JP5240681B2 - Photoelectric conversion element and manufacturing method thereof - Google Patents

Description

  The present invention relates to a photoelectric conversion element having a metal oxide semiconductor electrode on which a plurality of dyes are adsorbed, and a dye-sensitized solar cell incorporating the photoelectric conversion element.

At present, solar cells using single crystal, polycrystalline, or amorphous silicon semiconductors are used for electric products such as calculators and houses. However, high-precision processes such as plasma CVD and high-temperature crystal growth processes are used in the manufacture of solar cells using such silicon semiconductors, which requires a large amount of energy and is expensive and requires a vacuum. Manufacturing costs are high due to the need for equipment.

  Therefore, as a solar cell that can be manufactured at a low cost, for example, a dye-sensitized solar cell using a material in which a photosensitizing dye such as a ruthenium metal complex is adsorbed on an oxide semiconductor such as titanium oxide has been proposed. Yes. Specifically, the dye-sensitized solar cell has, for example, ruthenium on the transparent conductive layer side of a transparent insulating material such as a transparent glass plate or a transparent resin plate provided with a transparent conductive layer such as indium-added tin oxide (ITO). A negative electrode formed as a semiconductor layer with titanium oxide or the like adsorbed on the surface of a complex dye, and a transparent insulating material such as a transparent glass plate or a transparent resin plate provided with a metal layer or conductive layer such as platinum as a positive electrode Some of them are filled with electrolyte solution. When the dye-sensitized solar cell is irradiated with light, the electrons of the dye that absorbed the light are excited in the negative electrode, the excited electrons move to the semiconductor layer, and are further guided to the transparent electrode, and from the conductive layer in the positive electrode The electrolyte is reduced by electrons. The reduced electrolyte is oxidized by transferring electrons to the dye, and it is believed that the dye-sensitized solar cell generates electricity during this cycle.

  Currently, dye-sensitized solar cells have lower power generation energy efficiency with respect to irradiation light energy than silicon solar cells, and increasing the efficiency is an important issue in producing effective dye-sensitized solar cells. ing. The efficiency of the dye-sensitized solar cell is considered to be influenced by the characteristics of each element constituting the dye-sensitized solar cell and the combination of these elements, and various attempts have been made. In particular, efforts are being made on the interaction between a dye having a photosensitizing action and titanium oxide serving as a semiconductor layer, and a technique for preventing reverse current in an electrolytic solution of electrons once injected into titanium oxide.

WO94-05025 Publication Japanese Patent No. 3505414 JP 2000-268892 A JP 2000-243466 A JP 2002-343455 A Japanese Patent Laid-Open No. 2003-217688 JP 2003-249274 A JP 2003-249275 A JP 2003-249279 A JP 2001-223037 2006 (Spring) Proceedings of Electrochemical Society of Japan 2I04 “Fabrication of tandem dye-sensitized solar cell in cell”

Patent Document 1 describes a dye-sensitized solar cell in which a Ru complex, a brightener, and phthalocyanine are mixed and adsorbed. Patent Document 2 describes a photochemical cell in which the oxidation-reduction potentials of the dyes are different from each other and arranged such that the oxidation-reduction potential decreases from the semiconductor layer side toward the charge transport layer side. Since movement is performed, there is a problem in that movement efficiency decreases. Patent Documents 3 to 9 describe a photoelectric conversion device that absorbs light in a wide range of wavelengths using two or more kinds of dyes, but the adsorption amount of the dyes cannot be controlled in the film thickness direction. In the case of reacting dyes, the reaction conditions must be controlled for each dye, and there are problems such as the time required for adsorption, and the improvement in photoelectric conversion efficiency has not been sufficient. Patent Document 10 describes that a dye is adsorbed on a semiconductor in a supercritical fluid. In this case, the pressure is about 8 MPa and the temperature is 40 ° C. as supercritical conditions of carbon dioxide (CO ₂ ). Is described.

  The present invention performs adsorption of a dye on a semiconductor surface, which is a semiconductor electrode, in carbon dioxide gas in a supercritical state or under pressure, and prevents association or contact of the same or different kinds of dyes with the carbon dioxide gas. A device with high photoelectric conversion efficiency in which a dye is adsorbed in a short time to the back of a fine hole of a semiconductor electrode formed of a thin and wide area, and further to the back of a binding part of necked fine particles It is intended to obtain a dye-sensitized solar cell using

  The present invention relates to a photoelectric conversion element having a dye-sensitized semiconductor electrode in which at least two kinds of sensitizing dyes having different absorption wavelengths are adsorbed, wherein at least one of the sensitizing dyes is a carbon dioxide gas. It is adsorbed in a pressurized fluid containing carbon dioxide under temperature and pressure conditions where a supercritical fluid or carbon dioxide supercritical fluid is obtained, and at least two sensitizing dyes visible and near The photoelectric conversion element is characterized in that a difference in maximum absorption wavelength in an infrared light region is 90 nm or more.

  The present invention also provides a method for producing a photoelectric conversion element having a dye-sensitized semiconductor electrode in which at least two kinds of dyes having different absorption wavelengths are adsorbed, and visible light and near-infrared light between the sensitizing dyes. A sensitizing dye having a difference in maximum absorption wavelength in the optical region of 90 nm or more is selected, and at least one sensitizing dye is used at a temperature and pressure at which a supercritical fluid of carbon dioxide gas or a supercritical fluid of carbon dioxide gas is obtained. A method for producing a photoelectric conversion element comprising adsorbing a semiconductor in a pressurized fluid containing carbon dioxide under certain conditions.

  Furthermore, the present invention is a dye-sensitized solar cell comprising the above-described photoelectric conversion element.

Here, at least one sensitizing dye is a ruthenium complex, at least one sensitizing dye is a polymethine dye, or the maximum absorption wavelength of at least one sensitizing dye is 850 nm. It exists in the range of 1400 nm or more exceeding, and a preferable photoelectric conversion element is given. Further, a supercritical fluid containing a carbon dioxide gas and a solvent selected from C _{1 to} C ₄ alcohol, C _{1 to} C ₆ carbonate, C _{2 to} C ₆ ether, and C _{1 to} C ₄ nitrile is used as a sensitizing dye. Or making it adsorb | suck to a semiconductor in a pressurized fluid gives the manufacturing method of a preferable photoelectric conversion element.

  An example of the basic configuration of the photoelectric conversion element or dye-sensitized solar cell of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view showing an example of a photoelectric conversion element. On a substrate 1, different sensitizing dyes A and B are adsorbed on a conductive layer 2 and a semiconductor layer composed of one or more layers. It has a surface electrode 10 in which a semiconductor layer 3 in which dye A is mainly adsorbed and a semiconductor layer 4 in which dye B is mainly adsorbed, and a counter electrode 11 in which a conductive layer 6 is provided on a substrate 5. The electrolyte 7 is arranged between both electrodes. The dye adsorbing semiconductor layers 3 and 4 are also referred to as semiconductor electrodes because they constitute part of the electrodes. The dye adsorbing semiconductor layers 3 and 4 are coated and sintered as a single layer using titania or metal oxide fine particles, or are formed by a plurality of coatings and sintering, and in the film thickness direction. It is a semiconductor layer in which the amounts of adsorbed dyes A and B are different, and is composed of metal oxide particles such as titanium oxide particles and sensitizing dyes A and B existing so as to cover the surface of the particles. Light enters from the surface electrode 10 side. The dye-sensitized solar cell of the present invention has the same basic configuration as described above, but is made to work in an external circuit. And the method of using a photoelectric conversion element as a dye-sensitized solar cell may be a known method.

  The substrate 1 is not particularly limited as long as it is a transparent insulating material, and examples thereof include a normal glass plate and a plastic plate, and further, a flexible one may be used, for example, a PET resin. However, it is preferably a heat-resistant material that can withstand the step of baking titanium oxide with an upper limit of about 500 ° C., and a transparent glass plate can be mentioned.

  Next, a conductive layer 2 is provided on the surface of the substrate 1 so as not to impair the transparency of the base material. As the conductive layer, ITO, FTO, ATO known as a so-called transparent electrode, or a combination thereof is used. Moreover, it may be a metal layer having a thickness that does not impair the transparency. The method for providing these conductive layers is not particularly limited, and includes spin coating, bar coating, screen printing using sputtering, vapor deposition (including CVD and PVD), spraying, laser ablation, or pasted materials. Known techniques can be used. Among them, a spray method or a sputtering or vapor deposition method performed in a gas phase is suitable.

  On this, the dye adsorption semiconductor layers 3 and 4 are provided. Usually, after a metal oxide layer is formed as a semiconductor, a sensitizing dye is adsorbed thereto. As a metal oxide, what is known as a photoelectric conversion material can be used, and titanium oxide, zinc oxide, tungsten oxide, and the like can be used. Of these, titanium oxide is preferable. Titanium oxide may be titanium hydroxide such as anatase type, rutile type, brookite type, titanium hydroxide or hydrous titanium oxide. Further, at least one of each element of Nb, V, or Ta may be doped so as to have a weight concentration (as a metal element) of 30 ppm to 5% with respect to titanium oxide. The average particle diameter of such a metal oxide is 5 to 500 nm, preferably 10 to 200 nm.

  A metal oxide layer is formed on the transparent electrode 2, but the method is not particularly limited. For example, each method such as spin coating, printing, spray coating, or the like is used for pasting the metal oxide. May be. It is also possible to sinter for the purpose of sintering a metal oxide such as titanium oxide after film formation. Next, dyes for sensitization are adsorbed on the metal oxide to form dye adsorbing semiconductor layers 3 and 4 as dye adsorbing metal oxides. Dye adsorption may be performed by dissolving different dyes A and B in the same supercritical carbon dioxide fluid or fluid containing pressurized carbon dioxide and entrainer (solvent), or by dissolving them separately. You may make it adsorb | suck to.

  In the present invention, the dye-adsorbing semiconductor layers 3 and 4 are characterized, and the other layers or materials can be known structures or materials, and are not limited to those having the structure shown in FIG. Note that FIG. 1 shows an example in which the dye-adsorbing semiconductor layer is composed of two layers of the semiconductor layer 3 and the semiconductor layer 4. However, the dye-adsorbing semiconductor layer is not limited to two layers but may be one layer or more. May be. In the case of a single layer, a plurality of dyes are adsorbed in one layer, but if one of them is mainly adsorbed, the association and aggregation of the dyes will be reduced, resulting in a decrease in efficiency. The problem is greatly suppressed. Further, the sensitizing dye may be two kinds or three or more kinds, but it is preferable that the maximum absorption wavelengths are shifted from each other.

  The materials constituting the dye-adsorbing semiconductor layer 3 are a semiconductor and a dye. Usually, since the semiconductor is a metal oxide, preferably titanium oxide, the semiconductor may be represented by a metal oxide or titanium oxide. The dye for dye sensitization is not particularly limited, and may be a metal complex dye, an organic dye, a phthalocyanine dye, a porphyrin dye, a methine dye, or a mixture of these dyes. Preferably at least one dye is a metal complex dye, more preferably a ruthenium complex dye. Alternatively, at least one dye is a polymethine dye.

Examples of ruthenium complex dyes are those described in literature (for example, USP 4927721, JP-T 09-507334, JP-T 10-504521, JP-T 2002-512729, JP-B 2977773, etc.) Known ruthenium complex dyes that are soluble in supercritical CO ₂ or CO ₂ -containing solvents can be used. For example, cis-L ₂ -bis (2,2′-bipyridyl-4,4′-dicarboxylate) ruthenium (II) complex (where L is halogen, CN or SCN or NCS), preferably cis -Bisisothiocyanate-bis (2,2'-bipyridyl-4,4'-dicarboxylate) ruthenium (II) complex (hereinafter N3), cis-L ₂ -bis (2,2'-bipyridyl-4- Carboxylate-4′-carboxylic acid) ruthenium (II) -bistetrabutylammonium complex, preferably cis-bisisothiocyanate-bis (2,2′-bipyridyl-4-carboxylate-4′-carboxylic acid) ruthenium ( II) -Bistetrabutylammonium (N719), (2,2 ': 6', 2 "-terpyridine-4,4 ', 4" -tricarboxylate) ruthenium (II) tris (tetrabutylammonium ) Tris (isothiocyanate) (hereinafter Black Dye), cis-di (isothiocyanate)-(2,2'-bipyridyl-4,4 ' -Dicarboxylic acid) (4,4'-dimethyl-2,2'-bipyridyl) -ruthenium (II), cis-di (isothiocyanate)-(2,2'-bipyridyl-4,4'-dicarboxylic acid) ( 4,4'-dihexyl-2,2'-bipyridyl) -ruthenium (II), cis-di (isothiocyanate)-(2,2'-bipyridyl-4,4'-dicarboxylic acid) (4-methyl-4 '-Hexadecyl-2,2'-bipyridyl) -ruthenium (II), cis-di (isothiocyanate)-(2,2'-bipyridyl-4,4'-dicarboxylic acid) (4,4'-nonyl-2) , 2'-bipyridyl) -ruthenium (II).

  As the polymethine dye, known polymethine dyes such as those described in Patent Documents 2 to 9, which are soluble in the above solvent can be used.

  In the present invention, two or more kinds of dyes are used in order to make the wavelength range of photoelectric conversion as wide as possible and increase the conversion efficiency. A dye having a difference in maximum absorption wavelength of 90 nm or more between visible light and near infrared light of at least two sensitizing dyes is used. When using 3 or more types of pigment | dyes, any 2 types should just satisfy the said requirements.

And the pigment | dye to be used can be selected so that it may match with the wavelength range of the target light source. Such a dye preferably has an appropriate interlocking group for the surface of the semiconductor fine particles. Preferred linking groups include COOH group, SO ₃ H group, —P (O) (OH) ₂ group, —OP (O) (OH) ₂ group, —OH group or oxime, dioxime, hydroxyquinoline, salicylate and α. -Chelating groups with π conductivity such as ketoenolate. Among these, a COOH group is preferable. These groups may form a salt with an alkali metal or the like, or may form an internal salt. In the case of a polymethine dye, if the methine chain contains an acidic group as in the case where the methine chain forms a squalium ring or a croconium ring, this part may be used as a linking group.

Preferred dyes include dyes represented by the following formulas (I) and (II).

In the formula (I), n ₁ , n ₂ , and n ₃ represent integers from 0 to 6, but the total value of n ₁ , n ₂ , and n ₃ is an integer from 1 to 6. The dye having the maximum absorption wavelength exceeding 850 nm is preferably selected from integers having the above total value of 3 to 6. Y ₁ and Y ₂ are composed of any two or more elements selected from carbon, oxygen, nitrogen, sulfur, selenium, and tellurium. Rxn and Ryn (n is an integer from 1 to 4) are substituents connected to the methine group, and are hydrogen, C1 to C9 alkyl groups, and substituted alkyl groups. Rxn and Ryn or Rxn and Ryn ₊₁ are bonded to form a ring. An aliphatic structure may be constituted, and a cyclohexene ring, a cyclopentene ring, a squaric acid skeleton, or a croconic acid skeleton may be constituted. The methine moiety may be a methine unit and the same skeleton may be repeated, or it may have a methine moiety having a different substituent. Z ₁ and Z ₂ are hydrogen, an alkyl group, and a substituted alkyl group containing a linking group. The cyclic structure composed of C, Y ₁ and N ⁺ and the cyclic structure composed of C, Y ₂ and N are 5- to 7-membered rings, and are ring structures having adjacent rings and substituents. Also good. Preferably, an indole skeleton, an indolenine skeleton, a quinoline skeleton, a structure in which a condensed aromatic ring is adjacent, or a 5- to 7-membered ring containing azurenium, pyrylium, sulfur, oxygen, tellurium, or selenium may be used. The cyclic structure may have a linking group other than Z ₁ or Z ₂ . Z ₁ and Z ₂ do not have to be a linking group. There may be at least one linking group in the molecule.

式（II）において、n₂₁は１から６の整数を表す。Y₂₁は炭素、酸素、窒素、硫黄、セレン、テルルの中から選ばれる１種以上の元素、Y₂₂、Y₂₃、Y₂₄、Y₂₅は酸素、窒素、硫黄、セレン、テルルの中から選ばれるいずれかの元素で構成され、Y₂₄は結合基を置換基として持っていても良い。R₂₂、R₂₃はメチン基につながる置換基であり、水素、C1からC9のアルキル基、置換アルキル基である。メチン部分はメチン単位で同一骨格が繰り返しても良いし、異なる置換基をもつメチンユニットを有してもよい。また、同一又は異なるメチンユニット間の置換基同士が結合し、環状構造を有してもよい。Z₂₁は水素、アルキル基、結合基を含む置換アルキル基である。Y₂₁及びNを含む環状構造は、５〜７員環であってもよく、好ましくはインドール骨格、インドレニン骨格、キノリン骨格、縮合芳香環が隣接した構造又は、アズレニウム、ピリリウム、又は、硫黄、酸素、テルル、セレンを含む５〜７員環であっても良い。置換基を含むY₂₁及びNで構成される環の隣接環状構造に結合基X₂₁としてCOOH基、SO₃H基、OH基等があってもよい。結合基は分子の中に少なくとも１つあればよい。

In the formula (II), n ₂₁ represents an integer of 1 to 6. Y ₂₁ is one or more elements selected from carbon, oxygen, nitrogen, sulfur, selenium and tellurium; Y ₂₂ , Y ₂₃ , Y ₂₄ and Y ₂₅ are selected from oxygen, nitrogen, sulfur, selenium and tellurium Y ₂₄ may have a bonding group as a substituent. R ₂₂ and R ₂₃ are substituents connected to the methine group, and are hydrogen, a C1 to C9 alkyl group, and a substituted alkyl group. The methine moiety may be a methine unit and the same skeleton may be repeated, or it may have a methine unit having a different substituent. Further, substituents between the same or different methine units may be bonded to each other to have a cyclic structure. Z ₂₁ is a substituted alkyl group containing hydrogen, an alkyl group, and a linking group. The cyclic structure containing Y ₂₁ and N may be a 5- to 7-membered ring, preferably an indole skeleton, an indolenine skeleton, a quinoline skeleton, a structure in which a condensed aromatic ring is adjacent, or azurenium, pyrylium, or sulfur, It may be a 5- to 7-membered ring containing oxygen, tellurium and selenium. There may be a COOH group, SO ₃ H group, OH group or the like as the linking group X ₂₁ in the adjacent cyclic structure of the ring composed of Y ₂₁ and N containing a substituent. There may be at least one linking group in the molecule.

ここで、X^-はCl^-,I^-,ClO₄ ^-等のカウンターイオンである。 Some more specific examples of the dyes represented by the formulas (I) and (II) are shown in the following formulas (1) to (10).

Here, X ⁻ is a counter ion such as Cl ⁻ , I ⁻ , or ClO ₄ ⁻ .

In the present invention, at least one of these sensitizing dyes is adsorbed on a metal oxide such as titanium oxide, which is a semiconductor, using a pressurized fluid containing supercritical CO ₂ or pressurized CO ₂ . Here, pressurized fluid containing CO ₂ is, CO ₂ alone is supercritical CO ₂ temperature, it refers to the CO ₂ containing organic solvent solution in pressure. Therefore, the pressurized fluid containing CO ₂ may not be a supercritical fluid as a whole.

The organic solvent used for the pressurized fluid containing CO ₂ may be any organic solvent that can dissolve the dye, but preferably C ₁ -C ₄ alcohol, C ₁ -C ₆ carbonate, C ₂ -C _6. ethers or C ₁ -C ₄ nitriles. Specifically, methanol, ethanol, propanol and n-butanol, t-butanol, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, dimethyl ether, diethyl ether, dipropyl ether, tetrahydrofuran, tetrahydropyran, acetonitrile , Propionitrile, butyronitrile, isobutyronitrile, trimethylacetonitrile, and the like. These may be used in combination of two or more. In the case of C ₁ -C ₄ carbonate or C ₁ -C ₄ nitriles, number of carbon atoms contained in the carbonic acid group or nitrile group are excluded from the calculation. Above, C ₁ -C ₄ alcohols, C ₁ -C ₆ carbonate, C ₁ -C ₄ constituting the C ₂ -C ₆ ethers or C ₁ -C ₄ nitriles _{such, C 1 ~C 6, C 2} ~C 6 Etc. are preferably an alkyl group or an alkylene group having these carbon numbers. In addition, when it is an alkylene group, it can be a cyclic structure.

Since this organic solvent acts as an entrainer, it is also called an entrainer. Ratio of the organic solvent and CO ₂ pressurized fluid containing the CO ₂ is arbitrary, CO _2: As the organic solvent, 100: 1 to 0.5: 1, preferably 50: 1 to 1: 1, further The range of 10: 1 to 1: 1 is preferable.

Supercritical CO ₂ or CO ₂ alone when the supercritical CO ₂ pressurized fluid containing CO ₂ in the conditions to give (hereinafter, the former supercritical CO _2, called latter as pressurized fluid containing CO _2, and Both are collectively referred to as CO ₂ supercritical fluid) in a pressure range of 10 to 25 MPa, and in a temperature range of 40 to 60 ° C., better dye adsorption is achieved. Strictly speaking, the conditions for providing supercritical CO ₂ are 7.38 MPa and 31 ° C., so the above pressure and temperature may be satisfied. The concentration of the dye dissolved in the entrainer such as alcohol is not particularly limited, but is preferably in the range of 1 × 10 ⁻⁴ mol / L or more and 3 × 10 ⁻³ mol / L or less. Supercritical CO ₂ is known to have a very low surface tension, and so is a pressurized fluid containing CO ₂ . Therefore, it is considered that by adsorbing the dye in the CO ₂ supercritical fluid, the dye enters the fine pores of the metal oxide such as titanium oxide and can be effectively adsorbed. Although the details are unknown by mixing the dye in a large amount of CO ₂ supercritical fluid, it is thought that the dye can be effectively adsorbed by producing an anti-association effect that disperses the aggregated dye. . Alternatively, it is considered that by adsorbing a dye having a different molecular size, a small dye enters between large dyes and an association preventing effect is produced, thereby effectively adsorbing the dye.

In the present invention, by using a CO ₂ supercritical fluid, adsorption by changing the adsorption concentration of different dyes in the thickness direction of the titania film is performed by utilizing the difference in solubility in the fluid serving as the dye solvent . For example, a hardly soluble dye is used as the dye b, and is first adsorbed on the surface layer of the titania film on the 4 side in FIG. 1, and then the easily soluble dye is used as the dye a to suppress the dissolution of the dye b and form a film in a short time. By adsorbing to the back of the electrode, it is possible to create an electrode in which different dyes are dyed separately in the film thickness direction. It is difficult and time-consuming to impregnate two types of pigments having close solubility in the film thickness direction. When using a CO ₂ supercritical fluid, the difference in solubility for each dye can vary greatly depending on conditions such as the presence / absence of entrainer, type, mixing ratio with carbon dioxide, fluid temperature, pressure, etc. A plurality of different pigments can be easily dyed. The order of the adsorbed dye in the film thickness direction is as follows. Layer 3 in FIG. 1 is a short wavelength dye layer in which layer 3 adsorbs short wavelength dye A (which means a dye having maximum absorption on the short wavelength side), and layer 4 is long wavelength dye B. Even if it is a long wavelength dye layer that adsorbs, the layer 3 may be either a long wavelength dye layer that adsorbs the long wavelength dye A, or the layer 4 may be either a short wavelength dye layer that adsorbs the short wavelength dye B, Preferably, the layer 3 is a short wavelength dye layer and the layer 4 is a long wavelength dye layer.

  As a conventional method of adsorbing a sensitizing dye to a metal oxide layer such as titanium oxide, first, a conductive film 2 and then a metal oxide layer are formed on a substrate 1, and a metal oxide layer having a predetermined thickness is formed. An impregnation method in which the laminate is immersed in a dye solution in which a dye is dissolved in an appropriate solvent can be exemplified. However, in the impregnation method, due to the effect of the surface tension of the dye solution, the dye is not effectively adsorbed into the fine pores of the metal oxide such as titanium oxide. Dye-sensitized solar cells cannot be completely covered with dye molecules, causing problems such as insufficient dye adsorption and reverse current due to direct contact of the exposed titanium oxide surface with the electrolyte. In some cases, the photoelectric conversion efficiency is lowered. In addition, a dye having a binding group with good adsorptivity is aggregated due to the association of the binding groups, and it is difficult to adsorb the dye to the surface of the titanium oxide particles as close to a single layer as possible by the adsorption method.

Therefore, in the present invention, at least one dye is dissolved in a CO ₂ supercritical fluid, impregnated in a metal oxide layer, and adsorbed. In this case, a CO ₂ supercritical fluid in which two or more dyes are dissolved may be impregnated, or a CO ₂ supercritical fluid in which one dye is dissolved may be impregnated. In the latter case, it is preferable to prepare a fluid in which another dye is dissolved in a CO ₂ supercritical fluid having a different composition or condition and impregnate in two or more stages.

The adsorption of the dye using the CO ₂ supercritical fluid fluid can be performed, for example, by placing and impregnating a conductive layer-provided substrate provided with a metal oxide layer in the dye-containing CO ₂ supercritical fluid. FIG. 2 is a schematic diagram showing a pressure device used for the adsorption operation. In the pressure vessel 21, a substrate 22 with a conductive layer provided with a metal oxide layer is arranged on a holding table 24. A solution 23 in which a pigment is dissolved exists in the container 21 and is stirred by a stirrer 25. Carbon dioxide gas is introduced into the container and maintained at a predetermined pressure by the pressure regulating valve 26. The supercritical carbon dioxide gas fluid becomes a pressurized fluid mixed with the solution 23 and comes into contact with the substrate 22 for impregnation.

  In the present invention, it is preferable to rinse the semiconductor such as a metal oxide to which the dye is adsorbed as described above. As a method of the rinsing treatment, there is a method in which a metal oxide such as titanium oxide after adsorbing the dye is immersed in an alcohol such as methanol or ethanol to wash away the extra attached dye. The reason for performing the rinse treatment is to wash off excess dye, and details are unknown. However, when dye molecules adsorbed on the dye molecules so as to overlap further, for example, titanium oxide The dye molecules that do not come into contact with the metal oxide not only do not participate in power generation, but also have an effect of suppressing a decrease in photoelectric conversion efficiency due to absorption of incident light.

Not particularly limited as methods rinse, but rinsing with CO ₂ supercritical fluid are preferred. This is presumably because it is important to wash away such excess dye in the fine pores of a metal oxide such as titanium oxide. Specifically, the rinse treatment using supercritical CO ₂ includes a method in which a metal oxide such as titanium oxide adsorbed with a dye is placed in a supercritical CO ₂ fluid. Rinse treatment using a pressurized fluid containing CO ₂ is preferable. In this case, methanol, ethanol, propanol, n-butanol, t-butanol, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, dimethyl ether, diethyl ether, dipropyl ether, tetrahydrofuran and tetrahydropyran, acetonitrile, A metal oxide such as titanium oxide adsorbed in a pressurized fluid containing at least one organic solvent of propionitrile, butyronitrile, isobutyronitrile, and trimethylacetonitrile and CO ₂ , or a substrate on which this is laminated It can be done effectively by placing it. Moreover, the said pressure apparatus can be used also for this rinse process.

The condition of the rinsing process using the CO ₂ supercritical fluid is not particularly limited, and may be a condition capable of forming a supercritical state of carbon dioxide gas. Preferably, the pressure range is 10 to 25 MPa, and the temperature range is 40. ~ 60 ° C. In the rinsing process, conditions are set so that only a part of the adsorbed dye is washed away.

After completion of the rinsing treatment, the metal oxide adsorbed with the dye may be further adsorbed with carboxylic acid in a CO ₂ supercritical fluid. The effect of adsorbing carboxylic acids is known from J. Photochem. And Photobio. A, Chem. 164 (2004) 117. However, as in the case of dye adsorption and rinsing, it is important to effectively adsorb even inside the fine pores of a metal oxide such as titanium oxide. A dye-adsorbed metal oxide (which may be a substrate having a dye-adsorbed metal oxide layer) and a carboxylic acid are formed at a pressure range of 8-30 MPa and a temperature range of 40-60 ° C. Carboxylic acid can be effectively adsorbed by placing it in CO ₂ supercritical fluid. Preferred examples of the carboxylic acid include benzoic acid, acetic acid, anisic acid, and nicotinic acid. These carboxylic acids are preferably used in a state dissolved in an alcohol containing at least one of methanol, ethanol, propanol, and butanol, and the carboxylic acid concentration is in the range of 0.01 to 10 mol / L. It is preferable.

  As described above, the surface electrode 10 composed of the substrate 1, the transparent conductive film 2, and the dye-adsorbing semiconductor layer functions as a negative electrode. The other electrode (counter electrode) 11 acting as the positive electrode is disposed to face the surface electrode 10 as shown in FIG. The electrode serving as the positive electrode may be a conductive metal or the like, or may be a substrate 5 such as a normal glass plate or plastic plate provided with a conductive film 6 such as a metal film or a carbon film.

  An electrolyte layer is provided between the surface electrode 10 serving as the negative electrode and the counter electrode 11 serving as the positive electrode. The type of the electrolyte layer is not particularly limited as long as it contains a redox species for reducing the dye after photoexcitation and electron injection into the semiconductor, and may be a liquid electrolyte, which is well known. Or a gel electrolyte obtained by adding a pseudo-solid obtained by kneading an ionic liquid and a metal oxide.

For example, examples of the electrolyte used in the solution electrolyte, iodine and iodide (LiI, NaI, KI, CsI, metal iodide such as CaI _2, tetraalkylammonium iodide, pyridinium iodide, such as imidazolium iodide 4 the combination of the combination of grade ammonium compound iodine salt, etc.), bromine and a bromide (LiBr, NaBr, KBr, CsBr , CaBr 2 , etc. metal bromides, tetraalkylammonium bromide, quaternary ammonium compounds bromine salts such as pyridinium bromide, etc.), poly Examples thereof include sulfur compounds such as sodium sulfide, alkyl thiol, and alkyl disulfide, viologen dyes, hydroquinone, and quinone. The electrolyte may be used as a mixture.

Further, as the electrolyte, a molten salt electrolyte having a high boiling point is preferable. When the semiconductor electrode is composed of a dye-adsorbed titanium oxide layer, particularly excellent battery characteristics are exhibited by combining with a molten salt electrolyte. The molten salt electrolyte composition includes a molten salt. The molten salt electrolyte composition is preferably liquid at room temperature. The molten salt as the main component is an electrolyte that is liquid at room temperature or has a low melting point, and a general example thereof is “Electrochemistry”, 1997, Vol. 65, No. 11, p. Pyridinium salts, imidazolium salts, and triazolium salts described in No. 923. The molten salt may be used alone or in combination of two or more. Alkali metal salts such as LiI, NaI, KI, LiBF ₄ , CF ₃ COOLi, CF ₃ COONa, LiSCN, and NaSCN can also be used in combination. Usually, the molten salt electrolyte composition contains iodine. The molten salt electrolyte composition preferably has low volatility and preferably does not contain a solvent. The molten salt electrolyte composition may be used after gelation.

  When a solvent is used in the electrolytic solution, it is desirable that the compound has a low viscosity and high ion mobility and can exhibit excellent ionic conductivity. Examples of such solvents include carbonate compounds such as ethylene carbonate and propylene carbonate, heterocyclic compounds such as 3-methyl-2-oxazolidinone, ether compounds such as dioxane, diethyl ether and tetrahydrofuran, ethylene glycol dialkyl ether, propylene glycol Chain ethers such as dialkyl ether, polyethylene glycol dialkyl ether, polypropylene glycol dialkyl ether, alcohols such as methanol, ethanol, ethylene glycol monoalkyl ether, propylene glycol monoalkyl ether, polyethylene glycol monoalkyl ether, polypropylene glycol monoalkyl ether , Ethylene glycol, propylene glycol, polyethylene glycol Polypropylene glycol, polyhydric alcohols such as glycerin, acetonitrile, glutarodinitrile, methoxy acetonitrile, propionitrile, nitrile compounds such as benzonitrile, dimethyl sulfoxide, aprotic polar substances such as sulfolane, water and the like. These solvents can also be used as a mixture.

  The method for providing the electrolyte layer is not particularly limited. For example, a film-like spacer 7 may be disposed between both electrodes to form a gap, and an electrolyte may be injected into the gap. A method of stacking the positive electrode at an appropriate interval after applying the electrolyte may be used. It is desirable to seal both electrodes and their surroundings so that the electrolyte does not flow out, but the sealing method and the material of the sealing material are not particularly limited.

  The photoelectric conversion element of this invention or the dye-sensitized solar cell comprised from this has high photoelectric conversion efficiency.

  Hereinafter, the present invention will be described in more detail based on examples and comparative examples.

As a glass substrate with a transparent conductive film of 30 mm × 25 mm × 3 mm, a glass substrate with FTO (fluorine-doped tin oxide) film (trade name: Low-E glass) made of Japanese plate glass was used.
Next, a titanium oxide film was formed on the conductive film of the substrate with the conductive film. As titanium oxide, a commercially available titanium oxide paste (D paste made by Solaronics) was used. A laminated board in which a titanium oxide layer having a thickness of 15 μm was formed by coating this onto a conductive film of a substrate with a conductive film by a squeegee printing method in a range of 5 mm × 5 mm, drying and baking at 450 ° C. Obtained.

As the dye A, a commercially available ruthenium complex dye (Black Dye manufactured by Solaronics) was used. This was dissolved in ethanol to 3 × 10 ⁻⁴ mol / L. The dye was adsorbed by a method of immersion in a CO ₂ supercritical fluid (hereinafter referred to as SCF method). In the SCF method, as shown in FIG. 2, a 10 cc dye solution is placed in a 50 cc pressure vessel of a JASCO supercritical apparatus, and a laminated plate on which the titanium oxide layer is formed is placed in the vessel. The inside of the container was purged. Further, a CO ₂ supercritical fluid was formed by adjusting the predetermined temperature and pressure to 40 ° C. and 20 MPa, and the dye solution was held for 30 minutes while stirring with a stirrer. After removing the carbon dioxide gas and returning to a constant pressure, the laminate adsorbed with the dye was taken out from the pressure vessel. Incidentally, CO ₂ CO ₂ concentration in the supercritical fluid is about 60 wt%.

As the dye B, a polymethine dye represented by the above formula (6) was synthesized and used. This polymethine dye is described by FM Harmer, `` Heterocyclic Compounds-Cyanine Dyes and Related Compounds '', John Wiley and Sons. & Sons)-New York, London, 1964, DMSturmer, `` Heterocyclic Compounds-Special topics in cyclic chemistry '' , Chapter 18, Section 14, 482-515 Mitsugu, Tetrahedron Letter Vol.41, 2000, P1711-1715, etc., and 4-methylquinoline was reacted with iodoacetic acid, followed by N- [5- (phenyl (Amino) -2,4-pentadienylidene] aniline. This was dissolved in ethanol to 3 × 10 ⁻⁴ mol / L. The dye was adsorbed by the same SCF method as described above to prepare a laminate.

Next, the rinsing process was performed by a dipping method and a method using an SCF method. The dipping method was carried out by immersing the laminate adsorbing the dye several times in an ethanol solution at normal temperature and constant pressure. In the SCF method, a laminated plate that has adsorbed a dye is placed in the pressure vessel, ethanol is added to the extent that the laminated plate is not immersed, and the inside of the vessel is purged with carbon dioxide gas as in the case of adsorbing the dye. Was adjusted to form a CO ₂ supercritical fluid, and ethanol was held for 30 minutes while stirring with a stirrer. After removing the carbon dioxide gas and returning to a constant pressure, the laminated board rinsed from the pressure vessel was taken out.

Next, the rinsed laminate was placed in the pressure vessel, and ethanol containing 1% by weight of acetic acid was added to the extent that the laminate was not immersed. After the inside of the container was purged with carbon dioxide gas in the same manner as the dye adsorption, a CO ₂ supercritical fluid was formed by adjusting to a predetermined temperature and pressure, and this fluid was held for 30 minutes while stirring with a stirrer. After removing the carbon dioxide gas and returning to a constant pressure, the laminated board which processed the carboxylic acid from the pressure vessel was taken out.

  A sheet-like thermoplastic adhesive (product name: Mitsui DuPont Polychemical Co., Ltd .; High Milan Sheet) made of an ionomer resin with a thickness of 50μm on the 4mm outer periphery of 5mm x 5mm on which the titanium oxide film of this laminate was formed So that a gap of about 1 mm was provided at two locations on the outer periphery. This thermoplastic adhesive is not only a sealing material but also serves as a spacer between the two electrodes. Next, a glass substrate on which a platinum film having a thickness of 10 nm serving as a positive electrode was formed by a sputtering method was bonded through the thermoplastic adhesive film so that the platinum side was opposed to the titanium oxide side. From the gap between the thermoplastic adhesive films, an acetonitrile solution containing 0.5M LiI, 0.5M t-butylpyridine, and 0.05M iodine as the main component is filled between the substrate and the positive electrode using capillary action. It was. Immediately after filling the electrolyte, the gap was sealed with an epoxy resin adhesive to obtain a photoelectric conversion element.

  A photoelectric conversion element was obtained in the same manner as in Example 1 except that the dye B was adsorbed by the immersion method (hereinafter referred to as the Dip method). The Dip method was performed by immersing the laminate on which the titanium oxide layer was formed in a dye-dissolved ethanol solution at room temperature and constant pressure for 24 hours.

  A photoelectric conversion element was obtained in the same manner as in Example 1 except that NK3628 represented by the formula (1) was adsorbed as the dye B using the SCF method.

  A photoelectric conversion element was obtained in the same manner as in Example 1 except that NK3628 represented by the formula (1) was adsorbed as the dye B using the Dip method.

  A photoelectric conversion element was obtained in the same manner as in Example 1 except that NK3705 represented by the formula (10) was adsorbed by the SCF method as the dye A and Black Dye was adsorbed by the SCF method as the dye B.

  A photoelectric conversion element was obtained in the same manner as in Example 5 except that NK3705 represented by the formula (10) was adsorbed as the dye A by the Dip method.

  A photoelectric conversion element was obtained in the same manner as in Example 3 except that Black Dye was adsorbed as the dye A by the Dip method.

  A photoelectric conversion element was obtained in the same manner as in Example 1 except that Black Dye was adsorbed by the Dip method as the dye A.

Comparative Example 1
A laminate having a titanium oxide layer formed under the same conditions as in the example was obtained.
Black Dye was used as the dye. This was dissolved in ethanol to 3 × 10 ⁻⁴ mol / L. The laminate was immersed in this dye solution at room temperature for 24 hours to obtain a laminate on which the dye was adsorbed. Subsequent steps were performed in the same manner as in Example 1 to produce a photoelectric conversion element.

Comparative Example 2
As a dye A, Black Dye was adsorbed by the SCF method, and a laminate was obtained in which only one kind of dye was adsorbed without using the dye B. Subsequent steps were performed in the same manner as in Example 1 to produce a photoelectric conversion element.

Comparative Example 3
As a dye A, NK3705 was adsorbed by the Dip method, and a dyed plate was adsorbed without using the dye B to obtain a laminate. Subsequent steps were performed in the same manner as in Example 1 to produce a photoelectric conversion element.

Comparative Example 4
As Dye A, NK3628 was adsorbed using the Dip method, and Dye B was not used, and a laminated board adsorbing only one kind of dye was obtained. Subsequent steps were performed in the same manner as in Example 1 to produce a photoelectric conversion element.

Comparative Example 5
A dye represented by the formula (6) was adsorbed as the dye A by the Dip method, and a laminated board in which only one kind of dye was adsorbed without using the dye B was obtained. Subsequent steps were performed in the same manner as in Example 1 to produce a photoelectric conversion element.

Comparative Example 6
A laminate was obtained in which NK3705 was adsorbed as the dye A by the Dip method and Black Dye was adsorbed as the dye B by the Dip method. Subsequent steps were performed in the same manner as in Example 1 to produce a photoelectric conversion element.

Comparative Example 7
A laminate was obtained in which NK3705 was adsorbed as the dye A by the Dip method and NK3628 was adsorbed as the dye B by the Dip method. Subsequent steps were performed in the same manner as in Example 1 to produce a photoelectric conversion element.

Comparative Example 8
A laminate was obtained in which N719 was adsorbed as the dye A by the Dip method and Black Dye was adsorbed as the dye B by the Dip method. Subsequent steps were performed in the same manner as in Example 1 to produce a photoelectric conversion element.

Comparative Example 9
A laminate having N719 as the dye A adsorbed by the SCF method and Black Dye as the dye B adsorbed by the SCF method was obtained. Subsequent steps were performed in the same manner as in Example 1 to produce a photoelectric conversion element.

Comparative Example 10
A laminate was obtained in which Black Dye was adsorbed by Dip method as Dye A and NK3628 was adsorbed by Dip method as Dye B. Subsequent steps were performed in the same manner as in Example 1 to produce a photoelectric conversion element.

The photoelectric conversion elements prepared in Examples and Comparative Examples were used as dye-sensitized solar cells, and the battery characteristics were evaluated using AM1.5 simulated sunlight. Table 1 shows the production conditions of the photoelectric conversion elements and the IV measurement results (efficiency, Voc, Jsc, and FF). The difference in absorption wavelength is the difference (B _w -A _w ) between the maximum absorption wavelength A _w of dye A having the maximum absorption wavelength on the short wavelength side and the maximum absorption wavelength B _w of dye B having the maximum absorption wavelength on the long wavelength side. is there.

Remarks
Black: Black Dye (maximum absorption wavelength 620nm)
Formula (10): NK3705 (maximum absorption wavelength 426nm)
Formula (1): NK3628 (maximum absorption wavelength 752nm)
Formula (6): Polymethine dye (maximum absorption wavelength 930 nm)
N719: Ru complex dye (maximum absorption wavelength 570nm)

Sectional drawing which shows an example of a photoelectric conversion element Schematic diagram of supercritical equipment

Explanation of symbols

1: substrate, 2: transparent conductive film, 3: dye A adsorption metal oxide layer, 4: dye B adsorption metal oxide layer, 5: substrate, 6: conductive film, 7: electrolyte, 8: spacer, 10: Surface electrode, 11: Counter electrode, 21: Pressure vessel, 22: Laminated plate, 23: Treatment solution, 24: Laminated plate holder, 25: Stirrer, 26: Pressure adjustment valve

Claims (7)

In a photoelectric conversion element having a dye-sensitized semiconductor electrode in which at least two kinds of sensitizing dyes having different absorption wavelengths are adsorbed, at least one of the sensitizing dyes is a supercritical fluid of carbon dioxide gas or carbonic acid Adsorption of dyes for sensitization in the film thickness direction by adsorbing them in a pressurized fluid containing carbon dioxide under temperature and pressure conditions to obtain a supercritical fluid of gas and dyeing different dyes in the film thickness direction A photoelectric conversion element having a changed concentration and having a difference in maximum absorption wavelength of at least two sensitizing dyes in the visible light and near infrared light regions of 90 nm or more.   The photoelectric conversion element according to claim 1, wherein the at least one sensitizing dye is a ruthenium complex.   3. The photoelectric conversion element according to claim 1, wherein at least one sensitizing dye is a polymethine dye.   The photoelectric conversion device according to any one of claims 1 to 3, wherein the maximum absorption wavelength of at least one sensitizing dye is in the range of more than 850 nm and not more than 1400 nm. In a method for producing a photoelectric conversion element having a dye-sensitized semiconductor electrode in which at least two kinds of dyes having different absorption wavelengths are adsorbed, the maximum absorption wavelength in the visible light and near infrared light region between the dyes for sensitization Sensitizing dye having a difference of 90 nm or more is selected, and at least one sensitizing dye is carbon dioxide gas under a temperature and pressure condition at which a supercritical fluid of carbon dioxide gas or a supercritical fluid of carbon dioxide gas is obtained. Different dyes in the film thickness direction by separately adsorbing to a semiconductor in a pressurized fluid containing and separately adsorbing at least two kinds of dyes for sensitization. A method for producing a photoelectric conversion element, wherein the adsorption concentration is changed. The dye a sensitizing dye, a supercritical fluid containing a C ₁ -C ₄ alcohols, C ₁ -C ₆ carbonate, a solvent and carbon dioxide gas selected from among C ₂ -C ₆ ethers and C ₁ -C ₄ nitriles Or the manufacturing method of the photoelectric conversion element of Claim 5 made to adsorb | suck to a semiconductor in a pressurized fluid.   A dye-sensitized solar cell comprising the photoelectric conversion element according to claim 1.

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