JP5511490B2 - Method for forming photocatalytic film in dye-sensitized solar cell - Google Patents

Description

  The present invention relates to a method for forming a photocatalytic film in a dye-sensitized solar cell.

Generally, a dye-sensitized solar cell includes a transparent electrode in which a transparent conductive film is formed on a transparent substrate such as a glass plate, a counter electrode in which a transparent conductive film is similarly formed on the surface of the transparent substrate, and these It is composed of an iodine-based electrolyte layer disposed between both electrodes, and a photocatalytic film disposed between the two electrodes and on the surface of the transparent electrode. The photocatalytic film includes titanium oxide (TiO ₂ ) and the like. It is known that after forming the metal oxide, a photosensitizing dye such as ruthenium is adsorbed.

  In addition, titanium oxide fine particles are used as the photocatalyst, and a titanium oxide precursor is mixed in order to improve performance (for example, see Patent Document 1).

JP 2004-193321 A

  By the way, according to the thing of the said patent document 1, when forming the photocatalyst, after apply | coating the mixture of a titanium oxide and its precursor to the transparent electrode side, it is made to bake the whole. It was as high as about 450 ° C.

  As described above, since the firing temperature is high, there is a problem that a lightweight and inexpensive synthetic resin cannot be used as the transparent substrate. For those that are fired at low temperatures, the photocatalyst film does not contain a binder premised on a high firing temperature, such as a paste for high temperatures, and therefore a porous film cannot be obtained. There is a problem that the amount of adsorption at the time of adsorbing the dye is reduced, and the battery performance is lowered.

  Therefore, an object of the present invention is to provide a method for forming a photocatalyst film in a dye-sensitized solar cell that can use a material that is weak at high temperature such as a synthetic resin as a substrate and can improve battery performance.

In order to solve the above-described problems, a method for forming a photocatalytic film in a dye-sensitized solar cell of the present invention includes a transparent electrode, a counter electrode, an electrolyte layer disposed between both electrodes, and a transparent electrode between both electrodes. A method of forming a photocatalyst film in a dye-sensitized solar cell comprising a photocatalyst film disposed on the side,
A method of forming a photocatalyst film by applying a mixture containing photocatalyst fine particles and a precursor of the photocatalyst fine particles to the surface of the transparent electrode, and spraying superheated water vapor after firing.
Moreover, when applying the said mixture to the surface of a transparent electrode, it is the method of using an electrostatic spray method.

Further, in the above formation method, the photocatalytic fine particles are titanium oxide, tungsten oxide, tin oxide, zinc oxide or niobium oxide,
Further, the precursor is a metal alkoxide, metal acetylacetonate or metal carboxylate.

  According to the above formation method, when the photocatalyst film is formed on the surface of the transparent electrode, the mixture containing the photocatalyst fine particles and the precursor of the photocatalyst fine particles is applied to the surface of the transparent electrode, and after the application, the superheated steam is sprayed. Therefore, it is not necessary to heat the entire electrode, and therefore, a material having low heat resistance such as a synthetic resin can be used as a substrate material for the transparent electrode, thereby reducing the weight and cost of the solar cell itself. be able to.

  Also, since superheated water vapor is sprayed onto the photocatalyst film, binders premised on a high firing temperature such as high-temperature paste contained in the photocatalyst film can be removed, so even when a film substrate is used, the photocatalyst in the photocatalyst film can be removed. Since the bonding property between the fine particles is improved and the porous property can be ensured, the amount of the photosensitizing dye adsorbed in the photocatalyst film is increased, and the battery performance can be improved.

It is sectional drawing which shows schematic structure of the dye-sensitized solar cell which concerns on Example 1 of this invention. It is an external appearance perspective view of the vapor spray nozzle used for the formation method of the photocatalyst film in the solar cell of the Example 1. It is a side view explaining the formation method of the photocatalyst film | membrane in the dye-sensitized solar cell which concerns on Example 2 of this invention. It is a side view explaining the formation method of the photocatalyst film | membrane which concerns on the specific example of the Example 2. FIG.

  Hereinafter, a method for forming a photocatalyst film in a dye-sensitized solar cell according to an embodiment of the present invention will be described based on specific examples.

First, a schematic configuration of the dye-sensitized solar cell according to Example 1 will be described with reference to FIG.
As shown in FIG. 1, the dye-sensitized solar cell includes a transparent electrode 1 as a negative electrode, a counter electrode 2 as a positive electrode, an electrolyte layer 3 disposed between the electrodes 1 and 2, and both electrodes 1. , 2 and a photocatalyst film (also referred to as a photocatalyst layer or a power generation layer) 4 disposed on the transparent electrode 1 side.

  The transparent electrode 1 is composed of a transparent substrate 11 and a transparent conductive film 12 formed (arranged) on the surface of the transparent substrate 11, and the counter electrode 2 is formed on the surface of the transparent substrate 21 and the transparent substrate 21. The transparent conductive film 22 is formed (arranged).

  As each of the transparent substrates 11 and 21, a synthetic resin plate, a glass plate, or the like is used as appropriate, but a thermoplastic resin such as a polyethylene naphthalate (PEN) film is preferable in terms of weight reduction and price reduction. In addition to polyethylene naphthalate, polyethylene terephthalate, polyester, polycarbonate, polyolefin and the like can also be used.

Further, as the transparent conductive films 12 and 22, tin-added indium oxide (ITO) is preferably used. In addition, fluorine-added tin oxide (FTO), tin oxide (SnO ₂ ), and indium zinc oxide (IZO) are used. A thin film containing a conductive metal oxide such as zinc oxide (ZnO) can be used.

  As the electrolyte layer 3, for example, an iodine-based electrolyte is used. Specifically, an electrolyte component such as iodine, iodide ion or tertiary butyl pyridine dissolved in an organic solvent such as ethylene carbonate or methoxyacetonitrile is used. The electrolyte layer 3 is not limited to the electrolytic solution, and may be a solid electrolyte.

As the solid electrolyte, for example, is illustrated DMPImI (dimethylpropyl imidazolium iodide), but this addition, LiI, NaI, KI, CsI, metal iodide such as CaI _2, tetraalkylammonium iodide and quaternary ammonium compounds Bromide such as a combination of iodide such as iodine salt and I ₂ , metal bromide such as LiBr, NaBr, KBr, CsBr and CaBr ₂ , and bromide salt of quaternary ammonium compound such as tetraalkylammonium bromide and Br ₂ And the like can be used as appropriate.

  The photocatalyst film 4 is formed of an oxide semiconductor layer 41 to which a photosensitizing dye 42 is adsorbed. In the production thereof, a paste containing an oxide semiconductor which is photocatalyst fine particles, that is, metal oxide fine particles, is transparent. It is obtained by adsorbing the photosensitizing dye to the oxide semiconductor after coating on the surface of the electrode 1 and baking.

Examples of the oxide semiconductor include metal oxides such as titanium oxide (TiO ₂ ), tin oxide (SnO ₂ ), tungsten oxide (WO ₃ ), zinc oxide (ZnO), and niobium oxide (Nb ₂ O ₅ ). As photosensitizing dyes used, ruthenium complexes and iron complexes having a ligand containing a bipyridine structure or a terpyridine structure, metal complexes of porphyrins or phthalocyanines, or organic dyes such as eosin, rhodamine, merocyanine, coumarin, etc. Is used.

Next, a manufacturing method of the photocatalyst film 4 that is the gist of the present invention, that is, a forming method will be described.
First, metal oxide fine particles that are photocatalysts, their precursors, a viscous agent and a binder are dissolved in an alcohol solution to form a paste-like mixture, and then this paste-like mixture is formed on the surface of the transparent electrode 1, for example, by a squeegee method or After coating by screen printing, superheated steam is sprayed on this surface and fired (also referred to as sintering), whereby the photocatalytic film 4 is obtained.

  Here, the method of baking with superheated steam will be described in detail. As shown in FIG. 2, for example, the horizontal cross-sectional shape is a rectangular shape having a predetermined height (a predetermined width and a predetermined length opening) ) From the vapor spray nozzle 51 is sprayed onto the surface of the paste-like mixture to be a photocatalyst film coated on the surface of the film substrate that is the transparent substrate 11 (slowly supplied state) ) At this time, the relative moving speed between the vapor spray nozzle 51 and the transparent substrate 11 is in the range of several mm to 1000 mm / sec. Specifically, as indicated by an arrow a, the transparent substrate 11 is moved at an appropriate speed within a range of several mm to 1000 mm / sec. In this case, the photocatalytic film 4 can be formed continuously on the transparent substrate 11. Of course, the vapor spray nozzle 51 can be moved with respect to the transparent substrate 11.

  Further, the vapor spray nozzle 51 is formed in an elongated box shape in which the lower surface is opened and the upper side surface is provided with an opening (also referred to as a supply port) for saturated water vapor S, and an electric heater (not shown) is provided inside. ) Is arranged. Specifically, the ejection opening of the vapor spray nozzle 51 is elongated in the width direction perpendicular to the front-rear movement direction of the transparent substrate 11.

  Accordingly, when saturated steam S of 100 ° C. is supplied to the steam spray nozzle 51, it is heated to a predetermined temperature by an electric heater, for example, to a temperature of 350 to 550 ° C., and the superheated steam H is photocatalyzed from the ejection opening on the lower surface. It is supplied to the surface of the film 4. In this sense, it can be said that the steam spray nozzle 51 is provided with a superheated steam generator.

As the viscosity agent, ethylene glycol, acetylacetone or the like is used, and as the binder, polyethylene glycol or the like is used.
The counter electrode 2 has been described as having the transparent conductive film 22 formed on the surface of the transparent substrate 21, but a metal sheet such as aluminum, copper, or tin can also be used. In addition, the counter electrode may be configured by holding a gel-like solid electrolyte on a mesh electrode made of metal such as aluminum, copper, tin, or carbon or a conductive adhesive on one side of the transparent substrate 21. Even if the counter electrode 2 is configured by forming a layer so as to cover the transparent substrate 21 and transferring the separately formed brush-like carbon nanotube group to the transparent substrate 21 side through the adhesive layer. Good.

  Here, the case where a dye-sensitized solar cell (which is also a photoelectric conversion element) is assembled will be briefly described. After the transparent electrode 1 having the photocatalyst film 4 formed on the surface by the above-described method and the counter electrode 2 are aligned. The electrodes 1 and 2 are sealed with a heat-sealing film or a sealing material, and the liquid electrolyte is passed between the electrodes 1 and 2 through holes or gaps previously provided in the transparent electrode 1 or the counter electrode 2. It can be injected into.

In addition, when using a solid electrolyte, after superposing | stacking so that the photocatalyst film | membrane 4 and the electrolyte layer 3 may be pinched | interposed between both electrodes 1 and 2, the peripheral parts should just be heated and adhere | attached.
Hereinafter, a method for forming a photocatalyst film in a dye-sensitized solar cell according to a plurality of specific examples in which Example 1 is shown more specifically will be described.
[Specific Example 1]
First, a method for forming a photocatalytic film according to Example 1 will be described. Titanium oxide fine particles having a particle diameter of 20 nm (manufactured by Nippon Aerosil Co., Ltd .: P-25) 6.0 g, nitrated water 14.0 g adjusted to pH 2, and acetylacetone 2.2 g , 0.6 g of polyethylene glycol (# 20,000) and surfactant (octylphenol ethoxylate: specific examples include Triton X-100) diluted 100 times with pure water, paint shaker, etc. And kneading for about 6 hours to obtain a titanium oxide paste.

  And after apply | coating this titanium oxide paste to the surface of the PEN-ITO film which is the transparent electrode 1, superheated steam of 350-550 degreeC is sprayed on the surface (it can also be said to be exposed or irradiation). As described above, the spraying speed, that is, the moving speed of the transparent electrode 1 with respect to the steam spray nozzle 51 is in the range of several mm to 1000 mm / sec. It should be noted that high temperature superheated steam is sprayed while moving to the heat-sensitive film substrate (in other words, both move relatively), thus preventing the film substrate from being adversely affected by heat. obtain.

Moreover, in the case where firing is insufficient by one spraying of superheated steam, spraying may be performed a plurality of times.
Furthermore, in Example 1, since a paste such as polyethylene glycol is contained in the paste to be applied, baking by superheated steam spraying that can remove these binders is preferable. Further, by using ethylene glycol in place of polyethylene glycol, baking can be performed at a lower temperature.
[Specific Example 2]
Next, a method for forming a photocatalytic film according to specific example 2 will be described.

  As the titanium oxide paste in this forming method, the titanium oxide paste obtained in the specific example 1 described above was used as a photocatalyst precursor, with a metal alkoxide, that is, titanium alkoxide titanium (IV) isopropoxide (TTIP) 0.20 g. A mixture of 37.50 g of propanol was used.

  The mixture to be applied is not limited to this, and for example, titanium tetraethoxide, titanium tetrachloride, titanium hydroxide or the like can be used instead of TTIP as a photocatalyst precursor.

In the case where tin oxide (SnO ₂ ), tungsten oxide (WO ₃ ), zinc oxide (ZnO), niobium oxide (Nb ₂ O ₅ ), or the like is used as an oxide semiconductor other than titanium, the respective precursors are Used. The photocatalyst precursor does not necessarily match the material of the photocatalyst film. For example, when the photocatalyst is titanium oxide, a niobium oxide precursor can be used as the precursor.

  Furthermore, not only propanol but also t-butyl alcohol, ethoxyethanol, ethanol or the like may be used for the alcohol liquid as a solvent. Moreover, you may add diethanolamine, acetylacetone, etc. for the purpose of suppressing hydrolysis.

Here, specific numerical values will be described. Dye sensitization with a film thickness of about several μm and an effective diameter φ of 6 mm using a commercially available low-temperature titanium oxide paste without firing the photocatalytic film with superheated steam. When you create a solar cell, 1 sUN, the AM is under 1.5, the current density is 8.67mA / cm ^2, the open circuit voltage is 0.70 V, the fill factor is 0.61, the conversion efficiency was 3.68% On the other hand, in the case of the specific example 1, the current density was 13.2 mA / cm ² , the open circuit voltage was 0.72 V, the fill factor was 0.61, and the conversion efficiency was 5.79%. That is, it can be seen that the photocatalytic film forming method according to the present invention is excellent.

  According to the photocatalyst film forming method of Example 1, when the photocatalyst film 4 is formed on the surface of the transparent electrode 1, a mixture of metal oxide fine particles and an alcohol liquid as a photocatalyst is prepared, and then water, viscosity A paste-like mixture is obtained by adding an agent and a binder, and this mixture is applied to the surface of the transparent electrode 1, and then the application film is sprayed with superheated steam in the temperature range of 350 to 550 ° C. and fired. Therefore, it is not necessary to heat the entire electrode. That is, since a material having low heat resistance such as a synthetic resin can be used as the substrate material of the transparent electrode 1, the solar cell itself can be reduced in weight and price, and it is not necessary to heat the entire substrate. Therefore, since a large heating device is not required, the manufacturing equipment cost can be reduced.

  Also, since superheated water vapor is sprayed onto the photocatalyst film, binders premised on a high firing temperature such as high-temperature paste contained in the photocatalyst film can be removed, so even when a film substrate is used, the photocatalyst in the photocatalyst film can be removed. Since the bonding property between the fine particles is improved and the porous property can be secured, the amount of the photosensitizing dye adsorbed in the photocatalyst film is increased, and the battery performance can be improved.

Next, a method for forming a photocatalyst film in a dye-sensitized solar cell according to Example 2 of the present invention will be described.
In Example 1 described above, a paste-like mixture containing metal oxide fine particles as a photocatalyst and its precursor is applied to the surface of the transparent electrode by, for example, a squeegee method, and then sprayed with superheated steam and baked. As described above, in Example 2, this paste-like mixture was applied using an electrostatic spray method, and superheated steam was sprayed simultaneously with this application.

  That is, the method for forming a photocatalyst film according to Example 2 is a method for producing a transparent mixture of a metal oxide fine particle that is a photocatalyst, a precursor of the metal oxide fine particle, a viscosity agent, and a binder in an alcohol liquid. This is a method in which superheated steam is sprayed and fired while (simultaneously) being applied to the surface of the electrode, and an electrostatic spray method is used as a method for applying the mixture.

Here, the principle of the electrostatic spray method will be briefly described.
In this electrostatic spray method, as shown in FIG. 3, a needle electrode 62 is disposed at the center of a liquid spray nozzle 61 that sprays a solution toward the transparent electrode 1, and the needle electrode 62 and the transparent electrode 1 are connected to each other. A DC power source 64 having a predetermined voltage is connected between the application electrode 63 to be placed, and a positive voltage is applied to the needle electrode 62 side during spraying, thereby charging the spray liquid and negative application electrode. This is a method of spraying and adhering to the surface of the transparent electrode 1 disposed on the surface 63. In addition, the said transparent electrode 1 is mounted on the plane moving apparatus 65, and is comprised so that it can move to arbitrary positions. When the photocatalytic film is actually and continuously formed, the liquid spray nozzle 61 is naturally shaped and sized so as to correspond to the width of the transparent electrode 1 and the transparent electrode 1 is formed. A moving device that can move continuously in a predetermined direction is used. For example, the transparent electrode 1 is placed on a belt conveyor type (endless belt type) moving device.

  Application conditions by the electrostatic spraying method include: type of liquid spray nozzle, viscosity of coating solution, atomizing air pressure, pattern width, discharge amount, discharge pressure, moving speed, overlap width, liquid spray nozzle and transparent electrode The distance, the applied voltage, and the like can be mentioned, but these conditions vary depending on the equipment to be used. Therefore, the coating conditions are appropriately selected so that a desired film thickness can be obtained.

Next, a method for forming a photocatalytic film that is the gist of the present invention will be described.
First, the metal oxide fine particles used as a photocatalyst, its precursor, a viscous agent and a binder are dissolved in an alcohol solution to form a paste, and then the paste-like mixture is applied to the surface of the transparent electrode 1 by a spray spray method. At the same time, the surface of the photocatalyst film 4 applied to the surface of the film substrate which is the transparent substrate 11 is sprayed (slowly supplied) from the vapor spray nozzle onto this surface. . A photocatalytic film is formed by the heat of the superheated steam from the steam spray nozzle. Further, as described above, ethylene glycol, ethylene glycol, acetylacetone, or the like is used as the viscosity agent.
[Specific Example 1]
Specific example 1 will be described below.

  Here, the case where the superheated steam is sprayed from the steam spray nozzle immediately after spraying the titanium oxide paste from the liquid spray nozzle is described, and the spray nozzles 51 and 61 are moved relative to the transparent electrode 1. The case where it is made to explain is demonstrated.

  First, as shown in FIG. 4A, a titanium oxide paste containing photocatalyst fine particles is applied to the surface of the transparent substrate 12 from the liquid spray nozzle 61 on the PEN-ITO film that is the transparent electrode 1 using an electrostatic spray method. Apply (a glass substrate may be used instead of a film substrate).

  As a coating solution used in this electrostatic spraying method, for example, a mixture of titanium oxide fine particles having a particle diameter of 20 nm (manufactured by Nippon Aerosil Co., Ltd .: P-25) in ethanol was used. Here, although ethanol was used as the solvent, other alcohol solvents such as propanol and t-butanol may be used.

  As the application conditions by the electrostatic spray method, for example, a two-fluid liquid spray nozzle is used, the atomizing air pressure is 0.2 MPa, the discharge amount is 15 g / min, the distance between the liquid spray nozzle and the transparent electrode is 20 cm, The applied voltage was 20 kV, and the moving speed b of the liquid spray nozzle was 100 m / min.

Then, immediately after formation of the film by the electrostatic spray method, 550 ° C. superheated steam is sprayed on the film surface from the vapor spray nozzle 51 disposed adjacent to the liquid spray nozzle 61 on the downstream side, and the film is baked. Obtained a photocatalyst film of about 5 to 6 μm. Of course, the vapor spray nozzle 51 is also moved in the same direction and at the same speed. The liquid spray nozzle 51 has a jetting opening having substantially the same length (width direction orthogonal to the moving direction) as the vapor spray nozzle 61 described in the first embodiment.
[Specific Example 2]
Next, specific example 2 will be described.

  As a mixture which is a coating solution in the specific example 2, titanium oxide fine particles (manufactured by Nippon Aerosil: P-25) having a particle size of 20 nm as photocatalyst fine particles and titanium (IV) isopropoxide (TTIP) which is a photocatalyst precursor solution A test was performed using 0.20 g mixed with 37.50 g of propanol liquid and using a two-fluid spray nozzle as the liquid spray nozzle 61. However, the coating solution is not limited to this, and for example, titanium tetraethoxide, titanium tetrachloride, titanium hydroxide, or the like can be used as a precursor of the photocatalyst. Further, the photocatalyst fine particles are not limited to titanium, and zinc oxide, niobium oxide, tungsten oxide and the like can also be used. The solvent may be not only propanol but also t-butyl alcohol, ethoxyethanol, ethanol, or the like. Moreover, you may add diethanolamine, acetylacetone, etc. in order to suppress hydrolysis. And in this specific example 2, as shown in FIG.4 (b), about 5-6 micrometers photocatalyst film | membrane was obtained by spraying and baking superheated steam simultaneously with film formation by an electrostatic spray method. Of course, in this specific example 2, both the spray nozzles 51 and 61 are arranged so that the spray range from the liquid spray nozzle 61 and the spray range from the vapor spray nozzle 51 just overlap. As in the first specific example, both the spray nozzles 51 and 61 are moved in the same direction and at the same speed.

  By the way, spraying of the superheated steam in the specific examples 1 and 2 is performed by exposing the photocatalyst film to a place where the temperature is about 350 to 550 ° C. The superheated steam spraying condition (spraying speed) varies depending on the state of the film and the heat resistance of the film substrate to be used, but is in the range of several mm to 1000 mm / sec, for example. Further, when the thickness of the photocatalyst film cannot be sufficiently obtained by one spray application / superheated steam spray, the process is performed a plurality of times.

  Furthermore, an appropriate amount of a binder such as polyethylene glycol is mixed in the coating solution, but since these binders are removed by superheated steam, the photocatalyst film can be made porous and thick, and thus the battery Performance is improved.

By the way, when a dye-sensitized solar cell having an effective diameter φ of 6 mm is produced using a commercially available low-temperature titanium oxide paste without firing the photocatalyst film with superheated steam, the time required for forming the photocatalyst film is 20-30. The battery performance was about 1 minute under AM 1.5, the current density was 8.67 mA / cm ² , the open-circuit voltage was 0.70 V, the fill factor was 0.61, and the conversion efficiency was 3.6%. On the other hand, in the case of the specific example 1, the time required for forming the photocatalytic film is about several minutes, the current density is 9.80 mA / cm ² , the open-circuit voltage is 0.67 V, and the fill factor is 0.69. The conversion efficiency was 5.15%.

  In each of the above specific examples, the liquid spray nozzle 51 and the steam spray nozzle 61 have been described as having an ejection opening that is elongated in the width direction, but of course, a nozzle having a normal circular ejection opening In this case, in addition to the back-and-forth movement, it is reciprocated in the width direction.

  According to the method for forming a photocatalyst film according to the second embodiment, the photocatalyst film can be formed even without natural drying or a firing step using a heater or the like. In addition, by using superheated steam, the film and transparent conductive film can be baked without damaging them, so binders premised on a high baking temperature such as high-temperature paste contained in the photocatalyst film can be removed by heat. Therefore, even when a film substrate is used, the connectivity between the photocatalyst fine particles in the photocatalyst film can be improved and the porous property can be secured, so that the amount of photosensitizing dye adsorbed in the photocatalyst film increases. The battery performance can be improved.

DESCRIPTION OF SYMBOLS 1 Transparent electrode 2 Counter electrode 3 Electrolyte layer 4 Photocatalyst film | membrane 11 Transparent substrate 12 Transparent conductive film 21 Transparent substrate 22 Transparent conductive film 41 Oxide semiconductor layer 42 Photosensitizing dye 51 Vapor spray nozzle 61 Liquid spray nozzle

Claims (4)

A method for forming a photocatalyst film in a dye-sensitized solar cell comprising a transparent electrode, a counter electrode, an electrolyte layer disposed between both electrodes, and a photocatalyst film disposed between both electrodes and on the transparent electrode side There,
A mixture containing photocatalyst fine particles and a precursor of the photocatalyst fine particles is applied to the surface of the transparent electrode, and after the application, a photocatalytic film is formed by spraying superheated steam and baking. A method for forming a photocatalytic film in a dye-sensitized solar cell.   The method for forming a photocatalytic film in a dye-sensitized solar cell according to claim 1, wherein an electrostatic spray method is used when the mixture is applied to the surface of the transparent electrode.   3. The method for forming a photocatalyst film in a dye-sensitized solar cell according to claim 1, wherein the photocatalyst fine particles are titanium oxide, tungsten oxide, tin oxide, zinc oxide, or niobium oxide.   The method for forming a photocatalyst film in a dye-sensitized solar cell according to any one of claims 1 to 3, wherein the precursor is a metal alkoxide, a metal acetylacetonate, or a metal carboxylate.

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