JP2008034631A - Organic electroluminescence device and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL device which exhibits a high emission intensity, and by which a high color purity can be ensured. <P>SOLUTION: The organic EL device 1 has a light emitting layer 6 between a pair of electrodes 3 and 8. The light emitting layer 6 includes a host material 6a which has a light emitting unit having the light emitting function, a hole transport unit having the hole transport function, and an electron transport unit having the electron transport function in the identical molecule; and light emitting dopant 6b which is a light emitting material having an emission wavelength shorter than that of the host material 6a. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an organic electroluminescence device and an electronic apparatus.

  An electroluminescence element (hereinafter referred to as “EL element”) is expected to be used as a self-luminous flat display element. Among EL elements, organic EL elements, unlike inorganic EL elements, are not limited to AC driving and require a high voltage, and it is considered that multicolorization is relatively easy due to the diversity of organic compounds. Therefore, it is expected to be applied to full-color displays, and research and development is actively conducted.

  As a method of obtaining the three primary colors necessary for the production of the color panel, a method of combining a color filter with a white light emitting element (color filter method; see Patent Document 1), using a blue light emitting element having the highest energy among the three primary colors. A method of color-converting green to red (color conversion method), a method of separately coating light emitting elements of three primary colors (coloring method; see Patent Document 2), and the like have been proposed. Of these, the color filter method and the color conversion method do not require separate light emission colors compared to the separate color paint method, and the white or blue light-emitting surface can be formed on the entire panel, making the process easier. Become. However, the color filter method and the color conversion method have a large loss of light emission energy extraction, and the overall efficiency is still not sufficient.

On the other hand, the color-separation method requires a light-emission color color-separation technique, but the loss of emission energy extraction is less than the former two. Therefore, it can be said that it is a rational method that can fully utilize the merit of self-light emission if an element having high characteristics can be obtained for any of RGB. For organic EL devices with this structure, materials have been developed with the aim of achieving high brightness and high efficiency. Especially for green, the light-emitting layer is made by doping an 8-quinolinol complex of aluminum with a quinacridone derivative. Excellent properties have been obtained. For blue, excellent characteristics are obtained by using a distyrylarylene derivative in the light emitting layer. Both characteristics have a maximum luminance exceeding tens of thousands of cd / m ^2, and have come to the point where they can be put into practical use.
Japanese Patent Laid-Open No. 7-220871 JP 2000-136379 A

  However, the development of the remaining red light-emitting elements among the three primary colors is delayed compared to the previous two colors, and it still has sufficient characteristics even though active research and development has been conducted in various directions for practical application. An element is not obtained.

  As a method for obtaining a red light-emitting organic EL element, research and development aiming at high color purity, high light emission efficiency, and high brightness are being carried out from both doped and undoped types. The undoped type is a method of forming a light emitting layer with one light emitting material. On the other hand, the dope type is a method of forming a light emitting layer by adding a light emitting dopant (such as a fluorescent dye) as a guest material to a light emitting material as a host material.

  Among them, in the undoped type, although a light emitting material with relatively good color purity has been found, the luminance is low and it is difficult to apply to a color panel. On the other hand, the dope type can obtain relatively high luminance characteristics, but it is difficult to achieve high luminance while maintaining high color purity. In the doped organic EL element, the higher the ratio of the dopant to the host material, the more red light emission with good color purity can be obtained, but the luminance decreases. Conversely, the smaller the dopant concentration, the worse the color purity, but the luminance increases. In order to produce a display panel having a wide color reproduction region, it is necessary to give sufficient consideration to high color purity while achieving high luminance.

  As for the red organic EL element, application to a printer head (line head) is being studied. However, the printer head is required to have sufficient light emission luminance for exposing the photosensitive drum, and higher light emission luminance and light emission efficiency than those required for the display panel are required.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an organic EL device that has high emission luminance and can ensure high color purity. It is another object of the present invention to provide an electronic device such as an organic EL display or an optical printer that can achieve high luminance and high color purity by including such an organic EL device.

In order to solve the above problems, an organic electroluminescence device of the present invention is an organic electroluminescence device having a light emitting layer between a pair of electrodes, and the light emitting layer has a light emitting function in the same molecule. A host material which is a light emitting material having a light emitting unit, a hole transport unit having a hole transport function and an electron transport unit having an electron transport function, and a light emitting material having a light emission wavelength shorter than the light emission wavelength of the host material And a light-emitting dopant.
According to this configuration, the light emitting layer is doped with a light emitting dopant that emits light having a light emission energy higher (shorter wavelength) than that of the host material. Therefore, the host material is passed through the following two paths: (1) A path (electroluminescence) in which the host material emits light by electrons and holes injected into the light emitting layer, and (2) a light emitting dopant is emitted by the electrons and holes injected into the light emitting layer, and light emitted from the light emitting dopant is emitted. Light can be emitted by two paths: a path (photoluminescence) in which the host material is excited by energy to emit light (photoluminescence). For this reason, compared with the case where a host material is used independently, an organic EL device with high luminous efficiency can be provided. Further, since almost all the light emitted from the light emitting dopant is absorbed by the host material, only light having a wavelength caused by the host material is emitted from the light emitting layer. Therefore, problems such as color mixing due to doping with a light emitting dopant do not occur, and an organic EL device with high color purity is provided.

  Here, in the present invention, one kind or two or more kinds of light emitting materials can be used as the light emitting dopant. As these light emitting materials, either a low molecular material or a high molecular material can be used. When a low molecular material is used, a material having a fluorescence quantum efficiency close to 100% can be obtained, so that an organic EL device with high luminous efficiency can be realized. On the other hand, when the polymer material is used, the fluorescence quantum efficiency is inferior to that of the low-molecular material, but it has a merit in process such that the film can be formed by a wet method. For example, in the case of forming by a wet method, the dispersibility in a solvent is higher than that of a low-molecular material, and problems such as precipitation hardly occur.

  In the present invention, the “unit” refers to a molecule expressing a predetermined function or an assembly of the molecules, regardless of whether it is a high molecule or a low molecule.

In the present invention, it is desirable that the host material includes a light emitting unit having a red light emitting function.
As described above, a red organic EL device has not been obtained that has sufficient emission luminance as compared with green and blue organic EL devices, but if the configuration of the present invention is applied to a red organic EL device. It is possible to secure sufficient light emission brightness for all the colors of red, green and blue, and application to a full color display becomes possible. The red organic EL device is being considered for application to a line head. However, according to the organic EL device of the present invention, a line head having sufficient light emission luminance can be provided, and an image forming apparatus with high display quality ( Optical printer) can be realized.

In the present invention, the emission spectrum of the luminescent dopant preferably has a wavelength region that overlaps with the absorption spectrum of the host material.
According to this structure, the light radiated | emitted from the light emission dopant can be utilized effectively as energy for exciting a host material. That is, when the emission wavelength of the luminescent dopant and the absorption wavelength of the host material are far apart, the proportion of light emitted outside without exciting the host material increases, but the emission of the luminescent dopant as in the present invention. When the wavelength and the absorption wavelength of the host material are close to each other, almost all of the energy of the light emitted from the light-emitting dopant can be used for excitation of the host material, improving the luminous efficiency of the host material and emitting light The color purity of light emitted from the layer can be improved.

In the present invention, the emission spectrum when the emission layer is formed with the host material and the emission dopant and the emission spectrum when the emission layer is formed only with the host material coincide with each other with an overlap of 90% or more. Is desirable. Alternatively, the light emission chromaticity when the light emitting layer is formed with the host material and the light emitting dopant, and the light emission chromaticity when the light emitting layer is formed only with the host material coincide with each other up to two decimal places on the chromaticity coordinates. It is desirable to do.
According to this configuration, the spectrum or chromaticity of the light emitted from the light emitting layer is substantially the same as the spectrum or chromaticity of the light when the light emitting layer is formed of the host material alone, and the light emitting dopant is doped. Therefore, the color purity is hardly reduced.

In the present invention, the band gap of the host material is preferably narrower than the band gap of the light emitting dopant.
According to this configuration, the emission wavelength of the luminescent dopant can be made shorter than the emission wavelength of the host material.

In the present invention, it is preferable that the band gap of the host material exists inside the band gap of the light emitting dopant.
According to this configuration, electrons and holes injected into the light emitting layer are easily trapped by the light emitting dopant, and high light emission efficiency is realized. For example, when the host material HOMO (highest occupied molecular orbital) or LUMO (lowest unoccupied molecular orbital) is arranged outside the luminescent dopant HOMO or LUMO, electrons or holes are easily trapped by the host material. However, since the host material has a fluorescence quantum efficiency lower than that of the light emitting dopant, sufficient light emission efficiency cannot be achieved even if many electrons and holes are trapped. On the other hand, when the luminescent dopants HOMO and LUMO are arranged outside the host material HOMO and LUMO to make the luminescent dopant easily trap electrons and holes, the trapped electrons and holes contribute to light emission with a high probability. The excitation of the host material is also promoted by the light energy generated thereby. Therefore, higher light emission efficiency can be realized as compared with a case where light is emitted by trapping electrons and holes directly in the host material.

In the present invention, the fluorescence quantum efficiency of the luminescent dopant is preferably equal to or higher than the fluorescence quantum efficiency of the host material.
According to this configuration, high luminous efficiency can be realized.

In the present invention, the concentration of the light-emitting dopant with respect to the host material is preferably in the range of 1% by weight to 10% by weight.
When the concentration of the luminescent dopant is less than 1% by weight, the host material that is not excited by the injection of electrons and holes cannot be sufficiently excited. On the other hand, if the concentration of the luminescent dopant is larger than 10% by weight, the luminescence intensity of the luminescent dopant decreases due to concentration quenching, and the emission spectrum also shifts to the longer wavelength side.

In the present invention, the light emitting layer is preferably formed using a wet method.
According to this configuration, the light emitting layer can be formed with a simple apparatus as compared with the case where the light emitting layer is formed by vacuum deposition or the like. Note that as the wet method, a spin coating method, a droplet discharge method, a dip coating method, a roll coating method, or the like can be applied. This is preferable because a desired amount of material can be accurately disposed on the surface.

In the present invention, a hole injection layer is provided between one of the pair of electrodes and the light emitting layer, and the light emitting layer is dissolved between the hole injection layer and the light emitting layer. It is desirable to provide a hole transport layer insoluble in the solvent to be used.
According to this configuration, when the light emitting layer is formed by a wet method, the hole injection layer is not redissolved in the solvent for dissolving the light emitting layer, and a highly reliable organic EL device can be provided. Further, by providing a hole transport layer between the hole injection layer and the light emitting layer, the hole transport efficiency to the light emitting layer can be improved, and an organic EL device with higher light emission efficiency can be provided.

An electronic apparatus according to the present invention includes the above-described organic electroluminescence device according to the present invention.
According to this configuration, an electronic device with high luminous efficiency can be provided. Examples of such electronic devices include an organic EL display device (organic EL display) including the organic EL device as a display unit, and an image forming device (optical printer) including the organic EL device as a line head. Further, the present invention can be applied to an illumination device (backlight or the like) provided with the organic EL device as a surface light source. In particular, when the organic EL device of the present invention is applied to an organic EL display, an organic EL display with high luminance and high color purity can be provided.

  The present invention will be described below with reference to the drawings. In all the drawings below, the film thicknesses and dimensional ratios of the constituent elements are appropriately changed in order to make the drawings easy to see.

[Configuration of organic EL device]
FIG. 1 is a schematic configuration diagram showing an embodiment of an organic EL device of the present invention. The organic EL device 1 includes an anode 3 as a first electrode, a hole injection layer 4, a hole transport layer 5, a light emitting layer 6, and a cathode 8 as a second electrode on a base 2. The hole injection layer 4, the hole transport layer 5 and the light emitting layer 6 are formed of an organic material, and an organic functional layer 7 is formed of these organic layers. The organic functional layer 7 is sandwiched between the first electrode 3 and the second electrode 8, and the organic EL element 9 is formed by the first electrode 3, the organic functional layer 7, and the second electrode 8. Yes.

  A wiring for applying a drive voltage is connected to the first electrode 3 and the second electrode 8. When a driving voltage is applied between the electrodes through this wiring, electrons are injected from the second electrode 8 and holes are injected from the first electrode 8 into the light emitting layer 6, and move in the light emitting layer 6 by the applied electric field. And recombine. The energy released during the recombination generates excitons, and when the excitons return to the ground state, energy is emitted in the form of fluorescence or phosphorescence. The light emitted from the organic EL element 9 is emitted from the base body 2 made of, for example, a glass substrate and taken out to the outside (bottom emission method). In the following description, electrons and holes injected into the light emitting layer may be referred to as carriers.

  Here, as the hole injection layer 4, polyphenylene vinylene which is polytetrahydrothiophenylphenylene, 1,1-bis- (4-N, N-ditolylaminophenyl) cyclohexane, tris (8-hydroxyquinolinol) aluminum, Polystyrene sulfonic acid or the like is used. In particular, a mixture (PEDOT / PSS) of polyethylene dioxythiophene and polystyrene sulfonic acid is suitable.

  As the hole transport layer 5, polymer organic materials such as polyfluorene derivatives, polyparaphenylene vinylene derivatives, polyparaphenylene derivatives, polyvinylcarbazole, polythiophene derivatives, polyaniline derivatives, polymethylphenylsilane and the like are preferably used. It is done. The hole transport layer 5 has a LUMO (minimum unoccupied molecular orbital) level of the light emitting layer 6 and the hole injection layer in order to efficiently transport holes injected from the hole injection layer 4 to the light emitting layer 6. 4 is preferable. Further, in order to prevent electrons injected from the second electrode 8 into the light emitting layer 6 from passing through the light emitting layer without recombination, the HOMO (maximum occupied molecular orbital) level is set. What is arranged between the light emitting layer 6 and the hole injection layer 4 is preferable. By doing so, the luminous efficiency can be improved.

  The light emitting layer 6 includes a light emitting material 6 a that is a host material and a light emitting dopant 6 b that is a guest material doped in the light emitting material 6.

  The host material 6a is made of a light emitting material having a light emitting unit having a light emitting function, a hole transporting unit having a hole transporting function, and an electron transporting unit having an electron transporting function in the same molecule. As such a light emitting material, polyfluorene derivatives (PF), polyparaphenylene vinylene derivatives (PPV), polyphenylene derivatives (PP), polyphenylene derivatives (PF), which are known polymer light emitting materials capable of emitting fluorescence or phosphorescence. Polysilanes such as paraphenylene derivatives (PPP), polyvinylcarbazole (PVK), polythiophene derivatives, polydialkylfluorene (PDAF), polyfluorenebenzothiadiazole (PFBT), polyalkylthiophene (PAT), and polymethylphenylsilane (PMPS) Etc. can be used suitably.

  The light emitting dopant 6b is made of one or more kinds of light emitting materials capable of emitting light having a wavelength shorter than that of the host material 6a. Examples of such luminescent materials include known luminescent materials capable of emitting fluorescence or phosphorescence, dyes made of polymer materials such as perylene dyes, coumarin dyes, rhodamine dyes, rubrene, perylene, A dye made of a low molecular weight material such as 9,10-diphenylanthracene, tetraphenylbutadiene, Nile red, coumarin 6, quinacridone, or a mixture of one or more of these high molecular weight or low molecular weight light emitting materials is used. be able to.

  The light emitting dopant 6b excites (photoluminescence) the host material 6a by light energy generated by its own light emission. And thereby, the host material 6a which was not excited by carrier injection is made to contribute to light emission. In this case, all the light emitted from the light emitting dopant 6b is absorbed by the host material 6a and is not emitted to the outside. Accordingly, all the light emitted from the light emitting layer 6 becomes light having a wavelength corresponding to the light emission wavelength region (band gap energy) of the host material 6a.

  The light emitting dopant 6b desirably has a fluorescence quantum efficiency equal to or higher than that of the host material 6a. For example, it is desirable to have a fluorescence quantum efficiency of 80% or more. Moreover, it is desirable that the emission spectrum of the luminescent dopant 6b has a wavelength region that overlaps with the absorption spectrum of the host material 6a. As a result, the host material 6a that has not been excited by carrier injection can be reliably excited and contribute to light emission.

  The concentration of the light-emitting dopant 6b is desirably in the range of 1% by weight to 10% by weight. If the concentration is lower than 1% by weight, the host material 6a that has not been excited by carrier injection cannot be excited sufficiently. If the concentration is higher than 10% by weight, the emission intensity of the light-emitting dopant 6b is increased by concentration quenching. This is because the emission spectrum decreases and the emission spectrum shifts to the longer wavelength side.

  In the organic EL device 1 of FIG. 1, for example, the light emitting materials shown in [Chemical Formula 1] and [Chemical Formula 2] are used as the host material 6a and the light emitting dopant 6b. [Chemical Formula 1] is a polymer light emitting material having a red light emitting function, which is an example of the host material 6a, and [Chemical Formula 2] is a fluorescent dye having a yellow fluorescent color, which is an example of the light emitting dopant 6b. As the light-emitting dopant 6b, a green fluorescent dye as shown in [Chemical Formula 3] can be used, but has a light emission wavelength close to the absorption wavelength of the host material 6a from the viewpoint of improving the light emission rate and color purity. It is desirable to use the light emitting material of [Chemical Formula 2]. This is because if the emission wavelength of the light-emitting dopant 6b is separated from the absorption wavelength of the host material 6a, the proportion of light emitted outside without exciting the host material 6a increases.

FIG. 2 is a diagram showing a band diagram of the host material 6a and the light emitting dopant 6b in the light emitting layer 6. In FIG. As shown in FIG. 2, the light emitting dopant 6b has a larger band gap energy (HOMO-LUMO gap) E2 than the host material 6a. Some of the holes and electrons transported from the hole transport layer 5 and the cathode 8 cause the light emitting dopant 6b to emit light, and emit light L1 _EL corresponding to the band gap energy E2. The light L1 _EL is completely absorbed by the host material 6a and excites the host material 6a. And it is taken out as light L2 _PL corresponding to the band gap energy E1 of the host material 6a. On the other hand, the holes and electrons transported from the hole transport layer 5 and the cathode 8 cause the host material 6a to emit light and emit light L2 _EL corresponding to the band gap energy E1.

These lights L2 _PL and L2 _EL are both lights corresponding to the band gap energy E1 of the host material 6a, and have the same emission spectrum as when the light emitting dopant 6b is not doped. For example, when the host material 6a is composed of [Chemical Formula 1] and the light emitting dopant 6b is composed of [Chemical Formula 2], the emission spectrum of the light L emitted from the light emitting layer 6 is the same as the case where the light emitting layer 6 is formed of the host material alone. Compared with the overlap of 90% or more. When viewed in terms of chromaticity coordinates, the emission chromaticity of both coincides with two decimal places.

[Method for Manufacturing Organic EL Device]
Next, a method for manufacturing the organic EL device 1 will be described with reference to FIG.
First, as shown in FIG. 3A, the hole injection layer 4 is formed on the substrate 2 on which the first electrode 3 is formed using a wet method. As the wet method, a spin coating method, a droplet discharge method, a dip coating method, a roll coating method, or the like can be applied. Among these, the droplet discharge method is preferable because the use of the material is less wasteful and a desired amount of material can be accurately disposed at a desired position.

  Examples of the droplet discharge method (inkjet method) include a charge control method, a pressure vibration method, an electromechanical conversion method, an electrothermal conversion method, and an electrostatic suction method. In the charge control method, a charge is applied to a material by a charging electrode, and the flight direction of the material is controlled by a deflection electrode and discharged from a nozzle. In addition, the pressure vibration method applies an ultra-high pressure to the material and discharges the material to the tip of the nozzle. When the control voltage is not applied, the material moves straight and is discharged from the nozzle, and the control voltage is applied. Electrostatic repulsion occurs between the materials and the materials are scattered and not discharged from the nozzle. In addition, the electromechanical conversion method (piezo method) utilizes the property that a piezo element (piezoelectric element) deforms in response to a pulsed electric signal, and can be used in a space where material is stored by deformation of the piezo element. Pressure is applied through a flexible substance, and the material is pushed out from this space and discharged from the nozzle. In the electrothermal conversion method, a material is rapidly vaporized by a heater provided in a space in which the material is stored to generate bubbles, and the material in the space is discharged by the pressure of the bubbles. In the electrostatic attraction method, a minute pressure is applied in a space in which the material is stored, a meniscus of the material is formed on the nozzle, and an electrostatic attractive force is applied in this state before the material is drawn out. In addition to this, techniques such as a system that uses a change in the viscosity of a fluid due to an electric field and a system that uses a discharge spark are also applicable.

  For the hole injection layer 4, for example, a liquid material containing 3,4-polyethylenedioxythiophene / polystyrene sulfonic acid (PEDOT / PSS) which is a hole injection layer forming material is disposed on the first electrode 3, and this is used. It is formed by drying and firing. As a solvent for the hole injection layer forming material, a polar solvent such as isopropyl alcohol, N-methylpyrrolidone, 1,3-dimethyl-imidazolinone can be used.

  Next, as shown in FIG. 3B, the hole transport layer 5 is formed on the hole injection layer 4 by a wet method. For the hole transport layer 5, for example, a liquid material containing a polyfluorene derivative or the like, which is a hole transport layer forming material, provided with a crosslinkable functional group is disposed on the hole injection layer 4. It is formed by drying and baking (heat curing) in an atmosphere. As a solvent for the hole transport layer forming material, a nonpolar solvent that is insoluble in the hole injection layer 4 can be used in order to prevent re-dissolution of the hole injection layer 4.

  When the substrate 2 is placed on a hot plate or the like and heated in an inert gas atmosphere, a film insoluble in a nonpolar solvent (film of a hole transport layer forming material) is formed on the surface of the hole injection layer 4. . And the positive hole transport layer 5 is obtained by removing the soluble part of the surface of this film | membrane with nonpolar solvents, such as toluene. In addition, by using a material having a predetermined HOMO level and LUMO level as the hole transport layer forming material, the hole transport layer 5 can function as an electron block layer, thereby improving the efficiency of the organic EL device 1. Long life can be realized.

  Next, as shown in FIG. 3C, the light emitting layer 6 is formed on the hole transport layer 5 using a wet method. The light emitting layer 6 is formed, for example, by disposing a liquid material containing the host material 6a and the light emitting dopant 6b shown in [Chemical Formula 1] and [Chemical Formula 2] on the hole transport layer 5, and drying and baking the liquid material. To do. As a solvent for the light emitting material, a nonpolar solvent such as toluene can be used. Since the hole transport layer 5 is insoluble in the nonpolar solvent by the above-described treatment, the hole transport layer 5 and the hole injection layer can be formed even if such a liquid material is disposed on the hole transport layer 5. Layer 4 does not redissolve in the solvent.

  Next, as shown in FIG. 3D, the second electrode 8 is formed on the light emitting layer 6. The second electrode 8 can be formed, for example, by sequentially stacking calcium and aluminum by a vacuum deposition method. The calcium layer functions as an electron transport layer that transports electrons injected from the aluminum layer to the light emitting layer 6. As a result, the organic EL element 9 is formed on the substrate 2. Thereafter, a sealing process is performed as necessary to complete the organic EL device 1.

  As described above, according to the organic EL device 1 of the present embodiment, the light emitting layer 6 is doped with the light emitting dopant 6b that emits light having higher light emission energy (shorter wavelength) than the host material 6a. The host material 6a has the following two paths: (1) a path (electroluminescence) in which the host material emits light by electrons and holes injected into the light emitting layer 6, and (2) an electron injected into the light emitting layer 6 and The light-emitting dopant 6b can emit light by using holes, and the host material 6a can be excited by the energy of light emitted from the light-emitting dopant 6b to emit light (photoluminescence). For this reason, compared with the case where the host material 6a is used independently, the organic EL apparatus 1 with high luminous efficiency can be provided. Further, since almost all of the light emitted from the light emitting dopant 6b is absorbed by the host material 6a, only light having a wavelength caused by the host material 6a is emitted from the light emitting layer 6. Therefore, problems such as color mixing due to the doping of the light emitting dopant 6b do not occur, and the organic EL device 1 with high color purity is provided.

In this embodiment, since the band gap of the host material 6a exists inside the band gap of the light emitting dopant 6b, electrons and holes injected into the light emitting layer 6 are easily trapped by the light emitting dopant 6b. High luminous efficiency is realized. For example, when the HOMO or LUMO of the host material 6a is arranged outside the HOMO or LUMO of the light emitting dopant as shown in FIG. 4A or 4B, electrons or holes are transferred to the host material 6a. Although it is easy to be trapped, since the host material 6a has a lower fluorescence quantum efficiency than the light emitting dopant 6b, sufficient light emission efficiency cannot be realized even if many electrons and holes are trapped. On the other hand, when the HOMO and LUMO of the luminescent dopant 6b are arranged outside the HOMO and LUMO of the host material 6a to make the luminescent dopant 6b easily trap electrons and holes, the trapped electrons and holes emit light with a high probability ( L1 _EL ) contributes to the excitation of the host material 6a by the light energy generated thereby. Therefore, higher luminous efficiency can be realized as compared with the case where light is emitted by trapping electrons and holes directly in the host material 6a.

[Image forming apparatus]
Next, an image forming apparatus that is a first embodiment of an electronic apparatus including the organic EL device of the present invention will be described. FIG. 5 is a schematic configuration diagram illustrating an image forming apparatus 100 including the organic EL device 1 as a line head.

  The image forming apparatus 100 includes a photosensitive drum 16 as an image carrier in the vicinity of the travel path of the transfer medium 22. Around the photosensitive drum 16, an exposure device 15, a developing device 18, and a transfer roller 21 are sequentially arranged along the rotation direction of the photosensitive drum 16 (indicated by an arrow in the drawing). The photosensitive drum 16 is rotatably provided around the rotation shaft 17, and a photosensitive surface 16 </ b> A is formed on the outer peripheral surface of the photosensitive drum 16 at the central portion in the rotation axis direction. The exposure device 15 and the developing device 18 are arranged in a long axis shape along the rotation shaft 17 of the photosensitive drum 16, and the width in the long axis direction substantially coincides with the width of the photosensitive surface 16A.

  In this image forming apparatus 100, first, in the process of rotating the photosensitive drum 16, the surface of the photosensitive drum 16 (photosensitive surface 16 </ b> A) is positive (for example, positive) by a charging device (not shown) provided on the upstream side of the exposure device 15. Then, the exposure device 15 exposes the surface of the photosensitive drum 16 to form an electrostatic latent image LA on the surface. Further, the toner (developer) 20 is applied to the surface of the photosensitive drum 16 by the developing roller 19 of the developing device 18, and the toner image corresponding to the electrostatic latent image LA is formed by the electric attractive force of the electrostatic latent image LA. It is formed. The toner particles are positively (+) charged.

  After the toner image is formed by the developing device 18, the toner image comes into contact with a transfer medium (not shown) by further rotation of the photosensitive drum 16, and the transfer roller 21 reverses the toner particles of the toner image from the back surface of the transfer medium 22. A polar charge (here, negative (−) charge) is applied, and accordingly, toner particles forming a toner image are attracted to the transfer medium 22 from the surface of the photosensitive drum 16, and the toner image is transferred to the transfer medium 22. Is transferred to the surface.

  The exposure apparatus 15 includes a line head 1 having a plurality of organic EL elements 9 and an imaging optical element 12 having a plurality of lens elements 13 for imaging the light L emitted from the line head 1 at an erecting equal magnification. I have. The line head 1 and the imaging optical element 12 are held by a head case (not shown) while being aligned with each other, and are fixed on the photosensitive drum 16.

  The line head 1 includes a light emitting element array 10 in which a plurality of organic EL elements 9 are arranged along the rotation axis 17 of the photosensitive drum 16, and a drive element group including a drive element (not shown) that drives the organic EL elements 9. And a control circuit group 11 for controlling driving of these drive elements (drive element group). The organic EL element 9, the drive element group, and the control circuit group 11 are integrally formed on a long and thin element substrate (base) 2.

  The organic EL element 9 has the element structure shown in FIG. 1. The light emitting layer has a host material made of a red light emitting material shown in [Chemical Formula 1] and [Chemical Formula 2] or [Chemical Formula 3]. And a light-emitting dopant made of a yellow or green fluorescent dye. Then, red light L corresponding to the band gap energy of the host material is emitted from the element substrate 2 side to form an image on the photosensitive drum 16.

  The imaging optical element 12 is arranged (arranged) in a zigzag pattern in which the lens elements 13 having the same configuration as the SELFOC (registered trademark) lens element manufactured by Nippon Sheet Glass Co., Ltd. are arranged along the rotation axis 17 of the photosensitive drum 16. A lens element array 14 is provided.

  In the image forming apparatus 100, the organic EL element 9 formed on the line head 1 includes a light emitting layer containing the host material and the light emitting dopant shown in FIG. No image forming apparatus.

[Organic EL display device]
Next, an organic EL display device which is a second embodiment of an electronic apparatus including the organic EL device of the present invention will be described. FIG. 6 is a schematic configuration diagram of an organic EL display device 200 including the organic EL elements having the element structure shown in FIG. 1 as pixels in a matrix.

  The organic EL display device 200 includes a circuit element unit 30 including a thin film transistor as a circuit element, a pixel electrode (first electrode) 3 serving as an anode, an organic functional layer 7 including a light emitting layer, and a counter electrode serving as a cathode. (Second electrode) 8, a sealing portion 32, and the like are provided.

  For example, a glass substrate is used as the substrate 2. As a substrate in the present invention, in addition to a glass substrate, various known substrates used for electro-optical devices and circuit substrates such as a silicon substrate, a quartz substrate, a ceramic substrate, a metal substrate, a plastic substrate, and a plastic film substrate are applied. The

  On the base 2, a plurality of pixel areas A as light emitting areas are arranged in a matrix, and when performing color display, for example, corresponding to each color of red (Red), green (Green), and blue (Blue). Pixel areas A to be arranged are arranged in a predetermined arrangement. In each pixel region A, a pixel electrode 3 is arranged, and in the vicinity thereof, a signal line 42, a common power supply line 43, a scanning line 41, a scanning line for other pixel electrodes (not shown), and the like are arranged. As the planar shape of the pixel region A, an arbitrary shape such as a circle or an oval can be applied in addition to the rectangle shown in the figure.

  The sealing portion 32 prevents water and oxygen from entering and prevents the counter electrode 8 or the organic functional layer 7 from being oxidized, and includes a sealing substrate (or sealing can) 34 bonded to the base 2. The sealing substrate 34 is made of glass, metal, or the like, and the base 2 and the sealing substrate 34 are bonded together with a sealing agent. A desiccant is disposed inside the substrate 2, and an inert gas filling layer 33 filled with an inert gas is formed in a space formed between the substrates.

  In the pixel region A, a first thin film transistor 44 for switching in which a scanning signal is supplied to the gate electrode through the scanning line 41 and a holding for holding an image signal supplied from the signal line 42 through the thin film transistor 44. The capacitor cap, the driving second thin film transistor 45 to which the image signal held by the holding capacitor cap is supplied to the gate electrode, and the common supply line when electrically connected to the common power supply line 43 through the thin film transistor 45 A pixel electrode 3 into which a drive current flows from the electric wire 43 and an organic functional layer 7 sandwiched between the pixel electrode 3 and the counter electrode 8 are provided. The organic functional layer 7 includes a light emitting layer, and the organic EL element 9 which is a light emitting element includes the pixel electrode 3, the counter electrode 8, the organic functional layer 7, and the like.

  Here, among the organic EL elements 9, the organic EL element corresponding to the red pixel region A includes a host material made of a red light emitting material shown in [Chemical Formula 1] and [Chemical Formula 2] or [Chemical Formula 3]. A light emitting layer is provided that includes a light emitting dopant made of the indicated yellow or green fluorescent dye. For this reason, compared with the case where the light emitting layer is formed of the host material alone, the organic EL element has a higher light emission luminance.

  In the pixel area A, when the scanning line 41 is driven and the first thin film transistor 44 is turned on, the potential of the signal line 42 at that time is held in the holding capacitor cap, and the second capacitance is changed according to the state of the holding capacitor cap. The conductive state of the thin film transistor 45 is determined. In addition, a current flows from the common power supply line 43 to the pixel electrode 3 through the channel of the second thin film transistor 45, and further a current flows to the counter electrode 8 through the organic functional layer 7. And according to the electric current amount at this time, the organic functional layer 7 light-emits.

  In the organic EL display device 200, light emitted from the organic functional layer 7 to the base 2 side is transmitted through the circuit element unit 30 and the base 2 and emitted to the lower side (observer side) of the base 2. Light emitted from the functional layer 7 to the opposite side of the substrate 2 is reflected by the counter electrode 8, and the light passes through the circuit element unit 30 and the substrate 2 and is emitted to the lower side (observer side) of the substrate 2. (Bottom emission type). Note that light emitted from the counter electrode can be emitted by using a transparent material as the counter electrode 8 (top emission type). In this case, ITO, Pt, Ir, Ni, or Pd can be used as the transparent material for the counter electrode.

  In the organic EL display device 200, the organic EL element 9 formed in the red pixel region A includes a light emitting layer containing the host material and the light emitting dopant shown in FIG. An organic EL display device including red pixels with excellent purity is obtained.

  In the present embodiment, the present invention is applied to the organic EL element 9 formed in the red pixel region A. However, the present invention is applied to the organic EL element 9 in the green or blue pixel region A. You can also.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but it goes without saying that the present invention is not limited to such examples. Various shapes, combinations, and the like of the constituent members shown in the above-described examples are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

It is a schematic block diagram of the organic electroluminescent apparatus of this invention. It is a band diagram of the host material and light emission dopant which are contained in a light emitting layer. It is process drawing explaining the manufacturing method of an organic electroluminescent apparatus. It is a band diagram of the host material and light emission dopant which are contained in a light emitting layer. 1 is a schematic configuration diagram of an image forming apparatus that is an example of an electronic apparatus. It is a schematic block diagram of the organic electroluminescence display which is an example of an electronic device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Organic EL apparatus, 2 ... Base | substrate, 3 ... 1st electrode, 4 ... Hole injection layer, 5 ... Hole transport layer, 6 ... Light emitting layer, 6a ... Host material, 6b ... Light emitting dopant, 7 ... Organic functional layer , 8 ... second electrode, 9 ... organic EL element, 100 ... image forming apparatus (electronic device), 200 ... organic EL display device (electronic device), E1 ... band gap energy of host material, E2 ... band gap of luminescent dopant Energy, L1 _EL ... electroluminescence light emitted from the luminescent dopant, L2 _EL ... electroluminescence light emitted from the host material, L2 _PL ... photoluminescence light emitted from the host material

Claims (12)

An organic electroluminescence device having a light emitting layer between a pair of electrodes,
A host material in which the light emitting layer is a light emitting material having a light emitting unit having a light emitting function, a hole transporting unit having a hole transporting function, and an electron transporting unit having an electron transporting function in the same molecule; An organic electroluminescence device comprising: a light-emitting dopant that is a light-emitting material having an emission wavelength shorter than the emission wavelength.   The organic electroluminescence device according to claim 1, wherein the host material includes a light emitting unit having a red light emitting function.   3. The organic electroluminescence device according to claim 1, wherein an emission spectrum of the luminescent dopant has a wavelength region overlapping with an absorption spectrum of the host material.   The emission spectrum when the emission layer is formed of the host material and the emission dopant and the emission spectrum when the emission layer is formed of only the host material coincide with each other with an overlap of 90% or more. Item 4. The organic electroluminescence device according to Item 3.   The light emission chromaticity when the light emitting layer is formed with the host material and the light emitting dopant and the light emission chromaticity when the light emitting layer is formed only with the host material coincide with each other up to two decimal places on the chromaticity coordinates. The organic electroluminescence device according to claim 3.   The organic electroluminescent device according to claim 1, wherein a band gap of the host material is narrower than a band gap of the light emitting dopant.   The organic electroluminescence device according to claim 1, wherein the band gap of the host material exists inside the band gap of the light emitting dopant.   8. The organic electroluminescence device according to claim 1, wherein a fluorescence quantum efficiency of the light emitting dopant is equal to or higher than a fluorescence quantum efficiency of the host material. 9.   The organic electroluminescent device according to claim 1, wherein the concentration of the light-emitting dopant with respect to the host material is in the range of 1 wt% to 10 wt%.   The organic light-emitting device according to claim 1, wherein the light emitting layer is formed using a wet method.   A hole injection layer is provided between one electrode of the pair of electrodes and the light emitting layer, and a solvent that dissolves the light emitting layer is interposed between the hole injection layer and the light emitting layer. The organic electroluminescence device according to claim 10, wherein an insoluble hole transport layer is provided.   An electronic apparatus comprising the organic electroluminescence device according to any one of claims 1 to 11.

Images