JP2008016498A - White organic light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a white light emitting element which is fabricated by a convenient method and in which red light emission is achieved by one kind of fluorescence dye added to a single light emission layer, layer structure is simplified by emitting blue light from an electron transport layer, and difficulty of control is avoided by setting the addition of fluorescence dye at a low concentration when blue fluorescence dye is employed together with the red fluorescence dye. <P>SOLUTION: In the white organic light emitting element having at least an organic light emission layer and an electron transport layer between an anode and a cathode; the organic light emission layer contains a single fluorescence dye and emitting red light, and at least a part of the electron transport layer emits light having a peak wavelength of 400-500 nm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a white organic light emitting device. This white organic light emitting device has high definition and excellent visibility, and is useful for an organic electroluminescence (hereinafter referred to as organic EL) display that can be applied to a wide range of applications such as a display of a portable terminal or an industrial measuring instrument.

  As an example of a light emitting element applied to a display element, an organic EL element having a thin film laminated structure of an organic compound is known. An organic EL element is a thin-film self-luminous element and has excellent characteristics such as a low driving voltage, high resolution, and a high viewing angle. Therefore, various studies have been conducted for practical use thereof.

The organic EL element has a structure including at least an organic light emitting layer between an anode and a cathode.
The organic light emitting layer is where light is emitted by recombination of holes and electrons generated by applying a voltage to the anode and the cathode. The organic EL element has a structure in which one or more of a hole injection layer, a hole transport layer, an electron transport layer, and an electron injection layer are interposed as required. More specifically, for example, the following structures are exemplified.
(1) Organic light emitting layer (2) Hole injection layer / organic light emitting layer (3) Organic light emitting layer / electron transport layer (4) Hole injection layer / organic light emitting layer / electron transport layer (5) Hole injection layer / Hole transport layer / organic light emitting layer / electron transport layer (6) hole injection layer / hole transport layer / organic light emitting layer / electron transport layer / electron injection layer

  In the organic EL device having the above-described structures (1) to (6), the anode is connected to the organic light emitting layer (1, 3) or the hole injection layer (2, 4-6), and the organic light emitting layer ( 1, 2) The cathode is connected to the electron transport layer (3-5) or the electron injection layer (6).

  It is known that organic EL elements emit light in red, blue, and green depending on the type of pigment added to the organic light emitting layer. In order to realize a full color display, light emitting elements of three primary colors may be arranged in subpixels as pixels (pixels). However, since the characteristics of the light emitting elements of the respective colors are different from each other, the formation of the subpixel and the driving method thereof are complicated, which causes an increase in cost. Therefore, attempts have been made to obtain three primary colors from white light using a color filter. Therefore, realization of a multicolor or white light emitting organic EL element that can be used in a color filter system is desired.

There is a proposal of a method in which two or more light emitting layers are provided including a mixed layer type light emitting layer, and two or more kinds of dopants are contained, thereby obtaining two or more kinds of light emission (see, for example, Patent Document 1). .
Furthermore, a light-emitting element that can generate white light when a high voltage is applied by providing multiple light-emitting layers is disclosed.

  In addition, the light-emitting layer has a laminated structure in which a first light-emitting layer containing a fluorescent dye that emits blue light and a second light-emitting layer containing a fluorescent dye that emits green light are stacked. The first light-emitting layer, the second light-emitting layer, and the like There is also a proposal of a white light emitting element in which a fluorescent dye that emits red light is contained in at least one layer selected from organic layers (see, for example, Patent Document 2). The element described in Patent Document 2 also includes a plurality of light emitting layers containing a blue light emitting fluorescent dye, a green light emitting fluorescent dye, and a red light emitting fluorescent dye.

  There is also a proposal of an organic EL device that includes a hole transporting layer and an electron transporting light emitting layer, the electron transporting light emitting layer contains an electron transporting polymer compound and a plurality of types of fluorescent dyes, and emits white light. (For example, refer to Patent Document 3). The element of Patent Document 3 includes an electron transporting compound and fluorescent dyes that emit blue, green, yellow, and red, respectively, in a light emitting layer.

  In addition, the light-emitting layer has a hole transport layer and / or an electron transport layer adjacent to the light-emitting layer, and the light-emitting layer is composed of one or more layers including a blue light-emitting layer, and the light-emitting layer transports holes. There is also a proposal of an organic EL device including a hole injecting / transporting compound in a layer and / or an electron injecting / transporting compound in an electron transporting layer as a host compound (for example, see Patent Document 4). Here, the host compound is a blue light-emitting compound, and specifically, a phenylanthracene derivative is used. The white light-emitting element has this blue light-emitting layer and one or two light-emitting layers that emit light having a wavelength different from that of blue. The one or two light-emitting layers are hole injection transport layers. And an electron injecting and transporting layer.

There is also a proposal of an organic light emitting device characterized in that a blue light emitting layer and a green light emitting layer are sequentially laminated from the hole transport layer side, and the green light emitting layer has a region containing a red fluorescent dye (for example, (See Patent Document 5). The blue light emitting layer is doped with a blue fluorescent dye. The blue light emitting layer is formed from an electron transporting compound. The green light emitting layer is also made of an electron injecting and transporting compound.
In addition, a hole injection layer, a hole transport layer, a light emitting layer doped with a blue light-emitting compound, an electron transport layer, and an anode in this order from the cathode side, and the whole layer of the hole transport layer and / or the electron transport layer or A proposal of a white light emitting diode device in which a portion facing a blue light emitting layer is doped with a yellow light emitting compound (see, for example, Patent Document 6), a green light emitting compound is doped instead of the proposed yellow light emitting compound. There is also a proposal of a white light emitting diode device (see, for example, Patent Document 7). The hole transport layer of the device of Patent Document 6 is doped with a yellow dopant.

Republished patent WO98 / 08360 Japanese Patent No. 3366401 Japanese Patent Application Laid-Open No. 07-220871 JP 2001-52870 A Japanese Patent Application Laid-Open No. 07-142169 JP 2002-93583 A JP 2003-86380 A

The element described in Patent Document 1 requires two or more light-emitting layers for generating white light, each of which requires different dopants, so the configuration must be complicated, and the white light-emitting element can be manufactured at low cost. Can't get. There is also a problem that it is difficult to control the color tone.
The element described in Patent Document 2 also includes a plurality of light emitting layers containing a blue light emitting fluorescent dye, a green light emitting fluorescent dye, and a red light emitting fluorescent dye. The element of Patent Document 3 includes an electron transporting compound in the light emitting layer. And fluorescent dyes that emit blue, green, yellow, and red, respectively. However, these light emitting layers also have a problem that the colored light changes due to a small change in the dye concentration. In particular, in order to obtain the optimum white light, it is necessary to control the red fluorescent dye having low energy at a very low concentration, which is difficult to control.

  Also in Patent Document 4, two or three light emitting layers are provided in order to emit white light, and each light emitting layer uses a fluorescent dye for developing blue and other colors. Have the disadvantages of

  The element described in Patent Document 5 requires a plurality of light emitting layers, and each light emitting layer requires one or more fluorescent dyes. Therefore, the manufacturing process must be complicated. Since a slight change in voltage causes recombination of electrons and holes in different layers, a change in color occurs, resulting in a problem that the generated color changes depending on the state of the drive.

  In the device described in Patent Document 6, a blue fluorescent dopant is doped in the light emitting layer, and a yellow fluorescent dye is selectively doped in a part of the hole transport layer and / or the electron transport layer in contact therewith or the whole layer. Has been. Therefore, like the element described in Patent Document 1, the configuration must be complicated, and a white light emitting element cannot be obtained at low cost. There is also a problem that it is difficult to control the color tone.

  The device described in Patent Document 7 is also doped with a fluorescent dye in each of the light emitting layer, the hole transport layer, and the electron transport layer, and requires a different fluorescent dopant for each of the elements described in Patent Document 1. Therefore, the configuration must be complicated, and a white light emitting element cannot be obtained at a low cost. There is also a problem that it is difficult to control the color tone.

  Conventionally, for white light emission, a blue light emitting layer containing a blue light emitting dopant and a light emitting layer containing a red light emitting dopant have been used, and a plurality of light emitting layers have been required. On the other hand, making the electron transport layer emit blue light, which has not been possible in the past, includes a nitrogen-containing five-membered ring derivative in the electron transport layer, and the film thickness is set to 30 nm or more instead of the conventional 20 nm. It has been found that this can be achieved, and that complementary red light emission can be emitted outside the device by doping the light emitting layer with a red fluorescent dye.

  Based on this discovery, the present inventor realizes red light emission with one kind of fluorescent dye added to a single light emitting layer and causes the electron transport layer to emit blue light in order to solve the above problem. This simplifies the layer structure and avoids the difficulty of control due to the low concentration of the fluorescent dye added when the blue fluorescent dye is used together with the red fluorescent dye. An object is to provide an element.

  That is, the white light-emitting element of the present invention is an organic light-emitting element having at least an organic light-emitting layer and an electron transport layer between an anode and a cathode, and the organic light-emitting layer contains a single fluorescent dye and emits red light. At least a part of the transport layer emits light having a peak wavelength of 400 to 500 nm.

  According to the present invention, a high-efficiency white light-emitting element can be manufactured with high productivity with a simple configuration.

The white light emitting device of the present invention has at least a hole transport layer, an organic light emitting layer, and an electron transport layer between an anode and a cathode.
In order to cause the EL element to emit light, at least one of the anode and the cathode needs to be light transmissive, and the anode is preferably made of a material and a thickness such that the transmittance of emitted light is 80% or more, As the first electrode, a transparent electrode such as ITO (indium-tin oxide), In-Zn oxide, or ATO can be used. The thickness of the anode is preferably 10 to 500 nm.
The anode is provided on the transparent substrate.

  As the cathode, alkaline metals such as lithium and sodium, which are materials having a low work function, alkaline earth metals such as potassium, calcium, magnesium and strontium, or electron-injecting metals such as fluorides thereof, and other metals Alloys and compounds are used. Below that, a metal electrode having high reflectivity (a metal such as Al, Ag, Mo, or W or an alloy thereof, an amorphous metal or alloy such as NiP, NiB, CrP, or CrB, or a microcrystalline alloy such as NiAl) In this case, effective use of light emission of the organic EL layer due to low resistance and reflection can be achieved.

  Between the anode and the cathode, it has at least a hole transport layer, an organic light emitting layer, and an electron transport layer, and a hole injection layer and / or a hole transport layer may be provided between the anode and the organic light emitting layer, An electron injection layer may be provided between the electron transport layer and the cathode.

As the electroluminescent layer, a host compound added with one kind of red fluorescent dye is used. Examples of the host compound include metal complexes such as Alq ₃ , NA, BeBq ₂ , and DPVBi, TPD, naphthalimide derivatives, distyrylarylene derivatives, and conductive polymers. Examples of the conductive polymer include polyvinyl carbazole derivatives, polysilane derivatives, polythiophene derivatives, and the like.

  As a red fluorescent dye, 4- (dicyanomethylene) -2-methyl-6- (p-dimethylstyryl) -4H-pyran (DCM), 4,4-difluoro-1,3,5,7-tetraphenyl- 4-Bora-3a, 4a-diaza-s-indacene, propanedinitrile, Nile red and the like can be mentioned. The amount of the red fluorescent dye added to the host compound is preferably 0.5 to 10% by volume, and can be appropriately selected depending on the desired red intensity within this range.

  The electron transport layer is made of an electron transporting material that emits light having a peak wavelength of 400 to 500 nm. Examples of such a material include fluorene, bathophenanthroline, bathocuproine, anthraquinodimethane, diphenoquinone, imidazole, oligothiophene, Examples thereof include compounds having a structure such as phenylbenzimidazole, quinoline, and carbazole, compounds thereof, metal complex compounds, and nitrogen-containing five-membered ring derivatives.

  Examples of the metal complex compound include benzoxazole zinc complex, azomethine zinc complex, benzothiazole zinc complex, tri (2-methyl-8-hydroxyxylinato) aluminum complex, bis (2-methyl-8-quinolinato) (1-naphtholate). An aluminum complex, a bis (2-methyl-8-quinolinate) (o-cresolate) gallium complex, and the like can be given. As the nitrogen-containing five-membered ring derivative, oxazole, oxadiazole, thiadiazole, triazole and derivatives thereof are preferable. As an example.

  Specific examples of the nitrogen-containing five-membered ring derivative include 2,5-bis (1-phenyl) -1,3,4-oxazole, 2,5-bis (1-phenyl) -1,3,4-thiazole, 2,5-bis (1-phenyl) -1,3,4-oxadiazole, 2- (4′-tert-butylphenyl) -5- (4 ″ -biphenyl) -1,3,4-oxadi Azole, 2,5-bis (1-naphthyl) -1,3,4-oxadiazole, 1,4-bis [2- (5-phenylthiadiazolyl)] benzene, 2,5-bis (1- Naphthyl) -1,3,4-triazole, 3- (4-biphenylyl) -4-phenyl-5- (4-tert-butylphenyl) -1,2,4-triazole, and the like. , Polymer materials used in polymer organic electroluminescence devices It can also be used. Such polymeric materials include, for example polyparaphenylene and its derivatives, fluorene and its derivatives.

  Specific examples of the electron transport layer material are shown for illustrative purposes, and are not limited thereto.

  This electron transport layer is an electron transporting material that emits light having a peak wavelength of 400 to 500 nm. The electron transport layer did not emit light when the film thickness was 20 nm, which was conventionally employed, but when the film thickness was 30 nm or more, blue light emission of the electron transport layer could be obtained. Further, even if the film thickness exceeds 50 nm, there is no increase in the effect of obtaining blue light emission, and therefore the film thickness of the electron transport layer is preferably 30 to 50 nm.

  As the hole injection layer, aromatic amine compounds, starburst amines, benzidine amine multimers, copper phthalocyanine (CuPc), and the like can be used. As the hole transport layer, a starburst amine, an aromatic diamine, or the like can be used.

  In the case of providing a hole injection layer, a hole transport layer, and an electron injection layer as an EL light emitting device, any one can be used as long as it is generally used for a hole injection layer, a hole transport layer, and an electron injection layer of an EL light emitting device. Can also be used. For example, as the hole injection layer, an aromatic amine compound, a starburst amine, a benzidine amine multimer, copper phthalocyanine (CuPc), or the like can be used. As the hole transport layer, starburst amine, aromatic diamine, or the like can be used. The electron injection layer may be, for example, an alkali metal such as lithium or sodium, an alkaline earth metal such as potassium, calcium, magnesium, or strontium, or an electron injecting metal such as a fluoride thereof, or other metals. Materials such as alloys and compounds can be used.

  This white organic light emitting device is formed by depositing a transparent electrode on a substrate by vapor deposition, sputtering, etc., and using a resistance heating vapor deposition device or the like to sequentially form each desired layer including at least the organic light emitting layer and the electron transport layer without breaking the vacuum. A film may be formed.

  In order to produce a full-color display element using this white organic light-emitting element, a color filter corresponding to each color of red, green, and blue may be provided. Known color filters can be used for each color.

A schematic cross-sectional view showing the structure of the white organic light-emitting device of the present invention is shown in FIG.
A film made of In—Zn oxide (IZO) was formed as the anode 12 with a thickness of 200 nm on the substrate 11 by DC sputtering. A glass substrate was used as the substrate 11, an IZO fired body was used as the sputtering target, and a mixed gas of Ar and oxygen was used as the sputtering gas.

The substrate 11 having the anode 12 formed on the surface thus obtained was mounted in a resistance heating vapor deposition apparatus, and the hole transport layer 13, the organic light emitting layer 14, and the electron transport layer 15 were sequentially formed without breaking the vacuum. During film formation, the vacuum chamber internal pressure of the vapor deposition apparatus was reduced to 1 × 10 ⁻⁴ .

  As the hole transport layer, 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (α-NPD) was laminated to 80 nm. As the light emitting layer, 4,4′-bis [2,2′-diphenylvinyl) biphenyl (DPVBi) is used as a host compound, and 4- (dicyanomethylene) -2-methyl-6- (p-dimethyl) is used as a red fluorescent dye. Aminostyryl) -4H-pyran (DCM) was used, and the host compound and DCM were co-evaporated over the entire light emitting layer so that DCM was 5% by volume in the light emitting layer, thereby stacking 20 nm.

  The electron transport layer 15 was laminated to 40 nm using a nitrogen-containing five-membered ring derivative containing anthracene as a substituent. This compound is an electron transporting material that emits light having a peak at 400 to 500 nm.

  Thereafter, a cathode 16 composed of an Mg / Ag (10: 1 weight ratio) layer having a thickness of 200 nm was formed without breaking the vacuum.

  The laminate thus obtained was sealed with sealing glass and a UV curable adhesive in a glove box dry atmosphere (both oxygen and moisture were 10 ppm or less).

The resulting white organic light emitting device emitted white light with chromaticity (0.36, 0.40). When the voltage-instantaneous luminance characteristic of this element was measured, a luminance of 642 cd / m ² was obtained at a current density of 0.6 × 10 ⁻² A / cm ² .

  The white organic light-emitting device of the present invention is white light-emitting that exhibits high efficiency even with a simple configuration, and since it has a simple configuration, it exhibits stable product performance and is particularly useful for producing a full-color display device. .

It is a cross-sectional schematic diagram which shows an example of the structure of the white organic light emitting element of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Substrate 12 Anode 13 Hole transport layer 14 Organic light emitting layer 15 Electron transport layer 16 Cathode

Claims (3)

  In an organic light-emitting device having at least an organic light-emitting layer and an electron transport layer between an anode and a cathode, the organic light-emitting layer is a layer that emits red light containing a single fluorescent dye, and the electron transport layer is at least partially 400 to 400 A white organic light-emitting element that emits light having a peak wavelength of 500 nm.   The white organic light-emitting device according to claim 1, wherein the electron transport layer contains a nitrogen-containing five-membered ring derivative. The white organic light-emitting device according to claim 1 or 2, wherein the electron transport layer has a thickness of 30 to 50 nm.

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