metal is platinum instead of iridium are also attracting attention. With respect to this type of complex, many examples are known in which ligands are characterized.

  In either case, the light emission brightness and light emission efficiency of the light emitting device are greatly improved compared to conventional devices because the emitted light is derived from phosphorescence. There was a problem that it was lower than the conventional element. As described above, it is difficult for phosphorescent high-efficiency light-emitting materials to shorten the light emission wavelength and improve the light-emission lifetime of the device, and have not been able to achieve practically sufficient performance.

  In addition, regarding wavelength shortening, introduction of electron-withdrawing groups such as fluorine atoms, trifluoromethyl groups, and cyano groups into phenylpyridine as substituents, and picolinic acid and pyrazabole-based ligands as ligands However, with these ligands, the emission wavelength of the luminescent material is shortened to achieve a blue color, and a high-efficiency device can be achieved. There was a need to improve the trade-off.

  As a ligand, a metal complex in which a carbazole partial structure is introduced into the mother nucleus of phenylpyridine is known (see, for example, Patent Documents 1 and 2). In addition, a metal complex in which a partial structure of carbazole is introduced as a ligand into the mother nucleus of phenylpyrazole is known (for example, see Patent Document 3). As disclosed herein, by introducing a condensed ring structure composed of three or more rings containing heteroatoms into the structure of the ligand of the metal complex, the lifetime of the light emitting device can be improved. There is still room for improvement in terms of chromaticity.

  On the other hand, examples in which various substituents are introduced using phenylimidazole as a basic skeleton as a ligand are disclosed (for example, see Patent Documents 4 and 5).

  In addition, in an organic EL device having a light emitting layer containing a metal complex, the light emitting region in the light emitting layer, that is, the concentration of the content of the metal complex is controlled to control the light emitting position at the light emitting layer interface. The lifetime has been increased (for example, see Patent Documents 6 and 7).

However, these technologies do not show a significant improvement in the light emission lifetime, and there is room for improvement.
Japanese Patent Laid-Open No. 2004-67658 Japanese Patent Laid-Open No. 2005-23070 International Publication No. 04/085450 Pamphlet International Publication No. 05/007767 Pamphlet JP 2005-68110 A JP 2003-229272 A JP 2005-108730 A

  The objective of this invention is providing the organic electroluminescent element excellent in the light emission lifetime.

  The above object of the present invention is achieved by the following configurations.

  1. In an organic electroluminescence device having at least a light-emitting layer containing a host material and a dopant material between an opposing cathode and an anode, the dopant material is represented by the following general formula (1), and the content concentration of the dopant material emits light. An organic electroluminescence element, wherein the thickness decreases from the anode side to the cathode side in the thickness direction of the layer.

(In the formula, R ₁ represents a substituent. Z represents a group of nonmetallic atoms necessary to form a 5- to 7-membered ring. N1 represents an integer of 0 to _5. B _{1 to} B ₅ represent carbon. Represents an atom, nitrogen atom, oxygen atom or sulfur atom, at least one represents a nitrogen atom, M ₁ represents a group 8-10 metal in the periodic table, and X ₁ and X ₂ represent a carbon atom, nitrogen atom or Represents an oxygen atom, and L ₁ represents an atomic group forming a bidentate ligand together with X ₁ and X ₂ , m1 represents an integer of 1, 2 or 3, m2 represents an integer of 0, 1 or 2 (Where m1 + m2 is 2 or 3)
2. 2. The organic electroluminescence device as described in 1 above, wherein the concentration of the dopant material is gradually decreased from the anode side to the cathode side.

  3. 2. The organic electroluminescence device according to 1 above, wherein the concentration of the dopant material is continuously decreased from the anode side to the cathode side.

  4). 4. The organic electroluminescence device according to any one of 1 to 3, wherein m2 in the dopant material represented by the general formula (1) is 0.

5). 5. The organic according to any one of 1 to 4, wherein the nitrogen-containing heterocycle formed by B _{1 to} B ₅ in the dopant material represented by the general formula (1) is an imidazole ring. Electroluminescence element.

  6). 6. The organic electroluminescence device according to any one of 1 to 5, wherein in the light emitting layer, the ionization potential Iph of the host material and the ionization potential Ipd of the dopant material satisfy the following formula (1).

Formula (1) Iph-Ipd ≧ 0.7
7). A / B ≧ 1.5 is satisfied when the concentration of the dopant material contained on the anode side of the light emitting layer is A mass% and the concentration of the dopant material contained on the cathode side is B mass%. The organic electroluminescent element of any one of 1-6.

  8). The phosphorescence wavelength peak of the dopant material is 480 nm or less, The organic electroluminescence element described in any one of 1 to 7 above.

  9. The organic electroluminescence device according to any one of 1 to 8, further comprising another light emitting layer.

  10. 10. The organic electroluminescence device according to any one of 1 to 9, wherein the light emission is white.

  According to the present invention, an organic electroluminescence device having an excellent emission lifetime can be provided.

  Hereinafter, the present invention will be described in detail.

  The present invention relates to an organic electroluminescence device (hereinafter also referred to as an organic EL device) having at least a light emitting layer containing a host material and a dopant material between a cathode and an anode facing each other. The concentration of the dopant material is reduced from the anode side to the cathode side in the thickness direction of the light emitting layer.

  In the present invention, the gradual decrease from the anode side to the cathode side means that the dopant content is constant in the range of 2 nm or more.

  In the present invention, in order to decrease the dopant material content concentration from the anode side to the cathode side in the thickness direction of the light-emitting layer, in the co-evaporation of the host material and the dopant material, the deposition rate is changed by controlling the deposition temperature. A continuous decrease can be achieved. Moreover, the intended stepwise reduction can be achieved by controlling the shutter of the vapor deposition apparatus together with the change of the vapor deposition rate.

  Until now, in an organic EL device having a light emitting layer containing a dopant material, the light emitting region in the light emitting layer, that is, the light emission position at the light emitting layer interface is controlled by controlling the concentration of the content of the dopant material, It has been practiced to extend the life (for example, JP-A-2003-229272 and JP-A-2005-108730).

  In the case of a phosphorescent light emitting device using light emission from an excited triplet, the generation ratio of singlet excitons and triplet excitons is 1: 3 compared to a fluorescent light emitting device using light emission from an excited singlet. Since the upper limit of the quantum efficiency is 100%, in principle, the light emission efficiency is four times that of the excited singlet, and highly efficient light emission can be obtained. However, it is known that phosphorescent light-emitting elements have a poor life compared to fluorescent light-emitting elements, and in particular, blue phosphorescent light-emitting elements are still insufficient for practical use.

  As a result of intensive studies, we have found that a long-lived phosphorescent light-emitting device can be obtained with the dopant material represented by the general formula (1). As a result of further intensive studies, in the phosphorescent light emitting device using the dopant material represented by the general formula (1), a change in the doping concentration in the light emitting layer, specifically, a concentration gradient (anode) from the anode side to the cathode side. It was found that the light emission life was further extended by attaching a high concentration on the side and a low concentration on the cathode side, and the present invention was completed.

  Such a concentration gradient is confirmed by cutting the light emitting layer obliquely and measuring with TOF-SIMS. In the oblique cutting, as a pretreatment, an oblique cross section is prepared with Cycus NN04 (manufactured by Daipla Intes). When the light emitting layer contains a plurality of dopants, it can be distinguished by the difference in molecular weight.

  The TOF-SIMS measurement can be performed by using a time-of-flight secondary ion mass spectrometer TRIFT2 manufactured by Physical Electronics, Inc., and using In ions with an acceleration voltage of 25 kV (beam current is 2 nA) as primary ions.

  Although the cause of the surprising effect of the phosphorescent light emitting device according to the present invention has not been clarified in detail, the present inventors consider the factor as follows. However, the factor is not limited to this.

  In the light emitting layer, the dopant material exists in a state of being dispersed in the host material. When the difference between the ionization potential Ipd of the dopant material and the ionization potential Iph of the host material is large (for example, Iph−Ipd ≧ 0.7 eV), it is considered that the dopant material becomes a deep trap for holes. At this time, if the concentration of the dopant material contained in the light emitting layer is low, holes trapped in the dopant material having a small ionization potential cannot move to the adjacent dopant material contained in the light emitting layer, and the cathode It is thought that the hole is often trapped without being able to move to the side. For this reason, it is considered that the light emission is biased toward the anode side interface region of the light emitting layer, so that it is considered that deterioration in the anode side interface region of the light emitting layer is likely to occur. It is thought that.

  The ionization potential is defined as the energy required to emit electrons at the HOMO (highest occupied molecular orbital) level of a compound to the vacuum level. Specifically, electrons from a compound in a film state (layer state) This is the energy required for extraction, which can be measured directly by photoelectron spectroscopy. For example, it can be measured by ESCA 5600 UPS (ultraviolet photoemission spectroscopy) manufactured by ULVAC-PHI.

  In order to solve this problem, by increasing the concentration of the dopant material in the anode side interface region, the holes trapped in the dopant molecules on the anode side are moved to the cathode side, and the deterioration occurs only in the region on the anode side interface. The lifetime of the organic electroluminescent device was studied by extending the emission region to the cathode side, and the lifetime of the compound represented by the general formula (1), particularly the blue light emitting dopant material, was increased. The effect of was found to be surprisingly great.

  When the concentration of the dopant material contained on the anode side of the light emitting layer is A mass% and the concentration of the dopant material contained on the cathode side is B mass%, in the present invention, A / B ≧ 1.5 is satisfied. The upper limit is preferably 20, the upper limit is preferably 10, and the upper limit is more preferably 5.

Here, the anode side concentration (A mass%) means a dopant concentration contained within 1 nm of the thickness of the light emitting layer from the interface between the light emitting layer and the layer adjacent to the anode side of the light emitting layer. (B mass%) refers to the dopant concentration contained within 1 nm of the thickness of the light emitting layer from the interface between the light emitting layer adjacent to the cathode side and the light emitting layer, while the ionization potential Ipd of the dopant material When the difference in the ionization potential Iph of the host material is small (for example, Iph-Ipd <0.7), the hole can be moved to the cathode side because the trap of the hole by the dopant material is weak. In this case, it is considered that the effect of extending the lifetime is small in the organic EL element provided with the concentration gradient.

<< Dopant Material Represented by Formula (1) >>
In the dopant material represented by the general formula (1) of the present invention, examples of the substituent represented by R ₁ include an alkyl group (for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, a t-butyl group). , Pentyl group, hexyl group, octyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, etc.), cycloalkyl group (eg, cyclopentyl group, cyclohexyl group, etc.), alkenyl group (eg, vinyl group, allyl group, etc.) , Alkynyl groups (for example, ethynyl group, propargyl group, etc.), aromatic hydrocarbon ring groups (also called aromatic carbocyclic groups, aryl groups, etc.), for example, phenyl group, p-chlorophenyl group, mesityl group, tolyl group, xylyl Group, naphthyl group, anthryl group, azulenyl group, acenaphthenyl group, fluorenyl group, phenanthryl group, For example, pyridyl group, pyrimidinyl group, furyl group, pyrrolyl group, imidazolyl group, benzoimidazolyl group, pyrazolyl group, pyrazinyl group, triazolyl group (for example, 1, 2,4-triazol-1-yl group, 1,2,3-triazol-1-yl group, etc.), oxazolyl group, benzoxazolyl group, thiazolyl group, isoxazolyl group, isothiazolyl group, furazanyl group, 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 (one of the carbon atoms constituting the carboline ring of the carbolinyl group is a nitrogen atom) ), Quinoxalinyl group, Pyridazinyl group, triazinyl group, quinazolinyl group, phthalazinyl group, etc.), heterocyclic group (eg, pyrrolidyl group, imidazolidyl group, morpholyl group, oxazolidyl group, etc.), alkoxy group (eg, methoxy group, ethoxy group, propyloxy group, pentyl) Oxy group, hexyloxy group, octyloxy group, dodecyloxy group, etc.), cycloalkoxy group (eg, cyclopentyloxy group, cyclohexyloxy group, etc.), aryloxy group (eg, phenoxy group, naphthyloxy group, etc.), alkylthio group (For example, methylthio group, ethylthio group, propylthio group, pentylthio group, hexylthio group, octylthio group, dodecylthio group, etc.), cycloalkylthio group (for example, cyclopentylthio group, cyclohexylthio group, etc.), arylthio group ( For example, phenylthio group, naphthylthio group, etc.), alkoxycarbonyl group (eg, methyloxycarbonyl group, ethyloxycarbonyl group, butyloxycarbonyl group, octyloxycarbonyl group, dodecyloxycarbonyl group, etc.), aryloxycarbonyl group (eg, Phenyloxycarbonyl group, naphthyloxycarbonyl group, etc.), sulfamoyl group (for example, aminosulfonyl group, methylaminosulfonyl group, dimethylaminosulfonyl group, butylaminosulfonyl group, hexylaminosulfonyl group, cyclohexylaminosulfonyl group, octylaminosulfonyl group) , Dodecylaminosulfonyl group, phenylaminosulfonyl group, naphthylaminosulfonyl group, 2-pyridylaminosulfonyl group, etc.), acyl group (for example, Til group, ethylcarbonyl group, propylcarbonyl group, pentylcarbonyl group, cyclohexylcarbonyl group, octylcarbonyl group, 2-ethylhexylcarbonyl group, dodecylcarbonyl group, phenylcarbonyl group, naphthylcarbonyl group, pyridylcarbonyl group, etc.), acyloxy group ( For example, acetyloxy group, ethylcarbonyloxy group, butylcarbonyloxy group, octylcarbonyloxy group, dodecylcarbonyloxy group, phenylcarbonyloxy group, etc.), amide group (for example, methylcarbonylamino group, ethylcarbonylamino group, dimethylcarbonyl) Amino group, propylcarbonylamino group, pentylcarbonylamino group, cyclohexylcarbonylamino group, 2-ethylhexylcarbonylamino group, octylcal Bonylamino group, dodecylcarbonylamino group, phenylcarbonylamino group, naphthylcarbonylamino group, etc.), carbamoyl group (for example, aminocarbonyl group, methylaminocarbonyl group, dimethylaminocarbonyl group, propylaminocarbonyl group, pentylaminocarbonyl group, cyclohexyl) Aminocarbonyl group, octylaminocarbonyl group, 2-ethylhexylaminocarbonyl group, dodecylaminocarbonyl group, phenylaminocarbonyl group, naphthylaminocarbonyl group, 2-pyridylaminocarbonyl group, etc.), ureido group (for example, methylureido group, ethylureido) Group, pentylureido group, cyclohexylureido group, octylureido group, dodecylureido group, phenylureido group, naphthylureido group, 2-pyri Sulfinyl group (for example, methylsulfinyl group, ethylsulfinyl group, butylsulfinyl group, cyclohexylsulfinyl group, 2-ethylhexylsulfinyl group, dodecylsulfinyl group, phenylsulfinyl group, naphthylsulfinyl group, 2-pyridylsulfinyl group) Group), alkylsulfonyl group (for example, methylsulfonyl group, ethylsulfonyl group, butylsulfonyl group, cyclohexylsulfonyl group, 2-ethylhexylsulfonyl group, dodecylsulfonyl group, etc.), arylsulfonyl group or heteroarylsulfonyl group (for example, phenyl) Sulfonyl group, naphthylsulfonyl group, 2-pyridylsulfonyl group, etc.), amino group (for example, amino group, ethylamino group, dimethylamino group, butyryl) Group, cyclopentylamino group, 2-ethylhexylamino group, dodecylamino group, anilino group, naphthylamino group, 2-pyridylamino group, etc.), cyano group, nitro group, hydroxy group, mercapto group, silyl group (for example, trimethylsilyl group) , Triisopropylsilyl group, triphenylsilyl group, phenyldiethylsilyl group, etc.). Of these substituents, preferred are an alkyl group and an aryl group.

  Z represents a nonmetallic atom group necessary for forming a 5- to 7-membered ring. Examples of the 5- to 7-membered ring formed by Z include a benzene ring, naphthalene ring, pyridine ring, pyrimidine ring, pyrrole ring, thiophene ring, pyrazole ring, imidazole ring, oxazole ring, and thiazole ring. Of these, a benzene ring is preferred.

B ₁ .about.B ₅ represents a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom, at least one nitrogen atom. The aromatic nitrogen-containing heterocycle formed by these five atoms is preferably a monocycle. Examples include pyrrole ring, pyrazole ring, imidazole ring, triazole ring, tetrazole ring, oxazole ring, isoxazole ring, thiazole ring, isothiazole ring, oxadiazole ring, and thiadiazole ring. Of these, a pyrazole ring and an imidazole ring are preferable, and an imidazole ring is more preferable. These rings may be further substituted with the above substituents. Preferred as the substituent are an alkyl group and an aryl group, and more preferred is an aryl group.

L ₁ represents an atomic group that forms a bidentate ligand together with X ₁ and X ₂ . Specific examples of the bidentate ligand represented by X ₁ -L ₁ -X ₂ include, for example, substituted or unsubstituted phenylpyridine, phenylpyrazole, phenylimidazole, phenyltriazole, phenyltetrazole, pyrazabol, picolinic acid And acetylacetone.

  These groups may be further substituted with the above substituents.

  m1 represents an integer of 1, 2 or 3, m2 represents an integer of 0, 1 or 2, and m1 + m2 is 2 or 3. Especially, the case where m2 is 0 is preferable.

As the metal represented by M ₁ , a transition metal element of group 8 to 10 of the periodic table (also simply referred to as a transition metal) is used, among which iridium and platinum are preferable, and iridium is more preferable.

  In addition, the dopant material represented by General formula (1) of this invention does not need to have a polymeric group or a reactive group.

Among the dopant materials represented by the general formula (1), a dopant material represented by the following general formula (2) in which the nitrogen-containing heterocycle formed by B _{1 to} B ₅ is an imidazole ring is preferable.

In the general formula (2), R ₁ , R ₂ and R ₃ represent substituents and have the same meaning as the substituent represented by R ₁ in the general formula (1). Z, n1, M ₁ , X ₁ , X ₂ , L ₁ , m1, and m2 are synonymous with those in the general formula (1).

In the general formula (2), a dopant material in which R ₂ is represented by the following is more preferable.

R ₄ represents a substituent having a steric parameter value (Es value) of −0.5 or less.

  Here, the Es value is a steric parameter derived from chemical reactivity. The smaller this value, the more sterically bulky substituent can be said.

  Hereinafter, the Es value will be described. In general, in ester hydrolysis under acidic conditions, it is known that the influence of substituents on the progress of the reaction may only be considered as steric hindrance. The Es value is obtained by quantifying the steric hindrance.

The Es value of the substituent X is expressed by the following chemical reaction formula: X—CH ₂ COORX + H ₂ O → X—CH ₂ COOH + RXOH
The reaction rate constant kX for hydrolyzing an α-monosubstituted acetic acid ester derived from α-monosubstituted acetic acid in which one hydrogen atom of the methyl group of acetic acid is substituted with the substituent X represented by the formula And the following chemical reaction formula CH ₃ COORY + H ₂ O → CH ₃ COOH + RYOH
(RX is the same as RY) represented by the following formula from the reaction rate constant kH when the acetate corresponding to the α-monosubstituted acetate described above is hydrolyzed under acidic conditions.

Es = log (kX / kH)
The reaction rate decreases due to the steric hindrance of the substituent X, and as a result, kX <kH, so the Es value is usually negative. When the Es value is actually obtained, the above two reaction rate constants kX and kH are obtained and calculated by the above formula.

  Specific examples of Es values are given by Unger, S. et al. H. Hansch, C .; , Prog. Phys. Org. Chem. 12, 91 (1976). The specific numerical values are also described in “Structure-activity relationship of drugs” (Regional Chemistry Special Issue 122, Nankodo) and “American Chemical Society Reference Book, 'Exploring QSAR' p.81 Table 3-3”. There is. Next, a part is shown in Table 1.

  Here, it should be noted that the Es value as defined in this specification is not defined by defining that of a methyl group as 0, but by assuming that a hydrogen atom is 0, and an Es value where a methyl group is 0. Minus 1.24.

  In the present invention, the Es value is −0.5 or less. Preferably it is -7.0 or more and -0.6 or less. Most preferably, it is -7.0 or more and -1.0 or less.

  Specific examples of the dopant material represented by the general formula (1) according to the present invention are given below, but the present invention is not limited thereto.

  These metal complexes are described in, for example, Organic Letter, vol. 16, 2579-2581 (2001), Inorganic Chemistry, Vol. 30, No. 8, 1685-1687 (1991), J. Am. Am. Chem. Soc. , 123, 4304 (2001), Inorganic Chemistry, Vol. 40, No. 7, 1704-1711 (2001), Inorganic Chemistry, Vol. 41, No. 12, 3055-3066 (2002) , New Journal of Chemistry. 26, 1171 (2002), European Journal of Organic Chemistry, Vol. 4, pages 695-709 (2004), and further synthesized by applying methods such as references described in these documents. it can.

  In the present invention, the phosphorescence wavelength of a compound is the 0-0 band of the phosphorescence spectrum. The 0-0 band of the phosphorescence spectrum can be obtained by the following measurement method.

  The compound to be measured is dissolved in well-deoxygenated methylene chloride, put into a phosphorescence measurement cell, irradiated with excitation light at room temperature (25 ° C.), and the emission spectrum is measured. Moreover, about the compound which cannot be melt | dissolved in the said solvent type | system | group, you may use the arbitrary solvent which can melt | dissolve the compound.

  Next, the 0-0 band is determined. In the present invention, the emission maximum wavelength that appears on the shortest wavelength side in the phosphorescence spectrum chart obtained by the above-described measurement method is defined as the 0-0 band. If the phosphorescence spectrum is weak, noise and peaks can be separated and peak wavelengths can be read by performing a smoothing process. As the smoothing process, a Savitzky & Gray smoothing method or the like can be applied.

  In the present invention, the phosphorescence wavelength peak is preferably 480 nm or less.

  Next, the constituent layers of the organic EL device of the present invention will be described in detail.

  In this invention, although the preferable specific example of the layer structure of an organic EL element is shown below, this invention is not limited to these.

(I) Anode / light emitting layer / cathode (ii) Anode / hole transport layer / light emitting layer / cathode (iii) Anode / hole transport layer / light emitting layer / electron transport layer / cathode (iv) Anode / hole transport layer / Light emitting layer / hole blocking layer / electron transport layer / cathode (v) anode / hole injection layer / hole transport layer / light emitting layer / hole blocking layer / electron transport layer / cathode buffer layer / cathode (vi) anode / Hole injection layer / hole transport layer / hole transport layer A / light emitting layer / electron transport layer / cathode buffer layer / cathode.

<Light emitting layer>
The light emitting layer according to the present invention will be described.

  The light emitting layer according to the present invention is a layer that emits light by recombination of electrons and holes injected from an electrode, an electron transport layer, a hole transport layer, or the like, and the light emitting portion is in the layer of the light emitting layer. Alternatively, it may be the interface between the light emitting layer and the adjacent layer.

(Dopant material)
The light emitting layer of the organic EL device of the present invention contains a dopant material and a host material. In the present invention, it is preferable to use the aforementioned compound according to the present invention as a dopant material.

  Further, a plurality of known dopant materials may be used in combination. By using a plurality of dopant materials, it is possible to mix different light emission, thereby obtaining an arbitrary emission color. White light emission is possible by adjusting the kind of dopant material and the doping amount, and it can also be applied to illumination and backlight.

  Specific examples of known dopant materials include compounds described in the following documents.

  WO 00/70655 pamphlet, JP 2002-280178, JP 2001-181616, JP 2002-280179, JP 2001-181617, JP 2002-280180, JP 2001-247859, JP 2002-299060, JP 2001-313178, JP 2002-302671, JP 2001-345183, JP 2002-324679, International Publication No. 02/15645 pamphlet, JP 2002-332291 A, JP 2002-50484 A, JP 2002-332292 A, JP 2002-83684 A, JP 2002-540572 A, JP 2002-2002 A. No. 117978, JP 20 JP-A-2-338588, JP-A-2002-170684, JP-A-2002-352960, WO01 / 93642, JP-A-2002-50483, JP-A-2002-1000047, JP-A-2002. No. -173744, JP-A No. 2002-359082, JP-A No. 2002-17584, JP-A No. 2002-363552, JP-A No. 2002-184582, JP-A No. 2003-7469, JP-T-2002-525808. Gazette, JP2003-7471, JP2002-525833, JP2003-31366, JP2002-226495, JP2002-234894, JP2002-2335076 JP 2002-241751 A JP 2001-319779, JP 2001-319780, JP 2002-62824, JP 2002-1000047, JP 2002-203679, JP 2002-343572, JP 2002-203678 gazette etc.

(Host material)
As a material used for the light emitting layer, there is a host material in addition to the above dopant material.

  Here, in the present invention, the host material is defined as a compound having a phosphorescence quantum yield of phosphorescence emission of less than 0.01 at room temperature (25 ° C.) among compounds contained in the light emitting layer.

  The host material used in the present invention is not particularly limited in terms of structure, but representative examples include carbazole derivatives and triarylamine derivatives.

  Specific examples of the carbazole derivative, triarylamine derivative and the like are given below, but the present invention is not limited to these.

  As the host material, a compound that prevents the emission of light from being increased in wavelength and has a high Tg (glass transition temperature) is preferable. Here, high Tg means 100 degreeC or more.

  As specific examples of the host material, compounds described in the following documents are suitable. For example, Japanese Patent Application Laid-Open Nos. 2001-257076, 2001-313179, 2002-319491, 2001-357777, 2002-334786, 2002-8860, 2002-334787. Gazette, 2002-15871, 2002-334788, 2002-43056, 2002-334789, 2002-75645, 2002-105445, 2002-343568 No. 2002-141173, No. 2002-203683, No. 2002-363227, No. 2003-3165, No. 2002-234888, No. 2003-27048, No. 2002-255934, 2002-260861, JP same 2002-280183, JP same 2002-302516, JP same 2002-308837, JP same 2000-21572, JP same 2004-288381 Patent Publication.

《Hole transport layer》
The hole transport layer includes a material having a function of transporting holes, and in a broad sense, a hole injection layer and an electron blocking layer are also included in the hole transport layer. The hole transport layer can be provided as a single layer or a plurality of layers.

  There are no particular restrictions on the hole transport material, and conventionally known photoconductive materials are commonly used as hole charge injection and transport materials, and well-known materials used for hole injection layers and hole transport layers of EL devices. Any one can be selected and used.

  The hole transport material has one of hole injection or transport and electron barrier properties, and may be either organic or inorganic. For example, triazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, Examples thereof include stilbene derivatives, silazane derivatives, aniline copolymers, and conductive polymer oligomers, particularly thiophene oligomers.

  The above-mentioned materials can be used as the hole transport material, but it is preferable to use a porphyrin compound, an aromatic tertiary amine compound and a styrylamine compound, particularly an aromatic tertiary amine compound.

  Representative examples of aromatic tertiary amine compounds and styrylamine compounds include N, N, N ′, N′-tetraphenyl-4,4′-diaminophenyl; N, N′-diphenyl-N, N′— Bis (3-methylphenyl)-[1,1′-biphenyl] -4,4′-diamine (TPD); 2,2-bis (4-di-p-tolylaminophenyl) propane; 1,1-bis (4-di-p-tolylaminophenyl) cyclohexane; N, N, N ′, N′-tetra-p-tolyl-4,4′-diaminobiphenyl; 1,1-bis (4-di-p-tolyl) Aminophenyl) -4-phenylcyclohexane; bis (4-dimethylamino-2-methylphenyl) phenylmethane; bis (4-di-p-tolylaminophenyl) phenylmethane; N, N'-diphenyl-N, N ' − (4-methoxyphenyl) -4,4'-diaminobiphenyl; N, N, N ', N'-tetraphenyl-4,4'-diaminodiphenyl ether; 4,4'-bis (diphenylamino) quadriphenyl; N, N, N-tri (p-tolyl) amine; 4- (di-p-tolylamino) -4 '-[4- (di-p-tolylamino) styryl] stilbene; 4-N, N-diphenylamino- (2-diphenylvinyl) benzene; 3-methoxy-4′-N, N-diphenylaminostilbenzene; N-phenylcarbazole, and also two of those described in US Pat. No. 5,061,569. Having a condensed aromatic ring in the molecule, for example, 4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (NPD), JP-A-4-3086 4,4 ', 4 "-tris [N- (3-methylphenyl) -N-phenylamino] triphenylamine in which three triphenylamine units described in Japanese Patent No. 8 are linked in a starburst type ( MTDATA) and the like.

  Furthermore, a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain can also be used.

  In addition, inorganic compounds such as p-type-Si and p-type-SiC can also be used as the hole injection material and the hole transport material. The hole transport material preferably has a high Tg.

  This hole transport layer can be formed by thinning the hole transport material by a known method such as a vacuum deposition method, a spin coating method, a casting method, an ink jet method, or an LB method. Although there is no restriction | limiting in particular about the film thickness of a positive hole transport layer, Usually, it is about 5-5000 nm. The hole transport layer may have a single layer structure composed of one or more of the above materials.

  Further, a hole transport layer having a high p property doped with impurities can also be used. Examples thereof include JP-A-4-297076, JP-A-2000-196140, and JP-A-2001-102175; Appl. Phys. 95, 5773 (2004), and the like.

《Electron transport layer》
The electron transport layer is made of a material having a function of transporting electrons, and in a broad sense, an electron injection layer and a hole blocking layer are also included in the electron transport layer. The electron transport layer can be provided with a single layer or a plurality of layers.

  Conventionally, in the case of a single-layer electron transport layer and a plurality of layers, the following materials are used as the electron transport material (also serving as a hole blocking material) used for the electron transport layer adjacent to the cathode side with respect to the light emitting layer. It has been known. Further, the electron transport layer only needs to have a function of transmitting electrons injected from the cathode to the light emitting layer, and any material can be selected and used from conventionally known compounds.

  Examples of materials used for the electron transport layer (hereinafter referred to as electron transport materials) include heterocyclic tetracarboxylic acid anhydrides such as nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, naphthalene perylene, carbodiimides, Examples include fluorenylidenemethane derivatives, anthraquinodimethane and anthrone derivatives, and oxadiazole derivatives. Furthermore, in the above oxadiazole derivative, a thiadiazole derivative in which the oxygen atom of the oxadiazole ring is substituted with a sulfur atom, and a quinoxaline derivative having a quinoxaline ring known as an electron withdrawing group can also be used as an electron transport material.

  Furthermore, a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain can also be used.

In addition, metal complexes of 8-quinolinol derivatives such as tris (8-quinolinol) aluminum (Alq ₃ ), 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, bis (8-quinolinol) zinc (Znq), etc., and the central metals of these metal complexes are In, Mg Metal complexes replaced with Cu, Ca, Sn, Ga, or Pb can also be used as electron transport materials. In addition, metal-free or metal phthalocyanine, or those having terminal ends substituted with an alkyl group or a sulfonic acid group can be preferably used as the electron transport material. In addition, the distyrylpyrazine derivative exemplified as the material of the light emitting layer can also be used as an electron transport material, and similarly to the hole injection layer and the hole transport layer, inorganic such as n-type-Si and n-type-SiC. A semiconductor can also be used as an electron transport material.

  This electron transport layer can be formed by thinning the electron transport material by a known method such as a vacuum deposition method, a spin coating method, a casting method, an ink jet method, or an LB method. Although there is no restriction | limiting in particular about the film thickness of an electron carrying layer, Usually, it is about 5-5000 nm. This electron transport layer may have a single layer structure composed of one or more of the above materials.

  Alternatively, an impurity-doped electron transport layer having a high n property can be used. Examples thereof include JP-A-4-297076, JP-A-2000-196140, and JP-A-2001-102175; Appl. Phys. 95, 5773 (2004), and the like.

"anode"
As the anode according to the organic EL device of the present invention, an electrode having a work function (4 eV or more) metal, alloy, electrically conductive compound and a mixture thereof as an electrode material is preferably used. Specific examples of such electrode substances include metals such as Au, and conductive transparent materials such as CuI, indium tin oxide (ITO), SnO ₂ , and ZnO. Alternatively, an amorphous material such as IDIXO (In ₂ O ₃ —ZnO) capable of forming a transparent conductive film may be used.

  For the anode, these electrode materials may be formed into a thin film by a method such as vapor deposition or sputtering, and a pattern having a desired shape may be formed by a photolithography method, or when the pattern accuracy is not required (about 100 μm or more) ), A pattern may be formed through a mask having a desired shape when the electrode material is deposited or sputtered. When light emission is extracted from the anode, it is desirable that the transmittance be greater than 10%, and the sheet resistance as the anode is preferably several hundred Ω / □ or less. Further, although the film thickness depends on the material, it is usually selected in the range of 10 to 1000 nm, preferably 10 to 200 nm.

"cathode"
On the other hand, as the cathode according to the present invention, a cathode having a work function (4 eV or less) metal (referred to as an electron injecting metal), an alloy, an electrically conductive compound, and a mixture thereof is used. Specific examples of such electrode materials include sodium, sodium-potassium alloy, magnesium, lithium, magnesium / copper mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al ₂ O ₃ ) Mixtures, indium, lithium / aluminum mixtures, rare earth metals and the like.

Among these, from the viewpoint of electron injecting property and durability against oxidation, etc., a mixture of an electron injecting metal and a second metal which is a stable metal having a larger work function than this, for example, a magnesium / silver mixture, magnesium / Aluminum mixtures, magnesium / indium mixtures, aluminum / aluminum oxide (Al ₂ O ₃ ) mixtures, lithium / aluminum mixtures, aluminum and the like are preferred.

  The cathode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering. The sheet resistance as the cathode is preferably several hundred Ω / □ or less, and the film thickness is usually selected in the range of 10 to 1000 nm, preferably 50 to 200 nm. In order to transmit light, if either one of the anode or the cathode of the organic EL element is transparent or translucent, the light emission luminance is improved, which is convenient.

<< Substrate (also referred to as substrate, substrate, support, etc.) >>
The substrate of the organic EL device of the present invention is not particularly limited as to the type of glass, plastic and the like, and is not particularly limited as long as it is transparent. Examples of the substrate preferably used include glass and quartz. And a light transmissive resin film. A particularly preferable substrate is a resin film that can give flexibility to the organic EL element.

  Examples of the resin film include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyetherimide, polyetheretherketone, polyphenylene sulfide, polyarylate, polyimide, polycarbonate (PC), and cellulose. Examples include films made of triacetate (TAC), cellulose acetate propionate (CAP), and the like.

An inorganic or organic film or a hybrid film of both may be formed on the surface of the resin film, and it is preferably a high barrier film having a water vapor transmission rate of 0.01 g / m ² · day or less.

  The external extraction efficiency at room temperature for light emission of the organic electroluminescence device of the present invention is preferably 1% or more, more preferably 5% or more. Here, the external extraction quantum efficiency (%) = the number of photons emitted to the outside of the organic EL element / the number of electrons sent to the organic EL element × 100.

  When used in lighting applications, a film (such as an antiglare film) that has been roughened to reduce unevenness in light emission can be used in combination.

<Sealing>
As a sealing means used for sealing the organic EL element of the present invention, for example, there is a method of adhering a sealing member, an electrode, and a support base with an adhesive. The sealing member may be disposed so as to cover the display area of the organic EL element, and may be concave or flat. Moreover, transparency and electrical insulation are not particularly limited.

  Specific examples include a glass plate, a polymer plate / film, and a metal plate / film. Examples of the glass plate include soda lime glass, barium / strontium-containing glass, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, and quartz.

  Examples of the polymer plate include polycarbonate, acrylic, polyethylene terephthalate, polyether sulfide, and polysulfone. Examples of the metal plate include those made of one or more 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 the present invention, a polymer film and a metal film can be preferably used because the element can be thinned.

Further, the polymer film has an oxygen permeability of 10 ⁻³ ml / m ² · 24 hr · MPa or less and a water vapor permeability (25 ° C., relative humidity 90% RH) of 10 ⁻⁵ g / m ² · 24 hr or less. Is preferred. The sealing member is processed into a concave shape by sandblasting, chemical etching, or the like.

  Examples of the adhesive include photocuring and thermosetting adhesives having reactive vinyl groups such as acrylic acid oligomers and methacrylic acid oligomers, and moisture curing adhesives such as 2-cyanoacrylate. In addition, there are thermal and chemical curing types (two-component mixing) such as epoxy type. Moreover, hot-melt type polyamide, polyester, and polyolefin can be mentioned. Moreover, a cationic curing type ultraviolet curing epoxy resin adhesive can be mentioned. In addition, since an organic EL element may deteriorate by heat processing, what can be adhesive-hardened from room temperature to 80 degreeC is preferable. A desiccant may be dispersed in the adhesive. Application | coating of the adhesive agent to a sealing part may use commercially available dispenser, and may print like screen printing.

  It is also preferable to cover the electrode and the organic layer on the outer side of the electrode facing the support substrate with the organic layer interposed therebetween, and form an inorganic or organic layer in contact with the support substrate to form a sealing film. In this case, the material for forming the film may be any material that has a function of suppressing intrusion of elements that cause deterioration of the element such as moisture and oxygen. For example, silicon oxide, silicon dioxide, silicon nitride, or the like is used. it can. Further, in order to improve the brittleness of the film, it is preferable to have a laminated structure of these inorganic layers and layers made of organic materials.

《Protective film, protective plate》
In order to increase the mechanical strength of the device, a protective film or a protective plate may be provided on the outer side of the sealing film on the side facing the support substrate with the organic layer interposed therebetween or the sealing film. In particular, when the sealing is the sealing film, the mechanical strength is not necessarily high, and thus it is preferable to provide such a protective film and a protective plate. As the material that can be used for this, the same glass plate, polymer plate / film, metal plate / film, and the like used for the sealing can be used. It is preferable to use it.

<< Method for producing organic EL element >>
As an example of the method for producing the organic EL device of the present invention, a method for producing an organic EL device comprising an anode / hole injection layer / hole transport layer / light emitting layer / hole blocking layer / electron transport layer / cathode will be described. First, a desired electrode material, for example, a thin film made of a material for an anode is formed on a suitable support base by a method such as vapor deposition or sputtering so as to have a film thickness of 1 μm or less, preferably 10 to 200 nm. .

  Next, the organic compound thin film of the hole injection layer, the hole transport layer, the intermediate layer, and the light emitting layer, the hole blocking layer, and the electron transport layer, which are organic EL element materials, is formed thereon. As a method for thinning the organic compound thin film, there are a vapor deposition method and a wet process (spin coating method, casting method, ink jet method, printing method) as described above, but it is easy to obtain a uniform film and a pinhole. From the point of being difficult to form, a vacuum deposition method, a spin coating method, an ink jet method, and a printing method are particularly preferable. Further, different film forming methods may be applied for each layer.

When employing a vapor deposition method for film formation, the vapor deposition conditions vary depending on the type of compound used, but generally a boat heating temperature of 50 to 450 ° C., a degree of vacuum of 10 ⁻⁶ to 10 ⁻² Pa, and a vapor deposition rate of 0.01 to It is desirable to select appropriately within the range of 50 nm / second, substrate temperature −50 to 300 ° C., film thickness 0.1 nm to 5 μm, preferably 5 to 200 nm. After these layers are formed, a thin film made of a cathode material is formed thereon by a method such as vapor deposition or sputtering so as to have a film thickness of 1 μm or less, preferably 50 to 200 nm, and a cathode is provided. Thus, a desired organic EL element can be obtained.

  The organic EL element may be produced from a hole injection layer to a cathode consistently by a single evacuation, or may be taken out halfway and subjected to different film forming methods. At that time, it is necessary to consider that the work is performed in a dry inert gas atmosphere. It is also possible to reverse the layer order and reverse the layer order. When a DC voltage is applied to the multicolor display device thus obtained, light emission can be observed by applying a voltage of about 2 to 40 V with the anode as + and the cathode as-polarity. An alternating voltage may be applied. The alternating current waveform to be applied may be arbitrary.

<Application>
The organic electroluminescence element of the present invention can be used as a display device, a display, or various light sources.

  Illumination devices that use the organic EL element of the present invention as a light-emitting light source include home lighting, interior lighting, backlights for watches and liquid crystals, billboard advertisements, traffic lights, light sources for optical storage media, light sources for electrophotographic copying machines, Examples include, but are not limited to, a light source of an optical communication processor and a light source of an optical sensor.

  The organic EL element of the present invention may be used as a kind of lamp for illumination or exposure light source, a projection device that projects an image, or a type that directly recognizes a still image or a moving image. It may be used as a display device (display).

  The driving method when used as a display device for moving image reproduction may be either a simple matrix (passive matrix) method or an active matrix method.

  Moreover, it is possible to produce a full-color display device by using three or more organic EL elements of the present invention having different emission colors.

  Alternatively, it is also possible to extract a single emission color, for example, white emission using a color filter and extract B, G, and R light to make it full color.

  Furthermore, the emission color of the organic EL element can be converted to another color by using a color conversion filter to obtain a full color. In that case, the λmax of the organic EL emission is preferably 480 nm or less.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

Example 1
<< Preparation of Organic EL Elements 1-1 to 1-4 >>
Transparent support provided with this ITO transparent electrode after patterning on a substrate (NH45 manufactured by NH Techno Glass) made of ITO (indium tin oxide) with a thickness of 100 nm on a glass substrate of 100 mm × 100 mm × 1.1 mm as an anode The substrate was ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen gas, and subjected to UV ozone cleaning for 5 minutes.

  This transparent support substrate is fixed to a substrate holder of a commercially available vacuum deposition apparatus, while 200 mg of CuPc is put into a molybdenum resistance heating boat, and 200 mg of α-NPD is put into another molybdenum resistance heating boat, and another molybdenum resistance is added. 100 mg of H-1 was put into a heating boat, 100 mg of compound 1-79 was put into another resistance heating boat made of molybdenum, and 200 mg of BAlq was put into another resistance heating boat made of molybdenum, and attached to a vacuum deposition apparatus.

Next, after reducing the pressure of the vacuum chamber to 4 × 10 ⁻⁴ Pa, the heating boat containing CuPc was energized and heated, and deposited on the transparent support substrate at a deposition rate of 0.1 nm / second to form a 20 nm hole injection layer. Was provided. Further, the heating boat containing α-NPD was energized and heated, and was deposited on the hole injection layer at a deposition rate of 0.1 nm / second to provide a 20 nm hole transport layer.

  Next, the heating boat containing H-1 and the heating boat containing compound 1-79 are energized and heated, and deposited on the hole transport layer at a deposition rate of 0.1 nm / second and 0.012 nm / second. Co-evaporation is started, the heating boat containing compound 1-79 is adjusted, and light emission of 40 nm is performed so that the concentration of compound 1-79 contained in the light emitting layer on the cathode side is 3% by mass. A layer was provided. At this time, the concentration of the compound 1-79 in the light emitting layer continuously changes from the anode side to the cathode side.

  Then, the heating boat containing BAlq was energized and deposited on the light emitting layer at a deposition rate of 0.1 nm / second to provide an electron transport layer having a thickness of 30 nm. In addition, the substrate temperature at the time of vapor deposition was room temperature.

  Then, 0.5 nm of lithium fluoride was vapor-deposited as a cathode buffer layer, and also aluminum 110nm was vapor-deposited, the cathode was formed, and the organic EL element 1-1 was produced.

  In the production of the organic EL element 1-1, the same as the organic EL element 1-1 except that the content concentration of the compound 1-79 on the anode side and the content concentration of the compound 1-79 on the cathode side are shown in Table 2. Organic EL devices 1-2 to 1-4 were prepared by the method.

Ionization potential of H-1 (host material): 5.45 eV (calculation)
Ionization potential of compound 1-79 (dopant material): 4.33 eV (calculation).

<< Evaluation of Organic EL Elements 1-1 to 1-4 >>
The organic EL elements 1-1 to 1-4 are evaluated, and the results are shown in Table 3. The light emission lifetime of each element shown in Table 3 is determined by driving each organic EL element with a driving voltage (V) at which the front luminance is 1000 cd / m ² and taking the time until the luminance is halved. -4 was expressed as a relative value with 100.

  From Table 3, it can be seen that the organic EL device of the present invention has a long lifetime.

Example 2
<< Production of Organic EL Elements 2-1 to 2-4 >>
Transparent support provided with this ITO transparent electrode after patterning on a substrate (NH45 manufactured by NH Techno Glass) made of ITO (indium tin oxide) with a thickness of 100 nm on a glass substrate of 100 mm × 100 mm × 1.1 mm as an anode The substrate was ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen gas, and subjected to UV ozone cleaning for 5 minutes.

  This transparent support substrate is fixed to a substrate holder of a commercially available vacuum deposition apparatus, while 200 mg of CuPc is put into a molybdenum resistance heating boat, and 200 mg of α-NPD is put into another molybdenum resistance heating boat, and another molybdenum resistance is added. 100 mg of H-1 was placed in a heating boat, 100 mg of compound 1-99 was placed in another resistance heating boat made of molybdenum, and 200 mg of BAlq was placed in another resistance heating boat made of molybdenum, and attached to a vacuum deposition apparatus.

Next, after reducing the pressure of the vacuum chamber to 4 × 10 ⁻⁴ Pa, the heating boat containing CuPc was energized and heated, and deposited on the transparent support substrate at a deposition rate of 0.1 nm / second to form a 20 nm hole injection layer. Was provided. Further, the heating boat containing α-NPD was energized and heated, and was deposited on the hole injection layer at a deposition rate of 0.1 nm / second to provide a 20 nm hole transport layer.

  Next, the heating boat containing H-1 and the heating boat containing compound 1-99 were energized and heated, and deposited on the hole transport layer at a deposition rate of 0.1 nm / second and 0.012 nm / second. Co-evaporation is started, the heating boat containing compound 1-99 is adjusted, and light emission of 40 nm is performed so that the concentration of compound 1-99 contained in the light emitting layer on the cathode side is 3% by mass. A layer was provided. At this time, the concentration of compound 1-99 in the light emitting layer is continuously changed from the anode side to the cathode side.

  Then, the heating boat containing BAlq was energized and deposited on the light emitting layer at a deposition rate of 0.1 nm / second to provide an electron transport layer having a thickness of 30 nm. In addition, the substrate temperature at the time of vapor deposition was room temperature.

  Then, 0.5 nm of lithium fluoride was vapor-deposited as a cathode buffer layer, and also aluminum 110nm was vapor-deposited, the cathode was formed, and the organic EL element 2-1 was produced.

  In the production of the organic EL element 2-1, the same as the organic EL element 2-1, except that the concentration of the compound 1-99 on the anode side and the concentration of the compound 1-99 on the cathode side are as shown in Table 4. Organic EL elements 2-2 to 2-4 were prepared by the method.

Ionization potential of H-1 (host material): 5.45 eV (calculation)
Ionization potential of compound 1-99 (dopant material): 4.36 eV (calculation).

<< Evaluation of Organic EL Elements 2-1 to 2-4 >>
The organic EL elements 2-1 to 2-4 were evaluated, and the results are shown in Table 5. The light emission lifetime of each element shown in Table 5 is determined by driving each organic EL element with a driving voltage (V) at which the front luminance is 1000 cd / m ² and taking the time until the luminance is halved. -4 was expressed as a relative value with 100.

  From Table 5, it can be seen that the organic EL device of the present invention has a long lifetime.

Example 3
<< Preparation of organic EL elements 3-1 to 3-4 >>
Transparent support provided with this ITO transparent electrode after patterning on a substrate (NH45 manufactured by NH Techno Glass) made of ITO (indium tin oxide) with a thickness of 100 nm on a glass substrate of 100 mm × 100 mm × 1.1 mm as an anode The substrate was ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen gas, and subjected to UV ozone cleaning for 5 minutes.

  This transparent support substrate is fixed to a substrate holder of a commercially available vacuum deposition apparatus, while 200 mg of CuPc is put into a molybdenum resistance heating boat, and 200 mg of α-NPD is put into another molybdenum resistance heating boat, and another molybdenum resistance is added. 100 mg of H-1 was placed in a heating boat, 100 mg of compound 1-99 was placed in another resistance heating boat made of molybdenum, and 200 mg of BAlq was placed in another resistance heating boat made of molybdenum, and attached to a vacuum deposition apparatus.

Next, after reducing the pressure of the vacuum chamber to 4 × 10 ⁻⁴ Pa, the heating boat containing CuPc was energized and heated, and deposited on the transparent support substrate at a deposition rate of 0.1 nm / second to form a 20 nm hole injection layer. Was provided. Further, the heating boat containing α-NPD was energized and heated, and was deposited on the hole injection layer at a deposition rate of 0.1 nm / second to provide a 20 nm hole transport layer.

  Next, the heating boat containing H-1 and the heating boat containing compound 1-99 are energized and heated, and deposited on the hole transport layer at a deposition rate of 0.1 nm / second and 0.009 nm / second. Co-evaporation was started, the film thickness was 5 nm, and the heating boat containing H-1 and the heating boat containing compound 1-99 were energized and heated, and the deposition rate was 0.1 nm / sec. Co-evaporation was started on the hole transport layer at 006 nm / second, and a 35 nm-thick film was deposited to provide a 40 nm thick light-emitting layer. The concentration of compound 1-99 in the light emitting layer changes stepwise from the anode side to the cathode side.

  Then, the heating boat containing BAlq was energized and deposited on the light emitting layer at a deposition rate of 0.1 nm / second to provide an electron transport layer having a thickness of 30 nm. In addition, the substrate temperature at the time of vapor deposition was room temperature.

  Then, 0.5 nm of lithium fluoride was vapor-deposited as a cathode buffer layer, and also aluminum 110nm was vapor-deposited, the cathode was formed, and the organic EL element 3-1 was produced.

  In the production of the organic EL element 2-1, the same as the organic EL element 3-1, except that the content concentration of the compound 1-99 on the anode side and the content concentration of the compound 1-99 on the cathode side are shown in Table 6. Organic EL elements 3-2 to 3-4 were prepared by the method.

<< Evaluation of Organic EL Elements 3-1 to 3-4 >>
The light emission lifetime was evaluated in the same manner as in Example 1. The value is shown as a relative value when the organic EL element 3-4 is 100.

  From Table 7, it can be seen that the organic EL device of the present invention has a long lifetime.

Example 4
<< Production of Organic EL Elements 4-1 to 4-3 >>
After patterning on a substrate (NA-45 manufactured by NH Techno Glass Co., Ltd.) formed by depositing 100 nm of ITO (indium tin oxide) on a 100 mm × 100 mm × 1.1 mm glass substrate as an anode, this ITO transparent electrode was provided. The transparent support substrate was ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen gas, and subjected to UV ozone cleaning for 5 minutes.

  On this transparent support substrate, a solution obtained by diluting poly (3,4-ethylenedioxythiophene) -polystyrene sulfonate (PEDOT / PSS, Bayer, Baytron P Al 4083) to 70% with pure water at 3000 rpm for 30 seconds. After the film formation by spin coating, the film was dried at 200 ° C. for 1 hour to provide a first hole transport layer having a thickness of 30 nm.

  The substrate was transferred to a nitrogen atmosphere, and a solution of 50 mg α-NPD dissolved in 10 ml of toluene was formed on the first hole transport layer by spin coating at 1000 rpm for 30 seconds, and the second positive electrode was formed. A hole transport layer was formed.

  On this second hole transport layer, a solution prepared by dissolving 100 mg of H-1 and 10 mg of compound 1-99 in 10 ml of toluene was formed by spin coating at 1000 rpm for 30 seconds. A first light emitting layer having a thickness of 20 nm was obtained. Further, a solution obtained by dissolving 100 mg of H-1 in 10 ml of toluene was dropped on the light emitting layer, and a second light emitting layer was formed by spin coating under conditions of 1000 rpm and 30 seconds. At this time, the compound 1-99 is dissolved in the toluene solvent from the first light-emitting layer and diffused into the second light-emitting layer, whereby the content of the compound 1-99 is continuously changed. A light emitting layer was produced in which the content of compound 1-99 was larger than the content of compound 1-99 on the cathode side. The thickness of the combined light emitting layer of the first light emitting layer and the second light emitting layer was about 50 nm.

  Next, a solution obtained by dissolving 50 mg of (tBu) PBD in 10 ml of toluene on this light-emitting layer was formed by spin coating at 1000 rpm for 30 seconds, and vacuum-dried at 60 ° C. for 1 hour. The electron transport layer was about 25 nm.

This was attached to a vacuum deposition apparatus, and then the vacuum chamber was depressurized to 4 × 10 ⁻⁴ Pa. Lithium fluoride 1.0 nm was deposited as a cathode buffer layer and aluminum 110 nm was deposited as a cathode to form a cathode. Organic EL element 4 -1 was produced.

  As a comparative example, in the organic EL element 4-1, the content of the compound 1-99 contained in the toluene solution at the time of forming the first light emitting layer was 0 mg, and the compound contained in the toluene solution at the time of forming the second light emitting layer An organic EL element 4-2 was produced in the same manner except that the content of 1-99 was 10 mg. In this case, in the light emitting layer, the content concentration of the compound 1-99 on the anode side is smaller than the content concentration of the compound 1-99 on the cathode side.

  Further, as a comparative example, in the organic EL element 4-1, the content of compound 1-99 contained in the toluene solution at the time of forming the first light emitting layer was set to 5 mg, and the second light emitting layer was not formed in the same manner. Organic EL element 4-3 was produced. In this case, the light-emitting layer is uniform in that the concentration of compound 1-99 does not change from the anode side to the cathode side.

<< Evaluation of Organic EL Elements 4-1 to 4-3 >>
The light emission lifetime was evaluated in the same manner as in Example 1. The value is shown as a relative value when the organic EL element 4-3 is 100.

  From Table 8, it can be seen that the organic EL element of the present invention has a long life even in a coating type organic EL element.

Claims (10)

In an organic electroluminescence device having at least a light-emitting layer containing a host material and a dopant material between an opposing cathode and an anode, the dopant material is represented by the following general formula (1), and the content concentration of the dopant material emits light. An organic electroluminescence element, wherein the thickness decreases from the anode side to the cathode side in the thickness direction of the layer.

(In the formula, R ₁ represents a substituent. Z represents a group of nonmetallic atoms necessary to form a 5- to 7-membered ring. N1 represents an integer of 0 to _5. B _{1 to} B ₅ represent carbon. Represents an atom, nitrogen atom, oxygen atom or sulfur atom, at least one represents a nitrogen atom, M ₁ represents a group 8-10 metal in the periodic table, and X ₁ and X ₂ represent a carbon atom, nitrogen atom or Represents an oxygen atom, and L ₁ represents an atomic group forming a bidentate ligand together with X ₁ and X ₂ , m1 represents an integer of 1, 2 or 3, m2 represents an integer of 0, 1 or 2 (Where m1 + m2 is 2 or 3) 2. The organic electroluminescence device according to claim 1, wherein the concentration of the dopant material is gradually decreased from the anode side to the cathode side. 2. The organic electroluminescence device according to claim 1, wherein the concentration of the dopant material is continuously decreased from the anode side to the cathode side. The organic electroluminescent element according to any one of claims 1 to 3, wherein m2 in the dopant material represented by the general formula (1) is 0. The nitrogen-containing heterocyclic ring formed by B _{1 to} B ₅ in the dopant material represented by the general formula (1) is an imidazole ring, and any one of claims 1 to 4 2. The organic electroluminescence device according to item 1. The ionization potential Iph of the host material and the ionization potential Ipd of the dopant material satisfy the following formula (1) in the light-emitting layer, according to any one of claims 1 to 5. Organic electroluminescence device.
Formula (1) Iph-Ipd ≧ 0.7 A / B ≧ 1.5 is satisfied when the concentration of the dopant material contained on the anode side of the light emitting layer is A mass% and the concentration of the dopant material contained on the cathode side is B mass%. The organic electroluminescence device according to any one of items 1 to 6 of the range. The phosphorescence wavelength peak of the dopant material is 480 nm or less, The organic electroluminescence element according to any one of claims 1 to 7. The organic electroluminescence device according to any one of claims 1 to 8, further comprising another light emitting layer. The organic electroluminescence device according to any one of claims 1 to 9, wherein light emission is white.