JP2004146425A - Electrode substrate, photoelectric converter, and dye-sensitized solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode substrate having an excellent photoelectric conversion efficiency by suppressing a shielding fault on a surface of a metal wiring layer and suppressing circuit corrosion or reverse electron transfer due to the shielding fault, and to provide a photoelectric converter having the same and a dye-sensitized solar cell. <P>SOLUTION: The electrode substrate 1 includes the metal wiring layer 3 and a transparent electrode layer 4 on a transparent substrate 2. The layer 3 is formed along a wiring pattern formed with a groove on the substrate 2, or at least a part of the layer 3 reaches a height lower than the surface of the substrate 2. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrode substrate, a photoelectric conversion element, and a dye-sensitized solar cell.
[0002]
[Prior art]
Background of the Invention Solar cells as clean energy have attracted attention due to environmental issues and resource issues. However, conventional silicon-based solar cells have not been widely used because they have problems such as high production cost and insufficient supply of raw materials. Compound-based solar cells such as CIS-based cells have excellent characteristics such as extremely high conversion efficiency. However, problems such as cost and environmental load still hinder the widespread use.
[0003]
On the other hand, dye-sensitized solar cells have attracted attention as photoelectric conversion elements that are inexpensive and can achieve high conversion efficiency (for example, see Non-Patent Document 1). As a general structure of this photoelectric conversion element, a porous film using oxide semiconductor nanoparticles such as titanium dioxide is formed on a transparent conductive substrate and a sensitizing dye is supported on the porous film. And a counter electrode such as platinum-sputtered conductive glass, in which an organic electrolyte containing an oxidized / reduced species such as iodine / iodide ions is filled between both electrodes as a charge transfer layer. It has been reported that the semiconductor electrode has a porous film structure having a large specific surface with a roughness factor of> 1000, thereby increasing the light absorption rate, and a photoelectric conversion efficiency of 10% or more. In terms of cost, it is expected to be about one-half to one-sixth of current silicon-based solar cells. It does not necessarily require complicated and large-scale manufacturing equipment and does not contain harmful substances, so it is compatible with mass diffusion. It can be said that it has high potential as an affordable and mass-produced solar cell.
[0004]
As the transparent substrate used here, a glass substrate surface is generally coated with a transparent conductive film such as tin-added indium oxide (ITO) or fluorine-added tin oxide (FTO) in advance by a method such as vapor deposition or sputtering. However, since the specific resistance of ITO or FTO is about 10 ⁻⁴ to 10 ⁻³ Ω · cm, which is about 100 times the specific resistance of metals such as silver and gold, commercially available transparent conductive glass has low resistance. The value is high, and when used for a solar cell, particularly when a large area cell is used, the photoelectric conversion efficiency is significantly reduced.
As a method of lowering the resistance of the transparent conductive glass, it is conceivable to increase the thickness of the transparent conductive layer (ITO, FTO, etc.), but if the film is formed with a thickness sufficient to obtain a sufficient resistance value, the transparent conductive layer is formed. The light absorption by the layer is increased, and the transmission efficiency of the incident light through the window material is significantly reduced. As a result, the photoelectric conversion efficiency of the solar cell is also reduced.
[0005]
As a solution to such a problem, for example, a metal wiring layer is provided on the surface of a substrate with a transparent conductive layer used as a window electrode of a solar cell or the like so as not to significantly impair the aperture ratio, and the resistance of the substrate is reduced. (For example, refer to Japanese Patent Application No. 2001-400593). Further, when the metal wiring layer is provided on the substrate surface in this way, at least the metal wiring layer surface portion is provided in order to prevent corrosion of the metal wiring by the electrolytic solution and transfer of reverse electrons from the metal wiring layer to the electrolytic solution. It must be protected by some kind of shielding layer. Although the thickness of this shielding layer is not always required, it must be densely covered on the circuit surface.
[0006]
[Patent Document 1]
JP-A 1-220380 [Non-Patent Document 1]
B. O'Regan, M. Graetzel, Nature, vol. 353, Oct. 24, 1991, p737
[0007]
[Problems to be solved by the invention]
However, when there is a shadowed portion on the metal circuit surface when viewed from the film forming direction (for example, sneaking into the circuit wall), there is a possibility that a portion not covered by the shielding layer may occur, which may cause circuit corrosion. In addition, the cell characteristics may be significantly impaired due to the reverse electron transfer to the electrolyte. In particular, a sputtering method or a spray pyrolysis (SPD) method is preferably used as a method for forming a general film such as FTO, ITO, and TiO ₂ as a shielding layer. The membrane is extremely difficult. For example, when a circuit is formed by the additive plating method, the circuit wall shape may be tapered depending on the characteristics of a plating resist. Also, if there is a footing at the bottom of the resist pattern, it becomes a squat-shaped shadow after the circuit is formed. Thus, it is difficult to form a dense shielding layer thin film on a metal circuit surface.
[0008]
Further, in order to maintain an aperture ratio that does not impair light transmittance as much as possible and to provide sufficient conductivity, the metal wiring layer needs to have a certain height. When the wiring layer is formed, the surface of the substrate has many irregularities. For this reason, for example, in forming a semiconductor porous film for a dye solar cell, there is a problem that the uniformity of the film thickness is impaired, and the unevenness tends to cause cracking or peeling of the film.
[0009]
[Means for Solving the Problems]
The electrode substrate of the present invention is an electrode substrate having a metal wiring layer and a transparent conductive layer on a transparent substrate, wherein the metal wiring layer is formed along a wiring pattern grooved in the transparent substrate, At least a portion of the wiring layer has a height equal to or lower than the surface of the transparent substrate.
Preferably, at least the surface of the metal wiring layer is covered with a shielding layer.
It is preferable that the shielding layer contains at least one of a glass component, a metal oxide component, and an electrochemically inactive resin component.
A photoelectric conversion element according to the present invention includes the above electrode substrate.
The dye-sensitized solar cell of the present invention is characterized by comprising the above-mentioned photoelectric conversion element.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The electrode substrate of the present invention has a metal wiring layer and a transparent conductive layer on a transparent substrate, and FIG. 1 is a schematic sectional view showing one embodiment thereof.
The transparent substrate 2 used in the present invention has a wiring pattern that has been grooved by laser or etching. Further, the concave portion formed by the groove processing means a state reaching below the surface of the transparent substrate 2, and there is no limitation on the shape such as a lens shape, a concave shape, and a V-valley shape. Here, the term “surface” refers to the surface of the base material surface on which the semiconductor porous film or the like is formed and which is disposed to face the counter electrode.
As the transparent substrate 2, glass such as heat-resistant glass is generally used. In addition to glass, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), poly Examples thereof include a transparent plastic such as ether sulfone (PES), a polishing plate of ceramics such as titanium oxide and alumina, and a material having high light transmittance is preferable.
[0011]
In the present invention, the metal wiring layer 3 is formed along a wiring pattern grooved in the transparent substrate 2, and at least a part of the metal wiring layer 3 reaches a height below the surface of the transparent substrate 2. There is no particular limitation as long as it has a structure. For example, as shown in FIG. 1, the surface of the metal wiring layer 3 has the same height as the surface of the transparent substrate 2, and as shown in FIG. 2, the surface of the metal wiring layer 3 reaches a position higher than the surface of the transparent substrate 2. The metal wiring layer 3 may be formed entirely below the surface of the transparent substrate 2 (not shown). In any of the embodiments, when viewed from the direction in which the shielding layer 5 is formed, it is desirable that the shape be as smooth as possible with no noticeable unevenness, infiltration or voids. Further, it is preferable that the step between the surface of the metal wiring layer 3 and the surface of the transparent substrate 2 is smaller.
[0012]
The material for forming the metal wiring layer 3 is not particularly limited, but for example, gold, silver, platinum, aluminum, nickel, titanium, or the like can be used.
As a method of forming the metal wiring layer 3, various methods can be used without particular limitation, such as a printing method such as screen printing, a metal mask, and an inkjet method, such as a plating method, a sputtering method, and an evaporation method. . Particularly preferably, a method including at least one of a plating method and a printing method is selected. In addition, the height of the surface of the metal wiring layer 3 can be adjusted, for example, to be equal to the surface height of the transparent substrate 2 by polishing.
[0013]
In the present invention, the positional relationship between the metal wiring layer 3 and the transparent conductive layer 4 is not particularly limited. For example, as shown in FIG. 1, a structure in which a transparent conductive layer 4 is formed on a substrate on which a metal wiring layer 3 is disposed, or as shown in FIG. 3, a metal wiring on a substrate on which the transparent conductive layer 4 is disposed A structure in which the layer 3 is formed, or a structure in which the metal wiring layer 3 and the transparent conductive layer 4 are parallel as shown in FIG.
[0014]
The material for forming the transparent conductive layer 4 is not particularly limited, and examples thereof include tin-added indium oxide (ITO), tin oxide (SnO ₂ ), and fluorine-added tin oxide (FTO). It is preferable to select a material having a high rate as appropriate in accordance with the combination and use of the materials.
In addition, as a method for forming the transparent conductive layer 4, an appropriate method may be used according to a material for forming the transparent conductive layer 4 from a known method such as a sputtering method and an evaporation method.
[0015]
In the electrode substrate 1 of the present invention, in the case where the transparent conductive layer 4 is formed on the substrate on which the metal wiring layer 3 is arranged, the transparent conductive layer 4 may also serve as the shielding layer 5.
[0016]
As the shielding layer 5 formed on the surface of the conductive layer composed of the metal wiring layer 3 and / or the transparent conductive layer 4, at least one of a glass component, a metal oxide component, or an electrochemically inactive resin component is used. It is preferred to contain. The glass component is a low-melting amorphous or crystalline glass component such as lead oxide or lead borate, and the metal oxide component is titanium oxide, zinc oxide, or fluorine-added tin oxide (FTO). Examples of electrochemically inactive resin components such as tin-added indium oxide (ITO) include polyolefin-based resins, polyimide-based resins, and polybenzoxazole-based resins. These may be used alone or in combination of two or more. Can be used in combination.
[0017]
Although the formation range of the shielding layer 5 will be described later, in the case where the formation range of the shielding layer 5 is a wider range including the transparent portion where the surface of the metal wiring layer 3 and the transparent conductive layer 4 are arranged, the light transmission It is necessary to select a material and thickness that do not significantly impair the properties and electron transfer from the semiconductor porous film (that is, do not significantly lower the cell characteristics). Here, the shielding layer 5 made of a metal oxide component (oxide semiconductor) will be described in further detail. As a material, an electron transfer reaction rate with a redox species-containing electrolytic solution that comes into contact with a dye-sensitized solar cell Is required to be slow, excellent in light transmittance, and not hindering movement of generated photoelectrons. The material is not particularly limited as long as it satisfies such required characteristics, and examples thereof include titanium oxide, zinc oxide, niobium oxide, tin oxide, FTO, and ITO.
[0018]
The formation range of the shielding layer 5 is not particularly limited as long as it includes at least the surface of the metal wiring layer 3, and may be limited to only the surface of the metal wiring layer 3, or may be limited to the surface of the metal wiring layer 3 and the transparent conductive layer 4. May be wider than the area including the transparent portion where. Although the problem is small compared to the metal wiring layer 3, since the reverse electron transfer from the transparent conductive layer 4 has been pointed out, the shielding layer 5 has a wider area including the transparent portion where the transparent conductive layer 4 is disposed. By forming, more strict shielding is possible.
[0019]
The method for forming the shielding layer 5 is not particularly limited, and examples thereof include a method of forming a target compound or a precursor thereof by a dry method (vapor phase method) such as a sputtering method, an evaporation method, and a CVD method. Can be When a precursor such as a metal is formed into a film, the shielding layer 5 can be formed by oxidizing the film by a heat treatment or a chemical treatment.
[0020]
In the case of a wet method, a solution obtained by dissolving or dispersing a target compound or a precursor thereof is applied by a method such as spin coating, dipping, or blade coating, and then the target compound is subjected to heat treatment, chemical treatment, or the like. Thus, the shielding layer 5 can be formed. Examples of the precursor include salts and complexes having the constituent metal element of the target compound. Further, for the purpose of obtaining a dense film (shielding layer 5), it is preferable to be in a dissolved state rather than a dispersed state.
[0021]
In the case of the spray pyrolysis method (SPD) or the like, a substance serving as a precursor of the shielding layer 5 is sprayed toward the heated transparent substrate 2 having the transparent conductive layer 4 and thermally decomposed. The shielding layer 5 can be formed by changing to a target oxide semiconductor.
[0022]
As described above, according to the present invention, it is possible to suppress poor shielding of a shadowed portion at the time of film formation, such as an inverted tapered structure of the metal wiring layer 3 and a dive into the bottom portion, and to suppress a decrease in cell characteristics due to this. Can be. Further, regarding the uneven structure on the surface of the electrode substrate 1, the circuit thickness can be increased without increasing the level difference, so that the aperture ratio (non-wiring portion ratio) of the electrode substrate 1 can be increased and the resistance can be reduced. .
[0023]
Next, a dye-sensitized solar cell using the electrode substrate 1 will be described.
The dye-sensitized solar cell of the present invention includes, on the electrode substrate 1 described above, a working electrode including a dye-supported oxide semiconductor porous film, and a counter electrode disposed to face the working electrode, An electrolyte layer containing a redox couple is provided between the working electrode and the counter electrode.
[0024]
Examples of the material of the semiconductor porous film include titanium oxide (TiO ₂ ), tin oxide (SnO ₂ ), tungsten oxide (WO ₃ ), zinc oxide (ZnO), and niobium oxide (Nb ₂ O ₅ ). They can be used alone or in combination of two or more. Moreover, it can also be obtained from commercially available fine particles or a colloid solution obtained by a sol-gel method.
[0025]
As a method for producing a semiconductor porous film, for example, a screen printing method, an ink jet printing method, a roll coating method, a doctor blade method, a spin coating method, a spray coating method, and the like, using a colloid solution or a dispersion liquid (including an additive as necessary). In addition to coating using various coating methods, electrophoretic deposition of fine particles, combined use of a foaming agent, and compounding with polymer beads or the like (only the template component is removed later) can be applied.
[0026]
As the dye supported on the semiconductor porous film, a ruthenium complex containing a bipyridine structure, a terpyridine structure, or the like as a ligand, a metal-containing complex such as porphyrin or phthalocyanine, or an organic dye such as eosin, rhodamine, or merocyanine may be used. A material having an excitation behavior suitable for the application and the semiconductor to be used can be selected without particular limitation.
[0027]
As the electrolyte for forming the electrolyte layer, an organic solvent containing a redox couple, a molten salt at room temperature, or the like can be used.For example, acetonitrile, methoxyacetonitrile, propionitrile, propylene carbonate, diethyl carbonate, γ-butyrolactone, etc. Examples thereof include an organic solvent, a room temperature molten salt composed of a quaternized imidazolium-based cation and an iodide ion, a bistrifluoromethylsulfonylimide anion, and the like.
Further, a pseudo-solidified material, that is, a so-called gel electrolyte may be used by introducing an appropriate gelling agent into such an electrolytic solution.
[0028]
The redox couple is not particularly limited, and examples thereof include iodine / iodide ion and bromine / bromide ion. For example, specific examples of the former include iodide salts (lithium salts, quaternized Imidazolium salts, tetrabutylammonium salts and the like can be used alone or in combination) and iodine. Various additives such as tert-butylpyridine can be further added to the electrolyte as needed.
[0029]
Instead of the electrolyte layer formed from the electrolytic solution, a p-type semiconductor or the like can be used as the charge transport layer. Although there is no particular limitation on the p-type semiconductor, for example, a monovalent copper compound such as copper iodide or copper thiocyanide can be suitably used. In addition, various additives can be contained as required in terms of function and film formation. The method for forming the charge transport layer is not particularly limited, and examples thereof include a film forming method such as a casting method, a sputtering method, and a vapor deposition method.
[0030]
As the counter electrode, for example, various carbon-based materials, platinum, gold, and the like can be formed on a conductive or non-conductive substrate by a method such as evaporation or sputtering.
Further, when a solid charge transfer layer is used, a technique such as direct sputtering or coating on the surface thereof may be used.
[0031]
Since the dye-sensitized solar cell of the present invention has the above-described electrode substrate 1, corrosion of metal wiring due to the electrolytic solution and reverse electron transfer from the metal wiring layer 3 to the electrolytic solution are suppressed, and the output effect of the photoelectric conversion element is reduced. Is further improved.
[0032]
【Example】
(Example 1)
Grooves having a depth of 5 μm were formed in a lattice circuit pattern on the surface of a 100 × 100 mm glass with an FTO film by an etching method. The etching was performed using hydrofluoric acid after forming a pattern by photolithography. On this, a metal conductive layer (seed layer) was formed by sputtering to enable plating, and a metal wiring layer 3 was formed by additive plating. The metal wiring layer 3 was formed in a convex lens shape from the surface of the transparent substrate 2 to a height of 3 μm. The circuit width was 60 μm. From above, an FTO film having a thickness of 400 nm was formed as a shielding layer 5 by an SPD method to obtain an electrode substrate (i). The cross-sectional shape of the electrode substrate (i) conforms to FIG.
A titanium oxide dispersion having an average particle size of 25 nm was applied onto the electrode substrate (i), dried, and heated and sintered at 450 ° C. for 1 hour. This was immersed overnight in an ethanol solution of a ruthenium bipyridine complex (N3 dye) to carry the dye. A 50 μm-thick thermoplastic polyolefin resin sheet was interposed therebetween to face the platinum sputtered FTO substrate, and the resin sheet portion was thermally melted to fix the bipolar plates. An electrolyte injection port was previously opened on the platinum sputtering electrode side, and a methoxyacetonitrile solution containing 0.5M iodide and 0.05M iodine as a main component was injected between the electrodes. Further, the peripheral portion and the electrolyte injection port were completely sealed using an epoxy-based sealing resin, and a silver paste was applied to the current collecting terminal portion to obtain a test cell (i). When the photoelectric conversion characteristics of the test cell (i) were evaluated using simulated sunlight of AM1.5, the conversion efficiency was 2.8%.
[0033]
(Example 2)
A circuit pattern was engraved on a 100 × 100 mm heat-resistant glass surface using a laser engraving machine to form a metal wiring layer 3 similar to that of Example 1. From above, an FTO film having a thickness of 1000 nm was formed as a transparent conductive layer 4 and a shielding layer 5 by an SPD method to obtain an electrode substrate (ii). Note that the cross-sectional shape of the electrode substrate (ii) is similar to that of FIG. 2 except that the transparent conductive layer 4 reaches over the metal wiring.
Using the electrode substrate (ii), a test cell (ii) was produced in the same manner as in Example 1. When the photoelectric conversion characteristics of the test cell (ii) were evaluated using simulated sunlight of AM1.5, the conversion efficiency was 3.0%.
[0034]
(Example 3)
After the same metal wiring layer 3 as in Example 1 was formed on the heat-resistant glass surface, the metal wiring layer 3 was polished using a wafer polisher to approximately the same height as the substrate surface. From above, an FTO film having a thickness of 1000 nm was formed as the transparent conductive layer 4 and the shielding layer 5 by the SPD method. Further, a titanium oxide film was formed thereon with a thickness of 30 nm by a sputtering method to form an electrode substrate (iii) as a shielding layer 5. The cross-sectional shape of the electrode substrate (iii) is similar to that of FIG.
Using the electrode substrate (iii), a test cell (iii) was produced in the same manner as in Example 1. When the photoelectric conversion characteristics of the test cell (iii) were evaluated using simulated sunlight of AM1.5, the conversion efficiency was 3.1%.
[0035]
(Comparative Example 1)
A metal wiring layer 3 (gold circuit) was formed on a 100 mm square FTO glass substrate by an additive plating method. The metal wiring layer 3 (gold circuit) was formed in a lattice pattern on the substrate surface, and had a circuit width of 50 μm and a circuit thickness of 5 μm. An FTO film having a thickness of 300 nm was formed on this surface as a shielding layer 5 by an SPD method to obtain an electrode substrate (iv). When the cross section of the electrode substrate (iv) was confirmed using SEM and EDX, there was a sneak in at the bottom of the wiring, which was thought to be caused by the footing of the plating resist, and the FTO was not covered in the shadow part.
Using the electrode substrate (iv), a test cell (iv) was produced in the same manner as in Example 1. When the photoelectric conversion characteristics of the test cell (iv) were evaluated using simulated sunlight of AM1.5, the conversion efficiency was 0.3%.
[0036]
(Comparative Example 2)
Using a 100 mm square FTO glass substrate, a test cell (v) was produced in the same manner as in Example 1 with no wiring as a comparison. When the photoelectric conversion characteristics of the test cell (v) were evaluated using simulated sunlight of AM1.5, the conversion efficiency was 0.11%.
[0037]
From the above results, the test cells (i) to (iii) obtained in Examples 1 to 3 were all excellent in the photoelectric conversion efficiency, whereas the test cells obtained in Comparative Example 1 ( In iv), since the shielding by the shielding layer 5 was insufficient, the characteristics of the electrode substrate could not be brought out, and the conversion efficiency was not good.
Further, from comparison with Comparative Example 2, it was found that the test cell using the electrode substrate according to the embodiment of the present invention can greatly increase the photoelectric conversion efficiency in a large-area cell of 100 mm square class.
[0038]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the electrode substrate of this invention, in order to suppress the poor shielding of the surface of a metal wiring layer, the circuit corrosion and reverse electron transfer resulting from this can be suppressed, and also the circuit thickness can be reduced without increasing the unevenness of the electrode substrate surface. (Reducing the resistance of the electrode substrate). Therefore, since the function as a transparent substrate having high conductivity can be exhibited, the photoelectric conversion efficiency can be significantly increased, for example, in a large area cell of a 100 mm square class.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing one embodiment of an electrode substrate of the present invention.
FIG. 2 is a schematic sectional view showing an embodiment of the electrode substrate of the present invention.
FIG. 3 is a schematic sectional view showing an embodiment of the electrode substrate of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Electrode substrate, 2 ... Transparent substrate, 3 ... Metal wiring layer, 4 ... Transparent conductive layer, 5 ... Shielding layer

Claims (5)

An electrode substrate having a metal wiring layer and a transparent conductive layer on a transparent substrate,
An electrode substrate, wherein a metal wiring layer is formed along a wiring pattern grooved in a transparent substrate, and at least a part of the metal wiring layer reaches a height equal to or lower than the surface of the transparent substrate. 2. The electrode substrate according to claim 1, wherein at least a surface of the metal wiring layer is covered with a shielding layer. 3. The electrode substrate according to claim 1, wherein the shielding layer contains at least one of a glass component, a metal oxide component, and an electrochemically inactive resin component. A photoelectric conversion element comprising the electrode substrate according to claim 1. A dye-sensitized solar cell comprising the photoelectric conversion element according to claim 4.

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