JP2011054668A - Organic electroluminescence device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescence device improving an electrical failure without damaging electrical/optical characteristics. <P>SOLUTION: The organic electroluminescence device including at least an anode 1, a hole injection layer 2, a hole transport layer 3, a light-emitting layer 4, an electron transport layer 5 and a cathode 6 is concerned. The hole injection layer 2 is formed by using a coating method. The conductivity of the hole injection layer 2 is 1×10<SP>-5</SP>(S/cm) or more. A foreign matter can be coated efficiently because a coverage property to the foreign matter is better than a case when the hole injection layer 2 is formed by an evaporation method. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an organic electroluminescent element (organic EL element) that can be used for a backlight for liquid crystal display, a light source for illumination, and the like. Specifically, by using a coating type hole injection material having high conductivity, It relates to an organic electroluminescence device that reduces the occurrence of shorts without damaging the electrical characteristics even when it is formed on the film, and further, by selecting appropriate refractive index and extinction coefficient, optical characteristics are also achieved. The present invention relates to an organic electroluminescence device that does not lose.

  An organic electroluminescent element is a planar light emitting element characterized by exhibiting various emission colors by laminating thin films of several nm to several tens of nm. The luminescent color is determined by the luminescent material contained in the organic luminescent layer. Currently, luminescent materials that can be used are, for example, monochromatic luminescent materials such as blue, green, and red. Therefore, for example, when an organic electroluminescent element is applied as a light source for illumination, a light source including a plurality of luminescent colors is preferable. In particular, when applied to main lighting in a room, white light emission is performed. preferable. Here, the white light emission is light emission that substantially includes light having a wavelength in the visible light region, and can be obtained by, for example, a color mixture of two colors that are complementary colors of light blue and orange. .

  Here, when an organic electroluminescent element is considered as an illumination light source, the light emitting area is preferably large, and the size is required to be several centimeters to several tens of centimeters. On the other hand, the organic electroluminescence device currently in practical use is mainly used for display, but the pixel size is on the order of μm in both the active matrix type and the passive matrix type. Therefore, increasing the light emitting area has a problem of increasing electrical defects (leakage / short circuit).

  For this problem, Patent Documents 1 to 3 shown below have been proposed. In any patent document, the electrical failure is improved by forming a thick organic layer, but in any case, there is a problem of high voltage driving by forming a thick film. . In the invention described in Patent Document 1, a coating film is formed on ITO (coating film is formed by dissolving a vapor deposition material in a solvent), and there is no regulation of conductivity or refractive index, and driving voltage. Is a problem. In the invention described in Patent Document 2, the HIL material is deposited and then heat-treated to melt the material and embed the dust. The process is complicated and the drive voltage is high. It is a problem. Patent Document 3 has a problem in that the vapor deposition thick film and the drive voltage are high.

Furthermore, it is conceivable to form a thick film without increasing the driving voltage by using a material having high conductivity. As a result of an experiment using a passive matrix display, a pixel that seems to be derived from a high conductivity when evaluated using a material having a high conductivity, specifically, 1 × 10 ⁻⁵ (S / cm) or more. There was a problem that the edge of the (light emitting area) became unclear. Therefore, when considering application to a display, it is impossible to apply a material having high conductivity.

  In addition, since the organic electroluminescence device emits light in the state of being affected by optical interference, the optical film thickness design is very important in order to extract light efficiently. Here, when a thick film is simply formed, if a material with high conductivity is formed in a thick film, it is possible to reduce electrical defects such as leakage and short circuit without impairing electrical characteristics, It is not always an efficient organic electroluminescent element from an optical point of view. As a result of our diligent research, we have found that thick films can be formed without significant loss of optical properties when the refractive index of the material has a specific relationship.

JP 2002-75637 A JP 2000-91067 A JP 2003-257675 A

  The present invention has been made in view of the above points, and an object of the present invention is to provide an organic electroluminescence device having improved electrical defects without impairing electrical and optical characteristics.

The organic electroluminescent device according to claim 1 of the present invention is an organic electroluminescent device comprising at least an anode 1, a hole injection layer 2, a hole transport layer 3, a light emitting layer 4, an electron transport layer 5, and a cathode 6. The hole injection layer 2 is formed by a coating method, and its conductivity is 1 × 10 ⁻⁵ (S / cm) or more.

  The organic electroluminescence device according to claim 2 of the present invention is characterized in that, in claim 1, the thickness of the hole injection layer 2 is in the range of 20 to 200 nm.

The organic electroluminescent element according to claim 3 of the present invention is the organic electroluminescent element according to claim 1 or 2, wherein the refractive index (n _HIL ) of the hole injection layer 2 and the refractive index (n _HTL ) of the hole transport layer 3 are n _HIL. > N _HTL .

  An organic electroluminescent element according to a fourth aspect of the present invention is used in an organic EL lighting panel according to any one of the first to third aspects.

  In the first aspect of the invention, compared to the case where the hole injection layer is formed by a vapor deposition method, the coverage with respect to the foreign matter is better, so that the foreign matter can be efficiently covered and the electrical failure due to the foreign matter is reduced. In addition, since the conductivity of the hole injection layer is high, the device drive voltage is not increased even when the hole injection layer is formed in a thick film, and high power efficiency is achieved. It is possible to reduce electrical defects such as leaks and shorts while maintaining the above.

  According to the second aspect of the present invention, it is possible to suppress the defect occurrence rate of a large-area organic EL panel without reducing the light emission efficiency of the device.

In the invention of claim 3, since the refractive index (n _HIL ) of the hole injection layer and the refractive index (n _HTL ) of the hole transport layer are in a relationship of n _HIL > n _HTL , the luminous efficiency of the device is greatly reduced. It is something that can be avoided.

  In the invention of claim 4, an illumination panel having a large area and good luminous efficiency can be obtained.

It is the schematic of the layer structure which shows an example of embodiment of this invention. It is a graph which shows the relationship between the film thickness of a positive hole injection layer, and a total luminous flux ratio. It is a graph which shows the relationship between the size of a light emission area, and defect incidence. It is a graph which shows the relationship between the film thickness of a positive hole injection layer, and a total luminous flux ratio.

  Hereinafter, modes for carrying out the present invention will be described.

  The organic electroluminescent element of the present invention shown in FIG. 1 has a plurality of light emitting layers 4 (4a, 4b) having different colors such as an anode 1, a hole injection layer 2, a hole transport layer 3, and a luminescent color on the surface of a transparent substrate 10. ), An electron transport layer 5 and a cathode 6 are sequentially laminated.

  The substrate 10 is light-transmitting when light is emitted through the substrate 10, and may be slightly colored or ground glass in addition to being colorless and transparent. Good. For example, a transparent glass plate such as soda lime glass or non-alkali glass, a plastic film or a plastic plate produced by an arbitrary method from a resin such as polyester, polyolefin, polyamide, or epoxy, or a fluorine resin can be used. . Furthermore, it is also possible to use a material that has a light diffusion effect by containing particles, powder, bubbles, or the like having a refractive index different from that of the substrate matrix in the substrate 10 or imparting a shape to the surface. Further, when light is emitted without passing through the substrate 10, the substrate 10 does not necessarily have to be light transmissive, and any substrate 10 is used as long as the light emission characteristics, life characteristics, etc. of the element are not impaired. be able to. In particular, the substrate 10 having high thermal conductivity can be used in order to reduce a temperature rise due to heat generation of the element during energization.

The anode 1 is an electrode for injecting holes into the light emitting layer 4 through the hole injection layer 2 and the hole transport layer 3, and has a high work function metal, alloy, electrically conductive compound, or a mixture thereof. It is preferable to use an electrode material having a work function of 4 eV or more. Examples of the material of the anode 1 include metals such as gold, conductive materials such as CuI, ITO (indium-tin oxide), SnO ₂ , ZnO, IZO (indium-zinc oxide), PEDOT, and polyaniline. Examples thereof include a conductive polymer doped with a polymer and an optional acceptor, and a conductive light-transmitting material such as a carbon nanotube. The anode 1 can be produced, for example, by forming these electrode materials into a thin film on the surface of the substrate 10 by a method such as vacuum deposition, sputtering, or coating. In order to transmit the light emitted from the light emitting layer 4 to the outside through the anode 1, the light transmittance of the anode 1 is preferably set to 70% or more. Further, the sheet resistance of the anode 1 is preferably several hundred Ω / □ or less, and particularly preferably 100 Ω / □ or less. Here, the film thickness of the anode 1 varies depending on the material in order to control the light transmittance, sheet resistance, and other characteristics of the anode 1 as described above, but is set to a range of 500 nm or less, preferably 10 to 200 nm. It is good.

The hole injection layer 2 is provided in order to increase the hole injection efficiency from the anode 1 to the light emitting layer 4, and as a hole injection material, poly-3-hexylthiophene (P3HT) or poly (3 , 4-ethylenedioxythiophene) poly (styrene sulfonic acid) (PEDT: PSS), polyaniline (PANI), and the like can be used. The hole injection layer 2 can be formed by a coating method, and spin coating, spraying, screen printing, ink jet, or the like can be employed as the coating method. In this case, the hole injection layer 2 can be formed by applying a solution in which the hole injection material is dispersed or dissolved in a solvent such as water to the surface of the anode 1 and drying by heating or the like. The conductivity of the hole injection layer 2 is 1 × 10 ⁻⁵ (S / cm) or more. If the electrical conductivity is lower than this, the drive voltage of the organic electroluminescent element (device) becomes high, and there is a possibility that device characteristics such as a decrease in power efficiency may be lowered. Since the conductivity of the hole injection layer 2 is preferably as high as possible, it is not particularly limited. The conductivity of the hole injection layer 2 can be adjusted by the film forming conditions such as the type of the hole injection material to be used, annealing conditions (temperature and environment), additives (auxiliary solvent), etc. (Special Table 2006-518778). (See publicly known literature such as No. gazette). The thickness of the hole injection layer 2 is preferably in the range of 20 to 200 nm. If this film thickness is less than 20 nm, there is a risk that the function of covering the foreign matter will be reduced, and the reduction of electrical failure due to the foreign matter may not be sufficiently obtained. There is.

  The hole transport layer 3 has the ability to transport holes, has a hole injection effect from the anode 1, has an excellent hole injection effect with respect to the light emitting layer 4, and further has an electron anode 1. It is provided in order to prevent movement to the side. Examples of the hole transport material constituting the hole transport layer 3 include phthalocyanine derivatives, naphthalocyanine derivatives, porphyrin derivatives, N, N′-bis (3-methylphenyl)-(1,1′-biphenyl) -4,4′-. Aromatic diamine compounds such as diamine (TPD) and 4,4′-bis [N- (naphthyl) -N-phenyl-amino] biphenyl (α-NPD), oxazole, oxadiazole, triazole, imidazole, imidazolone, stilbene Derivatives, pyrazoline derivatives, tetrahydroimidazole, polyarylalkanes, butadiene, 4,4 ′, 4 ″ -tris (N- (3-methylphenyl) N-phenylamino) triphenylamine (m-MTDATA), However, the thickness of the hole transport layer 3 is not particularly limited. But not, it is preferably 5 to 100 nm.

The refractive index (n _HIL ) of the hole injection layer 2 and the refractive index (n _HTL ) of the hole transport layer 3 are preferably in a relationship of n _HIL > n _HTL. It is possible to prevent total reflection from occurring at the interface with the hole transport layer 3 and to prevent the light emission efficiency of the device from being greatly reduced. The relationship of n _HIL > n _HTL can be set by changing the type of hole injection material.

  The light emitting layer (organic light emitting layer) 4 is provided in order to recombine the holes injected from the anode 1 and the electrons injected from the cathode 6 to emit light. As a material that can be used for the light emitting layer 4, any material known as a material for an organic electroluminescent element can be used. For example, anthracene, naphthalene, pyrene, tetracene, coronene, perylene, phthaloperylene, naphthaloperylene, diphenylbutadiene, tetraphenylbutadiene, coumarin, oxadiazole, bisbenzoxazoline, bisstyryl, cyclopentadiene, quinoline metal complex, tris (8-hydroxy Quinolinato) aluminum complex, tris (4-methyl-8-quinolinato) aluminum complex, tris (5-phenyl-8-quinolinato) aluminum complex, aminoquinoline metal complex, benzoquinoline metal complex, tri- (p-terphenyl) -4-yl) amine, 1-aryl-2,5-di (2-thienyl) pyrrole derivative, pyran, quinacridone, rubrene, distyrylbenzene derivative, distyrylarylene derivative, distyle Triethanolamine derivatives and various fluorescent dyes, but include those including a material system and its derivatives of the foregoing, the present invention is not limited to these. Moreover, it is also preferable to mix and use the light emitting material selected from these compounds suitably. Further, not only a compound that emits fluorescence, typified by the above-described compound, but also a material system that emits light from a spin multiplet, for example, a phosphorescent material that emits phosphorescence, and a part thereof are included in a part of the molecule. A compound can also be used suitably. The organic layer made of these materials may be formed by a dry process such as vapor deposition or transfer, or may be formed by a wet process such as spin coating, spray coating, die coating, or gravure printing. . Although the thickness of the light emitting layer 4 is not specifically limited, It is preferable that it is 5-100 nm.

  The electron transport layer 5 has the ability to transport electrons, has an electron injection effect from the cathode 6, has an excellent electron injection effect with respect to the light emitting layer 4, and further has a positive effect on the cathode 6 side. It is provided to prevent movement. Examples of the electron transport material constituting the electron transport layer 5 include phenanthroline derivatives such as fluorene, bathophenanthroline, bathocuproine, anthraquinodimethane, diphenoquinone, oxazole, oxadiazole derivatives, triazole, imidazole, anthraquinodimethane, and the like. A compound, a metal complex compound, or a nitrogen-containing five-membered ring derivative. Specific metal complex compounds include tris (8-hydroxyquinolinato) aluminum, tri (2-methyl-8-hydroxyquinolinato) aluminum, tris (8-hydroxyquinolinato) gallium, bis (10- Hydroxybenzo [h] quinolinato) beryllium, bis (10-hydroxybenzo [h] quinolinato) zinc, bis (2-methyl-8-quinolinato) (o-cresolate) gallium, bis (2-methyl-8-quinolinato) ( 1-naphtholate) aluminum and the like, but not limited thereto. The nitrogen-containing five-membered ring derivative is preferably an oxazole, thiazole, oxadiazole, thiadiazole or triazole derivative. Specifically, 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-oxadiazole, 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-t-butylphenyl) -1,2,4-triazole, etc., but are not limited to these. The thickness of the layer 5 is not particularly limited, but is preferably 5 to 100 nm. There.

The cathode 6 is an electrode for injecting electrons into the light emitting layer 4 through the electron transport layer 5, and an electrode material made of a metal, an alloy, an electrically conductive compound, and a mixture thereof having a low work function is used. Preferably, the work function is 5 eV or less. Examples of the electrode material for the cathode 6 include alkali metals, alkali metal halides, alkali metal oxides, alkaline earth metals and the like, and alloys thereof with other metals such as sodium, sodium-potassium alloys, Examples include lithium, magnesium, a magnesium-silver mixture, a magnesium-indium mixture, an aluminum-lithium alloy, and an Al / LiF mixture. Aluminum, Al / Al ₂ O ₃ mixture, etc. can also be used. Furthermore, an alkali metal oxide, an alkali metal halide, or a metal oxide may be used as the base of the cathode 6, and one or more conductive materials such as metals may be stacked and used. For example, an alkali metal / Al laminate, an alkali metal halide / alkaline earth metal / Al laminate, an alkali metal oxide / Al laminate, and the like can be given as examples. Moreover, it is good also as a structure which takes out light from the cathode 6 side using the transparent electrode represented by ITO, IZO, etc. FIG. The organic layer at the interface of the cathode 6 may be doped with an alkali metal such as lithium, sodium, cesium, or calcium, or an alkaline earth metal. Moreover, the cathode 6 can be produced by, for example, forming these electrode materials into a thin film by a method such as a vacuum deposition method or a sputtering method. When light emission in the light emitting layer 4 is extracted from the anode 1 side, the light transmittance of the cathode 6 is preferably 10% or less. Conversely, when light is extracted from the cathode 6 side using the transparent electrode as the cathode 6 (including the case where light is extracted from both the anode 1 and the cathode 6), the light transmittance of the cathode 6 is set to 70% or more. It is preferable. In this case, the thickness of the cathode 6 varies depending on the material in order to control characteristics such as light transmittance of the cathode 6, but is usually 500 nm or less, preferably 100 to 200 nm.

  The organic electroluminescent element of the present invention as described above can be used as a panel for organic EL (electroluminescence) illumination. In this case, a terminal portion connected to the anode 1 and the cathode 6 is provided on the substrate 10, and the terminal portion can be formed so as to be connectable to an external power source.

  The present invention has a structure in which electrical failure is unlikely to occur, and provides an organic electroluminescent element suitable as an organic EL lighting panel. In addition, although an electrical failure is an important problem also in an organic EL display, since the illumination panel has a larger light emitting area than the display, it is a more important problem. In this case, in order to reduce electrical defects, the most essential solution is to reduce foreign matter on the substrate 10 as much as possible. However, since it is impossible to eliminate all foreign matter, It is important to develop a structure of an organic electroluminescent device that is less likely to cause electrical failure even in the presence of. An important guideline for reducing electrical defects is to realize a process and material system selection that covers the foreign matter on the substrate 10 and an element structure. Based on guidelines. However, in Patent Documents 1 to 3, there are problems in process, element characteristics, and the like, and thus improvement of electrical defects has been insufficient. In Japanese Patent Publication No. 2006-518778, it is described that PEDOT / PSS is formed as a buffer layer on ITO to approach the problem of electrical short circuit. Is to use high resistance (low conductivity, low conductivity) PEDOT / PSS. The reason why it is essential to use PEDOT / PSS with such a low conductivity is to avoid crosstalk in the organic EL display, but in the organic EL panel for illumination, the problem of crosstalk is essentially irrelevant. Therefore, there is no restriction on the conductivity of the hole injection layer 2 from the viewpoint of crosstalk (because the organic EL panel for illumination emits light with a large area as one pixel, there is no concept of crosstalk). Therefore, it is possible to use a high conductivity material as the material of the hole injection layer 2. When it is possible to use a high conductivity material, the drive voltage does not increase even if the film thickness is large, so that electrical defects can be sufficiently avoided within a range that does not deteriorate the device characteristics. The hole injection layer 2 may be formed with a film thickness.

  Hereinafter, the present invention will be described specifically by way of examples.

(Reference example)
An organic electroluminescent element having the following layer structure was formed. The reference example does not have a hole injection layer (HIL) (film thickness 0 nm).

Substrate 10: inorganic alkali glass substrate (thickness 0.7 mm)
Anode 1: ITO (thickness 150 nm)
Hole transport layer 3: NPD (thickness 40 nm), refractive index 1.8
First light emitting layer 4a: NPD: rubrene (thickness 20 nm)
Second light emitting layer 4b: TBADN: BCzVBi (thickness 30 nm)
Electron transport layer 5: Alq ₃ (thickness 30 nm)
Cathode 6: LiF / Al (thickness 1 nm / 80 nm)
Example 1
An organic electroluminescent element having the following layer structure was formed.

Substrate 10: inorganic alkali glass substrate (thickness 0.7 mm)
Anode 1: ITO (thickness 150 nm)
Hole injection layer 2: P3HT (thickness 200 nm), conductivity 1.1 × 10 ⁻⁵ S / cm, coating type injection layer, refractive index 1.95
Hole transport layer 3: NPD (thickness 40 nm)
Light emitting layer 4: TBADN: BCzVBi (thickness 50 nm)
Electron transport layer 5: Alq ₃ (thickness 30 nm)
Cathode 6: LiF / Al (thickness 1 nm / 80 nm)
The hole injection layer 2 was formed by applying a solution obtained by dispersing P3HT in a solvent (chlorobenzene) onto the anode 1 by spin coating and drying.

(Comparative Example 1)
An organic electroluminescent element having the following layer structure was formed.

Substrate 10: inorganic alkali glass substrate (thickness 0.7 mm)
Anode 1: ITO (thickness 150 nm)
Hole injection layer 2: NPD: MoO ₃ co-deposited film (20% doped, thickness 200 nm), conductivity 2.0 × 10 ⁻⁴ S / cm, refractive index 1.8
Hole transport layer 3: NPD (thickness 40 nm)
Light emitting layer 4: TBADN: BCzVBi (thickness 50 nm)
Electron transport layer 5: Alq ₃ (thickness 30 nm)
Cathode 6: LiF / Al (thickness 1 nm / 80 nm)
[Comparison of luminous efficiency]
For Example 1 and Comparative Example 1 above, the luminous efficiency was compared. The luminous efficiency was expressed as the ratio of the total luminous flux of Example 1 and Comparative Example 1 to the total luminous flux of the reference example. The total luminous flux was measured by a SLMS-CDS manufactured by Labsphere. The results are shown in Table 1.

[Defect occurrence rate]
50 pieces of each of Example 1 and Comparative Example 1 were prepared, and the defect occurrence rate was determined. Here, those having a current leakage amount of 150 mA or more or those having one or more dark spots having a diameter of 100 μm or more were defined as “defective”. The results are shown in Table 1.

実施例１では比較例１に比べて、基準例よりも発光効率を低下させずに不良率も低減させることができた。

In Example 1, compared with Comparative Example 1, it was possible to reduce the defect rate without lowering the light emission efficiency compared to the reference example.

(Example 2)
An organic electroluminescent element having the following layer structure was formed.

Substrate 10: inorganic alkali glass substrate (thickness 0.7 mm)
Anode 1: ITO (thickness 150 nm)
Hole injection layer 2: PEDT: PSS (thickness 200 nm), conductivity 1.4 × 10 ⁻⁵ S / cm, coating type injection layer Hole transport layer 3: NPD (thickness 40 nm)
First light emitting layer 4a: NPD: rubrene (thickness 35 nm)
Second light emitting layer 4b: TBADN: BCzVBi (thickness 30 nm)
Electron transport layer 5: Alq ₃ (thickness 30 nm)
Cathode 6: LiF / Al (thickness 1 nm / 80 nm)
The hole injection layer 2 was formed by applying PEDT: PSS (solvent is water) onto the anode 1 by spin coating and drying at 200 ° C. in the air.

(Example 3)
An organic electroluminescent element having the following layer structure was formed.

Substrate 10: inorganic alkali glass substrate (thickness 0.7 mm)
Anode 1: ITO (thickness 150 nm)
Hole injection layer 2: PEDT: PSS (thickness 200 nm), conductivity 3.8 × 10 ⁻⁴ S / cm, coating type injection layer Hole transport layer 3: NPD (thickness 40 nm)
First light emitting layer 4a: NPD: rubrene (thickness 35 nm)
Second light emitting layer 4b: TBADN: BCzVBi (thickness 30 nm)
Electron transport layer 5: Alq ₃ (thickness 30 nm)
Cathode 6: LiF / Al (thickness 1 nm / 80 nm)
The hole injection layer 2 was formed by applying PEDT: PSS similar to the above onto the anode 1 by spin coating and drying at 100 ° C. in a nitrogen atmosphere.

Example 4
An organic electroluminescent element having the following layer structure was formed.

Substrate 10: inorganic alkali glass substrate (thickness 0.7 mm)
Anode 1: ITO (thickness 150 nm)
Hole injection layer 2: PEDT: PSS (thickness 200 nm), conductivity 4.7 × 10 ⁻³ S / cm, coating type injection layer Hole transport layer 3: NPD (thickness 40 nm)
First light emitting layer 4a: NPD: rubrene (thickness 35 nm)
Second light emitting layer 4b: TBADN: BCzVBi (thickness 30 nm)
Electron transport layer 5: Alq ₃ (thickness 30 nm)
Cathode 6: LiF / Al (thickness 1 nm / 80 nm)
The hole injection layer 2 was formed by applying PEDT: PSS similar to that described above onto the anode 1 by spin coating and drying at 200 ° C. in a nitrogen atmosphere.

(Comparative Example 2)
An organic electroluminescent element having the following layer structure was formed.

Substrate 10: inorganic alkali glass substrate (thickness 0.7 mm)
Anode 1: ITO (thickness 150 nm)
Hole injection layer 2: PEDT: PSS (thickness 200 nm), conductivity 1.6 × 10 ⁻⁶ S / cm, coating type injection layer, addition of auxiliary solvent 1,4-dioxane Hole transport layer 3: NPD ( Thickness 40nm), refractive index 1.8
First light emitting layer 4a: NPD: rubrene (thickness 35 nm)
Second light emitting layer 4b: TBADN: BCzVBi (thickness 30 nm)
Electron transport layer 5: Alq ₃ (thickness 30 nm)
Cathode 6: LiF / Al (thickness 1 nm / 80 nm)
The hole injection layer 2 was formed by applying PEDT: PSS similar to that described above onto the anode 1 by spin coating and drying at 200 ° C. in the air.

  For Examples 2 to 4 and Comparative Example 2, the same luminous efficiency as above was measured. The results are shown in Table 2.

実施例２〜４のように、正孔注入層２の導電率が高い場合は、発光効率が大きく低下することはないのに対し、比較例２のように導電率が低い場合は、発光効率の低下が見られた。この原因として、導電率が低いことによる駆動電圧の上昇が考えられる。尚、正孔注入層２の膜厚と導電率とにおける電圧降下（駆動電圧の上昇）は以下の表３のような関係が見られる。

When the conductivity of the hole injection layer 2 is high as in Examples 2 to 4, the luminous efficiency is not greatly reduced, whereas when the conductivity is low as in Comparative Example 2, the luminous efficiency is Decrease was observed. As a cause of this, an increase in driving voltage due to low conductivity can be considered. The voltage drop (increase in drive voltage) in the film thickness and conductivity of the hole injection layer 2 has a relationship as shown in Table 3 below.

膜厚４００ｎｍ以上であると、電圧降下が大きいといえる。

It can be said that the voltage drop is large when the film thickness is 400 nm or more.

(Example 5)
An organic electroluminescent element having the following layer structure was formed.

Substrate 10: inorganic alkali glass substrate (thickness 0.7 mm)
Anode 1: ITO (thickness 150 nm)
Hole injection layer 2: P3HT, conductivity 1.1 × 10 ⁻⁵ S / cm, coating type injection layer, refractive index 1.95
Hole transport layer 3: NPD (thickness 40 nm), refractive index 1.8
First light emitting layer 4a: NPD: rubrene (thickness 20 nm)
Second light emitting layer 4b: TBADN: BCzVBi (thickness 30 nm)
Electron transport layer 5: Alq ₃ (thickness 30 nm)
Cathode 6: LiF / Al (thickness 1 nm / 80 nm)
The hole injection layer 2 was formed by applying a solution obtained by dispersing P3HT in a solvent (chlorobenzene) onto the anode 1 by spin coating and drying.

(Comparative Example 3)
An organic electroluminescent element having the following layer structure was formed.

Substrate 10: inorganic alkali glass substrate (thickness 0.7 mm)
Anode 1: ITO (thickness 150 nm)
Hole injection layer 2: PEDT: PSS, conductivity 1.4 × 10 ⁻⁵ S / cm, coating type injection layer, refractive index 1.5
Hole transport layer 3: NPD (thickness 40 nm), refractive index 1.8
First light emitting layer 4a: NPD: rubrene (thickness 20 nm)
Second light emitting layer 4b: TBADN: BCzVBi (thickness 30 nm)
Electron transport layer 5: Alq ₃ (thickness 30 nm)
Cathode 6: LiF / Al (thickness 1 nm / 80 nm)
The hole injection layer 2 was formed by applying PEDT: PSS similar to the above onto the anode 1 by spin coating and drying.

  About Example 5 and Comparative Example 3, the change of the luminous efficiency when the film thickness of the hole injection layer 2 was changed at 50 to 200 nm was measured. Luminous efficiency was evaluated as 1.00 with the same reference example. The results are shown in Table 4.

実施例５においては、正孔注入層２の膜厚が５０〜２００ｎｍの範囲において、基準例と同等もしくは基準例よりも高効率な特性が得られた。それに対して、比較例３においては、基準例よりも低い特性であった。尚、図２に、正孔注入層２の屈折率（ｎ_ＨＩＬ）と正孔輸送層３の屈折率（ｎ_ＨＴＬ）と陽極１の屈折率（ｎ_{ａｎｏｄｅ}）との関係が、（１）ｎ_{ａｎｏｄｅ}＞ｎ_ＨＴＬ＞ｎ_ＨＩＬの場合と、（２）ｎ_{ａｎｏｄｅ}＞ｎ_ＨＩＬ＞ｎ_ＨＴＬの場合と、（３）ｎ_ＨＩＬ＞ｎ_{ａｎｏｄｅ}＞ｎ_ＨＴＬの場合とについて、正孔注入層（ＨＩＬ）２の膜厚依存性について示す。（１）の場合のｎ_{ａｎｏｄｅ}＝２．０、ｎ_ＨＴＬ＝１．８、ｎ_ＨＩＬ＝１．５であり、（２）の場合のｎ_{ａｎｏｄｅ}＝２．０、ｎ_ＨＴＬ＝１．８、ｎ_ＨＩＬ＝１．９５であり、（３）の場合のｎ_{ａｎｏｄｅ}＝１．９、ｎ_ＨＴＬ＝１．８、ｎ_ＨＩＬ＝１．９５である。

In Example 5, in the range where the film thickness of the hole injection layer 2 is 50 to 200 nm, a characteristic equivalent to or higher than that of the reference example was obtained. On the other hand, Comparative Example 3 had lower characteristics than the reference example. FIG. 2 shows the relationship between the refractive index (n _HIL ) of the hole injection layer 2, the refractive index (n _HTL ) of the hole transport layer 3, and the refractive index (n _anode ) of the _anode 1 (1) n hole injection layer (HIL) 2 in the case of _anode > n _HTL > n _HIL , (2) in the case of n _anode > n _HIL > n _HTL , and (3) in the case of n _HIL > n _nano > n _HTL The film thickness dependence is shown. In the case of (1), n _nanode = 2.0, n _HTL = 1.8, n _HIL = 1.5, in the case of (2) n _nanode = 2.0, n _HTL = 1.8, n _HIL = 1.95, _nanode = 1.9, _nHTL = 1.8, and _nHIL = 1.95 in the case of (3).

(Example 6)
An organic electroluminescent element having the following layer structure was formed.

Substrate 10: inorganic alkali glass substrate (thickness 0.7 mm), light emitting area size 3 cm □ to 20 cm □
Anode 1: ITO (thickness 150 nm)
Hole injection layer 2: PEDT: PSS (thickness 0-800 nm), conductivity 3.8 × 10 ⁻⁴ S / cm, coating type injection layer Hole transport layer 3: NPD (thickness 40 nm)
First light emitting layer 4a: NPD: rubrene (thickness 35 nm)
Second light emitting layer 4b: TBADN: BCzVBi (thickness 30 nm)
Electron transport layer 5: Alq ₃ (thickness 30 nm)
Cathode 6: LiF / Al (thickness 1 nm / 80 nm)
The hole injection layer 2 was formed by applying PEDT: PSS similar to the above onto the anode 1 by spin coating and drying.

  For Example 6, the relationship between the size of the light emitting area and the defect occurrence rate was examined for each film thickness of 0 to 800 nm. The results are shown in FIG. From FIG. 3, when the thickness of the hole injection layer 2 is thicker than 20 nm, the defect occurrence rate can be suppressed to 10% or less in any light emitting area size.

(Example 7)
An organic electroluminescent element having the following layer structure was formed.

Substrate 10: inorganic alkali glass substrate (thickness 0.7 mm)
Anode 1: ITO (thickness 150 nm)
Hole injection layer 2: PEDT: PSS (thickness 0 to 800 nm), conductivity 3.8 × 10 ⁻⁴ S / cm, coating type injection layer, refractive index 1.5
Hole transport layer 3: NPD (thickness 40 nm), refractive index 1.8
First light emitting layer 4a: NPD: rubrene (thickness 35 nm)
Second light emitting layer 4b: TBADN: BCzVBi (thickness 30 nm)
Electron transport layer 5: Alq ₃ (thickness 30 nm)
Cathode 6: LiF / Al (thickness 1 nm / 80 nm)
The hole injection layer 2 was formed by applying PEDT: PSS similar to the above onto the anode 1 by spin coating and drying.

  For Example 7, the same luminous efficiency as described above was examined for each film thickness of 0 to 800 nm. The results are shown in Table 5 and FIG. As a result, although the high efficiency is maintained up to the thickness of the hole injection layer 2 up to 200 nm, the reduction in efficiency is remarkable at 400 nm and 800 nm. Therefore, in the range of 20 to 200 nm as the film thickness of the hole injection layer 2, it is confirmed that electrical defects are reduced without reducing the light emission efficiency.

DESCRIPTION OF SYMBOLS 1 Anode 2 Hole injection layer 3 Hole transport layer 4 Light emitting layer 5 Electron transport layer 6 Cathode

Claims (4)

In an organic electroluminescent device including at least an anode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode, the hole injection layer is formed using a coating method, and the conductivity is 1 The organic electroluminescent element characterized by being more than ^x10 < ^-5 > (S / cm).   2. The organic electroluminescence device according to claim 1, wherein the thickness of the hole injection layer is in the range of 20 to 200 nm. The organic electroluminescence according to claim 1 or 2, wherein the refractive index (n _HIL ) of the hole injection layer and the refractive index (n _HTL ) of the hole transport layer are in a relationship of n _HIL > n _HTL. element. The organic electroluminescent element according to claim 1, wherein the organic electroluminescent element is used for an organic EL lighting panel.

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