JP2009009740A - Dye-sensitized solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dye-sensitized solar cell in which utilization efficiency of light incident from a transparent substrate side is further improved and a high transfer efficiency can be obtained. <P>SOLUTION: The dye-sensitized solar cell 10 is provided with a transparent substrate 12a, a transparent conductive film 14a, and a conductive substrate installed opposed to the transparent conductive film 14a, and has a porous semiconductor layer 16 adsorbing dyes and an electrolyte 18. A silica particulate layer 22 which is obtained by coating a liquid in which silica particulates are dispersed in a silica film forming solution is formed on the surface of the transparent conductive film 14a side of the transparent substrate 12a. The porous semiconductor layer 16 is a dual-layer structure which consists of a porous titanium oxide layer 16a and a titanium oxide layer 16b denser than the porous titanium oxide layer 16a. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a dye-sensitized solar cell.

The dye-sensitized solar cell includes a transparent substrate, a transparent conductive film formed on the surface of the transparent substrate, and a conductive substrate provided to face the transparent conductive film, and the dye is interposed between the transparent conductive film and the conductive substrate. It is comprised so that it may have the porous semiconductor layer which adsorb | sucked, and electrolyte.
The dye-sensitized solar cell configured as described above is attracting attention as a low-cost solar cell because it is inexpensive and does not require large-scale equipment for production.

  However, the dye-sensitized solar cell currently has a sunlight conversion efficiency of about 11%, and further improvement in efficiency is required.

As one method for improving the conversion efficiency, for example, a depression is formed on the surface of a light-transmissive substrate member (corresponding to the transparent substrate) for the purpose of increasing the utilization efficiency of light incident from the transparent substrate side. And forming a recess in the transparent electrode film by forming a transparent electrode film (corresponding to the transparent conductive film) on the surface of the substrate member (see Patent Document 1).
JP 2006-100180 A

However, it is very difficult to obtain irregularities on the surface of the transparent substrate exceeding 0.1 μm by a normal transparent conductive film forming technique. Moreover, in order to make this unevenness | corrugation, the board | substrate etc. which used glass substrate itself in the shape of frosted glass are utilized. When forming a film on such a substrate due to the crystal sharpness on the surface of the transparent conductive film or the sharpness of the glass substrate tip, there is a problem that the film is difficult to form on the tip portion or penetrates the film, and the thin film solar cell And in the case of a dye-sensitized solar cell, this causes a decrease in efficiency. In addition, there is a concavo-convex substrate production technique in which silica produced by the reaction of raw material liquid components is deposited on the surface of a glass substrate using a liquid phase film forming technique of silica. . In addition, in the above-mentioned Patent Document 1, although there is a detailed reference to the shape of the unevenness, the degree of unevenness (surface roughness) and the method for forming the unevenness are not mentioned.
As described above, since the degree of unevenness formed on the surface of the transparent substrate is small in the above-described conventional technique, when used in a dye-sensitized solar cell, the utilization efficiency of light incident from the transparent substrate side is increased. But not always enough.
Further, it is considered that high sunlight conversion efficiency cannot always be obtained simply by forming irregularities on the surface of the transparent substrate.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a dye-sensitized solar cell that can increase the utilization efficiency of light incident from the transparent substrate side and obtain high conversion efficiency. And

The dye-sensitized solar cell according to the present invention includes a transparent substrate, a transparent conductive film formed on the surface of the transparent substrate, and a conductive substrate provided to face the transparent conductive film, In a dye-sensitized solar cell having a porous semiconductor layer and an electrolyte in which a dye is adsorbed between the conductive substrates,
A silica fine particle layer obtained by applying a liquid in which silica fine particles are dispersed in a silica film forming solution is formed and formed on the transparent conductive film side surface of the transparent substrate,
The porous semiconductor layer is composed of a porous titanium oxide layer and a titanium oxide layer denser than the porous titanium oxide layer disposed between the porous titanium oxide layer and the transparent conductive film It is a structure.

  The dye-sensitized solar cell according to the present invention is preferably characterized in that the irregularities on the surface of the transparent conductive film side of the silica fine particle layer are in the range of 0.3 to 3 μm in terms of arithmetic average value.

The dye-sensitized solar cell according to the present invention is preferably characterized in that the number of fine particles on the surface of the silica fine particle layer is 10,000 to 80,000 / mm ² .

  In the dye-sensitized solar cell according to the present invention, preferably, the porous semiconductor layer is a porous titanium oxide layer, and the porous titanium oxide layer disposed between the porous titanium oxide layer and the transparent conductive film. It has a two-layer structure of a titanium oxide layer that is denser than a quality titanium oxide layer.

  In the dye-sensitized solar cell according to the present invention, preferably, a titanium oxide layer denser than the porous titanium oxide layer immerses the transparent conductive film in an acid solution of a titanium oxide precursor, It is formed by irradiating.

  The dye-sensitized solar cell according to the present invention is preferably characterized in that the transparent conductive film is a tin oxide film doped with fluorine.

In the dye-sensitized solar cell according to the present invention, a silica fine particle layer obtained by applying a liquid in which silica fine particles are dispersed in a silica film forming solution is formed on the transparent conductive film side surface of the transparent substrate, and the porous semiconductor layer is Since it has a two-layer structure consisting of a porous titanium oxide layer and a titanium oxide layer that is denser than the porous titanium oxide layer disposed between the porous titanium oxide layer and the transparent conductive film, the unevenness is larger than before. Can be formed on the surface of the transparent substrate, and thus on the transparent conductive film, and the utilization efficiency of light incident from the transparent substrate side is high, and the conversion efficiency of sunlight is high.
The dye-sensitized solar cell according to the present invention further includes a porous titanium oxide layer in which the porous semiconductor layer is disposed between the porous titanium oxide layer and the porous titanium oxide layer and the transparent conductive film. Since it has a two-layer structure of a titanium oxide layer that is denser than the layer, voids that can occur between the irregularities and the porous semiconductor layer during manufacturing are reduced, or the irregularities are reliably covered with the porous semiconductor layer. be able to. Thereby, the conversion efficiency of sunlight is high.

  Embodiments of the present invention will be described below.

For example, as schematically shown in FIG. 1, the dye-sensitized solar cell 10 according to the present embodiment includes a transparent substrate 12a, a transparent conductive film 14a formed on the surface of the transparent substrate 12a, and a transparent conductive film 14a. A conductive substrate (in FIG. 1, the conductive substrate is composed of a conductive film 14b and a substrate 12b) provided opposite to each other, and a pigment (in FIG. 1, FIG. 1) is provided between the transparent conductive film 14a and the conductive substrate. The porous semiconductor layer 16 and the electrolyte 18 are adsorbed. In FIG. 1, reference numeral 20 indicates a separator provided for sealing the electrolyte 18 in the battery.
And the silica fine particle layer 22 obtained by apply | coating the liquid which disperse | distributed the silica fine particle in the silica film formation solution is formed in the transparent conductive film 14a side surface of the transparent substrate 12a.
The porous semiconductor layer 16 has a two-layer structure including a porous titanium oxide layer 16a and a titanium oxide layer 16b that is denser than the porous titanium oxide layer 16a.

The transparent substrate 12a and the substrate 12b may be plastic plates, for example, but are more preferably glass plates.
The silica fine particle layer 22 on the surface of the transparent substrate 12a is made of, for example, commercially available silica particles (spherical fine powder Seahoster manufactured by Nippon Shokubai Co., Ltd.) or silica gel particles (manufactured by Asahi Glass S-Tech Co., Ltd.) as an alkali barrier film of soda lime glass, for example. Disperse in a silica film-forming solution such as the silica thin film coating agent used (for example, OCD T-2 manufactured by Tokyo Ohka Kogyo Co., Ltd.), and heat this silica fine particle dispersion by a coating method such as spin coating or a spray method. The fine particles are spray-fixed on the substrate thus formed to be formed on the surface of the transparent substrate 12a.
In this case, when a glass plate is used as the transparent substrate 12a, it is preferable to use low-cost glass for building materials such as soda lime glass from the viewpoint of cost. In the soda lime glass as it is, the sodium (soda) component contained in the glass diffuses into the transparent conductive film and the resistance value increases, but by covering with the silica fine particle layer 22, diffusion can be prevented.

The silica fine particle layer 22 is applied with a non-uniform film thickness according to the application conditions or the lamination state of the silica fine particles, whereby irregularities are formed on the surface on the transparent conductive film 14a side. The thickness of the silica fine particle layer 22 is not particularly limited, and can be, for example, in the range of 0.5 to 8 μm.
When the unevenness is in the range of 0.3 to 3 μm in terms of arithmetic average value, it is more suitable for improving the utilization efficiency of sunlight. If the unevenness is significantly less than 0.3 μm, there is a risk that the difference in efficiency from the substrate without such unevenness may be lost, and if the unevenness is significantly greater than 3 μm, the conversion efficiency of sunlight may be reduced. The reason for the latter is not necessarily clear, but if the irregularities are extremely large, it becomes difficult to fix the silica fine particles with the silica film-forming material, and transparent conductive films are sequentially laminated in a thin film on the irregularities. The film 14a and the porous semiconductor layer 16 may be peeled off or voided, and there may be a problem such as a short circuit such as contact between the electrolytic solution and the transparent conductive film.
In obtaining the above irregularities, it is preferable to use silica fine particles having an average particle size in the range of 0.5 to 5 μm.
Further, the number of fine particles on the surface of the silica fine particle layer 22 is 10,000 to 80,000 particles / mm ² , and it is desirable that the silica fine particle layer 22 be applied at a density that does not overlap in two steps.

As the transparent conductive film 14a and the conductive film 14b, an appropriate material such as ITO (tin-doped indium film) may be used, but it is more preferable to use FTO (fluorine-doped tin oxide film). .
ITO is preferable as a transparent conductive material having a high light transmittance and a low sheet resistance, but by using FTO instead of this, a material having a specific resistance of about 3.5 × 10 ⁻⁴ (Ωcm) is low. The obtained thermal stability when the titanium oxide porous layer is heat-treated is higher.
As a method for obtaining the FTO transparent conductive film, there are various methods such as a spray method, a CVD method, a sputtering method, and a dip method. Among them, the spray method and the CVD method are excellent in terms of the characteristics of the obtained film, It also has economic efficiency. As a tin raw material used in these methods, SnCl ₄ , (CnH _{2n + 1} ) ₄ Sn (where n = 1 to 4), C ₄ H ₉ SnCl ₃ , (CH ₃ ) ₂ SnCl _{2 and the} like can be used. As a raw material for doping fluorine, NH ₄ F can be used in the spray method, HF, CCl ₂ F ₂ , CHClF ₂ , CH ₃ CHF ₂ , CF ₃ Br, or the like can be used in the CVD method. . By forming tin oxide using these raw materials, a transparent conductive film layer with an optimized amount of fluorine and chlorine can be formed.
By laminating the transparent conductive film 14a with a thickness of, for example, about 0.3 to 1.5 μm on the uneven surface of the silica fine particle layer 22, the transparent conductive film 14a has an uneven surface following the unevenness of the silica fine particle layer 22. Or, it is formed in a wave shape as a whole.

  The dye adsorbed on the porous semiconductor layer 16 has absorption at a wavelength of 400 nm to 1000 nm, and examples thereof include metal complexes such as ruthenium dye and phthalocyanine dye, and organic dyes such as cyanine dye.

  The electrolyte (electrolytic solution) 18 contains iodine, lithium ions, ionic liquid, t-butylpyridine, and the like. For example, in the case of iodine, an oxidation-reduction body composed of a combination of iodide ions and iodine can be used. The redox form contains an appropriate solvent that can dissolve the redox form.

For example, titanium, tin, zirconium, zinc, indium, tungsten, iron, nickel, silver, or other metal oxide can be used as the porous semiconductor layer 16 as a semiconductor material. Titanium oxide: titania) is more preferable.
The porous semiconductor layer 16 includes, for example, a porous titanium oxide layer 16a obtained by forming a film using fine particles having a diameter (diameter) of about 20 to 30 nm, a porous titanium oxide layer 16a, and a transparent conductive film 14a. For example, it has a two-layer structure composed of a titanium oxide layer 16b denser than the porous titanium oxide layer 16a obtained by forming a film using fine particles having a diameter (diameter) of, for example, about 10 nm or less.
Thereby, the unevenness | corrugation of the transparent conductive film 14a can be covered with sufficient coverage, that is, the void that may be generated between the unevenness and the porous semiconductor layer at the time of manufacturing is eliminated, or the unevenness is reliably ensured to be a porous semiconductor. Can be covered with layers. Further, by providing the dense titanium oxide layer 16b on the transparent conductive film 14a, it is possible to suppress the possibility that the transparent conductive film 14a comes into contact with the electrolyte 18 to cause a reverse electron reaction.
The thickness of each layer of the porous semiconductor layer 16 is not particularly limited, and the porous titanium oxide layer 16a can have a thickness of, for example, about 5 to 30 μm, and the dense titanium oxide layer 16b has, for example, 0 The thickness can be about 0.05 to 0.3 μm.

Each layer of the porous semiconductor layer 16 can be formed by a known appropriate method. In particular, the dense titanium oxide layer 16b can be formed by, for example, a sputtering method or an electrodeposition method. However, in the case of the former sputtering method, for example, if a film having a thickness larger than 10 nm is formed, the series resistance may increase and the operation as a battery may be deteriorated. On the other hand, in the case of the latter electrodeposition method, the conductivity of the obtained film is superior to that of the film obtained by sputtering. However, in this method, good characteristics are obtained by applying an equal electric field to the electrode. Since it is obtained, it is desirable that the transparent conductive film to be used is a flat film whose surface is polished, for example.
For this reason, in order to cover large irregularities with a dense titanium oxide layer 16b with a better coverage than the conventional one formed on the surface of the transparent conductive film 14a or the transparent substrate 12a, the dense titanium oxide layer 16b is more preferably It forms by the method of.
That is, titanium hydroxide, titanium isopropoxide, titanyl sulfate, titanyl nitrate, or the like is used as a raw material titanium oxide precursor. This titanium oxide precursor is diluted with, for example, 2-propanol and distilled water, and a glass substrate with a tin oxide transparent conductive film with unevenness is immersed in a solution whose pH is adjusted with an acid such as sulfuric acid, nitric acid or hydrochloric acid. Irradiate ultraviolet rays from the top. The form and crystallinity of crystals obtained by adjusting the pH can be controlled, and the pH around 1.5 at which anatase is formed after baking at 500 ° C. is more desirable. For example, by irradiating with ultraviolet rays for about 20 hours, a dense titanium oxide layer 16b having a thickness of about 0.1 to 0.2 μm is formed. When the film of the titanium oxide layer 16b is formed to have a thickness greatly exceeding 0.2 μm, the light transmittance may be reduced.

As the porous titanium oxide layer 16a, it is more preferable to form a highly permeable porous film on the dense titanium oxide layer 16b side, and form a highly scattering porous film thereon. .
A highly permeable porous membrane is obtained by forming a film by a method such as screen printing or squeegee using raw materials such as HT paste (manufactured by Solaronix) and PST-NR18 paste (manufactured by Catalyst Kasei Kogyo Co., Ltd.). In addition, a porous film having high scattering properties can be obtained by a method such as screen printing or squeegee using a raw material such as D paste (manufactured by Solaronix) or PST-200C paste (manufactured by Catalyst Kasei Kogyo Co., Ltd.). It can be obtained by forming a film.

In the dye-sensitized solar cell according to the present embodiment described above, a silica fine particle layer obtained by applying a liquid in which silica fine particles are dispersed in a silica film forming solution is formed on the transparent conductive film side surface of a transparent substrate. Therefore, it is possible to form a larger unevenness than the conventional one on the surface of the transparent substrate, and thus on the transparent conductive film, and the utilization efficiency of light incident from the transparent substrate side is high.
Further, the dye-sensitized solar cell according to the present embodiment includes a porous titanium oxide layer in which the porous semiconductor layer is disposed between the porous titanium oxide layer and the porous titanium oxide layer and the transparent conductive film. Since it has a two-layer structure of a titanium oxide layer that is denser than the layer, voids that can occur between the irregularities and the porous semiconductor layer during manufacturing are reduced, or the irregularities are reliably covered with the porous semiconductor layer. be able to.
Thereby, the dye-sensitized solar cell which concerns on this Embodiment has high conversion efficiency of sunlight.

  The present invention will be further described with reference to examples. In addition, this invention is not limited to the Example demonstrated below.

(Preparation of glass substrate)
A borosilicate glass having a planar size of 25 mm × 25 mm and a thickness of 1 mm was sufficiently washed and dried to obtain a glass substrate. Unevenness was formed on this substrate as follows.
100 μL of a solution prepared by mixing silica particles dispersed in ethylene glycol (Chihosta, Nippon Shokubai Co., Ltd.) and a solution that forms a silica film (OCD T-2, manufactured by Tokyo Ohka Kogyo Co., Ltd.) at a mass ratio of 1: 1. The concavo-convex film was formed by dropping on a glass substrate placed on a spin coater rotating at 5000 rpm with a pipette. Silica fine particles having four levels of 0.5, 1.5, 2.5, and 5 μm were used.

(Preparation of transparent conductive film)
A fluorine-doped tin oxide transparent conductive film was formed on the above substrate by the following method.
The fluorine-doped tin oxide film is prepared by adding ammonium fluoride for fluorine doping to a mixed solution of n-butyltin trichloride, water and ethanol, mixing oxygen gas with nitrogen gas as a carrier gas, and using a spray gun. Atomized and transported to a glass substrate heated to 450 ° C. to form a film by pyrolysis. The glass with FTO film thus obtained was sufficiently washed and dried.

(Preparation of titanium oxide layer)
A dense layer of titanium oxide was formed on the fluorine-doped tin oxide film by the following method.
The titanyl nitrate solution obtained by dissolving the gel obtained by dissolving titanium metal with hydrogen peroxide solution with nitric acid was diluted with 2-propanol and distilled water to obtain a solution adjusted to pH 1.6. A glass substrate with a fluorine-doped tin oxide film was immersed and irradiated with ultraviolet rays from the top. After irradiation for about 20 hours, a film (titanium oxide layer) of about 0.1 to 0.2 μm was formed.
A porous layer of titanium oxide was formed on the titanium oxide dense layer by the following method.
The titanium oxide fine particle paste was applied to an area of 0.5 cm × 0.5 cm by a squeegee method. As the titanium oxide porous membrane, a highly permeable porous membrane was formed to about 6 μm, and a highly scattering fine particle was formed to about 7 μm. Heat treatment was performed in an electric furnace at 500 ° C. for 1 hour. The film thickness obtained was approximately 13 μm.
The titanium oxide film is immersed in an ethanol solution containing N719 ((RuL ₂ (NCS) ₂ : 2TBA), L = 2,2'-bipyridyl-4,4'-dicarboxylic acid) dye for about 13 hours, Was adsorbed.

(Cell preparation)
The film was sealed with a 50 μm spacer using, as a counter electrode, an FTO having platinum in which the above-described dye-adsorbed titanium oxide film was formed by sputtering. Into this cell, an electrolyte prepared by adjusting 250 ml of I _{2 and} 580 mM of t-BuPy in acetonitrile was injected to produce a cell.

(Characteristic evaluation of solar cells)
The characteristics of the solar cell were measured by irradiating a dye-sensitized solar cell with AM1.5 and 100 mW / cm ² pseudo-sunlight using a solar simulator. The conversion efficiency of the solar cell was compared with that of a solar cell having the same configuration as that of the example (reference example: Experiment No1) except that the formation of irregularities by laminating silica particles on a glass substrate was omitted.

  A solar cell in which 1.5 μm silica particles are used and irregularities are formed by changing the number of laminated (fixed) silica particles, the short-circuit current, the open-circuit voltage, F.R. F. Table 1 summarizes the results of measuring the characteristics of (fill factor: shape factor) and conversion efficiency.

Table 2 shows the results of measuring the various characteristics of the silica particles with the number of laminated (fixed) particles of 50,000 / mm ² by changing the particle size of the silica fine particles. The numerical value is shown as a ratio to the reference example (experimental example / reference example).

  As a comparative example, Table 3 shows the results of measuring the characteristics of the solar cell prepared by the same method as in the above example except that the glass substrate was not formed with irregularities and the titania dense layer was not provided.

(Transmission electron micrograph of cross section of titania porous membrane)
Transmission electron micrographs of a cross section of the titania porous membrane (titanium oxide porous membrane) of Experiment No. 7 are shown in FIGS.
2 to 4, it can be seen that a dense titania layer is formed over the entire surface of the FTO film. It can also be seen that the depth of the irregularities on the surface of the FTO film, in other words, the height of the wave (swell) is about 1 to 2 μm.

It is a figure which shows typically the structure of the dye-sensitized solar cell which concerns on this Embodiment. It is a transmission electron microscope photograph of the cross section of the transparent substrate thru | or titania porous film of the dye-sensitized solar cell of an Example. It is the transmission electron micrograph which expanded the cross-section location shown by the arrow A in FIG. It is the transmission electron micrograph which expanded the cross-section location shown by the arrow B in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Dye-sensitized solar cell 12a Transparent substrate 12b Substrate 14a Transparent conductive film 14b Conductive film 16 Porous semiconductor layer 16a Porous titanium oxide layer 16b Dense titanium oxide layer 18 Electrolyte 20 Separator 22 Silica fine particle layer

Claims (5)

A transparent substrate, a transparent conductive film formed on the surface of the transparent substrate, and a conductive substrate provided opposite to the transparent conductive film are provided, and a dye is adsorbed between the transparent conductive film and the conductive substrate. In a dye-sensitized solar cell having a porous semiconductor layer and an electrolyte,
A silica fine particle layer obtained by applying a liquid in which silica fine particles are dispersed in a silica film forming solution is formed on the transparent conductive film side surface of the transparent substrate,
The porous semiconductor layer is composed of a porous titanium oxide layer and a titanium oxide layer denser than the porous titanium oxide layer disposed between the porous titanium oxide layer and the transparent conductive film A dye-sensitized solar cell having a structure.   2. The dye-sensitized solar cell according to claim 1, wherein irregularities on the surface of the silica fine particle layer on the transparent conductive film side are in an arithmetic average value of 0.3 to 3 μm. The dye-sensitized solar cell according to claim 1, wherein the number of fine particles on the surface of the silica fine particle layer is 10,000 to 80,000 particles / mm ² .   The titanium oxide layer denser than the porous titanium oxide layer is formed by immersing the transparent conductive film in an acid solution of a titanium oxide precursor and irradiating with ultraviolet rays. Item 2. The dye-sensitized solar cell according to Item 1.   The dye-sensitized solar cell according to claim 1, wherein the transparent conductive film is a tin oxide film doped with fluorine.

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