JP4954855B2 - Manufacturing method of dye-sensitized solar cell - Google Patents

Description

The present invention, conductive, high transparency, when a photoelectric conversion element, a process for the preparation of the dye-sensitized solar cell having a capable conductive glass reduce the leakage current.

Regarding such a conductive glass, there is a prior invention (Patent Document 1) that the inventor has previously applied for a patent.
FIG. 1 shows the conductive glass disclosed in the prior invention.
In FIG. 1, the code | symbol 11 shows a glass plate. The glass plate 11 is made of a plate glass such as soda glass, heat-resistant glass, quartz glass or the like having a thickness of about 1 to 5 mm.

  A transparent conductive film 12 that covers the entire surface of the glass plate 11 is provided on the glass plate 11. The transparent conductive film 12 is made of a transparent and conductive thin film such as ITO (tin oxide doped indium oxide) or FTO (fluorine doped tin oxide), and has a thickness of about 0.2 to 1 μm. The thin film is formed by a thin film forming method such as CVD.

On the transparent conductive film 12, a grid 13 made of a metal film is provided in close contact therewith. The grid 13 works together with the transparent conductive film 12 as a path for electrons generated in the oxide semiconductor porous film when the conductive glass is used in a dye-sensitized solar cell.
The grid 13 has, for example, a lattice shape as shown in FIG. 2 or a comb-like shape as shown in FIG.

  In the grid-like grid 13 shown in FIG. 2, an infinite number of rectangular openings 14, 14... Having a length of 450 to 2000 μm and a width of 2000 to 20000 μm are formed, and a line 15 made of a vertical and horizontal metal film forming a grid. The line width of is 10 to 1000 μm. In addition, a wide collector electrode 16 for current collection is formed on one side so as to extend in the vertical direction.

  In the comb-like grid 13 shown in FIG. 3, lines 15, 15... Made of a comb-like metal film and having a width of 10 to 1000 μm are formed in parallel with each other at intervals of 450 to 2000 μm, An infinite number of openings 14, 14... Are formed, and a wide collector electrode 16 for current collection is formed at one end thereof.

  The grid 13 is formed by, for example, a plating method, and is made of one or more alloys of metals such as gold, silver, platinum, chromium, nickel, and the thickness of the line 15 is 1 to 2. It is 20 μm, preferably 3 to 10 μm.

The aperture ratio of the grid 13 is 90 to 99%. The aperture ratio here is defined by the ratio of the total area of the line 15 in the unit area.
The total surface resistance (referred to as sheet resistance) including the transparent conductive film 12 and the grid 13 on the entire surface of such conductive glass is 1 to 0.01Ω / □, and transparent conductive materials such as ITO and FTO. Compared to the transparent conductive glass provided with a film, it is about 10 to 1/100. For this reason, it can be said that it is highly conductive glass.

Furthermore, in such a conductive glass, the average light transmittance of the whole surface is high. That is, since the conductivity is remarkably improved by the presence of the grid 13, the thickness of the transparent conductive film 12 can be reduced, and the aperture ratio of the grid 13 is 90 to 99%. This is because there is almost no blocking of incident light.
As described above, the conductive glass according to the invention of the prior application has high conductivity and transparency, and a dye-sensitized solar cell using the conductive glass may have high photoelectric conversion efficiency.

However, in the dye-sensitized solar cell assembled using this conductive glass, electrons may flow backward from the grid 13 to the electrolytic solution between the grid 13 and the electrolytic solution, and a leakage current may flow. This is because the energy level of the electrolytic solution is low when the energy level between the grid 13 and the electrolytic solution is compared.
In order to prevent this leakage current, a barrier layer made of a semiconductor or an insulator such as titanium oxide or tin oxide is newly provided at the interface between the grid 13 and the electrolytic solution, and the barrier layer moves from the grid 13 toward the electrolytic solution. It is expected that the leakage current that flows can be prevented.

This barrier layer can be formed by sputtering, complex sintering, spray pyrolysis, CVD, or the like.
However, in the barrier layer obtained by such a thin film formation method, there is a possibility that pinholes are inevitably generated, and when a pinhole is generated even at one place, a leakage current flows therefrom.

  In addition, since this barrier layer is also formed on the transparent conductive film 12 other than the grid 13, when the dye-sensitized solar cell is formed, electrons generated in the oxide semiconductor porous film are transferred to the transparent conductive film 12. Therefore, the amount of generated current decreases or the form factor (Fill Factor. FF) decreases.

  In order to solve such an inconvenience, it is only necessary to form a barrier layer only on the grid 13, but the problem of pinholes still remains, and the formation requires a troublesome work such as photolithography. There are drawbacks such as cost reduction. For this reason, the means of newly providing a barrier layer on the grid 13 is not practical.

Further, as the metal forming the grid 13, nickel is mainly used from the viewpoint of its forming means. However, when the grid 13 made of nickel is directly provided on the transparent conductive film 12 made of FTO or the like, the nickel forming the grid 13 is removed from the transparent conductive film 12 when this is left for a long time or when heat treatment is applied. In some cases, the transparent conductive film 12 may be deteriorated. For this reason, electrons flow backward from the transparent conductive film 12 to the electrolytic solution, a leakage current flows between the transparent conductive film 12 and the electrolytic solution, and the photoelectric conversion efficiency of the dye-sensitized solar cell is greatly reduced. there were.
Japanese Patent Application No. 2001-400593

  Therefore, an object of the present invention is to provide a transparent conductive film on a glass, and in a conductive glass provided with a grid made of a metal film on the transparent conductive film, this conductive glass is converted into a photoelectric conversion such as a dye-sensitized solar cell. An object of the present invention is to obtain means for preventing generation of leakage current flowing from the grid to the electrolytic solution and leakage current flowing from the transparent conductive film to the electrolytic solution when assembled into the element.

According to a first aspect of the present invention, there is provided a glass plate, a transparent conductive film provided on the glass surface, a grid made of a passivated metal film provided on the transparent conductive film, and the transparent conductive material. A working electrode having an oxide semiconductor porous film provided on the film; a counter electrode disposed opposite to the working electrode; and an electrolyte layer disposed between the working electrode and the counter electrode. A method for producing a dye-sensitized solar cell, in which a transparent conductive film is formed on the glass and a grid made of a passivated metal film is formed on the transparent conductive film to obtain a conductive glass. A method for producing a dye-sensitized solar cell, wherein the grid is heat-treated at 300 to 550 ° C. in an oxygen atmosphere.

The conductive glass according to the first invention is provided with a transparent conductive film on the glass surface, and a grid made of a passivated metal film on the transparent conductive film. Since the thickness of the transparent conductive film can be reduced and light is hardly blocked by the grid, the light transmittance is high.
In addition, since the grid is made of passivated metal, an insulating dense oxide film is formed on the surface of the grid, and this oxide film functions as a barrier layer. This glass is used as a dye-sensitized solar cell. When assembled, leakage current flowing from the grid toward the electrolyte is prevented. Therefore, the photoelectric conversion efficiency when using a dye-sensitized solar cell is high.
In particular, by setting the thickness of the oxide film formed on the surface of the grid to 10 to 500 nm, a leakage current preventing effect can be obtained, and the heat treatment time required for forming the oxide film is within a practical range. be able to.

  According to the manufacturing method of the conductive glass which concerns on 4th invention, it can heat-process in oxygen atmosphere and can form an oxide film on the surface of a grid actively. By performing the heat treatment at 120 to 550 ° C., a sufficiently thick oxide film can be obtained without melting the glass substrate itself.

  According to the sixth invention, by using the above-described conductive glass for a photoelectric conversion element such as a dye-sensitized solar cell, the photoelectric conversion efficiency is high.

(Embodiment)
A first example of an embodiment of the conductive glass of the present invention is a conductive glass having a structure shown in FIGS. 1 to 3, for example, in which the metal film forming the grid 13 is made of a passivated metal. .

  The passivating metal in the present invention is a metal that can form a dense oxide film on its surface in an oxidizing atmosphere such as the air, an alloy of the passivating metals, or the passivating metal and other metals. An alloy with metal. Specifically, aluminum, chromium, nickel, cobalt, titanium, manganese, molybdenum, tungsten, zinc, tin, nickel-chromium alloy, iron-nickel-chromium alloy, aluminum-tungsten alloy, nickel-zinc alloy, silver- Examples include alloys such as zinc alloys.

  Among these metals, since the additive method by plating is mainly adopted as a method of forming the grid 13, it is a metal that can be plated and it is preferable that the electrical resistance of the grid 13 itself is low. Most preferred are metals with low volume resistivity, such as nickel, chromium, cobalt, aluminum, titanium or alloys of these metals.

  The grid 13 may have a structure in which the inner layer is made of a metal other than a passivating metal such as gold, silver, or platinum, and the surface is made of the above-described passivating metal. The formation of the grid 13 whose surface is made of a passivated metal is made, for example, by first producing a grid precursor made of a metal other than a passivated metal such as gold, silver, platinum on the transparent conductive film 12 by a plating method or the like. Then, this grid precursor can be electroless-plated and coated with a passivating metal such as nickel, chromium or tin.

  The grid 13 made of the passivating metal is preferably formed by an additive method by plating as described above, but can also be formed by various thin film forming methods such as sputtering and vapor deposition.

  In the grid 13 made of such a passivated metal, an electrically insulating oxide film is naturally formed on the surface immediately after the grid 13 is formed, and this insulating oxide film serves as a barrier layer. It will function as a leakage current prevention layer. Also, when a dye-sensitized solar cell is assembled using this conductive glass, the oxide semiconductor porous film made of titanium oxide or the like is inevitably exposed to a high temperature on this conductive glass. An oxide film having a sufficient thickness is formed on the surface of the grid 13 and exhibits high barrier properties.

In order to form an oxide film on the surface of the grid 13, natural oxidation may be waited as described above, but preferably an oxide film is positively formed by heat treatment in an oxygen atmosphere. May be. The heat treatment varies depending on the type of passive metal, a temperature 300 to 550 ° C., preferably at 300 to 450 ° C., time 5 to 120 minutes, preferably on the 10 to 90 minutes condition. If the temperature is less than 300 ° C. and the time is less than 5 minutes, an oxide film having a sufficient thickness cannot be obtained. If the temperature exceeds 550 ° C., the glass plate 11 itself melts. When the time exceeds 120 minutes, the heat treatment is no longer excessive and uneconomical.

As described above, this heat treatment can also be performed by firing at the same temperature and time conditions when the oxide semiconductor porous film made of titanium oxide or the like is formed by firing.
The oxide film thus formed has a thickness of about 50 to 500 nm. If the thickness is less than 50 nm, the effect of preventing leakage current cannot be obtained, and if the thickness exceeds 500 nm, the effect reaches a peak, and the heat treatment time for forming the oxide film becomes long, which is not practical.

FIG. 4 shows an example of a dye-sensitized solar cell as a photoelectric conversion element using such conductive glass.
In FIG. 4, reference numeral 21 denotes the conductive glass shown in FIGS. An oxide semiconductor porous film 22 is provided on the grid 13 made of the passivated metal film of the conductive glass 21.

  This porous oxide semiconductor porous film 22 is configured by combining semiconducting metal oxide fine particles such as titanium oxide, tin oxide, tungsten oxide, zinc oxide, zirconium oxide, niobium oxide, etc. The porous body has fine pores and fine irregularities on the surface, and has a thickness of 5 to 50 μm.

As shown in FIG. 4, the oxide semiconductor porous film 22 is integrated with the grid 13 so as to fill the openings 14, 14... Of the grid 13 and cover the entire surface of the grid 13. Has been.
The formation of the oxide semiconductor porous film 22 includes screen printing, inkjet printing, roll coating, colloid liquid or dispersion liquid in which fine particles having an average particle diameter of 5 to 50 nm of the metal oxide are dispersed on the surface of the grid 13. It is performed by a method of applying by a coating means such as doctor coating or spray coating and sintering at 300 to 800 ° C.

  The oxide semiconductor porous film 22 carries a photosensitizing dye. This photosensitizing dye includes ruthenium complexes containing ligands such as bipyridine structure and terpyridine structure, metal complexes such as porphyrin and phthalocyanine, and organic dyes such as eosin, rhodamine and merocyanine. It can be appropriately selected according to the type of semiconductor.

    Reference numeral 23 is a counter electrode. The counter electrode 23 in this example is made of platinum, gold or the like on the surface of the metal foil of the metal foil laminated film 23a in which a metal foil such as copper foil or nickel foil is laminated on one surface of a plastic film such as polyimide or polyethylene terephthalate. What formed the electroconductive thin film 23b by vapor deposition, sputtering, etc. is used, and this electroconductive thin film 23b is arrange | positioned so that it may become the inner surface side of this solar cell, and it is the dye-sensitized solar cell of this example.

  In addition, as the counter electrode 23, a conductive substrate such as a metal plate or a nonconductive substrate 23 a such as a glass plate formed with a conductive film 23 b such as platinum, gold, or carbon may be used. When a p-type semiconductor is used as the hole transport layer, since the p-type semiconductor is solid, a conductive thin film such as platinum is directly formed on the p-type semiconductor by vapor deposition, sputtering, or the like, and this conductive thin film is used as the counter electrode 23. You can also.

An electrolyte is filled between the counter electrode 23 and the oxide semiconductor porous film 22 of the conductive glass 21 to form an electrolyte layer 24.
The electrolytic solution is not particularly limited as long as it is a non-aqueous electrolytic solution containing a redox pair. As the solvent, for example, acetonitrile, methoxyacetonitrile, propionitrile, ethylene carbonate, propylene carbonate, γ-butyrolactone and the like are used.
As a redox pair, for example, a combination of iodine / iodine ion, bromine / bromine ion and the like can be selected. As a counter ion when this is added as a salt, lithium ion, tetraalkyl ion, imidazolium is added to the above redox pair. Ions can be used. Moreover, you may add an iodine etc. as needed.

Moreover, you may use the solid thing which gelatinized such electrolyte solution with the suitable gelatinizer.
Further, instead of the electrolyte layer 24, a hole transport layer made of a p-type semiconductor may be used. For the p-type semiconductor, for example, a monovalent copper compound such as copper iodide or thiocyanic copper or a conductive polymer such as polypyrrole can be used, and copper iodide is particularly preferable. In the case of using a solid hole transport layer made of this p-type semiconductor or a gelled electrolyte, there is no fear of leakage of the electrolyte.

  In such a conductive glass, since the grid 13 made of a passivated metal film is provided on the transparent conductive film 12, the conductivity is high and the transparency is also high. Further, since the grid 13 is made of a passivating metal, a dense insulating oxide film is formed on the surface thereof, and this oxide film functions as a barrier layer, thereby preventing leakage current from being generated. Further, the oxide film can also prevent the grid 13 from being eroded by the electrolytic solution.

  Further, since this oxide film is extremely dense, pinholes are hardly generated in this film, and there is no fear of leakage current due to pinholes. In addition, it is not necessary to form a special barrier layer on the grid 13, so that the workability is high and the cost is advantageous.

Specific examples are shown below, but the present invention is not limited to these specific examples.

(Example 1)
This example 1 corresponds to the above-described embodiment.
A transparent conductive glass was prepared in which a transparent conductive film made of FTO having a thickness of 0.5 μm was provided on a glass plate having a thickness of 2 mm.

  A grid-like grid as shown in FIG. 2 was provided on the FTO of the transparent conductive glass. The types of metal forming the grid and the forming method thereof are as follows. For some metals, a barrier layer made of titanium oxide or FTO was formed for comparison.

Metal seed formation method 1. Aluminum vapor deposition method2. 2. Titanium sputtering method Chrome plating method4. 4. Cobalt plating method Nickel plating method6. 6. Gold plating method Platinum plating method8. Silver plating method9. Platinum plating method Barrier layer formation made of titanium oxide10. 10. Gold plating method Barrier layer formation made of titanium oxide Silver plating method Barrier layer formation made of titanium oxide12. Gold plating method Formation of barrier layer made of FTO13. Silver plating method Barrier layer formation made of FTO

The grid line thickness was 5 μm, the line width was 40 μm, the opening size was a rectangle of 860 μm length and 5000 μm width, and the aperture ratio was 95%.
The sheet resistance of the conductive glass thus obtained was 0.1 to 0.8Ω / □, and the light transmittance at a wavelength of 550 nm was 75 to 80%.

  Then, an oxide semiconductor porous film was formed on the conductive glass grid. The oxide semiconductor porous film is formed by dispersing fine particles of titanium oxide having a particle size of about 20 nm in acetylnitrile to form a paste, applying the paste on the grid to a thickness of 15 μm by the bar code method, and drying to 400 ° C. And baked for 1 hour. A ruthenium dye was supported on the oxide semiconductor porous film after firing.

As a counter electrode, a transparent conductive glass provided with a 5 μm thick FTO on a glass plate with a thickness of 2 mm is prepared, the conductive glass and the counter electrode are bonded together, and an iodine / iodide electrolyte is filled in the gap. A dye-sensitized solar cell was prepared as an electrolyte layer.
The planar size of the obtained solar cell was 10 mm × 10 mm.

About these solar cells, the leakage current which flows from a grid to electrolyte solution was measured. The measurement was performed by connecting a bipolar power source to the cell and measuring the amount of current while sweeping in the voltage range of 0 to 1V.
The results are shown in Table 1.

  The dry contact resistance in Table 1 is an evaluation of the surface condition when the metal is heated to high temperature and oxidized. When the surface is slightly rough, it is indicated by Δ, and when there is little roughness, it is indicated by ○. Those with no roughness were marked with ◎. In addition, the iodine resistance indicates chemical resistance against an electrolytic solution in which the redox couple is iodine / iodine ion, and the metal film having a thickness of 50 nm formed on the surface of the grid disappears even after contact with the electrolytic solution for one month. What did not do was set as (circle), and what disappeared was set as x.

Moreover, leakage current, what leakage current when the sweep voltage is 500mV is less than 0.01 mA / cm ² and ◎, and ○ those 0.01~0.05mA / cm ^2, 0.05mA / beyond the cm ^2, and 0.5 mA / cm ² or less of those of △ and was a × those exceeding 0.5 mA / cm ^2.

  From the results in Table 1, it can be seen that nickel is most preferable as the passivating metal forming the grid, and then aluminum is preferable.

(Example 2)
This Example 2 corresponds to the above-described embodiment, and examined the thickness and formation conditions of the oxide film on the surface of the passivated metal forming the grid.
First, two types of sample cells were produced.

Sample cell A
A substrate on the working electrode side in which a transparent conductive film made of FTO having a thickness of 500 nm was formed on the surface of a glass plate having a thickness of 2.0 mm, and a platinum foil having a thickness of 0.05 mm was attached. A glass plate was used as a counter electrode side substrate, these two substrates were sealed, and an electrolyte solution of iodine / iodide was filled in a gap between the substrates to obtain a sample cell A.

Sample cell B
As a substrate on the working electrode side, a transparent conductive film made of FTO having a thickness of 500 nm is formed on the surface of a glass plate having a thickness of 2.0 mm, and various passivating metals (nickel, chromium, aluminum) are formed on the transparent conductive film. , Cobalt, titanium) and a 1 μm-thick grid film was formed by a plating method to obtain a working electrode side substrate. This substrate was heat-treated in air at a temperature of 120 to 450 ° C. for a time of 5 to 120 minutes. Sample cell B was produced in the same manner as sample cell A, except that this working electrode side substrate was used.

  For sample cell A, the leakage current flowing from the transparent conductive film to the electrolyte was measured, and for sample cell B, the leakage current flowing from the grid to the electrolyte was measured. The leakage current was measured by a method in which a bipolar power source was connected between the transparent conductive film and the platinum foil, and the amount of current was measured while sweeping the applied voltage in the range of −1 to + 1V.

The amount of leakage current was evaluated by the amount of current when the sweep voltage was + 0.5V.
The leakage current value in the sample cell A is set as a reference value, a value having a large leakage current value in the sample cell B with respect to this reference value is set as x, a value approximately the same is set as △, and a value smaller than the reference value is set. A value of ○ was given, and a value of 1/10 or less of the reference value was evaluated as ◎.
Tables 2 to 6 show the relationship between this evaluation, the type of passivated metal, and the heat treatment conditions.

From the results shown in these tables, regardless of the type of the passivated metal, the leakage current is reduced by the heat treatment at a temperature of 120 to 450 ° C. for a time of 5 to 120 minutes. It can be seen that an oxide film having a thickness sufficient to prevent leakage current is formed on the surface. Furthermore, when the grid surface after heat treatment was observed with a field effect scanning electron microscope, the thickness of the oxide film was about 10 nm when evaluated as Δ in Tables 2 to 6, and about 50 nm when evaluated as ○. , 評 価 was evaluated to be about 100 nm.
In addition, in order to apply to an actual dye-sensitized solar cell, the thing more than evaluated as (triangle | delta) is required.

  The conductive glass of this invention can be used for a working electrode of a photoelectric conversion element such as a dye-sensitized solar cell, and a dye-sensitized solar cell having high photoelectric conversion efficiency can be produced.

The schematic sectional drawing which shows an example of embodiment of the electroconductive glass in this invention. The top view which shows an example of the planar shape of a grid. The top view which shows another example of the planar shape of a grid. The schematic sectional drawing which shows an example of the dye-sensitized solar cell using the conductive glass of this invention.

Explanation of symbols

  11 glass (glass plate), 12 transparent conductive film, 13 grid.

Claims (1)

A glass plate, a transparent conductive film provided on the glass surface, a grid made of a passivated metal film provided on the transparent conductive film, and an oxide semiconductor provided on the transparent conductive film A working electrode having a porous membrane;
A counter electrode disposed opposite to the working electrode;
A method for producing a dye-sensitized solar cell comprising an electrolyte layer disposed between the working electrode and a counter electrode,
When a transparent conductive film is formed on the glass and a grid made of a passivated metal film is formed on the transparent conductive film to obtain a conductive glass, the grid is heated at 300 to 550 ° C. in an oxygen atmosphere. The manufacturing method of the dye-sensitized solar cell characterized by processing.

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