JP2013016728A - Organic light-emitting element, light-emitting device, image formation device, display device, and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic light-emitting element capable of achieving high efficiency and low-voltage driving.SOLUTION: An organic light-emitting element having a cathode, an electron transport layer contacting with the cathode, a light-emitting layer, and an anode. The cathode contains at least one of an alkali metal, an alkali metal compound, an alkali earth metal, and an alkali earth metal compound, and a silver metal. The electron transport layer has a specific xanthone compound.

Description

  The present invention relates to an organic light emitting element, and a light emitting device, an image forming apparatus, a display apparatus, and an imaging apparatus using the organic light emitting element.

  An organic light emitting device is a device having a single layer or multiple layers of an organic compound layer including an anode, a cathode, and an organic light emitting material disposed between the two electrodes. In an organic light emitting device, light generated in a layer containing an organic light emitting material (hereinafter referred to as a light emitting layer) is emitted from one of an anode and a cathode. In Patent Document 1, light is emitted from a cathode, and a semi-transparent metal film using an alloy containing an alkali metal is used as the cathode for the purpose of improving electron injectability.

Japanese Patent Laid-Open No. 09-320763

  However, even when a cathode such as that of Patent Document 1 is used, sufficient electron injecting properties cannot be obtained depending on the material constituting the organic compound layer (hereinafter referred to as an electron transport layer) in contact with the cathode.

  An object of the present invention is to provide an organic light emitting device having high luminous efficiency and low driving voltage.

  The present invention is an organic light emitting device having a cathode, an electron transport layer in contact with the cathode, a light emitting layer, and an anode, wherein the cathode comprises an alkali metal, an alkali metal compound, an alkaline earth metal, and an alkaline earth. It contains at least one of a similar metal compound and silver metal, and the electron transport layer contains a material represented by the following structural formula (1).

In the formula (1), R _{1 to} R ₄ are a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, a substituted or unsubstituted phenyl group, a substituted or unsubstituted naphthyl group, a substituted or unsubstituted phenanthryl group, substituted or They are independently selected from an unsubstituted fluorenyl group, a substituted or unsubstituted triphenylenyl group, a substituted or unsubstituted chrysenyl group, a substituted or unsubstituted dibenzofuranyl group, and a substituted or unsubstituted dibenzothienyl group.

  According to the present invention, since the electron injection property from the cathode to the electron injection layer is improved, it is possible to provide an organic light emitting device having high luminous efficiency and low driving voltage.

It is a cross-sectional schematic diagram which shows an example of the organic light emitting element which concerns on Embodiment 1 of this invention. It is a cross-sectional schematic diagram which shows an example of the display apparatus which concerns on Embodiment 2 of this invention.

(Embodiment 1)
The organic light emitting device of the present invention has a first electrode (anode), a second electrode (cathode), a light emitting layer disposed between both electrodes, and an electron transport layer in contact with the cathode. .

  Hereinafter, the organic light-emitting device of the present invention will be described with reference to the drawings.

1A to 1C are schematic cross-sectional views of the organic light-emitting device of this embodiment.
An organic light emitting device 10 in FIG. 1A is configured by providing an anode 2, a light emitting layer 3, an electron transport layer 4, and a cathode 5 in this order on a substrate 1. The organic light emitting device 10 is useful when the light emitting layer 3 has all of hole injection / transport performance, electron injection / transport performance, and light emission performance. The organic light emitting device 10 is also useful when the light emitting layer 3 is mixed with a hole injecting and transporting material, an electron injecting and transporting material, and a light emitting material.

  The organic light emitting device 20 in FIG. 1B is configured by providing an anode 2, a hole transport layer 6, a light emitting layer 3, an electron transport layer 4, and a cathode 5 in this order on a substrate 1. The organic light emitting device 20 is a layer having a hole carrier transport function and a layer having a light emission function separated, and a compound having hole injection transport property, electron injection transport property, and light emission property. Can be used in combination in a timely manner. For this reason, the degree of freedom of material selection is greatly increased, and it is possible to effectively confine each charge or exciton in the central light emitting layer 3 to improve the light emission efficiency.

  The organic light emitting element 30 in FIG. 1C has a configuration in which the hole injection layer 7 is inserted between the anode 2 and the hole transport layer 6 in the organic light emitting element 20 in FIG. By providing the hole injection layer 7, the adhesion between the anode 2 and the hole transport layer 6 and the hole injection property are improved, which is effective for lowering the voltage.

  However, the organic light emitting elements 10, 20, and 30 shown in FIG. 1 have a very basic element configuration, and the present invention is not limited thereto. For example, various layer configurations such as a configuration in which an insulating layer, an adhesive layer or a light interference layer is provided at the interface between the electrode and the organic compound layer, and a configuration in which two or more hole transport layers are stacked with different HOMO energy levels be able to.

  In the present invention, the cathode 5 contains at least one of an alkali metal, an alkali metal compound, an alkaline earth metal, and an alkaline earth metal compound, and silver metal (Ag). Further, the electron transport layer 4 in contact with the cathode 5 contains a compound represented by the following structural formula (1).

In the formula (1), R _{1 to} R ₄ are a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, a substituted or unsubstituted phenyl group, a substituted or unsubstituted naphthyl group, a substituted or unsubstituted phenanthryl group, substituted or They are independently selected from an unsubstituted fluorenyl group, a substituted or unsubstituted triphenylenyl group, a substituted or unsubstituted chrysenyl group, a substituted or unsubstituted dibenzofuranyl group, and a substituted or unsubstituted dibenzothienyl group.

  The alkyl group having 1 to 4 carbon atoms is a methyl group, an ethyl group, a normal propyl group, an isopropyl group, a normal butyl group, a secondary butyl group, an isobutyl group, or a tertiary butyl group.

  The substituents that the phenyl group, naphthyl group, phenanthryl group, fluorenyl group, triphenylenyl group, chrycenyl group, dibenzofuranyl group, and dibenzothienyl group may have are shown below.

  First, a methyl group, an ethyl group, a normal propyl group, an isopropyl group, a normal butyl group, a secondary butyl group, an isobutyl group, and a tertiary butyl group.

  In addition, phenyl group, methylphenyl group, dimethylphenyl group, trimethylphenyl group, pentamethylphenyl group, triisopropylphenyl group, tertiary butylphenyl group, ditertiarybutylphenyl group, naphthylphenyl group, phenanthrylphenyl group, fluorene group Nylphenyl group, triphenylenylphenyl group, chrysenylphenyl group, dibenzofuranylphenyl group, dibenzothienylphenyl group, 9,9′-spirobi [fluoren] -ylphenyl group.

  Also, biphenyl group, ditertiary butyl biphenyl group, naphthyl biphenyl group, phenanthryl biphenyl group, fluorenyl biphenyl group, triphenylenyl biphenyl group, chrysenyl biphenyl group, dibenzofuranyl biphenyl group, dibenzothienyl biphenyl group .

  A naphthyl group, a ditert-butyl naphthyl group, a phenyl naphthyl group, and a biphenyl naphthyl group.

  A phenanthryl group, a phenylphenanthryl group, and a biphenylphenanthryl group.

  Further, they are a fluorenyl group, a phenylfluorenyl group, a biphenylfluorenyl group, and a 9,9'-spirobi [fluoren] -yl group.

  Further, they are a chrycenyl group, a phenyl chrysenyl group, and a biphenyl chrysenyl group.

  Further, they are a triphenylenyl group, a phenyltriphenylenyl group, and a biphenyltriphenylenyl group.

  Dibenzofuranyl group, tertiary butyl dibenzofuranyl group, ditertiary butyl dibenzofuranyl group, phenyl dibenzofuranyl group, biphenyl dibenzofuranyl group, naphthyl dibenzofuranyl group, phenanthryl dibenzofuranyl group, fluorene group Nyl dibenzofuranyl group, chrysenyl benzofuranyl group, triphenylenyl dibenzofuranyl group.

  Dibenzothienyl group, tertiary butyl dibenzothienyl group, ditertiary butyl dibenzothienyl group, phenyl dibenzothienyl group, biphenyl dibenzothienyl group, naphthyl dibenzothienyl group, phenanthryl dibenzothienyl group, fluorenyl dibenzothienyl group, chrysenyl group Nyl dibenzothienyl group and triphenylenyl dibenzothienyl group.

(About the properties of the compounds according to the present invention)
Since the xanthone compound represented by the formula (1) has a carbonyl group, it has a high electron affinity. In particular, the layer having a xanthone compound is preferably disposed adjacent to a cathode, particularly a cathode containing a reducing dopant such as an alkali metal, an alkali metal compound, an alkaline earth metal, or an alkaline earth metal compound. In this case, the reducing dopant and the carbonyl group interact with each other, so that the layer having the xanthone compound can easily receive electrons from the cathode.

  Examples of the alkali metal used in the present invention include lithium metal, sodium metal, potassium metal, and cesium metal. Examples of the alkali metal compound used in the present invention include oxides, fluorides and carbonates of the above alkali metals. That is, examples of the alkali metal oxide include lithium oxide, sodium oxide, potassium oxide, and cesium oxide. Examples of the alkali metal fluoride include lithium fluoride, sodium fluoride, potassium fluoride, and cesium fluoride. Examples of the alkali metal carbonate include lithium carbonate, sodium carbonate, potassium carbonate, and cesium carbonate.

  Examples of the alkaline earth metal used in the present invention include beryllium metal, magnesium metal, calcium metal, strontium metal, and barium metal. Examples of the alkaline earth metal compound used in the present invention include oxides, fluorides and carbonates of the above alkaline earth metals. That is, examples of the alkaline earth metal oxide include beryllium oxide, magnesium oxide, calcium oxide, strontium oxide, and barium oxide. Examples of the alkali metal fluoride include beryllium fluoride, magnesium fluoride, calcium fluoride, strontium fluoride, and barium fluoride. Examples of alkaline earth metal carbonates include beryllium carbonate, magnesium carbonate, calcium carbonate, strontium carbonate, and barium carbonate.

  In addition, since the xanthone compound is a skeleton having a planar structure, molecules easily overlap with each other and electron mobility is high. This is suitable for transporting electrons received from the cathode to the light emitting layer.

  From these properties, it can be said that the xanthone compound represented by the formula (1) is suitably responsible for the electron injection and transport functions. In particular, the layer having the xanthone compound represented by the formula (1) is desirably used as a layer in contact with the cathode.

Further, other characteristics of the xanthone compound include high S ₁ (singlet lowest excitation level) energy and T ₁ (triplet lowest excitation level) energy, and T ₁ energy is particularly high. Actually, a phosphorescence spectrum measurement was performed on a dilute toluene solution of a compound in which R _{1 to} R ₄ are hydrogen atoms in Formula (1) at 77 K, and T ₁ energy was obtained from the 0-0 band. As a result, the T ₁ energy of the compound is 3.0 eV (410 nm), and this value is sufficiently higher than blue (the maximum peak wavelength of the emission spectrum is 480 nm or less). Accordingly, the xanthone compound absorbs energy generated by recombination of electrons and holes in an organic light-emitting device that emits light in a blue to red region (600 nm to 620 nm or less) or a phosphorescent material. Can be suppressed. For this reason, it is useful as a layer adjacent to the light emitting layer.

  From the above, the electron transport layer having the compound represented by the formula (1) is preferably in contact with the light emitting layer, and can be applied to the structure to perform good electron transport and electron injection into the light emitting layer. It is thought that you can.

  Next, the substituent added to the xanthone compound according to the present invention will be described. By introducing an alkyl group or an aromatic ring group into a compound having high planarity such as a xanthone compound, solubility in a solvent, sublimation during vacuum deposition, and amorphousness in a thin film state can be improved. However, when the alkyl group has too many carbon atoms, the sublimation property is lowered, and therefore, the alkyl group preferably has 1 to 4 carbon atoms.

On the other hand, when the xanthone compound represented by the formula (1) is used in the electron transport layer adjacent to the light emitting layer in the phosphorescent light emitting device, it needs to have a higher T ₁ energy than the phosphorescent light emitting material. That is, when the phosphorescent material emits light in the blue to red region (450 nm or more and 620 nm or less), the T ₁ energy of the compound (1) according to the present invention is set corresponding to the emission color of the phosphorescent material. It is important to decide. In general, an alkyl substituent has a small influence on the T ₁ energy, whereas an aromatic ring substituent greatly changes the T ₁ energy of the entire compound. Therefore, in determining the T ₁ energy of the xanthone compound according to the present invention, attention was paid to the T ₁ energy of the aromatic ring substituent bonded to any _one of R _{1 to} R ₄ in the general formula (1).

Table 1 below shows the T ₁ energy (wavelength conversion value) of the main aromatic ring alone. Among them, aromatic ring structures preferably used are benzene, naphthalene, phenanthrene, fluorene, triphenylene, chrysene, dibenzofuran, dibenzothiophene, and pyrene.

Further, when the phosphorescent material emits light in a blue to green region (440 nm to 530 nm) by utilizing the high T ₁ energy characteristic of the xanthone compound represented by formula (1), R in formula (1) Preferred aromatic ring structures bonded to any of _{1 to} R ₄ are as follows. That is, they are benzene, naphthalene, phenanthrene, fluorene, triphenylene, chrysene, dibenzofuran and dibenzothiophene.

The substituent of the aromatic ring structure may further have a substituent unless significantly lowering the the T ₁ energy of the xanthone compounds according to the present invention.

(Explanation of specific compound structure)
The structural formulas of the xanthone compounds according to the present invention are specifically shown in Chemical formulas 3 to 5 below. In the present invention, this compound is used as a material for the electron transport layer in contact with the cathode. In that case, in order to improve the electron injecting property from the cathode, it is important that the cathode is in contact with many parts having high electron affinity. Specifically, when R ₁ and R ₂ in Formula (1) are substituted with an aryl group, R ₃ and R ₄ are preferably a hydrogen atom, a phenyl group, or an alkyl group having 1 to 4 carbon atoms. Further, it is preferable that a plurality of xanthone skeletons (units represented by the formula (1)) exist in the compound. Further, as described above, a linear shape is preferable from the viewpoint of electron mobility, and in that case, it is preferable that a unit represented by the formula (1) exists at the end of the molecule. These compounds are thought to increase the number of ketone groups in contact with the cathode and increase electron injectability. Incidentally, it is possible to appropriately adjusted depending on the size and number of units of the light emitting layer used energy of Compound (S ₁ energy and the T ₁ energy).

  The group A represented by Chemical Formula 3 in the above compound has a xanthone skeleton represented by the formula (1) at the center (in the long chain direction) of the compound. Those having a carbonyl structure with high electron affinity and symmetrical are uniform in electron distribution and have a property of transporting received electrons well. On the other hand, an asymmetric material has a property of increasing the amorphous property during film formation and, as a result, improving the stability of the film.

  Group B represented by Chemical Formula 4 has a xanthone skeleton represented by the formula (1) at the end (in the long chain direction) of the compound. This is because the number of locations where the carbonyl group and the cathode are in contact increases, so that the electron injecting property is enhanced.

  Group C represented by Chemical formula 5 has a xanthone skeleton represented by formula (1) at the center and at the end. This also has the characteristic that the electron injecting property is increased because the number of locations where the carbonyl group and the cathode are in contact with each other increases.

(Light emitting layer)
The light emitting material constituting the light emitting layer of the present invention may be a fluorescent material or a phosphorescent material, but the material of the present invention is particularly suitable for high-energy blue fluorescent materials, blue phosphorescent materials and green phosphorescent materials. Moreover, the material which comprises a light emitting layer may be two types, or may be three or more types including what is called assist material.

  Specific examples of the iridium complex used for the phosphorescent material of the present invention (Chemical formula 6) and specific examples of the host material (Chemical formula 7) are shown below, but the present invention is not limited thereto.

  Here, in addition to the compound of the present invention, conventionally known low molecular weight compounds and high molecular weight compounds can be used as necessary. Furthermore, a hole injection / transport material, a host material, a light emitting compound, an electron injection material, or the like can be used together.

  Examples of these compounds are given below.

  As the hole injecting and transporting material, a material having a high hole mobility is preferable so that holes can be easily injected from the anode and the injected holes can be transported to the light emitting layer. Low molecular and high molecular weight materials with hole injection and transport performance include triarylamine derivatives, phenylenediamine derivatives, stilbene derivatives, phthalocyanine derivatives, porphyrin derivatives, poly (vinylcarbazole), poly (thiophene), and other highly conductive materials. Molecule. These hole injecting and transporting materials can also be used for the hole transporting layer.

  Examples of the light-emitting material mainly related to the light-emitting function include the following materials in addition to the above-described phosphorescent guest material or derivatives thereof. That is, organoaluminum complexes such as fused ring compounds (for example, fluorene derivatives, naphthalene derivatives, pyrene derivatives, perylene derivatives, tetracene derivatives, anthracene derivatives, rubrene, etc.), quinacridone derivatives, coumarin derivatives, stilbene derivatives, tris (8-quinolinolato) aluminum , Organic beryllium complexes, and polymer derivatives such as poly (phenylene vinylene) derivatives, poly (fluorene) derivatives, and poly (phenylene) derivatives.

  As the electron injecting and transporting material, a material having a high electron mobility is preferable. For example, oxadiazole derivatives, oxazole derivatives, pyrazine derivatives, triazole derivatives, triazine derivatives, quinoline derivatives, quinoxaline derivatives, phenanthroline derivatives, organoaluminum complexes, and the like can be given. In addition, another layer may exist between the light emitting layer and the electron transport layer having the xanthone compound represented by the formula (1), and the above-described electron injecting / transporting material is used for the other layer. Also good.

Note that high hole mobility and high electron mobility indicate that the mobility is 10 ⁻⁵ cm ² / (V · S) or more. These values can be measured by the Time Of Flight (TOF) method.

  The anode material should have a work function as large as possible. For example, simple metals such as gold, platinum, silver, copper, nickel, palladium, cobalt, selenium, vanadium, tungsten, or an alloy combining these metals, tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide A metal oxide such as can be used. In addition, conductive polymers such as polyaniline, polypyrrole, and polythiophene can also be used. These electrode materials may be used alone or in combination of two or more. Moreover, the anode may be composed of a single layer or a plurality of layers.

  The cathode material includes silver (Ag) metal and at least one of at least an alkali metal, an alkali metal compound, an alkaline earth metal, and an alkaline earth metal compound. Ag has high electrical conductivity and high reflectivity. By containing an alkali metal, an alkali metal compound, an alkaline earth metal, or an alkaline earth metal compound, it interacts with the carbonyl group of the xanthone compound according to the present invention, and as a result, the electron injecting property is improved. In particular, the cathode preferably contains silver metal, cesium metal, cesium metal compound, magnesium metal, and magnesium metal compound, in order to further improve electron injectability.

  Although it does not specifically limit as a board | substrate used by this invention, Transparent substrates, such as opaque board | substrates, such as a metal board | substrate and a ceramic board | substrate, glass, quartz, a plastic sheet, are used. It is also possible to control the color light by using a color filter film, a fluorescent color conversion filter film, a dielectric reflection film or the like on the substrate. It is also possible to create a thin film transistor (TFT) on a substrate and connect it to create an element.

  Note that a protective layer or a sealing layer can be provided for the manufactured element in order to prevent contact with oxygen, moisture, or the like. Examples of the protective layer include diamond thin films, metal oxides such as silicon oxide and aluminum oxide, and inorganic material films such as metal nitrides such as silicon nitride. In addition, polymer films such as fluororesin, polyparaxylene, polyethylene, silicone resin, and polystyrene resin, and photo-curing resin are also included. Further, each of the inorganic material film and the polymer film may be a single layer, a plurality of layers, or a multilayer film in which an inorganic material film and a polymer film are laminated. Good. Further, the element itself can be packaged with an appropriate sealing resin or a low-melting-point metal material by covering glass, a gas-impermeable film, metal, or the like.

  The organic compound layer constituting the organic light emitting device of the present invention is formed by various methods. In general, a thin film is formed by vacuum vapor deposition, ionized vapor deposition, sputtering, or plasma CVD. Alternatively, it is dissolved in an appropriate solvent, and a thin film is formed by a known coating method (for example, spin coating, dipping, casting method, LB method, ink jet method, etc.). In particular, when a film is formed by a coating method, the film can be formed in combination with an appropriate binder resin.

  The binder resin can be selected from a wide range of binder resins, such as polyvinyl carbazole resin, polycarbonate resin, polyester resin, polyarylate resin, polystyrene resin, ABS resin, polybutadiene resin, polyurethane resin, acrylic resin, methacrylic resin. , Butyral resin, polyvinyl acetal resin, polyamide resin, polyimide resin, polyethylene resin, polyethersulfone resin, diallyl phthalate resin, phenol resin, epoxy resin, silicone resin, polysulfone resin, urea resin, etc. It is not something. In addition, these resins may be homopolymers or copolymer polymers. Furthermore, these resins may be used alone or in combination of a plurality of types. On the other hand, you may use together additives, such as a well-known plasticizer, antioxidant, and an ultraviolet absorber, as needed.

  The organic light emitting device of the present invention may have a so-called bottom emission structure that can extract light from the substrate side, or may have a so-called top emission structure that extracts light from the side opposite to the substrate side. A so-called tandem structure in which at least one structure corresponding to an element is stacked may be formed.

(Embodiment 2)
The organic light emitting device of the present invention can be used in a light emitting device or a display device. The light emitting device and the display device according to this embodiment further include a control circuit that controls light emission of the organic light emitting element, and causes the organic light emitting element to emit light by, for example, passive driving or active matrix driving. In the case of active matrix driving, a switching element such as a transistor or an MIM element is provided as a control circuit.

  Examples of the light emitting device include an illumination light source, an exposure light source of an electrophotographic image forming apparatus, and a backlight of a liquid crystal display device. When used in a lighting device, the number of organic light emitting elements may be one or plural. It is preferable to use a plurality of organic light emitting elements as an exposure light source of an electrophotographic image forming apparatus.

  FIG. 2A is a schematic perspective view of the display device according to the present embodiment. The display device according to the present embodiment includes a plurality of pixels 100 including organic EL elements. The plurality of pixels 100 are arranged in a matrix and form a display area 200. Note that a pixel means a region corresponding to a light emitting region of one light emitting element. In the display device of the present embodiment, the light emitting element is an organic light emitting element, and each pixel 100 is a display device in which one color organic light emitting element is disposed. Examples of the emission color of the organic light emitting element include red, green, and blue, and yellow and cyan may be used. In the display device of this embodiment, a plurality of pixel units each including a plurality of pixels having different emission colors (for example, a pixel that emits red, a pixel that emits green, and a pixel that emits blue) are arranged. The pixel unit is a minimum unit that enables light emission of a desired color by mixing colors of pixels.

  FIG. 2B is a schematic partial cross-sectional view taken along the line AB of FIG. One pixel has an organic light emitting element 40 including an anode 2, a hole transport layer 6, light emitting layers 3 R, 3 G, and 3 B, an electron transport layer 4, and a cathode 5 on a substrate 1. Yes. The organic light emitting device 40 of the present invention is a so-called top emission type display device having a reflection surface on the anode 2 for reflecting light emitted from the light emitting layer and traveling toward the anode 2 and emitting light from the cathode 5. . The organic light emitting device of the present invention can also be applied to a bottom emission type display device that extracts light from the substrate 1 side. Moreover, it is good also as an organic light emitting element provided in order of the cathode 5, the electron carrying layer 4, the light emitting layer 3R, 3G, 3B, the positive hole transport layer 6, and the anode 2 from the board | substrate 1 side.

  The light emitting layer 3R is a light emitting layer that emits red light, the light emitting layer 3G is a light emitting layer that emits green light, and the light emitting layer 3B is a light emitting layer that emits blue light. The light emitting layers 3R, 3G, and 3B are patterned in correspondence with pixels (organic light emitting elements 40) that emit red, green, and blue, respectively. Note that the hole transport layer 6 and the electron transport layer 4 may also be formed in a pattern for each pixel without being arranged in common across the pixels as illustrated in FIG.

  The anode 2 is also formed separately from the anode 2 of the adjacent pixel (organic light emitting element 40). The hole transport layer 6, the electron transport layer 4, and the cathode 5 may be formed in common with the adjacent pixel, or may be formed in a pattern for each pixel. Note that an insulating layer 50 is provided between the pixels (more specifically, the anode 2) in order to prevent the anode 2 and the cathode 5 from being short-circuited by a foreign substance. Furthermore, a protective layer for protecting the organic light emitting element from moisture or the like is provided on the cathode 5.

  In the display device of the present embodiment, the light emitting layer of the organic light emitting element 40 of the pixel 100 is patterned. However, for example, the light emitting layer may be formed as a white light emitting layer over all the pixels. In that case, color display may be performed using a color filter or the like.

  This display device is used in a display unit of a television receiver or a personal computer. In addition, the display device of the present embodiment may be disposed in a display unit or an electronic viewfinder of an imaging device such as a digital camera or a digital video camera. The imaging device further includes an imaging optical system for imaging and an imaging element such as a CMOS sensor.

  In addition, the display device of the present embodiment may be disposed in a display unit of a mobile phone, a display unit of a portable game machine, or the like, and further, a display unit of a portable music player, a personal digital assistant (PDA) You may arrange | position to the display part and the display part of a car navigation system.

  In addition, the display device of the present embodiment may be disposed on the operation panel unit of the image forming apparatus. The image forming apparatus further includes an exposure light source, a photoreceptor on which a latent image is formed by the exposure light source, and a charging unit that charges the photoreceptor. As described above, this exposure light source can be used as the light emitting device of this embodiment.

  Note that a method for manufacturing the display device of FIG. 2B will be described in detail in an embodiment described later.

  [Synthesis of Exemplary Compound A-1]

The following reagents and solvents were put into a 100 mL eggplant flask.
Xanthone (manufactured by Tokyo Chemical Industry Co., Ltd.): 5.0 g (26 mmol)
Bromine: 16 g (102 mmol)
Iodine: 50 mg (0.20 mmol)
Acetic acid: 20 mL

The reaction solution was heated to reflux for 5 hours with stirring at 100 ° C. under nitrogen. After completion of the reaction, chloroform and a saturated aqueous sodium sulfite solution were added to the reaction solution and stirred until the bromine color disappeared. Subsequently, the organic layer was separated, washed with a saturated aqueous sodium carbonate solution, dried over magnesium sulfate, and filtered. The solvent of the obtained filtrate was distilled off under reduced pressure, and the precipitated solid was purified by a silica gel column (toluene: 100%), 2.9 g of 2-bromoxanthone (yield 41%), 2,7-dibromoxanthone. 2.2 g was obtained (yield 25%).
Subsequently, the following reagents and solvent were charged into a 100 mL eggplant flask.
2,7-dibromoxanthone: 0.70 g (2.0 mmol)
4,4,5,5-tetramethyl-2- (9,9-dimethylfluoren-2-yl) -1,3,2-dioxaborolane: 1.4 g (4.8 mmol)
Tetrakis (triphenylphosphine) palladium (0): 0.23 g (0.20 mmol)
Toluene: 10 mL
Ethanol: 2mL
2M aqueous sodium carbonate solution: 5mL

The reaction solution was heated to reflux for 5 hours with stirring under nitrogen. After completion of the reaction, the organic layer was separated, dried over magnesium sulfate, and filtered. The solvent of the obtained filtrate was distilled off under reduced pressure, and the precipitated solid was purified by a silica gel column (chloroform: heptane = 1: 1). The obtained crystals were vacuum-dried at 150 ° C. and then purified by sublimation under conditions of 10 ⁻¹ Pa and 300 ° C. to obtain a high purity exemplary compound A-1.
580.2 which is M ^<+> of this compound was confirmed by MALDI-TOF MS.

Furthermore, the structure of this compound was confirmed by ¹ H-NMR measurement. ¹ H-NMR (CDCl ₃ , 500 MHz) δ (ppm): 8.68 (2H, d), 8.09 (2H, dd), 7.84 (2H, d), 7.80-7.76 ( 4H, m), 7.69 (2H, dd), 7.65 (2H, d), 7.48 (2H, dd), 7.40-7.33 (4H, m), 1.58 (12H) , S)

As for Example Compound A-1, was measured the T ₁ energy in the following manner. For a diluted toluene solution (1 × 10 ⁻⁵ M) of Exemplified Compound A-1, a phosphorescence spectrum was measured under an Ar atmosphere at 77 K and an excitation wavelength of 350 nm. When the T ₁ energy was determined from the peak wavelength of the 0-0 band (first emission peak) of the obtained phosphorescence spectrum, it was 487 nm in terms of wavelength.

  [Synthesis of Exemplary Compound B-1]

The following reagents and solvents were put into a 100 mL eggplant flask.
2-bromoxanthone: 0.55 g (2.0 mmol)
Boronic ester derivative 1: 1.1 g (2.4 mmol)
Tetrakis (triphenylphosphine) palladium (0): 0.23 g (0.20 mmol)
Toluene: 15 mL
Ethanol: 3mL
2M aqueous sodium carbonate solution: 5mL

The reaction solution was heated to reflux for 3 hours with stirring under nitrogen. After completion of the reaction, the precipitated solid was filtered and washed with water, methanol, and acetone. Subsequently, the obtained solid was dissolved in chlorobenzene by heating, and the solution was subjected to hot filtration to remove insoluble matters. The solvent of the filtrate was distilled off under reduced pressure, and the precipitated solid was recrystallized with a chlorobenzene / heptane system. The obtained crystals were vacuum-dried at 150 ° C. and then purified by sublimation under conditions of 10 ⁻¹ Pa and 370 ° C. to obtain a high purity exemplary compound B-1.

530.1 which is M ^<+> of this compound was confirmed by MALDI-TOF MS.

  [Synthesis of Exemplary Compound B-2]

The following reagents and solvents were put into a 50 mL eggplant flask.
2-bromoxanthone: 1.5 g (5.4 mmol)
Boronic ester derivative 2: 1.0 g (2.5 mmol)
Tetrakis (triphenylphosphine) palladium (0): 0.29 g (0.25 mmol)
Toluene: 10 mL
Ethanol: 2mL
2M sodium carbonate aqueous solution: 6mL

The reaction solution was heated to reflux with stirring for 12 hours under nitrogen. After completion of the reaction, the precipitated solid was filtered and washed with water, methanol, and acetone. Subsequently, the obtained solid was dissolved in chlorobenzene by heating, and the solution was subjected to hot filtration to remove insoluble matters. The solvent of the filtrate was distilled off under reduced pressure, and the precipitated solid was recrystallized with a chlorobenzene / heptane system. The obtained crystals were vacuum-dried at 150 ° C. and purified by sublimation under conditions of 10 ⁻¹ Pa and 370 ° C. to obtain 0.44 g of high-purity Example Compound B-2 (yield 33%).

542.2 which is M ^<+> of this compound was confirmed by MALDI-TOF MS (matrix assisted ionization-time-of-flight mass spectrometry).

Furthermore, the structure of this compound was confirmed by ¹ H-NMR measurement. ¹ H-NMR (CDCl ₃ , 500 MHz) δ (ppm): 8.65 (2H, d), 8.39 (2H, dd), 8.08 (2H, dd), 7.96 (2H, bs) , 7.78-7.74 (2H, m), 7.74-7.69 (4H, m), 7.65-7.58 (4H, m), 7.55 (2H, d), 7 .44-7.39 (2H, m)

The Exemplified Compound B-2, was measured the T ₁ energy in the following manner. With respect to a dilute toluene solution (1 × 10 ⁻⁵ M) of Exemplified Compound B-2, phosphorescence spectrum was measured in an Ar atmosphere at 77 K and an excitation wavelength of 350 nm. The T ₁ energy obtained from the peak wavelength of the 0-0 band (first emission peak) of the obtained phosphorescence spectrum was 443 nm in terms of wavelength.

  [Synthesis of Exemplified Compound C-2]

The following reagents and solvents were put into a 200 mL eggplant flask.
2-bromoxanthone: 5.0 g (18 mmol)
Bis (pinacolato) diboron: 5.5 g (22 mmol)
[1,1′-bis (diphenylphosphino) ferrocene] palladium (II) dichloride dichloromethane adduct: 0.74 g (0.91 mmol)
Potassium acetate: 3.2 g (33 mmol)
Dioxane: 40 mL

  The reaction solution was heated to reflux for 3 hours with stirring under nitrogen. After completion of the reaction, the precipitated salt was removed by filtration. The solvent of the obtained filtrate was distilled off under reduced pressure, and the precipitated solid was purified by a silica gel column (ethyl acetate: heptane = 1: 2) to obtain 5.1 g of intermediate 2 (yield 87%).

Subsequently, 4,4,5,5-tetramethyl-2- (9,9-dimethylfluoren-2-yl) -1,3,2-dioxaborolane used in the synthesis of Exemplary Compound A-1 in Synthesis Example 1 Exemplified Compound C-2 was obtained in the same manner as in the synthesis of Exemplified Compound A-1 in Synthesis Example 1 except that was changed to Intermediate 2.
MALDI-TOF MS confirmed 584.6 which is M ⁺ of this compound.

[Example 1]
The organic light-emitting device having the top emission structure shown in FIG. 1C was manufactured by the following method.
By sputtering, an aluminum alloy (AlNd) film and an indium tin oxide film were formed to a thickness of 100 nm and 10 nm, respectively, on a glass substrate (substrate 1) as a support, thereby forming an anode 2.

  Next, the substrate formed up to the anode 2 was successively ultrasonically washed with acetone and isopropyl alcohol (IPA). Next, the substrate was washed by boiling with IPA and then dried. Next, the surface of the substrate 1 was subjected to UV / ozone cleaning.

  Next, a compound H-1 shown below was formed on the anode 2 by vacuum deposition to form the hole injection layer 7. At this time, the thickness of the hole injection layer 7 was set to 160 nm.

  Next, the compound H-2 shown above was formed to a thickness of 10 nm on the hole injection layer 7 by a vacuum deposition method to form a hole transport layer 6.

  Next, the light emitting layer 3 is formed by co-evaporating the host (I-3) and the dopant (Ir-1) in a weight ratio of [I-3]: [Ir-1] = 9: 1. did. At this time, the thickness of the light emitting layer 3 was set to 30 nm.

  Next, 30 nm of A-1 was formed on the light emitting layer 3 to form the electron transport layer 4 by vacuum deposition.

  Next, silver metal and cesium carbonate were co-deposited as a cathode so that the cesium concentration in the layer was 2% by weight to form the cathode 5. At this time, the film thickness of the cathode 5 was 10 nm.

  Finally, the substrate 1 formed up to the cathode 5 in a glove box under a nitrogen atmosphere was sealed with a glass cap containing a desiccant. Thus, an organic light emitting device 30 was obtained.

About the obtained organic light emitting element, the luminous efficiency and voltage when a current having a current density of 10 mA / cm ² was applied were evaluated. The results are shown in Table 2.

[Example 2]
An organic light emitting device was prepared and evaluated in the same manner as in Example 1 except that Compound B-1 was used as the electron transport layer 4. The results are shown in Table 2.

[Example 3]
An organic light emitting device was prepared and evaluated in the same manner as in Example 1 except that Compound B-2 was used as the electron transport layer 4. The results are shown in Table 2.

[Example 4]
An organic light emitting device was prepared and evaluated in the same manner as in Example 1 except that Compound C-2 was used as the electron transport layer 4. The results are shown in Table 2.

[Comparative Example 1]
An organic light emitting device was prepared and evaluated in the same manner as in Example 1 except that Alq3 was used as the electron transport layer 4. The results are shown in Table 2.

[Example 5]
An organic light emitting device was prepared and evaluated in the same manner as in Example 3 except that the cathode 5 was formed by co-evaporating silver metal and magnesium metal at a weight ratio of 10: 1 as the cathode 5. The results are shown in Table 2.

  From the above, it can be seen that low voltage and high efficiency driving can be achieved by using the xanthone compound according to the present invention.

[Example 6]
The display device shown in FIG. 2 was produced by the following method. First, a TFT circuit (not shown) made of low-temperature polysilicon and controlling light emission of the organic light emitting element and a planarizing film (not shown) for flattening the TFT circuit were sequentially formed on the substrate 1. Next, the anode 2 was provided at a desired position on the planarizing film. Here, the TFT circuit is, for example, one in which (640 × 3 colors) × 480 pixels are two-dimensionally arranged with a diagonal size of 3.5 inches. The anode 2 was an electrode in which, for example, a reflective film made of a silver alloy with a thickness of 50 nm and an indium tin oxide film with a thickness of 20 nm were laminated in this order. The anode 2 provided in each pixel was connected to the TFT circuit through a contact hole (not shown) formed in the planarization film.

  Next, an acrylic resin film was formed on the substrate 1 including the anode 2 by coating with a spin coater. At this time, the thickness of the resin film was 1.5 μm. Next, the resin film was subjected to desired patterning by photolithography so that the insulating layer 50 was formed around the anode 2. At this time, an opening having a radius of 3 mm was provided.

  Next, the substrate 1 was sequentially ultrasonically washed with acetone and isopropyl alcohol (IPA). Next, the substrate 1 was dried by boiling with IPA and then dried. Next, the surface of the substrate 1 was subjected to UV / ozone cleaning. Next, after the treated substrate 1 is introduced into a vacuum apparatus, an organic compound layer and a cathode 5 which will be described later are formed, so that a plurality of organic light emitting elements having one of three colors (R, G, B) are emitted. A display device was prepared.

  First, a compound H-1 was formed by a vacuum deposition method to form a hole injection layer (not shown) common to all pixels. At this time, the thickness of the hole injection layer was set to 70 nm. Next, using a shadow mask, the compound H-2 was selectively formed in the region corresponding to the blue pixel, and the hole transport layer 6 was formed. At this time, the thickness of the hole transport layer 6 was set to 10 nm. Next, the compound BH-1 and the compound BD-1 shown below are co-deposited in a weight ratio of [Compound BH-1]: [Compound BD-1] = 95: 5, and the blue light emitting layer 3B is obtained. Formed. At this time, the thickness of the blue light emitting layer 3B was set to 35 nm.

  Next, using a shadow mask, the compound H-1 was further selectively formed in the region corresponding to the green pixel to form the hole transport layer 6, and the film thickness was adjusted. At this time, the thickness of the thin film selectively formed in the region corresponding to the green pixel was 60 nm. Next, the green light emitting layer 3G is formed by co-evaporating the host (I-3) and the dopant (Ir-3) in a weight ratio of [I-3]: [Ir-3] = 9: 1. did. At this time, the thickness of the green light emitting layer 3G was set to 20 nm.

  Next, using a shadow mask, the compound H-1 was further selectively formed in the region corresponding to the red pixel, and the thickness of the hole transport layer 6 was adjusted. At this time, the thickness of the thin film selectively formed in the region corresponding to the red pixel was 130 nm. Next, the compound RH-1 and the compound Ir-16 shown below are co-deposited so that the weight ratio of [Compound RH-1]: [Ir-16] = 90: 10 is obtained, and the red light emitting layer 3R Formed. At this time, the thickness of the red light emitting layer 3R was set to 30 nm.

  Next, the compound B-2 was formed into a film by the vacuum evaporation method, and the electron transport layer 4 common to all the pixels was formed. At this time, the thickness of the electron transport layer 4 was set to 30 nm. Next, a cathode 5 was formed by co-evaporation of silver metal and cesium carbonate so that the concentration of cesium carbonate in the layer was 2 wt% on the electron transport layer 4 by vacuum deposition. At this time, the film thickness of the cathode 5 was 13 nm. Next, a protective layer 60 was formed by depositing indium tin oxide on the cathode 5 by sputtering. At this time, the thickness of the protective layer 60 was set to 60 nm.

  Next, the substrate on which the organic light emitting element was formed was sealed with a glass cap containing a desiccant in a glove box under a nitrogen atmosphere. Finally, a circular deflecting plate (not shown) was provided on the glass cap for the purpose of preventing external light reflection. Thus, a display device was obtained.

  When the obtained display device was driven, a clear full-color moving image display with high luminance and good durability was obtained. Moreover, it was effective from the viewpoint of power consumption as a display device such as a mobile device having a limited power capacity.

2 Anode 3 Light emitting layer 4 Electron transport layer 5 Cathode

Claims (8)

An organic light emitting device having a cathode, an electron transport layer in contact with the cathode, a light emitting layer, and an anode,
The cathode includes at least one of an alkali metal, an alkali metal compound, an alkaline earth metal, and an alkaline earth metal compound, and silver metal;
The organic light-emitting device, wherein the electron transport layer includes a material represented by the following structural formula (1).

In the formula (1), R _{1 to} R ₄ are a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, a substituted or unsubstituted phenyl group, a substituted or unsubstituted naphthyl group, a substituted or unsubstituted phenanthryl group, substituted or They are independently selected from an unsubstituted fluorenyl group, a substituted or unsubstituted triphenylenyl group, a substituted or unsubstituted chrysenyl group, a substituted or unsubstituted dibenzofuranyl group, and a substituted or unsubstituted dibenzothienyl group.   The organic light emitting device according to claim 1, wherein the cathode includes at least one of cesium metal, cesium metal compound, magnesium metal, and magnesium metal compound, and silver metal. _3. The organic light-emitting device according to claim 1 _, wherein R _{3 and} R ₄ in the formula (1) are a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.   The organic light-emitting device according to claim 1, wherein the light-emitting material contained in the light-emitting layer is a phosphorescent light-emitting material.   5. A light-emitting device, comprising: the organic light-emitting element according to claim 1; and a control circuit that controls light emission of the organic light-emitting element.   An image forming apparatus comprising: the light emitting device according to claim 5; a photoconductor on which a latent image is formed by the light emitting device; and a charging unit that charges the photoconductor. A display device having a plurality of organic light emitting elements emitting different colors and a control circuit for controlling light emission of the organic light emitting elements,
The display device, wherein the organic light-emitting element is the organic light-emitting element according to claim 1.   An image pickup apparatus comprising the display device according to claim 7 and an image pickup element.

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