JP2006093002A - Photoelectric cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric cell with high photoelectric conversion efficiency and excellent durability. <P>SOLUTION: In the photoelectric cell in which a substrate having an electrode layer 1 on its surface and a semiconductor film 2 absorbing a photosensitive material formed on the surface of the electrode layer 1 and a substrate having an electrode layer 3 on its surface are arranged so that the electrode layer 1 and the electrode layer 3 are opposed to each other, and equipped with an electrolyte layer between the semiconductor film 2 and the electrode layer 3, the electrolyte layer contains at least one kind of ion-conduction promoting material selected from titanium oxide nanotube, fibrous titanium oxide, and carbon nanotube, and at least either of the substrates and the electrode layers have transparency. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a novel photovoltaic cell. More particularly, the present invention relates to a photoelectric cell having high photoelectric conversion efficiency.

  In recent years, since titanium oxide has a high band gap, it has been suitably used as a photocatalyst, and also as a so-called photoelectric conversion material that converts light energy into electric energy. Moreover, it has come to be used also for secondary batteries such as lithium batteries, hydrogen storage materials, proton conductive materials, and the like.

  The photoelectric conversion material is a material that can continuously extract light energy as electric energy, and is a material that converts light energy into electric energy using an electrochemical reaction between electrodes. When this photoelectric conversion material is irradiated with light, electrons are generated on one electrode side, move to the counter electrode, and the electrons moved to the counter electrode move as ions in the electrolyte and return to the one electrode. Since such energy conversion is performed continuously, it is used, for example, for solar cells.

  In general solar cells, first a semiconductor film for photoelectric conversion material is formed on a support such as a glass plate coated with a transparent conductive film as an electrode, and then another transparent conductive film is used as a counter electrode. A support such as a coated glass plate is provided, and an electrolyte is sealed between these electrodes.

  When the photosensitizer adsorbed on the semiconductor for photoelectric conversion material is irradiated with sunlight, the photosensitizer absorbs light in the visible region, the electrons in the photosensitizer are excited, and the excited electrons are applied to the semiconductor. The electrons then move to the counter electrode through the transparent conductive glass electrode, and the electrons transferred to the counter electrode reduce the redox system in the electrolyte. On the other hand, the photosensitizer that has moved electrons to the semiconductor is in an oxidant state, but this oxidant is reduced by the redox system in the electrolyte and returns to its original state. Thus, since electrons flow continuously, it functions as a solar cell using a semiconductor for photoelectric conversion materials.

  As such a photoelectric conversion material, a material in which a photosensitizing dye having absorption in a visible light region is adsorbed on the surface of a semiconductor film is used. For example, Japanese Patent Laid-Open No. 1-220380 (Patent Document 1) describes a solar cell having a color former layer such as a transition metal complex on the surface of a metal oxide semiconductor. Japanese Patent Application Laid-Open No. 5-504023 (Patent Document 2) discloses a solar cell having a photosensitizing dye layer such as a transition metal complex on the surface of a titanium oxide semiconductor layer doped with metal ions. .

Further, the applicant of the present application further uses a metal product semiconductor film having a pore volume in a specific range as disclosed in JP-A-11-339867 (Patent Document 3) as a photoelectric cell with improved photoelectric conversion efficiency. Japanese Laid-Open Patent Publication No. 2000-77691 (Patent Document 4) and Japanese Patent Application Laid-Open No. 2001-155791 (Patent Document 5) propose using metal oxide particles having a core cell structure. Japanese Patent Laid-Open No. 2002-319439 (Patent Document 6) proposes to use a metal oxide semiconductor film in combination with a porous metal oxide semiconductor film and a nonporous metal oxide semiconductor film. Further, in Japanese Patent Application Laid-Open No. 2003-168495 (Patent Document 7), when a semiconductor film using tubular titanium oxide (titanium oxide nanotubes) with low alkali content and high anatase crystallinity is used, light with high photoelectric conversion efficiency is used. It proposes that an electric cell can be obtained.
Japanese Patent Laid-Open No. 1-220380 Japanese National Patent Publication No. 5-504023 JP 11-339867 A JP 2000-77691 A JP 2001-155791 A JP 2002-319439 A JP 2003-168495 A

  In the solar cells described in Patent Documents 1 and 2, it is important for improving the light conversion efficiency that electrons are rapidly transferred from the photosensitizing dye layer excited by absorbing light to the titania film. If the electron transfer is not performed, the recombination of the ruthenium complex and the electrons occurs again, resulting in a problem that the light conversion efficiency is lowered.

  In recent years, due to the trend of space saving and miniaturization, a higher photoelectric conversion efficiency is required, and the photoelectric cells of Patent Documents 3 to 7 have been proposed. It was desired.

  In addition, it is desired to make the solar cell flexible, and the development of the solar cell using plastic as the substrate, and the problem of leakage during the long-term use of the liquid electrolyte in this case and the resulting performance degradation. There is also a need for this solution.

Under these circumstances, the present inventors have conducted further extensive research, and as a result, when an ion conduction promoting material composed of particles such as titanium oxide nanotubes is blended in the electrolyte layer (through these surfaces or through the tube). Proton conduction increases proton conductivity and reduces loss in proton transfer, improving electrolyte orientation, thereby improving ionic conductivity of the electrolyte layer and suppressing dark current generation As a result, it has been found that the photoelectric conversion efficiency is increased, and by adding an ion conduction promoter, the viscosity of the electrolyte is increased and gelled, and when such an electrolyte is used, there is no leakage of the electrolyte, The inventors have found that a photoelectric cell having excellent durability can be provided, and have completed the present invention.
(1) That is, the photoelectric cell according to the present invention is
A substrate having an electrode layer (1) on the surface and a semiconductor film (2) having a photosensitizer adsorbed on the surface of the electrode layer (1);
A substrate having an electrode layer (3) on the surface,
The electrode layer (1) and the electrode layer (3) are arranged so as to face each other,
In the photoelectric cell in which the electrolyte layer is provided between the semiconductor film (2) and the electrode layer (3),
The electrolyte layer comprises at least one ion conduction promoting material selected from titanium oxide nanotubes, fibrous titanium oxides, and carbon nanotubes;
At least one of the substrates and the electrode layer has transparency.
(2) The content of the ion conduction promoter in the electrolyte layer is in the range of 5 to 40% by weight.
(3) Fullerene and / or fullerene hydroxide is supported on the surface of the ion conduction promoting material.
(4) The electrolyte layer has a viscosity of 1000 cp or more.

  According to the present invention, since the electrolyte layer contains an ion conduction promoting agent, the orientation of the electrolyte is improved. Therefore, the ionic conductivity of the electrolyte layer is improved and the dark current can be prevented. When the liquid electrolyte is used, the efficiency is high, and the electrolyte is solidified (gelled), so that there is no leakage of the electrolyte and a photoelectric cell with excellent durability can be obtained.

The photoelectric cell according to the present invention will be specifically described below.
[Photoelectric cell]
The photoelectric cell according to the present invention comprises a substrate having an electrode layer (1) on the surface and a semiconductor film (2) adsorbing a photosensitizer on the surface of the electrode layer (1);
A substrate having an electrode layer (3) on the surface,
The electrode layer (1) and the electrode layer (3) are arranged so as to face each other,
In the photoelectric cell in which the electrolyte layer is provided between the semiconductor film (2) and the electrode layer (3),
The electrolyte layer comprises at least one ion conduction promoting material selected from titanium oxide nanotubes, fibrous titanium oxides, and carbon nanotubes;
At least one of the substrates and the electrode layer has transparency.

An example of such a photoelectric cell is shown in FIG.
FIG. 1 is a schematic cross-sectional view showing an embodiment of the photoelectric cell according to the present invention, which has a transparent electrode layer 1 on the surface of a transparent substrate 5 and adsorbs a photosensitizer on the surface of the transparent electrode layer 1. The substrate on which the semiconductor film 2 is formed and the substrate having the electrode layer 3 having reduction catalytic ability on the surface of the substrate 6 are arranged so that the electrode layers 1 and 3 face each other, and further the semiconductor film 2 and the electrode An electrolyte 4 is enclosed between the layer 3.

The substrates 5 and 6 used in the present invention may be hard or flexible.
Transparent substrate 5
As the transparent substrate 5, a transparent and insulating substrate such as a glass substrate or an organic polymer substrate such as PET can be used.

Board 6
In addition, the substrate 6 is not particularly limited as long as it has enough strength to be used, and in addition to an insulating substrate such as a glass substrate or an organic polymer substrate such as PET, metal titanium, metal aluminum, metal copper, metal nickel, etc. The conductive substrate can be used.

Transparent electrode layer 1
The transparent electrode layer 1 formed on the surface of the transparent substrate 5 includes tin oxide, tin oxide doped with Sb, F or P, indium oxide doped with Sn and / or F, antimony oxide, zinc oxide, noble metal, etc. Conventionally known electrodes can be used. Such a transparent electrode layer 1 can be formed by a conventionally known method such as a thermal decomposition method or a CVD method.

Electrode layer 3
The electrode layer 3 formed on the surface of the substrate 6 includes electrode materials such as platinum, rhodium, ruthenium metal, ruthenium oxide, tin oxide doped with tin oxide, Sb, F or P, Sn and / or F. Conventionally known electrodes such as an electrode obtained by plating or vapor-depositing the electrode material on the surface of a conductive material such as indium oxide or antimony oxide doped with carbon, or a carbon electrode can be used.

  Such an electrode layer 3 is formed by directly coating, plating, or vapor-depositing the electrode on the substrate 6 and forming a conductive layer from a conductive material by a conventionally known method such as a thermal decomposition method or a CVD method. The electrode material can be formed on the layer by a conventionally known method such as plating or vapor deposition.

These electrode layers usually have a reduction catalytic ability. For example, I ₃ ⁻ is reduced to 3I ⁻ by the reduction catalytic ability. The substrate 6 may be transparent like the transparent substrate 5, and the electrode layer 3 is the same as the transparent electrode layer 1. Alternatively, a transparent electrode may be used.

  It is preferable that the visible light transmittance of the transparent substrate 5 and the transparent electrode layer 1 is higher, specifically 50% or more, particularly preferably 90% or more. When the visible light transmittance is less than 50%, the photoelectric conversion efficiency may be lowered.

The resistance values of the transparent electrode layer 1 and the electrode layer 3 are each preferably 100 Ω / cm ² or less. When the resistance value of the electrode layer exceeds 100 Ω / cm ² , the photoelectric conversion efficiency may be lowered.

Semiconductor film 2
The semiconductor film 2 is formed on the transparent electrode layer 1 formed on the transparent substrate 5. The semiconductor film 2 may be formed on the electrode layer 3 formed on the substrate 6.

The thickness of the semiconductor film 2 is preferably in the range of 0.1 to 50 μm, more preferably 2 to 20 μm.
Moreover, it is preferable that the pore volume of the semiconductor film 2 is in the range of 0.05 to 0.8 ml / g and the average pore diameter is in the range of 2 to 250 nm. Within this range, it is possible to increase the adsorption amount of a spectral sensitizing dye, which will be described later, and to smooth the electron mobility in the film and to increase the photoelectric conversion efficiency.

  When the pore volume is smaller than the lower limit, the spectral sensitizing dye adsorption amount is low. When the pore volume is higher than the upper limit, the electron mobility in the film is lowered and the photoelectric conversion efficiency may be lowered.

  On the other hand, when the average pore diameter is smaller than the lower limit, the adsorption amount of the spectral sensitizing dye is decreased, and when the average pore diameter is higher than the upper limit, the electron mobility may be decreased and the photoelectric conversion efficiency may be decreased.

  The semiconductor film 2 is composed of titanium oxide. Preferably, it is composed of a titanium oxide binder derived from peroxotitanic acid acting as a binder and titanium oxide particles, and the titanium oxide particles are densely arranged in the film, and the binder fills the gaps between the particles. .

(i) Titanium oxide particles Titanium oxide particles have higher spectral sensitizing dye adsorption and higher electron mobility in the semiconductor film than other metal oxide particles, and are more stable, safe, and film-forming. Excellent characteristics such as being easy. As the titanium oxide particles, crystalline titanium oxides such as anatase-type titanium oxide, brookite-type titanium oxide, and rutile-type titanium oxide are preferable. Among them, anatase-type titanium oxide and brookite-type titanium oxide have a high band gap and high photoelectric conversion efficiency. A photoelectric cell can be obtained.

  As the anatase-type titanium oxide particles and brookite-type titanium oxide particles, those obtained by a conventionally known method can be used, and titanium oxide particles derived from peroxotitanic acid are preferred.

  Specifically, titanium oxide particles obtained by the following production method are suitable. First, hydrogen peroxide is added to a titanium compound aqueous solution, or a hydrated titanium oxide sol or gel, and heated to prepare peroxotitanic acid. In the present invention, peroxotitanic acid refers to titanium peroxide hydrated titanium and has absorption in the visible light region.

  Hydrated titanium oxide sol or gel is hydrolyzed by adding acid or alkali to titanium salt such as titanium halide, titanyl sulfate, titanium alkoxide such as tetraalkoxy titanium, titanium compound such as titanium hydride, etc. Depending on the condition, it is obtained by washing or washing and aging by heating.

Next, alkali, preferably ammonia and / or amine is added to peroxotitanic acid to make it alkaline, and then titanium oxide colloidal particles are obtained by heating and aging at a temperature range of 80 to 350 ° C. The titanium oxide colloidal particles obtained as necessary may be added as seed particles to peroxotitanic acid, and then the above steps may be repeated. The titanium oxide colloidal particles thus obtained are anatase-type titanium having high crystallinity by X-ray diffraction. In addition, as described in JP-A No. 2000-335919, brookite-type titanium oxide is prepared by preparing a sol or gel of titanic acid, peptizing by adding hydrogen peroxide, and then cations other than titanium. A peroxotitanic acid solution having an ion concentration of 1000 ppm or less is prepared by deionizing anions and / or anions, and an organic base and / or ammonia is added to the peroxotitanic acid solution to maintain the pH in the range of 8-14. However, it can be prepared by hydrothermal treatment in a temperature range of 120 ° C to 350 ° C.

The crystallite diameter of such crystalline titanium oxide is preferably in the range of 5 to 50 nm, more preferably 7 to 30 nm.
For example, the crystallite size of anatase-type titanium oxide particles can be determined by measuring the half width of the peak of the (1.0.1) plane by X-ray diffraction and calculating by the Debye-Scherrer equation. When the crystallite size of the anatase-type titanium oxide particles is less than 5 nm, the electron mobility in the particles decreases, and when it exceeds 50 nm, the adsorption amount of the spectral sensitizing dye decreases and the photoelectric conversion efficiency decreases.

  Moreover, the particle diameter of the titanium oxide particles can be measured by a laser Doppler type particle diameter measuring machine (manufactured by Nikkiso Co., Ltd .: Microtrac), and the average particle diameter is in the range of 5 to 600 nm, further 10 to 500 nm. It is preferable. Within this range, a semiconductor film having a desired film thickness can be formed with a small number of times, and the obtained semiconductor film is free from cracks and has a high pore diameter and pore volume. It is done.

  If the average particle diameter is less than the lower limit, cracks are likely to occur in the formed semiconductor film, and it is difficult to form a crack-free thick film having a film thickness described later with a small number of times, and the pore diameter of the semiconductor film In some cases, the pore volume decreases and the amount of spectral sensitizing dye adsorbed decreases. Further, when the average particle size is larger than the upper limit, the strength of the semiconductor film may be insufficient.

(ii) Binder (peroxotitanic acid)
The titanium oxide binder may be any of anatase type titanium oxide, brookite type titanium oxide, rutile type titanium oxide, and amorphous titanium oxide.

Such a titanium oxide binder component is derived from peroxotitanic acid obtained by adding hydrogen peroxide to a gel or sol of orthotitanic acid obtained by a titanium oxide sol and / or sol-gel method to dissolve hydrous titanic acid. And titanium oxide. (Peroxotitanic acid is decomposed into titanium oxide during semiconductor film formation)
When such a binder component is contained, the adhesion with the electrode is improved, the strength of the resulting semiconductor film is improved, and an adsorption layer of a photosensitizer can be formed on the surface of the titanium oxide particles. Furthermore, the contact area between the titanium oxide particles is increased, the electron mobility can be improved, and a photoelectric cell with high photoelectric conversion efficiency can be obtained.

The ratio of the titanium oxide binder component to the titanium oxide particles in the semiconductor film 2 is 0.03 to 0.50, preferably 0.1 to 0.00 in terms of weight ratio in terms of oxide (titanium oxide binder component / titanium oxide particles). It is desirable to be in the range of 3. Within this range, a porous semiconductor film capable of sufficiently adsorbing the photosensitizer can be formed. If the weight ratio is small (that is, the binder is small), the amount of adsorption of the photosensitizer becomes insufficient, and the adhesion to the substrate, the strength of the semiconductor film, etc. may be insufficient. On the other hand, when the weight ratio is higher than 0.50, there are too many binders, a porous semiconductor film may not be obtained, and the photosensitizer adsorption amount may not increase.

The semiconductor film 2 has a pore volume of 0.1 to 0.8 ml / g, preferably 0.2 to 0.8 ml / g, and an average pore diameter of 2 to 250 nm, preferably 5 to 100 nm. It is desirable. With such pore volume and average pore diameter, the photosensitizer adsorbed amount is high, the electron mobility in the film can be kept high, and a photoelectric cell with high photoelectric conversion efficiency can be obtained. .

  When the pore volume is small, the adsorption amount of the photosensitizer is low. When the pore volume is high, the electron mobility in the film is lowered, and the photoelectric conversion efficiency may be lowered. Also, when the average pore diameter is small, the amount of adsorption of the photosensitizer decreases, and when it is high, the electron mobility in the film may decrease and the photoelectric conversion efficiency may decrease.

  Such a semiconductor film 2 is formed, for example, by applying a coating liquid for forming a semiconductor film for a photoelectric cell comprising peroxotitanic acid as a precursor of a titanium oxide binder component, a titanium oxide particle-dispersed sol, and a dispersion medium onto an electrode. -It can be formed by drying. Peroxotitanic acid is prepared by adding hydrogen peroxide to a titanium compound aqueous solution, or a hydrated titanium oxide sol or gel, followed by heating.

  Any dispersion medium can be used as long as it can disperse peroxotitanic acid and titanium oxide particles and can be removed when dried. Alcohols are particularly preferred. In order to form a uniform film, the coating solution may further contain a film forming aid in order to densely fill the titanium oxide particles and further improve the adhesion to the electrode. . Examples of the film forming aid include polyethylene glycol, polyvinyl pyrrolidone, hydroxypropyl cellulose, polyacrylic acid, and polyvinyl alcohol.

As a coating method of the coating solution, it can be applied by a conventionally known method such as a dipping method, a spinner method, a spray method, a roll coater method, flexographic printing, and screen printing. The drying temperature may be any temperature that can remove the dispersion medium. If necessary, the coating film may be irradiated with ultraviolet rays to be cured. By irradiation with ultraviolet rays, peroxotitanic acid is decomposed into titanium oxide and cured. After curing the coating film by irradiating with ultraviolet rays, if necessary, at least one selected from inert gases belonging to Group 0 of the periodic table, such as O ₂ , N ₂ , H ₂ , neon, argon, krypton Annealing may be performed by irradiating ions of the gas. By irradiation with gas ions, these ions do not remain in the titanium oxide film, and many defects are formed on the surface of the titania particles, improving the crystallinity of the titanium oxide after annealing and promoting the bonding between the particles. For this reason, the bonding force with the photosensitizer increases, the amount of adsorption increases, and the electron mobility is improved by promoting the bonding of the particles, whereby the photoelectric conversion efficiency can be improved.

The film thickness of the semiconductor film thus obtained is preferably in the range of 0.1 to 50 μm.
The semiconductor film 2 as described above adsorbs the photosensitizer.
The photosensitizer is not particularly limited as long as it absorbs and excites light in the visible light region and / or infrared light region. For example, an organic dye, a metal complex, or the like can be used. .

  As the organic dye, a conventionally known organic dye having a functional group such as a carboxyl group, a hydroxyalkyl group, a hydroxyl group, a sulfone group, or a carboxyalkyl group in the molecule can be used. Specifically, xanthene, coumarin, acridine, tetraphenylmethane, quinone, eosin Y, dibromofluorescein, fluorescein, fluorescein, metal-free phthalocyanine, cyanine dyes, metarocyanine dyes, triphenylmethane dyes and uranin, eosin, Examples thereof include xanthene dyes such as rose bengal, rhodamine B, and dibromofluorescein. These organic dyes have a characteristic that the adsorption rate to the semiconductor film is fast.

Examples of the metal complex include metal phthalocyanines such as copper phthalocyanine and titanyl phthalocyanine described in JP-A-1-220380 and JP-A-5-504023, chlorophyll, hemin, ruthenium-tris (2,2 ′ -Bispyridyl-4,4'-dicarboxylate), cis- (SCN-)-bis (2,2'-bipyridyl-4,4'-dicarboxylate) ruthenium, ruthenium-cis-diaqua-bis (2, Ruthenium-cis-, such as 2'-bipyridyl-4,4'-dicarboxylate)
Examples include complexes of ruthenium, osmium, iron, zinc and the like, such as diaqua-bipyridyl complexes, porphyrins such as zinc-tetra (4-carboxyphenyl) porphine, and iron-hexocyanide complexes. These metal complexes are excellent in the effect of spectral sensitization and durability.

The above organic dyes and metal complexes may be used alone, or two or more kinds may be mixed and used, and an organic dye and a metal complex may be used in combination.
The method for adsorbing the photosensitizer is not particularly limited, and a solution obtained by dissolving the photosensitizer in a solvent is absorbed into the semiconductor film by a method such as a dipping method, a spinner method, or a spray method, and then dried. A general method such as can be adopted. Furthermore, you may repeat the said absorption process as needed. Further, the photosensitizer can be adsorbed to the semiconductor film by bringing the photosensitizer solution into contact with the substrate while heating and refluxing.

  As the solvent for dissolving the photosensitizer, any solvent that dissolves the photosensitizer can be used. Specifically, water, alcohols, toluene, dimethylformamide, chloroform, ethyl cellosolve, N-methylpyrrolidone, Tetrahydrofuran or the like can be used.

The amount of the photosensitizer adsorbed on the semiconductor film is preferably 50 μg or more per 1 cm ² of the specific surface area of the semiconductor film. When the amount of the photosensitizer is less than 50 μg, the photoelectric conversion efficiency may be insufficient.

  In the photoelectric cell according to the present invention, when the semiconductor film 2 is formed on the surface of the transparent electrode layer 1, the semiconductor film 2 and the electrode layer 3 are disposed to face each other, and the semiconductor film 2 is disposed on the surface of the electrode layer 3. If formed, the semiconductor film 2 and the transparent electrode layer 1 are arranged facing each other, the side surfaces are sealed with resin, an electrolyte containing an ion conduction promoting material is injected, and the injection port is sealed. Is done.

As an ion conductive promotor ion conduction promoting material, titanium oxide nanotubes, fibrous titanium oxide, at least one selected from the group consisting of carbon nanotubes is exemplified. When these are included, ion conduction is promoted, and high photoelectric conversion efficiency can be expressed. Although the reason is not clear, it is thought that these particles are linear long particles, the electrolyte is oriented on the surface of these particles, and electrons or ions flow through the shortest path, so that ion conduction is promoted. .

(i) Titanium oxide nanotube The titanium oxide nanotube used in the present invention is a tube-like particle made of titanium oxide, and the titanium oxide may be anatase, rutile, brookite, amorphous, or a mixture thereof. Usually, those having high crystallinity are suitable.

The titanium oxide nanotube has an outer diameter (Dout) of 5 to 40 nm, preferably 10 to 30 n.
m, the inner diameter (Din) is 4 to 30 nm, preferably 5 to 20 nm, the tube thickness is 1 to 20 nm, preferably 2 to 15 nm, and the length (L) is 25. -1000 nm, preferably in the range of 50-600 nm, and the ratio (L) / (Dout) of this length (L) to the outer diameter (Dout) is in the range of 5-200, preferably in the range of 10-100. It is desirable.

  Within this range, the titanium oxide nanotubes do not settle in the electrolyte, so that ion conduction can be promoted and the amount of fullerene supported can be increased.

When the outer diameter (Dout) of the titanium oxide nanotube is less than the lower limit, the inner diameter becomes correspondingly narrow, the electrolyte diffusion described later becomes insufficient, and it becomes difficult to promote ion conduction. In some cases, sufficient photoelectric conversion efficiency cannot be obtained. It is difficult to obtain a titanium oxide nanotube having an outer diameter (Dout) exceeding the upper limit, and the effect of being a tube is lost. In addition, when the inner diameter (Din) of the titanium oxide nanotube is less than the lower limit, sufficient photoelectric conversion efficiency may not be obtained as described above, and it is difficult to obtain the inner diameter (Din) exceeding the upper limit. In addition, there is no effect of being a tube. At this time, if the tube is thin, the crystal layer is thin, the crystal structure becomes loose, and sufficient photoelectric conversion efficiency may not be obtained. Even if the thickness of the tube is too thick, the ratio of the internal cavities is lowered, and the effect of using the nanotube is reduced.

  Furthermore, when the length (L) of the titanium oxide nanotube is less than the above lower limit, the reason is not necessarily clear, but the effect of improving ion conductivity may not be obtained because the particles themselves are short. When the length (L) of the titanium oxide nanotubes exceeds the above upper limit, the dispersibility in the electrolyte is lowered, and the titanium oxide nanotubes are localized in the electrolyte, so that the effect of improving ion conductivity becomes insufficient. There is.

When (L) / (Dout) is less than the above lower limit, the length is short, there is no meaning of adding a tube, and the effect of improving ion conductivity may not be obtained. If (L) / (Dout) exceeds the above upper limit, light scattering may increase, particles may be long and settle in the electrolyte, and electrolyte diffusion may be insufficient, resulting in sufficient photoelectric conversion efficiency. May not be obtained.

In the present invention, the alkali metal content in the titanium oxide nanotube is preferably 500 ppm or less, more preferably 200 ppm or less, and particularly preferably 100 ppm.
When the alkali metal content exceeds 500 ppm, the semiconductor function tends to decrease and the photoelectric conversion efficiency tends to decrease with time. The semiconductor function is a rectifying action that makes the flow of electrons and ions in one direction. In this case, a positive defect is generated in the semiconductor film, and the electron flow is inhibited by trapping the electrons. When this function is lowered, the flow of electrons is deteriorated and the photoelectric conversion efficiency is lowered.

  The method for producing a titanium oxide nanotube used in the present invention is not particularly limited as long as the above-described titanium oxide nanotube is obtained, and a conventionally known method can be adopted. Among them, the method disclosed in Japanese Patent Application Laid-Open No. 2003-168495 filed by the applicant of the present application can be suitably employed because a titanium oxide nanotube with high crystallinity can be obtained.

Fibrous titanium oxide Fibrous titanium oxide used in the present invention is a fibrous particle composed of titanium oxide. Titanium oxide may be anatase, rutile, brookite, amorphous, or a mixture thereof. Those having high crystallinity are preferred.

  The fibrous titanium oxide has a minor axis width (W) of 5 to 40 nm, preferably 8 to 30 nm. Further, the fibrous titanium oxide has a long axis length (L) of 25 to 1000 nm, preferably 50 to 600 nm. Furthermore, it is desirable that the fibrous titanium oxide has an aspect ratio (L / W) of 5 to 200, preferably 10 to 100. In such a range, the particles show a fibrous shape, and the fibrous titanium oxide does not settle in the electrolytic solution, the electrolyte has a high gelling effect, and can further promote ionic conduction, so the photoelectric conversion efficiency Can be increased.

  It is difficult to obtain a fibrous titanium oxide particle having a minor axis width (W) outside the above range. Moreover, even if it is obtained, if the width (W) of the minor axis is too large, the effect of precipitation of the fibrous titanium oxide in the electrolyte or gelation of the electrolyte may not be obtained. The effect of improving the conversion efficiency may not be obtained.

  If the long axis length (L) of the fibrous titanium oxide is short, the aspect ratio (L / W) also becomes small, there is no meaning of blending the fibrous particles, and the flow of electrons and ions is interrupted, Ion conduction promotion effect is insufficient.

  When the long axis length (L) of the fibrous titanium oxide exceeds the above upper limit, the dispersibility of the particles in the electrolyte is lowered and localized, so the effect of improving ion conductivity is insufficient. It may become.

When the aspect ratio (L / W) is smaller than the above lower limit, there is no meaning of using fibrous particles, and the particle length is too short, so that the ion conduction promoting effect is insufficient.
In some cases, it is difficult to obtain a material having an aspect ratio (L / W) exceeding the above upper limit. Even if it is obtained, the diffusion of the electrolyte is insufficient and sufficient photoelectric conversion efficiency cannot be obtained. is there.

  The alkali metal content in such a fibrous titanium oxide is also preferably 500 ppm or less, more preferably 200 ppm or less, particularly 100 ppm, similarly to the titanium oxide nanotube.

  The fibrous titanium oxide used in the present invention can be obtained by firing the above-described titanium oxide nanotubes at 350 to 900 ° C, preferably 500 to 750 ° C. By firing at a high temperature, the internal space of the titanium oxide nanotube is closed, and fibrous titanium oxide is obtained. At this time, fibrous titanium oxide having higher crystallinity can be obtained at a lower temperature when firing is performed under reduced pressure, preferably while evacuating.

  The titanium oxide nanotubes and fibrous titanium oxides used in the photoelectric cell of the present invention are preferably anatase-type titanium oxide, brookite-type titanium oxide, rutile-type titanium oxide and crystalline titanium oxides such as mixed crystals and eutectics thereof. Type titanium oxide and brookite type titanium oxide are preferred because of their high band gap.

The titanium oxide is not limited to titanium oxide represented by TiO ₂ , and may be, for example, low-order (that is, reduced) titanium oxide represented by TiO _n (n is less than 2). Further, part of oxygen may be substituted with nitrogen.

As the carbon nanotube, a conventionally known carbon nanotube can be used. The carbon nanotube is a single-layer or multi-layer tube-shaped material in which a hexagonal mesh graphene sheet is wound in a cylindrical shape.

The carbon nanotube used in the present application has an outer diameter (D) of 1 to 40 nm, more preferably 2 to 30.
It is in the range of nm, and the length (L) is preferably in the range of 10 to 1000 nm, more preferably in the range of 20 to 600 nm. As such a carbon nanotube, for example, a carbon nanotube manufactured by Nikkiso Co., Ltd. can be preferably used.

  By including the ion conduction promoting material as described above, the electrolyte may be gelled, but it is possible to suppress electrolyte leakage by gelation. Although the reason why the gelation of the electrolyte occurs due to the inclusion of the ionic conduction promoting agent in this way is not clear, there are + ions and − ions in the electrolyte, and when the ionic conduction promoting material is added, the Debye length is increased. This is considered to be due to the increase in length and percolation between particles. In other words, when positive or negative charged particles are dispersed in an ionic electrolyte, it is considered that electrical neutralization occurs and gels.

  It is preferable that fullerene or hydroxylated fullerene (fullerene in which an OH group is introduced into a carbon atom constituting the fullerene, hereinafter collectively referred to as fullerenes) is supported on the ion conduction promoting material.

The fullerenes used in the present invention are not particularly limited as long as they can be supported on titanium oxide nanotubes and / or carbon nanotubes and can improve ion conductivity. For example, C36, C60, C70, C76, C78, C80, C82, C84 etc. are mentioned. As such fullerenes, known ones can be used without particular limitation. (For example, refer to Japanese Patent Application Laid-Open No. 2002-151094) Further, those having a group such as —COOH, —OSO ₃ H, —SO ₃ H, —OPO (OH) ₂ introduced in addition to the hydroxyl group can be used. .

  When fullerenes are supported, the speed of movement (sometimes referred to as hopping) of the ion conduction promoting material surface of the electrolyte ions is improved, and the effect of suppressing dark current or improving photoelectric conversion efficiency can be further improved. it can.

  The supported amount of fullerenes is preferably in the range of 5 to 80 parts by weight, more preferably 10 to 60 parts by weight in terms of fullerene per 100 parts by weight of the ion conduction promoting material. Within this range, the fullerene effect is sufficiently exhibited.

  If the amount of fullerenes supported is small, the effect of improving the moving speed of the surface of the ion conduction promoting material for the electrolyte ions may not be sufficiently obtained. If the amount of fullerenes supported is too large, the moving speed of the surface of the ion conduction promoting material for the electrolyte ions may be reduced.

  Such a fullerene loading method is not particularly limited as long as a predetermined amount can be supported on an ion conduction promoting material such as a titanium oxide nanotube, a fibrous titanium oxide, or a carbon nanotube. For example, fullerene is dispersed in a solvent such as dimethylformamide, and a silane coupling agent is mixed therewith. Then, the ion conduction promoting material is dispersed in the dispersion, and ultrasonic waves are irradiated as necessary.

As the electrolyte , a mixture with at least one compound that forms a redox system with an electrochemically active salt is used.

Examples of the electrochemically active salt include quaternary ammonium salts such as tetrapropylammonium iodide. Examples of the compound forming the redox system, quinone, hydroquinone, iodine _{^{(I - / I - 3)}} , potassium iodide, bromine _{^{(Br - / Br - 3)}} , potassium bromide, and the like.

Such an electrolyte is usually dissolved in a solvent and used as an electrolytic solution.
Further, the electrolyte may be dissolved in the ionic liquid. An ionic liquid is a salt melted at room temperature, has a high ion density, and has a high ion mobility, and thus exhibits an extremely high ion conductivity. For this reason, it can also be used as an electrolyte matrix.

Examples of the ionic liquid include 2-methyl-1-pyrroline, 1-methylpyrazole, 1-ethylcarbazole and the like in addition to imidazolium salt, pyridinium salt, ammonium salt and the like. These can be made to have a high molecular weight, and can also be gelled if necessary.

  Moreover, in this invention, a solvent can also be mixed and used for the said electrolyte layer as needed. The solvent used at this time is preferably a solvent having a low solubility of the photosensitizer so that the photosensitizer adsorbed on the semiconductor film does not desorb and dissolve. Specific examples of solvents include water, alcohols, oligoethers, carbonates such as propion carbonate, phosphate esters, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, N-vinylpyrrolidone, sulfolane 66, sulfur compounds, and carbonic acid. Examples include ethylene, acetonitrile, valeronitrile and the like.

Also, the electrolyte concentration is not particularly limited, but it is generally desirable that the total concentration is in the range of 0.01 to 3 mol / l, preferably 0.1 to 2 mol / l.
In the present invention, since the above-described ion conduction promoting material is included, the electrolyte solution may be gelled as described above. However, in the present invention, there is no problem even if it is gelled. In particular, if it is gelled, it is convenient that there is no leakage of electrolyte.

Furthermore, in the present invention, a solid electrolyte can be used as the electrolyte.
Examples of solid electrolytes include CuI, CuBr, CuSCN, polyaniline, polypyrrole, polythiophene, arylamine-based polymers, polymers having acrylic groups and / or methacrylic groups, polyvinylcarbazole, triphenyldiamine polymers, L-valine derivative low molecular gels, poly Oligoethylene glycol methacrylate, poly (o-methoxy aniline)
, Poly (epichlorohydrin-Co-ethylene oxide), 2,2 ', 7,7'-tetorakis (N, N-di-P-methoxyphenyl-amine) -9,9'-spirobifluorene, perfluorosulfonate, etc. In addition to proton-conducting fluorine-based ion exchange resins, perfluorocarbon copolymers, perfluorocarbon sulfonic acids, etc., polyethylene oxide, and ionic gel methods such as imidazole cations and Br ⁻ , BF ₄ ⁻ , N ⁻ (SO ₂ CF ₃ ) ₂ which forms a counter ion and is polymerized by adding a vinyl monomer or PMMA monomer to this can also be suitably used. When using these solid electrolytes, the components constituting the solid electrolyte are dispersed or dissolved in a solvent, the ion conduction promoting material is further dispersed, and then the obtained dispersion is injected and injected between the electrodes. After removing the solvent as necessary, the entrance is sealed to form a photoelectric cell. Here, the solid electrolyte includes a gel electrolyte.

When the electrolyte is gel, the viscosity is 1000 cp or more, and further 2000 to 10,000 c.
It is preferable to be in the range of p. When the viscosity of the electrolyte is less than 1000 cp, there is no dissipation of the electrolyte, so that the photoelectric conversion efficiency does not decrease even when used for a long period of time and does not cause corrosion or the like.

  The content of the ion conduction promoting material in the electrolyte layer is preferably in the range of 5 to 40% by weight, more preferably 10 to 30% by weight as the solid content. If it exists in this range, while gelatinization fully occurs, the ionic conduction promotion effect can be heightened.

  When the content of the ionic conduction promoter in the electrolyte layer is less than 5% by weight as the solid content, the gelation may be insufficient when the liquid electrolyte is used, and the leakage of the electrolyte may not be prevented. In some cases, a sufficient conduction promoting effect may not be obtained.

If the content of the ion conduction promoting material in the electrolyte layer exceeds 40% by weight as the solid content, the electrolyte concentration becomes relatively low, so that the ion conductivity becomes insufficient.
[Example]
Hereinafter, although an example explains, the present invention is not limited by these examples.

[Example 1]
Formation of semiconductor film (A) 10 g of titanium hydride is suspended in 2 L of pure water, 800 g of 5 wt% hydrogen peroxide solution is added over 30 minutes, and then heated to 80 ° C. to dissolve and dissolve peroxotitanium. An acid solution was prepared.

  90% by weight of this solution was fractionated, and concentrated aqueous ammonia was added thereto to adjust the pH to 9, and the mixture was placed in an autoclave, hydrothermally treated at 250 ° C. for 5 hours under saturated vapor pressure, and colloidal titanium oxide particles (A ) Was prepared. It was anatase type titanium oxide having high crystallinity by X-ray diffraction. The crystallite size was 30 nm, and the average particle size was 40 nm.

Next, the titanium oxide colloidal particles (A) obtained above are concentrated to a concentration of 10% by weight, mixed with the peroxotitanic acid solution, and titanium in the mixture is 30% by weight in terms of TiO _2. A coating solution for forming a semiconductor film was prepared by adding hydroxypropylcellulose as a film forming aid so as to be a%. Next, the fluorine-doped tin oxide is applied to a transparent glass substrate formed as an electrode, dried naturally, and subsequently irradiated with 6000 mJ / cm ² of ultraviolet light using a low-pressure mercury lamp to decompose the peroxo acid and cure the film. It was. In addition, 30
The semiconductor film (A) was formed by heating at 0 ° C. for 30 minutes to decompose and anneal hydroxypropylcellulose.

The film thickness of the obtained semiconductor film (A) was 12 μm, the pore volume determined by the nitrogen adsorption method was 0.6 ml / g, and the average pore diameter was 18 nm.
Adsorption of photosensitizer Next, a ruthenium complex represented by cis- (SCN ⁻ ) -bis (2,2′-bipyridyl-4,4′-dicarboxylate) ruthenium (II) is used as a photosensitizer. An ethanol solution having a concentration of 3 × 10 ⁻⁴ mol / liter was prepared. This photosensitizer solution was applied onto the semiconductor film (A) using an rpm 100 spinner and dried. This coating and drying process was performed five times. The adsorption amount of the photosensitizer of the obtained semiconductor film was 200 μg / cm ² .

Production of Photoelectric Cell (A) Titanium oxide nanotube particles (TNT-1) were prepared as follows.
A titanium chloride aqueous solution was diluted with pure water to prepare a titanium chloride aqueous solution having a concentration of 5% by weight as TiO ₂ . This aqueous solution was neutralized and hydrolyzed by adding it to 15% by weight ammonia water whose temperature was adjusted to 5 ° C. The pH after addition of the aqueous titanium chloride solution was 10.5. Next, the produced gel was washed by filtration to obtain an orthotitanic acid gel having a concentration of 9% by weight as TiO ₂ .

After 100 g of this orthotitanic acid gel was dispersed in 2900 g of pure water, 800 g of hydrogen peroxide having a concentration of 35% by weight was added and heated at 85 ° C. for 3 hours with stirring to prepare a peroxotitanic acid aqueous solution. The concentration of the resulting aqueous peroxotitanic acid solution as TiO ₂ is 0.5.
% By weight.

Next, the mixture was heated at 95 ° C. for 10 hours to obtain a titanium oxide particle dispersion, and tetramethylammonium hydroxide (TMAH MW = 149.2) was added to the titanium oxide particle dispersion so that the molar ratio to TiO ₂ in the dispersion was 0.016. ) Was added. The pH of the dispersion at this time was 11. Next, hydrothermal treatment was performed at 230 ° C. for 5 hours to prepare a titanium oxide particle dispersion. The average particle diameter of the titanium oxide particles was 30 nm.

Then, the titanium oxide particle dispersion liquid, a concentration of 40 wt% KOH aqueous solution 70 g, TiO ₂ molar number (T _M) and the number of moles of alkali metal hydroxide (A _M) and the molar ratio of (A _M) / (T _M ) was added so as to be 10 and hydrothermally treated at 150 ° C. for 2 hours.

The obtained particles were sufficiently washed with pure water. At this time, the residual amount of K ₂ O was 0.9% by weight. After washing with pure water, an aqueous dispersion of particles (concentration of 5% by weight as TiO ₂ ) was added, and the same amount of cation exchange resin and anion exchange resin as the particles were added, and the mixture was heated at 60 ° C. for 24 hours. It processed and refine | purified, such as removal of an alkali. Subsequently, it was freeze-dried to prepare titanium oxide nanotube particles (TNT-1) (average particle outer diameter 10 nm, average particle inner diameter 7.5 nm, average particle length 180 nm).

Next, 0.5 mol of iodine was mixed with 0.6 mol of dimethylpropylimidazolium iodide (DMPI), which is an ionic liquid, and titanium oxide nanotube particles (TNT-1) were mixed therewith.
Was mixed so that the concentration as TiO ₂ would be 6% by weight, and the electrolyte (A) was sufficiently dispersed by irradiation with ultrasonic waves. This electrolyte (A) gelled when left standing for a while.

The electrode prepared above is used as one electrode, and fluorine-doped tin oxide as the other electrode is formed as an electrode. A transparent glass substrate carrying platinum is placed on the opposite side, and the side is sealed with a resin. The electrolyte (A) was sealed between the electrodes before gelation, and the electrodes were connected with lead wires to produce a photoelectric cell (A).

The photoelectric cell (A) is irradiated with light of 100 W / m ² with a solar simulator, Voc (voltage in an open circuit state), Joc (density of current that flows when the circuit is short-circuited), FF (curve) Factor) and η (conversion efficiency).

The results are shown in Table 1.
[Example 2]
Production of Photoelectric Cell (B) In Example 1, the concentration of titanium oxide nanotube particles (TNT-1) as TiO ₂ was 1
A photoelectric cell (B) was prepared in the same manner except that the electrolyte (B) was obtained by mixing to 7 wt%, and this was sealed between the electrodes.

Next, Voc (voltage in an open circuit state), Joc (density of current that flows when the circuit is short-circuited), FF (curve factor), and η (conversion efficiency) were measured.
The results are shown in Table 1.

[Example 3]
Production of Photoelectric Cell (C) In Example 1, titanium oxide nanotube particles (TNT-1) were mixed so that the concentration as TiO ₂ was 30% by weight to obtain an electrolyte (C), which was obtained between the electrodes. A photoelectric cell (C) was prepared in the same manner except that it was encapsulated.

Next, Voc (voltage in an open circuit state), Joc (density of current that flows when the circuit is short-circuited), FF (curve factor), and η (conversion efficiency) were measured. The results are shown in Table 1.
[Example 4]
Preparation of Photoelectric Cell (D) 5 g of fullerene hydroxide (Science Laboratories: C-60) was dispersed in 95 g of dimethylformamide, and 2 g of an isocyanate silane coupling agent (Shin-Etsu Silicon Co., Ltd.) was added thereto. Next, 10 g of titanium oxide nanotube particles (TNT-1) prepared in the same manner as in Example 1 were added to the fullerene dispersion, dispersed uniformly, separated by centrifugation, then dried, Titanium oxide nanotube particles (TNT-1) carrying oxide fullerene were obtained.

The supported amount of fullerene was 30 parts by weight per 100 parts by weight of titanium oxide nanotube particles (TNT-1) as a solid content.
Subsequently, the electrolyte (D) was similarly obtained in Example 1 except that fullerene-supported titanium oxide nanotube particles (TNT-1) were used instead of the titanium oxide nanotube particles (TNT-1).
Then, a photoelectric cell (D) was prepared.

Next, Voc (voltage in an open circuit state), Joc (density of current that flows when the circuit is short-circuited), FF (curve factor), and η (conversion efficiency) were measured. The results are shown in Table 1.
[Example 5]
Production of Photoelectric Cell (E) In Example 2, fullerene-supported titanium oxide nanotube particles (TNT-1) prepared in the same manner as in Example 4 were used instead of titanium oxide nanotube particles (TNT-1). Similarly, an electrolyte (E) was prepared, and then a photoelectric cell (E) was prepared.

Next, Voc (voltage in an open circuit state), Joc (density of current that flows when the circuit is short-circuited), FF (curve factor), and η (conversion efficiency) were measured. The results are shown in Table 1.
[Example 6]
Production of Photoelectric Cell (F) In Example 3, fullerene-supported titanium oxide nanotube particles (TNT-1) prepared in the same manner as in Example 4 were used instead of titanium oxide nanotube particles (TNT-1). Similarly, an electrolyte (F) was prepared, and then a photoelectric cell (F) was prepared.

Next, Voc (voltage in an open circuit state), Joc (density of current that flows when the circuit is short-circuited), FF (curve factor), and η (conversion efficiency) were measured. The results are shown in Table 1.
[Example 7]
Production of Photoelectric Cell (G) In Example 1, 0.5 mol of iodine was mixed with 0.6 mol of dimethylpropylimidazolium iodide (DMPI), which is an ionic liquid, as an electrolyte, and carbon nanotube particles ( Photoelectric cell (G) in the same manner except that electrolyte (G) in which CNT-1) is mixed so that the concentration as C (carbon) is 9% by weight and is sufficiently dispersed by irradiation with ultrasonic waves is used. )created.

Next, Voc (voltage in an open circuit state), Joc (density of current that flows when the circuit is short-circuited), FF (curve factor), and η (conversion efficiency) were measured. The results are shown in Table 1.
[Comparative Example 1]
Production of Photoelectric Cell (H) In Example 1, 0.5 mol of iodine was mixed with 0.6 mol of dimethylpropylimidazolium iodide (DMPI), which is an ionic liquid, instead of the electrolyte (A), and the electrolyte ( A photoelectric cell (H) was prepared in the same manner except that H) was used. (Titanium oxide nanotubes are not included)
Next, Voc (voltage in an open circuit state), Joc (density of current that flows when the circuit is short-circuited), FF (curve factor), and η (conversion efficiency) were measured. The results are shown in Table 1.

FIG. 1 is a schematic cross-sectional view showing an embodiment of a photoelectric cell according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Transparent electrode layer 2 ... Semiconductor film 3 ... Electrode layer 4 ... Electrolyte 5 ... Transparent substrate 6 ... Substrate

Claims (4)

A substrate having an electrode layer (1) on the surface and a semiconductor film (2) having a photosensitizer adsorbed on the surface of the electrode layer (1);
A substrate having an electrode layer (3) on the surface,
The electrode layer (1) and the electrode layer (3) are arranged so as to face each other,
In the photoelectric cell in which the electrolyte layer is provided between the semiconductor film (2) and the electrode layer (3),
The electrolyte layer comprises at least one ion conduction promoting material selected from titanium oxide nanotubes, fibrous titanium oxides, and carbon nanotubes;
At least one substrate and an electrode layer have transparency, The photoelectric cell characterized by the above-mentioned.   2. The photoelectric cell according to claim 1, wherein the content of the ion conduction promoting material in the electrolyte layer is in the range of 5 to 40 wt%.   The photoelectric cell according to claim 1, wherein fullerene and / or fullerene hydroxide is supported on the surface of the ion conduction promoting material.   The photoelectric cell according to claim 1, wherein the electrolyte layer has a viscosity of 1000 cp or more.

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