Photoelectric conversion element material for imaging and photoelectric conversion element

Abstract

Provided are: a material that provides high sensitivity and high resolution to a photoelectric conversion element for imaging; and a photoelectric conversion element for imaging, using said material. This material of a photoelectric conversion element for imaging is formed of an indolocarbazole compound having a fused ring structure of five rings having two heteroatoms, or an analog of said compound, and has, as a group substituting for a nitrogen atom or a heteroatom, an alkyl group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted π-electron excessive hetero-aromatic group, a linked aromatic group formed by linking 2-6 aromatic groups, or the like.

Description

[Technical Field]

[0001] The present invention relates to a material for a photoelectric conversion element for imaging and a photoelectric conversion element for imaging using the same.

[0002] In recent years, the development of organic electronics devices using thin films formed from organic semiconductors (also called organic charge transport materials) has progressed. Examples include electroluminescent devices, solar cells, transistor devices, and photoelectric conversion devices. In particular, the development of organic electroluminescent devices, which are electroluminescent devices made from organic materials, has progressed the most. As their application to smartphones, TVs, and other devices progresses, development aimed at further improving their functionality is also ongoing.

[0003] In the field of photoelectric conversion elements, progress has been made in the development and practical application of elements using PN junctions of inorganic semiconductors such as silicon. Studies are being conducted to improve the functionality of digital cameras and smartphone cameras, as well as for applications such as surveillance cameras and automotive sensors. However, challenges to meeting these diverse applications include increasing sensitivity and miniaturizing pixels (increasing resolution). Photoelectric conversion elements using inorganic semiconductors typically employ a method of placing color filters corresponding to the three primary colors of light, RGB, on the light-receiving section of the photoelectric conversion element to obtain color images. This method, which requires the RGB color filters to be placed on a flat surface, poses challenges in terms of the efficiency of incident light utilization and resolution (Non-Patent Documents 1 and 2).

[0004] As one solution to these issues with photoelectric conversion elements, development is underway on photoelectric conversion elements that use organic semiconductors instead of inorganic semiconductors (Non-Patent Documents 1 and 2). This takes advantage of the property of organic semiconductors, which allows them to selectively absorb only light in a specific wavelength range with high sensitivity, and it has been proposed to solve the problem of high sensitivity and high resolution by stacking photoelectric conversion elements made of organic semiconductors corresponding to the three primary colors of light. In addition, an element has been proposed in which a photoelectric conversion element made of an organic semiconductor and a photoelectric conversion element made of an inorganic semiconductor are stacked (Non-Patent Document 3).

[0005] Here, an organic semiconductor photoelectric conversion element is an element constructed by disposing a photoelectric conversion layer made of a thin film of an organic semiconductor between two electrodes, with a hole-blocking layer and / or an electron-blocking layer disposed between the photoelectric conversion layer and the two electrodes as needed. In this element, excitons are generated by absorbing light of a desired wavelength in the photoelectric conversion layer, and then holes and electrons are generated by charge separation of the excitons. The holes and electrons then migrate to the respective electrodes, converting light into an electrical signal. To accelerate this process, a bias voltage is typically applied between the two electrodes, but reducing the leakage current from the two electrodes caused by the application of the bias voltage presents a challenge. For these reasons, controlling the movement of holes and electrons within the photoelectric conversion element is key to achieving the desired characteristics of the photoelectric conversion element.

[0006] The organic semiconductors used in each layer of a photoelectric conversion element can be roughly divided into P-type organic semiconductors and N-type organic semiconductors, with P-type organic semiconductors being used as hole transport materials and N-type organic semiconductors being used as electron transport materials. In order to control the movement of holes and electrons within the above-mentioned photoelectric conversion element, various organic semiconductors with appropriate physical properties, such as hole mobility, electron mobility, energy value of the highest occupied molecular orbital (HOMO), and energy value of the lowest unoccupied molecular orbital (LUMO), have been developed. However, they do not yet have sufficient properties and have not yet been put to commercial use.

[0007] Patent Document 1 proposes a device that uses quinacridone as a P-type organic semiconductor in the photoelectric conversion layer, subphthalocyanine chloride as an N-type organic semiconductor, and an indolocarbazole derivative in a first buffer layer (considered to be synonymous with an electron blocking layer) disposed between the photoelectric conversion layer and an electrode. The application of the indolocarbazole derivative here is limited to the first buffer layer, and its applicability in the photoelectric conversion layer is unclear.

[0008] Patent Document 2 proposes a device in which a chrysenodithiophene derivative is used as a P-type organic semiconductor in a photoelectric conversion layer, and a fullerene or a subphthalocyanine derivative is used as an N-type organic semiconductor. Patent Document 3 proposes a device in which a benzodifuran derivative is used in an electron blocking layer disposed between a photoelectric conversion layer and an electrode.

[0009] However, there is a demand for photoelectric conversion elements for imaging with even higher sensitivity and resolution. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 2018-85427 [Patent Document 2] Japanese Patent Application Publication No. 2019-54228 [Patent Document 3] Japanese Patent Application Publication No. 2019-57704 [Non-patent literature]

[0011] [Non-Patent Document 1] NHK Giken R&D No.132, March 2012, pp4-11 [Non-patent document 2] NHK Giken R&D No.174, March 2019, pp4-17 [Non-patent document 3] 2019 IEEE International Electron Devices Meeting (IEDM), pp.16.6.1-16.6.4(2019) Summary of the Invention

[0012] Further improvements in sensitivity and resolution are required for imaging photoelectric conversion elements to improve the functionality of digital cameras and smartphone cameras, and to advance their application in surveillance cameras, automotive sensors, etc. In light of this current situation, the present invention aims to provide a material that achieves high sensitivity and high resolution in imaging photoelectric conversion elements, and an imaging photoelectric conversion element using the same.

[0013] As a result of extensive investigations, the present inventors have found that the process of generating holes and electrons due to charge separation of excitons in a photoelectric conversion layer, and the control of the movement of holes and electrons within a photoelectric conversion element, can be efficiently carried out by using an indolocarbazole derivative as a hole-transporting material, and have thus completed the present invention.

[0014] That is, the present invention relates to a material for an imaging photoelectric conversion element having a structure represented by the following general formula (1) or (2). [ka]

[0015] In general formulae (1) and (2), ring A independently represents a heterocycle represented by formula (1a) which is fused to an adjacent ring at any position. X is O, S, or N-Ar 2 Represents. Ar 1 and Ar 2 each independently represents an alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted π-electron rich heteroaromatic group having 4 to 30 carbon atoms, or a substituted or unsubstituted linking aromatic group formed by linking 2 to 6 aromatic groups selected from the aromatic hydrocarbon groups and π-electron rich heteroaromatic groups, provided that Ar 1 and Ar 2 When the linking aromatic group is composed only of aromatic hydrocarbon groups, Ar 1 and Ar 2 and cannot simultaneously be biphenyl groups. L represents a divalent substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted π-electron rich heteroaromatic group having 4 to 30 carbon atoms, or a linked aromatic group formed by linking 2 to 6 aromatic rings of an aromatic group selected from the aromatic hydrocarbon groups and the π-electron rich heteroaromatic groups. The above Ar 1 Or Ar 2It is a preferred embodiment that at least one of the above groups contains at least one substituted or unsubstituted tricyclic fused ring skeleton, and the tricyclic fused ring skeleton is preferably a substituted or unsubstituted carbazole, dibenzofuran, or dibenzothiophene skeleton, and more preferably a substituted or unsubstituted carbazole skeleton.

[0016] The photoelectric conversion element material preferably has a highest occupied molecular orbital (HOMO) energy level of −4.5 eV or less, or a lowest unoccupied molecular orbital (LUMO) energy level of −2.5 eV or more, as obtained by a structural optimization calculation using density functional theory calculation B3LYP / 6-31G(d).

[0017] In addition, the photoelectric conversion element material is 1×10 -6 cm 2 It is preferable that the material has a hole mobility of 1 / Vs or more, or is amorphous.

[0018] The material for a photoelectric conversion element can also be used as a hole transport material for an imaging photoelectric conversion element.

[0019] The present invention also relates to an imaging photoelectric conversion element having a photoelectric conversion layer and an electron blocking layer between two electrodes, wherein at least one of the photoelectric conversion layer and the electron blocking layer contains the above-mentioned material for photoelectric conversion elements.

[0020] The photoelectric conversion element of the present invention may contain an electron transporting material in the photoelectric conversion layer, and may contain the above-mentioned material for photoelectric conversion elements in the electron blocking layer.

[0021] The use of the material for photoelectric conversion devices of the present invention allows for appropriate movement of holes and electrons within a photoelectric conversion device for imaging, thereby reducing leakage current caused by application of a bias voltage when converting light into electrical energy, thereby enabling the production of a photoelectric conversion device that achieves a low dark current value and a high brightness / dark ratio. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic cross-sectional view showing an example of the structure of a photoelectric conversion element for imaging; DETAILED DESCRIPTION OF THE INVENTION

[0023] The photoelectric conversion element of the present invention has at least one organic layer between two electrodes. The organic layer contains a material for photoelectric conversion elements for imaging (also referred to as the material for photoelectric conversion elements or the material of the present invention) represented by the above general formula (1) or (2). If necessary, the element may have multiple organic layers containing the material for photoelectric conversion elements.

[0024] The above general formulas (1) and (2) will be explained below. Symbols common to general formulas (1) and (2) have the same meaning. Ring A represents a heterocycle represented by formula (1a) which is fused to an adjacent ring at any position.

[0025] In formula (1a), X is O, S, or N-Ar. 2 and preferably represents N-Ar 2 X is N-Ar 2 In this case, the five fused rings in general formula (1) represent an indolocarbazole skeleton, and there are five isomers represented by the following formulae (V), (W), (X), (Y), and (Z). Formula (V), (W), or (Y) is preferred. When X is O or S, there are isomers similar to those of the indolocarbazole skeleton. [ka]

[0026] In general formula (2), there are two fused rings of five rings and two rings A, but both X in formula (1a) are N-Ar 2When X is O or S, the five fused rings form an indolocarbazole skeleton, and there are the same isomers as above. The linking form of these indolocarbazole skeletons can be a combination of isomers of the same kind or a combination of isomers of different kinds, but a combination of isomers of the same kind is preferred. Note that when X is O or S, there are isomers similar to the indolocarbazole skeleton, and there are also combinations of isomers of different kinds with different X, but a combination of isomers of the same kind is preferred.

[0027] Examples of combinations of isomers of the same kind include the following formulae (21) to (27): Among these, formulae (21), (23) and (24) are preferred. [ka]

[0028] Examples of combinations of different isomers are shown below, but are not limited to these. [ka]

[0029] The above Ar 1 and Ar 2 are independently an alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted π-electron-rich heteroaromatic group having 4 to 30 carbon atoms, or a substituted or unsubstituted linking aromatic group formed by linking 2 to 6 aromatic rings of an aromatic group selected from the aromatic hydrocarbon groups and the π-electron-rich heteroaromatic groups. Preferably, they are a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted π-electron-rich heteroaromatic group having 4 to 20 carbon atoms, or a substituted or unsubstituted linking aromatic group formed by linking 2 to 4 aromatic rings of an aromatic group selected from the aromatic hydrocarbon groups and the π-electron-rich heteroaromatic groups. More preferred are substituted or unsubstituted aromatic hydrocarbon groups having 6 to 14 carbon atoms, substituted or unsubstituted π-electron-rich heteroaromatic groups having 4 to 14 carbon atoms, and substituted or unsubstituted linking aromatic groups formed by linking 2 to 4 aromatic rings of aromatic groups selected from the aromatic hydrocarbon groups and the π-electron-rich heteroaromatic groups. Also, Ar 1 and Ar 2 It is also preferable that at least one of the above is the π-electron rich heteroaromatic group, and is a substituted or unsubstituted linking aromatic group containing at least one of the above π-electron rich heteroaromatic group. Also, Ar 1 and Ar 2 When the linking aromatic groups are composed only of aromatic hydrocarbon groups, they are preferably different from each other, and Ar 1 and Ar 2 and are not both biphenyl groups. 1 and Ar 2 In the case where the linking aromatic group is composed only of aromatic hydrocarbon groups, it is preferable that

[0030] In general formula (2), L represents a divalent substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted π-electron-rich heteroaromatic group having 4 to 30 carbon atoms, or a linked aromatic group formed by linking 2 to 6 aromatic rings of an aromatic group selected from the aromatic hydrocarbon groups and the π-electron-rich heteroaromatic groups. Preferably, L represents a divalent substituted or unsubstituted aromatic hydrocarbon group having 6 to 14 carbon atoms, a substituted or unsubstituted π-electron-rich heteroaromatic group having 4 to 14 carbon atoms, or a linked aromatic group formed by linking 2 to 3 aromatic rings of an aromatic group selected from the aromatic hydrocarbon groups and the π-electron-rich heteroaromatic groups.

[0031] Ar 1 or Ar 2When is an alkyl group having 1 to 20 carbon atoms, the alkyl group having 1 to 20 carbon atoms may be any of linear, branched, and cyclic alkyl groups, and examples thereof include linear saturated hydrocarbon groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-octyl, n-dodecyl, n-tetradecyl, and n-octadecyl groups, branched saturated hydrocarbon groups such as isopropyl, isobutyl, neopentyl, 2-ethylhexyl, and 2-hexyloctyl groups, and saturated alicyclic hydrocarbon groups such as cyclopentyl, cyclohexyl, cyclooctyl, 4-butylcyclohexyl, and 4-dodecylcyclohexyl groups. Preferred examples include linear, branched, and cyclic alkyl groups having 1 to 10 carbon atoms.

[0032] Ar 1 or Ar 2 However, examples of unsubstituted aromatic hydrocarbon groups having 6 to 30 carbon atoms include monocyclic aromatic hydrocarbon groups such as benzene, bicyclic aromatic hydrocarbon groups such as naphthalene, tricyclic aromatic hydrocarbon groups such as indacene, biphenylene, phenalene, anthracene, phenanthrene, and fluorene, tetracyclic aromatic hydrocarbon groups such as fluoranthene, acephenanthrylene, aceanthrylene, triphenylene, pyrene, chrysene, tetraphene, tetracene, and pleiadene, and pentacyclic aromatic hydrocarbon groups such as picene, perylene, pentaphene, pentacene, tetraphenylene, and naphthaanthracene. Preferred examples include benzene, naphthalene, anthracene, phenanthrene, triphenylene, pyrene, chrysene, tetraphene, and tetracene. When L is an unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, the group is a divalent group.

[0033] Examples of the unsubstituted π-electron-rich heteroaromatic group having 4 to 30 carbon atoms include heteroaromatic groups having a pyrrole ring, a thiophene ring, and a furan ring, and examples thereof include nitrogen-containing aromatic groups having a pyrrole ring such as pyrrole, pyrrolopyrrole, indole, pyrroloindole, benzoindole, naphthopyrrole, isoindole, pyrroloisoindole, benzoisoindole, naphthisopyrrole, carbazole, benzocarbazole, indoloindole, carbazolocarbazole, and carboline, thiophene, and benzothiophene. Examples of the aromatic hydrocarbon group include sulfur-containing aromatic groups having a thiophene ring such as naphthothiophene, dibenzothiophene, benzothienonaphthalene, benzothienobenzothiophene, benzothienodibenzothiophene, dinaphthothiophene, dinaphthothienothiophene, and naphthobenzothiophene; and oxygen-containing aromatic groups having a furan ring such as furan, benzofuran, naphthofuran, dibenzofuran, benzofuronaphthalene, benzofurobenzofuran, benzofurodibenzofuran, dinaphthofuran, dinaphthofuranofuran, and naphthobenzofuran.

[0034] Preferred examples of the nitrogen-containing aromatic group having a pyrrole ring include carbazole, benzocarbazole, indoloindole, and carbazolocarbazole. Preferred examples of the sulfur-containing aromatic group having a thiophene ring include thiophene, dibenzothiophene, benzothienonaphthalene, benzothienobenzothiophene, benzothienodibenzothiophene, dinaphthothiophene, dinaphthothienothiophene, and naphthobenzothiophene. Preferred examples of the oxygen-containing aromatic group having a furan ring include dibenzofuran, benzofuronaphthalene, benzofurobenzofuran, benzofurodibenzofuran, dinaphthofuranofuran, and naphthobenzofuran.

[0035] Also, Ar 1 Or Ar 2It is also preferable that at least one of the above three-ring fused skeletons contains at least one substituted or unsubstituted tricyclic fused skeleton. Examples of the above three-ring fused skeleton include azafluorene, azaphenanthrene, azaanthracene, carbazole, dibenzofuran, and dibenzothiophene. Preferably, the tricyclic fused skeleton contains at least one carbazole, dibenzofuran, or dibenzothiophene skeleton, and more preferably, at least one carbazole skeleton. These skeletons may or may not have a substituent. The term "containing at least one substituted or unsubstituted tricyclic fused skeleton" means that the tricyclic fused skeleton contains at least one substituted or unsubstituted tricyclic fused skeleton, such as Ar 1 Or Ar 2 represents a substituted or unsubstituted π-electron-rich heteroaromatic group having 4 to 30 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 6 aromatic rings of an aromatic group selected from a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms and the π-electron-rich heteroaromatic group, and means that the group contains at least one of these skeletons.

[0036] Furthermore, it may be a π-electron-rich heteroaromatic group in which two or more rings selected from the above-mentioned nitrogen-containing aromatic group, sulfur-containing aromatic group, oxygen-containing aromatic group, etc. are condensed, for example, a group in which an aromatic having a pyrrole ring such as benzofurocarbazole or benzofurobenzocarbazole is condensed with an aromatic having a furan ring, a group in which an aromatic having a pyrrole ring such as benzothienocarbazole or benzothienobenzocarbazole is condensed with an aromatic having a thiophene ring, or a group in which an aromatic having a furan ring such as benzofurodibenzothiophene or benzofurobenzocarbazole is condensed with an aromatic having a thiophene ring. When L is an unsubstituted π-electron-rich heteroaromatic group, it is a divalent group.

[0037] Ar 1 , Ar 2 Alternatively, L may be a linking aromatic group formed by linking 2 to 6 of the above aromatic hydrocarbon groups or π-electron rich heteroaromatic groups. In this specification, a linking aromatic group refers to an aromatic group (meaning an aromatic hydrocarbon group or a π-electron-rich heteroaromatic group) in which carbon atoms in the aromatic rings are linked together by a single bond. The linking structure may be linear or branched. The aromatic group may be a hydrocarbon-based aromatic group or a π-electron-rich aromatic group, and multiple aromatic groups may be the same or different. An aromatic group that corresponds to a linking aromatic group is different from a substituted aromatic group.

[0038] Examples of the substituent that the aromatic hydrocarbon group, the π-electron-rich heteroaromatic group, and the linking aromatic group may have include an alkyl group having 1 to 20 carbon atoms. The alkyl group having 1 to 20 carbon atoms may be any of a linear, branched, or cyclic alkyl group, and is preferably a linear, branched, or cyclic alkyl group having 1 to 10 carbon atoms. Specific examples of the substituent include linear saturated hydrocarbon groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-octyl, n-dodecyl, n-tetradecyl, and n-octadecyl groups; branched saturated hydrocarbon groups such as isopropyl, isobutyl, neopentyl, 2-ethylhexyl, and 2-hexyloctyl groups; and saturated alicyclic hydrocarbon groups such as cyclopentyl, cyclohexyl, cyclooctyl, 4-butylcyclohexyl, and 4-dodecylcyclohexyl groups.

[0039] Preferred specific examples of the material for a photoelectric conversion element represented by general formula (1) of the present invention are shown below, but the material is not limited to these. [ka] [ka] [ka]

[0040] [ka] [ka] [ka]

[0041] [ka] [ka] [ka]

[0042] [ka] [ka] [ka]

[0043] [ka] [ka] [ka]

[0044] Preferred specific examples of the material for a photoelectric conversion element of the present invention represented by general formula (2) are shown below, but the material is not limited to these.

[0045] [ka] [ka] [ka]

[0046] [ka] [ka] [ka] [ka]

[0047] The photoelectric conversion element materials represented by the above general formulas (1) and (2) can be obtained by synthesizing them using commercially available reagents as raw materials through various organic synthesis reactions established in the field of organic synthetic chemistry, including coupling reactions such as Suzuki coupling, Stille coupling, Grignard coupling, Ullmann coupling, Buchwald-Hartwig reaction, and Heck reaction, followed by purification using known methods such as recrystallization, column chromatography, and sublimation purification, but the methods are not limited to these.

[0048] The material for photoelectric conversion devices of the present invention preferably has a HOMO energy level of −4.5 eV or less, more preferably in the range of −4.5 eV to −6.0 eV, as determined by structural optimization calculations using density functional theory calculation B3LYP / 6-31G(D).

[0049] The material for an imaging photoelectric conversion element of the present invention preferably has a LUMO energy level obtained by the structural optimization calculation of -2.5 eV or higher, more preferably in the range of -2.5 eV to -0.5 eV, and the difference (absolute value) between the HOMO energy level and the LUMO energy level is preferably in the range of 2.0 to 5.0 eV, more preferably in the range of 2.5 to 4.0 eV.

[0050] The material for a photoelectric conversion element of the present invention has a viscosity of 1×10 -6 cm 2 / Vs~1cm 2 / Vs, and preferably has a hole mobility of 1×10 -5 cm 2 / Vs~1cm 2 It is more preferable that the hole mobility is / Vs. The hole mobility can be evaluated by known methods such as a method using a FET transistor element, a time-of-flight method, or an SCLC method.

[0051] The material for a photoelectric conversion element of the present invention is preferably amorphous. The amorphous nature of the material can be confirmed by various methods, for example, by the absence of a peak detected by XRD or the absence of an endothermic peak detected by DSC.

[0052] Next, a photoelectric conversion element for imaging using the material for a photoelectric conversion element of the present invention will be described with reference to the drawings, but the structure of the photoelectric conversion element of the present invention is not limited to this.

[0053] 1 is a cross-sectional view schematically illustrating an example of the structure of an imaging photoelectric conversion element of the present invention, in which 1 represents a substrate, 2 represents an electrode, 3 represents an electron blocking layer, 4 represents a photoelectric conversion layer, 5 represents a hole blocking layer, and 6 represents an electrode. The structure is not limited to that shown in FIG. 1, and layers can be added or omitted as necessary.

[0054] The material for a photoelectric conversion device of the present invention can be used as an electron transporting material, in which case the material can be used in a photoelectric conversion layer or a hole blocking layer.

[0055] Each member and each layer of the photoelectric conversion element of the present invention will be described below. -substrate- A photoelectric conversion element using the material for a photoelectric conversion element of the present invention is preferably supported on a substrate. The substrate is not particularly limited, and may be made of, for example, glass, transparent plastic, quartz, or the like.

[0056] -electrode- The electrodes used in photoelectric conversion elements for imaging have the function of collecting holes and electrons generated in the photoelectric conversion layer. They also need the function of allowing light to enter the photoelectric conversion layer. Therefore, it is desirable that at least one of the two electrodes is transparent or translucent. The material used for the electrodes is not particularly limited as long as it is conductive. Examples include conductive transparent materials such as ITO, IZO, SnO2, ATO (antimony-doped tin oxide), ZnO, AZO (Al-doped zinc oxide), GZO (gallium-doped zinc oxide), TiO2, and FTO; metals such as gold, silver, platinum, chromium, aluminum, iron, cobalt, nickel, and tungsten; inorganic conductive materials such as copper iodide and copper sulfide; and conductive polymers such as polythiophene, polypyrrole, and polyaniline. These materials may be used in combination as needed, or two or more layers may be stacked.

[0057] -Photoelectric conversion layer- The photoelectric conversion layer is a layer in which holes and electrons are generated by charge separation of excitons generated by incident light. It may be formed of a single photoelectric conversion material, or may be formed in combination with a P-type organic semiconductor material, which is a hole-transporting material, or an N-type organic semiconductor material, which is an electron-transporting material. Two or more types of P-type organic semiconductors may be used, or two or more types of N-type organic semiconductors may be used. It is desirable that one or more of these P-type organic semiconductors and / or N-type semiconductors be a dye material capable of absorbing light of a desired wavelength in the visible region. The P-type organic semiconductor material, which is a hole-transporting material, can be a photoelectric conversion element material represented by the above formula (1) or (2).

[0058] The P-type organic semiconductor material may be any material having hole transport properties. It is preferable to use the material of the present invention represented by the above general formula (1) or general formula (2), but other P-type organic semiconductor materials may also be used. Furthermore, two or more materials represented by the above general formula (1) or general formula (2) may be mixed and used. Furthermore, the material of the present invention may be mixed with other P-type organic semiconductor materials. Other p-type organic semiconductor materials may be any material having hole transport properties, and examples thereof include compounds having a condensed polycyclic aromatic group such as naphthalene, anthracene, phenanthrene, pyrene, chrysene, naphthacene, triphenylene, perylene, fluoranthene, fluorene, and indene; compounds having a π-electron-rich aromatic group such as cyclopentadiene derivatives, furan derivatives, thiophene derivatives, pyrrole derivatives, benzofuran derivatives, benzothiophene derivatives, dinaphthothienothiophene derivatives, indole derivatives, pyrazoline derivatives, dibenzofuran derivatives, dibenzothiophene derivatives, carbazole derivatives, and indolocarbazole derivatives; aromatic amine derivatives, styrylamine derivatives, benzidine derivatives, porphyrin derivatives, phthalocyanine derivatives, and quinacridone derivatives. Examples of polymeric P-type organic semiconductor materials include polyphenylene vinylene derivatives, polyparaphenylene derivatives, polyfluorene derivatives, polyvinylcarbazole derivatives, and polythiophene derivatives. Polymeric P-type organic semiconductor materials may be mixed with the material of the present invention or a non-polymeric P-type organic semiconductor material, or two or more polymeric P-type organic semiconductor materials may be mixed together.

[0059] The N-type organic semiconductor material may be any material having electron transport properties, such as naphthalene tetracarboxylic acid diimide, perylene tetracarboxylic acid diimide, fullerenes, and azole derivatives such as imidazole, thiazole, thiadiazole, oxazole, oxadiazole, and triazole. Two or more N-type organic semiconductor materials may be mixed and used.

[0060] -Electron Blocking Layer- The electron blocking layer is provided to suppress dark current generated by electron injection from one electrode into the photoelectric conversion layer when a bias voltage is applied between the two electrodes. It also functions as a hole transporter, transporting holes generated by charge separation in the photoelectric conversion layer to the electrode. A single layer or multiple layers can be arranged as needed. The electron blocking layer can be made of a P-type organic semiconductor material, which is a hole transport material. Any material having hole transport properties can be used as the P-type organic semiconductor material. While the material of the present invention is preferably used as the P-type organic semiconductor material, other P-type organic semiconductor materials may also be used. Furthermore, a mixture of the material represented by the above general formula (1) and the material represented by general formula (2) may also be used. Furthermore, a mixture of the material of the present invention and other P-type organic semiconductor materials may also be used. Other p-type organic semiconductor materials may be any material having hole transport properties, and examples thereof include compounds having a condensed polycyclic aromatic group such as naphthalene, anthracene, phenanthrene, pyrene, chrysene, naphthacene, triphenylene, perylene, fluoranthene, fluorene, and indene; compounds having a π-electron-rich aromatic group such as cyclopentadiene derivatives, furan derivatives, thiophene derivatives, pyrrole derivatives, benzofuran derivatives, benzothiophene derivatives, dinaphthothienothiophene derivatives, indole derivatives, pyrazoline derivatives, dibenzofuran derivatives, dibenzothiophene derivatives, and carbazole derivatives; aromatic amine derivatives, styrylamine derivatives, benzidine derivatives, porphyrin derivatives, phthalocyanine derivatives, and quinacridone derivatives.

[0061] -Hole blocking layer- The hole-blocking layer is provided to suppress dark current generated by holes injected from one electrode into the photoelectric conversion layer when a bias voltage is applied between the two electrodes. It also functions as an electron transport layer, transporting electrons generated by charge separation in the photoelectric conversion layer to the electrode. A single layer or multiple layers can be arranged as needed. The hole-blocking layer can be made of an N-type organic semiconductor with electron transport properties. The N-type organic semiconductor material may be any material having electron transport properties, and examples thereof include polycyclic aromatic polycarboxylic anhydrides and imidized products thereof, such as naphthalene tetracarboxylic diimide and perylene tetracarboxylic diimide, fullerenes such as C60 and C70, azole derivatives such as imidazole, thiazole, thiadiazole, oxazole, oxadiazole, and triazole, tris(8-quinolinolato)aluminum(III) derivatives, phosphine oxide derivatives, nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, carbodiimides, fluorenylidenemethane derivatives, anthraquinodimethane and anthrone derivatives, bipyridine derivatives, quinoline derivatives, and indolocarbazole derivatives. Two or more N-type organic semiconductor materials may also be used in combination.

[0062] When producing the imaging photoelectric conversion element of the present invention, the method for forming each layer is not particularly limited, and they may be produced by either a dry process or a wet process. [Example]

[0063] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0064] Calculation example (HOMO and LUMO values) The HOMO and LUMO were calculated for the compound V1 and the compounds shown in Table 1. The calculations were performed using density functional theory (DFT) calculations, Gaussian calculation program, and B3LYP / 6-31G(d). The results are shown in Table 1. It can be said that all of the materials for photoelectric conversion elements of the present invention have preferable HOMO and LUMO values.

[0065] [Table 1]

[0066] Synthesis Example 1 [ka] At room temperature under a nitrogen atmosphere, starting material R1 (27.3 mmol), 1,3-diiodobenzene (13.6 mmol), tripotassium phosphate (110.7 mmol), and 1,2-cyclohexanediamine (9.6 mmol) were added to dioxane (100 ml) and stirred at 100°C for 3 hours. After cooling to room temperature, insoluble matter was filtered off, and the filtrate was concentrated. The concentrated residue was added to distilled water (100 ml) and stirred at room temperature. After 3 hours, the precipitate was collected by filtration and dried to obtain intermediate M1. The yield was 87%.

[0067] At room temperature under a nitrogen atmosphere, intermediate M1 (11.9 mmol), potassium carbonate (66.6 mmol), and CuI (38.1 mmol) were added to iodobenzene (50 ml) and stirred for 8 hours while heating to reflux. After cooling to room temperature, insoluble matter was filtered off, and the filtrate was added to methanol (100 ml) and stirred at room temperature. After 3 hours, the precipitate was collected by filtration. The resulting crude product was washed with meta-xylene to obtain the target compound DV1 as a yellow solid. The yield was 69%. The resulting powder was evaluated by XRD, but no peaks were detected, indicating that this compound was amorphous.

[0068] Synthesis Example 2 [ka] At room temperature under a nitrogen atmosphere, starting material R1 (15.6 mmol), 3-iodo-9-phenylcarbazole (15.6 mmol), CuI (1.6 mmol), tripotassium phosphate (62.4 mmol), and 1,2-cyclohexanediamine (14.8 mmol) were added to dioxane (100 ml) and stirred at 100°C for 5 hours. After cooling to room temperature, insoluble matter was filtered off, and the filtrate was concentrated. The concentrated residue was subjected to silica gel column chromatography (methylene chloride; hexane) to obtain intermediate M2. The yield was 42%.

[0069] Intermediate M2 (6.5 mmol), copper powder (16.1 mmol), and potassium carbonate (35.5 mmol) were added to iodobenzene (50 mL) at room temperature under a nitrogen atmosphere and stirred for 22 hours while heating to reflux. After cooling to room temperature, the mixture was concentrated under reduced pressure. The resulting residue was subjected to silica gel column chromatography (methylene chloride; hexane) to obtain the target compound V7 as a white solid. The yield was 81%. The resulting powder was characterized by XRD and found to be amorphous.

[0070] Synthesis Example 3 The same procedure as in Synthesis Example 2 was carried out, except that 2-iodo-9-phenylcarbazole was used instead of 3-iodo-9-phenylcarbazole, to obtain the target compound V5 as a white solid. The yield was 35%. The obtained powder was evaluated by XRD and found to be amorphous.

[0071] Synthesis Example 4 [ka] Sodium hydride (150 mmol) was added to a DMF solution (500 ml) of 3,2b-indolocarbazole (50 mmol) under a nitrogen atmosphere at room temperature, and the mixture was stirred at room temperature. After 30 minutes, 1-iodooctane (133 mmol) was added dropwise over 30 minutes at the same temperature. After stirring for 2 hours, the reaction solution was added dropwise to distilled water (1000 ml). The precipitate to be purified was collected by filtration and dried to obtain a crude product. The crude product was purified by recrystallization (isopropyl alcohol:hexane) to obtain the target compound Y2 as a yellow solid. The yield was 66%. The yellow solid was evaluated by XRD and found to be amorphous.

[0072] Synthesis Example 5 [ka] A 1,2-dichlorobenzene solution (50 mL) of 3,2b-indolocarbazole (12.1 mmol), 48.4 mmol of copper powder, anhydrous potassium carbonate (96.8 mmol), 18-crown-6 (2.42 mmol), and 4-iodooctylbenzene (36.3 mmol) was stirred at 200°C under a nitrogen atmosphere at room temperature. After 24 hours, tetrahydrofuran (150 mL) was added at room temperature, followed by filtration. The resulting mother liquor was concentrated. Methanol (300 mL) was added to the concentrated residue, and the resulting precipitate was collected by filtration and dried to obtain a crude product. The crude product was purified by recrystallization (isopropyl alcohol:hexane) to obtain the target compound Y3 as a yellow solid. The yield was 63%. XRD analysis of the resulting powder revealed that it was amorphous.

[0073] A sample was prepared in which a layer of compound DV1 with a thickness of approximately 3 μm was formed between a transparent electrode made of ITO and an aluminum electrode, and the hole mobility was measured using a time-of-flight apparatus. The hole mobility was 2 × 10 -4 cm 2 / Vs.

[0074] In the same manner as above, the hole mobility was evaluated for the compounds shown in Table 2. The results are shown in Table 2.

[0075] [Table 2]

[0076] Example 1 A glass substrate with an ITO electrode of 70 nm thickness was formed on it, and a vacuum of 4.0 × 10 -5 Compound DV1 was deposited as an electron blocking layer to a thickness of 100 nm at 2000 Pa. Next, a quinacridone thin film was deposited as a photoelectric conversion layer to a thickness of 100 nm. Finally, aluminum was deposited as an electrode to a thickness of 70 nm to prepare a photoelectric conversion element. When a voltage of 2 V is applied to ITO and aluminum electrodes, the current in the dark is 7.8 × 10 -12 A / cm 2 When a voltage of 2 V was applied and the ITO electrode was irradiated from a height of 10 cm with an LED adjusted to 1.6 μW and a wavelength of 500 nm, the current was 3.1 × 10 -6 A / cm 2 When a voltage of 2 V was applied to the transparent conductive glass side, the brightness ratio was 3.9 × 10 5 It was.

[0077] Comparative Example 1 A glass substrate with an ITO electrode of 70 nm thickness was formed on it, and a vacuum of 4.0 × 10 -5 A quinacridone film was formed at 100 Pa as a photoelectric conversion layer. Finally, an aluminum film was formed at 70 nm as an electrode, creating a photoelectric conversion element. When a voltage of 2 V was applied to the ITO and aluminum electrodes, the current in the dark was 6.3 × 10 -8 A / cm 2 When a voltage of 2 V was applied and the ITO electrode was irradiated from a height of 10 cm with an LED adjusted to 1.6 μW and a wavelength of 500 nm, the current was 8.6 × 10 -6 A / cm 2 The light-dark ratio when a voltage of 2 V was applied was 1.4 × 10 2 It was.

[0078] Example 2 A glass substrate with an ITO electrode of 70 nm thickness was formed on it, and a vacuum of 4.0 × 10 -5 Compound W1 was deposited as an electron blocking layer to a thickness of 10 nm at 1000 kJ / cm². Next, a 200 nm thick film of 2Ph-BTBT, F6-SubPc-OC6F5, and fullerene (C60) was co-deposited at a deposition rate ratio of 4:4:2 to form a photoelectric conversion layer. Subsequently, dpy-NDI was deposited at a thickness of 10 nm to form a hole blocking layer. Finally, a 70 nm thick aluminum film was deposited as an electrode to fabricate a photoelectric conversion element. When a voltage of 2.6 V was applied to ITO and aluminum electrodes, the current in the dark (dark current) was 6.3 x 10 -10 A / cm 2 In addition, when a voltage of 2.6 V was applied and the ITO electrode was irradiated from a height of 10 cm with an LED adjusted to 1.6 μW and a wavelength of 500 nm, the current (light current) was 3.0 × 10 -7 A / cm 2 The light-dark ratio when a voltage of 2.6 V was applied was 4.8 × 10 2 It was.

[0079] Examples 3 to 6 A photoelectric conversion element was prepared in the same manner as in Example 2, except that the compounds shown in Table 3 were used for the electron blocking layer.

[0080] Comparative Example 2 A photoelectric conversion element was fabricated in the same manner as in Example 2, except that the electron blocking layer was made of CzBDF. The results of the examples and comparative examples are shown in Table 3.

[0081] The compounds used in the examples and comparative examples are listed below. [ka]

[0082] [Table 3] [Explanation of symbols]

[0083] 1 electrode, 2 hole blocking layer, 3 photoelectric conversion layer, 4 electron blocking layer, 5 electrodes, 6 substrates

Claims

1. A material for a photoelectric conversion element for imaging, represented by the following general formula (1) or (2): 【Chemistry 1】 In formulae (1) and (2), ring A independently represents a heterocycle represented by formula (1a) which is fused to an adjacent ring at any position. X is O, S, or N-Ar ２ Represents. Ar １ and Ar ２ each independently represents an unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted π-electron rich heteroaromatic group having 4 to 14 carbon atoms, or a substituted or unsubstituted linking aromatic group formed by linking 2 to 6 aromatic rings of an aromatic group selected from the aromatic hydrocarbon group and the π-electron rich heteroaromatic group, provided that Ar １ and Ar ２ When Ar is a linking aromatic group composed only of aromatic hydrocarbon groups, １ and Ar ２ are not both biphenyl groups. In addition, at least one of Ar 1 and Ar 2 in general formula (1) contains at least one substituted or unsubstituted tricyclic fused ring skeleton. L represents a divalent substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted π-electron-rich heteroaromatic group having 4 to 30 carbon atoms, or a substituted or unsubstituted linking aromatic group formed by linking 2 to 6 aromatic rings of an aromatic group selected from the aromatic hydrocarbon groups and the π-electron-rich heteroaromatic groups.

2. Ar in the general formula (2) １ and Ar ２ 2. The material for an imaging photoelectric conversion element according to claim 1, wherein at least one of the groups above contains at least one substituted or unsubstituted tricyclic fused ring skeleton.

3. 3. The material for an imaging photoelectric conversion element according to claim 2, wherein the tricyclic fused ring skeleton is at least one selected from the group consisting of a carbazole skeleton, a dibenzofuran skeleton, and a dibenzothiophene skeleton.

4. 3. The material for an imaging photoelectric conversion element according to claim 2, wherein the tricyclic fused ring skeleton is a carbazole skeleton.

5. The material for an imaging photoelectric conversion element according to any one of claims 1 to 4, characterized in that the energy level of the highest occupied molecular orbital (HOMO) obtained by a structure optimization calculation using density functional calculation B3LYP / 6-31G(d) is -4.5 eV or less.

6. The material for an imaging photoelectric conversion element according to any one of claims 1 to 5, characterized in that the energy level of the lowest unoccupied molecular orbital (LUMO) obtained by a structural optimization calculation using density functional theory calculation B3LYP / 6-31G(d) is -2.5 eV or higher.

7. 1 x 10 －６ cm ２ 7. The material for an imaging photoelectric conversion element according to claim 1, wherein the material has a hole mobility of at least 1 / Vs.

8. 8. The material for an imaging photoelectric conversion element according to claim 1, which is amorphous.

9. 9. The material for an imaging photoelectric conversion element according to claim 1, which is used as a hole transport material for an imaging photoelectric conversion element.

10. 10. A photoelectric conversion element for imaging, comprising a photoelectric conversion layer and an electron blocking layer between two electrodes, wherein at least one of the photoelectric conversion layer and the electron blocking layer contains the material for a photoelectric conversion element for imaging according to any one of claims 1 to 9.

11. 11. The photoelectric conversion element for imaging according to claim 10, wherein the photoelectric conversion layer contains an electron transporting material.

12. 12. The imaging photoelectric conversion element according to claim 10, wherein the electron blocking layer contains a material for the imaging photoelectric conversion element.

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