KR100851519B1 - Iridium Complex with Improved Luminescent Properties and Organic Light-Emitting Diodes Containing Iridium Complex - Google Patents

Abstract

The present invention provides an iridium complex having an aryl derivative substituted with a halogen compound and a pyridine derivative introduced with an alkyl or alkoxy substituent as a main ligand, and an organic electroluminescent device for phosphorescence containing the iridium complex as a dopant of a light emitting layer. According to the present invention, the iridium complex compound synthesized by the main ligand and the secondary ligand introduced into the iridium has not only improved light emission characteristics, but also can be obtained by device doping the light emitting layer with the iridium complex compound to improve the light emission efficiency and the like. there was.

Iridium Complex, triplet, halogenated aryl pyridine, organic light emitting diode (OLED)

Description

Iridium Complex with Improved Luminescent Properties and Organic Light-Emitting Diodes Containing Iridium Complex}

1 is a schematic diagram illustrating a mechanism in which an aryl derivative substituted with a halogen atom and a pyridine derivative in which an alkyl or alkoxy substituent is introduced are prepared in an iridium complex in which a iridium complex is introduced into a main ligand according to an embodiment of the present invention;

2A and 2B are cross-sectional views schematically showing organic light emitting diodes having a single layer and a multilayer form to which iridium complexes synthesized according to the present invention are applied;

3 is a graph showing the results of UV-visible absorption spectrum measurement for iridium complexes synthesized according to Examples 3, 4, 5, and 6 of the present invention;

4 to 7 are graphs showing the results of measurement of photoluminescence (PL) intensity for iridium complexes synthesized according to Examples 3, 4, 5 and 6 of the present invention, respectively;

8A to 8B are graphs showing voltage-current density and voltage-emitting luminance measurement results for an electroluminescent device using an iridium complex compound synthesized according to Example 3 of the present invention as a dopant of a light emitting layer, respectively;

FIG. 9 is a graph showing electroluminescence (EL) intensity measurement results for an electroluminescent device using an iridium complex compound synthesized according to Example 3 of the present invention as a light guide layer;

FIG. 10 is a graph showing electroluminescence (EL) intensity measurement results for an electroluminescent device using Flrpic, an iridium complex compound known to exhibit blue light emission, as a dopant of a light emitting layer.

<Description of the symbols for the main parts of the drawings>

1000, 2000: organic light emitting display device 1100, 2100: substrate

1110 and 2110: first electrode 2120: buffer layer

2130: hole injection layer 2140: hole transport layer

1150, 2150: light emitting layer 2160: electron transport layer

2170: electron injection layer 1180, 2180: second electrode

The present invention relates to an iridium complex compound and an organic electroluminescent device comprising the same, and more particularly, to an iridium complex compound and an organic electroluminescent device comprising the same having improved luminous efficiency.

Recently, as the size of display devices increases, the demand for flat display devices such as liquid crystal displays (LCDs) and plasma display panels (PDPs) is increasing. These flat display devices have slower response speeds and limited viewing angles compared to CRTs, and thus, researches on other display devices have been conducted. One of them is an electroluminescent device.

Conventional electroluminescent devices are mainly used inorganic electroluminescent devices using a light emitting image generated when an electric field is applied to an inorganic semiconductor made of a pn junction such as ZnS, CdS, etc., but in the case of inorganic electroluminescent devices, a driving voltage of AC 220V or more is used. There is a problem that it is difficult to increase the size because the device is manufactured in a vacuum state, and in particular, it is difficult to obtain blue with high efficiency.

Due to these problems, research on organic light-emitting diodes (OLEDs) using organic materials is being conducted. An organic electroluminescent device is a display using an organic material that emits light by itself. When an electric field is applied to the organic material, electrons and holes are transferred from the cathode and the anode, respectively, and are combined in the organic material. Uses organic electroluminescence emitted by light. Compared with LCDs, organic light emitting diodes are attracting attention as next-generation display devices because they have a good viewing angle, low power consumption, and significantly improved response speeds to process high quality images.

The phenomenon of light emission in such an organic light emitting device can be classified into fluorescence and phosphorescence. When fluorescence is emitted from an organic molecule to a ground state from a singlet excited state, it emits light. Phosphorescence is a phenomenon in which organic molecules emit light when they fall from the triplet excited state to the ground state.

This will be described in detail as follows. Organic compounds doped in organic electroluminescent devices, including light emitting layers, share electrons between atomic carbon and other carbon atoms, or between atomic carbon and other atoms to form molecules through covalent bonds. State electron orbits (atomic orbital, AO) are converted to molecular orbitals (molecular orbital, MO). In molecular electron orbits, two pairs of atomic orbitals in the atomic state each participate to form a bonding orbital and an antibonding orbital, respectively. At this time, the band formed by many coupling orbits is called a valence band, and the die formed by many anti-bonding orbits is called a conduction band. The highest energy level of the valence band is called HOMO. The highest energy level of the conductive band is called Lowest Unoccupied Molecular Orbital (LUMO), and the energy difference between the energy of HOMO and LUMO is called the band gap.

However, electrons and holes injected into the organic light emitting layer constituting the organic light emitting device are recombined to form excitons, and the color of the color corresponding to the energy band gap of the light emitting layer in the process of converting the electrical energy of the excitons into light energy. Implement light. In this process, a single spin exciton with zero spin and triplet exciton with a spin of 1 are generated at a ratio of 1: 3. According to the selection rule for the electric dipole transition, the spin quantum number should not be changed when transitioning from the excited state to the ground state. Since the ground state of the organic molecules is the singlet state, the singlet excitons emit light and transition to the ground state. However, triplet excitons can't glow and transition. Therefore, in general, the maximum internal quantum efficiency of the organic light emitting diode doped with fluorescent dye is limited to 25%. However, when the spin-orbital coupling is large, the triplet excitons are phosphorescent to the ground state because the inter-system crossing occurs between the singlet and triplet states by mixing the singlet form and the triplet state. Can make a transition. After all, if the triplet excitons can be used to emit light, the internal quantum efficiency of the organic light emitting device can theoretically be improved to 100%.

As such, the phosphorescent organic electroluminescent device that can significantly improve the luminous efficiency of the organic light emitting device is S.R. Professor Forrest and M.E. of USC. It was developed by Thompson's team, especially since the spin-orbital bond is proportional to the square of the atomic number, and phosphorescent complexes of heavy atoms such as platinum (Pt), iridium (Ir), europium (Eu) and terbium (Tb) are phosphorescent. It is known that the efficiency is high. In the case of platinum complexes, the lowest triplet excitons are ligand-centered excitons (LC excitons), while the iridium complexes have the lowest energy triplet excitons. ligand charge transfer (MLCT). Thus, iridium complexes form larger spin-orbit bonds than platinum complexes, resulting in much shorter triplet exciton lifetimes and high phosphorescence efficiencies.

In this regard, C. Adachi et al. Described bis (2-phenylpyridine) iridium (III) acetylacetonate [(ppy) ₂ Ir (acac)], a green phosphorescent pigment with iridium as its central metal, with 3-phenyl-4- (1'- An organic electroluminescent device with a maximum luminous efficiency of 60 lm / W and a maximum internal quantum efficiency of 87% has been announced by doping naphthyl) -5-phenyl-1,2,4-triazole (TAZ). In addition, U.S. Universal Display Corp. (UDC) has announced that it has achieved high luminous efficiency of 82 lm / W by doping such a green phosphorescent dye into the light emitting layer and using a hole injection material developed by LG Chem. As described above, phosphorescent organic light emitting diodes emitting green and red light have been developed, but blue phosphorescent organic light emitting diodes having excellent luminous efficiency, color coordinates, and lifetimes have not been developed. For example, Flrpic (Iridium (III) bis [2,2 '(4'-difluorophenyl) -pyridinato-N, C2'] picolinate) has been developed recently, but it is still not a pure blue light emitting material in terms of color purity. There is a crowd.

The present invention has been proposed to solve the above problems, and an object of the present invention is to provide an iridium complex compound having a greatly improved blue light emission characteristics and luminous efficiency, particularly with respect to blue, and an organic light emitting device including the same. .

It is another object of the present invention to provide an iridium complex compound having an improved solubility in organic solvents, significantly improved heat resistance and excellent interfacial properties with an electrode, and an organic electroluminescent device comprising the same.

Other objects and advantages of the present invention will become more apparent from the following drawings and the configuration of the invention.

According to an aspect of the present invention having the above object, a pyridine derivative substituted with an alkyl group having 1 to 20 carbon atoms or an alkoxy group having 1 to 20 carbon atoms and an aryl derivative substituted with a halogen compound are provided as iridium complexes. do.

Iridium complex compound synthesized according to an embodiment of the present invention has a structure of formula (1).

Formula 1

는 피콜리닉산-N-oxide, 피페콜리닉산, 안트라닐릭산, 피라진산이다.)(Formula 1 R ₁ is an alkyl group having 1 to 20 carbon atoms or an alkoxy group having 1 to 20 carbon atoms; Ar is an aryl group; R ₂ is a halogen,

Are picolinic acid-N-oxide, pipecolinic acid, anthranilic acid and pyrazine acid.)

The aryl group introduced into the main chain of the iridium complex in the context of the present invention is phenyl, naphthalen, fluorene, carbazole, fluorene, phenazine, phenazine, phenanthroline ( phenanthroline, phenanthridine, permidine, acridine, acinnoline, cinnoline, quinazoline, quinoxaline, naphthydrine, phthalazine (phtalazine), quinolizine, indole, indazole, pyridazine, pyrazine, pyrimidine, pyridine, pyrazole, It is selected from the group consisting of imidazole, pyrrole, and particularly preferably an aryl group free of hetero atoms such as phenyl, naphthalene, and the like.

Especially preferably, R ₁ of Formula 1 is an alkyl group having 1 to 10 carbon atoms or an alkoxy group having 1 to 10 carbon atoms, and R ₂ of Formula 1 may include fluorine or chlorine.

On the other hand, according to another aspect of the present invention provides an organic electroluminescent device in which the iridium complex compound as described above is included in the light emitting layer.

The organic electroluminescent device according to the present invention includes, for example, a first electrode functioning as an anode, and a second electrode formed opposite to the first electrode and functioning as a cathode, and the light emitting layer includes: It is laminated between the second electrodes.

According to a preferred embodiment, the buffer layer between the first electrode and the light emitting layer of the organic light emitting device may be a multi-layer form further comprising an electron transfer layer and an electron injection layer between the light emitting layer and the second electrode. In this case, the buffer layer includes a hole injection layer stacked on top of the first electrode, and a hole transport layer stacked on top of the hole injection layer.

On the other hand, the iridium complex is included as a dopant that can interact with other host materials included in the light emitting layer, preferably contained in a concentration of 3 to 20% by weight based on the total amount of the light emitting layer.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

As described above, in the organic electroluminescent device, it is advantageous to use the light emitting material having the phosphorescent property rather than the light emitting material having the fluorescent property in terms of luminous efficiency. In the present invention, among the light emitting materials having such a phosphorescent property, not only the blue light emitting property and the light emitting efficiency are improved, but also an organic electroluminescent device comprising an iridium complex compound and an iridium complex compound having excellent solubility or compatibility with various organic solvents in the light emitting layer. Developed.

In the iridium complex according to the present invention, aromatic aryl derivatives and pyridine derivatives are introduced as main ligands, respectively, and are configured to exhibit improved blue light emission characteristics and luminous efficiency in comparison with the conventional blue light emission. According to a preferred embodiment, the iridium complex synthesized in the present invention has a structure of formula (1).

Formula 1

는 피콜리닉산-N-oxide, 피페콜리닉산, 안트라닐릭산, 피라진산이다.)(Formula 1 R ₁ is an alkyl group having 1 to 20 carbon atoms or an alkoxy group having 1 to 20 carbon atoms; Ar is an aryl group; R ₂ is a halogen,

Are picolinic acid-N-oxide, pipecolinic acid, anthranilic acid and pyrazine acid.)

As can be seen in the above formula (1), the iridium complex according to the present invention is an aromatic pyridine derivative introduced with an alkyl or alkoxy group and an aryl derivative introduced with a halogen compound as a main ligand. In the iridium complex compound exhibiting the phosphorescence property as in the present invention, the main ligand is a main factor for determining the emission color, and in particular, the emission property may be converted according to the electron density of nitrogen (N) contained in the ligand. In the case of the aromatic aryl derivative and the pyridine derivative introduced into the main ligand according to the present invention, the electron density of the nitrogen included in the structure is greatly increased compared to the conventionally developed iridium complex compound, thereby showing pure blue light emission.

The aryl group introduced into the main chain of the iridium complex synthesized according to the present invention includes phenyl, naphthalene, carbazole, fluorene, phenazine, phenanthroline, phenan Tridine (phenanthridine), acridine (acridine), sinoline (cinnoline), quinazoline (quinazoline), quinoxaline, naphthydrine, phthalazine (quintalzine), quinolizine , Indole, indazole, pyridazine, pyrazine, pyrimidine, pyridine, pyridine, pyrazole, imidazole , Pyrrole and the like, preferably phenyl, naphthalene, carbazole, fluorene and the like, but the present invention is not limited thereto.

Meanwhile, the aromatic aryl derivative and the pyridine derivative introduced into the main ligand according to the present invention may be substituted by various substituents such as alkyl groups, alkoxy groups, halogens and the like. As such, the iridium complex compound synthesized according to the present invention due to the substitution of various functional groups may be commonly used in organic solvents used, and when applied to organic electroluminescent devices, the interfacial characteristics with the electrodes may be improved.

Particularly as the substituent which may be substituted on the aromatic ring connected to pyridine in the context of the present invention, for example, an alkyl group having 1 to 20 carbon atoms, preferably having 1 to 10 carbon atoms, preferably having 1 to 20 carbon atoms, It contains an alkoxy group. Meanwhile, halogen atoms such as fluorine (F), chlorine (Cl), bromine (Br), and iodine (I) may be used as substituents on the aryl ring, and preferred halogen atoms include fluorine and chlorine.

)로는 피콜리닉산-N-옥사이드(picolinic acid N-oxide,

); 피라진산(pyrazine-2-carboxylic acid,

); 또는 피페콜리 닉산(pipecolinic acid,

), 안트라닐릭산 (anthranilic acid,

) 등이 포함될 수 있으나, 본 발명이 이들 보조리간드로만 한정되는 것은 아니다. On the other hand, the iridium complex synthesized according to the preferred embodiment of the present invention is an ancillary ligand (ancillary ligand) is introduced separately from the above-described main ligand. The auxiliary ligands are selected to adjust the fine color in the luminescence properties of the synthesized complex compound. In particular, it is preferable that the conjugated structure has a small conjugated structure so that the iridium complex compound of the present invention exhibits pure blue light emission. Secondary ligand that can be selected in connection with the present invention (

) Picolinic acid N-oxide (picolinic acid N-oxide,

); Pyrazine-2-carboxylic acid,

); Or pipecolinic acid,

), Anthranilic acid (anthranilic acid,

) May be included, but the present invention is not limited to these auxiliary ligands.

Next, the synthesis | combining process of the iridium complex compound which concerns on this invention is demonstrated. 1 is a schematic diagram illustrating a process of synthesizing the iridium complex of Chemical Formula 1 according to an embodiment of the present invention.

As shown, first, an aromatic boronic acid ((2)) such as a pyridine ((1)) derivative substituted with an alkyl or alkoxy group having 1 to 20 carbon atoms and a phenylboronic acid substituted with a halogen atom such as fluorine is replaced with K ₂ CO. _The arylpyridine ligand ((3)) is produced by Suzuki synthesis in ₃ and Pd (PPh ₃ ) ₄ and THF solvents. The arylpyridine dimer ((4)) can then be synthesized by dissolving the resulting mixture of arylpyridine zuligand and iridium chloride hydrate (IrCl ₃ -3H ₂ O) in a suitable solvent and then mixing. Finally, the obtained chlorine-crosslinked dimer ((4)) is mixed with an auxiliary ligand and an appropriate solvent, and an iridium complex compound having a pyridine derivative substituted with an alkyl group or an alkoxy group and an aryl group substituted with a halogen atom introduced into the main chain (( 5)) can be synthesized The iridium complex synthesized through the above method shows the maximum emission peak at approximately 470 nm as shown in the emission measurement results of FIGS. It was confirmed to have.

The iridium complex compound synthesized through the above-described method is a phosphorescent light emitting material having excellent light emission characteristics, and when used as a dopant of a light emitting layer of an organic light emitting diode, for example, pure blue light emission can be obtained. An organic electroluminescent device to which a complex compound can be applied will be described. 2A schematically illustrates an organic light emitting display device 1000 in a single layer type to which the above-described iridium complex compound may be applied according to an embodiment of the present invention. The single layer organic light emitting diode 1000 has a structure in which the substrate 1100, the first electrode 1110, the light emitting layer 1150, and the second electrode 1180 are sequentially stacked. The substrate 1100 may be made of a material such as, for example, glass or plastic.

Meanwhile, the first electrode 1110 and the second electrode 1180 serve as an anode and a cathode, respectively, and the first electrode 1110 is one part of the second electrode 1180, for example. Use materials with large work functions. In particular, in relation to the present invention, the first electrode 1110 is an effective material for injecting a hole, which is a positive-charged carrier, and is a metal, a mixed metal, an alloy, a metal oxide, or a mixed metal oxide or a conductive polymer. Can be. Specifically, the first electrode 1110 may be indium-tin oxide (ITO), fluorine doped tin oxide (FTO), ZnO-Ga ₂ O ₃ , or ZnO-Al ₂ O ₃ , SnO ₂ -Sb ₂ O ₃ Materials such as mixed metal oxides, conductive polymers such as polyaniline, polythiophene, and the like may be used, and according to a preferred embodiment, ITO.

In contrast, the second electrode 1180 may be formed of gold, aluminum, copper, silver, or an alloy thereof as an effective material for injecting electrons, which are negative-charged carriers; Aluminum, indium, calcium, barium, magnesium and alloys thereof, such as calcium / aluminum alloys, magnesium / silver alloys, aluminum / lithium alloys, and the like; Or in some cases, may be selected from metals belonging to rare earths, lanthanides, actinides, preferably aluminum, or aluminum / calcium alloys.

Meanwhile, in the light emitting layer 1150 stacked between the first electrode 1110 and the second electrode 1180, the above-described iridium complex compound synthesized according to the present invention is used as a dopant. In this regard, the light emitting layer 1150 includes a host, which is a light emitting material, to increase the light emitting efficiency by suppressing energy loss processes such as color purity change and quenching. In particular, since the iridium complex synthesized according to the present invention exhibits almost pure blue light emission, the host may be selected so that energy emitted from the host included in the light emitting layer 1150 can be transferred to the iridium complex compound, which is a dopant. According to the present invention, the host included in the emission layer 1150 may include both a host having a fluorescent characteristic and a host having a phosphorescent characteristic, but a host having a phosphorescent characteristic. Specifically, the host, which is a light emitting material in the blue region, may be, for example, poly (phenylenevinylene), polyvinylene (poly (fluorene)), and polyparaphenylene (poly (para-phenylene). ), PPP), polyalkylthiothio (poly (alkyllythiophene)), polypyridine (poly (pyridine), PPy), such as polymer materials, distyrylbenzene (DSB), distyrylbenzene derivative ( PESB), distyrylarylene (DSA), distyrylarylene derivatives, 1,2,3,4,5-pentaphenyl-1,3-cyclopentadiene (1,2,3,4,5- cyclopentadiene derivatives such as pentaphenyl-1,3-cyclopentadiene, PPCP), DPVBi (4,4'-bis (2,2'-diphenyl vinyl) -1,1'-biphenyl), DPVBi derivatives, spiro- Material such as DPVBi.

In particular, hosts having phosphorescent properties that can be used in connection with the present invention include aryl amines, carbazoles, and spiros. Specifically, 4,4-N, N-dicarbazole-biphenyl (4,4-N, N-dicarbazole-biphenyl, CBP), N, N-dicarbazoyl-3,5-benzene (N, N- dicarbazoyl-3,5-benzene, mCP), poly (vinylcarbazole, PVK), polyfluorene, 4,4'-bis [9- (3,6biphenylcarbazolyl)]-1- 1,1'-biphenyl4,4'-bis [9- (3,6-biphenylcarbazolyl)]-1-1,1'-biphenyl, 9,10-bis [(2 ', 7' -t-butyl) -9 ', 9' '-spirobifluorenyl anthracene, tetrafluorene (tetrafluorene) and the like may be included, preferably CBP and mCP may be used.

According to a preferred embodiment, the light emitting layer 1170 is laminated on top of the first electrode 1110 with a thickness of approximately 5 to 200 nm, preferably 50 to 10 nm, wherein the iridium complex synthesized according to the present invention is a dopant. It is included in a concentration of 3 to 20% by weight, preferably 5 to 10% by weight with respect to the light emitting layer 1170.

On the other hand, the iridium complex synthesized according to the present invention is not only the organic light emitting device 1000 in the form of a single layer described above, but also a multi-layer organic field provided with a separate layer for electron / hole transport between the light emitting layer and the electrode. 2B is a schematic cross-sectional view of an organic light emitting diode 2000 having a multi-layer type to which an iridium complex compound synthesized according to the present invention can be applied. As shown, the organic light emitting diode 2000 includes a substrate 2100, a first electrode 2110, a hole injection layer HIL 2130, and a hole transporting layer HTL 2140. A buffer layer 2120, a light emitting layer 2150, an electron transporting layer (ETL 2160), an electron injection layer (EIL 2170), and a second electrode 2180 sequentially stacked It has a form.

In the multilayer organic light emitting device having the above-described structure, the buffer layer 2120 stacked between the first electrode 2110 and the light emitting layer 2150 may be disposed between the material used as the first electrode 2110 and the light emitting layer 2150. Function to improve the interfacial properties of the or to supply holes to the light emitting layer 2150 stably. The buffer layer 2120 may be functionally divided into a hole injection layer 2130 and a hole transport layer 2140.

In this case, the hole injection layer 2130 constituting the buffer layer 2120 not only improves the interfacial property between the material such as ITO used as the first electrode 2110 and the organic material used as the hole transport layer 2140. The surface is coated on top of the uneven ITO to soften the surface of the ITO, thereby improving conductivity or luminous efficiency. In particular, the hole injection layer 2130 has a work function level of ITO and a hole transport layer 2140 in order to adjust the difference between the work function level of ITO and the like as the first electrode 2110 and the HOMO level of the hole transport layer 2140. As a material having a median value of HOMO level of), a material having a particularly suitable conductivity is selected. As a material forming the hole injection layer 2120 in relation to the present invention, copper-phthlalocyanine (CuPc), N, N'-dinaphthyl-N, N'-phenyl- (1,1'-biphenyl) -4,4 ' -diamine, NPD), α-NPD, 4,4 ', 4' '-tris [methylphenyl (phenyl) amino] triphenyl amine (m-MTDATA), 4,4', 4 ''-tris [1-naphthyl ( phenyl) amino] triphenyl amine (1-TNATA), 4,4 ', 4' '-tris [2-naphthyl (phenyl) amino] triphenyl amine (2-TNATA), 1,3,5-tris [N- ( Aromatic amines such as 4-diphenylaminophenyl) phenylamino] benzene (p-DPA-TDAB), poly (3,4-ethylene dixoythiophene) -poly (styrene sulfonate) (PEDOT), which is a polythiophene derivative as a conductive polymer, In particular, the embodiment of the present invention used PEDOT. The hole injection layer 2130 may be coated on the upper portion of the first electrode 2110 to a thickness of 20 ~ 200Å.

Meanwhile, a hole transport layer 2140 is formed on the hole injection layer 2130 to stably supply the holes introduced through the hole injection layer 2130 to the light emitting layer 2150, and the holes may be smoothly transported and transferred. The material of which the HOMO level of the hole transport layer 2140 is higher than the HOMO level of the light emitting layer 2150 is selected. Materials that can be used as the hole transport layer 2140 in the context of the present invention is N, N'-bis (3-methylphenyl) -N, N'-diphenyl- [1,1'-diphenyl-4,4'- diamine (TPD), α-TPD, N, N'-bis (1-naphthyl) -N, N'-biphenyl- [1,1'-biphenyl] -4,4'-diamine (TPB), N, N '-di (naphthalene-1-yl) -N, N'-diphenyl-benzidene (NPB), triphenylamine (TPA), bis [4- (N, N-diethylamino) -2-methylphenyl] (4-methylphenyl ) methane (MPMP), N, N, N ', N'-tetrakis (4-methylphenyl)-(1,1'-biphenyl) -4,4-diamine (TTB), N, N'-bis (4- Low molecular hole transport such as methylphenyl) -N, N'-bis (4-ethylphenyl)-[1,1 '-(3,3'-dimethyl) biphenyl] -4,4'-diamine (ETPD), or mixtures thereof Substance; Polymer hole transport materials such as polyvinylcarbazole, polyaniline, (phenylmethyl) polysilane, and the like can be used. The hole transport layer may be deposited on the hole injection layer 2130 to a thickness of about 10 to 100 nm.

However, each material substantially used in the hole injection layer and the hole transport layer includes both functions rather than having one function. That is, it should be noted that in the above, the material used as the hole injection layer not only improves the hole transport or transport but also the material used as the hole transport layer also improves the hole injection. As a result, in the above description, the materials used in the hole injection layer and the hole transport layer can be distinguished. However, such materials are only a matter of choice, and these materials are generally between the first electrode 2110 and the light emitting layer 2150. Is included in the buffer layer 2120.

Meanwhile, according to the present invention, the electron injection layer 2170 and the electron transfer layer 2160, which may correspond to the hole injection layer 2130 and the hole transfer layer 2140, are disposed between the emission layer 2150 and the second electrode 2180. Is formed. The electron injection layer 2170 is intended to induce smooth electron injection. Unlike other charge transfer layers, an alkali metal or alkaline earth metal ion form is used, such as LiF, BaF ₂ , CsF, etc., and the electron transport layer is formed by these metal cations. And may induce doping for 2160.

On the other hand, the electron transport layer 2160 is mainly composed of a material containing a chemical component that attracts electrons, for which high electron mobility is required, and stably supplies electrons to the light emitting layer 2150 through smooth electron transport. In this case, the particularly strong electron-receiver component may quench the electrons, so it is preferable to use an appropriate electron-receiving component to improve electron mobility. Electron transport layers that may be used in accordance with the present invention include Alq ₃ and oxadizole components. Specifically, Tris (8-hydroxyquinolinato) aluminum (Alq ₃ ); 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (DDPA); 2- (4-biphenyl) -5- (4-tert-butyl) -1,3,4-oxadizole (PBD), 3- (4-biphenyl) -4-phenyl-5- (4-tert-butyl) Azole compounds such as -1,2,4-triazole (TAZ); phenylquinozaline and the like. In the embodiment of the present invention, Alq ₃ was used as the electron transport layer 2160, and the electron transport layer 2160 may be stacked on the light emitting layer 2150 with a thickness of 5 to 150 nm.

Although not shown in the drawings, the lifespan of the device when the holes introduced through the hole injection layer 2130 and the hole transport layer 2140 pass through the light emitting layer 2150 to the second electrode 2180 is measured. Since the efficiency may be reduced, a hole blocking layer (HBL) having a very low HOMO level may be formed between the emission layer 2150 and the electron transport layer 2160. Materials that can be used in the hole blocking layer in the present invention include 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), and the light emitting layer (2150) to a thickness of about 5 ~ 150 nm It may be deposited on top of).

As described above, the iridium complex synthesized according to the present invention exhibits a wavelength corresponding to the pure blue region, and the electroluminescent device to which the improved iridium complex is applied as a dopant of the light emitting layer measures the electrical characteristics of FIGS. 8A to 8B. As can be seen from the results, it was confirmed that not only the electrical characteristics were greatly improved, but also light emission was shown in the blue region of about 470 nm as shown in FIG. 9.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples.

Example 1 Preparation of 2- (2,4-Difluorophenyl) -4-methylpyridine [(2- (2,4-Difluorophenyl) -4-methylpyridine)]

In a 100 mL three-necked flask, 2-bromo-4-methylpyridine (1.75 mL, 15.2 mmol, (1) in FIG. 1) and 2,4-diflurophenylboronic acid (3.00 g, 19 mmol, (2) in FIG. 1) were added. Put it in. Place a reflux apparatus in the flask containing the reagent and add the solvent under nitrogen. THF (57 mL) purified by sodium / benzophenone is used as a solvent, and an additional 4 M aqueous potassium carbonate solution (10 mL) and ethanol (1.9 mL) are added thereto. Here potassium carbonate acts as a base during the reaction. Then remove the gas from the flask containing the mixture with liquid nitrogen and add tetrakis (triphenylphosphine palladium) (1.10 g, 0.95 mmol) as reaction catalyst under nitrogen. The reaction mixture was refluxed at 85 ° C. for 15 hours, and the reaction was confirmed by TLC. After cooling the mixture to room temperature, the organic layer was extracted using diethyl ether (2 × 200 ml) and brine. Water remaining in the organic layer extracted with anhydrous magnesium sulfate (MgSO ₄ ) is removed, and the magnesium sulfate absorbed with water is filtered, and then the solvent is removed under reduced pressure. The obtained residue was separated by flash column chromatography (eluent; hexane / ethyl acetate = 4: 1, v / v) to obtain a liquid 2,4-difluorophenyl-4-methylpyridine ligand ((3) of FIG. 1). You can get it.

Yield: 81% (2.52 g)

¹ H-NMR (CDCl ₃ , δ ppm): 8.57 (d, 1H), 7.96 (m, 1H), 7.57 (s, 1H), 7.09 (d, 1H), 7.01 (t, 1H), 6.98 (t , 1H), 6.92 (m, 2H), 2.42 (s, -CH ₃ , 3H)

Example 2. Preparation of chloride-bridged dimer

In a 100 mL flask, IrCl ₃ 3H ₂ O (1.08 g, 3.05 mmol) and 2- (2,4-difluorophenyl) -4-methylpyridine (2.50 g, 12.2 mmol), which is the ligand synthesized in Example 1 ). To this, 2-ethoxyethanol (30 mL) and water (10 mL) were mixed in a 3: 1 ratio, added as a solvent, and the mixture was refluxed at 130 ° C for 24 hours. It can be seen that the product is in a solid state during the reaction and is cooled to room temperature when the reaction is completed. Then the product is filtered, washed with ethanol solution and dried in a vacuum oven as it is. The dried solid is a chlorine-crosslinked dimer which is yellow and is an intermediate of the final product ((4) of FIG. 1).

Yield: 85% (1.65 g)

Elemental Analysis: Calcd. for (C ₄₈ H ₃₂ Cl ₂ F ₈ Ir ₂ N ₄ ) n: C, 45.32; H, 2.54; N, 4.40. Found: C, 46.12; H, 2. 44; N, 4.46

Example 3 Preparation of Complex Compound Having Picolinic Acid-N-Oxide as Secondary Ligand

20 mL volumetric flask of chlorine-crosslinked dimer (0.102 g, 0.08 mmol), picolinic acid-N-oxide (0.033 g, 0.24 mmol) and Na ₂ CO ₃ (0.102 g, 0.96 mmol) obtained in Example ₂ After adding 2-ethoxyethanol (8 mL) as a solvent, reflux at 155 ℃ for 15 ~ 17 hours. After completion of the reaction by TLC, the mixture was cooled to room temperature, the solvent was removed under reduced pressure, and the organic layer was extracted with dichloromethane (2 × 100 ml) and brine. Anhydrous MgSO ₄ was added to the separated organic layer, the filtrate was dried, the filtrate was concentrated under reduced pressure, and the residue was separated by flash column chromatography (eluent; dichloro methane / methanol = 10: 1, v / v). The iridium complex compound (Fig. 1 (5)) into which -oxide was introduced was obtained. Hereinafter, the iridium complex compound obtained through this example is abbreviated as "Ir (dfpmpy) ₂ (picN)".

Yield: 75% (0.088 g)

¹ H-NMR (CDCl ₃ , δ ppm): 8.55 (d, 1H), 8.32 (d, 1H), 8.08 (d, 2H), 7.93 (t, 1H), 7.77 (d, 1H), 7.41 (t , 1H), 7.24 (d, 1H), 7.01 (d, 1H), 6.79 (d, 1H), 6.51-6.32 (m, 2H), 5.84 (d, 1H), 5.59 (d, 1H), 2.54 ( s, -CH ₃ , 6H)

Example 4 Preparation of Complex Compound Having Pipelinecholic Acid as Auxiliary Ligand

The chlorine-crosslinked dimer obtained in Example 2 (0.102 g, 0.08 mmol), pipecolic acid (0.030 g, 0.24 mmol) and Na ₂ CO ₃ (0.102 g, 0.96 mmol) were placed in a 20 mL round bottom flask. 2-ethoxyethanol (8 mL) was added as a solvent and refluxed at 158 ° C. for 15-17 hours. After completion of the reaction by TLC, the reaction mixture was cooled to room temperature to remove the solvent under reduced pressure, and the organic layer was extracted with dichloromethane (2 × 100 mL) and brine. Anhydrous MgSO ₄ was added to the separated organic layer, the filtrate was dried, the filtrate was concentrated under reduced pressure, and the residue was separated by flash column chromatography (eluent; dichloro methane / methanol = 10: 1, v / v). Iridium complex compound ((5) of FIG. 1) was obtained. Hereinafter, the iridium complex compound obtained through this example is abbreviated as "Ir (dfpmpy) ₂ (ppc)".

Yield: 73% (0.085 g)

¹ H-NMR (CDCl ₃ , δ ppm): 8.59 (d, 1H), 8.14 (s, 2H), 8.09 (d, 1H), 7.18 (m, 2H), 6.38 (m, 2H), 5.84 (d , 1H), 5.39 (d, 1H), 2.64 (d, -CH ₃ , 6H)

Example 5 Preparation of Complexes Having Anthranilic Acid as Auxiliary Ligand

The chlorine-crosslinked dimer obtained in Example 2 (0.102 g, 0.08 mmol), anthranilic acid (0.033 g, 0.24 mmol) and Na2CO3 (0.102 g, 0.96 mmol) were placed in a 20 mL flask and 2-ethoxyethanol (8 mL) was added as a solvent and refluxed at 158 ° C. for 15-17 hours. After completion of the reaction by TLC, the mixture was cooled to room temperature, concentrated under reduced pressure, and extracted with dichloromethane (2 × 100 mL) and brine. Anhydrous MgSO ₄ was added to the separated organic layer to remove moisture, and then filtered, and the solvent was removed under reduced pressure. The obtained residue was separated by flash column chromatography (eluent; hexane / ethylacetate = 2: 1, v / v) to obtain an iridium complex in which anthranilic acid was introduced as an auxiliary ligand (FIG. 1 (5)). Hereinafter, the iridium complex compound obtained through this example is abbreviated as "Ir (dfpmpy) ₂ (anth)".

Yield: 72% (0.085 g)

¹ H-NMR (CDCl ₃ , δ ppm): 8.02 (s, 1H), 7.84 (d, 1H), 7.71 (m, 1H), 7.64 (s, 1H), 7.36 (d, 1H), 6.74 (d , 1H), 6.62 (m, 1H), 6.52 (d, 1H), 6.35-6.47 (m, 1H), 6.01 (d, 1H), 5.82 (d, 1H), 4.38 (m, 1H), 2.44 ( d, -CH ₃ , 6H)

Example 6 Preparation of Complex Compounds Having Pyrazinic Acid as Secondary Ligand

Chlorine-crosslinked dimer obtained in Example 2 (0.508 g, 0.4 mmol), pyrazine-2-carboxylic acid (0.149 g, 1.2 mmol) and Na ₂ CO ₃ (0.509 g, 4.8 mmol) in a 50 mL volumetric flask After adding 2-ethoxyethanol (20 mL) as a solvent, reflux at 157 ℃ for 15 ~ 17 hours. After completion of the reaction by TLC, the mixture was cooled to room temperature, concentrated under reduced pressure, and extracted with dichloromethane (2 × 150 mL) and brine. Anhydrous MgSO ₄ was added to the separated organic layer to remove moisture, and then filtered, and the solvent was removed under reduced pressure. The obtained residue was separated by flash column chromatography (eluent; hexane / ethylacetate = 1: 2, v / v) to obtain an iridium complex compound (FIG. 1 (5)) into which pyrazine acid was introduced as an auxiliary ligand. Hereinafter, the iridium complex obtained through this example is abbreviated as "Ir (dfpmpy) ₂ (prz)".

Yield: 76% (0.440 g)

¹ H-NMR (CDCl ₃ , δ ppm): 9.46 (s, 1H), 8.72 (d, 1H), 8.48 (d, 1H), 8.08 (d, 2H), 7.76 (s, 1H), 7.24 (t , 1H), 7.04 (d, 1H), 6.84 (d, 1H), 6.54-6.32 (m, 2H), 5.84 (d, 1H), 5.55 (d, 1H), 2.60 (s, -CH ₃ , 6H )

Example 7 Measurement of Absorption Spectrum of Iridium Complex

In this embodiment, Ir (dfpmpy) ₂ (picN), Ir (dfpmpy) ₂ (ppc), Ir (dfpmpy) ₂ (anth), which are the iridium complexes synthesized through the procedures of Examples 3, 4, 5, and 6, respectively UV-visible absorption spectra were measured using a Shimadzu UV-3100 spectrometer in a state in which the Ir (dfpmpy) ₂ (prz) luminescent material was dissolved in chloroform.

Figure 3 is Ir (dfpmpy) ₂ (picN), Ir (dfpmpy) ₂ (ppc), Ir (dfpmpy) ₂ (anth), Ir (dfpmpy) ₂ , which is the iridium complex synthesized in Examples 3, 4, 5, 6 (prz) It is a graph which shows the measurement result of UV-visible absorption spectrum about light emitting material. Looking at the UV-visible absorption peak of the iridium complex synthesized according to the present invention, the ligands exhibit absorption wavelengths of 370 nm or less, which can be thought to be due to spin-allowed π-π * transition of the ligands themselves. Therefore, the weak shoulder in the region below 370 nm seen in the Ir (dfpmpy) ₂ (LX) complex can be attributed to the π-π * transition of the ligand and the wavelengths near 400 nm are spin-allowed metal to ligand charge transfer. band (MLCT). In particular, Ir (dfpmpy) ₂ (picN) and Ir (dfpmpy) ₂ (anth) show strong MLCT absorption peaks above 400 nm, which is expected to be a singlet due to strong spin-orbit coupling between Ir (III) metal and ligand. It can be seen that the triplet energy transfer is active.

Example 8. Determination of photoluminescence (PL) in solution of iridium complex

In this embodiment, Ir (dfpmpy) ₂ (picN), Ir (dfpmpy) ₂ (ppc), Ir (dfpmpy) ₂ (anth), which are the iridium complexes synthesized through the procedures of Examples 3, 4, 5, and 6, respectively The photoluminescence properties of Ir (dfpmpy) ₂ (prz) were measured by PL using Hitachi F-4500. PL was measured using the UV maximum absorption wavelength measured in each of the iridium-based light emitting materials as the excitation wavelength. In FIGS. 4, 5, 6 and 7, in particular, the iridium complex compound Ir (composite in Examples 3, 4, 5 and 6) was used. PL measurement results for dfpmpy) ₂ (picN), Ir (dfpmpy) ₂ (ppc), Ir (dfpmpy) ₂ (anth), Ir (dfpmpy) ₂ (prz) are shown graphically. Ir (dfpmpy) ₂ (picN), Ir (dfpmpy) ₂ (ppc), Ir (dfpmpy) ₂ (anth), Ir (dfpmpy) ₂ (prz) are 492 nm, 472 nm, 477 nm, 600 in chloroform solvent, respectively. It was shown that the emission wavelength of about nm. Ir (dfpmpy) ₂ (prz) predicted that the LUMO energy level would increase due to the introduction of a methyl group at the pyridine site, thus increasing the overall energy interval. Films doped with 5 wt% Ir (dfppy) ₂ (prz) in PMMA are known to show light at a wavelength of 554 nm. Films doped with Ir (dfpmpy) ₂ (prz) with methyl groups at the pyridine site are expected as 549 The blue shift was found to be about 5 nm by nm.

Ir (dfpmpy) ₂ (anth) and Ir (dfpmpy) ₂ (ppc) also show 474 nm and 477 nm in ethanol at 479 nm, respectively, ir (dfpmpy) ₂ (acac) and 520 nm Compared to Ir (dfpmpy) ₂ (pic) which shows the light of, it can be seen that it is blue shifted. In the case of Ir (dfpmpy) ₂ (prz), it was found to be red shifted to 626 nm compared with Ir (dfpmpy) ₂ (pic). In the case of pyrazine-2-carboxylic acid used as an auxiliary ligand, nitrogen is substituted for carbon at the para position of the pyridine group of picolinate. Can be estimated. For the remaining Ir (dfpmpy) ₂ (picN), Ir (dfpmpy) ₂ (anth), Ir (dfpmpy) ₂ (ppc) complexes, the nitrogen atom of the auxiliary ligand was sp ³ hybridized to the nitrogen atom of the picolinate (sp ² hybrid). Because of the small nature of the s orbitals, it can be presumed that ILET is blue shifted slightly compared to picolinate.

Ir (dfpmpy) ₂ (picN), Ir (dfpmpy) ₂ (anth), Ir (dfpmpy) ₂ (prz) were 466 nm in the film doped with 5wt% iridium complex in PMMA as compared to the chloroform solution. , Blue shifted up to 50 nm at 472 nm and 549 nm, and red shifted to 4 nm at 475 nm for Ir (dfpmpy) ₂ (ppc).

In addition, the PL was measured in chloroform, methylene chloride, and ethanol solvent, respectively.Il (dfpmpy) ₂ (anth) was positive solvatochromism at 474 nm in ethanol, and the remaining complexes Ir (dfpmpy) ₂ (picN), Ir (dfpmpy) ₂ (ppc ), Ir (dfpmpy) ₂ (prz) was negative solvatochromism at 515 nm, 477 nm and 626 nm in ethanol, respectively. In the film state, the film doped in PMMA was blue shifted from 20 nm up to 45 nm compared to the film without dope. Ir (dfpmpy) ₂ (picN) was found to be closest to the blue wavelength among the complexes, and Ir (dfpmpy) ₂ (prz) was the closest to the red wavelength and the solvent effect was the largest.

Example 9. Fabrication of phosphorescent organic electroluminescent device

Ir (dfpmpy) ₂ (picN), Ir (dfpmpy) ₂ (ppc), Ir (dfpmpy) ₂ (anth), Ir ( An organic light emitting display device was manufactured using dfpmpy) ₂ (prz) as a dopant of a light emitting layer.

In order to fabricate the organic light emitting device, first, the transparent electrode substrate coated with indium-tin oxide (ITO) on the glass substrate is thoroughly cleaned, and then the transparent electrode substrate coated with the ITO is coated with a photoresist resin and an etching solution ( etchant) was used to form the anode using a micromachining process and then washed again.

The hole injection layer was coated with a polythiophene derivative, poly (3,4-ethylenedioxythiophene) -poly (styrenesulfonate) (PEDOT), having a thickness of 100 고 and then baked at 110 ° C. for about 50 minutes. As the hole transport layer, NPB was vacuum deposited to a thickness of about 50 nm. In order to form the light emitting layer, CBP or mCP, which is widely used as a host material of a phosphorescent light emitting layer, is used as a host material of the light emitting layer, and Ir (dfpmpy) ₂ , which is an iridium complex compound of Examples 3, 4, 5, and 6, was used. (picN), Ir (dfpmpy) ₂ (ppc), Ir (dfpmpy) ₂ (anth), Ir (dfpmpy) ₂ (prz) were used as dopants for the light emitting layer, and the concentration of the dopant was about 5-10%. The light emitting layers were formed by vacuum deposition to a thickness of 20-100 nm, respectively, by evaporation.

BCP and Alq ₃ were vacuum deposited to a thickness of 20-60 nm as the hole blocking layer and the electron transporting layer, respectively. The thin film was sequentially formed by vacuum deposition of LiF, which is an electron injection layer, to form an Al electrode, which is a cathode, to fabricate an organic light emitting display device. The vacuum degree for vacuum deposition was deposited while maintaining the 4x10 ^-6 torr or less to form a thin film. During deposition, the film thickness and growth rate were controlled by using a crystal sensor. The emission area was 4 ㎜ and the driving voltage was a direct bias voltage.

Example 10 Measurement of Electro-optical Properties of Organic Electroluminescent Light Emitting Diode

Through Example 3, the electro-optical properties of the iridium complex compound Ir (dfpmpy) ₂ (picN) according to the present invention were measured for the organic light emitting device used as a dopant of the light emitting layer. The current density and the luminance according to the increase of the voltage of the organic light emitting diode manufactured according to Example 9 were measured using Keithley 236 Source Measurement and Minolta LS-100.

8A and 8B are graphs showing voltage-current density and voltage-luminescence luminance measurement results of phosphorescent organic light emitting diodes using Ir (dfpmpy) ₂ (picN) as a dopant, respectively. As shown, the organic light emitting device including the phosphorescent light emitting material synthesized according to the present invention starts to operate at a voltage of approximately 3.3 V, and as the voltage increases, the amount of carrier injected is increased, and as a result, the current It was found that the current density and the luminance increased exponentially.

FIG. 9 illustrates EL intensity measurement results of phosphorescent organic light emitting diodes using Ir (dfpmpy) ₂ (picN) as a dopant. As shown, it can be seen that the organic electroluminescent device in which the iridium complex compound synthesized according to the present invention is used as a dopant of the light emitting layer exhibits a maximum emission peak at about 470 nm, thereby greatly improving blue light emission characteristics.

Comparative Example: Measurement of physical properties of blue light-emitting phosphorescent organic electroluminescent device manufactured using Flrpic as a dopant

In this embodiment, organic electroluminescence using Flrpic (Iridium (III) bis [2-2 ', 4'-difluorophenyl) -pyridinato-N, C2'] picolinate, disclosed in US Pat. No. 6,835,469, is used as a dopant for the light emitting layer. EL intensity was measured for the device, and the measurement result is shown in FIG. As shown, Flrpic, reported as a phosphorescent compound of conventional blue emission, exhibited a maximum emission peak at about 475 nm. The blue luminescence properties and efficiency were found to be inferior to the iridium complex synthesized according to the present invention.

In the above, the present invention has been described based on the preferred embodiments of the present invention. However, the present invention is only intended to illustrate the present invention, but the present invention is not limited thereto. Rather, one of ordinary skill in the art to which the present invention pertains will be able to easily make various modifications and changes with reference to the embodiments described above. However, it will be apparent from the scope of the following claims that such modifications and variations fall within the scope of the present invention without departing from the spirit of the present invention.

The iridium complex compound synthesized according to the present invention has greatly improved light emission color and light emission efficiency compared to the known iridium-based light emitting materials, and can be easily dissolved in an organic solvent, thereby maintaining a large light emission area.

That is, the iridium complex of the present invention introduces a pyridine derivative substituted with an alkyl or alkoxy group and a phenyl derivative substituted with a halogen compound as a main ligand, and acetylacetone, picolinic acid-N-oxide, pipecolic acid, and anthra as a secondary ligand. By introducing nilic acid, pyrazine acid, and the like, a material capable of realizing a pure blue light emitting color as compared with a conventionally known iridium-based light emitting material can be used as a dopant of a light emitting layer, thereby making it possible to manufacture an organic phosphorescent device for blue phosphorescence.

In addition, the iridium complex compound of the present invention is soluble in general organic solvents and improves heat resistance characteristics by introducing various types of substituents into pyridine derivatives substituted with alkyl or alkoxy groups introduced into the main ligand and phenyl derivatives substituted with halogen compounds. It can be used as a light emitting material that is very excellent in interfacial properties with the electrode and excellent in thin film properties.

Claims (10)

Iridium complex compound having a structure of formula (1). Formula 1

(Formula 1 R ₁ is an alkyl group having 1 to 20 carbon atoms or an alkoxy group having 1 to 20 carbon atoms; Ar is an aryl group; R ₂ is a halogen,

Is picolinic acid-N-oxide or pipecolinic acid.) The method of claim 1, R ₁ of Formula 1 is an iridium complex compound, characterized in that an alkyl group having 1 to 10 carbon atoms or alkoxy group having 1 to 10 carbon atoms. The method of claim 2, The aryl group is phenyl, naphthalene, fluorene, carbazole, phenazine, phenanthroline, phenanthridine, acridine, acridine Cinoline, Quinazoline, Quinoxaline, Quinoxaline, Naphthydrine, Phtalazine, Quinolizine, Indole, Indazole, Pyridazine iridium complex selected from the group consisting of pyridazine, pyrazine, pyrimidine, pyridine, pyridine, pyrazole, imidazole and pyrrole . The method of claim 2, R ₁ in Formula 1 is an iridium complex, characterized in that the methyl group. The method of claim 2, R ₂ of Formula 1 is an iridium complex containing fluorine or chlorine. An organic electroluminescent device in which the iridium complex compound according to any one of claims 1 to 5 is contained in a light emitting layer. The method of claim 6, The organic light emitting diode includes a first electrode and a second electrode formed to face the first electrode, and the light emitting layer is stacked between the first electrode and the second electrode. device. The method of claim 7, wherein An organic electroluminescent device further comprising a buffer layer between the first electrode and the light emitting layer, and an electron transfer layer and an electron injection layer between the light emitting layer and the second electrode. The method of claim 8, The buffer layer may include a hole injection layer stacked on top of the first electrode, and a hole transport layer stacked on top of the hole injection layer. The method of claim 6, The iridium complex compound is an organic electroluminescent device, characterized in that included as a dopant of the light emitting layer.

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