WO2013176156A1

WO2013176156A1 - Electron-donating organic material, material for photovoltaic power element using same, and photovoltaic power element using same

Info

Publication number: WO2013176156A1
Application number: PCT/JP2013/064149
Authority: WO
Inventors: 渡辺伸博; 北澤大輔; 山本修平
Original assignee: 東レ株式会社
Priority date: 2012-05-25
Filing date: 2013-05-22
Publication date: 2013-11-28
Also published as: TW201406811A; JPWO2013176156A1

Abstract

The purpose of the present invention is to provide a photovoltaic power element with high photoelectric conversion efficiency. Provided are an electron-donating organic material that comprises a structural unit represented by general formula (1) and a photovoltaic power element using the material. [Chemical formula 1] (In general formula (1), R1 represents a substitutable aryl group or a substitutable heteroaryl group.)

Description

Electron donating organic material, photovoltaic device material using the same, and photovoltaic device

The present invention relates to an electron donating organic material, a material for a photovoltaic device using the same, and a photovoltaic device using the material.

Solar cells are attracting attention as an effective solution to the increasing energy problem as an environmentally friendly electric energy source. Currently, inorganic materials such as single crystal silicon, polycrystalline silicon, amorphous silicon, and compound semiconductors are used as semiconductor materials for photovoltaic elements of solar cells. However, solar cells manufactured using inorganic semiconductors have not been widely used in general households because of high costs. The high cost factor is mainly in the process of manufacturing a semiconductor thin film under vacuum and high temperature. Therefore, organic solar cells using organic semiconductors and organic dyes such as conjugated polymers and organic crystals are being studied as semiconductor materials expected to simplify the manufacturing process.

However, an organic solar cell using a conjugated polymer or the like has the biggest problem that the photoelectric conversion efficiency is lower than that of a conventional solar cell using an inorganic semiconductor, and has not yet been put into practical use. The photoelectric conversion efficiency of organic solar cells using conventional conjugated polymers is mainly due to the low solar absorption efficiency and the excitons that are difficult to separate the electrons and holes generated by sunlight. This is because a state is formed and a trap for trapping carriers (electrons and holes) is easily formed, so that the generated carriers are easily trapped in the trap and the mobility of carriers is low.

Conventional photoelectric conversion elements using organic semiconductors are Schottky type, electron accepting organic materials (n-type organic semiconductors) and electron donating properties, which join an electron donating organic material (p-type organic semiconductor) and a metal having a low work function. It can be classified into a heterojunction type in which an organic material (p-type organic semiconductor) is joined. In these elements, only the organic layer (about several molecular layers) at the junction contributes to the photocurrent generation, so that the photoelectric conversion efficiency is low, and its improvement is a problem.

As a method for improving photoelectric conversion efficiency, a bulk heterojunction in which an electron-accepting organic material (n-type organic semiconductor) and an electron-donating organic material (p-type organic semiconductor) are mixed to increase the bonding surface contributing to photoelectric conversion There is a type (for example, see Non-Patent Document 1). Among them, the conjugated polymer used as the electron donating organic material (p-type organic semiconductor), a fullerene or fullerene derivative, such as other C ₆₀ of the conductive polymer having the semiconductor characteristics of the n-type as the electron accepting organic material The used photoelectric conversion material is reported (for example, refer nonpatent literature 2).

In order to efficiently absorb radiant energy over a wide range of the solar spectrum and improve photoelectric conversion efficiency, electron donating properties with a narrow band gap by introducing electron donating groups and electron withdrawing groups into the main chain skeleton Organic materials have been reported (for example, see Non-Patent Documents 3 and 4). As this electron-withdrawing group, a thienopyrrole-4,6-dione skeleton having an imide group or a thienoisoindole-5,7-dione skeleton is used, Narrow band gap electron-donating organic materials in which an oligothiophene skeleton, a cyclopentadithiophene skeleton, or a benzodithiophene skeleton is combined as an electron-donating group have been reported (see Patent Document 1 and Non-Patent Documents 4 to 16).

WO2011 / 063534

Narrow bandgap electron-donating organic material combining the above-described electron-withdrawing group with a thienopyrrole dione skeleton and the electron-donating group with an oligothiophene skeleton, a cyclopentadithiophene skeleton, or a benzodithiophene skeleton (Patent Document 1, Non-Patent Document) In 5 to 15), the solubility in an organic solvent necessary for coating the power generation layer is poor, and in order to improve the solubility, an alkyl side chain is introduced on the nitrogen of the thienopyrrole dione skeleton. However, it was thought that the introduction of an excessive alkyl group having no carrier transporting ability would reduce the carrier mobility of the electron donating organic material.

Examples of the alkyl group on the nitrogen include a straight chain structure such as a butyl group, a hexyl group, an octyl group, and a dodecyl group (Patent Document 1, Non-Patent Documents 5 to 13), a 2-ethylhexyl group, a 3,7-dimethylhexyl group, A branched chain structure such as 2-butyloctyl group (Patent Document 1, Non-Patent Documents 6, 8 to 10, 14) is used. A relatively short alkyl group such as a butyl group cannot secure sufficient solubility in an organic solvent, and the compatibility with an electron accepting material typified by fullerene also decreases, so that sufficient photoelectric conversion efficiency can be obtained. (Non-patent document 9).

Furthermore, in a narrow bandgap electron donating organic material in which a conventional alkyl group is introduced into the thienopyrrole dione skeleton, the highest occupied molecular orbital (HOMO) level becomes shallow, and the open voltage of the solar cell characteristics decreases.

That is, in a conventional photovoltaic device using an electron-donating organic material having a thienopyrrole dione skeleton in which an alkyl side chain is introduced on nitrogen, any of solubility in an organic solvent, high carrier mobility, and deep HOMO Was insufficient, and only those with low photoelectric conversion efficiency were obtained. An object of the present invention is to provide a photovoltaic device having high photoelectric conversion efficiency, and to provide an electron-donating organic material satisfying all of solubility in an organic solvent, high carrier mobility, and deep HOMO.

As a result of examining various structures of substituents on the thienopyrrole dione skeleton, aryl and heteroaryl groups were introduced on nitrogen in order to satisfy the solubility in organic solvents, high carrier mobility, and deep HOMO formation. I found out that I should do.

That is, the present invention relates to an electron donating organic material containing a thienopyrrole dione structural unit in which an aryl group or a heteroaryl group is introduced on the nitrogen represented by the general formula (1), and a photovoltaic device using the same. is there.

(In the general formula (1), R ¹ represents an optionally substituted aryl group or an optionally substituted heteroaryl group.)

According to the present invention, a photovoltaic device with high photoelectric conversion efficiency can be provided.

The schematic diagram which showed the one aspect | mode of the photovoltaic device of this invention. The schematic diagram which showed another aspect of the photovoltaic element of this invention.

The electron donating organic material of the present invention includes a structural unit represented by the general formula (1).

(In the general formula (1), R ¹ represents an optionally substituted aryl group or an optionally substituted heteroaryl group.)
The aryl group or heteroaryl group introduced onto the nitrogen of this thienopyrrole dione skeleton makes it possible to partially destroy the planarity of the conjugated polymer, so that both solubility in organic solvents and high carrier mobility can be achieved. It will be possible. Here, the partial planarity of the conjugated polymer is partially broken by the twist between the aryl group or heteroaryl group introduced on the nitrogen of the conjugated polymer main chain skeleton and the thienopyrrole dione skeleton. This means that the planarity of the whole conjugated polymer is slightly lowered while maintaining the pi-conjugated plane of the case. Furthermore, by arranging an electron-withdrawing group on the aryl group or heteroaryl group on nitrogen, it is considered possible to deepen the HOMO level of the conjugated polymer (this may be called deep HOMO). .

Here, the aryl group refers to, for example, an aromatic hydrocarbon group such as a phenyl group, a naphthyl group, a biphenyl group, a phenanthryl group, an anthryl group, a terphenyl group, a pyrenyl group, a fluorenyl group, and a perylenyl group. In order to maintain the high carrier mobility of the electron donating organic material, a phenyl group having a small molecular size is particularly preferably used.

The heteroaryl group includes, for example, thienyl group, furyl group, pyrrolyl group, imidazolyl group, pyrazolyl group, oxazolyl group, pyridyl group, pyrazyl group, pyrimidyl group, quinolinyl group, isoquinolyl group, quinoxalyl group, acridinyl group, indolyl group. A heteroaromatic cyclic group having an atom other than carbon, such as a group, a carbazolyl group, a benzofuran group, a dibenzofuran group, a benzothiophene group, a dibenzothiophene group, a benzodithiophene group, a silole group, a benzosilole group, and a dibenzosilole group; The number of carbon atoms in the heteroaryl group is preferably 2 or more and 8 or less in order to maintain carrier mobility. Here, the carbon number of the heteroaryl group represents the number of carbon atoms contained in the aromatic ring, and even if a non-aromatic carbon is included as a substituent, it is not included in the carbon number of the heteroaryl group.

^Examples of the substituent of the aryl group or heteroaryl group when the aryl group or heteroaryl group has a substituent include an alkyl group (R ^1S1 ), an alkoxy group (R ^1S2 ), and a halogen (R ^1S3 ). Note that halogen is not a group, but in the present invention, it is treated as one type of group (hereinafter, the same applies to substituents on other structural formulas). In addition, when a phenyl group is used as the aryl group, the position of the substituent is preferably in the ortho position or the meta position, and since an appropriate twist can be generated in the phenyl group and the main chain structure, an excessive alkyl side chain is introduced. Thus, the solubility of the conjugated polymer can be improved.

Here, the alkyl group (R ^1S1 ) is, for example, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, or a dodecyl group. The saturated aliphatic hydrocarbon group may be linear, branched, or cyclic, and may be unsubstituted or substituted. Examples of the substituent when substituted include an alkoxy group and halogen. The number of carbon atoms of the alkyl group (R ^1S1 ) is preferably 6 or less in order to maintain sufficient carrier mobility of the electron donating organic material. Here, carbon contained in the substituent in the alkyl group is not included in the number of carbon atoms of the alkyl group (R ^1S1 ). As the substituent for the alkyl group (R ^1S1 ), fluorine is particularly preferably used to deepen the HOMO level of the conjugated polymer.

In addition, the alkoxy group (R ^1S2 ) is a group in which an aliphatic hydrocarbon group is bonded via an ether bond such as a methoxy group, an ethoxy group, a propoxy group, or a butoxy group, and the alkoxy group (R ^1S2 ) The aliphatic hydrocarbon group may be unsubstituted or may have a substituent. Examples of the substituent in the case of having a substituent include the above aryl group, the above heteroaryl group, and halogen. The preferable carbon number range of the alkoxy group (R ^1S2 ) is preferably 6 or less as in the case of the alkyl group (R ^1S1 ). In this case as well, the carbon number contained in the substituent of the aliphatic hydrocarbon group is not included in the number of carbon atoms of the alkoxy group (R ^1S2 ).

The halogen (R ^1S3 ) that can be applied to the present invention is any one of fluorine, chlorine, bromine, and iodine. Among these, fluorine is particularly preferably used because it can deepen the HOMO level of the electron-donating organic material by being introduced as a substituent of the aryl group or heteroaryl group.

The electron donating organic material including the structure represented by the general formula (1) is preferably composed of the structure represented by the general formula (2).

(In the general formula (2), X represents a divalent linking group capable of maintaining a conjugated structure. N represents the degree of polymerization and represents a range of 2 to 1,000.)
By setting n to 2 or more and 1,000 or less, the carrier mobility of the electron-donating organic material can be increased, and an effective carrier path can be formed in the aforementioned bulk heterojunction thin film, so that the photoelectric conversion efficiency is increased. be able to. For ease of synthesis, n is preferably less than 100. The degree of polymerization can be determined by dividing the weight average molecular weight by the molecular weight (calculated value) of the repeating unit. The weight average molecular weight can be determined by measuring using GPC (gel permeation chromatography) and converting to a polystyrene standard sample.

In the general formula (2), X is a divalent linking group capable of maintaining a conjugated structure. Here, the divalent linking group capable of maintaining a conjugated structure is a linking group that itself has a conjugated structure, and the conjugated structures on both sides of two bonding sites can be continued through the linking group. Say that. Preferred examples of the linking group X include thiophene derivatives such as oligothiophene, benzodithiophene, and cyclopentadithiophene. Among these, the band gap can be narrowed and high carrier mobility can be maintained. The benzodithiophene or cyclopentadithiophene represented by 3) is more preferably used.

(In general formula (3), R ² to R ⁵ may be the same or different and each represents an optionally substituted alkyl group, alkoxy group, aryl group, or heteroaryl group.)
The alkyl group, alkoxy group, aryl group, and heteroaryl group are as described above except for the preferred carbon number range. In order to maintain the carrier mobility of the conjugated polymer, R ² to R ⁵ are particularly preferably an alkyl group or alkoxy group having 12 or less carbon atoms.

Specific examples of the electron donating organic material including the structure represented by the general formula (1) include the following structures. In the following structural formula, n is preferably in the range of 2 or more and 1,000 or less for the same reason as in the case of the general formula (2).

The electron-donating organic material containing the structural unit represented by the general formula (1) is, for example, the polymerization method described in Non-Patent Document 5 or the polymerization method described in Non-Patent Document 8. Obtainable.

The electron donating organic material containing the structural unit represented by the general formula (1) of the present invention is a material exhibiting p-type semiconductor characteristics, and is used as a photovoltaic element material in an organic semiconductor layer in a photovoltaic element. Preferably used. The electron donating organic material containing the structural unit represented by the general formula (1) of the present invention may be used as a material for a photovoltaic device comprising (i-1) alone, or (i-2) It may be used as a photovoltaic device material in combination with other electron-donating organic materials, or (ii) used as a photovoltaic device material in combination with an electron-accepting organic material exhibiting n-type semiconductor characteristics. Also good. Among them, it is preferable to combine with an electron-accepting organic material (the embodiment (ii)) because higher photoelectric conversion efficiency can be obtained. In the embodiment (ii), other electron donating organic materials in the embodiment (i-2) may be used in combination. In addition, the specific aspect of the organic-semiconductor layer and photovoltaic element using these materials for photovoltaic elements is mentioned later.

In the case where the electron donating organic material containing the structural unit represented by the general formula (1) is used as a material for a photovoltaic device in combination with another electron donating organic material (the embodiment (i-2)) Examples of other electron-donating organic materials that can be used in combination include polythiophene polymers, benzothiadiazole-thiophene derivatives, benzothiadiazole-thiophene copolymers, poly-p-phenylene vinylene polymers, poly- Conjugated polymers such as p-phenylene polymer, polyfluorene polymer, polypyrrole polymer, polyaniline polymer, polyacetylene polymer, polythienylene vinylene polymer, H ₂ phthalocyanine (H ₂ Pc ), Phthalocyanine derivatives such as copper phthalocyanine (CuPc) and zinc phthalocyanine (ZnPc), porphyrin Derivatives, N, N′-diphenyl-N, N′-di (3-methylphenyl) -4,4′-diphenyl-1,1′-diamine (TPD), N, N′-dinaphthyl-N, N ′ -Triarylamine derivatives such as diphenyl-4,4'-diphenyl-1,1'-diamine (NPD), carbazole derivatives such as 4,4'-di (carbazol-9-yl) biphenyl (CBP), oligothiophene Examples thereof include low molecular organic compounds such as derivatives (terthiophene, quarterthiophene, sexithiophene, octithiophene, etc.).

When the electron-donating organic material containing the structural unit represented by the general formula (1) is used as a material for a photovoltaic device in combination with an electron-accepting organic material exhibiting n-type semiconductor characteristics (the mode (ii) above) ), For example, 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), 3,4,9,10-perylenetetracarboxylic dianhydride (NTCDA) PTCDA), 3,4,9,10-perylenetetracarboxylic bisbenzimidazole (PTCBI), N, N′-dioctyl-3,4,9,10-naphthyltetracarboxydiimide (PTCDI-C8H), 2- ( 4-Biphenylyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole (PBD), oxazole derivatives such as 2,5-di (1-naphthyl) -1,3,4-oxadiazole (BND), 3- (4-biphenylyl) -4-phenyl-5- (4-t -Butylphenyl) -1,2,4-triazole (TAZ) and other triazole derivatives, phenanthroline derivatives, phosphine oxide derivatives, fullerene compounds (C ₆₀ , C ₇₀ , C ₇₆ , C ₇₈ , C ₈₂ , C ₈₄ , C ₉₀ , C ₉₄ and the like, [6,6] -phenyl C61 butyric acid methyl ester ([6,6] -PCBM), [5,6] -phenyl C61 butyric acid methyl ester ( [5,6] -PCBM), [6,6] -phenyl C61 butyric acid hexyl ester ([6,6] -PCBH), [6 ] - phenyl C61 butyric acid dodecyl ester ([6,6] -PCBD), phenyl C71 butyric acid methyl ester _(PC 70 BM), phenyl C85 butyric acid methyl ester _(PC 84 BM)), carbon nanotubes ( CNT), a derivative in which a cyano group is introduced into a poly-p-phenylene vinylene polymer (CN-PPV), and the like. Among these, fullerene compounds are preferably used because of their high charge separation speed and electron transfer speed. Among fullerene compounds, C ₇₀ derivatives (such as the above PC ₇₀ BM) are more preferable because they are excellent in light absorption characteristics and can obtain higher photoelectric conversion efficiency.

When the electron-donating organic material containing the structural unit represented by the general formula (1) is used as a material for a photovoltaic device in combination with an electron-accepting organic material exhibiting n-type semiconductor characteristics (the mode (ii) above) ), The content ratio (weight fraction) of the electron-donating organic material and the electron-accepting organic material is not particularly limited, but the weight fraction of the electron-donating organic material: electron-accepting organic material is 1:99 to 99. Is preferably in the range of 1:90, more preferably in the range of 10:90 to 90:10, and still more preferably in the range of 20:80 to 60:40.

When the electron-donating organic material containing the structural unit represented by the general formula (1) is used as a material for a photovoltaic device in combination with an electron-accepting organic material exhibiting n-type semiconductor characteristics (the mode (ii) above) The preferred form of the organic semiconductor layer in the organic semiconductor layer will be described later. There is no particular limitation on the mixing method in the case of adopting the form used by mixing, but after adding it to the solvent at a desired ratio, one or more methods such as heating, stirring and ultrasonic irradiation are combined. And a method of dissolving in a solvent. Electron-donating organic material in the case of a mixed form: The weight fraction of the electron-accepting organic material is as described above, and in the case of a form in which the electron-donating organic material and the electron-accepting organic material are stacked. (Including the case of a laminated structure of two or more layers) means the content ratio of the electron donating organic material and the electron accepting organic material in the entire laminated layer.

In order to further improve the photoelectric conversion efficiency, the electron-donating organic material and / or the electron-accepting organic material preferably has a small amount of impurities that can trap carriers, and the electron-donating organic material It is preferable to remove as much as possible in the production process of the electron-accepting organic material. In the present invention, the electron-donating organic material containing the structural unit represented by the general formula (1) and the purification method for removing impurities from the electron-accepting organic material are not particularly limited. A crystal method, a sublimation method, a reprecipitation method, a Soxhlet extraction method, a molecular weight fractionation method by GPC, a filtration method, an ion exchange method, a chelate method and the like can be used. In general, a column chromatography method, a recrystallization method, and a sublimation method are preferably used for purification of a low molecular weight organic material. On the other hand, for purification of high molecular weight compounds, reprecipitation method, Soxhlet extraction method, molecular weight fractionation method by GPC is preferably used when removing low molecular weight components, and reprecipitation method or the like when removing metal components. A chelate method or an ion exchange method is preferably used. A plurality of these methods may be combined.

Next, the photovoltaic element of the present invention will be described. The photovoltaic element of the present invention has at least a positive electrode and a negative electrode, and an organic semiconductor layer containing the material for a photovoltaic element of the present invention between them. FIG. 1 is a schematic view showing an example of the photovoltaic element of the present invention. In FIG. 1, reference numeral 1 is a substrate, reference numeral 2 is a positive electrode, reference numeral 3 is an organic semiconductor layer containing the photovoltaic element material of the present invention, and reference numeral 4 is a negative electrode.

The organic semiconductor layer 3 contains the photovoltaic element material of the present invention. That is, the electron-donating organic material containing the structural unit represented by the general formula (1) is included. Here, when the electron donating organic material containing the structural unit represented by the general formula (1) is used in combination with an electron accepting organic material exhibiting n-type semiconductor characteristics (the embodiment (ii)), these There are modes in which organic materials are mixed and used, but it is preferable to adopt a mode in which they are used in combination. That is, a bulk heterojunction photovoltaic device that can increase the bonding surface between an electron-donating organic material and an electron-accepting organic material that contribute to photoelectric conversion efficiency by mixing an electron-donating organic material and an electron-accepting organic material Is preferable. In this bulk heterojunction organic power generation layer, it is preferable that the electron-donating organic material containing the structural unit represented by the general formula (1) and the electron-accepting organic material are phase-separated in a nanometer size. The domain size of this phase separation structure is not particularly limited, but is usually 1 nm or more and 50 nm or less.

In addition, in the case where the electron-donating organic material containing the structural unit represented by the general formula (1) is used in combination with an electron-accepting organic material exhibiting n-type semiconductor characteristics (the embodiment (ii)), When the corresponding electron-donating organic material and electron-accepting organic material are laminated, the layer containing the electron-donating organic material exhibiting p-type semiconductor characteristics is on the positive electrode side, and the electron-accepting property exhibiting n-type semiconductor characteristics The layer containing an organic material is preferably on the negative electrode side. An example of the photovoltaic element in such a case is shown in FIG. Reference numeral 5 denotes a layer containing an electron donating organic material containing the structural unit represented by the general formula (1), and reference numeral 6 denotes a layer containing an electron accepting organic material. The organic semiconductor layer preferably has a thickness of 5 nm to 500 nm, more preferably 30 nm to 300 nm. When stacked, the layer containing the electron-donating organic material of the present invention preferably has a thickness of 1 nm to 400 nm, more preferably 15 nm to 150 nm.

In the photovoltaic device of the present invention, it is preferable that either the positive electrode 2 or the negative electrode 4 has light transmittance. The light transmittance of the electrode is not particularly limited as long as incident light reaches the organic semiconductor layer 3 and an electromotive force is generated. Here, the electrode represents a positive electrode or a negative electrode. The light transmittance in the present invention is a value obtained by [transmitted light intensity (W / m ² ) / incident light intensity (W / m ² )] × 100 (%). The thickness of the electrode may be in a range having light transmittance and conductivity, and is preferably 20 nm to 300 nm although it varies depending on the electrode material. The other electrode is not necessarily light-transmitting as long as it has conductivity, and the thickness is not particularly limited.

As the electrode material, it is preferable to use a conductive material having a high work function for one electrode and a conductive material having a low work function for the other electrode. An electrode using a conductive material having a large work function is a positive electrode. Conductive materials with a large work function include metals such as gold, platinum, chromium and nickel, transparent metal oxides such as indium, tin and molybdenum, and composite metal oxides (indium tin oxide (ITO)). Indium zinc oxide (IZO) and the like are preferably used. Here, the conductive material used for the positive electrode 2 is preferably one that is in ohmic contact with the organic semiconductor layer 3. Furthermore, when a hole transport layer described later is used, it is preferable that the conductive material used for the positive electrode 2 is in ohmic contact with the hole transport layer.

An electrode using a conductive material with a low work function is a negative electrode, but as the conductive material with a low work function, alkali metal or alkaline earth metal, specifically lithium, magnesium, calcium, etc. are used. . Tin, silver, and aluminum are also preferably used. Furthermore, an electrode made of an alloy made of the above metal or a laminate of the above metal is also preferably used. Further, it is possible to improve the extraction current by introducing a metal fluoride such as lithium fluoride or cesium fluoride into the interface between the negative electrode 4 and the electron transport layer. Here, the conductive material used for the negative electrode 4 is preferably one that is in ohmic contact with the organic semiconductor layer 3.

The substrate 1 is a substrate on which an electrode material and an organic semiconductor layer can be laminated according to the type and application of the photoelectric conversion material, for example, inorganic materials such as alkali-free glass and quartz glass, polyester, polycarbonate, polyolefin, polyamide, polyimide, polyphenylene A film or plate produced by an arbitrary method from an organic material such as sulfide, polyparaxylene, epoxy resin or fluorine resin can be used. In the case where light is incident from the substrate side, it is preferable that each substrate described above has a light transmittance of about 80%.

In the present invention, a hole transport layer may be provided between the positive electrode 2 and the organic semiconductor layer 3. Examples of the material for forming the hole transport layer include conductive polymers such as polythiophene polymers, poly-p-phenylene vinylene polymers, polyfluorene polymers, phthalocyanine derivatives (H ₂ Pc, CuPc, ZnPc, etc.) ), Low molecular organic compounds exhibiting p-type semiconductor properties such as porphyrin derivatives are preferably used. In particular, polyethylenedioxythiophene (PEDOT), which is a polythiophene polymer, or PEDOT to which polystyrene sulfonate (PSS) is added is preferably used. The thickness of the hole transport layer is preferably 5 nm to 600 nm, more preferably 30 nm to 200 nm.

In the photovoltaic device of the present invention, an electron transport layer may be provided between the organic semiconductor layer 3 and the negative electrode 4. The material for forming the electron transport layer is not particularly limited, but the above-described electron-accepting organic materials (NTCDA, PTCDA, PTCDI-C8H, oxazole derivatives, triazole derivatives, phenanthroline derivatives, phosphine oxide derivatives, fullerene compounds, Organic materials exhibiting n-type semiconductor properties such as CNT and CN-PPV are preferably used. The thickness of the electron transport layer is preferably 5 nm to 600 nm, more preferably 30 nm to 200 nm.

Further, the photovoltaic element of the present invention may form a series junction by laminating two or more organic semiconductor layers via one or more intermediate electrodes. For example, a laminated structure of substrate / positive electrode / first organic semiconductor layer / intermediate electrode / second organic semiconductor layer / negative electrode can be given. Such a configuration is sometimes called a tandem configuration. By adopting the tandem configuration in this way, the open circuit voltage can be improved. Note that the hole transport layer described above may be provided between the positive electrode and the first organic semiconductor layer and between the intermediate electrode and the second organic semiconductor layer, and between the first organic semiconductor layer and the intermediate electrode. The above-described electron transport layer may be provided between the second organic semiconductor layer and the negative electrode.

In such a tandem configuration, at least one of the organic semiconductor layers contains the photovoltaic device material of the present invention, and the other layers are represented by the general formula (1) in order not to reduce the short-circuit current. It is preferable to include an electron-donating organic material having a different band gap from the electron-donating organic material containing a structural unit. Examples of the electron-donating organic material used in such a case include the above-described polythiophene polymer, benzothiadiazole-thiophene derivative, benzothiadiazole-thiophene copolymer, poly-p-phenylene vinylene polymer, poly-p. -Conjugated polymers such as phenylene polymers, polyfluorene polymers, polypyrrole polymers, polyaniline polymers, polyacetylene polymers, polythienylene vinylene polymers, phthalocyanine derivatives, porphyrin derivatives, triaryls Low molecular organic compounds such as amine derivatives, carbazole derivatives, oligothiophene derivatives and the like can be mentioned.

In addition, the material for the intermediate electrode used here is preferably a material having high conductivity, for example, the above-mentioned metals such as gold, platinum, chromium, nickel, lithium, magnesium, calcium, tin, silver, aluminum, and transparent Metal oxides such as indium, tin, and molybdenum, composite metal oxides (indium tin oxide (ITO), indium zinc oxide (IZO), etc.), alloys composed of the above metals, and laminates of the above metals , Polyethylenedioxythiophene (PEDOT), and those obtained by adding polystyrene sulfonate (PSS) to PEDOT. The intermediate electrode preferably has a light transmission property, but even a material such as a metal having a low light transmission property can often ensure a sufficient light transmission property by reducing the film thickness.

Next, a method for manufacturing the photovoltaic element of the present invention will be described with an example. A transparent electrode such as ITO (corresponding to a positive electrode in this case) is formed on the substrate by sputtering or the like. Next, a solution is prepared by dissolving an electron-donating organic material containing the structural unit represented by the general formula (1) and, if necessary, a material for a photoelectric conversion element containing an electron-accepting organic material in a solvent. To form an organic semiconductor layer.

The solvent used at this time is preferably an organic solvent, for example, methanol, ethanol, butanol, toluene, xylene, o-chlorophenol, acetone, ethyl acetate, ethylene glycol, tetrahydrofuran, dichloromethane, chloroform, dichloroethane, chlorobenzene, dichlorobenzene, Examples include chlorobenzene, chloronaphthalene, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, and γ-butyrolactone. Two or more of these may be used.

When the organic semiconductor layer is formed by mixing the electron-donating organic material containing the structural unit represented by the general formula (1) and the electron-accepting organic material, the structural unit represented by the general formula (1) is included. An electron-donating organic material and an electron-accepting organic material are added to a solvent in a desired ratio, dissolved by using a method such as heating, stirring, and ultrasonic irradiation to form a solution, which is applied onto a transparent electrode. In this case, the photoelectric conversion efficiency of the photovoltaic element can be improved by using a mixture of two or more solvents. This is because, as described above, a structure in which an electron-donating organic material and an electron-accepting material are phase-separated at a nanometer size is preferable for improving the conversion efficiency, and such a phase-separated structure can be formed by a solvent. It is. As the solvent to be combined in such a case, an optimal combination type can be selected depending on the types of the electron donating organic material and the electron accepting organic material to be used. When using the electron donating organic material containing the structural unit represented by the general formula (1), chloroform and chlorobenzene are mentioned as preferred solvents to be combined among the above. In this case, the mixing volume ratio of each solvent is preferably in the range of chloroform: chlorobenzene = 5: 95 to 95: 5, and more preferably in the range of chloroform: chlorobenzene = 10: 90 to 90:10.

When an organic semiconductor layer is formed by stacking an electron donating organic material and an electron accepting organic material containing the structural unit represented by the general formula (1), for example, a solution of an electron donating organic material is applied. After forming a layer having an electron-donating organic material, a solution of the electron-accepting organic material is applied to form a layer. Here, when the electron-donating organic material and the electron-accepting organic material are low molecular weight substances having a molecular weight of about 1000 or less, it is possible to form a layer using a vapor deposition method.

For organic semiconductor layer formation, spin coating, blade coating, slit die coating, screen printing coating, bar coater coating, mold coating, printing transfer method, dip pulling method, ink jet method, spray method, vacuum deposition method, etc. This method may be used, and the formation method may be selected according to the characteristics of the organic semiconductor layer to be obtained, such as film thickness control and orientation control. For example, when spin coating is performed, the electron donating organic material containing the structural unit represented by the general formula (1) and the electron accepting organic material have a concentration of 1 to 20 g / l (in the general formula (1)). The electron donating organic material and the electron accepting organic material having the structure represented by the general formula (1) with respect to the volume of the solution containing the electron donating organic material, the electron accepting organic material and the solvent having the structure represented by Weight) is preferable, and by setting this concentration, a homogeneous organic semiconductor layer having a thickness of 5 to 200 nm can be easily obtained.

In order to remove the solvent, the formed organic semiconductor layer may be annealed under reduced pressure or under an inert atmosphere (in a nitrogen or argon atmosphere). A preferable temperature for the annealing treatment is 40 ° C to 300 ° C, more preferably 50 ° C to 200 ° C. Further, by performing the annealing process that applies heat, the effective area where the stacked layers permeate and contact each other at the interface increases, and the short-circuit current can be increased. This annealing treatment may be performed after the formation of the negative electrode.

Next, a metal electrode such as Al (corresponding to a negative electrode in this case) is formed on the organic semiconductor layer by vacuum deposition or sputtering. When the metal electrode is vacuum-deposited using a low molecular organic material for the electron transport layer, it is preferable that the metal electrode is continuously formed while maintaining the vacuum.

When a hole transport layer is provided between the positive electrode and the organic semiconductor layer, a desired p-type organic semiconductor material (such as PEDOT) is applied on the positive electrode by spin coating, bar coating, blade casting, or the like. Then, the solvent is removed using a vacuum thermostat or a hot plate to form a hole transport layer. In the case of using a low molecular organic material such as a phthalocyanine derivative or a porphyrin derivative, it is also possible to apply a vacuum vapor deposition method using a vacuum vapor deposition machine.

When an electron transport layer is provided between the organic semiconductor layer and the negative electrode, a desired n-type organic semiconductor material (such as fullerene derivatives) or an n-type inorganic semiconductor material (such as titanium oxide gel) is spin-coated on the organic semiconductor layer. After coating by a coating method, a casting method using a blade, a spray method, or the like, the solvent is removed using a vacuum thermostat or a hot plate to form an electron transport layer. When using a low molecular organic material such as a phenanthroline derivative or C _60, it is also possible to apply a vacuum deposition method using a vacuum deposition machine.

The photovoltaic element of the present invention can be applied to various photoelectric conversion devices using a photoelectric conversion function, an optical rectification function, and the like. For example, it is useful for photovoltaic cells (such as solar cells), electronic devices (such as optical sensors, optical switches, phototransistors), optical recording materials (such as optical memories), and the like.

Hereinafter, the present invention will be described more specifically based on examples. In addition, this invention is not limited to the following Example. Of the compounds used in the examples and the like, those using abbreviations are shown below.
ITO: indium tin oxide PEDOT: polyethylene dioxythiophene PSS: polystyrene sulfonate PC ₇₀ BM: phenyl C71 butyric acid methyl ester Eg: band gap HOMO: highest occupied molecular orbital Isc: short circuit current density Voc: open circuit voltage FF: fill Factor η: Photoelectric conversion efficiency For the ¹ H-NMR measurement, an FT-NMR apparatus (JEOL JNM-EX270 manufactured by JEOL Ltd.) was used.

Further, the average molecular weight (number average molecular weight, weight average molecular weight) was calculated by an absolute calibration curve method using a polystyrene standard sample using a GPC apparatus (manufactured by TOSOH Co., Ltd., which was fed with chloroform, high-speed GPC apparatus HLC-8320GPC). . The degree of polymerization n was calculated by the following formula.
Degree of polymerization n = [(weight average molecular weight) / (molecular weight of repeating unit (calculated value))]
The band gap (Eg) was calculated from the light absorption edge wavelength by the following equation. The light absorption edge wavelength was measured using a U-3010 type spectrophotometer manufactured by Hitachi, Ltd. for a thin film formed on a glass by spin coating using chloroform as a solvent to a thickness of about 60 nm. It was obtained from an ultraviolet-visible absorption spectrum (measurement wavelength range: 300 to 900 nm) of the obtained thin film.
Eg (eV) = 1240 / light absorption edge wavelength of thin film (nm)
m
Note that whether the material is an electron-donating organic material or an electron-accepting organic material (p-type semiconductor characteristics or n-type semiconductor characteristics) can be specified by performing FET measurement or energy level measurement on the above-described thin film.

Synthesis example 1
Compound A-1 was synthesized by the method shown in Formula 1. The compound of formula 1 (1-g) was synthesized with reference to the method described in Advanced Functional Materials, 2011, Vol. 21, pp. 718-728.

To 50 ml of acetic acid solution of 4.5 g (26.1 mmol) of thiophenedicarboxylic acid (manufactured by Frontier Scientific), 25 g (156 mmol) of bromine was slowly added and stirred at room temperature for 1 hour and at 60 ° C. for 6 hours. After completion of the stirring, a saturated aqueous sodium thiosulfate solution was slowly added to the reaction solution until the color of the reaction solution disappeared, and the mixture was left at 0 ° C. for 12 hours. The precipitated solid was filtered off and recrystallized from acetone / water to give 5.7 g (yield 66%) of compound (1-b) as a white solid. The measurement result of ¹³ C-NMR of the compound (1-b) is shown below.
¹³ C-NMR (67.5 MHz, DMSO-d ₆ ): 162.46, 135.11, 114.39 ppm.

80 ml of acetic anhydride (manufactured by Wako Pure Chemical Industries, Ltd.) was added to 4.9 g (14.9 mmol) of the above compound (1-b), and the mixture was heated to reflux for 6 hours. After the reaction solution was distilled off under reduced pressure, the precipitated solid was washed with hexane and dried to obtain 3.4 g (yield 74%) of compound (1-c) as a white solid. The measurement result of ¹³ C-NMR of the compound (1-c) is shown below.
¹³ C-NMR (67, 5 MHz, CDCl ₃ ): 153.78, 133.66, 116.99 ppm
To a solution of orthotoluidine (manufactured by Tokyo Chemical Industry Co., Ltd.) 343 mg (3.2 mmol) in dimethylformamide (15 ml) was added 936 mg (3.0 mmol) of the above compound (1-c) at room temperature, and the mixture was stirred at 70 ° C. for 3 hours. . After completion of the reaction, the solvent was distilled off under reduced pressure to obtain 1.3 g (crudely purified product) of compound (1-e) as a white solid. Compound (1-e) was directly used in the next reaction. The measurement result of ¹ H-NMR of the compound (1-e) is shown below.
¹ H-NMR (270 MHz, DMSO-d ₆ ): 9.96 (s, 1H), 7.40 (d, J = 8.4 Hz, 1H), 7.25-7.11 (m, 3H), 2.28 (s, 3H) ppm.

800 mg of sodium acetate (manufactured by Wako Pure Chemical Industries, Ltd.) was added to 1.3 g of the above compound (1-e) in acetic anhydride solution (20 ml), and the mixture was stirred at 80 ° C. for 5 hours. The reaction solution was slowly poured into methanol (200 ml), stirred for a while at room temperature, and then the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography (eluent, chloroform) gave 960 mg (yield 80%) of compound (1-f) as a white solid. The measurement results of ¹ H-NMR and ¹³ C-NMR of the compound (1-f) are shown below.
¹ H-NMR (270 MHz, CDCl ₃ ): 7.4-7.3 (m, 3H), 7.14 (d, J = 7.6 Hz, 1H), 2.21 (s, 3H) ppm.
¹³ C-NMR (67.5 MHz, CDCl ₃ ): 159.09, 136.65, 134.32, 131.1, 130.33, 129.5, 128.2, 126.8, 113.95, 18 .01 ppm.

When 60 mg (0.15 mmol) of the compound (1-f) and 115 mg (0.15 mmol) of the compound (1-g) were dissolved in 10 ml of toluene (manufactured by Wako Pure Chemical Industries, Ltd.), tris (dibenzylidene) was dissolved. Acetone) dipalladium (manufactured by Tokyo Chemical Industry Co., Ltd.) 4 mg and tris (2-methylphenyl) phosphine (manufactured by Tokyo Chemical Industry Co., Ltd.) 7 mg were added, and the mixture was stirred at 100 ° C. for 12 hours under a nitrogen atmosphere. Subsequently, 10 mg of bromobenzene (manufactured by Tokyo Chemical Industry Co., Ltd.) was added and stirred at 100 ° C. for 1 hour. Next, 40 mg of tributyl (2-thienyl) tin (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and the mixture was further stirred at 100 ° C. for 1 hour. After completion of the stirring, the reaction mixture was cooled to room temperature and poured into 100 ml of methanol. The precipitated solid was collected by filtration and washed with methanol, water, and acetone in this order. Subsequently, it wash | cleaned in order of acetone and hexane using the Soxhlet extractor. Next, the obtained solid was dissolved in chloroform, passed through Celite (manufactured by Nacalai Tesque), and then a silica gel column (free solution, chloroform), and then the solvent was distilled off under reduced pressure. The obtained solid was dissolved again in chloroform and then reprecipitated in methanol to obtain Compound A-1 (84 mg). The weight average molecular weight was 29,800, the number average molecular weight was 14,200, and the degree of polymerization n was 43. The light absorption edge wavelength was 680 nm, the band gap (Eg) was 1.82 eV, and the highest occupied molecular orbital (HOMO) level was −5.34 eV.

Synthesis example 2
Compound A-2 was synthesized by the method shown in Formula 2.

To a solution of dimethylformamide (15 ml) in 400 mg (3.2 mmol) of 4-fluoro-2-methylaniline (manufactured by Aldrich) was added 936 mg (3.0 mmol) of the above compound (1-c) at room temperature. Stir. After completion of the reaction, the solvent was distilled off under reduced pressure to obtain 1.3 g of the compound (2-b) (crude product) as a white solid. Compound (2-b) was directly used in the next reaction. The measurement result of ¹ H-NMR of the compound (2-b) is shown below.
¹ H-NMR (270 MHz, DMSO-d ₆ ): 7.28 (m, 2H), 6.95 (dd, J = 8.6 Hz and 2.7 Hz, 1H), 2.25 (s, 3H) ppm.

800 mg of sodium acetate (manufactured by Wako Pure Chemical Industries, Ltd.) was added to 1.3 g of the above compound (2-b) in acetic anhydride solution (20 ml) and stirred at 80 ° C. for 5 hours. The reaction solution was slowly poured into methanol (200 ml), stirred for a while at room temperature, and then the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography (eluent, chloroform) gave 875 mg (yield 70%) of compound (2-c) as a white solid. The measurement result of ¹ H-NMR of the compound (2-c) is shown below.
¹ H-NMR (270 MHz, CDCl ₃ ): 7.31 (m, 1H), 7.10 (m, 1H), 6.90 (d, J = 8.6 Hz, 1H), 2.17 (s, 3H) ppm.

When 63 mg (0.15 mmol) of the compound (2-c) and 115 mg (0.15 mmol) of the compound (1-g) were dissolved in 10 ml of toluene (manufactured by Wako Pure Chemical Industries, Ltd.), tris (dibenzylidene) was dissolved. Acetone) dipalladium (manufactured by Tokyo Chemical Industry Co., Ltd.) 4 mg and tris (2-methylphenyl) phosphine (manufactured by Tokyo Chemical Industry Co., Ltd.) 7 mg were added, and the mixture was stirred at 100 ° C. for 12 hours under a nitrogen atmosphere. Subsequently, 10 mg of bromobenzene (manufactured by Tokyo Chemical Industry Co., Ltd.) was added and stirred at 100 ° C. for 1 hour. Next, 40 mg of tributyl (2-thienyl) tin (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and the mixture was further stirred at 100 ° C. for 1 hour. After completion of the stirring, the reaction mixture was cooled to room temperature and poured into 100 ml of methanol. The precipitated solid was collected by filtration and washed with methanol, water, and acetone in this order. Subsequently, it wash | cleaned in order of acetone and hexane using the Soxhlet extractor. Next, the obtained solid was dissolved in chloroform, passed through Celite (manufactured by Nacalai Tesque), and then a silica gel column (free solution, chloroform), and then the solvent was distilled off under reduced pressure. The obtained solid was dissolved again in chloroform and then reprecipitated in methanol to obtain Compound A-2 (79 mg). The weight average molecular weight was 42,800, the number average molecular weight was 21,200, and the degree of polymerization n was 61. The light absorption edge wavelength was 680 nm, the band gap (Eg) was 1.82 eV, and the highest occupied molecular orbital (HOMO) level was −5.41 eV.

Synthesis example 3
Compound A-3 was synthesized by the method shown in Formula 3.

To a dimethylformamide solution (10 ml) of 338 mg (2.1 mmol) of 2-aminobenzotrifluoride (manufactured by Tokyo Chemical Industry Co., Ltd.), 624 mg (2.0 mmol) of the above compound (1-c) was added at room temperature, and 70 ° C. Stir for 3 hours. After completion of the reaction, the solvent was distilled off under reduced pressure to obtain 950 mg (crudely purified product) of compound (3-b) as a white solid. Compound (3-b) was directly used in the next reaction.

To 950 mg of acetic anhydride solution (10 ml) of the above compound (3-b), 500 mg of sodium acetate (manufactured by Wako Pure Chemical Industries, Ltd.) was added and stirred at 80 ° C. for 5 hours. The reaction solution was slowly poured into methanol (100 ml) and stirred for a while at room temperature, and then the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography (eluent, chloroform) gave 592 mg (yield 65%) of compound (3-c) as a white solid. The measurement result of ¹ H-NMR of the compound (3-c) is shown below.
¹ H-NMR (270 MHz, CDCl ₃ ): 7.83 (d, J = 7.6 Hz, 1H), 7.68 (m, 2H), 7.31 (d, J = 7.6 Hz, 1H) ppm .

When 68 mg (0.15 mmol) of the compound (3-c) and 115 mg (0.15 mmol) of the compound (1-g) were dissolved in 10 ml of toluene (manufactured by Wako Pure Chemical Industries, Ltd.), tris (dibenzylidene) was dissolved. Acetone) dipalladium (manufactured by Tokyo Chemical Industry Co., Ltd.) 4 mg and tris (2-methylphenyl) phosphine (manufactured by Tokyo Chemical Industry Co., Ltd.) 7 mg were added, and the mixture was stirred at 100 ° C. for 12 hours under a nitrogen atmosphere. Subsequently, 10 mg of bromobenzene (manufactured by Tokyo Chemical Industry Co., Ltd.) was added and stirred at 100 ° C. for 1 hour. Next, 40 mg of tributyl (2-thienyl) tin (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and the mixture was further stirred at 100 ° C. for 1 hour. After completion of the stirring, the reaction mixture was cooled to room temperature and poured into 100 ml of methanol. The precipitated solid was collected by filtration and washed with methanol, water, and acetone in this order. Subsequently, it wash | cleaned in order of acetone and hexane using the Soxhlet extractor. Next, the obtained solid was dissolved in chloroform, passed through Celite (manufactured by Nacalai Tesque), and then a silica gel column (free solution, chloroform), and then the solvent was distilled off under reduced pressure. The obtained solid was dissolved again in chloroform and then reprecipitated in methanol to obtain Compound A-3 (80 mg). The weight average molecular weight was 34,100, the number average molecular weight was 12,200, and the degree of polymerization n was 46. The light absorption edge wavelength was 672 nm, the band gap (Eg) was 1.85 eV, and the highest occupied molecular orbital (HOMO) level was −5.46 eV.

Synthesis example 4
Compound A-4 was synthesized by the method shown in Formula 4. The compound (4-d) described in Formula 4 was synthesized with reference to the method described in Macromolecules 2007, 40, 1981-1986.

To a solution of 233 mg (2.1 mmol) of 4-fluoroaniline (manufactured by Tokyo Chemical Industry Co., Ltd.) in dimethylformamide (10 ml) is added 624 mg (2.0 mmol) of the above compound (1-c) at room temperature, and 70 ° C. for 3 hours. Stir. After completion of the reaction, the solvent was distilled off under reduced pressure to obtain 850 mg (crude product) of compound (4-b) as a white solid. Compound (4-b) was directly used in the next reaction.

400 mg of sodium acetate (manufactured by Wako Pure Chemical Industries, Ltd.) was added to 850 mg of acetic anhydride solution (10 ml) of the above compound (4-b), and the mixture was stirred at 80 ° C. for 5 hours. The reaction solution was slowly poured into methanol (100 ml) and stirred for a while at room temperature, and then the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography (eluent, chloroform) gave 570 mg (yield 70%) of compound (4-c) as a white solid. The measurement result of ¹ H-NMR of the compound (4-c) is shown below.
¹ H-NMR (270 MHz, CDCl ₃ ): 7.35 (m, 1H), 7.18 (m, 1H), 1.55 (s, 3H) ppm.

When 61 mg (0.15 mmol) of the compound (4-c) and 109 mg (0.15 mmol) of the compound (4-d) were dissolved in 5 ml of toluene (manufactured by Wako Pure Chemical Industries, Ltd.), tris (dibenzylidene) was dissolved. Acetone) dipalladium (manufactured by Tokyo Chemical Industry Co., Ltd.) 4 mg and tris (2-methylphenyl) phosphine (manufactured by Tokyo Chemical Industry Co., Ltd.) 7 mg were added, and the mixture was stirred at 100 ° C. for 12 hours under a nitrogen atmosphere. Subsequently, 10 mg of bromobenzene (manufactured by Tokyo Chemical Industry Co., Ltd.) was added and stirred at 100 ° C. for 1 hour. Next, 40 mg of tributyl (2-thienyl) tin (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and the mixture was further stirred at 100 ° C. for 1 hour. After completion of the stirring, the reaction mixture was cooled to room temperature and poured into 100 ml of methanol. The precipitated solid was collected by filtration and washed with methanol, water, and acetone in this order. Subsequently, it wash | cleaned in order of acetone and hexane using the Soxhlet extractor. Next, the obtained solid was dissolved in chloroform, passed through Celite (manufactured by Nacalai Tesque), then a silica gel column (free solution: chloroform), and then the solvent was distilled off under reduced pressure. The obtained solid was dissolved again in chloroform and then reprecipitated in methanol to obtain Compound A-4 (68 mg). The weight average molecular weight was 32,000, the number average molecular weight was 12,200, and the degree of polymerization n was 50. The light absorption edge wavelength was 739 nm, the band gap (Eg) was 1.68 eV, and the highest occupied molecular orbital (HOMO) level was −5.49 eV.

Synthesis example 5
Compound B-1 was synthesized by the method shown in Formula 5. The compound (5-a) described in Formula 5 was synthesized with reference to the method described in Advanced Functional Materials, 2011, Vol. 21, pp. 71-728.

When 63 mg (0.15 mmol) of the compound (5-a) and 116 mg (0.15 mmol) of the compound (1-g) were dissolved in 10 ml of toluene (manufactured by Wako Pure Chemical Industries, Ltd.), tris (dibenzylidene) was dissolved. Acetone) dipalladium (manufactured by Tokyo Chemical Industry Co., Ltd.) 4 mg and tris (2-methylphenyl) phosphine (manufactured by Tokyo Chemical Industry Co., Ltd.) 7 mg were added, and the mixture was stirred at 100 ° C. for 12 hours under a nitrogen atmosphere. Subsequently, 10 mg of bromobenzene (manufactured by Tokyo Chemical Industry Co., Ltd.) was added and stirred at 100 ° C. for 1 hour. Next, 40 mg of tributyl (2-thienyl) tin (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and the mixture was further stirred at 100 ° C. for 1 hour. After completion of the stirring, the reaction mixture was cooled to room temperature and poured into 100 ml of methanol. The precipitated solid was collected by filtration and washed with methanol, water, and acetone in this order. Subsequently, it wash | cleaned in order of acetone and hexane using the Soxhlet extractor. Next, the obtained solid was dissolved in chloroform, passed through Celite (manufactured by Nacalai Tesque), and then a silica gel column (free solution, chloroform), and then the solvent was distilled off under reduced pressure. The obtained solid was dissolved again in chloroform and then reprecipitated in methanol to obtain Compound B-1 (79 mg). The weight average molecular weight was 65,000, the number average molecular weight was 26,100, and the degree of polymerization n was 91. The light absorption edge wavelength was 670 nm, the band gap (Eg) was 1.85 eV, and the highest occupied molecular orbital (HOMO) level was -5.23 eV.

Synthesis Example 6
Compound B-2 was synthesized by the method shown in Formula 6. The compound (6-a) described in Formula 6 was synthesized with reference to the method described in Advanced Functional Materials, 2011, Vol. 21, pp. 71-728.

A toluene / dimethylformamide solution (50 ml / 10 ml) of 1.18 g (2.0 mmol) of the above compound (6-a) and 2.2 g (6.0 mmol) of tributyl (2-thienyl) tin (manufactured by Tokyo Chemical Industry Co., Ltd.) ) 100 mg of dichlorobis (triphenylphosphine) palladium catalyst (manufactured by Tokyo Chemical Industry Co., Ltd.) was added and refluxed for 8 hours under nitrogen. The reaction solution was cooled to room temperature, 50 ml of water was added, and the organic layer was washed twice with water and then with saturated brine. The solvent was dried over anhydrous magnesium sulfate and then filtered, and the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography (eluent, hexane: ethyl acetate = 20: 1) gave compound (6-b) as a yellow solid (900 mg, yield 75%). The measurement result of ¹ H-NMR of the compound (6-b) is shown below.
¹ H-NMR (270 MHz, CDCl ₃ ): 8.02 (d, J = 3.4 Hz, 2H), 7.43 (d, J = 3.4 Hz, 2H), 7.12 (t, J = 7 .3 Hz, 2H), 3.55 (d, J = 7.3 Hz, 2H), 1.89 (brs, 1H), 1.4-1.2 (m, 34H), 0.86 (m, 6H) ) Ppm.

To a chloroform solution (50 ml) of 837 mg (1.4 mmol) of the above compound (6-b) was added 498 mg (2.8 mmol) of N-bromosuccinimide (manufactured by Tokyo Chemical Industry Co., Ltd.), and the mixture was stirred at room temperature for 6 hours. After adding 50 ml of water, the organic layer was washed twice with water and then once with saturated brine, dried over anhydrous magnesium sulfate, and the solvent was evaporated under reduced pressure. The crude product was purified by silica gel column chromatography (eluent, hexane: chloroform = 1: 1) to obtain compound (6-c) as a yellow solid (820 mg, yield 78%). The measurement result of ¹ H-NMR of the compound (6-c) is shown below.
¹ H-NMR (270 MHz, CDCl ₃ ): 7.66 (d, J = 4.1 Hz, 2H), 7.07 (J = 4.1 Hz, 2H), 3.53 (d, J = 7.3 Hz) , 2H), 1.87 (brs, 1H), 1.4-1.1 (m, 34H), 0.86 (m, 6H) ppm.

When 113 mg (0.15 mmol) of the compound (6-c) and 116 mg (0.15 mmol) of the compound (1-g) were dissolved in 10 ml of toluene (manufactured by Wako Pure Chemical Industries, Ltd.), tris (dibenzylidene) was dissolved. Acetone) dipalladium (manufactured by Tokyo Chemical Industry Co., Ltd.) 4 mg and tris (2-methylphenyl) phosphine (manufactured by Tokyo Chemical Industry Co., Ltd.) 7 mg were added, and the mixture was stirred at 100 ° C. for 12 hours under a nitrogen atmosphere. Subsequently, 10 mg of bromobenzene (manufactured by Tokyo Chemical Industry Co., Ltd.) was added and stirred at 100 ° C. for 1 hour. Next, 40 mg of tributyl (2-thienyl) tin (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and the mixture was further stirred at 100 ° C. for 1 hour. After completion of the stirring, the reaction mixture was cooled to room temperature and poured into 100 ml of methanol. The precipitated solid was collected by filtration and washed with methanol, water, and acetone in this order. Subsequently, it wash | cleaned in order of acetone and hexane using the Soxhlet extractor. Next, the obtained solid was dissolved in chloroform, passed through Celite (manufactured by Nacalai Tesque), and then a silica gel column (free solution, chloroform), and then the solvent was distilled off under reduced pressure. The obtained solid was dissolved again in chloroform and then reprecipitated in methanol to obtain Compound B-2 (72 mg). The weight average molecular weight was 45,300, the number average molecular weight was 22,000, and the degree of polymerization n was 44. The light absorption edge wavelength was 658 nm, the band gap (Eg) was 1.88 eV, and the highest occupied molecular orbital (HOMO) level was −5.35 eV.

Synthesis example 7
Compound B-3 was synthesized by the method shown in Formula 7.

When 63 mg (0.15 mmol) of the compound (5-a) and 109 mg (0.15 mmol) of the compound (4-d) were dissolved in 5 ml of toluene (manufactured by Wako Pure Chemical Industries, Ltd.), tris (dibenzylidene) was dissolved. Acetone) dipalladium (manufactured by Tokyo Chemical Industry Co., Ltd.) 4 mg and tris (2-methylphenyl) phosphine (manufactured by Tokyo Chemical Industry Co., Ltd.) 7 mg were added, and the mixture was stirred at 100 ° C. for 12 hours under a nitrogen atmosphere. Subsequently, 10 mg of bromobenzene (manufactured by Tokyo Chemical Industry Co., Ltd.) was added and stirred at 100 ° C. for 1 hour. Next, 40 mg of tributyl (2-thienyl) tin (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and the mixture was further stirred at 100 ° C. for 1 hour. After completion of the stirring, the reaction mixture was cooled to room temperature and poured into 100 ml of methanol. The precipitated solid was collected by filtration and washed with methanol, water, and acetone in this order. Subsequently, it wash | cleaned in order of acetone and hexane using the Soxhlet extractor. Next, the obtained solid was dissolved in chloroform, passed through Celite (manufactured by Nacalai Tesque), and then a silica gel column (free solution, chloroform), and then the solvent was distilled off under reduced pressure. The obtained solid was dissolved again in chloroform and then reprecipitated in methanol to obtain Compound B-3 (50 mg). The weight average molecular weight was 19,400, the number average molecular weight was 11,000, and the degree of polymerization n was 29. The light absorption edge wavelength was 752 nm, the band gap (Eg) was 1.65 eV, and the highest occupied molecular orbital (HOMO) level was −5.28 eV.

Example 1
The above A-1 (1 mg) and PC ₇₀ BM (4 mg, manufactured by Solenne) were added to a sample bottle containing 0.25 ml of chlorobenzene, and an ultrasonic cleaner (US-2 manufactured by Inoue Seieido Co., Ltd.) Name), and output 120W) for 30 minutes to obtain a solution A.

A glass substrate on which a 120-nm thick ITO transparent conductive layer serving as a positive electrode was deposited by sputtering was cut into 38 mm × 46 mm, and then ITO was patterned into a 38 mm × 13 mm rectangular shape by photolithography. The obtained substrate was subjected to ultrasonic cleaning for 10 minutes with an alkali cleaning solution (“Semico Clean” EL56 (trade name), manufactured by Furuuchi Chemical Co., Ltd.), and then washed with ultrapure water.

After this substrate was UV / ozone treated for 30 minutes, a PEDOT: PSS aqueous solution (0.8% by weight of PEDOT, 0.5% by weight of PPS) serving as a hole transport layer was formed on the substrate to a thickness of 60 nm by spin coating. did. After heating and drying at 200 ° C. for 5 minutes using a hot plate, the above solution A was dropped onto the PEDOT: PSS layer, and an organic semiconductor layer having a thickness of 100 nm was formed by spin coating. Thereafter, the substrate on which the organic semiconductor layer is formed and the cathode mask are placed in a vacuum vapor deposition apparatus, and the vacuum in the apparatus is exhausted again until the vacuum level becomes 1 × 10 ⁻³ Pa or less, and the negative electrode is formed by resistance heating. The aluminum layer to be formed was deposited so as to have a thickness of 80 nm and an area intersecting with the stripe-like ITO layer was 5 mm × 5 mm. As described above, a photovoltaic element having a power generation layer area of 5 mm × 5 mm was produced. As described above, a photovoltaic device having an area where the stripe-shaped ITO layer intersects with the aluminum layer was 5 mm × 5 mm was produced.

The positive and negative electrodes of the photovoltaic device thus fabricated were connected to a picoammeter / voltage source 4140B manufactured by Hewlett-Packard Co., and simulated sunlight (from Yamashita Denso Co., Ltd., simplified) from the ITO layer side in the atmosphere. Type solar simulator YSS-E40, spectrum shape: AM1.5, intensity: 100 mW / cm ² ), and the current value was measured when the applied voltage was changed from −1V to + 2V. At this time, the short-circuit current density (value of the current density when the applied voltage is 0 V) is 6.45 A / cm ² , the open circuit voltage (value of the applied voltage when the current density is 0) is 0.97 V, and the fill factor (FF) was 0.60, and the photoelectric conversion efficiency calculated from these values was 3.75%. The fill factor and photoelectric conversion efficiency were calculated by the following equations.
Fill factor = IVmax (mA · V / cm ² ) / (Short-circuit current density (mA / cm ² ) × Open circuit voltage (V))
(Here, IVmax is the value of the product of the current density and the applied voltage at the point where the product of the current density and the applied voltage becomes maximum when the applied voltage is between 0 V and the open circuit voltage value.)
Photoelectric conversion efficiency = [(short circuit current density (mA / cm ² ) × open voltage (V) × fill factor) / pseudo sunlight intensity (100 mW / cm ² )] × 100 (%)
The fill factor and photoelectric conversion efficiency in the following examples and comparative examples were all calculated by the above formula.

Example 2
A photovoltaic device was prepared in the same manner as in Example 1 except that A-2 was used in place of A-1, and current-voltage characteristics were measured. At this time, the short-circuit current density was 7.83 mA / cm ² , the open-circuit voltage was 0.98 V, and the fill factor (FF) was 0.54. The photoelectric conversion efficiency calculated from these values was 4.14%. .

Example 3
A photovoltaic device was prepared in the same manner as in Example 1 except that A-3 was used in place of A-1, and current-voltage characteristics were measured. At this time, the short-circuit current density was 7.23 mA / cm ² , the open-circuit voltage was 0.98 V, the fill factor (FF) was 0.50, and the photoelectric conversion efficiency calculated from these values was 3.54%. .

Example 4
A photovoltaic device was produced in the same manner as in Example 1 except that A-4 was used instead of A-1, and current-voltage characteristics were measured. At this time, the short-circuit current density was 7.68 mA / cm ² , the open-circuit voltage was 0.94 V, the fill factor (FF) was 0.46, and the photoelectric conversion efficiency calculated from these values was 3.32%. .

Comparative Example 1
A photovoltaic device was prepared in the same manner as in Example 1 except that B-1 was used instead of A-1, and current-voltage characteristics were measured. The short-circuit current density at this time was 6.10 mA / cm ² , the open-circuit voltage was 0.96 V, and the fill factor (FF) was 0.45. The photoelectric conversion efficiency calculated from these values was 2.64%. .

Comparative Example 2
A photovoltaic device was produced in the same manner as in Example 1 except that B-2 was used in place of A-1, and current-voltage characteristics were measured. At this time, the short-circuit current density was 2.45 mA / cm ² , the open-circuit voltage was 0.76 V, the fill factor (FF) was 0.56, and the photoelectric conversion efficiency calculated from these values was 1.04%. .

Comparative Example 3
A photovoltaic device was produced in the same manner as in Example 1 except that B-3 was used in place of A-1, and current-voltage characteristics were measured. At this time, the short-circuit current density was 5.43 mA / cm ² , the open-circuit voltage was 0.80 V, the fill factor (FF) was 0.41, and the photoelectric conversion efficiency calculated from these values was 1.78%. .

As is clear from Table 1, the photovoltaic devices (Examples 1 to 4) produced using the electron donating organic material having the structure represented by the general formula (1) were produced under the same conditions. The photoelectric conversion efficiency was higher than those of the photovoltaic devices (Comparative Examples 1 to 3).

1: Substrate 2: Positive electrode 3: Organic semiconductor layer 4: Negative electrode 5: Layer having an electron-donating organic material 6: Layer having an electron-accepting organic material

Claims

An electron-donating organic material containing a structural unit represented by the general formula (1).

(In the general formula (1), R 1 represents an optionally substituted aryl group or an optionally substituted heteroaryl group.)
2. The electron donating organic material according to claim 1, comprising a structure represented by the general formula (2).

(In the above general formula (2), X represents a divalent linking group capable of maintaining a conjugated structure. N represents the degree of polymerization and represents a range of 2 to 1,000.)
The electron donating organic material according to claim 2, wherein X in the general formula (2) includes a cyclopentadithiophene structure or a benzodithiophene structure represented by the general formula (3).

(In general formula (3), R 2 to R 5 may be the same or different and each represents an optionally substituted alkyl group, alkoxy group, aryl group, or heteroaryl group.)
A photovoltaic device material comprising the electron donating organic material according to any one of claims 1 to 3.
The photovoltaic device which has an organic-semiconductor layer containing the material for photovoltaic devices of Claim 4 between the negative electrode and the positive electrode.