JP4869759B2 - Organic electroluminescence device - Google Patents

Description

  The present invention relates to an organic electroluminescent element (also simply referred to as an element, a light emitting element, or an EL element) that can emit light by converting electric energy into light.

Today, research and development on various display elements are active. Among them, organic electroluminescence (EL) elements are attracting attention as promising display elements because they can emit light with high luminance at a low voltage.
In general, an organic EL element is composed of a light emitting layer or a counter electrode sandwiching a plurality of organic layers including a light emitting layer, and electrons injected from a cathode and holes injected from an anode are recombined in the light emitting layer, One that uses light emission from the generated exciton, or one that uses light emission from the exciton of another molecule generated by energy transfer from the exciton.
However, further improvements in luminous efficiency and luminance are strongly demanded from the viewpoint of energy saving and durability improvement.

Since the organic EL element is a self-luminous surface light source, it can be used as a white light source, for example. An ideal white light source has coordinates on the CIE chromaticity diagram of (0.33, 0.33), as defined by the Commission Internationale de l'Eclairage (CIE). White light emission can be obtained by light emission of light emitting materials of three colors of blue, green, and red, or light emitting materials of two colors having a complementary color relationship.
As a white light emitting element, white light emission with low voltage, high luminance, and high chromaticity is desired. In order to lower the voltage and increase the brightness, it is desired to use a phosphorescent light emitting material having higher luminous efficiency than the fluorescent light emitting material (see, for example, Patent Documents 1, 2, and 3). In order to improve efficiency, it is desired to develop a phosphorescent material that emits blue light and to develop an element that effectively emits light from the blue phosphorescent material. The reason for this is that when the blue emission intensity is low, it is necessary to adjust the green or red phosphorescence emission intensity, which is known to emit light with high efficiency, in order to obtain the desired chromaticity. In addition, the light emission efficiency as a light emitting element is reduced.
Further, in the white light emitting element, there is a problem that chromaticity deteriorates when energy transfer (blue → green → red) occurs between the light emitting materials, and improvement has been desired. Patent Document 3 discloses a white light-emitting element using phosphorescent light-emitting materials for blue, green, and red light-emitting layers, respectively. However, the luminous efficiency and chromaticity are still insufficient, and further improvement has been desired.
JP 2001-319780 A Japanese Patent Application Laid-Open No. 2004-28877 JP-T-2004-522276

  An object of this invention is to provide the organic electroluminescent element excellent in luminous efficiency and chromaticity.

In view of the above circumstances, the present inventors have conducted extensive research and found that the above problems can be solved, thereby completing the present invention.
That is, the present invention is achieved by the following means.

< 1 > An organic electroluminescent device having a plurality of organic compound layers including at least one light emitting layer between an anode and a cathode, wherein at least one phosphorescent light emitting material is formed on at least the same layer of the light emitting layers. at least two comprises a light emitting material and a host material and the light emitting layer and the anode has an organic compound layer of the three layers between the ionization potential of the light-emitting layer Ip1, the organic compound layer of the three layers including the ionization potential in order of proximity to the light-emitting layer, when the Ip2, Ip3, I p 4, wherein (1): Ip1>Ip2>Ip3> satisfy the relation of I p 4, and the light emitting layer and a cathode has an organic compound layer of the three layers between the electron affinity of the light emitting layer Ea1, the electron affinity of the organic compound layer of the three layers in order of proximity to the light-emitting layer, when the Ea2, Ea3, E a 4 ,formula( ): Ea1 <Ea2 <Ea3 <meets the relationship E a 4, the organic electroluminescent device, characterized in, that the barrier is less than 0.4eV between adjacent layers.

<2> The organic electroluminescent element as described in <1> above, wherein the organic compound layer adjacent to the anode side of the light emitting layer has an ionization potential (Ip2) of 6.2 to 5.3 eV.
<3> The organic electroluminescence according to the above <1> or <2>, wherein an electron affinity (Ea2) of an organic compound layer adjacent to the cathode side of the light emitting layer is 2.2 to 3.1 eV element.
<4> When a voltage is applied between the anode and the cathode, the at least two light-emitting materials contained in the same layer, above, characterized in that at least two emit light <1> - The organic electroluminescent element of any one of < 3 >.

< 5 > The organic electroluminescence according to any one of <1> to < 4 >, wherein at least one of the at least two light emitting materials is a blue light emitting material. element.
< 6 > The organic electroluminescent element as described in < 5 > above, wherein the blue light emitting material is a phosphorescent light emitting material.
< 7 > The organic electroluminescent element according to any one of <1> to < 6 >, wherein the organic electroluminescent element is white light emission.

< 8 > The concentration of the at least two light emitting materials contained in the same layer is 2% by mass or less, and the total concentration of the at least two light emitting materials contained in the same layer is 3% by mass. The organic electroluminescent element according to any one of the above items <1> to < 7 >, wherein:

  ADVANTAGE OF THE INVENTION According to this invention, the organic EL element excellent in high luminous efficiency and chromaticity can be provided.

Hereinafter, the present invention will be described in detail.
The organic electroluminescent element of the present invention has a plurality of organic compound layers including at least one light emitting layer between an anode and a cathode, and at least one phosphorescent light emitting material is formed in at least the same layer among the light emitting layers. An organic compound layer having three layers between the light emitting layer and the anode, the ionization potential of the light emitting layer being Ip1, and the organic compound having the three layers the ionization potential of the layers in the order from the layer adjacent to the luminescent layer, when the Ip2, Ip3, I p 4, wherein (1): Ip1>Ip2>Ip3> satisfy the relation of I p 4, and the light emitting has an organic compound layer of the three layers between the layer and the cathode, the electron affinity of the light emitting layer Ea1, the electron affinity of the organic compound layer of the three layers in the order from the layer adjacent to the luminescent layer, Ea2, Ea3, It was E a 4 To come formula (2): Ea1 <Ea2 < Ea3 < meets the relationship E a 4, a barrier between adjacent layers is not more than 0.4 eV, and wherein.
By setting it as the said structure, the organic EL element excellent in high luminous efficiency and chromaticity can be obtained.

The organic electroluminescent device of the present invention, between the light emitting layer and the anode (anode side),及Beauty, between the emitting layer and the cathode (cathode side), an organic compound layer and 3 Soyu child Therefore The potential barrier between adjacent layers can be reduced, and the light emission efficiency and light emission luminance can be increased.
The organic electroluminescent device of the present invention has an organic compound layer in each of between the light emitting layer and two electrodes, further, the organic compound layer, Ru provided adjacent to the light emitting layer and electrodes.
The barrier between the adjacent layers is 0 . 3 eV or less is particularly preferable.

  Here, the “ionization potential of each layer” in the light emitting device of the present invention means an ionization potential of a material having the lowest ionization potential among materials contained in the layer of 10% by mass or more. As the ionization potential in this specification, a value measured at room temperature and in the atmosphere using AC-1 (manufactured by Riken Keiki Co., Ltd.) is adopted. The measurement principle of AC-1 is described in Chiyaya Adachi et al., “Organic thin film work function data collection” issued by CMC Publishing Co., Ltd. 2004.

  In addition, the “electron affinity of each layer” in the light emitting device of the present invention means the electron affinity of a material having the highest electron affinity among materials contained in 10% by mass or more in the layer. The electron affinity in the present invention is calculated from the excitation energy and the value of the ionization potential obtained by measuring the ultraviolet-visible absorption spectrum of the film used for measuring the ionization potential, obtaining the excitation energy from the energy at the long wavelength end of the absorption spectrum. In this specification, an ultraviolet-visible absorption spectrum measured with a UV3100 spectrophotometer manufactured by Shimadzu Corporation is used.

The number (n-1) of the organic compound layers on the anode side in the light emitting device of the present invention preferably has 3 to 5 layers from the viewpoint of reducing the potential barrier between layers and reducing the manufacturing cost. It is more preferable to have 3 to 4 layers.
Also, the organic compound layer (m-1) on the cathode side preferably has 3 to 5 layers from the viewpoint of reducing the potential barrier between layers and reducing the manufacturing cost, and has 3 to 4 layers. Is more preferable.
The number of the organic compound layers of the two electrodes may be the same or different.
In the present invention, the number of the organic compound layers of the two electrodes is the same number of three layers.

  When the light emitting layer in the light emitting device of the present invention is a single layer, the ionization potential (Ip1) of the light emitting layer is preferably 6.4 eV or less, more preferably 6.3 eV or less, and particularly preferably 6.2 eV or less. In addition, the electron affinity (Ea1) of the light emitting layer is preferably 2.1 eV or more, more preferably 2.2 eV or more, and particularly preferably 2.3 eV or more.

The ionization potential (Ip2) of the organic compound layer adjacent to the anode side of the light emitting layer is preferably 6.2 to 5.3 eV, more preferably 6.1 to 5.4 eV, and particularly preferably 6.0 to 5.5 eV. preferable.
The ionization potential (Ip3, 4,..., N) of another organic compound layer provided between the light emitting layer and the anode is preferably 5.8 eV or less, more preferably 5.7 eV or less, and 5.6 eV or less. Particularly preferred.

The electron affinity (Ea2) of the organic compound layer adjacent to the cathode side of the light emitting layer is preferably 2.2 to 3.1 eV, more preferably 2.3 to 3.0 eV, and particularly preferably 2.4 to 2.9 eV. preferable.
The electron affinity (Ea3, 4,..., M) of the other organic compound layer (electron transport layer) provided between the light emitting layer and the cathode is preferably 2.6 eV or more, more preferably 2.7 eV or more, 2.8 eV or more is particularly preferable.

  The relationship between the ionization potential or the electron affinity in the present invention is controlled by selecting and combining the materials showing the above ionization potential or electron affinity from the materials constituting each layer.

In addition, when a voltage is applied to the element of the present invention, it is preferable that at least two of the at least two light emitting materials contained in the same layer emit light.
When at least two of the at least two light emitting materials emit light, light emitting elements having various hues can be obtained.
Here, the determination of whether light is emitted is performed as follows. First, an emission spectrum obtained when each luminescent material is independently formed on a glass substrate is irradiated with ultraviolet rays, and the wavelength at the maximum value of the emission spectrum of each material is examined. Subsequently, the spectrum when a voltage is applied to the element of the present invention is observed, and the intensity at the wavelength at the maximum value of the emission spectrum of each material examined earlier is 1 / of the maximum value of the emission spectrum of the element of the present invention. If it is 10 or more, it is determined that the luminescent material emits light.

Furthermore, in the structure of the element of the present invention, at least one of the at least two light emitting materials is preferably a blue light emitting material, and more preferably a blue phosphorescent light emitting material.
With the above-described structure, the light-emitting element of the present invention can emit white light, and the application range such as illumination and liquid crystal backlight can be expanded.

  The substrate, the anode and the cathode that can be used in the present invention are not particularly limited and can be appropriately selected from known ones. However, due to the properties of the light emitting element, at least one of the anode and the cathode must be transparent. Is preferred.

  As an aspect of lamination of the organic compound layer in the present invention, an aspect in which a hole transport layer, a light emitting layer, and an electron transport layer are laminated in this order from the anode side is preferable. Further, a charge blocking layer or the like may be provided between the hole transport layer and the light-emitting layer, or between the light-emitting layer and the electron transport layer. A hole injection layer may be provided between the anode and the hole transport layer, and an electron injection layer may be provided between the cathode and the electron transport layer.

The light-emitting layer receives holes from the anode, the hole injection layer, or the hole transport layer when an electric field is applied, receives electrons from the cathode, the electron injection layer, or the electron transport layer, and recombines holes and electrons. It is a layer which has the function to provide and to emit light.
The host material in the light emitting layer in the present invention may be one type or two or more types, and in the case of two or more types, for example, a configuration in which an electron transporting host material and a hole transporting host material are mixed. Is mentioned. In addition to the charge transporting host material, the light emitting layer may further contain a host material that does not have a charge transporting property and does not emit light.
The material used for the host material is not particularly limited and can be appropriately selected from known materials. For example, as the electron transporting host material and the hole transporting host material, materials used for the electron transport layer and the electron injection layer, materials used for the hole transport layer and the hole injection layer, respectively, can be preferably used. .

The light-emitting element of the present invention includes at least two light-emitting materials including at least one phosphorescent light-emitting material and a host material in the same light-emitting layer.
The phosphorescent material is not particularly limited and can be appropriately selected from known materials. Examples include those described in JP-A-2004-221068 (0051) to (0057), among which ortho-metalated metal complexes or porphyrin metal complexes are preferred.

  Examples of the above-mentioned orthometalated metal complex include, for example, Akio Yamamoto, “Organic Metal Chemistry: Fundamentals and Applications”, pages 150 and 232, Hankabo (published in 1982) and Yersin's “Photochemistry and Photophysics of Coordination Compounds” pages 71-77, pages 135-146, Springer-Verlag (published in 1987), etc. The use of the orthometalated metal complex as a light emitting material in the light emitting layer is advantageous in terms of high luminance and excellent light emission efficiency.

  There are various ligands that form the ortho-metalated metal complex, which are also described in the above documents. Among them, preferred ligands include 2-phenylpyridine derivatives, 7,8- Examples include benzoquinoline derivatives, 2- (2-thienyl) pyridine derivatives, 2- (1-naphthyl) pyridine derivatives, and 2-phenylquinoline derivatives. These derivatives may have a substituent if necessary. The orthometalated metal complex may have other ligands in addition to the above ligands.

The orthometalated metal complex used in the present invention can be obtained from Inorg. Chem. 1991, No. 30, page 1685, 1988, No. 27, page 3464. 1994, 33, 545, Inorg. Chim. Acta, 1991, 181, 245; Organomet. Chem. , 1987, 335, 293, J. Am. Am. Chem. Soc. 1985, No. 107, p. 1431 and the like can be synthesized by various known methods.
Among the ortho-metalated complexes, compounds that emit light from triplet excitons can be suitably used in the present invention from the viewpoint of improving luminous efficiency. Of the porphyrin metal complexes, a porphyrin platinum complex is preferred.

  The content of the host material in the light emitting layer is not particularly limited, but 90 to 99.9% by mass is preferable, 95 to 99.9% by mass is more preferable, and 97 to 99.9% by mass. % Is particularly preferred.

In the present invention, a light emitting element of any color can be obtained by using at least two different light emitting materials including at least one phosphorescent light emitting material. The white light-emitting element can select at least two different light-emitting materials including at least one phosphorescent light-emitting material, and more particularly, three or more light-emitting materials can be selected to produce white light with higher light emission efficiency and higher luminance. It is preferable from the viewpoint of obtaining an element. These luminescent materials can be appropriately selected from the above examples.
For example, a white light-emitting element can be obtained by combining a blue light-emitting material and an orange light-emitting material in complementary colors as two types of light-emitting materials, and three different types of blue light-emitting material, green light-emitting material, and red light-emitting material. A white light emitting element can be obtained by appropriately selecting the above light emitting materials.
Among them, the blue light emitting material is preferably a material having a maximum light emission wavelength (wavelength when the light emission intensity becomes maximum) of 400 to 500 nm, more preferably 420 to 490 nm, and particularly preferably 430 to 470 nm.
Moreover, as a green luminescent material, 500-570 nm is preferable, 500-560 nm is more preferable, 500-550 nm is especially preferable.
Moreover, as a red luminescent material, 580-670 nm is preferable, 590-660 nm is more preferable, 600-650 nm is especially preferable.

The light emitting layer of the light emitting device of the present invention may be a single layer or a plurality of layers.
When producing the white light emitting device of the present invention, when two kinds of light emitting materials are used, it is necessary to contain the two kinds of light emitting materials together with the host material in the same layer among the light emitting layers. In the case where a light emitting material is used, even if three kinds of light emitting materials are included in the same layer, a layer containing two kinds of light emitting materials and a layer containing another one kind of light emitting material are used. May be laminated separately.
In any case, the number of layers can be reduced as compared with the case where at least two kinds of light-emitting materials contained are all contained in separate layers, and a light-emitting element can be easily produced.

  Further, the light emitting layer in the present invention contains at least two kinds of light emitting materials, and at least one of the light emitting materials needs to be a phosphorescent light emitting material. In addition to the phosphorescent light emitting material, a fluorescent light emitting material is used. Can also be used in combination. There is no restriction | limiting in particular as an example of the fluorescent luminescent material which can be used by this invention, It can select from a well-known thing suitably. Examples include those described in JP-A No. 2004-146067 [0027], JP-A No. 2004-103577 [0057], and the like, but the present invention is not limited thereto.

  Furthermore, in the present invention, it is preferable that the concentration of each light emitting material is 5% by mass or less and the total concentration of all the light emitting materials is 10% by mass or less. Furthermore, it is more preferable that each light emitting material is 0.03% or more and 3% or less, and the total concentration of all the light emitting materials is 5% by mass or less, and further, 0.1% or more and 2% or less, The total concentration of all luminescent materials is preferably 3% by mass or less.

When the light emitting material includes a blue material, the lowest excited triplet energy (hereinafter referred to as T ₁ ) of the material used as the host is:
60 kcal / mol (251.4 kJ / mol) or more and 90 kcal / mol (377.1 kJ / mol) or less is preferable, 63 kcal / mol (264 kJ / mol) or more and 85 kcal / mol (356.2 kJ / mol) or less is more preferable, and 65 kcal / Mol (272 kJ / mol) to 80 kcal / mol (335.2 kJ / mol) is more preferable, and 66 kcal / mol (276.5 kJ / mol) to 80 kcal / mol (335.2 kJ / mol) is particularly preferable.
When T ₁ of the host material is smaller than T ₁ of the light emitting material, excitons formed in the light emitting material move to the host, which is not preferable. Here, considering the case where the light emitting material is a blue material having a light emission peak at a short wavelength, the T ₁ of the blue material is large, so that it has the above T ₁ from the viewpoint of not moving excitons to the host material. A host material is preferred.

  Constituent elements such as a substrate, electrodes, organic layers, and other layers in the organic electroluminescent device of the present invention are described in, for example, [0013] to [0082] of JP-A-2004-221068, JP-A-2004-214178. [0017] to [0091], JP 2004-146067 [0024] to [0035], JP 2004-103577 [0017] to [0068], JP 2003-323987 [0014]. [0062], JP-A-2002-305083, [0015] to [0077], JP-A-2001-172284, [0008] to [0028], JP-A-2000-186094, [0013] to [0075], Those described in [0016] to [0118] of JP-T-2003-515897 are the present invention. It can be applied similarly. However, the present invention is not limited to these.

  The organic electroluminescence device of the present invention emits light by applying a direct current (which may include an alternating current component as necessary) voltage (usually 2 to 15 volts) or a direct current between the anode and the cathode. Obtainable.

  An important characteristic value of the organic electroluminescence device is external quantum efficiency (luminescence efficiency). The external quantum efficiency is calculated by “external quantum efficiency φ = number of photons emitted from the device / number of electrons injected into the device”, and it can be said that the larger this value, the more advantageous the device in terms of power consumption.

  Further, the external quantum efficiency of the light emitting element can be calculated from the result and the relative luminous efficiency curve obtained by measuring the light emission luminance, the light emission spectrum, and the current density. That is, the number of input electrons can be calculated using the current density value. The emission luminance can be converted into the number of photons emitted by integral calculation using the emission spectrum and the relative visibility curve (spectrum). From these, the external quantum efficiency (%) can be calculated by “(number of emitted photons / number of electrons input to the device) × 100”.

In the present invention, a source measure unit 2400 manufactured by Keithley Co. is used to apply a DC constant voltage to the EL element to emit light, and an emission spectrum is measured using a spectral radiance meter SR-3 manufactured by Topcon Co., Ltd. Obtain the external quantum efficiency and CIE chromaticity coordinates (x, y) at m ² .

  The driving method of the organic electroluminescence device of the present invention is described in JP-A-2-148687, JP-A-6-301355, JP-A-5-29080, JP-A-7-134558, JP-A-8-234658, and JP-A-8-2441047. The driving methods described in each publication, Japanese Patent No. 2784615, US Pat. Nos. 5,828,429, 6023308, and the like can be applied.

  The light emitting device of the present invention includes a display device, a display (for example, full color display), a backlight, electrophotography, an illumination light source, a recording light source (for example, a light source array), an exposure light source, a reading light source, a sign, a signboard, an interior, and light. It can be suitably used in the field of communication and the like.

  The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[Comparative Example 1]
An indium tin oxide (ITO) transparent conductive film (manufactured by Geomatic Co., Ltd.) formed on a glass substrate with a thickness of 150 nm was patterned using photolithography and hydrochloric acid etching to form an anode. The patterned ITO substrate is cleaned in the order of ultrasonic cleaning with acetone, water with pure water, and ultrasonic cleaning with isopropyl alcohol, then dried with nitrogen blow, and finally with ultraviolet ozone cleaning. installed. Thereafter, the inside of the vapor deposition apparatus was evacuated.

  Subsequently, 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (α-NPD) shown below is heated in the vapor deposition apparatus, and the vapor deposition rate is 0.2 nm / second. Vapor deposition was performed to form a 40 nm-thick hole transport layer.

Subsequently, 4,4′-N, N′-dicarbazole-biphenyl (CBP) as a host material contained in the light emitting layer and iridium (blue light emitting material) are formed on the hole transport layer formed as described above. III) Bis [(4,6-difluorophenyl) -pyridinate-N, C2] picolinate (Firpic), green light emitting material tris (2-phenylpyridine) iridium (Ir (ppy) ₃ ), red light emitting material The light emitting layer was formed by heating the dopant A and co-depositing it. The CBP deposition rate is controlled to 0.2 nm / second, and the emission is 30 nm with a film containing 1.5% by weight, 0.5% by weight of Ir (ppy) _{3 and} 0.5% by weight of dopant A. The layer was laminated on the hole transport layer.

  Further, aluminum (III) bis (2-methyl-8-quinolinato) 4-phenylphenolate (BAlq) represented by the following formula is deposited at a deposition rate of 0.1 nm / second, and an electron having a thickness of 30 nm is formed. A transport layer was laminated on the light emitting layer.

Thereafter, lithium fluoride (LiF) is deposited on the electron transport layer at a deposition rate of 0.1 nm / second and a thickness of 1 nm to form an electron injection layer, and further, aluminum is deposited at a deposition rate of 0.5 nm / second. A cathode having a thickness of 150 nm was formed.
Also, aluminum lead wires were connected from the anode and the cathode, respectively.
During vapor deposition, monitoring was performed using a crystal oscillation type film formation controller so as to obtain a desired film thickness.

The laminated body obtained here was put in a glove box substituted with nitrogen gas without being exposed to air. A moisture absorbent (manufactured by SAES Getters) was affixed to a stainless steel sealing cover provided with a recess on the inside in the glove box. This sealing cover was sealed using an ultraviolet curable adhesive (XNR5516HV, manufactured by Chiba Nagase) as an adhesive.
As described above, an organic EL element of Comparative Example 1 was obtained.

[Comparative Example 2]
Similar to Comparative Example 1, the ITO transparent conductive film deposited on the glass substrate was patterned and washed, and placed in a vacuum evaporation apparatus. Thereafter, the inside of the vapor deposition apparatus was evacuated.

  Subsequently, copper phthalocyanine (CuPc) shown below was heated in the vapor deposition apparatus, and vapor deposition was performed at a vapor deposition rate of 0.1 nm / second to form a 10 nm thick hole injection layer.

  Next, α-NPD was heated on the hole injection layer formed as described above, and vapor deposition was performed at a deposition rate of 0.2 nm / second to form a hole transport layer having a thickness of 30 nm.

Subsequently, on the hole transport layer formed as described above, as a host material contained in the light emitting layer, CBP, Firepic of blue light emitting material, Ir (ppy) ₃ of green light emitting material, and red light emitting material The dopant A was heated and a light emitting layer was formed by co-evaporation. The CBP deposition rate is controlled to 0.2 nm / second, and the emission is 30 nm with a film containing 1.5% by weight, 0.5% by weight of Ir (ppy) _{3 and} 0.5% by weight of dopant A. The layer was laminated on the hole transport layer.

  Subsequently, BAlq was deposited at a deposition rate of 0.1 nm / second, and a hole blocking layer having a thickness of 10 nm was laminated on the light emitting layer.

  Subsequently, on the hole blocking layer, tris (8-hydroxyquinolinato) aluminum (III) (Alq) shown below was deposited at a deposition rate of 0.2 nm / second, and an electron transport layer having a thickness of 35 nm. Formed.

Thereafter, lithium fluoride (LiF) is deposited on the electron transport layer at a deposition rate of 0.1 nm / second and a thickness of 1 nm to form an electron injection layer, and further, aluminum is deposited at a deposition rate of 0.5 nm / second. A cathode having a thickness of 150 nm was formed.
During vapor deposition, monitoring was performed using a crystal oscillation type film formation controller so as to obtain a desired film thickness.

Next, aluminum lead wires were connected to the anode and the cathode, respectively.
The laminated body obtained here was put in a glove box substituted with nitrogen gas without being exposed to air. A moisture absorbent (manufactured by SAES Getters) was affixed to a stainless steel sealing cover provided with a recess on the inside in the glove box. This sealing cover was sealed using an ultraviolet curable adhesive (XNR5516HV, manufactured by Chiba Nagase) as an adhesive.
As described above, an organic EL element of Comparative Example 2 was obtained.

[Comparative Example 3]
In Comparative Example 2, comparison was made in the same manner as in Comparative Example 2 except that the host material contained in the light emitting layer was changed from CBP to 4,4′-N, N′-dicarbazole-biphenyl (mCP) shown below. The organic EL element of Example 3 was created.

[Example 1]
Similar to Comparative Example 1, the ITO transparent conductive film deposited on the glass substrate was patterned and washed, and placed in a vacuum evaporation apparatus. Thereafter, the inside of the vapor deposition apparatus was evacuated.

Subsequently, CuPc was heated in the vapor deposition apparatus, and vapor deposition was performed at a vapor deposition rate of 0.1 nm / second to form a first hole transport layer having a thickness of 10 nm.
Next, α-NPD was heated on the first hole transport layer formed as described above, and vapor deposition was performed at a deposition rate of 0.2 nm / second to form a second hole transport layer having a thickness of 30 nm. .
Subsequently, 4,4 ′, 4 ″ -tris (N-carbazolyl) -triphenylamine (TCTA) shown below is heated on the second hole transport layer formed as described above, and the deposition rate is 0. Vapor deposition was performed at 2 nm / second to form a third hole transport layer having a thickness of 10 nm.

Subsequently, on the third hole transport layer formed as described above, the host material mCP, the blue light emitting material Irpic, the green light emitting material Ir (ppy) _3, and the red light emitting material contained in the light emitting layer. The dopant A was heated and a light emitting layer was formed by co-evaporation. The deposition rate of mCP is controlled to 0.2 nm / second, and a 30 nm thick light emitting layer containing 1.5% by mass of Ferpic, 0.5% by mass of Ir (ppy) _{3 and} 0.5% of dopant A Was laminated on the hole transport layer.

  Further, ETM-1 shown below was deposited at a deposition rate of 0.1 nm / second, and a first electron transport layer having a thickness of 10 nm was laminated on the light emitting layer.

  Subsequently, BAlq was deposited at a deposition rate of 0.1 nm / second, and a second electron transport layer having a thickness of 10 nm was stacked on the first electron transport layer.

  Subsequently, Alq was deposited on the second electron transport layer at a deposition rate of 0.2 nm / second to form a third electron transport layer having a thickness of 25 nm.

Thereafter, lithium fluoride (LiF) is deposited on the electron transport layer at a deposition rate of 0.1 nm / second and a thickness of 1 nm to form an electron injection layer, and further, aluminum is deposited at a deposition rate of 0.5 nm / second. A cathode having a thickness of 150 nm was formed.
During vapor deposition, monitoring was performed using a crystal oscillation type film formation controller so as to obtain a desired film thickness.

Next, aluminum lead wires were respectively connected from the anode and the cathode.
The laminated body obtained here was put in a glove box substituted with nitrogen gas without being exposed to air. A moisture absorbent (manufactured by SAES Getters) was affixed to a stainless steel sealing cover provided with a recess on the inside in the glove box. This sealing cover was sealed using an ultraviolet curable adhesive (XNR5516HV, manufactured by Chiba Nagase) as an adhesive.
As described above, an organic EL element of Example 1 was obtained.

[Evaluation of material properties]
(1) Ionization potential Each compound used for the organic compound layer was deposited on a glass substrate so as to have a thickness of 50 nm. The ionization potential of this membrane was measured with an ultraviolet photoelectron analyzer AC-1 manufactured by Riken Keiki Co., Ltd. under normal temperature and normal pressure. In addition, about the ionization potential of ETM-1, it measured by MUL-010HI made from PHI using the film | membrane vapor-deposited on the gold substrate in thickness of 50 nm.

(2) Electron affinity The ultraviolet-visible absorption spectrum of the film used for measuring the ionization potential was measured with a UV3100 spectrophotometer manufactured by Shimadzu Corporation, and the excitation energy was determined from the energy at the long wavelength end of the absorption spectrum. The electron affinity was calculated from the excitation energy and the value of the ionization potential.
These results are shown in Table 1 below.

  Using these measured values, the ionization potential of each layer in Comparative Examples 1 to 3 and Example 1 is summarized as shown in the following table.

[Evaluation of organic electroluminescence device]
A direct voltage was applied to the organic EL element to emit light using the source measure unit 2400 type (manufactured by Keithley) for each of the obtained Comparative Examples 1 to 3 and Example 1. The external quantum efficiency (η ₁₀₀₀ ) (%) at ₁₀₀₀ cd / m ² was determined, the emission spectrum was measured using SR-3 (manufactured by Topcon), and the CIE 1964 chromaticity coordinates (x, y) were determined. The closer the CIE chromaticity coordinate value is to an ideal white light source (0.33, 0.33), the better. These values are shown in Table 6.

In comparison between Comparative Examples 1 and 2, it can be seen that the efficiency is improved by increasing the number of layers. In comparison between Comparative Examples 2 and 3, a comparison was made using a high T ₁ host material (CBP: 60 kcal / mol; mCP: 67 kcal / mol) in order to prevent exciton migration from the blue material to the host material. In Example 3, it can be seen that when the number of layers between the light emitting layer cathodes and between the light emitting layer anodes is two, both the luminous efficiency and chromaticity are insufficient.
On the other hand, in Example 1 having three electron transport layers and three hole transport layers, as can be seen from Table 6, it can be seen that an element having good luminous efficiency and chromaticity is obtained.
In Example 1, the same effect can be obtained even when an element is created using ETM-2 or ETM-3 instead of HTM-1 and ETM-1 shown below instead of TCTA. The ionization potential and electron affinity of these materials are as shown in Table 7 below.
This can reduce the difference in ionization potential between adjacent layers in the range from the organic layer closest to the anode to the light emitting layer, and is adjacent in the range from the organic layer closest to the cathode to the light emitting layer. It can be presumed that the difference in electron affinity of the layers could be reduced.
As described above, by producing a light-emitting element having the structure of the present invention, an element with high efficiency and good chromaticity can be obtained.

Claims (8)

An organic electroluminescence device having a plurality of organic compound layers including at least one light emitting layer between an anode and a cathode, wherein at least one phosphorescent material is included in at least the same layer of the light emitting layers. wherein the two light-emitting materials and host materials, and ionization of Ip1, the three-layer organic compound layer has an organic compound layer of the three layers, the ionization potential of the light-emitting layer between the light emitting layer and the anode the potential in the order closer to the light-emitting layer, when the Ip2, Ip3, I p 4, wherein (1): Ip1>Ip2>Ip3> satisfy the relation of I p 4, and, between the light emitting layer and the cathode has an organic compound layer of the three layers, the electron affinity of the light emitting layer Ea1, the electron affinity of the organic compound layer of the three layers in order of proximity to the light-emitting layer, when the Ea2, Ea3, E a 4, wherein (2): a1 <Ea2 <Ea3 <meets the relationship E a 4, the organic electroluminescent device, characterized in, that the barrier is less than 0.4eV between adjacent layers. The organic electroluminescence device according to claim 1, wherein an ionization potential (Ip2) of an organic compound layer adjacent to the anode side of the light emitting layer is 6.2 to 5.3 eV. The organic electroluminescence device according to claim 1 or 2, wherein an electron affinity (Ea2) of an organic compound layer adjacent to the cathode side of the light emitting layer is 2.2 to 3.1 eV. 4. The light emitting device according to claim 1, wherein when a voltage is applied between the anode and the cathode, at least two of the at least two light emitting materials included in the same layer emit light . 2. The organic electroluminescent element according to item 1 . Wherein the at least two light-emitting materials, organic electroluminescent device according to any one of claims 1 to 4, characterized in that at least one luminescent material is a blue luminescent material. 6. The organic electroluminescent element according to claim 5 , wherein the blue light emitting material is a phosphorescent light emitting material. It is white light emission, The organic electroluminescent element of any one of Claims 1-6 characterized by the above-mentioned. The concentration of the at least two light emitting materials included in the same layer is 2% by mass or less, and the total concentration of the at least two light emitting materials included in the same layer is 3% by mass or less. The organic electroluminescent element according to any one of claims 1 to 7 , wherein