JP2016183290A - Copolymer, photoelectric conversion element, and solar battery module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copolymer capable of improving the light resistance of a photoelectric conversion element, a photoelectric conversion element having high light resistance, a solar batter, and a solar battery module.SOLUTION: Provided is a copolymer having a repeating unit represented by formula (I) and a repeating unit represented by formula (II)[D denotes a doner-based monomer unit; A1 denotes an acceptor-based monomer; A2 denotes an acceptor-based monomer unit; Rand Rdenote respectively independently monovalent organic groups; L denotes an alkenylene group, an alkynylene group, a bivalent aromatic hydrocarbon group or a bivalent aromatic heterocyclic group capable of having a substituent (where, the carbon atom position at the α site in the carbon atom composing the L has not substituent or is substituted by a fluorine atom).SELECTED DRAWING: None

Description

  The present invention relates to a copolymer, a photoelectric conversion element, a solar cell, and a solar cell module.

  A π-conjugated polymer is used as a semiconductor material for organic electronic devices such as organic solar cells, organic EL elements, organic thin film transistors, and organic light emitting sensors. In particular, in an organic solar cell, it is desired to improve sunlight absorption efficiency, and it is important to develop a polymer that can absorb light having a long wavelength (600 nm or more). In order to achieve a longer absorption wavelength, an example in which a copolymer of a donor monomer and an acceptor monomer (hereinafter sometimes referred to as a copolymer) is used for a photoelectric conversion element has been reported.

  Specifically, Non-Patent Document 1 describes a photoelectric conversion element using a copolymer having an imidothiophene unit and a dithienocyclopentadiene unit. Non-Patent Documents 1, 2, 3 and Patent Document 1 describe photoelectric conversion elements using a copolymer having an imidothiophene unit and a dithienosilole unit. Further, Non-Patent Document 2 describes a photoelectric conversion element using a copolymer having an imidothiophene unit and a dithienogermol unit.

International Publication No. 2012/102390 Pamphlet

J. et al. Mater. Chem. , 2011, 21, 3895-3902 J. et al. Am. Chem. Soc. , 2011, 133, 10062-10065 Chem. Commun. , 2011, 47, 4920-4922.

  Since the organic thin film solar cell is assumed to be used in an environment exposed to sunlight, for practical use of the organic thin film solar cell, it is desired to improve not only the conversion efficiency but also the exposure stability. However, according to the study by the present inventors, the organic thin film solar cell using the copolymer described in Patent Literature 1 and Non-Patent Literatures 1 to 3 is irradiated with light when the solar cell is produced or used. It has been found that there is a possibility that the conversion efficiency is lowered as it is done. This is mainly because the copolymer of the material constituting the photoelectric conversion element of the organic thin film solar cell is deteriorated by light.

  An object of this invention is to provide the copolymer which can solve the said problem and can improve the light resistance of a photoelectric conversion element, and a photoelectric conversion element, a solar cell, and a solar cell module with high light resistance.

  As a result of intensive studies to solve the above problems, the present inventors can solve the above problem by using a copolymer having a specific repeating unit in addition to the repeating unit of a donor monomer unit and an acceptor monomer unit. The present invention has been found and the present invention has been achieved. That is, the gist of the present invention is as follows.

[1] A copolymer having a repeating unit represented by the following formula (I) and a repeating unit represented by the following formula (II) different from the following formula (I).

(In formula (I), D represents a donor monomer unit, A1 represents an acceptor monomer unit. In formula (II), A2 represents an acceptor monomer unit, and R ¹ and R ² are each independent. And L represents an optionally substituted alkenylene group, alkynylene group, divalent aromatic hydrocarbon group or divalent aromatic heterocyclic group (provided that Among the carbon atoms constituting L, the carbon atom located at the α-position has no substituent or is substituted with a fluorine atom)).
[2] The copolymer according to [1], wherein D in the formula (I) is a structural unit represented by the following formula (III).

(In Formula (III), Ring 1 and Ring 2 each independently represent an aromatic hydrocarbon ring which may have a substituent or an aromatic heterocyclic ring which may have a substituent. X ¹ is Q ¹ (R ³⁾ represents (R ^4), X ² is a single bond, O, S, N (R 5), or Q ² (R ⁶⁾ represents a (R ⁷⁾ .Q ¹ and Q ² represents an atom selected from Group 14 elements of the periodic table, and R ^{3 to} R ⁷ each represents a hydrogen atom or a monovalent organic group.)
[3] The copolymer according to [1] or [2], wherein A1 in the formula (I) is a structural unit represented by the following formula (V).

(In formula (V), X ³ represents an atom selected from Group 16 elements of the periodic table, and R ⁸ represents a hydrogen atom or a monovalent organic group.)
[4] The copolymer according to any one of [1] to [3], wherein A1 and A2 in the formula (I) and the formula (II) are the same structural unit.
[5] The copolymer according to any one of [1] to [4], wherein L in the formula (II) is a divalent aromatic heterocyclic group.
[6] The copolymer according to [5], wherein L in the formula (II) is any group represented by the following formulas (XI) to (XIII).

(In Formula (XI), Formula (XII), and Formula (XIII), R ^{21 to} R ²⁶ each independently represent a hydrogen atom or a fluorine atom. In Formula (XI), n is 1 to 3). Represents an integer.)
[7] A photoelectric conversion element having at least a pair of electrodes and an active layer between the pair of electrodes on a substrate, wherein the active layer is any one of [1] to [6] A photoelectric conversion element containing a copolymer.
[8] A solar cell having the photoelectric conversion element according to [7].
[9] A solar cell module having the solar cell according to [8].

According to the present invention, it is an object to provide a copolymer capable of improving the light resistance of a photoelectric conversion element, and a photoelectric conversion element, a solar cell, and a solar cell module having high light resistance.

It is sectional drawing which shows typically the structure of the photoelectric conversion element as one Embodiment of this invention. It is sectional drawing which shows typically the structure of the solar cell as one Embodiment of this invention. It is sectional drawing which shows typically the structure of the solar cell module as one Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail. The description of the constituent requirements described below is an example (representative example) of an embodiment of the present invention, and the present invention is not specified in these contents unless it exceeds the gist.

<1. Copolymer according to the present invention>
By using the copolymer according to the present invention in, for example, an active layer of a photoelectric conversion element, a photoelectric conversion element having high light resistance can be provided. Although the reason for this is not clear, the copolymer according to the present invention has an appropriate solubility and carrier balance by having two or more specific structural units to be described later, and improves the π-stacking property between molecules, thereby improving the structure. Is considered to improve light resistance.

  The copolymer according to the present invention has a repeating unit represented by the following formula (I) and a repeating unit represented by the following formula (II) different from the following formula (I).

  In formula (I), D represents a donor monomer unit, and A1 represents an acceptor monomer unit. In the present invention, the donor monomer unit means a monomer unit having a small ionization potential and a strong tendency to donate electrons. The acceptor monomer unit means a monomer unit having a large electron affinity and a strong tendency to accept electrons. Specifically, D is a monomer unit having an ionization potential smaller than that of A1.

  The donor monomer unit is not particularly limited as long as it has the above-mentioned characteristics, for example, thiophene, bithiophene, terthiophene, quarterthiophene, thienothiophene, dithienothiophene, benzodithiophene, cyclopentadithiophene, Examples include dithienosilol, dithienogermol, indacenodithiophene, dithioenopyrrole, carbazole, arylamine, and isothianaphthene. Moreover, the donor-type monomer unit as described in a nonpatent literature (Macromolecules 2012,45,607-632) is mentioned.

  The donor monomer unit may have a substituent. The substituent that the donor monomer unit may have is not particularly limited, and is an aliphatic hydrocarbon group, an aromatic hydrocarbon group, an aliphatic heterocyclic group, an aromatic heterocyclic group, an alkoxy group, an aryloxy group. A group, an amino group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkylcarbonyl group, an arylcarbonyl group, an alkylthio group, an arylthio group, or a halogen atom. The number of substituents that the donor monomer unit may have is not particularly limited, and may have a plurality of substituents as long as substitution is possible. Further, when the donor monomer unit has a plurality of substituents, the substituents may have two or more kinds of substituents.

  Among these, D is preferably a structural unit represented by the following formula (III) because it is easily fixed on the same plane and is easily increased in wavelength by π conjugation.

  In formula (III), ring 1 and ring 2 each independently represent an aromatic hydrocarbon ring which may have a substituent or an aromatic heterocycle which may have a substituent.

  The aromatic hydrocarbon ring is not particularly limited, but is preferably an aromatic hydrocarbon having 6 to 30 carbon atoms. Specifically, monocyclic aromatic hydrocarbon such as benzene ring; condensed polycyclic such as naphthalene ring, indane ring, indene ring, phenanthrene ring, fluorene ring, anthracene ring, azulene ring, pyrene ring, perylene ring And aromatic hydrocarbons. Of these, a benzene ring or a naphthalene ring is preferable.

  The aromatic heterocyclic ring is not particularly limited, but is preferably an aromatic heterocyclic group having 2 to 30 carbon atoms. Specifically, monocyclic aromatic heterocycles such as thiophene ring, furan ring, pyridine ring, pyrimidine ring, thiazole ring, oxazole ring, triazole ring; or benzothiophene ring, benzofuran ring, benzothiazole ring, benzoxazole ring , Condensed polycyclic aromatic heterocycles such as benzotriazole ring and thiadiazolopyridine ring. Of these, a thiophene ring, a pyridine ring, a pyrimidine ring, a thiazole ring or an oxazole ring is preferable.

  The substituent that the aromatic hydrocarbon ring and the aromatic heterocyclic ring may have is not particularly limited, and examples thereof include the substituent that the donor monomer unit may have as described above. You may have a some substituent in the possible range. Moreover, when an aromatic hydrocarbon ring or an aromatic heterocyclic ring has a some substituent, you may have 2 or more types of substituents.

  Among these, the ring 1 and the ring 2 are each independently more preferably an aromatic hydrocarbon having 2 to 6 carbon atoms or an aromatic heterocyclic ring having 2 to 6 carbon atoms. The following aromatic heterocycles are particularly preferred. Specific examples include a furan ring or a thiophene ring, and a thiophene ring is particularly preferable.

In formula (III), X ¹ represents Q ¹ (R ³ ) (R ⁴ ). Q ¹ represents an atom selected from Group 14 elements of the periodic table, preferably a carbon atom, a silicon atom, or a germanium atom.

R ³ and R ⁴ each represent a group bonded to Q ¹ , and each independently represents a hydrogen atom or a monovalent organic group. R ³ and R ⁴ may be the same group or different from each other.

  The monovalent organic group is not particularly limited, but may have an aliphatic hydrocarbon group that may have a substituent, an aromatic hydrocarbon group that may have a substituent, or a substituent. And an aliphatic heterocyclic group which may be substituted or an aromatic heterocyclic group which may have a substituent.

  Examples of the aliphatic hydrocarbon group include a linear aliphatic hydrocarbon group, a branched aliphatic hydrocarbon group, and a cyclic aliphatic hydrocarbon group. The number of carbon atoms of the aliphatic hydrocarbon group is preferably 1 or more, more preferably 3 or more, still more preferably 4 or more, while the number of carbons is preferably 30 or less. , 20 or less, more preferably 16 or less, and particularly preferably 12 or less.

  Examples of the linear aliphatic hydrocarbon group include a linear alkyl group, a linear alkenyl group, and a linear alkynyl group.

  The linear alkyl group is not particularly limited, and examples thereof include n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, An n-undecyl group or an n-dodecyl group may be mentioned.

  The straight-chain alkenyl group is not particularly limited, and examples thereof include 2-butenyl group, 3-butenyl group, 4-pentenyl group, 5-hexenyl group, 6-heptenyl group, 7-octenyl group, 8-nonenyl group, A 9-decenyl group, a 10-undecenyl group, an 11-dodecenyl group, or a 12-tridecenyl group may be mentioned.

  The straight-chain alkynyl group is not particularly limited, but 2-butynyl group, 3-butynyl group, 4-pentynyl group, 5-hexynyl group, 6-heptynyl group, 7-octynyl group, 8-noninyl group, 9- A decynyl group, 10-undecynyl group, or 11-dodecynyl group is mentioned.

  Examples of the branched aliphatic hydrocarbon group include a branched alkyl group, a branched alkenyl group, and a branched alkynyl group.

  Examples of the branched alkyl group include a branched primary alkyl group, a branched secondary alkyl group, and a branched tertiary alkyl group. The branched primary alkyl group means a branched alkyl group having two hydrogen atoms bonded to a carbon atom having a free valence. The branched secondary alkyl group means a branched alkyl group having one hydrogen atom bonded to a carbon atom having a free valence. The branched tertiary alkyl group means a branched alkyl group having no hydrogen atom bonded to a carbon atom having a free valence. Here, the free valence refers to a substance that can form a bond with another free valence as described in the organic chemistry / biochemical nomenclature (above) (Revised 2nd edition, Nankodo, 1992).

  The branched primary alkyl group is not particularly limited, and examples thereof include 2-ethylhexyl group, 2-methylpropyl group, 2-ethylhexyl group, 2,2-dimethylpropyl group, 2-methylbutyl group, 2-ethylbutyl group, 2,4-dimethylhexyl group, 2-methylpentyl group, 2,4,4-trimethylpentyl group, 2,3-dimethylbutyl group, 2,6-dimethylheptyl group, 2,2-dimethylbutyl group, 2 -Methylheptyl group, 2-butyloctyl group, 2-methylnonyl group, 2-propylpentyl group, 2-methylundecyl group, 2-methyloctyl group, 2-methyldecyl group or 2,5-dimethylhexyl group .

  The branched secondary alkyl group is not particularly limited. For example, 1-methylpropyl group, 1-methylbutyl group, 1-methylheptyl group, 1-propylpentyl group, 1-ethylhexyl group, 1-methylpentyl group, 1-ethylpentyl group, 1-methyloctyl group, 1-ethylbutyl group, 1-ethyl-2-methylpropyl group, 1,5-dimethylhexyl group, 1-butylheptyl group, 1,2-dimethylpropyl group, 1 , 3-dimethylbutyl group, 1-ethyloctyl group, 1-propylhexyl group, 1,2-dimethylpentyl group, 4-ethyl-1-methyloctyl group, 4-methyl-1-propylhexyl group, 1,3 -Dimethylpentyl group, 1-ethyl-2-methylpentyl group, 1,2-dimethylpentyl group, 1-butylhexyl group, 1,3,5-trimethylhexyl Group, 3-ethyl-1,5-dimethyl-nonyl group or a 1-propylheptyl group.

  The branched tertiary alkyl group is not particularly limited, and examples thereof include a t-butyl group, 1- (1-methylethyl) -1-methylpentyl group, 1-ethyl-1,3,3-trimethylbutyl group, 1-ethyl-1,3-dimethylpentyl group, 3-ethyl-1,1-dimethylpentyl group, 2-ethyl-1,1-dimethylpentyl group, 1,1,3,4-tetramethylpentyl group, 1 , 1,3,3-tetramethylpentyl group, 1,1,4-trimethylhexyl group, 1,1,3-trimethylhexyl group, 1,1,2-trimethylhexyl group, 1,1-diethyl-2- Methylpropyl group, 1-ethyl-1,2-dimethylpropyl group, 1,1-dipropylpentyl group, 1,1,5-trimethylhexyl group, 1-butyl-1-ethylhexyl group, 1,1,4- Trimethylpentyl 1- (2-methylpropyl) -1-methylpentyl group, 1,3-dimethyl-1- (2-methylpropyl) butyl group, 3-methyl-1- (2-methylpropyl) butyl group, 1- Ethyl-1-propylpentyl group, 1-ethyl-1,2,2-trimethylpropyl group, 1,1,2,3,3-pentamethylhexyl group, 1,1-dimethylnonyl group, 1-ethyl-1 , 4-dimethylpentyl group, 1,1,2-trimethylpropyl group, 1,1-dimethylheptyl group, 1-ethyl-1-methylpentyl group, 1,1-dimethyldecyl group, 1,1-dimethyloctyl group 1,1-bis (1-methylethyl) -2-methylpropyl group, 1- (1-methylethyl) -1,2-dimethylbutyl group, 1- (2-methylpropyl) -1,3,3 A trimethylbutyl group, -Ethyl-1,3-dimethylbutyl group, 1,1-diethylpropyl group, 1,1-dimethylpentyl group, 1-propyl-1,2-dimethylbutyl group, 2-methyl-1- (1-methylethyl ) Propyl group, 1,1-dipropylbutyl group, 1,1,3,3-tetramethylbutyl group, 1,4-dimethyl-1- (2-methylpropyl) pentyl group, 1-butyl-1,4 -Dimethylpentyl group, 1-butyl-1-ethylpentyl group, 1-butyl-1-methylpentyl group, 1-ethyl-1-methylhexyl group, 1-methyl-1-propylpentyl group, 1-ethyl-1 -A methylpropyl group or a 1,1,2,2-tetramethylpropyl group is mentioned.

  The branched alkenyl group is not particularly limited, and examples thereof include a 2-methyl-2-propenyl group, a 3-methyl-3-butenyl group, and a 4-methyl-2-hexenyl group.

  The branched alkynyl group is not particularly limited, and examples thereof include a 1-methyl-2-propynyl group, a 2-methyl-3-butynyl group, and a 4-methyl-2-hexynyl group.

  The aromatic hydrocarbon group is not particularly limited, and examples thereof include a monocyclic aromatic hydrocarbon group, a polycyclic aromatic hydrocarbon group, and a condensed polycyclic aromatic hydrocarbon group. The aromatic hydrocarbon group preferably has 6 or more carbon atoms, while the carbon number is preferably 30 or less, more preferably 20 or less, and particularly preferably 14 or less. Specific examples include a phenyl group, a naphthyl group, an indanyl group, an indenyl group, a fluorenyl group, an anthracenyl group, and an azulenyl group. Of these, a phenyl group is preferred.

  The aliphatic heterocyclic group is not particularly limited, but the aliphatic heterocyclic group preferably has 2 or more carbon atoms, while the carbon number is preferably 30 or less, and 14 or less. Is more preferably 10 or less, and particularly preferably 6 or less. Specific examples include an oxetanyl group, a pyrrolidinyl group, a tetrahydrofuryl group, a tetrahydrothienyl group, a piperidinyl group, a tetrahydropyranyl group, and a tetrahydrothiopyranyl group.

  The aromatic heterocyclic group is not particularly limited, and examples thereof include a monocyclic aromatic heterocyclic group, a polycyclic aromatic heterocyclic group, and a condensed polycyclic aromatic heterocyclic group. The aromatic heterocyclic group preferably has 2 or more carbon atoms, while the carbon number is preferably 30 or less, more preferably 20 or less, and particularly preferably 14 or less. preferable. Specifically, thienyl, furanyl, pyridyl, pyrrolyl, imidazolyl, pyrimidyl, thiazolyl, oxazolyl, isoxazolyl, isothiazolyl, pyrazolyl, triazolyl, benzothiophenyl, benzofuranyl, benzothiazolyl Group, benzoxazolyl group or benzotriazolyl group. Among these, a thienyl group, a pyridyl group, a pyrimidyl group, a thiazolyl group, or an oxazolyl group can be given.

  In addition, the substituent which the above-mentioned aliphatic hydrocarbon group, aromatic hydrocarbon group, aliphatic heterocyclic group, and aromatic heterocyclic group may have is not particularly limited. For example, an aliphatic hydrocarbon group, an aromatic hydrocarbon group, an aliphatic heterocyclic group, or an aromatic heterocyclic group, an alkoxy group, an aryloxy group, an amino group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkylcarbonyl group, An arylcarbonyl group, an alkylthio group, an arylthio group, or a halogen atom is exemplified. Moreover, you may have 2 or more types of substituents. Furthermore, these substituents may further have another substituent.

Among the above, R ³ and R ⁴ are each independently a linear aliphatic hydrocarbon group having 4 to 12 carbon atoms or a branched aliphatic hydrocarbon group having 4 to 12 carbon atoms. It is preferable that For example, an n-octyl group, 2-ethylhexyl group, etc. are mentioned.

In the above formula (III), X ² represents a single bond, O, S, N (R ⁵ ), or Q ² (R ⁶ ) (R ⁷ ). Q ² represents an atom selected from Group 14 elements of the periodic table, and examples thereof include a carbon atom, a silicon atom, or a germanium atom, and a silicon atom is particularly preferable.

R ⁵ represents a group bonded to N, and R ⁶ and R ⁷ each independently represents a group bonded to Q ² . R ^{5 to} R ⁷ are each a hydrogen atom or a monovalent organic group, and specific examples thereof include the groups described for R ³ and R ⁴ , and preferred groups are also the same.

Among these, X ² is preferably a single bond, O, S, Q ² (R ⁶ ) (R ⁷ ). In addition, in order to obtain good intermolecular carrier transfer without excessively increasing the steric hindrance on ring 1 and ring 2, X ² is more preferably a single bond, O or S, and particularly preferably a single bond. .

Among the above-mentioned donor monomer units represented by the formula (III), both ring 1 and ring 2 are thiophene rings, X ¹ is Q ¹ (R ³ ) (R ⁴ ), and X ² is It is preferably a structural unit represented by the following formula (IV) which is a single bond.

In formula (IV), Q ¹ has the same meaning as Q ¹ listed in the description of formula (III).

In formula (IV), R ³ and R ⁴ have the same meanings as R ³ and R ⁴ mentioned in the description of formula (III).

  In the above formula (I), A1 represents an acceptor monomer unit as described above. The acceptor monomer unit is not particularly limited as long as it has the properties as an acceptor. For example, benzothiadiazole, naphthobisthiadiazole, diketopyrrolopyrrole, thienothiophene, thiazole, thiadiazole, oxazole, oxadiazole, Examples include pyridine, pyrimidine, quinoxaline, thienopyrazine, imidothiophene, and fluorobenzene. Moreover, the acceptor-type monomer unit of a nonpatent literature (Macromolecules 2012,45,607-632) is mentioned.

  These acceptor monomer units may have a substituent. The substituent that the acceptor monomer unit may have is not particularly limited, and examples thereof include the substituent that the donor monomer unit described above may have.

  Among these, A1 is preferably a structural unit represented by the following formula (V).

In the formula (V), X ³ represents an atom selected from Group 16 elements of the periodic table, and specifically represents an oxygen atom, a sulfur atom, a selenium atom, or a tellurium atom. Among these, from the viewpoint of ease of synthesis, X ³ is preferably an oxygen atom or a sulfur atom, and particularly preferably a sulfur atom.

In formula (V), R ⁸ may be a hydrogen atom or a monovalent organic group. The monovalent organic group is not particularly limited, but may have an aliphatic hydrocarbon group that may have a substituent, an aromatic hydrocarbon group that may have a substituent, or a substituent. And an aliphatic heterocyclic group which may be substituted and an aromatic heterocyclic group which may have a substituent. Specific groups of the aliphatic hydrocarbon group, the aromatic hydrocarbon group, the aliphatic heterocyclic group, and the aromatic heterocyclic group are not particularly limited, but are the groups described above for R ³ and R ^4. And the same groups. Moreover, the substituent which these groups may have also includes the same substituents as those described for R ³ and R ⁴ described above.

Among these, R ⁸ is preferably a linear aliphatic hydrocarbon group which may have a substituent or an aromatic hydrocarbon group which may have a substituent. When R ⁸ is an aromatic hydrocarbon group, the aromatic hydrocarbon group preferably has an alkoxy group or an aliphatic hydrocarbon group as a substituent in order to improve solubility and conversion efficiency.

  In addition, the preferable form of the repeating unit represented by the formula (I) which the copolymer according to the present invention has is preferably a structural unit represented by the above formula (III) and A1 represented by the above formula (V). Is a combination.

  Below, the specific form of the repeating unit represented by the formula (I) which the copolymer which concerns on this invention has is illustrated. However, in the present invention, the repeating unit represented by the formula (I) is not limited to the following.

  As described above, the copolymer according to the present invention has a repeating unit represented by the following formula (II).

In formula (II), L is an alkenylene group, an alkynylene group, a divalent aromatic hydrocarbon group, or a divalent aromatic heterocyclic group, which may have a substituent. However, the carbon atom located in the α-position among the carbon atoms constituting L does not have a substituent or is substituted with a fluorine atom. In the present invention, the carbon atom located at the α-position among the carbon atoms constituting L is a thiophene ring having R ¹ among the carbon atoms constituting L described in formula (II). And a carbon atom located next to the carbon atom bonded to the thiophene ring having R ² .

  The alkenylene group is not particularly limited, but is preferably an alkenylene group having 2 to 8 carbon atoms. For example, a vinylene group is mentioned.

  The alkynylene group is not particularly limited, but an alkynylene group having 2 to 8 carbon atoms is preferable. For example, an ethynylene group can be mentioned.

  The divalent aromatic hydrocarbon group is not particularly limited and may be any of monocyclic, polycyclic and condensed polycyclic. The monocyclic aromatic hydrocarbon group is not particularly limited, and examples thereof include phenylene and fluorophenylene groups. Examples of the polycyclic aromatic hydrocarbon group include a biphenylene group, a terphenylene group, and a quaterphenylene group. Examples of the condensed polycyclic aromatic hydrocarbon group include naphthylene and anthracenylene groups.

  The divalent aromatic heterocyclic group is not particularly limited, and may be monocyclic, polycyclic, or condensed polycyclic. Examples of the monocyclic aromatic heterocyclic group include pyrrolenylene, furanylene, and thienylene groups. Examples of the polycyclic aromatic heterocyclic group include bipyrrolenylene, terpyrrolenylene, bifuranylene, terfuranylene, bithienylene group, and tertienylene group. Examples of the condensed polycyclic aromatic heterocyclic group include indoleylene, benzofuranylene, benzothienylene, and thienothienylene groups.

In addition, in addition to the structural unit represented by the said formula (I), the copolymer which concerns on this invention has the following advantages by having the structural unit represented by the said formula (II). That is, the structural unit represented by the formula (II) has a thiophene ring having a substituent (R ¹ ) at a specific position and a thiophene ring having a substituent (R ² ) at a specific position. Therefore, the solubility of the polymer is improved by a synergistic effect with the structural unit represented by the above formula (I), and when the polymer is used in the active layer, the molecules are regularly arranged and the structure is stable. It is thought that. In particular, in the structural unit represented by the above formula (II), L bonded to these thiophene rings is located between the thiophene ring having the substituent R ¹ and the thiophene ring having the substituent R ^2. Therefore, it is considered that the steric hindrance between the two substituents (R ¹ and R ² ) is less likely to occur, and the π stacking property between molecules is improved.

In addition, as described above, the alkenylene group, alkynylene group, divalent aromatic hydrocarbon group, and divalent aromatic heterocyclic group may have a substituent, but in the carbon atoms constituting L, And the carbon atom located at the α-position has no substituent or is substituted with a fluorine atom, L, a thiophene ring having the substituent R ^1, and a thiophene ring having the substituent R ² Since the steric hindrance is suppressed, it is considered that high intermolecular π stacking property can be obtained. As a result, it is considered that the intermolecular arrangement is stabilized and the light resistance of the photoelectric conversion element is improved by using the copolymer according to the present invention in the active layer of the photoelectric conversion element.

  In addition, the substituent which the carbon atom other than the carbon atom located at the α-position among the carbon atoms constituting L may have is not particularly limited, and examples thereof include an aliphatic hydrocarbon group and an aromatic carbon group. A hydrogen group, an aromatic heterocyclic group, an alkoxy group or a halogen atom is exemplified.

  Among these, from the viewpoints that adjacent rings are likely to be coplanar, improve intramolecular carrier movement, have excellent π stack between molecules, and improve carrier movement between molecules, L is represented by the following formula: A group represented by any one of (XI) to (XIII) is preferable.

In formula (XI), formula (XII) and formula (XIII), R ^{21 to} R ²⁶ each independently represents a hydrogen atom or a fluorine atom. Moreover, in formula (XI), n represents the integer of 1-3. Among these, L is preferably a group represented by the above formula (XI), and n is particularly preferably 2.

In formula (II), R ¹ and R ² each independently represents a monovalent organic group. The monovalent organic group is not particularly limited, but has an aliphatic hydrocarbon group that may have a substituent, an aromatic hydrocarbon group that may have a substituent, and a substituent. Examples thereof include an aliphatic heterocyclic group which may be substituted, an aromatic heterocyclic group which may have a substituent, and an alkoxy group which may have a substituent. By using R ¹ and R ² as the above group, the solubility of the copolymer having the structural unit in the solvent is improved as compared with the case where R ¹ and R ² are hydrogen atoms. Therefore, for example, when the copolymer according to the present invention is used in an active layer of a photoelectric conversion element as described later, an improvement in processability can be expected, and an active layer having a uniform film quality can be formed. In addition, as described above, the copolymer having the structural unit is easily oriented in a certain direction by having a substituent at a specific position, so that it contributes to a longer wavelength and the carrier movement proceeds smoothly. Thus, improvement in conversion efficiency can be expected. It is also considered that the π stacking property between molecules is improved.

The aliphatic hydrocarbon group, aromatic hydrocarbon group, aliphatic heterocyclic group, and aromatic heterocyclic group are not particularly limited, but specifically, the same groups as those described for R ³ and R ⁴ Is mentioned.

  The alkoxy group is not particularly limited, but the number of carbon atoms of the alkoxy group is preferably 1 or more, more preferably 3 or more, particularly preferably 5 or more, while 30 or less. It is preferably some, more preferably 20 or less, and particularly preferably 14 or less. Specific examples include a hexyloxy group, an octyloxy group, a nonyloxy group, a decyloxy group, a dodecyloxy group, and a tetradecyloxy group.

R ¹ and R ² are preferably each independently an aliphatic hydrocarbon group or an alkoxy group in order to further suppress steric hindrance among the groups described above, and when used as an organic thin film solar cell. An aliphatic hydrocarbon group is particularly preferable because the open circuit voltage tends to increase.

Further, in order to suppress steric hindrance and improve conversion efficiency, R ¹ and R ² are straight aliphatic hydrocarbon groups having 6 to 14 carbon atoms among aliphatic hydrocarbon groups. Is preferred. Specifically, an n-octyl group, an n-decyl group, or an n-dodecyl group can be given.

  In formula (II), A2 represents an acceptor monomer unit. A2 is not particularly limited, and specific examples include the acceptor monomer units listed in A1. A1 and A2 may be the same acceptor monomer units or different acceptor monomer units. However, A1 and A2 are preferably the same structural unit in order to suppress carrier traps in the molecule and cause carrier movement smoothly. From the above viewpoint, when A1 is a repeating unit represented by the above formula (V), A2 is preferably a structural unit represented by the following formula (VI).

In the formula (VI), X ⁴ represents an atom selected from Group 16 elements of the periodic table, and specifically includes an oxygen atom, a sulfur atom, a selenium atom, or a tellurium atom, among which an oxygen atom or A sulfur atom is preferred, and a sulfur atom is particularly preferred.

In formula (VI), R ⁹ represents a hydrogen atom or a monovalent organic group. The monovalent organic group is not particularly limited, but may have an aliphatic hydrocarbon group that may have a substituent, an aromatic hydrocarbon group that may have a substituent, or a substituent. And an aliphatic heterocyclic group which may be substituted or an aromatic heterocyclic group which may have a substituent. The aliphatic hydrocarbon group, the aromatic hydrocarbon group, the aliphatic heterocyclic group, and the aromatic heterocyclic group are not particularly limited, but include the same groups as R ^8, and preferred groups are also listed as R ⁸ . And the same groups as those mentioned above. R ⁹ in the formula (VI) may be the same as or different from R ⁸ in the formula (V), but R ⁸ and R ⁹ are preferably the same group.

  Below, the form of the copolymer which concerns on this invention is illustrated. However, the copolymer according to the present invention is not limited to the following.

  In the copolymer according to the present invention, the repeating unit represented by the above formula (I) and the repeating unit represented by the above formula (II) can be arbitrarily selected. Is a structural unit represented by the above formula (IV), A1 in the above formula (I) is a structural unit represented by the above formula (V), and A2 in the above formula (II) is A copolymer that is a structural unit represented by the above formula (VI) is preferable.

  The arrangement state of the repeating unit represented by the above formula (I) and the repeating unit represented by the above formula (II) in the copolymer according to the present invention may be alternating, block or random. That is, the copolymer according to the present invention may be an alternating copolymer, a block copolymer, or a random copolymer. In addition, a copolymer having an intermediate structure among these copolymers, for example, a random copolymer having a block property may be used. Also included are copolymers and dendrimers that are branched in the main chain and have three or more terminal portions. Among these, a block copolymer or a random copolymer is preferable because it is easy to synthesize and regularity can be lowered, and the solubility of the copolymer is improved and the storage stability of the ink in which the copolymer is dissolved is improved. In view of this, a random copolymer is more preferable.

  In addition, the copolymer according to the present invention may have two or more kinds of repeating units represented by the above formula (I). Similarly, you may have 2 or more types of repeating units represented by the said formula (II).

  The terminal portion of the polymer having the repeating unit represented by the formula (I) and the repeating unit represented by the formula (II) is not particularly limited, but may be an aromatic hydrocarbon ring, an aromatic heterocyclic ring, or hydrogen. It is preferably end-gapped with atoms.

  Further, in the copolymer having the repeating unit represented by the formula (I) and the repeating unit represented by the formula (II), the ratio of each repeating unit is not particularly limited, but the repeating unit represented by the formula (I) The ratio of the repeating unit represented by the formula (II) to the unit is such that the units represented by the formula (II) are sufficiently π-stacked so that many intermolecular carrier paths are formed, and light is irradiated. Even when a part is damaged, the decrease in photoelectric conversion efficiency is suppressed, so that it is preferably 0.1 or more, more preferably 0.3 or more, and particularly preferably 0.4 or more. preferable. On the other hand, the ratio of the repeating unit represented by the formula (II) to the repeating unit represented by the formula (I) increases the contribution of the π stack and increases the solubility as the unit represented by the formula (II) increases. In order to be considered to become low, it is preferably 10 or less, more preferably 8 or less, and particularly preferably 3 or less.

  In addition, the copolymer according to the present invention includes a repeating unit other than the repeating unit represented by the formula (I) and the repeating unit represented by the formula (II) as long as the effects of the present invention are not impaired. May be. Although the repeating unit which may be specifically contained is not particularly limited, the donor monomer unit and the acceptor monomer mentioned in D and A1 in the above formula (I) and A2 in the formula (II) And repeating units composed of units.

The polystyrene-reduced weight average molecular weight (Mw) of the copolymer according to the present invention is not particularly limited, but is usually 5.0 × 10 ³ or more, preferably 1.0 × 10 ⁴ or more, more preferably 1.5 ×. 10 ⁴ or more, more preferably 2.0 × 10 ⁴ or more, still more preferably 3.0 × 10 ⁴ or more, and particularly preferably 4.0 × 10 ⁵ or more. On the other hand, it is preferably 1.0 × 10 ⁷ or less, more preferably 1.0 × 10 ⁶ or less, and particularly preferably 5.0 × 10 ⁵ or less. The weight average molecular weight is preferably in this range from the viewpoint of increasing the light absorption wavelength, from the viewpoint of realizing high absorbance, from the viewpoint of realizing high carrier movement, and from the viewpoint of solubility in an organic solvent.

The polystyrene-reduced number average molecular weight (Mn) of the copolymer according to the present invention is not particularly limited, but is usually 3.0 × 10 ³ or more, preferably 5.0 × 10 ³ or more, more preferably 8.0 ×. 10 ³ or more, more preferably 1.0 × 10 ⁴ or more, and particularly preferably 2.0 × 10 ⁴ or more. On the other hand, preferably 1.0 × 10 ⁷ or less, more preferably 1.0 × 10 ⁶ or less, further preferably 5.0 × 10 ⁵ or less, even more preferably 2.0 × 10 ⁵ or less, and particularly preferably 1 0.0 × 10 ⁵ or less. The number average molecular weight is preferably in this range from the viewpoint of increasing the light absorption wavelength, from the viewpoint of realizing high absorbance, from the viewpoint of realizing high carrier movement, and from the viewpoint of solubility in an organic solvent.

  The molecular weight distribution (PDI, (weight average molecular weight / number average molecular weight (Mw / Mn))) of the copolymer according to the present invention is usually 1.0 or more, preferably 1.1 or more, more preferably 1.2 or more, Preferably it is 1.3 or more. On the other hand, it is usually 50.0 or less, preferably 20.0 or less, more preferably 15.0 or less, and still more preferably 10.0 or less. The molecular weight distribution is preferably in this range in that the solubility of the copolymer can be in a range suitable for coating.

  The polystyrene-reduced weight average molecular weight, number average molecular weight, and molecular weight distribution of the copolymer according to the present invention can be determined by gel permeation chromatography (GPC). Specifically, two Polymer Laboratories GPC columns (PLgel MIXED-B 10 μm inner diameter 7.5 mm, length 30 cm) are connected in series as a column, LC-10AT (manufactured by Shimadzu Corporation) as a pump, and an oven It can be measured by using CTO-10A (manufactured by Shimadzu Corp.), a differential refractive index detector (manufactured by Shimadzu Corp .: RID-10A), and a UV-vis detector (manufactured by Shimadzu Corp .: SPD-10A). As a measuring method, a copolymer (1 mg) to be measured is dissolved in chloroform (200 mg), and 1 μL of the obtained solution is injected into a column. Using o-dichlorobenzene as the mobile phase, measurement is performed at 80 ° C. and a flow rate of 1.0 mL / min. For the analysis, LC-Solution (manufactured by Shimadzu Corporation) is used.

  The solubility of the copolymer according to the present invention is not particularly limited, but preferably the solubility in chlorobenzene at 25 ° C. is usually 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 1% by mass or more. On the other hand, it is usually 30% by mass or less, preferably 20% by mass. High solubility is preferable because a thicker film can be formed by coating.

  The copolymer according to the present invention preferably has an appropriate interaction between molecules. In the present specification, the interaction between molecules means that the distance between polymer chains is shortened by an interaction such as π-π stacking between molecules. The stronger the interaction, the higher the mobility and / or crystallinity, and the more suitable the semiconductor material is. That is, in a copolymer that interacts between molecules, electron transfer between molecules is likely to occur. For example, when the copolymer according to the present invention is used in an active layer in a photoelectric conversion element, a p-type semiconductor compound in the active layer is used. It is considered that holes generated at the interface between the n-type semiconductor compound and the n-type semiconductor compound can be efficiently transported to the electrode (anode).

  An example of a crystallinity measuring method is an X-ray diffraction method (XRD). In this specification, having crystallinity means that an X-ray diffraction spectrum obtained by XRD measurement has a diffraction peak. Having crystallinity is considered to mean that it has a laminated structure in which molecules are arranged, and is preferable in that the active layer described later tends to be thickened. XRD measurement can be performed based on a method described in a known document (X-ray crystal analysis guide (applied physics selection book 4)).

The hole mobility (sometimes referred to as hole mobility) of the copolymer according to the present invention is usually 1.0 × 10 ⁻⁷ cm ² / Vs or more, preferably 1.0 × 10 ⁻⁶ cm ² / Vs or more. More preferably, it is 1.0 × 10 ⁻⁵ cm ² / Vs or more, and particularly preferably 1.0 × 10 ⁻⁴ cm ² / Vs or more. On the other hand, the hole mobility of the copolymer according to the present invention is usually 1.0 × 10 ⁴ cm ² / Vs or less, preferably 1.0 × 10 ³ cm ² / Vs or less, and more preferably 1.0 × 10 6. ² cm ² / Vs or less, particularly preferably 1.0 × 10 cm ² / Vs or less. When the hole mobility is in this range, the copolymer according to the present invention is suitably used as a semiconductor material. Further, in order to obtain high conversion efficiency in the photoelectric conversion element, it is important to balance the mobility of the n-type semiconductor compound and the mobility of the p-type semiconductor compound. When the copolymer according to the present invention is used as a p-type semiconductor compound in a photoelectric conversion element, from the viewpoint of bringing the hole mobility of the copolymer according to the present invention close to the electron mobility of the n-type semiconductor compound, the copolymer according to the present invention is positive. The hole mobility is preferably within this range. As a method for measuring the hole mobility, there is an FET method. The FET method can be performed by a method described in a known document (Japanese Patent Laid-Open No. 2010-045186).

  The copolymer according to the present invention preferably has high storage stability in a solution state. High storage stability means that it is difficult to aggregate when made into a solution. More specifically, 2 mg of the copolymer according to the present invention was placed in a 2 mL screw vial, dissolved in o-xylene to a concentration of 1.5% by mass, and then cooled to room temperature. Then, it is preferable not to gel for 5 minutes or more, and it is more preferable not to gel for 1 hour or more.

  The impurities in the copolymer according to the present invention are preferably as few as possible. In particular, when a copolymer having a repeating unit represented by the formula (1) is synthesized, when a transition metal catalyst such as palladium or copper is used, these may remain in the copolymer. If these metal catalysts remain in the copolymer, exciton traps due to the heavy atom effect of the transition metal occur and charge transfer is inhibited. As a result, when the copolymer according to the present invention is used in a photoelectric conversion element, There is a risk of reducing the conversion efficiency. Therefore, the concentration of the transition metal catalyst is usually 1000 ppm or less, preferably 500 pm or less, more preferably 100 ppm or less per 1 g of copolymer. On the other hand, it is usually larger than 0 ppm and may be 1 ppm or more, or 3 ppm or more.

  The impurities contained in the copolymer can be measured by, for example, ICP mass spectrometry. ICP mass spectrometry can be carried out by a method described in a known document (“Plasma ion source mass spectrometry” (Academic Publishing Center)). Specifically, about palladium atom and copper atom, after wet-decomposing the sample, Pd and Sn in the decomposition solution are analyzed by a calibration curve method using an ICP mass spectrometer (ICP mass spectrometer 7500ce type manufactured by Agilent Technologies). It can be quantified.

<2. Method for producing copolymer according to the present invention>
The method for producing the copolymer of the present invention is not particularly limited. The compound represented by the following formula (VII), the compound represented by the formula (VIII), the compound represented by the formula (IX), and the formula A method of polymerizing the compound represented by (X) in the presence of an appropriate catalyst if necessary.
When producing a copolymer in which A1 in formula (I) and A2 in formula (II) are the same, a compound represented by formula (VII), a compound represented by formula (VIII), A compound represented by the formula (IX) (or a compound represented by the formula (X)) can be produced according to a polymerization reaction described later. In the case of producing a copolymer in which A1 in formula (I) and A2 in formula (II) are different, as an example, a compound represented by formula (VII) and a formula (IX) Intermediate 1 obtained by a polymerization reaction with a compound, a compound represented by formula (VIII), and an intermediate 2 obtained by a polymerization reaction with a compound represented by formula (X). The copolymer according to the present invention can be produced by synthesizing the intermediate 1 and the intermediate 2 by the polymerization reaction described later.

In the above formula (VII), D has the same meaning as D in the above formula (I). In the above formula (VIII), L, R ¹ and R ² are as defined L in above-mentioned formula (II), and R ¹ and R ^2. In formula (IX), A1 has the same meaning as A1 in formula (I). In the above formula (X), A2 has the same meaning as A2 in the above formula (II).

Y1 to Y8 in the formula (VII) to the formula (X) can be appropriately selected according to the kind of the polymerization reaction and are not particularly limited, but are independently a halogen atom, an alkylstannyl group, or an alkylsulfo group. , Arylsulfo group, arylalkylsulfo group, boric acid ester residue, sulfonium methyl group, phosphonium methyl group, phosphonate methyl group, monohalogenated methyl group, boric acid residue (-B (OH) ₂ ), formyl group, An alkenyl group or an alkynyl group is represented.

  The halogen atom is not particularly limited, but is preferably a bromine atom or an iodine atom.

  The borate ester residue is not particularly limited, and examples thereof include a group represented by the following formula.

  In the formula, Me represents a methyl group, and Et represents an ethyl group.

  The alkylstannyl group is not particularly limited, and examples thereof include a group represented by the following formula.

  In the formula, Me represents a methyl group, and Bu represents a butyl group.

  The alkenyl group is not particularly limited, but for example, an alkenyl group having 2 to 12 carbon atoms is preferable.

Among the above, Y1 to Y8 are each independently a halogen atom, an alkylstannyl group, from the viewpoint of the synthesis of the compounds represented by the formulas (VII) to (X) and the ease of reaction. A boric acid ester residue or a boric acid residue (—B (OH) ₂ ) is preferable.

Examples of the reaction method used for the polymerization of the copolymer of the present invention include Suzuki-Miyaura cross-coupling reaction method, Stille coupling reaction method, Yamamoto coupling reaction method, Grignard reaction method, Heck reaction method, Sonogashira reaction method, FeCl _{3 and the} like. A reaction method using an oxidizing agent, a method using an electrochemical oxidation reaction, a reaction method by decomposition of an intermediate compound having an appropriate leaving group, and the like. Among these, the Suzuki-Miyaura coupling reaction method, the Stille coupling reaction method, the Yamamoto coupling reaction method, and the Grignard reaction method are preferable in terms of easy structure control. In particular, the Suzuki-Miyaura cross-coupling reaction method, the Stille coupling reaction method, and the Grignard reaction method are preferable from the viewpoint of easy availability of materials and easy reaction operation. These reactions are described in "Cross Coupling-Fundamentals and Industrial Applications (CMC Publishing)", "Transition Metal Catalyzed Reactions for Organic Synthesis (edited by Jiro Jiro: edited by Organic Synthetic Chemical Society)", "For Organic Synthesis" The reaction can be carried out according to a method described in known literature such as “catalytic reaction 103 (Teijiro Hatakeyama: Tokyo Kagaku Dojin)”.

  As described above, Y1 to Y8 in the formulas (VII) to (X) may be appropriately selected to perform the polymerization reaction. For example, Y1 to Y4 in the formula (VII) and the formula (VIII) are alkylstannyl groups, and Y5 to Y8 in the formula (IX) and the formula (X) are used as a halogen atom. What is necessary is just to react according to conditions. Moreover, Y1-Y4 in Formula (VII) and Formula (VIII) is a borate ester residue or boric acid residue, Y5-Y8 in Formula (IX) and Formula (X) is a halogen atom, and is known as Suzuki. -The reaction may be performed according to the conditions of the Miyaura coupling reaction. Furthermore, Y1 to Y4 in formula (VII) and formula (VIII) are used as silyl groups, Y5 to Y8 in formula (IX) and formula (X) are used as halogen atoms, and the reaction is carried out according to known Hiyama coupling reaction conditions. Just do it. As a catalyst for the coupling reaction, for example, a combination of a transition metal such as palladium and a ligand (for example, a phosphine ligand such as triphenylphosphine) can be used.

  In addition, it is preferable to further end-treat the copolymer obtained by the polymerization reaction. By performing the terminal treatment of the copolymer, the residual amount of the terminal residues (Y1 to Y8 described above) of the copolymer can be reduced. By performing such a terminal treatment, halogen atoms, alkylstannyl groups, and the like in the obtained copolymer can be reduced. Therefore, when the copolymer according to the present invention is used for a photoelectric conversion element, conversion efficiency and durability are improved. This is preferable because of improved properties.

  Moreover, the process of isolate | separating a copolymer is normally performed after a polymerization reaction. When the terminal treatment of the copolymer is performed, it is preferable to perform a step of separating the copolymer after the terminal treatment. If necessary, further copolymer separation and purification may be performed prior to copolymer termination. From the viewpoint of obtaining the copolymer in a shorter processing step, it is preferable to carry out the terminal treatment of the copolymer, separation of the copolymer and purification of the copolymer in this order after the polymerization reaction.

  As a method for separating the copolymer, for example, the reaction solution and a poor solvent are mixed to precipitate the copolymer, or the active species in the reaction solution is quenched with water or hydrochloric acid, and then the copolymer is extracted with an organic solvent. Examples include a method of distilling off the organic solvent.

  Examples of the purification method of the copolymer include known methods such as reprecipitation purification, extraction using a Soxhlet extractor, gel permeation chromatography, or metal removal using a scavenger.

<2-1. Method for Producing Compound Represented by Formula (VII) to Formula (X)>
The method for producing the compounds represented by the formulas (VII) to (X) is not particularly limited, but can be carried out with reference to known examples. Known examples include Polymer, 1990, 31, 1379-1383, Adv. Mater. , 2007, 19, 4160-4165, Macromolecules, 2010, 43, 6936-6938, Adv. Mater. , 2011, 23, 3315-3319, Angew. Chem. Int. Ed. 2012, 51, 2068-2071, J. MoI. Mater. Chem. , 2011, 21, 3895-3902, J. Am. Am. Chem. Soc. , 2011, 133, 10062-10065 or Chem. Commun. , 2011, 47, 4920, WO2013 / 180243, and the like.

<3. Photoelectric conversion element>
The copolymer according to the present invention can be used as a material for a photoelectric conversion element. Specifically, by using the copolymer according to the present invention as a p-type semiconductor material for an active layer of a photoelectric conversion element, high conversion efficiency and high exposure can be obtained. A photoelectric conversion element having stability can be provided. Hereinafter, an embodiment of a photoelectric conversion element using the copolymer according to the present invention will be described.

  The photoelectric conversion element according to the present invention includes at least a base material, a pair of electrodes formed on the base material, and an active layer formed between the pair of electrodes. Hereinafter, an embodiment of a photoelectric conversion element according to the present invention will be described with reference to FIG.

  As shown in FIG. 1, one embodiment of the photoelectric conversion element according to the present invention includes a lower electrode 101, a lower buffer layer 102, an active layer 103, an upper buffer layer 104, and an upper electrode on a substrate 106. 105 have a layer structure in which are sequentially formed. In the present invention, the lower electrode means an electrode laminated on the substrate 106 side, and the upper electrode means an electrode laminated above the lower electrode when the substrate 106 is used as the bottom. . In the present invention, the lower electrode 101 and the upper electrode 105 may be collectively referred to as a pair of electrodes. In addition, the lower buffer layer 102 and the upper buffer layer 104 are not essential components, and may be provided arbitrarily, and may include only one of the lower buffer layer 102 and the upper buffer layer 104. Moreover, the photoelectric conversion element may optionally have another layer other than the above. Hereinafter, each component of the photoelectric conversion element will be described.

<3-1. Substrate 106>
The photoelectric conversion element 107 is usually formed on a base material 106 that serves as a support. There is no particular limitation on the material of the substrate 106. Preferable examples of the material of the substrate 106 include inorganic materials such as quartz, glass, sapphire, and titania, and flexible substrates. Specific examples of the flexible substrate include, but are not limited to, polyethylene terephthalate, polyethylene naphthalate, polyethersulfone, polyimide, nylon, polystyrene, polyvinyl alcohol, ethylene vinyl alcohol copolymer, fluororesin film, vinyl chloride. Or polyolefin such as polyethylene; organic material (resin substrate) such as cellulose, polyvinylidene chloride, aramid, polyphenylene sulfide, polyurethane, polycarbonate, polyarylate, polynorbornene, or epoxy resin; paper material such as paper or synthetic paper; stainless steel, Examples thereof include composite materials such as a metal foil such as titanium or aluminum whose surface is coated or laminated in order to impart insulation.

  Examples of the glass include soda glass, blue plate glass, and non-alkali glass. Among these, alkali-free glass is preferable in that there are few eluted ions from the glass.

  There is no restriction | limiting in the shape of the base material 106, For example, things, such as plate shape, a film form, or a sheet form, can be used.

  Although there is no restriction | limiting in the film thickness of the base material 106, Usually, it is 5 micrometers or more, Preferably it is 20 micrometers or more, On the other hand, it is 20 mm or less normally, Preferably it is 10 mm or less. It is preferable that the thickness of the substrate is 5 μm or more because the possibility that the strength of the photoelectric conversion element is insufficient is reduced. It is preferable that the thickness of the substrate 106 is 20 mm or less because the cost is suppressed and the mass is not increased. In addition, the film thickness when the material of the base material 106 is glass is usually 0.01 mm or more, preferably 0.1 mm or more, and is usually 1 cm or less, preferably 0.5 cm or less. It is preferable that the glass substrate has a film thickness of 0.01 mm or more because the mechanical strength increases and it is difficult to break. Moreover, it is preferable that the film thickness of the glass substrate is 0.5 cm or less because the mass does not increase.

<3-2. Pair of electrodes (lower electrode 101 and upper electrode 105)>
The pair of electrodes (101, 106) has a function of collecting holes and electrons generated by light absorption. Accordingly, the pair of electrodes includes an electrode suitable for collecting holes (hereinafter sometimes referred to as an anode) and an electrode suitable for collecting electrons (hereinafter sometimes referred to as a cathode). It is preferable to use it. Any one of the pair of electrodes may be translucent, and both may be translucent. Translucency means that sunlight passes through 40% or more. Further, the solar light transmittance of the transparent electrode is preferably 70% or more in order to allow light to reach the active layer through the transparent electrode. The light transmittance can be measured with a normal spectrophotometer.

  The anode is an electrode generally made of a conductive material having a work function higher than that of the cathode and having a function of smoothly extracting holes generated in the active layer.

  Examples of anode materials include conductive metal oxides such as nickel oxide, tin oxide, indium oxide, indium tin oxide (ITO), indium-zirconium oxide (IZO), titanium oxide, indium oxide, and zinc oxide. A metal such as gold, platinum, silver, chromium or cobalt, or an alloy thereof; These substances are preferable because they have a high work function, and further, a conductive polymer material represented by PEDOT: PSS in which a polythiophene derivative is doped with polystyrene sulfonic acid can be stacked. When laminating such a conductive polymer, the work function of this conductive polymer material is high, so even if it is not a material with a high work function as described above, it is suitable for cathodes such as Al and Mg. Metals can also be widely used. PEDOT: PSS in which a polythiophene derivative is doped with polystyrene sulfonic acid, or a conductive polymer material in which polypyrrole, polyaniline, or the like is doped with iodine or the like can also be used as an anode material.

  When the anode is a transparent electrode, it is preferable to use a light-transmitting conductive metal oxide such as ITO, zinc oxide or tin oxide, and ITO is particularly preferable.

  The film thickness of the anode is not particularly limited, but is usually 10 nm or more, preferably 20 nm or more, and more preferably 50 nm or more. On the other hand, it is usually 10 μm or less, preferably 1 μm or less, more preferably 500 nm or less. When the thickness of the anode is 10 nm or more, the sheet resistance is suppressed, and when the thickness of the anode is 10 μm or less, light can be efficiently converted into electricity without decreasing the light transmittance. When the anode is a transparent electrode, it is necessary to select a film thickness that can achieve both light transmittance and sheet resistance.

  The sheet resistance of the anode is not particularly limited, but is usually 1Ω / □ or more, on the other hand, 1000Ω / □ or less, preferably 500Ω / □ or less, more preferably 100Ω / □ or less.

  Examples of the anode forming method include a vacuum film forming method such as a vapor deposition method or a sputtering method, or a wet coating method in which an ink containing nanoparticles or a precursor is applied to form a film.

  The cathode is generally an electrode made of a conductive material having a low work function, and having a function of smoothly extracting electrons generated in the active layer 103. The cathode is adjacent to the electron extraction layer.

  Examples of cathode materials include platinum, gold, silver, copper, iron, tin, zinc, aluminum, indium, chromium, lithium, sodium, potassium, cesium, calcium, and magnesium, and alloys thereof; lithium fluoride And inorganic salts such as cesium fluoride and metal oxides such as nickel oxide, aluminum oxide, lithium oxide, and cesium oxide. These materials are preferable because they are materials having a low work function. Similarly to the anode, a material having a high work function can be used for the cathode by using an n-type semiconductor such as titania having conductivity as the electron extraction layer. From the viewpoint of electrode protection, the cathode material is preferably a metal such as platinum, gold, silver, copper, iron, tin, aluminum, calcium or indium, or an alloy using these metals such as indium / tin oxide. .

  The film thickness of the cathode is not particularly limited, but is usually 10 nm or more, preferably 20 nm or more, more preferably 50 nm or more. On the other hand, it is usually 10 μm or less, preferably 1 μm or less, more preferably 500 nm or less. When the film thickness of the cathode is 10 nm or more, the sheet resistance is suppressed, and when the film thickness of the cathode is 10 μm or less, light can be efficiently converted into electricity without decreasing the light transmittance. When the cathode is a transparent electrode, it is necessary to select a film thickness that achieves both light transmittance and sheet resistance.

  The sheet resistance of the cathode is not particularly limited, but is usually 1000Ω / □ or less, preferably 500Ω / □ or less, and more preferably 100Ω / □ or less. Although there is no restriction on the lower limit, it is usually 1Ω / □ or more.

  As a method for forming the cathode, there are a vacuum film formation method such as a vapor deposition method or a sputtering method, or a wet coating method in which an ink containing nanoparticles or a precursor is applied to form a film.

  Furthermore, the anode and the cathode may have a laminated structure of two or more layers. In addition, characteristics (electric characteristics, wetting characteristics, etc.) may be improved by performing surface treatment on the anode and the cathode.

<3-3. Active layer 103>
The active layer 103 is a layer that contains a p-type semiconductor compound and an n-type semiconductor compound and undergoes photoelectric conversion. Specifically, when the photoelectric conversion element 107 receives light, the light is absorbed by the active layer 103, electricity is generated at the interface between the p-type semiconductor material and the n-type semiconductor material, and the generated electricity is extracted from the anode and the cathode. It is.

  As the layer structure of the active layer 103, a thin film stack type in which a layer containing a p-type semiconductor compound and a layer containing an n-type semiconductor compound are stacked, or a layer in which a p-type semiconductor compound and an n-type semiconductor compound are mixed is used. A bulk heterojunction type. Note that the bulk heterojunction active layer may have a structure in which a layer containing a p-type semiconductor compound and / or a layer containing an n-type semiconductor compound is further stacked in addition to the mixed layer. From the viewpoint that high photoelectric conversion efficiency can be expected, a bulk heterojunction type is preferable.

  The p-type semiconductor compound contained in the active layer 103 contains the copolymer according to the present invention. When the active layer 103 contains the copolymer according to the present invention, a photoelectric conversion element having high conversion efficiency and high exposure stability can be obtained.

  The active layer 103 may contain other p-type semiconductor compounds in addition to the copolymer according to the present invention as long as the effects according to the present invention are not impaired. The other p-type semiconductor compound may be a low molecular organic compound or a high molecular compound. These p-type semiconductor compounds are not particularly limited, but for example, those described in known literatures such as International Publication No. 2011-016430 or Japanese Unexamined Patent Publication No. 2012-191194 can be used.

  The n-type semiconductor compound is not particularly limited. For example, a fullerene compound; a quinolinol derivative metal complex represented by 8-hydroxyquinoline aluminum; a condensed ring tetracarboxylic acid such as naphthalenetetracarboxylic acid diimide or perylenetetracarboxylic acid diimide. Acid diimides; perylene diimide derivatives, terpyridine metal complexes, tropolone metal complexes, flavonol metal complexes, perinone derivatives, benzimidazole derivatives, benzoxazole derivatives, thiazole derivatives, benzthiazole derivatives, benzothiadiazole derivatives, oxadiazole derivatives, thiadiazole derivatives, Triazole derivatives, aldazine derivatives, bisstyryl derivatives, pyrazine derivatives, phenanthroline derivatives, quinoxaline derivatives, benzoquinoline derivatives, Pyridine derivatives, borane derivatives; anthracene, pyrene, total fluoride condensed polycyclic aromatic hydrocarbons such as naphthacene or pentacene; single-walled carbon nanotubes, n-type polymer (n-type polymer semiconductor material), and the like.

  Among them, fullerene compounds, borane derivatives, thiazole derivatives, benzothiazole derivatives, benzothiadiazole derivatives, N-alkyl-substituted naphthalenetetracarboxylic acid diimides, N-alkyl-substituted perylene diimide derivatives or n-type polymer semiconductor materials are preferable. More preferred are fullerene compounds, N-alkyl substituted perylene diimide derivatives, N-alkyl substituted naphthalene tetracarboxylic acid diimides or n-type polymer semiconductor compounds, and fullerene compounds are particularly preferred. These compounds are not particularly limited, but for example, those described in known literature such as International Publication No. 2011-016430 or Japanese Unexamined Patent Publication No. 2012-191194 can be used. In addition, a kind of compound may be used among the above, and a mixture of a plurality of kinds of compounds may be used. Among these, it is particularly preferable to use 60 PCBM, 70 PCBM or a mixture thereof.

  The thickness of the active layer 103 is not particularly limited, but is usually 10 nm or more, preferably 50 nm or more, and is usually 1 μm or less, preferably 500 nm or less, more preferably 200 nm or less. A thickness of the active layer 103 of 10 nm or more is preferable because the uniformity of the film is maintained and a short circuit is hardly caused. In addition, it is preferable that the thickness of the active layer 103 is 1 μm or less because the internal resistance is reduced, and further, the charge diffusion is improved without the pair of electrodes being separated too much.

  A method for forming the active layer 103 is not particularly limited, but is preferably formed by a coating method because productivity is improved. Specifically, the active layer 103 is preferably formed by applying an active layer forming ink containing a copolymer according to the present invention.

  As the coating method, any method can be used. For example, spin coating method, reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, air knife coating method, wire barber coating method, pipe Examples include a doctor method, an impregnation / coating method, and a curtain coating method.

  When forming a laminated type active layer, an active layer forming ink containing at least a copolymer according to the present invention as a p-type semiconductor compound and an active layer ink containing an n-type semiconductor compound are used, respectively, by a coating method. An active layer may be formed by stacking a p-type semiconductor-containing layer and an n-type semiconductor-containing layer. On the other hand, when forming a bulk hetero type active layer, an active layer forming ink containing at least a copolymer according to the present invention and an n type semiconductor compound as a p type semiconductor compound is used, and a bulk hetero type active layer is formed by a coating method. An active layer may be formed.

  The above-mentioned ink for forming an active layer usually contains a solvent in addition to the above-mentioned compound. The solvent is not particularly limited, but for example, aliphatic hydrocarbons such as hexane, heptane, octane, isooctane, nonane or decane; aromatic such as toluene, xylene, mesitylene, cyclohexylbenzene, chlorobenzene or orthodichlorobenzene Hydrocarbons; cycloaliphatic hydrocarbons such as cyclopentane, cyclohexane, methylcyclohexane, cycloheptane, cyclooctane, tetralin or decalin; lower alcohols such as methanol, ethanol or propanol; acetone, methyl ethyl ketone, cyclopentanone or cyclohexanone Aliphatic ketones such as acetophenone or propiophenone; esters such as ethyl acetate, butyl acetate or methyl lactate; chloroform, Methylene, dichloroethane, halogenated hydrocarbons such as trichloroethane or trichlorethylene; ethers such as ethyl ether and tetrahydrofuran or dioxane; or an amide such as dimethylformamide or dimethylacetamide, and the like.

  Among them, aromatic hydrocarbons such as toluene, xylene, mesitylene, cyclohexylbenzene, chlorobenzene or orthodichlorobenzene; cycloaliphatic carbonization such as cyclopentane, cyclohexane, methylcyclohexane, cycloheptane, cyclooctane, tetralin or decalin Hydrogens; ketones such as acetone, methyl ethyl ketone, cyclopentanone or cyclohexanone; halogen hydrocarbons such as chloroform, methylene chloride, dichloroethane, trichloroethane or trichloroethylene; or ethers such as ethyl ether, tetrahydrofuran or dioxane. More preferably, non-halogen aromatic hydrocarbons such as toluene, xylene, mesitylene or cyclohexylbenzene; non-halogen ketones such as cyclopentanone or cyclohexanone; aromatic ketones such as acetophenone or propiophenone; tetrahydrofuran, cyclohexane Alicyclic hydrocarbons such as pentane, cyclohexane, methylcyclohexane, cycloheptane, cyclooctane, tetralin or decalin; ketones such as acetone, methyl ethyl ketone, cyclopentanone or cyclohexanone; or non-halogens such as 1,4-dioxane Aliphatic ethers. Particularly preferred are non-halogen aromatic hydrocarbons such as toluene, xylene, mesitylene or cyclohexylbenzene.

  As the solvent, one kind of solvent may be used alone, or any two or more kinds of solvents may be used in any ratio. When two or more kinds of solvents are used in combination, it is preferable to combine a low boiling point solvent having a boiling point of 60 ° C. or higher and 150 ° C. or lower and a high boiling point solvent having a boiling point of 180 ° C. or higher and 250 ° C. or lower. Examples of combinations of low and high boiling solvents include non-halogen aromatic hydrocarbons and alicyclic hydrocarbons, non-halogen aromatic hydrocarbons and aromatic ketones, ethers and alicyclic carbonization. Examples thereof include hydrogens, ethers and aromatic ketones, aliphatic ketones and alicyclic hydrocarbons, or aliphatic ketones and aromatic ketones. Specific examples of preferred combinations include toluene and tetralin, xylene and tetralin, toluene and acetophenone, xylene and acetophenone, tetrahydrofuran and tetralin, tetrahydrofuran and acetophenone, methyl ethyl ketone and tetralin, methyl ethyl ketone and acetophenone, and the like.

  In addition to the compounds described above, the active layer forming ink may contain other additives as long as the effects of the present invention are not impaired.

<3-4. Lower buffer layer 102, upper buffer layer 104>
As described above, the photoelectric conversion element according to this embodiment includes the lower buffer layer 102 between the lower electrode 101 and the active layer 103, and the upper buffer layer 104 between the upper electrode 105 and the active layer 103. . The lower buffer layer 102 and the upper buffer layer 104 each have a function of improving the electron extraction efficiency from the active layer 103 to the cathode or the hole extraction efficiency from the active layer 103 to the anode. Note that a buffer layer having a function of improving the electron extraction efficiency from the active layer 103 to the cathode is referred to as an electron extraction layer, and a buffer layer having a function of improving the electron extraction efficiency from the active layer 103 to the cathode is referred to as a hole extraction layer. As described above, the lower buffer layer 102 and the upper buffer layer 104 are not essential components, and the organic thin film solar cell element 4 may not include the lower buffer layer 102 and the upper buffer layer 104. Moreover, you may have only any one layer.

  Either the lower buffer layer 102 or the upper buffer layer 104 may be an electron extraction layer or a hole extraction layer, but when the lower electrode 101 is a cathode and the upper electrode 105 is an anode, the lower buffer layer 102 is an electron extraction layer. The upper buffer layer 104 is a hole extraction layer. On the other hand, when the lower electrode 101 is an anode and the upper electrode 105 is a cathode, the lower buffer layer 102 is a hole extraction layer and the upper buffer layer 104 is an electron extraction layer.

<3-4-1. Electron extraction layer>
The material of the electron extraction layer is not particularly limited as long as it is a material that improves the efficiency of extracting electrons from the active layer 103 to the cathode, and examples thereof include inorganic compounds and organic compounds.

  Examples of inorganic compounds include salts of alkali metals such as Li, Na, K or Cs; n-type semiconductor oxides such as titanium oxide (TiOx) and zinc oxide (ZnO). Among them, the alkali metal salt is preferably a fluoride salt such as LiF, NaF, KF or CsF, and the n-type semiconductor oxide is preferably zinc oxide (ZnO). Although the operation mechanism of such a material is unknown, it is conceivable to reduce the work function of the cathode when combined with a cathode made of Al or the like and increase the voltage applied to the solar cell element.

  Examples of organic compounds include phosphine compounds having a double bond between a phosphorus atom and a group 16 element such as triarylphosphine oxide compounds; substituents such as bathocuproin (BCP) or bathophenanthrene (Bphen) A phenanthrene compound in which the 1-position and the 10-position may be substituted with a heteroatom; a boron compound such as triarylboron; an organometallic such as (8-hydroxyquinolinato) aluminum (Alq3) Oxide; Compound having 1 or 2 ring structure which may have a substituent such as oxadiazole compound or benzimidazole compound; naphthalenetetracarboxylic anhydride (NTCDA) or perylenetetracarboxylic anhydride Such as (PTCDA), such as dicarboxylic anhydride Aromatic compounds having a slip dicarboxylic acid structure.

  The thickness of the electron extraction layer is usually 0.1 nm or more, preferably 1 nm or more, more preferably 10 nm or more. On the other hand, it is usually 400 nm or less, preferably 200 nm or less. When the film thickness of the electron extraction layer is 0.1 nm or more, it functions as a buffer material. When the film thickness of the electron extraction layer is 400 nm or less, electrons are easily extracted and the photoelectric conversion efficiency is improved. Can improve.

  The LUMO energy level of the material of the electron extraction layer is not particularly limited, but is usually −4.0 eV or more, preferably −3.9 eV or more. On the other hand, it is usually −1.9 eV or less, preferably −2.0 eV or less. It is preferable that the LUMO energy level of the material for the electron extraction layer is −1.9 eV or less because charge transfer can be promoted. It is preferable that the LUMO energy level of the material for the electron extraction layer is −4.0 eV or more in terms of preventing reverse electron transfer to the n-type semiconductor material.

  The HOMO energy level of the material for the electron extraction layer is not particularly limited, but is usually −9.0 eV or more, preferably −8.0 eV or more. On the other hand, it is usually −5.0 eV or less, preferably −5.5 eV or less. The HOMO energy level of the material for the electron extraction layer is preferably −5.0 eV or less from the viewpoint of preventing movement of holes.

  As a method for calculating the LUMO energy level and the HOMO energy level of the material of the electron extraction layer, a cyclic voltammogram measurement method may be mentioned. For example, it can implement with reference to the method as described in well-known literature (International Publication 2011/016430).

  When the material of the electron extraction layer is an organic compound, the glass transition temperature (hereinafter sometimes referred to as Tg) of this compound as measured by the DSC method is not particularly limited, but is not observed, or It is preferable that it is 55 degreeC or more. That the glass transition temperature is not observed by the DSC method means that there is no glass transition temperature. Specifically, the determination is made based on the presence or absence of a glass transition temperature of 400 ° C. or lower. A material in which the glass transition temperature by the DSC method is not observed is preferable in that it has high thermal stability.

  Among the compounds having a glass transition temperature of 55 ° C. or higher as measured by the DSC method, the glass transition temperature is preferably 65 ° C. or higher, more preferably 80 ° C. or higher, more preferably 110 ° C. or higher, particularly preferably. A compound having a temperature of 120 ° C. or higher is desirable. On the other hand, the upper limit of the glass transition temperature is not particularly limited, but is usually 400 ° C. or lower, preferably 350 ° C. or lower, more preferably 300 ° C. or lower. Moreover, it is preferable that the material of an electron taking-out layer is a thing by which the glass transition temperature by DSC method is not observed below 30 degreeC or more and less than 55 degree | times.

  The glass transition temperature in the present specification is defined as a point at which specific heat changes in an amorphous solid, which is a temperature at which local molecular motion is started by thermal energy. When the temperature rises further than Tg, the solid structure changes and crystallization occurs (the temperature at this time is defined as the crystallization temperature (Tc)). When the temperature rises further, it generally melts at the melting point (Tm) and changes to a liquid state. However, these phase transitions may not be observed due to molecular decomposition or sublimation at high temperatures.

  The DSC method is a thermophysical property measurement method (differential scanning calorimetry method) defined in JIS K-0129 “General Rules for Thermal Analysis”. In order to determine the glass transition temperature more clearly, it is desirable to measure after rapidly cooling a sample once heated to a temperature higher than the glass transition temperature. For example, the measurement can be carried out by a method described in a known document (International Publication No. 2011/016430).

  When the glass transition temperature of the compound used for the electron extraction layer is 55 ° C. or higher, the structure of this compound is difficult to change against external stress such as applied electric field, flowing current, stress due to bending or temperature change. It is preferable in terms of durability. Furthermore, since there is a tendency that the crystallization of the thin film of the compound does not proceed easily, the stability of the electron extraction layer is improved by making it difficult for the compound to change between the amorphous state and the crystalline state in the operating temperature range. Therefore, it is preferable in terms of durability. This effect becomes more prominent as the glass transition temperature of the material is higher.

  There is no restriction | limiting in the formation method of an electronic taking-out layer. For example, when a material having sublimation property is used, it can be formed by a vacuum deposition method or the like. Further, for example, when a material soluble in a solvent is used, it can be formed by a wet coating method such as spin coating or inkjet.

When the electron extraction layer is formed by a coating method, a surfactant may be further contained in the coating solution. By using the surfactant, the occurrence of dents due to adhesion of fine bubbles or foreign matters and / or uneven coating in the drying process is suppressed. Known surfactants (cationic surfactants, anionic surfactants, nonionic surfactants) can be used as the surfactant. Of these, silicon-based surfactants, acetylenic diol-based surfactants, and fluorine-based surfactants are preferable. In addition, as surfactant, only 1 type may be used and 2 or more types may be used together by arbitrary combinations and a ratio.
Specifically, for example, when an alkali metal salt is used as a material for the electron extraction layer, the electron extraction layer can be formed by using a vacuum film formation method such as vacuum deposition or sputtering. Especially, it is desirable to form an electron taking-out layer by vacuum vapor deposition by resistance heating. By using vacuum deposition, damage to other layers such as an active layer can be reduced.

  On the other hand, for metal oxides of n-type semiconductors, for example, when zinc oxide ZnO is used as the material for the electron extraction layer, a vacuum film formation method such as sputtering can be used. It is desirable to form the extraction layer. For example, Sol-Gel Science, C.I. J. et al. Brinker, G.M. W. According to the sol-gel method described by Scherer, Academic Press (1990), an electron extraction layer composed of zinc oxide can be formed. In this case, the film thickness is usually 0.1 nm or more, preferably 2 nm or more, more preferably 5 nm or more, and usually 1 μm or less, preferably 100 nm or less, more preferably 50 nm or less. If the electron extraction layer is too thin, the effect of improving the electron extraction efficiency is not sufficient, and if it is too thick, the electron extraction layer tends to deteriorate the characteristics of the device by acting as a series resistance component.

<3-4-2. Hole extraction layer>
The material for the hole extraction layer is not particularly limited as long as it is a material capable of improving the efficiency of extracting holes from the active layer 103 to the anode. Specifically, conductive polymers in which polythiophene, polypyrrole, polyacetylene, triphenylenediamine, polyaniline, etc. are doped with sulfonic acid and / or iodine, polythiophene derivatives having a sulfonyl group as a substituent, conductive organics such as arylamine Examples thereof include compounds, copper oxide, nickel oxide, manganese oxide, molybdenum oxide, vanadium oxide, metal oxide such as tungsten oxide, Nafion, and a p-type semiconductor described later. Among them, a conductive polymer doped with sulfonic acid is preferable, and (3,4-ethylenedioxythiophene) poly (styrenesulfonic acid) (PEDOT: PSS) in which a polythiophene derivative is doped with polystyrene sulfonic acid is more preferable. It is. A thin film of metal such as gold, indium, silver or palladium can also be used. A thin film of metal or the like may be formed alone or in combination with the above organic material.

  The film thickness of the hole extraction layer is usually 0.1 nm or more. On the other hand, it is usually 400 nm or less, preferably 200 nm or less. When the film thickness of the hole extraction layer is 0.1 nm or more, it functions as a buffer material. When the film thickness of the hole extraction layer is 400 nm or less, holes are easily extracted, Conversion efficiency can be improved.

There is no restriction | limiting in the formation method of a positive hole taking-out layer. For example, when a material having sublimation property is used, it can be formed by a vacuum deposition method or the like. For example, when a material soluble in a solvent is used, it can be formed by a wet coating method such as a spin coating method or an ink jet method. When a semiconductor material is used for the hole extraction layer, the precursor may be converted into a semiconductor compound after forming the layer using the precursor, similarly to the low-molecular organic semiconductor compound of the active layer.
Especially, when using PEDOT: PSS as a material of a hole taking-out layer, it is preferable to form a hole taking-out layer by the method of apply | coating a dispersion liquid. Examples of the dispersion of PEDOT: PSS include CLEVIOSTM series manufactured by Heraeus, ORGACONTM series manufactured by Agfa, and the like.

  When the hole extraction layer is formed by a coating method, a surfactant may be further contained in the coating solution. By using the surfactant, the occurrence of dents due to adhesion of fine bubbles or foreign matters and / or uneven coating in the drying process is suppressed. Known surfactants (cationic surfactants, anionic surfactants, nonionic surfactants) can be used as the surfactant. Of these, silicon-based surfactants, acetylenic diol-based surfactants, and fluorine-based surfactants are preferable. In addition, as surfactant, only 1 type may be used and 2 or more types may be used together by arbitrary combinations and a ratio.

<3-5. Manufacturing method of photoelectric conversion element>
A photoelectric conversion element 107 having the configuration shown in FIG. 1 is formed on a base 106 by a lower electrode 101, a lower buffer layer 102, an active layer 103, an upper buffer layer 104, and an upper electrode in accordance with the method described above for each layer. It can be manufactured by sequentially stacking 105. In the case of manufacturing the photoelectric conversion element having the tandem structure shown in FIG. 2, the lower electrode 101, the lower buffer layer 102, the first active layer 108, the intermediate layer 109, and the second active element are formed on the substrate 106. The layer 110, the upper buffer layer 104, and the upper electrode 105 can be sequentially stacked.

  After laminating the lower electrode 101 and the upper electrode 105, the photoelectric conversion element is usually in a temperature range of 50 ° C. or higher, preferably 80 ° C. or higher, usually 300 ° C. or lower, preferably 280 ° C. or lower, more preferably 250 ° C. or lower. It is preferable to heat (this step is referred to as an annealing treatment step).

  Performing the annealing process at a temperature of 50 ° C. or higher improves adhesion between the layers of the photoelectric conversion element, for example, adhesion between the lower buffer layer 102 and the lower electrode 101 and / or the lower buffer layer 102 and the active layer 103. This is preferable because the effect of By improving the adhesion between the layers, the thermal stability and durability of the photoelectric conversion element can be improved. In addition, the self-organization of the active layer can be promoted by the annealing process. It is preferable to set the temperature of the annealing treatment step to 300 ° C. or lower because the possibility that the organic compound in the active layer 103 is thermally decomposed is reduced. In the annealing treatment step, stepwise heating may be performed within the above temperature range.

  The heating time is usually 1 minute or longer, preferably 3 minutes or longer, and usually 3 hours or shorter, preferably 1 hour or shorter. The annealing treatment step is preferably terminated when the open-circuit voltage, the short-circuit current, and the fill factor, which are parameters of the solar cell performance, reach a constant value. Further, the annealing treatment step is preferably performed under normal pressure and in an inert gas atmosphere.

  As a heating method, the photoelectric conversion element may be placed on a heat source such as a hot plate, or the photoelectric conversion element may be placed in a heating atmosphere such as an oven. The heating may be performed batchwise or continuously.

  Although the thermal treatment and durability of the photoelectric conversion element can be improved by the annealing treatment step, the fullerene compound is aggregated during the annealing treatment step and phase separation is promoted, so that the photoelectric conversion efficiency may be lowered. . However, since the active layer 103 contains an additive, aggregation of the fullerene compound during the annealing process is suppressed by the additive. Thus, the photoelectric conversion element 107 with higher photoelectric conversion efficiency after performing an annealing process can be obtained by making the active layer 103 contain an additive.

  Each layer constituting the photoelectric conversion element according to the present invention is not particularly limited and can be formed by a sheet-to-sheet (sheet-fed) method, or a roll-to-roll method, for the following reasons, It is preferable to form by a roll-to-roll method.

  The roll-to-roll method is a method in which a flexible base material wound in a roll shape is fed out and processed intermittently or continuously until it is taken up by a take-up roll. is there. According to the roll-to-roll method, it is possible to batch-process long substrates on the order of km, so that the production method is more suitable for mass production than the sheet-to-sheet method.

  The size of the roll that can be used in the roll-to-roll method is not particularly limited as long as it can be handled by a roll-to-roll manufacturing apparatus, but the outer diameter is usually 5 m or less, preferably 3 m or less. Preferably, it is 1 m or less, usually 10 cm or more, preferably 20 cm or more, more preferably 30 cm or more. The outer diameter of the roll core is usually 4 m or less, preferably 3 m or less, more preferably 0.5 m or less, usually 1 cm or more, preferably 3 cm or more, more preferably 5 cm or more, still more preferably 10 cm or more, particularly preferably 20 cm or more. When these diameters are not more than the above upper limit, it is preferable in terms of high handleability of the roll, and when it is more than the lower limit, the layer formed in each of the following steps is less likely to be broken by bending stress. Is preferable. The width of the roll is usually 5 cm or more, preferably 10 cm or more, more preferably 20 cm or more, and is usually 5 m or less, preferably 3 m or less, more preferably 2 m or less. When the width is not more than the upper limit, it is preferable from the viewpoint of high handleability of the roll.

<3-6. Photoelectric conversion characteristics>
The photoelectric conversion characteristics of the photoelectric conversion element 107 can be obtained as follows. The photoelectric conversion element 107 is irradiated with light having an AM 1.5G condition with a solar simulator at an irradiation intensity of 100 mW / cm ² , and current-voltage characteristics are measured. From the obtained current-voltage curve, photoelectric conversion characteristics such as photoelectric conversion efficiency (PCE), short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF), series resistance, and shunt resistance can be obtained.

  The photoelectric conversion efficiency of the photoelectric conversion element according to the present invention is not particularly limited, but is usually 1% or more, preferably 1.5% or more, more preferably 2% or more. On the other hand, there is no particular limitation on the upper limit, and the higher the better.

Moreover, as a method for measuring the durability of the photoelectric conversion element, a method for obtaining a maintenance ratio of the photoelectric conversion efficiency before and after exposing the photoelectric conversion element to the atmosphere can be mentioned.
(Maintenance rate) = (Photoelectric conversion efficiency after N hours of atmospheric exposure) / (Photoelectric conversion efficiency immediately before atmospheric exposure)

In order to put a photoelectric conversion element into practical use, it is important to have high photoelectric conversion efficiency and high durability in addition to simple and inexpensive manufacture. From this viewpoint, the maintenance rate of photoelectric conversion efficiency before and after exposure to the atmosphere for one week is preferably 60% or more, more preferably 80% or more, and the higher the better.

<4. Solar cell>
The photoelectric conversion element according to the above-described embodiment is preferably used as a solar cell, particularly a solar cell element of a thin film solar cell. FIG. 2 is a cross-sectional view schematically showing the configuration of a thin-film solar cell as one embodiment of the present invention. As shown in FIG. 2, the thin film solar cell 14 of this embodiment includes a weather-resistant protective film 1, an ultraviolet cut film 2, a gas barrier film 3, a getter material film 4, a sealing material 5, and a photoelectric conversion element. 6, a sealing material 7, a getter material film 8, a gas barrier film 9, and a back sheet 10 are provided in this order. And a thin film solar cell is normally irradiated with light from the side (downward in the figure) in which the weather-resistant protective film 1 was formed, and the photoelectric conversion element 6 generates electric power. Note that the thin-film solar cell does not need to have all of these constituent members, and each constituent member may be arbitrarily selected and provided.

  There are no particular restrictions on these constituent members constituting the thin-film solar cell and the manufacturing method thereof, and well-known techniques can be used. For example, the thing described in well-known literatures, such as international publication 2011/016430 or Japan Unexamined-Japanese-Patent No. 2012-191194, can be used.

  There is no special restriction | limiting in the use of the solar cell which concerns on this invention, especially the thin film solar cell 14 mentioned above, It can use for arbitrary uses. Examples include solar cells for building materials, solar cells for automobiles, solar cells for spacecrafts, solar cells for home appliances, solar cells for mobile phones, solar cells for toys, and the like.

  The solar cell according to the present invention, particularly a thin-film solar cell, may be used as it is, or for example, a solar cell may be installed on a substrate and used as a solar cell module. For example, as shown in FIG. 3, the solar cell module 13 having the thin film solar cell 14 on the base 12 can be installed and used at a place of use. For the substrate 12, a well-known technique can be used, for example, those described in International Publication No. 2011-016430 or Japanese Unexamined Patent Publication No. 2012-191194. For example, when a building material plate is used as the substrate 12, a solar cell panel can be produced as the solar cell module 13 by providing the thin film solar cell 14 on the surface of the plate.

  Hereinafter, embodiments of the present invention will be described by way of examples. However, the present invention is not limited to these examples as long as the gist thereof is not exceeded. The items described in the examples were measured by the following methods.

[Method for measuring weight average molecular weight and number average molecular weight]
The polystyrene equivalent weight average molecular weight (Mw) and number average molecular weight (Mn) were determined by gel permeation chromatography (GPC). The molecular weight distribution (PDI) represents Mw / Mn.

Gel permeation chromatography (GPC) measurement was performed under the following conditions.
Column: PolymerLaboratories GPC column (PLgel MIXED-B 10 μm inner diameter 7.5 mm, length 30 cm) used in series connected Pump: LC-10AT (manufactured by Shimadzu Corporation)
Oven: CTO-10A (manufactured by Shimadzu Corporation)
Detector: differential refractive index detector (manufactured by Shimadzu Corporation, RID-10A) and UV-vis detector (manufactured by Shimadzu Corporation, RID-10A) and UV-vis detector (manufactured by Shimadzu Corporation, SPD-10A)
Sample: 1 μL of 1 mg sample dissolved in orthodichlorobenzene (200 mg)
Mobile phase: orthodichlorobenzene
Flow rate: 1.0 mL / min
Temperature: 80 ° C
Analysis: LC-Solution (manufactured by Shimadzu Corporation)

<Synthesis Example 1: Synthesis of Copolymer 1>
[Synthesis Example: 3,3 ′ ″-didodecyl-5,5 ′ ″-bis (trimethylstannyl) -2,2 ′: 5 ′, 2 ″: 5 ″, 2 ′ ″-quarterthiophene (Synthesis of Compound E2)

  3,3 ′ ″-didodecyl-2 obtained in reference to a non-patent document (Angew. Chem. Int. Ed., 2012, 51, 2068-2071) in a 100 mL two-necked eggplant flask under a nitrogen atmosphere. , 2 ′: 5 ′, 2 ″: 5 ″, 2 ′ ″-Quarterthiophene (Compound E1) (203 mg, 0.304 mmol) was added and dissolved in tetrahydrofuran (THF, 20.0 mL). Cooled to. A tetrahydrofuran / hexane solution of lithium diisopropylamide (LDA) (manufactured by Kanto Chemical Co., Inc., concentration 1.3 M, 0.23 mL, 1.0 eq) was added dropwise and stirred for about 30 minutes. A solution of trimethyltin chloride in tetrahydrofuran (Aldrich, 1.0 M, 0.3 mL, 1.0 eq) was added dropwise, and the mixture was stirred for about 30 minutes and cooled to -78 ° C. After dropwise addition of a tetrahydrofuran solution of trimethyltin chloride (Aldrich, 1.0 M, 0.3 mL, 1.0 eq), a tetrahydrofuran / hexane solution of lithium diisopropylamide (LDA) (Kanto Chemical Co., concentration 1.3 M, 0) .23 mL, 1.0 eq) was added dropwise, stirred for about 30 minutes, and slowly warmed to room temperature. After cooling to −50 ° C., a tetrahydrofuran solution of trimethyltin chloride (Aldrich, 1.0 M, 0.3 mL, 1.0 eq) was added dropwise, and then a tetrahydrofuran / hexane solution of lithium diisopropylamide (LDA) (manufactured by Kanto Chemical Co., Inc.). , Concentration 1.3M, 0.23 mL, 1.0 eq) was added dropwise, stirred for about 30 minutes, and heated to -20 ° C. This operation was repeated 5 times, and it was confirmed that the reaction had progressed completely. Water was added to the reaction solution, and the precipitated solid was filtered. The crude product is ultrasonically washed in methanol, filtered and dried under vacuum to give 3,3 ′ ″-didodecyl-5,5 ′ ″-bis (trimethylstannyl) -2,2 ′. : 5 ′, 2 ″: 5 ″, 2 ′ ″-quarterthiophene (Compound E2) was obtained as a brown solid.

Compound E2: 1H-NMR (400 MHz, solvent: deuterated chloroform): δ 7.14 (d, 4H, J = 3.6 Hz), δ 7.11 (s, 2H), δ 7.04 (d, 4H, J = 3) .6 Hz), δ2.81 (t, 4H, J = 7.6 Hz), δ1.73—-1.65 (m, 4H), δ1.46-1.28 (m, 36H), δ0.90 ( t, 6H, J = 6.8 Hz), δ 0.41 (s, 18H).

1,3-dibromo-5- (n-octyl) obtained by referring to a method described in a known document (Organic Letters 2004, 6, 3381-3384) as a monomer in a 50 mL two-necked eggplant flask under a nitrogen atmosphere. ) -4H-thieno [3,4-c] pyrrole-4,6- (5H) -dione (compound E4 (imidothiophene dibromide), 136.7 mg, 0.323 mmol), 3,3 ′ ″-didodecyl −5,5 ′ ″-bis (trimethylstannyl) -2,2 ′: 5 ′, 2 ″: 5 ″, 2 ′ ″-quarterthiophene (Compound E2) (32.6 mg, 0.032 mmol) ) And 4,4-bis (2-ethylhexyl) -2,6-bis (trimethyltin) -dithieno [3,2-b: 2 ′, 3 obtained by referring to the method described in WO2013 / 180243 ' -D] Silole (compound E3) (220.8 mg, 0.291 mmol) was added, and tetrakis (triphenylphosphine) palladium (0) (9.7 mg, 3 mol%), a triphenylphosphine-containing heterogeneous palladium complex catalyst Pd-EnCatTPP30 (Aldrich, 12.7 mg, 3 mol%), toluene (10 mL), and N, N-dimethylformamide (2.5 mL) were added, and the mixture was stirred at 95 ° C. for 1 hour and then at 105 ° C. for 2 hours. did. The reaction solution was diluted 4-fold with toluene, trimethyl (phenyl) tin (0.06 mL) was added, and the mixture was heated and stirred at 105 ° C. for 1.5 hours. Further, bromobenzene (1.8 mL) was added, and the mixture was added at 105 ° C. Stir with heating for hours. The reaction solution was cooled, 1 mL of methanol was added, and the deposited precipitate was collected by filtration and dissolved in chloroform. Diamine silica gel (manufactured by Fuji Silysia Chemical) was added and stirred for 30 minutes at room temperature, and then passed through a short column of acidic silica gel. Solution by concentrating, copolymer-1 of interest, was obtained in yield 81%. The weight average molecular weight Mw of the obtained copolymer 1 was 81000, and PDI was 2.6.

<Synthesis Example 2: Synthesis of Copolymer 2>

  1,3-dibromo-5- (n-octyl) obtained by referring to a method described in a known document (Organic Letters 2004, 6, 3381-3384) as a monomer in a 50 mL two-necked eggplant flask under a nitrogen atmosphere. ) -4H-thieno [3,4-c] pyrrole-4,6- (5H) -dione (compound E4 (imidothiophene dibromide), 142.2 mg, 0.336 mmol), 2,2′-didodecyl-5 , 5′-bis (trimethylstannyl) -2,2′-bithiophene (Compound E5) (28.4 mg, 0.033 mmol) and 4,4-obtained by referring to the method described in WO2013 / 180243 Bis (2-ethylhexyl) -2,6-bis (trimethyltin) -dithieno [3,2-b: 2 ′, 3′-d] silole (compound E 3) (220.8 mg, 0.302 mmol) was added, and tetrakis (triphenylphosphine) palladium (0) (9.7 mg, 3 mol%), triphenylphosphine-containing heterogeneous palladium complex catalyst Pd-EnCatTPP30 (Aldrich) Manufactured, 12.7 mg, 3 mol%), toluene (10 mL), and N, N-dimethylformamide (2.5 mL) were added and stirred at 105 ° C. for 3 hours. The reaction solution was diluted 4 times with toluene, trimethyl (phenyl) tin (0.08 mL) was added as a terminal treatment, and the mixture was heated and stirred at 105 ° C. for 1 hour, and further bromobenzene (1.8 mL) was added to 105 ° C. And stirred for 4 hours. The reaction solution was cooled, methanol was added, and the deposited precipitate was collected by filtration and dissolved in chloroform. Diamine silica gel (manufactured by Fuji Silysia Chemical) was added and stirred for 30 minutes at room temperature, and then passed through a short column of acidic silica gel. By concentrating the solution, the target copolymer 2 was obtained in a yield of 80%. The weight average molecular weight Mw of the obtained copolymer 2 was 51000, and PDI was 2.2.

<Synthesis Example 3: Synthesis of Copolymer 3>

  1,3-dibromo-5- (n-octyl) obtained by referring to a method described in a known document (Organic Letters 2004, 6, 3381-3384) as a monomer in a 50 mL two-necked eggplant flask under a nitrogen atmosphere. ) -4H-thieno [3,4-c] pyrrole-4,6- (5H) -dione (compound F1 (imidothiophene dibromide), 138 mg, 0.33 mmol) and the method described in WO2013 / 180243. Compound E1 (255 mg, 0.34 mmol) obtained in this manner was added, and tetrakis (triphenylphosphine) palladium (0) (12 mg, 3 mol%), triphenylphosphine-containing heterogeneous palladium complex catalyst Pd-EnCatTPP30 (Aldrich) Manufactured, 23 mg, 3 mol%), toluene (5.3 mL) and N, N-dimethylformamide (1.3 mL) were added, and the mixture was stirred at 90 ° C. for 1 hour and then at 100 ° C. for 10 hours. After the reaction solution was diluted 4-fold with toluene and heated and stirred at 100 ° C. for another 0.5 hours, as a terminal treatment, trimethyl (phenyl) tin (0.3 mL) was added and heated and stirred at 100 ° C. for 8 hours. Bromobenzene (1.5 mL) was further added, and the mixture was heated and stirred at 100 ° C. for 8 hours. The reaction solution was poured into methanol, and the deposited precipitate was collected by filtration. The obtained solid was dissolved in chloroform, diamine silica gel (Fuji Silysia Chemical) was added, and the mixture was stirred for 1 hour at room temperature and passed through a short column of acidic silica gel. The solution was concentrated, recrystallized using chloroform / ethyl acetate as a solvent, and the deposited precipitate was filtered off to obtain the target copolymer 3 in a yield of 75%. The weight average molecular weight Mw of the obtained copolymer 3 was 137K, and PDI was 3.3.

<Synthesis Example 4: Synthesis of Copolymer 4>

  Under a nitrogen atmosphere, 4,7-bis (5-bromo-) obtained in a 50 mL two-necked eggplant flask as a monomer by referring to a method described in a known document (Adv. Mater. 2014, 26, 2586-2591). 4- (2-decyltetradecyl) -2-thienyl) -5,6-difluoro-2,1,3-benzothiadiazole (Compound E6) (115 mg, 0.098 mmol) and 5,5′-bis (trimethylsta) Nyl) -2,2′-bithiophene (Compound E7) (Aldrich, 49.4 mg, 0.1 mmol) was added, and tetrakis (triphenylphosphine) palladium (0) (3.4 mg, 3 mol%), tri Phenylphosphine-containing heterogeneous palladium complex catalyst Pd-EnCatTPP30 (manufactured by Aldrich, 4.7 mg, mol%), toluene (4 mL), and N, placed N- dimethylformamide (1 mL), and stirred for 4 hours at 115 ° C.. After the reaction solution was diluted 4 times with toluene, trimethyl (phenyl) tin (0.03 mL) was added as a terminal treatment, and the mixture was heated and stirred at 115 ° C. for 2 hours. Further, bromobenzene (0.9 mL) was added, and the mixture was stirred with heating at 115 ° C. for 3 hours. Ethyl acetate was poured into the reaction solution, and the deposited precipitate was collected by filtration. The obtained solid was dissolved in chloroform, diamine silica gel (Fuji Silysia Chemical) was added, and the mixture was stirred for 1 hour at room temperature and passed through a short column of acidic silica gel. By concentrating the solution, the target copolymer 4 was obtained in a yield of 88%. The weight average molecular weight Mw of the obtained copolymer 4 was 53.6K, and PDI was 3.9.

<Synthesis Example 5: Synthesis of Copolymer 5>

  1,3-Dibromo-5- (n-octyl)-obtained as a monomer in a 10 mL Schlenk tube under a nitrogen atmosphere with reference to a method described in a known document (Organic Letters 2004, 6, 3381-3384). 4H-thieno [3,4-c] pyrrole-4,6- (5H) -dione (compound E4 (imidothiophene dibromide), 12.6 mg, 0.03 mmol), known literature (Polymer, 1990, 31, 1379) -1383), 4,4′-didodecyl-5,5′-bis (trimethylstannyl) -2,2′-bithiophene (compound E2) (30.3 mg, 0.03 mmol) was added. Tetrakis (triphenylphosphine) palladium (0) (1.0 mg, 3 mol%), triphenylphospho A fin-containing heterogeneous palladium complex catalyst Pd-EnCatTPP30 (manufactured by Aldrich, 1.4 mg, 3 mol%), toluene (1 mL), and N, N-dimethylformamide (0.25 mL) were added, and at 105 ° C. for 1 hour, Subsequently, the mixture was stirred at 115 ° C. A solid insoluble in the organic solvent was precipitated in the system.

<Example 1: Production of photoelectric conversion elements 1-1 and 1-2>
Copolymer 1 obtained in Synthesis Example 1 as a p-type semiconductor compound, and a mixture of fullerene compounds PC61BM (phenyl C61 butyric acid methyl ester) and PC71BM (phenyl C71 butyric acid methyl ester) as an n-type semiconductor compound (Frontier Carbon Co., Ltd., nanom spectra E123) was dissolved in a mixed solvent of o-xylene and tetralin (volume ratio 9: 1) in a nitrogen atmosphere to a concentration of 2.4% by mass. Note that the mass ratio of the p-type semiconductor compound to the n-type semiconductor compound was p-type semiconductor compound: n-type semiconductor compound = 1: 2. This solution was stirred and mixed on a hot stirrer at a temperature of 80 ° C. for 1 hour. The solution after stirring and mixing was filtered through a 1 μm polytetrafluoroethylene (PTFE) filter to obtain an ink for coating an active layer.

  A glass substrate (manufactured by Geomatic Co., Ltd.) patterned with an indium tin oxide (ITO) transparent conductive film is subjected to ultrasonic cleaning with acetone, followed by ultrasonic cleaning with isopropanol, followed by drying with nitrogen blow and UV-ozone treatment. went.

Next, a mixed solvent of 2-methoxyethanol (Aldrich) and ethanolamine (Aldrich) at a concentration of 105 mg / mL of zinc (II) acetate dihydrate (Wako Pure Chemical Industries) (volume ratio 100: The solution (about 0.1 mL) dissolved in 3) was spin-coated at a speed of 3000 rpm, subjected to UV-ozone treatment, and then heated in an oven at 200 ° C. for 15 minutes to form an electron extraction layer.
The substrate on which the electron extraction layer was formed was brought into a glove box, heat-treated at 150 ° C. for 3 minutes in a nitrogen atmosphere, and after cooling, the ink for active layer application (0.12 mL) produced as described above was spin-coated. An active layer having a thickness of 200 nm was formed. Then, it heated at 140 degreeC for 10 minute (s) on the hotplate.
The substrate on which the active layer was formed was taken out of the glove box, allowed to stand in the atmosphere (25 ° C., humidity 1% or less) for 3 hours under light shielding, and then brought back into the glove box.
Further, a molybdenum trioxide (MoO ₃ ) film having a thickness of 1.5 nm is formed on the active layer as a hole extraction layer, and then a silver film having a thickness of 100 nm is formed as an upper electrode by resistance heating vacuum deposition. A 5 mm square photoelectric conversion element was produced by sequentially forming a film. The photoelectric conversion element 1-1 produced in this way was evaluated by measuring the current-voltage characteristics as described above, and the photoelectric conversion efficiency (PCE) when the active layer was not exposed was obtained.

  In addition, holes are taken out in the same manner as described above except that the substrate formed up to the active layer is taken out of the glove box and then left in the atmosphere (25 ° C., humidity 1% or less) for 3 hours under irradiation of a fluorescent lamp. A layer and an upper electrode were formed, and a photoelectric conversion element 1-2 was produced. The conversion efficiency of the photoelectric conversion element 1-2 thus obtained was determined. Moreover, as a maintenance rate at the time of exposure, the photoelectric conversion efficiency (PCE) of the photoelectric conversion element 1-2 in which the active layer is exposed with respect to the photoelectric conversion efficiency (PCE) of the photoelectric conversion element 1-1 in which the active layer is not exposed. The ratio was calculated. These results are shown in Table 1. The above conversion efficiency was obtained by the following equation.

PCE (photoelectric conversion efficiency%) = Pmax / Pin × 100 = Voc × Jsc × FF / Pin × 100
FF = Pmax / (Voc × Jsc)
Here, the open circuit voltage Voc is the voltage value (V) when the current value = 0 (mA / cm ² ), and the short circuit current density Jsc is the current density when the voltage value = 0 (V) ( mA / cm ² ). The form factor (FF) is a factor representing the internal resistance, and is represented by the following expression when the maximum output point is Pmax.

<Comparative Example 1: Production of photoelectric conversion elements 2-1 and 2-2>
Photoelectric conversion elements 2-1 and 2-2 were prepared and converted in the same manner as in Example 1 except that the copolymer 2 obtained in Synthesis Example 2 was used instead of the copolymer 1 obtained in Synthesis Example 1. Efficiency and maintenance rate were determined. The obtained results are shown in Table 1.

<Comparative Example 2: Production of photoelectric conversion elements 3-1 and 3-2>
Photoelectric conversion elements 3-1 and 3-2 were produced in the same manner as in Example 1 except that the copolymer 3 obtained in Synthesis Example 3 was used instead of the copolymer 1 obtained in Synthesis Example 1, and conversion was performed. Efficiency and maintenance rate were determined. The obtained results are shown in Table 1.

<Comparative Example 3: Production of photoelectric conversion elements 4-1 and 4-2>
Photoelectric conversion elements 4-1 and 4-2 were produced and converted in the same manner as in Example 1 except that the copolymer 4 obtained in Synthesis Example 3 was used instead of the copolymer 1 obtained in Synthesis Example 1. Efficiency and maintenance rate were determined. The obtained results are shown in Table 1.

[Table 1]

  From the results shown in Table 1, it can be confirmed that the conversion efficiency maintenance ratio of the photoelectric conversion elements manufactured in Comparative Examples 1 to 3 is 64 to 74%, and the light resistance is low. On the other hand, it was confirmed that the photoelectric conversion element using the copolymer according to the present invention produced in Example 1 did not show a decrease in conversion efficiency even when the active layer was exposed and had high light resistance. it can.

DESCRIPTION OF SYMBOLS 101 Lower electrode 102 Lower buffer layer 103 Active layer 104 Upper buffer layer 105 Upper electrode 106 Base material 107 Photoelectric conversion element 1 Weatherproofing protective film 2 UV cut film 3,9 Gas barrier film 4,8 Getter material film 5,7 Sealing material 6 Solar cell element 10 Back sheet 12 Base material 13 Solar cell unit 14 Thin film solar cell

Claims (9)

A copolymer having a repeating unit represented by the following formula (I) and a repeating unit represented by the following formula (II) different from the following formula (I).

(In formula (I), D represents a donor monomer unit, A1 represents an acceptor monomer unit. In formula (II), A2 represents an acceptor monomer unit, and R ¹ and R ² are each independent. And L represents an optionally substituted alkenylene group, alkynylene group, divalent aromatic hydrocarbon group or divalent aromatic heterocyclic group (provided that Among the carbon atoms constituting L, the carbon atom located at the α-position has no substituent or is substituted with a fluorine atom)). The copolymer according to claim 1, wherein in the formula (I), D is a structural unit represented by the following formula (III).

(In Formula (III), Ring 1 and Ring 2 each independently represent an aromatic hydrocarbon ring which may have a substituent or an aromatic heterocyclic ring which may have a substituent. X ¹ is Q ¹ (R ³⁾ represents (R ^4), X ² is a single bond, O, S, N (R 5), or Q ² (R ⁶⁾ represents a (R ⁷⁾ .Q ¹ and Q ² represents an atom selected from Group 14 elements of the periodic table, and R ^{3 to} R ⁷ each represents a hydrogen atom or a monovalent organic group.) The copolymer according to claim 1 or 2, wherein A1 in the formula (I) is a structural unit represented by the following formula (V).

(In formula (V), X ³ represents an atom selected from Group 16 elements of the periodic table, and R ⁸ represents a hydrogen atom or a monovalent organic group.)   The copolymer according to any one of claims 1 to 3, wherein A1 and A2 in the formula (I) and the formula (II) are the same structural unit.   The copolymer according to any one of claims 1 to 4, wherein L in the formula (II) is a divalent aromatic heterocyclic group. The copolymer according to claim 5, wherein L in the formula (II) is any group represented by the following formulas (XI) to (XIII).

(In Formula (XI), Formula (XII), and Formula (XIII), R ^{21 to} R ²⁶ each independently represent a hydrogen atom or a fluorine atom. In Formula (XI), n is 1 to 3). Represents an integer.)   A photoelectric conversion element comprising at least a pair of electrodes and an active layer between the pair of electrodes on a substrate, wherein the active layer contains the copolymer according to any one of claims 1 to 6. A photoelectric conversion element.   A solar cell comprising the photoelectric conversion element according to claim 7.   A solar cell module comprising the solar cell according to claim 8.

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