Organic electroluminescent device
11594700 · 2023-02-28
Assignee
Inventors
Cpc classification
International classification
Abstract
To provide a material for an organic EL device that is excellent in hole injection and transport abilities, electron blocking ability, thin film stability, and durability, as a material for an organic EL device with high efficiency and high durability, and also to provide an organic EL device having a high efficiency, a low driving voltage, and a long lifetime by combining the material with various materials for an organic EL device that is excellent in hole and electron injection and transport abilities, electron blocking ability, thin film stability, and durability. An organic electroluminescent device comprising at least an anode, a hole transport layer, a light emitting layer, an electron transport layer and a cathode in this order, wherein the hole transport layer comprises a carbazole compound of the following general formula (1), and the light emitting layer comprises a blue light emitting dopant. ##STR00001##
Claims
1. An organic electroluminescent device comprising at least an anode, a hole transport layer, an electron blocking layer, a light emitting layer, an electron transport layer and a cathode in this order; wherein the electron blocking layer comprises a carbazole compound of the general formula (1) ##STR00077## wherein Ar.sub.1 to Ar.sub.3 may be the same or different, and represent a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, or a substituted or unsubstituted condensed polycyclic aromatic group; R.sub.1 to R.sub.6 may be the same or different, and represent a deuterium atom, a fluorine atom, a chlorine atom, a cyano group, a nitro group, a linear or branched alkyl group of 1 to 6 carbon atoms that may have a substituent, a cycloalkyl group of 5 to 10 carbon atoms that may have a substituent, a linear or branched alkenyl group of 2 to 6 carbon atoms that may have a substituent, a linear or branched alkyloxy group of 1 to 6 carbon atoms that may have a substituent, a cycloalkyloxy group of 5 to 10 carbon atoms that may have a substituent, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted condensed polycyclic aromatic group, a substituted or unsubstituted aryloxy group, or a disubstituted amino group substituted with a group selected from an aromatic hydrocarbon group, an aromatic heterocyclic group, and a condensed polycyclic aromatic group, where the respective groups may bind to each other via a single bond, a substituted or unsubstituted methylene group, an oxygen atom, or a sulfur atom to form a ring, and the respective groups may bind to the benzene ring binding with R.sub.1 to R.sub.6 via a linking group such as substituted or unsubstituted methylene, an oxygen atom, a sulfur atom, or a monosubstituted amino group to form a ring; r.sub.4 and r.sub.5 represent an integer of 0 to 4, and r.sub.1, r.sub.2, r.sub.3, and r.sub.6 represent an integer of 0 to 3; and n represents 0 or 1; and wherein the light emitting layer comprises a blue light emitting dopant, wherein the blue light emitting dopant is a pyrene derivative, or an amine derivative having a condensed ring structure of the following general formula (2a-a), (2a-b), (2b-a), (2b-b), (2b-c), (2b-d), (2c-a), or (2c-b): ##STR00078## ##STR00079## wherein A.sub.1 represents a divalent group of a substituted or unsubstituted aromatic hydrocarbon, a divalent group of a substituted or unsubstituted aromatic heterocyclic ring, a divalent group of substituted or unsubstituted condensed polycyclic aromatics, or a single bond; Ar.sub.4 and Ar.sub.5 may be the same or different, and represent a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, or a substituted or unsubstituted condensed polycyclic aromatic group, where Ar.sub.4 and Ar.sub.5 may bind to each other via a single bond, substituted or unsubstituted methylene, an oxygen atom, or a sulfur atom to form a ring; R.sub.7 to R.sub.10 may be the same or different, and represent a hydrogen atom, a deuterium atom, a fluorine atom, a chlorine atom, cyano, nitro, linear or branched alkyl of 1 to 6 carbon atoms that may have a substituent, cycloalkyl of 5 to 10 carbon atoms that may have a substituent, linear or branched alkenyl of 2 to 6 carbon atoms that may have a substituent, linear or branched alkyloxy of 1 to 6 carbon atoms that may have a substituent, cycloalkyloxy of 5 to 10 carbon atoms that may have a substituent, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted condensed polycyclic aromatic group, substituted or unsubstituted aryloxy, or a disubstituted amino group substituted with a group selected from an aromatic hydrocarbon group, an aromatic heterocyclic group, and a condensed polycyclic aromatic group, where the respective groups may bind to each other via a single bond, substituted or unsubstituted methylene, an oxygen atom, or a sulfur atom to form a ring, and the respective groups may bind to the benzene ring binding with R.sub.7 to R.sub.10 via a linking group such as substituted or unsubstituted methylene, an oxygen atom, a sulfur atom, or a monosubstituted amino group to form a ring; R.sub.13 represents a hydrogen atom, a deuterium atom, a fluorine atom, a chlorine atom, cyano, nitro, linear or branched alkyl of 1 to 6 carbon atoms that may have a substituent, cycloalkyl of 5 to 10 carbon atoms that may have a substituent, linear or branched alkenyl of 2 to 6 carbon atoms that may have a substituent, linear or branched alkyloxy of 1 to 6 carbon atoms that may have a substituent, cycloalkyloxy of 5 to 10 carbon atoms that may have a substituent, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted condensed polycyclic aromatic group, or substituted or unsubstituted aryloxy; R.sub.14 and R.sub.15 may be the same or different, and represent linear or branched alkyl of 1 to 6 carbon atoms that may have a substituent, cycloalkyl of 5 to 10 carbon atoms that may have a substituent, linear or branched alkenyl of 2 to 6 carbon atoms that may have a substituent, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted condensed polycyclic aromatic group, or substituted or unsubstituted aryloxy, where the respective groups may bind to each other via a linking group such as a single bond, substituted or unsubstituted methylene, an oxygen atom, a sulfur atom, or a monosubstituted amino group to form a ring; and X and Y may be the same or different and represent an oxygen atom or a sulfur atom.
2. The organic electroluminescent device according to claim 1, wherein the hole transport layer includes a benzidine derivative, 1,1-bis[4-(di-4-tolylamino)phenyl]cyclohexane, a triphenylamine derivative having two triphenylamine skeletons as a whole molecule; a triphenylamine derivative having four triphenylamine skeletons as a whole molecule, or a triphenylamine derivative having three triphenylamine skeletons as a whole molecule.
3. The organic electroluminescent device according to claim 1, wherein the blue light emitting dopant is a pyrene derivative.
4. The organic electroluminescent device according to claim 1, wherein the electron transport layer includes a compound of the following general formula (3) having a pyrimidine ring structure: ##STR00080## wherein Ar.sub.6 represents a substituted or unsubstituted aromatic hydrocarbon group, or a substituted or unsubstituted condensed polycyclic aromatic group; Ar.sub.7 and Ar.sub.8 may be the same or different, and represent a hydrogen atom, a substituted or unsubstituted aromatic hydrocarbon group, or a substituted or unsubstituted condensed polycyclic aromatic group; Ar.sub.9 represents a substituted or unsubstituted aromatic heterocyclic group; and R.sub.16 to R.sub.19 may be the same or different, and represent a hydrogen atom, a deuterium atom, a fluorine atom, a chlorine atom, cyano, trifluoromethyl, linear or branched alkyl of 1 to 6 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, or a substituted or unsubstituted condensed polycyclic aromatic group, where Ar.sub.7 and Ar.sub.8 are not simultaneously a hydrogen atom.
5. The organic electroluminescent device according to claim 1, wherein the light emitting layer includes an anthracene derivative.
6. The organic electroluminescent device according to claim 2, wherein the light emitting layer includes an anthracene derivative.
Description
BRIEF DESCRIPTION OF DRAWINGS
(1)
DESCRIPTION OF EMBODIMENTS
(2) The following presents specific examples of preferred compounds among the carbazole compounds of the general formula (1) preferably used in the organic EL device of the present invention. The present invention, however, is not restricted to these compounds.
(3) ##STR00011## ##STR00012## ##STR00013## ##STR00014## ##STR00015##
(4) The following presents specific examples of preferred compounds among the amine derivatives having a condensed ring structure of the general formula (2) preferably used in the organic EL device of the present invention. The present invention, however, is not restricted to these compounds.
(5) ##STR00016## ##STR00017## ##STR00018## ##STR00019## ##STR00020## ##STR00021## ##STR00022##
(6) The amine derivatives having a condensed ring structure described above can be synthesized by a known method (refer to PTL 6, for example).
(7) The following presents specific examples of preferred compounds among the compounds having a pyrimidine ring structure of the general formula (3) preferably used in the organic EL device of the present invention. The present invention, however, is not restricted to these compounds.
(8) ##STR00023## ##STR00024## ##STR00025## ##STR00026## ##STR00027## ##STR00028## ##STR00029## ##STR00030## ##STR00031## ##STR00032## ##STR00033## ##STR00034## ##STR00035## ##STR00036## ##STR00037## ##STR00038## ##STR00039## ##STR00040## ##STR00041## ##STR00042## ##STR00043## ##STR00044## ##STR00045## ##STR00046## ##STR00047## ##STR00048## ##STR00049## ##STR00050## ##STR00051## ##STR00052## ##STR00053## ##STR00054## ##STR00055## ##STR00056## ##STR00057## ##STR00058## ##STR00059## ##STR00060## ##STR00061## ##STR00062## ##STR00063## ##STR00064## ##STR00065## ##STR00066##
(9) The compounds described above having a pyrimidine ring structure can be synthesized by a known method (refer to PTL 7, for example).
(10) The carbazole compounds of the general formula (1) were purified by methods such as column chromatography, adsorption using, for example, a silica gel, activated carbon, or activated clay, recrystallization or crystallization using a solvent, and a sublimation purification method. The compounds were identified by an NMR analysis. A melting point, a glass transition point (Tg), and a work function were measured as material property values. The melting point can be used as an index of vapor deposition, the glass transition point (Tg) as an index of stability in a thin-film state, and the work function as an index of hole transportability and hole blocking performance.
(11) Other compounds used for the organic EL device of the present invention were purified by methods such as column chromatography, adsorption using, for example, a silica gel, activated carbon, or activated clay, recrystallization or crystallization using a solvent, and a sublimation purification method, and finally purified by a sublimation purification method.
(12) The melting point and the glass transition point (Tg) were measured by a high-sensitive differential scanning calorimeter (DSC3100SA produced by Bruker AXS) using powder.
(13) For the measurement of the work function, a 100 nm-thick thin film was fabricated on an ITO substrate, and an ionization potential measuring device (PYS-202 produced by Sumitomo Heavy Industries, Ltd.) was used.
(14) The organic EL device of the present invention may have a structure including an anode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode successively formed on a substrate, optionally with an electron blocking layer between the hole transport layer and the light emitting layer, a hole blocking layer between the light emitting layer and the electron transport layer, and an electron injection layer between the electron transport layer and the cathode. Some of the organic layers in the multilayer structure may be omitted, or may serve more than one function. For example, a single organic layer may serve as the hole injection layer and the hole transport layer, or as the electron injection layer and the electron transport layer, and so on. Further, any of the layers may be configured to laminate two or more organic layers having the same function, and the hole transport layer may have a two-layer laminated structure, the light emitting layer may have a two-layer laminated structure, the electron transport layer may have a two-layer laminated structure, and so on. The organic EL device of the present invention is preferably configured such that the electron blocking layer is provided between the hole transporting layer and the light emitting layer.
(15) Electrode materials with high work functions such as ITO and gold are used as the anode of the organic EL device of the present invention. The hole injection layer of the organic EL device of the present invention may be made of, for example, material such as starburst-type triphenylamine derivatives and various triphenylamine tetramers; porphyrin compounds as represented by copper phthalocyanine; accepting heterocyclic compounds such as hexacyano azatriphenylene; and coating-type polymer materials, in addition to the carbazole compounds of the general formula (1). These materials may be formed into a thin film by a vapor deposition method or other known methods such as a spin coating method and an inkjet method.
(16) Examples of material used for the hole transport layer of the organic EL device of the present invention can be benzidine derivatives such as N,N′-diphenyl-N,N′-di(m-tolyl)benzidine (TPD), N,N′-diphenyl-N,N′-di(α-naphthyl)benzidine (NPD), and N,N,N′,N′-tetrabiphenylylbenzidine; 1,1-bis[4-(di-4-tolylamino)phenyl]cyclohexane (TAPC); triphenylamine derivatives having two triphenylamine skeletons as a whole molecule; triphenylamine derivatives having four triphenylamine skeletons as a whole molecule; and triphenylamine derivatives having three triphenylamine skeletons as a whole molecule, in addition to the carbazole compounds of the general formula (1). These may be individually deposited for film forming, may be used as a single layer deposited mixed with other materials, or may be formed as a laminate of individually deposited layers, a laminate of mixedly deposited layers, or a laminate of the individually deposited layer and the mixedly deposited layer. These materials may be formed into a thin-film by using a vapor deposition method or other known methods such as a spin coating method and an inkjet method.
(17) The material used for the hole injection layer or the hole transport layer may be obtained by p-doping materials such as trisbromophenylamine hexachloroantimony, and radialene derivatives (refer to PTL 8, for example) into a material commonly used for these layers, or may be, for example, polymer compounds each having, as a part of the compound structure, a structure of a benzidine derivative such as TPD.
(18) The carbazole compounds of the general formula (1) are used as the electron blocking layer of the organic EL device of the present invention. These may be individually deposited for film forming, may be used as a single layer deposited mixed with other hole transporting materials, or may be formed as a laminate of individually deposited layers, a laminate of mixedly deposited layers, or a laminate of the individually deposited layer and the mixedly deposited layer. These materials may be formed into a thin-film by a vapor deposition method or other known methods such as a spin coating method and an inkjet method.
(19) Examples of a hole transporting material that can be mixed or can be used at the same time with the carbazole compounds of the general formula (1) can be compounds having an electron blocking effect, including, for example, carbazole derivatives such as 4,4′,4″-tri(N-carbazolyl)triphenylamine (TCTA), 9,9-bis[4-(carbazol-9-yl)phenyl]fluorene, 1,3-bis(carbazol-9-yl)benzene (mCP), and 2,2-bis(4-carbazol-9-ylphenyl)adamantane (Ad-Cz); and compounds having a triphenylsilyl group and a triarylamine structure, as represented by 9-[4-(carbazol-9-yl)phenyl]-9-[4-(triphenylsilyl)phenyl]-9H-fluorene.
(20) Examples of material used for the light emitting layer of the organic EL device of the present invention can be the amine derivative having a condensed ring structure of the general formula (2) and the pyrene derivative. Examples of a light emitting material that can be mixed or can be used at the same time with the amine derivative of the general formula (2) and the pyrene derivative can be various metal complexes such as quinolinol derivative metal complexes including Alq.sub.3, anthracene derivatives, bis(styryl)benzene derivatives, oxazole derivatives, and polyparaphenylene vinylene derivatives. Further, the light emitting layer may be made of a host material and a dopant material. Examples of the host material can be thiazole derivatives, benzimidazole derivatives, and polydialkyl fluorene derivatives, in addition to the above light-emitting materials. Examples of the dopant material that can be mixed or can be used at the same time with a blue light emitting dopant such as the amine derivative having a condensed ring structure of the general formula (2) and the pyrene derivative can be quinacridone, coumarin, rubrene, perylene, derivatives thereof, benzopyran derivatives, indenophenanthrene derivatives, rhodamine derivatives, and aminostyryl derivatives. These may be individually deposited for film forming, may be used as a single layer deposited mixed with other materials, or may be formed as a laminate of individually deposited layers, a laminate of mixedly deposited layers, or a laminate of the individually deposited layer and the mixedly deposited layer.
(21) As the light emitting layer of the organic EL device of the present invention, it is preferable to use the amine derivative having a condensed ring structure of the general formula (2) or the pyrene derivative as a dopant material, and it is more preferable to use the amine derivative having a condensed ring structure of the general formula (2) as a dopant material.
(22) Further, examples of the light emitting material may be delayed fluorescent-emitting material such as a CDCB derivative of PIC-TRZ, CC2TA, PXZ-TRZ, 4CzIPN or the like (refer to NPL 3, for example).
(23) These materials may be formed into a thin-film by using a vapor deposition method or other known methods such as a spin coating method and an inkjet method.
(24) The hole blocking layer of the organic EL device of the present invention may be formed by using hole blocking compounds such as various rare earth complexes, triazole derivatives, triazine derivatives, and oxadiazole derivatives, in addition to metal complexes of phenanthroline derivatives such as bathocuproin (BCP), and the metal complexes of quinolinol derivatives such as aluminum(III) bis(2-methyl-8-quinolinate)-4-phenylphenolate (hereinafter referred to as BAlq). These materials may also serve as the material of the electron transport layer. These may be individually deposited for film forming, may be used as a single layer deposited mixed with other materials, or may be formed as a laminate of individually deposited layers, a laminate of mixedly deposited layers, or a laminate of the individually deposited layer and the mixedly deposited layer. These materials may be formed into a thin-film by using a vapor deposition method or other known methods such as a spin coating method and an inkjet method.
(25) Examples of material used for the electron transport layer of the organic EL device of the present invention can be preferably the compounds having a pyrimidine ring structure of the general formula (3). These may be individually deposited for film forming, may be used as a single layer deposited mixed with other electron transport materials, or may be formed as a laminate of individually deposited layers, a laminate of mixedly deposited layers, or a laminate of the individually deposited layer and the mixedly deposited layer. These materials may be formed into a thin-film by using a vapor deposition method or other known methods such as a spin coating method and an inkjet method.
(26) Examples of the electron transporting material that can be mixed or can be used at the same time with the compounds having a pyrimidine ring structure of the general formula (3) can be metal complexes of quinolinol derivatives including Alq.sub.3 and BAlq, various metal complexes, triazole derivatives, triazine derivatives, oxadiazole derivatives, pyridine derivatives, pyrimidine derivatives, benzimidazole derivatives, thiadiazole derivatives, anthracene derivatives, carbodiimide derivatives, quinoxaline derivatives, pyridoindole derivatives, phenanthroline derivatives, and silole derivatives.
(27) Examples of material used for the electron injection layer of the organic EL device of the present invention can be alkali metal salts such as lithium fluoride and cesium fluoride; alkaline earth metal salts such as magnesium fluoride; and metal oxides such as aluminum oxide. However, the electron injection layer may be omitted in the preferred selection of the electron transport layer and the cathode.
(28) The cathode of the organic EL device of the present invention may be made of an electrode material with a low work function such as aluminum, or an alloy of an electrode material with an even lower work function such as a magnesium-silver alloy, a magnesium-indium alloy, or an aluminum-magnesium alloy.
(29) The following describes an embodiment of the present invention in more detail based on Examples. The present invention, however, is not restricted to the following Examples.
Example 1
Synthesis of 3,6-bis(9′-phenyl-9′H-carbazole-3-yl)-9-phenyl-9H-carbazole (Compound 1-1)
(30) Under a nitrogen atmosphere, 3,6-dibromo-9-phenyl-9H-carbazole (1.6 g), 9-phenyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)-9H-carbazole (2.4 g), tetrakistriphenylphosphine palladium (0.23 g), 2 M potassium carbonate aqueous solution (6 ml), toluene (20 ml), and ethanol (5 ml) were added into a reaction vessel at reflux temperature, and the mixture was heated and stirred for 5 hours. After cooling to 40° C., the reaction solution was filtered and concentrated under reduced pressure to obtain a crude product. The crude product was purified by recrystallization (solvent: toluene/methanol), and dried to obtain a white powder of 3,6-bis(9′-phenyl-9′H-carbazole-3-yl)-9-phenyl-9H-carbazole (Compound 1-1; 1.76 g; yield 60.9%).
(31) The structure of the obtained white powder was identified by NMR.
(32) .sup.1H-NMR (CDCl.sub.3) detected 35 hydrogen signals, as follows.
(33) δ(ppm)=8.56 (2H), 8.49 (2H), 8.24-8.26 (2H), 7.79-7.81 (4H), 7.62-7.67 (12H), 7.43-7.55 (11H), 7.30-7.33 (2H).
(34) ##STR00067##
Example 2
Synthesis of 3,6-bis(9′-phenyl-9′H-carbazole-3-yl)-9-(phenyl-D5)-9H-carbazole (Compound 1-2)
(35) Under a nitrogen atmosphere, 3,6-dibromo-9-(phenyl-d5)-9H-carbazole (26.1 g), 9-phenyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)-9H-carbazole (48.7 g), tetrakistriphenylphosphine palladium (2.23 g), 2 M potassium carbonate aqueous solution (95 ml), toluene (326 ml), and ethanol (82 ml) were added into a reaction vessel at reflux temperature, and the mixture was heated and stirred for 6.5 hours. After cooling to a room temperature, methanol (650 ml) was added and a crude product was obtained by filtration. The crude product was purified by silica gel and dissolved in toluene (1130 ml). The crude product obtained by concentrating the solution under reduced pressure was purified by recrystallization (solvent: toluene/hexane), washed with methanol and dried to obtain a white powder of 3,6-bis(9′-phenyl-9′H-carbazole-3-yl)-9-(phenyl-d5)-9H-carbazole (Compound 1-2; 32.3 g; yield 69%).
(36) The structure of the obtained white powder was identified by NMR.
(37) .sup.1H-NMR (CDCl.sub.3) detected 30 hydrogen signals, as follows.
(38) δ(ppm)=8.70 (2H), 8.60 (2H), 8.28 (2H), 7.83-7.86 (4H), 7.65-7.66 (8H), 7.49-7.54 (6H), 7.36-7.42 (4H), 7.27 (2H).
(39) ##STR00068##
Example 3
Synthesis of 9′-phenyl-9-[4-(9-phenyl-9H-carbazole-3-yl)-phenyl]-9H,9′H-[3,3′]bicarbazolyl (Compound 1-7)
(40) Under a nitrogen atmosphere, 9-phenyl-9H,9′H-[3,3′]bicarbazolyl (12.9 g), 4-bromo-iodobenzene (13.4 g), a copper powder (0.64 g), potassium carbonate (8.34 g), sodium hydrogen sulfite (0.49 g), and o-dichlorobenzene (50 ml) were added into a reaction vessel. The mixture was heated and stirred at 170° C. for 6.5 hours. After cooling to 90° C., toluene (200 ml) was added and the mixture was filtered. The crude product obtained by concentrating the filtrate under reduced pressure was purified by recrystallization (solvent: methanol), and dried to obtain a white powder of 9-(4-bromophenyl)-9′-phenyl-9H,9′H-[3,3′]bicarbazolyl (17.3 g; yield 97%).
(41) Under a nitrogen atmosphere, 9-(4-bromophenyl)-9′-phenyl-9H,9′H-[3,3′]bicarbazolyl (17.0 g), 9-phenyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)-9H-carbazole (12.3 g), tetrakistriphenylphosphine palladium (1.74 g), 2 M potassium carbonate aqueous solution (23 ml), toluene (160 ml), and ethanol (40 ml) were added into a reaction vessel at reflux temperature, and the mixture was heated and stirred for 13 hours. After cooling to a room temperature, toluene (100 ml) and water (150 ml) were added and stirred, and then the organic layer was separated with a separatory funnel. The organic layer was dried over magnesium sulfate. The obtained crude product was concentrated under reduced pressure, and then purified by column chromatography (carrier: silica gel, eluent: n-hexane/toluene) to obtain a pale yellow powder of 9′-phenyl-9-[4-(9-phenyl-9H-carbazol-3-yl)-phenyl]-9H,9TH-[3,3′]bicarbazolyl (10.4 g; yield 48%).
(42) The structure of the obtained pale yellow powder was identified by NMR.
(43) .sup.1H-NMR (CDCl.sub.3) detected 35 hydrogen signals, as follows.
(44) δ(ppm)=8.56-8.61 (3H), 8.26-8.30 (3H), 8.04-8.08 (2H), 7.81-7.85 (3H), 7.73-7.76 (2H), 7.64-7.69 (8H), 7.58 (1H), 7.48-7.53 (5H), 7.36-7.44 (5H), 7.25-7.31 (3H).
(45) ##STR00069##
Example 4
(46) The glass transition points of the carbazole compounds of the general formula (1) were measured using a high-sensitive differential scanning calorimeter (DSC3100SA produced by Bruker AXS).
(47) TABLE-US-00001 Glass transition point Compound of Example 1 157° C. Compound of Example 2 160° C. Compound of Example 3 148° C.
(48) The carbazole compounds of the general formula (1) have glass transition points of 100° C. or higher, demonstrating that the compounds have a stable thin-film state.
Example 5
(49) A 100 nm-thick vapor-deposited film was fabricated on an ITO substrate using the carbazole compounds of the general formula (1), and a work function was measured using an ionization potential measuring device (PYS-202 produced by Sumitomo Heavy Industries, Ltd.).
(50) TABLE-US-00002 Work function Compound of Example 1 5.76 eV Compound of Example 2 5.77 eV Compound of Example 3 5.81 eV
(51) As the results show, the carbazole compounds of the general formula (1) have desirable energy levels compared to the work function 5.4 eV of common hole transport materials such as NPD and TPD, and thus possess desirable hole transportability.
Example 6
(52) The organic EL device, as shown in
(53) Specifically, the glass substrate 1 having ITO having a film thickness of 150 nm formed thereon was subjected to ultrasonic washing in isopropyl alcohol for 20 minutes and then dried for 10 minutes on a hot plate heated to 200° C. Thereafter, after performing a UV ozone treatment for 15 minutes, the glass substrate 1 with ITO was installed in a vacuum vapor deposition apparatus, and the pressure was reduced to 0.001 Pa or lower. Subsequently, as the hole injection layer 3 covering the transparent anode 2, an electron acceptor (Acceptor-1) of the structural formula below and Compound (HTM-1) of the structural formula below were formed in a film thickness of 5 nm by dual vapor deposition at a vapor deposition rate that satisfies a vapor deposition rate ratio of Acceptor-1/HTM-1=3/97. As the hole transport layer 4 on the hole injection layer 3, Compound (HTM-1) of the structural formula below was formed in a film thickness of 45 nm. As the electron blocking layer 5 on the hole transport layer 4, Compound (1-1) of the structural formula below was formed in a film thickness of 10 nm. As the light emitting layer 6 on the electron blocking layer 5, Compound (2-1) of the structural formula below and Compound (EMH-1) of the structural formula below were formed in a film thickness of 20 nm by dual vapor deposition at a vapor deposition rate that satisfies a vapor deposition rate ratio of Compound (2-1)/EMH-1=5/95. As the electron transport layer 7 on the light emitting layer 6, Compound (3-125) of the structural formula below and Compound (ETM-1) of the structural formula below were formed in a film thickness of 30 nm by dual vapor deposition at a vapor deposition rate that satisfies a vapor deposition rate ratio of Compound (3-125)/ETM-1=50/50. As the electron injection layer 8 on the electron transport layer 7, lithium fluoride was formed in a film thickness of 1 nm. Finally, aluminum was vapor-deposited in a thickness of 100 nm to form the cathode 9. The characteristics of the organic EL device were measured in the atmosphere at ordinary temperature. Table 1 summarizes the results of measurement of emission characteristics when applying a DC voltage to the fabricated organic EL device.
(54) ##STR00070## ##STR00071## ##STR00072##
Example 7
(55) An organic EL device was fabricated under the same conditions used in Example 6, except that the compound (1-1) of the structural formula above was replaced with the compound (1-2) of the structural formula below as material of the electron blocking layer 5. The characteristics of the organic EL device thus fabricated were measured in the atmosphere at an ordinary temperature. Table 1 summarizes the results of emission characteristics measurements performed by applying a DC voltage to the fabricated organic EL device.
(56) ##STR00073##
Example 8
(57) An organic EL device was fabricated under the same conditions used in Example 6, except that the compound (1-1) of the structural formula above was replaced with the compound (1-7) of the structural formula below as material of the electron blocking layer 5. The characteristics of the organic EL device thus fabricated were measured in the atmosphere at an ordinary temperature. Table 1 summarizes the results of emission characteristics measurements performed by applying a DC voltage to the fabricated organic EL device.
(58) ##STR00074##
Comparative Example 1
(59) For comparison, an organic EL device was fabricated under the same conditions used in Example 6, except that the compound (1-1) of the structural formula above was replaced with the compound (HTM-1) of the structural formula above as material of the electron blocking layer 5. The characteristics of the organic EL device thus fabricated were measured in the atmosphere at an ordinary temperature. Table 1 summarizes the results of emission characteristics measurements performed by applying a DC voltage to the fabricated organic EL device.
(60) Table 1 summarizes the results of measurement of a device lifetime using the organic EL devices fabricated in Examples 6 to 8 and Comparative Example 1. The device lifetime was measured as a time elapsed until the emission luminance of 2,000 cd/m.sup.2 (initial luminance) at the start of emission was attenuated to 1,900 cd/m.sup.2 (corresponding to 95% when taking the initial luminance as 100%: Attenuation to 95%) when carrying out constant current driving.
(61) TABLE-US-00003 TABLE 1 Luminous Power Lifetime Electron Voltage Luminance efficiency efficiency of device, blocking [V] [cd/m.sup.2] [cd/A] [lm/W] attenuation layer (@10 mA/cm.sup.2) (@10 mA/cm.sup.2) (@10 mA/cm.sup.2) (@10 mA/cm.sup.2) to 95% Example 6 Compound 1-1 3.57 750 7.50 6.61 189 hours Example 7 Compound 1-2 3.59 754 7.54 6.60 186 hours Example 8 Compound 1-7 3.59 756 7.56 6.61 182 hours Comparative HTM-1 3.60 637 6.37 5.60 163 hours Example 1
(62) As shown in Table 1, the luminous efficiency upon passing a current with a current density of 10 mA/cm.sup.2 was 7.50 to 7.56 cd/A for the organic EL devices in Examples 6 to 8, which was higher than 6.37 cd/A for the organic EL device in Comparative Example 1. Further, the power efficiency was 6.60 to 6.61 lm/W for the organic EL devices in Examples 6 to 8, which was higher than 5.60 lm/W for the organic EL device in Comparative Example 1. The device lifetime (95% attenuation) was 182 to 189 hours for the organic EL devices in Examples 6 to 8, showing achievement of a far longer lifetime than 163 hours for the organic EL device in Comparative Example 1.
Example 9
(63) An organic EL device was fabricated under the same conditions used in Example 6, except that the compound (HTM-1) of the structural formula above was replaced with the compound (HTM-2) of the structural formula below as material of the hole injection layer 3 and the hole transport layer 4. The characteristics of the organic EL device thus fabricated were measured in the atmosphere at an ordinary temperature. Table 2 summarizes the results of emission characteristics measurements performed by applying a DC voltage to the fabricated organic EL device.
(64) ##STR00075##
Example 10
(65) An organic EL device was fabricated under the same conditions used in Example 6, except that the compound (HTM-1) of the structural formula above was replaced with the compound (HTM-3) of the structural formula below as material of the hole injection layer 3 and the hole transport layer 4. The characteristics of the organic EL device thus fabricated were measured in the atmosphere at an ordinary temperature. Table 2 summarizes the results of emission characteristics measurements performed by applying a DC voltage to the fabricated organic EL device.
(66) ##STR00076##
Comparative Example 2
(67) For comparison, an organic EL device was fabricated under the same conditions used in Example 6, except that the compound (HTM-1) of the structural formula above was replaced with the compound (HTM-2) of the structural formula above as material of the hole injection layer 3 and the hole transport layer 4, and the compound (1-1) of the structural formula above was replaced with the compound (HTM-2) of the structural formula above as material of the electron blocking layer 5. The characteristics of the organic EL device thus fabricated were measured in the atmosphere at an ordinary temperature. Table 2 summarizes the results of emission characteristics measurements performed by applying a DC voltage to the fabricated organic EL device.
Comparative Example 3
(68) For comparison, an organic EL device was fabricated under the same conditions used in Example 6, except that the compound (HTM-1) of the structural formula above was replaced with the compound (HTM-3) of the structural formula above as material of the hole injection layer 3 and the hole transport layer 4, and the compound (1-1) of the structural formula above was replaced with the compound (HTM-3) of the structural formula above as material of the electron blocking layer 5. The characteristics of the organic EL device thus fabricated were measured in the atmosphere at an ordinary temperature. Table 2 summarizes the results of emission characteristics measurements performed by applying a DC voltage to the fabricated organic EL device.
(69) Table 2 summarizes the results of measurement of a device lifetime using the organic EL devices fabricated in Examples 9 to 10 and Comparative Examples 2 to 3. The device lifetime was measured as a time elapsed until the emission luminance of 2,000 cd/m.sup.2 (initial luminance) at the start of emission was attenuated to 1,900 cd/m.sup.2 (corresponding to 95% when taking the initial luminance as 100%: Attenuation to 95%) when carrying out constant current driving.
(70) TABLE-US-00004 TABLE 2 Hole injection Luminous Power Lifetime layer Electron Voltage Luminance efficiency efficiency of device, Hole transport blocking [V] [cd/m.sup.2] [cd/A] [lm/W] attenuation layer layer (@10 mA/cm.sup.2) (@10 mA/cm.sup.2) (@10 mA/cm.sup.2) (@10 mA/cm.sup.2) to 95% Example 9 HTM-2 Compound 1-1 3.59 756 7.56 6.61 193 hours Example 10 HTM-3 Compound 1-1 3.59 745 7.45 6.53 180 hours Comparative HTM-2 HTM-2 3.60 644 6.44 5.63 165 hours Example 2 Comparative HTM-3 HTM-3 3.62 642 6.42 5.58 151 hours Example 3
(71) As shown in Table 2, the luminous efficiency upon passing a current with a current density of 10 mA/cm.sup.2 was 7.45 to 7.56 cd/A for the organic EL devices in Examples 9 to 10, which was higher than 6.42 to 6.44 cd/A for the organic EL devices in Comparative Examples 2 to 3. Further, the power efficiency was 6.53 to 6.61 lm/W for the organic EL devices in Examples 9 to 10, which was higher than 5.58 to 5.63 lm/W for the organic EL devices in Comparative Examples 2 to 3. The device lifetime (95% attenuation) was 180 to 193 hours for the organic EL devices in Examples 9 to 10, showing achievement of a far longer lifetime than 151 to 165 hours for the organic EL devices in Comparative Examples 2 to 3.
(72) It was found that the organic EL device of the present invention can achieve an organic EL device having high luminous efficiency and a long lifetime compared to the conventional organic EL devices by combining a carbazole compound having a specific structure and a specific light emitting material (dopant) so that carrier balance inside the organic EL device is improved, and further by combining the compounds so that the carrier balance matches the characteristics of the light emitting material.
INDUSTRIAL APPLICABILITY
(73) In the organic EL device of the present invention in which a carbazole compound having a specific structure and a specific light emitting material (dopant) are combined, luminous efficiency can be improved, and also durability of the organic EL device can be improved to attain potential applications for, for example, home electric appliances and illuminations. 1 Glass substrate 2 Transparent anode 3 Hole injection layer 4 Hole transport layer 5 Electron blocking layer 6 Light emitting layer 7 Electron transport layer 8 Electron injection layer 9 Cathode