JP2012241099A - Conjugated polymer, electron-releasing organic material employing the same, material for photovoltaic element and photovoltaic element - Google Patents

Abstract

A photovoltaic device having high photoelectric conversion efficiency is provided.
A photovoltaic device material comprising a conjugated polymer having a specific structure.
[Selection figure] None

Description

  The present invention relates to a conjugated polymer, an electron-donating organic material, a photovoltaic device material and a photovoltaic device using the conjugated polymer.

    Solar cells are attracting attention as an environmentally friendly electrical energy source and an influential energy source for increasing energy problems. 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 ordinary households because of high costs compared with power generation methods such as thermal power generation and nuclear power generation. 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 slow.

  Conventional photoelectric conversion elements using organic semiconductors can be generally classified into the following element configurations at present. A Schottky type that joins an electron-donating organic material (p-type organic semiconductor) and a metal having a low work function, and an electron-accepting organic material (n-type organic semiconductor) and an electron-donating organic material (p-type organic semiconductor). Heterojunction type. 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), was used C ₆₀ derivatives such other PCBM conductive polymer having semiconductor properties of n-type as the electron accepting organic material A photoelectric conversion material has been reported (for example, see Non-Patent Document 2).

  In addition, in order to efficiently absorb radiant energy over a wide range of the solar spectrum, photoelectric conversion materials using organic semiconductors with an electron-donating group and an electron-withdrawing group introduced into the main chain to narrow the band gap have been reported. (For example, see Non-Patent Documents 3 to 6). However, sufficient photoelectric conversion efficiency has not been obtained.

J. et al. J. et al. M.M. Halls, C.I. A. Walsh, N .; C. Greenham, E.I. A. Marsegla, R.M. H. Frind, S.M. C. Moratti, A.M. B. Homes, "Nature", 1995, 376, 498 G. Yu, J. et al. Gao, J .; C. Hummelen, F.M. Wudl, A.W. J. et al. Heeger, "Science", 1995, 270, 1789 E. Bundgaard, F.M. C. Krebs, "Solar Energy Materials & Solar Cells", 2007, 91, 954. S. Xiao, A .; C. Stuart, S.A. Liu, W .; By You, "ACS Applied Materials & Interfaces", 2009, Volume 1, p. 1613 L. Huo, J. et al. Hou, H.H. Chen, S.M. Zhang, Y. et al. Jiang, T .; L. Chen, Y. et al. Yang, “Macromolecules”, 2009, 42, 6564 H. Zhou, L .; Yang, S .; Xiao, S .; Liu, W .; You, “Macromolecules”, 2010, 43, 811

  As described above, all of the conventional organic solar cells have a problem of low photoelectric conversion efficiency. An object of this invention is to provide a photovoltaic device with high photoelectric conversion efficiency.

  That is, the present invention is a conjugated polymer having a structure represented by the following general formula (1), an electron donating organic material, a photovoltaic element material and a photovoltaic element using the conjugated polymer.

(R ¹ and R ² may be the same or different and are selected from hydrogen, deuterium, alkyl group, alkoxy group, ester group, aryl group, heteroaryl group, and halogen. R ³ and R ⁴ are the same. However, it may be different, and is an alkyl group having 6 or more carbon atoms, n represents a range of 5 or more and 1000 or less, and A is selected from structures represented by any one of the following general formula (2) )

(R ^{5 to} R ²³ may be the same or different, and are selected from hydrogen, deuterium, alkyl groups, alkoxy groups, ester groups, aryl groups, heteroaryl groups, and halogens.)

  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 conjugated polymer of the present invention has a structure represented by the following general formula (1).

In the general formula (1), R ¹ and R ² may be the same or different and are selected from hydrogen, deuterium, alkyl group, alkoxy group, ester group, aryl group, heteroaryl group, and halogen. R ³ and R ⁴ may be the same or different and are alkyl groups having 6 or more carbon atoms. n represents the range of 5 or more and 1000 or less. A is selected from structures represented by any one of the following general formula (2).

  Here, the alkyl group is, for example, a saturated aliphatic group such as methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group. The hydrocarbon group may be linear, branched, or cyclic, and may be unsubstituted or substituted. From the viewpoint of heat resistance, the alkyl group preferably has 30 or less carbon atoms, more preferably 20 or less. Examples of the substituent when substituted include the following alkoxy groups, ester groups, aryl groups, heteroaryl groups, and halogens.

  The alkoxy group refers to, for example, an aliphatic hydrocarbon group via an ether bond such as a methoxy group, an ethoxy group, a propoxy group, or a butoxy group, and the aliphatic hydrocarbon group may be unsubstituted or substituted. Absent. From the viewpoint of heat resistance, the alkoxy group preferably has 30 or less carbon atoms, more preferably 20 or less. Examples of the substituent when substituted include the following aryl groups, heteroaryl groups, and halogens.

  The ester group refers to, for example, an aliphatic hydrocarbon group or an aromatic hydrocarbon group via an ester bond such as a methyl ester group, an ethyl ester group, a butyl ester group, or a phenyl ester group.

  The aryl group represents, 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, which is unsubstituted. But it can be replaced. The number of carbon atoms of the aryl group is preferably 6 or more and 30 or less from the viewpoint of processability. Examples of the substituent when substituted include the above alkyl group, alkoxy group, the following heteroaryl group, and halogen.

  The heteroaryl group is, for example, thienyl group, thienothienyl group, furyl group, pyrrolyl group, imidazolyl group, pyrazolyl group, oxazolyl group, pyridyl group, pyrazyl group, pyrimidyl group, quinolinyl group, isoquinolyl group, quinoxalyl group, acridinyl A heteroaromatic group having an atom other than carbon, such as a group, an indolyl 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, or a dibenzosilole group This can be unsubstituted or substituted. Examples of the substituent in the case of substitution include the above alkyl group, alkoxy group, aryl group, and the following halogen.

  Halogen is any one of fluorine, chlorine, bromine and iodine. N represents the degree of polymerization and is in the range of 5 or more and 1000 or less. The degree of polymerization can be determined from the weight average molecular weight. The weight average molecular weight can be determined by measuring using GPC (gel permeation chromatography) and converting to a polystyrene standard sample.

  Since the conjugated polymer represented by the general formula (1) is excellent in light absorption characteristics and hole transportability, it can be preferably used as an electron donating organic material in a photovoltaic device.

  A bulk heterojunction type photovoltaic device is known as a method for increasing the photoelectric conversion efficiency of a photovoltaic device, which increases the bonding surface contributing to photoelectric conversion by mixing an electron-accepting organic material and an electron-donating organic material. ing. In bulk heterojunction photovoltaic devices, the electron-donating organic material and the electron-accepting organic material are not completely compatible with each other in order to form a path for electrons and holes (carrier path). It is preferable.

  Further, the photoelectric conversion efficiency of the photovoltaic element greatly depends on the orientation state of the electron donating organic material. When the π plane of the electron donating organic material is oriented parallel to the photovoltaic element substrate, it is possible to efficiently absorb incident light and at the same time move electrons and holes efficiently.

The conjugated polymer having the structure represented by the general formula (1) in the present invention enables both the above-described nano-level phase separation formation and ideal alignment state formation. The main chain structure of the conjugated polymer having the structure represented by the general formula (1) includes a benzo [2,1-b: 3,4-b ′] dithiophene skeleton having R ^{1 to} R ⁴ and a general formula It has a divalent linking group represented by (2).

The first component, the benzo [2,1-b: 3,4-b ′] dithiophene skeleton, has high planarity and thus easily causes aggregation due to π-π stacking, and is a phase suitable for the above-described bulk heterojunction. It is considered that a separation structure is easily formed. Further, by introducing an alkyl group having 6 or more carbon atoms at the positions of R ³ and R ⁴ , the above-mentioned nano-level phase separation formation and ideal orientation state formation can be realized while ensuring solubility. It becomes possible.

Here, introduction of an alkyl group having 6 or more carbon atoms at the positions of R ³ and R ⁴ means that the alkyl group is directly bonded to the dithiophene skeleton, and the polymer described in Non-Patent Document 4 (Comparative Example 1) or non- Even if an alkyl group having 6 or more carbon atoms is introduced via a thiophene skeleton as in the polymer described in Patent Document 6 (Comparative Example 3), the above effect cannot be obtained.

  The divalent linking group represented by the general formula (2), which is the second component, is an electron-withdrawing skeleton, and can narrow the band gap and efficiently absorb light on the long wavelength side. Is. The divalent linking group represented by the general formula (2) is bonded directly to the benzo [2,1-b: 3,4-b ′] dithiophene skeleton which is the first component, thereby It is possible to maintain the formation of nano-level phase separation and ideal alignment.

  Here, the polymer described in Non-Patent Document 5 (Comparative Example 2) and the polymer described in Non-Patent Document 6 (Comparative Example 3) are diketopyrrolopyrrole and benzothiophene or benzothiadiazole and benzothiophene via thiophene. The above effects are difficult to obtain because they are bonded and not directly bonded.

  Examples of the conjugated polymer having the structure represented by the general formula (1) include the following structures. In the following structure, n is in the range of 5 to 1000.

  In addition, the conjugated polymer which has a structure represented by General formula (1) is compoundable by the method similar to the method described in the said nonpatent literature 4-6, for example.

The electron donating organic material of the present invention may be composed only of a conjugated polymer having a structure represented by the general formula (1), or may contain other electron donating organic materials. Examples of other electron-donating organic materials include polythiophene polymers, poly-p-phenylene vinylene polymers, poly-p-phenylene polymers, polyfluorene polymers, polypyrrole polymers, polyaniline polymers. Conjugated polymers such as polyacetylene polymers, polythienylene vinylene polymers, phthalocyanine derivatives such as H ₂ phthalocyanine (H ₂ Pc), copper phthalocyanine (CuPc), 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′-diphenyl- Triarylamine derivatives such as 4,4′-diphenyl-1,1′-diamine (NPD), 4,4′-di (carbazole-9) Yl) biphenyl (CBP) as an electroluminescent host carbazole derivatives such as, oligothiophene derivatives (terthiophene, quarter thiophene, sexithiophene include low molecular organic compound of octyl thiophene etc.) and the like.

  Since the conjugated polymer having the structure represented by the general formula (1) exhibits p-type semiconductor characteristics, an electron-accepting organic material (n-type) is required to obtain higher photoelectric conversion efficiency as a photovoltaic device material. It is preferable to combine with an organic semiconductor.

The electron-accepting organic material used in the present invention is an organic material exhibiting n-type semiconductor characteristics. For example, 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), 3,4,9,10- Perylenetetracarboxylic dianhydride (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), 2,5-di (1-naphthyl) -1,3 , 4-oxadiazole (BND) and other oxazole derivatives, 3- (4-biphenylyl) -4-phenyl-5- (4-t- Triazole derivatives such as butylphenyl) -1,2,4-triazole (TAZ), phenanthroline derivatives, phosphine oxide derivatives, fullerene compounds (C ₆₀ , C ₇₀ , C ₇₆ , C ₇₈ , C ₈₂ , C ₈₄ , C ₉₀ , _Examples thereof include unsubstituted ones such as C94.

[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), [6,6] -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, etc.), carbon nanotube (CNT), poly-p-phenylene vinylene-based polymer derivative (CN-PPV), etc. Is mentioned.

Among these, fullerene compounds are preferably used because of their high charge separation speed and electron transfer speed. Among the fullerene compounds, C ₇₀ derivatives (such as the PC 70 _BM) because excellent light absorption characteristics, it is possible to obtain a relatively high photoelectric conversion efficiency, more preferred.

  In the photovoltaic device material of the present invention, the content ratio (weight fraction) of the electron-donating organic material and the electron-accepting organic material is not particularly limited. The rate is preferably in the range of 1 to 99:99 to 1, more preferably in the range of 10 to 90:90 to 10, still more preferably in the range of 20 to 60:80 to 40.

  It is preferable to use a mixture of an electron-donating organic material and an electron-accepting organic material. Although it does not specifically limit as a mixing method, After adding to a solvent in a desired ratio, the method of making it melt | dissolve in a solvent combining 1 type or multiple types of methods, such as a heating, stirring, and ultrasonic irradiation, is mentioned. . As will be described later, when the photovoltaic element material forms a single organic semiconductor layer, the above-mentioned content ratio is the content ratio of the electron-donating organic material and the electron-accepting organic material contained in the single layer. When the organic semiconductor layer has a laminated structure of two or more layers, it means the content ratio of the electron donating organic material and the electron accepting organic material in the whole organic semiconductor layer.

  In order to further improve the photoelectric conversion efficiency, it is preferable to remove impurities that can trap carriers as much as possible. In the present invention, the method for removing impurities from the conjugated polymer having the structure represented by the general formula (1) and the electron-accepting organic material is not particularly limited, but column chromatography, recrystallization, Sublimation method, reprecipitation method, Soxhlet extraction method, molecular weight fractionation method by GPC (gel permeation chromatography), filtration method, ion exchange method, 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, an ion exchange method, and a column chromatography method are preferably used. A plurality of these methods may be combined.

  Next, the photovoltaic element of the present invention will be described. The photovoltaic device of the present invention has at least a positive electrode and a negative electrode, and includes the photovoltaic device material 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, an electron donating organic material including a conjugated polymer having a structure represented by the general formula (1) and an electron accepting organic material are included. These materials may be mixed or laminated, but are preferably mixed. The aforementioned “bulk heterojunction type” indicates this mixed type. When they are mixed, the electron-donating organic material and the electron-accepting organic material are compatible or phase-separated at the molecular level, but are preferably phase-separated at the nano-level. The domain size of this phase separation structure is not particularly limited, but is usually 1 nm or more and 50 nm or less. When laminated, the layer having an electron-donating organic material exhibiting p-type semiconductor characteristics is preferably on the positive electrode side, and the layer having an electron-accepting organic material exhibiting n-type semiconductor characteristics is preferably on the negative electrode side.

  An example of the photovoltaic element in the case where the organic semiconductor layer 3 is laminated is shown in FIG. Reference numeral 5 denotes a layer having an electron donating organic material containing a conjugated polymer having a structure represented by the general formula (1), and reference numeral 6 denotes a layer having 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 laminated, the layer having the electron donating organic material containing the conjugated polymer having the structure represented by the general formula (1) has a thickness of 1 nm to 400 nm among the above thicknesses. It is preferably 15 nm to 150 nm.

  The organic semiconductor layer 3 may contain a conjugated polymer having a structure represented by the general formula (1) and an electron-donating organic material (p-type organic semiconductor) other than the electron-accepting organic material. . Examples of the electron donating organic material (p-type organic semiconductor) used here include those exemplified above.

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 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 transparency 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 an 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.

  In addition, it is possible to improve the extraction current by introducing a metal fluoride such as lithium fluoride or cesium fluoride or a metal carbonate such as cesium carbonate at 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. Furthermore, when an electron transport layer described later is used, it is preferable that the conductive material used for the negative electrode 4 is in ohmic contact with the electron transport layer.

  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. When light is incident from the substrate side and used, 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. As a material for forming the hole transport layer, 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 hole transport layer preferably has a thickness of 5 nm to 600 nm, more preferably 30 nm to 200 nm.

  Further, it is preferable to treat the hole transport layer with a fluorous compound (an organic compound having one or more fluorine atoms in the molecule), and the photoelectric conversion efficiency can be further improved. Examples of fluorous compounds include benzotrifluoride, hexafluorobenzene, 1,1,1,3,3,3-hexafluoro-2-propanol, perfluorotoluene, perfluorodecalin, perfluorohexane, 1H, 1H, 2H, 2H-hepta. Decafluoro-1-decanol (F-decanol) and the like can be mentioned.

  More preferably, benzotrifluoride, perfluorohexane, or F-decanol is used. As a treatment method, the above-mentioned fluorous compound is mixed in advance with the material for forming the hole-transporting layer and then the hole-transporting layer is formed, or the hole-transporting layer is formed and then the above-mentioned fluorous compound is contacted Examples thereof include spin coating, dip coating, blade coating, vapor deposition, and steam treatment.

  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, A compound exhibiting n-type semiconductor properties such as CNT and CN-PPV) and titanium oxide is preferably used. The thickness of the electron transport layer is preferably 5 nm to 600 nm, more preferably 30 nm to 200 nm.

  In the photovoltaic device of the present invention, two or more organic semiconductor layers may be stacked (tandemized) via one or more intermediate electrodes to form a series junction. For example, a laminated structure of substrate / positive electrode / first organic semiconductor layer / intermediate electrode / second organic semiconductor layer / negative electrode can be given. By laminating 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 hole transport layer described above may be provided between the second organic semiconductor layer and the negative electrode.

  In the case of such a laminated structure, at least one of the organic semiconductor layers contains the material for a photovoltaic device 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 conjugated polymer having a structure.

  Examples of such an electron-donating organic material include the polythiophene polymer, poly-p-phenylene vinylene polymer, poly-p-phenylene polymer, polyfluorene polymer, polypyrrole polymer, polyaniline described above. Polymer, polyacetylene polymer, polythienylene vinylene polymer, benzothiadiazole polymer (for example, PCPDTBT (poly [2,6- (4,4-bis- (2-ethylhexyl) -4H-cyclopenta [ 2,1-b; 3,4-b ′] dithiophene) -alt-4,7- (2,1,3-benzothiadiazole)]) and PSBTBT (poly [(4,4-bis- (2-ethylhexyl)). ) Dithiono [3,2-b: 2 ′, 3′-d] silole -2,6-diyl-alt- (2,1,3-benzothiadiazole) -4,7-diyl])) conjugated polymers and the like.

Further, phthalocyanine derivatives such as H ₂ phthalocyanine (H ₂ Pc), copper phthalocyanine (CuPc), zinc phthalocyanine (ZnPc), porphyrin derivatives, N, N′-diphenyl-N, N′-di (3-methylphenyl)- Tria such as 4,4′-diphenyl-1,1′-diamine (TPD), N, N′-dinaphthyl-N, N′-diphenyl-4,4′-diphenyl-1,1′-diamine (NPD) Low molecular organic compounds such as reelamine derivatives, carbazole derivatives such as 4,4′-di (carbazol-9-yl) biphenyl (CBP), oligothiophene derivatives (terthiophene, quarterthiophene, sexithiophene, octithiophene, etc.) Is 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, molybdenum and titanium, composite metal oxides (indium tin oxide (ITO), indium zinc oxide (IZO), etc.), alloys composed of the above metals and the above metals Examples include laminates, 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, an example is given and demonstrated about the manufacturing method of the photovoltaic device of this invention. 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 conjugated polymer having a structure represented by the general formula (1) and, if necessary, a material for a photovoltaic device including other electron donating organic materials and electron accepting organic materials are dissolved in a solvent. A solution is made and applied onto the transparent electrode 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, trichlorobenzene, chloronaphthalene, dimethylformamide, dimethyl sulfoxide, Examples thereof include N-methylpyrrolidone and γ-butyrolactone. Two or more of these may be used.

  Moreover, photoelectric conversion efficiency can be improved more by containing the above-mentioned fluorous compound. Fluorous compounds (fluorus solvents) that are liquid at normal temperature and pressure are preferred, and the above-mentioned benzotrifluoride, perfluorohexane, and F-decanol are more preferably used. The content of the fluoro compound is preferably 0.01 to 20% by volume, more preferably 0.1 to 2% by volume, based on the total amount of the solvent. Further, the content of the fluorous solvent is preferably 0.01 to 30% by weight, more preferably 0.1 to 4% by weight in the total solvent.

  When an organic semiconductor layer is formed by mixing an electron-donating organic material containing an conjugated polymer having a structure represented by the general formula (1) and an electron-accepting organic material, the organic semiconductor layer is represented by the general formula (1). An electron-donating organic material containing a conjugated polymer having a structure and an electron-accepting organic material are added to a solvent at a desired ratio, and dissolved using a method such as heating, stirring, or ultrasonic irradiation to form a solution. Apply on 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 presumably because the electron-donating organic material and the electron-accepting organic material undergo phase separation at the nano level, and a carrier path that forms a path for electrons and holes is formed. As the solvent to be combined, 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 an electron-donating organic material containing a conjugated polymer having a structure represented by the general formula (1), chloroform and chlorobenzene are mentioned as preferred solvents to be combined. In this case, the mixing volume ratio of each solvent is preferably in the range of chloroform: chlorobenzene = 5: 95 to 95: 5, more preferably in the range of chloroform: chlorobenzene = 10: 90 to 90:10.

  Further, when an organic semiconductor layer is formed by laminating an electron donating organic material containing a conjugated polymer having a structure represented by the general formula (1) and an electron accepting organic material, for example, an electron donating organic material After forming a layer having an electron-donating organic material by applying the above solution, a layer 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 concentration of electron donating organic material including a conjugated polymer having the structure represented by the general formula (1) and the electron accepting organic material is 1 to 20 g / l (general Conjugation 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 including the conjugated polymer having the structure represented by the formula (1) The weight of the electron-donating organic material and the electron-accepting organic material containing the polymer is preferable, and a homogeneous organic semiconductor layer having a thickness of 5 to 200 nm can be obtained by using this concentration.

  In order to remove the solvent, the formed organic semiconductor layer may be subjected to an annealing treatment under reduced pressure or in 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 treatment, 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 a photovoltaic cell (such as a solar cell), an electronic element (such as an optical sensor, an optical switch, a phototransistor, and a photoconductor), an optical recording material (such as an optical memory), 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 PCE: photoelectric conversion efficiency.

For ¹ H-NMR measurement, an FT-NMR apparatus (JEOL JNM-EX270 manufactured by JEOL Ltd.) was used. Moreover, the average molecular weight (number average molecular weight, weight average molecular weight) was calculated by an absolute calibration curve method using a GPC apparatus (manufactured by TOSOH Co., Ltd., to which chloroform was fed, high-speed GPC apparatus HLC-8220 GPC). The degree of polymerization n was calculated by the following formula.
Degree of polymerization n = [(weight average molecular weight) / (molecular weight of repeating unit)]
The light absorption edge wavelength is an ultraviolet-visible absorption spectrum (measurement wavelength) of a thin film formed on glass with a thickness of about 60 nm using a U-3010 spectrophotometer manufactured by Hitachi, Ltd. (Range: 300-900 nm). The band gap (Eg) was calculated from the light absorption edge wavelength by the following equation. The thin film was formed by spin coating using chloroform as a solvent.
Eg (eV) = 1240 / light absorption edge wavelength (nm)
In addition, the highest occupied molecular orbital (HOMO) level was determined by using a surface analyzer (in-air ultraviolet photoelectron spectrometer AC-2 type, manufactured by Riken Kikai Co., Ltd.) for a thin film formed on ITO glass with a thickness of about 60 nm. ). The thin film was formed by spin coating using chloroform as a solvent.

Synthesis example 1
Compound A-1 was synthesized by the method shown in Formula 1.

  20.29 g of compound (1-a) (manufactured by Wako Pure Chemical Industries, Ltd.) was added to a mixed solution of chloroform (162 ml) / acetic acid (72 ml), 74.1 g of bromine was added under a nitrogen atmosphere, The mixture was stirred at 60 ° C. for 1 hour and heated to reflux for 9 hours. After distilling off chloroform, 300 ml of water was added, and the solid was collected by filtration and washed with water and methanol in this order. The obtained solid was recrystallized from ethanol to obtain 45.43 g of compound (1-b).

  45.43 g of the above compound (1-b) and zinc powder (23.6 g) were added to a mixed solution of ethanol (472 ml) / acetic acid (113 ml) / hydrochloric acid (concentration 3M, 9.4 ml) / water (47 ml), and nitrogen was added. The mixture was heated to reflux for 2.5 hours under an atmosphere. Ethanol was distilled off, water was added, the solid was collected by filtration, and the resulting solid was dissolved in chloroform. The resulting solution was washed with water and dried over magnesium sulfate, and chloroform was distilled off. The obtained solid was purified by column chromatography (filler: silica gel, eluent: hot hexane) and then recrystallized from hexane to obtain 24.82 g of compound (1-c).

  3.56 g of the above compound (1-c), sodium iodide (8.24 g), copper (I) iodide (0.1 g), N, N′-dimethylethylenediamine (0.12 ml) were mixed with o-xylene (0.12 ml). 200 ml) / bis (2-methoxyethyl) ether (50 ml), and the mixture was refluxed for 3 days under a nitrogen atmosphere. The solid was filtered off from the obtained suspension, and the solvent was distilled off under reduced pressure. The obtained solid was purified by column chromatography (filler: silica gel, eluent: hot hexane) to obtain 4.1 g of compound (1-d).

  4.1 g of the above compound (1-d) and 8-hexadecine (manufactured by Tokyo Chemical Industry Co., Ltd.) (8.2 ml), palladium acetate (0.22 g) and tributylamine (7 ml) are added to dimethylformamide (40 ml) at 110 ° C. in a nitrogen atmosphere. Stir for 12 hours. Ether and water were added to the resulting solution to separate the organic layer, washed with water and dried over magnesium sulfate, and the solvent was distilled off under reduced pressure. The obtained oil was purified by column chromatography (filler: silica gel, eluent: hexane) to obtain 1.63 g of compound (1-e).

1.63 g of the above compound (1-e) was dissolved in 40 ml of dimethylformamide, 2.8 g of N-bromosuccinimide was added, and the mixture was stirred at room temperature for 1 day. Ether and water were added to the resulting solution to separate the organic layer, washed with water and dried over magnesium sulfate, and the solvent was distilled off under reduced pressure. The obtained oil was purified by column chromatography (filler: silica gel, eluent: hexane) to obtain 1.66 g of compound (1-f). The ¹ H-NMR measurement result of the compound (1-f) is shown.
¹ H-NMR (CDCl ₃ , ppm): 7.39 (s, 2H), 2.89 (t, 4H), 1.65 to 1.31 (m, 20H), 0.90 (t, 6H) .

  4.3 g of compound (1-g) (manufactured by Tokyo Chemical Industry Co., Ltd.) and 10 g of bromine were added to 150 ml of 48% hydrobromic acid and stirred at 120 ° C. for 3 hours. After cooling to room temperature, the precipitated solid was filtered through a glass filter and washed with 1000 ml of water and 100 ml of acetone. The obtained solid was vacuum-dried at 60 ° C. to obtain 6.72 g of compound (1-h).

5.3 g of the above compound (1-h) is added to 70 ml of 1,4-dioxane, and 10.6 g of bis (pinacolatodiboron) and 0.88 g of [bis (diphenylphosphino) ferrocene] dichloropalladium under a nitrogen atmosphere. After adding 5.3 g of potassium acetate, the mixture was stirred at 80 ° C. for 5 hours. The solid was filtered off from the obtained suspension, and the solvent was distilled off under reduced pressure. The obtained solid was recrystallized from hexane to obtain 3.29 g of compound (1-i). The ¹ H-NMR measurement result of compound (1-i) is shown.
_{^{1 H-NMR (CDCl 3,}} ppm): 8.14 (s, 2H), 1.45 (s, 24H).

  706 mg of the above compound (1-f) and 503 mg of the above compound (1-i) were dissolved in 18 ml of toluene. 10 ml of water, 3.59 g of potassium carbonate, 75 mg of tetrakis (triphenylphosphine) palladium (0) and 1 drop of Aliquat 336 (manufactured by Aldrich) were added thereto, and the mixture was stirred at 100 ° C. for 9 hours under a nitrogen atmosphere. Next, 1 g of bromobenzene was added and stirred at 100 ° C. for 2 hours, 1 g of phenylboronic acid was added, and the mixture was stirred at 100 ° C. for 2 hours. 500 ml of methanol was added to the obtained solution, and the generated solid was collected by filtration and washed with methanol, acetone, hot water and hot acetone in this order. The obtained solid was added to 400 ml of acetone and heated to reflux for 30 minutes. The solid obtained by filtration while hot was dissolved in chloroform, passed through a silica gel short column (eluent: chloroform), concentrated, and reprecipitated with methanol to obtain 600 mg of compound A-1 (yield 88%). ). The weight average molecular weight was 28600, the number average molecular weight was 15800, and the degree of polymerization n was 55.1. The light absorption edge wavelength was 705 nm, the band gap (Eg) was 1.76 eV, and the highest occupied molecular orbital (HOMO) level was −5.12 eV.

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

When 0.46 g of the compound (1-f) of Synthesis Example 1 was dissolved in 10 ml of tetrahydrofuran and cooled to −78 ° C., a 1.6 M concentration n-butyllithium hexane solution (manufactured by Wako Pure Chemical Industries, Ltd.) 1.2 ml was dripped and it stirred at -78 degreeC for 1 hour. Next, 0.5 g of trimethyltin chloride was added, and the reaction solution was further stirred at room temperature for 1 day, and then water and diethyl ether were added. The organic layer was washed 3 times with water and then dried over magnesium sulfate, and the solvent was distilled off under reduced pressure to obtain 0.47 g of compound (2-a). The ¹ H-NMR measurement result of the compound (2-a) is shown.
¹ H-NMR (CDCl ₃ , ppm): 7.48 (s, 2H), 3.03 (t, 4H), 1.63-1.31 (m, 20H), 0.90 (t, 6H) , 0.44 (s, 18H).

  197 mg of the above compound (2-a) and compound (2-b) (synthesized by the method described in Journal of the American Chemical Society, 2009, Vol. 131, pages 7792-7799) 131 mg was dissolved in 20 ml of toluene. To this, 2 ml of dimethylformamide and 16 mg of tetrakis (triphenylphosphine) palladium (0) were added, and the mixture was stirred at 120 ° C. for 1 day in a nitrogen atmosphere. 500 ml of methanol was added to the resulting solution, and the generated solid was collected by filtration and washed with methanol, acetone, hot water and acetone in this order. The obtained solid was dissolved in chloroform, passed through a silica gel short column (eluent: chloroform), concentrated, and reprecipitated with methanol to obtain 180 mg of compound A-2 (yield 93%). The weight average molecular weight was 4,900, the number average molecular weight was 3,500, and the degree of polymerization n was 7.0. The light absorption edge wavelength was 762 nm, the band gap (Eg) was 1.63 eV, and the highest occupied molecular orbital (HOMO) level was -4.96 eV.

Example 1
1 mg of the above A-1 and 4 mg of PC ₇₀ BM (manufactured by Solen) are added to a sample bottle containing 0.25 ml of chlorobenzene, and an ultrasonic cleaning machine (US-2 (trade name) manufactured by Inoue Seieido Co., Ltd.) The solution A was obtained by ultrasonic irradiation for 30 minutes in an output of 120 W).

A glass substrate on which an ITO transparent conductive layer serving as a positive electrode having a thickness of 120 nm 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 evaporation apparatus, and the vacuum is exhausted again until the degree of vacuum in the apparatus becomes 1 × 10 ⁻³ Pa or less. An aluminum layer was deposited to a thickness of 80 nm. 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 3.66 mA / cm ² , the open circuit voltage (value of the applied voltage when the current density is 0) is 0.78 V, and the fill factor (FF) was 0.61, and the photoelectric conversion efficiency calculated from these values was 1.7%. The fill factor and photoelectric conversion efficiency were calculated by the following equations.
Fill factor = IVmax (mW / 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 comparative examples were all calculated by the above formula.

Example 2
A photovoltaic device was produced 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 3.82 mA / cm ² , the open-circuit voltage was 0.90 V, the fill factor (FF) was 0.67, and the photoelectric conversion efficiency calculated from these values was 2.3%. .

Comparative Example 1
Instead of A-1, the following B-1 (ACS Applied Materials & Interfaces, 2009, Volume 1, pages 1613-1621: synthesized, weight average molecular weight: 12000, synthesized in the method described in B1 (ACS Applied Materials & Interfaces, 2009, Volume 1, pages 1613-1621) A photovoltaic device was prepared in the same manner as in Example 1 except that the number average molecular weight was 10,000 and the polymerization degree n was 12.9.) A current-voltage characteristic was measured. The short-circuit current density at this time was 1.52 mA / cm ² , the open circuit voltage was 0.72 V, the fill factor (FF) was 0.40, and the photoelectric conversion efficiency calculated from these values was 0.44%. .

Comparative Example 2
Instead of A-1, the following B-2 (synthesized by the method described in Macromolecules, 2009, Vol. 42, pages 6564-6571. Weight average molecular weight is 15400, number average molecular weight is 10200, polymerization degree A photovoltaic device was produced in the same manner as in Example 1 except that n was 16.5.), and current-voltage characteristics were measured. The short-circuit current density at this time was 4.52 mA / cm ² , the open-circuit voltage was 0.68 V, the fill factor (FF) was 0.45, and the photoelectric conversion efficiency calculated from these values was 1.38%. .

Comparative Example 3
Instead of A-1, it was synthesized by the method described in the following B-3 (Macromolecules, 2010, 43, 811-820. Weight average molecular weight was 12000, number average molecular weight was 9000, polymerization degree A photovoltaic device was produced in the same manner as in Example 1 except that n was 10.9.), and current-voltage characteristics were measured. At this time, the short-circuit current density was 1.82 mA / cm ² , the open circuit voltage was 0.72 V, the fill factor (FF) was 0.41, and the photoelectric conversion efficiency calculated from these values was 0.54%. .

DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Positive electrode 3 Organic-semiconductor layer 4 Negative electrode 5 The layer which has an electron-donating organic material containing the conjugated polymer which has a structure represented by General formula (1) 6 The layer which has an electron-accepting organic material

Claims (6)

A conjugated polymer having a structure represented by the following general formula (1).

(R ¹ and R ² may be the same or different and are selected from hydrogen, deuterium, alkyl group, alkoxy group, ester group, aryl group, heteroaryl group, and halogen. R ³ and R ⁴ are the same. However, it may be different, and is an alkyl group having 6 or more carbon atoms, n represents a range of 5 or more and 1000 or less, and A is selected from structures represented by any one of the following general formula (2) )

(R ^{5 to} R ²³ may be the same or different, and are selected from hydrogen, deuterium, alkyl groups, alkoxy groups, ester groups, aryl groups, heteroaryl groups, and halogens.) An electron donating organic material comprising the conjugated polymer according to claim 1. A material for a photovoltaic device comprising an electron-accepting organic material and the electron-donating organic material according to claim 2. The photovoltaic element material according to claim 3, wherein the electron-accepting organic material is a fullerene compound. The fullerene compound material for photovoltaic devices according to claim 4, wherein the C ₇₀ derivative. A photovoltaic element having at least a positive electrode and a negative electrode, wherein the photovoltaic element comprises the photovoltaic element material according to any one of claims 3 to 5 between the negative electrode and the positive electrode.

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