JP2005285428A - Photosensitized solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photosensitized solar cell having high adhesiveness of a semiconductor electrode and high light utilization efficiency. <P>SOLUTION: This invention provides the photosensitized solar cell comprising a plastic substrate containing a fiber-like metal oxide, a transparent electrode layer provided on the plastic substrate, a semiconductor electrode provided on the transparent electrode layer and carrying a dye on its surface, a counter substrate spaced from and opposing to the semiconductor electrode, a conductive layer provided on the counter substrate and an electrolyte layer having electrolyte provided between the semiconductor electrode and the conductive layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photosensitized solar cell.

  As a general photosensitized solar cell, a transparent electrode provided on a transparent substrate, a semiconductor electrode supported on the transparent electrode and having a dye supported on the surface of metal oxide fine particles, and a semiconductor provided on a counter substrate Some include a counter electrode facing the electrode and an electrolyte layer interposed between the two substrates.

  Such a photosensitized solar cell operates through the following process. That is, the light incident from the transparent electrode side reaches the dye carried on the surface of the semiconductor electrode and excites this dye. The excited dye quickly passes electrons to the semiconductor electrode. On the other hand, the positively charged dye by losing electrons is electrically neutralized by receiving electrons from ions diffused from the electrolyte layer. The ions that have passed the electrons diffuse to the counter electrode and receive the electrons. The photosensitized solar cell is operated by using a transparent electrode and a counter electrode facing the transparent electrode as a negative electrode and a positive electrode, respectively.

  Recently, a photosensitized solar cell in which a semiconductor electrode is formed on a plastic substrate has been reported (see, for example, Patent Document 1 and Patent Document 2). Photosensitized solar cells using such plastic substrates are expected to be used for purposes other than conventional ones, taking advantage of their lightweight and flexible characteristics. For example, Patent Document 1 and Patent Document 2 include a resin substrate. It is described that conductive fine particles are dispersed to impart conductivity. However, when a plastic substrate is used, when the semiconductor electrode is formed, there is a problem that the semiconductor electrode is peeled off even in a relatively low temperature thermal process of about 50 to 100 degrees due to the difference in linear expansion coefficient between the plastic and the semiconductor. Exists. Further, in the process of adsorbing the dye on the surface of the semiconductor electrode, there is a problem that the semiconductor electrode peels off due to swelling of the plastic substrate when immersed in the alcohol solution of the dye.

In addition, the photosensitized solar cell has a problem that not all incident light can excite the dye on the surface of the semiconductor electrode, and the light utilization efficiency is low.
JP 2003-297442 A (page 3-11, FIG. 1) JP 2003-297443 A (page 3-14, FIG. 1)

  As described above, conventionally, there has been a problem that a semiconductor electrode is peeled off and a problem that light utilization efficiency is low.

  In view of these problems, an object of the present invention is to provide a photosensitized solar cell having high adhesion of semiconductor electrodes and high light utilization efficiency.

  Therefore, the present invention provides a plastic substrate containing a fibrous metal oxide, a transparent electrode layer provided on the plastic substrate, a semiconductor electrode provided on the transparent electrode layer and having a dye supported on the surface, and a semiconductor electrode And a counter substrate disposed to be spaced apart from each other, a conductive layer provided on the counter substrate, and an electrolyte layer having an electrolyte provided between the semiconductor electrode and the conductive layer. A sensitized solar cell is provided.

  In the present invention, the metal oxide material may be at least one selected from the group consisting of silica, alumina, zirconia, titania, and magnesia.

  In the present invention, the ratio x1 / x2 between the linear expansion coefficient x1 of the plastic substrate material and the linear expansion coefficient x2 of the metal oxide material may be 2 or more and 50 or less.

  In the present invention, the weight of the metal oxide material may be 20 wt% or more and 90 wt% or less with respect to the weight of the plastic substrate material.

  In the present invention, the material of the plastic substrate may be at least one selected from the group consisting of polycarbonate, polyethylene terephthalate, polyethylene naphthalate, and polyacrylate.

  In the present invention, the metal oxide may have a diameter of 0.8 μm or more and 50 μm or less.

  According to the present invention, it is possible to provide a photosensitized solar cell with high adhesion of semiconductor electrodes and high light utilization efficiency.

  Hereinafter, embodiments of the present invention will be described in detail.

  In the photosensitized solar cell according to the embodiment of the present invention, a transparent electrode layer and a semiconductor electrode having a dye supported on the surface are stacked on a transparent substrate, and the transparent substrate is coated with a fibrous metal oxide. Including plastic substrate.

  As described above, conventionally, there have been a problem that the transparent substrate and the semiconductor electrode are peeled off due to a temperature change during the process of the transparent substrate and swelling with respect to the solvent, and a problem that the light utilization efficiency is low.

  Therefore, in this embodiment, a fibrous metal oxide is included in the plastic substrate. As a result, even when there is a temperature change during the process, the plastic has a high coefficient of linear expansion, but the metal oxide has a low coefficient of linear expansion, so the overall degree of expansion of the substrate is small, and the semiconductor electrode is also difficult to expand. This film can prevent peeling. Also, when immersed in a dye solution, the plastic swells similarly, but the metal oxide hardly swells, the degree of swelling of the substrate is reduced as a whole, and the film peeling of the semiconductor electrode can be prevented.

  Furthermore, the metal oxide fiber randomly dispersed in the substrate refracts light, so that incident light is refracted randomly, so that the optical path length in the semiconductor electrode can be increased, and the incident light Can be used effectively. As a result, it becomes possible to improve the light utilization efficiency.

In this embodiment, what is contained in the plastic substrate is a fibrous metal oxide. The metal oxide is used because the linear expansion coefficient is close to that of the n-type semiconductor and the n-type semiconductor film can be peeled off and problems such as cracks can be solved. The metal oxide includes silica (SiO ₂ ).

Further, in the present embodiment, the fibrous form refers to a fiber having an average aspect ratio of 1: 5 or more, a rod-shaped chopped strand (diameter of several μm, length of about several tens of μm) obtained by cutting glass fibers, Fibrous alumina (linear expansion coefficient: 5.3 × 10 ⁻⁶ / ° C.), magnesia (10 × 10 ⁻⁶ / ° C.), silica (7.4 × 10 ⁻⁶ / ° C.), silica glass (0. 41 × 10 ⁻⁶ / ° C.), titania (8.5 × 10 ⁻⁶ / ° C.), zircon (4.3 × 10 ⁻⁶ / ° C.), zirconium oxide (10 × 10 ⁻⁶ / ° C.), etc. Can do. The fiber shape may be a rod shape or a curved shape. The length may also be about several tens of μm to several mm or several tens of mm. The reason why a fibrous material is used as the metal oxide in the present embodiment is that the fibrous oxide interacts with the surrounding oxide as compared with the spherical oxide, and the expansion of the plastic having a large linear expansion coefficient of nearly one digit. This is because the overall linear expansion coefficient can be lowered. In addition, since the fibrous metal oxide has its fibers randomly present in the plastic substrate, the light transmitted through the substrate is refracted randomly without regularity. In addition, since the light is refracted more than the spherical substance is present, the optical path length in the solar cell can be increased.

  Any method can be used as a method for including a fibrous metal oxide in a plastic substrate. For example, after forming a fibrous metal oxide into a sheet, it is impregnated with a liquid resin precursor. There are a method of curing by curing, a method in which a fibrous metal oxide is mixed into a resin precursor, and the resin is molded into a sheet and then cured.

  In the present embodiment, silica, alumina, zirconia, titania, magnesia, or the like can be used as the metal oxide. In particular, it can be said that silica and titania are more desirable because they are easily formed into a fiber and have high strength.

  In this embodiment, the ratio x1 / x2 between the linear expansion coefficient x1 of the plastic substrate material and the linear expansion coefficient x2 of the metal oxide material may be 2 or more and 50 or less. By setting it to 2 or more, it becomes possible to effectively suppress the expansion of the plastic substrate, and by setting it to 50 or less, it is possible to effectively prevent peeling of the interface between the plastic and the metal oxide.

  In the present embodiment, the weight of the metal oxide material may be 20 wt% or more and 90 wt% or less with respect to the weight of the plastic substrate material. By setting it to 20% by weight or more, the linear expansion coefficient of the entire plastic substrate including the metal oxide can be made close to that of the semiconductor electrode, and by setting it to 90% by weight or less, flexibility and resistance to bending are maintained. I can do it.

  In this embodiment, the plastic substrate material is polycarbonate, polyethylene terephthalate, polyethylene naphthalate, polyacrylate, epoxy resin, polyimide resin, alicyclic resin, styrene acrylonitrile resin, cycloolefin resin, alicyclic polyolefin resin. An alicyclic acrylic resin, a polyester resin, a fluorine resin, a vinyl ester resin, or the like can be used. Polycarbonate, polyethylene terephthalate, polyethylene naphthalate, and polyacrylate are particularly preferable because of their high transparency and flexibility.

  In the present embodiment, the diameter of the metal oxide may be 0.8 μm or more and 50 μm or less. By setting the diameter of the metal oxide to 0.8 μm or more, incident light can be refracted and the optical path length in the semiconductor electrode can be increased, so that the energy of the incident light can be used effectively. Further, by setting the thickness to 50 μm or less, it is possible to obtain an effect that the fiber metal oxide can be uniformly present in the plastic substrate and the optical path length can be sufficiently obtained.

  Next, an embodiment of a photosensitized solar cell using a plastic substrate containing such a fibrous metal oxide will be described.

  In this embodiment, a plastic substrate containing a fibrous metal oxide having a light-receiving surface, a transparent electrode layer formed on one surface of the plastic substrate, a dye formed on the surface and formed on the transparent electrode layer An adsorbed semiconductor electrode, a counter substrate facing the semiconductor electrode, a conductive layer formed on a surface of the counter substrate facing the semiconductor electrode, and an electrolyte layer present between the conductive layer and the semiconductor electrode In this structure, sunlight enters from a plastic substrate.

  Hereinafter, the transparent electrode layer, the semiconductor electrode, the dye, the counter substrate, the conductive layer, and the electrolyte layer will be described.

(A) Transparent electrode layer The transparent conductive layer preferably has little absorption in the visible light region and has conductivity. The transparent conductive layer is preferably a tin oxide film doped with ITO, fluorine or indium, or a zinc oxide film doped with fluorine or indium. Further, from the viewpoint of improving conductivity and preventing an increase in resistance, it is desirable to wire a low-resistance metal matrix in combination with the transparent conductive layer.

(A) Semiconductor electrode The semiconductor electrode is preferably composed of a transparent semiconductor with little absorption in the visible light region. As such a semiconductor, a metal oxide semiconductor is preferable. Specifically, oxides of transition metals such as titanium, zirconium, hafnium, strontium, tin, zinc, indium, yttrium, lanthanum, vanadium, niobium, tantalum, chromium, molybdenum or tungsten, SrTiO ₃ , CaTiO ₃ , BaTiO ₃ Perovskites such as MgTiO ₃ and SrNb ₂ O ₆ , composite oxides or mixtures of these oxides, and GaN. As a method for forming the semiconductor electrode, a method of forming a film of a paste dispersed in water with a doctor blade or a screen printer, a method of forming a film by spraying the paste with a spray, a spin coating method, or the like can be used.

(C) Dye As the dye adsorbed on the surface of the semiconductor electrode, for example, a ruthenium-tris transition metal complex, a ruthenium-bis transition metal complex, an osmium-tris transition metal complex, an osmium-bis type Examples include transition metal complexes, ruthenium-cis-diaqua-bipyridyl complexes, phthalocyanines, porphyrins, and the like. Examples of the method for adsorbing the dye include a method in which the semiconductor electrode is adsorbed on the surface of the semiconductor electrode by an ester bond by being immersed in a dye solution dissolved in a medium such as ethanol.

(D) Counter substrate The counter substrate preferably has little absorption in the visible light region.

(E) Conductive layer The conductive layer is formed of, for example, a tin oxide film, a tin oxide film doped with fluorine, a zinc oxide film, a metal such as platinum, gold, or silver, or carbon, porous carbon, or the like. Can do. In view of durability against the electrolyte, platinum is most preferable. By reducing the thickness of these conductive layers, a transparent conductive layer with little absorption in the visible light region can be obtained.

(F) Electrolyte Layer The electrolyte contains, for example, iodine (I) and includes a reversible redox pair consisting of I ⁻ and I ₃ ⁻ . The reversible redox _couple can be supplied from a mixture of iodine molecules (I ₂ ) and iodide.

  Such a redox pair desirably exhibits a redox potential that is about 0.1 to 0.6 V lower than the oxidation potential of the dye described later. In the redox pair showing a redox potential 0.1 to 0.6 V lower than the oxidation potential of the dye, for example, a reducing species such as I- can receive holes from the oxidized dye. By containing such a redox pair in the electrolyte, the speed of charge transport between the semiconductor electrode and the conductive layer can be increased, and the open-circuit voltage can be increased.

  Examples of the iodide in the electrolyte include an alkali metal iodide, an organic compound iodide, and a molten salt of iodide.

  Examples of the molten salt of iodide include iodides of heterocyclic nitrogen-containing compounds such as imidazolium salts, pyridinium salts, quaternary ammonium salts, pyrrolidinium salts, pyrazolidium salts, isothiazolidinium salts, and isoxazolidinium salts. Etc. can be used.

  As the alkali metal iodide, lithium iodide, sodium iodide, potassium iodide, or the like can be used.

  Trimethylamine, triethylamine, tripropylamine, etc. can be used as the iodide of the organic compound.

  The content of iodine molecules in the electrolyte is preferably 0.01 mol / L or more and 3 mol / L or less. Iodine is mixed with iodide in the electrolyte and acts as a reversible redox pair. Therefore, by setting the iodine content to 0.01 mol / L or more, a sufficient redox pair can be obtained and electric charges can be transported. On the other hand, by setting it as 3 mol / L or less, the light absorption of a solution can be reduced and light can be efficiently given to a semiconductor electrode. The iodine content is more preferably 0.03 mol / L or more and 1.0 mol / L or less.

  The electrolyte may be either liquid or gel and can contain an organic solvent. By containing the organic solvent, the viscosity of the electrolyte can be further reduced, so that the electrolyte can easily penetrate into the n-type semiconductor electrode.

  Examples of the organic solvent that can be used include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC); chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; γ-butyrolactone, acetonitrile, propionic acid Examples include methyl and ethyl propionate. Furthermore, cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran; chain ethers such as dimethoxyethane and diethoxyethane; nitrile solvents such as acetonitrile, propionitrile, glutaronitrile, and methoxypropionitrile It is done. These organic solvents can be used alone or as a mixture of two or more.

  The content of the organic solvent is not particularly limited, but is preferably 80% by weight or less in the electrolyte. If the content of the organic solvent exceeds 80% by weight, performance may be deteriorated due to volatilization. The content of the organic solvent is more preferably 30% by weight or less.

  When setting it as a gel-like electrolyte layer, in addition to the electrolyte mentioned above, you may contain a gelatinizer.

  In addition, materials such as an inorganic hole transport layer and an organic hole transport layer that do not contain iodine may be used.

  The photosensitized solar cell of this embodiment may be manufactured, for example, by the method described below.

  First, a substrate having a light receiving surface and including a fibrous metal oxide is prepared, and a transparent electrode layer and a semiconductor electrode are sequentially formed on one surface thereof. Then, the dye is adsorbed on the surface of the semiconductor electrode. On the other hand, a counter substrate having a conductive layer provided on the surface is prepared, and the battery unit is assembled by disposing the conductive layer and the above-described semiconductor electrode so as to face each other.

  Next, an electrolyte is injected into the gap between the semiconductor electrode and the conductive layer to form an electrolyte layer. Moreover, you may make an electrolyte precursor gelatinize as a gel-like electrolyte layer. Subsequently, the photosensitized solar cell of this embodiment is obtained by sealing the battery unit.

  In order to obtain a gel electrolyte layer, it is preferable to heat the battery unit during gelation of the electrolyte precursor. It is preferable that the temperature of heat processing shall be in the range of 50-200 degreeC. This is due to the following reason. That is, when the heat treatment temperature is lower than 50 ° C., the degree of polymerization of the gel is lowered, and it may be difficult to form a gel. On the other hand, when heat treatment is performed at a high temperature exceeding 200 ° C., the decomposition of the dye is likely to occur. More preferably, the heat treatment temperature is 70 to 150 ° C.

  Hereinafter, specific examples will be described in more detail with reference to the drawings.

(Example 1)
As metal oxide, 30 parts by weight of glass cloth in which glass fibers having a diameter of 5 μm made of SiO ₂ (linear expansion coefficient: 7.4 × 10 ⁻⁶ / ° C.) are vertically and horizontally woven are used. The above-mentioned metal oxide was impregnated with a composition obtained by mixing 100 parts by weight of 138 g of resin and 174 g of oiled shell Ep806 with 3 parts by weight of imidazole catalyst Shikoku Kasei Co., Ltd. C17Z used as a resin curing catalyst. It was sandwiched between two Teflon (R) treated glass substrates and heated at 150 degrees for 8 hours. After curing, a plastic substrate 1 having a thickness of 0.5 mm was obtained.

As shown in FIG. 1A, an ITO film 2 (transparent electrode layer 2) was formed on a plastic substrate 1 by sputtering. The thickness of the ITO film 2 was about 0.10 μm. On the ITO film 2, a titania paste manufactured by Swiss Solaronics (for nano-cide DL low-temperature curing) was formed into a size of 1 cm × 1 cm using a 50 μm metal mask. The titania film was naturally dried, and then heated while being pressurized with a hot press at 50 degrees for 20 kN for 30 minutes. Two types of the substrates were prepared, and a scotch tape test was performed by attaching and removing the scotch tape on the titania film. As a result, the titania film did not peel off the substrate and showed high adhesion. 3 × 10 ⁻⁴ mol / l cis-bis (thiocyanato) -N, N-bis (2,2′-dipyridyl-4,4′-dicarboxylic acid) -ruthenium (II) dihydrate) Was immersed in an ethanol solution for 10 hours, and a dye was adsorbed on the surface of titania 3 to obtain a semiconductor electrode 4.

  As shown in FIG. 1B, a plastic substrate 1 on which a semiconductor electrode 4 is formed and a counter substrate 6 having a conductive layer 5 formed by sputtering platinum are bonded together with a sealing resin 7 at an interval of about 40 μm. . A methoxypropionitrile solution of 1-methyl-3-hexylimidazolium iodide 500 mM, LiI 500 mM, and t-butylpyridine 580 mM was injected as an electrolyte 9 using the injection nozzle 8 from the remaining injection port (FIG. 1 (c )).

  As shown in FIG.1 (d), when the inlet 10 was plugged and efficiency was measured, it was 4.3%. Ten similar cells were prototyped, but all 10 cells showed almost the same efficiency. In this embodiment, it is considered that the light passing through the plastic substrate 1 is refracted and the light can be taken in efficiently.

(Comparative Example 1)
A titania film was prepared in the same manner as in Example 1 except that a PET film containing no metal oxide was used as the plastic substrate 1. When the scotch tape test was performed on the titania film in the same manner as in Example 1, the titania film was peeled off without being adhered. In addition, after the titania film was formed, the dye was adsorbed and the semiconductor electrode 4 was formed in the same manner as in Example 1. As a result, the titania film was peeled off during the adsorption, and only 4 out of 10 were prototyped. I could not. The efficiency of this cell was measured and found to be 3.8%. In Comparative Example 1, unlike Example 1, it is considered that the efficiency was lowered because the light passing through the plastic substrate 1 could not be used efficiently.

(Example 2)
A pair of glass plates is sandwiched between 50 parts by weight of a glass fiber made of SiO ₂ used as a metal oxide and having a diameter of about 2 to 3 μm and a length of several millimeters, and polymerized with 50 parts by weight of methyl methacrylate (MMA) used as a plastic material. A solution mixed with 1 part by weight of azoisobutyronitrile (AIBN) used as an initiator was further poured between the glass plates. After curing this at 100 degrees for 30 minutes, the glass substrate was peeled off to produce a plastic substrate 1 containing glass fibers. Others were made in the same manner as in Example 1 to produce solar cells. The energy conversion efficiency of this solar cell was measured and found to be 4.4%. Also, 10 similar cells were prototyped, and all 10 cells showed almost the same efficiency. Further, when the adhesion of the titania film was measured by the Scotch tape test in the same manner as in Example 1, there was no peeling of the film.

(Example 3)
30 parts by weight of glass fiber chopped strand made of SiO ₂ used as a metal oxide and having a diameter of 2 to 3 μm and a length of 10 to 15 μm, and 70 parts by weight of polycarbonate pellets used as a plastic material are extruded and molded at 250 degrees to form a sheet having a thickness of 1 mm Thus, a plastic substrate 1 was produced. Others were made in the same manner as in Example 1 to produce solar cells. The energy conversion efficiency of this solar cell was measured and found to be 4.3%. In addition, although 10 similar cells were prototyped, all 10 cells showed almost the same efficiency. Further, when the adhesion of the titania film was measured by the Scotch tape test in the same manner as in Example 1, there was no peeling of the film.

It is sectional drawing which shows an example of the manufacturing process of the dye-sensitized solar cell which concerns on embodiment of this invention. It is sectional drawing which shows an example of the dye-sensitized solar cell which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Plastic substrate containing fibrous metal oxide 2 ... Transparent electrode layer 3 ... Titanium oxide fine particle 4 ... Semiconductor electrode 5 ... Conductive layer 6 ... Opposite substrate 7, 10 ... Epoxy resin 8 ... Injection nozzle 9 ... Electrolyte 11 ... Incident light

Claims (6)

A plastic substrate containing a fibrous metal oxide;
A transparent electrode layer provided on the plastic substrate;
A semiconductor electrode provided on the transparent electrode layer and having a dye supported on the surface;
A counter substrate disposed to face and separate from the semiconductor electrode;
A conductive layer provided on the counter substrate;
A photosensitized solar cell comprising: an electrolyte layer having an electrolyte provided between the semiconductor electrode and the conductive layer.   2. The photosensitized solar cell according to claim 1, wherein the metal oxide material is at least one selected from the group consisting of silica, alumina, zirconia, titania, and magnesia.   2. The photosensitizing type according to claim 1, wherein a ratio x1 / x2 between a linear expansion coefficient x1 of the plastic substrate material and a linear expansion coefficient x2 of the metal oxide material is 2 or more and 50 or less. Solar cell.   2. The photosensitized solar cell according to claim 1, wherein the weight of the metal oxide material is 20 wt% or more and 90 wt% or less with respect to the weight of the plastic substrate material.   2. The photosensitized solar cell according to claim 1, wherein the material of the plastic substrate is at least one selected from the group consisting of polycarbonate, polyethylene terephthalate, polyethylene naphthalate, and polyacrylate. The photosensitized solar cell according to claim 1, wherein the metal oxide has a diameter of 0.8 μm to 50 μm.

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