JP2010257734A - Method of evaluating organic el element, and method of manufacturing organic el element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaluation method capable of precisely measuring emission efficiency of an organic EL element. <P>SOLUTION: The organic EL element is configured by pinching a laminate made of a plurality of organic functional layers including light-emitting layers pinched by an anode and a cathode. In the evaluation method, with the laminate formed on a transparent substrate, a fluorescence spectrum is measured by a spectrographic method to obtain an emission quantum yield. In this method, the emission quantum yield to be an indicator of emission efficiency of the organic EL element is measured in a state of the laminate, so that precise measurement and evaluation can be carried out. Therefore, an evaluation method capable of precisely measuring emission efficiency of the organic EL element can be provided. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an evaluation method for an organic EL (Electro Luminescence) element and a manufacturing method using the evaluation method.

Organic EL displays using organic EL elements that are self-luminous devices are said to be more advantageous in terms of thinning and lower power consumption than liquid crystal displays that require an external light source such as a backlight. In order to increase the degree of perfection as a product, it is expected to improve these advantages.
In particular, from the viewpoint of low power consumption, there is a demand for an organic EL element having high current efficiency that shows the coupling efficiency between holes and electrons. In other words, there has been a demand for an organic EL element that has high luminous efficiency per drive current and excellent energy conversion efficiency.
Conventionally, the light emission efficiency of an organic EL element has been generally measured by passing an electric current through an organic EL element having an anode electrode and a cathode electrode attached thereto, that is, a completed organic EL element to emit light. Because it had to be built up to the finished state, it was inefficient. For this reason, in view of this point, more efficient methods have been proposed.

For example, Patent Document 1 discloses a method of measuring the fluorescence spectrum or light absorption spectrum of a light emitting layer in the state of a single light emitting layer and using it as an indicator of the light emission efficiency of an organic EL element. According to the method, in the manufacturing process of the organic EL element, when the light emitting layer (single layer) is formed, the light emitting layer is irradiated with light having a wavelength indicating the maximum fluorescence intensity from the light source installed in the apparatus. The fluorescence spectrum of the light emitted from the light emitting layer is measured according to the irradiated light. In addition, according to this method, since it is not necessary to complete the organic EL element, the luminous efficiency can be measured efficiently.
That is, in the evaluation method, the light emission efficiency of the organic EL element is estimated by measuring the light emission quantum yield in the single light emitting layer using a spectroscopic method.

Japanese Patent No. 3992582

However, it has been difficult to estimate the accurate light emission efficiency of the organic EL element from the light emission quantum yield in the single light emitting layer. Specifically, the organic EL element generally has a multilayer structure including a plurality of organic functional layers such as a hole injection layer and an electron transport layer in addition to the light emitting layer. It was difficult to estimate the light emission efficiency of the organic EL element having a multilayer structure from the quantum yield. In particular, in the case of a multilayer structure, in addition to the use of materials other than the light emitting material constituting the light emitting layer, an interface is formed between each organic functional layer. It had an effect on properties. For example, when there is roughness (distortion) at the interface, the roughness may cause quenching, and the light emission efficiency of the organic EL element may decrease. In addition, for example, at the interface of the functional layer in contact with the light emitting layer, the light emission efficiency may be reduced due to quenching (electric field quenching) due to excimer generation.
That is, the conventional evaluation method has a problem that it is difficult to accurately measure the light emission efficiency of the organic EL element. In other words, there has been a problem that an evaluation method capable of accurately and efficiently measuring the light emission efficiency of the organic EL element is not known. Therefore, there has been a problem that it is difficult to produce an organic EL element having excellent luminous efficiency using an appropriate evaluation method.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following application examples or forms.

(Application example)
(A) forming a plurality of organic functional layers including at least a light emitting layer on a transparent substrate; and (b) irradiating a laminate comprising the plurality of organic functional layers with light having a predetermined wavelength; (C) measuring the fluorescence spectrum of the fluorescence emitted by the laminate in response to the irradiated light, and deriving the emission quantum yield of the laminate, Evaluation method.

According to this evaluation method, since the organic EL element is evaluated in the state of a laminated body, more accurate evaluation can be performed than the conventional evaluation method that has been evaluated with a single light emitting layer. In other words, accurate light emission efficiency can be obtained by measuring the light emission quantum yield in the state of the same laminate as the actual device configuration.
Therefore, it is possible to provide an evaluation method capable of accurately measuring the light emission efficiency of the organic EL element. Furthermore, since the evaluation is performed in a state where a plurality of organic functional layers are laminated on the transparent substrate, it is not necessary to form a cathode and an anode electrode, and the evaluation can be performed efficiently.
Therefore, it is possible to provide an evaluation method capable of accurately and efficiently measuring the light emission efficiency of the organic EL element.

The transparent substrate is a quartz substrate, and in steps (b) and (c), an integrating sphere including a light source unit that emits light of a predetermined wavelength and a light receiving unit that senses fluorescence emitted from the laminate. The predetermined wavelength is preferably a wavelength at the maximum fluorescence intensity, which is measured in advance and at which the fluorescence emitted from the light emitting layer has the maximum fluorescence intensity.
Further, in each of the reference laminate that is a laminate in the organic EL element that is the reference for evaluation and the evaluation laminate that is the laminate in the organic EL element that is the evaluation target, steps (a) to (c) are performed. It is preferable to further include (d) a step of comparing the emission quantum yield in the evaluation laminate and the emission quantum yield in the reference laminate.

  In the evaluation method described above, the evaluation laminate is formed so that the ratio of the emission quantum yield in the evaluation laminate and the emission quantum yield in the reference laminate satisfies ≧ 1.0. Manufacturing method of EL element.

1 is a perspective view of an organic EL panel according to Embodiment 1. FIG. (A)-(d) Sectional drawing which shows the basic composition of a laminated body (organic EL element). The schematic diagram of the measuring device of the light emission quantum yield. The figure which shows the one aspect | mode of the laminated body in (a), (b) evaluation example. The flowchart figure which shows the flow of the evaluation method of a laminated body (organic EL element).

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the scale of each layer and each part is different from the actual scale so that each layer and each part can be recognized on the drawing.

(Embodiment)
"Outline of organic EL panel"
FIG. 1 is a perspective view showing a schematic configuration of an organic EL panel according to the present embodiment.
First, a schematic configuration of an organic EL panel 100 as an organic EL display using an organic EL element according to an embodiment of the present invention will be described.

The organic EL panel 100 is configured by sandwiching an organic EL element between the element substrate 1 and the counter substrate 30. The periphery of the element substrate 1 and the counter substrate 30 are bonded by a sealing material 25, and the internal organic EL element is sealed. In addition, the area surrounded by the sealing material 25 is a display area V in plan view.
In the display area V, a plurality of pixels P each made of an organic EL element are arranged in a matrix. Specifically, pixels P of three colors of red, green, and blue are periodically arranged.
The organic EL panel 100 is a top emission type organic EL panel that emits display light emitted from these pixels P from the counter substrate 30 side.
In addition, the element substrate 1 is formed with an overhang region in which one side extends from the outer shape of the counter substrate 30. In the overhang region, a terminal portion 13 for inputting various signals including image signals from the outside and a drive circuit (not shown) for driving each pixel P are formed.

Here, the organic EL element which comprises each pixel P is formed in the element substrate 1 side. Specifically, the anode (pixel electrode), the laminated body, and the cathode (common electrode) are laminated in this order from the element substrate 1 side, and light is emitted from the cathode side made of a transparent electrode.
In this specification, a multilayer structure composed of a plurality of organic functional layers including a light emitting layer is referred to as a “laminated body”, and an element in a completed state in which a cathode and an anode are attached to the laminated body is referred to as an “organic EL element. ".
In addition, a light emitting layer that emits red color light is formed on the stacked body in the red pixel P. Similarly, a light emitting layer that emits green color light is formed on the stack of green pixels P, and a light emitting layer that emits blue color light is formed on the stack of blue pixels P.
Note that each light emitting layer is not limited to the three-color system that emits light of different colors of red, green, and blue. For example, the light emitting layer is a single white color and each pixel has a red, green, and blue color filter. A color filter method may be used.
Further, the emission type is not limited to the top emission type in which light is extracted from the cathode side, but may be a bottom emission type in which light is emitted from the anode side through the element substrate 1. The bottom emission type has a simpler structure than the top emission type, so that the manufacturing efficiency is high and the yield can be improved.

"Configuration of organic EL element (laminated body)"
2A to 2D are cross-sectional views showing the basic configuration of the laminate (organic EL element) according to this embodiment.
According to the evaluation method according to the present invention, it is possible to evaluate laminated bodies having various configurations as shown in FIGS.
The laminated body L1 shown in FIG. 2A has a two-layer laminated structure of a hole injection layer 3 as an organic functional layer and a light emitting layer 5. In addition, although mentioned later for details, when measuring the light emission quantum yield accompanying evaluation of luminous efficiency, the laminated body L1 is formed on a quartz substrate. Specifically, the light emission quantum yield is measured in a state where the hole injection layer 3 and the light emitting layer 5 are laminated in this order on a quartz substrate.
Moreover, as shown by a dotted line, an organic EL element including the multilayer body L1 is formed by forming an anode and a cathode so as to sandwich the multilayer body L1. In other words, by laminating the anode, the hole injection layer 3, the light emitting layer 5, and the cathode in this order, an organic EL element including the multilayer body L1 is formed.

The laminated body L2 shown in FIG. 2B includes a hole transport layer 4 as an organic functional layer in addition to the configuration of the laminated body L1 in FIG. Specifically, the multilayer body L2 has a three-layer structure in which a hole injection layer 3, a hole transport layer 4, and a light emitting layer 5 are stacked in this order.
According to the laminated body L2, since the hole transport layer 4 is provided, the charge transport function and the light emission function are substantially separated, so that electrons and holes in the light emission layer 5 are recombined more efficiently. It becomes possible. As in the case of the stacked body L1, when measuring the emission quantum yield, the stacked body L2 is formed on a quartz substrate.
Moreover, as shown by a dotted line, an organic EL element including the multilayer body L2 is formed by forming an anode and a cathode so as to sandwich the multilayer body L2. In other words, by laminating the anode, the hole injection layer 3, the hole transport layer 4, the light emitting layer 5, and the cathode in this order, an organic EL element including the multilayer body L2 is formed. The

The laminated body L3 shown in FIG. 2C includes an electron transport layer 7 as an organic functional layer in addition to the configuration of the laminated body L1 in FIG. Specifically, the multilayer body L3 has a three-layer structure in which the hole injection layer 3, the light emitting layer 5, and the electron transport layer 7 are laminated in this order.
According to the stacked body L3, since the electron transport layer 7 is provided, the charge transport function and the light emission function are substantially separated, so that electrons and holes in the light emission layer 5 can be recombined more efficiently. Is possible. As in the case of the stacked body L1, when measuring the emission quantum yield, the stacked body L3 is formed on a quartz substrate.
Moreover, as shown by a dotted line, an organic EL element including the multilayer body L3 is formed by forming an anode and a cathode so as to sandwich the multilayer body L3. In other words, by laminating the anode, the hole injection layer 3, the light emitting layer 5, the electron transporting layer 7, and the cathode in this order, an organic EL element including the multilayer body L3 is formed. .

A laminate L4 shown in FIG. 2D includes a hole blocking layer 6 as an organic functional layer in addition to the configuration of the laminate L3 in FIG. Specifically, the laminate L4 has a four-layer structure in which a hole injection layer 3, a light emitting layer 5, a hole blocking layer 6, and an electron transport layer 7 are laminated in this order.
The hole blocking layer 6 is an organic functional layer that plays a role of blocking holes moving from the light emitting layer 5 from reaching the cathode and a function of efficiently transporting injected electrons toward the light emitting layer 5. It is. According to the stacked body L4 including the hole blocking layer 6, electrons and holes in the light emitting layer 5 can be recombined more efficiently. As in the case of the stacked body L1, when measuring the emission quantum yield, the stacked body L4 is formed on a quartz substrate.
Moreover, as shown by a dotted line, an organic EL element including the laminate L4 is formed by forming an anode and a cathode so as to sandwich the laminate L4. In other words, the anode L, the hole injection layer 3, the light emitting layer 5, the hole blocking layer 6, the electron transport layer 7, and the cathode are stacked in this order to provide the stacked body L4. An organic EL element is formed.

Moreover, the structure of a laminated body is not limited to the laminated bodies L1-L4 mentioned above, The structure which combined these and the structure which added another functional layer may be sufficient. In other words, it may be a multilayer structure including at least a light emitting layer and having a plurality of organic functional layers laminated. For example, the stacked body L3 in FIG. 2C may have a configuration in which the hole transport layer 4 in FIG. 2B is added between the hole injection layer 3 and the light emitting layer 5.
In the following description, the generic name of the laminated bodies L1 to L4 is also referred to as “laminated body L”.

"Materials for organic functional layers"
The material of each organic functional layer constituting the laminate L described above may be a material that can form a multilayer structure, and may be a low molecular material or a polymer material. In addition, when using a low molecular material, it is preferable to form each organic functional layer using vapor deposition methods, such as a vacuum vapor deposition method, for example. Further, a laser transfer method may be used.
In the present embodiment, a laminate is formed using a polymer material. Specifically, the laminate is formed by an inkjet method using a solution in which a polymer material (solute) is dissolved in a solvent as ink. In addition, application | coating of a solution is not limited to the inkjet method, What is necessary is just the method which can apply | coat a solution. For example, a dispenser method such as a jet dispenser method or a needle dispenser method can also be used. Alternatively, a casting method or a spin coating method may be used.

Hereinafter, preferable examples of the polymer material as the material of each organic functional layer will be listed.
First, the solvent of the solution will be described.
As the solvent, aromatic solvents such as toluene, benzene, xylene, trimethylbenzene, tetralin, 3-phenoxytoluene, cyclohexylbenzene, dichlorobenzene, and trichlorobenzene can be used. Further, ether solvents such as tetrahydrofuran, ethyl ether, diisopropyl ether, ethylene glycol, ethylene glycol diethyl ether, dioxane, and anisole, and halogenated hydrocarbon solvents such as methylene chloride, chloroform, and carbon tetrachloride may be used. Also, hydrocarbon solvents such as pentane, hexane, heptane and cyclohexane, ketone solvents such as acetone, N-methyl-2-pyrrolidinone, methyl ethyl ketone, tetralone and cyclohexanone, and ester solvents such as ethyl acetate and butyl acetate. Also good. Further, alcohol solvents such as methanol, ethanol and isopropyl alcohol, nitrile solvents such as acetonitrile, amide solvents such as dimethylformamide and dimethylacetamide, sulfur compound solvents such as dimethyl sulfoxide, and water may be used.
A solution obtained by mixing two or more of these solvents may be used as the solvent.

Subsequently, the material of the hole injection layer 3 will be described.
As a material of the hole injection layer 3, polythiophene, polyaniline, polypyrrole, 3,4-polyethylenediosithiophene / polystyrene sulfonic acid (PEDOT / PSS) can be used. Further, these substances are used as a solution in a glycol solvent such as ethylene glycol or diethylene glycol. As a preferred example, PEDOT / PSS is dissolved in an ether solvent.
Also, copper phthalocyanine TAPC, (1,1-bis [4- (di-p-tolyl) ami.nophenyl] cyclohexane)) TPD N, N'-diphenyl-N, N'-bis- (3-methylphenyl) -1,1′biphenyl-4,4′-diamine, α-NPDN, N′-diphenyl-N, N′-bis- (1-naphthyl) -1,1′biphenyl-4,4′-diamine, m -MTDATA, 4,4 ', 4 "-tris (3-methylphenylphenylamino) triphenylamine 2-TNATA, 4,4', 4" -tris (N, N- (2-naphthyl) phenylamino) tri Phenylamine TCTA, Tris- (4-carbazoyl-9-yl-phenyl) -amine spiro TAD, (DTP) DPPD, HTM1, Tri-p-tolylamineHTM2,1,1-bis [(di-4-tolylamino) phenyl] CyclohexaneTPT1, 1,3,5-tris (4-pyridyl) -2,4,6-triazinTPTE, triphenylamine-tetramer, and the like can also be used.

Next, the material of the hole transport layer 4 will be described.
Examples of the material for the hole transport layer 4 include polyfluorene derivatives (PF), polyparaphenylene vinylene derivatives (PPV), polyparaphenylene derivatives (PPP), polyvinylcarbazole (PVK), polythiophene derivatives, polymethylphenylsilane (PMPS). ) -Containing polymer organic materials such as polysilanes can be used. Further, materials used for the hole injection layer, for example, materials such as TAPC, TPD, α-NPD, m-MTDATA, 2-TNATA, TCTA, spiro TAD, (DTP) DPPD, HTM1, and TPTE may be used. .

Next, the material of the light emitting layer 5 will be described.
First, a polyfluorene derivative, a polyphenylin derivative, or a polyphenylene vinylene derivative can be used as the high-molecular fluorescent material. Preferable examples include ADS109GE, ADS111RE, and ADS136BE (all are trademarks) manufactured by American Dice Source.
When a low molecular material is used, the light emitting layer 5 is composed of a host material and a guest material.
As host materials, CBP (4,4′-bis (9-dicarbazolyl) -2,2′-biphenyl), BAlq (Bis- (2-methyl-8-quinolinolate) -4- (phenylphenolate) aluminium), mCP (N, N-dicarbazolyl-3,5-benzene: CBP derivative), CDBP (4,4'-bis (9-carbazolyl) -2,2'-dimethyl-biphenyl), DCB (N, N'-Dicarbazolyl- 1,4-dimethene-benzene), P06 (2,7-bis (diphenylphosphine oxide) -9,9-dimethylfluorene), SimCP (3,5-bis (9-carbazolyl) tetraphenylsilane), UGH3 (W-bis (triphenylsilyl) ) benzene) or the like.
As phosphorescent materials in guest materials, Ir (ppy) 3 (Fac-tris (2-phenypyridine) iridium), Ppy2Ir (acac) (Bis (2-phenyl-pyridinato-N, C2) iridium (acetylacetone), Bt2Ir (acacone) ) (Bis (2-phenylbenxothiozolato-N, C2 ') iridium (III) (acetylacetonate)), Btp2Ir (acac) (Bis (2-2'-benzothienyl) -pyridinato-N, C3) Iridium (acetylacetonate), FIrpic ( Iridium-bis (4,6difluorophenyl-pyridinato-N, C.2.)-Picolinate), Ir (pmb) 3 (Iridium-tris (1-phenyl-3-methylbenzimidazolin-2-ylidene-C, C (2) ' ), FIrN4 ((((Iridium (III) bis (4,6-difluorophenylpyridinato) (5- (pyridin-2-yl) -tetrazolate), Firaz ((Iridium (III) bis (4,6-difluorophenylpyridinato) (5- (pyridine-2-yl) -1,2,4-triazo-late), PtOEP (2,3,7,8,12,13,17,18-Octaethyl-21H, 23H-porphine, platinum (II), etc. Can be used.

As the fluorescent material in the guest material, Alq3 (8-hydroxyquinolinate) aluminum, rubrene, perylene, 9,10-diphenylanthracene, tetraphenylbutadiene, Nile red, coumarin 6, quinacridone, and the like can be used.
Note that the host material is not limited to the method of doping the guest material, and these materials may be used alone as the light emitting layer.

Next, the material of the hole blocking layer 6 will be described.
As the hole blocking layer 6, BALq, OXD-1, 1,5-tri (5- (4-tert-butylphenyl) -1,3,4-oxadiazole), BCP (Bathocuproine), PBD ( 2- (4-biphenyl) -5- (4-tert-butylphenyl) -1,2,4-oxadiazole, TAZ (3- (4-biphenyl) -5- (4-tert-butylphenyl)- 1,2,4-triazole, DPVBi4,4'-bis (1,1-diphenylethenyl) biphenyl, BND 2,5-bis (1-naphthyl) -1,3,4-oxadiazole, DTVBi 4, 4′-bis (1,1-bis (4-methylphenyl) ethenyl) biphenyl, BBD 2,5-bis (4-biphenylyl) -1,3,4-oxadiazole, etc. can be used. An oxadiazole polymer compound or a triazole polymer compound may be used.

Next, the material of the electron transport layer 7 will be described.
As the electron transport layer 7, Alq3 (8-hydroxyquinolinate) aluminum, oxadiazole derivative, oxazole derivative, phenanthoroline derivative, anthraquinodimethane derivative, benzoquinone derivative, naphthoquinone derivative, anthraquinone derivative, tetracyanoanthraquinodimethane Derivatives, fluorenone derivatives, diphenyldicyanoethylene derivatives, diphenoquinone derivatives, hydroxyquinoline derivatives, and the like can be used. The material of the hole blocking layer 6 described above can also be used as the material of the electron transport layer 7.

Next, materials for the anode and the cathode that are required when each laminate is used as an organic EL element will be described.
As the anode, a transparent electrode such as ITO (Indium Tin Oxide) or ZnO (zinc oxide) can be used.
As the cathode, lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, aluminum, copper, silver, gold or the like, or an alloy thereof can be used. Alternatively, a multilayer body in which aluminum (Al) is stacked on a layer made of cesium carbonate (Cs2CO3) or lithium fluoride (LiF), or an alloy such as magnesium silver (MgAg) may be used. In the case of the top emission type, since light is emitted from the cathode side, a half-mirror-like metal thin film formed so thin as to allow light to pass through the aforementioned alloy such as MgAg is used as the cathode.

"Measurement method of luminescence quantum yield"
FIG. 3 is a schematic diagram of an apparatus for measuring the emission quantum yield.
Here, a method for measuring the emission quantum yield of the laminate described in FIG. 2 will be described.

As shown in FIG. 3, the light emission quantum yield of the stacked body L is measured using a measuring apparatus 200 including an integrating sphere 110.
The measuring device 200 includes an integrating sphere 110, a light source device 120, an irradiation light spectroscope 130, a spectroscopic detector 140, an analysis computer 150, etc., and measures the fluorescence spectrum by using a spectroscopic method. It is a measuring device that derives the light emission quantum yield from the result by software processing.
The integrating sphere 110 is a sphere in which one surface of the sphere is a diffuse reflection surface, and includes a light incident port 111, a sample carry-in port 112, a light receiving sensor 113 as a light receiving unit, and the like. In FIG. 3, a side sectional view of the integrating sphere 110 is shown.
The light source device 120 includes a light source such as a xenon lamp or a halogen lamp, and a power supply circuit for lighting these light sources.
The irradiation light spectroscope 130 splits light emitted from the light source of the light source device 120 and outputs light having a predetermined wavelength to the light guide tube 135 as irradiation light having a predetermined intensity.
The light guide tube 135 is a light guide tube (unit) such as a glass fiber, and guides the irradiation light generated by the irradiation light spectroscope 130 to the light incident port 111 of the integrating sphere 110.

A light incident port 111 is provided on the upper surface (ceiling side) of the integrating sphere 110, and a sample carry-in port 112 is formed on the lower surface (bottom surface). The light receiving sensor 113 is composed of an optical sensor such as a CCD (Charge Coupled Device), and is arranged in the middle of the side surface of the integrating sphere 110.
A laminated body L formed on the quartz substrate 10 as a transparent substrate is set inside the sample carry-in port 112, and the laminated body L has an end portion ( Irradiation light (outlined arrow) is emitted from the light source unit. The transparent substrate is not limited to the quartz substrate 10 and may be a transparent substrate, for example, inorganic glass. The laminated body L is excited by the irradiation light and emits fluorescence corresponding to the wavelength and intensity of the irradiation light. The emitted fluorescence has a substantially uniform intensity distribution in the integrating sphere 110 including the installation site of the light receiving sensor 113 and is detected (detected) by the light receiving sensor 113. In addition, it is not limited to the laminated body L which radiates | emits fluorescence, The laminated body L which radiates | emits phosphorescence may be sufficient. In other words, the stacked body L may emit phosphorescence.
Further, in the integrating sphere 110, a light shielding plate 114 is formed on a straight line connecting the light incident port 111 and the light receiving sensor 113 so that the irradiation light does not directly enter the light receiving sensor 113.

The fluorescence sensing data sensed by the light receiving sensor 113 is input to the spectroscopic detector 140, and the fluorescence spectrum is measured. Then, the fluorescence spectrum measurement data is transmitted to the analysis computer 150.
The analysis computer 150 is installed with a program for deriving the emission quantum yield. The analysis computer 150 starts the program, inputs the wavelength and intensity of the irradiation light, and the fluorescence spectrum measurement data from the spectroscopic detector 140 to derive the emission quantum yield.
In the present embodiment, the emission quantum yield is defined as the ratio of the number of emitted photons to the absorbed photons in the laminate L. The derived light emission quantum yield is an index indicating the light emission efficiency, and is represented by a numerical value within 0 to 1.0. The larger the numerical value, the higher the light emission efficiency.

“Evaluation Method of Laminate and Manufacturing Method of Organic EL Element”
4 (a) and 4 (b) are diagrams showing an aspect of the laminated body in the evaluation example, and correspond to FIG. 2 (b). FIG. 5 is a flowchart showing a flow of a method for evaluating a laminated body (organic EL element).
First, the structure of the laminated body in an evaluation example is demonstrated using FIG. 4 (a), (b).

In the evaluation method according to the present embodiment, for the flow of performing comparative evaluation after obtaining the respective light emission quantum yields using the reference laminate as a reference for evaluation determination and the evaluation laminate of the evaluation target to be evaluated. Prior to the description of the evaluation method, the configuration of the laminated body in the evaluation example based on the laminated body L2 described in FIG.
The reference laminate L2a in FIG. 4A is the same as the laminate L2 in FIG. 2B, but is referred to as a reference laminate L2a here for convenience of explanation. Moreover, the evaluation laminated body L2b of FIG.4 (b) differs from the reference | standard laminated body L2a only in the structure of a positive hole transport layer. In detail, the light emitting material which comprises the light emitting layer 5 is added to the positive hole transport layer 4b of the evaluation laminated body L2b. In other words, the hole transport layer 4b is composed of a mixed material obtained by adding a light emitting material to the material that constitutes the original hole transport layer. The structure of the evaluation laminated body L2b other than this point is the same as that of the reference laminated body L2a.

Subsequently, the flow of the evaluation method will be described with reference to FIG.
In step S1, the reference laminate L2a is set on the integrating sphere 110 of the measuring apparatus 200 of FIG.
In step S2, the light emission quantum yield is measured by irradiating the reference laminate L2a with illumination light. Here, the wavelength of the illumination light as the predetermined wavelength is determined in advance according to the color light emitted from the single light emitting layer 5 in the reference laminate L2a. This may be determined based on, for example, the absorption spectrum of the light emitting layer 5 provided by the vendor, or may be determined by measuring the absorption spectrum of only the light emitting layer 5 using the measuring device 200. It is preferable to use a wavelength that exhibits the maximum fluorescence intensity in the fluorescence emitted from the single light emitting layer 5.

In step S3, the evaluation laminated body L2b is set on the integrating sphere 110 of the measuring apparatus 200 of FIG.
In step S4, the evaluation stacked body L2b is irradiated with illumination light, and the emission quantum yield is measured. The illumination light is the same as the illumination light described in step S2. In other words, the irradiation light having the same wavelength and the same intensity as the irradiation light in step S2 is irradiated.
In step S5, the light emission quantum yield in the evaluation laminated body L2b is compared with the light emission quantum yield in the reference laminated body L2a. Specifically, when the ratio between the emission quantum yield in the evaluation stacked body L2b and the emission quantum yield in the reference stacked body L2a satisfies ≧ 1.0 (S5: Yes), the evaluation ends. If the ratio is less than 1.0 (S5: No), the process proceeds to step S6. In other words, the evaluation step ends when the correlation between the light emission quantum yields satisfies the following mathematical formula (1).
Emission quantum yield of evaluation laminate L2b / Emission quantum yield of reference laminate L2a ≧ 1.0 (1)

In step S6, the evaluation laminated body L2b is replaced with another sample prepared in advance, or a new evaluation laminated body L2b is created, and the process returns to step S3.
Another sample is a sample having a different configuration or manufacturing method from the evaluation laminate L2b evaluated first. For example, the samples may be different in the amount of the light emitting material added to the hole transport layer 4b, or may be samples manufactured by different manufacturing methods even if the layers are the same material.
In addition, when newly creating, the evaluation laminated body L2b evaluated first, such as making the addition amount of the light emitting material different or adjusting the interface state between the hole transport layer 4b and the light emitting layer 5 by the production method, The samples are different in structure and manufacturing method.

In the evaluation step, the comparison up to the emission quantum yield in step S5 corresponds to the evaluation method in the present embodiment. And the branching routine including the mathematical expression (1) in step S5 and step S6 corresponds to the manufacturing method in the present embodiment.
In the above description, the configuration based on the laminate L2 in FIG. 2B has been described as an evaluation example, but the configuration is not limited to this, and the configuration based on any laminate L in FIG. May be. In addition, for example, evaluation can be performed between different stacked bodies L, such as the stacked body L1 and the stacked body L4.

As described above, according to the evaluation method and the manufacturing method according to the present embodiment, the following effects can be obtained.
According to this evaluation method, the light emission quantum yield, which is an index of the light emission efficiency of the organic EL element, is measured in the state of the laminated body L. Measurement and evaluation can be performed. In other words, accurate light emission efficiency can be obtained by measuring the light emission quantum yield in the state of the same stacked body L as the actual element configuration.
Therefore, it is possible to provide an evaluation method capable of accurately measuring the light emission efficiency of the organic EL element. In particular, since the light emission capability as an organic EL element is not uniquely determined only by the light emitting layer, the light emission of the element can be evaluated by evaluating in the state of a laminate including an organic functional layer such as a hole injection layer. The ability of efficiency can be determined.
Furthermore, since the evaluation is performed in a state where a plurality of organic functional layers are laminated on the transparent substrate, it is not necessary to form a cathode and an anode electrode, and the evaluation can be performed efficiently. Further, the measurement of the light emission quantum yield can be easily performed because it is only necessary to set the quartz substrate on which the laminate L is formed in the integrating sphere 110 of the measuring apparatus 200.
Therefore, it is possible to provide an evaluation method capable of accurately and efficiently measuring the light emission efficiency of the organic EL element.

In addition, by setting the wavelength of the irradiation light to the wavelength at the maximum fluorescence intensity at which the fluorescence emitted from the light emitting layer 5 has the maximum fluorescence intensity, the SN ratio of the measured fluorescence spectrum is increased, so that more accurate emission quantum collection is achieved. The rate can be determined.
Moreover, since the process (step S5) which compares the light emission quantum yield in an evaluation laminated body with the light emission quantum yield in a reference | standard laminated body is included, the light emission efficiency of an evaluation laminated body and the light emission efficiency of a reference | standard laminated body are obtained. Comparative evaluation is possible.
Therefore, it is possible to improve the evaluation laminated body so that the luminous efficiency of the evaluation laminated body is higher than the luminous efficiency of the reference laminated body.

Moreover, according to the manufacturing method using the evaluation method described above, the ratio between the emission quantum yield in the evaluation laminate and the emission quantum yield in the reference laminate satisfies ≧ 1.0 (Equation (1)). In addition, an evaluation laminate is formed.
That is, by satisfying the mathematical formula (1) using the evaluation method, an evaluation laminated body having higher luminous efficiency than the reference laminated body can be manufactured.
Therefore, it is possible to provide an evaluation method capable of manufacturing an organic EL element having excellent light emission efficiency and a manufacturing method using the evaluation method.

  Note that the present invention is not limited to the above-described embodiment, and various modifications and improvements can be added to the above-described embodiment. A modification will be described below.

(Modification)
This will be described with reference to FIG.
In the said embodiment, although the light emitting layer 5 in each laminated body L demonstrated as what is single layer structure, it may be comprised from multiple layers.
For example, the light-emitting layer 5 may be a stacked light-emitting layer in which a plurality of light-emitting layers that emit a plurality of different color lights are stacked. Moreover, the boundary (interface) of each layer in the laminated light emitting layer may not be clearly separated, and both materials may be mixed.
For example, when a low molecular material is used, when the light emitting layer 5 is vapor deposited, a plurality of vapor deposition sources are provided, and a material corresponding to a plurality of different colored lights is set in each vapor deposition source, whereby the light emitting layer is formed by co-vapor deposition. 5 may be formed. In the case of a polymer material, the light emitting layer 5 may be formed using a solution in which materials corresponding to a plurality of different colored lights are dissolved together.
According to these configurations, it is possible to efficiently form a light-emitting layer that emits white light or the like in which a plurality of color lights are mixed, and according to the evaluation method of the present application, a laminate including these light-emitting layers. The luminous efficiency of (organic EL element) can be measured accurately.

Example 1
“Examples of different configurations of laminates”
The reference laminated body L2a of FIG. 4A and the evaluation laminated body L2b of FIG. 4B were manufactured as follows and evaluated along the flowchart of FIG.
The constituent materials of each organic functional layer in the reference laminate L2a are as follows.
PEDOT / PSS was used for the hole injection layer 3.
For the hole transport layer 4, TFB was used.
A polyfluorene derivative was used for the light emitting layer 5.

Moreover, the manufacturing method of each organic functional layer is as follows.
A method for forming the hole injection layer 3.
A PEDOT / PSS in which 3,4-polyethylenedioxythiophene, which is a polythiophene derivative, is dispersed in polystyrene sulfonic acid on a quartz substrate, and further dispersed in water by spin coating, to form a 50 nm hole. An injection layer 3 was obtained.
A method for forming the hole transport layer 4.
Poly (2,7- (9,9-di-n-octylfluorene)-(1,4-phenylene-((4-methylphenyl) imino) 1,4-phenylene-((4-methylphenyl) imino- 1,4-phenylene) (TFB) is dissolved in a xylene solution, applied onto the hole injection layer 3 by spin coating, and then heated at 180 ° C. for 1 hour in a nitrogen atmosphere to transport 20 nm holes. Layer 4 was obtained.
A method for forming the light emitting layer 5.
On the hole transport layer 4, a blue light emitting polyfluorene derivative of 60 nm was formed by spin coating, and then heated at 100 ° C. for 30 minutes in a nitrogen atmosphere to form the light emitting layer 5.

The constituent materials of each organic functional layer in the evaluation laminate L2b are as follows.
PEDOT / PSS was used for the hole injection layer 3.
For the hole transport layer 4b, a material obtained by adding a polyfluorene derivative to TFB was used.
A polyfluorene derivative was used for the light emitting layer 5.
That is, the configuration of the evaluation stacked body L2b is different from the configuration of the reference stacked body L2a only in the hole transport layer 4b.
Moreover, the manufacturing method of the evaluation laminated body L2b differs only in the manufacturing method of the reference | standard laminated body L2a, and the manufacturing method of the positive hole transport layer 4b. The manufacturing method of the positive hole transport layer 4b is shown below.
A film forming method of the hole transport layer 4b.
Poly (2,7- (9,9-di-n-octylfluorene)-(1,4-phenylene-((4-methylphenyl) imino) 1,4-phenylene-((4-methylphenyl) imino- 1,4-phenylene) (TFB) and a polyfluorene derivative, which is a blue light-emitting material, are mixed in a 50:50 weight ratio and dissolved in a xylene solution. After coating, heating was performed at 180 ° C. for 1 hour in a nitrogen atmosphere to obtain a 20 nm hole transport layer 4b.

The measurement and evaluation results of the reference laminate L2a and the evaluation laminate L2b were as follows. The wavelength of the illumination light was 365 nm.
The emission quantum yield of the reference laminate L2a was 0.70 (70%).
The light emitting quantum yield of the evaluation laminated body L2b was 0.84 (84%).
When this result was substituted into Formula (1), it was 0.84 / 0.70 = about 1.2, and the condition of 1.0 or more was satisfied.

Furthermore, an anode and a cathode were formed on each laminate, and current was actually passed to measure current efficiency. Moreover, ITO was used for the anode and Ca / Al was used for the cathode. Note that current efficiency is also one of the indexes that represent light emission efficiency.
The current efficiency of the reference laminate L2a was 3.3 cd / A.
The current efficiency of the evaluation laminated body L2b was 4.3 cd / A.
Further, the current efficiency of the evaluation laminated body L2b / the current efficiency of the reference laminated body L2a = 4.3 / 3.3 = 1.3, which is a ratio substantially equal to about 1.2 obtained by the equation (1). It was confirmed that In other words, it was confirmed that the evaluation result by the laminate substantially coincides with the evaluation result in the completed state.

(Example 2)
"Examples of different laminate manufacturing methods"
Also in Example 2, the evaluation was performed in the same manner as in Example 1 using the reference laminate L2a in FIG. 4A and the evaluation laminate L2b in FIG. 4B.
In Example 2, only the manufacturing method of evaluation laminated body L2b differs from Example 1. FIG. Specifically, after forming the hole transport layer 4b of the evaluation laminate L2b, a cleaning process for cleaning the surface of the layer is added. Except for this point, the configuration, manufacturing method, and evaluation method of the reference laminate L2a are the same as in Example 1.

The cleaning process added after the film formation of the hole transport layer 4b is as follows.
The hole transport layer 4b was baked at 100 ° C. for 30 minutes, and then rinsed with toluene in an inert atmosphere.
And following the washing | cleaning process, the measurement result of the light emission quantum yield of the evaluation laminated body L2b which formed the light emitting layer 5 into a film with the manufacturing method mentioned above was as follows.
The light emission quantum yield of the evaluation laminated body L2b was 0.95 (95%).
When this result was substituted into Equation (1), 0.95 / 0.70 = 1.36, which satisfied the condition of 1.0 or more.

Furthermore, an anode and a cathode were formed on each laminate, and current was actually passed to measure current efficiency.
The current efficiency of the evaluation laminated body L2b was 5.4 cd / A.
That is, by adding the cleaning process, the current efficiency of the evaluation stacked body L2b is improved from 4.3 cd / A in Example 1 to 5.4 cd / A. This is considered to be because the impurities on the surface of the hole transport layer 4b are removed by the cleaning process, and the extinction portion is reduced.

  DESCRIPTION OF SYMBOLS 3 ... Hole injection layer, 4 ... Hole transport layer, 5 ... Light emitting layer, 6 ... Hole blocking layer, 7 ... Electron transport layer, 110 ... Integrating sphere, 113 ... Light receiving sensor as light receiving part, 200 ... Measuring apparatus , L, L1 to L4 ... laminate, L2a ... reference laminate, L2b ... evaluation laminate.

Claims (4)

(A) forming a plurality of organic functional layers including at least a light emitting layer on a transparent substrate;
(B) irradiating light having a predetermined wavelength to the laminate composed of the plurality of organic functional layers;
(C) measuring the fluorescence spectrum of the fluorescence emitted by the laminate in response to the irradiated light, and deriving the emission quantum yield of the laminate, Evaluation method. The transparent substrate is a quartz substrate;
The steps (b) and (c) are performed in an integrating sphere including a light source unit that emits light of the predetermined wavelength and a light receiving unit that senses fluorescence emitted from the laminate.
2. The method for evaluating an organic EL element according to claim 1, wherein the predetermined wavelength is a wavelength at a maximum fluorescence intensity measured in advance so that the fluorescence emitted from the light emitting layer has a maximum fluorescence intensity. (A) to (c) in each of the reference laminate that is the laminate in the organic EL element that is a criterion for evaluation and the evaluation laminate that is the laminate in the organic EL element that is an evaluation target. )
(D) The organic EL device according to claim 1, further comprising a step of comparing the emission quantum yield in the evaluation laminate with the emission quantum yield in the reference laminate. Evaluation method.   The evaluation method according to claim 3, wherein the evaluation laminate is adjusted so that a ratio of the emission quantum yield in the evaluation laminate and the emission quantum yield in the reference laminate satisfies ≧ 1.0. A method for producing an organic EL element, comprising forming the organic EL element.

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