JP2011233507A - Substrate with porous titanium oxide coating film formed thereon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous titanium oxide coating film, which allows ions and electrons to travel efficiently while suppressing reverse electron transfer and facilitates light diffusion, thereby making possible to produce a dye-sensitized solar cell with a large conversion efficiency.SOLUTION: A porous titanium oxide coating film includes rod-like, tubular or fibrous titanium oxide structures (A) and titania nanoparticles (B), and has continuous or gradual concentration gradients of the titanium oxide structures (A) and titania nanoparticles (B) in a thickness direction thereof. When formed on a substrate, it is preferable that the porous titanium oxide coating film has a continuous or gradual concentration gradient such that the concentration of the titanium oxide structures (A) at a point away from the interface of the coating film and the substrate in the coating film becomes higher as the point becomes closer to the top surface of the coating film in the thickness direction of the coating film.

Description

  The present invention relates to a substrate on which a porous titanium oxide coating film used for a photoelectric conversion element such as a dye-sensitized solar cell is formed, and a dye-sensitized solar cell using the same.

  Solar cells are attracting attention as environmentally friendly power generation devices, and silicon-based semiconductors using pn junctions are widely known. However, silicon-based solar cells require a high vacuum and a high temperature during production, and it is difficult to reduce the cost, which has hindered their spread.

  While development of a lower cost solar cell is awaited, a dye-sensitized solar cell using a titanium dioxide modified with a dye as an active electrode has been reported by Gretzel et al. (See Patent Document 1). Dye-sensitized solar cells are attracting attention as solar cells that can be easily manufactured at low cost.

  As the porous titanium oxide coating used in this dye-sensitized solar cell, those containing high-aspect-ratio titania nanotubes and titania nanoparticles transport the generated electrons at high speed because the titania nanotubes are highly conductive. Therefore, improvement in conversion efficiency is expected.

  However, although titania nanotubes have high conductivity, reverse electron transfer to the electrolytic solution occurs, which may cause a decrease in open circuit voltage, and there is a problem that an increase in short circuit current and a decrease in open circuit voltage are offset. In addition, high-aspect-ratio titania nanotubes are thought to have the function of ensuring the light scattering effect of visible light and ion paths, but their functions are not fully expressed because appropriate concentration distribution with titania nanoparticles is not achieved. The conversion efficiency was not improved sufficiently.

Japanese Patent Publication No. 8-15097

  The present invention provides a porous oxidation capable of producing a dye-sensitized solar cell with high conversion efficiency by suppressing reverse electron transfer, enabling efficient transfer of ions and electrons, and facilitating light diffusion. It aims at providing the board | substrate with which the titanium coating film was formed.

In view of the above-mentioned object, as a result of intensive studies, in a substrate on which a porous titanium oxide coating film including a rod-like, tubular, fibrous or plate-like titanium oxide structure (A) and titania nanoparticles (B) is formed, By increasing the concentration of the titanium oxide structure (A) and decreasing the concentration of titania nanoparticles (B) as the porous titanium oxide coating film moves from the interface with the substrate toward the outermost surface of the coating film. The present inventors have found that a porous titanium oxide coating film that solves the above problems can be obtained, and has completed the present invention. That is, the present invention has the following configuration.
Item 1. A substrate on which a porous titanium oxide coating film containing a rod-like, tubular, fibrous or plate-like titanium oxide structure (A) and titania nanoparticles (B) is formed,
As the porous titanium oxide coating film moves from the interface with the substrate toward the outermost surface of the coating film, the concentration of the titanium oxide structure (A) increases and the concentration of titania nanoparticles (B) decreases. Features
A substrate on which a porous titanium oxide coating film is formed.
Item 2. The porous titanium oxide coating film is
The concentration of the titanium oxide structure (A) at a depth in the range of 0 to 10% of the thickness of the coating film from the outermost surface is 20 to 100% by weight,
The concentration of the titanium oxide structure (A) at a depth in the range of 90 to 100% of the thickness of the coating film from the outermost surface is 0 to 80% by weight.
A substrate on which the porous titanium oxide coating film according to Item 1 is formed.
Item 3. Item 3. The substrate on which the porous titanium oxide coating film according to Item 1 or 2 is formed, wherein the average aspect ratio of the titanium oxide structure (A) is 3 to 200,000.
Item 4. Any one of Items 1 to 3, wherein the titanium oxide structure (A) is at least one selected from the group consisting of a titania-coated nanoscale carbon tube (A1), a titania nanotube (A2), and a titania nanorod (A3). A substrate on which the described porous titanium oxide coating film is formed.
Item 5. Item 5. The substrate on which the porous titanium oxide coating film according to Item 4 is formed, wherein the titania nanotube (A2) is a titania nanotube (A2b) in which titania nanoparticles are continuous.
Item 6. Item 5. The substrate on which the porous titanium oxide coating film according to Item 4 is formed, wherein the titania nanotube (A2) is a titania nanotube (A2c) containing 30% or more of titania having a crystal form of a magnetic phase structure.
Item 7. Item 7. A substrate on which a porous titanium oxide coating film according to any one of Items 1 to 6 having an insulating oxide film on the surface of a titanium oxide structure (A) is formed.
Item 8. Claim | item 8. The board | substrate with which the porous titanium oxide coating film in any one of claim | item 1 -7 in which a porous titanium oxide coating film has an insulating oxide film on the surface was formed.
Item 9. An electrode substrate comprising a substrate on which the porous titanium oxide coating film according to any one of Items 1 to 8 is formed,
The substrate has a structure in which a resin substrate or a glass substrate and a transparent conductive film are integrated,
The porous titanium oxide coating film is formed on a transparent conductive film, and
An electrode substrate in which a pigment is supported on the porous titanium oxide coating film.
Item 10. An electrode substrate comprising: a substrate on which the porous titanium oxide coating film according to any one of Items 1 to 8 is formed; and a mesh electrode formed on the substrate on which the porous titanium oxide coating film is formed. There,
The mesh electrode is formed so as to contact and cover the porous titanium oxide coating film,
The substrate is a resin substrate or a glass substrate,
An electrode substrate in which a pigment is supported on the porous titanium oxide coating film.
Item 11. Item 11. The electrode substrate according to Item 10, wherein the mesh electrode does not react with iodine ions and bromine ions, or has corrosion resistance against iodine ions and bromine ions.
Item 12. Item 12. The item 10 or 11, wherein the mesh electrode comprises at least one selected from the group consisting of titanium, gold, platinum, tungsten, niobium, tantalum, carbon, stainless steel, and titania having a crystalline form of a Magneli phase structure. Electrode substrate.
Item 13. Claim | item 9-12 A dye-sensitized solar cell provided with the electrode substrate in any one of.
Item 14. A porous titanium oxide coating film comprising a rod-like, tubular, fibrous or plate-like titanium oxide structure (A) and titania nanoparticles (B),
The concentration of the titanium oxide structure (A) increases and the concentration of the titania nanoparticles (B) decreases as it goes from one surface to the other surface.
Porous titanium oxide coating.

  According to the present invention, a porous material capable of producing a dye-sensitized solar cell with high conversion efficiency by suppressing reverse electron transfer, enabling efficient movement of ions and electrons, and facilitating light diffusion. A quality titanium oxide coating film can be provided.

It is an electron microscope (TEM) photograph of one iron-carbon complex which comprises the carbonaceous material obtained in Example 1 of Unexamined-Japanese-Patent No. 2002-338220. It is an electron microscope (TEM) photograph which shows the presence state of the iron-carbon composite in the carbonaceous material obtained in Example 1 of Unexamined-Japanese-Patent No. 2002-338220. It is the electron microscope (TEM) photograph which made the iron-carbon composite_body | complex obtained in Example 1 of Unexamined-Japanese-Patent No. 2002-338220 into the shape of a ring. In addition, the black triangle ((triangle | delta)) shown in the photograph of FIG. 3 has shown the EDX measurement point for composition analysis. The schematic diagram of the TEM image of a carbon tube is shown, (a-1) is a schematic diagram of the TEM image of a cylindrical nano flake carbon tube, (a-2) is the TEM image of the multi-layer carbon nanotube of a nested structure FIG. It is an electron microscope (SEM) photograph which shows the surface shape of the titania covering nanoscale carbon tube (A1) by which the surface of rod-like or fibrous carbon was coat | covered with the coating layer which a titania nanoparticle continues. It is a schematic diagram explaining the movement of electrons in a titania-coated nanoscale carbon tube (A1) in which the surface of a rod-like or fibrous carbon is coated with a coating layer in which titania nanoparticles are continuous. It is an electron microscope (SEM) photograph which shows the surface shape of the titania-coated nanoscale carbon tube when it is not sufficiently covered with a coating layer composed of continuous titania nanoparticles. It is a schematic diagram explaining the movement of electrons in the titania-coated nanoscale carbon tube when it is not sufficiently covered with a coating layer composed of continuous titania nanoparticles. It is an electron microscope (SEM) photograph which shows the surface shape of the titania nanotube (A2b) which a titania nanoparticle becomes continuous. It is a schematic diagram explaining the movement of the electron in the titania nanotube (A2b) which a titania nanoparticle becomes continuous. It is a schematic diagram which shows the concept of the titania nanotube in which (a) well-known titania nanotube and (b) titania nanoparticle continue. Note that (a) includes a roll of titania nanosheets. As for titania nanorods (A3b), (a) one containing a plurality of crystallized parts, (b) one containing a plurality of short crystals (length of 50 nm or less), and (c) main It is a schematic diagram which shows the concept of what contains a short crystal | crystallization (length is 50 nm or less) in a crystal | crystallization (length is larger than 50 nm). It is a schematic sectional drawing which shows an example of the electrode substrate of aspect 1 (front contact structure) of this invention. In aspect 1 (front contact structure) of this invention, it is a schematic sectional drawing which shows an example of the electrode substrate in the case of having an insulating oxide film on the surface of a titanium oxide structure (A). In addition, the case where the insulating oxide film coat | covers the surface of a titanium oxide structure (A), and also the pigment | dye is adsorb | sucking to the surface is shown. In aspect 1 (front contact structure) of this invention, it is a schematic sectional drawing which shows an example of an electrode substrate in case it has an insulating oxide film on the surface of a titanium oxide structure (A) and a titania nanoparticle (B). In addition, the case where the insulating oxide film coat | covers the surface of a titanium oxide structure (A) and a titania nanoparticle (B), and also the pigment | dye is adsorb | sucking to the surface is shown. It is a schematic sectional drawing which shows an example of the electrode substrate of aspect 2 (back contact structure) of this invention. In aspect 2 (back contact structure) of this invention, it is a schematic sectional drawing which shows an example of the electrode substrate in the case of having an insulating oxide film on the surface of a titanium oxide structure (A). In addition, the case where the insulating oxide film coat | covers the surface of a titanium oxide structure (A), and also the pigment | dye is adsorb | sucking to the surface is shown. In aspect 2 (back contact structure) of this invention, it is a schematic sectional drawing which shows an example of an electrode substrate in the case of having an insulating oxide film on the surface of a titanium oxide structure (A) and a titania nanoparticle (B). In addition, the case where the insulating oxide film coat | covers the surface of a titanium oxide structure (A) and a titania nanoparticle (B), and also the pigment | dye is adsorb | sucking to the surface is shown. 2 is an electron microscope (TEM) photograph of an end portion of a titania nanotube (A2b) produced in Example 1. FIG. 2 is an electron microscope (TEM) photograph of the central part of the titania nanotube (A2b) produced in Example 1. FIG. 4 is an electron microscope (TEM) photograph of the titania-coated nanoscale carbon tube (A1) produced in Example 3. FIG. 6 is an electron microscope (SEM) photograph showing the surface shape of a titania nanotube (A2c) produced in Example 4. FIG. 4 is an electron microscope (TEM) photograph of a central portion of a titania nanotube (A2c) produced in Example 4. 4 is an electron microscope (TEM) photograph of an end portion of a titania nanotube (A2c) produced in Example 4.

1. Substrate on which a porous titanium oxide coating film is formed A substrate on which the porous titanium oxide coating film of the present invention is formed comprises a rod-like, tubular, fibrous or plate-like titanium oxide structure (A) and titania nanoparticles (B Is a substrate on which a porous titanium oxide coating film is formed. Furthermore, as the porous titanium oxide coating film moves from the interface with the substrate to the outermost surface of the coating film, the concentration of the titanium oxide structure (A) increases and the concentration of the titania nanoparticles (B) decreases. Is.

In the present invention, “titanium oxide” or “titania” does not mean only titanium dioxide, but dititanium trioxide (Ti ₂ O ₃ ); titanium monoxide (TiO); Ti ₄ O ₇ , Ti ₅ O. _It includes those having a composition deficient in oxygen from titanium dioxide represented by ₉ etc. Further, as represented by the terminal OH group, a group other than Ti—O—Ti resulting from the synthesis of titanium oxide may be included.

1-1. Titanium oxide structure (A)
The titanium oxide structure (A) used in the present invention is not particularly limited as long as it is rod-shaped, tubular, fibrous, or plate-shaped. Specifically, any of titania-coated nanoscale carbon tube (A1), titania nanotube (A2), and titania nanorod (A3) may be used.

  Further, the shape of the titanium oxide structure (A) is not particularly limited, but the average diameter orthogonal to the major axis is 5 to 500 nm from the viewpoint of efficiently transmitting electrons while having a sufficient surface area. The average length of the major axis is preferably from 0.1 to 1000 μm, and the average aspect ratio (average length of the major axis / average diameter perpendicular to the major axis) is preferably 3 to 200,000, and the average diameter perpendicular to the major axis is 7 to 300 nm. The average length of the major axis is preferably 1 to 50 μm, and the average aspect ratio (average length of major axis / average diameter perpendicular to the major axis) is more preferably 10 to 3,000. In addition, in this invention, when using a tubular thing as a titanium oxide structure (A), the diameter means an outer diameter. Moreover, the average diameter, average length, and average aspect ratio of the titanium oxide structure (A) can be measured, for example, by observation with an electron microscope (SEM or TEM).

  Furthermore, the titanium oxide structure (A) preferably has an insulating oxide film on the surface. The oxide that can be used for the insulating oxide film is not particularly limited, but the electron conduction band energy level is closer to the vacuum energy level than the electron conduction band energy level of the titanium oxide structure (A). There may be used one that can tunnel electrons from the dye to the titanium oxide structure (A). For example, magnesium oxide, aluminum oxide, silicon oxide, zirconium oxide, hafnium oxide, yttrium oxide, nickel oxide, chromium oxide, manganese oxide, copper oxide, germanium oxide, gallium oxide, etc. may be used. Aluminum oxide is preferred. These oxides can be used alone or in combination of two or more.

  The thickness of the insulating oxide film is not particularly limited, but is preferably 0.1 to 100 nm, particularly 0.1 to 10 nm, and more preferably 0.5 to 5 nm in order to prevent reverse electron transfer.

  The method for forming the insulating oxide film on the surface of the titanium oxide structure (A) is not particularly limited. For example, sputtering, dipping, spraying, vapor deposition, ion plating, plasma CVD Law. Among these, since the insulating oxide film can be formed up to the details of the titanium oxide structure (A), the dipping method is preferable. Specifically, the precursor of the insulating oxide is about 0.001 to 1 mol / L. What is necessary is just to immerse a titanium oxide structure (A) in the solution to contain, and to bake after that.

  Examples of the precursor of the insulating oxide include an alkoxide, a halide, an oxo halide, a carbonyl, an organic complex, and the like of a metal constituting the oxide. Specifically, for example, magnesium ethoxide, aluminum isopropoxide, aluminum butoxide, yttrium isopropoxide or the like may be used.

  The firing conditions are not particularly limited, but may be about 300 to 600 ° C., particularly about 450 to 550 ° C., about 1 to 60 minutes, particularly about 10 to 30 minutes.

<(A1) Titania-coated nanoscale carbon tube>
As the titania-coated nanoscale carbon tube (A1), for example, those described in JP 2010-24133 A can be used. Specifically, the surface of rod-like or fibrous carbon is coated with a coating layer composed of continuous titania nanoparticles.

  “Continuous” means that the titania nanoparticles are in close contact with the adjacent titania nanoparticles to form a coating layer as a whole, thereby forming an appropriate surface for supporting the dye. . It does not have a titanium oxide layer having a substantially smooth surface.

The rod-like or fibrous carbon rod-like or fibrous carbon is not particularly limited, but it is preferable to use a nanoscale carbon tube. The nanoscale carbon tube is preferably formed of a conductive material.

  In addition, this rod-like or fibrous carbon has a mean diameter perpendicular to the long axis of about 1 to 100 nm, since it can produce a titanium oxide-coated carbon material that is as fine as possible, has a large surface area, and has a long and continuous titanium oxide. It is preferable that the average length of the shaft is about 0.1 to 1000 μm and the average aspect ratio (average length of the long axis / average diameter perpendicular to the long axis) is about 5 to 1000000, and the average diameter orthogonal to the long axis is More preferably, the average length of the major axis is about 0.1 to 1000 μm, and the average aspect ratio (average length of the major axis / average diameter perpendicular to the major axis) is about 5 to 10,000. In addition, the average diameter orthogonal to the long axis, the average length of the long axis, and the average aspect ratio can be measured, for example, by observation with an electron microscope (SEM or TEM) of 10,000 times or more.

  The nano-scale carbon tube refers to a carbon tube having a nano-sized diameter, and iron or the like may be included in the inner space of the carbon tube.

As such a nanoscale carbon tube,
(I) single-walled carbon nanotubes or multi-walled carbon nanotubes,
(II) an amorphous nanoscale carbon tube developed by the present applicant,
(III) Nano flake carbon tube,
(IV) (a) a carbon tube selected from the group consisting of nano-flake carbon tubes and nested multi-walled carbon nanotubes and (b) iron carbide or iron, and 10 of the space in the tube of the carbon tube (a) An iron-carbon composite filled with iron carbide or iron of (b) in a range of -90%;
(V) These 2 or more types of mixtures etc. can be illustrated.

  The carbon nanotube (I) is a hollow carbon material in which a graphite sheet (that is, a carbon atom plane or graphene sheet having a graphite structure) is closed like a tube, its diameter is nanometer scale, and the wall structure has a graphite structure. is doing. Among the carbon nanotubes (I), those whose wall structure is closed in a tube shape with a single graphite sheet are called single-walled carbon nanotubes, and each of a plurality of graphite sheets is closed in a tube shape and is nested. What is present is called a nested multi-walled carbon nanotube. In the present invention, both of these single-walled carbon nanotubes and nested multi-walled carbon nanotubes can be used.

  The single-walled carbon nanotube preferably has an average diameter orthogonal to the major axis of about 1 to 10 nm, an average length of the major axis of about 0.1 to 500 μm, and an average aspect ratio of about 10 to 500,000. More preferably, the average diameter orthogonal to each other is about 1 to 10 nm, the average length of the major axis is about 0.1 to 500 μm, and the average aspect ratio is about 10 to 50,000.

  The nested multi-wall carbon nanotubes preferably have an average diameter orthogonal to the major axis of about 1 to 100 nm, an average length of the major axis of about 0.1 to 500 μm, and an average aspect ratio of about 1 to 500,000. More preferably, the average diameter orthogonal to the major axis is about 1 to 100 nm, the average length of the major axis is about 0.1 to 500 μm, and the average aspect ratio is about 5 to 10,000.

  The amorphous nanoscale carbon tube (II) is described in WO00 / 40509 (Japanese Patent No. 3355442), has a main skeleton made of carbon, has a diameter of 0.1 to 1000 nm, and has an amorphous structure. A nanoscale carbon tube having a linear shape and having a plane interval (d002) of a carbon network plane (002) measured by a diffractometer method in an X-ray diffraction method (incident X-ray: CuKα) ) Is 3.54 mm or more, particularly 3.7 mm or more, the diffraction angle (2θ) is 25.1 degrees or less, particularly 24.1 degrees or less, and the full width at half maximum of the 2θ band is 3.2 degrees or more, particularly 7 .0 degrees or more.

  The amorphous nanoscale carbon tube (II) is a thermally decomposable resin having a decomposition temperature of 200 to 900 ° C. in the presence of a catalyst comprising at least one metal chloride such as magnesium, iron, cobalt, nickel, etc. For example, it can be obtained by exciting polytetrafluoroethylene, polyvinylidene chloride, polyvinylidene fluoride, polyvinyl alcohol or the like.

  The shape of the thermally decomposable resin as a starting material may be any shape such as a film shape, a sheet shape, a powder shape, or a lump shape. For example, when obtaining a carbon material in which a thin amorphous nanoscale carbon tube is formed on a substrate, excitation treatment may be performed under appropriate conditions with a thermally decomposable resin applied or placed on the substrate. .

  As the excitation treatment, for example, heating is performed in an inert atmosphere, preferably in a temperature range of about 450 to 1800 ° C. and at or above the thermal decomposition temperature of the raw material, and in a temperature range of about room temperature to about 3000 ° C. and the thermal decomposition temperature of the raw material. The process of plasma processing etc. can be illustrated by the above.

  The amorphous nanoscale carbon tube (II) is a nanoscale carbon nanotube having an amorphous structure (amorphous structure), has a hollow linear shape, and has a highly controlled pore. The shape is mainly a cylinder, a quadrangular prism, etc., and at least one of the tips often has no cap (open). When the tip is closed, the shape is often flat.

  The amorphous nanoscale carbon tube (II) preferably has an average outer diameter of about 1 to 100 nm, an average length of about 0.1 to 1000 μm, an average aspect ratio of about 1 to 1000000, and an average outer diameter of 1. It is more preferable that the average length is about 0.1 to 1000 μm, and the average aspect ratio is about 5 to 10,000.

  Here, “amorphous structure” means a carbonaceous structure consisting of an irregular carbon network plane, not a graphite structure consisting of a continuous carbon layer of regularly arranged carbon atoms. The graphene sheets are irregularly arranged. From an image obtained by a transmission electron microscope, which is a typical analysis technique, the nanoscale carbon tube having an amorphous structure according to the present invention has a planar extent of the carbon network plane of the diameter of the amorphous nanoscale carbon tube (II). Less than 1 time. As described above, the amorphous nanoscale carbon tube (II) has an amorphous structure in which a large number of fine graphene sheets (carbon network surface) are irregularly distributed instead of a graphite structure on the wall portion. Is not continuous over the entire length in the tube longitudinal direction, but is discontinuous. In particular, the length of the carbon network surface constituting the outermost layer is less than 20 nm, particularly less than 5 nm.

Amorphous carbon generally does not exhibit X-ray diffraction, but exhibits broad reflection. In the graphitic structure, the carbon mesh planes are regularly stacked, so the carbon mesh plane spacing (d ₀₀₂ ) is narrowed, and the broad reflection shifts to the high angle side (2θ) and becomes gradually sharper (in the 2θ band). The full width at half maximum becomes narrower), and it can be observed as a d ₀₀₂ diffraction line (d ₀₀₂ = 3.354 mm when regularly stacked due to the graphite positional relationship).

In contrast, an amorphous structure generally does not exhibit X-ray diffraction as described above, but partially exhibits very weak coherent scattering. The theoretical crystallographic characteristics of the amorphous nanoscale carbon tube (II) according to the present invention measured by the diffractometer method in the X-ray diffraction method (incident X-ray = CuKα) are defined as follows: The carbon mesh plane spacing (d ₀₀₂ ) is 3.54 mm or more, more preferably 3.7 mm or more; the diffraction angle (2θ) is 25.1 degrees or less, more preferably 24.1 degrees or less. The half width of the 2θ band is 3.2 degrees or more, more preferably 7.0 degrees or more.

Typically, the amorphous nanoscale carbon tube (II) has a diffraction angle (2θ) by X-ray diffraction in the range of 18.9 to 22.6 degrees, and the carbon network plane spacing (d ₀₀₂ ) is 3. The half-width of the 2θ band is in the range of 7.6 to 8.2 degrees.

The term “straight” which is one term representing the shape of the amorphous nanoscale carbon tube (II) is defined as follows. That is, when the length of a transmission electron microscope according amorphous nanoscale carbon tubes (II) image is L, the length of time that extended the amorphous nanoscale carbon tubes (II) was L _0, L / L _It shall mean a shape characteristic in which ₀ is 0.9 or more.

  The tube wall portion of the amorphous nanoscale carbon tube (II) has an amorphous structure composed of a plurality of fine carbon network planes (graphene sheets) oriented in all directions. It has an advantage that it has an active point or is excellent in affinity with the resin.

  Further, the iron-carbon composite (IV) is described in JP-A No. 2002-338220 (Patent No. 3569806), and is selected from the group consisting of (a) nano-flake carbon tubes and nested multi-layer carbon nanotubes. And (b) iron carbide or iron. The carbon tube (a) is filled with iron carbide or iron (b) in a range of 10 to 90% of the space in the tube. That is, 100% of the space in the tube is not completely filled, and the iron carbide or iron is filled in the range of 10 to 90% of the space in the tube (that is, partially). It is characterized in that it is filled in). The wall portion is a patchwork-like or machete-like (so-called paper match-like) nanoflake carbon tube.

  In this specification, the “nano flake carbon tube” is a graphite sheet composed of a plurality of (usually many) flake-like graphite sheets assembled in a patchwork shape or a papier-like shape. It refers to a carbon tube made of aggregate.

Such iron-carbon composite (IV) is obtained according to the method described in JP-A-2002-338220.
(1) Ratio when the pressure is adjusted to 10 ⁻⁵ Pa to 200 kPa in an inert gas atmosphere, the oxygen concentration in the reactor is A (liter), and the oxygen amount is B (Ncc). A step of heating the iron halide to 600 to 900 ° C. in a reaction furnace adjusted to a concentration at which B / A is 1 × 10 ⁻¹⁰ to 1 × 10 ⁻¹ ; and (2) an inert gas in the reaction furnace. And a heat decomposable carbon source is introduced at a pressure of 10 ⁻⁵ Pa to 200 kPa and a heat treatment is performed at 600 to 900 ° C.

  Here, “Ncc”, which is a unit of the oxygen amount B, means a volume (cc) when converted to a standard state of gas at 25 ° C.

  The iron-carbon composite (IV) is composed of (a) a carbon tube selected from the group consisting of nano flake carbon tubes and nested multi-walled carbon nanotubes, and (b) iron carbide or iron, The space inside the carbon tube (that is, the space surrounded by the tube wall) is not completely filled, but a part of the space, more specifically about 10 to 90%, especially 30 to About 80%, preferably about 40 to 70%, is filled with iron carbide or iron.

  In the iron-carbon composite (IV), as described in JP-A-2002-338220, the carbon portion is cooled at a specific rate after the production steps (1) and (2) are performed. It becomes a nano flake carbon tube, and after performing manufacturing process (1) and (2), it heat-processes in inert gas, and becomes a multi-layer carbon nanotube of a nested structure by cooling with a specific cooling rate.

  The iron-carbon composite (IV) composed of the nano flake carbon tube (a-1) and iron carbide or iron (b) is typically cylindrical, but such a cylindrical iron-carbon composite. FIG. 3 shows a transmission electron microscope (TEM) photograph of a cross section substantially perpendicular to the longitudinal direction (obtained in Example 1 of JP-A-2002-338220), and FIG. 1 shows a side TEM photograph. .

  Moreover, the schematic diagram of the TEM image of such a cylindrical nano flake carbon tube is shown to (a-1) of FIG. In (a-1) of FIG. 4, 100 schematically shows a TEM image in the longitudinal direction of the nano flake carbon tube, and 200 shows a TEM image in a cross section substantially perpendicular to the longitudinal direction of the nano flake carbon tube. This is shown schematically.

  The nano flake carbon tube (a-1) constituting the iron-carbon composite (IV) typically has a hollow cylindrical shape, and when the cross section is observed by TEM, the arc-shaped graphene sheet image is concentric. Each graphene sheet image forms a discontinuous ring. When the longitudinal direction of the graphene sheet image is observed with a TEM, a substantially straight graphene sheet image has many parallel to the longitudinal direction. The graphene sheet images are arranged in layers, and each graphene sheet image has a feature that it is not continuous over the entire length in the longitudinal direction but is discontinuous.

  More specifically, the nano flake carbon tube (a-1) constituting the iron-carbon composite (IV) has a longitudinal direction as apparent from 200 in FIGS. 3 and 4 (a-1). When the cross section perpendicular to the TEM is observed by a TEM, a large number of arc-shaped graphene sheet images are concentrically (multi-layered tube shape), but each graphene sheet image is a complete image as shown in 210 and 214, for example. A closed ring is not formed, but a discontinuous ring is formed. Some graphene sheet images may be branched as indicated by 211. At the discontinuity point, the plurality of arc-shaped TEM images constituting one discontinuous ring may have a partially disturbed layer structure as indicated by 222 in FIG. As shown in 223, there may be a gap between adjacent graphene sheet images, but a large number of arc-shaped graphene sheet images observed by TEM form a multilayer tube structure as a whole. Yes.

  Further, as apparent from 100 of FIGS. 1 and 4 (a-1), when the longitudinal direction of the nano flake carbon tube (a-1) is observed with a TEM, a large number of substantially linear graphene sheet images are obtained. The graphene sheet images 110 are arranged over the entire length in the longitudinal direction of the iron-carbon composite (IV), although the graphene sheet images 110 are arranged in multiple layers substantially parallel to the longitudinal direction of the iron-carbon composite (IV) used in the present invention. It is not continuous and is discontinuous along the way. Some graphene sheet images may be branched as indicated by reference numeral 111 in FIG. Further, at the discontinuous point, among the TEM images arranged in a layered manner, the TEM image of one discontinuous layer is at least partly adjacent to the adjacent graphene sheet image as indicated by 112 in (a-1) of FIG. In some cases, they may overlap each other or may be slightly separated from adjacent graphene sheet images as indicated by 113, but a large number of substantially linear TEM images form a multilayer structure as a whole.

  The structure of the nano flake carbon tube (a-1) is greatly different from the conventional multi-walled carbon nanotube. That is, as indicated by reference numeral 400 in FIG. 4A-2, the multi-walled carbon nanotube (a-2) having a nested structure has substantially a TEM image of a cross section perpendicular to the longitudinal direction, as indicated by reference numeral 410. As shown by 300 in FIG. 4 (a-2), a straight graphene sheet image 310, etc., which is a concentric tube that is a complete circular TEM image, is continuous over the entire length in the longitudinal direction. It is a structure arranged in parallel (concentric cylindrical or nested structure).

  Although the details have not been fully elucidated yet, the nano-flake carbon tube (a-1) constituting the iron-carbon composite (IV) has a large number of flake-like graphene sheets in the form of patchwork or tension. It seems to form a tube as a whole.

  Such a nano flake carbon tube (a-1) and an iron-carbon composite (IV) made of iron carbide or iron (b) encapsulated in the space in the tube are described in Japanese Patent No. 2546114. The structure of the carbon tube is greatly different from that of the composite in which the metal is included in the space in the tube of the multi-walled carbon nanotube (a-2) having such a nested structure.

  When the nano-flake carbon tube (a-1) constituting the iron-carbon composite (IV) is observed with a TEM, each of the substantially linear graphene sheet images oriented in the longitudinal direction is individually The length of the graphene sheet image is usually about 2 to 500 nm, particularly about 10 to 100 nm. That is, as indicated by 100 in (a-1) of FIG. 4, a large number of TEM images of the substantially linear graphene sheet indicated by 110 are gathered to obtain a TEM image of the wall portion of the nanoflake carbon tube (a-1). The length of each substantially linear graphene sheet image is usually about 2 to 500 nm, particularly about 10 to 100 nm.

  Thus, in the iron-carbon composite (IV), the outermost layer of the nano flake carbon tube (a-1) constituting the wall portion is a discontinuous graphene sheet that is not continuous over the entire length in the tube longitudinal direction. The length of the outermost carbon network surface is usually about 2 to 500 nm, particularly about 10 to 100 nm.

The carbon portion of the wall portion of the nano-flake carbon tube (a-1) constituting the iron-carbon composite (IV) has a tube-like shape as a whole with a plurality of flake-shaped graphene sheets oriented in the longitudinal direction as described above. However, when measured by the X-ray diffraction method, the carbon fiber has an average distance (d ₀₀₂ ) between the carbon network surfaces of 0.34 nm or less.

  Further, the thickness of the wall portion made of the nano-flake carbon tube (a-1) of the iron-carbon composite (IV) is 49 nm or less, particularly about 0.1 to 20 nm, preferably about 1 to 10 nm, It is substantially uniform over the entire length.

  As described above, the carbon tube constituting the iron-carbon composite (IV) obtained by performing the specific heating step after performing the steps (1) and (2) is a multi-layer carbon nanotube having a nested structure. (A-2).

  In the nested multi-walled carbon nanotube (a-2) thus obtained, a TEM image of a cross section perpendicular to the longitudinal direction forms a substantially complete circle, as indicated by 400 in FIG. 4 (a-2). And a graphene sheet image that is continuous over the entire length in the longitudinal direction thereof is arranged in parallel (a concentric cylindrical or nested structure).

The carbon portion of the wall portion of the multi-walled carbon nanotube (a-2) having a nested structure constituting the iron-carbon composite (IV) has an average distance (d ₀₀₂₎ between the carbon network surfaces when measured by an X-ray diffraction method. ) Has a graphite structure of 0.34 nm or less.

  Further, the thickness of the wall portion composed of the multi-walled carbon nanotube (a-2) having a nested structure of the iron-carbon composite (IV) is 49 nm or less, particularly about 0.1 to 20 nm, preferably about 1 to 10 nm. And substantially uniform over the entire length.

  In the present specification, the filling ratio of the space portion in the carbon tube selected from the group consisting of the nano flake carbon tube (a-1) and the multi-layer carbon nanotube (a-2) with a nested structure by iron carbide or iron (b) ( 10 to 90%), the iron-carbon composite (IV) is observed with a transmission electron microscope, and the area of the image of the space of each carbon tube (that is, the space surrounded by the tube wall of the carbon tube), It is the ratio of the area of the image of the part filled with iron carbide or iron (b).

  As for the filling form of iron carbide or iron (b), there are a form in which the space in the carbon tube is continuously filled, a form in which the space in the carbon tube is intermittently filled, etc. Filled intermittently. Therefore, the iron-carbon composite (IV) should also be referred to as a metal-encapsulated carbon complex, an iron compound-encapsulated carbon complex, iron carbide, or an iron-encapsulated carbon complex.

  The iron carbide or iron (b) included in the iron-carbon composite (IV) is oriented in the longitudinal direction of the carbon tube, has high crystallinity, and is filled with iron carbide or iron (b). The ratio of the area of the TEM image of crystalline iron carbide or iron (b) to the area of the TEM image in the range (hereinafter referred to as “crystallization rate”) is generally about 90 to 100%, particularly 95 to 100%. Degree.

  The high crystallinity of the iron carbide or iron (b) encapsulated means that the TEM images of the inclusions are arranged in a lattice when observed from the side of the iron-carbon composite (IV). It is clear, and it is also clear from the fact that a clear diffraction pattern is obtained in electron beam diffraction.

  Further, the inclusion of iron carbide or iron (b) in the iron-carbon composite (IV) can be easily confirmed by an electron microscope and EDX (energy dispersive X-ray detector).

  The iron-carbon composite (IV) that can be used in the present invention is less curved, linear, and has a uniform thickness over the entire length of the wall portion. And has a homogeneous shape. The shape is columnar and mainly cylindrical.

  The iron-carbon composite (IV) preferably has an average outer diameter of about 1 to 100 nm, an average length of about 0.1 to 1000 μm, an average aspect ratio of about 1 to 1000000, and an average outer diameter of 1. It is more preferable that the average length is about 0.1 to 1000 μm, and the average aspect ratio is about 5 to 10,000.

  The term “linear”, which is one term representing the shape of the iron-carbon composite (IV), is defined as follows. That is, a carbonaceous material containing an iron-carbon composite (IV) is observed in a range of 200 to 2000 nm by a transmission electron microscope, the length of the image is W, and the length when the image is linearly extended When the thickness is Wo, it means a shape characteristic in which the ratio W / Wo is 0.8 or more, particularly 0.9 or more.

  The iron-carbon composite (IV) has the following properties when viewed as a bulk material. That is, in the present invention, iron is contained in a range of 10 to 90% of the space in the tube of the carbon tube selected from the nano flake carbon tube (a-1) and the multi-walled carbon nanotube (a-2) having the nested structure as described above. Alternatively, the iron-carbon composite (IV) filled with iron carbide (b) is not a trace amount that can be barely observed by microscopic observation, but is a bulk material containing a large number of the iron-carbon composite (IV). Thus, it is obtained in a large amount in the form of a carbonaceous material containing an iron-carbon composite (IV), or a material to be called iron carbide or an iron-containing carbonaceous material.

  An electron micrograph of a carbonaceous material composed of the nano-flake carbon tube (a-1) produced in Example 1 of JP-A-2002-338220 and iron carbide (b) filled in the space in the tube, As shown in FIG.

  As can be seen from FIG. 2, in the carbonaceous material containing the iron-carbon composite (IV), basically, in almost all (particularly 99% or more) carbon tubes, the space portion (that is, carbon) It is normal that 10 to 90% of the space (space surrounded by the tube wall of the tube) is filled with iron carbide or iron (b), and there is substantially no carbon tube in which the space is not filled. . However, in some cases, a small amount of carbon tubes not filled with iron carbide or iron (b) may be present.

  Moreover, in the carbonaceous material containing iron-carbon composite (IV), the iron-carbon composite in which iron or iron carbide (b) is filled in 10 to 90% of the space in the carbon tube as described above. Although (IV) is a main component, soot may be included in addition to the iron-carbonaceous complex (IV). In such a case, components other than the iron-carbonaceous complex (IV) are removed to improve the purity of the iron-carbonaceous complex (IV) in the carbonaceous material, and the iron-carbon complex is substantially improved. A carbonaceous material consisting only of (IV) can also be obtained.

  Also, unlike materials that could only be confirmed in microscopic amounts by conventional microscopic observation, a carbonaceous material containing iron-carbon composite (IV) can be synthesized in large quantities, and its weight should be easily set to 1 mg or more. Can do.

The carbonaceous material is attributed to iron or iron carbide (b) contained in powder X-ray diffraction measurement in which X-rays of CuKα are irradiated with an irradiation area of 25 mm ² or more with respect to 1 mg of the carbonaceous material. Of the peaks at 40 ° <2θ <50 °, the peak showing the strongest integrated intensity is Ia, and 26 ° <2θ <27 attributed to the average distance (d ₀₀₂ ) between the carbon network surfaces of the carbon tubes. In the case of the integrated intensity Ib of the peak at °, the ratio R (= Ia / Ib) of Ia to Ib is preferably about 0.35 to 5, particularly about 0.5 to 4, more preferably 1 It is about ~ 3.

In this specification, the ratio of Ia / Ib is referred to as an R value. When the carbonaceous material containing the iron-carbon composite (IV) is observed with an X-ray irradiation area of 25 mm ² or more in the X-ray diffraction method, this R value has a peak intensity as an average value of the entire carbonaceous material. In order to be observed, it is not the inclusion rate or filling rate in one iron-carbon composite (IV) that can be measured by TEM analysis, but the entire carbonaceous material that is an aggregate of iron-carbon composite (IV). The average value of iron carbide or iron (b) filling rate or inclusion rate is shown.

  In addition, the average filling rate as the whole carbonaceous material containing many iron-carbon composites (IV) observes a several visual field by TEM, and the several iron-carbon composite (IV) observed in each visual field. The average filling rate of iron carbide or iron (b) can be measured, and the average filling rate of a plurality of visual fields can be calculated. When measured by such a method, the average filling rate of iron carbide or iron (b) as a whole carbonaceous material composed of the iron-carbon composite (IV) used in the present invention is about 10 to 90%, particularly 40 to 40%. About 70%.

  The iron or iron carbide (b) is iron-encapsulated by acid treatment of the iron-carbon composite (IV) partially encapsulated in the inner space of the nanoflake carbon tube (a-1). Iron carbide (b) is dissolved and removed, and a hollow nanoflake carbon tube (III) in which iron or iron carbide (b) is not present in the space in the tube can be obtained.

  Examples of the acid used for the acid treatment include hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, and the like, and the concentration is preferably about 0.1 to 2N. As an acid treatment method, various methods can be used. For example, 1 g of iron-encapsulated nanoflake carbon tube is dispersed in 100 ml of 1N hydrochloric acid, and stirred at room temperature for 6 hours, followed by filtration and separation. Thereafter, the same treatment is performed twice with 100 ml of 1N hydrochloric acid to obtain a hollow nanoflake carbon tube (III).

  The basic configuration of the nano flake carbon tube (III) is not particularly changed by this acid treatment. Therefore, also in the hollow nano flake carbon tube (III) in which iron or iron carbide (b) does not exist in the inner space of the tube, the length of the carbon network surface constituting the outermost surface is 500 nm or less, particularly 2 ~ 500 nm, in particular 10-100 nm.

Covering layer The covering layer is composed of a series of titania nanoparticles.

  The crystal structure of the titania nanoparticles is not particularly limited, but preferably contains at least one selected from the group consisting of anatase-type titanium oxide, rutile-type titanium oxide and brookite-type titanium oxide, and has activity against light. From a high point, what contains anatase type titanium oxide is more preferable. The crystal structure of titania nanoparticles can be measured by, for example, X-ray diffraction method, Raman spectroscopic analysis or the like.

  The average particle diameter of the titania nanoparticles is preferably 1 to 200 nm, more preferably 1 to 50 nm from the viewpoint that more dye can be adsorbed and light can be absorbed. However, from the viewpoint of the light confinement effect inside the battery, titanium oxide particles having a large light scattering may be used in combination. In addition, an average particle diameter can be measured by electron microscope (SEM) observation etc., for example.

  The thickness of the coating layer is preferably 2 to 500 nm, more preferably 5 to 200 nm, from the viewpoint of preventing leakage current. In addition, the thickness of a coating layer can be measured by electron microscope (SEM or TEM) observation etc., for example.

Titania-coated nanoscale carbon tube (A1)
In the titania-coated nanoscale carbon tube (A1), the surface of rod-like or fibrous carbon is covered with a coating layer in which titania nanoparticles are connected. Thereby, as shown in FIG. 5, the fine unevenness | corrugation exists in the surface of a rod-shaped or fibrous titanium oxide covering carbon material. By using a titanium oxide-coated carbon material having fine irregularities on the surface for a dye-sensitized solar cell, a large amount of the dye can be supported and incident light can be efficiently absorbed. Then, electrons can be efficiently generated, and as shown in FIG. 6, the electrons can be efficiently transported to the transparent electrode through the carbon as the core material.

  When a titania-coated nanoscale carbon tube (A1) that is not sufficiently covered with a coating layer and has a large exposed carbon area as shown in FIG. 7 is used, light is absorbed as shown in FIG. The electrons generated by this cause reverse electron transfer from the carbon into the electrolyte solution, so that the electrons cannot be carried efficiently. From such a viewpoint, in the titania-coated nanoscale carbon tube (A1), the coverage of the titania nanoparticles on the surface of the rod-like or fibrous carbon is preferably 70 to 100%, particularly preferably 85 to 100%. The surface element ratio of carbon / titanium is preferably 0/100 to 70/30 (atomic ratio), more preferably 0/100 to 50/50 (atomic ratio). In addition, the surface coverage (ratio of the portion covered with the coating layer on which the titania nanoparticles are continuous on the surface of the carbon) can be determined by observation with an electron microscope (SEM or TEM), etc. The surface element ratio can be measured, for example, by X-ray photoelectron spectroscopy.

  The titania-coated nanoscale carbon tube (A1) preferably has a powder resistance of 10 Ω · m or less, more preferably 5 Ω · m or less, more preferably 1Ω from the point of obtaining a larger current. -What is m or less is still more preferable. The powder resistance is preferably smaller, and the lower limit is not particularly limited, but is about 0.0001 Ω · m. The method for measuring the titanium oxide-coated carbon material is not particularly limited. For example, the titanium oxide-coated carbon material is processed into a flat plate having a thickness of 0.3 mm at a pressure of 10 MPa, and a current value flowing by applying a voltage of 1 V between pellets is measured. Can be measured.

The titania-coated nanoscale carbon tube (A1) preferably has a specific surface area of 50 m ² / g or more from the viewpoint of increasing the surface area, carrying a large amount of dye, and efficiently absorbing incident light. Is more preferably 70 m ² / g or more, more preferably 80 m ² / g or more. The specific surface area is preferably larger, and the upper limit is not particularly limited, but is about 3000 m ² / g. The specific surface area can be measured by the BET method or the like.

Production method In addition, the titania-coated nanoscale carbon tube (A1) is formed by a method including a step of forming a coating layer in which titania nanoparticles are continuous on a surface of a rod-like or fibrous carbon by precipitation reaction from a titanium fluoro complex. It is obtained by forming a coating layer composed of titania nanoparticles.

  Even a sol-gel method using titanium alkoxide as a raw material or a wet method using titanium tetrachloride or the like as a raw material can form a coating layer in which titania nanoparticles are continuous on the surface of rod-like or fibrous carbon. A method of depositing titania nanoparticles by a precipitation reaction from is preferred.

  Specifically, for example, rod-like or fiber-like carbon is treated with an acid such as nitric acid, sulfuric acid, hydrochloric acid, and then dispersed in a solvent containing a dispersant, and then titanium fluorocomplex and boric acid, aluminum chloride, etc. In this method, titanium oxide is precipitated by adding a fluoride ion scavenger or the like. Thereafter, heat treatment may be performed at 300 to 550 ° C. in order to strengthen the bond between titanium oxides.

  Here, the titanium fluoro complex is not particularly limited, and examples thereof include ammonium hexafluorotitanate, hexafluorotitanic acid, and potassium hexafluorotitanate.

  Although it does not restrict | limit especially as said solvent, For example, the solvent etc. which a titanium fluoro complex melt | dissolves, such as water, the mixed solvent of water and alcohol, etc. are mentioned.

Further, as the dispersant, sodium naphthalene sulfonate formalin condensate-based dispersant,
Anionic dispersants such as polycarboxylate-based dispersants, maleic acid α-olefin copolymer salt-based dispersants, anionic surfactants; cationic properties such as quaternary ammonium salt-based dispersants and alkylamine salts Dispersants; Nonionic dispersants such as cellulose dispersants, polyvinyl alcohol dispersants, and polyether dispersants; and other dispersants such as amphoteric surfactants. Among these, nonionic dispersants are preferable, and polyether dispersants are more preferable.

  In the above, as the titania-coated nanoscale carbon tube (A1), the rod-like or fibrous carbon surface has been described as being coated with a coating layer in which titania nanoparticles are continuous, but other forms, for example, A material in which the surface of a rod-like or fibrous carbon is coated with a smooth titania layer can also be used.

<(A2) Titania nanotube>
The titania nanotube (A2) may be a known titania nanotube (A2a), a titania nanotube (A2b) in which titania nanoparticles are linked, or a titania nanotube (A2c) containing 30% or more of titanium oxide having a crystal form of a magneli phase. Etc.

Known titania nanotube (A2a)
When known titania nanotubes are used, for example, those described in Japanese Patent Nos. 3513738 and 398533 may be used.

Titania nanotubes composed of a series of titania nanoparticles (A2b)
As the titania nanotube (A2b) in which titania nanoparticles are connected, for example, those described in JP 2010-24132 A can be used. Specifically, those described below can be used.

  “Continuous” means that titania nanoparticles are in intimate contact with adjacent titania nanoparticles, thereby forming an appropriate surface for supporting the dye. In addition, it is not a titania nanotube which has a substantially smooth surface like a well-known titania nanotube (A2a).

  In the titania nanotube (A2b) in which the titania nanoparticles are connected, the titania nanoparticles are connected so as to form a tubular shape to form the titania nanotube. Accordingly, as shown in FIG. 9, fine irregularities exist on the surface of the titania nanotube (A2b) in which the titania nanoparticles are continuous. As a result, a large amount of dye is supported and incident light can be efficiently absorbed. Then, electrons are generated efficiently, and the adjacent titania nanoparticles are in intimate contact with each other as shown in FIG. 10. Therefore, the electrons can be efficiently transferred to the transparent electrode through the adjacent titania nanoparticles.

  The crystal structure of the titania nanoparticles is not particularly limited, but preferably contains at least one selected from the group consisting of anatase-type titanium oxide, rutile-type titanium oxide and brookite-type titanium oxide, and has activity against light. From a high point, what contains anatase type titanium oxide is more preferable. The crystal structure of titania nanoparticles can be measured by, for example, X-ray diffraction or Raman spectroscopic analysis. In addition to anatase-type titanium oxide, rutile-type titanium oxide, and brookite-type titanium oxide, titania nanoparticles further include at least one selected from the group consisting of trivalent titanium oxide and tetravalent titanium oxide. It is preferable to include.

In addition to the above, the titania nanoparticles preferably include titania having a crystal form of a Magneli phase structure. Although the specific configuration of the titania having the crystal form of the Magneli phase structure is not clear, it is represented by a composition formula: Ti _n O _2n-1 (n: 4 to 10) and has a conductivity equivalent to that of a metal. I have it. By including titania having a crystal form of this magnetic phase structure, the conductivity of the titania nanotube (A2b) can be improved.

  The average particle diameter of the titania nanoparticles is preferably 1 to 200 nm, more preferably 1 to 50 nm from the viewpoint that more dye can be adsorbed and light can be absorbed. In addition, an average particle diameter can be measured by electron microscope (SEM or TEM) observation etc., for example.

The titania nanotube (A2b) preferably has a specific surface area of 20 m ² / g or more, and has a specific surface area of 70 m ² / g or more from the viewpoint of carrying a large amount of dye and efficiently absorbing incident light. Is more preferable, and more preferably 80 m ² / g or more. The specific surface area is preferably larger, and the upper limit is not particularly limited, but is about 3000 m ² / g. The specific surface area can be measured by the BET method or the like.

The titania nanotube (A2b) preferably has a powder resistance of 3 × 10 ⁶ Ω · m or less, preferably 1 × 10 ⁵ Ω · m or less, from the point of obtaining a larger current. More preferred. The powder resistance is preferably as small as possible, and the lower limit is not particularly limited, but is about 0.1 Ω · m. The method for measuring the powder resistance of the titania nanotube (A2b) is not particularly limited. For example, a current flowing by applying a voltage of 1 V between the pellets processed into a plate having a thickness of 0.3 mm at a pressure of 10 MPa. It can be measured by measuring the value.

  The thickness of the titania nanotube (A2b) is preferably about 2 to 500 nm, more preferably about 5 to 200 nm from the viewpoint of preventing leakage current. The wall thickness means the difference between the outer diameter and inner diameter of the titania nanotube (A2b). Moreover, the thickness of the titania nanotube (A2b) can be measured, for example, by observation with an electron microscope (SEM or TEM).

  The titania nanotube (A2b) as described above can be obtained, for example, by a method of eliminating nanoscale carbon existing in the titania-coated nanoscale carbon tube (A1). This has the advantage that titania has an anatase type crystal structure and adhesion is increased. Here, the nanoscale carbon tube may be eliminated, and the method is not particularly limited, but it is easy to eliminate the oxidation. For example, in the case of heating in air to cause oxidation to disappear, the heating temperature is preferably 450 ° C. or higher, more preferably 550 ° C. or higher, further preferably 600 to 750 ° C., particularly preferably 600 to 700 ° C. .

Titania nanotube (A2c) containing 30% or more of titania having a crystalline form of the magnetic phase
The titania nanotube (A2c) is composed of titania nanoparticles, and 30% or more of the titanium oxide fine particles are titania having a crystalline form of a Magneli phase structure. The titania nanotube (A2b) also includes titania having a crystal form of a magnetic phase structure, but the amount is small and does not exceed 30%.

  The average particle diameter of the titania nanoparticles constituting the titania nanotube (A2c) is 1 to 100 nm, preferably 30 to 80 nm. Thus, by setting the average particle diameter of titania nanoparticles within the above range, the active specific surface area can be increased, so that more dye can be adsorbed and light can be easily absorbed. In addition, the average particle diameter of a titania nanoparticle can be measured by electron microscope (SEM or TEM) observation etc., for example.

  In the titania nanotube (A2c), 30% or more, preferably 50% or more, and more preferably 70% or more of the titania nanoparticles are titanium oxide having a crystalline form of a Magneli phase structure. Conductivity can be improved by using 30% or more of the titania nanoparticles as titania having a crystal form of a magnetic phase structure.

The titania having the crystal form of the magnetic phase structure contained in the titania nanotube (A2c) is represented by the general formula (1):
TiOx
(Wherein x is 1.75 to 1.95)
Among them, those having x of 1.75 to 1.85 have the same degree of conductivity as metal. Specifically, for _{example, Ti 4 O 7, Ti 5} O 9, Ti 6 O 11, Ti 8 O 15 and the like. Among these, T ₄ O ₇ having higher conductivity is preferable. These titanias having the crystal form of the Magneli phase structure may be used alone or in combination of two or more.

  The titania nanotube (A2c) may contain anatase-type titania, rutile-type titania, brookite-type titania and the like in addition to the titanium oxide having the crystal form of the above-mentioned magnetic phase structure. In the case of containing titania other than titania having a crystalline form of the magnetic phase structure, among the above three types, anatase titania is preferable because of its high activity against light. Of the above three types, only one type may be used, or two or more types may be used.

  The crystal structure of titania nanoparticles can be measured by, for example, X-ray diffraction, electron beam diffraction, Raman spectroscopic analysis, or the like.

  The thickness of the titania nanotube (A2c) is preferably about 1 to 250 nm, more preferably about 5 to 200 nm from the viewpoint of preventing leakage current. The wall thickness means the difference between the outer diameter and the inner diameter of the titania nanotube (A2c). Moreover, the thickness of the titania nanotube (A2c) can be measured, for example, by observation with an electron microscope (SEM or TEM).

  Moreover, the titania nanotube (A2c) may have a smooth surface or may have irregularities. When the surface has irregularities, it is preferable to use titania nanotubes (A2c) in which titania nanoparticles are connected.

  If the titania nanotube (A2c) is made of a series of titania nanoparticles, fine irregularities can be formed on the surface of the titania nanotube (A2c). Thus, if titania nanotubes (A2c) having fine irregularities on the surface are used for a dye-sensitized solar cell, a large amount of the dye is supported, incident light is efficiently absorbed, and electrons are efficiently generated. be able to. In addition, since the titania nanotube (A2c) contains a large amount of titania having a crystal form of a magnetic phase structure, electrons can be efficiently transferred to the transparent electrode through the adjacent titania.

The titania nanotube (A2c) preferably has a specific surface area of 20 m ² / g or more, and has a specific surface area of 70 m ² / g or more, from the viewpoint of carrying a large amount of dye and absorbing incident light efficiently. Is more preferable, and more preferably 80 m ² / g or more. The specific surface area is preferably larger, and the upper limit is not particularly limited, but is about 3000 m ² / g. The specific surface area can be measured by the BET method or the like.

The titania nanotube (A2c) preferably has a powder resistance of 3 × 10 ⁶ Ω · m or less, preferably 1 × 10 ⁵ Ω · m or less, from the point of obtaining a larger current. More preferred. The powder resistance is preferably as small as possible, and the lower limit is not particularly limited, but is about 1 × 10 ⁻⁶ Ω · m or less Ω · m. The method for measuring the powder resistance of the titania nanotube (A2c) is not particularly limited. For example, a current flowing by applying a voltage of 1 V between the pellets processed into a plate having a thickness of 0.3 mm at a pressure of 10 MPa. It can be measured by measuring the value.

  The titania nanotube (A2c) can be produced, for example, by a method in which the titania-coated nanoscale carbon tube (A1) is heat-treated at 950 ° C. or lower in a reducing atmosphere. That is, in the method for producing titania nanotubes (A2b), the heat treatment atmosphere may be a reducing atmosphere. Thereby, a titania nanotube (A2c) having a large specific surface area and a large amount of titania having a crystalline form of a Magneli phase in titania nanoparticles can be obtained.

  The reducing atmosphere is not particularly limited, but may be an atmosphere having a reducing gas. Examples of the reducing gas include hydrogen, carbon monoxide, nitric oxide, unsaturated hydrocarbon gases (acetylene, ethylene, etc.), saturated hydrocarbon gases (methane, ethane, propane, etc.), hydrogen , At least one selected from the group consisting of carbon monoxide and acetylene is preferable. As described above, by performing the heat treatment in a reducing atmosphere, it is possible to increase the content of titania having a crystal form of the magnetic phase structure in the obtained titania nanotube (A2c).

  In the present invention, the reducing atmosphere does not necessarily need to be an atmosphere made of only the reducing gas, and may contain, for example, an inert gas such as nitrogen or argon. When setting it as the atmosphere containing an inert gas, the reducing gas should just contain 50 mol% or more.

  Even when heat treatment is performed in a reducing atmosphere, when the heat treatment temperature described later is not satisfied, that is, when heat treatment is performed at a high temperature, titania nanoparticles are aggregated, and the average particle diameter is about 1 μm or more. For this reason, the active specific surface area cannot be increased, and sufficient conductivity cannot be obtained.

  The heat treatment temperature is 950 ° C. or lower, preferably 650 to 850 ° C. As described above, when the heat treatment temperature is too high, the titanium oxide fine particles are aggregated and the average particle diameter is about 1 μm or more.

  In addition, even when heat-treated at 950 ° C. or lower, when it is not in a reducing atmosphere, for example, when heat-treated in the air or under an inert atmosphere, the titania nanotube (A2c) obtained contains titania having a crystalline form of the magnetic phase structure. The amount cannot be large enough.

<(A3) Titania nanorods>
The titania nanorod (A3) may be a known titania nanorod (A3a) or a titania nanorod (A3b) having a large aspect ratio.

Titania nanorods with large aspect ratio (A3b)
The titania nanorod (A3b) is a plate-like structure having a plurality of titanium oxide crystals and an aspect ratio of 10 or more. Moreover, the arithmetic average roughness (Ra) of the side surface in the longitudinal direction is less than 10% of the average width.

  “Plate” means that the length (long side) is larger than the width (short side), and it does not necessarily have to be a complete plane, and may be a curved surface. However, cylinders (tubes) are excluded.

  The “titanium oxide structure containing a plurality of titanium oxide crystals” is usually a polycrystalline body. In the present invention, the titania nanorod (A3b) is intended to be composed of a plurality of plate-like crystals. That is, as shown in FIG. 11A, the titania nanorod (A3b) is not a conventionally known titanium oxide nanotube having a cylindrical shape and a crystal plane extending from end to end of the titanium oxide structure in the longitudinal direction. As shown in FIG. 11B, the particulate crystals are not continuous.

The titania nanorods (A3b) are preferably linear and less bent from the viewpoint of improving the dispersibility because the titania nanorods (A3b) are not easily entangled with each other. Specifically, when the length of the titanium oxide structure image by electron microscope observation (SEM or TEM) is L and the length when the titanium oxide structure is stretched is L ₀ , L / L ₀ A shape characteristic with a value of 0.7 or more is preferable.

  The titania nanorods (A3b) preferably have parallel long sides facing each other. In this specification, the term “parallel” does not need to be completely parallel, and includes those that are substantially parallel. Specifically, it is preferable that the angle formed by the long sides facing each other is 0 to 10 ° except for the end 100 nm of the titania nanorod (A3b).

The shape of the titania nanorod (A3b) (L / L ₀ and the angle formed between the long sides facing each other) can be measured, for example, by observation with an electron microscope (SEM or TEM).

  Moreover, the titania nanorod (A3b) has an arithmetic average roughness (Ra) of the side surface in the longitudinal direction of less than 10%, preferably about 0 to 5% of the average width. Specifically, the calculated average roughness (Ra) of the longitudinal side surface is less than 5 nm, preferably about 0 to 3 nm. In addition, the arithmetic mean roughness of the side surface in the longitudinal direction can be measured, for example, by measuring the linear shape or curved shape of the surface of the titania nanorod (A3b) using an image analyzer from an electron micrograph of TEM.

  The titania nanorod (A3b) contains a plurality of titania crystals. In this specification, “containing a plurality of titania crystals” specifically includes, as shown in FIG. 12 (a), those containing a plurality of partially crystallized ones, as shown in FIG. 12 (b). As shown in Fig. 12 (c), a long crystal in a main crystal (longer than 50 nm) contains a plurality of types of short crystals (longer than 50 nm). It is a concept including any of those containing short crystals (length is 50 nm or less).

  More specifically, it is preferable to contain 30% or more, particularly 50% or more of crystals having a length in the longitudinal direction of 50 nm or less. Thus, by containing 30% or more of crystals having a length in the longitudinal direction of 50 nm or less, aggregation is unlikely to occur while achieving both strength, conductivity, and specific surface area.

The specific crystal structure of the titania nanorod (A3b) is not particularly limited, but preferably contains at least one of anatase type, brookite type, and TiO ₂ -B type, and includes anatase type and / or TiO 2. It is more preferable to include _2- B type, and it is more preferable to include at least anatase type. The crystal structure of the titania nanorod (A3b) can be measured by, for example, X-ray diffraction, electron beam diffraction, Raman spectroscopic analysis, or the like.

The titania nanorod (A3b) has a specific surface area of preferably 15 m ² / g or more, more preferably 20 m ² / g or more, from the viewpoint that it can carry a large amount of dye and can absorb incident light efficiently. The specific surface area is preferably larger, and the upper limit is not particularly limited, but is about 3000 m ² / g. The specific surface area can be measured by the BET method or the like.

  The content of the alkali metal in the titania nanorod (A3b) is preferably 2000 ppm or less, more preferably 500 ppm or less, from the viewpoint of ensuring activity. In addition, when heat resistance is required, since it may be preferable that there is much Na, alkali metal content should just be set suitably according to the objective. The alkali metal content can be measured by ion chromatography, ICP emission spectroscopic analysis, or the like.

In the titania nanorod (A3b), the powder resistance under 10 MPa is preferably 3 × 10 ⁶ Ω · m or less and more preferably 1 × 10 ⁵ Ω · m or less from the viewpoint of obtaining a larger current. The powder resistance is preferably as small as possible, and the lower limit is not particularly limited, but is about 0.1 Ω · m. The method for measuring the powder resistance of the titania nanorod (A3b) is not particularly limited. For example, a current flowing by applying a voltage of 1 V between the pellets processed into a plate having a thickness of 0.3 mm at a pressure of 10 MPa. It can be measured by measuring the value.

  The titania nanorod (A3b) does not lose its shape even in a high temperature region of about 500 to 900 ° C., and can maintain a specific surface area and an aspect ratio. That is, the titania nanorod (A3b) can maintain a high specific surface area, dispersibility in a solution, and high strength even at a high temperature.

The manufacturing method of the titania nanorod (A3b) is, for example,
(1) A step of bringing a 3 to 20 mol / L aqueous alkali solution into contact with titania nanoparticles having an average particle diameter of 50 nm or less at a temperature higher than 160 ° C.

  In the step (1), specifically, although not limited thereto, titania nanoparticles having an average particle diameter of 50 nm or less are added to an alkaline aqueous solution of 3 to 20 mol / L, and then from 160 ° C. What is necessary is just to heat to high temperature.

  As the alkaline aqueous solution, an aqueous solution of an alkali metal hydroxide is preferable from the viewpoint of dissolving the surface of the raw material titanium oxide and promoting the reaction. In addition, it is good also as an aqueous solution containing 2 or more types of alkalis as an alkali, and it is more preferable to set it as the aqueous solution which contains 50 weight% or more of sodium hydroxide. When an alkali other than sodium hydroxide is included as the alkali, for example, potassium hydroxide, lithium hydroxide or the like may be used in combination with sodium hydroxide.

  The concentration of the alkaline aqueous solution is such that the titania nanorods (A3b) composed of plate-like titania crystals having a large aspect ratio are produced without taking a long time by dissolving the surface of the raw material titanium oxide and maintaining the fluidity of the reaction solution. From the point which can be performed, it is 3-20 mol / L, Preferably it is about 5-15 mol / L. In addition, when using the aqueous solution containing 2 or more types of alkalis, the density | concentration of aqueous alkali solution is the sum total of the density | concentration of all the alkalis.

  The form of titania nanoparticles used is not particularly limited. Known or commercially available titania nanoparticles may be used as they are, or when the particle size is large, they may be used by dry or wet pulverization using a planetary ball mill, paint shaker or the like.

  Moreover, it is preferable that the titania nanoparticles exhibit at least anatase type.

  The average particle diameter of the titania nanoparticles to be used is 50 nm or less, preferably 30 nm or less from the viewpoint that the titania nanorod (A3b) of the present invention can be produced at a lower temperature and in a shorter time. If the average particle diameter of the titania nanoparticles used is too large, it is difficult to produce titania nanorods (A3b). The average particle size of the titania nanoparticles is preferably small, and the lower limit is not particularly set, but is usually about 3 nm. The average particle diameter of titania nanoparticles can be measured, for example, by observation with an electron microscope (SEM or TEM).

  The amount of titania nanoparticles added to the aqueous alkaline solution is not particularly limited, but is about 0.01 to 1 mol / L, preferably 0.05 to 0.00, from the viewpoint of balancing the fluidity and productivity of the reaction solution. What is necessary is just 5 mol / L.

  The temperature at which the aqueous alkali solution and the titania nanoparticles are brought into contact is a temperature higher than 160 ° C. The upper limit of the contact temperature is not particularly limited, but is usually 370 ° C., which is the critical point of water. The temperature is preferably about 180 to 370 ° C, more preferably about 200 to 300 ° C. If the contact temperature is too low, titania nanorods (A3b) cannot be produced, and a massive structure in which titania nanoparticles are aggregated or an extremely small titania nanorod is entangled to produce only a massive structure as a whole. That is, a titania nanorod having a high aspect ratio and high dispersibility cannot be obtained. In Patent No. 3513738 and Patent No. 3985533, it is difficult to produce a tube-shaped product at 160 ° C. or higher (Patent No. 3513738 [0024] and Patent No. 3985533 [0024]). On the other hand, when the contact is made at a low temperature, the titania nanorods are entangled with each other, so that a high aspect ratio and high dispersibility titania nanorod cannot be obtained. Further, if the contact temperature is too high, it is not desirable in terms of the amount of energy used and safety.

  The time for contacting the aqueous alkali solution with the titania nanoparticles is not particularly limited, and may be about 1 to 24 hours.

  The preferred range of the average particle diameter, contact temperature, and contact time of the titania nanoparticles has a correlation, and when using titania nanoparticles having a larger average particle diameter, it is preferable to increase the contact temperature. For example, when the titania nanoparticles having an average particle diameter of 7 nm are used and the contact time is 12 hours, the contact temperature may be set to a temperature higher than 160 ° C., but the contact time is determined using titania nanoparticles having an average particle diameter of 25 nm. In the case of 12 hours, the contact temperature is preferably 185 ° C. or higher.

In the method for producing titania nanorods (A3b), after the above step (1),
(2) It is preferable to include a step of bringing the titania nanorod (A3b) obtained in the step (1) into contact with at least one selected from the group consisting of water, an acid, and an ion exchange resin.

  Specifically, when water or acid is used, for example, the titania nanorod (A3b) obtained in step (1) may be added to water or an acidic aqueous solution, and an ion exchange resin is used. For this, the liquid containing the product may be passed through a column filled with an ion exchange resin, or only mixed with the ion exchange resin and stirred.

  When an alkali metal hydroxide is used as the alkaline aqueous solution, an alkali metal may be contained in the titania nanorods obtained in the step (1). By this step, the alkali metal contained in the titania nanorods may be contained. Can be removed.

  The acid is preferably a protonic acid capable of exchanging protons with alkali metal ions. Specific examples include general inorganic acids or organic acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, acetic acid, citric acid, formic acid, and oxalic acid. These acids may be used individually by 1 type, and may be used in combination of 2 or more type.

  Examples of the ion exchange resin include cation exchange resins such as Diaion (manufactured by Mitsubishi Chemical Corporation; registered trademark) and Amberlite (made by Rohm and Haas). These ion exchange resins may be used individually by 1 type, and may be used in combination of 2 or more type.

  Among water, acid, and ion exchange resin, it is preferable to use an acid from the viewpoint that the alkali metal contained in the titania nanorod (A3b) obtained in step (1) can be removed in a short time. Nitric acid, acetic acid, oxalic acid and the like are more preferable. However, when using an acid, after making the titania nanorod (A3b) obtained at the process (1) contact with an acid, it is preferable to wash the titania nanorod (A3b) with water to remove the acid.

  The time for contacting the titania nanorod (A3b) obtained in the step (1) with at least one selected from the group consisting of water, acid and ion exchange resin may be about 1 to 48 hours, and is sufficiently alkaline. If it is necessary to remove the metal, 8 hours or more is more desirable.

In the method for producing titania nanorods (A3b), after the above step (2),
(3) It is preferable to include a step of firing the titania nanorod (A3b) obtained in step (2) at 150 ° C. or higher.

  The titania nanorod (A3b) obtained in the step (2) may be dried by hot air drying, reduced pressure drying or the like that is generally performed, but is preferably heated and fired. Thereby, the dehydration reaction of the Ti—OH group remaining in the titania nanorod (A3b) can be performed.

  The firing temperature is preferably 150 ° C. or higher from the viewpoint that the Ti—OH group remaining in the titania nanorod (A3b) can be dehydrated, and 300 ° C. or higher from the point that the crystallinity of the titania nanorod (A3b) can be improved. Is more preferable. The upper limit of the firing temperature is not particularly limited, but is usually about 1000 ° C.

1-2. Titania nanoparticles (B)
There is no restriction | limiting in particular as a titania nanoparticle (B), What is necessary is just to use a well-known or commercially available thing.

  The crystal structure of the titania nanoparticle (B) is not particularly limited, but preferably contains at least one selected from the group consisting of anatase-type titanium oxide, rutile-type titanium oxide and brookite-type titanium oxide. Those containing anatase-type titanium oxide are more preferred because of their high activity against. The crystal structure of the titania nanoparticle (B) can be measured by, for example, an X-ray diffraction method, Raman spectroscopic analysis, or the like.

  The average particle diameter of the titania nanoparticles (B) is preferably 1 to 500 nm, more preferably 5 to 100 nm, from the viewpoint that more dye can be adsorbed and light can be absorbed. However, from the viewpoint of the light confinement effect inside the battery, titanium oxide particles having a large particle size and large light scattering may be used in combination. In addition, the average particle diameter of a titania nanoparticle (B) can be measured by electron microscope (SEM) observation etc., for example.

1-3. Porous titanium oxide coating film The porous titanium oxide coating film of the present invention comprises the above-described titanium oxide structure (A) and titania nanoparticles (B), and the titanium oxide structure ( The concentration of A) increases and the concentration of titania nanoparticles (B) decreases.

  Specifically, the porous titanium oxide coating film has a titanium oxide structure (at a depth in the range of 0 to 10% of the thickness of the coating film from the outermost surface on the side where the content of the titanium oxide structure (A) is high. The content of A) is 20 to 100% by weight, particularly 70 to 100% by weight, and the depth is in the range of 90 to 100% of the thickness of the coating film from the outermost surface on the side where the content of titanium oxide structure (A) is high. The content of the titanium oxide structure (A) in is preferably 0 to 80% by weight, more preferably 0 to 30% by weight. In addition, each content in the whole porous titanium oxide coating film of the present invention is not particularly limited, but the titanium oxide structure (A) is about 5 to 80% by weight, preferably 10 to 50% by weight. The titania nanoparticles (B) may be about 20 to 95% by weight, preferably about 50 to 90% by weight.

  The porous titanium oxide coating film of the present invention is preferably as thick as possible so that it can absorb more incident light when used as a solar cell electrode, but the electrolyte penetrates deep into the electrode film or is homogeneous. From the standpoint of securing good film formability, it is better to be as thin as possible. From the effects of these contradictory phenomena, the thickness is preferably about 1 to 80 μm, particularly about 5 to 50 μm.

1-4. Substrate on which the porous titanium oxide coating film is formed The substrate on which the porous titanium oxide coating film of the present invention is formed is one in which the porous titanium oxide coating film of the present invention is formed on the substrate. Here, as the porous titanium oxide coating film moves from the interface with the substrate toward the outermost surface of the coating film, the concentration of the titanium oxide structure (A) increases and the concentration of the titania nanoparticles (B) decreases. Is.

  Thus, the titanium oxide structure (A) is formed near the surface of the coating film by having a concentration gradient in which the concentration of the titanium oxide structure (A) increases as it approaches the outermost surface from the interface with the substrate. Many titania nanoparticles (B) can be increased in the vicinity of the interface with the substrate. Thereby, since there are many titania nanoparticles (B) in the interface vicinity with a board | substrate, light can be absorbed more efficiently. Moreover, since there are many titanium oxide structures (A) in the vicinity of the surface, ions and electrons can be more efficiently carried to the vicinity of the electrode. Furthermore, by adopting a configuration in which there are many titania nanoparticles (B) in the vicinity of the interface with the substrate and many titanium oxide structures (A) in the vicinity of the surface, the light incident from the substrate side is irradiated with the titanium oxide structure ( Since A) is reflected and light can be confined in the coating film, light can be used efficiently.

  Specifically, the porous titanium oxide coating film has a titanium oxide structure (A) concentration of 20 to 100 at a depth ranging from 0 to 10% of the thickness of the coating film from the outermost surface (the side opposite to the substrate). % By weight, particularly 70 to 100% by weight, the concentration of the titanium oxide structure (A) at a depth ranging from the outermost surface (opposite side of the substrate) to 90 to 100% of the thickness of the coating film, 0 to 80% by weight, In particular, the content is preferably 0 to 30% by weight.

  When producing the porous titanium oxide coating film of the present invention on a substrate, a composition comprising a titanium oxide structure (A) and titania nanoparticles (B) having different concentrations is not particularly limited. May be prepared and applied and dried on an appropriate substrate in order from the one with the lowest concentration of the titanium oxide structure (A). At this time, the composition may be dried each time it is applied, or all the compositions may be applied and then dried together. The total thickness of the porous titanium oxide coating film may be 1 to 80 μm, preferably about 5 to 50 μm.

  There is no restriction | limiting in particular as a board | substrate, It has a smooth surface at normal temperature, The surface may be a plane or a curved surface, and may deform | transform by stress. Specific examples of the substrate that can be used include various glasses, and transparent resins such as PET (polyethylene terephthalate) and PEN (polyethylene naphthalate) that have a transparent conductive function. Moreover, in the case of using the porous titanium oxide coating film of the present invention as a negative electrode material for a dye-sensitized solar cell and collecting current from the surface side (back contact), the substrate is necessarily provided with a transparent conductive function. There is no need to use conductive aluminum, titanium, chromium, stainless steel or the like as a current collecting member, and a simple transparent substrate such as various types of glass or transparent resin may be used. However, it is preferable to use a glass substrate when firing at a temperature of 300 ° C. or higher, such as a step of forming an insulating oxide film described later.

  There are no particular restrictions on the application method, and conventional methods such as screen printing, dip coating, spray coating, spin coating, and squeegee method may be employed.

  The drying conditions are not particularly limited, but may be 100 to 500 ° C., preferably 200 to 300 ° C. for 1 to 10 hours, preferably 1 to 3 hours.

  Furthermore, in the substrate on which the porous titanium oxide coating film of the present invention is formed, the porous titanium oxide coating film preferably has an insulating oxide film on the surface. The oxide that can be used for the insulating oxide film is not particularly limited, but the electron conduction band energy level is closer to the vacuum energy level than the electron conduction band energy level of the titanium oxide structure (A). There may be used one that can tunnel electrons from the dye to the titanium oxide structure (A). For example, magnesium oxide, aluminum oxide, silicon oxide, zirconium oxide, hafnium oxide, yttrium oxide, nickel oxide, chromium oxide, manganese oxide, copper oxide, germanium oxide, gallium oxide, etc. may be used. Aluminum oxide is preferred. These oxides can be used alone or in combination of two or more.

  The thickness of the insulating oxide film is not particularly limited, but is preferably 0.1 to 100 nm, particularly 0.1 to 10 nm, and more preferably 0.5 to 5 nm in order to prevent reverse electron transfer.

  The method for forming the insulating oxide film on the surface of the porous titanium oxide coating film is not particularly limited. For example, sputtering method, dipping method, spray method, vapor deposition method, ion plating method, plasma CVD method, etc. Etc. Among these, since the insulating oxide film can be formed up to the details of the titanium oxide structure (A), the dipping method is preferable. Specifically, the precursor of the insulating oxide is about 0.001 to 1 mol / L. What is necessary is just to immerse the porous titanium oxide coating film of this invention formed on the board | substrate in the solution to contain, and to bake after that.

  Examples of the precursor of the insulating oxide include an alkoxide, a halide, an oxo halide, a carbonyl, an organic complex, and the like of a metal constituting the oxide. Specifically, for example, magnesium ethoxide, aluminum isopropoxide, aluminum butoxide, or yttrium isopropoxide may be used.

  The firing conditions are not particularly limited, but may be about 300 to 600 ° C., particularly about 450 to 550 ° C., about 1 to 60 minutes, particularly about 10 to 30 minutes.

2. When forming an electrode substrate for an electrode substrate dye-sensitized solar cell, the porous titanium oxide coating film of the present invention is formed on a resin substrate or a glass substrate (particularly, a transparent substrate made of a resin substrate or a glass substrate). Form and carry the dye. However, it is preferable to use a glass substrate when firing at a temperature of 300 ° C. or higher, such as a step of forming an insulating oxide film described later.

  The resin substrate is not particularly limited as long as it is transparent. For example, polyester such as polyethylene naphthalate resin substrate (PEN resin substrate) and polyethylene terephthalate resin substrate (PET resin substrate); polyamide; polysulfone; polyethersulfone; Examples include ether ether ketone, polyphenylene sulfide, polycarbonate, polyimide, polymethyl methacrylate, polystyrene, cellulose triacetate, and polymethylpentene.

  There is no restriction | limiting in particular also as a glass substrate, What is necessary is just to use a well-known or commercially available thing, and any of colorless or colored glass, meshed glass, a glass block etc. may be sufficient.

  As this resin substrate or glass substrate, one having a thickness of about 0.05 to 10 mm may be used.

  In the present invention, the porous titanium oxide coating film may be directly formed on the surface of the resin substrate or the glass substrate, but may be formed via a transparent conductive film.

  Examples of the transparent conductive film include a tin-doped indium oxide film (ITO film), a fluorine-doped tin oxide film (FTO film), an antimony-doped tin oxide film (ATO film), an aluminum-doped zinc oxide film (AZO film), and a gallium-doped zinc oxide. Examples include a film (GZO film). By passing through these transparent conductive films, in the case of a structure for collecting current from the resin substrate or glass substrate side (front contact), it becomes easy to take out the generated current to the outside. The film thickness of these transparent conductive films is preferably about 0.02 to 10 μm.

  Examples of the electrode of the present invention include the following two embodiments.

<Aspect 1: Front contact structure (FIGS. 13A to 13C)>
The porous titanium oxide coating film of the present invention can be formed on a resin substrate or a glass substrate via a transparent conductive film to form the electrode of the present invention (for example, FIG. 13A). That is, in aspect 1, the substrate having a structure in which a resin substrate or a glass substrate (in particular, a transparent substrate made of a resin substrate or a glass substrate) and a transparent conductive film are integrated is used as the substrate, and the porous titanium oxide of the present invention is used. A coating film is formed on the transparent conductive film. The resin substrate, the glass substrate and the transparent conductive film are as described above. The porous titanium oxide coating film of the present invention may have an insulating oxide film on at least one surface of the titanium oxide structure (A) and titania nanoparticles (B) (FIGS. 13B and C). ). In addition, if an insulating oxide film is formed on the surfaces of both the titanium oxide structure (A) and the titania nanoparticles (B), a porous titanium oxide coating film having an insulating oxide film on the surface as a whole. be able to.

  Specifically, an electrode may be formed as follows.

  First, a transparent conductive film is formed on a resin substrate or a glass substrate by a vacuum deposition method, an ion plating method, a CVD method, a sputtering method, a sol-gel method, a nanoparticle composite, or the like. The surface resistance of the substrate thus obtained is 50 Ω / sq. The following is preferable.

  And what is necessary is just to form the porous titanium oxide coating film of this invention on it. In addition, what is necessary is just to employ | adopt the method similar to the method mentioned above as the method of forming a porous titanium oxide coating film. Further, when the same insulating oxide film as described above is formed on the surface of the titanium oxide structure (A) and the titania nanoparticle (B), a porous titanium oxide coating film is similarly formed. Good. The above-described method may be adopted as a method for forming the insulating oxide film. Thereafter, a dye may be further adsorbed.

<Aspect 2: Back contact structure (FIGS. 14A to 14C)>
A porous titanium oxide coating film of the present invention is directly formed on a resin substrate or a glass substrate, and a porous conductive film or a mesh electrode may be further formed thereon to form the electrode substrate of the present invention (for example, FIG. 14A). The resin substrate and the glass substrate are as described above. Moreover, when forming the porous titanium oxide coating film of this invention on a resin substrate or a glass substrate, the method similar to the said aspect 1 is employable. And like the aspect 1, in the porous titanium oxide coating film of this invention, even if it has an insulating oxide film in the at least 1 surface of a titanium oxide structure (A) and a titania nanoparticle (B), Good (FIGS. 14B and C).

  As the porous conductive film that can be used in the aspect 2, ions that are not affected by (do not react with) ions contained in the electrolyte such as iodine ions and bromine ions, or ions contained in the electrolyte such as iodine ions and bromine ions. Although it will not specifically limit if it is the electroconductive material which has the corrosion resistance with respect to, For example, the titania etc. which have the crystal form of titanium, gold | metal | money, platinum, tungsten, niobium, tantalum, carbon, stainless steel, and a Magneli phase structure are mentioned. By forming these porous conductive films, in the case of a current collecting (back contact) structure from the surface (surface opposite to the resin substrate or glass substrate) of the porous titanium oxide coating film, the generated current is It is easy to take out outside. The surface resistance of these porous conductive films is not particularly limited, but is 10 Ω / sq. The film thickness is not particularly limited, but is preferably 150 nm or more.

  What is necessary is just to form a porous electrically conductive film by thin film formation methods, such as a sputtering method, further on the porous titanium oxide coating film formed on the resin substrate or the glass substrate.

  Moreover, as a material which comprises the mesh electrode which can be used in aspect 2, it is not attacked by the ion contained in electrolyte solutions, such as an iodine ion and a bromine ion (it does not react), or in electrolyte solutions, such as an iodine ion and a bromine ion If it is an electroconductive material which has the corrosion resistance with respect to the ion contained in, it will not specifically limit. Specific examples include titanium, gold, platinum, tungsten, niobium, tantalum, carbon, stainless steel, titania having a crystalline form of a Magneli phase structure, and the like. By laminating mesh electrodes made of these materials, current is collected from the surface of the porous titanium oxide coating film (surface opposite to the resin substrate or glass substrate) as in the case of the porous conductive film ( In the case of a back contact structure, it is easy to take out the generated current to the outside. These mesh electrodes preferably have electrical contact with the porous titanium oxide coating film with low resistance, and are also firmly bonded mechanically, and at the same time, ions from the electrolyte side Those that do not hinder the entry of are preferable.

  Further on the porous titanium oxide coating film formed on the resin substrate or the glass substrate, for example, the mesh electrode forms the porous titanium oxide coating film on the resin substrate or the glass substrate by the method described above. In this case, after the titania material is applied by a printing method or the like, the porous titanium oxide coating film is in a soft state with a solvent or the like and in a state in which dimensional stability is maintained. On top of this, holding the mesh electrode that leaves the electrode margin, and applying a drying treatment, necking treatment, or sintering treatment, it has low resistance to electrical contact with the porous titanium oxide coating film. Further, it is possible to obtain a mesh electrode having a back contact structure that is firmly bonded mechanically.

  In the case of adopting aspect 1 (front contact structure), it is preferable to use titania nanotubes (A2), particularly titania nanotubes (A2b) in which titania nanoparticles are connected, as the titanium oxide structure (A). These are because the light transmittance is high and the conversion efficiency of the resulting dye-sensitized solar cell is improved.

  On the other hand, when Aspect 2 is adopted, it is preferable to form a mesh electrode among the porous conductive film and the mesh electrode. A mesh-like electrode is preferred as the electrode of aspect 2 if it is generally easily available and has a coarse network so that it does not hinder the permeation of electrolyte ions and can ensure good electrical contact with the porous titanium oxide coating film. That is, the porous titanium oxide coating film of the present invention is formed on a resin substrate or a glass substrate (in particular, a transparent substrate made of a resin substrate or a glass substrate), and is further in contact with the porous titanium oxide coating film. It is preferable to form a mesh electrode so as to cover it. By taking such a structure, the amount of the titanium oxide structure (A) that easily absorbs visible light is reduced on the side close to the resin substrate or glass substrate side of the porous titanium oxide coating film. Light arrival with less loss is possible, and the amount of highly conductive titanium oxide structure (A) is increased on the side close to the mesh electrode to enable smooth electron transfer from the mesh electrode side. Can do. Thereby, the conversion efficiency of the dye-sensitized solar cell obtained can be improved.

  In addition, in the case of adopting the aspect 2, since it is possible to reach light with little loss to the active material due to the structure, it is not necessary to consider the light transmittance of the titanium oxide structure (A) to be used. Can be widely selected from other excellent physical properties such as properties and ion conductivity. That is, examples of the titanium oxide structure (A) include titania-coated nanoscale carbon tubes (A1), titania nanotubes (A2c) containing 30% or more of titania having a crystalline form of a Magneli phase structure, and particularly titania-coated nanoscale carbon tubes. It is preferable to use (A1) or the like.

  As described above, when using titania nanotubes (A2b) or the like in which titania nanoparticles are connected, depending on the type of titanium oxide structure (A) to be used, embodiment 1 is designated as titania-coated nanoscale carbon tube (A1), When using materials with excellent physical properties such as electrical conductivity and ionic conductivity, such as titania nanotubes (A2c) containing 30% or more of titania having a crystalline form of the magnetic phase structure, use Mode 2 That's fine. However, it is most preferable that the titania-coated nanoscale carbon tube (A1) is used as the titanium oxide structure (A) and the mode 2 is adopted.

  As described above, the dye may be adsorbed after the porous titanium oxide coating film of the present invention is formed on the resin substrate or the glass substrate. In addition, when a coating film is formed on the surfaces of the titanium oxide structure (A) and the titania nanoparticles (B) using the same insulating oxide film as described above, What is necessary is just to adsorb | suck a pigment | dye. In the case of aspect 2 (back contact structure), electrical contact between the porous titanium oxide coating and the porous conductive film or mesh electrode is ensured, and the transmitted light is a dye in the porous titanium oxide coating. If the film thickness is sufficiently absorbed, there are no particular restrictions on the production procedure, but the porous titanium oxide coating film is wetted after the printing process after the porous titanium oxide coating film is formed and before the dye is attached. It is preferable that the temperature is increased after the mesh electrode is deposited in a state where the mesh electrode is in a state of being heated. That is, by depositing the mesh electrode in a wet state after printing the porous titanium oxide coating, the solvent is evaporated or decomposed and removed, and the titania nanoparticles are necked together. Alternatively, it is sintered and electrode material is taken into the deposition shrinkage and intermolecular bonds that accompany these processes, making it possible to form a strong contact between the porous titanium oxide coating and the electrode material, and good electrical contact Is done. In addition, when an insulating oxide film similar to that described above is formed on the surfaces of the titanium oxide structure (A) and the titania nanoparticles (B), a coating film is formed and wetted after the printing process. Then, after depositing the mesh-like electrode, the temperature may be raised and dried in the same manner to adsorb the dye.

  The dye is not particularly limited as long as it has absorption characteristics in the visible region and the near infrared region and improves (sensitizes) the light absorption efficiency of the porous titanium oxide coating film. Dyes, semiconductors and the like are preferable. In addition, in order to give adsorptivity to the porous titanium oxide coating film, carboxyl group, hydroxyl group, sulfonyl group, phosphonyl group, carboxylalkyl group, hydroxyalkyl group, sulfonylalkyl group, phosphonylalkyl in the dye molecule Those having a functional group such as a group are preferred.

  As the metal complex dye, for example, a ruthenium, osmium, iron, cobalt, zinc, mercury complex (for example, mellicle chromium), metal phthalocyanine, chlorophyll, or the like can be used. Examples of organic dyes include, but are not limited to, cyanine dyes, hemicyanine dyes, merocyanine dyes, xanthene dyes, triphenylmethane dyes, metal-free phthalocyanine dyes, and the like. As a semiconductor that can be used as a dye, an amorphous semiconductor having a large i-type light absorption coefficient, a direct transition semiconductor, a fine particle semiconductor that exhibits a quantum size effect and efficiently absorbs visible light, and the like are preferable. Usually, one of various semiconductors, metal complex dyes and organic dyes, or two or more kinds of dyes can be mixed in order to make the wavelength range of photoelectric conversion as wide as possible and increase the conversion efficiency. Moreover, the pigment | dye to mix and its ratio can be selected so that it may match with the wavelength range and intensity distribution of the target light source.

  As a method for adsorbing the dye to the porous titanium oxide coating, for example, a method in which a solution in which the dye is dissolved in a solvent is applied on the porous titanium oxide coating by spray coating or spin coating and then dried. Can be formed. In this case, the substrate may be heated to an appropriate temperature. Moreover, the method of immersing and adsorbing a porous titanium oxide coating film in a solution can also be used. The immersion time is not particularly limited as long as the dye is sufficiently adsorbed, but is preferably 10 minutes to 30 hours, more preferably 1 to 20 hours. Moreover, you may heat a solvent and a board | substrate when immersing as needed. The concentration of the dye in the case of a solution is about 0.01 to 100 mmol / L, preferably about 0.1 to 10 mmol / L.

  The solvent to be used is not particularly limited, but water and an organic solvent are preferably used. Examples of the organic solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and t-butanol; acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, and the like. Nitriles; aromatic hydrocarbons such as benzene, toluene, o-xylene, m-xylene, p-xylene; aliphatic hydrocarbons such as pentane, hexane, heptane; alicyclic hydrocarbons such as cyclohexane; acetone, methyl ethyl ketone Ketones such as diethyl ketone and 2-butanone; ethers such as diethyl ether and tetrahydrofuran; ethylene carbonate, propylene carbonate, nitromethane, dimethylformamide, dimethyl sulfoxide, hexamethylphosphoamide, dimethoxy Ethane, γ-butyrolactone, γ-valerolactone, sulfolane, dimethoxyethane, adiponitrile, methoxyacetonitrile, dimethylacetamide, methylpyrrolidinone, dimethylsulfoxide, dioxolane, sulfolane, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, ethyl phosphate Dimethyl, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, tridecyl phosphate, tris phosphate (trifluoromethyl), tris phosphate (pentafluoroethyl), Examples thereof include triphenyl polyethylene glycol phosphate and polyethylene glycol.

  In order to reduce the interaction such as aggregation between the dyes, a colorless compound having properties as a surfactant may be added to the dye adsorption liquid and co-adsorbed to the semiconductor layer. Examples of such colorless compounds include steroid compounds such as cholic acid having a carboxyl group or sulfo group, deoxycholic acid, chenodeoxycholic acid, taurodeoxycholic acid, sulfonates, and the like.

  It is preferable to remove the unadsorbed dye by washing immediately after the adsorption step. Washing is preferably performed using acetonitrile, an alcohol solvent or the like in a wet washing tank.

  After adsorbing the dye, a semiconductor using an amine, a quaternary ammonium salt, a ureido compound having at least one ureido group, a silyl compound having at least one silyl group, an alkali metal salt, an alkaline earth metal salt, etc. The surface of the layer may be treated. Examples of preferred amines include pyridine, 4-t-butylpyridine, polyvinylpyridine and the like. Examples of preferred quaternary ammonium salts include tetrabutylammonium iodide, tetrahexylammonium iodide and the like. These may be used by dissolving in an organic solvent, or may be used as they are in the case of a liquid.

3. Dye-sensitized solar cell In the present invention, a counter electrode (counter electrode) is formed on the porous titanium oxide coating film of the electrode of the present invention, and a photoelectric conversion element is formed by filling between these electrodes with an electrolytic solution.

  The counter electrode may have a single layer structure made of a conductive material, or may be composed of a conductive layer and a substrate. The substrate is not particularly limited, and the material, thickness, dimensions, shape, and the like can be appropriately selected according to the purpose. For example, metal, colorless or colored glass, meshed glass, glass block, etc. are used. Resin may be used. Examples of such resins include polyesters such as polyethylene terephthalate, polyamide, polysulfone, polyether sulfone, polyether ether ketone, polyphenylene sulfide, polycarbonate, polyimide, polymethyl methacrylate, polystyrene, cellulose triacetate, and polymethylpentene. Alternatively, the counter electrode may be formed by applying, plating, or vapor-depositing (PVD, CVD) a conductive material directly on the charge transport layer.

  As the conductive material, a metal having a small specific resistance, such as a metal such as platinum, gold, nickel, titanium, aluminum, copper, silver, or tungsten; a carbon material; or a conductive organic material is used.

  A metal lead may be used for the purpose of reducing the resistance of the counter electrode. The metal lead is preferably made of a metal such as platinum, gold, nickel, titanium, aluminum, copper, silver or tungsten, and particularly preferably made of aluminum or silver.

  In the present invention, before forming the counter electrode, for the purpose of improving the light absorption efficiency of the electrode of the present invention, it is preferable to support (adsorb, contain, etc.) the dye on the porous titanium oxide coating film. The dye and the method for supporting the dye are as described above.

  The dye-sensitized solar cell of the present invention can be manufactured by modularizing the photoelectric conversion element and providing predetermined electrical wiring.

  The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Example 1
<Preparation of titania nanotube (A2b)>
A titania nanotube (A2b) was produced in the same manner as in Example 1 of JP2010-24132A. Specifically, it is as follows.

  To 0.96 g of nanoscale carbon tube (average diameter: 35 nm, average length: 5 μm, average aspect ratio: 143), 69 g of nitric acid 150 g was added and held at 90 to 95 ° C. for 6 hours. This was filtered, washed with distilled water until the filtrate reached pH 6-7, and then dried.

  This was dispersed in 100 g of distilled water containing 3.7 g of a polyether dispersant using an ultrasonic homogenizer. To this nanoscale carbon dispersion liquid, ammonium hexafluorotitanate diluted to 1.0 M and boric acid diluted to 1.0 M were added so that the respective concentrations would be 0.20 M and 0.4 M. After standing for a period of time, it was filtered and dried to obtain a structure in which the surface of the nanoscale carbon tube was coated with titanium oxide.

  When this structure was measured by X-ray photoelectron spectroscopy, the carbon / titanium atomic ratio was 0.1 and only a small amount of carbon was detected. When observed with an electron microscope (SEM), the surface coverage of titanium oxide was about 98%. In addition, the surface where the smooth portion without unevenness of 1 nm or more (the portion of the carbon tube not covered with titanium oxide) is continuously present for 5 nm or more is regarded as the portion where the carbon tube is not covered and the surface is exposed. The coverage was measured.

  Whereas X-ray diffraction and Raman spectroscopy reflect information down to a depth of a few micrometers, X-ray photoelectron spectroscopy does not expose nanoscale carbon tubes because it is an analysis of a few nanometers on the surface, It can be seen that titanium oxide is coated.

  This titanium oxide-coated nanoscale carbon tube was baked in air at 600 ° C. for 1 hour, and the nanoscale carbon tube disappeared to obtain a titania nanotube (A2b) in which particulate titanium oxide was continuous.

  When the crystal phase of the structure after firing was identified by X-ray diffraction and Raman spectroscopy, the anatase type was mainly used.

  Further, no graphite peak derived from the nanoscale carbon tube was observed.

  Further, when the structure was observed with an electron microscope (SEM and TEM), the results shown in FIGS. 9, 15 and 16 were obtained. Titanium oxide fine particles having a thickness of 5 to 20 nm gathered and the thickness was about 30 to 50 nm. The tube had an average diameter of 80 to 150 nm, an average length of about 1000 to 10000 nm, and an average aspect ratio of about 10 to 100.

  In addition, when electron beam diffraction measurement was performed at points A to C in FIG. 15 (end portion of the titanium oxide structure) and D to F in FIG. 16 (center portion of the titanium oxide structure), the following Table 1 was obtained. The following structure was confirmed.

Moreover, when the specific surface area was measured by BET method, it was a large specific surface area of 95 m < ² > / g.

<Manufacture of photoelectric conversion elements>
[Preparation of paste]
4.8 g of titania nanoparticles (P-25) manufactured by Nippon Aerosil Co., Ltd. are suspended in 2.1 g of an aqueous nitric acid solution having a pH of 0.7, 0.105 g of polyethylene glycol (molecular weight 500,000) is added as a thickener, and Triton-X100 (poly (oxyethylene) = octylphenyl ether; manufactured by Roche Diagnostics Co., Ltd.) as a surfactant was diluted 10-fold, 0.14 g was added, and these were added to agate A paste for the first application was prepared by kneading in a mortar.

  The paste for the second application was applied for the first time except that 3.6 g of titania nanoparticles (P-25) and 1.2 g of titania nanotubes (A2b) were used instead of 4.8 g of titania nanoparticles (P-25). It was produced in the same manner as the paste for use.

  Similarly, pastes for the third to fifth coatings were prepared by changing the mixing ratio of titania nanoparticles (P-25) and titania nanotubes (A2b). Table 2 shows the mixing ratios of the pastes for the first to fifth coatings.

[Film formation]
The above-mentioned paste for the first application was sequentially applied to a transparent glass substrate with a transparent electrode using a screen printer. The first film thickness was about 3 μm. It applied similarly about the paste for the 2nd time-the 5th time application. The obtained coating film was baked at 500 ° C. for 1 hour to produce an electrode film having a thickness of 15 μm.

[Manufacture of photoelectric conversion elements]
After the electrode film having a film thickness of 15 μm obtained as described above was immersed in an absolute ethanol solution of 5 × 10 ⁻⁵ mol / l ruthenium complex (RuL ₂ (NCS) ₂ ) dye (N3Dye) at room temperature for 18 hours. And dried to produce an oxide porous electrode.

  Next, a counter electrode plated with platinum is attached to a transparent glass substrate with a transparent electrode through a spacer, and 0.6 mol / l lithium iodide, 0.06 mol / l iodine, 0.5 mol are used as an electrolyte in the meantime. An acetonitrile solution containing / l 4-tert-butylpyridine was injected to prepare a photoelectric conversion element.

Comparative Example 1
The paste for the fifth application (titania nanotube (A2b) 100% by weight) prepared in Example 1 was continuously applied 5 times to obtain a coating film having a film thickness of 15 μm composed of only titania nanotubes (A2b). A photoelectric conversion element was produced in the same manner as in Example 1.

Comparative Example 2
The first application paste (titania nanoparticles (P-25) 100% by weight) prepared in Example 1 was applied five times in succession to obtain a coating film having a film thickness of 15 μm composed of only titania nanoparticles (P-25). Other than that, a photoelectric conversion element was fabricated in the same manner as in Example 1.

Comparative Example 3
The paste for the third coating prepared in Example 1 (50% by weight of titania nanoparticles (P-25) + 50% by weight of titania nanotubes (A2b)) was applied five times in succession, and the coating thickness was 15 μm with no composition gradient. A film was obtained, and a photoelectric conversion element was produced in the same manner as in Example 1 except for the above.

Example 2
<Preparation of titania nanotube (A2a)>
After adding 40 g of distilled water to 0.5 g of titanium oxide fine particles having an average particle diameter of 7 nm and stirring, 16 g of NaOH was added and further stirred for 5 minutes (concentration of titanium oxide: 0.16 mol / L, concentration of alkaline aqueous solution: 10 mol / L). When this mixed solution was placed in a PTFE-lined SUS316 pressure vessel and allowed to stand in a 250 ° C. heating furnace for 12 hours, a white precipitate was obtained.

  The precipitate was vigorously stirred in 500 ml of distilled water and then filtered under reduced pressure three times, and then stirred in 500 g of 1M hydrochloric acid for 24 hours. Further, the operation of stirring the obtained substance in 500 ml of distilled water and then filtering under reduced pressure was repeated 5 times. The resulting white cake was dried under reduced pressure at 150 ° C. and further heat-treated (fired) at 500 ° C. .4 g of white material was obtained.

When this material was observed by SEM and TEM, it was made of titanium oxide polycrystal and had a large aspect ratio (average aspect ratio: 77) with an average width of 65 nm and an average length of 5 μm (L / L _0). : 0.7 or more), it was found that the long sides facing each other are parallel (the angle formed is 0 to 10 °) and is a plate-like substance.

  Moreover, when the arithmetic average roughness of the side surface in the longitudinal direction was measured for the obtained titanium oxide structure using image processing of a TEM photograph, it was 0.6 nm (0.9% of the average width).

When the specific surface area of the obtained titanium oxide structure was measured by the BET method, it was 30 m ² / g, and when the alkali content was measured by ICP emission spectrometry, it was below the detection limit (500 ppm or less).

  When the obtained titanium oxide structure was baked at 800 ° C., the average length was 3 μm, but the shape having a large aspect ratio (average aspect ratio: 46) was maintained, and the heat resistance was excellent. It was found. Moreover, when X-ray crystal structure analysis was performed, it turned out that it is an anatase type.

<Manufacture of photoelectric conversion elements>
An electrode film having a thickness of 15 μm was prepared in the same manner as in Example 1 except that titania nanotube (A2a) was used instead of titania nanotube (A2b). Further, a photoelectric conversion element was produced in the same manner as in Example 1.

Example 3
<Production of titania-coated nanoscale carbon tube (A1)>
To 0.96 g of nanoscale carbon tube (average diameter: 35 nm, average length: 5000 nm, average aspect ratio: 143), 69 g of nitric acid 150 g was added and held at 90-95 ° C. for 6 hours. This was filtered, washed with distilled water until the filtrate reached pH 6-7, and then dried.

  This was dispersed in 100 g of distilled water containing 3.7 g of a polyether dispersant using an ultrasonic homogenizer. To this nanoscale carbon dispersion liquid, ammonium hexafluorotitanate diluted to 1.0 M and boric acid diluted to 1.0 M were added so that the respective concentrations would be 0.20 M and 0.4 M. After standing for a period of time, it was filtered and dried to obtain a structure in which the surface of the nanoscale carbon tube was coated with titanium oxide.

  When the TG-DTA measurement was performed, the nanoscale carbon tube burned violently around 550 ° C, whereas the manufactured nanoscale carbon tube surface covered with titanium oxide burned slowly from 550 ° C to 700 ° C. did. This is considered that the nanoscale carbon tube was covered with titanium oxide and combustion was suppressed.

  When the crystal phase was identified by the X-ray diffraction method and the Raman spectroscopic analysis about the produced structure and the structure which baked this structure at 500 degreeC for 1 hour, it was an anatase type. A graphite peak derived from the nanoscale carbon tube was also observed.

  On the other hand, in the X-ray photoelectron spectroscopic analysis, the atomic ratio of carbon / titanium was 0.1 and only a small amount of carbon was detected. When observed with an electron microscope (SEM), the surface coverage of titanium oxide was about 98%. In addition, the surface where the smooth portion without unevenness of 1 nm or more (the portion of the carbon tube not covered with titanium oxide) is continuously present for 5 nm or more is regarded as the portion where the carbon tube is not covered and the surface is exposed. The coverage was measured.

  Whereas X-ray diffraction and Raman spectroscopy reflect information down to a depth of a few micrometers, X-ray photoelectron spectroscopy does not expose nanoscale carbon tubes because it is an analysis of a few nanometers on the surface, It can be seen that titanium oxide is coated.

  When the structure was observed with SEM and TEM, the results shown in FIGS. 5 and 17 were obtained, and the titanium oxide fine particles of 5 to 20 nm gathered to cover the thickness of about 30 to 50 nm, and the average diameter was 80 to 150 nm. The fiber had an average length of about 1000 to 10000 nm and an average aspect ratio of about 10 to 100.

When the specific surface area was measured by the BET method, it was a large specific surface area of 73 m ² / g.

<Manufacture of photoelectric conversion elements>
An electrode film having a thickness of 15 μm was prepared in the same manner as in Example 1 except that the titania-coated nanoscale carbon tube (A1) was used instead of the titania nanotube (A2b). Further, a photoelectric conversion element was produced in the same manner as in Example 1.

Example 4
<Production of titania nanotube (A2c)>
To 0.96 g of nanoscale carbon tube (average diameter: 35 nm, average length: 5 μm, average aspect ratio: 143), 69 g of nitric acid 150 g was added and held at 90 to 95 ° C. for 6 hours. This was filtered, washed with distilled water until the filtrate reached pH 6-7, and then dried.

  This was dispersed in 100 g of distilled water containing 3.7 g of a polyether dispersant using an ultrasonic homogenizer. To this nanoscale carbon dispersion liquid, ammonium hexafluorotitanate diluted to 1.0 M and boric acid diluted to 1.0 M were added so that the respective concentrations would be 0.20 M and 0.4 M. After standing for a period of time, it was filtered and dried to obtain a structure in which the surface of the nanoscale carbon tube was coated with titanium oxide.

  When this structure was measured by X-ray photoelectron spectroscopy, the carbon / titanium atomic ratio was 0.1 and only a small amount of carbon was detected. When observed with an electron microscope (SEM), the surface coverage of titanium oxide was about 98%. In addition, the surface where the smooth portion without unevenness of 1 nm or more (the portion of the carbon tube not covered with titanium oxide) is continuously present for 5 nm or more is regarded as the portion where the carbon tube is not covered and the surface is exposed. The coverage was measured.

  Whereas X-ray diffraction and Raman spectroscopy reflect information down to a depth of a few micrometers, X-ray photoelectron spectroscopy does not expose nanoscale carbon tubes because it is an analysis of a few nanometer parts of the surface, It can be seen that titanium oxide is coated.

  This titanium oxide-coated nanoscale carbon tube was baked at 750 ° C. for 2 hours to eliminate the nanoscale carbon tube, thereby obtaining a titania nanotube (A2c) containing 30% or more of titania having a crystalline form of a Magneli phase structure. . Note that the firing atmosphere was an atmosphere made of only hydrogen gas by introducing hydrogen gas at 0.1 L / min.

Manufacturing titania nanotubes (A2c), was identified crystalline phase by X-ray diffractometry and Raman spectroscopic analysis, about 50% were Magneli phase _(Ti 4 _{O 7).}

  Further, no graphite peak derived from the nanoscale carbon tube was observed.

  Moreover, when the structure was observed with an electron microscope (SEM and TEM), the results were as shown in FIGS. 18 to 20, and titanium oxide fine particles having an average particle diameter of 30 to 60 nm were assembled to have a thickness of about 30 to 200 nm. It was a tube having an average diameter of about 50 to 300 nm, an average length of about 1000 to 10,000 nm, and an average aspect ratio of about 20 to 200.

  In addition, when electron beam diffraction measurement was performed at points A to C in FIG. 19 (center portion of the titanium oxide structure) and D to F in FIG. 20 (end portions of the titanium oxide structure), the following Table 3 was obtained. The following structure was confirmed.

<Manufacture of photoelectric conversion elements>
An electrode film having a thickness of 15 μm was prepared in the same manner as in Example 1 except that titania nanotube (A2c) was used instead of titania nanotube (A2b). Further, a photoelectric conversion element was produced in the same manner as in Example 1.

Example 5
<Formation of insulating oxide film on titania nanotube (A2b)>
The titania nanotube (A2b) produced in Example 1 was used as the titania nanotube (A2b).

  A titanium oxide paste obtained by mixing 3.0 g of titania nanotubes (A2b), 1.5 g of ethyl cellulose and 10 g of α-terpineol was prepared from FTO (fluorine-doped tin oxide) glass (manufactured by Nippon Sheet Glass Co., Ltd., resistance: 10Ω / sq). It was applied so that the thickness was 14 μm.

  Then, the titania electrode was produced by drying at 125 degreeC and baking at 500 degreeC for 1 hour. This titania electrode was immersed in a solution in which 0.61 g of magnesium ethoxide was dissolved in 20 mL of 2-propanol (magnesium ethoxide: 0.15 mol / L) at 60 ° C. for 30 minutes. Thereafter, the titania electrode was immersed in hot water at 80 ° C. for 1 minute and then baked at 450 ° C. for 20 minutes to obtain an insulation-coated titania electrode in which a 1 nm thick magnesium oxide film was coated on the titania layer of the titania electrode. In this insulating coated titania electrode, the surface of the titania nanotube (A2b) in the titania layer was also coated with a magnesium oxide film having a thickness of 1 nm.

<Manufacture of photoelectric conversion elements>
The Titania nanotube (A2b) coated with the magnesium oxide film was peeled off from the FTO glass of the above-described insulation-coated titania electrode.

  An electrode film having a thickness of 15 μm was prepared in the same manner as in Example 1 except that the titania nanotube (A2b) coated with the peeled magnesium oxide film was used instead of the titania nanotube (A2b). Further, a photoelectric conversion element was produced in the same manner as in Example 1.

Example 6
<Manufacture of photoelectric conversion elements>
[paste]
As the titanium oxide structure, the titania nanotube (A2c) produced in Example 4 was used. And as a paste for porous titanium oxide coating film preparation, the same 1st-5th paste as what was used in Example 4 was used.

[Film formation]
The paste for the first application was sequentially applied to a glass substrate with a screen printer. The first film thickness was about 3 μm. It applied similarly about the paste for the 2nd time-the 5th time application.

[Production of electrode substrate]
After coating 5 times, the temperature is raised and held at 200 ° C. for 10 minutes. As a film form that can maintain the dimensional stability while maintaining a wet state, mesh titanium is secured on it, and an electrode margin is secured. And put it on. The obtained coating film with back contact electrode was baked at 500 ° C. for 1 hour to prepare an electrode film having a thickness of 15 μm.

[Dye adsorption]
After the electrode film having a film thickness of 15 μm obtained as described above was immersed in an absolute ethanol solution of 5 × 10 ⁻⁵ mol / l ruthenium complex (RuL ₂ (NCS) ₂ ) dye (N3Dye) at room temperature for 18 hours. And dried to adsorb the dye to the porous titanium oxide coating film.

[Manufacture of photoelectric conversion elements]
A platinum-plated counter electrode is bonded to a transparent glass substrate with a transparent electrode through a spacer, and 0.6 mol / l lithium iodide, 0.06 mol / l iodine, 0.5 mol / l An acetonitrile solution containing 4-tert-butylpyridine was injected to produce a photoelectric conversion element.

Example 7
An electrode having a porous titanium oxide coating film having a thickness of 15 μm, as in Example 6, except that the titania-coated nanoscale carbon tube (A1) produced in Example 3 was used instead of the titania nanotube (A2c). A substrate was produced. Further, a photoelectric conversion element was produced in the same manner as in Example 6.

Experimental Example When the photoelectric conversion elements of Examples 1 to 7 and Comparative Examples 1 to 3 were irradiated with pseudo-sunlight (1 kW / m ² ) and the current-voltage characteristics were measured, the results shown in Table 4 below were obtained. It was.

Claims (14)

A substrate on which a porous titanium oxide coating film containing a rod-like, tubular, fibrous or plate-like titanium oxide structure (A) and titania nanoparticles (B) is formed,
As the porous titanium oxide coating film moves from the interface with the substrate toward the outermost surface of the coating film, the concentration of the titanium oxide structure (A) increases and the concentration of titania nanoparticles (B) decreases. Features
A substrate on which a porous titanium oxide coating film is formed. The porous titanium oxide coating film is
The concentration of the titanium oxide structure (A) at a depth in the range of 0 to 10% of the thickness of the coating film from the outermost surface is 20 to 100% by weight,
The concentration of the titanium oxide structure (A) at a depth in the range of 90 to 100% of the thickness of the coating film from the outermost surface is 0 to 80% by weight.
A substrate on which the porous titanium oxide coating film according to claim 1 is formed. The board | substrate with which the porous titanium oxide coating film of Claim 1 or 2 in which the average aspect-ratio of a titanium oxide structure (A) is 3-200000 was formed. The titanium oxide structure (A) is at least one selected from the group consisting of titania-coated nanoscale carbon tubes (A1), titania nanotubes (A2), and titania nanorods (A3). A substrate on which the porous titanium oxide coating described in 1 is formed. The substrate on which the porous titanium oxide coating film according to claim 4 is formed, wherein the titania nanotube (A2) is a titania nanotube (A2b) in which titania nanoparticles are continuous. The substrate on which the porous titanium oxide coating film according to claim 4 is formed, wherein the titania nanotube (A2) is a titania nanotube (A2c) containing 30% or more of titania having a crystal form of a magnetic phase structure. The board | substrate with which the porous titanium oxide coating film in any one of Claims 1-6 which has an insulating oxide film on the surface of a titanium oxide structure (A) was formed. The board | substrate with which the porous titanium oxide coating film in any one of Claims 1-7 in which a porous titanium oxide coating film has an insulating oxide film on the surface was formed. An electrode substrate comprising a substrate on which the porous titanium oxide coating film according to claim 1 is formed,
The substrate has a structure in which a resin substrate or a glass substrate and a transparent conductive film are integrated,
The porous titanium oxide coating film is formed on a transparent conductive film, and
An electrode substrate in which a pigment is supported on the porous titanium oxide coating film. An electrode substrate comprising: a substrate on which the porous titanium oxide coating film according to claim 1 is formed; and a mesh electrode formed on the substrate on which the porous titanium oxide coating film is formed. Because
The mesh electrode is formed so as to contact and cover the porous titanium oxide coating film,
The substrate is a resin substrate or a glass substrate,
An electrode substrate in which a pigment is supported on the porous titanium oxide coating film. The electrode substrate according to claim 10, wherein the mesh electrode does not react with iodine ions and bromine ions, or has corrosion resistance against iodine ions and bromine ions. The mesh electrode is made of at least one selected from the group consisting of titanium, gold, platinum, tungsten, niobium, tantalum, carbon, stainless steel, and titania having a crystalline form of a magnetic phase structure. Electrode substrate. A dye-sensitized solar cell comprising the electrode substrate according to claim 9. A porous titanium oxide coating film comprising a rod-like, tubular, fibrous or plate-like titanium oxide structure (A) and titania nanoparticles (B),
The concentration of the titanium oxide structure (A) increases and the concentration of the titania nanoparticles (B) decreases as it goes from one surface to the other surface.
Porous titanium oxide coating.

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