JP2012243629A - Film forming method, film body, and dye-sensitized solar cell - Google Patents

Abstract

A method for forming a porous film made of an inorganic material that does not require a firing step, a film-forming body manufactured by the film-forming method, and a dye-sensitized solar cell provided with the film-forming body.
[MEANS FOR SOLVING PROBLEMS] (1) A porous film of an inorganic substance is formed on a base material by spraying inorganic fine particles onto the base material to join the base material and the fine particles, and joining the fine particles to each other. 23, the small particles 21 having an average particle size r <1 μm and the large particles 26 having an average particle size R ≧ 1 μm are used as the fine particles, and the average particle size r of the small particles 21 is An operation in which the relative ratio (r / R) of the large particle 26 to the average particle size R satisfies the relationship of (1/1000) ≦ (r / R) ≦ (1/5), and the operation of spraying the small particle 21 is large. A film forming method in which the operation of spraying the diameter particles 26 is performed simultaneously or alternately.
[Selection] Figure 2

Description

  The present invention relates to a film forming method for forming a porous film made of an inorganic substance on a substrate, a film forming body obtained by the film forming method, and a dye-sensitized solar cell including the film forming body.

  For a photoelectrode of a dye-sensitized solar cell (DSC), a porous film made of an oxide semiconductor such as titanium oxide to which a photosensitizing dye such as a ruthenium metal complex is adsorbed is used (Patent Document 1). As a conventional method of forming a porous film, a slurry or paste containing oxide semiconductor particles is applied onto a base material, and this is fired at a temperature below the melting point of the oxide semiconductor, whereby oxide semiconductor particles The film is formed in a state where they are in weak contact with each other. By adding a binder such as ethyl cellulose to the slurry or paste before coating, the viscosity of the slurry or paste was adjusted, and the porosity of the film to be formed was increased to increase the adsorption area of the photosensitizing dye. Usually, a porous film is used.

  In order to improve the photoelectric conversion efficiency of a dye-sensitized solar cell, a method of surface-treating fine particles constituting a porous film is known. As a representative example, a method of forming a new titanium oxide film on a porous film by immersing the porous film made of titanium oxide formed as described above in a titanium tetrachloride aqueous solution and pulling it up, followed by heat treatment Is known (Non-Patent Document 1). This titanium oxide film is considered to play a role of enhancing the adhesion between titanium oxide particles constituting the porous film while providing a clean surface to the porous film.

Japanese Patent No. 334559

Published by Technical Education Publishing Company Modularization, material development and evaluation technology for dye-sensitized solar cells P. 89-93

  However, a porous film formed by a baking method at 500 ° C. for about 1 hour has a problem that the adhesion between the oxide semiconductor particles is weak and the electron conductivity remains low. This is because the firing temperature is much lower than the melting point of the oxide semiconductor (the melting point of titanium oxide is 1700 to 1800 ° C.), so that the particle surface does not melt and the contact area between the particles remains small. . For example, if the particle has a shape close to a sphere, the contact area of the interface (grain boundary) between the two particles is extremely small. Moreover, when a binder is mix | blended in a slurry or a paste, the contact of particle | grains will reduce further and there exists a problem that the electronic conductivity of the porous film formed into a film remains low.

  Since the base material which supports the conventional porous membrane needs to be a material which can be baked, it is difficult to use a plastic or a resin film as a base material. In addition, there is a problem that the time required for the firing process increases the time required for the entire manufacturing process of the porous membrane.

  The present invention has been made in view of the above circumstances, and a method for forming a porous film made of an inorganic substance, which does not require a firing step, a film formed body manufactured by the film forming method, and a film formed body thereof An object is to provide a dye-sensitized solar cell provided.

According to a first aspect of the present invention, there is provided a method for forming a film on a base material by spraying inorganic fine particles onto a base material to join the base material and the fine particles and joining the fine particles to each other. In the method of forming a porous film of an inorganic substance, small particles having an average particle diameter r <1 μm and large particles having an average particle diameter R ≧ 1 μm are used as the fine particles. The relative ratio (r / R) between the particle diameter r and the average particle diameter R of the large particles satisfies the relationship of (1/1000) ≦ (r / R) ≦ (1/5), and the small particle The operation of spraying and the operation of spraying the large-diameter particles are performed simultaneously or alternately.
The film forming method according to claim 2 of the present invention is the film forming method according to claim 1, wherein the small-diameter particles are bonded to each other by causing the large-diameter particles to collide with the small-diameter particles sprayed on the base material. The film forming method according to claim 3 of the present invention is characterized in that, in claim 1 or 2, from the surface of the base material until the film thickness of the porous film reaches 40%. The spraying speed of the large-diameter particles or the small-diameter particles is made faster than the spraying speed of the large-diameter particles or the small-diameter particles until the film thickness reaches 100% after the porous film thickness of 40%. To do.
The film forming method according to a fourth aspect of the present invention is characterized in that, in any one of the first to third aspects, an average particle diameter r of the small diameter particles is 1 nm to 100 nm.
The film forming method according to claim 5 of the present invention is characterized in that, in any one of claims 1 to 4, an average particle diameter R of the large particles is 1 μm to 100 μm.
The film forming method according to claim 6 of the present invention is characterized in that, in any one of claims 1 to 5, the inorganic substance is an oxide semiconductor.
The film forming method according to claim 7 of the present invention is the film forming method according to any one of claims 1 to 6, wherein the inorganic substance is an oxide semiconductor, and the small-diameter particles and the large-diameter particles are different from each other. It is characterized by being an oxide semiconductor.
The film forming method according to claim 8 of the present invention is characterized in that, in any one of claims 1 to 7, the base material is made of a resin.
The film forming method according to claim 9 of the present invention is characterized in that, in any one of claims 1 to 8, the substrate is a film made of a resin.
The film forming body according to claim 10 of the present invention is obtained by the film forming method according to any one of claims 1 to 9.
The film-forming body according to an eleventh aspect of the present invention is characterized in that, in the tenth aspect, the content of the large-diameter particles in the porous film is 30% by volume or less.
The film-forming body according to claim 12 of the present invention is characterized in that, in any one of claims 10 and 11, the porosity of the porous film is 50% or more.
The film-forming body according to claim 13 of the present invention is characterized in that, in any one of claims 10 to 12, the porous film has at least a crystalline part on the surface.
A film-forming body according to a fourteenth aspect of the present invention is characterized in that, in any one of the tenth to thirteenth aspects, the porosity of the porous film increases in the film thickness direction away from the substrate. .
A dye-sensitized solar cell according to claim 15 of the present invention includes the film-forming body according to any one of claims 10 to 14.

According to the film forming method of the present invention, a conventional baking process is not required. For this reason, a plastic, a resin film, etc. with comparatively low heat resistance can be used as a base material. Furthermore, since a baking process is unnecessary at the time of manufacture and the required time for film formation can be shortened, it is excellent in manufacturing characteristics.
Further, in the film forming method of the present invention, mixed particles composed of small-sized particles and large-sized particles are sprayed onto the substrate, so that the large-sized particles collide with the small-sized particles accumulated on the surface of the substrate and the small-sized particles are used as the base. It can be reliably bonded to the material surface or another adjacent small particle. As a result, a porous film can be formed more easily than in the past. That is, even when fine particles are sprayed at a lower speed than in the past, a porous film can be reliably formed.
According to the film forming body of the present invention, since the porous film is firmly bonded to the surface of the base material, it is possible to reduce the possibility that the porous film is peeled off from the base material. In addition, since the inorganic particles constituting the porous film are reliably bonded to each other, the strength is high and the electron conductivity is excellent. By this bonding, voids serving as dye adsorption sites are formed in the porous film, so that the dye adsorption property is excellent. Since the voids are also suitable for diffusing the electrolyte, the diffusibility of the electrolyte is excellent.
The film-forming body of the present invention is useful as a component of a photoelectrode because a porous film having excellent characteristics is disposed on the surface of a substrate.
Since the dye-sensitized solar cell of the present invention includes the film forming body, it is excellent in photoelectric conversion efficiency. Moreover, if a film-forming body using a flexible substrate such as a resin film is used, a deformable dye-sensitized solar cell can be obtained.

It is a schematic diagram which shows the film forming apparatus which can be used for this invention. It is typical sectional drawing which shows an example of a film forming process. It is typical sectional drawing which shows an example of a film forming process. It is typical sectional drawing which shows an example of a film forming process. It is an example of the electron micrograph (TEM photograph) of the surface of the film forming body concerning this invention. It is an example of the electron micrograph (TEM photograph) of the surface of the film forming body concerning this invention. It is an example of the electron micrograph (TEM photograph) of the surface of the porous titanium oxide layer formed by baking. It is an example of the electron micrograph (TEM photograph) of the surface of the porous titanium oxide layer formed by baking. It is an example of the electron micrograph (SEM photograph) of the film forming body concerning this invention. It is an example of the electron micrograph (SEM photograph) of the film forming body concerning this invention. It is typical sectional drawing which shows the change of the porosity in the porous film which comprises the film forming body of this invention. It is an example of the electron micrograph (SEM photograph) of the film forming body concerning this invention.

The present invention will be described in detail below.
<< Film Formation Method >>
In the film forming method of the present invention, inorganic fine particles are sprayed onto a base material to join the base material and the fine particles, and the fine particles are joined to each other, whereby the porous inorganic material is formed on the base material. This is a method of forming a film.

Examples of the inorganic substance include metal particles such as Pt, Ag, and Au, semiconductor particles such as Si, CdS, CdSe, CdTe, PbS, PbSe, ZnO, TiO ₂ , In ₂ O ₃ , SnO ₂ , and BaTiO ₃ , and Well-known composite inorganic particle etc. are mentioned.
As the inorganic substance, an oxide semiconductor excellent in electron conductivity and dye supporting property is preferable. Examples of the oxide semiconductor include titanium oxide (TiO ₂ ), zinc oxide (ZnO), and strontium titanate (SrTiO ₃ ). Among these, titanium oxide that is excellent in electron conductivity when a porous film is formed is preferable.

In general, titanium oxides used industrially are roughly classified into anatase type and rutile type, and brookite type and amorphous titanium oxide are also known. In the present invention, when titanium oxide is used as the inorganic substance constituting the porous membrane, the small-diameter particles are preferably anatase-type titanium oxide, and the large-diameter particles are preferably rutile-type titanium oxide. A porous film formed by this combination tends to have a strength suitable for a photoelectrode of a dye-sensitized solar cell. Thus, it is preferable that the small particle and the large particle are different oxide semiconductors.
Unlike the so-called green compact, the porous film constituting the film-forming body according to the present invention is stronger than the green compact and is more difficult to peel from the substrate than the green compact.

  In addition to anatase-type titanium oxide, rutile-type titanium oxide, brookite-type titanium oxide, or amorphous titanium oxide may be used as the small-diameter particles. In addition to the rutile type titanium oxide, anatase type titanium oxide, brookite type titanium oxide or amorphous titanium oxide may be used as the large particle.

The average particle size r of the small particles is less than 1 μm (r <1 μm), the average particle size R of the large particles is 1 μm or more (R ≧ 1 μm), and the average particle size r of the small particles is The relative ratio (r / R) to the average particle size R of the large particles is
The relationship of (1/1000) ≦ (r / R) ≦ (1/5) is satisfied.

The average particle diameter r of the small diameter particles is less than 1 μm and is not particularly limited as long as the above relationship is satisfied. For example, it is preferably 1.0 nm or more and less than 1000 nm (1 μm), more preferably 1.0 nm or more and 500 nm or less, and further preferably 1.0 nm or more and 100 nm or less. A suitable average particle diameter r when the anatase-type titanium oxide is used as the small-diameter fine particles is the same as the above range.
By being at least the lower limit of the above range, a larger amount of dye (sensitizing dye) can be supported, and voids in which the electrolyte solution can more easily diffuse are easily formed in the porous film.
When the upper limit of the above range is preferably less than 1 μm, more preferably 500 nm or less, and still more preferably 100 nm or less, the small diameter particles tend to be joined. As a result, the electronic conductivity and strength of the porous film can be further improved.

The average particle diameter R of the large particles is 1 μm or more, and is not particularly limited as long as the above relationship is satisfied. For example, it is preferably 1.0 μm or more and 100 μm or less, more preferably 1.0 μm or more and 50 μm or less, further preferably 1.0 μm or more and 10 μm or less, and particularly preferably 1.0 μm or more and 5.0 μm or less. . A suitable average particle diameter R when the rutile titanium oxide is used as the large-sized fine particles is also the same as the above range.
By being above the lower limit of the above range, the energy with which the large particles collide with the small particles can be increased when the mixed particles are sprayed onto the substrate. As a result, in the film formation by spraying, the bonding between the small diameter particles, the bonding between the small diameter particles and the base material, or the bonding between the small diameter particles and the large diameter particles can be performed more reliably. As a result, the electronic conductivity and strength of the porous film can be further improved.
By being below the upper limit of the said range, it can prevent that a large diameter particle scrapes off the porous membrane currently formed on the said base material at the time of film forming. Thereby, since the film formation can be steadily advanced by the spraying, the film formation speed can be increased. Moreover, it is easy to be in the state joined by the said small diameter particle | grains.

The average particle diameter r of the small particle is obtained as an average value of the particle diameters measured by observing a plurality of small particles with an electron microscope. In this case, the larger the number of small-diameter particles to be measured, the better. However, for example, 10 to 50 particles may be measured and the average may be obtained. Or the method of determining as a peak value of the particle diameter (volume average diameter) distribution obtained by the measurement of the laser diffraction type particle size distribution measuring apparatus is also mentioned.
The average particle size R of the large particles is obtained by the same measuring method as the average particle size r of the small particles.

When the average particle diameter r of the small particle is measured by a particle size distribution measuring device and a particle size distribution curve of the small particle is drawn, fitting is performed assuming that the number of peaks in the range of the average particle diameter of less than 1 μm is one. ,preferable.
On the other hand, when it is more mathematically or logically appropriate to fit the number of the peaks as a plurality (for example, 2 to 5), the fitted particle size distribution curve with the number of the peaks as a plurality. May be drawn. In this case, there are first small diameter particles, second small diameter particles, third small diameter particles,... Having a plurality of average particle diameters r1, r2, r3. The plurality of small diameter particles are collectively referred to as a small diameter particle group. About the average particle diameter of each small diameter particle belonging to the small diameter particle group, the average particle diameter obtained by weighting by the abundance ratio of each small diameter particle corresponds to the “average particle diameter r of the small diameter particle” of the present invention. To do.

  The half width (full width at half maximum) of the peak in the particle size distribution curve of the small particle is preferably 1.0 nm or more and less than 1000 nm (1 μm), more preferably 1.0 nm or more and 500 nm or less, and further preferably 1.0 nm or more and 100 nm or less. preferable. It is preferable to use small-diameter particles having a peak with a narrow half-value width because it is easy to estimate the speed at the time of the spraying and the energy of the collision related to the speed, and the control of the spraying conditions becomes easier.

  The half width of the peak in the particle size distribution curve of the small particle is preferably determined based on the fitted distribution curve assuming that the number of the peak is one in the range of the average particle size of less than 1 μm. On the other hand, if it is more mathematically or logically appropriate to fit the number of the peaks as a plurality (for example, 2 to 5), the number of the peaks is set to a plurality, and the above-mentioned half for each peak. The price range may be obtained. Also in this case, the half width of each peak is preferably in the above range.

When measuring the average particle size R of the large particles with a particle size distribution measuring device and drawing a particle size distribution curve of the large particles, fitting is performed assuming that the number of peaks in the range of the average particle size of 1 μm or more is one. It is preferable.
On the other hand, when it is more mathematically or logically appropriate to fit the number of the peaks as a plurality (for example, 2 to 5), the fitted particle size distribution curve with the number of the peaks as a plurality. May be drawn. In this case, the first large particle, the second large particle, the third large particle, etc. having a plurality of average particle diameters R1, R2, R3,. Become. These multiple large particles are collectively referred to as a large particle group. For the average particle size of each large particle belonging to the large particle group, the average particle size obtained by averaging the weighted ratios of the abundance ratio of each large particle is the “average particle size of large particles” of the present invention. r ”.

  The full width at half maximum (full width at half maximum) of the large particle in the particle size distribution curve is preferably 1.0 μm to 100 μm, more preferably 1.0 μm to 50 μm, and still more preferably 1.0 μm to 10 μm. It is preferable to use large-diameter particles having a peak with a narrow half-value width, because it becomes easy to estimate the speed at the time of spraying and the energy of the collision related to the speed, and control of the spraying conditions becomes easier.

  The full width at half maximum of the peak in the particle size distribution curve of the large particle is preferably determined based on the fitted distribution curve assuming that the number of the peak is one in the range of the average particle size of 1 μm or more. On the other hand, if it is more mathematically or logically appropriate to fit the number of the peaks as a plurality (for example, 2 to 5), the number of the peaks is set to a plurality, and the above-mentioned half for each peak. The price range may be obtained. Also in this case, the half width of each peak is preferably in the above range.

  The relative ratio (r / R) of the average particle size r of the small particles and the average particle size R of the large particles satisfies the relationship of (1/1000) ≦ (r / R) ≦ (1/5). . The relative ratio preferably satisfies the relationship of (1/750) ≦ (r / R) ≦ (1/10), and the relationship of (1/500) ≦ (r / R) ≦ (1/20) is satisfied. It is more preferable to satisfy | fill, and it is still more preferable to satisfy | fill the relationship of (1/250) <= (r / R) <= (1/30).

When the relative ratio satisfies the relationship, the difference between the average particle diameter r of the small particle and the average particle diameter R of the large particle becomes clearer. When the small particle and the large particle are made of the same inorganic substance (for example, titanium oxide), the difference in the average particle size becomes clearer because the weight of the individual particles of the small particle and the individual particles of the large particle This means that the difference becomes clearer.
In the present invention, it is preferable to clarify the difference in weight, because it is possible to more easily set spraying conditions considering the difference in weight. For example, when the difference in weight is relatively large, when the mixed particles are sprayed onto the base material to form a film, the collision energy given by the large particles to the small particles is significantly higher than the collision energy between the small particles. Can be large. That is, in the film formation process, the sprayed large-diameter particles collide with the small-diameter particles that have reached the base material or another adjacent particle, so that the collided small-diameter particles become the base material or By pressing or rubbing against another adjacent particle, the small diameter particle and the base material, or the small diameter particle and the adjacent another particle can be more reliably joined.

However, if the difference in weight is extremely large, the collided small-diameter particles may be shattered and it may be difficult to form a porous film. Further, when the difference in weight is extremely small, the degree to which the energy given by the large particle colliding with the small particle when the small particle is bonded to the base material or the adjacent another particle contributes, It becomes relatively small. In this case, the mechanism that collides with and joins the base material or other adjacent particles by the kinetic energy inherent to the sprayed small-diameter particles prevails.
By setting the relative ratio (r / R) to satisfy the above relationship, the difference in weight can be within an appropriate range, and a porous film having further improved strength and electronic conductivity can be formed on the substrate. Can be formed into a film.

  In the film forming method of the present invention, the operation of spraying the small particle and the operation of spraying the large particle are performed simultaneously or alternately.

  When carrying out simultaneously, it is preferable that the nozzle for spraying the small-diameter particles and the nozzle for spraying the large-diameter particles are brought close to each other and the jets blown from the nozzles are sprayed so as to at least partially overlap each other. Thereby, on the said base material, a large diameter particle can be made to collide more reliably with respect to a small diameter particle. As a result, the strength and electronic conductivity of the porous film formed on the substrate can be further enhanced.

  As another method in the case of carrying out at the same time, mixed particles in which small particles and large particles are mixed in advance may be prepared, and the mixed particles may be sprayed onto the substrate. Also by this method, the large-diameter particles can be more reliably collided with the small-diameter particles on the base material, and the strength and electronic conductivity of the porous film may be further enhanced.

In the mixed particles, the mixing ratio of small particles: large particles is preferably 0.1 parts by weight: 99.9 parts by weight to 50 parts by weight: 50 parts by weight, and 0.5 parts by weight: 99.5 parts. More preferably, it is more preferably from 25 parts by weight: 75 parts by weight, more preferably from 99 parts by weight to 20 parts by weight: 80 parts by weight.
When it is in the above range, the large-diameter particles can be more reliably collided with the small-diameter particles on the substrate. As a result, the strength and electronic conductivity of the porous film formed on the substrate can be further enhanced.

In the case of alternately carrying out, the small diameter particles are first sprayed onto the substrate, then the large diameter particles are sprayed, the small diameter particles are sprayed again, and then the large diameter particles are sprayed again.
The number of times of alternately repeating the operation of spraying the small particle and the operation of spraying the large particle is not particularly limited, and may be appropriately repeated according to the film thickness of the porous film to be formed.

In general, the larger the number of repetitions, the lower the porosity of the porous film can be made. This is because the larger the number of repetitions, the higher the probability that the large particle breaks the small particle.
Each spraying time and spraying speed may be the same or different. The longer the time for spraying the small-diameter particles, the larger the amount that the porous film becomes thicker at that time. The longer the time for spraying the large-diameter particles, the lower the porosity of the porous film that has been formed so far, so that a denser film can be obtained.

In the operation of spraying small-diameter particles, the spraying time t, spraying speed s, spraying angle, spraying distance, jet stream thickness, and the like are appropriately set according to the average particle diameter r of the small-diameter particles used and the type of substrate. The Usually, the longer the spraying time t, the faster the film forming speed, and the higher the spraying speed s, the lower the porosity of the porous film to be formed (the higher the density).
In the operation of spraying large-diameter particles, the spraying time T, spraying speed S, spray angle, spraying distance, thickness of the sprayed spray, and the like are appropriately determined according to the average particle diameter R of the large-diameter particles used and the type of the substrate. Is set. Usually, the longer the spraying time T or the larger the spraying speed S, the lower the porosity of the porous film to be formed (the higher the density).
The jet refers to an aerosol in which small diameter particles and / or large diameter particles are dispersed in a carrier gas.

The relative relationship between the spraying time t of the small particle and the spraying time T of the large particle is influenced by the difference between the average particle diameters r and R, but it cannot be generally stated, but the film is formed more reliably. From the viewpoint, it is preferable to satisfy t ≦ T.
The relative relationship between the spraying speed s for small-diameter particles and the spraying speed S for large-diameter particles is influenced by the difference between the average particle diameters r and R of each other. From the viewpoint, it is preferable that s ≧ S. Moreover, when it is this relative relationship (s> = S), the effect which reduces that a large-diameter particle | grain breaks up and is taken in in a porous membrane can also be show | played.

In the film forming method of the present invention, it is preferable to form the film by joining the small-diameter particles to the small-diameter particles sprayed on the base material so that the large-diameter particles collide with each other.
By causing the large-diameter particles to collide with the small-diameter particles, the small-diameter particles can be bonded more reliably. As a result, the strength and electronic conductivity of the porous material can be further enhanced.

  As a method of joining the small-diameter particles more reliably, there is a method of increasing the spraying speed s of small-diameter particles and / or increasing the spraying speed S of large-diameter particles or increasing the spraying time T of large-diameter particles. It is done.

From the viewpoint of preferentially joining the small-diameter particles, preventing the small-diameter particles from being excessively crushed, and preventing the small-diameter particles from detaching from the base material, the spraying speed s of the small-diameter particles is the average of the small-diameter particles used. Although depending on the particle diameter r, 10 to 650 m / s is preferable, 10 to 250 m / s is more preferable, and 10 to 150 m / s is still more preferable.
From the viewpoint of preferentially joining the small-diameter particles, preventing the small-diameter particles from being excessively crushed, and preventing the small-diameter particles from detaching from the base material, the large-diameter particles to be used are used as the spraying speed S of the large-diameter particles. 10 to 650 m / s is preferable, 10 to 250 m / s is more preferable, and 10 to 150 m / s is still more preferable.

  In the process of forming the porous film, the spraying speed of the large-diameter particles or the small-diameter particles until the film thickness of the porous film reaches 40% from the surface of the substrate is determined by the film thickness of the porous film. A region of 40% thickness of the porous membrane from the surface of the base material (region A) by making it faster than the spraying speed of the large diameter particles or the small diameter particles until the film thickness reaches 100% after 40%. Can be made lower than the porosity of a region (region B) having a thickness of 40% or more and a thickness of 100% after the porous membrane. That is, a porous film in which the region A is more dense than the region B can be formed. This is because the probability of crushing or crushing small-diameter particles on the substrate increases as the spraying speed of large-diameter particles or small-diameter particles increases. In addition, the position where the film thickness is 100% indicates the surface of the porous film where the film formation is completed.

  Here, “the spraying speed of the large-diameter particles or the small-diameter particles from the surface of the base material until the film thickness of the porous film reaches 40%” (the former) and “the film thickness of the porous film after 40% “Large particle or small particle spraying speed until reaching a film thickness of 100%” (the latter) is compared. At this time, when the former is the spraying speed of the large diameter particles, the latter is also the spraying speed of the large diameter particles, and when the former is the spraying speed of the small diameter particles, the latter is also the spraying speed of the small diameter particles. That is, the former and the latter are compared with respect to the spraying speed of the same kind of fine particles.

In addition, “the spraying speed” in the above (the former) means an average spraying speed from the surface of the base material to the film thickness of 40% of the porous film. That is, in the film forming process of the region A, after spraying under the condition of the spraying speed a1 (m / second) and the spraying time t1 (second), the condition of the spraying speed a2 (m / second) and the spraying time t2 (second) When the film is formed by spraying, the average spraying speed is [{a1 × t1 ÷ (t1 + t2)} + {a2 × t2 ÷ (t1 + t2)}] (m / sec).
Similarly, the “spraying speed” in the above (the latter) means an average spraying speed from 40% of the porous film to 100% of the film thickness. That is, in the film forming process of the region B, after spraying under the condition of spraying speed b1 (m / second) and spraying time t3 (second), the condition of spraying speed b2 (m / second) and spraying time t4 (second) When the film is formed by spraying, the average spraying speed is [{b1 × t3 ÷ (t3 + t4)} + {b2 × t4 ÷ (t3 + t4)}] (m / sec).

In addition to the method described above in which the spraying speed at the initial stage of the film forming process is higher than the spraying speed at the later stage of the film forming process, the spraying time of the large diameter particles at the initial stage of the film forming process can be The same effect may be obtained by a method of making the spraying time longer than the above.
That is, in the process of forming the porous film, the time for spraying the large-diameter particles from the surface of the base material until the film thickness of the porous film reaches 40% is defined as the film thickness of the porous film of 40%. Thereafter, the porosity of the region A can be made lower than the porosity of the region B by making it longer than the spraying time of the large diameter particles until the film thickness reaches 100%. That is, a porous film in which the region A is more dense than the region B can be formed. This is because the probability that the fine particles sprayed on the base material are crushed or the degree of pulverization increases as the spraying time of the large-diameter particles is increased.

Here, the area A and the area B are described as being divided, but it is not always necessary to divide these two areas. For example, regions C1 to C10 obtained by dividing a region from the surface of the base material to the film thickness of the porous film 100% in 10% increments in the film thickness direction are sequentially formed from the region C1 to the region C10. In the process of performing the process, as described above, the porosity in which the porosity is gradually increased from the region C1 to the region C10 by gradually decreasing the spraying speed of the large diameter particles or the small diameter particles. A film can be formed.
Similarly, in the process of sequentially forming the film from the region C1 to the region C10, as described above, by gradually reducing the spraying time of the large-diameter particles, the region C1 to the region C10 are stepped. A porous film with an increased porosity can be formed.
Needless to say, by further finely dividing the film in the film thickness direction, for example, by setting a region divided in 1 to 10% increments in the film thickness direction, it is more continuous from the substrate surface toward the film thickness of 100%. A porous film with an increased porosity can be formed.

In the film forming method of the present invention, the porosity is stepwise or continuously from the substrate surface toward the film thickness of 100% without changing the spraying speed or spraying time stepwise as described above. An increased porous membrane may be formed. In other words, even when a film is formed with a constant spraying speed or spraying time, a porous film with a porosity increasing stepwise or continuously may be formed from the surface of the substrate toward a film thickness of 100%. . This is because, as the film forming process proceeds, the integrated value of the impact energy received by the region formed in the early stage of the film forming process is larger than the integrated value of the impact energy received by the region formed in the latter part of the film forming process. This is thought to be due to the increase in the size. In general, the region where the integrated value is large increases the degree of crushing of the fine particles constituting the region.
However, it is possible to increase the porosity more reliably in the direction from the substrate surface to the surface of the porous film, by changing the spraying speed or spraying time stepwise as described above, preferable.

The film forming method of the present invention is a method for forming a porous film in which fine particles are bonded onto a base material by spraying small diameter particles and large diameter particles simultaneously or alternately onto the base material.
The fine particles may include small-sized particles and particles obtained by pulverizing small-sized particles, and large-sized particles and particles obtained by pulverizing large-sized particles.

According to the film forming method of the present invention, the relative ratio satisfies the relationship of (1/1000) ≦ (r / R) ≦ (1/5), so that among the fine particles constituting the porous film, the small diameter The ratio of particles broken by particles and / or small-diameter particles can be 50% by volume or more. The range of the relative ratio is set to a suitable range, or the spraying speed s for small-sized particles, the spraying time t for small-sized particles, the spraying speed S for large-sized particles, or the spraying time T for large-sized particles are adjusted to suitable ranges. By doing so, the ratio can be further increased. In other words, the content ratio of the large-diameter particles and / or the particles obtained by breaking the large-diameter particles in the porous film formed on the substrate can be 50% by volume or less, preferably 40% by volume or less. More preferably 30% by volume or less. This is thought to be because the large-sized particles sprayed onto the substrate during film formation are repelled outside after the collision without forming a porous film.
The smaller the content ratio of the large-sized particles in the porous film and the particles in which the large-sized particles are crushed, the more the particle diameters of the fine particles constituting the porous film can be made uniform. This is preferable because conductivity can be increased.

Fine particles larger than the small-sized particles before spraying are obtained by observing a cross section in the film thickness direction of the porous film with an electron microscope. Is determined to be a large particle or a particle in which the large particle is broken, and the content rate may be obtained. When calculating | requiring the said content rate, it calculates | requires as a percentage of the area which the particle | grains which the large diameter particle contained in the unit area of the said cross section or the large diameter particle crushed accounted for. The larger the unit volume, the more accurately reflects the content of the porous film, and it may be, for example, 100 μm ² .

The said base material in particular is not restrict | limited, For example, the transparent base material used for the photoelectrode of a dye-sensitized solar cell is mentioned.
Examples of the transparent substrate include a substrate made of glass or plastic, a resin film, and the like.

  Examples of the glass that is the material of the substrate include soda lime glass, borosilicate glass, quartz glass, borosilicate glass, Vycor glass, non-alkali glass, blue plate glass, and white plate glass.

  Examples of the plastic as the material of the base material include polyacrylic resin, polycarbonate resin, polyester resin, polyimide resin, polystyrene resin, polyvinyl chloride resin, and polyamide resin. Among these, polyester resins, particularly polyethylene terephthalate (PET), are produced and used in large quantities as transparent heat-resistant films. From the viewpoint of producing a thin, light and flexible dye-sensitized solar cell, the substrate is preferably a PET film.

  The surface of the base material is preferably coated with a metal oxide used for a transparent conductive substrate of a known dye-sensitized solar cell. For example, indium oxide / tin oxide (ITO), fluorine-doped tin oxide (FTO), zinc oxide, tin oxide, antimony-doped tin oxide (ATO), indium oxide / zinc oxide (IZO), gallium oxide / zinc oxide (GZO) Etc. may be formed in advance on the surface of the substrate. When the layer made of these metal oxides is formed on the surface of the substrate, the porous film is preferably formed by being laminated on the metal oxide layer. The metal oxide layer may be a single layer or a plurality of layers.

Examples of the method for spraying the small-sized particles and the large-sized particles on the substrate include an aerosol deposition method (AD method) using a carrier gas, an electrostatic fine particle coating method in which fine particles are accelerated by electrostatic force, a cold spray method, and the like. Among these methods, the AD method is preferred because it is easy to adjust the spraying speed and it is easy to adjust the strength and film thickness of the porous film to be formed.
The small diameter particles and the large diameter particles may be sprayed from the same nozzle or from different nozzles. The timing of spraying the small diameter particles and the large diameter particles may be performed simultaneously or alternately.

The AD method is a method in which fine particles are accelerated from a subsonic speed to a supersonic speed by a carrier gas such as helium and sprayed onto a substrate. At least a part of the fine particles colliding with the surface of the base material bites into the surface of the base material and is not easily peeled off. Further, due to this collision, a new surface is formed on the surface of the base material and the surface of the fine particles, and the base material and the fine particles are joined mainly on the new surface. Subsequently, by continuing the spraying, another fine particle collides with the fine particle that has digged into the surface of the substrate. Due to the collision of the fine particles, a new surface is formed on the surface of the fine particles, and the fine particles are joined mainly on the new surface. At this time, by appropriately adjusting the speed of spraying, it is possible to adjust the degree of crushing of the small diameter particles and the large diameter particles. Usually, the higher the speed of spraying, the greater the degree of breakage of small and large particles.
In the collision between the fine particles, a temperature rise that causes the fine particles to melt hardly occurs. Therefore, a grain boundary layer made of vitreous substantially does not exist at the interface where the fine particles are joined. By continuing the spraying of the fine particles, a porous film is formed in which a large number of fine particles are gradually bonded to the substrate surface. Since the formed porous film has sufficient strength and electronic conductivity as a photoelectrode of a dye-sensitized solar cell, baking by baking is not required.
As a method of adjusting the spraying speed, for example, the opening diameter of the spray nozzle (the diameter of the opening or the length of one side of the opening) can be adjusted. As the opening diameter is increased, the spraying speed can be decreased. As the opening diameter is decreased, the spraying speed can be increased. For example, it is possible to easily accelerate to about several hundreds m / s by blowing fine particles (small particle or large particle) conveyed through a gas through a nozzle opening having an opening diameter of 1 mm or less.

In the present invention, “fine particles are bonded” means a state in which new surfaces are formed on the surfaces of adjacent fine particles and are in close contact with each other. This close contact state can also be expressed as a state of being fused and bonded (fused). In many cases, there is substantially no grain boundary layer made of vitreous formed by melting the particle surface on the surface where the particles are bonded to each other.
Usually, when observed with an electron microscope, it can be seen that the “joined state” and the “contact state” are clearly different. When a SEM photograph is taken at a magnification (for example, 50,000 to 200,000 times) that allows observation of the entire fine particles (the entire fine particles enter the observation field of view), a gap is formed at the boundary between the fine particles in the bonded state. A state of close contact is observed.

  FIG. 2 is a schematic cross-sectional view showing an example of a process for forming a film by the film forming method according to the present invention. The operation of spraying the small-diameter particles 21 and the operation of spraying the large-diameter particles 26 on the surface of the base material 24 is performed simultaneously or alternately to show that the porous film 23 is formed by bonding the fine particles 22 to each other. ing. However, the relative sizes of the small-diameter particles 21, the large-diameter particles 26, and the fine particles 22 in FIG. 2 are merely examples, and are not limited thereto. Although the porous film 23 is drawn so as to be composed of fine particles 22 smaller than the small-diameter particles 21, the fine particles 22 are not necessarily smaller than the small-diameter particles 21, and the small-diameter particles 22 and / or the large-diameter particles are not necessarily included. The porous film 23 may be formed in a state where the original shape is maintained without being broken.

  FIG. 3 is a schematic cross-sectional view showing an example of a process for forming a film by performing only the operation of spraying the small-diameter particles 31. Small particles 31 are sprayed onto the surface of the substrate 34, and the small particles 31 and the fine particles 32 made of particles obtained by pulverizing the small particles 31 form the thin film 33. The thin film 33 is a porous film or a dense thin film. In order to form a film by spraying only the small-diameter particles 31, it is necessary to increase the spraying speed and apply a large kinetic energy for breaking the small-diameter particles 31. However, it is usually not easy to adjust the degree to which the small diameter particles 31 are crushed. In particular, when using small-diameter particles 31 whose average particle diameters are not uniform, it is difficult to control the degree of crushing by spraying. For this reason, even if the thin film 33 becomes a porous film, it is not easy to control the porosity. When the small-diameter particles 31 are crushed excessively, the thin film 33 becomes a dense film and the porosity is extremely small. In addition, as shown in FIG. 4, when the small-diameter particles 41 are sprayed weakly so as not to be crushed, the small-diameter particles 41 are often simply deposited without being bonded to the base material 44. The small-diameter particles 41 deposited on the base material 44 become so-called green compacts 45. The green compact 45 is a fragile deposit that easily peels from the substrate 44.

In the present invention, the speed of the small diameter particles accelerated by the carrier gas is preferably 10 to 650 m / s, more preferably 10 to 250 m / s, and still more preferably 10 to 150 m / s.
By being below the upper limit of the above range, the porous film can be more easily formed without excessively crushing when the small-diameter particles to be sprayed collide with the base material or fine particles already bonded.
By being above the lower limit of the above range, the sprayed small-diameter particles can be reliably bonded to the base material or the already bonded fine particles to form a porous film having sufficient strength and electron conductivity. Easy to do.
The speed of the small-diameter particles accelerated by the carrier gas may be appropriately adjusted in the above range according to the type of the substrate, the average particle diameter r of the small-diameter particles, the kind of the inorganic substance forming the small-diameter particles, and the like.

In the present invention, the speed of the large particles accelerated by the carrier gas is preferably 10 to 650 m / s, more preferably 10 to 250 m / s, and still more preferably 10 to 150 m / s.
By being larger than the lower limit of the above range, when the large-diameter particles to be sprayed collide with the fine particles already sprayed on the base material, the collision energy for more surely joining the fine particles is given more sufficiently. be able to. As a result, it is possible to more easily form a porous film having sufficient strength and electron conductivity.
It is suitable for supporting the pigment by preventing excessively pulverizing the fine particles when the large-sized particles to be sprayed collide with the fine particles already sprayed on the base material by being below the upper limit of the above range. It is easier to form a porous film having a high porosity.
The speed of the large-sized particles accelerated by the carrier gas is appropriately determined depending on the type of the base material, the average particle size R of the large-sized particles, the kind of the inorganic substance forming the small-sized particles and the large-sized particles, and the like. Adjust it.

The film forming method of the present invention is a method capable of forming a film in a room temperature environment. Here, normal temperature refers to a temperature that is sufficiently lower than the melting point of the small and large particles, and is substantially 200 ° C. or lower.
It is preferable that the temperature of the normal temperature environment is equal to or lower than the melting point of the base material. When the base material is made of resin, the temperature of the room temperature environment is preferably less than the Vicat softening temperature.

  In the film forming method of the present invention, for example, the ultrafine particle beam deposition method and apparatus disclosed in International Publication No. WO01 / 27348A1, or the brittle material ultrafine particle low temperature molding method and apparatus disclosed in Japanese Patent No. 32655481, The present invention may be applied without departing from the spirit of the present invention.

  In these known AD methods, it is important to preliminarily apply an internal strain to the fine particles to determine whether or not cracks will occur by pretreating the fine particles to be sprayed with a ball mill or the like. By adding this internal strain, the sprayed fine particles can be easily crushed and deformed when colliding with the base material or already bonded fine particles, and as a result, a dense film can be formed. Yes.

  In the film forming method of the present invention, it is not necessary to apply internal strain in advance to the small particle and large particle to be sprayed. The small diameter particles and the large diameter particles have an appropriate strength, so that the small diameter particles and the large diameter particles are not excessively pulverized during spraying to form a porous film in which voids are sufficiently formed inside. it can. Thereby, a porous film having a large specific surface area can be formed.

  On the other hand, when a film is formed by spraying small-diameter particles to which internal strain has been applied in advance, a very dense thin film having a small porosity is obtained. Such a dense thin film hardly adsorbs a dye (sensitizing dye) and is inappropriate for use as a photoelectrode.

  In the film forming method of the present invention, an aerosol generator used in the ultrafine particle beam deposition method in order to prevent the small particles and large particles from aggregating to form secondary particles before spraying, A classifier and / or a disintegrator may be used.

  In the film forming method of the present invention, the porosity of the porous film to be formed can be adjusted by the spraying speed and spray angle of the small particle or large particle, but the average particle diameter r or the large particle of the small particle can be adjusted. By setting the average particle diameter R to a suitable range as described above, it can be adjusted more effectively.

  When preparing mixed fine particles in which the small diameter particles or large diameter particles are mixed in advance, the preparation method is not particularly limited. For example, the small diameter particles and the large diameter particles may be uniformly mixed with a ball mill or the like before spraying on the substrate.

<< Film body >>
The film-forming body of the present invention comprises at least a porous film formed by the film-forming method described above and the base material.

The porous film is a porous film having voids (also referred to as pores or pores) that can carry the dye of the dye-sensitized solar cell.
The porosity of the porous film (also referred to as porosity, porosity, or porosity) is preferably 50% or more, more preferably 50 to 85%, and still more preferably 50 to 80%.
If it is at least the lower limit of the above range, more dye can be supported. The intensity | strength of a porous membrane can be strengthened more as it is below the upper limit of the said range.

In the present specification and claims, the porosity means “percentage occupied by the volume of the void per unit volume of the formed thin film”. This porosity is calculated by porosity = bulk specific gravity / true specific gravity × 100 (%). The bulk specific gravity is obtained by dividing the mass per unit volume of the porous membrane by the mass of the inorganic substance particles per unit volume (theoretical value), and the true specific gravity is the specific gravity of the inorganic substance particles (theoretical value). ). The porosity can be measured by a known gas adsorption test or mercury intrusion test as a method for analyzing fine structure characteristics.
Further, when the porous film according to the present invention has a different porosity in the film thickness direction, the “porosity of the porous film” is “average of the film thickness direction of the porous film” unless a specific region is clearly indicated. Mean void ratio ".

The porous membrane is formed on the substrate, and the thickness of the porous membrane is preferably 1 μm to 200 μm, preferably 2 μm to 100 μm, and 5 μm to 50 μm. More preferably it is.
When it is at least the lower limit of the above range, the probability that the dye supported on the porous film absorbs light energy can be further increased, and the photoelectric conversion efficiency in the dye-sensitized solar cell can be further improved. Further, when the amount is not more than the upper limit of the above range, the exchange between the bulk electrolyte (electrolyte in the solar battery cell) and the electrolyte in the porous film is more efficiently performed by diffusion, and the photoelectric conversion efficiency can be further improved. .

The porous film preferably has a crystalline part at least on the surface. When at least a part of the surface is crystalline, the photoelectric conversion efficiency of the dye-sensitized solar cell including the film-formed body on which the porous film is formed as a photoelectrode can be further improved. The reason for this is considered to be that the electron conductivity is further increased due to the crystallinity and / or the efficiency of electron transfer between the dye and the inorganic substance is further increased.
Here, “crystalline” means that the fine particles of the inorganic substance forming the porous film are regularly arranged like crystals. However, this does not mean that the atoms constituting the inorganic particles form a complete crystal. As described later, the crystallinity can be confirmed by observing regular parallel lines (stripes) when the surface of the porous film is observed with an electron microscope and a TEM photograph is taken. .
Further, the “surface of the porous membrane” means the surface on the opposite side when the surface where the porous membrane is in contact with the base material is the “back surface”. That is, the surface on which the particles are sprayed is called “surface”.

  It is more preferable that the entire surface of the porous film is crystalline, but the effect can be achieved even when a part of the surface is crystalline and the other part is amorphous (non-crystalline). Moreover, it is more preferable that it is crystalline not only on the surface of the porous membrane but also in the thickness direction of the porous membrane.

Whether a part or all of the surface of the porous film is crystalline can be confirmed by observing the surface of the porous film with an electron microscope. For example, when a regular and parallel stripe pattern as shown in FIGS. 5 to 6 is observed by taking a TEM photograph, it can be said that at least the surface region is crystalline. On the other hand, when the surface or film thickness direction is amorphous (non-crystalline), such a striped pattern cannot be observed. For example, FIG. 7 to FIG. 8 are TEM photographs of the surface of a porous titanium oxide layer produced by using a titanium oxide paste manufactured by Pexel, which can be formed by low-temperature firing (110 ° C. for 5 minutes), but the striped pattern is not observed. .
Whether the porous film is crystalline in the film thickness direction can be confirmed by, for example, X-ray diffraction.

  It is preferable that the porosity of the porous film constituting the film-forming body of the present invention is increased stepwise or continuously in the film thickness direction away from the substrate.

  FIG. 11 shows a state in which the porosity of the porous film 23 is continuously increased in the film thickness direction away from the base material 24. By forming a porosity gradation in this way, a region with a lower porosity (a region with higher density) is placed close to the substrate, so that the dye excited by light is transferred from the substrate to the substrate. Electrons can be more easily conducted and the photoelectric conversion efficiency can be further improved. In addition, by arranging a region with a higher porosity (region with a lower density) away from the base material, the sunlight scattering effect can be enhanced and the utilization efficiency of sunlight is increased. Conversion efficiency is further improved. As a result, the photoelectric conversion efficiency of the dye-sensitized solar cell using the film-forming body provided with the porous film 23 as a photoelectrode can be further improved.

As a method for investigating that the porosity of the porous film is increased stepwise or continuously in the film thickness direction away from the substrate, the cross section of the porous film in the film thickness direction is observed with an electron microscope. It is confirmed that the degree of bonding of the fine particles constituting the region close to the base material is larger than the degree of bonding of the fine particles constituting the region close to the surface of the porous film, and is in a denser state. That's fine. Alternatively, it is confirmed that the void volume (porosity) in the region close to the base material is smaller than the void volume (porosity) in the region close to the surface of the porous membrane, and is in a denser state. That's fine.

For example, in the film thickness direction of the porous film, the degree of bonding of the fine particles in the region from the surface of the base material to the film thickness of the porous film is 40% or more. What is necessary is just to confirm that it is larger than the grade of the said microparticle joining in the area | region to 100% of thickness. Alternatively, the volume of voids (porosity) included in the region up to 40% of the film thickness of the porous film is the volume of voids included in the region of 40% after the film thickness of the porous film up to 100% ( What is necessary is just to confirm that the porosity is small.

The titanium oxide paste manufactured by Pexel is commercially available as a porous titanium oxide layer can be formed by low-temperature baking at 110 ° C. for 5 minutes. Moreover, it is known that a porous semiconductor layer can be formed by the low-temperature firing (see Chemistry Letters Vol. 36, No. 6 (2007), etc.).
Such low-temperature baking is a mild temperature compared to the conventional baking temperature of 500 ° C., but it is still difficult to use a resin substrate or a resin film as a base material.

Examples of a method for obtaining a photoelectrode for a dye-sensitized solar cell by adsorbing the dye to the porous film constituting the film-forming body of the present invention include the following methods.
First, a dye described later is dissolved in a solvent, and a tetrabutylammonium cation (hereinafter sometimes referred to as TBA) is further added to prepare a dye solution. The film forming body can be used as a photoelectrode by immersing the film forming body in this dye solution and adsorbing the dye and TBA to the porous film.

  The said pigment | dye is not specifically limited, The sensitizing dye generally used for the dye-sensitized solar cell can be used. Examples of the dye include cis-di (thiocyanato) -bis (2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium (II) (hereinafter sometimes referred to as N3), N3 bis-TBA salt ( N719), tri (thiocyanato)-(4,4 ′, 4 ″ -tricarboxy-2,2 ′: 6 ′, 2 ″ -terpyridine) ruthenium tris-tetrabutylammonium salt (black dye) Ruthenium dye systems, etc.). Examples of the dye include coumarin, polyene, cyanine, hemicyanine, thiophene, indoline, xanthene, carbazole, perylene, porphyrin, phthalocyanine, merocyanine, catechol and squarylium. Various organic pigments can be mentioned. Furthermore, a donor-acceptor composite dye combining these dyes is also used as the dye.

As a solvent used for preparing the dye solution, it is possible to use one or a mixture of two or more of various solvents such as alcohol, nitrile, ether, ester, ketone, hydrocarbon, halogenated hydrocarbon and the like. it can.
Examples of the alcohol include methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol, t-butyl alcohol, and ethylene glycol.
Examples of the nitrile include acetonitrile and propionitrile.
Examples of the ether include dimethyl ether, diethyl ether, ethyl methyl ether, and tetrahydrofuran.
Examples of the ester include ethyl acetate, propyl acetate, and butyl acetate.
Examples of the ketone include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone.
Examples of the hydrocarbon include pentane, hexane, heptane, octane, cyclohexane, toluene, and xylene.
Examples of the halogenated hydrocarbon include methylene chloride and chloroform.

  When N3 or N719 is used as the dye, it is preferable to use, for example, a mixed solvent of t-butyl alcohol (t-BuOH) and acetonitrile (MeCN) as a solvent for preparing the dye solution.

The TBA cation added to the dye solution is preferably added to the dye solution in a state where a hydroxylated TBA or a TBA salt is dissolved or dispersed in an appropriate solvent.
Examples of the TBA salt include brominated TBA (TBAB) and iodinated TBA (TBAI).

  The amount of TBA cation added to the dye solution is preferably in the range of 0.1 to 3.0 equivalents, more preferably in the range of 0.3 to 2.5 equivalents, per mole of the dye contained in the dye solution. A range of 0.5 to 1.5 equivalents is more preferable. When the amount of TBA cation added is less than 0.1 equivalent, the effect of adding TBA cation is insufficient, and the photoelectric conversion efficiency becomes the same as when TBA cation is not added. When the added amount of TBA cation exceeds 3.0 equivalents, the effect of adding TBA cation reaches its peak, which is not preferable.

  In the dye solution, the concentration of the dye is not particularly limited, but is usually preferably in the range of 0.05 to 1.0 mM, more preferably in the range of 0.1 to 0.5 mM.

  The method for immersing the film-forming body in the dye solution is not particularly limited, and the film-forming body is immersed in the dye solution in a container, held at a constant temperature for a certain time, and then the film-forming body is pulled up. Is mentioned. In addition, a method of continuously charging, dipping and pulling up while moving the film-forming body into the dye solution is also included.

  The temperature of the dye solution at the time of immersion is not particularly limited. The temperature is preferably 10 to 90 ° C. The immersion time is preferably 30 minutes to 50 hours. What is necessary is just to set the combination of immersion temperature and immersion time according to the combination of the kind of inorganic substance which comprises the pigment | dye to be used and a porous membrane.

After immersion, the film-forming body is pulled up from the dye solution, and excess dye is washed with alcohol and dried as necessary.
By the above operation, a photoelectrode for a dye-sensitized solar cell in which the dye and TBA are adsorbed on the porous film constituting the film-forming body according to the present invention is obtained.

  The dye-sensitized solar cell of the present invention is provided with the film-formed body or a photoelectrode comprising the film-formed body. As the member other than the photoelectrode, a counter electrode, a separator, an electrolyte (electrolyte), and the like used in known dye-sensitized solar cells can be used.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited by these examples.

  Table 1 shows the average particle diameter of the particles used in the operation for spraying the small-diameter particles, the average particle diameter of the particles used in the operation for spraying the large-diameter particles, and the spraying speed. Table 2 shows the characteristics of a film obtained by spraying fine particles on a glass substrate on which a transparent conductive film (FTO) is formed by AD method under each condition shown in Table 1.

In Example 1, mixed particles in which small particles and large particles shown in Table 1 were mixed in advance at a weight ratio of 10:90 were prepared, and these were simultaneously sprayed from the same nozzle to form a film by the AD method.
In Comparative Example 3, small-diameter particles in which small-diameter particles having an average particle diameter of 30 nm and small-diameter particles having an average particle diameter of 200 nm were mixed at 45:55 (weight ratio) were prepared, and these were simultaneously sprayed from the same nozzle by the AD method. A film was formed.

As the large particles in Table 1, rutile type titanium oxide particles (rutile degree 95%, average particle size 2.31 μm, purity 99.9%, manufactured by Mitsuwa Chemical Co., Ltd.) were used.
As the small-diameter particles in Table 1, anatase-type titanium oxide particles (model number = P25, rutile conversion rate 30%, average particle size about 30 nm, manufactured by Nippon Aerosil Co., Ltd.) were used.
As small-diameter particles in Table 1, rutile type titanium oxide particles (model number = R310, average particle size of about 200 nm, manufactured by Sakai Chemical Industry Co., Ltd.) were used.

The conditions of the AD method used here are as follows.
A film was formed using the film forming apparatus 10 shown in FIG. In the film forming chamber 1, the mixed particles 4 were sprayed from the nozzle 2 having a rectangular opening of 5 mm × 0.5 mm to the glass substrate 3 at a subsonic to supersonic jet speed shown in Table 1.
Helium, which is a carrier gas, was supplied from the cylinder 5 to the carrier pipe 6, and the flow rate was adjusted by the mass flow controller 7. Fine particles for spraying were loaded into the aerosol generator 8, dispersed in a carrier gas, conveyed to the crusher 9 and the classifier 11, and sprayed from the nozzle 2 onto the substrate 3. A pump 12 is connected to the film forming chamber 1, and the film forming chamber is set to a negative pressure.
In order to prevent the formation of secondary particles (aggregated particles), fine particles from which moisture was previously removed by vacuum drying were used. During spraying for about 10 minutes, the stage 13 was moved horizontally so that a porous film having a uniform thickness was formed on the glass substrate 3.

[Comparative Example 6]
The same glass substrate on which a transparent conductive film (FTO film) was formed on the surface was used as in Example 1. A titanium oxide paste was applied onto the glass substrate by a doctor blade method and baked at 110 ° C. for 5 minutes in an air atmosphere to form a porous titanium oxide layer having a thickness of 10 μm on the transparent conductive film.

  Next, the glass substrates formed in Example 1, Comparative Example 3 and Comparative Example 6 were immersed in an alcohol solution of a dye (N719, manufactured by Solaronics) prepared at 0.3 mM at room temperature for 24 hours. Next, after lightly washing the photoelectrode consisting of a porous film carrying a pigment and a glass substrate with alcohol, a 30 μm-thick silicon rubber spacer is placed around the thin film, and an electrolyte solution (Iodolyte 50, manufactured by Solaronics) is used. Poured. Subsequently, a counter electrode made of glass with platinum coating was placed over the glass so as not to enter air, and the photoelectrode and the counter electrode were sandwiched with a double clip and pressed to obtain a simple cell of a dye-sensitized solar cell. The effective area was 4 mm square.

[Evaluation of photoelectric conversion efficiency]
Using a solar simulator (AM1.5, 100 mW / cm ² ) equipped with an IV characteristic measurement device, the photoelectric conversion efficiency of each simple cell produced was evaluated.
As a result, the photoelectric conversion efficiencies of Example 1, Comparative Example 3, and Comparative Example 6 were 7.06%, 0.2%, and 5.70% in this order. From this result, it is clear that the film-forming body provided with the porous film of Example 1 is excellent as a photoelectrode.

  Thus, the reason why the photoelectric conversion efficiency of the dye-sensitized solar cell according to Example 1 is excellent is that the porous film of the film forming body constituting the dye-sensitized solar cell has strength, electron conductivity, dye adsorbability, and electrolyte solution. It is because it is excellent in diffusibility.

[Observation of cross section of porous film in thickness direction]
When the cross section of the porous film of the film-formed body produced in Example 1 was observed with an electron microscope and an SEM photograph was taken (see FIG. 9), it was confirmed that the fine particles constituting the porous film were joined together. It could be confirmed. FIG. 9 is an image of a surface obtained by smoothly cutting a fracture surface of a porous membrane by ion milling at a magnification of about 100,000 times. It can be seen that the new surfaces of the fine particles are bonded together. The SEM photograph which imaged this cross section by about 20,000 times magnification is shown in FIG. When this SEM photograph is analyzed, the porous film is mainly composed of small-diameter particles and fine particles obtained by pulverizing the small-diameter particles, and the large-diameter particles contained in the porous film are 30% of the porous film. It was estimated that:

  Moreover, when the cross section of the film thickness direction of the film production body produced in Example 1 was observed with the electron microscope, and the SEM photograph was taken (refer FIG. 12), the volume (void ratio) of the space | gap of the said porous film is It was confirmed that the film thickness was higher in the film thickness direction away from the substrate. In other words, it was confirmed that the degree of bonding between the fine particles in the region close to the substrate (region A) was larger than the degree of bonding between the fine particles in the region close to the film surface (region B). That is, the porosity of region B is larger than the porosity of region A.

[Measurement of porosity]
The porosity of the porous membrane of the membrane produced in Example 1 was 55% as measured by the nitrogen adsorption method. Table 2 shows the porosity of the films measured in the same manner and obtained in Comparative Examples 1 and 3. In Comparative Examples 2, 4, and 5, since no film was formed, it was impossible to measure the porosity.

[Film crystallinity]
Moreover, the surface of the porous film of the film-forming body created in Example 1 was observed with an electron microscope, and a TEM photograph was taken. The photographs are shown in FIGS. Since a regular and parallel stripe pattern was observed in the portion corresponding to the titanium oxide particles, it was judged that at least the surface of the region was crystalline. Similarly, regular and parallel stripes were not observed on the surfaces of the porous titanium oxide layer of Comparative Example 6 and the thin films of Comparative Examples 1 to 5, and thus were determined not to be crystalline. TEM photographs of the surface of the porous titanium oxide layer of Comparative Example 6 are shown in FIGS.

  From the above, it is apparent that the film forming method of the present invention does not require a baking step, and therefore the time required for film formation can be shortened. Moreover, since it can form into a film at normal temperature, it is clear that a porous film | membrane can be formed on base materials, such as a plastics and a resin film.

  The film forming method of the present invention can be widely used for the production of dye-sensitized solar cells.

DESCRIPTION OF SYMBOLS 1 ... Film forming chamber, 2 ... Nozzle, 3 ... Base material, 4 ... Mixed particle, 5 ... Gas cylinder, 6 ... Transfer pipe, 7 ... Mass flow controller, 8 ... Aerosol generator, 9 ... Crusher, 10 ... Product made Membrane device, 11 ... classifier, 12 ... pump, 13 ... stage, 21 ... small particle, 22 ... fine particle, 23 ... porous membrane, 24 ... substrate, 26 ... large particle, 31 ... small particle, 32 ... fine particle 33 ... Thin film, 34 ... Base material, 41 ... Small diameter particle, 44 ... Base material, 45 ... Green compact.

Claims (15)

This is a method for forming a porous film of an inorganic substance on the base material by spraying inorganic fine particles onto the base material so as to join the base material and the fine particles and joining the fine particles to each other. And
As the fine particles, small particles having an average particle diameter r <1 μm and large particles having an average particle diameter R ≧ 1 μm are used.
The relative ratio (r / R) between the average particle size r of the small particles and the average particle size R of the large particles is
Satisfies the relationship of (1/1000) ≦ (r / R) ≦ (1/5),
An operation for spraying the small diameter particles and an operation for spraying the large diameter particles are performed simultaneously or alternately.   2. The film forming method according to claim 1, wherein the small-diameter particles sprayed on the base material are bonded to each other by forming the large-diameter particles to collide with each other to form a film. .   The spraying speed of the large-diameter particles or the small-diameter particles from the surface of the base material until the film thickness of the porous film reaches 40% is from 40% of the porous film to 100% of the film thickness. The film forming method according to claim 1, wherein the film is formed at a speed higher than a spraying speed of the large diameter particles or the small diameter particles.   The average particle diameter r of the said small diameter particle is 1 nm-100 nm, The film forming method as described in any one of Claims 1-3 characterized by the above-mentioned.   The average particle diameter R of the said large diameter particle is 1 micrometer-100 micrometers, The film forming method as described in any one of Claims 1-4 characterized by the above-mentioned.   The said inorganic substance is an oxide semiconductor, The film forming method as described in any one of Claims 1-5 characterized by the above-mentioned.   The film formation according to claim 1, wherein the inorganic substance is an oxide semiconductor, and the small-diameter particles and the large-diameter particles are oxide semiconductors having different crystal systems. Method.   The said base material consists of resin, The film forming method as described in any one of Claims 1-7 characterized by the above-mentioned.   The film forming method according to claim 1, wherein the base material is a film made of a resin.   A film forming body obtained by the film forming method according to any one of claims 1 to 9.   The film forming body according to claim 10, wherein a content ratio of the large-diameter particles in the porous film is 30% by volume or less.   The film-forming body according to claim 10 or 11, wherein the porosity of the porous film is 50% or more.   The film-forming body according to any one of claims 9 to 11, wherein the porous film has a crystalline part at least on a surface thereof.   The film-forming body according to any one of claims 10 to 13, wherein the porosity of the porous film increases in the film thickness direction away from the substrate.   A dye-sensitized solar cell comprising the film-forming body according to any one of claims 10 to 14.