JP5178794B2 - Novel compound and organic electroluminescent element, display device and lighting device using the same - Google Patents

Description

  Embodiments described herein relate generally to a novel compound and an organic electroluminescent element, a display device, and a lighting device using the same.

  In recent years, organic electroluminescent elements (hereinafter also referred to as organic EL elements) have attracted attention as light-emitting technologies for next-generation displays and illumination. In the early days of research on organic EL elements, fluorescence has been mainly used as the light emission mechanism of the organic layer. However, in recent years, attention has been focused on organic EL elements using phosphorescence with higher internal quantum efficiency.

  In recent years, the mainstream of a light emitting layer of an organic EL element using phosphorescence is a host material made of an organic material doped with a light emitting metal complex having iridium or platinum as a central metal. However, since iridium complexes and platinum complexes are rare metals and expensive, there is a problem that the organic EL element using them is expensive. On the other hand, since the copper complex similarly exhibits phosphorescence emission and is inexpensive, it can be expected that the cost can be suppressed if it is used as a light emitting material.

  So far, an organic EL device using a copper complex as a light emitting material has been disclosed, but it has a problem that a method for synthesizing the copper complex to be used is complicated. Further, in order to apply to illumination that emits white light or RGB full-color display, a material that emits blue light with high efficiency is required.

JP 2008-179697 A

  The problem to be solved by the present invention is a copper complex that is inexpensive, easy to synthesize, and exhibits a short emission wavelength, and an organic electroluminescence element, a display device, and an illumination device using the copper complex as a light emission dopant Is to provide.

In order to achieve the above object, according to an embodiment, a compound represented by the following general formula (1) is provided:

(In the formula, Cu ⁺ is a copper ion. N is each independently an integer of 0 to 5, at least one n is an integer of 1 to 5. X ⁻ is a counter ion, X Is BF ₄ or ClO ₄ ).

FIG. 1 is a cross-sectional view illustrating an organic electroluminescent device according to an embodiment. FIG. 2 is a circuit diagram illustrating the display device according to the embodiment. FIG. 3 is a cross-sectional view illustrating the lighting device according to the embodiment. FIG. 4 is a diagram showing a ¹ H-NMR spectrum of [Cu (py) ₂ (pF-PPh ₃ ) ₂ ] BF ₄ . FIG. 5 is a diagram showing a PL spectrum of [Cu (py) ₂ (pF-PPh ₃ ) ₂ ] BF ₄ . FIG. 6 is a diagram showing an EL spectrum of the organic electroluminescence device according to the example. FIG. 7 is a diagram illustrating light emission characteristics of the organic electroluminescent device according to the example.

  Hereinafter, embodiments will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view illustrating an organic electroluminescent device according to an embodiment.

  The organic electroluminescent element 10 has a structure in which an anode 12, a hole transport layer 13, a light emitting layer 14, an electron transport layer 15, an electron injection layer 16 and a cathode 17 are sequentially formed on a substrate 11. The hole transport layer 13, the electron transport layer 15, and the electron injection layer 16 are formed as necessary.

  Hereinafter, each member of the organic electroluminescent element according to the embodiment will be described in detail.

  The light emitting layer 14 is a layer having a function of receiving holes from the anode side and electrons from the cathode side, and providing a field for recombination of holes and electrons to emit light. The host material in the light emitting layer is excited by the energy of this bond. When energy is transferred from the host material in the excited state to the light emitting dopant, the light emitting dopant enters the excited state, and light is emitted when the light emitting dopant returns to the ground state again.

The light emitting layer 14 has a configuration in which a host material made of an organic material is doped with a light emitting metal complex (hereinafter referred to as a light emitting dopant). In the present embodiment, a copper complex represented by the following general formula (1) is used as the luminescent dopant.

The copper complex represented by the general formula (1) has a structure in which pyridine and triphenylphosphine are coordinated to Cu ⁺ . At least one of the phenyl groups in the triphenylphosphine is substituted with one or more fluorine atoms. In the formula (1), Cu ⁺ is a copper ion. n means the number of fluorine atoms in the phenyl group, each independently an integer of 0 to 5, and at least one n is an integer of 1 to 5. X ⁻ is a counter ion, and X is BF ₄ or ClO ₄ .

  By using a copper complex as a luminescent dopant, an organic EL element can be produced at a lower cost than when an iridium complex or a platinum complex is used. Moreover, the copper complex shown by the said General formula (1) is easily compoundable compared with the other copper complex whose use as a light emission dopant is known.

  Furthermore, the copper complex represented by the general formula (1) has an emission wavelength on the short wavelength side as compared with other copper complexes whose use as a luminescent dopant is known. Therefore, when the copper complex of the general formula (1) is used as a light emitting dopant, light emission closer to blue can be obtained.

  In addition, even when the copper complex represented by the general formula (1) is used as a light emitting dopant, an organic EL element having luminous efficiency and luminance equal to or higher than those of conventional organic EL elements is obtained. Can be provided.

Specific examples of the copper complex represented by the general formula (1) include a copper complex [Cu] in which triphenylphosphine (pF-PPh ₃ ) in which fluorine is introduced at the para position of pyridine and a phenyl group is coordinated to a copper ion. _{(py) 2 (pF-PPh} 3) 2] BF 4 and the like. In the present specification, pF means that fluorine is introduced at the para position of the phenyl group. The structure of [Cu (py) ₂ (pF-PPh ₃ ) ₂ ] BF ₄ is shown below.

Hereinafter, a synthesis scheme of [Cu (py) ₂ (pF-PPh ₃ ) ₂ ] BF ₄ is shown as an example, but other copper complexes represented by the general formula (1) can be synthesized in the same manner. .

As the host material, it is preferable to use a material with high energy transfer efficiency to the luminescent dopant. Host materials used in the case of using a phosphorescent dopant as the luminescent dopant are roughly classified into a low molecular system and a high molecular system. The light emitting layer containing the low molecular weight host material is formed mainly by vacuum co-evaporation of the low molecular weight host material and the light emitting dopant. The light emitting layer containing the polymer host material is formed mainly by applying a solution in which the polymer host material and the light emitting dopant are mixed. A typical example of the low molecular weight host material is 1,3-bis (carbazol-9-yl) benzene (mCP). A typical example of the polymer host material is polyvinyl carbazole (PVK). In this embodiment, 4,4′-bis (9-dicarbazolyl) -2,2′-biphenyl (CBP) is also used as the host material.
, P-bis (triphenylsilyl) benzene (UGH2) and the like can be used.

  When a host material having a strong hole transporting property is used, there is a problem that the carrier balance between the holes and electrons in the light emitting layer cannot be achieved and the light emission efficiency is lowered. Therefore, an electron injecting / transporting material may be further contained in the light emitting layer. Conversely, when a host material having a strong electron transporting property is used, a hole injection / transport material may be further contained in the light emitting layer. With such a configuration, the carrier balance between holes and electrons in the light emitting layer can be achieved, and the light emission efficiency can be improved.

  A method for forming the light emitting layer 14 is not particularly limited as long as it is a method capable of forming a thin film. For example, a spin coating method can be used. A solution containing a light-emitting dopant and a host material is applied to a desired film thickness and then heated and dried with a hot plate or the like. As the solution to be applied, one previously filtered with a filter may be used.

  The thickness of the light emitting layer 14 is preferably 10 to 100 nm. The ratio of the host material and the light emitting dopant in the light emitting layer 14 is arbitrary as long as the effects of the present invention are not impaired.

  The substrate 11 is for supporting other members. The substrate 11 is preferably one that is not altered by heat or an organic solvent. Examples of the material of the substrate 11 include inorganic materials such as alkali-free glass and quartz glass, polyethylene, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide, polyamide, polyamideimide, liquid crystal polymer, cycloolefin polymer, and the like. Examples thereof include plastics, polymer films, and metal substrates such as stainless steel (SUS) and silicon. In order to extract light emission, it is preferable to use a transparent substrate made of glass, synthetic resin, or the like. There is no restriction | limiting in particular about the shape of the board | substrate 11, a structure, a magnitude | size, etc., It can select suitably according to a use, an objective, etc. The thickness of the substrate 11 is not particularly limited as long as it has sufficient strength to support other members.

  The anode 12 is stacked on the substrate 11. The anode 12 injects holes into the hole transport layer 13 or the light emitting layer 14. The material of the anode 12 is not particularly limited as long as it has conductivity. Usually, a transparent or translucent conductive material is formed by vacuum deposition, sputtering, ion plating, plating, coating, or the like. For example, a conductive metal oxide film, a translucent metal thin film, or the like can be used as the anode 12. Specifically, conductive glass made of indium tin oxide, zinc oxide, tin oxide, and indium tin oxide (ITO), fluorine-doped tin oxide (FTO), indium zinc oxide, or the like, which is a composite thereof, is used. A produced film (NESA or the like), gold, platinum, silver, copper, or the like is used. In particular, a transparent electrode made of ITO is preferable. Further, as an electrode material, polyaniline and a derivative thereof, which is an organic conductive polymer, polythiophene and a derivative thereof, or the like may be used. In the case of ITO, the film thickness of the anode 12 is preferably 30 to 300 nm. If it is thinner than 30 nm, the conductivity is lowered, the resistance is increased, and the luminous efficiency is lowered. If it is thicker than 300 nm, ITO becomes inflexible, and cracks occur when stress is applied. The anode 12 may be a single layer or may be a laminate of layers made of materials having different work functions.

  The hole transport layer 13 is arbitrarily disposed between the anode 12 and the light emitting layer 14. The hole transport layer 13 is a layer having a function of receiving holes from the anode 12 and transporting them to the light emitting layer side. As a material of the hole transport layer 13, for example, a polythiophene polymer such as poly (ethylenedioxythiophene): poly (styrene sulfonic acid) [hereinafter referred to as PEDOT: PSS] which is a conductive ink is used. However, the present invention is not limited to this. The method for forming the hole transport layer 13 is not particularly limited as long as it is a method capable of forming a thin film. For example, a spin coating method can be used. After the solution of the hole transport layer 13 is applied to a desired film thickness, it is heated and dried with a hot plate or the like. As the solution to be applied, one previously filtered with a filter may be used.

  The electron transport layer 15 is optionally laminated on the light emitting layer 14. The electron transport layer 13 is a layer having a function of receiving electrons from the electron injection layer 16 and transporting them to the light emitting layer 14. Examples of the material of the electron transport layer 15 include tris [3- (3-pyridyl) -mesityl] borane [hereinafter referred to as 3TPYMB], tris (8-hydroxyquinolinolato) aluminum complex (Alq3), bathophenanthroline ( BPhen) or the like can be used, but is not limited thereto. The method for forming the electron transport layer 15 is the same as that for the hole transport layer 13.

  The electron injection layer 16 is optionally stacked on the electron transport layer 15. The electron injection layer 16 is a layer having a function of receiving electrons from the cathode 17 and injecting them into the electron transport layer 15 or the light emitting layer 14. As a material of the electron injection layer 16, for example, CsF, LiF, or the like can be used, but is not limited thereto. The method for forming the electron injection layer 16 is the same as that for the hole transport layer 13.

  The cathode 17 is laminated on the light emitting layer 14 (or the electron transport layer 15 or the electron injection layer 16). The cathode 17 injects electrons into the light emitting layer 14 (or the electron transport layer 15 or the electron injection layer 16). Usually, a transparent or translucent conductive material is formed by vacuum deposition, sputtering, ion plating, plating, coating, or the like. Examples of the electrode material include a conductive metal oxide film and a metal thin film. When the anode 12 is formed using a material having a high work function, it is preferable to use a material having a low work function for the cathode 17. Examples of the material having a low work function include alkali metals and alkaline earth metals. Specific examples include Li, In, Al, Ca, Mg, Li, Na, K, Yb, and Cs.

  The cathode 17 may be a single layer or may be a laminate of layers made of materials having different work functions. Moreover, you may use the alloy of 2 or more types of metals. Examples of the alloy include a lithium-aluminum alloy, a lithium-magnesium alloy, a lithium-indium alloy, a magnesium-silver alloy, a magnesium-indium alloy, a magnesium-aluminum alloy, an indium-silver alloy, and a calcium-aluminum alloy.

  The film thickness of the cathode 17 is preferably 10 to 150 nm. When the film thickness is thinner than the above range, the resistance becomes too large. When the film thickness is thick, it takes a long time to form the cathode 17, and the adjacent layers are damaged and the performance deteriorates.

  As described above, the organic electroluminescence device having the structure in which the anode is stacked on the substrate and the cathode is disposed on the side opposite to the substrate has been described, but the substrate may be disposed on the cathode side.

FIG. 2 is a circuit diagram showing a display device according to an embodiment of the present invention.
The display device 20 shown in FIG. 2 has a configuration in which the pixels 21 are arranged in a circuit in which horizontal control lines (CL) and vertical signal lines (DL) are arranged in a matrix. The pixel 21 includes a light emitting element 25 and a thin film transistor (TFT) 26 connected to the light emitting element 25. One terminal of the TFT 26 is connected to the control line, and the other terminal is connected to the signal line. The signal line is connected to the signal line driving circuit 22. The control line is connected to the control line drive circuit 23. The signal line drive circuit 22 and the control line drive circuit 23 are controlled by a controller 24.

FIG. 3 is a cross-sectional view showing an illumination device according to an embodiment of the present invention.
The lighting device 100 has a configuration in which an anode 107, an organic EL layer 106, and a cathode 105 are sequentially stacked on a glass substrate 101. The sealing glass 102 is disposed so as to cover the cathode 105 and is fixed using the UV adhesive 104. A desiccant 103 is installed on the surface of the sealing glass 102 on the cathode 105 side.

<Synthesis of _{[Cu (py) 2 (pF} -PPh 3) 2] BF 4>
(Reaction I)
A 100 mL three-necked flask is charged with tetrakis (acetonitrile) copper (I) tetrafluoroborate (0.21 g, 0.68 mmol), tris (p-fluorophenyl) phosphine (0.43 g, 1.35 mmol), and vacuumed. Drying was performed. The inside of the three-necked flask was replaced with nitrogen, and 30 mL of nitrogen bubbled chloroform was added using a nitrogen-substituted syringe. Immediately after the addition of chloroform, the solution became cloudy and undissolved residue was confirmed, but after 10 minutes it was completely dissolved and became a transparent solution. After stirring for 7 hours at room temperature, the reaction solution was filtered to remove insolubles. The solvent of the reaction solution was distilled off and vacuum drying was performed to obtain 0.40 g of [Cu (CH ₃ CN) ₂ (pF-PPh ₃ ) ₂ ] BF ₄ as a target substance.

The reaction scheme of the above reaction I is shown below.

(Reaction II)
[Cu (CH ₃ CN) ₂ (pF-PPh ₃ ) ₂ ] BF ₄ (0.084 g) was placed in a 50 mL three-necked flask and vacuum-dried. The inside of the three-necked flask was replaced with nitrogen, and 1 mL of nitrogen bubbled chloroform was added using a nitrogen-substituted syringe. After confirming complete dissolution, 1 mL of pyridine was added. After stirring at room temperature for 5 hours, the reaction solution was filtered to remove insolubles. After the solvent of the filtrate was distilled off, vacuum drying was performed to obtain [Cu (py) ₂ (pF-PPh ₃ ) ₂ ] BF ₄ as a white solid as a target substance. The obtained [Cu (py) ₂ (pF-PPh ₃ ) ₂ ] BF ₄ was dissolved in deuterated chloroform, and a proton nuclear magnetic resonance spectrum was measured. The chemical shifts (ppm) of the peak positions were as follows: 8.46 (double line), 7.78 (triple line), 7.36 (triple line), 7.19 (multiple line), 6.99 (triple line).

The reaction scheme of the above reaction II is shown below.

FIG. 4 shows the ¹ H-NMR spectrum (CDCl ₃ , 270 MHz) of [Cu (py) ₂ (pF-PPh ₃ ) ₂ ] BF ₄ synthesized by the above method.

<Measurement of PL spectrum>
The obtained by the synthesis method described above _{[Cu (py) 2 (pF} -PPh 3) 2] BF 4, it was measured photoluminescence (PL) spectra. The measurement was performed using a multichannel detector PMA-11 manufactured by Hamamatsu Photonics at room temperature and in a solid state. The result is shown in FIG. When excited with ultraviolet light having an excitation wavelength of 365 nm, blue-green light was emitted with an emission peak of 498 nm.

<Production of organic EL element>
The synthesized [Cu (py) ₂ (pF-PPh ₃ ) ₂ ] BF ₄ was used as a light emitting dopant to produce an organic EL device. The layer structure of this element is as follows.

ITO 100 nm / PEDOT: PSS 45 nm / PVK: OXD-7: [Cu (py) ₂ (pF-PPh ₃ ) ₂ ] BF ₄ 65 nm / 3TPYMB 50 nm / CsF 1 nm / Al 150 nm.

  The cathode is a transparent electrode made of ITO (indium tin oxide) having a thickness of 100 nm.

  As the material for the hole transport layer, an aqueous solution of poly (ethylenedioxythiophene): poly (styrene sulfonic acid) [PEDOT: PSS], which is a conductive ink, was used. A hole transport layer was formed to a thickness of 45 nm by applying an aqueous solution of PEDOT: PSS by spin coating and heating and drying.

As the material of the light emitting layer, polyvinyl carbazole [PVK] as a host material and 1,3-bis (2- (4-tertiarybutylphenyl) -1,3,4-oxydiazol-5-yl) benzene as an electron transport material [OXD-7] and [Cu (py) ₂ (pF-PPh ₃ ) ₂ ] BF ₄ were used as a light-emitting dopant. PVK is a hole transporting host material and OXD-7 is an electron transporting material. Therefore, by using a mixture of these as the host material, electrons and holes can be efficiently injected into the light emitting layer when a voltage is applied. Weighed PVK: OXD-7: [Cu (py) ₂ (pF-PPh ₃ ) ₂ ] BF ₄ = 60: 30: 10 by weight ratio, and applied a solution obtained by dissolving them in chlorobenzene by spin coating. The light emitting layer was formed to a thickness of 65 nm by heating and drying.

  The electron transport layer was formed to a thickness of 50 nm by vacuum deposition of tris [3- (3-pyridyl) -mesityl] borane [3TPYMB]. The electron injection layer was formed of CsF having a thickness of 1 nm, and the cathode was formed of Al having a thickness of 150 nm.

<Measurement of EL spectrum>
About the organic EL element produced as mentioned above, the electroluminescence (EL) spectrum at the time of voltage application was measured. The measurement was performed using a high-sensitivity multichannel spectrometer C10027-01 manufactured by Hamamatsu Photonics. The result is shown in FIG. An EL spectrum having an emission peak at 520 nm was obtained. From the above results, it was found that the copper complex according to the embodiment of the present invention is useful as a light emitting dopant of the organic EL device.

<Light emission characteristics of organic EL element>
The organic EL element produced as described above was examined for light emission characteristics. FIG. 7A is a diagram showing the relationship between the voltage of the element and the current density. FIG. 7B is a diagram showing the relationship between the voltage of the element and the luminance. FIG. 7C is a diagram showing the relationship between the voltage of the element and the light emission efficiency. Luminous efficiency was determined by simultaneously performing luminance measurement and current and voltage measurement. The luminance was measured using a Si photodiode S7610 with a visibility filter manufactured by Hamamatsu Photonics. The current and voltage were measured using a semiconductor parameter analyzer 4156b manufactured by HEWLETT PACKARD.

As the voltage was applied, the current density increased and light emission started at 6V. The luminance was 11.6 cd / cm ^{2 at} 10 V, and the maximum luminous efficiency was 0.51 cd / A.

  From the above result, it turned out that the copper complex which concerns on embodiment is useful as a light emission dopant of an organic EL element.

  According to the above-described embodiment or example, a copper complex that is inexpensive, easy to synthesize, and exhibits a short emission wavelength, and an organic electroluminescence element, a display device, and an illumination device that use the copper complex as a light-emitting dopant are provided. Can be provided.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10 ... Organic electroluminescent element, 11 ... Board | substrate, 12 ... Anode, 13 ... Hole transport layer, 14 ... Light emitting layer, 15 ... Electron transport layer, 16 ... Electron injection layer, 17 ... Cathode, 20 ... Display apparatus, 21 ... Pixel, 22 ... Signal line drive circuit, 23 ... Control line drive circuit, 24 ... Controller, 25 ... Light emitting element, 26 ... TFT, 100 ... Lighting device, 101 ... Glass substrate, 102 ... Sealing glass, 103 ... Drying agent, 104 ... UV adhesive, 105 ... cathode, 106 ... organic EL layer, 107 ... anode.

Claims (5)

Compound represented by the following general formula (1):

(In the formula, Cu ⁺ is a copper ion. N is each independently an integer of 0 to 5, at least one n is an integer of 1 to 5. X ⁻ is a counter ion, X Is BF ₄ or ClO ₄ ). An anode and a cathode spaced apart from each other;
An organic electroluminescent device comprising a light emitting layer disposed between the anode and the cathode and comprising a host material and a light emitting dopant,
An organic electroluminescent device comprising the compound according to claim 1 as the light-emitting dopant.   The organic electroluminescence device according to claim 2, wherein the host material is a low molecule or a polymer.   A display device comprising the organic electroluminescent element according to claim 2.   An illuminating device comprising the organic electroluminescent element according to claim 2.

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