JP2006278112A - Dye-sensitized solar cell and dye-sensitized solar cell module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance photoelectric transfer efficiency of a dye-sensitized solar cell. <P>SOLUTION: This dye-sensitized solar cell has at least a conductive substrate, a porous semiconductor layer adsorbing a sensitized dye, a carrier transport layer, and a counter electrode in this order. The sensitized dye comprises two kinds of sensitized dye having different absorption peak wavelengths in an absorption spectrum, and the molecular weight of the sensitized dye having the absorption peak wavelength on the short wavelength side is smaller than the molecular weight of the sensitized dye having the absorption peak wavelength on the long wavelength side. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a dye-sensitized solar cell and a dye-sensitized solar cell module. More specifically, the present invention relates to a dye-sensitized solar cell having high photoelectric conversion efficiency and a dye-sensitized solar cell module exhibiting excellent performance even in a structure in which it is integrated.

  Present solar power generation is put to practical use mainly for silicon-based solar cells using single crystal silicon, polycrystalline silicon, and amorphous silicon. However, silicon-based solar cells have problems such as high energy consumption in the manufacturing process and high manufacturing costs. Furthermore, when it is spread as it is, a shortage of silicon as a raw material becomes a problem.

  Accordingly, attention has been focused on dye-sensitized solar cells. This dye-sensitized solar cell is sandwiched between, for example, a porous electrode (porous semiconductor layer) made of a semiconductor carrying a sensitizing dye formed on a transparent conductive film on a transparent substrate, a counter electrode, and the electrodes. It is mainly composed of a carrier transport layer. This solar cell is expected as a next-generation solar cell because of its simplicity of manufacturing method and low material cost.

  J. et al. Am. Ceram. Soc. , 80 (12) 3157-3171 (1997) (Non-Patent Document 1) describes a method for producing a dye-sensitized solar cell in which a sensitizing dye such as a transition metal complex is adsorbed on the surface of a titanium oxide porous electrode. Has been. In this method, a porous electrode formed on a transparent conductive film on a transparent substrate is immersed in a solution in which a sensitizing dye is dissolved, whereby the sensitizing dye is supported on the porous electrode. Thereafter, a redox electrolyte is dropped, and a counter electrode is stacked on the porous electrode to produce a solar cell.

In the solar cell, when the semiconductor electrode is irradiated with visible light, the sensitizing dye on the surface of the semiconductor electrode absorbs light, thereby exciting electrons in the dye molecule and injecting excited electrons into the semiconductor electrode. . Therefore, electrons are generated on the semiconductor electrode side, and the electrons move through the electric circuit to the counter electrode. The electrons that have moved to the counter electrode are carried by holes or ions in the carrier transport layer and return to the sensitizing dye on the porous electrode surface. Such a process is repeated to extract electric energy with high energy conversion efficiency.
However, in order to put it to practical use as a solar cell, further improvement in conversion efficiency is desired.

  As one cause of the deterioration of the characteristics of the dye-sensitized solar cell, it is considered that injected carriers flow into the carrier transport layer from the surface of the semiconductor electrode not covered with the dye. For example, Japanese Patent Application Laid-Open No. 2001-102103 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2000-323192 (Patent Document 2) prevent the movement of a dye and a carrier on the surface of a semiconductor electrode in order to suppress the flow of the carrier. A technique for supporting a substance to be carried is described. As a molecule for preventing carrier movement, a silicon compound, a tin compound, a sulfone compound, a sulfonate, a sulfate ester salt, and a phosphate ester-containing polymer are used. In Japanese Patent Laid-Open No. 2004-119279 (Patent Document 3), for the same purpose, alkoxysilane, chlorosilane, silanol, pyridines, and imidazoles each containing a fluorine atom are supported on the surface of the semiconductor electrode.

JP 2001-102103 A JP 2000-323192 A JP 2004-119279 A J. et al. Am. Ceram. Soc. , 80 (12) 3157-3171 (1997)

  However, when a substance that prevents the movement of these carriers is supported on the porous electrode surface, the light absorbed by these substances is not extracted as electrical energy. Therefore, the subject that the photoelectric conversion efficiency fell occurred.

  Thus, according to the present invention, a conductive substrate, a porous semiconductor layer on which the sensitizing dye is adsorbed, a carrier transport layer, and a counter electrode are provided in this order, and the sensitizing dye has an absorption spectrum. The molecular weight of the sensitizing dye having the absorption peak wavelength on the short wavelength side is smaller than the molecular weight of the sensitizing dye having the absorption peak wavelength on the long wavelength side. A dye-sensitized solar cell is provided.

  Furthermore, according to the present invention, there is provided a dye-sensitized solar cell module in which two or more dye-sensitized solar cells are connected in series.

  According to the present invention, the two types of sensitizing dyes can reduce the portion of electrons flowing from the porous semiconductor layer to the carrier transport layer, so the ratio of charges flowing in the opposite direction from the porous semiconductor layer to the carrier transport layer can be reduced. Can be reduced. As a result, the short circuit current, the open circuit voltage, and the photoelectric conversion efficiency can be increased.

In the following, the background to the present invention will be described.
A dye-sensitized solar cell having a conductive substrate, a porous semiconductor layer (semiconductor electrode) in which a sensitizing dye is adsorbed on the conductive substrate, a carrier transport layer, and a counter electrode in this order is provided on the surface of the porous semiconductor layer. When the dye-sensitive material absorbs light, electrons in the dye molecule are excited, the excited electrons are injected into the porous semiconductor layer, and electric energy is obtained by taking out the electrons. However, there is a portion not covered with the sensitizing dye on the surface of the porous semiconductor layer, and electrons injected from the sensitizing dye flow from the portion not covered with the sensitizing dye to the carrier transport layer (reversely). Current). This phenomenon reduces the photoelectric conversion efficiency.

  Moreover, the electrons injected from the sensitizing dye occupy the conduction band bottom level of the porous semiconductor layer. When these electrons return to the LUMO level or HOMO level of the sensitizing dye, a reverse flow of electrons occurs, and the open circuit voltage may decrease. That the absorption peak wavelength of the sensitizing dye is short means that the energy gap between the LUMO level and the HOMO level is large, and the LUMO level is high and the HOMO level is low. If the HOMO level decreases, the energy gap between the conduction band bottom level and the HOMO level increases, and the reverse flow of electrons from the porous semiconductor layer to the HOMO level of the sensitizing dye is suppressed. Conceivable. The same can be said for the LUMO level. Therefore, since the open circuit voltage is larger when the absorption peak wavelength is short, the sensitizing dye having the absorption peak wavelength on the short wavelength side is more sensitive than the sensitizing dye having the absorption peak wavelength on the long wavelength side. The reverse current prevention effect is great.

In the dye-sensitized solar cell of the present invention, among the two types of dyes, the absorption peak wavelength is on the short wavelength side, and the size of the sensitizing dye molecule considered to have a large reverse current prevention effect is smaller. Therefore, the sensitizing dye whose absorption peak wavelength is on the short wavelength side is increased between the sensitizing dye whose absorption peak wavelength is adsorbed on the porous semiconductor layer is on the long wavelength side, or the absorption peak wavelength is on the long wavelength side. It can also be adsorbed in pores where dyes are difficult to adsorb, and as a result, the surface of the porous semiconductor layer can be more widely coated with sensitizing dyes. Therefore, by supporting a sensitizing dye with a small molecular weight having an absorption peak wavelength on the short wavelength side, it is possible to reduce the portion of electrons flowing from the porous semiconductor layer to the carrier transport layer, so that from the porous semiconductor layer to the carrier transport layer. The proportion of charges flowing in the opposite direction can be reduced. As a result, the short circuit current and the open circuit voltage can be increased.
Below, each component of a dye-sensitized solar cell is demonstrated.

(Conductive substrate)
In the present invention, the porous semiconductor layer is formed on a conductive substrate.
As the conductive substrate, a substrate having conductivity itself such as a metal substrate, or a substrate such as glass or plastic having a conductive layer on the surface thereof can be used. In the latter case, preferable conductive materials include metals such as gold, platinum, silver, copper, aluminum, and indium, conductive carbon, indium tin composite oxide, fluorine-doped tin oxide, and zinc oxide. These conductive materials can be formed on the substrate by a conventional method. The thickness of the conductive layer is preferably about 0.02 to 5 μm.

The conductive substrate preferably has a lower surface resistance. For example, the surface resistance is preferably 40 Ω / sq or less. Moreover, the film thickness of this support body will not be specifically limited if an appropriate intensity | strength can be provided to a porous semiconductor layer.
When the conductive substrate side is the light receiving surface, the substrate is preferably transparent.

  Taking into account the above points and satisfying the mechanical strength, a typical support is a laminate in which a conductive layer made of fluorine-doped tin oxide is laminated on a transparent substrate made of soda-lime float glass. .

  In consideration of cost, flexibility, etc., a transparent polymer sheet provided with the conductive layer may be used. Examples of the transparent polymer sheet include tetraacetyl cellulose (TAC), polyethylene terephthalate (PET), polyphenyl sulfide (PPS), polycarbonate (PC), polyarylate (PA), polyether imide (PEI), phenoxy resin, and the like. It is done.

Metal leads may be added to reduce the resistance of the conductive substrate. The material of the metal lead wire is preferably platinum, silver, copper, aluminum, indium, nickel, titanium, or the like. The metal lead wire may be formed on the support substrate by sputtering, vapor deposition or the like before forming a transparent conductive layer such as tin oxide or ITO, or may be formed after the conductive layer is provided. However, it should be noted that the metal lead wire may reduce the amount of incident light.
Further, when the conductive substrate is not a light receiving surface, a metal substrate such as platinum, silver, copper, aluminum, indium, nickel, titanium, tantalum, tungsten, or molybdenum may be used.

(Porous semiconductor layer)
The porous semiconductor layer is usually composed of an aggregate of semiconductor fine particles.

Any fine semiconductor particles can be used as long as they are generally used for photoelectric conversion materials. For example, titanium oxide, zinc oxide, tin oxide, iron oxide, niobium oxide, zirconium oxide, cerium oxide, tungsten oxide, silicon oxide, aluminum oxide, nickel oxide, barium titanate, strontium titanate, cadmium sulfide, lead sulfide, sulfide Examples thereof include zinc, indium phosphide, copper-indium sulfide (CuInS ₂ ), CuAlO ₂ , and SrCu ₂ O ₂ . Among these, titanium oxide, zinc oxide, tin oxide, and niobium oxide are preferable, and titanium oxide is particularly preferable from the viewpoint of stability and safety.

  Titanium oxide includes titanium hydroxide, hydrous titanium oxide and the like in addition to various narrowly defined titanium oxides such as anatase-type titanium oxide, rutile-type titanium oxide, amorphous titanium oxide, metatitanic acid, and orthotitanic acid.

  The semiconductor fine particles may be single crystal, polycrystalline, or amorphous. Among these, polycrystal is preferable from the viewpoint of stability, difficulty of crystal growth, production cost, and the like. In particular, polycrystalline semiconductor fine particles of fine powder (nano to microscale) are preferable.

  Further, two or more kinds of particles having different particle sizes may be mixed and used. In this case, the material of each particle may be the same or different. The ratio of the average particle sizes of different particle sizes should have a difference of 10 times or more. Particles having a large particle size (for example, 100 to 500 nm) can be used for the purpose of scattering incident light and increasing the light capture rate. In particular, when fine particles of different types of semiconductors are used, it is more effective to improve the light capture rate if the fine particles of semiconductor particles having a strong adsorption action are made smaller.

The thickness of a porous semiconductor layer is not specifically limited, For example, about 0.1-100 micrometers is mentioned. From another point of view, a porous semiconductor layer having a large surface area is preferable, for example, about 10 to 200 m ² / g.
Further, the porosity of the porous semiconductor layer is preferably 40 to 80%. If it is less than 40%, it is not preferred because the dye solution is difficult to permeate, so that it is difficult to adsorb the dye.

(Titanium oxide production method)
Titanium oxide, which is the most preferable form of semiconductor fine particles, can be produced according to methods described in various documents. For example, as a production method, “New synthesis method: Synthesis of monodispersed particles by sol-gel method and control of size form” Vol. 35, No. 9, pages 1012 to 1018 (1995) can be cited as representative examples. Can do. Also suitable is a method obtained by hydrolyzing a chloride developed by Degussa.

  Among the titanium oxides used in the present invention, the anatase type and the rutile type can take any form depending on the production method and thermal history, but the anatase type is common. The anatase type has a shorter light absorption wavelength than the rutile type, and the degree of decrease in photoelectric conversion by ultraviolet light is small. Therefore, a high anatase type content is preferable, and the ratio is preferably 80% or more.

(Method for producing porous semiconductor layer)
Examples of the method for forming the porous semiconductor layer include a method of applying a suspension containing semiconductor fine particles on a transparent conductive film, and drying and / or firing.
The above method will be specifically described.

  First, the semiconductor fine particles are suspended in a suitable solvent. Examples of such a solvent include glyme solvents such as ethylene glycol monomethyl ether, alcohols such as isopropyl alcohol, alcohol mixed solvents such as isopropyl alcohol / toluene, water, and the like. Further, instead of these suspensions, a commercially available titanium oxide paste (Ti-nanoxide, D, T / SP, D / SP, manufactured by Solaronix) may be used.

  Examples of the method for applying the suspension to the substrate for forming the porous semiconductor layer include known methods such as a doctor blade method, a squeegee method, a spin coating method, and a screen printing method. Thereafter, the coating solution is dried and baked. The temperature, time, atmosphere, etc. necessary for drying and firing can be appropriately adjusted according to the type of substrate and semiconductor fine particles used. For example, in the range of about 500-800 degreeC under air | atmosphere or inert gas atmosphere, about 10 second-about 12 hours are mentioned. Drying and firing may be performed only once at a single temperature, or may be performed twice or more by changing the temperature. When there are a plurality of semiconductor layers, semiconductor fine particle suspensions having different average particle diameters may be prepared, and the coating, drying, and firing steps may be performed twice.

  After forming a porous semiconductor layer on a conductive substrate, for example, for the purpose of improving electrical connection between semiconductor fine particles, increasing the surface area of the porous semiconductor layer, and reducing defect levels on the semiconductor fine particles. When the semiconductor layer is made of titanium oxide, the porous semiconductor layer may be pretreated with an aqueous titanium tetrachloride solution.

(Sensitizing dye)
Two types of sensitizing dyes are adsorbed on the porous semiconductor layer.
As the sensitizing dye, an organic dye or a metal complex dye can be used. Examples of organic dyes include azo dyes, quinone dyes, quinone imine dyes, quinacridone dyes, squarylium dyes, cyanine dyes, merocyanine dyes, triphenylmethane dyes, xanthene dyes, porphyrin dyes, and perylene dyes. Examples thereof include dyes, indigo dyes, and naphthalocyanine dyes.

  In the metal complex dye, Cu, Ni, Fe, Co, V, Sn, Si, Ti, Ge, Cr, Zn, Ru, Mg, Al, Pb, Mn, In, Mo, Y, Zr, Nb, Sb, La, W, Pt, Ta, Ir, Pd, Os, Ga, Tb, Eu, Rb, Bi, Se, As, Sc, Ag, Cd, Hf, Re, Au, Ac, Tc, Te, Rh, etc. Examples thereof include a pigment having a metal. In particular, phthalocyanine dyes, ruthenium bipyridine dyes, and the like are preferable.

  Among the sensitizing dyes, the molecular weight of the sensitizing dye having the absorption peak wavelength on the short wavelength side is preferably 50 or more smaller than the molecular weight of the sensitizing dye having the absorption peak wavelength on the long wavelength side. Furthermore, it is preferable that it is small in the range of 80-1200.

  Moreover, 650-2000 are preferable and, as for the molecular weight of the sensitizing dye whose absorption peak wavelength exists in a long wavelength side among sensitizing dyes, it is more preferable that it is 700-1500. On the other hand, the sensitizing dye whose absorption peak wavelength is on the short wavelength side is preferably 150 to 900, and more preferably 200 to 700.

  A sensitizing dye having an absorption peak wavelength on the short wavelength side preferably has an absorption peak wavelength in the light wavelength region of 350 to 510 nm. The sensitizing dye having an absorption peak wavelength on the long wavelength side preferably has an absorption peak wavelength in the light wavelength region of 500 to 800 nm. Moreover, it is preferable that the difference of the absorption peak wavelength of two sensitizing dyes is 10-400 nm.

  The ratio of the two sensitizing dyes is such that the molar ratio of the sensitizing dye having the absorption peak wavelength on the short wavelength side is 0.1 to 10 with respect to the sensitizing dye having the absorption peak wavelength on the long wavelength side. It is preferable that it is in the range of 0.2-4. If the sensitizing dye having an absorption peak wavelength on the short wavelength side is less than 0.1, it is not preferable because the light on the short wavelength side cannot be sufficiently absorbed, and if it exceeds 10, the light on the long wavelength side can be sufficiently absorbed. Since it disappears, it is not preferable.

  Among the sensitizing dyes, the sensitizing dye having an absorption peak wavelength on the long wavelength side is more preferably a ruthenium-based metal complex dye or a terpyridine-based ruthenium complex, and particularly a Ruthenium 535 dye (compound 1, molecular weight) represented by the following structural formula. 705, absorption peak wavelength 538 nm, manufactured by Solaronix), Ruthenium 535-bisTBA dye (compound 2, molecular weight 1203, absorption peak wavelength 535 nm, manufactured by Solaronix), Ruthenium620-1H3TBA dye (compound 3, molecular weight 1363, absorption peak wavelength 620 nm, Solaronix) Are preferable.

  Sensitizing dyes whose absorption peak wavelength is on the short wavelength side include, for example, NK-3985 (compound 4, molecular weight 357, absorption maximum wavelength 472 nm, manufactured by Hayashibara Biochemical Laboratories) represented by the following structural formula, NKX-2311 (compound 5, molecular weight 418, absorption maximum wavelength 504 nm, manufactured by Hayashibara Biochemical Laboratory), NKX-2586 (compound 6, molecular weight 444, absorption maximum wavelength 470 nm, manufactured by Hayashibara Biochemical Laboratory), NKX-2569 (compound 7, molecular weight 387) , Absorption maximum wavelength 489 nm, manufactured by Hayashibara Biochemical Laboratory), NKX-2577 (compound 8, molecular weight 394, absorption maximum wavelength 470 nm, manufactured by Hayashibara Biochemical Laboratory), NKX-2510 (compound 9, molecular weight 338, absorption maximum wavelength) 430 nm, manufactured by Hayashibara Biochemical Research Institute), NKX-2398 (compound 10, molecular weight 367, absorption maximum wavelength 49) nm, manufactured by Hayashibara Biochemical Laboratories), NKX-2393 (compound 11, molecular weight 437, absorption maximum wavelength 500 nm, manufactured by Hayashibara Biochemical Research Institute), NKX-2553 (compound 12, molecular weight 242, absorption maximum wavelength 455 nm, Hayashibara organism Chemical Laboratory), NKX-2554 (compound 13, molecular weight 362, absorption maximum wavelength 460 nm, Hayashibara Biochemical Laboratory), NKX-2590 (compound 14, molecular weight 562, absorption maximum wavelength 430 nm, Hayashibara Biochemistry Research Institute) ), NKX-2595 (compound 15, molecular weight 602, absorption maximum wavelength 500 nm, manufactured by Hayashibara Biochemical Laboratories), NKX-2672 (compound 16, molecular weight 550, absorption maximum wavelength 454 m, manufactured by Hayashibara Biochemical Research Institute), NKX- 2718 (compound 17, molecular weight 471, absorption maximum wavelength 460 nm, Hayashibara Biochemical Research) NKX-2656 (compound 18, molecular weight 607, absorption maximum wavelength 490 nm, manufactured by Hayashibara Biochemical Laboratories), S0313 (compound 19, molecular weight 352, absorption maximum wavelength 426 nm, manufactured by Nippon Siebel Hegner), S0312 (compound 20, Molecular weight 385, absorption maximum wavelength 426 nm, manufactured by Nippon Siebel Hegner, Inc., S0294 (compound 21, molecular weight 336, absorption maximum wavelength 428 nm, manufactured by Nippon Siebel Hegner), S0308 (compound 22, molecular weight 282, absorption maximum wavelength 454 nm, manufactured by Nippon Siebel Hegner, Inc.) ), S0280 (Compound 23, molecular weight 316, absorption maximum wavelength 476 nm, manufactured by Nippon Siebel Hegner), S0279 (Compound 24, molecular weight 330, absorption maximum wavelength 479 nm, manufactured by Nippon Siebel Hegner), S0056 (Compound 25, molecule Quantity 316, absorption maximum wavelength 487 nm, manufactured by Nippon Siebel Hegner, Inc., S0285 (compound 26, molecular weight 344, absorption maximum wavelength 491 nm, manufactured by Nippon Siebel Hegner), Coumarin 343 (compound 27, molecular weight 285, absorption maximum wavelength 409 nm, manufactured by Nippon Siebel Hegner) ), Coumarin 4 (compound 28, molecular weight 176, absorption maximum wavelength 372 nm, manufactured by Nippon Shibel Hegner), Nippon Kayaku Co., Ltd. dye (compound 29, molecular weight 377, absorption maximum wavelength 420, 440 nm), and the like.

  In order to firmly adsorb to the porous semiconductor layer, the sensitizing dye preferably has an interlock group such as a carboxyl group, an alkoxy group, a sulfone group, an ester group, a mercapto group, or a phosphonyl group in the molecule. In the case of having an interlock group, the sensitizing dye can be firmly fixed to the porous semiconductor layer through this group. As a result, the movement of electrons between the excited sensitizing dye and the conductor of the porous semiconductor layer can be facilitated. In other words, the electrical coupling between the sensitizing dye and the porous semiconductor layer can be improved.

  Further, it is preferable that the sensitizing dye has a large extinction coefficient because a large amount of light can be absorbed in a small amount. In particular, it is preferable that the absorption coefficient of the sensitizing dye having the absorption peak wavelength on the short wavelength side is larger than that of the sensitizing dye having the absorption peak wavelength on the long wavelength side. The absorption coefficient of a sensitizing dye having an absorption peak wavelength on the short wavelength side is preferably 2000 or more.

(Sensitivity dye adsorption method)
The sensitizing dye can spectrally sensitize the semiconductor by being adsorbed to the porous semiconductor layer. The adsorption of the sensitizing dye may be performed on the semiconductor fine particles for forming the porous semiconductor layer or on the porous semiconductor layer. In general, it is preferable to adsorb the porous semiconductor layer after forming it because the adsorbability of the sensitizing dye is improved rather than adsorbing to the semiconductor fine particles.

  As a method of adsorbing the sensitizing dye to the semiconductor (semiconductor fine particles or porous semiconductor layer), a well-dried semiconductor is immersed in a solution containing the sensitizing dye, or the dye solution is applied to the semiconductor and adsorbed. The method of letting it be mentioned. Of these, a method of adsorbing a sensitizing dye to a semiconductor by dipping is common.

As a solvent for the dye solution, a solvent capable of dissolving the sensitizing dye to be used is preferable. Specific examples include organic solvents such as alcohol, toluene, acetonitrile, THF, chloroform, and dimethylformamide. Usually, it is preferable to use a purified solvent. In order to improve the solubility of the sensitizing dye, the dissolution temperature may be increased, or two or more different solvents may be mixed. The dye concentration in the solvent can be adjusted according to the sensitizing dye used, the type of solvent, and the conditions of the dye adsorption method. The concentration of the sensitizing dye is preferably 1 × 10 ⁻⁵ mol / liter or more.

  In the present invention, it is necessary to adsorb two types of sensitizing dyes to the porous semiconductor layer. As an adsorption method, there is a method in which a dye solution in which two kinds of sensitizing dyes are dissolved in the same solvent is prepared, and a porous semiconductor layer is immersed in the dye solution. In addition, after the porous semiconductor layer is immersed in a dye solution in which one kind of sensitizing dye is dissolved and the dye is adsorbed, the porous semiconductor layer is immersed in a solution in which the other sensitizing dye is dissolved, and the other There is a method of adsorbing the dye. When adsorbing the dyes separately, the order of adsorbing the dyes is preferably to adsorb the dye having the absorption peak wavelength on the short wavelength side after adsorbing the sensitizing dye having the absorption peak wavelength on the long wavelength side.

If the adsorption amount of the sensitizing dye is small, the sensitizing effect may be insufficient. On the contrary, if the amount is large, the dye not adsorbed on the porous semiconductor layer may float, which may reduce the sensitizing effect and cause an efficiency effect. The adsorption amount of the sensitizing dye is preferably in the range of 10 ⁻⁴ to 10 ⁻³ mol / cm ³ per porous semiconductor layer.

  If necessary, a relatively low-molecular coadsorbing compound can be added to prevent sensitizing dyes or between sensitizing dyes and additives and to give sensitizing dyes a certain direction. Also good. Examples of the co-adsorbing compound include steroid compounds such as cholic acid having a carboxyl group or a carboxylic anhydride group.

  Unadsorbed sensitizing dye may be removed by washing immediately after the adsorption step. As the cleaning agent, an organic solvent having a relatively high volatility is preferably used. Examples of the organic solvent include alcohols such as methanol and ethanol, and solvents that are relatively easy to dry, such as acetonitrile and acetone.

  Further, after removing the unadsorbed sensitizing dye, the surface of the semiconductor fine particles may be treated with an organic basic compound in order to make the adsorption state more stable, thereby promoting the removal of the unadsorbed sensitizing dye. Examples of the organic basic compound include derivatives such as bipyridine and quinoline. In the case of a liquid, the organic basic compound may be used as it is. In the case of a solid, it is preferably used after being dissolved in a solvent (for example, the same solvent as the dye solution).

(Counter electrode)
The counter electrode can constitute a pair of electrodes together with a semiconductor electrode (porous semiconductor layer). Usually, it is formed on a support substrate. The counter electrode may have a configuration including a laminated body in the order of a conductive layer and a catalyst layer from the support substrate side.
Examples of the supporting substrate include a transparent or opaque substrate that can be usually used as a substrate for a solar cell.

Next, the conductive layer may be transparent or opaque. For example, an N-type or P-type elemental semiconductor (eg, silicon, germanium, etc.) or a compound semiconductor (eg, GaAs, InP, ZnSe, CsS, etc.); a metal such as gold, platinum, silver, copper, aluminum, etc .; titanium, tantalum And a high melting point metal such as tungsten; and a layer made of a transparent conductive material such as ITO, SnO ₂ , CuI, and ZnO. The thickness of the conductive layer is suitably about 0.1 to 0.5 μm. These conductive layers can be formed by a conventional method.

Examples of the catalyst layer include platinum, carbon black, ketjen black, carbon nanotube, fullerene and the like. In the case of platinum, the catalyst layer can be formed on a support substrate coated with a conductive layer by a method such as sputtering, thermal decomposition of chloroplatinic acid, or electrodeposition. As for the thickness of the catalyst layer which consists of platinum, about 0.5-1000 nm is mentioned.
Note that when the catalyst layer has high electrical conductivity, the conductive layer may not be provided.

(Carrier transport layer)
The carrier transport layer is preferably composed of a conductive material capable of transporting electrons, holes and / or ions. For example, hole transport materials such as polyvinyl carbazole and triphenylamine; electron transport materials such as tetranitrophlorenone; conductive polymers such as polythiophene and polypyrrole; ionic conductors such as liquid electrolyte and polymer electrolyte; copper iodide, thiocyanin Examples include inorganic p-type semiconductors such as copper acid.
Among the above conductive materials, a conductive material that can transport ions, that is, an ionic conductor is preferable.

(Liquid electrolyte)
The liquid electrolyte preferably includes a redox electrolyte.
In general, the redox electrolyte is not particularly limited as long as it can be used in a battery, a solar battery or the like. Specific examples include redox electrolytes such as I ⁻ / I ₃ ⁻ system, Br ₂ ⁻ / Br ₃ ⁻ system, Fe ²⁺ / Fe ³⁺ system, and quinone / hydroquinone system.

Specific examples of the redox electrolyte include combinations of metal iodides such as lithium iodide (LiI), sodium iodide (NaI), potassium iodide (KI), calcium iodide (CaI) and iodine (I ₂ ). A tetraalkylammonium salt such as tetraethylammonium iodide (TEAI), tetrapropylammonium iodide (TPAI), tetrabutylammonium iodide (TBAI), tetrahexylammonium iodide (THAI), etc., and odor A combination of metal bromide such as lithium bromide (LiBr), sodium bromide (NaBr), potassium bromide (KBr), calcium bromide (CaBr) and bromine is preferable. Among these, a combination of LiI and I ₂ is particularly preferable.

Examples of the liquid electrolyte solvent include carbonates such as propylene carbonate, nitriles such as acetonitrile, alcohols such as ethanol, water, aprotic polar substances, and the like. Among these, carbonate compounds and nitriles Compounds are particularly preferred.
Two or more of these solvents can be used in combination.

Various additives may be contained in the liquid electrolyte. Additives include nitrogen-containing aromatic compounds such as t-butylpyridine (TBP), dimethylpropylimidazole iodide (DMPII), methylpropylimidazole iodide (MPII), ethylmethylimidazole iodide (EMII), ethyl Imidazole salts such as imidazole iodide (EII) and hexylmethylimidazole iodide (HMII) may be added.
The electrolyte concentration in the liquid electrolyte is preferably in the range of 0.1 to 1.5 mol / liter, particularly preferably in the range of 0.1 to 0.7 mol / liter.

(Polymer electrolyte)
Next, the polymer electrolyte is preferably composed of a redox species and a solid substance capable of dissolving the redox species or binding to at least one substance constituting the redox species. Examples of the solid material include polyethylene oxide, polypropylene oxide, polyethylene succinate, poly-β-propiolactone, polyethyleneimine, polyalkylene sulfide, and the like, or a crosslinked product thereof, polyphosphazene, polysiloxane. In addition, a polymer functional group such as polyvinyl alcohol, polyacrylic acid, polyalkylene oxide, or the like having a polyether segment or oligoalkylene oxide structure added as a side chain or a copolymer thereof can be mentioned. Those having an alkylene oxide structure as a side chain and those having a polyether segment structure as a side chain are preferred.
As the redox species, the same ones as mentioned for the liquid electrolyte can be used.

  In order to contain the redox species in the solid substance, for example, a method of polymerizing a monomer that becomes a polymer compound in the coexistence with the redox species, a solid such as a polymer compound is used as a solvent as necessary. Examples include a method of dissolving and adding a redox species to the resulting solution to remove the solvent. The content of the redox species can be appropriately selected according to the required ionic conductivity performance.

(spacer)
A spacer may be used to prevent contact between the counter electrode and the porous semiconductor layer. Examples of the spacer include a polymer film such as polyethylene. When the porous semiconductor layer is made of titanium oxide, the film thickness is suitably about 10 to 50 μm considering the film thickness and the ion mobility of the carrier transport layer.
Two or more dye-sensitized solar cells (unit cells) may be connected in series to form a dye-sensitized solar cell module. This module can achieve high conversion efficiency.

The following examples and comparative examples will be described based on FIG. 1 which is a schematic cross-sectional view showing the layer structure of the dye-sensitized solar cell of the present invention. In FIG. 1, 1 and 9 are support substrates, 2 and 8 are transparent conductive films, 3 is a platinum layer, 4 is a carrier transport layer, 5 is dye I (sensitizing dye whose absorption peak wavelength is on the long wavelength side), 6 Is Dye II (sensitizing dye whose absorption peak wavelength is on the short wavelength side), 7 is a porous semiconductor, and e ⁻ and arrows indicate the flow of electrons. The transparent conductive film 2 and the platinum layer 3 are collectively referred to as a counter electrode.

Example 1
-Production of porous semiconductor layer On the transparent conductive film 8 side of the support substrate 9 of a 1.1 mm-thick glass plate (manufactured by Nippon Sheet Glass Co., Ltd.) on which a SnO ₂ film having a thickness of 1 μm was deposited as the transparent conductive film 8, A titanium oxide paste (manufactured by Solaronix, Tinanoxide D / SP) was applied on the transparent conductive film 8 with a film thickness of about 10 μm and an area of about 10 mm × 10 mm by screen printing. The obtained coating film was preliminarily dried at 100 ° C. for 30 minutes, and then baked at 500 ° C. for 40 minutes in an air atmosphere, whereby titanium oxide having a thickness of 8 μm was obtained as the porous semiconductor layer 7.

Adsorption of sensitizing dye Tris (isothiocyanato) -ruthenium (II) -2 as sensitizing dye 5 (dye I),
2 ′: 6 ′, 2 ″ -terpyridine-4,4 ′, 4 ″ -tricarboxylic acid tris-tetrabutylammonium salt (compound 3, molecular weight 1363, absorption peak wavelength 620 nm, trade name Ruthenium 620-1H3TBA, Solaronix) Was dissolved in a mixed solvent of acetonitrile (manufactured by Kishida Chemical Co., Ltd.) and 2-butanol (manufactured by Kishida Chemical Co., Ltd.) so as to have a concentration of 2 × 10 ⁻⁴ mol / liter. To this solution, deoxycholic acid (manufactured by Aldrich) was added and dissolved at a concentration of 2 × 10 ⁻² mol / liter to obtain a dye I adsorption solution.
Further, NKX-2311 (compound 5, molecular weight 418, absorption maximum wavelength 504 nm, manufactured by Hayashibara Biochemical Laboratories) was used as sensitizing dye 6 (dye II) so that the concentration of dye I was 2 × 10 ⁻⁴ mol / liter. It was made to melt | dissolve in the solution for adsorption | suction and the solution for adsorption | suction of the pigment | dye I and the pigment | dye II was obtained.
The glass plate was immersed in the obtained dye I and dye II adsorption solution for about 20 hours to adsorb the dye I and dye II to the porous semiconductor layer. Then, it was dried at about 70 ° C. for about 10 minutes.

Preparation of redox electrolyte solution Lithium iodide (Aldrich) was added to a concentration of 0.1 mol / liter, and dimethyl-propylimidazolium iodide (Shikoku Chemicals) was adjusted to a concentration of 0.6 mol / liter. Iodine (manufactured by Aldrich) was dissolved in acetonitrile (manufactured by Aldrich) to a concentration of 0.05 mol / liter to prepare a redox electrolyte solution used as the carrier transport layer 4.

-Production of solar cell A platinum film was deposited by 1 μm on the transparent conductive film 2 side of the support substrate 1 (the same substrate as the glass plate) provided with the transparent conductive film 2 to form a platinum layer 3 as a counter electrode.
This counter electrode and the porous semiconductor layer obtained above were stacked with a spacer for preventing a short circuit therebetween. An oxidation-reduction electrolyte was injected from the gap between the support substrates 1 and 9, and the side surfaces thereof were sealed with resin. Subsequently, the solar cell was obtained by attaching a lead wire to each electrode.
The obtained solar cell was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and characteristics (Jsc, Voc, FF, photoelectric conversion efficiency) were measured. The results are shown in Table 1.

Example 2
A solar cell was produced in the same manner as in Example 1 except that NKX-2569 (compound 7, molecular weight 387, absorption maximum wavelength 489 nm, manufactured by Hayashibara Biochemical Laboratories) was used as the dye II, and the characteristics were measured. It was. The results are shown in Table 1.

Example 3
A solar cell was prepared and characteristics were measured in the same manner as in Example 1 except that NKX-2554 (Compound 13, molecular weight 362, absorption maximum wavelength 460 nm, manufactured by Hayashibara Biochemical Laboratories) was used as Dye II. It was. The results are shown in Table 1.

Example 4
A solar cell was prepared and characteristics were measured in the same manner as in Example 1 except that NKX-2718 (compound 17, molecular weight 471, absorption maximum wavelength 460 nm, manufactured by Hayashibara Biochemical Laboratories) was used for Dye II. It was. The results are shown in Table 1.

Example 5
A solar cell was produced in the same manner as in Example 1 except that NKX-2656 (compound 18, molecular weight 607, absorption maximum wavelength 490 nm, manufactured by Hayashibara Biochemical Laboratories) was used as the dye II, and the characteristics were measured. It was. The results are shown in Table 1.

Comparative Example 1
A solar cell was produced in the same manner as in Example 1 without using the dye II, and the characteristics were measured. The results are shown in Table 1.

Example 6
An integrated dye-sensitized solar cell module in which four unit cells shown in FIG. 2 are connected in series was produced. The manufacturing process is shown below.
A 10 cm × 10 cm glass substrate with SnO ₂ manufactured by Nippon Sheet Glass Co., Ltd. was used as the support 21 (transparent conductive film 22 = fluorine-doped tin oxide). Patterning was performed by irradiating SnO ₂ with laser light (YAG laser) and evaporating SnO ₂ so as to form a strip having a width of 10 mm and an interval between adjacent unit cells of 350 μm.
A porous semiconductor layer 23 was formed on the support by the same method as in Example 1, and the size of the semiconductor layer of the unit cell was 10 mm wide × 90 mm long × 15 μm thick.

Tris (isothiocyanato) -ruthenium (II) -2,2 ′: 6 ′, 2 ″ -terpyridine-4,4 ′, 4 ″ -tricarboxylic acid tris-tetrabutylammonium salt (trade name Ruthenium 620-) 1H3TBA (manufactured by Solaronix) was dissolved in a mixed solvent of acetonitrile (manufactured by Kishida Chemical Co., Ltd.) and 2-butanol (manufactured by Kishida Chemical Co., Ltd.) so as to have a concentration of 2 × 10 ⁻⁴ mol / liter. To this solution, deoxycholic acid (manufactured by Aldrich) was added and dissolved so as to have a concentration of 2 × 10 ⁻² mol / liter.

Further, NKX-2554 (compound, absorption maximum wavelength 460 nm, manufactured by Hayashibara Biochemical Laboratories) was added and dissolved as dye II to a concentration of 2 × 10 ⁻⁴ mol / liter to prepare a dye adsorption solution. .
Next, the sensitizing dye was adsorbed on the porous semiconductor layer by immersing the glass plate in the obtained adsorption solution for about 20 hours. Thereafter, the porous semiconductor layer was washed and dried with ethanol (Aldrich).

Further, a support 29 having a transparent conductive film 26 similar to the patterned support 21 is prepared, and the platinum layer 25 (with a film thickness of about 3000 nm is formed by sputtering so that the same pattern as SnO ₂ is formed. (Counter electrode) was formed.
The insulation layer 28 is made of DuPont Himiran 1855 cut out at 1 mm × 95 mm, and the two supports are bonded together in the shape of FIG. 2 and heated in an oven at about 100 ° C. for 10 minutes for pressure bonding. did. Thereafter, a commercially available conductive paste (made by Fujikura Kasei Co., Ltd., trade name “Dotite”) is injected into the gap between the insulating layers from an sealing port (not shown) provided in the support substrate 29 and dried, thereby connecting the connection layer 27. Formed.

  Lithium iodide (manufactured by Aldrich) to a concentration of 0.1 mol / liter, dimethyl-propylimidazolium iodide (manufactured by Shikoku Kasei) to a concentration of 0.6 mol / liter, and a concentration of 0.05 Mole / liter iodine (manufactured by Aldrich) was dissolved in acetonitrile (manufactured by Aldrich) to prepare a redox electrolyte used as the carrier transport layer 24.

A dye-sensitized solar cell module was manufactured by injecting an oxidation-reduction electrolytic solution by a capillary effect from the electrolytic solution sealing port 10 and sealing the peripheral portion with an epoxy resin.
The obtained solar cell was irradiated with light having an intensity of 1 kW / m ² (AM1.5 solar simulator), and the characteristics were measured. The results are shown in Table 1.

Comparative Example 2
A dye-sensitized solar cell module was produced in the same manner as in Example 6 without using Dye II, and the characteristics were measured. The results are shown in Table 1.

  From the results shown in Table 1, it can be seen that in the example of the present invention, the conversion efficiency is improved as the open circuit voltage and the short circuit current are improved as compared with the comparative example. Therefore, according to the present invention, a dye-sensitized solar cell having excellent conversion efficiency was obtained.

It is a schematic diagram which shows the dye-sensitized solar cell of this invention. It is a schematic diagram which shows the dye-sensitized solar cell module of this invention.

Explanation of symbols

1, 9, 21, 29 Support substrate 2, 8, 22, 26 Transparent conductive film 3, 25 Platinum layer 4, 24 Carrier transport layer 5 Sensitizing dye I
6 Sensitizing dye II
7, 23 Semiconductor layer 27 Connection layer 28 Insulating layer (spacer)

Claims (10)

  A conductive substrate, a porous semiconductor layer adsorbing a sensitizing dye, a carrier transport layer, and a counter electrode in this order at least on the conductive substrate, wherein the sensitizing dye has different absorption peak wavelengths in the absorption spectrum 2 A dye sensitizing dye comprising a sensitizing dye having a absorption peak wavelength on the short wavelength side and a molecular weight of the sensitizing dye having a absorption peak wavelength on the short wavelength side, which is composed of a seed sensitizing dye and having a absorption peak wavelength on the long wavelength side. Sensitive solar cell.   The dye sensitizing dye according to claim 1, wherein the molecular weight of the sensitizing dye having the absorption peak wavelength on the short wavelength side is 50 or more smaller than the molecular weight of the sensitizing dye having the absorption peak wavelength on the long wavelength side. Solar cell.   The dye-sensitized solar cell according to claim 1, wherein the dye having the absorption peak wavelength on the long wavelength side has a molecular weight of 650 to 2,000.   2. The dye-sensitized solar cell according to claim 1, wherein the dye having the absorption peak wavelength on the short wavelength side has a molecular weight of 150 to 900. 3.   The dye-sensitized solar cell according to any one of claims 1 to 4, wherein the dye having the absorption peak wavelength on the short wavelength side has an absorption peak wavelength in a light wavelength region of 300 to 510 nm.   The dye-sensitized solar cell according to any one of claims 1 to 5, wherein the dye having the absorption peak wavelength on the long wavelength side is a ruthenium pyridine complex.   The dye-sensitized solar cell according to any one of claims 1 to 6, wherein the dye having the absorption peak wavelength on the long wavelength side is a terpyridine-based ruthenium complex.   The dye-sensitized solar cell according to any one of claims 1 to 7, wherein the porous semiconductor layer is made of titanium oxide.   The dye-sensitized solar cell according to claim 8, wherein the porous semiconductor layer has a porosity of 40 to 80%.   A dye-sensitized solar cell module in which two or more dye-sensitized solar cells according to any one of claims 1 to 9 are connected in series.

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