JP5027432B2 - Dye-sensitized solar cell and method for producing the same - Google Patents

Description

  The present invention relates to a dye-sensitized solar cell and a method for producing the same.

  A dye-sensitized solar cell using a dye such as Ru dye has a relatively high conversion efficiency while being inexpensive and easy to manufacture.

On the other hand, the present inventor has reported that the absorbance of the Ru dye is increased by the action of Ag particles (Non-patent Document 1).
Manabu Ihara et al., Journal of Physical Chemistry Part B (1997), Vol. 101, p. 5153

  Conventional dye-sensitized solar cells are not yet sufficiently energy efficient in view of practical application, and further improvement in energy conversion efficiency has been strongly demanded for a long time. Moreover, although the said nonpatent literature 1 has shown that the light absorbency of Ru pigment | dye increases when Ru pigment | dye and Ag particle | grains are vacuum-deposited on a quartz substrate, a Ru pigment | dye and Ag particle | grains are porous like titania. As a result of the study by the present inventors, it has been clarified that the energy conversion efficiency of the dye-sensitized solar cell does not necessarily improve even if it is supported on the material film.

  Then, an object of this invention is to provide the dye-sensitized solar cell with improved energy conversion efficiency, and its manufacturing method.

  The present invention relates to a dye-sensitized solar cell comprising a porous film containing a metal oxide and a photoelectrode having a dye supported thereon, a counter electrode, and an electrolyte layer interposed between the photoelectrode and the counter electrode. The photoelectrode comprises a surface-modified metal particle comprising a metal particle supported on a porous film and a surface-modifying compound having a functional group that is disposed on the surface of the metal particle and generates a chemical bond with the metal in the metal particle. In addition.

  The dye-sensitized solar cell according to the present invention expresses higher energy conversion efficiency than before by supporting the surface-modified metal particles modified with the specific compound on the porous film in the photoelectrode. It became possible. In the surface modifying compound, it is considered that a functional group that generates a chemical bond with a metal in the metal particle is mainly arranged on the surface of the metal particle by forming a chemical bond with the metal in the metal particle.

  In dye-sensitized solar cells, an electric current is generated when electrons excited by absorption of the dye flow into a porous film containing a metal oxide. In the case of dye-sensitized solar cells, however, they are excited. It is thought that the generation of so-called reverse current, in which electrons flow toward the charge transport material of the electrolyte, is a major factor in reducing energy conversion efficiency. In the case of the present invention, the present inventors have obtained the effect of improving the energy conversion efficiency as a result of the reverse current being suppressed by the presence of the surface modifying compound between the metal particles, the dye and the electrolyte. Is estimating.

  The maximum absorption wavelength in the plasmon absorption of the surface-modified metal particles is preferably equal to or less than the maximum absorption wavelength in the charge transfer absorption band of the dye. Thereby, the effect of energy conversion efficiency improvement becomes more remarkable.

  The functional group possessed by the surface modification compound is preferably an amino group or a mercapto group. In this case, it is more preferable that the surface modification compound further has a carboxyl group or a hydroxyl group. When the surface modification compound has these functional groups, a chemical bond is generated with a metal oxide such as titanium oxide, and the metal particles are easily supported inside the porous film. At the same time, the surface modifying compound is more reliably interposed between the porous film and the metal particles. Thereby, the effect of energy conversion efficiency improvement becomes more remarkable.

  The surface-modified metal particles are preferably capable of forming a colloidal solution in water-soluble alcohol. Thereby, the effect of energy conversion efficiency improvement becomes more remarkable.

The metal particles are preferably Ag particles. In this case, the electrolyte layer more preferably contains an iodine-based redox pair. Thereby, the effect of energy conversion efficiency improvement becomes more remarkable. Ag exhibits a relatively high solubility in an electrolyte layer containing an iodine-based redox couple (I ₃ ⁻ / I ⁻ ). Therefore, considering the operational stability and the like, Ag particles are treated with an iodine-based redox couple. It is generally considered difficult to use in combination. However, in the case of Ag particles modified with the specific surface modifying compound as in the present invention, it is possible to achieve particularly high energy conversion efficiency by combining iodine-based redox pairs. It became clear as a result of examination by et al.

  The present invention also provides a dye-sensitized solar cell comprising a porous film containing a metal oxide and a photoelectrode having a dye supported thereon, a counter electrode, and an electrolyte layer interposed between the photoelectrode and the counter electrode. In the production method of the method, the step of forming the photoelectrode comprises surface-modified metal particles having a metal particle and a surface-modifying compound having a functional group that is disposed on the surface of the metal particle and generates a chemical bond with the metal in the metal particle. A step of impregnating a porous membrane with a colloidal solution dispersed in a water-soluble alcohol, removing the water-soluble alcohol from the impregnated colloidal solution, and supporting the surface-modified metal particles on the porous membrane is included.

  The manufacturing method according to the present invention can be suitably employed for manufacturing the dye-sensitized solar cell according to the present invention. According to this manufacturing method, it is possible to easily manufacture a dye-sensitized solar cell with improved energy conversion efficiency.

  According to the present invention, a dye-sensitized solar cell with improved energy conversion efficiency is provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

  FIG. 1 is a schematic cross-sectional view showing one embodiment of a dye-sensitized solar cell according to the present invention. A dye-sensitized solar cell 100 shown in FIG. 1 includes a transparent substrate 11, a transparent conductive film 12 formed on the transparent substrate 11, a photoelectrode 1 formed on the transparent conductive film 12, and a transparent substrate 15. The transparent conductive film 13 formed on the transparent substrate 15, the counter electrode 3 formed on the transparent conductive film 13, the electrolyte layer 5 interposed between the photoelectrode 1 and the counter electrode 3, the photoelectrode 1 and the electrolyte layer 5 and a seal portion 20 provided around 5.

The photoelectrode 1 has a porous film mainly composed of an aggregate of metal oxide fine particles, and a dye and surface-modified metal particles are supported on the porous film. As the metal oxide constituting the porous film, titania (TiO ₂ ) is preferable. A metal complex is preferable as the dye, and a Ru dye is preferably used among the metal complexes. The Ru dye can be used without particular limitation as long as it is a dye made of a Ru complex and can generate an electromotive force when used in a dye-sensitized solar cell. Specific examples of suitable Ru dyes include [Ru (dc b py) ₂ (NCS) ₂ ] · 2H ₂ O.

  The surface-modified metal particle has a metal particle and a surface-modifying compound having a functional group that is disposed on the surface of the metal particle and generates a chemical bond with the metal in the metal particle. As the metal particles, Ag particles mainly composed of Ag are preferably used. Usually, Ag particles contain at least 50 atomic percent Ag. The average particle diameter of the metal particles is preferably 0.1 to 500 nm in order to develop appropriate plasmon absorption and to reliably increase energy conversion efficiency.

It is preferable that λ _M ≦ λ _d, where λ _M is the maximum absorption wavelength in the plasmon absorption measured in the air of the surface-modified metal particles and λ _d is the maximum absorption wavelength or less in the charge transfer absorption band of the dye. Here, in particular, it is preferable that λ _M of the surface-modified metal particles supported on the porous film in the photoelectrode 1 is λ _d or less. As λ _M approaches λ _d , the absorbance of the dye in the photoelectrode 1 tends to increase. More preferably, λ _M and λ _d satisfy the relationship of λ _d −λ _M ≦ 100 nm. When the difference between λ _d and λ _M exceeds 100 nm, the effect of increasing the absorbance of the dye tends to decrease.

It is possible to control λ _M to satisfy the above conditions by the type and particle size of the metal particles, the type of surface modification compound, the heat treatment with the surface modification compound supported, etc. It is.

  The surface-modified metal particles are preferably capable of forming a colloidal solution in a water-soluble alcohol (preferably ethanol). The surface-modified metal particles capable of forming a colloidal solution in water-soluble alcohol have a high affinity with the metal oxide constituting the porous film and are easily and uniformly supported on the porous film.

  A surface modification compound is a compound which has 1 or 2 or more of functional groups which produce | generate a chemical bond with the metal in a metal particle. As this functional group, a mercapto group and an amino group are preferable. More preferably, the surface modifying compound has one or more carboxyl groups or hydroxyl groups. In the surface-modified metal particles, most of these functional groups react with the metal in the metal particles or the metal oxide in the porous film to produce thioether, carboxylic acid ester, ether or the like. Conceivable.

The surface modifying compound is represented by, for example, the following general formula (1) or (2).
X-R-SH (1)
X—R—NH ₂ (2)

  In formulas (1) and (2), R represents a linear or branched alkylene group, and X represents a carboxyl group or a hydroxyl group. Specific examples of the surface modifying compound represented by the formula (1) include 16-mercaptohexadecanoic acid and 3-mercaptopropionic acid.

The electrolyte layer 5 is composed of an electrolytic solution in which a redox couple is dissolved in a predetermined solvent. As the redox pair, iodine-based (I ₃ ⁻ / I ⁻ ), cobalt-based (Co ²⁺ / Co ³⁺ ), or the like is used, and an iodine-based redox pair is particularly preferable.

  As the transparent substrates 11 and 15, glass substrates are preferably used. It is possible to replace the transparent substrate 15 located on the counter electrode side with a non-transparent substrate. The transparent conductive films 12 and 13 are made of a transparent conductor such as ITO. The counter electrode 3 is preferably an electrode formed by depositing a noble metal such as Pt. The seal portion 20 is provided mainly for the purpose of preventing leakage of the electrolyte solution in the electrolyte layer 5 to the outside, and is formed using a polymer sheet, a polymer adhesive, or the like.

  The photoelectrode 1 is formed by, for example, impregnating a porous film with a step of forming a porous film containing a metal oxide and a colloidal solution in which the surface-modified metal particles are dispersed in a water-soluble alcohol (preferably ethanol). And removing the water-soluble alcohol from the impregnated colloidal solution to support the surface-modified metal particles on the porous film and the method of supporting the dye on the porous film. . Either the step of supporting the surface-modified metal particles on the porous membrane or the step of supporting the dye on the porous membrane may be performed first. Alternatively, a dye may be further added to the colloidal solution so that both are supported on the porous film in parallel.

  A colloidal solution in which surface-modified metal particles are dispersed can be prepared, for example, by reducing metal ions while stirring in a reaction solution containing metal ions and a surface-modifying compound. In this case, when a solvent other than a water-soluble alcohol such as chloroform is used as a solvent for the reaction solution, the solvent is replaced with a water-soluble alcohol through a step of removing the reaction solvent by centrifugation or the like. A colloidal solution using as a dispersion medium is prepared.

  The porous membrane can be impregnated with the colloidal solution by a method of immersing the porous membrane in the colloidal solution at room temperature. After impregnation, the water-soluble alcohol is removed by leaving at room temperature or heating as necessary. As a result, the surface-modified metal particles are supported on the porous film. The removal of the water-soluble alcohol is preferably performed without heating or by heating to 200 ° C. or lower. When the porous membrane after impregnation is heated to 200 ° C. or higher, the surface modification compound is decomposed and the effect of improving the energy conversion efficiency tends to be reduced. Therefore, after impregnation, the porous film is preferably used as a photoelectrode of a solar cell without heating to a temperature exceeding 200 ° C.

  The formation of the porous film and the loading of the dye can be easily performed by those skilled in the art by appropriately referring to conventionally known methods.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

1. Absorbance improvement by surface modified Ag particles of Ru dye supported on titania porous membrane (1) Preparation of colloidal solution of surface modified metal particles AgNO ₃ 0.15g dissolved in water and phase transfer catalyst ( The organic phase in which C ₈ H ₁₇ ) ₄ NBr was dissolved in chloroform was stirred in a reaction vessel at room temperature for 1 hour to move Ag ions to the organic phase, and then the aqueous phase was removed. Next, 0.23 g of 16-mercaptohexadecanoic acid as a surface modifying compound was added to the organic phase and stirred for 15 minutes. Thereafter, an aqueous solution of NaBH ₄ as a reducing agent was mixed with the organic phase and stirred at room temperature for 12 hours. As a result, Ag ions in the organic phase were reduced, and a colloidal solution in which Ag particles (surface-modified Ag particles) whose surface was coated with 16-mercaptohexadecanoic acid was dispersed was generated.

  After removing the aqueous phase, Ag particles were precipitated from the colloidal solution by centrifugation, and after removing the supernatant, ethanol was added to obtain a colloidal solution using ethanol as a dispersion medium.

  Two types of colloidal solutions were also prepared in which Ag particles (“Finesphere SVE001” (trade name) manufactured by Nippon Paint Co., Ltd.) whose surface was coated with a surface modifying compound having an amino group were dispersed in ethanol.

(2) Plasmon absorption characteristics of surface-modified Ag particles supported on a titania porous film and absorbance of Ru dye A paste containing titania powder is applied onto a quartz substrate by a spin coating method to form a thin film, which is 450 ° C. Was sintered to form a titania porous film. The porous membrane was immersed in the colloidal solution for about 4 days, and the removed porous membrane was heat-treated in a nitrogen atmosphere. The maximum absorption wavelength in plasmon absorption of the surface-modified Ag particles supported on the porous film was changed by appropriately adjusting the heating temperature within the range of 230 to 580 ° C. and the heating time within the range of 3 to 20 minutes.

The porous film after the heat treatment was immersed in a Ru dye solution for 12 hours, and the taken out porous film was dried to form a photoelectrode in which the Ru dye and surface-modified Ag particles were supported on the titania porous film. . At the time of immersion, [Ru (dc b py) ₂ (NCS) ₂ ] · 2H ₂ O (maximum absorption wavelength in the charge transfer absorption band: 540 nm) manufactured by Kojima Chemical Co., Ltd., which is a Ru dye, is manufactured by Wako Pure Chemical Industries, Ltd. A solution obtained by dissolving in dehydrated ethanol at a concentration of 1 × 10 ⁻³ M and diluting it to 3 × 10 ⁻⁴ M was used.

  The light absorption spectrum of the formed photoelectrode was measured, and the ratio (increase rate) of the absorbance of the Ru dye at 520 nm to the absorbance of the Ru dye alone was determined.

  FIG. 2 shows a graph in which the rate of increase in absorbance is plotted against the maximum absorption wavelength of plasmon absorption of the surface-modified Ag particles. In the figure, “thiol” is plotted in the case of surface-modified Ag particles prepared using 16-mercaptohexadecanoic acid, and “amine 1” is plotted in the case of surface-modified Ag particles prepared using a surface-modified compound having an amino group. Or “amine 2”. As shown in FIG. 2, it was confirmed that the absorbance of the Ru dye supported on the titania porous membrane was greatly increased by supporting the surface-modified Ag particles. It was also confirmed that the increase rate tends to improve as the absorption maximum wavelength of plasmon absorption of the surface-modified Ag particles approaches 540 nm, which is the absorption maximum wavelength of the Ru dye. Furthermore, the increasing rate of the absorbance also tended to increase as the peak area of plasmon absorption increased.

2. Preparation and Evaluation of Dye-Sensitized Solar Cell A dye-sensitized solar cell was prepared as follows using a colloidal solution of surface-modified Ag particles prepared using a surface-modifying compound having an amino group.

  First, a titania porous film formed in the same manner as described above was immersed in a colloidal solution of surface-modified Ag particles for 5 hours, and the taken out porous film was dried at room temperature. Thereafter, the porous membrane was immersed in the same Ru dye solution as described above for 12 hours and then dried at room temperature to form a photoelectrode in which the Ru dye and surface-modified Ag particles were supported on the titania porous film. Photoelectrodes were similarly formed using several types of colloidal solutions with different Ag particle concentrations. Moreover, the light absorbency in 520 nm of the formed photoelectrode was measured.

  A counter electrode is formed by forming Pt on a glass substrate having a transparent conductive film formed on the surface, and this is bonded to a glass substrate on which a transparent conductive film and a photoelectrode are formed with a polymer adhesive film interposed therebetween. It was. Then, an electrolyte solution containing an iodine-based redox couple was injected from an electrolyte solution injection hole provided in the glass substrate on the counter electrode side to form an electrolyte layer. The electrolyte used was 3-methoxypropionitrile manufactured by Wako Pure Chemical Industries, Ltd. as a solvent, and 0.5M 4-tert-butylpyridine (Aldrich), 0.1M lithium iodide (Wako Pure) Yakuhin Kogyo Co., Ltd.), 0.1 M iodine (manufactured by Kanto Chemical Co., Inc.), and 0.6 M dimethylpropylimidazolium iodide (SOLARONIX) were dissolved and used.

About the produced dye-sensitized solar cell, quantum yield (IPCE) and energy conversion efficiency ((eta)) were evaluated as follows. Evaluation was made for each case where 100 mW / cm ² was 1.0 sun and the light intensity was 1.0 sun or 0.4 sun.

Quantum efficiency The short-circuit current and the incident monochromatic light intensity when monochromatic light was incident were measured, and the quantum yield (IPCE) was calculated from these values. Monochromatic light was incident using a spectrometer manufactured by Koken Kogyo. The diffraction grating of the spectroscope was 600 line / mm, the slit width was 2.0 mm, and the half-value width of emitted light was 12 nm.

Energy conversion efficiency A dye-sensitized solar cell equipped with a mask having an opening of 5 mm × 5 mm was irradiated with simulated sunlight of AM1.5 calibrated to 100 mW / cm ² using a reference cell. The current-voltage characteristics at this time were measured, the short-circuit current density (Isc), the open electromotive force (Voc), and the fill factor (ff) were determined, and the energy conversion efficiency (η) was calculated from these values.

  As shown in Table 1, the battery of the example using the surface-modified Ag particles is different from the comparative example in which the Ag particles are not used in terms of energy conversion efficiency (η), short-circuit current density (Isc), and quantum yield ( ICPE) peak value was greatly improved.

It is a schematic sectional drawing which shows one Embodiment of the dye-sensitized solar cell which concerns on this invention. It is the graph which plotted the increase rate of the light absorbency of Ru pigment | dye with respect to the maximum absorption wavelength of the plasmon absorption of surface-modified Ag particle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Photoelectrode, 3 ... Counter electrode, 5 ... Electrolyte layer, 11 ... Transparent substrate, 12 ... Transparent conductive film, 13 ... Transparent conductive film, 15 ... Transparent substrate, 20 ... Seal part, 100 ... Dye-sensitized solar cell.

Claims (8)

In a dye-sensitized solar cell comprising a porous film containing a metal oxide and a photoelectrode having a dye supported thereon, a counter electrode, and an electrolyte layer interposed between the photoelectrode and the counter electrode,
The photoelectrode is a surface-modified metal particle comprising a metal particle supported on the porous film and a surface-modifying compound having a functional group that is disposed on the surface of the metal particle and generates a chemical bond with the metal in the metal particle. A dye-sensitized solar cell, further comprising:   The dye-sensitized solar cell according to claim 1, wherein an absorption maximum wavelength in plasmon absorption of the surface-modified metal particles is not more than an absorption maximum wavelength in a charge transfer absorption band of the dye.   The dye-sensitized solar cell according to claim 1 or 2, wherein the functional group is a mercapto group or an amino group.   The dye-sensitized solar cell according to claim 3, wherein the surface modifying compound further has a carboxyl group or a hydroxyl group.   The dye-sensitized solar cell according to any one of claims 1 to 4, wherein the surface-modified metal particles can form a colloidal solution in a water-soluble alcohol.   The dye-sensitized solar cell according to any one of claims 1 to 5, wherein the metal particles are Ag particles.   The dye-sensitized solar cell according to claim 6, wherein the electrolyte layer includes an iodine-based redox pair. A method for producing a dye-sensitized solar cell, comprising a porous film containing a metal oxide and a photoelectrode having a dye supported thereon, a counter electrode, and an electrolyte layer interposed between the photoelectrode and the counter electrode In
The step of forming the photoelectrode comprises
A porous colloidal solution in which surface-modified metal particles including a metal particle and a surface-modifying compound having a functional group that forms a chemical bond with the metal in the metal particle is dispersed in a water-soluble alcohol. A production method comprising impregnating a membrane, removing the water-soluble alcohol from the impregnated colloidal solution, and supporting the surface-modified metal particles on the porous membrane.

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