JP2013163708A - Ink composition for organic el and method for producing organic el element using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink composition for organic ELs that contains 1,3,5-tris[N, N-bis(4'-methyl-4-biphenylyl)amino]benzene (compound A), which is a substance with hole transport performance and of poor solubility, and can suitably make a film by printing.SOLUTION: An ink composition for organic ELs includes a substance with hole transport performance, printed on a substrate 10 to form a hole transport layer 30 in an organic EL element S1 in which an organic layer 60 having the hole transport layer 30 and an light emitting layer 40 is formed on the substrate 10. The ink composition for organic ELs includes compound A as a substance, and a solvent which contains 1-bromonaphthalene as a component of a maximum weight, and compound A is dissolved or dispersed homogeneously in the solvent.

Description

  The present invention relates to a substance having a hole transporting property printed on a substrate in order to form a hole transport layer in an organic EL device formed by forming an organic layer including a hole transport layer and a light emitting layer. It is related with the manufacturing method of the organic EL element using the ink composition for organic EL containing, and such an ink composition for organic EL.

  In general, an organic EL element is formed on a substrate by sequentially laminating a lower electrode, an organic layer, and an upper electrode from the substrate side. Here, the organic layer generally has a layered structure in which a hole transport layer and a light emitting layer made of an organic EL (electroluminescence) material are sequentially stacked from the lower electrode side (substrate side). .

  These electrodes and each layer of the organic EL element are formed by a film forming method in a vacuum atmosphere such as sputtering or vapor deposition. On the other hand, in recent years, film formation by printing has also been proposed from the standpoint of reducing material waste due to sputtering and vapor deposition and reducing costs.

  Here, in the hole transport layer of the organic layer, 1,3,5-tris [N, N-bis (4′-methyl-4-biphenylyl) amino] benzene (a substance having a hole transport property) ( As the molecular structural formula, see FIG. 2 described later) is employed (see Patent Document 1). Hereinafter, this substance is referred to as Compound A.

  However, since this compound A is difficult to dissolve in a solvent and is hardly soluble, it is difficult to form a printing ink, so that it has been conventionally formed by vacuum deposition.

  On the other hand, as a method for forming a film by printing in an organic EL element, a method for printing an ink composition made of a polymerizable conductive material has been proposed (see Patent Document 2). In this product, the printed matter is polymerized by light irradiation or the like.

JP 2010-56364 A JP 2007-197587 A

  However, in forming an organic layer in an organic EL element by printing, when a polymerizable material such as Patent Document 2 described above is used, unpolymerized portions remain after film formation, which may reduce reliability. is there. Therefore, the above-described compound A is desired to be formed by printing. As described above, since this compound A is hardly soluble, film formation by printing has not been realized.

  The present invention has been made in view of the above problems, and provides an organic EL ink composition that includes Compound A, which is a poorly soluble substance having hole transportability, and can be appropriately formed into a film by printing. And it aims at providing the manufacturing method of the organic EL element using the said ink composition for organic EL.

  In order to achieve the above-mentioned object, the inventors have intensively studied to make the solvent capable of dissolving the compound A at a temperature below the flash point of the solvent to a concentration necessary for film formation by printing.

  In the case where the compound A is dissolved at a temperature equal to or higher than the flash point of the solvent, printing is performed at a temperature equal to or higher than the flash point in order to prevent the precipitation of the compound A. Then, when oxygen is present in the atmosphere during printing, the solvent may ignite during the printing.

  Therefore, attention was focused on a solvent that can dissolve compound A at a temperature below the flash point of the solvent to a concentration necessary for film formation by printing. And based on this attention point, as a result of examining solubility, film-forming property, etc. about various solvents, it discovered that 1-bromo naphthalene was suitable as a solvent.

The invention according to claim 1 was created based on the results of this study, and an organic layer (60) including a hole transport layer (30) and a light emitting layer (40) on a substrate (10). Organic EL ink composition containing a substance having a hole transporting property printed on the substrate (10) in order to form the hole transport layer (30) in the organic EL element (S1) formed by forming Because
It comprises a compound A represented in FIG. 2 described later as a substance and a solvent containing 1-bromonaphthalene as the most multiple amount component, and the compound A is dissolved or uniformly dispersed in the solvent. And

  In 1-bromonaphthalene in the present invention, compound A dissolves at a concentration sufficient for film formation by printing at a flash point (109 ° C.) or less of 1-bromonaphthalene. Therefore, according to the present invention, it is possible to provide an organic EL ink composition that includes the compound A that is a poorly soluble substance but has a hole transport property and can be appropriately formed by printing.

In the invention according to claim 3, an organic layer (layer) in which a lower electrode (20), a hole transport layer (30), and a light emitting layer (40) are laminated on a substrate (10) in this order from the substrate (10) side. 60), a method for producing an organic EL device in which the upper electrode (50) is formed in order, a preparation step of preparing an organic EL ink composition containing a substance having hole transportability, and hole transport A printing step of printing an organic EL ink composition to form the layer (30),
In the preparation step, the organic EL ink composition includes a compound A represented in FIG. 2 described later as a substance, and a solvent containing 1-bromonaphthalene as the most multiple amount component. An ink composition dissolved or uniformly dispersed in a solvent is prepared, and in the printing step, printing is performed at a temperature of 109 ° C. or lower which is a flash point of 1-bromonaphthalene.

  According to this, it is possible to provide a method for producing an organic EL device using the organic EL ink composition that includes the compound A that is a hole-transporting but hardly soluble substance and can be appropriately formed by printing. .

  In addition, the code | symbol in the bracket | parenthesis of each means described in the claim and this column is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.

It is a schematic sectional drawing which shows schematic sectional structure of the organic EL element concerning embodiment of this invention. It is a figure which shows the chemical structure of the compound A which comprises the positive hole transport layer in FIG. It is process drawing which shows the manufacturing method of the organic EL element in the said embodiment. It is a graph which shows the solubility characteristic with respect to the various solvent of the compound A. It is a graph which shows the relationship between the temperature in 1-bromo naphthalene, and the melt | dissolution density | concentration of the compound A. It is a graph which shows the luminance characteristic of the organic EL element of embodiment, and the organic EL element of a comparative example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other are given the same reference numerals in the drawings in order to simplify the description.

(First embodiment)
FIG. 1 is a diagram showing a schematic cross-sectional configuration of an organic EL element S1 according to the first embodiment of the present invention. The organic EL element S1 roughly includes an organic layer 60 in which a lower electrode 20, a hole transport layer 30, and a light emitting layer 40 are stacked in this order from the substrate 10 side, and an upper electrode 50 in that order. It becomes.

  Specifically, the organic EL element S of the present embodiment includes a lower electrode 20 as an anode disposed on one surface of a transparent substrate 10 and a hole transport layer disposed on a surface opposite to the substrate 10 in the lower electrode 20. 30, a light emitting layer 40 disposed on the surface of the hole transport layer 30 opposite to the upper electrode 20, and an upper electrode 50 serving as a cathode disposed on the surface of the light emitting layer 40 opposite to the hole transport layer 30. Here, the organic layer 60 is constituted by the hole transport layer 30 and the light emitting layer 40.

  The substrate 10 is made of a transparent substrate made of glass or plastic. The lower electrode 20 is transparent or translucent. As a constituent material of the lower electrode 20, a known conductive substance that is transparent or translucent and can form an electrode can be employed. In this embodiment, the lower electrode 20 made of indium tin oxide (ITO) is employed.

  A hole transport layer 30 is disposed on the surface of the lower electrode 20 opposite to the substrate 10. The hole transport layer 30 is configured as a film formed of the compound A shown in FIG. Specifically, the hole transport layer 30 is formed by a printing method using the compound A.

  With respect to this printing method, for example, a spin coating method, an ink jet method, a screen printing method, a spray method and the like can be mentioned. In the present embodiment, deaeration treatment is performed in a vacuum after printing in order to obtain a uniform film (for example, a thickness of several tens of nm) by suppressing the precipitation of needle crystals of Compound A during printing.

  In the hole transport layer 30 formed of the compound A, the hole transport layer 30 is not dissolved in a solvent when the polymer light emitting layer 40 is formed on the hole transport layer 30 by a printing method. . Therefore, the degree of freedom in selecting the constituent material of the light emitting layer 40 can be improved.

  The light emitting layer 40 is made of a polymer material having a LUMO value of less than 2.6 eV, such as polyfluorene. The light emitting layer 40 may be a single layer or may be configured by laminating a plurality of layers.

  In general, a material exhibiting an LUMO value of less than 2.6 eV has a higher molecular weight than a material having an LUMO value of 2.6 eV or more and is a polymer, and therefore cannot be formed by a vacuum deposition method. Therefore, the polymer light emitting layer 40 is formed by the same printing method as that for the hole transport layer 30. As a result, it is possible to reduce the vacuum vapor deposition step during the manufacturing process of the organic EL element S1 as compared with the configuration employing the light emitting layer 40 made of a low molecular material.

  The upper electrode 50 is in contact with the light emitting layer 40 and has a three-layer structure in which an electron injection layer 51, a first metal layer 52, and a second metal layer 53 are laminated in this order from the light emitting layer 40 side.

  As the electron injection layer 51, a material capable of forming an electric double layer at the interface with the light emitting layer 40 and thereby reducing the electron injection barrier can be employed. Such materials include alkali metal or alkaline earth metal fluorides. In the present embodiment, the electron injection layer 51 is made of LiF, which is an alkali metal fluoride.

  For the first metal layer 52, a material that can reduce the electron injection barrier at the interface with the light emitting layer 40 made of a polymer material (polymer material having a LUMO value of less than 2.6 eV) can be used. Examples of such a material include a metal having a small work function (in other words, a metal having a work function close to the LUMO value of the polymer of the light emitting layer 40), specifically, an alkali metal or an alkaline earth metal.

  In the present embodiment, the first metal layer 52 is made of Ca (work function 2.87 eV), which is an alkaline earth metal. The second metal layer 53 can be made of a material that is stable in the air and has low resistance. In the present embodiment, the second metal layer 53 is made of Al.

  In such an organic EL element S1, an electric field is applied between the lower electrode 20 serving as an anode and the upper electrode 50 serving as a cathode, so that holes are formed from the lower electrode 20 via the hole transport layer 30, whereas Electrons are respectively injected and transported from the electrode 50 to the light emitting layer 40, and electrons and holes are recombined in the light emitting layer 40, and the light emitting layer 40 emits light by the energy at that time. The emitted light is extracted from the substrate 10 side, for example.

  Next, a manufacturing method of the organic EL element S1 will be described with reference to FIG. In this manufacturing method, the organic EL 60 and the upper electrode 50 in which the lower electrode 20, the hole transport layer 30 and the light emitting layer 40 are laminated in this order from the substrate 10 side are formed on the substrate 10 in order, whereby the organic EL Element S1 is manufactured.

  First, in the substrate preparation step, the substrate 10 is prepared. Next, in the lower electrode formation step, the lower electrode 20 is formed by sputtering or the like. In the present embodiment, the lower electrode 20 made of ITO is formed by sputtering.

  Next, the hole transport layer 30 is formed. First, an organic EL ink composition containing a substance having a hole transporting property is prepared (preparation step). In this ink composition preparation step, the organic EL ink composition is composed of the compound A shown in FIG. 2 and a solvent containing 1-bromonaphthalene as the most multiple amount component, and the compound A is a solvent. An ink composition prepared by dissolving or uniformly dispersing in is prepared.

  Specifically, Compound A is dissolved in a solvent at a temperature of 109 ° C. or lower, which is the flash point of 1-bromonaphthalene. In 1-bromonaphthalene, compound A is dissolved at 0.5% by weight or more at a flash point of 109 ° C. or lower. This dissolved concentration is sufficient for film formation by printing. The hole transport layer 30 needs to have a film thickness of at least about several tens of nanometers. However, if the dissolution concentration is less than 0.5% by weight, the film thickness cannot be ensured.

  In the printing step, the organic EL ink composition is printed on the lower electrode 20 in order to form the hole transport layer 30. In this printing, each printing method described above is employed, and printing is performed at a temperature of 109 ° C. or lower, which is the flash point of 1-bromonaphthalene. In addition, this printing may be performed in the air, but it is desirable that the printing be performed in an inert gas such as nitrogen in order to minimize oxygen in the atmosphere.

  Next, the solvent is removed from the printed ink composition and dried. At this time, the solvent may be removed by heating, but it is desirable to deaerate at room temperature. In this embodiment, vacuum deaeration is performed and the solvent is removed.

  Subsequently, in the heat drying step, the material is heated and sufficiently dried. Thus, the hole transport layer 30 made of the compound A is formed on the lower electrode 20. Next, in the light emitting layer forming step, as described above, the polymer light emitting layer 40 is formed on the hole transport layer 30 by a printing method. In this way, the organic layer 60 is completed.

  Next, the electron injection layer 51, the first metal layer 52, and the second metal layer 53 are sequentially formed on the light emitting layer 40 by an evaporation method, thereby forming the upper electrode 50. Thus, the organic EL element S1 of this embodiment is completed.

  By the way, according to this embodiment, compound A and 1-bromonaphthalene are used as an organic EL ink composition containing a substance having a hole transporting property printed on the substrate 10 in order to form the hole transporting layer 30. And an organic EL ink composition in which Compound A is dissolved or uniformly dispersed in a solvent.

  As described above, the film thickness of the hole transport layer 30 is required to be several tens of nm or more. For this purpose, the concentration of the solute in the solvent is required to be at least 0.5% by weight or more. In that respect, in 1-bromonaphthalene, compound A is dissolved at a concentration (0.5% by weight or more) sufficient for film formation by printing below the flash point (109 ° C.) of 1-bromonaphthalene.

  Therefore, according to the ink composition for organic EL of the present embodiment, the hole transport layer 30 can be appropriately formed by printing, including the compound A that has a hole transport property but is a hardly soluble substance. An ink composition for organic EL is provided.

  And in the said manufacturing method of this embodiment, the preparation process which prepares the ink composition for organic EL which consists of the solvent which contains the compound A and 1-bromo naphthalene as a maximum multiple amount component, and the flash point of 1-bromo naphthalene. And a printing step of printing the organic EL ink composition to form the hole transport layer 30 at a certain temperature of 109 ° C. or lower.

  Here, even if the printing process is performed in an inert gas atmosphere, it is difficult to completely eliminate oxygen and it is difficult to avoid the presence of a small amount of oxygen. For this reason, even if oxygen is present in the printing atmosphere, the ink composition of this embodiment does not ignite because printing can be performed at a temperature below the flash point of the solvent. And sufficient film formation can be performed and the positive hole transport layer 30 which ensured the film thickness is formed.

  Further, in the manufacturing method of the present embodiment, after the printing step, the solvent is removed from the printed organic EL ink composition by performing vacuum deaeration at room temperature, and then drying by heating is performed to form holes. A transport layer 30 is formed.

  According to the study of the present inventor, when the solvent is removed from the printed organic EL ink composition by heating and evaporation, the needle crystals of the compound A are partially generated and the film quality is not uniform. It is easy to become. On the other hand, according to the study by the present inventor, it is easy to form a uniform film if the solvent is removed by vacuum degassing.

[Examples of solvent studies]
Next, examination examples conducted by the present inventor for various solvents will be described in selecting a solvent that can dissolve the compound A at a temperature below the flash point of the solvent to a concentration necessary for film formation by printing. Based on the following study example, 1-bromonaphthalene was reached.

  FIG. 4 shows the dissolution characteristics of Compound A in various solvents obtained as a result of the study of the present inventors. Here, the calculated solubility value Δδ shown on the horizontal axis in FIG. 4 was used as an index corresponding to the type of solvent.

  The calculated solubility value Δδ is an intrinsic physical property value of the solvent determined by the well-known Hansen method solubility parameter calculation. The smaller the value, the easier the compound A dissolves. That is, in FIG. 4, it means that the compound A is a solvent that is easily dissolved from the center of the horizontal axis toward the left side, and the compound A is a solvent that is less soluble as it goes to the right side.

  Also, the dissolution temperature (0.5 wt%) on the left vertical axis in FIG. 4 indicates the temperature at which Compound A is dissolved in a solvent at 0.5 wt% required for film formation. The relationship between the solubility calculated value Δδ and the dissolution temperature (unit: ° C.) is obtained by actual measurement, and is shown by a thick solid line graph in FIG. Moreover, the white triangular plot on the said solid line graph has shown the value of 1-bromo naphthalene. Further, the flash point (unit: ° C.) on the right vertical axis in FIG. 4 is an intrinsic physical property value of the solvent, and the relationship between the calculated solubility value Δδ and the flash point is shown by a broken line graph.

  In FIG. 4, the value circled is the value of 1-bromonaphthalene. As can be seen from this, 1-bromonaphthalene is the only solvent that can achieve the dissolution concentration (0.5% by weight) necessary for film formation below the flash point. On the other hand, with other solvents, a dissolution concentration of 0.5% by weight cannot be realized unless the temperature exceeds the flash point of the solvent. Thus, the present inventor selected 1-bromonaphthalene as a solvent.

  Regarding the relationship between the solvent temperature of 1-bromonaphthalene and the dissolved concentration of Compound A, as shown in FIG. 5, there is a linearly increasing proportional relationship between the temperature and the concentration. A concentration of 5% by weight is achieved, and at 109 ° C. a concentration of 1% by weight is achieved. That is, the ink composition of the present embodiment contains the compound in a ratio of 0.5 wt% to 1 wt% with respect to the total weight of the compound A and the solvent.

[Concrete example]
Next, the effect of this embodiment will be described in more detail with reference to a specific example of this embodiment.

  After forming ITO as a lower electrode 20 with a thickness of 150 nm on one surface of a transparent substrate 10 made of glass or the like, 1-bromonaphthalene (95% or more) as the organic EL ink composition is formed thereon. An ink composition having 0.5% by weight of Compound A dissolved therein was printed by spin coating.

  After this printing, the solvent is quickly removed by vacuum degassing at a vacuum degree of 0.1 Pa or less, and then a drying treatment is performed at 150 ° C. for 1 hour in a nitrogen atmosphere having a dew point temperature of −60 ° C. or less. A hole transport layer 30 having a thickness of 30 nm was formed.

  Next, Poly [(9,9-dioctylfluorenyl-2,7-diyl) -co- (1,4-benzo- {2,1 ′, 3} -thiazole)] (ADS233YE) manufactured by American Dye Source Co., Ltd. A polymer light emitting material having a weight average molecular weight of 40,000 after purification was dissolved in a xylene solvent to prepare a coating solution, and this coating solution was applied onto the hole transport layer 30 by spin coating. And it was set as the light emitting layer 40 of thickness 100nm by drying this at 120 degreeC.

  Next, LiF having a thickness of 1 nm was formed as the electron injection layer 51 by vacuum deposition, and then a first metal layer 52 made of Ca having a thickness of 2 nm was formed. Next, Al having a thickness of 100 nm was formed as the second metal layer 53 by a vacuum deposition method.

  Finally, the element was sealed by adhering a metal can (not shown) and the substrate 10 on which the element was formed in a glove box with a photocurable resin. Thus, an organic EL element S1 as a specific example of the present embodiment was produced.

(Comparative example)
As a comparative example, an organic EL device was produced in the same manner as in the above specific example except that the compound A was formed with a film thickness of 30 nm by a vacuum vapor deposition method and used as the hole transport layer 30.

  The luminance characteristics of the organic EL element S1 of the specific example thus formed and the organic EL element of the comparative example were evaluated. The result is shown in FIG.

As initial luminance characteristics, a current density (unit: mA / cm ² ) and luminance (unit: cd / m ² ) when a DC voltage of 10 V was applied between the upper and lower electrodes 10 and 50 were measured. Further, as luminance durability, the initial luminance is set to 1000 cd / m ² , the luminance after DC driving for 200 hours in an 85 ° C. environment is obtained, and the luminance decreases from the initial luminance of 1000 cd / m ^2. Expressed as a percentage.

As shown in FIG. 6, the initial luminance characteristics in the organic EL element S1 of the specific example of this embodiment are a current density of 25.9 mA / cm ² and a luminance of 1534 cd / m ² , and the initial luminance characteristics in the comparative example are The current density was 24.7 mA / cm ² and the luminance was 1710 cd / m ² . As for luminance durability, the present embodiment was 73% and the comparative example was 75%.

  As described above, the organic EL element S1 in which the hole transport layer 30 is formed by printing using the ink composition of the present embodiment has initial characteristics as compared with those in which the hole transport layer 30 is formed by conventional vacuum deposition. In addition, it was confirmed that the luminance characteristics were comparable with durability.

(Other embodiments)
In the above-described embodiment, the organic layer 60 is formed by laminating the hole transport layer 30 and the light emitting layer 40 in this order from the substrate 10 side. However, an electron is further provided between the light emitting layer 40 and the upper electrode 50. A transport layer may be interposed, and this electron transport layer may also constitute the organic layer 60.

  Further, in the above specific example, 1-bromonaphthalene having a purity of 95% or more was used as the solvent, but the solvent contains 1-bromonaphthalene as the most multiple amount component, and can be used for forming a film by printing below the flash point. What is necessary is just to be able to ensure a necessary dissolution concentration. Of course, 100% of 1-bromonaphthalene may be used.

DESCRIPTION OF SYMBOLS 10 Substrate 20 Lower electrode 30 Hole transport layer 40 Light emitting layer 50 Upper electrode 60 Organic layer

Claims (5)

In order to form the hole transport layer in the organic EL element (S1) formed by forming the organic layer (60) including the hole transport layer (30) and the light emitting layer (40) on the substrate (10). An organic EL ink composition containing a substance having a hole transporting property printed on the substrate,
Compound A represented by the following chemical formula 1 as the substance:

A solvent containing 1-bromonaphthalene as the most multiple amount component,
An ink composition for organic EL, wherein the compound A is dissolved or uniformly dispersed in the solvent.   2. The organic EL device according to claim 1, wherein the compound A is contained in a ratio of 0.5 wt% to 1 wt% with respect to a total weight of the compound A and the solvent. Ink composition. On the substrate (10), an organic layer (60) in which a lower electrode (20), a hole transport layer (30) and a light emitting layer (40) are laminated in order from the substrate side, and an upper electrode (50) are sequentially formed. A method for producing an organic EL element formed by:
A preparation step of preparing an organic EL ink composition containing a substance having a hole transporting property;
Printing the organic EL ink composition to form the hole transport layer, and
In the preparation step, as the organic EL ink composition, the compound A represented by the following chemical formula 2 as the substance:

A solvent containing 1-bromonaphthalene as the most multiple component, and preparing an ink composition in which the compound A is dissolved or uniformly dispersed in the solvent,
In the said printing process, it prints at the temperature below 109 degreeC which is a flash point of 1-bromo naphthalene, The manufacturing method of the organic EL element characterized by the above-mentioned.   In the preparation step, the compound A is contained in the organic EL ink composition in a proportion of 0.5 wt% to 1 wt% with respect to the total weight of the compound A and the solvent. What is prepared, The manufacturing method of the organic EL element of Claim 3 characterized by the above-mentioned.   After the printing step, the solvent is removed from the printed organic EL ink composition by performing vacuum deaeration at room temperature, and then drying by heating is performed to form the hole transport layer. The manufacturing method of the organic EL element of Claim 3 or 4 characterized by these.

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