JP6327951B2 - Charge generation material and organic electroluminescence device - Google Patents

Description

  The present invention relates to a charge generation material and an organic electroluminescence element.

  In recent years, organic electroluminescence elements, which are self-luminous light emitting elements, have been actively developed. An organic electroluminescence element (hereinafter referred to as an organic EL element) is an element that emits light from a light emitting material containing an organic compound in a light emitting layer by recombining holes and electrons injected from an anode and a cathode in the light emitting layer. is there.

  A general organic EL device includes a light emitting layer and a structure in which a plurality of layers having different characteristics such as a hole transport layer that transports holes and electrons as carriers and an electron transport layer are stacked on the light emitting layer. . Conventionally, in an organic EL element, various compounds have been studied as a material for each layer in order to improve the light emission characteristics and extend the lifetime.

  For example, Patent Document 1 discloses a tetracoordinate boron compound that is suitably used as a host material for a light emitting layer.

  On the other hand, in order to further improve the light emission efficiency, an organic EL element having a multi-stack structure in which a plurality of light emitting layers are stacked via a charge generation layer has been proposed. In such a multi-stack type organic EL device, when a predetermined voltage is applied, each charge generation layer injects holes in the cathode direction of the device and injects electrons in the anode direction, thereby Light is emitted as if the light emitting layers are electrically connected in series to improve the light emission efficiency.

JP 2007-35791 A

  Here, conventionally, in an organic EL element using a compound known as a charge generation material for a charge generation layer, there has been a problem that light emission efficiency and drive voltage are not sufficiently lowered. Therefore, there has been a demand for a charge generation material that can improve the light emission efficiency of the organic EL element and reduce the driving voltage.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is a new and improved device capable of improving the light emission efficiency of the organic EL element and lowering the driving voltage. Another object of the present invention is to provide a charge generating material and an organic EL device using the charge generating material.

上記一般式（１）において、
Ａｒ_１は、置換もしくは無置換のアリール（ａｒｙｌ）基、または置換もしくは無置換のヘテロアリール（ｈｅｔｅｒｏａｒｙｌ）基である。 In order to solve the above problems, according to one aspect of the present invention, there is provided a charge generation material containing a tetracoordinate boron compound represented by the following general formula (1).

In the general formula (1),
Ar ₁ is a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group.

  According to this configuration, by using the charge generation material for an organic EL element, the light emission efficiency of the organic EL element can be improved and the driving voltage can be lowered.

Ar ₁ may have at least one deuterium or electron withdrawing group as a substituent.

  According to this configuration, since the charge generation capability of the charge generation material is improved, the light emission efficiency of the organic EL element can be further improved and the drive voltage can be further reduced.

Ar ₁ may have at least one electron-withdrawing group having a Hammett substituent constant σ greater than 0.07 as a substituent.

  According to this configuration, since the charge generation capability of the charge generation material is improved, the light emission efficiency of the organic EL element can be further improved and the drive voltage can be further reduced.

上記一般式（２）において、
Ａｒ_１およびＡｒ_２は、互いに独立して、置換もしくは無置換のアリール基、または置換もしくは無置換のヘテロアリール基である。 In order to solve the above problems, according to another aspect of the present invention, a charge generation material including a tetracoordinate boron compound represented by the following general formula (2) is provided.

In the above general formula (2),
Ar ₁ and Ar ₂ are each independently a substituted or unsubstituted aryl group or a substituted or unsubstituted heteroaryl group.

  According to this configuration, by using the charge generation material for an organic EL element, the light emission efficiency of the organic EL element can be improved and the driving voltage can be lowered.

At least one of Ar ₁ and Ar ₂ may have at least one deuterium or electron withdrawing group as a substituent.

  According to this configuration, since the charge generation capability of the charge generation material is improved, the light emission efficiency of the organic EL element can be further improved and the drive voltage can be further reduced.

At least one of Ar ₁ and Ar ₂ may have at least one electron withdrawing group having a Hammett substituent constant σ greater than 0.07 as a substituent.

  According to this configuration, since the charge generation capability of the charge generation material is improved, the light emission efficiency of the organic EL element can be further improved and the drive voltage can be further reduced.

上記一般式（３）において、
Ｘは、Ｎ−Ｒ_３またはＳであり、
Ｒ_１〜Ｒ_３は、互いに独立して、置換もしくは無置換のアリール基、または置換もしくは無置換のヘテロアリール基である。 Moreover, in order to solve the said subject, according to another viewpoint of this invention, the charge generation material containing the tetracoordinate boron compound represented by following General formula (3) is provided.

In the general formula (3),
X is N—R ₃ or S;
R _{1 to} R ₃ are each independently a substituted or unsubstituted aryl group or a substituted or unsubstituted heteroaryl group.

  According to this configuration, by using the charge generation material for an organic EL element, the light emission efficiency of the organic EL element can be improved and the driving voltage can be lowered.

At least one of R _{1 to} R ₃ may have at least one deuterium or electron withdrawing group as a substituent.

  According to this configuration, since the charge generation capability of the charge generation material is improved, the light emission efficiency of the organic EL element can be further improved and the drive voltage can be further reduced.

At least one of R _{1 to} R ₃ may have at least one electron withdrawing group having a Hammett's substituent constant σ greater than 0.07 as a substituent.

  According to this configuration, since the charge generation capability of the charge generation material is improved, the light emission efficiency of the organic EL element can be further improved and the drive voltage can be further reduced.

  The electron-withdrawing group includes, independently of each other, a halogen atom, a methyl group substituted with at least one halogen atom, a cyano group, and a sulfonic acid group. Any functional group selected from the group may be used.

  According to this configuration, since the charge generation capability of the charge generation material is improved, the light emission efficiency of the organic EL element can be further improved and the drive voltage can be further reduced.

  The LUMO level of the tetracoordinate boron compound may be -6.0 eV or more and -3.4 eV or less.

  According to this configuration, by using the charge generation material for an organic EL element, the light emission efficiency of the organic EL element can be improved and the driving voltage can be lowered.

  Moreover, in order to solve the said subject, according to another viewpoint of this invention, the organic electroluminescent element which contains the said charge generation material in a charge generation layer is provided.

  According to this configuration, the light emission efficiency of the organic EL element can be improved and the drive voltage can be reduced.

  As described above, according to the present invention, the light emission efficiency of the organic EL element can be improved and the drive voltage can be lowered.

It is the schematic which shows an example of the organic EL element which concerns on one Embodiment of this invention. It is the schematic of the organic electroluminescent element produced using the electric charge generation material which concerns on one Embodiment of this invention.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<Charge generating material according to one embodiment of the present invention>
First, a charge generation material according to an embodiment of the present invention will be described. The charge generation material according to an embodiment of the present invention includes a tetracoordinate boron compound represented by any one of the following general formulas (1) to (3).

In the general formula (1), Ar ₁ is a substituted or unsubstituted aryl group or a substituted or unsubstituted heteroaryl group.

In the general formula (2), Ar ₁ and Ar ₂ are each independently a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group.

In the general formula (3), X is N—R ₃ or S, and R _{1 to} R ₃ are each independently a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group. is there.

  Here, it is known that the tetracoordinate boron compound is suitable as a host material of the light emitting layer as disclosed in Patent Document 1, for example. Specifically, in Patent Document 1, by imparting a bipolar property to a tetracoordinate boron compound and providing a hole transporting ability and an electron transporting ability, from each of the anode side and the cathode side. It has characteristics suitable as a host material for the light emitting layer into which holes and electrons are injected.

  However, in patent document 1, sufficient examination was not carried out about the other suitable use of a tetracoordinate boron compound. Therefore, the present inventors have studied in detail about the characteristics of the tetracoordinate boron compound, and as a result, by giving the acceptor property to the tetracoordinate boron compound, the present invention can be suitably used as a charge generation material. I found out that I can.

  Here, the charge generation material is used in a charge generation layer of a multi-stack type organic EL element. When a predetermined voltage is applied to the organic EL element, holes are injected in the cathode direction of the element, and the anode direction It fulfills the function of injecting electrons. For this reason, it is preferable that the charge generation material includes a compound which is deficient in electrons and has a high electron acceptor property. More specifically, the charge generation material preferably includes a compound having a low LUMO (Lowest Unoccupied Molecular Orbital) value.

Since the tetracoordinate boron compound represented by any one of the general formulas (1) to (3) has B (C ₆ F ₅ ) ₃ which is a strong organometallic Lewis acid, it is coordinated. The boron at the center is in a strong electron deficiency state. Therefore, the tetracoordinate boron compound represented by any one of the general formulas (1) to (3) has a strong acceptor property and a low LUMO value, and thus is suitably used as the above-described charge generation material. be able to.

  The tetracoordinate boron compound represented by any one of the general formulas (1) to (3) preferably has at least one deuterium or electron withdrawing group as a substituent.

Specifically, in the general formula (1), Ar ₁ preferably has at least one deuterium or an electron withdrawing group as a substituent. In the general formula (2), Ar ₁ and Ar ₂ At least one of them preferably has at least one deuterium or electron withdrawing group as a substituent. In the general formula (3), at least one of R _{1 to} R ₃ is a heavy group as a substituent. It is preferable to have at least one hydrogen or electron withdrawing group.

  When the tetracoordinate boron compound represented by any one of the general formulas (1) to (3) has at least one deuterium or electron withdrawing group as a substituent, the boron at the coordination center is further It becomes an electron deficient state. Therefore, the tetracoordinate boron compound represented by any one of the above general formulas (1) to (3) has a higher acceptor property and a lower LUMO value. Further improvement can be achieved.

  Note that, in the tetracoordinate boron compound according to the present embodiment, as the number of deuterium or electron withdrawing groups as a substituent is larger, boron at the coordination center of the tetracoordinate boron compound is more electron deficient. Become. Therefore, the tetracoordinate boron compound according to this embodiment has a lower LUMO value when the number of deuterium or electron withdrawing groups as a substituent is larger, and further improves the charge generation ability of the charge generation material. More preferable.

  In addition, the tetracoordinate boron compound represented by any one of the general formulas (1) to (3) has at least one electron-withdrawing group having a Hammett substituent constant σ greater than 0.07 as a substituent. It is preferable to have the above.

Specifically, in the general formula (1), Ar ₁ preferably has at least one electron withdrawing group having a Hammett's substituent constant σ greater than 0.07 as a substituent. ), At least one of Ar ₁ and Ar ₂ preferably has at least one electron-withdrawing group having a Hammett's substituent constant σ greater than 0.07 as a substituent. In the general formula (3), , R _{1 to} R ₃ preferably have at least one electron-withdrawing group having a Hammett's substituent constant σ larger than 0.07 as a substituent.

  Here, the Hammett's rule is an index showing the strength of electron withdrawing and electron donating properties of the functional group from the difference between the reaction rate to benzoic acid and the reaction rate to benzoic acid substituted with a functional group. . Specifically, in the Hammett rule, the electron withdrawing property and electron donating property of the substituent are evaluated by the value of Hammett's substituent constant σ, and the value of σ increases toward the positive side with σ = 0 as a boundary. The electron-withdrawing property is strong, and the larger the value on the negative side, the stronger the electron donating property.

  The Hammett's substituent constant σ is defined in two ways, the para effect and the meta effect, depending on the position of the substituent. In this specification, the Hammett's substituent constant σ is “0. “Greater than 07” means that Hammett's substituent constant σ is larger than 0.07 in both the para effect and the meta effect.

  The tetracoordinate boron compound represented by any one of the general formulas (1) to (3) has at least one electron withdrawing group having a Hammett's substituent constant σ greater than 0.07 as a substituent. Thus, boron at the coordination center can be further brought into an electron-deficient state. Therefore, the tetracoordinate boron compound represented by any one of the above general formulas (1) to (3) has a higher acceptor property and a lower LUMO value. Further improvement can be achieved.

  However, when the tetracoordinate boron compound represented by any one of the above general formulas (1) to (3) is substituted with an electron-withdrawing group having a weak electron-withdrawing property, boron electrons at the coordination center Little effect on deficiency. Therefore, the electron withdrawing group which the tetracoordinate boron compound according to the present embodiment has as a substituent preferably has strong electron withdrawing properties that greatly affect the electron deficiency state of boron at the coordination center. The electron withdrawing strength of such an electron withdrawing group is, for example, σ> 0.07 in Hammett's substituent constant σ.

  In the tetracoordinate boron compound according to this embodiment, the stronger the electron withdrawing property of the electron withdrawing group as a substituent (that is, the larger the Hammett's substituent constant σ), the more boron in the coordination center. It becomes an electron deficient state. Therefore, the tetracoordinate boron compound according to the present embodiment has a higher LUMO value when it has an electron withdrawing group having a stronger electron withdrawing property (that is, Hammett's substituent constant σ is larger) as a substituent. This is preferable because the charge generation capability of the charge generation material can be further improved.

  Here, the electron withdrawing group which the tetracoordinate boron compound according to the present embodiment has as a substituent specifically includes a halogen atom, a methyl group substituted with at least one halogen atom, a cyano group, and A sulfonic acid group or the like may be used. Since the tetracoordinate boron compound according to the present embodiment has at least one electron-withdrawing group having such a high electron-withdrawing property as a substituent, the LUMO value can be lowered. It is possible to improve the charge generation ability.

  Note that, specifically, the LUMO level of the tetracoordinate boron compound according to the present embodiment is preferably −6.0 eV or more and −3.4 eV or less. When the LUMO level of the tetracoordinate boron compound according to this embodiment is within the above-described range, the tetracoordinate boron compound according to this embodiment can further improve the charge generation ability of the charge generation material. it can.

  Below, the structure of the compounds 1-24 which are a specific example of the tetracoordinate boron compound which concerns on this embodiment mentioned above is shown. However, the tetracoordinate boron compound according to the present embodiment is not limited to the following compounds.

  As described above, the charge generation material according to this embodiment includes a tetracoordinate boron compound represented by any one of the above general formulas (1) to (3). The tetracoordinate boron compound represented by any one of the above general formulas (1) to (3) has a strong acceptor property and a low LUMO value, and therefore improves the charge generation ability of the charge generation material. Can do. Therefore, the charge generation material according to the present embodiment can be suitably used for the charge generation layer of the organic EL element, and the light emission efficiency of the organic EL element can be improved and the drive voltage can be reduced.

<Organic EL Device According to One Embodiment of the Present Invention>
Next, an organic EL element according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic view showing an example of an organic EL element according to an embodiment of the present invention.

  As shown in FIG. 1, an organic EL element 100 according to an embodiment of the present invention includes a substrate 101, an anode 103 disposed on the substrate 101, a first light emitting unit 110 disposed on the anode 103, A charge generation layer 105 disposed on the first light emission unit (unit) 110; a second light emission unit 120 disposed on the charge generation layer 105; and a cathode 107 disposed on the second light emission unit. .

  Here, the first light emitting unit 110 includes a first hole injection layer 111 disposed on the anode 103, a first hole transport layer 113 disposed on the first hole injection layer 111, and a first positive electrode. First light-emitting layer 115 disposed on hole transport layer 113, first electron transport layer 117 disposed on first light-emitting layer 115, and first electron injection layer disposed on first electron transport layer 117 119.

  The second light emitting unit 120 includes a second hole injection layer 121 disposed on the charge generation layer 105, a second hole transport layer 123 disposed on the second hole injection layer 121, and a second A second light-emitting layer 125 disposed on the hole-transporting layer 123; a second electron-transporting layer 127 disposed on the second light-emitting layer 125; and a second electron injection disposed on the second electron-transporting layer 127 Layer 129.

  The structure of the organic EL element 100 shown in FIG. 1 is merely an example, and the organic EL element according to the present embodiment is not limited to the structure of FIG. For example, in the organic EL element 100, some layers may be omitted or other layers may be added. Furthermore, each layer of the organic EL element 100 may be formed of a plurality of layers.

  Moreover, the organic EL element 100 according to the present embodiment may further include a plurality of charge generation layers and a plurality of light emitting units. For example, the organic EL element 100 includes a third light emitting unit disposed between the second light emitting unit 120 and the cathode 107, and a charge generation layer sandwiched between the second light emitting unit 120 and the third light emitting unit. May be further provided.

  As the substrate 101, for example, a transparent glass (glass) substrate, a semiconductor substrate such as silicon (Si), or a resin substrate such as a polymer compound can be used.

  The anode 103 is disposed on the substrate 101 and supplies holes to the first hole injection layer 111. The anode 103 can be formed of, for example, a metal, an alloy, a metal oxide, a conductive compound, or the like having a high work function, and specifically, indium tin oxide (ITO), indium zinc oxide (IZO), or the like. It is formed using. The film thickness of the anode 103 can be appropriately selected depending on the material, but is, for example, 100 nm to 500 nm.

The first hole injection layer 111 is disposed on the anode 103 and facilitates injection of holes from the anode 103 to the first hole transport layer 113. The first hole injection layer 111 is formed of, for example, 4,4 ′, 4 ″ -Tris [2-naphthyl (phenyl) amino] triphenylamine (2-TNATA), N, N, N ′, N′-Tetrakis (3 -Methylphenyl) -3,3'-dimethylbenzidine (HMTPD), Dipyrazino [2,3-f: 2 ', 3'-h] quinoxaline-2,3,6,7,10,11-hexacarbonitril (HAT (CN)) ₆ ) and the like. In addition, although the film thickness of the 1st positive hole injection layer 111 can be suitably selected with material, it is 10 nm-100 nm, for example.

  The first hole transport layer 113 is disposed on the first hole injection layer 111 and transports holes injected from the anode 103 to the first light emitting layer 115. The first hole transport layer 113 is formed of, for example, N, N′-Bis (3-methylphenyl) -N, N′-diphenylbenzidine (TPD), 4,4 ′, 4 ″ -Tris (N-carbazolyl) triphenylamine ( TCTA), N, N′-Di (1-naphthyl) -N, N′-diphenylbenzidine (NPD) and the like. In addition, although the film thickness of the 1st positive hole transport layer 113 can be suitably selected with materials, it is 10 nm-150 nm, for example.

  The first light emitting layer 115 is a layer that is disposed on the first hole transport layer 113 and emits light by providing a field for recombination of holes and electrons. Specifically, the first light emitting layer 115 is formed by including a dopant material which is a light emitting material in a host material. Note that a known fluorescent material and phosphorescent material can be used as the dopant material. For example, the first light-emitting layer 115 uses 9,10-Di (2-naphthyl) anthracene (ADN) as a host material. In addition, as a dopant material, 2,5,8,11-Tetra-t-butylperylene (TBP) is included. In addition, the film thickness of the 1st light emitting layer 115 is although it does not specifically limit, For example, they are 10 nm-100 nm.

The first electron transport layer 117 is disposed on the first light emitting layer 115 and transports electrons injected from the charge generation layer 105 to the first light emitting layer 115. The first electron transport layer 117 is formed of, for example, Tris (8-hydroxyquinolinato) aluminum (Alq ₃ ), 3- (4-Biphenylyl) -4-phenyl-5- (4-tert-butylphenyl) -4H-1,2, 4-triazole (TAZ) and the like are formed. In addition, although the film thickness of the 1st electron carrying layer 117 can be suitably selected with materials, it is 5 nm-100 nm, for example.

The first electron injection layer 119 is disposed on the first electron transport layer 117 and facilitates injection of electrons from the charge generation layer 105 to the first electron transport layer 117. The first electron injection layer 119 includes, for example, lithium fluoride (LiF), sodium chloride (NaCl), cesium fluoride (CsF), lithium oxide (Li ₂ O), barium oxide (BaO), and the like. . In addition, although the film thickness of the 1st electron injection layer 119 can be selected suitably with materials, it is 0.1 nm-10 nm, for example.

  The charge generation layer 105 is disposed on the first electron injection layer 119, supplies electrons to the first light emitting layer 115 on the anode 103 side, and supplies holes to the second light emitting layer 125 on the cathode 107 side. Specifically, the charge generation layer 105 includes a metal doping layer formed on the first electron injection layer 119 and an acceptor layer disposed on the metal doping layer.

  The metal doping layer includes an organic compound and a metal that functions as an electron-donating dopant, and supplies electrons to the first light-emitting layer 115 on the anode 103 side. Specifically, the metal doping layer preferably includes one or more metals selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals, or compounds of the metals. For example, the metal included in the metal doping layer may be lithium (Li), cesium (Cs), or the like. The metal doping layer may be formed as a metal layer that does not contain an organic compound and is made of a metal that functions as an electron-donating dopant.

  The acceptor layer is formed of the charge generation material according to an embodiment of the present invention, and supplies holes to the second light emitting layer 125 on the cathode 107 side. Since the tetracoordinate boron compound included in the charge generation material according to an embodiment of the present invention has strong acceptor properties and a low LUMO value, the charge generation layer 105 can have high charge generation ability. Therefore, the organic EL element 100 according to this embodiment has improved light emission efficiency and reduced drive voltage.

  The second hole injection layer 121 is disposed on the charge generation layer 105 and facilitates injection of holes from the charge generation layer 105 to the second hole transport layer 123. The second hole injection layer 121 can be formed with the same material and thickness as the first hole injection layer 111. The first hole injection layer 111 and the second hole injection layer 121 may be formed of the same material and film thickness, or may be formed of different materials and film thicknesses.

  The second hole transport layer 123 is disposed on the second hole injection layer 121 and transports holes injected from the charge generation layer 105 to the second light emitting layer 125. The second hole transport layer 123 can be formed with the same material and film thickness as the first hole transport layer 113. The first hole transport layer 113 and the second hole transport layer 123 may be formed of the same material and film thickness, or may be formed of different materials and film thicknesses.

  The second light emitting layer 125 is a layer that is disposed on the second hole transport layer 123 and emits light by providing a field for recombination of holes and electrons. The second light emitting layer 125 can be formed with the same material and thickness as the first light emitting layer 115. Note that the first light emitting layer 115 and the second light emitting layer 125 may be formed of the same material and film thickness, or may be formed of different materials and film thicknesses.

  The second electron transport layer 127 is disposed on the second light emitting layer 125 and transports electrons injected from the cathode 107 to the second light emitting layer 125. The second electron transport layer 127 can be formed using the same material and thickness as the first electron transport layer 117. Note that the first electron transport layer 117 and the second electron transport layer 127 may be formed of the same material and film thickness, or may be formed of different materials and film thicknesses.

  The second electron injection layer 129 is disposed on the second electron transport layer 127 and transports electrons injected from the cathode 107 to the second light emitting layer 125. The second electron injection layer 129 can be formed with the same material and thickness as the first electron injection layer 119. Note that the first electron injection layer 119 and the second electron injection layer 129 may be formed of the same material and film thickness, or may be formed of different materials and film thicknesses.

  The cathode 107 is disposed on the second electron injection layer 129 and supplies electrons to the second electron injection layer 129. The cathode 107 is formed of, for example, a metal, an alloy, a metal oxide, a conductive compound, or the like having a low work function. Specifically, the cathode 107 is formed of a metal such as aluminum (Al) and a transparent material such as indium tin oxide (ITO) or indium zinc oxide (IZO). The film thickness of the cathode 107 can be appropriately selected depending on the material, but is, for example, 100 nm to 500 nm.

  In the structure of the organic EL element 100 shown in FIG. 1, the material for forming each layer excluding the acceptor layer of the charge generation layer 105 is not particularly limited, and is a known organic EL element material. It is also possible to use.

  Here, each layer of the organic EL element 100 according to the embodiment of the present invention described above can be formed by selecting an appropriate film forming method according to the material such as vacuum deposition, sputtering, or various coating methods. .

  For example, electrode layers such as the anode 103 and the cathode 107 may be formed by using an electron beam evaporation method, a hot filament evaporation method, a vacuum deposition method, a sputtering method, or a plating method. ) Method (electroplating method and electroless plating method) or the like.

  The first hole injection layer 111, the first hole transport layer 113, the first light emitting layer 115, the first electron transport layer 117, the first electron injection layer 119, the charge generation layer 105, and the second hole injection layer 121. Each of the second hole transport layer 123, the second light emitting layer 125, the second electron transport layer 127, the second electron injection layer 129, and the like may be formed by, for example, a physical vapor deposition method (PVD method) such as a vacuum deposition method. ), A printing method such as a screen printing method and an ink jet printing method, a laser transfer method, and a coating method such as a spin coat method.

  The example of the configuration of the organic EL element 100 according to this embodiment has been described above.

  Hereinafter, the charge generation material according to an embodiment of the present invention and the organic EL element including the charge generation material will be specifically described with reference to examples and comparative examples. In addition, the Example shown below is an example to the last, Comprising: The charge generation material and organic electroluminescent element which concern on one Embodiment of this invention are not limited to the following example.

[Synthesis of tetracoordinate boron compounds]
First, a method for synthesizing a tetracoordinate boron compound included in the charge generation material according to the present embodiment will be specifically described by exemplifying methods for synthesizing the above compounds 1 to 3, 7 and 14. Note that the synthesis method described below is merely an example, and the synthesis method of the tetracoordinate boron compound included in the charge generation material according to the present embodiment is not limited to the following example.

(Synthesis of Compound 3)
Compound 3 which is a tetracoordinate boron compound according to this embodiment was synthesized according to the following reaction formula 1.

  To a pentane solution (300 ml) of tris (pentafluorophenyl) borane (5 g, 9.8 mmol) set to 0 ° C. (300 ml), benzothiazole (0.3 ml, 2.8 mmol). ) Was added dropwise. After the addition, the mixture was stirred at 0 ° C. for 1 hour and further stirred at room temperature for 24 hours. After the reaction, the product was filtered off, washed with pentane, and then vacuum dried to obtain Compound A (1.9 g, yield 95%).

When NMR (Nuclear Magnetic Resonance) measurement was performed on the synthesized compound A, the chemical shift value of Compound A measured by ¹ H-NMR (400 MHz, CDCl ₃ ) measurement was δ 9.44. (D, 1H), δ 8.03 (m, 2H), and δ 7.63 (m, 2H). Moreover, the chemical shift value of the compound A measured by ¹⁹ F-NMR measurement is δ-133.9 (t, 6F), δ-155.4 (t, 3F), δ-163.4 (m, 6F). )Met. Furthermore, when the HRMS (High-Resolution Mass Spectrometry) measurement was performed with respect to the compound A synthesized, the molecular weight of the compound A measured was 646.999. Therefore, Compound A was identified as C ₂₅ H ₅ BF ₁₅ NS (molecular weight 646.9983).

  In addition, benzene / tetrahydrofuran (200 ml at a volume ratio of 10/1) was added to compound A (1.2 g, 1.8 mmol), and the mixture was cooled to -10 ° C. After cooling, methyllithium (2 ml, 2.3 mmol) was added dropwise to the mixture, and the mixture was further stirred overnight at room temperature. After completion of the reaction, the solvent was volatilized and concentrated, and production was performed with an alumina column to obtain Compound 3 (750 mg, 66% yield).

When NMR measurement was performed on the synthesized compound 3, the chemical shift value of the compound A measured by ¹ H-NMR (400 MHz, CDCl ₃ ) measurement was δ8.06 (m, 1H), δ7.89. (M, 1H), δ 6.39 (m, 2H). Further, the chemical shift values of Compound 3 measured by ¹⁹ F-NMR measurement are δ-130.8 (m, 1F), δ-131.8 (m, 4F), δ-137.5 (m, 1F). ), Δ-144.4 (m, 1F), δ-154.9 (m, 1F), δ-155.7 (m, 2F), and δ-162.5 (m, 4F). Met. Furthermore, when the HRMS measurement was performed with respect to the compound 3 synthesized, the molecular weight of the compound 3 measured was 626.9933. Therefore, compound 3 _was identified as a _{C 25 H4BF 14 NS (626.9937)} .

  Note that AVANCE III 300 manufactured by BRUKER was used for the NMR measurement, and JMS-700 manufactured by JEOL was used for the HRMS measurement.

(Synthesis of Compound 1)
Compound 1 was synthesized in the same manner as in the synthesis of Compound 3, except that benzothiazole was changed to thiazole.

(Synthesis of Compound 2)
Compound 2 was synthesized in the same manner as in the synthesis of Compound 3 except that benzothiazole was changed to 4-trifluoromethylthiazole (4- (Trifluoromethyl) thiazole).

(Synthesis of Compound 7)
Compound 2 was synthesized in the same manner except that benzothiazole was changed to 6-trifluoromethylbenzothiazole (6- (Trifluoromethyl) benzothiazole) in the synthesis of Compound 3.

(Synthesis of Compound 14)
Compound 14 was synthesized in the same manner except that benzothiazole was changed to 1-phenylimidazole in the synthesis of Compound 3.

  Compounds 1 to 3, 7 and 14 synthesized above were subjected to NMR measurement and HRMS measurement, respectively, and their structures were identified. Similarly, AVANCE III 300 manufactured by BRUKER was used for NMR measurement, and JMS-700 manufactured by JEOL was used for HRMS measurement. The yields, molecular weights (calculated values), and molecular weights (HRMS measured values) of the compounds 1 to 3, 7 and 14 synthesized above are summarized in Table 1.

  Referring to the results shown in Table 1, the synthesized compounds 1 to 3, 7 and 14 have the calculated molecular weight and the molecular weight of the HRMS measurement result consistent with high accuracy. It can be seen that 7 and 14 could be synthesized.

[Production of organic EL element]
Next, the organic EL element which concerns on one Embodiment of this invention was produced in the following procedures using vacuum deposition. The structure and manufacturing method of the organic EL element described below are merely examples, and the structure and manufacturing method of the organic EL element according to this embodiment are not limited to the following examples.

Example 1
First, an ITO-glass substrate that had been patterned and cleaned in advance was subjected to a surface treatment using ozone. The film thickness of the ITO film on the glass substrate was 130 nm. Immediately after the ozone treatment, N, N′-Di (1-naphthyl) -N, N′-diphenylbenzidine (NPD) was formed as a hole transport material with a film thickness of 70 nm on the ITO film.

Next, Tris (8-hydroxyquinolinato) aluminum (Alq ₃ ) was formed to a thickness of 50 nm as a light-emitting material, and lithium fluoride (LiF) was formed to a thickness of 0.5 nm as an electron injection material. Subsequently, after depositing aluminum (Al) with a thickness of 100 nm, the compound 1 was deposited with a thickness of 10 nm as a charge generation material (CGM) to form a charge generation layer.

Next, NPD was formed to a thickness of 70 nm on the charge generation layer as a hole transport material. Next, Alq ₃ was formed to a thickness of 50 nm as a light emitting material, and lithium fluoride was formed to a thickness of 0.5 nm as an electron injection material. Then, aluminum was formed into a film with a film thickness of 100 nm as a cathode, and the organic EL element 200 was produced.

(Example 2)
An organic EL device was produced in the same manner as in Example 1 except that Compound 2 was used instead of Compound 1 used in Example 1.

(Example 3)
An organic EL device was produced in the same manner as in Example 1 except that Compound 3 was used instead of Compound 1 used in Example 1.

Example 4
An organic EL device was produced in the same manner as in Example 1 except that Compound 7 was used instead of Compound 1 used in Example 1.

(Example 5)
An organic EL device was produced in the same manner as in Example 1 except that Compound 14 was used instead of Compound 1 used in Example 1.

(Comparative example)
An organic EL device was produced in the same manner as in Example 1 except that HAT (CN) ₆ having the following structure was used instead of Compound 1 used in Example 1. HAT (CN) ₆ is a general charge generating material.

  The schematic diagram of Examples 1-5 of the produced organic EL element 200 and a comparative example is shown in FIG. The produced organic EL element 200 is, for example, disposed on the substrate 201, the anode 203 disposed on the substrate 201, the first hole transport layer 205 disposed on the anode 203, and the first hole transport layer 205. The first light emitting layer 207, the first electron injection layer 209 disposed on the first light emitting layer 207, the charge generation layers 211 and 213 disposed on the first electron injection layer 209, and the charge generation layers 211 and 213 Second hole transport layer 215, second light emitting layer 217 disposed on second hole transport layer 215, second electron injection layer 219 disposed on second light emitting layer 217, and second electron injection layer 219 comprises a cathode 221 disposed on 219.

[Evaluation results]
The evaluation results of the produced organic EL elements 200 of Examples 1 to 5 and Comparative Examples 1 to 4 are shown in Table 2 below. Note that a C9920-11 luminance alignment characteristic measuring device manufactured by Hamamatsu Photonics was used for evaluating the light emission characteristics of the produced organic EL element 200. In Table 1 below, the driving voltage and the light emission efficiency were measured at a current density of 10 mA / cm ² .

Referring to the results shown in Table 2, Examples 1 to 5 using the charge generation materials (compounds 1 to 3, 7 and 14) according to the present embodiment are obtained by using a general charge generation material (HAT-CN ₆ ). It can be seen that the light emission efficiency is improved and the drive voltage is reduced compared to the comparative example used.

  Further, Example 2 using Compound 2 having an electron withdrawing group (trifluoromethyl group) as a charge generation material differs from Compound 2 only in that it does not have an electron withdrawing group (trifluoromethyl group). It can be seen that the light emission efficiency is improved and the drive voltage is reduced as compared with Example 1 using Compound 1. Similarly, Example 4 using the compound 7 having an electron withdrawing group (trifluoromethyl group) as a charge generation material is that the compound 7 has no electron withdrawing group (trifluoromethyl group). It can be seen that the light emission efficiency is improved and the drive voltage is reduced as compared with Example 3 using a different compound 3. Therefore, the tetracoordinate boron compound according to the present embodiment has an electron accepting group as a substituent, so that acceptability is enhanced, and the charge generation ability of the charge generation material is improved. It can be seen that the driving voltage can be reduced by improving the driving voltage.

  In the above-described example, the organic EL element using the charge generation material according to an embodiment of the present invention has been described. However, the present invention is not limited to the above-described example. For example, the charge generation material according to an embodiment of the present invention can be used for other light-emitting elements or light-emitting devices. The organic EL elements shown in FIGS. 1 and 2 can be used for a passive-matrix driving type organic EL display, but an active-matrix driving type. It can also be used for organic EL displays.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 100 Organic EL element 101 Substrate 103 Anode 105 Charge generation layer 107 Cathode 110 1st light emission unit 111 1st hole injection layer 113 1st hole transport layer 115 1st light emission layer 117 1st electron transport layer 119 1st electron injection layer 120 2nd light emitting unit 121 2nd hole injection layer 123 2nd hole transport layer 125 2nd light emitting layer 127 2nd electron transport layer 129 2nd electron injection layer

Claims (12)

A charge generating material comprising a tetracoordinate boron compound represented by the following general formula (1).

In the general formula (1),
Ar ₁ is a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group. The charge generation material according to claim 1, wherein Ar ₁ has at least one deuterium or electron withdrawing group as a substituent. The charge generation material according to claim 2, wherein Ar ₁ has at least one electron withdrawing group having a Hammett's substituent constant σ larger than 0.07 as a substituent. A charge generation material comprising a tetracoordinate boron compound represented by the following general formula (2).

In the above general formula (2),
Ar ₁ and Ar ₂ are each independently a substituted or unsubstituted aryl group or a substituted or unsubstituted heteroaryl group. 5. The charge generating material according to claim 4, wherein at least one of Ar ₁ and Ar ₂ has at least one deuterium or electron withdrawing group as a substituent. 6. The charge generation material according to claim 5, wherein at least one of Ar ₁ and Ar ₂ has at least one electron withdrawing group having a Hammett's substituent constant σ greater than 0.07 as a substituent. A charge generating material comprising a tetracoordinate boron compound represented by the following general formula (3).

In the general formula (3),
X is N—R ₃ or S;
R _{1 to} R ₃ are each independently a substituted or unsubstituted aryl group or a substituted or unsubstituted heteroaryl group. The charge generating material according to claim 7, wherein at least one of R _{1 to} R ₃ has at least one deuterium or electron withdrawing group as a substituent. 9. The charge generation material according to claim 8, wherein at least one of R _{1 to} R ₃ has at least one electron withdrawing group having a Hammett's substituent constant σ larger than 0.07 as a substituent.   The electron withdrawing group is, independently of each other, any functional group selected from the group consisting of a halogen atom, a methyl group substituted with at least one halogen atom, a cyano group, and a sulfonic acid group. The charge generation material according to any one of claims 3, 6 and 9.   The charge generation material according to any one of claims 1 to 10, wherein a LUMO level of the tetracoordinate boron compound is -6.0 eV or more and -3.4 eV or less. The organic electroluminescent element which contains the charge generation material as described in any one of Claims 1-11 in a charge generation layer.

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