Photoelectric conversion element containing photoelectric conversion element material

Abstract

Provided is a photoelectric conversion element in which a photoelectric conversion element material with which high sensitivity and high resolution can be achieved is used. The photoelectric conversion element comprises two electrodes and one or more organic layers disposed between the electrodes, wherein a photoelectric conversion element material represented by general formula (1) is used in at least one of the organic layers. In the formula: X1 represents O, S, or N-R1; R1 represents an alkyl group having 1 to 20 carbon atoms, an aromatic hydrocarbon group having 6 to 30 carbon atoms, or a heteroaromatic group having 3 to 17 carbon atoms; and Ar1 to Ar3 each independently represent a deuterium, an alkyl group having 1 to 20 carbon atoms, an aromatic hydrocarbon group having 6 to 30 carbon atoms, a heteroaromatic group having 3 to 17 carbon atoms, a tricyclic condensed ring structure represented by any one of formulae (2a) to (2e), or the like.

Description

Photoelectric conversion element containing material for photoelectric conversion element

[0001] The present invention relates to a photoelectric conversion element containing a predetermined material for a photoelectric conversion element, and particularly to a photoelectric conversion element useful for an imaging device.

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

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

[0004] As one solution to these problems with photoelectric conversion elements, development is underway to 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 problems 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, a device 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, a photoelectric conversion element using an organic semiconductor is an element configured by having 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 a photoelectric conversion 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 move to the respective electrodes, converting light into an electrical signal. To accelerate this process, a technique of applying a bias voltage between the two electrodes is commonly used, but one challenge is reducing the leakage current from the two electrodes caused by the application of the bias voltage. For these reasons, controlling the movement of holes and electrons within the photoelectric conversion element can be said to be the key to achieving the desired characteristics of the photoelectric conversion element.

[0006] 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 in the above-mentioned photoelectric conversion element, various organic semiconductors having 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, these do not have sufficient properties and have not yet been put to commercial use.

[0007] Patent Document 1 proposes a device using a derivative in which phenoxazine is substituted at both ends of a biscarbazole in an electron blocking layer disposed between a photoelectric conversion layer and an electrode. Patent Documents 2 and 3 propose devices using a naphthalene derivative in which a carbazole skeleton is linked as a three-ring fused structure in an electron blocking layer disposed between a photoelectric conversion layer and an electrode. Patent Document 4 proposes a device using a carbazole derivative in which a carbazole skeleton is linked as a three-ring fused structure in an electron blocking layer disposed between a photoelectric conversion layer and an electrode. Patent Document 5 proposes a device using a spirofluorene derivative in which an acridine skeleton is linked as a three-ring fused structure in an electron blocking layer disposed between a photoelectric conversion layer and an electrode.

[0008] JP 2011-228614 A JP 2019-055919 A ​​WO2018 / 235780 A JP 2015-153910 A JP 2011-82507 A

[0009] NHK Giken R&D No. 132, pp. 4-11 (March 2012) NHK Giken R&D No. 174, pp. 4-17 (March 2019) 2019 IEEE International Electron Devices Meeting (IEDM), pp. 16.6.1-16.6.4 (2019)

[0010] For example, further improvement in sensitivity and resolution is a challenge for photoelectric conversion elements for imaging to be applied to digital cameras, smartphone cameras with high functionality, surveillance cameras, automotive sensors, etc. In light of this current situation, an object of the present invention is to provide a material that realizes high sensitivity and high resolution in photoelectric conversion elements, and a photoelectric conversion element using the same.

[0011] As a result of extensive research, 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 process of moving holes and electrons within a photoelectric conversion element, can be efficiently carried out by using a compound having a specific three-ring fused ring structure, and have thus completed the present invention.

[0012] That is, the present invention provides a photoelectric conversion element having one or more organic layers between two electrodes, wherein at least one of the organic layers contains a material for photoelectric conversion elements represented by the following general formula (1):

[0013] In general formula (1), X １ are each independently O, S, or N-R １ and X １ are each independently preferably represented by O or S, and more preferably represented by O.

[0014] R １each independently represents an alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or a substituted or unsubstituted heteroaromatic group having 3 to 17 carbon atoms.

[0015] Ar １ ~Ar ３ each independently represents deuterium, 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 heteroaromatic group having 3 to 17 carbon atoms, or a group having a tricyclic fused ring structure represented by any one of the following formulas (2a) to (2e), or represents a substituted or unsubstituted linked aromatic group formed by linking 2 to 5 substituted or unsubstituted aromatic hydrocarbon groups having 6 to 30 carbon atoms, substituted or unsubstituted heteroaromatic groups having 3 to 17 carbon atoms, or any one of the following formulas (2a) to (2e): However, when the tricyclic fused ring structure is contained at a terminal, it is each independently represented by the above formula (2c) or (2d), and when it is not at a terminal and there are two bonding sites, it is represented by the above formula (2a), (2b), or (2e). Preferably, the group is deuterium, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, a substituted or unsubstituted heteroaromatic group having 3 to 12 carbon atoms, or a group having a tricyclic fused ring structure represented by any one of the following formulas (2a) to (2e), or is represented by a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, a substituted or unsubstituted heteroaromatic group having 3 to 17 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking two or three of any of the following formulas (2a) to (2e).

[0016] Here, * indicates the point of attachment.

[0017] Ar ４ independently represent hydrogen, deuterium, an alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 5 of these aromatic groups.

[0018] X ２ are each independently a single bond, O, S, or N—R ２ and X ２ is preferably represented by a single bond, O, or S.

[0019] R 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, or a substituted or unsubstituted heteroaromatic group having 3 to 17 carbon atoms.

[0020] s and t independently represent the number of substitutions, and s and t independently represent an integer of 0 to 2, and preferably s and t independently represent 0 to 1.

[0021] Furthermore, a represents the number of substitutions and is an integer of 1 or 2.

[0022] However, when a=1, Ar １ ~Ar ３ Among them, it is preferred that at least one contains a group having a tricyclic fused ring structure of any one of the above formulas (2a) to (2e), and at least two contain a group having a tricyclic fused ring structure of any one of the above formulas (2a) to (2e). １ ~Ar ３ When any one of the above is a linking aromatic group, the linking aromatic group may contain two groups having a tricyclic fused ring structure of any one of the above formulas (2a) to (2e).

[0023] Also, a=1 and Ar １ ~Ar ３ It is also preferred that at least one of Ar contains a group having a tricyclic fused ring structure represented by the above formula (2c), １ ~Ar ３ It is more preferable that at least two of Ar include a group having a tricyclic fused ring structure represented by the above formula (2c). ２ or Ar ３ When the group contains a group having a tricyclic fused ring structure of any one of the above formulae (2a) to (2e), s and t, which represent the number of substitutions, are not 0 but 1 or 2.

[0024] In the above general formula (1), Ar １ preferably contains any one of the ring structures represented by the following general formulas (3a) to (3m), and Ar １ is more preferably any of the ring structures represented by the following general formulas (3a) to (3m).

[0025] Ar １ is represented by the above general formula (3b), it is preferable that it is bonded at a bonding position such as that shown in the following general formula (3b-1) or (3b-2), examples of which include the following (P38) or (P39). Here, * represents the point of attachment to N in formula (1).

[0026] Ar １ It is also preferred that R 1 contains at least one substituted or unsubstituted heteroaromatic group having 3 to 17 carbon atoms and containing an oxygen or sulfur atom.

[0027] The material for photoelectric conversion elements represented by the general formula (1) has an energy level of the highest occupied molecular orbital (HOMO) obtained by a structural optimization calculation using density functional theory calculation B3LYP / 6-31G(d) of −4.0 eV or less, an energy level of the lowest unoccupied molecular orbital (LUMO) obtained by the structural optimization calculation of −2.5 eV or more, and a density of 1×10 －６ cm ２ It is preferable that the HOMO energy level is −4.5 eV or less and −5.2 eV or more.

[0028] The material for a photoelectric conversion element represented by the above general formula (1) can be used as a hole transport material in a photoelectric conversion element for imaging.

[0029] The present invention also relates to a photoelectric conversion element for imaging, which has a photoelectric conversion layer and an electron blocking layer between two electrodes, and is characterized in that at least one of the photoelectric conversion layer and the electron blocking layer contains a material for photoelectric conversion elements represented by general formula (1) above.

[0030] Here, in the present invention, the material for a photoelectric conversion element represented by the above general formula (1) is preferably contained in the electron blocking layer or photoelectric conversion layer of a photoelectric conversion element, and in that case, it is preferably contained as a hole transport material. The above material for a photoelectric conversion element is preferably used in the electron blocking layer. Furthermore, when the above material for a photoelectric conversion element is contained in the electron blocking layer, the photoelectric conversion layer preferably contains an electron transport material, and in particular, it is preferable to contain a fullerene derivative as the electron transport material. Furthermore, in that case, it is preferable that the photoelectric conversion layer further contains a material having a skeleton containing at least two thiophene rings as a hole transport material.

[0031] Furthermore, in the present invention, when the material for a photoelectric conversion element represented by the above general formula (1) is used in the electron blocking layer of a photoelectric conversion element, the absolute value of the energy level difference (|h1-e1|) between the HOMO energy level (h1) of a hole-transporting material used in a photoelectric conversion layer adjacent to the electron blocking layer and the HOMO energy level (e1) of the material for a photoelectric conversion element represented by general formula (1) contained in the electron blocking layer is preferably 1.0 eV or less, and more preferably 0.8 eV or less. Furthermore, when the photoelectric conversion element material represented by the general formula (1) is used in the photoelectric conversion layer of a photoelectric conversion element, the absolute value of the energy level difference (|h2-e2|) between the HOMO energy level (h2) of the hole transport material used in the electron blocking layer adjacent to the photoelectric conversion layer and the HOMO energy level (e2) of the photoelectric conversion element material represented by the general formula (1) contained in the photoelectric conversion layer is preferably 1.0 eV or less, more preferably 0.8 eV or less. When the photoelectric conversion layer contains multiple materials, the hole transport material contained in the photoelectric conversion layer refers to a material that has a volume fraction of at least 5% and has the highest HOMO energy level among the materials contained in the photoelectric conversion layer. Similarly, when the electron blocking layer contains multiple materials, the hole transport material contained in the electron blocking layer refers to a material that has a volume fraction of at least 5% and has the highest HOMO energy level among the materials contained in the electron blocking layer.

[0032] The photoelectric conversion element material of the present invention can realize appropriate movement of holes and electrons within the photoelectric conversion element, thereby reducing leakage current that occurs due to application of a bias voltage when converting light into electrical energy in the photoelectric conversion element. As a result, a photoelectric conversion element that realizes a low dark current value and a high contrast ratio can be obtained, and is particularly useful as a photoelectric conversion element material for a photoelectric conversion film stack-type imaging device.

[0033] 1 is a schematic cross-sectional view showing an example of the structure of a photoelectric conversion element for imaging;

[0034] The imaging photoelectric conversion element of the present invention has at least one organic layer (i.e., one or more organic layers) between two electrodes. In the present invention, at least one of the organic layers contains the material for photoelectric conversion elements represented by the general formula (1). Preferably, in an imaging photoelectric conversion element having a photoelectric conversion layer and an electron blocking layer between two electrodes, the material for photoelectric conversion elements represented by the general formula (1) is contained in at least one of the photoelectric conversion layer and the electron blocking layer. Hereinafter, the material for photoelectric conversion elements represented by the general formula (1) may be referred to as the material for photoelectric conversion elements of the present invention, or simply as the material for photoelectric conversion elements, the material of the present invention, or the compound represented by the general formula (1).

[0035] The compound represented by the above general formula (1) will be explained below.

[0036] X １ are each independently O, S, or N-R １ and X １ are each independently preferably represented by O or S, and more preferably represented by O.

[0037] R １ 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, or a substituted or unsubstituted heteroaromatic group having 3 to 17 carbon atoms.

[0038] R １When is an unsubstituted alkyl group having 1 to 20 carbon atoms, the alkyl group may be any of linear, branched, and cyclic alkyl groups, and is preferably a linear, branched, or cyclic alkyl group having 1 to 10 carbon atoms. Specific examples 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, tert-butyl, neopentyl, 2-ethylhexyl, and 2-hexyloctyl groups; and saturated alicyclic hydrocarbon groups such as cyclopentyl, cyclohexyl, cyclooctyl, 4-butylcyclohexyl, and 4-dodecylcyclohexyl groups. The alkyl group having 1 to 20 carbon atoms may be any of linear, branched, and cyclic alkyl groups.

[0039] R １ For unsubstituted aromatic hydrocarbon compounds having 6 to 30 carbon atoms, the number of carbon atoms is preferably 6 to 18. Examples of aromatic hydrocarbon compounds having 6 to 30 carbon atoms include groups derived from monocyclic aromatic hydrocarbons such as benzene, bicyclic aromatic hydrocarbons such as naphthalene, tricyclic aromatic hydrocarbons such as indacene, biphenylene, phenalene, anthracene, phenanthrene, and fluorene, tetracyclic aromatic hydrocarbons such as fluoranthene, acephenanthrylene, aceanthrylene, triphenylene, pyrene, chrysene, tetraphene, tetracene, and pleiadene, and pentacyclic aromatic hydrocarbons such as picene, perylene, pentaphene, pentacene, tetraphenylene, and naphthaanthracene. Preferred are groups derived from benzene, naphthalene, anthracene, phenanthrene, triphenylene, or pyrene, and more preferred are groups derived from benzene, naphthalene, anthracene, phenanthrene, pyrene, or triphenylene.

[0040] R １For the unsubstituted heteroaromatic group having 3 to 17 carbon atoms, the number of carbon atoms is preferably 3 to 12, and more preferably 6 to 12. Examples of the heteroaromatic group having 3 to 17 carbon atoms include groups derived from nitrogen-containing aromatic compounds having a pyrrole ring, such as pyrrole, pyrrolopyrrole, indole, isoindole, pyrroloisoindole, and carboline, as well as thiophene, benzothiophene, dibenzothiophene, furan, benzofuran, dibenzofuran, carbazole, indolocarbazole, pyridine, pyrimidine, quinoline, isoquinoline, quinazoline, and quinoxaline. Preferred are groups derived from thiophene, benzothiophene, dibenzothiophene, furan, benzofuran, dibenzofuran, or carbazole, and more preferably dibenzothienyl, dibenzofuranyl, or carbazolyl.

[0041] Ar １ ~Ar ３ are each independently deuterium, 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 heteroaromatic group having 3 to 17 carbon atoms, or a group having a tricyclic fused ring structure represented by any one of the above formulas (2a) to (2e), or a substituted or unsubstituted linked aromatic group formed by linking 2 to 5 substituted or unsubstituted aromatic hydrocarbon groups having 6 to 30 carbon atoms, substituted or unsubstituted heteroaromatic groups having 3 to 17 carbon atoms, or any one of the above formulas (2a) to (2e). However, when the tricyclic fused ring structure is contained at a terminal, it is each independently represented by the above formula (2c) or (2d), and when it is not at a terminal and there are two bonding sites, it is represented by the above formula (2a), (2b), or (2e). Preferably, the group is deuterium, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, a substituted or unsubstituted heteroaromatic group having 3 to 12 carbon atoms, or a group having a tricyclic fused ring structure represented by any one of the following formulas (2a) to (2e), or is represented by an aromatic hydrocarbon group having 6 to 18 carbon atoms, a heteroaromatic group having 3 to 17 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking two or three of any one of the following formulas (2a) to (2e).

[0042] Ar １ ~Ar ３When R is an alkyl group having 1 to 20 carbon atoms, the number of carbon atoms is preferably 1 to 10. Examples of alkyl groups having 1 to 20 carbon atoms include R １ This is the same as in the case described above. １ ~Ar ３ When R is an unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, the number of carbon atoms is preferably 6 to 18. Examples of aromatic hydrocarbon groups having 6 to 30 carbon atoms include R １ This is the same as in the case described above. １ ~Ar ３ When R is an unsubstituted heteroaromatic group having 3 to 17 carbon atoms, the number of carbon atoms is preferably 6 to 12. Examples of heteroaromatic groups having 3 to 17 carbon atoms include R １ In addition to the cases described above, groups having a tricyclic fused ring structure represented by the formulas (2a) to (2e) above can be mentioned. １ ~Ar ３ In the case of an unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, an unsubstituted heteroaromatic group having 3 to 17 carbon atoms, and an unsubstituted linked aromatic group formed by linking 2 to 5 groups represented by the formulas (2a) to (2e), the number of links is preferably 2 to 3, and more preferably 2. １ ~Ar ３ is a linking aromatic group, Ar １ ~Ar ３ and the group represented by formula (1) may be bonded via an aromatic hydrocarbon group or a heteroaromatic group contained in the linking aromatic group, or via any of the groups represented by formulas (2a) to (2e), and may be bonded at both ends or in a branched manner.

[0043] Ar ４ Ar independently represents deuterium, an alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 5 of these aromatic groups. ４ When R is an alkyl group having 1 to 20 carbon atoms, the number of carbon atoms is preferably 1 to 10. Examples of alkyl groups having 1 to 20 carbon atoms include R １ This is the same as in the case described above. ４When R is an unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, the number of carbon atoms is preferably 6 to 18. Examples of aromatic hydrocarbon groups having 6 to 30 carbon atoms include R １ This is the same as the case described above.

[0044] X ２ are each independently a single bond, O, S, or N—R ２ and X ２ is preferably represented by a single bond, O, or S.

[0045] R ２ R 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, or a substituted or unsubstituted heteroaromatic group having 3 to 17 carbon atoms. ２ When R is an unsubstituted alkyl group having 1 to 20 carbon atoms, the number of carbon atoms is preferably 1 to 10. Examples of alkyl groups having 1 to 20 carbon atoms include R １ This is the same as in the case described above. ４ When R is an unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, the number of carbon atoms is preferably 6 to 18. Examples of aromatic hydrocarbon groups having 6 to 30 carbon atoms include R １ This is the same as in the case described above. ４ When R is an unsubstituted heteroaromatic group having 3 to 17 carbon atoms, the number of carbon atoms is preferably 3 to 12. Examples of heteroaromatic groups having 3 to 17 carbon atoms include R １ This is the same as the case described above.

[0046] s and t independently represent the number of substitutions, and s and t independently represent an integer of 0 to 2, and preferably s and t independently represent 0 to 1.

[0047] a represents the number of substitutions and is an integer of 1 or 2. However, when a=1, Ar １ ~Ar ３ Among Ar, it is preferred that at least one contains a group having a tricyclic fused ring structure of any one of the above formulas (2a) to (2e), and at least two contain a group having a tricyclic fused ring structure of any one of the above formulas (2a) to (2e). １ ~Ar ３When any one of the above is a linking aromatic group, the linking aromatic group may contain two groups having a tricyclic fused ring structure of any one of the above formulas (2a) to (2e).

[0048] Also, a=1 and Ar １ ~Ar ３ It is also preferred that at least one of Ar contains a group having a tricyclic fused ring structure represented by the above formula (2c), １ ~Ar ３ It is more preferable that at least two of the above groups contain a group having a tricyclic fused ring structure represented by the above formula (2c).

[0049] Ar １ preferably contains any one of the ring structures represented by the formulas (3a) to (3m), and Ar １ is more preferably any of the ring structures represented by the general formulae (3a) to (3m).

[0050] Of the ring structures represented by the formulae (3a) to (3m), (3b), (3e), (3f), (3g), (3h), (3i), and (3m) are preferred, and (3b), (3e), (3f), (3h), and (3m) are more preferred.

[0051] Ar １ It is also preferred that the heteroaromatic group contains at least one substituted or unsubstituted heteroaromatic group having 3 to 17 carbon atoms and containing an oxygen or sulfur atom. Examples include heteroaromatic groups containing a furan ring or a thiophene ring and having a ring in which the furan ring or the thiophene ring is fused with an aromatic hydrocarbon ring, and the fused aromatic hydrocarbon ring may be singular or plural, but is not limited thereto.

[0052] In this specification, the term "unsubstituted linked aromatic group" refers to an aromatic group in which two or more aromatic groups are linked by single bonds and are selected from the aromatic hydrocarbon groups, aromatic groups of heteroaromatic groups, and groups having a tricyclic fused ring structure represented by the formulas (2a) to (2e). These linked aromatic groups may be linear or branched. The linking position when the benzene rings are linked may be ortho, meta, or para, but para- or meta-linking is preferred. The aromatic group may be an aromatic hydrocarbon group, a heteroaromatic group, or a group having a tricyclic fused ring structure represented by the formulas (2a) to (2e), and the multiple aromatic groups may be the same or different.

[0053] In this specification, examples of the substituent with which an aromatic hydrocarbon group or the like may be substituted, such as a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, include deuterium, a cyano group, and an alkyl group having 1 to 20 carbon atoms.

[0054] Among these, when the substituent is an alkyl group having 1 to 20 carbon atoms, the alkyl group may be any of linear, branched, and cyclic alkyl groups, and is preferably a linear, branched, or cyclic alkyl group having 1 to 10 carbon atoms. Specific examples 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, tert-butyl, neopentyl, 2-ethylhexyl, and 2-hexyloctyl groups; and saturated alicyclic hydrocarbon groups such as cyclopentyl, cyclohexyl, cyclooctyl, 4-butylcyclohexyl, and 4-dodecylcyclohexyl groups. In the present invention, the substituent is bonded to a carbon atom or a heteroatom constituting the aromatic ring.

[0055] 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 invention is not limited thereto. The numbers in parentheses represent the compound numbers.

[0056] The photoelectric conversion element material of the present invention can be obtained by synthesizing it 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, and then purifying it using known methods such as recrystallization, column chromatography, and sublimation purification, but is not limited to these methods.

[0057] The material for photoelectric conversion elements of the present invention preferably has an energy level of the highest occupied molecular orbital (HOMO) obtained by a structure optimization calculation using density functional theory calculation B3LYP / 6-31G(D) of −4.0 eV or less, more preferably in the range of −5.0 eV to −4.5 eV.

[0058] Furthermore, the energy level of the lowest unoccupied molecular orbital (LUMO) obtained by the above structural optimization calculation is preferably −2.5 eV or higher, and more preferably in the range of −2.5 eV to −0.9 eV.

[0059] In the material for photoelectric conversion devices of the present invention, 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.

[0060] The material for a photoelectric conversion element of the present invention preferably has a viscosity of 1×10 －６ cm ２ / Vs ~ 1 cm ２ / Vs, and more preferably 2×10 －５ cm ２ / Vs ~ 1 × 10 －１ cm ２ The hole mobility can be evaluated by a known method such as a method using a FET transistor element, a time-of-flight method, or an SCLC method.

[0061] 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 detecting no peaks in an XRD method or no endothermic peaks in a DSC method.

[0062] Next, an imaging photoelectric conversion element using the material for a photoelectric conversion element of the present invention will be described, but the structure of the imaging photoelectric conversion element of the present invention is not limited thereto.

[0063] Figure 1 is a cross-sectional view schematically illustrating the structure of an imaging photoelectric conversion element using the imaging photoelectric conversion element material of the present invention, where 1 represents a substrate, 2 an electrode, 3 an electron blocking layer, 4 a photoelectric conversion layer, 5 a hole blocking layer, and 6 an electrode. The structure of Figure 1 is not limited to this, and layers can be added or omitted as needed. A structure opposite to that of Figure 1 is also possible, i.e., an electrode 6, a hole blocking layer 5, a photoelectric conversion layer 4, an electron blocking layer 3, and an electrode 2 are laminated in this order on a substrate 1, and in this case, layers can also be added or omitted as needed. In the imaging photoelectric conversion element described above, layers that constitute the laminate structure on the substrate other than electrodes such as an anode and a cathode may be collectively referred to as organic layers.

[0064] Each member and each layer of the photoelectric conversion element of the present invention will be described below.

[0065] -Substrate- The photoelectric conversion element is preferably supported on a substrate. There are no particular limitations on the substrate, and it is possible to use substrates made of, for example, glass, transparent plastic, quartz, etc.

[0066] - Electrode - The electrode has the function of collecting holes and electrons generated in the photoelectric conversion layer. It also needs to have 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 semi-transparent. In addition, the material used as the electrode is not particularly limited as long as it is conductive, but examples thereof include ITO, IZO, SnO ２ , ATO (antimony-doped tin oxide), ZnO, AZO (Al-doped zinc oxide), GZO (gallium-doped zinc oxide), TiO ２Examples of the conductive material include transparent conductive materials such as fluorine-containing tetrahydrofuran (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. A mixture of these materials may be used as needed. Two or more layers may also be laminated.

[0067] -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 P-type organic semiconductors may be used, or two or more 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 that has the function of absorbing light of a desired wavelength in the visible region. The material for a photoelectric conversion element of the present invention can be used as the P-type organic semiconductor material, which is a hole-transporting material.

[0068] The P-type organic semiconductor material may be any material having hole transport properties, and it is preferable to use the photoelectric conversion element material of the present invention, but other P-type organic semiconductor materials may also be used. Furthermore, two or more compounds represented by the above general formula (1) (photoelectric conversion element material of the present invention) may be mixed and used. Furthermore, the above compound may be mixed with other P-type organic semiconductor materials.

[0069] The other P-type organic semiconductor material may be any material having hole transport properties, and examples thereof include aromatic compounds such as naphthalene derivatives, anthracene derivatives, phenanthrene derivatives, pyrene derivatives, chrysene derivatives, naphthacene derivatives, triphenylene derivatives, perylene derivatives, fluoranthene derivatives, fluorene derivatives, 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, aromatic amine derivatives, styrylamine derivatives, benzidine derivatives, porphyrin derivatives, phthalocyanine derivatives, and quinacridone derivatives.

[0070] Furthermore, a polymeric P-type organic semiconductor material may be used. Examples of such a polymeric P-type organic semiconductor material include polyphenylene vinylene derivatives, polyparaphenylene derivatives, polyfluorene derivatives, polyvinylcarbazole derivatives, and polythiophene derivatives. Furthermore, a mixture of two or more selected from the compound represented by formula (1), P-type organic semiconductor materials, and polymeric P-type organic semiconductor materials may be used.

[0071] The N-type organic semiconductor material may be any material having electron transport properties, and examples thereof include naphthalene tetracarboxylic acid diimide, perylene tetracarboxylic acid diimide, fullerenes (fullerene derivatives), and azole derivatives such as imidazole, thiazole, thiadiazole, oxazole, oxadiazole, and triazole. Two or more materials selected from the N-type organic semiconductor materials may be mixed and used.

[0072] -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. The electron blocking layer also functions as a hole transport layer, transporting holes generated by charge separation in the photoelectric conversion layer to the electrode. A single layer or multiple layers may be arranged as needed. The electron blocking layer may be formed using a P-type organic semiconductor material, which is a hole transport material. Any material having hole transport properties may be used as the P-type organic semiconductor material. The compound represented by the general formula (1) above is preferably used, but other P-type organic semiconductor materials may also be used. Furthermore, the compound represented by the general formula (1) may be mixed with other P-type organic semiconductor materials or polymeric P-type organic semiconductor materials, such as those described above.

[0073] -Hole Blocking Layer- The hole blocking layer is provided to suppress dark current generated when holes are injected from one electrode into the photoelectric conversion layer when a bias voltage is applied between the two electrodes. The hole blocking layer also functions as an electron transport layer, transporting electrons generated by charge separation in the photoelectric conversion layer to the electrode, and a single layer or multiple layers can be arranged as needed. The hole blocking layer can be made of an N-type organic semiconductor having 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 (fullerene derivatives) 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, carbodiimide, fluorenylidenemethane derivatives, anthraquinodimethane and anthrone derivatives, bipyridine derivatives, quinoline derivatives, indolocarbazole derivatives, etc. Two or more materials selected from the N-type organic semiconductor materials may also be mixed and used.

[0074] The hydrogen in the material of the present invention may be deuterium, i.e., hydrogen on the aromatic ring in the general formulas (1), (2a), (2b), (2c), (2d), (2e), (3a), (3b), (3c), (3d), (3e), (3f), (3g), (3h), (3i), (3j), (3k), and (3m), as well as Ar １ , Ar ２ , Ar ３ , Ar ４ , R １ , and R ２ Some or all of the hydrogen atoms on the alkyl group or aromatic ring may be deuterium atoms, including those of the following substituents: Furthermore, some or all of the hydrogen atoms in the compounds used as the N-type organic semiconductor material and the P-type organic semiconductor material may be deuterium atoms.

[0075] When producing the imaging photoelectric conversion element of the present invention, the method for forming each layer is not particularly limited, and the layer may be produced by either a dry process or a wet process. If necessary, the organic layer containing the material for a photoelectric conversion element of the present invention may be a multi-layer structure.

[0076] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0077] Calculation Example: Calculation of HOMO and LUMO Values ​​The HOMO and LUMO were calculated for the above compounds P1, P4, P20, P38, P39, P41, P50, P51, P52, P55, P63, P64, and P65. The calculations were performed using density functional theory (DFT), a Gaussian calculation program, and structural optimization calculations using density functional calculation B3LYP / 6-31G(d). The results are shown in Table 1. It can be said that all of the materials of the present invention have preferable HOMO and LUMO values.

[0078] For comparison, the HOMO and LUMO of Compounds H1, H2, H3, H4, and H5 were calculated in the same manner as above. The results are shown in Table 1.

[0079]

[0080] The synthesis of compounds P1, P39, and P51 will be described below as representative examples. Other compounds were also synthesized in a similar manner.

[0081] Synthesis Example 1 (Synthesis of Compound P1) A 300 ml three-neck flask was charged with T1 (16.0 mmol), T2 (6.9 mmol), bis(tri-tert-butylphosphine)palladium(0) (0.6 mmol), and sodium tert-butoxide (21.1 mmol) and 40 ml of xylene was added. The mixture was then stirred at 150°C for 6 hours. After cooling to room temperature, the reaction mixture was concentrated to dryness and purified by column chromatography. Compound 1 (white solid) was obtained by reprecipitation with xylene and isopropanol. The yield was 67%. The solid obtained was evaluated by XRD, but no peak was detected. This confirmed that compound P1 was amorphous. APCI-TOFMS m / z 590 [M+1] ＋

[0082] Synthesis Example 2 (Synthesis of Compound P39) Compound P39 (white solid) was obtained in the same manner as in Synthesis Example 1, except that T1 was replaced with T3 and T2 with T4. The yield was 21%. The obtained solid was evaluated by XRD, but no peak was detected. APCI-TOFMS m / z 679 [M+1] ＋

[0083] Synthesis Example 3 (Synthesis of Compound P51) Compound P51 (white solid) was obtained in the same manner as in Synthesis Example 1, except that T3 was replaced with T5. The yield was 43%. The obtained solid was evaluated by XRD, but no peak was detected. APCI-TOFMS m / z 591 [M+1] ＋

[0084] Measurement of Charge Mobility Compound 1 was formed as an organic layer by vacuum deposition on an electrode made of ITO with a thickness of 110 nm formed on a glass substrate under conditions of a film thickness of approximately 3 μm. Next, using a device in which aluminum (Al) was formed to a thickness of 70 nm as an electrode, charge mobility was measured by the time-of-flight method. The hole mobility was 1.3 × 10 －４ cm ２ / Vs.

[0085] The hole mobility of each compound was measured in the same manner as above, except that Compound 1 was replaced with the compound shown in Table 2. The results are shown in Table 2.

[0086]

[0087] Example 1 A vacuum chamber was placed on an electrode made of ITO with a thickness of 70 nm formed on a glass substrate. －５ Compound P1 was deposited as an electron blocking layer at 100 Pa to a thickness of 10 nm. Next, as a photoelectric conversion layer, 2Ph-BTBT (hole transport material), F6-SubPc-OC6F5 (dye material), and fullerene (C60, electron transport material) were co-deposited to a thickness of 200 nm at a deposition rate ratio of 4:4:2 to form a film. Subsequently, dpy-NDI was deposited to a thickness of 10 nm to form a hole blocking layer. Finally, aluminum was deposited as an electrode to a thickness of 70 nm to prepare a photoelectric conversion element. When a voltage of 2.6 V was applied using ITO and aluminum as electrodes, the current in the dark (dark current) was 3.7 × 10 －１０ A / cm ２ In addition, when a voltage of 2.6 V was applied and light was irradiated from a height of 10 cm onto the ITO electrode side using an LED adjusted to 1.6 μW and with 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 8.1 × 10 ２ These results are shown in Table 3.

[0088] Examples 2 to 13 Photoelectric conversion elements were prepared in the same manner as in Example 1, except that the compounds shown in Table 3 were used for the electron blocking layer.

[0089] Comparative Examples 1 to 5 Photoelectric conversion elements were prepared in the same manner as in Example 1, except that the compounds shown in Table 3 were used for the electron blocking layer. The results of Examples 1 to 13 and Comparative Examples 1 to 5 are shown in Table 3.

[0090] The calculation results of the HOMO and LUMO of the compounds used in the examples and comparative examples other than the compounds shown in the above-mentioned Table 1 are shown in Table 4. As in the previous case, the calculations were performed using density functional theory (DFT) calculations, Gaussian calculation program, and structural optimization calculations using density functional calculation B3LYP / 6-31G(d).

[0091]

[0092]

[0093] The results in Table 3 show that the photoelectric conversion element using the compound of the present invention exhibits a low dark current value and a high light-to-dark ratio.

[0094] The material for a photoelectric conversion element for imaging of the present invention can realize appropriate movement of holes and electrons within the photoelectric conversion element, thereby making it possible to reduce leakage current that occurs due to application of a bias voltage when converting light into electrical energy, and as a result, a photoelectric conversion element that achieves a low dark current value and a high light-to-dark ratio can be obtained. The material of the present invention is useful as a material for a photoelectric conversion element in a photoelectric conversion film stack-type imaging device.

[0095] 1 Substrate, 2 Electrode, 3 Electron blocking layer, 4 Photoelectric conversion layer, 5 Hole blocking layer, 6 Electrode

Claims

1. A photoelectric conversion element having one or more organic layers between two electrodes, wherein at least one of the organic layers contains a material for photoelectric conversion elements represented by the following general formula (1): In the formula, X １ are each independently O, S, or N-R １ Represents R １ 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, or a substituted or unsubstituted heteroaromatic group having 3 to 17 carbon atoms. １ ~Ar ３ are each independently deuterium, 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 heteroaromatic group having 3 to 17 carbon atoms, or a group having a tricyclic fused ring structure represented by any one of the following formulas (2a) to (2e), or a substituted or unsubstituted linked aromatic group formed by linking 2 to 5 substituted or unsubstituted aromatic hydrocarbon groups having 6 to 30 carbon atoms, substituted or unsubstituted heteroaromatic groups having 3 to 17 carbon atoms, or any one of the following formulas (2a) to (2e), provided that when the tricyclic fused ring structure is contained at a terminal, it is each independently represented by the following formula (2c) or (2d), and when it is not at a terminal and there are two bonding sites, it is represented by the above formula (2a), (2b), or (2e). * indicates the point of attachment. ４ X independently represent hydrogen, deuterium, an alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 5 of these aromatic groups. ２ are each independently a single bond, O, S, or N—R ２ Represents R 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, or a substituted or unsubstituted heteroaromatic group having 3 to 17 carbon atoms. s and t independently represent the number of substitutions, and s and t independently represent an integer of 0 to 2. a represents the number of substitutions, and is an integer of 1 or 2. However, when a=1, Ar １ ~Ar ３ At least one of the groups contains a group having a tricyclic fused ring structure of any one of the above formulas (2a) to (2e).

2. In the above general formula (1), Ar １ The photoelectric conversion element according to claim 1, wherein the ring structure is represented by any one of the following general formulas (3a) to (3m):

3. In the above general formula (1), X ２ The photoelectric conversion element according to claim 1 , wherein is represented by a single bond, O, or S.

4. In the above general formula (1), Ar １ 2. The photoelectric conversion element according to claim 1, wherein the heteroaromatic group has at least one substituted or unsubstituted heteroaromatic group having 3 to 17 carbon atoms and containing an oxygen or sulfur atom.

5. In the above general formula (1), Ar １ 2. The photoelectric conversion element according to claim 1, wherein is a ring structure represented by any one of the general formulae (3a) to (3m).

6. In the above general formula (1), a = 1 and Ar １ ~Ar ３ 2. The photoelectric conversion element according to claim 1, wherein at least two of the groups contain a group having a tricyclic fused ring structure represented by any one of the formulas (2a) to (2e).

7. In the above general formula (1), a = 1 and Ar １ ~Ar ３ The photoelectric conversion element according to claim 1 , wherein at least one of the groups contains a group having a tricyclic fused ring structure represented by the formula (2c).

8. In the above general formula (1), Ar １ ~Ar ３ The photoelectric conversion element according to claim 7 , wherein at least two of the groups contain a group having a tricyclic fused ring structure represented by the formula (2c).

9. The photoelectric conversion element according to claim 1, characterized in that the material for photoelectric conversion elements represented by the general formula (1) has an energy level of the highest occupied molecular orbital (HOMO) obtained by a structural optimization calculation using density functional calculation B3LYP / 6-31G(d) of -4.0 eV or less.

10. The photoelectric conversion element according to claim 1, characterized in that the material for photoelectric conversion elements represented by the general formula (1) has an energy level of the lowest unoccupied molecular orbital (LUMO) of -2.5 eV or higher, as obtained by a structural optimization calculation using density functional calculation B3LYP / 6-31G(d).

11. The material for a photoelectric conversion element represented by the general formula (1) is 1×10 －６ cm 2 2. The photoelectric conversion element according to claim 1, wherein the photoelectric conversion element has a hole mobility of at least 1 / Vs.

12. The photoelectric conversion element according to claim 1, wherein the material for photoelectric conversion elements represented by the general formula (1) is amorphous.

13. The photoelectric conversion device according to claim 1, wherein the material for photoelectric conversion devices represented by the general formula (1) is used as a hole transport material.

14. A photoelectric conversion element for imaging, having a photoelectric conversion layer and an electron blocking layer as organic layers between two electrodes, characterized in that the electron blocking layer contains the material for photoelectric conversion elements represented by the above general formula (1).

15. The photoelectric conversion element according to claim 14, wherein the absolute value of the HOMO energy level difference between the material for photoelectric conversion elements represented by the general formula (1) and the hole transport material contained in the photoelectric conversion layer is 1.0 eV or less.

16. The photoelectric conversion element according to claim 14, wherein the photoelectric conversion layer contains an electron transporting material.

17. The photoelectric conversion element according to claim 16, wherein the photoelectric conversion layer contains a fullerene derivative as an electron transporting material.

18. The photoelectric conversion element according to claim 16, wherein the photoelectric conversion layer contains a material having a skeleton containing at least two thiophene rings as a hole transporting material.

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