JP2013214565A - Aromatic diiodonium salts, charge transport film composition, charge transport film ink, and charge transport film manufacturing method using these - Google Patents

Abstract

（Ａｒ₁は置換または非置換の２価の芳香族基であり、Ａｒ₂およびＡｒ₃は同一でも異なっていてもよく、置換または非置換の１価の芳香族基である。Ａｒ₂₁，Ａｒ_22，Ａｒ₂₃およびＡｒ₂₄のうち、少なくとも１つは、電子吸引性置換基を有する１価の芳香族基であり、残りは同一でも異なっていてもよく、置換または非置換の１価の芳香族基である。）
【選択図】 なしAn aromatic diiodonium salt that has an oxidizing power exceeding that of an acceptor material made of a conventional aromatic monoiodonium salt, is soluble in an organic solvent, and can be suitably used for wet film formation.
An aromatic diiodonium salt represented by the following general formula 1.
[Chemical 1]

(Ar ₁ is a substituted or unsubstituted divalent aromatic group, Ar ₂ and Ar ₃ may be the same or different, and are substituted or unsubstituted monovalent aromatic groups. Ar ₂₁ , Ar _At least one of _22, Ar ₂₃ and Ar ₂₄ is a monovalent aromatic group having an electron-withdrawing substituent, and the rest may be the same or different, and a substituted or unsubstituted monovalent aromatic A group.)
[Selection figure] None

Description

  The present invention relates to an aromatic diiodonium salt used for a charge transport film in a device such as an organic EL (electroluminescent) element, a composition for a charge transport film containing the same, an ink for a charge transport film, and charge transport using the same. The present invention relates to a film manufacturing method.

  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. The organic light emitting material's molecular design makes it easy to obtain full color light emission of red, green, and blue, and it is thin, lightweight, self-luminous at low direct current voltage, high speed response, high contrast, and less blurring. Therefore, organic EL elements are expected as next-generation flat panel displays that replace liquid crystal displays, and are being put into practical use as next-generation display devices such as mobile phone displays and televisions.

  In addition, it is also applied to thin flat luminaires, and is expected as next-generation lighting that is gentle on eyes unlike point-emitting LEDs.

  The basic organic EL device has a transparent conductive substrate and a laminated structure including a hole injection layer, a hole transport layer, an organic light emitting layer, an electron transport layer, and a cathode sequentially provided thereon. And it is moisture-proof sealed. The transparent conductive substrate includes a transparent substrate made of a glass plate or a plastic film, and an anode formed thereon. As the anode, for example, a light transmissive conductive material such as patterned ITO (indium tin composite oxide). A sex membrane is used.

  When the hole transporting layer functions as a hole transporting electron blocking layer or a hole transporting electron blocking layer is provided between the organic light emitting layer, electrons as carriers are confined in the light emitting layer and transported by electrons. When the layer functions as an electron transporting hole blocking layer or an electron transporting hole blocking layer is provided between the organic light emitting layer and the electron transporting layer, holes as carriers are confined in the light emitting layer. The density of holes and electrons in the light emitting layer is increased, the recombination probability of holes and electrons is improved, and the light emission intensity and efficiency can be increased.

  When the hole injection into the organic light emitting layer is dominant over the electron injection and the hole transporting property of the organic light emitting layer is stronger than the electron transporting property, the region where holes and electrons recombine is closer to the cathode side. The hole transporting electron blocking layer can be omitted. On the contrary, when electron injection into the organic light emitting layer is dominant and the electron transporting property is stronger than the hole transporting property of the organic light emitting layer, the recombination region is closer to the anode side. May be unnecessary.

  Organic substances should be used as the main component not only in the organic light emitting layer, but also in the hole injection layer, hole transport layer, hole transport electron block layer, electron transport hole block layer, electron transport layer, and electron injection layer. There are many. Examples of these commercially available organic EL materials are also listed in the catalog of Luminescence Technology in Taiwan, the catalog of American Dye Sources in Canada, the catalog of SIGMA-ALDRICH in the United States, and the Organic and Printed Electronics materials in the web catalog. Has been.

  A semiconductor layer such as an inorganic oxide may be used as a layer such as a hole injection layer. The electron injection layer is often used by doping an organic material with a metal element such as an alkali metal, an alkaline earth metal, or a rare earth, or a salt or metal complex thereof.

  A conventionally used method for forming an organic layer in an organic EL element is a mask vapor deposition method. In this method, since a low molecular material is deposited using a mask, it is difficult to form an organic layer on a large-area substrate. The reason for this is the deflection or thermal expansion of the vapor deposition mask. Moreover, it is difficult to align a large-area vapor deposition mask with high accuracy, and the apparatus cost is high.

  In order to form a light emitting layer on a large-area substrate at a low cost, for example, there is a method of separately coating the light emitting layers of each color by a coating method such as a continuous nozzle printing method or a wet film forming method such as an ink jet method. . In the wet film-forming method, an ink containing an organic solvent selected from aromatic hydrocarbons containing 6-membered rings such as toluene, xylene and ethyl anisolebenzoate; aromatic ethers and aromatic esters is generally used. Used. Therefore, if each layer serving as a base of the light emitting layer is insoluble in such an organic solvent, the light emitting layer can be formed by a wet film forming method.

  For example, an ink made of an aqueous suspension containing fine particles of a polythiophene-based conductive polymer poly (3,4-ethylenedioxythiophene) / poly (styrenesulfonic acid) (hereinafter abbreviated as PEDOT / PSS) is used. Thus, a hole injection layer insoluble in an organic solvent can be formed. The ratio of PEDOT to PSS in the aqueous suspension is about 1: 6 to 1:20.

PSS acts as an acceptor and binder for PEDOT, and PEDOT / PSS has high conductivity. For this reason, an organic EL element which can be driven at a low voltage is obtained by forming a hole injection layer using PEDOT / PSS ink. As the volume resistivity of the PEDOT / PSS film used for the organic EL element, a material having a high PSS concentration is often used in order to prevent a leak current between pixels, but generally from 1 × 10 ⁵ Ω · cm to 3 .4 × 10 ⁶ Ω · cm level is low. Although it is advantageous in that a low-resistance film can be obtained in this way, various problems are associated with the use of PEDOT / PSS ink.

  For example, since the PEDOT / PSS ink has strong acidity, the metal part of the drive wiring in the manufacturing apparatus or the element may corrode or decompose the metal complex used in the light emitting layer. In addition, PEDOT / PSS has a hygroscopic property, and a problem due to moisture occurs when drying is insufficient. Al is generally used for the cathode in the device and the wiring on the TFT substrate, and the cathode and the wiring are easily corroded by moisture and acid. Further, since the fine particles are used as an aqueous suspension in which the fine particles are suspended in an aqueous medium, the PEDOT / PSS ink is likely to aggregate and repel. If the PEDOT / PSS ink is diluted with alcohol or the like and then used, aggregation or gelation may occur and uniform film formation may not be achieved.

  Therefore, there has been a demand for an organic solvent-based ink that can form a uniform film and that can be dried quickly, and that can provide a low-resistance hole injection layer that is insoluble in an organic solvent after film formation.

  In a low molecular vapor deposition type organic EL element, a low molecular hole transport material serving as a host is doped with a low molecular dopant material serving as an acceptor by co-evaporation to form a low resistance hole injection layer. The hole transport material as a host is cationized by depriving electrons by acceptor molecules. As a result, the carrier density increases and the resistance of the hole injection layer decreases.

Examples of a material for obtaining a low-resistance hole injection layer include fragrances such as 4,4 ′, 4 ″ -tris [2-naphthyl (phenylamino)] triphenyl-amine (abbreviated as 2-TNATA). A compound in which an electron-withdrawing acceptor molecule is doped in a host compound of a group III tertiary amine is known. Examples of the electron-accepting acceptor molecule include 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (hereinafter abbreviated as F4-TCNQ) and 2- (6- Dicyanomethylene-1,3,4,5,7,8-hexafluoro-6H-naphthalene-ylidene) malononitrile (hereinafter abbreviated as F6-TNAP) and the like (for example, see Patent Document 1 and Patent Document 2). . When a similar host compound is doped with a Lewis acid such as tetraphenylantimony bromide or FeCl ₃ as an acceptor material, a low-resistance hole transport material is obtained (for example, see Non-Patent Document 1). .

However, F4-TCNQ, F6-TNAP, and the like having a cyano group in the aromatic ring are likely to have mutagenicity because they easily intercalate into the DNA strand, and FeCl ₃ is highly corrosive.

  A vapor deposition film or a sputtering film of an inorganic semiconductor material selected from molybdenum oxide, vanadium oxide, nickel oxide, tungsten oxide, or the like may be used for the hole injection layer. In this case, the protrusions on the anode surface cannot be sufficiently covered, or large particles adhere to the device and the device is likely to be short-circuited.

  Fluorine-substituted phthalocyanines are known as materials having an electron affinity of about 5 to 6 eV (hereinafter abbreviated as Ea). For example, 1, 2, 3, 4, 8, 9, 10, 11, 15, Ea of 16,17,18,22,23,24,25-hexadecafluoro-29H, 31H-phthalocyanine copper (II) (hereinafter abbreviated as F16CuPc) is about 5.3 eV. When the hole injection layer is formed using a material having such a small energy gap and large light absorption, EL emission is strongly absorbed when the film thickness is increased.

  When a hole transport layer, a light emitting layer, etc. are laminated on a hole injection layer containing a low molecular weight compound by a wet method using a solution, depending on the type of the solvent contained in the solution, the lower hole injection layer May dissolve and mix. When the light emitting layer is formed by a wet method, it is required that the solvent of the solution to be used does not dissolve the lower layer (hole injection layer). The hole-injecting layer insoluble in the solvent can be formed using, for example, a crosslinked compound.

  In order to obtain a hole injection layer combining an organic solvent-soluble crosslinkable hole transporting polymer and an organic solvent soluble acceptor material, a hole transporting polymer having a crosslinkable group that can be cross-linked by heat or light. It has been proposed to use a material (see, for example, Patent Document 3). In this, a specific aromatic monoiodonium salt is blended as an acceptor material. Further, a method of forming a hole injection layer insoluble in an organic solvent by mixing the above acceptor material with a hole transporting polymer material and forming a film and then reacting it with light or heat has been studied (for example, Patent Documents 4, 5 and 6).

Many iodonium salts are used as fungicides and antibacterial agents, but are known to be relatively low in toxicity to mammals (Chemical Reviews, 1996, pages 1123 to 1178, page 1170. 1171, 1996). An aromatic monoiodonium salt used as a conventional acceptor material is a compound represented by the following formula MN, and is considered to be soluble in an organic solvent and relatively high in safety.

  In this aromatic monoiodonium salt, the iodonium cation takes electrons from the hole-transporting polymer material and becomes cationized by ultraviolet irradiation or heating, and decomposes itself. The decomposition product on the cation side volatilizes by heating. In addition to increasing the types of hole-transportable polymer materials and acceptor materials that can be doped, the development of iodonium salt materials other than conventional aromatic monoiodonium salts is also required to expand the range of heat treatment temperature and hole transport capability. Yes.

  For example, it is disclosed that a long-life EL device can be obtained by blending a 0.2 wt% acceptor material with a polyfluorene-based light emitting polymer material and using it for forming a hole injection layer (for example, patents) Reference 4). In addition, the hole injection material having the ionization energy Ip (also referred to as ionization potential) estimated to be about 5 eV is blended with the above-mentioned aromatic monoiodonium salt in an amount of 9 to 29% by weight. When formed, it is disclosed that a long-life EL element that can be driven at a low voltage can be obtained (see, for example, Patent Documents 5 and 6). It is disclosed that an EL device in which a hole injection layer is formed using a cross-linked polymer as a hole transporting material has a longer lifetime than a non-cross-linked polymer used in the hole injection layer. (For example, refer to Patent Document 6).

In Patent Document 5, a low-resistance layer can be obtained by blending the above-mentioned aromatic monoiodonium salt in a ratio of 5: 1 (weight percentage: 16.6 wt%) with a non-crosslinked hole transporting polymer. Have been described. In this case, the compound used as the non-crosslinked hole transporting polymer has a tetraphenylparaphenylenediamine structure, and Ip is estimated to be about 5 eV from the structure. The resistivity of the layer after heat treatment at 230 ° C. is 5.3 × 10 ⁷ Ωcm, which is three orders of magnitude lower than when no aromatic monoiodonium salt is contained (2.4 × 10 ¹⁰ Ωcm).

As described above, the volume resistivity of the PEDOT / PSS film generally used for the organic EL element is about 1 × 10 ⁵ Ω · cm to about 3.4 × 10 ⁶ Ω · cm. In order to form a hole injection layer having a low volume resistivity comparable to this using an aromatic monoiodonium salt, it is necessary to further increase the concentration of the aromatic monoiodonium salt. The aromatic monoiodonium salt contained at a high concentration is likely to diffuse into adjacent layers, and the conductivity of the hole injection layer may become unstable due to the residue. Moreover, the cracked gas containing aromatic iodine is scattered in the atmosphere. In order to avoid such a problem, an acceptor material that can form a hole injection layer having a low resistance even when contained in an extremely small amount is required.

  In order to efficiently inject holes into a host material of a high-purity blue light-emitting layer having an Ip of about 6 eV and an energy gap between Ip and Ea of 3 eV or more, it is necessary to prevent exciplex light emission at the interface It is desirable that the hole transport material has an Ip of about 6 eV. There is a need for acceptor materials with high oxidizing power that can easily cationize such high Ip hole transport materials to obtain low resistance films.

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

Applied Physics Letters 72, 2147 (1998)

  The present invention provides an aromatic diiodonium salt which has an oxidizing power exceeding that of an acceptor material composed of a conventional aromatic monoiodonium salt, is soluble in an organic solvent and can be suitably used for wet film formation, and such an aromatic diiodonium salt. It is an object of the present invention to provide a composition for a charge transport film and an ink for a charge transport film.

According to the first aspect of the present invention, an aromatic diiodonium salt represented by the following general formula 1 is provided.

(Here, Ar ₁ is a substituted or unsubstituted divalent aromatic group, Ar ₂ and Ar ₃ may be the same or different, and are substituted or unsubstituted monovalent aromatic groups. Ar _At least one of ₂₁ , Ar _22, Ar ₂₃ and Ar ₂₄ is a monovalent aromatic group having an electron-withdrawing substituent, and the rest may be the same or different, and may be substituted or unsubstituted 1 Valent aromatic group.)
According to a second aspect of the present invention, a charge transport film composition comprising a charge transport compound selected from a hole transport compound and a luminescent compound, and the above-mentioned aromatic diiodonium salt. Is provided.

  According to a third aspect of the present invention, there is provided a charge transport film ink comprising the above-mentioned aromatic diiodonium salt and an organic solvent, and a method for producing a charge transport film using them.

  According to an embodiment of the present invention, an aromatic diiodonium salt having an oxidizing power exceeding that of an acceptor material made of a conventional aromatic monoiodonium salt, soluble in an organic solvent, and suitable for wet film formation, such an aromatic Provided are a charge transport film composition containing a group diiodonium salt, a charge transport film ink, and a method for producing a charge transport film using them.

Schematic which shows the structure of an organic EL element. The ¹ H-NMR chart of the aromatic Jiyodoniumu salt of Example. The enlarged view of the < ¹ > H-NMR chart of the aromatic diiodonium salt of an Example. ¹⁹ F-NMR of the aromatic diiodonium salt of the examples. The infrared absorption spectrum of the aromatic diiodonium salt of an Example. Schematic which shows the structure of the sample for measuring the volume resistivity of a charge transport film | membrane. The graph which shows the relationship between the density | concentration of the aromatic diiodonium salt in the solid content melt | dissolved in the ink for charge transport films | membranes, and the volume resistivity of a charge transport film | membrane. The graph which shows the relationship between the density | concentration of the aromatic diiodonium salt in the solid content melt | dissolved in the ink for charge transport films | membranes, and the volume resistivity of a charge transport film | membrane. The graph which shows the relationship between the density | concentration of the aromatic diiodonium salt in the solid content melt | dissolved in the ink for charge transport films | membranes, and the volume resistivity of a charge transport film | membrane. The graph which shows the relationship between the density | concentration of the aromatic diiodonium salt in the solid content melt | dissolved in the ink for light emitting layers, and the emitted light intensity of a light emitting layer.

  Embodiments of the present invention will be described below.

  The aromatic diiodonium salt according to one embodiment has a larger oxidizing power than the conventional aromatic monoiodonium salt and can easily cationize the hole transport material. Therefore, the hole injection layer in the organic EL device, It is used for a charge transport film having a hole transport property such as 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. The illustrated 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. And 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.

<Board>
As the substrate 1, for example, an insulating transparent glass plate having a thickness of about 0.5 to 1.1 mm and an excellent gas barrier property, a flexible glass sheet having a thickness of about 50 microns, or a plastic film is used. 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 low-resistance conductive polymer film such as PEDOT / PSS may be formed on a transparent conductive oxide thin film or a metal mesh film such as a nickel alloy to form the anode 2.

  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. Some types of blue light-emitting dopant materials and host materials have a large Ip of 6 eV or more. When such a material is used together with the anode having a small Ip as described above, the energy barrier for hole injection from the anode 2 to the light emitting layer 6 becomes a large value of 1 eV or more. In order to lower the energy barrier for hole injection and increase the efficiency of hole injection from the anode 2 to the hole injection layer 3, it is effective to increase the Ip by treating the anode surface.

  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, or surface treatment with a fluorine-based silane coupling agent. Alternatively, the metal atom on the surface of the anode 2 may be halogenated to treat the surface of the anode. Such treatment can be achieved, for example, by generating a halogen radical 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, Ip on the surface of the anode 2 is increased to 5.7 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 material compound having low resistance and 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 the value of Ip of the material of the anode 2 and the hole. It is preferably between the values of Ip of the material of the transport layer 4. Alternatively, the hole injection layer 3 is formed using a material having a value of 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. May be. In this case, holes can be injected into the hole transport layer through the lowest free electron orbit (LUMO) of the material.

  As the hole injection layer 3, for example, a vapor-deposited film or a coated printed film of a hole transporting compound containing an aromatic tertiary amine having an Ip of about 5 to 6 eV can be used. A vapor-deposited film of metal phthalocyanines such as copper phthalocyanine is also preferably used as the hole injection layer 3.

  The hole transporting compound is selected from, for example, an aromatic tertiary amine compound, a carbazole ring, a thiophene ring, a benzo [C] [1,2,5] thiadiazole ring, a benzene ring, a naphthalene ring, and an anthracene ring. It is a compound containing an aromatic ring structure and may be any of a low molecular compound, an oligomer, and a polymer. The hole transporting compounds may be used alone or in combination of two or more. Here, the low molecular weight compound preferably refers to a compound having a molecular weight of 400 or more and less than 10,000, the oligomer refers to a compound in which the structure serving as a repeating unit is polymerized to about several tens, and the polymer serves as a repeating unit. A compound whose structure is several dozen or more.

  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 high hole transporting ability, amorphousness and high glass transition temperature is preferably used. Specifically, 2-TNATA, 2,2 ′, 7,7′-tetrakis [N-naphthalenyl (phenyl) -amino] -9,9-spirobifluorene (hereinafter abbreviated as Spiro NPD) and the like. is there.

  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 can be formed by using a cross-linked hole transporting compound and 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 transporting polymer, any hole transporting polymer material into which a crosslinking group capable of crosslinking with light, heat or acid can be used can be used. For example, the compound (HT-A) shown below ). 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. .

  The crosslinkable hole transporting compound is crosslinked by heat or light to form the hole injection layer 3 that is insoluble or hardly soluble in the organic solvent. Such a hole injection layer is not dissolved and mixed by an organic solvent. For this reason, a multilayer laminated film can be easily formed by 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. 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 exciton near the interface between the hole injection layer 3 and the light emitting layer 5 is suppressed from being deactivated by absorbing energy in the hole injection layer 3 having a high hole carrier density. Reduction is reduced. Further, the diffusion of impurities and ions in the hole injection layer 3 to the light emitting layer 5 is limited, and thereby the deterioration of the light emitting layer 5 is reduced, and the life and the drive voltage are prevented from increasing.

  The hole transport layer 4 can be formed using, for example, a hole transporting low-molecular compound containing an aromatic tertiary amine having a high hole transport capability. Alternatively, the hole transport layer 4 may be formed using a cross-linked hole transport polymer that contains an aromatic tertiary amine having a high hole transport capability and is insolubilized 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. 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. Such characteristics are suitable as a hole transport layer in contact with the blue light emitting layer.

  Further, in order to prevent a decrease in luminous efficiency and color purity, the material used for the hole transport layer 4 is desirably a material that does not form an exciplex with the light emitting dopant material. The value of Ip of the material of the hole transport layer 4 is between the value of Ip of the hole injection layer 3 and the value of Ip of the host in the light emitting layer 5, and Ip of the light emitting dopant material in the light emitting layer 5 It is desirable to be deeper than the value of.

  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 that is at least 0.3 eV smaller than the material used for the light emitting layer 5.

  When the hole transport layer 4 having a low electron mobility is used, it is possible to suppress the leakage of electrons to the hole injection layer 3 and the anode 2 and improve the light emission efficiency. 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. It is an electron trap type light emitting dopant material having a high emission quantum yield and a material in which Ip is equal to or higher than that of the hole transport material and does not become a hole trap, and Ea is larger than the hole transport material and becomes an electron trap. is there. With such a material, the electron mobility of the hole transport layer 4 is lower than the hole mobility, and the light emission efficiency is improved by the emission of the dopant material.

  The hole transport layer 4 containing the light emitting dopant material also functions as a light emitting layer. For example, a normal hole transporting layer can be formed, and a hole transporting 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 elution of the dopant material, it is preferable to dope a cross-linked electron trap light-emitting dopant material into the hole transporting host material having a cross-linking group. The host material and the dopant material are cross-linked to insolubilize the hole-transporting light-emitting layer, and the elution of the dopant material is prevented.

As a bridge | crosslinking type electron trap light emission dopant, the compound (PF-1) shown below is mentioned, for example. This compound (PF-1) is a crosslinked polymer having a hexenyl group having a crosslinked, polymerizable double bond at the 9-position of fluorene. The 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 that is doped into the compound (HT-C) or the like. .

  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 due to the hole transport layer 4 in contact with the light emitting layer 5 can be prevented.

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

  Examples of fluorescent light-emitting materials include anthracene derivatives, benzoanthracene derivatives, dibenzoanthracene derivatives, styryl derivatives, carbazole derivatives, aluminum oxine complexes, complexes that exhibit thermally activated delayed fluorescence including copper, polyfluorene copolymers, and poly Various fluorescent light emitting materials such as phenoxazine copolymer can be used. The fluorescent light emitting material may be a low molecular compound having a 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 is dissolved in a solvent at a concentration of 1% by mass or more to obtain a solution. 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 having an Ea level shallower than that of the dopant material Ea and the light emitting dopant easily traps electrons is also preferable as the host material.

  When a hole transporting material and an electron transporting material are mixed to form a host material, the hole transporting 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 transporting material preferably has an Ea smaller than that of the light emitting dopant material and has an Eg larger than that of the light emitting dopant material. By adjusting the blending ratio of the hole transporting material and the electron transporting material, the carrier balance between holes and electrons injected into the light emitting layer 5 can be adjusted to be close to 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.

  In the case where 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 provision of the hole blocking electron transport layer leads to the cathode 7. Hole leakage, and absorption of exciton energy by the cathode 7 is 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 lowering an energy barrier and resistance for injecting electrons from the cathode 7 to the light emitting layer 5. Further, the excitons generated in the light emitting layer 5 are prevented from diffusing to the cathode 7 and quenching.

  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-6-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 compound such as phenyldi (1-pyrenyl) phosphine, or the like is used for forming the electron transport layer 6. May be.

  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 co-evaporation or the like. An organic radical compound having a small Ip can also be mixed and applied as a donor. The material of the electron transport layer is anionized by the donor to increase the carrier density, 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 an alkali metal such as Li, Ba, or Cs having an Ip of 3 eV or less, a rare earth such as an alkaline earth metal or Yb, or a compound thereof 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 a non-light-emitting spot is easily formed and corroded. 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. The sealing plate 9 can be bonded to the cathode 2 and the cathode terminal portion 11 on 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 the organic EL element 15 is caused to emit light by applying a DC voltage, the anode 2 is connected to the positive electrode of the power source 12 through the wiring 13 and the cathode terminal portion 11 is connected to the power source 12 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.

<Aromatic diiodonium salt according to this embodiment>
The aromatic diiodonium salt according to this embodiment is contained in a hole transporting 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. It acts suitably as an acceptor material. Such an aromatic diiodonium salt of this embodiment is represented by the following general formula 1.

Here, Ar ₁ is a substituted or unsubstituted divalent aromatic group, and Ar ₂ and Ar ₃ may be the same or different, and are substituted or unsubstituted monovalent aromatic groups. At least one of Ar ₂₁ , Ar _22, Ar _23, and Ar ₂₄ is a monovalent aromatic group having an electron-withdrawing substituent, and the rest may be the same or different, and may be substituted or unsubstituted. It is a monovalent aromatic group.

The aromatic diiodonium salt concerning one Embodiment is comprised from the aromatic diiodonium cation shown by the following general formula 1c, and the aromatic borate anion shown by the following general formula 1a.

  As shown in the general formula 1c, in the cation of the aromatic diiodonium salt according to one embodiment, two electron-withdrawing aryliodonium groups are bonded to one aromatic group. Since two aryliodonium groups are contained, the cation of the aromatic diiodonium according to the present embodiment has the lowest free electron orbit (hereinafter abbreviated as LUMO) level as compared with the conventionally used aromatic monoiodonium. Is low and has strong oxidizing power.

  Due to this, the aromatic diiodonium salt of the present embodiment can quickly cationize a charge transporting compound such as a hole transporting compound or a light emitting compound. Among charge transporting compounds used for a hole transport layer, a light emitting layer, and the like suitable for a blue light emitting device, there are those having a large energy gap (Eg) of 3 eV or more and a large ionization potential (Ip) of about 6 eV. It is difficult for electrons to be extracted from a charge transporting compound having such a large energy gap and ionization potential. Even such a charge transporting compound is easily cationized by the aromatic diiodonium salt of the present embodiment. As a result, a charge transport film having a low resistance can be obtained.

In the aromatic diiodonium cation represented by the general formula 1c, the divalent aromatic group introduced as Ar ₁ is a divalent group derived from a benzene derivative and a divalent group derived from a heteroaromatic ring. Any of these may be used. 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 a thiophene ring and a pyrrole ring.

  Some of the hydrogen atoms in these divalent aromatic groups are selected from a methyl group, a 2,5-dimethyl group, a methoxy group, an isopropyl group, and an alkoxy group such as a tert-butyl group and a methoxy group. It may be substituted with 4 or less aliphatic hydrocarbon groups. If the aliphatic hydrocarbon group to be introduced has 4 or less carbon atoms, the decomposition product (cation) after taking electrons from the hole transporting compound or the light emitting compound is volatilized by heating at about 200 ° C. Can do. With such a heating temperature, the hole transporting compound and the light emitting compound in the charge transport film are not thermally decomposed.

The monovalent aromatic group introduced into the general formula 1c as Ar ₂ and Ar ₃ may be either a monovalent group derived from a benzene derivative or a monovalent group derived from a heteroaromatic ring. . Examples of the monovalent aromatic group derived from the benzene derivative include phenyl. Examples of the monovalent aromatic group derived from the heteroaromatic ring include monovalent groups derived from a heteroaromatic ring such as a thienyl group, a pyrrolyl group, and a pyridyl group. The hydrogen atom in such a monovalent aromatic group may be substituted with an aliphatic hydrocarbon group having 4 or less carbon atoms for the same reason as described above.

On the other hand, in the aromatic borate anion represented by the general formula 1a, at least one of Ar ₂₁ , Ar _22, Ar ₂₃ and Ar ₂₄ is a monovalent aromatic group having an electron-withdrawing substituent. . In order to delocalize the negative charge on the boron atom on the aromatic group and enhance the stability, it is more preferable that two or more monovalent aromatic groups have an electron-withdrawing substituent.

  The monovalent aromatic group includes a monovalent group derived from a benzene ring such as phenyl group, naphthyl group, anthryl group, phenanthrenyl group, biphenyl group, fluoren-2-yl group, and thienyl group, pyridyl group, phenanthroline group. Any of groups derived from a heteroaromatic ring such as quinoxalin-6-yl group, but since negative charges can be delocalized more uniformly and stability is improved, phenyl group, naphthyl group Those derived from such a benzene ring are preferred.

  Examples of the electron-withdrawing substituent include a cyano group, a nitro group, a fluorine group, and a trifluoromethyl group. Due to the presence of the electron-withdrawing substituent, the negative charge of the borate anion does not concentrate on the boron atom, but delocalizes on the aromatic ring having the electron-withdrawing substituent. As a result, it becomes difficult to be attacked by cations and stability is improved.

Specific examples of the aromatic group having an electron-withdrawing substituent include a 4-cyanophenyl group, a pentafluorophenyl group, a 3,4,5-trifluorophenyl group, and a 3,5-trifluoromethylphenyl group. 1,3,4,5,7,8-heptafluoronaphthalen-2-yl group. At least one group of Ar ₂₁ , Ar _22, Ar ₂₃ and Ar ₂₄ can be any substituted or unsubstituted aromatic group as long as the other group has an electron-withdrawing substituent. When introducing a substituent for the purpose of adjusting the dispersibility and diffusibility in the charge transport film, the substituent has an electron-withdrawing substituent in consideration of reducing the density of the charge transport film and lowering the transportability. It is desirable that the substituent not to be used is an aliphatic hydrocarbon group or aliphatic ether group having about 1 to 10 carbon atoms.

  Since the aromatic borate anion has a three-dimensional molecule, when it is used as a counter ion of a cationization site such as an aromatic tertiary amine site of a hole transporting compound, it is electrostatically close to the cation site. It is difficult to bond strongly. For this reason, it becomes difficult to constrain the movement of holes, and it is considered that high conductivity can be imparted to the hole transporting compound.

In the aromatic borate anion represented by the above general formula 1a, Ar ₂₁ , Ar _22, Ar ₂₃ can be obtained by arbitrarily combining aromatic groups having substituents having different numbers and types of electron-withdrawing substituents and different electron-withdrawing forces. And Ar ₂₄ can be introduced. In this case, the ionization potential on the anion side can be adjusted so that an ionization potential larger than the ionization potential of the hole transporting compound or the light emitting compound can be obtained.

In addition, a divalent borate anion in which two aromatic borate anions are condensed by dimerizing one of the aromatic rings Ar ₂₁ , Ar _22, Ar ₂₃ and Ar ₂₄ as a common aromatic ring is used as a counter anion. You can also. In that case, the molar ratio of the cation and the counter anion of the aromatic diiodonium salt is 1: 1.

The aromatic diiodonium salt according to one embodiment can be synthesized, for example, according to the following synthesis route 1.

In synthesis route 1, aromatic diiodonium salt 7 is synthesized using iodosobenzene represented by compound 3 as a starting material. The aromatic diiodonium salt 7 has an unsubstituted divalent aromatic group (paraphenylene group) as Ar ₁ in the above general formula 1, and an unsubstituted monovalent aromatic group (phenyl group) as Ar 1. ₂ and corresponds to one in which an arbitrary monovalent aromatic group is introduced as Ar ₃ . The second intermediate 5 can be synthesized from the starting material with reference to the method described in The Journal of Organic Chemistry, 57, 6810, 1992.

Specifically, first, trifluoromethanesulfonic acid (TfOH) is reacted with the starting material to obtain the first intermediate 4, and then the second intermediate 5 is synthesized using the arylene compound Ar ₃ H.

The arylene compound Ar ₃ H replacing the first intermediate 4 can be selected from, for example, toluene, p-xylene, anisole, isopropylbenzene, and tert-butylbenzene. A part of hydrogen atoms in Ar ₃ contained in the arylene compound Ar ₃ H may be substituted with a substituent such as a methyl group, a 2,5-dimethyl group, a methoxy group, an isopropyl group, or a tert-butyl group. . By introducing Ar ₃ having a substituent into the cation, the solubility of the aromatic diiodonium salt in the solvent can be adjusted. Furthermore, when Ar ₃ has a substituent, the compatibility of the aromatic diiodonium salt and the hole transporting material in the ink and in the film can be enhanced.

  An aromatic diiodonium salt 7 can be synthesized by exchanging the tosylate anion in the second intermediate 5 with the borate anion salt 6. Anion exchange can be performed in an aqueous alcohol such as aqueous methanol, but is not limited thereto.

  The iodosylbenzene of compound 3 as a starting material can be changed to, for example, diacetoxyiodobenzene. Further, trifluoromethanesulfonic acid (TfOH) can be changed to, for example, toluenesulfonic acid.

Synthesis route 2 shows an example of a method for synthesizing an aromatic diiodonium salt according to another embodiment.

In the synthesis route 2, an aromatic diiodonium salt 11 is synthesized using an aromatic diiodoso compound represented by compound 8 as a starting material. In the aromatic diiodonium salt 11, the same substituted or unsubstituted monovalent aromatic group is introduced as Ar ₂ and Ar ₃ in the aforementioned general formula 1, and an arbitrary divalent aromatic group is defined as Ar _1. It corresponds to what you have. As described above, Ar ₁ may be any of a divalent group derived from a benzene derivative and a divalent group derived from a heteroaromatic ring. Similarly, Ar ₂ and Ar ₃ may be either a monovalent group derived from a benzene derivative or a monovalent group derived from a heteroaromatic ring. However, Ar ₃ is the same monovalent group as Ar ₂ .

In the synthesis of the aromatic diiodonium salt 11, first, toluenesulfonic acid is reacted with the starting material to obtain the first intermediate 9 (Mendeleev Communications, Vol. 2, pages 159-160, 1992). Next, the second intermediate 10 is synthesized using the arene compound Ar ₂ H under the same conditions as in the above-described synthesis route 1. Specifically, 2 equivalents of the arene compound Ar ₂ H are reacted in 2,2,2-trifluoroethanol or the like. As a result, a second intermediate 10 composed of a diiodonium tosylate salt having the same aromatic group Ar ₂ at both ends is synthesized.

As the arene compound Ar ₂ H, the same compounds described in the synthesis route 1 can be used. As described above, some of the hydrogen atoms in Ar ₂ contained in the arene compound Ar ₂ H may be substituted with an aliphatic hydrocarbon group having 4 or less carbon atoms.

Next, an aromatic diiodonium salt 11 having the same aromatic group Ar ₂ at both ends of the cation is synthesized by exchanging the tosylate anion in the second intermediate 10 using the borate anion salt 6. Can do.

  Here, the diiodosylarene compound of Compound 8 as a starting material can be changed to, for example, a bis (diacetoxyiodo) arene compound. In the diiodosylbenzene compound, the site where the two iodosyl groups are bonded is not particularly limited, and may be any of the para position, the meta position, and the ortho position. The site where the two diacetoxyiodo groups in the bis (diacetoxyiodo) benzene compound are bonded may be in the para position, the meta position, or the ortho position.

After obtaining the first intermediate 9 according to the aforementioned synthesis route 2, the aromatic diiodonium salt 14 according to another embodiment can also be synthesized according to the method shown in the synthesis route 3.

The aromatic diiodonium salt 14 is different from the general formula 1 in that substituted or unsubstituted monovalent aromatic groups introduced as Ar ₂ and Ar ₃ are different from each other, and any divalent aromatic group is represented by Ar Corresponds to what you have as ₁ . As described above, Ar ₁ may be any of a divalent group derived from a benzene derivative and a divalent group derived from a heteroaromatic ring. Similarly, Ar ₂ and Ar ₃ may be either a monovalent group derived from a benzene derivative or a monovalent group derived from a heteroaromatic ring.

In the synthesis of the aromatic diiodonium salt 14, arene compounds Ar ₂ H and Ar ₃ H having different aromatic groups Ar ₂ and Ar ₃ , respectively, are prepared. Ar ₂ and Ar ₃ are each a substituted or unsubstituted monovalent aromatic group, and a substituent similar to Ar ₃ as described in Synthesis Route 1 may be introduced. As shown in the synthesis route 3, the arenes Ar ₂ H and Ar ₃ H are reacted with 1 equivalent each in order with respect to the first intermediate 9. As a result, a second intermediate 13 composed of a tosylate anion salt of a diiodonium cation is synthesized.

  Next, the borate anion salt 14 of aromatic diiodonium can be synthesized by exchanging the tosylate anion in the second intermediate 13 using the borate anion salt 6.

  In addition, in the above-mentioned synthesis routes 1, 2, and 3, although Li salt is used as the borate anion salt 6, it is not limited to this. Salts containing other cations such as Na salt and Ka salt can also be used.

In the aromatic diiodonium salt in one embodiment, the aromatic diiodonium cation represented by the general formula 1c may have substituted or unsubstituted metaphenylene as Ar ₁ . Such an aromatic diiodonium salt can be synthesized, for example, according to Synthesis Route 4 shown below.

First, an intermediate 17 is synthesized from meta-dimethoxybenzene 15 as a starting material using 2, for example, 2,2,2-trifluoroethanol using Koser's reagent represented by compound 16. For the synthesis here, for example, a method described in Tetrahedron, Vol. 66, pages 5775-5785, 2010 can be referred to. Ar ₄₁ in compound 16 is, for example, a phenyl group, and part of the hydrogen atoms may be substituted with an aliphatic hydrocarbon group having 4 or less carbon atoms.

  Subsequently, anion exchange is performed in aqueous alcohol, and the aromatic diiodonium salt 18 is obtained.

The Li salt 8 of the aromatic borate anion can be synthesized, for example, according to the synthesis route 5 shown below.

Using tribromoborane (BBr ₃ ) as a starting material, Ar ₂₁ -Cu, Ar ₂₂ -Cu, Ar ₂₃ -Cu, and Ar ₂₄ -Cu are reacted in order of 1 equivalent each. Ar ₂₁ , Ar ₂₂ , Ar ₂₃ , and Ar ₂₄ may be the same or different, and at least one of them is an aromatic group having an electron-withdrawing substituent.

Ar ₂₁ -Cu, Ar ₂₂ -Cu, Ar ₂₃ -Cu, and Ar ₂₄ -Cu used in the reaction are described, for example, in Journal of Organometallic Chemistry, Vol. 681, 2003, pages 134 to 142 [Cu (Mes)] Toluene coordination complex of copper arene such as ₅ · Toluene or [Cu (C ₆ F ₅ )] ₄ · η ^2- (Toluene) ₂ complex. Such compounds can be synthesized using, for example, CuCl and the corresponding Grignard reagent as raw materials.

Examples of aromatic diiodonium cations that can be synthesized by the same method according to the synthesis routes 1 to 4 described above are summarized in Table 1 below. In Table 1 below, Ar ₁ , Ar ₂ and Ar ₃ in the cation represented by the following general formula 1c are shown. Examples of aromatic borate anions that can be synthesized by the same method according to the synthesis route 5 are shown in Table 2 below. In Table 2 below, Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ in the anion represented by the following general formula 1a are shown.

  The aromatic diiodonium salt of the present embodiment can be synthesized by arbitrarily combining the aromatic diiodonium cation represented by the general formula 1c and the aromatic borate anion represented by the general formula 1a.

The aromatic diiodonium salt of this embodiment also has a hole transporting ability, and can be used alone to form a film. When heated at a high temperature of 200 ° C. or higher during drying after film formation, it is likely to decompose and volatilize. For example, a compound represented by the following formula 2 decomposes by generating heat at 236.7 ° C. or higher when heated at 20 ° C./min by DSC (Differential Scanning Calorimetry) measurement.

The compound represented by the above formula 2, in the following general formula 1, as Ar _1, Ar _2, and Ar _3, respectively paraphenylene group, a phenyl group and a para-tert- butylphenyl group, is introduced, Ar _21, Ar ₂₂ , Ar ₂₃ and Ar ₂₄ are all compounds having a pentafluorophenyl group introduced therein.

<Composition for charge transport film>
The aromatic diiodonium salt of the present embodiment as described above is used as a hole injection layer, a hole transport layer, an electron block hole transport layer, a hole transport compound and a luminescent compound used in the light emitting layer as described above. The charge transport film composition of this embodiment is obtained by mixing with a charge transport compound selected from the group consisting of:

  Any hole-transporting compound or light-emitting compound can be used as the charge-transporting compound, but an aromatic tertiary amine, a carbazole ring, a thiophene ring, a benzo [C] [1,2,5] thiadiazole ring, , A benzene ring, a naphthalene ring or an anthracene ring.

  The charge transporting compound may be a low molecular compound or a polymer as long as it has properties such as solubility, film-forming property, heat resistance, hole transporting property, and light emitting property.

  When a low molecular weight compound is used, there is a problem that it tends to evaporate during the heat treatment of the film depending on the pressure of the atmosphere and the heat treatment temperature. However, evaporation can be prevented 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. The aromatic diiodonium salt of this embodiment is By cationizing the charge transporting compound, the hole carrier density can be increased, and the resistance of the resulting charge transport film can be reduced.

  In addition, the charge transporting compound may be a vinyl group, an allyl group, an isobutenyl group, a vinyl ether group, an epoxy group, an oxetane group, a benzocyclobutene group, a thienyl group, an alkoxysilane group, a thiol group, and an ene group that crosslink with light, heat, or acid. It may have a crosslinkable group such as a combination with a group.

  Since the aromatic diiodonium salt according to the present embodiment acts as a cationic polymerization initiator by light or heat, in the case of a cationic polymerizable crosslinking group such as a vinyl ether group, an epoxy group, or an oxetane group, a crosslinking reaction is performed. Is promoted. Crosslinking is completed at a lower temperature and in a shorter time, and a charge transport film that is insoluble in the solvent is formed. Therefore, even when heat treatment is performed in the atmosphere, it is possible to suppress oxidative degradation of the hole transport compound and the like. . 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.

  When the aromatic diiodonium salt and the charge transporting compound as described above are mixed in a solid state, the charge transport film composition of the present embodiment is a powder. The powder can be compression-molded to obtain granules of the composition for a charge transport film. When an aromatic diiodonium salt and a charge transporting compound are dissolved in an organic solvent and then dried by spray drying, freeze drying, vacuum distillation, cast drying, etc., a solid charge transport film composition A thing is obtained. It is also possible to obtain a powder, granule, or film-shaped composition for a charge transport film by subjecting this solid to an appropriate treatment. The solid charge transport film composition of this embodiment can be stored for a long period of time under light shielding at room temperature or lower.

<Ink for charge transport film>
The charge transport film composition of this embodiment is dissolved in an organic solvent to obtain the charge transport film ink of this embodiment. The charge transport film ink may contain a charge transport compound such as the above-described hole transport compound or luminescent compound. The first solution containing the diiodonium salt of the present embodiment and the second solution containing a charge transporting compound such as a hole transporting compound or a light emitting compound are prepared and used in a desired ratio. May be mixed to obtain an ink for a charge transport film.

  The organic solvent used in the ink preferably has a boiling point of 80 to 220 ° C. and good drying properties. 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 1,3-dimethoxybenzene (boiling point 217 ° C.) and other aromatic ether solvents; methyl benzoate (boiling point 198-200 ° C.), ethyl benzoate (Boiling point 211-213 ° C.), ester solvents such as methyl cyclohexanecarboxylate (boiling point 183 ° C.), butyl acetate (boiling point 126 ° C.), and isoamyl acetate (boiling point 142 ° C.); cyclohexanone (boiling point 157 ° C.), cyclopentanone (Boiling point 130 ° C.) and ketone solvents such as acetophenone (boiling point 202 ° C.); C 1-9 aliphatic monohydric alcohols such as 1-octanol and 1-nonanol (boiling point 214 ° C.); cyclopentanol (boiling point 140 ° C.), cyclohexanol (boiling point 161 ° C.) And monovalent alicyclic alcohol solvents having 5 to 8 carbon atoms such as cycloheptanol (boiling point 185 ° C.) and cyclooctanol (boiling point 209 ° C.).

  When these solvents are used, it is desirable to adjust them to boiling points and viscosities according to coating methods and printing methods, either alone or with appropriate mixing with other organic solvents.

  Note that alicyclic alcohols having 9 or more carbon atoms and divalent or higher alicyclic alcohols are not suitable because the film has a relatively high boiling point and the film is difficult to dry.

  When 1/4 or more of the total capacity of the solvent is selected from alicyclic ketones and monovalent alicyclic alcohols, it is possible to reduce coloring and alteration of the ink. Thereby, the storage stability of the ink becomes higher. The presence of such a solvent suppresses the oxidation reaction and charge transfer of the hole transport compound by the aromatic diiodonium salt.

  Examples of the alicyclic ketone include alicyclic ketone compounds having 5 to 10 carbon atoms. For example, cyclohexanone has a boiling point of 160 ° C. or less that is easily dried during spin coating, dissolves a charge transporting compound composed of an aromatic compound, and is ionic such as an onium salt such as an iodonium salt or a cationized charge transporting compound. Excellent solubility in compounds.

  As monovalent aliphatic alcohol, a C5-C8 alicyclic alcohol is mentioned, for example. When 1/3 or more of the total capacity of the ink is selected from alicyclic ketones and monovalent alicyclic alcohols having 5 to 8 carbon atoms, the above-described effects are further enhanced.

  A solvent having a carbonyl group such as cyclohexanone or a solvent containing an alcoholic hydroxyl group such as cyclopentanol or cyclooctanol is coordinated around an iodonium cation in an aromatic diiodonium salt, thereby forming a cation and a hole transporting compound. Separated from. Charge transfer is suppressed, and oxidation and coupling of the charge transporting compound due to radical reaction are prevented. As a result, it is considered that the coloring of the solution is suppressed and the stability is enhanced.

  The ink for a charge transport film of this embodiment can be formed by any wet film forming method. Examples thereof include spin coating, die coating, capillary coating, gravure printing, flexographic printing, offset printing, screen printing, continuous nozzle printing, and ink jet printing.

  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. When a hole transporting or light emitting polymer is used as the charge transporting compound, the ink viscosity may be adjusted by adjusting the weight average molecular weight of the polymer. Alternatively, the viscosity of the ink can be lowered by adding a fluorine-based solvent having a low surface tension. Examples of the fluorine-based solvent include NOVEC 7300 or 7500 manufactured by 3M.

  For example, when a printing method such as an inkjet method or a continuous nozzle printing method is used, a smooth film is formed in the pixels surrounded by the partition walls. The ink printed by such a printing method preferably contains a mixture of a first good solvent having a low boiling point and viscosity and a second solvent having a high boiling point and viscosity.

  By adjusting the viscosity, surface tension, and solvent composition of the ink as described above and suppressing ink repelling, the smoothness of the resulting charge transport film is enhanced.

After the wet film formation, the substrate is dried by heating using a hot plate or an oven in the air, under reduced pressure, or in an inert gas atmosphere. Charge transporting compounds such as a hole transporting compound and a light emitting compound are cationized by depriving electrons from the dication of the aromatic diiodonium salt of this embodiment, and a low resistance charge transporting film is obtained. For example, when an aromatic diiodonium salt represented by the following formula 2 is mixed with the crosslinked hole transporting polymer HT-A, the volume resistivity of the film can be adjusted over about 9 digits. Therefore, it is effective for controlling the carrier balance of the injected charge. The resistivity of the charge transport film can be controlled by adjusting the concentration of the aromatic diiodonium salt.

  Conditions such as the appropriate heating temperature, time, and pressure of the drying atmosphere include the decomposition temperature of the aromatic diiodonium salt, the boiling point and vapor pressure of the solvent used, the crystallization temperature of the hole-transporting compound and the luminescent compound, and the crosslinking group. It can be appropriately selected depending on the type and the like. However, the heating temperature is required to be lower than the temperature at which crystallization, sublimation, or decomposition of the hole transporting compound or the light emitting compound in the ink occurs. Usually, it is dried by heating at 150 to 250 ° C. for about 10 minutes to 2 hours under atmospheric pressure, inert atmosphere or reduced pressure.

  When a crosslinkable compound is used as the hole transporting compound or the light emitting compound, it can be easily laminated by forming a film by a wet method. When the hole transport layer and the light-emitting layer of the organic EL element can be stacked by the wet film formation method, low-cost production can be performed without using an expensive vacuum deposition apparatus. In addition, the present invention can also be applied to the production of organic devices such as organic photovoltaic cells and organic light emitting transistors using multilayer films.

  If necessary, a patterned charge transport film can be obtained. Specifically, the charge transport film ink of this embodiment is formed into a wet film, heated and dried to form a coating film, and then pattern exposure is performed on a predetermined region of the coating film. The pattern exposure can be performed by, for example, light irradiation through a photomask, or scanning with laser light or LED light. Only the exposed portion of the coating film selectively crosslinks and becomes insoluble or hardly soluble in the organic solvent to form a charge transport film. Since the unexposed part of the coating film is soluble in the organic solvent, the unexposed part can be dissolved and removed with the organic solvent. Thereafter, by heating and drying to remove volatile components, a patterned low-resistance charge transport film can be obtained.

  By performing such patterning, the charge transport film in a predetermined region can be removed. Specifically, it is a hole injection layer or the like in a region not related to light emission, such as a sealing adhesive part, a terminal connection part, and a driving circuit part for adhering to the moisture-proof cover glass of the organic EL panel. As a result, it is possible to selectively form a charge transport film only in a desired light emitting area.

  Further, by making the hole injection layer in the light emitting pixel into a fine division pattern, it is possible to diffuse light escaping in the film surface direction at the pattern end face and improve the light extraction efficiency outside the element.

  The ink for a charge transport film of this embodiment can be 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.

  When the charge transport film ink of this embodiment is used to form the hole injection layer 3, the hole density of the hole injection layer 3 can be increased. Since the aromatic diiodonium salt of the present embodiment is contained, there is little risk of mutation and corrosion as in the case of using a conventional acceptor material, and a film generated by repelling at the time of coating and printing an aqueous dispersion. There is little occurrence of uneven thickness.

  As described above, when the coating film containing the aromatic diiodonium salt of the present embodiment together with the charge transporting compound is heat-treated, the charge transporting compound is cationized by depriving electrons. As a result, the carrier density of the hole transport layer is increased, and a charge transport film having a low resistance can be obtained. Further, it is possible to easily obtain a relatively thick hole injection layer of 100 nm or more by various coating methods and printing methods. In this case, the short circuit of the element can be suppressed by covering the projection of the anode. Moreover, the hole injection layer formed using the charge transport film ink of the present embodiment strongly absorbs visible light like a copper phthalocyanine vapor deposition film even when the thickness of the hole injection layer is as large as 100 nm or more. Compared with the hole injection material to be used, the transmittance of EL light is also increased.

  The aromatic diiodonium salt of this embodiment has higher oxidizing power than the aromatic monoiodonium salt conventionally used as an acceptor material. For this reason, the force which draws an electron from a charge transporting compound having a large Ip, which has not been easily cationized in the past, is strong and can be easily cationized.

  When used for forming the hole injection layer 3, the resistance can be reduced by 1 to 2 digits if the concentration of the aromatic diiodonium salt is 1% by mass or more of the total solid content of the ink. In order to further reduce by 4 to 7 digits or more, the concentration of the aromatic diiodonium salt is more preferably 5% by mass or more based on the total solids of the ink. On the other hand, if the aromatic diiodonium salt is excessively present in the ink, a hole transporting compound or anion cationized by heating after film formation is likely to precipitate, and the film after heat treatment may become cloudy. Although depending on the type of solvent, such an inconvenience can be avoided by using an aromatic diiodonium salt in an amount of 20 to 30% by mass or less of the total solid content of the ink or using a mixed solvent having high solubility.

  Aromatics can also be used when shortening the heating or light irradiation time of the hole injection layer or hole transport layer crosslinked and insolubilized with a hole transporting material having a cationically polymerizable substituent, or reducing the temperature of the heat treatment for crosslinking. The concentration of the diiodonium salt may be less than 30% by mass of the total solid content of the ink.

  When used to form a hole transport layer or hole transport electron blocking layer in contact with the light emitting layer, the generated cation radical of the hole transporting material deactivates excitons near the light emitting layer interface and absorbs EL light. Therefore, it is desirable that the amount of the aromatic diiodonium salt is less than 5% by mass of the total solid content of the ink.

  More preferably, the content is 2% by mass or less in order to achieve both low resistance and light emission intensity.

  Similarly, in the case where the hole transporting light emitting layer containing the light emitting dopant material or the light emitting layer 5 is used, the amount of the aromatic diiodonium salt is 2% by mass or less based on the total solid content of the ink. Preferably, the hole transporting ability of the hole transporting light emitting layer is enhanced, and crosslinking by light or heat is promoted.

  Further, when the amount of the aromatic diiodonium salt is suppressed to about 1% by mass of the total solid content of the ink, the decrease in emission intensity is further reduced.

  By using the charge transport film ink containing the aromatic diiodonium salt of the present embodiment, the hole transport charge transport such as the hole injection layer 3, the hole transport layer 4, and the light emitting layer 5 in the organic EL element. The film can be formed with a low volume resistivity.

  Specific examples of the aromatic diiodonium salt, the charge transport film composition, and the charge transport film ink are shown below.

  Aromatic diiodonium salts were synthesized and their properties were investigated.

  First, 0.5 g (2.27 mmol) of iodosylbenzene and methylene chloride (5.7 mL) 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 an intermediate compound represented by the following chemical formula (1-[(4-tert-butylphenyl) [(trifluoromethanesulfonyl) oxy] iodo] -4- [phenyl [(trifluoromethanesulfonyl) Oxy] iodo] benzene.

  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)
FIG. 2 shows a ¹ H-NMR chart, and FIG. 3 shows a ¹ H-NMR enlarged chart. 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 central benzene ring. The top four proton signals 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.

FIG. 4 is a chart of ¹⁹ F-NMR. The 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.

The white crystals obtained here were identified as [4- (phenyliodonio) phenyl] (4-tert-butylphenyl) iodonium bistetrakis (pentafluorophenyl) borate represented by the following formula 2.

In this compound, a paraphenylene group, a phenyl group, and a para tert-butylphenyl group are introduced as Ar ₁ , Ar _2, and Ar ₃ in the following general formula 1, respectively, and Ar ₂₁ , Ar ₂₂ , Ar _23, and Ar ₂₄ are introduced. All of these are aromatic diiodonium salts in which a pentafluorophenyl group is introduced.

  With respect to the obtained aromatic diiodonium salt, the LUMO level of the cation component was determined. Specifically, AM1 was calculated as a basis function by molecular orbital calculation software MOPAC7. As a result, the LUMO level of the cation component of the aromatic diiodonium salt of this example was −8.37 eV.

A conventional aromatic monoiodonium salt represented by the following formula MN was similarly found to have a LUMO level of the cation component of -5.42 eV. The aromatic diiodonium salt of this example was confirmed to have a lower LUMO level of the cation component and higher oxidizing power than the conventional aromatic monoiodonium salt.

A charge transport film composition was prepared using the aromatic diiodonium salt 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 was 30% by mass of the total solid content of the ink. This solid charge transport film composition was not changed after one month in a light-shielded state at room temperature.

  Further, 37 mg of the 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 promotion of oxidation reaction and crosslinking of the crosslinked hole transporting polymer, the solution was prepared in the dark.

  When the mixture was further stirred at 60 ° C. for 1 hour and cooled to room temperature, the color of the solution changed to dark blue. The coloring of the solution is presumed to be due to the formation of a charge transfer complex of an aromatic diiodonium salt and a cross-linked polymeric holey polymer.

  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 stirring at room temperature under light shielding to obtain a light brown transparent solution. It is presumed that the solvent was decolored by coordination of the solvent cyclopentanol with the cation of the charge transfer complex.

  The light brown transparent solution was further dried under reduced pressure to obtain a charge transport film composition comprising about 59 mg of a light brown solid.

  Using the same aromatic diiodonium salt and crosslinked hole transporting polymer as described above, an ink for charge transport film was prepared using anisole as a solvent.

  First, a cross-linked hole transporting polymer and an aromatic diiodonium salt were mixed to obtain a powder of a composition for a charge transport film. The amount of the aromatic diiodonium salt was 15% by mass of the total solid content of the ink. 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 1 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 seems that charge transfer complexes were formed in the ink over time.

  Using the same aromatic diiodonium salt and cross-linked hole transporting polymer as described above, the solvent was changed to a mixed solvent of anisole and cyclohexanone to prepare an ink for a charge transport film.

  First, a cross-linked hole transporting polymer and an aromatic diiodonium salt were mixed to obtain a powder of a composition for a charge transport film. The amount of the aromatic diiodonium salt was 25% by mass of the total solid content of the ink.

  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 2 was obtained by dissolving the aforementioned powder of the composition for a charge transport film in the obtained mixed solvent so as to have a solid content of 1.2% by mass. In ink 2, 3/5 of the solvent is cyclohexanone.

  This ink 2 was colorless and transparent during preparation, and no change occurred after 4 days in a yellow light clean room. Since cyclohexanone, which is an alicyclic ketone, accounts for 3/5 of the solvent, in ink 2, coloring components such as charge transfer complexes with aromatic diiodonium and oxides of hole transporting polymers are not formed. Presumed to be.

  Using the same aromatic diiodonium salt and crosslinked hole transporting polymer as described above, the solvent was changed to tetralin to prepare an ink for a charge transport film.

  First, a cross-linked hole transporting polymer and an aromatic diiodonium salt were mixed to obtain a powder of a composition for a charge transport film. The amount of the aromatic diiodonium salt was 10% by mass of the total solid content of the ink. 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 3 was colorless and transparent during the preparation, but when left in a yellow light clean room, the color changed to blue and transparent after 4 days.

  Using the same aromatic diiodonium salt and crosslinked hole transporting polymer as described above, the solvent was changed to a mixed solvent of tetralin and cyclopentanol to prepare an ink for a charge transport film.

  First, a cross-linked hole transporting polymer and an aromatic diiodonium salt were mixed to obtain a powder of a composition for a charge transport film. The amount of the aromatic diiodonium salt was 15% by mass of the total solid content of the ink.

  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 4 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. In ink 4, 1/4 of the solvent capacity is cyclopentanol.

  This ink 4 was colorless and transparent during preparation, and no change occurred even after 4 days in a yellow light clean room. Since cyclopentanol, which is a monovalent alicyclic alcohol, occupies a quarter of the solvent, it is presumed that in ink 4, the formation of colored components such as charge transfer complexes is suppressed.

Comparative Example 1

  A conventional charge transport film composition was prepared using a conventional aromatic monoiodonium salt and a crosslinked hole transporting polymer. The aromatic monoiodonium salt is a compound represented by the aforementioned formula MN. The crosslinked hole transporting polymer is represented by the above formula (HT-A), and its weight average molecular weight is 56,000.

  First, a crosslinked hole transporting polymer and an aromatic monoiodonium salt were mixed to obtain a powder of a composition for a charge transport film. The amount of the aromatic monoiodonium salt was 20% by mass of the total solid content of the ink. 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 5 was colorless and transparent during preparation, but was left in a yellow light clean room and colored light brown after 4 days.

  A charge transport film was formed using the charge transport film ink containing the aromatic diiodonium salt of the present embodiment represented by the above-described formula 2, and the volume resistivity was measured by fabricating a hole-only device.

  FIG. 6 is a schematic diagram showing the configuration of a sample used for resistivity measurement. In the sample 20 shown in the figure, a charge transport film 23 is formed on a glass substrate 21 having striped anodes 22 by spin coating, and an unnecessary film at an end serving as a terminal is wiped off. On the top, a stripe-shaped counter electrode 24 is provided so as to be orthogonal to the anode 22.

  The anode 22 was formed by etching an ITO film (thickness 150 nm) formed by sputtering to a width of 2 mm. The counter electrode 24 was formed by vapor-depositing an Al film (thickness 120 nm) through a shadow mask having holes in a 2 mm width stripe. The striped anode 22 and the striped counter electrode 24 face each other with a 2 mm square area through the charge transport film 23.

  The charge transport film ink used for forming the charge transport film 23 is a solution obtained by dissolving the above-mentioned aromatic diiodonium salt in cyclohexane. The amount of aromatic diiodonium salt in the ink was 3% by mass. The charge transport film ink was spin-coated on the glass substrate 21 on which the anode 22 was formed, and dried under reduced pressure for 1 hour to obtain a charge transport film 23. The thickness of the charge transport film 23 was 56 nm.

  A voltage was applied between the anode 22 and the counter electrode 24 to measure the current flowing between the electrodes, 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.

  The wiring resistance of the anode line made of ITO is insignificantly larger than the Al film of the counter electrode and cannot be ignored when a large current is passed. 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 face each other with a 2 mm square area through 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.

The actual voltage (actual electric field) and volume resistivity are summarized in Table 3 below.

As shown in Table 3 above, the charge transport film formed using the charge transport film ink containing the aromatic diiodonium salt of the present embodiment has an actual electric field of 2.0 × 10 ^{5 to} 5.0 ×. The volume resistance value at 10 ⁵ V / cm is 2.9 × 10 ^{9 to} 1.1 × 10 ⁹ Ω · cm.

Comparative Example 2

  A charge transport film is formed using an ink for a charge transport film that does not contain the aromatic diiodonium salt of this embodiment and contains only a crosslinked hole transporting polymer, and its volume resistivity and residual film ratio due to toluene rinsing Was measured.

  For the measurement of the volume resistivity, the same sample as in Example 7 was used 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 was prepared by dissolving a cross-linked hole transport polymer in anisole. The crosslinked hole transporting polymer is represented by the above formula (HT-A), and its weight average molecular weight is 427,000, and the amount of the crosslinked hole transporting polymer in the ink is about 1 mass. %.

  The charge transport film 23 was formed by spin-coating the charge transport film ink of this comparative example on the glass substrate 21 on which the anode 22 was formed, and heating at 200 ° C. for 30 minutes. The heating here was performed in an Ar inert atmosphere under light shielding. The thickness of the obtained charge transport film was 89 nm.

The volume resistivity of the charge transport film was determined by the same method as described above. The actual voltage (real electric field) and volume resistivity are summarized in Table 4 below.

As shown in Table 4 above, the charge transport film formed using the charge transport film ink not containing the aromatic diiodonium salt of the present embodiment has an actual electric field of 2.0 × 10 ^{5 to} 5.0. The volume resistivity at × 10 ⁵ V / cm is 1.7 × 10 ^{11 to} 1.4 × 10 ¹⁰ Ω · cm. Compared with the result of the above-mentioned Table 3, it turns out that the charge transport film | membrane of only the hole transportable polymer HT-A which does not contain the aromatic diiodonium salt of a comparative example has large resistance.

The charge transport film formed using the charge transport film ink of this comparative example was examined for solvent resistance. Specifically, the charge transport film having an initial film thickness (T ₀ ) was rinsed with 3 ml of toluene, and the film thickness (T ₁ ) after drying at 3000 rpm for 1 minute was measured.

The residual film ratio calculated by ((T ₁ / T ₀ ) × 100) was 39%. In general, the residual film ratio is required to be 98% or more in order to suppress the mixing of soluble components into the laminated film during lamination by wet film formation such as a light emitting layer. Even when a cross-linked hole transporting polymer is contained, when the charge transport film ink of this embodiment does not contain the aromatic diiodonium salt, the resulting charge transport film has extremely low solvent resistance. It has been shown.

Comparative Example 3

  A charge transport film was formed using a charge transport film ink containing the conventional aromatic monoiodonium salt represented by the formula MN and a cross-linked hole transport polymer, and the volume resistivity was measured.

  For the measurement of the volume resistivity, the same sample as in Example 7 was used except that the material of the charge transport film 23 was different. In preparing the charge transport film ink used for forming the charge transport film 23, first, the crosslinked hole transport polymer was dissolved in ethyl benzoate to obtain a solution having a solid content of 1.7% by mass. The used cross-linked hole transporting polymer is represented by the above formula (HT-A), and its weight average molecular weight is 427,000. An aromatic monoiodonium salt was added to an ethyl benzoate solution of a crosslinked hole transporting polymer in an amount of 25% by mass of the total solid content of the ink to obtain an ink for a charge transport film of this comparative example.

  The charge transport film 23 was formed by spin-coating the charge transport film ink of this comparative example on the glass substrate 21 on which the anode 22 was formed, and heating at 230 ° C. for 60 minutes. The heating here was performed in the atmosphere under yellow light. The obtained charge transport film had a thickness of 55 nm.

When the volume resistivity of the charge transport film was obtained by the same method as described above, the volume resistivity when the actual voltage (real electric field) was 1.1 V (2.0 × 10 ⁵ V / cm) was 3.4. × 10 ⁸ Ω · cm.

  A charge transport film was formed using the charge transport film ink containing the aromatic diiodonium salt of the present embodiment represented by the above-described formula 2 and a crosslinked hole transporting polymer, and the volume resistivity was measured. .

  For the measurement of the volume resistivity, the same sample as in Example 7 was used except that the material of the charge transport film 23 was different. In preparing the charge transport film ink used to form the charge transport film 23, first, a cross-linked hole transport polymer is dissolved in a mixed solvent containing tetralin and cyclopentanol in a volume ratio of 7: 3. Thus, a solution having a solid content of about 1% by mass was obtained. The used cross-linked hole transporting polymer is represented by the above formula (HT-A), and its weight average molecular weight is 279,000. To the obtained solution, an aromatic diiodonium salt was added in an amount of 15% by mass of the total solid content of the ink, to obtain a charge transport film ink used in this example.

  The charge transport film 23 was formed by spin-coating the above-described ink for charge transport film on the glass substrate 21 on which the anode 22 was formed, and heating at 200 ° C. for 30 minutes. The heating here was performed in the atmosphere under yellow light. The thickness of the obtained charge transport film was 44 nm.

When the volume resistivity of the charge transport film was determined by the same method as described above, the volume resistivity when the actual voltage (real electric field) is 0.88 V (2.0 × 10 ⁵ V / cm) is 2. It was 1 × 10 ⁷ Ω · cm. Compared with the charge transport film obtained in Comparative Example 3 described above, it can be seen that the charge transport film obtained in this example has low resistance even at a heat treatment temperature lower by 30 ° C. and half the heat treatment time.

Comparative Example 4

  A charge transport film is formed using a conventional aromatic monoiodonium salt represented by the above formula MN and a crosslinkable hole transport polymer ink, and the residual film ratio after toluene rinsing is measured. did.

  The sample used for the measurement is the same as in Example 7 except that the material of the charge transport film 23 is different, the end of the film is not wiped, and the counter electrode 24 is not provided. In preparing the charge transport film ink used for forming the charge transport film 23, first, a crosslinked hole transporting polymer was dissolved in anisole to prepare a solution having a solid content of about 1% by mass. The crosslinked hole transporting polymer used here is represented by the above formula (HT-A), and its weight average molecular weight is 427,000. To the crosslinked hole transporting polymer anisole solution, an aromatic monoiodonium salt was added in an amount of 1% by mass of the total solid content of the ink to obtain an ink for a charge transport film used in this comparative example.

The charge transport film 23 was formed by spin-coating the charge transport film ink of this comparative example on the glass substrate 21 on which the anode 22 was formed, and heating at 200 ° C. for 30 minutes. The heating here was performed under an inert atmosphere and light shielding. The charge transport film thus obtained had an initial film thickness (T ₀ ) of 54 nm.

The charge transport film was rinsed with 3 ml of toluene, and the film thickness (T ₁ ) after drying at 3000 rpm for 1 minute was measured. The residual film ratio calculated by ((T ₁ / T ₀ ) × 100) was 96%.

  A charge transport film is formed using the charge transport film ink containing the aromatic diiodonium salt of the present embodiment represented by Formula 2 and a cross-linked hole transport polymer, and the remaining film ratio after toluene rinsing Was measured.

  For the measurement of the remaining film ratio, the same sample as in Comparative Example 4 described above was used except that the material of the charge transport film 23 was different. In preparing the charge transport film ink used for forming the charge transport film 23, first, a crosslinked hole transporting polymer was dissolved in anisole to prepare a solution having a solid content of about 1% by mass. The crosslinked hole transporting polymer used here is represented by the above formula (HT-A), and its weight average molecular weight is 427,000. To the anisole solution, an aromatic diiodonium salt was added in an amount of 1% by mass of the total solid content of the ink to obtain an ink for a charge transport film used in this example.

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 heating at 200 ° C. for 30 minutes. The heating here was performed in an Ar atmosphere under light shielding. The charge transport film thus obtained had an initial film thickness (T ₀ ) of 47 nm.

The charge transport film was rinsed with 3 ml of toluene, and the film thickness (T ₁ ) after drying at 3000 rpm for 1 minute was measured. The remaining film ratio calculated by ((T ₁ / T ₀ ) × 100) was 98% to 100%.

  The value of the remaining film ratio is 2% or more higher than that in Comparative Example 4 using the charge transport film ink containing the conventional aromatic monoiodonium salt. Therefore, it can be seen that the charge transport film obtained by using the charge transport film ink of this example does not dissolve even when a light emitting layer is formed thereon by a coating method, and is less likely to be mixed.

  Further, when compared with the result of Comparative Example 2, the aromatic diiodonium salt of the present embodiment has an effect of sufficiently promoting crosslinking even with a low addition amount of 1% by mass with respect to the crosslinked hole transporting polymer. I understand.

  The relationship between the concentration of the aromatic diiodonium salt in the charge transport film ink used for forming the charge transport film and the volume resistivity of the charge transport film formed using the charge transport film ink was investigated.

  For the measurement of the volume resistivity, the same sample as in Example 7 was used except that the material of the charge transport film 23 was different. In preparing the charge transport film ink used for forming the charge transport film 23, the cross-linked hole transport polymer and the aromatic diiodonium salt of the present embodiment represented by the above-described formula 2 are mixed with the concentration of the aromatic diiodonium salt. Is dissolved in anisole so that the total solid content of the ink is 0% by mass, 1% by mass, 5% by mass, 15% by mass, and 20% by mass to prepare an ink for a charge transport film having a solid content of about 1% by mass. did. The used cross-linked hole transporting polymer is represented by the above formula (HT-A), and its weight average molecular weight is 427,000.

  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 heating at 200 ° C. for 30 minutes. The heating here was performed in an Ar inert atmosphere under light shielding.

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 described above. The concentration of the aromatic diiodonium salt in the solid content dissolved in the charge transport film ink and the volume resistivity of the charge transport film are summarized in Table 5 below and plotted in the graph of FIG.

  It can be seen that the volume resistivity is drastically lowered when the aromatic diiodonium salt is contained, and the degree of reduction is moderated when the concentration of the aromatic diiodonium salt is further increased.

  (For the value of the 1% by mass mixed film, a PEDOT / PSS aqueous dispersion (HC Stark BYTRON PVP AI4083) was spin-coated on the ITO electrode and dried to form an 80 nm film, which was used as an anode. The value measured with was measured.)

  Relationship between concentration of aromatic diiodonium salt in ink for charge transport film using mixed solvent used for formation of charge transport film and volume resistivity of charge transport film formed using ink for charge transport film I investigated.

  For the measurement of the volume resistivity, the same sample as in Example 7 was used except that the material of the charge transport film 23 was different. In preparing the charge transport film ink used for forming the charge transport film 23, a mixed solvent containing cyclohexanone and anisole in a volume ratio of 8: 2 is represented by the cross-linked hole transport polymer and the above-described formula 2. The aromatic diiodonium salt of this embodiment is dissolved so that the concentration of the aromatic diiodonium salt is 0% by mass, 5% by mass, 10% by mass, and 20% by mass with respect to the total solids of the ink. A 2.2% by mass charge transport film ink was prepared. The used cross-linked hole transporting polymer is represented by the above formula (HT-A), and its weight average molecular weight is 210,000. In the charge transport film ink used in this example, 4/5 of the solvent capacity is cyclohexanone.

  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 drying by heating at 200 ° C. for 30 minutes. The heating here was performed under an Ar inert atmosphere and light shielding. The thickness of the obtained charge transport film was 184 to 189 nm.

For each charge transport film, the volume resistivity (Ω · cm) when the electric field strength applied between the electrodes was 2.0 × 10 ⁵ V / cm was determined by the same method as in Example 7 above. . The concentration of the aromatic diiodonium salt in the solid content dissolved in the charge transport film ink and the volume resistivity of the charge transport film formed using the same are summarized in Table 6 below and plotted in the graph of FIG. .

  In the charge transport film ink used in Example 10 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. Due to the use of a mixed solvent of cyclohexanone and anisole, dispersibility of non-cationized part and cationized part of HT-A and cations and anions derived from aromatic diiodonium salt is improved, compared with the case of using a single solvent. A highly transparent film was also obtained. In addition, even when the concentration of the aromatic diiodonium salt in the charge transport film ink is smaller than that in Example 10, a volume resistance value comparable to that in Example 10 is obtained.

  A light-emitting layer made of a low molecular weight coating type blue hole-transporting light-emitting material is formed as a charge transport film, and the concentration of the aromatic diiodonium salt in the charge transport film (light-emitting layer) ink used for the formation and the charge transport film The relationship between the concentration of the aromatic diiodonium salt in the ink for the charge transport film and the intensity of the fluorescent light peak was investigated.

A sample similar to that in Example 7 described above was used except that the material of the charge transport film 23 having a volume resistivity was different. In preparing the charge transport film ink used for forming the charge transport film 23, the low molecular weight coating type hole transporting blue light emitting material represented by the following formula 8 and the aromatic diiodonium salt of the present embodiment represented by the formula 2 are used. Is dissolved in toluene so that the aromatic diiodonium salt concentration becomes 0% by mass, 1% by mass, 2% by mass, and 5% by mass of the total solid content of the ink, and a charge transport film having a solid content of 3.0% by mass An ink was prepared.

  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 drying by heating at 200 ° C. for 30 minutes. The heating here was performed in an Ar inert atmosphere under light shielding. The thickness of the obtained charge transport film was 169 to 177 nm. Since the light emitting material is contained, the charge transport film formed here can be referred to as a light emitting layer.

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

Even when a low molecular weight hole transporting compound is used, if the aromatic diiodonium salt of this embodiment is contained, a low resistance charge transporting film can be formed. Moreover, even when the concentration of the aromatic diiodonium salt is as small as about 5.0% by mass of the total solid content of the ink, a low resistance of about 1.0 × 10 ⁵ Ω · cm or less can be achieved.

  Further, the emission peak intensity was examined for each light emitting layer. Specifically, excitation was performed with light having a wavelength of 337 nm using a spectrofluorimeter, and an emission spectrum having a fluorescence peak wavelength of 446 nm was obtained. The emission peak intensity of each light emitting layer is shown in FIG. From the results of FIG. 10, by doping the aromatic diiodonium salt of this embodiment at a concentration of 0.2 to 5 wt%, it becomes possible to control the resistance reduction of 1 to 9 digits while maintaining strong fluorescence emission, It turns out that the aromatic diiodonium salt of this embodiment is applicable also to a light emitting layer.

Comparative Example 5

  A charge transport film is formed using an ink for a charge transport film containing a conventional polythiophene-based hole injection polymer (aqueous dispersion of PEDOT / PSS (HC Star BYTRON PVP CH8000)), and the volume resistivity is increased. It was measured.

  For the measurement of the volume resistivity, the same sample as in Example 7 was used 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 a conventional polythiophene-based hole injection polymer (PEDOT / PSS aqueous dispersion (HC Star BYTRON PVP CH8000)).

  The charge transport film 23 is spin-coated with a PEDOT / PSS aqueous dispersion through a 0.45 micron syringe filter on the glass substrate 21 on which the anode 22 is formed, and is heated and dried in the atmosphere at 20 ° C. for 15 minutes. Formed by. The film thickness of the obtained charge transport film was 84 nm.

When the volume resistivity of the charge transport film was determined by the same method as in Example 7, the volume resistivity when the actual voltage (actual electric field) was 1.65 V (2.0 × 10 ⁵ V / cm) was Although it was 2.3 × 10 ⁶ Ω · cm, a lot of unevenness occurred in film thickness due to ink repelling.

Comparative Example 6

  A charge transport film was formed using a charge transport film ink containing the conventional aromatic monoiodonium salt represented by the formula MN and a cross-linked hole transport polymer, and the volume resistivity was measured.

  For the measurement of the volume resistivity, the same sample as in Example 7 was used except that the material of the charge transport film 23 was different. In preparing the charge transport film ink used for forming the charge transport film 23, the crosslinked hole transporting polymer and the aromatic monoiodonium salt are mixed with anisole so that the aromatic monoiodonium salt is 20% by mass of the total solid content of the ink. The ink for charge transport film | membrane used for this comparative example with a solid content rate of about 1 mass% was prepared. The used cross-linked hole transporting polymer is represented by the above formula (HT-A), and its weight average molecular weight is 427,000.

  The charge transport film 23 was formed by spin-coating the charge transport film ink of this comparative example on the glass substrate 21 on which the anode 22 was formed, and heating at 200 ° C. for 30 minutes. The heating here was performed in an Ar inert atmosphere under light shielding. The thickness of the obtained charge transport film was 81 nm.

When the volume resistivity of the charge transport film was determined by the same method as in Example 7, the volume resistivity when the actual voltage (actual electric field) was 1.9 V (2.0 × 10 ⁵ V / cm) was 1.4 × 10 ⁶ Ω · cm. Compared to Example 10 using the aromatic diiodonium salt of the present invention, the volume resistivity is about 3 times, and a low resistance charge transporting film can be obtained by using diiodonium salt having strong oxidizing power. Recognize.

  A charge transport film is formed using an ink for a charge transport film comprising the aromatic diiodonium salt of the present embodiment represented by Formula 2 above, a cross-linked hole transporting polymer and a cross-linked light-emitting polymer, and photocrosslinking The remaining film rate after the subsequent toluene rinse was measured.

The sample used for the measurement is the same as in Example 7 except that the material of the charge transport film 23 is different, the end of the film is not wiped, and the counter electrode 24 is not provided. The charge transport film ink used for forming the charge transport film 23 is an anisole solution containing a crosslinkable hole transportable polymer, a crosslinkable light emitting polymer, and an aromatic diiodonium salt in a mass ratio of 94: 5: 1. is there. The solid content in the anisole solution was 1% by mass. The used cross-linked hole transporting polymer is represented by the following formula (HT-C), and its weight average molecular weight is 131,000. Moreover, the used crosslinking type light emitting polymer is represented by a following formula (PF-1), and the weight average molecular weight is 85,000.

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 irradiating it with ultraviolet rays in the atmosphere to crosslink. From a handy ultraviolet lamp (Funakoshi UVGL-25) as a light source, 365 nm ultraviolet rays of about 400 mJ / cm ² were irradiated for 155 seconds through a quartz photomask provided with a 0.5 mm wide stripe pattern made of a chromium film. The charge transport film thus obtained had an initial film thickness (T ₀ ) of 70 nm.

After the charge transport film was rinsed with 3 ml of toluene and dried at 3000 rpm for 1 minute, the film thickness (T ₁ ) of the stripe pattern was 63 nm. The residual film ratio calculated by ((T ₁ / T ₀ ) × 100) was 90%.

  Further, when excited with light having a wavelength of 330 nm using a Shimadzu RF5300PC fluorescence spectrophotometer, blue light emission having a fluorescence peak wavelength of 420 nm was obtained.

  A hole injection layer was formed using the charge transport film ink of this embodiment, and an organic EL device was produced.

  In preparing the charge transport film ink, first, an anisole solution containing a crosslinkable hole transport polymer and the aromatic diiodonium salt of the present embodiment represented by the above-described formula 2 in a mass ratio of 95: 5 is prepared. did. The solid content in the anisole solution was 2% by mass. The used cross-linked hole transporting polymer is represented by the above formula (HT-A), and its weight average molecular weight is 427,000. A hole injection layer is formed using the charge transport film ink thus prepared.

  A glass substrate having a patterned ITO film as an anode was prepared. The glass substrate was washed with water with a neutral detergent and then with ultraviolet ozone. The above-described ink for charge transport film was spin-coated on the glass substrate after washing, and the film on the electrode terminal was wiped off. Then, it mounted on the hotplate heated at 200 degreeC, and heated for 60 minutes in nitrogen atmosphere. As a result, the crosslinked hole transporting polymer was crosslinked and insolubilized to form a 30 nm thick hole injection layer.

  A cross-linked hole transporting polymer similar to that described above was dissolved in anisole to prepare a solution having a solid content of 2% by mass, whereby an ink for a hole transporting layer was obtained. The hole transport layer ink was spin-coated on the hole injection layer and heated on a hot plate heated to 200 ° C. in a nitrogen atmosphere for 60 minutes. As a result, the cross-linked hole transporting polymer was cross-linked to form a hole transport layer. The film thickness of the obtained hole transport layer was 20 nm.

A light emitting layer ink containing a compound represented by the following formula TPBI and a compound represented by the following formula Ir (mppy) ₃ at a mass ratio of 95: 5 was prepared. The solid content in the light emitting layer ink was 3% by mass.

  After the ink for the light emitting layer was spin-coated on the hole transport layer and the film on the electrode terminal was wiped off, the light emitting layer was formed by heating and drying in nitrogen at 150 ° C. for 15 minutes. The film thickness of the obtained light emitting layer was 70 nm.

  On the light emitting layer, Ba was deposited by mask vapor deposition with a thickness of 4 nm, and then Al was continuously deposited by mask vapor deposition with a thickness of 150 nm to form a cathode. This cathode is connected to a cathode terminal portion on the substrate.

The laminated structure including the hole injection layer, the hole transport layer, and the light emitting layer was sealed with a sealing plate, and the anode and the cathode terminal portion were connected to a power source by wiring to produce an organic EL element. The obtained organic EL element flowed a current of 62 mA / cm ^{2 at} 10 V and emitted green light with a luminance of 13910 cd / m ² .

  The aromatic diiodonium salt of the present embodiment includes an organic EL element, an organic light emitting transistor, an organic EL laser, and a hole injection layer, a hole transport layer, and a light emitting layer in an organic element such as an organic photovoltaic cell and an organic thin film solar cell, It can be used when a charge transport film such as a photoactive layer is formed by coating printing. In particular, the resistance of the hole injection layer and the hole transport layer can be reduced, and the carrier balance between the holes and electrons in the light emitting layer of the organic EL element can be adjusted. Moreover, in a p-i-n junction type or bulk heterojunction type organic photovoltaic cell or organic thin-film solar cell, the resistance of the hole transporting p-type layer can be reduced and the loss of photovoltaic and photocurrent can be suppressed. Can do. Further, by reducing the resistance of the photoactive layer, the active layer can be made thicker, the amount of light absorption can be increased, and the photocurrent can be increased. Moreover, in addition to being able to laminate a multilayer film by coating printing, it can be preferably used for forming a patterned charge transport film.

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; Material 11 ... Cathode terminal; 12 ... Power source; 13 ... Wiring; 14 ... Laminated structure 15 ... Organic EL element; 20 ... Sample; 21 ... Glass substrate; 22 ... Anode 23 ... Charge transport film;

Claims (13)

An aromatic diiodonium salt represented by the following general formula 1.

(Here, Ar ₁ is a substituted or unsubstituted divalent aromatic group, Ar ₂ and Ar ₃ may be the same or different, and are substituted or unsubstituted monovalent aromatic groups. Ar _At least one of ₂₁ , Ar _22, Ar ₂₃ and Ar ₂₄ is a monovalent aromatic group having an electron-withdrawing substituent, and the rest may be the same or different, and may be substituted or unsubstituted 1 Valent aromatic group.) In the general formula 1, Ar ₁ is paraphenylene, Ar ₂ is phenyl, Ar ₃ is para tert-butylphenyl, and Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ are all pentafluorophenyl. The aromatic diiodonium salt according to claim 1, wherein   A charge transport film composition comprising: a charge transport compound selected from a hole transport compound and a light emitting compound; and the aromatic diiodonium salt according to claim 1 or 2.   The charge transport film composition according to claim 3, wherein the charge transport compound is a low molecular compound.   The charge transport film composition according to claim 3, wherein the charge transporting compound is a crosslinked or non-crosslinked polymer.   A charge transport film ink comprising the aromatic diiodonium salt according to claim 1 or 2 and an organic solvent.   The charge transport film ink according to claim 6, further comprising a charge transport compound selected from a hole transport compound and a light-emitting compound.   8. The charge transport film ink according to claim 7, wherein the charge transporting compound is a low molecular compound.   8. The charge transport film ink according to claim 7, wherein the charge transporting compound is a crosslinked or non-crosslinked polymer.   The at least 1/4 of the total capacity of the organic solvent is at least one selected from alicyclic ketones and monovalent aliphatic alcohols, according to any one of claims 7 to 9. Ink for charge transport film.   The ink for a charge transport film according to claim 10, wherein the alicyclic ketone is cyclohexanone.   The charge transport film ink according to claim 10, wherein the monovalent aliphatic alcohol is a monovalent alicyclic alcohol having 5 to 8 carbon atoms.   13. A method for producing a charge transport film, comprising: forming a film by a wet film formation method using the charge transport film ink according to claim 6; and drying by heat treatment.

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