JP2014169418A - Ink for charge transport membrane, aromatic oligo iodonium salt usable to charge transport membrane, and method for producing charge transport membrane using the ink for charge transport membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink for a charge transport membrane comprising an acceptor material including an aromatic iodonium salt and a charge transport material, and having high storage stability.SOLUTION: Provided is an ink for a charge transport membrane comprising: an acceptor material including an aromatic iodonium salt; a charge transport material having charge transportability; and a solvent. The solvent includes substituted or non-substituted alicyclic ketone and/or substituted or non-substituted alicyclic monohydric alcohol in 1/4 or more by a volume ratio.

Description

  The present invention relates to an ink for a charge transport film used for forming an organic charge transport film in a device such as an organic electroluminescent element (hereinafter also referred to as an organic EL element). The present invention also relates to an aromatic oligoiodonium salt that can be used in a charge transport film ink and a method for producing a charge transport film using the charge transport film ink.

  An organic EL element is an element that emits light by injecting electrons and holes into a thin film of a light emitting material containing an organic fluorescent material or a phosphorescent material and recombining them. A flat panel display using an organic EL element can easily obtain full color light emission of red, green and blue by the molecular design of the organic light emitting material. In addition, it is advantageous in that it is thin, lightweight, and emits light at a low direct current voltage. Further, there are advantages such as a high-speed response and a high-contrast moving image obtained by high contrast. Therefore, a display using an organic EL element is expected as a next-generation display that replaces a liquid crystal display. In particular, research and development has been vigorously conducted and put into practical use as next-generation display devices such as mobile phones and televisions.

Moreover, the organic EL element is also applied to a thin flat lighting device. Unlike point-emitting LEDs, illumination using organic EL elements is also expected as next-generation illumination that is gentle on the eyes.
A general method for manufacturing an organic EL element is performed by a mask vapor deposition method through a shadow mask. First, a transparent conductive film such as ITO (indium tin composite oxide) is formed on a glass plate by sputtering, and then patterned to form an anode. On the obtained anode, an organic layer composed of an organic hole injection layer, an organic hole transport layer, an organic light emitting layer, an organic electron transport layer and the like and a metal cathode are sequentially formed by a mask vapor deposition method. Finally, the obtained laminate is hermetically sealed with a glass plate or a metal plate.

The layer structure of the organic layer has been improved and changed as appropriate in order to improve the luminous efficiency and extend the lifetime. For example, a hole transport electron blocking layer may be provided between the hole transport layer and the organic light emitting layer, or an electron transport hole blocking layer may be provided between the organic light emitting layer and the electron transport layer.
When the hole transport property of the organic light emitting layer is stronger than the electron transport property, the recombination region of holes and electrons is shifted to the cathode side. In order to prevent deactivation of excitons by the metal cathode and penetration of holes into the cathode, a hole blocking electron transport layer may be provided and a hole transport electron blocking layer may not be provided. Conversely, when the electron transport property of the organic light emitting layer is stronger than the hole transport property, the recombination region is closer to the anode side. In order to prevent electrons from penetrating into the anode, a hole transporting electron blocking layer may be provided, and the electron transporting hole blocking layer may not be provided.

As a problem when the organic layer is formed by a vacuum evaporation method using a low molecular material, if there is a foreign object on the pixel electrode of the substrate, the film thickness of the part where the incident of the evaporation material is blocked It can be thinned. As a result, an electrical short circuit tends to occur between the anode and the cathode, which can cause defects.
Moreover, advanced technology is required to form a deposited film having a uniform composition on a large-area substrate by co-evaporation. Therefore, a film with non-uniform characteristics may be formed on the substrate.
For example, in order to reduce the resistance of the hole injection layer or the electron injection layer, co-evaporation may be performed using an acceptor material or a donor material containing an alkali metal component. In such a case, or when co-evaporating the host material and the light emitting dopant material in the light emitting layer, if a vapor deposition film having a uniform composition cannot be obtained, the resistance value of the film and the emission color will vary. Deterioration due to current concentration and element destruction may occur.

Further, patterning using a mask vapor deposition method tends to cause misalignment of the alignment accuracy due to deflection of the vapor deposition mask or thermal expansion, and advanced technology is required for high definition. In addition, this method has a problem that a large vacuum apparatus is required when a film is formed on a large area substrate for a large TV or the like, and the cost is increased.
In view of this, various methods for separately painting sub-pixels made of red, blue and green, or red, blue, green and white have been studied in the production of a light emitting layer of a large area color display. Examples of such a method include an inkjet method using a soluble low molecular weight material or a polymer material, a continuous nozzle printing method, a flexographic printing method, a laser thermal transfer method, and the like.

In order to prevent an electrical short circuit between the anode and the cathode caused by foreign matters or protrusions on the substrate, at least one organic layer is formed using a wet film formation method (for example, coating, printing, etc.). It is effective. The wet film forming method is excellent in coverage. In addition, it is desired that as many layers as possible can be formed by a wet film forming method in order to reduce the cost.
However, in order to form a light-emitting layer containing a low-molecular or high-molecular light-emitting material by a wet film formation method, each layer serving as a base of the light-emitting layer may not be dissolved in the organic solvent used in the ink for the light-emitting layer. is necessary.

As the organic solvent used in the ink for the light emitting layer, a solvent capable of dissolving the material of the light emitting layer is appropriately used. Generally, an aromatic hydrocarbon type such as toluene, xylene, anisole, or an aromatic ether type is used. An organic solvent such as an aromatic ester is used.
For this reason, a material that is hardly soluble in an organic solvent is used for the layer serving as the base of the light emitting layer. In the case where the base layer of the light emitting layer is a hole injection layer, for example, a conductive polymer (hereinafter, PEDOT / PSS) made of poly (3,4-ethylenedioxythiophene) and poly (styrenesulfonic acid). An aqueous suspension of fine particles, also referred to as PEDOT / PSS ratio (about 1: 6 to 1:20), is used as the ink for the hole injection layer. Since the film formed of this ink is hardly soluble in an organic solvent, mixing with the light emitting layer can be prevented.

  However, the ink containing PEDOT / PSS has strong acidity and is corrosive. Furthermore, since the film formed using this ink has high hygroscopicity, it may corrode the metal part of the machine. Further, if the substrate is left in a humid atmosphere after film formation, there is a risk of corroding the metal wiring on the substrate. In addition, since the ink containing PEDOT / PSS is an aqueous suspension of fine particles, it also has a problem that it is easily repelled during application. In order to avoid this problem, the aqueous suspension is diluted with alcohol or the like to lower the surface tension. However, in this case, the ink tends to cause aggregation and gelation, resulting in uniform formation. There was a further problem that the film could not be formed.

  Therefore, in order to form a laminated film in organic devices such as organic EL elements and organic thin-film solar cells without any problems by a wet film formation method, it is excellent in film formability and drying property, and the film is insoluble in an organic solvent after film formation. Alternatively, there is a need for charge transport film inks that are sparingly soluble. Moreover, it is preferable that a film having low resistance is obtained by the ink for charge transport film.

In a low molecular vapor deposition type organic EL device, a low molecular hole transport material as a host and a low molecular dopant material as an acceptor are co-evaporated to form a hole injection layer with low resistance. The hole transport material as a host is deprived of electrons by the acceptor molecule and becomes cationized, thereby increasing the carrier density and lowering the resistance.
Examples of the low molecular hole transport material include aromatic tertiary amines such as 4,4 ′, 4 ″ -tris [2-naphthyl (phenylamino)] triphenyl-amine (abbreviated as 2-TNATA). It is done. Moreover, as a low molecular dopant material, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (hereinafter also referred to as F4-TCNQ; Patent Document 1) and 2- ( 6-Dicyanomethylene-1,3,4,5,7,8-hexafluoro-6H-naphthalene-ylidene) malononitrile (hereinafter also referred to as F6-TNAP; Patent Document 2), etc. Is mentioned.

When the hole injection layer is formed into a wet film, the hole transporting polymer is doped with a Lewis acid such as tetraphenylantimony bromide (Non-patent Document 1) or FeCl ₃ as an acceptor material. A hole injection layer having a low thickness is formed.
However, these acceptor compounds are PRTR-regulated substances that are harmful to the human body, and Lewis acids such as FeCl ₃ have a problem that they are highly corrosive.
In addition, when a solvent-soluble low molecular weight compound is formed into a hole injection layer by a wet method, and a hole transport layer, a light emitting layer, or the like is stacked thereon by a wet method, it is stacked on the hole transport layer. As a solvent for the material to be used, it was necessary to use a solvent that does not dissolve the hole injection layer.

Therefore, when forming a hole injection layer by a coating printing method, a low molecule or oligomer having a crosslinking group that is soluble in an organic solvent as a material but can be insolubilized by crosslinking with heat or light after film formation. Alternatively, use of a hole transport material made of a polymer in combination with an acceptor material soluble in an organic solvent has been studied.
As an acceptor material soluble in an organic solvent, an aromatic monoiodonium salt represented by the following formula (MNPFPB) is known. This is also used as a photocationic polymerization catalyst and is said to be relatively safe (Patent Document 3). Aromatic monoiodonium salts are also mixed as an acceptor material for increasing the stability of the light emitting layer of the organic EL device and for reducing the resistance of the hole injection layer (Patent Documents 4 to 7).

  When a salt represented by the formula (MNPFPB) is mixed in a hole transport material containing an aromatic tertiary amine, etc., and irradiated with ultraviolet rays or heated, an iodonium cation constituting the salt represented by the formula (MNPFPB) Takes electrons from the HOMO (highest occupied orbit) of the hole transport material and cationizes the hole transport material. At that time, the iodonium cation is reduced and decomposed into an aromatic compound or an aromatic iodine compound, and most of the decomposition components are volatilized from the film by heating.

In Example 13 of Patent Document 5, a film is formed using a composition in which an acceptor material (0.2 wt%) represented by Formula 1 and a polyfluorene-based light emitting polymer material (1.5 wt%) are dissolved in toluene. A long-life EL element is obtained using the light emitting layer.
In Patent Documents 6 and 7, by mixing 9 to 29% by mass of an aromatic monoiodonium salt represented by the above formula (MNPFPB) in a low-molecular or polymer hole transport material, it can be driven at a low voltage. A long-life EL element is obtained.

In Example 11 of Patent Document 6, a non-crosslinked hole transporting polymer having a tetraphenylparaphenylenediamine structure (the ionization potential (hereinafter also referred to as Ip) is estimated to be about 5 eV) is 5: 1. It is described that an anisole solution ink was prepared by mixing the compound represented by the above formula (MNPFPB) at a mass ratio. The film obtained by spin coating is heat-treated at 230 ° C. for 15 minutes to obtain a resistivity of 5.3 × 10 ⁷ Ωcm. It can be seen that the resistance decreased by three orders of magnitude compared to 2.4 × 10 ¹⁰ Ωcm when the compound represented by the above formula (MNPFPB) was not mixed.

In Patent Document 7, a crosslinkable hole transporting polymer is mixed with a compound represented by the above formula (MNPFPB) to prepare an ethyl benzoate solution ink, which is spin-coated to form a hole injection layer. Is formed. It is described that the EL element thus obtained has a longer lifetime than when a non-crosslinked hole transporting polymer is used.
However, the ink described in Patent Document 7 includes an aromatic iodonium salt having a high oxidizing power and a hole transport material that is a low molecule or a polymer that is easily oxidized. When such an ink uses an aromatic solvent such as toluene or anisole as a solvent, oxidation proceeds in a short time even at room temperature, and the ink tends to be colored black-brown and has a problem in storage stability.

Further, an ink prepared by mixing an aromatic iodonium salt as an acceptor material with a polymer hole transport material at a concentration of several tens of mass% or more in an aromatic solvent such as toluene or an aromatic ether solvent such as anisole. In this case, when the ink was spin-coated, the obtained film sometimes phase separated and became cloudy. This is probably because toluene and anisole have a low ability to dissolve a hole transport material in which a cation or a charge transfer complex is formed.
Therefore, there is a demand for an ink that has a high storage stability, is difficult to be colored, and can form a highly transparent film.

Japanese Patent No. 4024754 Special table 2009-521110 Japanese Patent No. 3816112 JP 2012-84909 A JP 2005-179634 A JP 2006-233162 A JP 2010-192474 A

Applied Physics Letters 72, 2147 (1998)

  In view of the above background, the present invention provides an ink for a charge transport film including an acceptor material containing an aromatic iodonium salt and a charge transport material having a charge transport property, and having high storage stability. With the goal. It is another object of the present invention to provide an ink for a charge transport film that can provide a highly transparent film and can provide a low resistance film even when the content of the acceptor material is small. It is another object of the present invention to provide a method for producing a charge transport film using an aromatic oligoiodonium salt that can be used in the charge transport film ink and the charge transport film ink.

According to a first aspect of the present invention,
An acceptor material comprising an aromatic iodonium salt;
A charge transport material having charge transport properties;
A charge transport film ink containing a solvent, wherein the solvent contains a substituted or unsubstituted alicyclic ketone and / or a substituted or unsubstituted alicyclic monohydric alcohol in a volume ratio of 1/4 or more. The

According to a second aspect of the present invention, there is provided an aromatic oligoiodonium salt represented by the following general formula (2):

here,
Ar ₁ and Ar ₂ are substituted or unsubstituted phenyl groups;
Ar ₃ is a substituted or unsubstituted phenylene group;
n is an integer of 2 or more representing the degree of polymerization.

According to a third aspect of the present invention,
Using the charge transport film ink to form a film by a wet film formation method;
There is provided a method for producing a charge transport film comprising heat-treating the obtained film.

  ADVANTAGE OF THE INVENTION According to this invention, it is an ink for charge transport films containing the acceptor material containing an aromatic iodonium salt, and the charge transport material which has charge transportability, Comprising: The ink with high storage stability can be provided. In addition, it is possible to provide an ink for a charge transport film that can provide a highly transparent film and that can provide a low resistance film even when the content of the acceptor material is small. Furthermore, an aromatic oligoiodonium salt that can be used for the charge transport film ink and a method for producing a charge transport film using the charge transport film ink can also be provided.

Sectional drawing which shows the structure of an organic EL element. ¹ H-NMR chart of an aromatic diiodonium salt (DIPFPB) obtained in Example 1. ¹ H-NMR enlarged chart of aromatic diiodonium salt (DIPFPB) obtained in Example 1. ¹⁹ F-NMR chart of the aromatic diiodonium salt (DIPFPB) obtained in Example 1. The infrared absorption spectrum of the aromatic diiodonium salt (DIPFPB) obtained in Example 1. ¹ H-NMR chart of an aromatic oligoiodonium salt (OligoITfO) obtained in Example 2. ¹ H-NMR enlarged chart of an aromatic oligoiodonium salt (OligoITfO) obtained in Example 2. ¹⁹ F-NMR chart of the aromatic oligoiodonium salt (OligoITfO) obtained in Example 2. ¹ H-NMR chart of the aromatic oligoiodonium salt (OligoIPFPB) obtained in Example 2. ¹ H-NMR enlarged chart of an aromatic oligoiodonium salt (OligoIPFPB) obtained in Example 2. ¹⁹ F-NMR chart of the aromatic oligoiodonium salt (OligoIPFPB) obtained in Example 2. The infrared absorption spectrum of the aromatic oligoiodonium salt (OligoIPFPB) obtained in Example 2. The figure which shows the relationship between the density | concentration of cyclooctanol in a mixed solvent, and the viscosity of a mixed solvent. Schematic which shows the structure of the sample for measuring the volume resistivity of a charge transport film | membrane. The figure which shows the relationship between the density | concentration of the aromatic diiodonium salt (DIPFPB) in the ink solid content for charge transport films | membranes, and the volume resistivity of a charge transport film | membrane. The figure which shows the relationship between the density | concentration of the aromatic diiodonium salt (DIPFPB) in the ink solid content for charge transport films | membranes, and the volume resistivity of a charge transport film | membrane.

Hereinafter, first, the basic configuration and the manufacturing method of the organic EL element will be described, and then the charge transport film ink according to the embodiment and the aromatic iodonium salt contained in the ink will be described.
The ink for a charge transport film according to an embodiment of the present invention can be applied to a charge transport layer in an organic EL element. In particular, it can be applied to improve the hole transport capability of a charge transport layer having a hole transport property such as a hole injection layer, a hole transport layer, a hole transport electron blocking layer, and a light emitting layer.

<Basic structure of organic EL element and manufacturing method thereof>
First, a basic configuration of an organic EL element and a manufacturing method thereof will be described with reference to FIG. FIG. 1 is a cross-sectional view showing the configuration of the organic EL element. The organic EL element 15 includes a substrate 1 and a laminated structure 14 including an anode 2, a hole injection layer 3, a hole transport layer 4, a light emitting layer 5, an electron transport layer 6, and a cathode 7 provided thereon. Have. The cathode 7 is electrically connected to a cathode terminal portion 11 provided on the substrate 1. The laminated structure 14 on the substrate 1 is covered with a sealing plate 9, and the end of the sealing plate 9 is fixed to the substrate 1 with an adhesive 10. A desiccant sheet 8 is attached to the inner wall of the upper surface of the sealing plate 9, and the anode 2 and the cathode terminal portion 11 are connected to a power source 12 by wiring 13.

(substrate)
As the substrate 1, for example, an insulating transparent glass plate having a thickness of about 0.5 to 1.1 mm and excellent in gas barrier properties, a flexible glass sheet having a thickness of about 50 microns, or a plastic film, etc. Can be used. A flexible substrate in which a metal foil such as aluminum or stainless steel is coated with an insulating material may be used as the substrate 1. Further, a silicon substrate on which a minute driving circuit is formed or a sapphire substrate having excellent heat dissipation can be used as the substrate 1.
An opaque material may be used as the substrate 1. In this case, light can be extracted out of the organic EL element 15 by configuring the cathode 7 using a light-transmitting material.

(anode)
The anode 2 on the substrate 1 can be formed of a thin film of a transparent conductive oxide such as ITO (indium tin composite oxide) or IZO (indium zinc composite oxide). Alternatively, the anode 2 may be formed using a semi-transparent metal thin film made of gold or platinum having high conductivity. Furthermore, a transparent electrode having a surface resistance of 10 ohms / square or less, which is a transparent conductive oxide thin film sandwiched with a low resistance silver alloy thin film having a thickness of 20 nm or less, is laminated and formed by sputtering or the like. 2 can also be used.

  ITO used as the anode 2 has a small Ip of about 4.8 eV when the surface treatment for increasing the work function is not performed. Depending on the type, the blue light emitting dopant material of the light emitting layer 5 and the host material Ip may be as large as 6 eV or more. When the light emitting layer material having a large Ip is used together with the anode having a small Ip as described above, when holes are injected from the anode 2 into the light emitting layer 5 through the hole injection layer 3 or the hole transport layer 4. The energy barrier becomes a large value of 1 eV or more. In order to lower the energy barrier of hole injection and increase the hole injection efficiency from the anode 2 to the light emitting layer 5 through the hole injection layer 3, the surface of the anode 2 is treated to increase Ip, and from the anode 2 It is effective to reduce the energy barrier between layers up to the light emitting layer 5.

  Examples of the treatment applied to the surface of the anode 2 include plasma treatment with argon gas or oxygen gas, ultraviolet irradiation ozone treatment, surface treatment with a fluorine-based silane coupling agent, molybdenum oxide, tungsten oxide, or ammonium thereof. Examples thereof include a method in which a compound solution is applied with a thickness on the order of nm and heat-treated in an oxidizing atmosphere. Alternatively, the surface of the anode 2 may be treated by halogenating metal atoms on the surface of the anode 2. Such treatment can be achieved, for example, by generating halogen radicals by irradiating ultraviolet rays or plasma in a vapor atmosphere of an organic chlorine compound or an organic fluorine compound. By performing the surface treatment as described above, the Ip on the surface of the anode 2 increases to about 5.6 eV or more, and the hole injection efficiency from the anode 2 to the hole injection layer 3 is increased.

(Hole injection layer)
The hole injection layer 3 is preferably formed using a hole transporting compound having a low resistance and a high Ip. This increases the efficiency of hole injection into the hole transport layer 4. The thickness of the hole injection layer 3 is generally about 0.5 to 100 nm. When the thickness of the hole injection layer 3 is large, unevenness and foreign matter on the surface of the anode 2 are covered and smoothed, so that an electrical short circuit is prevented.

  The material used for the hole injection layer 3 desirably has a high hole transport capability in addition to a high hole density or hole mobility, and its Ip is positive with the value of Ip of the material of the anode 2. It is preferably between the values of Ip of the material of the hole transport layer 4. Alternatively, a material having an electron affinity (hereinafter also referred to as Ea) between Ip of the material of the anode 2 and Ip of the material of the hole transport layer 4 and having Ea of about 5 to 6 eV is used. The hole injection layer 3 may be formed. In this case, holes can be injected into the hole transport layer 4 through the lowest free electron orbit (LUMO) of the material.

As the hole injection layer 3, for example, a vapor deposition film or a coated printing film containing an aromatic tertiary amine having an Ip of about 5 to 6 eV as a hole transporting compound can be used.
The hole transporting compound includes, for example, an aromatic tertiary amine compound or an aromatic ring structure selected from a carbazole ring, a thiophene ring, a benzothiadiazole ring, a benzene ring, a naphthalene ring, an anthracene ring, and a chrysene ring. It is a compound and any of a low molecular weight compound, an oligomer, and a polymer may be sufficient. The hole transporting compounds may be used alone or in combination of two or more.

Here, the low molecular compound is preferably a compound having a molecular weight of 400 or more and less than 10,000. An oligomer refers to a compound obtained by polymerizing several tens or less of a structure serving as a repeating unit. A polymer refers to a compound obtained by polymerizing several tens or more of a structure serving as a repeating unit.
As the hole transporting low molecular weight compound, for example, an aromatic tertiary amine compound such as a starburst type or an oligomer type having a hole transporting ability and an amorphous property and a high glass transition temperature is preferably used. Specifically, 2-TNATA and 2,2 ′, 7,7′-tetrakis [N-naphthalenyl (phenyl) -amino] -9,9-spirobifluorene (hereinafter abbreviated as spiro-NPD), etc. is there.
A vapor deposition film containing metal phthalocyanines such as copper phthalocyanine is also preferably used as the hole injection layer 3.

As an example of an oligomer, N, N′-bis [4 ′-(diphenylamino) -1,1′-biphenyl-4-yl] -N, N′-diphenyl- in which four triphenylamine structural units are connected Examples thereof include 1,1′-biphenyl-4,4′-diamine.
Examples of polymers include poly (9,9-dioctylfluorenyl-2,7-diyl) -co- (N, N′-bis {p-butylphenyl} -1,1′-biphenylene-4,4 And a copolymer such as' -diamine).

When the layer immediately above the hole injection layer 3 is formed by vapor deposition, it is not required that the hole injection layer 3 is insoluble in an organic solvent. In this case, a film formed by applying a solution containing a non-crosslinked hole transporting compound can be used as the hole injection layer 3.
When manufacturing an organic EL element, the layers may be laminated on the substrate in the reverse order as described above, that is, in the order of cathode, electron transport layer, light emitting layer, hole transport layer, hole injection layer, and anode. . If the layers up to the hole transport layer previously laminated on the substrate are insoluble in the coating solvent for the hole injection layer, a solution containing a non-crosslinked type hole transport compound is used. The hole injection layer 3 may be formed.

Examples of the non-crosslinked hole transport polymer include the following compound (HT-B).

  On the other hand, when the layer immediately above the hole injection layer 3 is formed by a wet method using a solution, the hole injection layer 3 is required to be insoluble in the solvent (organic solvent) of the solution. The The hole-injecting layer 3 insoluble in the solvent contains a cross-linked hole transporting compound and can be formed by cross-linking with light or heat.

Examples of the crosslinkable hole transporting low molecular weight compound include those in which two or more crosslinking groups such as vinyl groups are introduced into the hole transporting low molecular weight compound (HT-B) as described above. . As the crosslinkable hole transportable polymer, any hole transportable polymer material into which a crosslinkable group capable of crosslinking with light, heat or acid can be used. For example, the compound (HT-A) shown below can be used. ). Since the compound (HT-A) has an Ip of about 5.8 eV, holes are injected well from the hole injection layer 3 formed using this compound into the hole transport layer having a high Ip. .

  Since a crosslinkable hole transporting compound is crosslinked by heat or light, the use of such a compound forms the hole injection layer 3 that is insoluble or hardly soluble in an organic solvent. Such a hole injection layer is not dissolved by an organic solvent and mixed with other layers. For this reason, a multilayer laminated structure can be easily formed by using a wet film forming method using a solution.

(Hole transport layer)
The hole transport layer 4 is provided between the hole injection layer 3 and the light emitting layer 5 in order to lower the energy barrier from the hole injection layer 3 to the light emitting layer 5 and promote hole transport. Also called. The thickness of the hole transport layer 4 is generally about 5 to 30 nm. The hole transport layer 4 provides the following effects. For example, leakage of electrons injected into the light emitting layer 5 into the hole injection layer 3 and the anode 2 is suppressed. In addition, the excitons in the vicinity of the interface between the hole injection layer 3 and the light emitting layer 5 are suppressed from being absorbed by the hole injection layer 3 having a high hole carrier density and deactivated. As a result, a decrease in luminous efficiency is reduced. Further, the diffusion of impurities and ions in the hole injection layer 3 to the light emitting layer 5 is limited. Thereby, the deterioration of the light emitting layer 5 is reduced, and the decrease of the element life and the increase of the driving voltage are suppressed.

The hole transport layer 4 can be formed using, for example, a hole transporting low molecular weight compound such as an aromatic tertiary amine having a high hole transport capability. Alternatively, the hole transport layer 4 may be formed using an aromatic tertiary amine having a high hole transport capability and a crosslinked hole transport polymer for insolubilization in a solvent.
When the light emitting layer 5 immediately above the hole transport layer 4 is formed by vapor deposition, the hole transport layer 4 does not necessarily need to be insoluble in an organic solvent. In this case, the hole transport layer 4 can also be formed using a solvent-soluble low molecular weight compound or a non-crosslinked polymer.

On the other hand, when the light emitting layer 5 immediately above the hole transport layer 4 is formed by a wet method using a solution, the hole transport layer 4 is insoluble or hardly soluble in the solvent (organic solvent) of the solution. It is required to be. The hole transport layer 4 insoluble in the solvent can be formed using, for example, a low molecular weight compound insoluble in the solvent used in the solution for the light emitting layer. Alternatively, a film in which a cross-linked hole transporting polymer is cross-linked and insoluble or hardly soluble is used as the hole transport layer 4. Specific examples of the compound suitable for forming the hole transport layer 4 include a compound (HT-C) shown below. This compound (HT-C) has an Ip of about 6.0 eV and an Ea of 2.7 eV. A compound having such characteristics is suitable as a compound contained in the hole transport layer in contact with the blue light-emitting layer.

In addition, in order to prevent a decrease in light emission efficiency and color purity, the material used for the hole transport layer 4 is desirably a material that does not emit unnecessary long wavelength light by forming an exciplex with the light emitting dopant material. It is. The Ip value of the material contained in the hole transport layer 4 is between the Ip value of the material contained in the hole injection layer 3 and the Ip value of the host material contained in the light emitting layer 5, and in the light emitting layer 5 It is desirable to be larger than the Ip value of the light emitting dopant material.
The energy barrier between the hole transport layer 4 and the light emitting layer 5 prevents the electrons in the light emitting layer 5 from leaking to the hole injection layer 3, and as a result, the light emission efficiency is increased. In order to sufficiently obtain such an effect, it is preferable to form the hole transport layer 4 using a material having Ea which is 0.3 eV or less smaller than the material used for the light emitting layer 5.

  When the hole transport layer 4 having a low electron mobility is used, the leakage of electrons to the hole injection layer 3 and the anode 2 is suppressed, and the light emission efficiency can be improved. In order to obtain the hole transport layer 4 having a low electron mobility, for example, the following material is doped in a small amount into the hole transport layer 4. That is, Ip is equal to or higher than that of the hole transport material (does not act as a hole trap), Ea is larger than the hole transport material (acts as an electron trap), and the emission quantum It is an electron trap type light emitting dopant material with a high yield. By including such a material, the electron mobility of the hole transport layer 4 becomes lower than the hole mobility, and the light emission efficiency is improved.

The hole transport layer 4 containing a light emitting dopant material also functions as a light emitting layer. For example, a normal hole transport layer can be formed, and a hole transport light emitting layer (not shown) can be formed thereon.
The hole transporting light emitting layer containing a low molecular electron trap light emitting dopant is soluble in an organic solvent. When the electron-transporting light-emitting layer or the hole-blocking electron-transporting layer is laminated on the hole-transporting light-emitting layer by a wet method, the dopant material is eluted from the hole-transporting light-emitting layer, and other layers May be mixed with. In order to prevent the elution of the dopant material, it is preferable to dope a hole-transporting host material having a cross-linking group with a cross-linkable electron trap light-emitting dopant material. When the host material and the dopant material are cross-linked, the hole transporting light emitting layer is insolubilized and the elution of the dopant material from the hole transporting light emitting layer is prevented.

As a bridge | crosslinking type electron trap type | mold light emission dopant, the following compound (PF-1) is mentioned, for example. This compound (PF-1) is a crosslinked polymer having a hexenyl group having a crosslinkable and polymerizable double bond at the 9-position of fluorene. Compound (PF-1) has an Ip of about 6.1 eV and an Ea of 3.2 eV, and is suitable as a bridging electron trap type blue light-emitting dopant doped in the aforementioned compound (HT-C) or the like. Yes.

  Even if the value of Ea is about the same as that of the host material of the light emitting layer 5, any material can be used as the hole transport layer material as long as the hole mobility is one digit or more larger than the electron mobility. When a phosphorescent material is used for the light emitting layer 5, it is desirable to use a material having a lowest excited triplet level larger than the lowest excited triplet level of the phosphorescent material for the hole transport layer 4. Thereby, quenching of excitons in the light emitting layer due to the hole transport layer 4 in contact with the light emitting layer 5 can be suppressed.

(Light emitting layer)
The light emitting layer 5 on the hole transport layer 4 includes, for example, a light emitting material having various EL emission colors such as red, green, blue, yellow, or white having strong fluorescence or phosphorescence. The light emitting layer 5 is usually formed with a thickness of about 5 to 100 nm.

Examples of fluorescent materials include anthracene derivatives, benzoanthracene derivatives, dibenzoanthracene derivatives, styryl derivatives, carbazole derivatives, aluminum oxine complexes, thermally activated delayed fluorescent materials, polyfluorene-based copolymers, and polyphenoxazine copolymers And various fluorescent light emitting materials. The fluorescent light emitting material may be a low molecular compound having a weight average molecular weight of about 10,000 or less, or a high molecular compound having a weight average molecular weight of about 10,000 to several million.
In addition, a phosphorescent complex containing heavy atoms such as iridium, platinum, and rhenium can be used as the light-emitting material.

It is preferable that the light emitting material used when the light emitting layer 5 is formed by a wet method can be used by dissolving in a solvent at a concentration of 1% by mass or more. Moreover, it is also required to be a material that can be applied with such a solution to obtain a smooth film.
Although the light emitting layer 5 may be formed using a light emitting material alone, it is preferable to use a light emitting dopant material having a small Eg mixed in a light emitting host material having a large energy gap (Eg). In this case, concentration quenching and excimer light emission due to aggregation of the light emitting material can be prevented, and the light emission intensity can be increased.

When a single material is used as the host material, it is preferable that the Ip level of the host material is deeper than the Ip of the light emitting dopant material, and the light emitting dopant easily traps holes. A material in which the level of Ea is shallower than that of the dopant material and the light-emitting dopant easily traps electrons is also preferable as the host material.
When a hole transport material and an electron transport material are mixed to form a host material, the hole transport material preferably has an Ip higher than that of the light emitting dopant material and has a larger Eg than the light emitting dopant material. On the other hand, the electron transport material preferably has an Ea smaller than the light emitting dopant material and an Eg larger than the light emitting dopant material. By adjusting the blending ratio of the hole transport material and the electron transport material, the carrier balance between the holes and electrons injected into the light emitting layer 5 can be adjusted to approach 1. This leads to an improvement in luminous efficiency.

(Hole block electron transport layer)
Although not shown, a hole blocking electron transport layer can be provided between the light emitting layer 5 and the electron transport layer 6. When the thickness of the hole block electron transport layer is about 5 to 50 nm, the holes that escape from the light emitting layer 5 to the cathode 7 side are confined, and the ratio of electrons to holes injected into the light emitting layer 5 is set to 1. Can be approached.
When the hole transport capability of the light emitting layer 5 is higher than the electron transport capability, and the light emitting region due to recombination of holes and electrons is close to the cathode 7, the cathode 7 is provided by providing a hole blocking electron transport layer. Hole leakage to the cathode, and absorption of exciton energy by the cathode 7 can be suppressed. As a result, luminous efficiency can be increased.

For example, in the case of forming a hole block electron transport layer for a blue light emitting element, it has Ip that is at least 0.3 eV or more than the light emitting material and Eg that is 3 eV or more, and absorbs visible light emission from the light emitting layer 5. It is preferable to use a material that does not.
Examples of the material used for forming the hole block electron transport layer include bathophenanthroline, bathocuproin, 1,3,5-tris (N-phenylbenzimidazol-2-yl) benzene (hereinafter abbreviated as TPBI), tris. Compounds having a nitrogen-containing heterocycle such as [3- (3-pyridyl) -mesityl] borane, and phosphine such as 2,7-bis (diphenylphosphoryl) -9,9′-spirobi (9H-fluorene) Examples thereof include oxide compounds, dimers thereof, and derivatives having a substituent.

(Electron transport layer)
The electron transport layer 6 has a thickness of about 1 to 50 nm and can be provided between the light emitting layer 5 and the cathode 7 or between the hole block electron transport layer (not shown) and the cathode 7. The electron transport layer 6 has an action of reducing an energy barrier and resistance when electrons are injected from the cathode 7 into the light emitting layer 5. Further, the excitons generated in the light emitting layer 5 are prevented from being quenched by diffusing to the cathode 7.

For the formation of the electron transport layer 6, for example, 1,10-phenanthroline derivatives such as bathocuproin and bathophenanthroline, benzimidazole derivatives such as TPBI, bis (10-benzoquinolinolato) Be complex, bis (2- (2- (2- Hydroxyphenyl) -4-methyl-pyridine) Be complex, tris (8-hydroxyquinoline) Al complex, tris (4-methyl-fluoro-8-hydroxyquinoline) Al complex, bis (2-methyl-8-quinolinato)- A metal complex such as 4-phenylphenolate aluminum or a compound having a nitrogen-containing heterocycle such as 4,4′-biscarbazole biphenyl can be used.
In addition, an aromatic boron compound such as tris [3- (3-pyridyl) -mesityl] borane, an aromatic silane compound, an aromatic phosphine oxide compound such as phenyldi (1-pyrenyl) phosphine oxide, and the like are used as the material for the electron transport layer 6. It may be used as

  In the electron transport layer 6, an alkali metal such as Cs, Na, Li, or Ba or an alkaline earth metal can be doped as a donor by a co-evaporation method. These metals can also be doped by dissolving a salt such as Cs or Li carbonate together with the material of the electron transport layer and applying the resulting solution. Alternatively, an organic radical compound having a small Ip can be used as a donor mixed with the electron transport layer material and applied. When the material of the electron transport layer is anionized by the donor, the carrier density is increased, and the resistance of the charge transport layer is further decreased. As a result, an organic EL element that can be driven at a lower voltage is obtained.

(cathode)
The cathode 7 is usually composed of a metal vapor deposition film having low resistance and high light reflectance. For example, an Al film or an Ag film can be used as the cathode 7. The cathode can also be formed using a light transmissive material. In this case, a transparent electrode material or the like is laminated on a metal cathode of about 10 nm or less.
At the interface between the cathode 7 and the electron transport layer 6, a layer made of alkali metal such as Li, Ba, Cs such as Li, Ba, Cs, rare earth such as Yb, or a compound thereof having an Ip of 3 eV or less is several nm. It is preferable to form with thickness. As a result, electrons are efficiently injected from the cathode 7 into the electron transport layer 6.

(Sealing)
If moisture is present in the organic EL element 15, a local battery is formed and corrosion is likely to occur, thereby causing a non-light-emitting spot. Therefore, it is required to avoid the influence of moisture as much as possible. For example, by adhering the desiccant sheet 8 to the upper surface of the inner wall of the sealing plate 9, the influence of moisture can be avoided. The desiccant sheet 8 is attached to the sealing plate 9 in, for example, an inert gas, and the sealing plate 9 is a substrate using an adhesive 10 having a high barrier property against oxygen and water vapor as illustrated. 1 is bonded to the anode 2 and the cathode terminal portion 11 on the substrate 1. The laminated structure 14 formed on the substrate 1 is thus sealed by the sealing plate 9.

Alternatively, a passivation layer (not shown) having a high barrier property against water vapor or oxygen may be directly formed on the cathode 7 and sealed. As the passivation layer, for example, a metal oxide, metal nitride, or metal oxynitride CVD (chemical deposition) film, ALE (atomic layer epitaxial growth) film, sputtered film, reactive vapor deposition film, etc. can be used. Specific examples include SiO _x , SiON, SiN, InZnO, InZnGaO, and SiAlON.

(Drive)
For example, when a direct current voltage is applied to cause the organic EL element 15 to emit light, as shown in FIG. Connect to the negative pole. Although not shown, an alternating voltage can be applied to cause the organic EL element 15 of this embodiment to emit light. In this case, the organic EL element 15 emits light while a positive voltage is applied to the anode 2 and a negative voltage is applied to the cathode terminal portion 11.

<Ink for charge transport film>
Hereinafter, the charge transport film ink according to the embodiment will be described.
The charge transport film ink according to the embodiment is:
An acceptor material comprising an aromatic iodonium salt;
A charge transport material having charge transport properties;
Containing a solvent.

  The solvent used in the ink contains a substituted or unsubstituted alicyclic ketone and / or a substituted or unsubstituted alicyclic monohydric alcohol in a volume ratio of 1/4 or more. The volume ratio here is a value when the volume of the solvent is 1.

  The ink for a charge transport film according to the embodiment is an ink obtained by dissolving a mixed composition of an acceptor material containing an aromatic iodonium salt and a charge transport material in a solvent. Also, a first solution containing an aromatic iodonium salt and a second solution containing a charge transport material are respectively prepared and mixed at a desired ratio when used to obtain a charge transport film ink. Also good.

  The organic solvent used for coating printing of the organic EL material varies depending on the coating printing method, but a solvent having a boiling point of about 80 to 220 ° C. is used from the viewpoint of drying. For example, aromatic solvents such as toluene (boiling point 110 ° C.), xylene (boiling point 144 ° C.), mesitylene (boiling point 165 ° C.), and tetralin (boiling point 207 ° C.); anisole (boiling point 154 ° C.), 1,4-dimethoxybenzene (Boiling point 213 ° C), 4-methoxyanisole (boiling point 175 ° C), and aromatic ether solvents including anisole solvents such as 1,3-dimethoxybenzene (boiling point 217 ° C); methyl benzoate (boiling point 198-200 ° C) ), Ester solvents such as ethyl benzoate (boiling point 211-213 ° C.), methyl cyclohexanecarboxylate (boiling point 183 ° C.), butyl acetate (boiling point 126 ° C.), and isoamyl acetate (boiling point 142 ° C.); acetophenone (boiling point 202 ° C. ) And other aromatic ketone solvents.

However, when an aromatic iodonium salt is used as an acceptor material, an aromatic iodonium salt having a strong oxidizing power and a charge transporting material that is easily oxidized are mixed to form an ink, which causes a problem in storage stability.
For example, an aromatic solvent such as toluene, xylene, tetralin or the like, an aromatic ether solvent such as anisole, 4-methoxybenzene, 1,3-dimethoxybenzene, or the like is used as an ink solvent, and aromatic iodonium and a charge transport material are used therefor. When a solution is prepared by mixing, a charge transfer complex is immediately formed and colored even at room temperature. Furthermore, the oxidation and cross-linking of the charge transport material progresses with time, and dark coloring and precipitation may occur.

In addition, when an ink obtained by mixing a charge transport material having a group that easily causes oxidative polymerization or crosslinking and an aromatic iodonium salt is used for relief printing, the charge transport material is polymerized or crosslinked by absorbing external light during printing. Promoted. As a result, the viscosity of the ink increases on the printing plate, and the ink may harden.
As a result of intensive studies, the present inventors have determined that the ink contains a solvent containing alicyclic ketone and / or alicyclic monohydric alcohol in a volume ratio of ¼ or more, more preferably 以上 or more. It was found that the storage stability can be enhanced by suppressing the coloring and alteration of the ink.

The alicyclic compound has higher solubility of the aromatic compound constituting the charge transport material than the linear compound, and is less likely to form a charge transfer complex than the aromatic solvent. In addition, the oxygen of the ketone or alcohol is coordinated to the iodonium cation of the aromatic iodonium salt, whereby the reaction between the aromatic iodonium salt and the charge transport material is suppressed, and the stability of the aromatic iodonium salt is increased.
The alicyclic ketone may be substituted or unsubstituted. Preferred alicyclic ketones include alicyclic ketone compounds having 5 to 10 carbon atoms constituting the ring, and more preferably 5 to 8 carbon atoms constituting the ring. An alicyclic ketone having the number of carbon atoms in the above range is preferable in that a solvent that can be dried at an appropriate speed according to the printing coating method can be selected and a smooth film can be easily obtained.

Examples of the alicyclic ketone compound include 4-tertiarybutylcyclohexanone (boiling point 225.1 ° C.), 4-propylcyclohexanone (boiling point 202.6 ° C.), cyclooctanone (boiling point 195 ° C. to 197 ° C.), cyclohepta. Non (boiling point 180 ° C.), 2-methylcyclohexanone (boiling point 165 ° C.), cyclohexanone (boiling point 157 ° C.), cyclopentanone (boiling point 131 ° C.) and the like.
For example, cyclohexanone has a boiling point of 160 ° C. or less that is easily dried during spin coating, and dissolves a charge transporting compound that is an aromatic compound. Furthermore, it is particularly excellent because of its high solubility in ionic salts such as onium salts such as iodonium salts and cationized charge transporting compounds.

Preferable examples of the alicyclic monohydric alcohol include alicyclic alcohols having 5 to 10 carbon atoms constituting the ring, and the number of carbon atoms constituting the ring is preferably 5 to 8. preferable. Monovalent alicyclic alcohols are preferable in that the film can be dried at an appropriate rate because the boiling point is relatively low compared to divalent or higher alicyclic alcohols. Moreover, the monovalent | monohydric aliphatic alcohol whose number of the carbon atoms which comprise a ring is the said range is also preferable for the same reason.
For example, 3-cyclohexene-1-methanol (boiling point 192 ° C.), 2-cyclohexen-1-ol (boiling point 166 ° C.), 2-methylcyclohexanol (boiling point 165-167 ° C.), 4-methylcyclohexanol, 3,5 -Alicyclic monovalent dimethylcyclohexanol (boiling point 186 ° C), cyclopentanol (boiling point 140 ° C), cyclohexanol (boiling point 161 ° C), cycloheptanol (boiling point 185 ° C), cyclooctanol (boiling point 209 ° C), etc. Examples include alcohol solvents.

  In addition, both alicyclic ketone and alicyclic monohydric alcohol may be contained in the solvent, and either one may be contained. When both the alicyclic ketone and the alicyclic monohydric alcohol are contained in the solvent, the total content thereof is preferably ¼ or more and 1 or less in a volume ratio with respect to the solvent. When 1/3 or more of the total capacity of the ink solvent is an alicyclic ketone and / or a monovalent alicyclic alcohol, the above-described effect is further enhanced. Further, when the alicyclic ketone and / or the monovalent alicyclic alcohol is more than 1/2 and less than 1 of the total capacity of the ink solvent, the above-described effects are further enhanced and preferable.

When a compound having a carbonyl group such as cyclohexanone or a compound containing an alcoholic hydroxyl group such as cyclopentanol or cyclooctanol is used as a solvent, these compounds are coordinated around the iodonium cation in the aromatic iodonium salt. As a result, the iodonium cation and the charge transport material are separated from each other, and the charge transfer is considered to be suppressed. Therefore, the generation of radical cations in the charge transport material is suppressed, and the progress of oxidation and coupling of the charge transport material is also suppressed. As a result, it is considered that the deterioration of the ink such as coloring is suppressed and the stability is improved.
Since the coordinated compound (solvent) is removed by drying or heat treatment after film formation, it does not adversely affect the resistance of the film.

In addition, when an aromatic iodonium salt is mixed in an ink at a high concentration, the film may become cloudy after film formation. For example, in the case of an ink in which an aromatic iodonium salt and a hole transport polymer HT-A are dissolved in a single solvent of anisole or tetralin, the concentration of the aromatic iodonium salt is about 10% by mass or more of the total solid content of the ink. It may become cloudy after film formation.
However, when the solvent containing the alicyclic ketone of this embodiment is used, the dispersibility at the time of forming the ink material is improved, and such inconvenience is avoided. For example, in an ink in which an aromatic iodonium salt and a hole transport polymer HT-A are dissolved in a mixed solvent of cyclohexanone: anisole (volume ratio 8: 2), the concentration of the aromatic iodonium salt is 30% by mass of the total solid content of the ink. But it doesn't become cloudy.

  The ink for a charge transport film of this embodiment can be formed by any wet film forming method. Examples include spin coating, die coating, capillary coating, electrostatic coating, gravure printing, relief printing (relief printing), offset printing, screen printing, continuous nozzle printing, and ink jet printing. It is done.

  It is desirable to adjust the viscosity of the ink so that the viscosity is suitable for the coating printing method and apparatus to be used. The viscosity of the ink can be adjusted by adjusting the mixing ratio of solvents having different viscosities. Other organic solvents include organic solvents such as aromatic hydrocarbons such as toluene, xylene and tetralin, aromatic ethers such as anisole, and aromatic ester solvents such as methyl benzoate. When a polymer material such as hole transporting property or light emitting property is used as the charge transporting compound, the viscosity of the ink can be adjusted by adjusting the average molecular weight of the polymer. Alternatively, the surface tension of the ink can be lowered by adding a fluorine solvent or a surfactant having a low surface tension. Examples of the fluorinated solvent include 3M's Novec 7300 and Novec 7500. However, the viscosity of an ink in which a low molecular weight compound is dissolved in a solvent is almost the same as the viscosity of the solvent, and even if the solution has a high concentration, the viscosity does not increase like a polymer. Therefore, it has been difficult to prepare a high-viscosity ink suitable for printing using a low molecular compound.

  When the printing method is used, the viscosity of the ink is preferably 3 mPa · s to 200 mPa · s at 23 ° C., and more preferably about 30 mPa · s to 150 mPa · s in the relief printing method. If cyclooctanol having a high viscosity of about 150 mPa · s is selected as the alicyclic monohydric alcohol, a mixed solvent having the above viscosity can be obtained.

In addition, for example, when a printing method such as an inkjet method or a continuous nozzle printing method is used, it is also desired that a smooth film be formed in the pixels surrounded by the partition wall in order to suppress light emission unevenness. . The ink printed by such a printing method contains a first good solvent having a low boiling point and viscosity and a second good solvent having a higher boiling point and viscosity. The first good solvent and the second good solvent Can be mixed at any ratio without phase separation in order to prevent separation of the solution during drying and to obtain a smooth membrane.
By adjusting the viscosity, surface tension, solvent composition, and the like of the ink as described above and suppressing ink repelling, the smoothness of the resulting charge transport film is enhanced.

Hereinafter, components other than the solvent contained in the charge transport film ink according to the embodiment will be described in order.
1. Aromatic iodonium salt The ink according to the embodiment contains an aromatic iodonium salt. The aromatic iodonium salt is mixed in a charge transport film such as a hole injection layer, a hole transport layer, a hole transport electron blocking layer, and a light emitting layer in the organic EL element as described above, and light such as ultraviolet rays is mixed. By being irradiated or heat-treated, it suitably acts as an acceptor material.

The aromatic iodonium salt contained in the ink according to the embodiment preferably contains a cation represented by the following general formula I.

here,
Ar ₁ and Ar ₂ are substituted or unsubstituted monovalent aromatic groups;
Ar ₃ is a substituted or unsubstituted divalent aromatic group;
n is an integer of 0 or more.

The aromatic iodonium salt preferably contains a salt represented by the following general formula (1).

here,
Ar ₁ , Ar ₂ , Ar ₃ and n are as defined in general formula I above;
Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ each independently represent a substituent, and at least one of Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ is a substituent containing an electron-withdrawing group;
Two or more of Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ may be bonded to each other to form a ring.

Specific examples and preferred ranges of the aromatic groups represented by Ar ₁ , Ar ₂ and Ar ₃ and the substituents represented by Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ include the following aromatic monoiodonium salts, aromatic As described in the description of the aromatic diiodonium salt and aromatic oligoiodonium salt.
n is preferably an integer of 0 to 10, more preferably an integer of 0 to 5, and particularly preferably 1 to 3 because high oxidizing power and solubility can be obtained.

  The aromatic iodonium salt contained in the ink of the present invention is preferably selected from aromatic monoiodonium salts, aromatic diiodonium salts and aromatic oligoiodonium salts. Hereafter, each aromatic iodonium salt in case a cation is represented by the said general formula I is demonstrated.

(Aromatic monoiodonium salt)
Aromatic mono- iodonium salts according to one embodiment of the present invention is a salt comprising a cation of the general formula I _0. The cation represented by the general formula I ₀ corresponds to the case where n = 0 in the general formula I.

Here, Ar ₁ and Ar ₂ may be the same or different, and are substituted or unsubstituted monovalent aromatic groups. Of these, a 5-membered or 6-membered aromatic group is preferably used.
The monovalent aromatic group introduced into the general formula I ₀ as Ar ₁ and Ar ₂ may be the same or different, and is a condensed hetero ring such as a substituted or unsubstituted naphthyl group or a quinoline ring. Monovalent groups derived from aromatic rings can also be used, but monovalent groups derived from substituted or unsubstituted benzene derivatives, and substituted or unsubstituted 5- or 6-membered heteroaromatics One of the monovalent groups derived from the ring is more preferable because the molecular weight is smaller and the decomposition product after the heat treatment tends to volatilize. Examples of the monovalent aromatic group derived from the benzene derivative include a phenyl group, a tolyl group, an isopropylphenyl group, a t-butylphenyl group, a xylyl group, a mesityl group, and a methoxyphenyl group. Specific examples of the monovalent group derived from a 5-membered or 6-membered heteroaromatic ring include a thienyl group, a pyrrolyl group, and a pyridyl group.

Examples of the substituent introduced into the aromatic group represented by Ar ₁ and Ar ₂ for the purpose of improving solubility include alkyl groups such as methyl, isopropyl and tertiary butyl groups, and alkoxy such as methoxy groups Group, and an aliphatic hydrocarbon group having 4 or less carbon atoms is preferable.
The aromatic iodonium salt is mixed with a charge transport material and a solvent to form an ink, and is formed into a film by coating or printing as a charge transport layer such as a hole injection layer. Thereafter, heat treatment is performed so that the iodonium cation in the aromatic iodonium salt takes electrons from the charge transport material and cationizes the charge transport material. In addition to heat treatment, the reaction can be accelerated by ultraviolet irradiation.

The heat treatment is performed by heating to a temperature of 100 ° C. or higher, preferably about 130 ° C. to 250 ° C. in the atmosphere, in an inert gas atmosphere such as nitrogen or argon, or under reduced pressure. The iodonium cation removes electrons from the charge transport material and undergoes reductive decomposition to generate decomposition products (for example, iodoaryl, etc.), but the carbon atoms of the substituents introduced into Ar ₁ and Ar ₂ of the aromatic iodonium salt If the number is 4 or less, the decomposition product has a small increase in molecular weight and can be evaporated. Therefore, the decomposition product is volatilized from the film and easily removed by heat treatment.
When the heat treatment temperature is less than 100 ° C., the decomposition product may not be sufficiently volatilized from the film. Further, the cationization of the charge transport material becomes insufficient, and there may be problems such as the resistance cannot be lowered sufficiently and the heat treatment takes a long time. On the other hand, when the heat treatment temperature exceeds 250 ° C., the charge transport material may deteriorate or decompose.

The group introduced into the aromatic iodonium salt as Ar ₁ and Ar ₂ is preferably an aromatic ring such as a substituted or unsubstituted phenyl group or thienyl group from the viewpoint of stability. Table 1 below shows specific examples in the case where Ar ₁ and Ar ₂ in the monoiodonium cation represented by the general formula I ₀ are phenyl group derivatives or thienyl group derivatives. The combination of Ar ₁ and Ar ₂ is not limited to the case shown in Table 1, and those listed as Ar ₁ and Ar _{2 in} Table 1 and other aromatic groups can be arbitrarily combined.

As the counter anion of the cation represented by the general formula I _0, borate anions represented by the general formula B are preferably used.

Here, Ar ₂₁ , Ar _22, Ar ₂₃ and Ar ₂₄ each independently represent a substituent _, and at least one of Ar ₂₁ , Ar _22, Ar ₂₃ and Ar ₂₄ is a substituent containing an electron-withdrawing group. . Two or more of Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ may be bonded to each other to form a ring.
The electron-withdrawing group of the substituent containing an electron-withdrawing group in Ar ₂₁ , Ar _22, Ar _23, and Ar ₂₄ is not particularly limited as long as it has an electron-withdrawing group, but a halogen atom such as fluorine, trifluoromethyl, and the like. It is preferably selected from a group, a perfluoroalkyl group, a nitro group, a cyano group, a carbonyl group, a sulfonyl group, and the like.

It is preferable that the carbon atom adjacent to the boron atom of the borate anion forms a conjugated double bond. Thereby, the negative charge of the borate anion can be delocalized to suppress the reaction with the cation, and the stability of the borate anion can be enhanced.
Therefore, one or more aromatic hydrocarbon groups such as phenyl group, biphenyl group, condensed aromatic hydrocarbon groups such as naphthyl group, and one or more heteroaromatic groups such as pyridyl group, pyrimidyl group, pyrazinyl group, thienyl group, etc. More preferably, the group substituted with an electron-withdrawing substituent is contained in at least one of Ar ₂₁ , Ar _22, Ar _23, and Ar ₂₄ . More preferably, the two or more substituents contain an electron withdrawing group. Even more preferably, the three or more substituents contain electron withdrawing groups. It is particularly preferable that all of Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ are substituents containing an electron-withdrawing group.

Of Ar ₂₁ , Ar _22, Ar _23, and Ar ₂₄ , the group that does not contain an electron-withdrawing group may be an arbitrary substituent. Such substituents include, for example, a phenyl group having 1 to 10 carbon atoms, a tolyl group, a xylyl group, a mesityl group, a naphthyl group, and biphenyl from the viewpoint of adjusting the dispersibility and diffusibility in the charge transport film. And aromatic groups such as benzyl groups, aliphatic hydrocarbon groups and aliphatic ether groups having about 1 to 10 carbon atoms, and aromatic groups substituted with them.
Also, two or more adjacent groups of Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ may be bonded to each other to form a ring. For example, adjacent phenyl groups may be bonded to form a dibenzoborol ring.

The substituents represented by Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ are preferably bulky groups. Specific examples of the bulky substituent include a pentafluorophenyl group, a 3,4,5-trifluorophenyl group, and a 3,5-trifluoromethylphenyl group. These groups form borate anions having a radius of 0.6 nm or more centering on boron.
The borate anion remains as a counter ion at the cationization site of the charge transport material after heat treatment of the membrane. Borate anions having a large radius are difficult to diffuse in the membrane. Moreover, the approach by the Coulomb force with the cationization site | part of a positive hole transport material is inhibited, and the movement of the positive hole on a positive hole transport material becomes difficult to be restrained. As a result, the resistance of the film is lower.

Other examples of Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ include those described in Chapter 2 of Highly Fluorous tetraarylborate Anions; Versatile Counteranions for Homogeneous cataiysis in Novel reaction Media (ISBN 90-393-3274-6) Examples include groups constituting the described borates.

In addition to the above, the counter anions of the aromatic iodonium of the general formula I included in the charge transport film ink according to the present embodiment include US2011 / 0278559, WO2011 / 132702, JP2005-179634, and JP2006-233162. Various anions described as counter anions of onium salts, monovalent anions such as Cl, Br, I, PF ₄ , PF ₆ , BF ₄ , SbF ₆ , ClO ₄ , AsF ₆ , triflate, ionic liquid Anions such as bis (perfluoroalkylsulfonyl) imides and 2,2,2-trifluoro-N- (trifluoromethanesulfonyl) acetamide used in the above can also be used. An anion in which the boron atom in the borate anion is replaced with gallium can also be used, but the borate anion is excellent in stability.

In the borate anion represented by the general formula B, Ar ₂₁ , Ar _22, Ar _23, and Ar ₂₄ may be arbitrarily combined with substituents having different numbers of electron-withdrawing groups or groups having different electron-withdrawing forces. Can do.

Table 2 shows examples in which all four substituents Ar ₂₁ , Ar _22, Ar ₂₃ and Ar ₂₄ contain an electron-withdrawing group. Anion A16 in Table 2 shows an example where Ar _{21 and} Ar _22, Ar ₂₃ and Ar ₂₄ are bonded to each other to surround a boron atom to form a spiro ring.
Table 3 shows an example of a combination of a group containing an electron withdrawing group and a group not containing an electron withdrawing group in a combination of Ar ₂₁ , Ar _22, Ar ₂₃ and Ar ₂₄ .
The combination of Ar ₂₁ , Ar _22, Ar _23, and Ar ₂₄ is not limited to the combinations shown in Table 2 and Table 3, and can be appropriately selected and combined from the groups described in Table 2 and Table 3 and other groups. .

When the molar ratio of the cations in the monoiodonium salt is 1, the counter-anion molar ratio is represented by 1 / (anion valence).
Various aromatic monoiodonium salts are commercially available as cationic polymerization initiators and photoacid generators, and onium salts of diphenyliodonium derivatives which may have various counter anions and substituents can be used. A typical example includes a salt represented by the following formula (MNPFPB).

(Aromatic diiodonium salt)
Next, the aromatic diiodonium salt concerning one Embodiment of this invention is demonstrated.
Aromatic Jiyodoniumu salt used in the present invention is a salt comprising a cation represented by the following general formula I _1. Cation of the general formula I ₁ corresponds to the case where n = 1 in the general formula I. Aromatic diiodonium salts are particularly preferred from the viewpoint of solubility.

In the aromatic di-iodonium cation represented by the above general formula I _1, defined and preferred examples of Ar ₁ and Ar ₂ is the same as in the case of mono iodonium cation. The divalent aromatic group introduced as Ar ₃ may be either a divalent group derived from a benzene derivative or a divalent group derived from a heteroaromatic ring. Examples of the divalent aromatic group derived from the benzene derivative include paraphenylene and metaphenylene. Examples of the divalent aromatic group derived from the heteroaromatic ring include divalent heteroaromatic groups such as thienylene group, pyridylene group, and furylene group.

  Some of the hydrogen atoms in these divalent aromatic groups are fatty acids having 4 or less carbon atoms selected from methyl group, 2,5-dimethyl group, methoxy group, isopropyl group, tertiary butyl group, methoxy group and the like. It may be substituted with a group hydrocarbon group.

In Table 4 below, specific examples of phenyl group derivatives, thienyl group derivatives, phenylene group derivatives as Ar ₃ , and thienylene groups as Ar ₁ and Ar ₂ in the diiodonium cation represented by the above general formula I ₁ are shown as examples. Is shown. The combination of Ar ₁ , Ar ₂ and Ar ₃ is not limited to the combinations shown in Table 4, and can be appropriately selected from the groups shown in Table 4 and other groups.

Examples of the counter anion of the diiodonium cation include the same as those of the monoiodonium cation, and a borate anion is preferably used. The molar ratio of the anion is represented by 2 / (anion valence) when the molar ratio of the cation is 1.
To synthesize the borate salt of di-iodonium cations are triflate salt of an aromatic di-iodonium cation of the general formula I _1, tosylate salt or bromide salt is first synthesized. The resulting salt is then reacted with an alkali metal salt of a borate such as lithium tetra (pentafluorophenyl) borate ethyl ether complex in an aqueous alcohol such as aqueous methanol to exchange the anion for the borate anion.

  The synthesis of the triflate salt, tosylate salt, and bromide salt can be performed with reference to the following documents. Triflate salt [reference for synthesis from iodosylbenzene: The Journal of Organic Chemistry, 57, 6810-6814 (1992), Mendelev Communications, 2, 159-160 (1992)], or Tosylate salts [References on synthesis methods: Tetrahedron, 66, 5775-5785 (2010)], or bromide salts [References on synthesis methods using para-phenylene diiodosoacetate as a starting material: Journal of Polymer science: Polymer Letters Edition, 14, 65-71 (1976)].

As an example of a typical aromatic diiodonium salt, a compound represented by the following formula (DIPFPB) showing a synthesis method in Examples is given.

(Aromatic oligoiodonium salt)
Next, the aromatic oligoiodonium salt concerning one Embodiment of this invention is demonstrated.
Aromatic oligo iodonium salt used in the present invention is a salt comprising a cation represented by the following general formula I _2. Cation of the general formula I ₂ corresponds to the case n is an integer of 2 or more in the general formula I.

Here, n is an integer of 2 or more representing a repeating unit.
Specific examples and preferred ranges of Ar ₁ , Ar ₂ and Ar ₃ are the same as in the case of the aromatic iodonium cation represented by the aforementioned general formulas I ₀ and I ₁ .
Specific examples and preferred ranges of the counter anion of the oligoiodonium cation are the same as those of the monoiodonium cation and diiodonium cation, and a borate anion is preferably used. The molar ratio of the counter anion in the oligoiodonium salt is represented by (n + 1) / (valence of the anion) when the molar ratio of the cation is 1.

The aromatic oligoiodonium salt only needs to contain at least a salt containing an oligoiodonium cation having a repeating unit number n of 2 or more and 10 or less, and may be in a state where salts having different n are mixed. When the salt having different n is an aromatic oligoiodonium salt mixed, the average degree of polymerization is preferably 2 to 10, and more preferably 2 to 4.
The borate salt of oligoiodonium cation can be synthesized with reference to ORGANIC LETTERS Vol. 1, No. 2, pages 253-255 (1999). Specifically, the formula to synthesize a triflate salt of oligo iodonium cation represented by I _2, then in the same manner as in the synthesis of Jiyodoniumu salt, in an aqueous alcohol such as aqueous methanol or a polar organic solvent Reaction with an alkali metal salt of borate such as lithium tetra (pentafluorophenyl) borate ethyl ether complex. Finally, the anion is exchanged for the borate anion.

The aromatic iodonium cation used in the present invention has a strong oxidizing action.
Using the molecular orbital calculation software MOPAC7, the level of the lowest free orbital (abbreviated as LUMO) of the iodonium cation represented by the following general formula Ia was calculated using AM1 as a basis function. The degree of polymerization n was varied in the range of 0-4. The results are shown below. In the results shown below, the numerical value in parentheses represents the LUMO level when the vacuum order is 0.

n = 0 (−5.6 eV), n = 1 (−8.5 eV), n = 2 (−10.9 eV), n = 3 (−12.4 eV), n = 4 (−13.7 eV).
From the calculation results, it is predicted that the higher the number of iodonium cations bonded to the aromatic ring, the lower the LUMO level and the stronger the oxidizing power.

  Therefore, aromatic diiodonium cations and aromatic oligoiodonium cations are considered to have a lower LUMO level and stronger oxidizing power than aromatic monoiodonium cations. Therefore, when an aromatic diiodonium cation or an aromatic oligoiodonium cation is used, it can be easily cationized by taking electrons from a charge transport material having a larger ionization potential. As a result, it is considered that the resistance of the charge transport layer can be lowered.

The aromatic monoiodonium salt, diiodonium salt and oligoiodonium salt according to this embodiment also act as a cationic polymerization initiator by applying light or heat. When the charge transport material is a charge transport material having a cationically polymerizable cross-linking group such as a vinyl ether group, an epoxy group, or an oxetane group, the aromatic iodonium salt according to this embodiment is mixed and irradiated with light or heated. The crosslinking reaction can be promoted by performing a treatment such as the above. Therefore, a charge transport film that is insoluble or hardly soluble in a solvent can be formed at a lower temperature or in a shorter time, and the multilayer coating can be easily applied and laminated.
As a result, organic devices such as organic EL elements, organic photovoltaic cells, and organic light-emitting transistors having a multilayer structure can be manufactured at low cost by using wet methods such as coating and printing.

The present invention also relates to an aromatic oligoiodonium salt represented by the following general formula (2).

here,
Ar ₁ and Ar ₂ are substituted or unsubstituted phenyl groups;
Ar ₃ is a substituted or unsubstituted phenylene group;
n is an integer of 2 or more representing the degree of polymerization.

Specific examples of Ar ₁ , Ar ₂ and Ar ₃ include the same groups as those listed in Tables 1 and 4 above.
n is preferably from 2 to 10, and more preferably from 2 to 4. The aromatic oligoiodonium salt may simultaneously contain iodonium cations having different degrees of polymerization n. In that case, the average degree of polymerization of the iodonium cation is preferably 2 to 10, and more preferably 2 to 4.

2. Charge Transport Material Hereinafter, the charge transport material contained in the charge transport film ink according to the embodiment will be described.

  The charge transport material contained in the charge transport film ink according to the embodiment is a material included in the charge transport layer of the organic EL element as described above. Examples of the charge transport layer include a hole injection layer, a hole transport layer, an electron block hole transport layer, and a light emitting layer. The charge transporting material is soluble in a solvent, and any charge transporting material usually used in the art can be used as long as it has charge transporting properties. It is preferable that it is a compound which has property.

  The charge transporting material may be any of a low molecular material, an oligomer material, and a polymer material, and it is preferable to use a material having good wet film forming properties. As the charge transport material, a charge transport compound may be used alone, or two or more kinds may be used in combination. The solubility of the charge transport material in the solvent is desirably at least 0.1% by mass, more preferably 1% by mass.

  As a hole transporting low molecular weight compound that can be applied or printed, for example, a highly amorphous starburst type, spiro type, oligomer type, or polymer type aromatic tertiary amine compound is preferably used. Specific examples of starburst type aromatic tertiary amine compounds include tris [4- [phenyl (3-methylphenyl) amino] phenyl] amine and the like, and specific examples of spiro type aromatic tertiary amine compounds. 2,2 ′, 7,7′-tetrakis [N-naphthalenyl (phenyl) -amino] -9,9-spirobifluorene (hereinafter abbreviated as spiro-NPD) and the like.

Specific examples of the hole transporting oligomer include N, N′-bis [4 ′-(diphenylamino) -1,1′biphenyl-4-yl] -N, N in which four triphenylamine structural units are connected. Examples include '-diphenyl-1,1'-biphenyl-4,4'-diamine.
Specific examples of hole transporting polymers include poly (3,4-ethylenedioxythiophene), poly (3-hexylthiophene-2,5-diyl), and poly (9,9-dioctylfluorenyl-2). , 7-diyl) -co- (N, N′-bis {p-butylphenyl} -1,1′-biphenylene-4,4′-diamine) and the like.

A light-emitting compound can also be used as long as it has characteristics such as wet film-forming properties, heat resistance, hole transport properties, or light-emitting properties. The light emitting compound may be a low molecular compound or a polymer.
Depending on the pressure and temperature of the atmosphere, the film may evaporate under vacuum and at a high temperature during heat drying of the film containing a low molecular compound or heat treatment for crosslinking. However, evaporation can be suppressed by using an amorphous and highly soluble hole transporting low molecular weight compound or oligomer having a molecular weight of 500 or more, more preferably a molecular weight of 800 or more.

When the film formed with the ink containing the aromatic iodonium salt according to the embodiment is heat-treated, the aromatic iodonium salt takes electrons from the charge transport material and cationizes the charge transport material. As a result, the hole carrier density in the charge transport material is increased, and a charge transport film having a volume resistivity as low as several to seven orders of magnitude can be obtained.
In addition, the charge transporting compound constituting the charge transporting material may have a crosslinkable group that crosslinks with light, heat, or acid. Examples of such a crosslinkable group include a vinyl group, an allyl group, and an isobutenyl group. , Vinyl ether group, epoxy group, oxetane group, benzocyclobutene group, thienyl group, alkoxysilane group, and a combination of thiol group and ene group.

  The present invention also relates to a composition for a charge transport film comprising a charge transport compound and an aromatic oligoiodonium salt. The charge transporting compound contained in this composition is as described above as the charge transporting material, and the aromatic oligoiodonium salt is also as described above.

<Method for producing charge transport film>
The charge transport film ink according to the embodiment is applied to the formation of the hole injection layer 3, the hole transport layer 4 or the light emitting layer 5 in the organic EL element shown in FIG. Can do. Specifically, the method for producing a charge transport film of the present invention includes forming a film by a wet film formation method using the charge transport film ink according to the above embodiment, and heat-treating the obtained film. including.
When the hole injection layer is a film having a thickness of 100 nm or more and low resistance, an effect of suppressing the short circuit of the element by covering the projection of the anode can be expected.

The charge transport film of this embodiment may be heat-treated on the hot plate or in the oven after formation, in the air, under reduced pressure, or in an inert gas atmosphere. Thereby, the charge transport material is cationized, the hole carrier density is increased, and the resistance of the film is lowered.
The resistivity of the charge transport film can be adjusted by the solid content of the aromatic iodonium salt mixed in the ink. Usually, it can be used by adjusting in the range of 0.5 mass% to 30 mass%.

  When the ink according to the embodiment is used for forming the hole injection layer 3, the aromatic iodonium salt is not included by adjusting the aromatic iodonium salt concentration in the total solid content of the ink to about 1% by mass. In comparison, the volume resistivity can be reduced by 1 to 2 digits. When 5% by mass or more is mixed, the resistivity can be reduced by about 4 to 7 orders of magnitude compared to an unmixed film.

For example, a case where a film is formed by spin coating an ink in which an aromatic diiodonium salt (DIPFPB) is mixed with a cross-linked hole transporting polymer (HT-A) will be examined. In a film not mixed with (DIPFPB), the volume resistivity takes a high value of the order of 1 × 10 ¹¹ Ω · cm or more, whereas when (DIPFPB) is mixed in a solid content of 10% by mass or more, 1 × 10 ⁵ Ω -The volume resistivity can be as low as cm order.
By using a similar hole transporting polymer or a low molecular material containing a hole transporting group such as an aromatic tertiary amine in combination with an aromatic iodonium salt, the resistance of the film can be lowered. By applying such a film to the hole injection layer or the transport layer of the EL element, the driving voltage of the EL element can be reduced.

  When the solid content of the aromatic iodonium salt in the ink is higher than 30% by mass, the rate of decrease in the film resistance tends to be saturated. When aromatic iodonium salts are mixed at a high concentration, the concentration of counter anions in the film also increases, so that the distance between the hole transporting compounds is increased, and hole hopping is suppressed. Therefore, the concentration of the aromatic iodonium salt in the total solid content of the ink is usually 30% by mass or less (or at most, less than the amount of the substance corresponding to half of the cationized units in the charge transport material).

  When mixing aromatic iodonium salts to increase the hole transport capability of the hole transport layer or hole transport electron blocking layer in contact with the light emitting layer, the cation radical of the generated hole transport material is near the interface of the light emitting layer. Excitons may be deactivated or EL light may be absorbed. Therefore, the amount of aromatic iodonium salt is desirably 20% by mass or less, more preferably 5% by mass or less, based on the total solid content of the ink.

Similarly, in the case of mixing an aromatic iodonium salt for the purpose of increasing the hole transporting ability of the hole transporting light emitting layer containing the light emitting dopant material or the light emitting layer, the amount of aromatic iodonium salt is the total solid content of the ink. It is preferable that it is 5 mass% or less of 3 mass% or less.
Conditions such as the appropriate heating temperature, time, and pressure of the drying atmosphere in the heat treatment after wet film formation include the decomposition temperature of the aromatic iodonium salt, the volatilization temperature of the decomposition product, the boiling point and vapor pressure of the solvent used, and charge transport. It selects suitably according to the crystallization temperature of a crystalline compound, the kind of crosslinking group, etc.
However, the heating temperature is preferably lower than the temperature at which crystallization, sublimation, or decomposition of the charge transporting compound in the ink occurs, and is preferably equal to or higher than the temperature at which the solvent has a vapor pressure sufficient for drying.

The normal heat treatment is performed at 100 ° C. or higher, more preferably at 130 to 250 ° C. for 10 seconds to 2 hours, even more preferably 10 at atmospheric pressure, in an inert atmosphere such as nitrogen or argon, or under reduced pressure. It takes about one hour from a minute.
If the time is too short or the heat treatment temperature is too low, a decomposition product of the cation component of the aromatic iodonium salt may remain in the film.
Further, if the time is too long or the heat treatment temperature is too high, the emission spectrum of the charge transport material may change or be altered.
Examples of the heating process include a hot plate, a clean oven, an infrared ray, a halogen heater, and microwave heating, but the hot plate is excellent for uniform heating.

  The substrate on which the charge transport film is applied and printed may be placed on a hot plate or the like in the air immediately after the application printing and dried while sucking volatile vapor. In a glove box where the coating film is preliminarily heated and dried on a hot plate at a temperature (for example, 80 ° C. to 100 ° C.) at which the coating film is hardly oxidized and deteriorated, and then replaced with an inert atmosphere with argon or nitrogen gas. Alternatively, it may be heated to a higher temperature (for example, 100 ° C. to 250 ° C.) in a clean oven or a vacuum oven and dried completely. Moreover, you may perform the crosslinking process above glass transition temperature.

  Moreover, in the charge transport film of the present embodiment, a patterned charge transport film can be produced as necessary. Specifically, after wet film formation is performed using the charge transport film ink containing the aromatic iodonium salt and the cross-linked charge transport material according to the embodiment, pattern exposure is performed on a predetermined region of the coating film. According to pattern exposure, for example, exposure can be selectively performed by ultraviolet light irradiation through a photomask, or scanning with laser light or LED light. Only the exposed portion of the coating film is selectively photocationically polymerized or crosslinked by photoreaction or thermal reaction to form a charge transport film insoluble or hardly soluble in the organic solvent.

The unexposed part of the coating film can be dissolved and removed with an organic solvent. Thereafter, by heating and drying to remove volatile components, a patterned charge transport film having a low resistance can be obtained.
By performing such patterning, the charge transport film in an unnecessary region can be dissolved and removed after the ink is applied over a wide range by a die coating method or the like that does not require much cost. Specifically, areas that are not related to light emission, such as a sealing adhesion area for bonding to a moisture-proof cover glass, a terminal connection area, and an area on a drive circuit, on an organic EL panel substrate that is multifaceted to a large glass substrate It is effective to remove the charge transport film.

As a result, it is possible to selectively form a charge transport film only in a desired light emitting area.
Also, by making the hole injection layer and hole transporting light emitting layer in the light emitting pixel into a finely divided pattern, light escaping in the film surface direction at the pattern end face is diffused, and the light extraction efficiency to the outside of the element is improved. Is also possible.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, the content of this invention is not limited by this.
<1. Synthesis of aromatic iodonium salt>
Example 1
Aromatic diiodonium salts were synthesized and their properties were investigated.
First, 0.5 g (2.27 mmol) of iodosylbenzene and 5.7 mL of methylene chloride were mixed in a Schlenk flask under an argon atmosphere to obtain a suspension. The suspension was stirred while cooling with ice, and 0.4 mL (4.57 mmol) of trifluoromethanesulfonic acid was added dropwise. This was stirred at room temperature for 22 hours to obtain a reaction mixture. After the reaction mixture was ice-cooled, tert-butylbenzene 0.304 g (2.27 mmol) was added dropwise to bring the liquid temperature back to room temperature.

  After reacting with stirring at room temperature for 4 hours, the solvent in the reaction mixture was distilled off under reduced pressure to obtain a black tar-like product. Ether was added to the tar-like material to precipitate crystals, and suction filtration was performed to collect the precipitate. The precipitate was washed with ether and dried under reduced pressure to obtain 0.84 g of white powder. The yield was 44.2%.

The analysis result of the obtained white powder is shown below.
¹ H-NMR (CD ₃ OD, ppm) δ 1.31 (s, 9H), 7.52 to 7.59 (m, 4H), 7.70 to 7.74 (m, 1H), 8.09 to 8.11 (m, 2H), 8.19 to 8.21 (m, 2H), 8.25 (bs, 4H)
¹⁹ F-NMR (CD3OD, ppm) δ 80.0 (CF ₃ )
The white powder obtained here was identified as an intermediate compound [4- (phenyliodonio) phenyl] (4-tert-butylphenyl) iodonium bistriflate represented by the following chemical formula.

0.3 g (0.36 mmol) of the obtained intermediate compound was dissolved in 3.0 mL of methanol under an argon atmosphere. To the obtained methanol solution, 3.0 mL of ion-exchanged water was added to prepare an intermediate solution, which was heated to 50 ° C.
On the other hand, lithium tetrakis (pentafluorophenyl) borate-ethyl ether complex 0.89 g (0.72 mmol, 70% manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in ion-exchanged water to prepare a solution. The obtained solution was added dropwise to the above-mentioned intermediate solution and reacted at 50 ° C. for 1 hour with stirring.

  Crystals were confirmed in the mixture after the reaction. After returning the temperature of the mixture containing crystals to room temperature, the mixture was diluted with 10 mL of ion-exchanged water. Crystals were collected by suction filtration, washed with ion-exchanged water, and dried under reduced pressure at 50 ° C. As a result, 0.66 g of white crystals was obtained, and the yield was 97.2%. About 0.4 g of this white crystal was dissolved in 1 mL of anisole at room temperature. Similarly, about 0.4 g of this white crystal was dissolved in 1 mL of cyclohexanone at room temperature.

The analysis results of the obtained white crystals are shown below.
¹ H-NMR (CD ³ OD, ppm) δ 1.30 (s, 9H), 7.51 to 7.59 (m, 4H), 7.69 to 7.73 (m, 1H), 8.09 ( d, J = 8.4 Hz, 2H), 8.19 (d, J = 7.6 Hz, 2H), 8.26 (bs, 4H)
¹⁹ F-NMR (CD ₃ OD, ppm) δ-133.8 (Ar-F), -165.7 (Ar-F), -169.6 (Ar-F)
2 shows a ¹ H-NMR chart of the aromatic diiodonium salt (DIPFPB) obtained in Example 1, and FIG. 3 shows an enlarged chart of ¹ H-NMR in FIG. The peak at 1.30 ppm indicates the presence of a tert-butyl group. The peak from 7.5 ppm to 8.3 ppm indicates the proton signal on the benzene ring of [4- (phenyliodonio) phenyl] (4-tert-butylphenyl) iodonium, and the peak at 8.26 ppm is The signals of four protons on the benzene ring are shown. The peak near 3.3 ppm is due to the methyl group in the solvent, and the peak near 4.9 ppm is due to the hydroxy group in the solvent.

4 is a ¹⁹ F-NMR chart of an aromatic diiodonium salt (DIPFPB) obtained in Example 1. FIG. Three peaks in the vicinity of −134 ppm, −166 ppm, and −170 ppm indicate the presence of fluorine in three different environments that tetrakispentafluorophenyl borate has.
FIG. 5 shows an infrared absorption spectrum (measured by the diffuse reflection method) of the aromatic diiodonium salt (DIPFPB) obtained in Example 1.

The white crystals obtained here were a compound represented by the following formula: [4- (phenyliodonio) phenyl] (4-tert-butylphenyl) iodonium bis [tetrakis (pentafluorophenyl)] borate (hereinafter referred to as DIPFPB). Also identified).

(Example 2)
An aromatic oligoiodonium salt (OligoIPFPB) was synthesized and its characteristics were investigated.
First, an intermediate compound (OligoITfO) represented by the following formula was synthesized with reference to ORGANIC LETTERS Vol. 1, No. 2, pages 253-255, 1999.

Under argon atmosphere, 2.4 g (7.5 mmol, manufactured by Tokyo Chemical Industry) of diacetyliodosylbenzene was added as powder to 13.5 mL of trifluoromethanesulfonic acid cooled to 0 ° C. in a Schlenk flask, and then returned to room temperature. Stir for 2 hours. To this, 4.02 g (29.95 mmol) of tert-butylbenzene was added dropwise, followed by stirring at room temperature for 20 hours.
The reaction mixture was poured into ice water, and the precipitated brown precipitate was collected by suction filtration. After the precipitate was dispersed in ether under stirring, the precipitate was collected by suction filtration, washed with ether and then dried under reduced pressure to obtain 1.3 g of a light ocher powder.

The analysis result of the intermediate compound (OligoITfO) of the obtained light ocher powder is shown below.
¹ H-NMR (CD ₃ OD, ppm) δ 1.26 to 1.32 (m), 7.50 to 7.61 (m), 7.68 to 7.76 (m), 7.87 to 7. 94 (m), 8.06 to 8.13 (m), 8.17 to 8.35 (m)
¹⁹ F-NMR (CD3OD, ppm) δ-79.9 (CF3)
FIG. 6 shows a ¹ H-NMR chart of the aromatic oligoiodonium salt (OligoITfO) obtained in Example 2. FIG. 7 shows an enlarged view around 1.26 to 1.32 ppm in FIG. The tip of the tert-Bu peak at 1.26 to 1.32 ppm is broken into a plurality of pieces, indicating that it is an oligomer. Also, if the integral value 9.0 of the signal corresponding to tert-Bu at 1.25 to 1.35 ppm is 9H, it corresponds to four hydrogens in the aromatic ring sandwiched between two iodonium of 8.25 ppm or more The signal integration is 12H. By dividing this by 4, the average degree of polymerization n is calculated to be 3.0. The average molecular weight was calculated as iodonium cation content 945.85 + triflate content 148.95 × 4 = 1541.65.
The peak near 3.3 ppm is due to the methyl group in the solvent, and the peak near 4.8 ppm is due to the hydroxy group in the solvent.

FIG. 8 shows a ¹⁹ F-NMR chart of the aromatic oligoiodonium salt (OligoITfO) obtained in Example 2. The peak appearing at −79.9 ppm indicates the fluorine of trifluoromethanesulfonate.

Next, an aromatic oligoiodonium salt (OligoIPFPB) represented by the following formula was synthesized, and the characteristics were measured.

  After dissolving 1.3 g (about 0.84 mmol) of OligoITfO in 17 mL of methanol in a Schlenk flask under an argon atmosphere, 17 mL of ion-exchanged water was added and heated to 50 ° C. A solution prepared from 4.33 g (3.48 mmol, 70% manufactured by Tokyo Chemical Industry) of lithium tetrakis (pentafluorophenyl) borate-ethyl ether complex and 35 mL of ion-exchanged water and 2.5 mL at 50 ° C. were added thereto. Stir for hours. Thereafter, the mixture was further stirred at room temperature for 15 hours.

  After completion of the reaction, 50 mL of ion exchange water was added for dilution, and the supernatant was removed by decantation. Thereto was added 70 mL of ion-exchanged water, and the crystals were dispersed in an ultrasonic bath. The obtained crystals were collected by suction filtration, dissolved in 100 mL of acetone, and insoluble matters were removed by suction filtration. After the solvent was distilled off, ion-exchanged water cooled with ice was added to the remaining tar-like product to crystallize the tar-like product. The crystals were pulverized in ion-exchanged water, and then collected by suction filtration and washed with ion-exchanged water. Subsequently, it dried under reduced pressure at 50 degreeC and obtained 2.9g of off-white powder (OligoIPFPB).

About 0.2 g or more of this white crystal was dissolved in 1 mL of anisole at room temperature. This white crystal was similarly dissolved in about 1 g of cyclohexanone at room temperature in an amount of about 0.5 g or more.
The analysis results of the obtained grayish white powder (OligoIPFPB) are shown below.

¹ H-NMR (CD ₃ OD, ppm) δ 1.25 to 1.35 (m), 7.47 to 7.61 (m), 7.66 to 7.75 (m), 7.84 to 7. 94 (m), 8.03 to 8.11 (m), 8.13 to 8.21 (m, 2H), 8.22 to 8.37 (m, 12H)
¹⁹ F-NMR (CD3OD, ppm) δ-133.8 (Ar-F), -165.6 (Ar-F), -169.5 (Ar-F)
FIG. 9 shows a ¹ H-NMR chart of (OligoIPFPB) obtained in Example 2. FIG. 10 shows an enlarged view of the vicinity of 1.25 to 1.35 ppm in FIG. The tip of the tert-Bu peak at 1.25 to 1.35 ppm is broken into multiple pieces, indicating that it is an oligomer.

If the integral value 0.792 corresponding to tert-Bu at 1.25 to 1.35 ppm is 9H, it corresponds to four hydrogens in an aromatic ring sandwiched between two iodonium at 8.2 ppm or more. The integrated value 1.0 of the signal is 11.36H. By dividing this by 4, the average degree of polymerization n is calculated to be 2.84.
The peak near 3.3 ppm is due to the methyl group in the solvent, and the peak near 4.8 ppm is due to the hydroxy group in the solvent.

FIG. 11 shows a ¹⁹ F-NMR chart of (OligoIPFPB) obtained in Example 2. The peaks at -133.8 ppm, -165.6 ppm and -169.5 ppm indicate the fluorine group of tetrapentafluorophenyl borate.
FIG. 12 shows an infrared absorption spectrum (measured by the diffuse reflection method) of (OligoIPFPB) obtained in Example 2.
From the above results, (OligoIPFPB) was identified as an aromatic oligoiodonium salt having an average degree of polymerization of 2.84.

<2. Preparation of ink and evaluation of storage stability>
(Example 3)
A charge transport film composition was prepared using the aromatic diiodonium salt (DIPFPB) obtained in Example 1 and a crosslinked hole transporting polymer. The used cross-linked hole transporting polymer is represented by the following chemical formula (HT-A) and has a weight average molecular weight of 279,000. First, a crosslinkable polymeric holey polymer and an aromatic diiodonium salt were mixed to obtain a charge transport film composition. The blending amount of the aromatic diiodonium salt (DIPFPB) was 30% by mass of the total solid content of the ink.

37 mg of the resulting solid charge transport film composition was dissolved in anisole at room temperature to obtain a light green transparent solution having a solid content of 0.7% by mass. In order to avoid photodegradation of aromatic diiodonium salt by external light and oxidation reaction of crosslinked hole transporting polymer and promotion of crosslinking, the solution was prepared in the dark.
Furthermore, when it stirred at 60 degreeC for 1 hour and it cooled to room temperature, the color of the solution changed to dark blue. The coloration of the solution is presumed to be due to the charge transfer complex being formed by the aromatic diiodonium salt and the cross-linked polymeric holey polymer, and the polymer being oxidized.

When the deep blue solution was dried under reduced pressure, about 37 mg of a greenish blue solid was obtained. This was dissolved in 1.5 ml of cyclopentanol while being stirred at room temperature under light shielding to obtain a light brown transparent solution. It is presumed that the charge transfer complex was eliminated and the color disappeared by coordination of the solvent cyclopentanol to the cation of the charge transfer complex.
From the above results, it was found that anisole, which is an aromatic ether, promotes coloring of ink, and cyclopentanol, which is an alicyclic monohydric alcohol, suppresses coloring of ink.

(Comparative Example 1)
A charge transport film ink was prepared using an aromatic monoiodonium salt and a crosslinked hole transporting polymer.
As the aromatic monoiodonium salt, the compound represented by the aforementioned formula (MNPFPB) (manufactured by Tokyo Chemical Industry) was used. As the cross-linked hole transporting polymer, the compound represented by the above formula (HT-A) is used, and its weight average molecular weight is 427,000.

First, a crosslinkable hole transporting polymer and an aromatic monoiodonium salt are mixed so that the concentration of the aromatic monoiodonium salt is 20% by mass of the total solid content to obtain a powder of the composition for a charge transport film. It was. This powder was dissolved in anisole in a glass sample tube to prepare a solution having a solid content of about 1% by mass.
This ink 1 was colorless and transparent during the preparation, but was left in a yellow light clean room and colored a deep blue after one day.

(Comparative Example 2)
A charge transport film ink was prepared using an aromatic monoiodonium salt and a crosslinked hole transporting polymer.
As the aromatic monoiodonium salt, the compound represented by the above formula (MNPFPB) was used. As the cross-linked hole transporting polymer, the compound represented by the above formula (HT-A) was used, and its weight average molecular weight was 56,000.

First, a crosslinkable hole transporting polymer and an aromatic monoiodonium salt are mixed so that the concentration of the aromatic monoiodonium salt is 20% by mass of the total solid content to obtain a powder of the composition for a charge transport film. It was. This powder was dissolved in tetralin in a glass sample tube to prepare a solution having a solid content of about 1% by mass.
This ink 2 was colorless and transparent during preparation, but was left in a yellow light clean room and colored light brown after 4 days.

Example 4
A charge transport film ink was prepared in the same manner as in Comparative Examples 1 and 2 described above by changing the solvent to a mixed solvent of cyclohexanone and anisole.
In preparing the ink, first, a mixed solvent in which cyclohexanone and anisole were mixed at a volume ratio of 8: 2 in a glass sample tube was prepared. Next, the crosslinkable hole transporting polymer (weight average molecular weight 200,000) represented by the above formula (HT-A) and the aromatic monoiodonium salt (MNPFPB) are mixed with the total solid content of (MNPFPB). The charge transport film ink 3 was prepared by dissolving in a mixed solvent so that the total solid content in the ink was 1.3% by mass.

  In ink 3, 4/5 of the solvent is cyclohexanone. This ink 3 was colorless and transparent during preparation, and was colorless and transparent even after one month passed in a yellow light clean room, and no change occurred. In ink 3, cyclohexanone which is an alicyclic ketone accounts for 4/5 of the solvent. For this reason, it is presumed that the formation of colored components such as the formation of a charge transfer complex by an aromatic monoiodonium salt and a hole transporting polymer or the formation of an oxidized form of a hole transporting polymer is suppressed.

(Example 5)
A charge transport film ink was prepared in the same manner as in Comparative Examples 1 and 2 described above by changing the solvent to a mixed solvent of tetralin and cyclohexanol.
As the aromatic monoiodonium salt, the compound represented by the above formula (MNPFPB) was used. As the cross-linked hole transporting polymer, the compound represented by the above formula (HT-A) was used, and its weight average molecular weight was 56,000.

First, a crosslinkable hole transporting polymer and an aromatic monoiodonium salt (MNPFPB) are mixed so that the concentration of (MNPFPB) is 20% by mass of the total solids, and the powder of the charge transport film composition is mixed. Obtained.
Meanwhile, tetralin and cyclohexanol were mixed at a volume ratio of 2: 1 in a glass sample tube to prepare a mixed solvent. Ink 4 was prepared by dissolving the aforementioned powder of the composition for a charge transport film in the obtained mixed solvent so that the solid content was about 1% by mass.

This ink 4 was colorless and transparent during the preparation, and was colorless and transparent and remained unchanged even after being left in a clean room for 4 days.
In ink 4, cyclohexanol, which is an alicyclic monohydric alcohol, accounts for 1/3 of the solvent. For this reason, it is presumed that the formation of colored components such as the formation of charge transfer complexes by aromatic monoiodonium salts and a hole transporting polymer or the formation of an oxidized form of a hole transporting polymer was suppressed.

(Example 6)
A charge transport film ink was prepared in the same manner as in Comparative Examples 1 and 2 described above by changing the solvent to a mixed solvent of tetralin and cyclooctanol.
As the aromatic monoiodonium salt, the compound represented by the above formula (MNPFPB) was used. As the cross-linked hole transporting polymer, the compound represented by the above formula (HT-A) was used, and its weight average molecular weight was about 56,000.

First, a crosslinkable hole transporting polymer and an aromatic diiodonium salt are mixed so that the concentration of the aromatic monoiodonium salt is 20% by mass of the total solid content, thereby obtaining a powder of the composition for a charge transport film. It was.
Meanwhile, in a glass sample tube, tetralin and cyclooctanol were mixed at a volume ratio of 2: 1 to prepare a mixed solvent. Ink was obtained by dissolving the aforementioned powder of the charge transport film composition in the resulting mixed solvent so that the solid content was about 1% by mass.

  This ink 5 was colorless and transparent during the preparation, and was colorless and transparent even after one month passed in the yellow light clean room, and no change occurred. In ink 5, cyclooctanol, which is an alicyclic monohydric alcohol, accounts for 1/3 of the solvent. For this reason, it is presumed that the formation of colored components such as the formation of a charge transfer complex by an aromatic monoiodonium salt and a hole transporting polymer or the formation of an oxidized form of a hole transporting polymer is suppressed.

(Comparative Example 3)
A charge transport film ink was prepared using an aromatic diiodonium salt and a cross-linked hole transporting polymer using anisole as a solvent.
As the aromatic diiodonium salt, the compound represented by the formula (DIPFPB) synthesized in Example 1 was used. As the cross-linked hole transporting polymer, the compound represented by the above formula (HT-A) was used, and its weight average molecular weight was about 279,000.

First, a crosslinkable hole transporting polymer and an aromatic diiodonium salt are mixed so that the concentration of the aromatic diiodonium salt is 15% by mass of the total solid content, thereby obtaining a powder of the composition for a charge transport film. It was.
This powder was dissolved in anisole in a glass sample tube to prepare a solution having a solid content of 1% by mass.
The ink 6 was colorless and transparent during the preparation, but turned into a light blue transparent solution after 15 hours in a yellow light clean room, and changed to a blue transparent solution after 4 days. It is considered that a charge transfer complex of an aromatic diiodonium salt and a hole transporting polymer was formed in the ink with the passage of time.

(Example 7)
A charge transporting film ink was prepared using an aromatic diiodonium salt and a cross-linked hole transporting polymer using cyclohexanone as a solvent.
As the aromatic diiodonium salt, the compound represented by the formula (DIPFPB) synthesized in Example 1 was used. As the cross-linked hole transporting polymer, the compound represented by the above formula (HT-A) was used, and its weight average molecular weight was about 279,000.

First, a crosslinkable hole transporting polymer and an aromatic diiodonium salt are mixed so that the concentration of the aromatic diiodonium salt is 25% by mass of the total solid content to obtain a powder of the composition for a charge transport film. It was.
This powder was dissolved in anisole in a glass sample tube to prepare a solution having a solid content of 1.28% by mass.

  The ink 7 was colorless and transparent during preparation, but remained colorless and transparent after 5 days in a yellow light clean room. The solvent of ink 7 is 100% cyclohexanone. It is presumed that cyclohexanone suppressed the formation of colored components such as the formation of a charge transfer complex by an aromatic diiodonium salt and a hole transporting polymer or the formation of an oxidized form of a hole transporting polymer.

(Example 8)
A charge transport film ink was prepared in the same manner as in Example 7 except that the solvent was changed to a mixed solvent of anisole and cyclohexanone.
As the aromatic diiodonium salt, the compound represented by the above formula (DIPFPB) was used. As the cross-linked hole transporting polymer, the compound represented by the above formula (HT-A) was used, and its weight average molecular weight was about 279,000.

First, a cross-linked hole transporting polymer and an aromatic diiodonium salt were mixed so that the concentration of the aromatic diiodonium salt was 25% by mass of the total solid content, thereby obtaining a powder of the composition for a charge transport film. .
On the other hand, in a glass sample tube, anisole and cyclohexanone were mixed at a volume ratio of 2: 3 to prepare a mixed solvent. Ink 8 was obtained by dissolving the aforementioned powder of the charge transport film composition in the resulting mixed solvent so that the solid content was 1.2% by mass.

  This ink 8 was colorless and transparent during the preparation, and no change occurred even after one month in the yellow light clean room. In ink 8, cyclohexanone, which is an alicyclic ketone, accounts for 3/5 of the solvent. For this reason, it is presumed that the formation of colored components such as the formation of a charge transfer complex by the aromatic diiodonium salt and the hole transporting polymer or the formation of an oxidant of the hole transporting polymer is suppressed.

(Comparative Example 4)
A charge transport film ink was prepared in the same manner as in Example 7 except that the solvent was changed to tetralin.
As the aromatic diiodonium salt, the compound represented by the above formula (DIPFPB) was used. As the cross-linked hole transporting polymer, the compound represented by the above formula (HT-A) was used, and its weight average molecular weight was about 279,000.

First, a cross-linked hole transporting polymer and an aromatic diiodonium salt were mixed so that the concentration of the aromatic diiodonium salt was 10% by mass of the total solid content, thereby obtaining a powder of the composition for a charge transport film. .
This powder was dissolved in tetralin in a glass sample tube to prepare a solution having a solid content of about 1% by mass.
The ink 9 was colorless and transparent during preparation, but when left in a yellow light clean room, the color changed to blue and transparent after 4 days.

Example 9
A charge transport film ink was prepared in the same manner as in Example 7 except that the solvent was changed to a mixed solvent of tetralin and cyclopentanol.
As the aromatic diiodonium salt, the compound represented by the above formula (DIPFPB) was used. As the cross-linked hole transporting polymer, the compound represented by the above formula (HT-A) was used, and its weight average molecular weight was about 279,000.

First, a cross-linked hole transporting polymer and an aromatic diiodonium salt were mixed so that the concentration of the aromatic diiodonium salt was 15% by mass of the total solid content to obtain a powder of the composition for a charge transport film. .
On the other hand, tetralin and cyclopentanol were mixed in a volume ratio of 3: 1 in a glass sample tube to prepare a mixed solvent. Ink 10 was obtained by dissolving the above-described composition powder for charge transport film in the obtained mixed solvent so that the solid content was about 1% by mass.

  This ink 10 was colorless and transparent during preparation, and no change occurred even after 4 days in a yellow light clean room. In ink 10, cyclopentanol, which is a monovalent alicyclic alcohol, accounts for ¼ of the solvent. Therefore, it is presumed that the formation of colored components such as the formation of a charge transfer complex by an aromatic diiodonium salt and a hole transporting polymer or the formation of an oxidized form of a hole transporting polymer is suppressed.

(Example 10)
A charge transport film ink was prepared in the same manner as in Example 7 except that the crosslinked hole transporting polymer was changed to a hole transporting light emitting material which is a low molecular compound.
As the aromatic diiodonium salt, the compound represented by the above formula (DIPFPB) was used. As a hole transporting light emitting material which is a low molecular weight compound, a material containing a hole transporting aromatic tertiary amine represented by the following formula (LHBE-A) and a blue light emitting anthracene ring in the molecule. It was used.

As the solvent, a mixed solvent in which cyclohexanone and anisorule were mixed at a volume ratio of 8: 2 was used. Ink 11 was obtained by dissolving the aforementioned powder of the charge transport film composition in this mixed solvent so that the solid content was about 5% by mass.
This ink 11 was light yellow and transparent during the preparation, and no change occurred even after 1 month of light-shielding storage. In ink 11, cyclohexanone, which is a monovalent alicyclic ketone, occupies 4/5 of the solvent. Therefore, the formation of colored components such as the formation of charge transfer complexes by the aromatic diiodonium salts and low molecular hole transport materials containing aromatic tertiary amines and the formation of oxidants of the low molecular hole transport materials is suppressed. Presumed to have been.

(Comparative Example 5)
A charge transport film ink was prepared using an aromatic oligoiodonium salt, a crosslinked hole transporting polymer, and anisole as a solvent.
As the aromatic oligoiodonium salt, (OligoIPFPB) synthesized in Example 2 was used. As the cross-linked hole transporting polymer, the compound represented by the above formula (HT-A) was used, and its weight average molecular weight was about 279,000.

First, a crosslinkable hole transporting polymer and an aromatic oligoiodonium salt are mixed so that the concentration of the aromatic diiodonium salt is 15% by mass of the total solid content, thereby obtaining a powder of the composition for a charge transport film. It was.
This powder was dissolved in anisole in a glass sample tube to prepare a solution having a solid content of 1% by mass.
The ink 12 turned dark blue immediately after preparation. Since (OligoIPFPB) has a strong oxidizing power, it is considered that a charge transfer complex or an oxidant was immediately formed in the ink.

(Example 11)
An ink for a charge transport film was prepared using an aromatic oligoiodonium salt, a crosslinked hole transporting polymer, and a mixed solvent of tetralin and cyclopentanol as a solvent.
As the aromatic oligoiodonium salt, (OligoIPFPB) synthesized in Example 2 was used. As the cross-linked hole transporting polymer, the compound represented by the above formula (HT-A) was used, and its weight average molecular weight was about 279,000.

First, a crosslinkable hole transporting polymer and an aromatic oligoiodonium salt are mixed so that the concentration of the aromatic oligoiodonium salt is 20% by mass of the total solid content to obtain a powder of the composition for a charge transport film. It was.
On the other hand, in a glass sample tube, tetralin and cyclopentanol were mixed at a volume ratio of 7: 3 to prepare a mixed solvent. Ink 13 was obtained by dissolving the above-mentioned composition powder for charge transport film in the obtained mixed solvent so as to have a solid content of about 1% by mass.
This ink 13 was colorless and transparent during preparation, and became slightly light yellow after 4 days in a yellow light clean room, but hardly changed. In ink 13, cyclopentanol, which is a monovalent alicyclic alcohol, accounts for ¼ or more of the solvent. Therefore, in the case of the ink 12, the ink 13 was immediately colored, whereas in the ink 13, the formation of a charge transfer complex or a hole transporting polymer by an aromatic oligoiodonium salt and a hole transporting polymer containing an aromatic tertiary amine. It is presumed that the formation of colored components, such as the formation of oxidants, was suppressed.

(Example 12)
Ink solvents having different viscosities were prepared by changing the mixing ratio of cyclooctanol and tetralin.
FIG. 13 shows the relationship between the concentration of cyclooctanol in the mixed solvent of cyclooctanol and tetralin and the viscosity of the mixed solvent. The viscosity of the solvent was measured at 23 ° C. with HAAKE viscoelasticity measurement rheology evaluation apparatus MARS. The viscosity in the case of 100% cyclooctanol was 153 mPa · s.

  When the concentration of cyclooctanol, which is an alicyclic monohydric alcohol, is reduced from 1/4 to 7/10 of the total volume of the mixed solvent, a mixed solvent having a viscosity of 3 mPa · s to 20 mPa · s suitable for the ink jet system can be obtained. . It can also be seen that in order to obtain a mixed solvent having a viscosity of about 30 mpa · s or more and 150 mPa · s suitable for the relief printing method, the cyclooctanol concentration should be 78% or more of the total volume of the mixed solvent.

The viscosity of the ink in which the low molecular weight material such as the compound represented by the formula (LHBE-A) is dissolved is approximately equal to the viscosity of the solvent. Therefore, when an aromatic solvent such as tetralin or an aromatic ether solvent such as anisole is used alone, an ink having a viscosity suitable for coating or printing cannot be obtained.
Therefore, when using a low molecular weight compound or a polymer with a low weight average molecular weight as a charge transport material, use a mixed solvent in which alicyclic monohydric alcohol having a high viscosity is mixed with 1/4 or more of the total capacity of the solvent. By doing so, it is possible to produce a highly stable ink having a viscosity suitable for various printing methods and suppressing discoloration or oxidation during storage or use.

<3. Measurement of volume resistivity of charge transport film>
(Example 13)
The volume resistivity of a charge transport film formed using a charge transport film ink containing a mixed solvent, a crosslinked hole transporting polymer, and an aromatic monoiodonium salt was examined.
As the charge transport film ink used for forming the charge transport film, the ink 3 prepared in Example 4 was used. That is, the ink is obtained by dissolving a cross-linked hole transporting polymer and an aromatic monoiodonium salt in a mixed solvent of cyclohexanone and anisole.

  The ink is a cross-linked hole transporting polymer (weight average molecular weight 200,000) represented by the above (HT-A) as a charge transporting material in a mixed solvent in which cyclohexanone and anisole are mixed at a volume ratio of 8: 2. ) And an aromatic monoiodonium salt represented by (MNPFPB) as an acceptor material. At this time, the concentration of (MNPFPB) was set to 20% by mass of the total solid content of the ink, and the total solid content of the ink was set to 1.3% by mass.

The volume resistivity of the charge transport film produced using the ink was measured by producing a hole-only device.
FIG. 14 is a schematic diagram showing the configuration of the sample used for measuring the volume resistivity.
In the sample 20 shown in the figure, a charge transport film 23 is formed on a glass substrate 21 having a striped anode 22 by spin coating. A striped counter electrode 24 is provided on the charge transport film 23 so as to be orthogonal to the anode 22 after the unnecessary film on the periphery of the substrate serving as a terminal is wiped off.

  The anode 22 was formed by etching an ITO film (thickness 150 nm) formed by sputtering to a width of 2 mm. The charge transport film 23 was formed by spin-coating the charge transport film ink 3 on the anode 22 after alkali cleaning and ultraviolet ozone cleaning of the glass substrate 21 on which the anode 22 was formed. The solvent was volatilized and removed by heating on a hot plate at 200 ° C. for 30 minutes, and the acceptor material and the charge transport material in the charge transport film 23 were reacted. The heating here was performed in an air atmosphere in a yellow light clean room. The film thickness of the obtained charge transport film was 82 nm, and a crosslinked film hardly soluble in toluene was obtained. The counter electrode 24 was formed by vapor-depositing an Al film (thickness 120 nm) through a shadow mask having a hole with a 2 mm width stripe. The striped anode 22 and the striped counter electrode 24 are opposed to each other in a 2 mm square area via the charge transport film 23.

About the sample produced as mentioned above, the volume resistivity of the charge transport film | membrane was calculated | required with the following method.
A voltage was applied between the anode 22 and the counter electrode 24, the current flowing between the electrodes was measured, and the resistance of the charge transport film 23 was obtained. For measurement of current-voltage characteristics, an organic EL external quantum efficiency measuring device C9920-12 (manufactured by Hamamatsu Photonics) was used, and a voltage was applied at a speed of 0.1 V / 0.8 seconds.

  Since the wiring resistance of the anode line made of ITO is much larger than that of the Al film of the counter electrode, it cannot be ignored when a large current flows. Considering the wiring resistance of the ITO anode line, the actual voltage applied to the charge transport film is obtained by subtracting the product of the resistance value 45Ω of the anode line, which is the voltage drop due to the anode line, and the measured current from the measured voltage. . As described above, the anode and the counter electrode are opposed to each other in a 2 mm square area via the charge transport film. The value of the actual electric field (V / cm) applied to the 2 mm square charge transport film is obtained by dividing the actual voltage applied to the corresponding film by the film thickness. The volume resistivity (Ω · cm) is calculated by dividing the electric field value by the current density value.

Similarly, the volume resistivity of a charge transport film (a film transparent at 85.7 nm) prepared using an ink prepared so that the concentration of (MNPFPB) is 25% by mass of the total solid content was also obtained. .
Their volume resistivity at an actual electric field of 2 × 10 ⁵ V / cm is summarized in Table 5 below.

(Comparative Example 6)
The relationship between the concentration of the aromatic diiodonium salt and the volume resistivity of the charge transport film was examined for the charge transport film formed using the charge transport film ink using anisole as a solvent.
For the measurement of the volume resistivity, the same measurement sample as in Example 13 was used except that the material of the charge transport film 23 was different. The ink for a charge transport film was prepared by dissolving a crosslinked hole transporting polymer as a charge transport material and an aromatic diiodonium salt represented by the above (DIPFPB) as an acceptor material in anisole. At this time, the concentration of (DIPFPB) is 0% by mass, 1% by mass, 5% by mass, 15% by mass, and 20% by mass, and the solid content in the ink is about 1% by mass. I did it. The used cross-linked hole transporting polymer was a compound represented by the above formula (HT-A), and its weight average molecular weight was 427,000.

The anode 22 was produced in the same manner as in Example 13. The charge transport film 23 was formed by spin-coating the charge transport film ink of this example on the glass substrate 21 on which the anode 22 was formed and washed. The solvent was volatilized and removed by heating at 200 ° C. for 30 minutes, and the acceptor material in the charge transport film 23 was reacted with the charge transport material.
The heating here was performed in an Ar inert atmosphere under light shielding. After heating, the charge transport film formed from the ink mixed with (DIPFPB) having a total solid content of 15% by mass or more formed a cross-linked film hardly soluble in the cloudy toluene. The counter electrode 24 was formed in the same manner as in Example 13.

For each charge transport film, the volume resistivity (Ω · cm) when the electric field strength applied to the film between the electrodes was 2.0 × 10 ⁵ V / cm was determined by the same method as in Example 13. The concentration of aromatic diiodonium salt (DIPFPB) in the solid content of the charge transport film ink and the volume resistivity of the charge transport film are summarized in Table 6 below and plotted in the graph of FIG.

It can be seen that the volume resistivity is drastically decreased when the aromatic diiodonium salt (DIPFPB) is contained, and the degree of decrease is moderated when the concentration of (DIPFPB) is further increased.
In addition, the measured value of the film | membrane produced from the ink which mixed 1 mass% of (DIPFPB) spin-coats the PEDOT / PSS aqueous dispersion (HC Star BYTRON PVP AI4083) on an ITO electrode, and dries. This is a value measured with a hole-only device using the 80 nm film formed as a positive electrode.

(Example 14)
The volume resistivity of a charge transport film formed using a charge transport film ink containing a mixed solvent, a cross-linked hole transport polymer, and an aromatic diiodonium salt was examined.
The volume resistivity was measured in the same manner as in Example 13 except that the material of the charge transport film 23 was different. The charge transport film ink comprises a mixed solvent containing cyclohexanone and anisole in a volume ratio of 8: 2, a cross-linked hole transporting polymer as a charge transport material, and an aroma represented by the above (DIPFPB) as an acceptor material. It was prepared by dissolving a group diiodonium salt. At this time, the concentration of (DIPFPB) is 0% by mass, 5% by mass, 10% by mass, and 20% by mass of the total solid content of the ink, and the solid content ratio in the ink is approximately 2.2% by mass. I made it. The used cross-linked hole transporting polymer was a compound represented by the above formula (HT-A), and its weight average molecular weight was 210,000. In the charge transport film ink used in this example, 4/5 of the solvent capacity is cyclohexanone.

The anode 22 was produced in the same manner as in Example 13. The charge transport film 23 was formed by spin-coating the charge transport film ink of this example on the glass substrate 21 on which the anode 22 was formed and washed. The solvent was volatilized and removed by heating and drying at 200 ° C. for 30 minutes, and the acceptor material and the charge transport material in the charge transport film 23 were reacted.
The heating here was performed under an Ar inert atmosphere and light shielding. The obtained charge transport film had a film thickness of 184 to 189 nm, was a transparent, and hardly crosslinked toluene film. When a mixed solvent containing cyclohexanone and anisole at a volume ratio of 8: 2 was used, a transparent film was obtained when the concentration of DIPFPB with respect to the total solid content of the ink was 30% by mass or less. The counter electrode 24 was formed in the same manner as in Example 13.

The volume resistivity (Ω · cm) when the electric field strength applied to the charge transport film between the electrodes was 2.0 × 10 ⁵ V / cm by the same method as in Example 13 described above. ) The concentration of the aromatic diiodonium salt in the solid content of the charge transport film ink and the volume resistivity of the charge transport film are summarized in Table 7 below and plotted in the graph of FIG.

  In the charge transport film ink used in Comparative Example 6 described above, the total amount of the solvent is anisole, whereas in the charge transport film ink used in this example, 4/5 of the capacity of the solvent is Cyclohexanone. The use of a mixed solvent of cyclohexanone and anisole improves the dispersibility of the non-cationized and cationized portions of (HT-A), and the cations and anions derived from aromatic diiodonium salts. A film having higher transparency than that obtained was obtained. Moreover, even when the concentration of the aromatic diiodonium salt in the charge transport film ink is smaller than that in Comparative Example 6, a volume resistance value comparable to that in Comparative Example 6 is obtained.

(Example 15)
The volume resistivity of a charge transport film formed using an ink for a charge transport film containing cyclohexanone, a crosslinked hole transporting polymer, and an aromatic diiodonium salt was examined.
The volume resistivity was measured in the same manner as in Example 13 except that the material of the charge transport film 23 was different. The charge transport film ink used for forming the charge transport film 23 is the same as the ink used in Example 7.

  The ink for a charge transport film dissolves, in cyclohexanone, a crosslinked hole transporting polymer as a charge transport material and an aromatic diiodonium salt represented by the formula (DIPFPB) synthesized in Example 1 as an acceptor material. It was prepared by. At this time, the concentration of (DIPFPB) was set to 25% by mass of the total solid content of the ink, and the solid content rate in the ink was set to about 1.28% by mass. The used cross-linked hole transporting polymer was a compound represented by the above formula (HT-A), and its weight average molecular weight was 279,000.

The anode 22 was produced in the same manner as in Example 13. The charge transport film 23 was formed by spin-coating the charge transport film ink of this example on the glass substrate 21 on which the anode 22 was formed and washed. The solvent was volatilized and removed by heating at 200 ° C. for 30 minutes to react the acceptor material in the charge transport film 23 with the charge transport material.
The heating here was performed in an air atmosphere and yellow light in a clean room. The resulting charge transport film had a thickness of 75 nm, and a transparent crosslinked film hardly soluble in toluene was obtained. The counter electrode 24 was formed in the same manner as in Example 13.

When the volume resistivity (Ω · cm) of the charge transport film was determined by the same method as in Example 13, it was 9.6 × when the actual electric field strength applied to the charge transport film was 2.0 × 10 ⁵ V / cm. When it was 10 ⁵ Ω · cm and 4.0 × 10 ⁵ V / cm, it was 3.8 × 10 ⁵ Ω · cm, which was a low resistance value.

(Example 16)
The volume resistivity of a charge transport film formed using a charge transport film ink containing a mixed solvent, a cross-linked hole transport polymer and an aromatic oligoiodonium salt was examined.
The volume resistivity was measured in the same manner as in Example 13 except that the material of the charge transport film 23 was different. The charge transport film ink used for forming the charge transport film 23 is the same as the ink used in Example 11.

  The charge transporting film ink was synthesized in a mixed solvent containing tetralin and cyclopentanol in a volume ratio of 7: 3, a cross-linked hole transporting polymer as a charge transporting material, and a compound synthesized in Example 2 as an acceptor material ( It was prepared by dissolving an aromatic oligoiodonium salt represented by OligoIPFPB). At this time, the concentration of (OligoIPFPB) was set to 20 mass% of the total solid content of the ink, and the solid content ratio in the ink was set to about 1.15 mass%. The used cross-linked hole transporting polymer was a compound represented by the above formula (HT-A), and its weight average molecular weight was 279,000. In the charge transport film ink used in this example, 1/4 or more of the capacity of the solvent is cyclopentanol.

The anode 22 was produced in the same manner as in Example 13. The charge transport film 23 was formed by spin-coating the charge transport film ink of this example on the glass substrate 21 on which the anode 22 was formed and washed. The solvent was removed by heating and drying at 200 ° C. for 30 minutes, and the OligoIPFPB in the charge transport film 23 and the charge transport material were reacted.
The heating here was performed under an Ar inert atmosphere and light shielding. The thickness of the obtained charge transport film was 57 nm, and a substantially transparent crosslinked film hardly soluble in toluene was obtained. The counter electrode 24 was formed in the same manner as in Example 13.

When the volume resistivity (Ω · cm) of the charge transport film was determined by the same method as in Example 13, when the actual electric field strength applied to the charge transport film was 5.0 × 10 ⁵ V / cm, 1.1 was obtained. × 10 ⁶ Ω · cm, a low resistance value.

(Comparative Example 7)
As the charge transport film, a light-emitting layer containing a coating-type hole-transporting blue light-emitting material, which is a low-molecular compound, is formed. The concentration of the aromatic diiodonium salt in the ink used for the formation and the volume resistance of the charge-transport film The relationship with rate was examined. Toluene was used as the solvent for the ink.
The volume resistivity was measured in the same manner as in Example 13 except that the material of the charge transport film 23 was different.

  The ink for the charge transport film is the formula synthesized in Example 1 as the hole transporting blue light-emitting material represented by the formula (LHBE-A) used in Example 10 as the charge transport material and the acceptor material in toluene. It was prepared by dissolving an aromatic diiodonium salt represented by (DIPFPB). At this time, the aromatic diiodonium salt concentration was set to 0% by mass and 1% by mass of the total solid content of the ink, and the solid content rate in the ink was set to 3.0% by mass.

The anode 22 was produced in the same manner as in Example 13. The charge transport film 23 was formed by spin-coating the charge transport film ink of this example on the glass substrate 21 on which the anode 22 was formed. The solvent was removed by heating and drying at 200 ° C. for 30 minutes, and the acceptor material in the charge transport film 23 and the charge transport material were reacted.
The heating here was performed in an Ar inert atmosphere under light shielding. The thickness of the obtained charge transport film was 175 to 177 nm and was transparent. The counter electrode 24 was formed in the same manner as in Example 13.

In the same manner as in Example 13, the volume resistivity (Ω ···) for each charge transport film when the actual electric field strength applied to the charge transport film between the electrodes is 2.0 × 10 ⁵ V / cm. cm). The relationship between the concentration of the aromatic diiodonium salt in the solid content of the charge transport film ink and the volume resistivity of the charge transport film is summarized in Table 8 below.

(Example 17)
A light-emitting layer containing a coating-type hole-transporting blue light-emitting material, which is a low-molecular compound, is formed as a charge transport film, and the concentration of aromatic diiodonium salt in the ink used for the formation and the volume resistivity of the charge transport film I investigated the relationship with.
The charge transport film ink is a hole transporting blue light emitting material represented by the formula (LHBE-A) used in Example 10 as a charge transport material in a mixed solvent in which cyclohexanone and anisole are mixed at 8: 2. And an aromatic diiodonium salt represented by the formula (DIPFPB) as an acceptor material. At this time, the concentration of the aromatic diiodonium salt was set to 0% by mass and 1% by mass of the total solid content of the ink, and the solid content ratio in the ink was set to 5.0% by mass.

The anode 22 was produced in the same manner as in Example 13. The charge transport film 23 was formed by spin coating the charge transport film ink of this example on the glass substrate 21 on which the anode 22 was formed and washed. The solvent was removed by heating and drying at 200 ° C. for 30 minutes, and the acceptor material in the charge transport film 23 and the charge transport material were reacted.
The heating here was performed in an Ar inert atmosphere under light shielding. The thickness of the obtained charge transport film was 165 to 174 nm and was transparent.

The volume resistivity (Ω · cm) when the electric field strength applied to the charge transport film between the electrodes is 2.0 × 10 ⁵ V / cm by the same method as in Example 12 described above. ) The relationship between the concentration of the aromatic diiodonium salt in the solid content of the charge transport film ink and the volume resistivity of the charge transport film is summarized in Table 9 below.

  When a hole transporting light emitting layer is prepared using an ink obtained by mixing a hole transporting light emitting material which is a low molecular compound and an aromatic diiodonium salt, the aromatic diiodonium salt concentration relative to the ink is 0. It is preferably 5% by mass to 5% by mass, and more preferably 3% by mass or less. From the above results, it can be seen that a decrease in resistance of 2 to 3 digits can be achieved within this preferable concentration range. Further, by comparing with Comparative Example 6, it can be seen that the resistance of the film is lower when a mixed solvent of cyclohexanone and anisole is used than when a toluene solvent is used.

  According to the embodiment and the examples, it is possible to provide a charge transport film ink having high storage stability. Further, when a charge transport film is formed using an ink containing an aromatic iodonium salt according to the present invention, a film having a lower resistance can be obtained. In particular, the resistance of the hole injection layer or the hole transport layer can be reduced by using the charge transport film of the present invention as a hole injection layer or a hole transport layer.

The charge transport film of the present invention can be applied to organic elements such as organic EL elements, organic light emitting transistors, organic EL lasers, pin junction type or bulk heterojunction type organic photovoltaic cells, and organic thin film solar cells. . As a result, the driving voltage of the organic EL element can be reduced, and the photovoltaic power and photocurrent of the organic photovoltaic cell or organic thin film solar cell can be increased.
Furthermore, the ink for a charge transport film of the present invention is particularly useful when a coating printing method that can be carried out at a low cost is applied.

  DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Anode, 3 ... Hole injection layer, 4 ... Hole transport layer, 5 ... Light emitting layer, 6 ... Electron transport layer, 7 ... Cathode, 8 ... Desiccant sheet, 9 ... Sealing plate, 10 DESCRIPTION OF SYMBOLS ... Adhesive, 11 ... Cathode terminal part, 12 ... Power supply, 13 ... Wiring, 14 ... Laminated structure, 15 ... Organic EL element, 20 ... Sample, 21 ... Glass substrate, 22 ... Anode, 23 ... Charge transport film, 24 ... cathode.

Claims (14)

An acceptor material comprising an aromatic iodonium salt;
A charge transport material having charge transport properties;
A charge transport film ink containing a solvent, wherein the solvent contains a substituted or unsubstituted alicyclic ketone and / or a substituted or unsubstituted alicyclic monohydric alcohol in a volume ratio of 1/4 or more. The ink for a charge transport film according to claim 1, wherein the aromatic iodonium salt contains a cation represented by the following general formula I:

here,
Ar ₁ and Ar ₂ are substituted or unsubstituted monovalent aromatic groups;
Ar ₃ is a substituted or unsubstituted divalent aromatic group;
n is an integer of 0 or more. The ink for a charge transport film according to claim 1, wherein the aromatic iodonium salt is represented by the following general formula (1):

here,
Ar ₁ , Ar ₂ , Ar ₃ and n are as defined in the general formula I;
Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ each independently represent a substituent, and at least one of Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ is a substituent containing an electron-withdrawing group;
Two or more of Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ may be bonded to each other to form a ring. The charge transport film ink according to claim 2, wherein all of Ar ₂₁ , Ar ₂₂ , Ar _23, and Ar ₂₄ are substituents containing an electron-withdrawing group.   The charge transport film ink according to claim 1, wherein the alicyclic ketone is a 5- to 8-membered alicyclic ketone.   The charge transport film ink according to claim 5, wherein the alicyclic ketone is cyclohexanone.   The charge transport film ink according to claim 1, wherein the solvent further contains an aromatic hydrocarbon-based, aromatic ether-based, or aromatic ester-based organic solvent.   The charge transport film ink according to claim 1, wherein the solvent includes an alicyclic monohydric alcohol and has a viscosity at 23 ° C. of 3 mPa · s to 150 mPa · s.   The charge transport film ink according to claim 8, wherein the alicyclic monohydric alcohol is cyclooctanol.   The charge transport film ink according to claim 1, wherein the charge transport material has a hole transport property and / or a light emission property.   The charge transport film ink according to claim 1, wherein the charge transport material is a low molecular material or a polymer material. Aromatic oligoiodonium salt represented by the following general formula (2):

here,
Ar ₁ and Ar ₂ are substituted or unsubstituted phenyl groups;
Ar ₃ is a substituted or unsubstituted phenylene group;
n is an integer of 2 or more representing the degree of polymerization.   The composition for charge transport films containing a charge transportable compound and the aromatic oligoiodonium salt of Claim 12. Forming a film by a wet film-forming method using the charge transport film ink according to any one of claims 1 to 11,
A method for producing a charge transport film, comprising heat-treating the obtained film.

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