JP2004342375A - Luminous body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent element with high light-taking-out efficiency. <P>SOLUTION: A difference of an admittance of a light-taking-out part (L) consisting of a transparent substrate (A), a transparent conductive layer (B), and a hole transport layer (C), from a refraction index of a luminous layer (D) is controlled to be as small as possible. To be more precise, the light-taking-out part (L) and the luminous layer (D) are designed so as to make small a difference between the admittance of the light-taking-out part (L) and the refraction index of the luminous layer (D) in their real term as well as imaginary term. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００６７】
実施例１と２の場合のように｜ｘ−α｜及び｜ｙ―β｜が０．５以下の場合には、有機エレクトロルミネッセンス素子の発光輝度が、比較例１の場合のように｜ｘ−α｜又は｜ｙ―β｜が該制限範囲を逸脱している場合に比較して高いことが分かる。実施例１、２及び比較例１においてその視感平均透過率及び表面抵抗値に大きな違いはない。
そこで実施例１及び２が示す高い発光輝度は、光取り出し部（Ｌ）のアドミッタンスと発光層（Ｄ）の屈折率差を小さくし、光取り出し効率を向上させたことによるものであると考えることができる。
【００６８】
【発明の効果】
透明基板（Ａ）、透明導電層（Ｂ）、正孔輸送層（Ｃ）からなる光取り出し部（Ｌ）のアドミッタンスと発光層（Ｄ）の屈折率との差を制限することにより、従来に比較して発光輝度が高い有機エレクトロルミネッセンス素子を提供することができる。
【図面の簡単な説明】
【図１】透明導電性薄膜積層体の一例を示す断面図
【図２】有機エレクトロルミネッセンス素子の一例を示す平面図
【図３】有機エレクトロルミネッセンス素子の一例を示す平面図
【符号の説明】
１０ 透明基体
２０ 高屈折率薄膜層
３０ 銀または銀合金薄膜層
４０ 透明導電性薄膜層
５０ 有機薄膜層
６０ 陰極
７０ 正孔輸送層
８０ 発光層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an organic luminous body.
[0002]
[Prior art]
An organic electroluminescent element that has recently attracted attention as an organic light emitting body is a thin and self-luminous type light emitting element. At present, a liquid crystal display device mainly used in the thin display field requires a light source because the liquid crystal itself does not emit light. Therefore, there is a limit to the reduction in thickness. On the other hand, the market demands a further reduction in the thickness of the display device. As described above, the organic electroluminescence element does not require a light source because it can emit light as described above, and is advantageous for thinning as compared with a liquid crystal display device. Japanese Patent Publication No. 64-7635 (Patent Document 1), There is a disclosure in JP-A-8-188772 (Patent Document 2) and the like. For this reason, the organic electroluminescence element is listed as a promising candidate as a next-generation display element. Recently, it has begun to be used for display screens of small mobile terminals such as mobile phones, and the market is expected to expand in the future.
[0003]
However, the organic electroluminescence element has a problem that the light extraction efficiency is low, and it is not sufficient to cope with the energy saving of the display, which has a great demand as well as the reduction in thickness.
[0004]
[Patent Document 1] Japanese Patent Publication No. 64-7635
[Patent Document 2] JP-A-8-188772
[0005]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to provide an organic luminous body having high light extraction efficiency.
[0006]
[Means for Solving the Problems]
The present inventors have studied and found that the light extraction efficiency of the organic electroluminescent device is low because light generated in the light emitting layer passes through the hole transport layer, the transparent electrode layer and the transparent substrate, and the organic In the process of going out of the luminescence element, it was found that light was reflected at the transparent substrate / transparent electrode interface, the transparent electrode / hole transport layer interface, and the hole transport layer / light emitting layer interface. Further, the light extraction layer and the light emitting layer are so formed as to reduce the difference between the admittance of the portion where the transparent substrate (A), the transparent conductive layer (B) and the hole transport layer (C) are integrated, and the refractive index of the light emitting layer. It has been found that by designing the configuration of (1), reflection can be reduced, and an organic electroluminescence element having high light extraction efficiency can be obtained, and the present invention has been completed. That is, the present invention
(1) A luminous body having a transparent substrate (A), a transparent conductive layer (B), a hole transport layer (C), and a luminescent layer (D),
The admittance of the light extraction portion (L) arranged in the order of the transparent substrate (A) / transparent conductive layer (B) / hole transport layer (C) is Y = x + iy, and the refractive index of the light emitting layer (D) is η. _D = Α + iβ
| X-α | is 0.5 or less and | y-β | is 0.5 or less
It is a luminous body characterized by the following.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
(Configuration of luminous body)
The luminous body of the present invention comprises at least a transparent substrate (A), a transparent conductive layer (B), a hole transport layer (C), a luminescent layer (D), and a cathode (E). The transparent substrate (A) / transparent conductive layer (B) / hole transport layer (C) / light-emitting layer (D) / cathode (E) are arranged in this order.
[0008]
The luminous body of the present invention does not require that the transparent substrate (A), the transparent conductive layer (B), the hole transport layer (C), the luminescent layer (D), and the cathode (E) are directly laminated. For example, the luminous body of the present invention comprises a transparent conductive layer (B) and a hole transport layer (C) in order to increase the efficiency of hole transfer from the transparent conductive layer (B) to the hole transport layer (C). May have a hole injection layer (C1). Further, the luminous body has an electron injection layer (E1) between the light emitting layer (D) and the cathode (E) in order to increase the efficiency of electron transfer from the cathode (E) to the light emitting layer (D). It does not matter. The structure of the luminous body having the hole injection layer (C1) and the electron injection layer (E1) is as follows: transparent substrate (A) / transparent conductive layer (B) / hole injection layer (C1) / hole transport layer (C). / Light-emitting layer (D) / electron injection layer (E1) / cathode (E).
[0009]
In the present invention, the transparent conductive layer (B) is preferably a laminate of a high refractive index thin film layer (a) and a metal thin film layer (b). Specifically, a repeating unit having a structure of a high refractive index thin film layer (a) / a metal thin film layer (b) is repeatedly laminated one to four times, and further on the metal thin film layer (b) located on the outermost surface thereof. It is preferable that the laminate is formed by laminating the high refractive index thin film layers (a).
[0010]
When a laminate of a high-refractive-index thin film layer (a) and a metal thin film layer (b) is used as the transparent conductive layer (B), the structure is compared with a case where a single transparent conductive layer (B) is employed. In many cases, a transparent conductive layer having a low surface electric resistance and a high transmittance can be easily obtained.
However, the effect of the present invention can be exerted when the transparent conductive layer (B) has a single layer or any of the above-mentioned multilayer structures.
[0011]
(Admittance of luminous body)
In the present invention, the admittance of the light extraction portion (L) having the structure of the transparent substrate (A) / the transparent conductive layer (B) / the hole transport layer (C) is Y = x + iy, and the refraction of the light emitting layer (D). Rate η _D = Α + iβ, | x−α | is 0.5 or less and | y−β | is 0.5 or less.
More preferably, | x-α | is 0.4 or less, and | y-β | is 0.4 or less, and still more preferably, | x-α | is 0.3 or less, and | y-β | 0.3 or less.
[0012]
In order to extract as much of the light emitted from the light emitting layer (D) as possible, the light emitted from the light emitting layer (D) passes through the hole transport layer (C), the transparent conductive layer (B), and the transparent substrate (A). The interface between the light emitting layer (D) and the hole transport layer (C), the interface between the hole transport layer (C) and the transparent conductive layer (B), and the transparent conductive layer ( It is preferable that the reflectance at the interface between B) and the transparent substrate (A) is as small as possible.
[0013]
The thicknesses of the transparent conductive layer (B) and the hole transport layer (C) in the organic electroluminescence element are film thicknesses that cause optical interference, and the transparent conductive layer (B) and the hole transport layer ( The thickness of C) is also within the range.
[0014]
The reflection phenomenon at the interface when the thicknesses of the transparent conductive layer (B) and the hole transport layer (C) are such as to cause optical interference is as follows. That is, the light reflected at the interface is reflected again at another interface, and travels to the outside again. Then, the light is partially transmitted at the previous interface and partially reflected. This process is repeated countless times. Similar phenomena also occur at other interfaces. For example, light traveling outward from the light emitting layer (D) is partially transmitted and partially reflected at the interface between the transparent substrate (A) and the transparent conductive layer (B). The reflected light partially transmits at the interface between the transparent conductive layer (B) and the hole transport layer (C), but partially reflects and returns to the outside. Further, the reflected light partially passes and partially reflects at the interface between the transparent substrate (A) and the transparent conductive layer (B).
[0015]
Therefore, it is difficult to discuss the reflectivity of light passing through a stacked body having a layer having a thickness that causes optical interference. Conversely, it is difficult to derive the relationship between the thickness of each layer and the reflectance.
[0016]
On the other hand, when discussing the characteristics of light passing through a laminated body formed by laminating films having a thickness causing optical interference, it is convenient and effective to use the admittance of the laminated body. That is, comparing the admittance of the light extraction portion (L) composed of the transparent substrate (A), the transparent conductive layer (B) and the hole transport layer (C) with the admittance of the light emitting layer (D), C) and the interface between the transparent conductive layer (B) and the hole transport layer (C) and the interface between the transparent substrate (A) and the transparent conductive layer (B), respectively. Without separately discussing the reflectivity, it is possible to obtain the conditions of each layer necessary for improving the light extraction efficiency.
[0017]
In the present invention, in order to increase the amount of light extracted from the light-emitting layer (D) through the light extraction portion (L) to the outside, the light extraction portion (L) has no interface inside the light extraction portion (L). Assuming that the admittance is a layer of Y = x + iy, if the reflectivity at the interface between the light emitting layer (D) and the light extraction part (L) is made as small as possible, the light is extracted from the light extraction part (L) to the outside. The amount of light that is emitted increases. In order to realize this matter, the refractive index η of the light emitting layer (D) _D = Α + βi and the admittance Y = x + yi of the light extraction unit (L) may be made closer. That is, it is necessary to reduce both the differences | x−α | and | y−β |
[0018]
(Calculation of admittance)
In the present invention, the admittance of the laminate is obtained by calculation. Examples of calculation software that can be used include, but are not limited to, Essential Macleod [Thin Film Center Inc]. In order to determine the admittance, the film thickness, the refractive index, the incident angle of light, and the wavelength of incident light of each layer of the target laminate are input parameters.
[0019]
The film thickness of each layer is a value obtained from a value measured by a stylus film thickness meter using a sample in which the thin film is formed under the same conditions. By the way, with a stylus film thickness meter, with respect to a film thickness of 40 nm or less, the accuracy limit of the apparatus is reached, and the film thickness cannot be accurately evaluated. For this reason, a film is usually formed to have a thickness of 40 nm or more, preferably 100 nm or more, and the value is read accurately. Since the film thickness is proportional to the film formation time, the film thickness of each thin film in the sample can be determined based on the accurately determined film thickness and time.
[0020]
The refractive index of each layer is a value measured by an ellipsometer using a sample in which the thin film is formed under the same conditions.
[0021]
As the incident angle of light, an optimum angle may be selected depending on the application. In the case of an organic electroluminescence element, light is emitted from the light emitting layer (D) in all directions. However, considering that the intensity of light incident perpendicular to the light extraction portion (L), that is, at an incident angle of 0 °, is the highest, it is most preferable to set the incident angle of light to 0 ° in the calculation.
[0022]
The wavelength of the incident light may be selected to be optimal according to the application.
For example, in the case of an organic electroluminescent element that emits green light, 550 nm located substantially at the center of the green wavelength may be selected as the light wavelength.
[0023]
(Transparent substrate A)
As the transparent substrate (A) in the present invention, a glass plate and a molded polymer can be used.
[0024]
As the transparent polymer molded substrate used in the present invention, those in a film state and a plate state are mainly used, and it is preferable that they have excellent transparency and have sufficient mechanical strength according to the application. Here, “excellent in transparency” means that the luminous transmittance is 40% or more in the thickness in the used state. Further, an antireflection layer or an antiglare layer may be formed on the surface opposite to the main surface of the transparent polymer molded substrate.
[0025]
As the transparent substrate in a film state, a polymer film is preferably used. Specifically, polyimide, polysulfone (PSF), polyethersulfone (PES), polyethylene terephthalate (PET), polymethylene methacrylate (PMMA), polycarbonate (PC), polyetheretherketone (PEEK), polypropylene (PP ), Triacetyl cellulose (TAC) and the like. Among them, polyethylene terephthalate (PET), polycarbonate (PC), polyethersulfone (PES), and polyimide are particularly preferably used.
[0026]
There is no particular limitation on the thickness of the film. Usually, it is about 20 to 500 μm.
[0027]
Examples of the plate-shaped transparent substrate include a molded polymer and a molded glass. The transparent polymer molded article is more preferably used because it is lighter and harder to break than glass. Examples of preferable materials include acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate resins, and the like, but are not limited to these resins. Above all, PMMA can be suitably used because of its high transparency in a wide wavelength region and high mechanical strength.
[0028]
A transparent polymer molded article is often provided with a hard coat layer for reasons such as increasing the surface hardness or adhesion.
[0029]
As the glass molded body, those having almost no surface warpage or scratches and excellent in thermal stability are generally used. For the active matrix driving method, alkali-free glass (white glass) is used because alkali elution from the glass may greatly affect the performance of the active element. For the simple matrix drive system, inexpensive soda-lime glass (blue plate glass) can be used. The method for manufacturing a glass plate includes a float method, a download method, a fusion method, and the like. Alkali-free glass is produced using a download method or a fusion method, and soda-lime glass is produced using a float method.
[0030]
There is no particular limitation on the thickness of the plate-shaped transparent substrate, as long as sufficient mechanical strength and rigidity for maintaining flatness without bending are obtained. Usually, it is about 0.3 to 10 mm.
[0031]
Further, a layer for improving gas barrier properties and a layer for improving solvent resistance may be formed on the surface of the transparent substrate. For the purpose of improving gas barrier properties, silicon oxides and silicon nitrides are generally used as inorganic materials, and ethylene vinyl acetate compounds (EVA) and polyvinyl acetate compounds (PVA) are generally used as organic materials. , But is not limited to this. For the purpose of improving the solvent resistance, a general hard coat layer is often used. Further, an antireflection layer or an antiglare layer may be formed on the surface of the transparent substrate.
[0032]
(Transparent conductive layer (B))
The transparent conductive layer (B) in the present invention is a multilayer laminate composed of a high refractive index thin film layer (a) and a metal thin film layer (b), and a conductive high refractive index thin film layer (a). It may be a monolayer.
[0033]
(High refractive index thin film layer a)
It is preferable that the material used for the transparent high-refractive-index thin film layer (a) has excellent transparency as much as possible. Here, “excellent in transparency” means that when a thin film having a thickness of about 100 nm is formed, the luminous transmittance of the thin film is 60% or more. The high-refractive-index material is a material having a refractive index for light of 550 nm of 1.4 or more. These may be mixed with impurities depending on the application.
[0034]
Examples of materials that can be suitably used for the transparent high refractive index thin film layer include oxides of indium and tin (ITO), oxides of cadmium and tin (CTO), and aluminum oxide (Al). ₂ O ₃ ), Zinc oxide (ZnO) ₂ ), Oxides of zinc and aluminum (AZO), magnesium oxide (MgO), thorium oxide (ThO ₂ ), Tin oxide (SnO) ₂ ), Lanthanum oxide (LaO) ₂ ), Silicon oxide (SiO ₂ ), Indium oxide (In) ₂ O ₃ ), Niobium oxide (Nb ₂ O ₃ ), Antimony oxide (Sb ₂ O ₃ ), Zirconium oxide (ZrO) ₂ ), Cesium oxide (CeO) ₂ ), Titanium oxide (TiO) ₂ ), Bismuth oxide (Bi ₂ O ₃ ).
[0035]
Further, a transparent high refractive index sulfide may be used. Specifically, zinc sulfide (ZnS), cadmium sulfide (CdS), antimony sulfide (Sb ₂ S ₃ ) And the like.
[0036]
Among transparent high-refractive-index thin film materials, among others, ITO, TiO ₂ , And AZO are particularly preferred. ITO and AZO have conductivity and a refractive index in the visible region as high as about 2.0, and hardly absorb in the visible region. TiO ₂ Is an insulator and has a small absorption in the visible region, but has a large refractive index for visible light of about 2.3.
[0037]
There is no particular limitation on the percentage of tin contained in the ITO used. Usually, it is 0 to 50% by mass. The ratio of aluminum contained in AZO used is not particularly limited. However, if the content ratio of aluminum is too low, the non-resistance value of the AZO film may become too large. When laminated on the outermost surface, the contact resistance with the outside may become too large. If the content of aluminum is too high, the transmittance of the AZO film, particularly the transmittance for light having a wavelength of 300 to 500 (nm), may decrease. Therefore, the ratio of aluminum contained in AZO is preferably about 1 to 5 (% by mass).
[0038]
In the case where the transparent conductive layer (B) is a single-layer body composed of the high refractive index thin film layer (a) having conductivity, the material used preferably has a low specific resistance. Usually, ITO or AZO is preferably used. The preferred specific resistance of the transparent high refractive index thin film layer (a) located on the outermost surface is 1 × 10 ^-6 (Ω · cm) or more, 1 × 10 ^-3 (Ω · cm) or less. More preferably, 1 ×× 10 ^-6 (Ω · cm) or more, 1 × 10 ^-4 (Ω · cm) or less, still more preferably 1 × 10 ^-6 (Ω · cm) or more, 1 × 10 ^-5 (Ω · cm) or less.
[0039]
The thickness of the transparent high-refractive-index thin film layer is determined in consideration of the transmittance and electric conductivity of the entire transparent electrode. Usually, it is about 0.5 to 100 nm
[0040]
(Metal thin film layer b)
The material of the metal thin film layer (b) used in the present invention is silver or a silver alloy. Silver has a specific resistance of 1.59 × 10 ^-6 (Ω · cm), which is most preferably used in the present invention because it has the best electrical conductivity among all materials and the thin film has excellent visible light transmittance. However, silver has a problem that it lacks stability when it is formed into a thin film and agglomerates. When the transparent conductive thin film laminate according to the present invention is manufactured using silver, and further, an organic electroluminescence element is manufactured using the stacked body, and a light emission test is performed. Non-light-emitting portions are easily generated. For this reason, silver alloys are often used for the purpose of increasing stability. Specific examples of metals other than silver used in the silver alloy include gold, copper, palladium, platinum, indium, tin, and neodymium. Among them, an alloy of silver and gold, an alloy of silver, palladium, and copper, and an alloy of silver, gold, and neodymium are preferably used. The amount of metal contained in the silver to form the alloy depends on the application. If the amount is too small, the effect of increasing the stability may not be obtained. If the amount is too large, the optical properties and the electrical properties may decrease.
[0041]
For example, the preferred gold content in an alloy of silver and gold is 0.1-20% by mass, preferably 0.5-15% by mass, and even more preferably 1.0-10% by mass. The preferred content of palladium and copper in the alloy of silver, palladium and copper is 0.3 to 2% by mass, preferably 0.5 to 2% by mass, and more preferably 1.0 to 1.5% by mass. %. The preferable content of gold and neodymium in the alloy of silver, gold and neodymium is 0.3 to 2% by mass, preferably 0.5 to 2% by mass, and more preferably 1.0 to 1.5% by mass. % By mass. When a transparent conductive thin film laminate is prepared using these silver alloys, and it is used as an organic electroluminescent element as a transparent electrode, and a light emission test is performed, non-light-emitting portions are less likely to occur as compared with the case where pure silver is used. Become.
[0042]
The thickness of the metal thin film layer made of silver or a silver alloy is determined in consideration of durability, light transmittance, and electrical conductivity when current is applied to the entire transparent electrode, depending on the material used and the application. . For example, when a silver alloy containing 5% by mass of gold is used as a material and used as a transparent electrode of an organic electroluminescence element, in order to sufficiently obtain durability when an electric current is applied, the silver alloy metal thin film layer needs to be formed. The thickness is at least 9 to 20 nm, more preferably 10 to 20 nm, and even more preferably 11 to 20 nm. When the thickness is equal to or less than the above-described thickness, when an organic electroluminescent element is manufactured and a light emission test is performed, a dot-shaped non-light-emitting portion which is presumed to be caused by deterioration of the transparent electrode occurs in the light-emitting portion. On the other hand, when the thickness is within the above range, the above-mentioned problem hardly occurs, and a practical transparent electrode can be provided.
[0043]
(Hole transport layer (C))
Known materials can be used for the hole transport layer (C). For example, a diamine-based organic compound is preferably used because of its excellent hole transporting ability. Among them, N, N'-diphenyl-N, N '-(3-methylphenyl) -1,1'-biphenyl-4,4'-diamine (abbreviated as TPD) is excellent in hole transport ability and widely transports holes. Used as a material.
[0044]
(Light-emitting layer (D))
The material used for the light emitting layer (D) contained a red light emitting dye such as, for example, 4- (dicyanomethylene) -2-methyl-6- (4-dimethylaminostyryl) -tetrahydropyran (abbreviation: DCM1). , N-vinylcarbazole (abbreviation: PVK), aluminum quinolinol complex (8-hydroxyquinoline aluminum) (abbreviation: Alq3), 1,2,3,4,5-pentaphenyl-1,3-cyclopentadiene (abbreviation: PPCP) , 2- (4-biphenylyl-)-5- (4-t-butylphenyl) -1,3,4-oxadiazole (abbreviation PBD), N-N'-bis (2,5-t-butyl) Phenyl) -3,4,9,10-perylenedicarboximide (abbreviation BPPC).
[0045]
The hole transport layer (C) and the light emitting layer (D) may be formed by a conventionally known physical vapor deposition method such as a vacuum evaporation method or an ionization evaporation method, or by dispersing a desired material in an appropriate solvent and spinning. After applying by a method such as coating, a wet method of drying may be used.
[0046]
The thickness of each of the hole transport layer (C) and the light emitting layer (D) is usually 30 to 200 nm.
[0047]
(Cathode E)
The material used for the cathode is an alloy of magnesium and silver, an alloy of magnesium and aluminum, and the like. For forming these cathodes, a conventionally known physical film forming method such as a vacuum evaporation method or a sputtering method may be used.
[0048]
The thickness of the cathode is usually about 5 to 500 nm.
[0049]
Further, an appropriate electron transport layer may be inserted between the light emitting layer (D) and the cathode to further improve the light emitting efficiency.
[0050]
(Thin film formation method)
The transparent high-refractive-index thin film layer and the silver or silver alloy thin film layer may be formed by a conventionally known method such as a vacuum evaporation method, an ion plating method, and a sputtering method.
[0051]
For forming the transparent high refractive index thin film layer, an ion plating method or a sputtering method is suitably used. In the ion plating method, a desired metal or sintered body is resistance-heated in a reaction gas plasma or heated by an electron beam to perform vacuum deposition. In the sputtering method, a desired metal or a sintered body is used as a target, an inert gas such as argon or neon is used as a sputtering gas, and a gas necessary for a reaction is added to perform sputtering. For example, when an ITO thin film is formed, DC magnetron sputtering is performed in oxygen gas using an oxide of indium and tin as a sputtering target.
[0052]
For the metal thin film layer, a vacuum evaporation method or a sputtering method is suitably used. In the vacuum evaporation method, a metal thin film can be easily formed by using a desired metal as an evaporation source and performing heating evaporation by resistance heating, electron beam heating, or the like. When a sputtering method is used, a desired metal material is used as a target, an inert gas such as argon or neon is used as a sputtering gas, and a metal thin film is formed using a DC sputtering method or a high-frequency sputtering method. Can be. In order to increase the deposition rate, a DC magnetron sputtering method or a high-frequency magnetron sputtering method is often used.
[0053]
(Evaluation of composition and composition)
The atomic composition of the thin film layer surface of the transparent conductive thin film laminate produced by the above-described method is as follows: Auger electron spectroscopy (AES), X-ray fluorescence (XRF), X-ray microanalysis (XMA), charged particles Excitation X-ray analysis (RBS), X-ray photoelectron spectroscopy (XPS), vacuum ultraviolet photoelectron spectroscopy (UPS), infrared absorption spectroscopy (IR), Raman spectroscopy, secondary ion mass spectroscopy (SIMS), It can be measured by low energy ion scattering spectroscopy (ISS) or the like. Further, the atomic composition and the film thickness in the film can be examined by performing Auger electron spectroscopy (AES) or secondary ion mass spectrometry (SIMS) in the depth direction.
[0054]
(Element evaluation)
In order to evaluate the luminous characteristics of the luminous body, the luminous body may be actually prepared and examined. For example, a method for producing an organic electroluminescent element is such that a hole transport layer (C), a light emitting layer (D) and a cathode are formed on a transparent conductive thin film of a transparent electrode by using a transparent electrode / hole transport layer (C) / light emitting layer ( D) / Laminated in a cathode configuration.
[0055]
As the material used for the hole transport layer (C), for example, a diamine-based organic compound is preferably used because of its excellent hole transport ability. Among them, N, N'-diphenyl-N, N '-(3-methylphenyl) -1,1'-biphenyl-4,4'-diamine (abbreviated as TPD) is excellent in hole transport ability and widely transports holes. Used as a material.
[0056]
The material used for the light emitting layer (D) contained a red light emitting dye such as, for example, 4- (dicyanomethylene) -2-methyl-6- (4-dimethylaminostyryl) -tetrahydropyran (abbreviation: DCM1). , N-vinylcarbazole (abbreviation: PVK), aluminum quinolinol complex (8-hydroxyquinoline aluminum) (abbreviation: Alq3), 1,2,3,4,5-pentaphenyl-1,3-cyclopentadiene (abbreviation: PPCP) , 2- (4-biphenylyl-)-5- (4-t-butylphenyl) -1,3,4-oxadiazole (abbreviation PBD), N-N'-bis (2,5-t-butyl) Phenyl) -3,4,9,10-perylenedicarboximide (abbreviation BPPC).
[0057]
The hole transport layer (C) and the light emitting layer (D) may be formed by a conventionally known physical vapor deposition method such as a vacuum evaporation method or an ionization evaporation method, or by dispersing a desired material in an appropriate solvent and spinning. After applying by a method such as coating, a wet method of drying may be used.
[0058]
The thickness of each of the hole transport layer (C) and the light emitting layer (D) is usually 30 to 200 nm.
[0059]
The material used for the cathode is an alloy of magnesium and silver, an alloy of magnesium and aluminum, and the like. For forming these cathodes, a conventionally known physical film forming method such as a vacuum evaporation method or a sputtering method may be used.
[0060]
The thickness of the cathode is usually about 5 to 500 nm. Further, an appropriate electron transport layer may be inserted between the light emitting layer and the cathode to further improve the light emitting efficiency.
[0061]
The organic electroluminescent device manufactured by the above method is made to emit light, and the pass / fail is determined based on the light emitting state. The device is driven by applying a voltage of 10 V, and the luminance is measured. In the present invention, the luminance is 2000 cd / m ² The above cases are considered to be acceptable.
[0062]
【Example】
(Example 1)
(Preparation of transparent conductive thin film laminate)
As the transparent substrate (A), a glass plate [manufactured by Corning, model number 7059, size 50 mm × 50 mm, thickness 1.1 mm] was prepared.
Using a Kapton tape as a mask, a transparent conductive thin film having a width of 3 mm and a length of 50 mm was formed so as to be parallel to one side of the transparent substrate (A). A plurality of samples were prepared under the same conditions, and different samples were used for a current resistance test and an organic electroluminescence evaluation test. The film was formed under the following conditions.
Using a direct current magnetron sputtering method, a thin film layer (a) made of an oxide of indium and tin and a thin film layer (b) of an alloy of silver and gold were formed on the transparent polymer molded substrate (A) by A / a [thickness]. 40 nm] / b [thickness 10 nm] / a [thickness 80 nm] / b [thickness 10 nm] / a [thickness 40 nm] to form a transparent electrode. The thin film layer made of an oxide of indium and tin constitutes a transparent high refractive index thin film layer, and the thin film layer of silver and gold alloy constitutes a metal thin film layer. In forming a thin film layer composed of an oxide of indium and tin, as a target, an indium oxide-tin oxide sintered body [In ₂ O ₃ : SnO ₂ = 90: 10 (mass ratio)], and an argon / oxygen / hydrogen mixed gas (total pressure 266 mPa, oxygen partial pressure 8 mPa, hydrogen partial pressure 5 mPa) was used as a sputtering gas. In forming the alloy thin film layer of silver, palladium, and copper, an alloy of silver, palladium, and copper [Ag: Au = 95: 5 (mass ratio)] was used as a target, and argon gas (total pressure) was used as a sputtering gas. 266 mPa). FIG. 1 shows a cross-sectional view of the formed transparent conductive thin film.
Note that the film thickness of the thin film layer described in this example is a value obtained from a value measured using a stylus film thickness meter on a sample in which the thin film is formed under the same conditions. By the way, with a stylus film thickness meter, with respect to a film thickness of 40 nm or less, the accuracy limit of the apparatus is reached, and the film thickness cannot be accurately evaluated. For this reason, a film is usually formed to have a thickness of 40 nm or more, preferably 100 nm or more, and the value is read accurately. Since the film thickness is proportional to the film forming time, the film thickness of each thin film in the sample is determined based on the accurately determined film thickness and time.
[0063]
(Evaluation of transparent conductive thin film laminate)
The surface resistance and the luminous average transmittance of the transparent conductive thin film laminate prepared above were measured.
[0064]
(Organic electroluminescent element evaluation test)
Subsequently, an organic electroluminescence device was produced using the obtained transparent conductive thin film laminate as a transparent electrode, and a light emission test was performed. That is, an organic thin film layer was formed in a square shape with dimensions of 5 mm × 5 mm on a transparent electrode, and then a cathode having a width of 3 mm was formed so as to be orthogonal to the transparent electrode. The positional relationship between the transparent electrode, the organic thin film layer, and the cathode is as described in FIG.
The organic thin film layer and the cathode were formed as follows. First, N, N′-diphenyl-N, N ′-(3-methylphenyl) -1,1 ′ was formed as a hole transport layer (C) on a transparent conductive thin film of a transparent electrode by a vacuum heating evaporation method. A biphenyl-4,4'-diamine (abbreviation: TPD) layer [50 nm] was formed. Subsequently, an 8-hydroxyquinoline aluminum (abbreviation: Alq3) layer [50 nm] was formed thereon as a light emitting layer using a vacuum heating evaporation method. Further, a magnesium layer [2 nm] was formed thereon as a cathode by using a vacuum heating evaporation method. FIG. 3 shows a cross-sectional view of the formed organic electroluminescence element.
A DC voltage of 10 V was applied between the anode and the cathode of the organic electroluminescence element, and the emission luminance was measured.
[0065]
(Calculation of admittance)
The refractive indices of the transparent substrate (A), the high refractive index thin film layer (a), the metal thin film layer (b), the hole transport layer (C), and the light emitting layer (D) were measured by an ellipsometer. As for the high refractive index thin film layer (a), the metal thin film layer (b), the hole transport layer (C), and the light emitting layer (D), each of the thin film layers having a thickness of 20 to 100 (nm) is a glass plate. A sample formed thereon was prepared, and the refractive index of the thin film layer was measured.
In the present invention, the admittance was determined by setting the incident angle of light to 0 ° and the wavelength of light to 550 nm.
(Example 2)
The operation was performed in the same manner as in Example 1 except for the following.
On the transparent polymer molded substrate (A), a thin film layer (a) composed of an oxide of indium and tin and a thin film layer (b) of an alloy of silver and gold were subjected to A / a [thickness of 40 nm] / b [thickness]. 10 nm] / a [thickness 100 nm] / b [thickness 10 nm] / a [thickness 40 nm] in this order to form a transparent electrode.
(Comparative Example 1)
On the transparent polymer molded substrate (A), a thin film layer (a) composed of an oxide of indium and tin and a thin film layer (b) of an alloy of silver and gold were subjected to A / a [thickness of 40 nm] / b [thickness]. 10 nm] / a [thickness 120 nm] / b [thickness 10 nm] / a [thickness 40 nm] were stacked in this order to form a transparent electrode.
Table 1 shows the results of the above Examples and Comparative Examples.
[0066]
[Table 1]

[0067]
When | x−α | and | y−β | are equal to or less than 0.5 as in Examples 1 and 2, the emission luminance of the organic electroluminescent element is | x as in Comparative Example 1. It can be seen that −α | or | y−β | is higher than the case where the value is outside the limit range. In Examples 1 and 2 and Comparative Example 1, there is no significant difference in the luminous average transmittance and the surface resistance value.
Therefore, it is considered that the high light emission luminance shown in Examples 1 and 2 is due to the fact that the difference between the admittance of the light extraction part (L) and the refractive index of the light emitting layer (D) is reduced, and the light extraction efficiency is improved. Can be.
[0068]
【The invention's effect】
By limiting the difference between the admittance of the light extraction portion (L) composed of the transparent substrate (A), the transparent conductive layer (B) and the hole transport layer (C) and the refractive index of the light emitting layer (D), An organic electroluminescence element having a higher light emission luminance can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating an example of a transparent conductive thin film laminate.
FIG. 2 is a plan view showing an example of an organic electroluminescence element.
FIG. 3 is a plan view illustrating an example of an organic electroluminescence element.
[Explanation of symbols]
10 Transparent substrate
20 High refractive index thin film layer
30 Silver or silver alloy thin film layer
40 Transparent conductive thin film layer
50 Organic thin film layer
60 cathode
70 hole transport layer
80 Light emitting layer

Claims (1)

A luminous body having a transparent substrate (A), a transparent conductive layer (B), a hole transport layer (C), and a light emitting layer (D),
The admittance of the light extraction portion (L) arranged in the order of transparent substrate (A) / transparent conductive layer (B) / hole transport layer (C) is Y = x + iy, and the refractive index of the light emitting layer (D) is η _D = | x-α | is 0.5 or less and | y-β | is 0.5 or less when α + iβ is satisfied.

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