JP5754889B2 - Titanium oxide structure - Google Patents

Description

  The present invention relates to a titanium oxide structure used for a photoelectric conversion element such as a dye-sensitized solar cell, a method for producing the same, and a photoelectric conversion element using the titanium oxide structure.

  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 titanium dioxide particles modified with a dye as an active electrode has been reported by Gretzell et al. (See Patent Document 1). Dye-sensitized solar cells are attracting attention as solar cells that can be easily manufactured at low cost.

  However, at present, there is a demand for further improvement in performance, and one of them is improvement in conductivity.

In order to improve conductivity, it is effective to increase the specific surface area of the active electrode made of titanium oxide, that is, to reduce the average particle diameter of the titanium oxide particles. In addition, among titanium oxides, titanium oxide having a crystalline form of a magnetic phase structure has a structure in which oxygen is released from titanium dioxide (TiOx; x = 1.75 to 1.95), and has high conductivity. Since it has characteristics such as high corrosion resistance, it is expected that high performance can be achieved by using titanium oxide having a crystalline form of a magnetic phase structure as a catalyst for a fuel cell and an electrode plate for an electric device. Further, among the titanium oxide having a crystalline form of Magneli phase structure, Ti ₄ O ₇ has been known that most high conductivity since (1, Non-Patent Document 1), a Ti ₄ O ₇ Various studies have been made to obtain this.

Conventionally, titanium oxide having a crystalline form of a magnetic phase structure such as Ti ₄ O ₇ has been produced by high-temperature annealing at 1000 ° C. or more using titanium oxide particles or the like as a starting material (see, for example, Patent Document 2). However, since it was produced at a high temperature, the titanium oxide fine particles aggregated, and only particles having an average particle diameter of 100 μm or more were obtained. Moreover, in patent document 2, in order to obtain favorable electroconductivity, the average particle diameter of about 100-150 micrometers is made appropriate, and the subject to make it small to a nanometer order is not suggested at all.

  Further, in Patent Document 3, the titanium oxide fine particles having a diameter of about 1 micron are obtained by using titanium oxide fine particles (average particle size: several tens of nm) as a starting material. There is no suggestion of a problem of reducing the average particle diameter of the titanium oxide particles to the nanometer order.

  On the other hand, as a titanium oxide structure composed of titanium oxide fine particles having a small average particle diameter, for example, an average particle of about several tens of nanometers can be obtained by coating the surface of carbon nanotubes (CNT) with titanium oxide fine particles and by a method such as heat treatment. There is known a method for obtaining a titanium oxide structure comprising titanium oxide fine particles having a diameter and having a crystal form of a magnetic phase structure (see Patent Document 4).

  However, at present, there is no known method for obtaining a titanium oxide structure comprising titanium oxide fine particles having a small average particle diameter and containing a large amount of titanium oxide having a crystalline form of a conductive magnetic phase structure.

Japanese Patent Publication No. 8-15097 Special table 2008-539538 gazette Japanese Patent No. 3955620 JP 2010-24132 A

Monolithic Ti4O7 Ebonex Ceramic

  An object of this invention is to provide the titanium oxide structure which consists of a titanium oxide fine particle which has a small average particle diameter, and can produce a highly conductive dye-sensitized solar cell.

As a result of intensive studies in view of the above object, a titanium oxide structure that solves the above problems can be obtained by heat-treating an aggregate of titanium oxide having an average particle diameter of 1 to 100 nm at 950 ° C. or lower in a reducing atmosphere. As a result, the present invention has been completed. That is, the present invention has the following configuration.
Item 1. Titanium oxide fine particles having an average particle diameter of 1 to 100 nm are connected,
30% or more of the titanium oxide fine particles are titanium oxide having a crystal form of a Magneli phase structure .
Tubular titanium oxide structure.
Item 2. Titanium oxide having a crystalline form of the magnetic phase structure is represented by the general formula (1):
TiOx
(Wherein x is 1.75 to 1.95)
In shown the titanium oxide structure according to claim 1.
Item 3 . Item 3. The titanium oxide structure according to Item 1 or 2 , further comprising at least one selected from the group consisting of anatase-type titanium oxide, rutile-type titanium oxide, and brookite-type titanium oxide .
Item 4 . Item 4. The titanium oxide structure according to any one of Items 1 to 3, wherein the thickness is 1 to 250 nm.
Item 5 . A process of heat-treating titanium oxide-coated nanoscale carbon having a rod-like or fibrous nanoscale carbon surface coated with a coating layer made of titanium oxide having an average particle diameter of 1 to 100 nm at 950 ° C. or lower in a reducing atmosphere. comprising a method for producing a titanium oxide structure according to any one of claim 1-4.
Item 6 . Item 6. The method for producing a titanium oxide structure according to Item 5 , wherein the reducing atmosphere contains 50 to 100 mol% of a reducing gas.
Item 7 . Item 7. The production of the titanium oxide structure according to Item 6 , wherein the reducing gas is at least one selected from the group consisting of hydrogen, carbon monoxide, nitric oxide, unsaturated hydrocarbon gas, and saturated hydrocarbon gas. Method.
Item 8 . Item 6. A dye is applied to the surface of an active substance containing the titanium oxide structure according to any one of Items 1 to 4 or the titanium oxide structure obtained by the method for producing a titanium oxide structure according to any one of Items 5 to 7. A photoelectric conversion element which is supported.

  According to the present invention, an oxide capable of producing a dye-sensitized solar cell having high conductivity by containing a large amount of titanium oxide having a crystal form of a magnetic phase structure and comprising titanium oxide fine particles having a small average particle diameter. A titanium structure can be provided.

It is a graph showing that Ti ₄ O ₇ has the highest conductivity among the titanium oxides having a crystal form of a magnetic phase structure. It is a schematic diagram explaining the movement of an electron in the case of using the titanium oxide structure which a particulate titanium oxide continues. 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. 6 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. 2 is an electron microscope (SEM) photograph showing the surface shape of the titanium oxide structure of Example 1. FIG. 2 is an electron microscope (TEM) photograph of the central portion of the titanium oxide structure of Example 1. FIG. 2 is an electron microscope (TEM) photograph of an end portion of the titanium oxide structure of Example 1. FIG.

1. Titanium oxide structure The rod-like, tubular or fibrous titanium oxide structure of the present invention is composed of titanium oxide fine particles having an average particle diameter of 1 to 100 nm, and 30% or more of the titanium oxide fine particles have a crystalline form of a magnesium phase structure. It is essential to be titanium oxide having In the present specification, “titanium oxide” does not only refer to titanium dioxide, but also includes oxygen-deficient titanium dioxide such as Ti ₂ O ₃ and Ti ₄ O ₇ .

  The average particle diameter of the titanium oxide fine particles constituting the titanium oxide structure of the present invention is 1 to 100 nm, preferably 30 to 80 nm. Thus, by setting the average particle diameter of the titanium oxide fine particles 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 the titanium oxide fine particles can be measured, for example, by observation with an electron microscope (SEM or TEM).

  In the titanium oxide structure of the present invention, 30% or more, preferably 50% or more, and more preferably 70% or more of the titanium oxide fine particles are titanium oxide having a crystalline form of a magnetic phase structure. Conductivity can be improved by using 30% or more of the titanium oxide fine particles as titanium oxide having a crystalline form of a Magneli phase structure.

Titanium oxide having a crystalline form of the magnetic phase structure 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 titanium oxides having a crystalline form of the magnetic phase structure may be used alone or in combination of two or more.

  The titanium oxide structure of the present invention may contain anatase-type titanium oxide, rutile-type titanium oxide, brookite-type titanium oxide, and the like in addition to the above-described titanium oxide having the crystal form of the magnetic phase structure. In the case where titanium oxide other than titanium oxide having a crystal form of the magnetic phase structure is included, anatase type titanium oxide is preferable among the above three types 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 the titanium oxide fine particles can be measured, for example, by X-ray diffraction, electron beam diffraction, Raman spectroscopic analysis or the like.

  The shape of the titanium oxide structure of the present invention may be any of a rod shape, a tubular shape, and a fibrous shape. Among these, a tubular one is preferable because the active surface area can be increased.

  In addition, the titanium oxide structure of the present invention has a sufficient surface area and efficiently transmits electrons, so that the average diameter orthogonal to the major axis is 5 to 500 nm, and the average length of the major axis is 0.1. ˜1000 μm, average aspect ratio (average length of major axis / average diameter orthogonal to major axis) of 3 to 200,000 is preferable, average diameter orthogonal to major axis is 5 to 500 nm, and average length of major axis Is more preferably 0.1 to 1000 μm, and an average aspect ratio (average length of long axis / average diameter orthogonal to long axis) of 3 to 5000, average diameter orthogonal to long axis is 7 to 300 nm, long More preferably, the average length of the shaft is 1 to 50 μm and the average aspect ratio is 10 to 3000. In addition, in this invention, when using a tubular thing as a titanium oxide structure, the diameter means an outer diameter. The average diameter, average length, and average aspect ratio of the titanium oxide structure can be measured by, for example, observation with an electron microscope (SEM).

  When the titanium oxide structure of the present invention is tubular, the thickness is preferably about 1 to 250 nm, more preferably about 5 to 200 nm from the viewpoint of preventing leakage current. The wall thickness refers to the difference between the outer diameter and the inner diameter of the tubular titanium oxide structure. Moreover, the thickness of the titanium oxide structure of the present invention can be measured, for example, by observation with an electron microscope (SEM or TEM).

  In the present invention, the titanium oxide structure may have a smooth surface or may have irregularities. When the surface has irregularities, it is preferable to use a titanium oxide structure in which titanium oxide fine particles are continuous. Here, the term “continuous” means that the titanium oxide fine particles are in close contact with the adjacent titanium oxide fine particles, and is not simply in a state obtained by mixing.

  If the titanium oxide structure of the present invention is composed of continuous titanium oxide particles, fine irregularities can be formed on the surface of the rod-like, tubular or fibrous titanium oxide structure of the present invention. In this way, if a titanium oxide structure having fine irregularities on the surface is used for a dye-sensitized solar cell, a large amount of dye is supported, incident light is efficiently absorbed, and electrons are efficiently generated. Can do. In addition, since the titanium oxide structure of the present invention contains a large amount of titanium oxide having a crystalline form of the magnetic phase structure, as shown in FIG. 2, the electrons are efficiently transferred to the transparent electrode through the adjacent titanium oxide. Can do. In FIG. 2, for convenience, the titanium oxide structure is formed of only one atomic layer, but is not limited thereto.

The titanium oxide structure of the present invention 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. Some are 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 titanium oxide structure of the present invention preferably has a powder resistance of 3 × 10 ⁶ Ω · m or less under 10 MPa from the viewpoint of obtaining a larger current, and is 1 × 10 ⁵ Ω · m or less. Those are 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 titanium oxide structure is not particularly limited. For example, the current value is processed by applying a voltage of 1 V between the pellets after processing into a plate having a thickness of 0.3 mm at a pressure of 10 MPa. It can be measured by measuring.

2. Method for Producing Titanium Oxide Structure The titanium oxide structure of the present invention includes a step of heat-treating an aggregate of titanium oxide having an average particle diameter of 1 to 100 nm at 950 ° C. or lower in a reducing atmosphere. As a result, a titanium oxide structure having a large specific surface area and a large amount of titanium oxide having a crystal form of a magnetic phase structure in the titanium oxide fine particles can be obtained because the average particle diameter is composed of fine titanium oxide fine particles of about 1 to 100 nm. .

<Aggregates of titanium oxide>
The aggregate of titanium oxide is not particularly limited as long as it is a rod-like, tubular or fiber-shaped titanium oxide fine particle having an average particle diameter of 1 to 100 nm, preferably 30 to 80 nm, and contains carbon or the like. May be. Examples thereof include titanium oxide-coated nanoscale carbon, titanium oxide nanotubes, titanium oxide nanorods, and titanium oxide nanowires. Among these, titanium oxide-coated nanoscale carbon is preferable because titanium oxide having a crystalline form of a magnetic phase structure is easily formed by being in sufficient contact with a reducing solid and being burnt down at a low temperature. When titanium oxide fine particles are used instead of an aggregate of titanium oxide, at least one selected from the group consisting of a divalent titanium oxide and a trivalent titanium oxide unless heat treatment is performed at a high temperature of 1000 ° C. or higher. A titanium oxide structure containing a seed of titanium oxide (particularly titanium oxide having a crystalline form of a Magneli phase) cannot be obtained. Further, when heat treatment is performed at 1000 ° C. or more using titanium oxide fine particles, the titanium oxide fine particles 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 titanium oxide-coated nanoscale carbon is obtained by coating the surface of a rod-like or fibrous nanoscale carbon with a coating layer made of titanium oxide having an average particle diameter of 1 to 100 nm.

  The titanium oxide-coated nanoscale carbon is obtained, for example, by forming a coating layer made of titanium oxide fine particles on the surface of a rod-like or fibrous nanoscale carbon by a precipitation reaction from a titanium fluoro complex.

  Specifically, for example, rod-like or fibrous nanoscale carbon is treated with an acid such as nitric acid, sulfuric acid, hydrochloric acid, etc., and then dispersed in a solvent containing a dispersant. In this method, a fluoride ion scavenger such as aluminum is added to deposit titanium oxide.

  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.

  In addition, as the dispersant, anionic dispersion such as sodium naphthalenesulfonate formalin condensate-based dispersant, polycarboxylate-based dispersant, maleic acid α-olefin copolymer salt-based dispersant, anionic surfactant, etc. Agents; Cationic dispersants such as quaternary ammonium salt dispersants and alkylamine salts; Nonionic dispersants such as cellulose dispersants, polyvinyl alcohol dispersants, polyether dispersants; amphoteric surfactants, etc. Other dispersants and the like. Among these, nonionic dispersants are preferable, and polyether dispersants are more preferable.

  The method for producing the titanium oxide-coated nanoscale carbon is not limited to the above method, and for example, 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 may be used. However, from the viewpoint of producing a titanium oxide structure having a large specific surface area in which titanium oxide fine particles are connected, a method of depositing titanium oxide by a precipitation reaction from a titanium fluoro complex is preferable.

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

  In addition, this rod-like or fibrous nanoscale carbon has an average diameter of about 1 to 100 nm perpendicular to the major axis, and the major axis, since it can produce a structure that is as fine as possible and has a large surface area and a long continuous titanium oxide. The average length is preferably about 0.1 to 1000 μm and the average aspect ratio is about 5 to 1000000, the average diameter orthogonal to the long axis is about 1 to 100 nm, and the long axis average length is 0.1 to 1000 μm. More preferably, the average aspect ratio is about 5 to 10,000, the average diameter orthogonal to the major axis is about 1 to 50 nm, the average length of the major axis is about 1 to 50 μm, and the average aspect ratio is about 10 to 10,000. More preferred. 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).

Nanoscale carbon tube The nanoscale 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) amorphous nanoscale carbon tube,
(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.

< Carbon nanotube >
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. 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 perpendicular to the axis 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, and the average diameter perpendicular to the major axis is about 1 to 5 nm. More preferably, the long axis has an average length of about 1 to 100 μm and an average aspect ratio of about 15 to 30000. Particularly, the average diameter perpendicular to the long axis is about 1 to 2 nm, and the average length of the long axis is 1. Those having an average aspect ratio of about 20 to 20000 are preferable.

  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, and the average diameter orthogonal to the major axis is More preferably, the average length of the major axis is about 1 to 50 nm, the average length of the major axis is about 1 to 100 μm, and the average aspect ratio is about 10 to 10,000. In particular, the average diameter orthogonal to the major axis is about 1 to 40 nm. Those having a length of about 1 to 20 μm and an average aspect ratio of about 10 to 10,000 are preferable.

< Amorphous nanoscale carbon tube >
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. The nanoscale carbon tube has a linear shape, and in the X-ray diffraction method (incident X-ray: CuKα), the plane interval (d002) of the carbon network plane (002) measured by the diffractometer method is It 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. It is characterized by being at least degrees.

  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 higher than or equal to the thermal decomposition temperature of the raw material, and in a temperature range of about room temperature to 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. ˜100 nm, average length is about 0.1 to 1000 μm, average aspect ratio is about 5 to 10000, average outer diameter is about 1 to 50 nm, average length is about 1 to 50 μm, average aspect ratio Is more preferably about 10 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 method, the nanoscale carbon tube having an amorphous structure that can be used in the present invention has a planar spread of the carbon network plane of the amorphous nanoscale carbon tube (II). Less than 1 times the diameter. 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.

< Iron-carbon composite >
An iron-carbon composite (IV) that can be used in the present invention is described in JP-A-2002-338220 (Patent No. 3569806), and (a) a nano-flake carbon tube and a multi-layer carbon nanotube with a nested structure A carbon tube selected from the group consisting of (b) iron carbide or iron, and 10 to 90% of the space in the tube of the carbon tube (a) is filled with iron carbide or iron (b). ing. 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. 5 shows a transmission electron microscope (TEM) photograph of a cross section almost perpendicular to the longitudinal direction (obtained in Example 1 of Japanese Patent Laid-Open No. 2002-338220), and FIG. 3 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. 6, 100 schematically shows a TEM image in the longitudinal direction of the nanoflake carbon tube, and 200 shows a TEM image in a cross section substantially perpendicular to the longitudinal direction of the nanoflake 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 nanoflake carbon tube (a-1) constituting the iron-carbon composite (IV) that can be used in the present invention is apparent from 200 in FIGS. 5 and 6 (a-1). In addition, when a cross section perpendicular to the longitudinal direction is observed with a TEM, a large number of arc-shaped graphene sheet images are concentrically (multi-layered tube shape). As shown, a continuous ring that is completely closed is not formed, but a discontinuous ring that is interrupted 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.

  In addition, as is clear from 100 in FIGS. 3 and 6 (a-1), when the longitudinal direction of the nanoflake 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 points, 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 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 400 in FIG. 6A-2, the multi-walled carbon nanotube (a-2) having a nested structure has a TEM image of a cross section perpendicular to the longitudinal direction substantially as indicated by 410. A straight graphene sheet image 310 or the like that is a concentric tube that is a complete circular TEM image and is continuous over the entire length in the longitudinal direction, as indicated by 300 in FIG. 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. 6, 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. 6 (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) is straight with little curvature and has a uniform thickness over the entire length of the wall, so it has a uniform shape over the entire length. Have. 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. ˜100 nm, average length is about 0.1 to 1000 μm, average aspect ratio is about 5 to 10000, average outer diameter is about 1 to 50 nm, average length is about 1 to 400 μm, average aspect ratio Is more preferably about 10 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, the carbonaceous material containing the iron-carbon composite (IV) used in the present invention is observed in a range of 200 to 2000 nm square by a transmission electron microscope, the length of the image is W, and the image is linear. When the length when stretched is Wo, the shape characteristic means that 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 iron-carbon composite (IV), or a material that should be called iron carbide or iron-containing carbonaceous material.

  A carbonaceous material that can be used in the present invention comprising the nanoflake carbon tube (a-1) produced in Example 1 of JP-A-2002-338220 and iron carbide (b) filled in the space in the tube. An electron micrograph is shown in FIG.

  As can be seen from FIG. 4, in the carbonaceous material containing the iron-carbon composite (IV) used in the present invention, basically, in almost all (particularly 99% or more) carbon tubes, the space 10% to 90% of the portion (that is, the space surrounded by the tube wall of the carbon tube) is filled with iron carbide or iron (b), and there is substantially no carbon tube in which the space portion is not filled. It is normal. However, in some cases, a small amount of carbon tubes not filled with iron carbide or iron (b) may be present.

  In the carbonaceous material used in the present invention, the iron-carbon composite (IV) in which iron or iron carbide (b) is filled in 10 to 90% of the space in the carbon tube as described above is mainly used. Although it is a component, soot may be contained in addition to the iron-carbonaceous composite (IV). In such a case, components other than the iron-carbonaceous composite are removed to improve the purity of the iron-carbonaceous composite (IV) in the carbonaceous material, and the iron-carbon composite (IV) is substantially improved. It is also possible to obtain a carbonaceous material consisting of only the above.

  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 with 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 made of iron-carbon composite (IV) is about 10 to 90%, particularly about 40 to 70%. .

< Nano flake carbon tube >
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.

Titanium oxide-coated nanoscale carbon The titanium oxide-coated nanoscale carbon thus obtained has a titanium oxide coverage of 70 to 100% on the surface of the rod-like or fiber-like nanoscale carbon from the viewpoint of preventing leakage current. In particular, it is 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 formed by continuous particulate titanium oxide on the surface of the carbon) can be determined by, for example, observation with an electron microscope (SEM or TEM) or the carbon / The surface element ratio of titanium can be measured by, for example, X-ray photoelectron spectroscopy.

<Reducing atmosphere>
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, the content of titanium oxide having a crystal form of the magnetic phase structure in the obtained titanium oxide structure can be increased.

  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, if the heat treatment temperature described later is not satisfied, that is, when heat treatment is performed at a high temperature, the titanium oxide fine particles 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.

<Heat treatment temperature>
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, if it is not a reducing atmosphere described later, for example, when heat-treated in the air or under an inert atmosphere, titanium oxide having a crystalline form of a magnesium phase structure in the obtained titanium oxide structure The content of cannot be increased sufficiently.

3. Photoelectric conversion element The photoelectric conversion element of the present invention comprises at least a conductive substrate, a semiconductor layer, a charge transport layer, and a counter electrode.

  The conductive substrate usually has an electrode layer on the 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. Colorless or colored 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. In addition, the board | substrate in this invention has a smooth surface at normal temperature, The surface may be a plane or a curved surface, and may deform | transform by stress.

The material of the conductive film that acts as an electrode is not particularly limited, and examples thereof include a metal such as gold, silver, chromium, copper, tungsten, and titanium, a metal thin film, and a conductive film made of a metal oxide. As the metal oxide, for example, Indium Tin Oxide (ITO (In ₂ O ₃ : Sn)), or Fluorine doped Tin Oxide (FTO (SnO ₂ )) obtained by doping a metal oxide such as tin or zinc with a small amount of another metal element. : F)), Aluminum doped Zinc Oxide (AZO (ZnO: Al)), Antimony doped Tin Oxide (ATO (SnO ₂ : Sb)), and the like are preferably used.

  The film thickness of the conductive film is usually 100 to 10,000 nm, preferably 300 to 2000 nm. The surface resistance (resistivity) is appropriately selected, but is usually 0.5 to 500 Ω / sq, preferably 1 to 50 Ω / sq.

  The method for forming the conductive film is not particularly limited, and a known method can be appropriately employed depending on the type of metal or metal oxide used. Usually, a vacuum deposition method, an ion plating method, a CVD method, a sputtering method, or the like is used. In either case, it is desirable that the substrate temperature be formed within a range of 20 to 700 ° C.

  The counter electrode (counter electrode) in the photoelectric conversion element of the present invention 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.

  As the semiconductor layer, one made of the above-described titanium oxide structure of the present invention is used. However, the orientation direction of the titanium oxide structure of the present invention is not particularly limited, and the longitudinal direction does not necessarily have to be oriented in a specific direction such as substantially perpendicular to the substrate. Further, the semiconductor layer is not necessarily composed of only the titanium oxide structure of the present invention, and may be mixed with, for example, titanium oxide fine particles, known titanium oxide nanotubes, and the like.

  The method for forming the semiconductor layer on the conductive substrate is not particularly limited, and examples thereof include a method of preparing a paste containing the titanium oxide structure of the present invention, applying the paste on the conductive substrate, and baking it. . At this time, water, an organic solvent, or the like can be used as a solvent for the paste.

  The organic solvent is not particularly limited as long as it can disperse the titanium oxide structure of the present invention. For example, alcohols such as ethanol, methanol and terpineol, and glycols such as ethylene glycol, polyethylene glycol, propylene glycol and polypropylene glycol can be used. These solvents are usually mixed and used in consideration of dispersibility, volatility, and viscosity. The proportion of the solvent in the paste is 50 to 90% by weight, particularly 60 to 75%, from the viewpoint of imparting fluidity during coating, maintaining the thickness after coating, and forming porous titanium oxide. % By weight is preferred.

  As a component of the dispersion liquid, a thickener or the like may be included in addition to the above solvent.

  Examples of the thickener include alkyl celluloses such as methyl cellulose and ethyl cellulose. Among these, alkyl cellulose, particularly ethyl cellulose can be preferably used.

  The proportion of the thickener in the paste is preferably 2 to 20% by weight, particularly 3 to 15% by weight from the viewpoint of balancing the fluidity during coating and the thickness after coating.

  The proportion of titanium oxide in the paste is preferably 10 to 50% by weight, particularly 10 to 30% by weight, from the viewpoint of the balance between the fluidity at the time of coating and the thickness after coating, as described above. Further, in the titanium oxide, when the titanium oxide structure of the present invention and another titanium oxide are used in combination, the titanium oxide structure of the present invention is added in an amount of 0.1 to 90% by weight (further 0.2 to 70% by weight). % (Particularly 0.3 to 50% by weight). The remainder is preferably the above-mentioned titanium oxide fine particles or known titanium oxide nanotubes.

  In the photoelectric conversion element of the present invention, a semiconductor layer having a dye supported (adsorbed, contained, etc.) on the semiconductor layer is used for the purpose of improving the light absorption efficiency of the semiconductor layer.

  The dye is not particularly limited as long as it has absorption characteristics in the visible region and near infrared region, and improves (sensitizes) the light absorption efficiency of the semiconductor layer. However, metal complex dyes, organic dyes, natural dyes, semiconductors, etc. Is preferred. In addition, in order to impart adsorptivity to the semiconductor layer, a functional group such as a carboxyl group, a hydroxyl group, a sulfonyl group, a phosphonyl group, a carboxylalkyl group, a hydroxyalkyl group, a sulfonylalkyl group, or a phosphonylalkyl group is included in the dye molecule. Those having a group are preferably used.

  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, or a fine particle semiconductor that exhibits a quantum size effect and efficiently absorbs visible light is 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 semiconductor layer, for example, a solution in which the dye is dissolved in a solvent is applied on the semiconductor layer by spray coating, spin coating, or the like, and then dried. In this case, the substrate may be heated to an appropriate temperature. Alternatively, a method in which the semiconductor layer is immersed in a solution and adsorbed can 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 forming a solution is about 1 to 1000 mmol / L, preferably about 10 to 500 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.

  The charge transport layer contains a charge transport material having a function of replenishing electrons to the oxidant of the dye. The charge transport material used in the present invention is a charge transport material in which ions are involved. A solution in which a redox counter ion is dissolved, a gel electrolyte composition in which a polymer matrix gel is impregnated with a solution of a redox pair, a solid electrolyte composition, etc. Is mentioned.

The electrolyte solution as a charge transport material involving ions is preferably composed of an electrolyte, a solvent, and an additive. Examples of the electrolyte used in the electrolytic solution, iodine and iodide (LiI, NaI, KI, CsI, metal iodide such as CaI _2, tetraalkylammonium iodide, pyridinium iodide, quaternary ammonium such as imidazolium iodide A combination of bromine and bromide (metal bromide such as LiBr, NaBr, KBr, CsBr, CaBr, CaBr ₂ , quaternary ammonium compound bromide such as tetraalkylammonium bromide, pyridinium bromide, etc.) Examples thereof include metal complexes such as Russianate-ferricyanate and ferrocene-ferricinium ions, sulfur compounds such as sodium polysulfide and alkylthiol-alkyldisulfides, viologen dyes, and hydroquinone-quinone. Among them, an electrolyte obtained by combining I ₂ and LiI or a quaternary ammonium compound iodine salt such as pyridinium iodide or imidazolium iodide is preferable. The electrolyte may be used as a mixture.

  Any solvent can be used as long as it is generally used in electrochemical cells and batteries. Specifically, acetic anhydride, methanol, ethanol, tetrahydrofuran, propylene carbonate, nitromethane, acetonitrile, dimethylformamide, dimethyl sulfoxide, hexamethylphosphoamide, ethylene carbonate, dimethoxyethane, γ-butyrolactone, γ-valerolactone, sulfolane, dimethoxy Ethane, propiononitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, dimethylacetamide, methylpyrrolidinone, dimethyl sulfoxide, dioxolane, sulfolane, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, ethyldimethyl phosphate, tributyl phosphate, phosphorus Tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, phosphoric acid Tridecyl, tris phosphate (trifluoromethyl), tris phosphate (pentafluoroethyl), triphenyl polyethylene glycol phosphate, polyethylene glycol, and the like can be used. In particular, propylene carbonate, ethylene carbonate, dimethyl sulfoxide, dimethoxyethane, acetonitrile, γ-butyrolactone, sulfolane, dioxolane, dimethylformamide, dimethoxyethane, tetrahydrofuran, adiponitrile, methoxyacetonitrile, methoxypropionitrile, dimethylacetamide, methylpyrrolidinone, dimethylsulfoxide Dioxolane, sulfolane, trimethyl phosphate, triethyl phosphate and the like are preferable. Also, room temperature molten salts can be used. Here, the room temperature molten salt is a salt composed of an ion pair that is melted at room temperature (that is, in a liquid state) and usually has a melting point of 20 ° C. or lower and is a liquid at a temperature exceeding 20 ° C. Is a salt. The solvent may be used alone or in combination of two or more.

  Further, it is preferable to add a basic compound such as 4-t-butylpyridine, 2-picoline, or 2,6-lutidine to the above-described molten salt electrolyte composition or electrolytic solution. A preferable concentration range when adding the basic compound to the electrolytic solution is 0.05 to 2 mol / L. When added to the molten salt electrolyte composition, the basic compound preferably has an ionic group. The blending ratio of the basic compound with respect to the entire molten salt electrolyte composition is preferably 1 to 40% by mass, more preferably 5 to 30% by mass.

  As a material that can be used as a polymer matrix, there is no particular limitation as long as a solid state or a gel state is formed by a polymer matrix alone, or by adding a plasticizer, a supporting electrolyte, or a plasticizer and a supporting electrolyte. Commonly used so-called polymer compounds can be used.

  Examples of the polymer compound exhibiting characteristics as the polymer matrix include hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, ethylene, propylene, acrylonitrile, vinylidene chloride, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, and methyl acrylate. And polymer compounds obtained by polymerizing or copolymerizing monomers such as ethyl acrylate, methyl methacrylate, styrene, and vinylidene fluoride. These polymer compounds may be used alone or in combination. Among these, a polyvinylidene fluoride polymer compound is particularly preferable.

  The charge transport layer can be formed by one of two methods. The first method is a method in which a semiconductor layer and a counter electrode are bonded together, and a liquid charge transport layer is sandwiched between the gaps. The second method is a method in which a charge transport layer is provided directly on the semiconductor layer, and a counter electrode is provided thereafter.

  In the case of the former method, when sandwiching the charge transport layer, a normal pressure process using capillary action by dipping or the like, or a vacuum process in which the gas phase in the gap is replaced with a liquid phase at a pressure lower than normal pressure can be used. .

  When a wet charge transport layer is used in the latter method, a counter electrode is usually applied in an undried state and measures for preventing liquid leakage at the edge portion are taken. Moreover, when using a gel electrolyte composition, you may solidify by methods, such as superposition | polymerization, after apply | coating this with a wet method. Solidification may be performed before or after applying the counter electrode.

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

Example 1
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 tubular titanium oxide structure in which particulate titanium oxide was continuous. Note that the firing atmosphere was an atmosphere made of only hydrogen gas by introducing hydrogen gas at 0.1 L / min.

Experimental example 1
The titanium oxide structure after firing was prepared in Example 1, 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 shown in FIGS. 7 to 9 were obtained, 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. 8 (center portion of the titanium oxide structure) and D to F in FIG. 9 (end portion of the titanium oxide structure), the following Table 1 was obtained. The following structure was confirmed.

  Furthermore, the solar cell was evaluated using the titanium oxide structure produced in Example 1 as the negative electrode of the dye-sensitized solar cell.

  3.0 g of titanium oxide (ST-21 (average particle diameter 20 nm) manufactured by Ishihara Sangyo Co., Ltd.), 1.5 g of ethyl cellulose and 10 g of α-terpineol were mixed, and the titanium oxide structure produced in Example 1 was further mixed. The titanium oxide paste obtained by adding 5% by weight of titanium oxide is 14 μm in thickness on FTO (fluorine-doped tin oxide) glass (manufactured by Nippon Sheet Glass Co., Ltd., resistance: 10Ω / sq). It applied so that it might become.

  Then, the titanium oxide electrode was produced by drying at 125 degreeC and baking at 500 degreeC for 1 hour. Ruthenium dye (Rutenium535-bis-TBA (N719) manufactured by Solaronix) is adsorbed on the obtained titanium oxide electrode, and an electrolytic solution between Pt sputtered conductive glass (manufactured by Geomatic Co., Ltd., resistance: 2Ω / sq) (Iodolyte AN-50 manufactured by Solaronix) was enclosed.

When the cell was irradiated with simulated sunlight (100 mW / cm ² ) and the short-circuit current was measured with a multimeter (manufactured by ADMTT), a current density of 17.2 mA / cm ² was obtained.

Example 2
A titanium oxide structure was obtained in the same manner as in Example 1 except that the firing temperature was 850 ° C.

Experimental example 2
The titanium oxide structure after firing prepared in Example 2, was identified crystalline phase by X-ray diffractometry and Raman spectroscopic analysis, was nearly 100% Magneli phase (Ti 4 _{O 7).}

  Further, when the structure was observed with an electron microscope (SEM and TEM), titanium oxide fine particles having an average particle diameter of 50 to 80 nm gathered to have a thickness of about 50 to 200 nm, an average diameter of about 100 to 300 nm, and an average length. Was a tube having an average aspect ratio of about 10 to 100.

Furthermore, when the short circuit current of the photovoltaic cell was measured in the same manner as in Example 1, a current density of 18.2 mA / cm ² was obtained.

Example 3
A titanium oxide structure was obtained in the same manner as in Example 1 except that carbon monoxide gas was introduced at 0.1 L / min to make the firing atmosphere an atmosphere consisting of only carbon monoxide gas.

Experimental example 3
The titanium oxide structure after firing prepared in Example 3, was identified crystalline phase by X-ray diffractometry and Raman spectroscopic analysis, was nearly 100% Magneli phase (Ti 4 _{O 7).}

  Further, when the structure was observed with an electron microscope (SEM and TEM), titanium oxide fine particles having an average particle diameter of 50 to 80 nm gathered to have a thickness of about 50 to 200 nm, an average diameter of about 100 to 300 nm, and an average length. Was a tube having an average aspect ratio of about 10 to 100.

Furthermore, when the short circuit current of the photovoltaic cell was measured in the same manner as in Example 1, a current density of 18.2 mA / cm ² was obtained.

Example 4
A titanium oxide structure was obtained in the same manner as in Example 1 except that the calcination atmosphere was changed to an atmosphere consisting of acetylene gas only by introducing acetylene gas at 0.1 L / min.

Experimental Example 4
The titanium oxide structure after firing prepared in Example 4, was identified crystalline phase by X-ray diffractometry and Raman spectroscopic analysis, was nearly 100% Magneli phase (Ti 4 _{O 7).}

  Further, when the structure was observed with an electron microscope (SEM and TEM), titanium oxide fine particles having an average particle diameter of 50 to 80 nm gathered to have a thickness of about 50 to 200 nm, an average diameter of about 100 to 300 nm, and an average length. Was a tube having an average aspect ratio of about 10 to 100.

Furthermore, when the short circuit current of the photovoltaic cell was measured in the same manner as in Example 1, a current density of 18.2 mA / cm ² was obtained.

Comparative Example 1
Titanium oxide fine particles having an average particle diameter of 20 nm were fired at 850 ° C. for 2 hours. Note that the firing atmosphere was an atmosphere made of only hydrogen gas by introducing hydrogen gas at 0.1 L / min.

Comparative Experiment Example 1
The titanium oxide structure after firing was prepared in Comparative Example 1, was identified crystalline phase by X-ray diffractometry and Raman spectroscopic analysis, Magneli phase (Ti 4 _{O 7)} were not present.

  Further, when the structure was observed with an electron microscope (SEM and TEM), the average diameter was about 30 to 50 nm.

Furthermore, when the short circuit current of the photovoltaic cell was measured in the same manner as in Example 1, a current density of 13.6 mA / cm ² was obtained.

Comparative Example 2
Comparative Example 1 was performed except that the firing temperature was 1100 ° C.

Comparative Experiment Example 2
The titanium oxide structure after firing was prepared in Comparative Example 2, was identified crystalline phase by X-ray diffractometry and Raman spectroscopic analysis, about 80% were Magneli phase (Ti 4 _{O 7).}

  Further, when the structure was observed with an electron microscope (SEM and TEM), the titanium oxide fine particles were aggregated, and the average diameter was about 1000 to 1500 nm.

Furthermore, when the short circuit current of the photovoltaic cell was measured in the same manner as in Example 1, a current density of 14.3 mA / cm ² was obtained.

Comparative Example 3
A titanium oxide structure was obtained in the same manner as in Example 1 except that the firing atmosphere was in the air.

Comparative Experiment Example 3
The titanium oxide structure after firing was prepared in Comparative Example 3, was identified crystalline phase by X-ray diffractometry and Raman spectroscopic analysis, about 16% were Magneli phase (Ti 4 _{O 7).}

  Further, when the structure was observed with an electron microscope (SEM and TEM), titanium oxide fine particles having an average particle diameter of 30 to 50 nm gathered to have a thickness of about 30 to 200 nm, an average diameter of about 50 to 300 nm, and an average length. Was about 1000 to 10000 nm and the average aspect ratio was about 20 to 200.

Furthermore, when the short circuit current of the photovoltaic cell was measured in the same manner as in Example 1, a current density of 15.8 mA / cm ² was obtained.

  The results of the above examples and comparative examples are shown in Table 2.

Claims (8)

Titanium oxide fine particles having an average particle diameter of 1 to 100 nm are connected,
30% or more of the titanium oxide fine particles are titanium oxide having a crystal form of a Magneli phase structure.
Tubular titanium oxide structure. Titanium oxide having a crystalline form of the magnetic phase structure is represented by the general formula (1):
TiOx
(Wherein x is 1.75 to 1.95)
The titanium oxide structure of Claim 1 shown by these. Furthermore, the titanium oxide structure of Claim 1 or 2 containing at least 1 sort (s) chosen from the group which consists of anatase type titanium oxide, rutile type titanium oxide, and brookite type titanium oxide. The titanium oxide structure according to any one of claims 1 to 3 , wherein the thickness is 1 to 250 nm. A process of heat-treating titanium oxide-coated nanoscale carbon having a rod-like or fibrous nanoscale carbon surface coated with a coating layer made of titanium oxide having an average particle diameter of 1 to 100 nm at 950 ° C. or lower in a reducing atmosphere. The manufacturing method of the titanium oxide structure in any one of Claims 1-4 provided with these. The method for producing a titanium oxide structure according to claim 5 , wherein the reducing atmosphere contains 50 to 100 mol% of a reducing gas. 7. The titanium oxide structure according to claim 6 , wherein the reducing gas is at least one selected from the group consisting of hydrogen, carbon monoxide, nitric oxide, an unsaturated hydrocarbon gas, and a saturated hydrocarbon gas. Production method. On the surface of the active substance containing the titanium oxide structure according to any one of claims 1 to 4 or the titanium oxide structure obtained by the method for producing a titanium oxide structure according to any one of claims 5 to 7 , A photoelectric conversion element which carries a dye.

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