JP2010209131A - New photosensitizer and photoelectromotive element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new photosensitizer which is capable of absorbing light widely in a visible region and of increasing a transformation efficiency and which is used suitably for dye sensitized solar cells. <P>SOLUTION: The photosensitizer comprises a metal complex expressed by general formula (I): ML<SP>1</SP>L<SP>2</SP>X<SB>n</SB>(wherein, M is a transition metal of the periodic table group VIII; L<SP>1</SP>and L<SP>2</SP>are the same or different, each at least a ligand containing an aromatic ring or a pyridine ring, and at least one of the both contains a COOH group or an OH group) and has an HOMO ranging -5.2 to -4.9 eV and an LUMO ranging -3.7 to -3.45 and also a gap of HOMO/LUMO ranging 1.20 to 1.55 eV as calculated by the use of a program calculation (the DFT calculation) in a quantum chemistry. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a novel photosensitizer, and more particularly to a novel photosensitizer that is suitably used for a dye-sensitized solar cell. The present invention also relates to a photovoltaic device using the photosensitizer.

The dye-sensitized solar cell element announced by Gretzell et al. In 1991 is a wet solar cell using a titanium oxide porous thin film spectrally sensitized by a ruthenium complex as a working electrode, and can obtain performance equivalent to that of a silicon solar cell. Has been reported (see Non-Patent Document 1). Since this method can use an inexpensive oxide semiconductor such as titania without purifying it with high purity, it can provide an inexpensive dye-sensitized solar cell element, and since the absorption of the dye is broad, it is visible. It has the advantage of being able to convert light in almost all wavelength regions of light into electricity, and has attracted attention.
However, a known ruthenium complex dye absorbs visible light but hardly absorbs infrared light having a wavelength longer than 700 nm, and thus has a low photoelectric conversion ability in the infrared region. Therefore, in order to further increase the conversion efficiency, development of a dye having absorption not only in the visible light but also in the infrared region has been desired.
On the other hand, the black die can absorb light up to 920 nm, but has a small extinction coefficient. Therefore, in order to obtain a high current value, it is necessary to increase the amount adsorbed on the titanium oxide porous thin film. Although there are various methods for increasing the amount of adsorption to the titanium oxide porous thin film, it is generally possible to increase the thickness of the thin film (see Non-Patent Document 2). When the thickness of the thin film is increased, the conversion efficiency cannot be increased greatly because the open-circuit voltage value is decreased and the FF is decreased due to an increase in reverse electron transfer and a decrease in the electron density in the thin film.
Moreover, although the pigment | dye which has light absorption to about 900 nm is obtained with the ligand containing a quinoline ring and a naphthidine ring, the fall of an extinction coefficient is a subject like a black die (nonpatent literature 3). reference).

B. O'Regan, M. Gratzel, "Nature" (UK), 1991, 353, p. 737 M. Gratzel, “Journal of American Chemical Society”, 2001, 123, p. 1613 "Inorganic Chemistry", 2006, 45, 10131

  There has been a demand for a dye (photosensitizer) having a large absorption coefficient that absorbs light in a wide range of visible light and has a high light absorption even in an extremely thin thin film.

  As a result of extensive studies on metal complex dyes in order to solve the above problems, the present inventors have reached the present invention.

That is, the present invention comprises a metal complex represented by the general formula (I), and has a HOMO of −5.2 to −4.9 eV and a LUMO of −3. The present invention relates to a photosensitizer characterized by being in the range of 7 to -3.45 and having a HOMO / LUMO gap in the range of 1.20 to 1.55 eV.
ML ¹ L ² X _n (I)
(Here, M represents a Group 8 transition metal in the periodic table, L ¹ and L ² are ligands containing at least an aromatic ring or a pyridine ring, which may be the same or different, and L ¹ or L ² contains at least one COOH group or OH group.)

（ここで、Ｒ^１、Ｒ^２は同一でも異なっていても良く、少なくともどちらか一方がＣＯＯＨを含む基である。同一でない場合、他方は、水素、炭素数１〜３０のアルキル基、アルケニル基、アリール基、アラルキル基、アルコキシ基またはアミノ基を表す。）

（Ｒ^２１〜Ｒ^３２はそれぞれ独立に、水素、炭素数１〜３０のアルキル基、アルケニル基、アリール基、アルコキシ基、ＯＨ基、ハロゲン、アミノ基、シアノ基またはニトロ基を示す。Ｙは、Ｏ、ＳまたはＮＲ^１３を示す。Ｒ^１３は炭素数１〜３０のアルキル基、アリール基またはアラルキル基を表す。）

（式（III）中、Ｒ^３３〜Ｒ^３５は、それぞれ同一でも異なっていても良く、水素、炭素数１〜３０のアルキル基、炭素数２〜３０のアルコキシアルキル基、炭素数１〜３０のパーフルオロアルキル基、炭素数６〜３０のアリール基、または炭素数７〜３０のアラルキル基を表す。Ｒ^３６は、水素、シアノ基、炭素数１〜２０のアルキル基、炭素数１〜２０のパーフルオロアルキル基、または炭素数６〜１５のアリール基を表し、Ｒ^３６同士が結合して環を形成してもよい。） The present invention, in the general formula (I), L ¹ represents one of the bidentate ligands containing quinoline represented by the following general formula (II), L ² is represented by the following general formula (a) ~ indicates one of the ligands represented by (g), X is independently a halogen atom, CN, NCS, SCN, an ionic ligand selected from NCO and NCN _2, ^{L 2} has the formula ( In cases other than a) and formula (g), n = 2 independently represents any bidentate ligand represented by the following general formula (III), and L ² represents formula (a) or formula (g). Is an ionic ligand selected from a halogen atom, CN, NCS, SCN, NCO and NCN ₂ , and relates to the photosensitizer described above, wherein n = 1.

(Here, R ¹ and R ² may be the same or different, and at least one of them is a group containing COOH. When they are not the same, the other is hydrogen, an alkyl group having 1 to 30 carbon atoms, or an alkenyl group. Represents an aryl group, an aralkyl group, an alkoxy group or an amino group.)

(R ^{21 to} R ³² each independently represents hydrogen, an alkyl group having 1 to 30 carbon atoms, an alkenyl group, an aryl group, an alkoxy group, an OH group, a halogen, an amino group, a cyano group, or a nitro group. Y represents Represents O, S or NR ^13. R ¹³ represents an alkyl group having 1 to 30 carbon atoms, an aryl group or an aralkyl group.

(In the formula (III), R ^{33 to} R ³⁵ may be the same or different and are each hydrogen, an alkyl group having 1 to 30 carbon atoms, an alkoxyalkyl group having 2 to 30 carbon atoms, or an alkyl group having 1 to 30 carbon atoms. A perfluoroalkyl group, an aryl group having 6 to 30 carbon atoms, or an aralkyl group having 7 to 30 carbon atoms, R ³⁶ is hydrogen, a cyano group, an alkyl group having 1 to 20 carbon atoms, or an alkyl group having 1 to 20 carbon atoms. (It represents a perfluoroalkyl group or an aryl group having 6 to 15 carbon atoms, and R ³⁶ may be bonded to form a ring.)

  The present invention further relates to a photovoltaic device having at least one metal oxide semiconductor layer, wherein the metal oxide semiconductor layer contains the photosensitizer described above.

  The photosensitizer of the present invention can absorb light widely in the visible region and increase the conversion efficiency of the photovoltaic element.

It is an example of the cross section of a photovoltaic device. 1 is a ¹ H-NMR spectrum of photosensitizer 1.

  The present invention will be described below.

  The photosensitizer of the present invention comprises a metal complex represented by the general formula (I), and has a HOMO calculated using a quantum chemical program calculation (DFT calculation) of −5.2 to −4.9 eV, preferably Is in the range of −5.15 to −4.95, more preferably −5.1 to −4.95, and the LUMO is −3.7 to −3.45 eV, preferably −3.65 to −3. 45, more preferably in the range of −3.65 to −3.5, and the HOMO / LUMO gap is 1.20 to 1.55 eV, preferably 1.25 to 1.55, more preferably 1.30. It is characterized by being in the range of ˜1.50.

  The quantum chemical calculation was performed using commercially available GAUSSIAN03. In the CPCM solvent model, DFT (density functional theory) / TD-DFT calculation considering the solvent (ethanol) was performed. The calculation method: DFT / B3LYP, basis function: LANL2DZ was applied to the structure optimization and the energy level of the electronic structure / molecular orbitals.

  Here, in photoexcitation of the photosensitizer, when excited electrons are injected into the oxide semiconductor, the oxidant of the generated dye reacts with iodine, and the dye is reduced to the original ground state. If it exceeds -4.9 eV, it will be close to the redox level of iodine, the reaction rate will decrease, and if this reaction is rate limiting, the current value will decrease.

  In the photoexcitation of the photosensitizer, the generated excited electrons are injected into the oxide semiconductor. However, when the LUMO of the dye is lower than −3.7 eV, the value is close to the conduction band level of the oxide semiconductor. It has been found that efficiency decreases. In this case, in addition to a decrease in current value, a decrease in voltage value is also expected.

  Furthermore, the HOMO / LUMO gap is between 1.20 and 1.55. When the gap is lower than 1.20, the HOMO and iodine redox levels, and the LUMO and oxide semiconductor conduction band levels match. Deteriorates and decreases efficiency. On the other hand, if it is larger than 1.55, the light absorption region of the dye can only absorb light in the short wavelength region, so that a sufficient current value cannot be obtained.

The photosensitizer of the present invention is required to satisfy the above-mentioned quantum chemistry program calculation, and is specifically a metal complex represented by the following general formula (I).
ML ¹ L ² X _n (I)

  In the general formula (I), M represents a Group 8 transition metal in the periodic table, among which a transition metal selected from Ru, Os and Fe is preferable, and Ru is particularly preferable.

L ¹ represents any one of bidentate ligands containing a quinoline represented by the following general formula (II).

Here, R ¹ and R ² may be the same or different, and at least one of them is a group containing COOH. When R ¹ and R ² are not the same, the other represents hydrogen, an alkyl group having 1 to 30 carbon atoms, an alkenyl group, an aryl group, an aralkyl group, an alkoxy group, or an amino group. Here, the group containing COOH represents a group represented by -Z-COOH in addition to a COOH group (Z represents a divalent hydrocarbon group such as an alkylene group having 1 to 30 carbon atoms, an alkenylene group, an arylene group, They may be included at the same time).

Specific examples of L ¹ include the following compounds, but are not limited thereto.

In the general formula (I), L ² represents any of the ligands represented by the following general formulas (a) to (g).

Here, R ^{21 to} R ³² each independently represent hydrogen, an alkyl group having 1 to 30 carbon atoms, an alkenyl group, an aryl group, an alkoxy group, an OH group, a halogen, an amino group, a cyano group, or a nitro group, and Y Represents O, S or NR, and R represents an alkyl group having 1 to 30 carbon atoms, an aryl group or an aralkyl group.

  Specific examples of the formula (a) include, but are not limited to, the following.

  Specific examples of the formula (b) include, but are not limited to, the following.

  Specific examples of the formula (c) include, but are not limited to, the following.

  Specific examples of the formula (d) include, but are not limited to, the following.

  Specific examples of the formula (e) include, but are not limited to, the following.

  Specific examples of the formula (f) include the following, but are not limited thereto.

  Specific examples of formula (g) include the following, but are not limited thereto.

In the general formula (I), X is an ionic ligand independently selected from a halogen atom, CN, NCS, SCN, NCO and NCN ₂ , and L ² is other than the formula (a) and the formula (g) Is independently n = 2 or any of the bidentate ligands of formula (IIIa) or (IIIb) represented by the following general formula (III), and L ² represents formula (a) or formula (g ) Represents an ionic ligand selected from a halogen atom, CN, NCS, SCN, NCO and NCN ₂ , and n = 1.

In the case of general formula (IIIa), R ^{33 to} R ³⁵ may be the same as or different from each other, and are hydrogen, an alkyl group having 1 to 30 carbon atoms, an alkoxyalkyl group having 2 to 30 carbon atoms, or 1 to 30 carbon atoms. A perfluoroalkyl group, an aryl group having 6 to 30 carbon atoms, or an aralkyl group having 7 to 30 carbon atoms.
The alkyl group having 1 to 30 carbon atoms may be linear or branched, and specifically includes methyl, ethyl, i-propyl, n-propyl, butyl, s-butyl, t- Examples include butyl group, hexyl group, octyl group, nonyl group, dodecyl group, icosyl group, docosyl group and the like. Specific examples of the alkoxyalkyl group having 2 to 30 carbon atoms include methoxymethyl group, methoxyethyl group, methoxypropyl group, ethoxymethyl group, ethoxybutyl group, ethoxyhexyl group, ethoxynonyl group, propoxymethyl group, butoxymethyl. Group, hexyloxymethyl group, nonyloxymethyl group, dodecyloxyethyl group and the like. Specific examples of the C 1-30 perfluoroalkyl group include —CF ₃ , —C ₂ F ₅ , —iC ₃ F _{7, and the} like. Specific examples of the aryl group having 6 to 30 carbon atoms include a phenyl group and a naphthyl group. Specific examples of the aralkyl group having 7 to 30 carbon atoms include benzyl group, phenethyl group, phenylbutyl group, phenylnonyl group, and naphthylnonyl group. More specifically, the following functional groups are mentioned.

In the general formula (IIIb), R ³⁶ represents hydrogen, a cyano group, an alkyl group having 1 to 20 carbon atoms, a perfluoroalkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 15 carbon atoms. Or it may form a ring R ³⁶ mutually coupled.
The alkyl group having 1 to 20 carbon atoms may be linear or branched. Specifically, methyl group, ethyl group, i-propyl group, n-propyl group, butyl group, s-butyl group, t- A butyl group, a hexyl group, an octyl group, a nonyl group, a dodecyl group, etc. are mentioned. Specific examples of the C 1-20 perfluoroalkyl group include —CF ₃ , —C ₂ F ₅ , —iC ₃ F _{7, and the} like. Specific examples of the aryl group having 6 to 15 carbon atoms include a phenyl group and a naphthyl group. Specific examples include the functional groups shown below.

Moreover, as if to R ³⁶ mutually coupled to form a ring, and specific examples thereof include functional groups shown below.

Next, a typical method for synthesizing the photosensitizer of the present invention will be described, but the present invention is not limited to this method.
The case where ruthenium is used as M in the general formula (I) will be described below as an example. First, a method of introducing X after sequentially reacting ligands L ¹ and L ² with a ruthenium precursor is preferably used. As the ruthenium precursor, ruthenium chloride, dichloro (p-cymene) ruthenium dimer, diiodo (p-cymene) ruthenium dimer, or the like can be used. The reactions of L ¹ and L ² may be added sequentially to carry out the reaction, or may be carried out by adding at the same time. When performing the reaction sequentially, either L ¹ or L ² may be added first.

As a reaction solvent, a general organic solvent, water, and the like can be used. Preferably, alcohol solvents such as ethanol, methanol, butanol, amide solvents such as dimethylformamide (DMF), dimethylacetamide, dimethyl sulfoxide, propylene carbonate A polar solvent such as N-methylpyrrolidone can be used.
The reaction temperature is not particularly limited, but heating is preferable for the reaction to proceed, and it is particularly preferable to perform the reaction in the range of 50 to 250 ° C. When the reaction is performed sequentially, the reaction temperature of the first stage reaction and the second stage reaction can be changed. For heating, an oil bath, a water bath, a microwave heating device, or the like can be used.
Although reaction time is not specifically limited, Usually, it is 1 minute-several days, Preferably it is 5 minutes-1 day, It is preferable to change time with a heating apparatus.

  About X, it can introduce | transduce by adding corresponding ammonium salt, a metal salt, etc., and reacting. Reaction time and reaction temperature are not particularly limited

Next, the photovoltaic element of the present invention will be described.
As an example of the photovoltaic element of the present invention, for example, an element having a cross section shown in FIG. In this element, a semiconductor layer 3 on which a photosensitizer of the present invention is adsorbed is disposed on a transparent conductive substrate 1, an electrolyte layer 4 is disposed between the semiconductor layer 3 and the counter electrode substrate 2, and the periphery is sealed. Sealed with a material 5. Note that the lead wire is connected to the conductive portions of the transparent conductive substrate 1 and the counter electrode substrate 2 so that power can be taken out.

  A transparent conductive substrate is usually produced by laminating a transparent conductive layer on a transparent substrate. The transparent substrate is not particularly limited, and the material, thickness, dimensions, shape, and the like can be appropriately selected according to the purpose.For example, colorless or colored glass, netted glass, glass blocks, etc. are used. A colorless or colored resin having transparency may be used. Specific examples of such resins include polyesters such as polyethylene terephthalate, polyamide, polysulfone, polyether sulfone, polyether ether ketone, polyphenylene sulfide, polycarbonate, polyimide, polymethyl methacrylate, polystyrene, cellulose triacetate, and polymethylpentene. Etc. In the present invention, the term “transparent” means having a transmittance of 10 to 100%, and the term “substrate” in the present invention has a smooth surface at room temperature, and the surface is flat or curved. It may be deformed by stress.

The transparent conductive layer that forms the conductive layer of the electrode is not particularly limited as long as it fulfills the object of the present invention. For example, a conductive thin film made of metal such as gold, silver, chromium, copper, tungsten, or a metal oxide is used. Examples include membranes. Examples of the metal oxide include Indium Tin Oxide (ITO (In ₂ O ₃ : Sn)), Fluorine doped Tin Oxide (FTO (SnO ₂ : F)) in which tin oxide or zinc oxide is slightly doped with other metal elements. ), Aluminum doped Zinc Oxide (AZO (ZnO: Al)) and the like are preferably used.
The film thickness is usually 10 nm to 10 μm, preferably 100 nm to 2 μm. The surface resistance (resistivity) is appropriately selected depending on the use of the substrate of the present invention, but is usually 0.5 to 500 Ω / sq, preferably 2 to 50 Ω / sq.

  As the counter electrode, platinum, a carbon electrode, or the like can be usually used. The material of the substrate is not particularly limited, and the material, thickness, dimensions, shape and the like can be appropriately selected according to the purpose. For example, colorless or colored glass, meshed glass, glass block, etc. are used, colorless or A colored transparent resin may be used. Specific examples of such resins include polyesters such as polyethylene terephthalate, polyamide, polysulfone, polyether sulfone, polyether ether ketone, polyphenylene sulfide, polycarbonate, polyimide, polymethyl methacrylate, polystyrene, cellulose triacetate, and polymethylpentene. Etc. A metal plate or the like can also be used as the substrate.

The semiconductor layer used in the photovoltaic device of the present invention is not particularly limited, for _example, TiO 2, _ZnO, such as a layer made of SnO 2, _Nb 2 _{O 5} and the like, made of inter alia _TiO 2, ZnO A layer is preferred.
The semiconductor used in the present invention may be single crystal or polycrystalline. As the crystal system, anatase type, rutile type, brookite type and the like are mainly used, and anatase type is preferable.
A known method can be used for forming the semiconductor layer. As a method for forming the semiconductor layer, the semiconductor nanoparticle dispersion, the sol solution, or the like can be obtained by coating on a substrate by a known method. The coating method in this case is not particularly limited, and examples include a method of obtaining a thin film by a casting method, a spin coating method, a dip coating method, a bar coating method, and various printing methods including a screen printing method. .
Although the thickness of a semiconductor layer is arbitrary, it is 0.5-50 micrometers normally, Preferably it is 1-20 micrometers.

As a method of adsorbing the photosensitizer of the present invention to the semiconductor layer, for example, a method in which a solution obtained by dissolving a photosensitizer in a solvent is applied on the semiconductor layer by spray coating or spin coating and then dried. Can be formed. In this case, the substrate may be heated to an appropriate temperature. Alternatively, a method of immersing and adsorbing a semiconductor layer in a solution in which a photosensitizer is dissolved can be used. The immersion time is not particularly limited as long as the photosensitizer is sufficiently adsorbed, but is preferably 10 minutes to 30 hours, more preferably 1 to 20 hours. Moreover, you may heat a solvent and a board | substrate when immersing as needed. The concentration of the photosensitizer in the case of a solution is about 0.01 to 100 mmol / L, preferably about 0.1 to 50 mmol / L.
As the solvent, alcohols, ethers, nitriles, esters, hydrocarbons and the like can be used.

Further, in order to reduce the interaction such as aggregation between the photosensitizers, a colorless compound having properties as a surfactant may be added and co-adsorbed on the semiconductor layer. Examples of such colorless compounds include steroid compounds such as cholic acid having a carboxyl group or sulfo group, deoxycholic acid, chenodeoxycholic acid, taurodeoxycholic acid, sulfonates, and the like.
The unadsorbed photosensitizer is preferably removed by washing immediately after the adsorption step. Washing is preferably performed using acetonitrile, an alcohol solvent or the like in a wet washing tank.
The adsorption amount of the photosensitizer is calculated from the light absorption amount of the alkaline solution after desorbing the photosensitizer from the semiconductor layer with a strong alkaline solution.
Further, the adsorption amount to the semiconductor surface, can be adsorbed in the range of ^{1.0 × 10 -8 mol / cm 2} ~1.0 × 10 -6 mol / cm 2.

  After adsorbing the photosensitizer, amines, quaternary ammonium salts, ureido compounds having at least one ureido group, silyl compounds having at least one silyl group, alkali metal salts, alkaline earth metal salts, etc. are used. Then, the surface of the semiconductor layer may be treated. Examples of preferred amines include pyridine, 4-t-butylpyridine, polyvinylpyridine and the like. Examples of preferred quaternary ammonium salts include tetrabutylammonium iodide, tetrahexylammonium iodide and the like. These may be used by dissolving in an organic solvent, or may be used as they are in the case of a liquid.

The electrolyte used in the present invention is not particularly limited, and may be either a liquid system or a solid system, and desirably exhibits reversible electrochemical redox characteristics. Here, showing reversible electrochemical redox characteristics means that an electrochemical redox reaction can occur reversibly in the potential region where the photovoltaic element acts. Typically, it is usually desirable to be reversible in the potential region of −1 to +2 Vvs NHE with respect to the hydrogen reference electrode (NHE).
The ionic conductivity of the electrolyte is usually 1 × 10 ⁻⁷ S / cm or more, preferably 1 × 10 ⁻⁶ S / cm or more, more preferably 1 × 10 ⁻⁵ S / cm or more at room temperature.
The thickness of the electrolyte layer is not particularly limited, but is preferably 1 μm or more, more preferably 10 μm or more, and preferably 3 mm or less, more preferably 1 mm or less.
The electrolyte is not particularly limited as long as the above-described conditions are satisfied, and those known in this technical field can be used for both liquid and solid systems.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[Example 1]
(1) Quantum chemical calculation of photosensitizer 1 Quantitative chemical calculation software Gaussian 03 was used to calculate photosensitizer 1 synthesized below. HOMO: -4.95 eV, LUMO: -3.50 eV Met.
(2) Synthesis of Photosensitizer 1 Compound 1 was synthesized according to the literature (Inorganica Chimica Acta 351, 283 (2003) and New J. Chem., 26,963, (2002)).
Dichloro (p-cymene) ruthenium dimer (1 mmol: 0.61 g) and compound 1 (2 mmol: 0.50 g) were dissolved in DMF (50 ml) and stirred at 80 ° C. for 2 hours under an argon atmosphere. Subsequently, 4,4′-bis (dimethylamino) -2,2′-bipyridine (2 mmol: synthesized according to the literature (Organometallics 27,1765 (2008))) was added, and 150 ° C. for 5 hours under argon. Heating and stirring were performed. Further, ammonium thiocyanate (1.5 g) was added, and the mixture was heated and stirred for 4 hours.
After completion of the reaction, the reaction mixture was concentrated under reduced pressure, and the resulting residue was dispersed in water and filtered to obtain the desired product as a crude product. An aqueous solution of n-butylammonium hydroxide in methanol was added to dissolve the target product, followed by column purification (Sephadex LH-20). The main component is obtained, concentrated under reduced pressure, diluted with water, adjusted to pH 2 with dilute HNO ₃ aqueous solution, the produced dark red precipitate is recovered by filtration, and the desired photosensitizer 1 is obtained by drying under reduced pressure. Obtained in 45% yield. Photosensitizer 1 was identified by MS spectrum (m / z 709) and ¹ H-NMR spectrum. FIG. 2 shows the ¹ H-NMR spectrum of photosensitizer 1.

[Example 2]
(1) Quantum chemical calculation of photosensitizer 2 When the photosensitizer 2 was calculated using the quantum chemical calculation software Gaussian 03, HOMO: −5.01 eV and LUMO: −3.66 eV.
(2) Synthesis of Photosensitizer 2 Compound 2 was synthesized according to the literature (Inorganica Chimica Acta 351, 283 (2003) and New J. Chem., 26,963, (2002)).
Dichloro (p-cymene) ruthenium dimer (1 mmol: 0.61 g) and compound 2 (2 mmol: 0.59 g) were dissolved in DMF (50 ml) and stirred at 80 ° C. for 2 hours under an argon atmosphere. Subsequently, 4,4′-bis (dimethylamino) -2,2′-bipyridine (2 mmol) was added, and the mixture was heated and stirred under argon at 150 ° C. for 5 hours. Further, ammonium thiocyanate (1.5 g) was added, and the mixture was heated and stirred for 4 hours.
After completion of the reaction, the reaction mixture was concentrated under reduced pressure, and the resulting residue was dispersed in water and filtered to obtain the desired product as a crude product. An aqueous solution of n-butylammonium hydroxide in methanol was added to dissolve the target product, followed by column purification (Sephadex LH-20). The main component is obtained, concentrated under reduced pressure, diluted with water, adjusted to pH 2 with dilute HNO ₃ aqueous solution, and the resulting dark red precipitate is collected by filtration, and the desired photosensitizer 2 is obtained by drying under reduced pressure. Obtained in 65% yield. Photosensitizer 2 was identified by MS spectrum (m / z 755) and ¹ H-NMR spectrum.

[Example 3]
(1) Quantum chemical calculation of photosensitizer 3 When the photosensitizer 3 was calculated using the quantum chemical calculation software Gaussian 03, HOMO: −5.07 eV and LUMO: −3.55 eV.
(2) Synthesis of photosensitizer 3 Dichloro (p-cymene) ruthenium dimer (1 mmol: 0.61 g) and compound 1 (2 mmol: 0.59 g) were dissolved in DMF (50 ml), and the reaction was performed under an argon atmosphere. Stir at 2 ° C. for 2 hours. Subsequently, 4,4′-dimethoxy-2,2′-bipyridine (2 mmol) was added, and the mixture was heated and stirred at 150 ° C. for 5 hours under argon. Further, ammonium thiocyanate (1.5 g) was added, and the mixture was heated and stirred for 4 hours.
After completion of the reaction, the reaction mixture was concentrated under reduced pressure, and the resulting residue was dispersed in water and filtered to obtain the desired product as a crude product. An aqueous solution of n-butylammonium hydroxide in methanol was added to dissolve the target product, followed by column purification (Sephadex LH-20). The main component is obtained, concentrated under reduced pressure, diluted with water, adjusted to pH 2 with dilute HNO ₃ aqueous solution, the resulting dark red precipitate is collected by filtration, and the desired photosensitizer 3 is obtained by drying under reduced pressure. Obtained in 65% yield. Photosensitizer 3 was identified by MS spectrum (m / z 919) and ¹ H-NMR spectrum.

[Example 4]
(Production of photovoltaic elements and measurement of conversion efficiency)
A photovoltaic device based on sensitization of a titanium dioxide film supported on a conductive substrate was produced as follows (see FIG. 1).
After colloidal TiO ₂ particles (particle size: 20-30 nm) are applied on conductive glass (fluorine-doped SnO ₂ , 10Ω) and baked at 450 ° C. for 30 minutes (film thickness: 10 μm), light is applied on it. TiO ₂ particles (particle size: 300 to 400 nm) were applied and baked at 520 ° C. for 1 hour (film thickness: 6 to 8 μm). These two layers were immersed in a TiCl ₄ solution for 30 minutes and then heated at 450 ° C. for 30 minutes.
The obtained film was immersed in the novel dye (photosensitizer) / ethanol solution (3.0 × 10 ⁻⁴ mol / L) for 15 hours to form a dye layer. The obtained substrate and the Pt surface of the glass with the Pt thin film are combined, and an acetonitrile solution containing 0.5 mol / L lithium iodide and 0.05 mol / L iodine is soaked by capillary action, and the periphery is an epoxy adhesive. Sealed with. A lead wire was connected to the conductive layer portion of the transparent conductive substrate and the counter electrode.
For comparison, a solar cell using a ruthenium dye (comparative example) (Rutenium 535-bisTBA: manufactured by SOLARONIX) generally used in a photovoltaic cell as a dye was prepared.
Table 1 shows the result of measuring the incident photon-current conversion efficiency (IPCE) by irradiating the cell thus obtained with monochromatic light of pseudo-sunlight 900 nm.
From Table 1, when the conventional ruthenium dye was used, absorption was not shown in the infrared region of 900 nm, but when the photosensitizer of the present invention was used (Example 1-3), the same region. Showed clear absorption.

DESCRIPTION OF SYMBOLS 1 Transparent conductive substrate 2 Counter electrode substrate 3 Semiconductor layer 4 which adsorbed photosensitizer 4 Electrolyte layer 5 Seal

  The photosensitizer of the present invention can absorb light widely in the visible region and increase the conversion efficiency, and is suitably used for a dye-sensitized solar cell.

Claims (3)

It consists of a metal complex represented by the general formula (I), and has a HOMO of −5.2 to −4.9 eV and a LUMO of −3.7 to −3. 45. A photosensitizer characterized by being in the range of 45 and having a HOMO / LUMO gap in the range of 1.20 to 1.55 eV.
ML ¹ L ² X _n (I)
(Here, M represents a Group 8 transition metal in the periodic table, L ¹ and L ² are ligands containing at least an aromatic ring or a pyridine ring, which may be the same or different, and L ¹ or L ² contains at least one COOH group or OH group.) In the general formula (I), L ¹ represents any of the bidentate ligands containing a quinoline represented by the following general formula (II), and L ² is represented by the following general formulas (a) to (g). X is an ionic ligand independently selected from a halogen atom, CN, NCS, SCN, NCO and NCN ₂ , wherein L ² is a group represented by the formula (a) and the formula ( When other than g), n = 2 independently represents any bidentate ligand represented by the following general formula (III), and when L ² is the formula (a) or the formula (g), _{2. The} photosensitizer according to claim 1, wherein the photosensitizer is an ionic ligand selected from a halogen atom, CN, NCS, SCN, NCO, and NCN ₂ , and n = 1.

(Here, R ¹ and R ² may be the same or different, and at least one of them is a group containing COOH. When they are not the same, the other is hydrogen, an alkyl group having 1 to 30 carbon atoms, or an alkenyl group. Represents an aryl group, an aralkyl group, an alkoxy group or an amino group.)

(R ^{21 to} R ³² each independently represents hydrogen, an alkyl group having 1 to 30 carbon atoms, an alkenyl group, an aryl group, an alkoxy group, an OH group, a halogen, an amino group, a cyano group, or a nitro group. Y represents Represents O, S or NR ^13. R ¹³ represents an alkyl group having 1 to 30 carbon atoms, an aryl group or an aralkyl group.

(In the formula (III), R ^{33 to} R ³⁵ may be the same or different and are each hydrogen, an alkyl group having 1 to 30 carbon atoms, an alkoxyalkyl group having 2 to 30 carbon atoms, or an alkyl group having 1 to 30 carbon atoms. A perfluoroalkyl group, an aryl group having 6 to 30 carbon atoms, or an aralkyl group having 7 to 30 carbon atoms, R ³⁶ is hydrogen, a cyano group, an alkyl group having 1 to 20 carbon atoms, or an alkyl group having 1 to 20 carbon atoms. (It represents a perfluoroalkyl group or an aryl group having 6 to 15 carbon atoms, and R ³⁶ may be bonded to form a ring.)   A photovoltaic device having at least one metal oxide semiconductor layer, wherein the metal oxide semiconductor layer includes the photosensitizer according to claim 1.

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