JPWO2014115763A1 - Film-forming method, porous film, photoelectrode, and dye-sensitized solar cell - Google Patents

Abstract

In this film forming method, in the solvent containing the raw material compound, the fine particles of the inorganic substance using the raw material compound as a raw material are synthesized and the aggregated particles obtained by agglomerating the fine particles are used. A porous particle is produced through a step of strengthening the bonding between the fine particles, the porous particle is sprayed onto the base material, the base material and the porous particle are joined, and the porous particles are joined together. Thus, the method includes forming a porous film made of the inorganic substance on the base material.

Description

The present invention includes a film forming method for forming a porous film made of the particles on the substrate by spraying the particles onto the substrate, the porous film formed by the film forming method, and the porous film. And a dye-sensitized solar cell including the photoelectrode.
This application claims priority on January 22, 2013 based on Japanese Patent Application No. 2013-009210 for which it applied to Japan, and uses the content here.

As a method of forming a porous film that constitutes the photoelectrode of a dye-sensitized solar cell, a paste in which titanium oxide particles are mixed with a binder such as a polymer is applied on a substrate, and this is fired to form a porous film. How to do is known. This method has an advantage that a porous film can be easily obtained. However, since the substrate material is required to have heat resistance, there is a problem that the substrate to be used is substantially limited to the glass substrate.
Then, it replaces with the method of baking a paste, and the method of spraying a titanium oxide particle on a board | substrate and obtaining the film forming body which consists of titanium oxide is also examined. Examples of such a method include a spray method, a cold spray method, an electrostatic spray method, a thermal spray method, and an aerosol deposition method (AD method).

  Patent documents 1-3 are mentioned as conventional AD method. In Patent Document 1, as the titanium oxide particles to be sprayed (ultrafine particle brittle material), secondary particles aggregated to about 50 nm to 1 μm by firing primary particles having a particle size of about several tens of nm are used. . The secondary particles have a characteristic that they are easily broken and crushed from the interface by an impact sprayed on the substrate. For this reason, according to the AD method of Patent Document 1, a dense film-formed body (dense film) having a theoretical density of 95% or more is obtained.

  In Patent Documents 2 to 3, an AD method for obtaining a porous film, not a dense film, is proposed by changing the method for producing secondary particles used in the AD method of Patent Document 1. Specifically, first, primary particles are dispersed in a solution having a binder such as a high molecular polymer, and an aggregate obtained by drying and solidifying the primary particles is obtained. Is sintered strongly to obtain a porous sintered body in a large lump. Next, this sintered body is crushed with a mortar and further passed through a 25 μm mesh to obtain secondary particles adjusted to a size of about 20 μm that can be sprayed. It is reported that a porous film can be obtained by spraying the secondary particles so as to collide with the substrate at an angle of 60 °.

Japanese Patent No. 3265481 Japanese Patent No. 4103470 Japanese Patent No. 4626829

  However, in the method for preparing secondary particles (spraying particles) described in Patent Documents 2 to 3, even if the particle diameter is adjusted to 25 μm or less and adjusted to an average particle diameter of 20 μm by passing through a mesh, there is a variation in particle diameter. Since it is large, the bonding strength and porosity of the secondary particles in the formed porous film vary. In addition, when the secondary particles have an average particle size of about 20 μm, not only a film forming effect for forming a film but also a blasting effect for scraping the formed film occurs, so that the film forming efficiency is low (the film forming speed is low). Therefore, it is relatively difficult to increase the film thickness. When spraying for a long time in order to obtain a thick porous film, the probability that the large-diameter particles that have barely passed through the mesh will be sprayed increases, and the risk of cracking in the porous film being formed increases. Narrowing the opening of the mesh to remove large-diameter particles from the spray particles is not a practical solution because the mesh becomes clogged and it becomes difficult to prepare a large amount of spray particles.

  The present invention has been made in view of the above circumstances, and a film forming method capable of forming a thick porous film more easily than the conventional one, a porous film manufactured by the film forming method, and the porous film And a dye-sensitized solar cell provided with the photoelectrode.

[1] In a solvent containing a raw material compound, the fine particles of the inorganic substance using the raw material compound as a raw material are synthesized and aggregated particles obtained by aggregating the fine particles are used. By producing porous particles through a step of strengthening bonding, spraying the porous particles on a base material, joining the base material and the porous particles, and joining the porous particles to each other, A film forming method comprising forming a porous film made of the inorganic substance on the substrate.
That is, in the solvent containing the raw material compound, the fine particles of the inorganic material using the raw material compound as a raw material are synthesized and the aggregated particles obtained by aggregating the fine particles are used to bond the fine particles in the aggregated particles. The inorganic particles are formed on the base material by spraying the porous particles produced through the strengthening process onto the base material, thereby joining the base material and the porous particle and joining the porous particles to each other. A film forming method comprising forming a porous film made of a substance.
[2] In the step of strengthening the bonding between the fine particles, the fine particles in the aggregated particles are bonded to each other by not packing the aggregated particles closely, and the film formation according to the above [1] Method.
In the step of strengthening the bonding between the fine particles, the fine particles in the aggregated particles are bonded together without bonding the aggregated particles by not packing the aggregated particles closely. The film forming method according to [1].
[3] In the step of strengthening the bonding between the fine particles, by firing at a temperature range of a temperature at which the fine particles are in contact with each other by a solid-phase reaction and a temperature range that can be bonded to the melting point of the inorganic substance. The film forming method according to [1] or [2], wherein the fine particles are bonded to each other.
[4] In the step of strengthening the bonding between the fine particles, a reactive compound containing a metal or a semiconductor constituting the fine particles and the aggregated particles are mixed, and the fine particles are chemically bonded via the reactive compound. The film forming method according to any one of [1] to [3], wherein the film forming method is bonded to the film.
[5] The film forming method according to any one of [1] to [4], wherein an average particle diameter of the aggregated particles and the porous particles is 200 nm to 2 μm.
[6] The film forming method according to any one of [1] to [5], wherein an average particle diameter of the fine particles is 10 nm to 100 nm.
[7] The porous particles to be sprayed onto the base material do not include porous particles having a particle size of 5 μm or more, according to any one of [1] to [6], Film forming method.
That is, the film forming method according to any one of [1] to [6], wherein the porous particles to be sprayed do not include porous particles having a particle diameter of 5 μm or more. [8] The film forming method according to any one of [1] to [7], wherein the porous film is a porous film for a photoelectrode of a dye-sensitized solar cell.
[9] A porous film formed by the film forming method according to any one of [1] to [8].
[10] A photoelectrode comprising the porous film according to [9].
[11] A dye-sensitized solar cell comprising the photoelectrode according to [10].

  According to the film forming method of the present invention, primary particles (fine particles) are grown by a liquid phase synthesis method, and secondary particles (aggregated particles) obtained by aggregating the primary particles are used. There is no need to crush a large lump of sintered particles in a mortar and no need to pass through a mesh. Aggregated particles having a uniform particle diameter can be obtained by growing the fine particles while stirring in the reaction solution for liquid phase synthesis and further aggregating the fine particles. Aggregated particles are in a porous state in which fine particles are partially bonded. Even if the porous particles obtained through the bonding step for strengthening the bonding between the fine particles collide with the substrate, the porous particles can be maintained. As a result, a porous film having a high porosity can be obtained. In addition, since the porous particles have the same particle size as the aggregated particles, large particles are not mixed in the sprayed particles, and the blasting effect hardly occurs, so that a thick porous film is efficiently formed. be able to. Further, even when a thick porous film is formed, the porosity of the region close to the substrate and the region away from the substrate can be made the same, and the porosity of the entire film can be made uniform.

  The porous membrane of the present invention has high structural strength because the entire membrane is formed of porous particles having a uniform particle size. Furthermore, it has a high porosity throughout the membrane. For this reason, the photoelectrode which increased dye adsorption amount than before is obtained. As a result, the photoelectrode and dye-sensitized solar cell provided with the porous film of the present invention have excellent photoelectric conversion efficiency.

It is a schematic block diagram of the film forming apparatus applicable to the film forming method of 1st embodiment of this invention. It is a plot figure which shows the change of the pigment | dye adsorption amount with respect to the change of the film thickness of a porous film.

Hereinafter, the present invention will be described with reference to the drawings based on preferred embodiments, but the present invention is not limited to such embodiments.
In the present specification, the fine particles mean particles (primary particles) made of an inorganic substance. Aggregated particles refer to particles formed by agglomerating the fine particles. The porous particles are particles obtained by firing the aggregated particles.
<Film forming method>
The film forming method according to the first embodiment of the present invention synthesizes fine particles (primary particles) made of an inorganic substance using a raw material compound as a raw material in a solvent containing the raw material compound (in a liquid phase raw material). Aggregated particles obtained by aggregating the fine particles are used.

  The aggregated particles may be synthesized by a conventionally known hydrothermal synthesis method, or commercially available products may be used. A commercial product of the aggregated particles can be purchased from, for example, Teika Corporation. As a conventionally known hydrothermal synthesis method, a method in which a solid reactant and a solvent or an aqueous solution acting as a reactant are placed in an autoclave and treated under high temperature and high pressure conditions can be applied. By this treatment, the solid reactants dissolve and react with each other or react with the components of the aqueous solution, whereby the target fine particles can be precipitated. At this time, by changing the temperature, the type and concentration of the aqueous solution, the pH, the stirring, and the like, it is possible to control the obtained particle shape and aggregation state. Examples of such conventionally known hydrothermal synthesis methods include the methods described in the following references.

<References> ・ Synthesis of ceramic powder by hydrothermal method, Kazumichi Yanagisawa, Nichias Technical Time Report 2008 No.2 No. 353, pp1-7.・ Effects of conditioning conditions on the properties of anatase-type titania solid solution nanoparticles, Masanori Hirano, Aichi Institute of Technology Research Report, No. 12, 2010

The liquid phase raw material includes a solvent and a raw material compound to be dissolved or dispersed in the solvent. The raw material compound is a compound containing an inorganic substance constituting the fine particles. For example, fine particles comprising titanium oxide and aggregated particles in which the fine particles are aggregated can be obtained by a hydrothermal synthesis method using water as the solvent and TiCl ₄ as the raw material compound.
Although the said inorganic substance is not restrict | limited in particular, For example, the material of the porous film which comprises the photoelectrode of a conventionally well-known dye-sensitized solar cell is mentioned. Specific examples include metals or semiconductors such as titanium and zinc, salts of the metals or semiconductors, and halides of the metals or semiconductors.

  The average particle diameter (average of major axis) of the fine particles (primary particles) constituting the aggregated particles is not particularly limited, but is preferably 1 nm to 100 nm, more preferably 5 nm to 70 nm, and still more preferably 10 nm to 40 nm. When the average particle diameter of the fine particles is 1 nm or more, porous aggregated particles can be easily obtained, and a porous film having a specific surface area sufficient for adsorbing the sensitizing dye can be formed. When the average particle size of the fine particles is 100 nm or less, the bonding force between the fine particles constituting the aggregated particles can be increased, and aggregated particles having high physical strength can be obtained.

  Examples of the method for obtaining the average particle size of the fine particles include a method of measuring and averaging the long diameters of a plurality of fine particles by SEM observation. The larger the number of measurements when calculating the average, the better. However, for example, with respect to 30 to 100 aggregated particles, a method of calculating the average value by measuring the major axis of about 10 fine particles each.

  The aggregated particles are secondary particles obtained by further aggregating fine particles obtained by the liquid phase synthesis method. The average particle diameter (average of the major axis) of the aggregated particles is not particularly limited, but is preferably 0.1 μm to 5 μm, more preferably 0.2 μm to 2 μm, and still more preferably 0.5 μm to 1.5 μm. When the average particle diameter of the aggregated particles is 0.1 μm or more, a structurally strong porous film different from the green compact can be easily obtained. That is, a sufficient film forming effect can be easily obtained. When the average particle size of the aggregated particles is 5 μm or less, it is possible to sufficiently suppress the blasting effect of scraping the porous film formed by the previously sprayed aggregated particles with the aggregated particles sprayed later.

  As a method for obtaining the average particle size of the aggregated particles, for example, a method of determining the peak value of the volume average particle size distribution obtained by measurement with a laser diffraction particle size distribution measuring device or the major axis of a plurality of aggregated particles by SEM observation. The method of measuring and averaging is mentioned. The larger the number of measurements when calculating the average, the better. However, for example, there is a method of calculating the average value by measuring the major axis of 30 to 100 aggregated particles. The particle size of the aggregated particles is preferably measured by the SEM observation.

In the present embodiment, in order to increase the structural strength of the aggregated particles, a bonding process for strengthening the bonding between the fine particles constituting the aggregated particles is performed. As this joining treatment, it is preferable to fire the aggregated particles without using a binder containing a polymer as in Patent Documents 2 to 3, and only the aggregated particles are fired (only the aggregated particles are It is more preferable to fire alone. Here, the high molecular polymer means a polymer having a molecular weight (Mw) of 1000 or more.
Since the firing in the present embodiment is performed for the purpose of strengthening the bonding between the already aggregated fine particles, it is not necessary to perform the firing in a state where the aggregated particles are closely packed. Rather, in order to prevent unnecessary bonding between the agglomerated particles, it is preferable to fire in a state where the agglomerated particles are not closely packed. Specifically, it is preferable to perform firing in a state where the density of the aggregated particles is 3.7 to 4.1 g / cm ³ . This is particularly important and will be explained in more detail below.

The binder used in conventional baking is used for the purpose of aggregating particles that are not yet bonded. Furthermore, in order to ensure the aggregation state of the particles, it is necessary to densely pack the particles to which the binder is attached before firing. The binder burns out after firing and has a function of assisting strong sintering of the particles. However, it is extremely difficult to control the size of the sintered body (large lump) obtained after firing. For this reason, the process which crushes a sintered compact and arranges (classifies) further to a desired size using a filter etc. is indispensable.
On the other hand, the agglomerated particles in the present embodiment do not require the binder because the fine particles, which are primary particles, are already bonded before firing. By firing the agglomerated particles without using the binder, the agglomerated particles are bonded together more firmly without binding the agglomerated particles, and the structural strength of the agglomerated particles is increased. Enhanced porous particles can be obtained. At this time, since the binder is not used, a large lump (sintered body) formed by firmly bonding the aggregated particles (secondary particles) to each other is not formed. The conventional sintered body needs to be crushed later, but this trouble does not occur in this embodiment. In the present embodiment, by not using the binder, it is possible to obtain porous particles having a uniform particle size even after firing, similarly to the aggregated particles.

The temperature range of the baking is not particularly limited as long as it is a temperature capable of strengthening the bonding between the fine particles, but the temperature is higher than the temperature at which the portion where the fine particles are in contact with each other by a solid-phase reaction, and the inorganic A temperature range below the melting point of the substance is preferred. Here, the term “solid phase reaction” refers to a location where the fine particles are in contact with each other in a temperature range below the melting point temperature of the fine particles, where atom diffusion and recombination occur at the locations where the fine particles are in contact with each other. Refers to the reaction of binding.
When the aggregated particles are made of titanium oxide, the firing temperature is preferably 400 to 1000 ° C, more preferably 500 to 800 ° C, and still more preferably 500 to 600 ° C. At this firing temperature, the firing time is preferably 1 hour to 24 hours, more preferably 3 hours to 12 hours, and even more preferably 5 hours to 12 hours.

  The average particle diameter of the porous particles is preferably substantially the same as that of the aggregated particles. As described above, even if the aggregated particles are fired, the aggregated particles are hardly bound to each other as long as the binder is not used and the firing temperature and the firing time are as described above. Further, even if the aggregated particles are attached to each other by the firing, the adhesion is not strong, and therefore it can be easily returned to the original size of the aggregated particles by lightly understanding.

Wherein at density of the porous particles is not particularly limited but is preferably 3.3~4.2g / cm ^3, more preferably 3.5~4.2g / cm ^3, is 3.7~4.1g / cm ³ Further preferred.
When the density is in the above range, a porous film having a high porosity can be easily obtained.

When the porous particles are made of titanium oxide, the Mohs hardness of the porous particles is preferably in the range of 5.5 to 6.0.
When the Mohs hardness is in the above range, the porous particles can be suppressed from being pulverized by spraying, and a porous film maintaining the porosity of the porous particles can be easily formed.

In order to increase the structural strength of the agglomerated particles, bonding by chemical treatment can be performed instead of the firing as a treatment for strengthening the bonding between the fine particles constituting the agglomerated particles.
Specifically, for example, a reactive compound containing a metal or a semiconductor constituting the fine particles is used, the reactive compound is mixed with the aggregated particles, and the fine particles are chemically bonded via the reactive compound. can do. As the reactive compound, a compound whose reaction is accelerated by light or heat can be used.

When the fine particles are fine particles made of titanium oxide, examples of the reactive compound include TiCl ₄ . By dipping the agglomerated particles in an aqueous solution of TiCl ₄ having a concentration of 0.05 to 0.1 mol / L for 30 minutes and heating at 60 to 100 ° C. for 30 minutes to 2 hours (or irradiating UV light with heating) The bond between the fine particles in the aggregated particles can be strengthened. In this case, it is possible to prevent the agglomerated particles from being joined by heating the aqueous solution while stirring so that the agglomerated particles are not bonded to form a large lump.

<Film formation by AD method>
Hereinafter, a method for forming a porous membrane according to a first embodiment of the present invention will be described with reference to FIG.
The drawings used in the following description are schematic, and the length, width, thickness ratio, and the like are not necessarily the same as the actual ones, and can be changed as appropriate.

  FIG. 1 is a configuration diagram of a film forming apparatus 60 applicable to the present embodiment. However, the film forming apparatus used in the film forming method of the present embodiment is not limited to the configuration shown in FIG. 1 as long as it is an apparatus capable of spraying the porous particles, which are the raw material of the porous film, onto the base material.

<Film forming device>
The film forming apparatus 60 includes a gas cylinder 55, a transfer pipe 56, a nozzle 52, a base 63, and a film forming chamber 51.
The gas cylinder 55 is filled with a gas for accelerating the porous particles 54 and spraying it on the base material 53 (hereinafter referred to as a carrier gas).
One end of a transfer pipe 56 is connected to the gas cylinder 55. The carrier gas supplied from the gas cylinder 55 is supplied to the carrier pipe 56.

  The transport pipe 56 is provided with a mass flow controller 57, an aerosol generator 58, a disintegrator 59 and a classifier 61 that can appropriately adjust the dispersion degree of the porous particles 54 in the transport gas, in order from the front side. It has been. By the crusher 59, the state in which the porous particles 54 adhere to each other due to moisture or the like can be solved. Further, even if there are porous particles that have passed through the crusher 59 in an attached state, the particles can be removed by the classifier 61.

  The mass flow controller 57 can adjust the flow rate of the carrier gas supplied from the gas cylinder 55 to the carrier pipe 56. The aerosol generator 58 is loaded with porous particles 54. In the case of producing a porous film for a dye-sensitized solar cell, a sensitizing dye may be adsorbed in advance on the porous particles 54 before spraying. The porous particles 54 are dispersed in the carrier gas supplied from the mass flow controller 57 and conveyed to the crusher 59 and the classifier 61.

  The nozzle 52 is disposed such that an opening (not shown) faces the base material 53 on the base 63. The other end of the transport pipe 56 is connected to the nozzle 52. The carrier gas containing the porous particles 54 is injected from the opening of the nozzle 52 onto the base material 53.

  The base material 53 is placed on the upper surface 73 of the base 63 so that one surface 72 of the base material 53 comes into contact therewith. Further, the other surface 71 (film forming surface) of the substrate 53 faces the opening of the nozzle 52. The porous particles 54 injected together with the carrier gas from the nozzle 52 collide with the film forming surface, and a porous film made of the porous particles 54 is formed.

  In the member constituting the base 63 of the film forming apparatus 60, the collision energy between the porous particles 54 is appropriately controlled on the film forming surface 71 according to the average particle diameter, hardness, and spraying speed of the porous particles 54. Preferably, it is made of a material. With such a member, the adhesion of the porous particles 54 to the film-forming surface 71 is improved, and the porous particles 54 to be deposited are easily joined together, so that a porous film having a high porosity can be easily formed. It can be formed into a film.

  The base material 53 is preferably made of a material that allows the sprayed porous particles 54 to bite into the film-forming surface 71 and to adhere to the porous particles 54 without penetrating. Examples of such a substrate 53 include a resin film (resin sheet). Since the film can be formed at room temperature according to the AD method, the substrate 53 is not required to have high heat resistance. More specific selection of the base material 53 may be appropriately performed according to the material of the porous particles 54, the film forming conditions such as the spraying speed, and the use of the porous film.

The film forming chamber 51 is provided for film formation in a reduced pressure atmosphere. A vacuum pump 62 is connected to the film forming chamber 51, and the inside of the film forming chamber 51 is depressurized as necessary.
The film forming chamber 51 is provided with a base exchange means (not shown).

<Blowing method>
Hereinafter, an example of a method for spraying the porous particles 54 will be described.
First, the vacuum pump 62 is operated to depressurize the film forming chamber 51. The pressure in the film forming chamber 51 is not particularly limited, but is preferably set to 5 to 1000 Pa. By reducing the pressure to this extent, convection in the film forming chamber 51 is suppressed, and it becomes easy to spray the porous particles 54 onto predetermined positions on the film forming surface 71.

Next, the carrier gas is supplied from the gas cylinder 55 to the carrier pipe 56, and the flow rate and flow rate of the carrier gas are adjusted by the mass flow controller 57. As the carrier gas, for example, a general gas such as O ₂ , N ₂ , Ar, He, or air can be used.
What is necessary is just to set suitably the flow velocity and flow volume of carrier gas according to the material of the porous particle 54 sprayed from the nozzle 52, average particle diameter, flow velocity, and flow volume.

  The porous particles 54 are loaded into the aerosol generator 58, and the porous particles 54 are dispersed in the carrier gas flowing in the carrier pipe 56 and accelerated. The porous particles 54 are ejected from the opening of the nozzle 52 at a subsonic to supersonic speed, and are laminated on the film forming surface 71 of the substrate 53. At this time, the spraying speed of the porous particles 54 onto the film forming surface 71 can be set to 10 to 1000 m / s, for example. However, the speed is not particularly limited, and may be set as appropriate according to the material of the base material 53.

  By continuing the spraying until the porous film made of the porous particles 54 reaches a predetermined film thickness, the porous particles 54 are successively applied to the porous particles 54 that have digged into the film forming surface 71 of the substrate 53. Colliding with each other, a new surface is formed on the surfaces of the porous particles 54 by the collision of the porous particles 54, and the porous particles 54 are joined to each other on the new surface. When the porous particles 54 collide with each other, a temperature rise that causes the entire porous particles 54 to melt does not occur. Therefore, a glassy grain boundary layer is hardly formed on the new surface.

When the porous film of the porous particles 54 reaches a predetermined film thickness (for example, 1 μm to 100 μm), the spraying of the porous particles 54 from the nozzle 52 is stopped.
Through the above steps, a porous film having a predetermined film thickness made of porous particles 54 is formed on the film forming surface 71 of the substrate 53.

  Although the film formation method by AD method was illustrated above, the film formation method of this invention is not limited to AD method. Even if a porous film is formed by spraying the porous particles onto a substrate using a conventionally known powder spraying method, such as a spray method, a cold spray method, an electrostatic spray method, or a spraying method. Good.

<Porous membrane>
The porous film of the second embodiment of the present invention is a porous film formed on a substrate by the film forming method of the first embodiment. This porous film has high structural strength because the entire film is formed of porous particles having a uniform particle diameter. Furthermore, it has a high porosity throughout the membrane. For this reason, the photoelectrode which increased dye adsorption amount than before is obtained. As a result, the photoelectrode and dye-sensitized solar cell provided with the porous film of the present invention have excellent photoelectric conversion efficiency.
The use of the porous film of the present embodiment is not limited to the photoelectrode, but can be widely applied to the use of substance adsorption and substance support using a porous structure.

<< Photoelectrode >>
The photoelectrode of the third embodiment of the present invention is a photoelectrode in which a sensitizing dye is adsorbed on the porous film of the second embodiment. The kind of sensitizing dye is not particularly limited, and conventionally known dyes can be applied. In the third embodiment, the porous film is preferably formed on a transparent conductive substrate.

  The photoelectrode of the third embodiment can be produced by a conventional method except that the porous film of the second embodiment is used.

《Dye-sensitized solar cell》
The dye-sensitized solar cell according to the fourth embodiment of the present invention includes the photoelectrode according to the third embodiment, a counter electrode, and an electrolytic solution or an electrolyte layer. The electrolytic solution is preferably sealed with a sealing material between the photoelectrode and the counter electrode.

  As the substrate on which the porous film constituting the photoelectrode is formed, a resin film or a resin sheet having a transparent conductive film formed on the surface can be used. As the resin (plastic), those having visible light permeability are preferable, and examples thereof include polyacryl, polycarbonate, polyester, polyimide, polystyrene, polyvinyl chloride, and polyamide. Among these, polyester, particularly polyethylene terephthalate (PET), is produced and used in large quantities as a transparent heat-resistant film. By using such a resin substrate, a thin and light flexible dye-sensitized solar cell can be manufactured.

  As the electrolytic solution, an electrolytic solution used in a conventionally known dye-sensitized solar cell can be applied. A redox couple (electrolyte) is dissolved in the electrolytic solution. The electrolyte solution may contain other additives such as fillers and thickeners without departing from the spirit of the present invention.

  Further, an electrolyte layer (solid electrolyte layer) may be applied instead of the electrolytic solution. The electrolyte layer has a function similar to that of the electrolytic solution, and is in a gel or solid state. As the electrolyte layer, for example, a solution obtained by gelling or solidifying the electrolyte solution by adding a gelling agent or a thickener to the electrolyte solution and removing the solvent as necessary can be applied. By using the gel or solid electrolyte layer, there is no possibility of the electrolyte solution leaking from the dye-sensitized solar cell.

  The dye-sensitized solar cell of the fourth embodiment can be manufactured by a conventional method except that the photoelectrode of the third embodiment is used.

  The porous film of the second embodiment constituting the photoelectrode of the third embodiment has a structural strength, structural uniformity, porosity, porosity that is higher than that of a porous film formed by a conventional powder spraying method. Excellent uniformity and dye adsorption. As a result, the durability and photoelectric conversion efficiency of the photoelectrode of the third embodiment and the dye-sensitized solar cell of the fourth embodiment can be improved.

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

[Example 1]
Commercially available agglomerated particles made of TiO ₂ aggregated until fine particles having an average primary particle size of about 15 nm were about 1 μm were purchased and used. The aggregated particles were washed with purified water or the like, spread on a bat and dried so that the aggregated particles were not packed closely. The dried aggregated particles having an average particle diameter of about 1 μm were put in a reagent bottle and temporarily stored.
Next, 10 g of the dried powdery agglomerated particles was put in an alumina container having a volume of 150 cm ³ . At this time, no pressure was applied to the powder, and a certain amount of gaps were included between the particles. At this time, no binder is used.
In this state, calcination was performed at 500 ° C. for 5 hours in an air atmosphere to obtain porous particles made of TiO ₂ having an average particle diameter of about 1 μm, which was the same as the aggregated particles.
The density of the obtained porous particles was 3.8 g / cm ³ .
The porous particles were sprayed onto the PEN substrate on which ITO was formed by AD method to form a porous film made of TiO ₂ . The film thickness could be arbitrarily adjusted in the range of 0.1 μm to 30 μm.

[Example 2]
Commercially available agglomerated particles made of TiO ₂ aggregated until fine particles having an average primary particle diameter of about 30 nm were about 1 μm were purchased and used. The aggregated particles were washed with purified water or the like, spread on a bat and dried so that the aggregated particles were not packed closely. The dried aggregated particles having an average particle diameter of about 1 μm were put in a reagent bottle and temporarily stored.
Next, 10 g of the dried powdery agglomerated particles was put in an alumina container having a volume of 150 cm ³ . At this time, no pressure was applied to the powder, and a certain amount of gaps were included between the particles. At this time, no binder is used.
In this state, calcination was performed at 500 ° C. for 5 hours in an air atmosphere to obtain porous particles made of TiO ₂ having an average particle diameter of about 1 μm, which was the same as the aggregated particles.
The density of the obtained porous particles was 4.0 g / cm ³ .
The porous particles were sprayed onto the PEN substrate on which ITO was formed by AD method to form a porous film made of TiO ₂ . The film thickness could be arbitrarily adjusted in the range of 0.1 μm to 30 μm.

[Example 3]
Commercially available agglomerated particles made of TiO ₂ aggregated until fine particles having an average primary particle size of about 15 nm were about 1 μm were purchased and used. The aggregated particles were washed with purified water or the like, spread on a bat and dried so that the aggregated particles were not packed closely. The dried aggregated particles having an average particle diameter of about 1 μm were put in a reagent bottle and temporarily stored.
Next, 10 g of the dried powdery agglomerated particles was put in an alumina container having a volume of 150 cm ³ . At this time, no pressure was applied to the powder, and a certain amount of gaps were included between the particles. At this time, no binder is used.
In this state, calcination was performed at 300 ° C. for 5 hours in an air atmosphere to obtain porous particles made of TiO ₂ having an average particle diameter of about 1 μm, which was the same as the aggregated particles.
The density of the obtained porous particles was 3.7 g / cm ³ .
The porous particles were sprayed onto the PEN substrate on which ITO was formed by AD method to form a porous film made of TiO ₂ . The film thickness could be arbitrarily adjusted in the range of 0.1 μm to 30 μm.

[Comparative Example 1]
Produced by a known flame fusion method, an average primary particle size calcined particles with an average of TiO ₂ particles and the primary particle size of about 15nm was mixed TiO ₂ particles 2μm 10:90 (volume ratio) The porous particles made of TiO ₂ were formed by spraying the mixed particles on the PEN substrate on which ITO was formed by using the AD method. The film thickness could be arbitrarily adjusted in the range of 0.1 μm to 30 μm.
However, since the film as it is sprayed without binding the TiO ₂ particles of primary particles, the bonding of the TiO ₂ particles are in the obtained porous film, depending only on the collision energy at the time of spraying Yes. For this reason, it is necessary to spray strongly in order to obtain sufficient collision energy. However, when strongly sprayed, the porosity of the porous film decreases, and in an extreme case, it becomes a dense film. The collision energy also depends on the size of the particles to be sprayed and the material (hardness) of the substrate. Thus, it is not impossible to adjust the porosity only by the strength of the collision energy, but it is very difficult.

[Comparative Example 2]
Using TiO ₂ particles having an average primary particle diameter of 15 nm prepared by a known flame melting method, the particles are used without firing, and the particles are formed on the PEN substrate on which ITO is formed by AD method. To make a porous film made of TiO ₂ . However, only a structurally fragile green compact was obtained.

[Comparative Example 3]
TiO ₂ particles having an average primary particle diameter of 15 nm prepared by a known flame melting method and polyethylene glycol (PEG) (Mw: 6000): as a binder were mixed at 97: 3 (weight ratio). This mixture was dried and solidified at room temperature to obtain an aggregate in which primary particles were aggregated. After this aggregate was fired at 500 ° C. for 5 hours, the resulting sintered mass was crushed with a mortar and passed through a 25 μm mesh to produce porous particles made of TiO ₂ .
The average particle diameter of the obtained porous particles was about 10 μm. Using the porous particles, the porous particles were sprayed onto a PEN substrate on which ITO was formed by AD method to form a film (film thickness: 1.8 μm) made of TiO ₂ .
Subsequently, an attempt was made to form a porous film having a thickness of 10 μm or more. However, a large number of large-diameter particles exceeding 10 μm were mixed in the particles to be sprayed, and the blasting action was dominant. Couldn't get.

<Measurement of specific surface area>
A plurality of porous films having different film thicknesses were produced by the film forming methods of Example 1, Example 2, and Comparative Example 1, and the porosities thereof were compared. The comparison of the porosity was evaluated by comparing the dye adsorption amount. Specifically, each porous film is immersed in a solution containing N719 dye to adsorb the dye, and then the porous film is immersed in another solvent to remove the dye adsorbed on the porous film. Released. The amount of the desorbed dye was measured, and the porosities were compared by calculating the dye adsorption amount (dye adsorption density) per unit volume of each porous film. The result is shown in FIG.

  In the porous membranes obtained by the film forming methods of Example 1 and Example 2, the dye adsorption density did not change even when the film thickness changed, and was almost constant. This indicates that the porosity is constant even when the thickness of the porous film is changed. Further, the porous membrane of Example 1 has a higher dye adsorption density and a larger specific surface area than Example 2. This indicates that the specific surface area is increased because the average particle diameter of the primary particles used in the film forming method of Example 1 is smaller than that of Example 2. Therefore, it was shown that the porosity of the obtained porous film can be controlled by adjusting the average particle diameter of the primary particles used in the film forming method of the present invention.

  On the other hand, in the porous film obtained by the film forming method of Comparative Example 1, the dye adsorption density changed depending on the film thickness, and the dye adsorption density decreased as the film became thicker. This suggests that brittle deformation of the particles occurred during film formation, and the porous structure of the porous film was crushed and densified.

<Measurement of photoelectric conversion efficiency η>
The porous film obtained by the film forming method of Example 1, Example 2, Comparative Example 1 and Comparative Example 3 was used as a photoelectrode of a dye-sensitized solar cell, and its conversion efficiency was measured. A glass substrate with platinum on one side was used as the counter electrode. Using N719 as the dye and AN50 (manufactured by Solaronics) as the electrolyte, solar cells were produced by a conventional method. The photoelectric conversion efficiency of each solar battery cell provided with each porous film was measured using a commercially available solar simulator. The results are shown in Table 1.

  As a result of the measurement, the solar cell using the porous film of Example 1 and Example 2 showed higher photoelectric conversion efficiency than the solar cell using the porous film of Comparative Example 1. This result is considered to reflect that the dye adsorption density (porosity) of the porous films of Example 1 and Example 2 is higher than that of Comparative Example 1. Moreover, since the porous film of Comparative Example 3 was thin, the photoelectric conversion efficiency was low. From this result, it was shown that the porous film obtained by the film forming method of the present invention is useful as a photoelectrode of a dye-sensitized solar cell.

[Summary of Examples and Comparative Examples]
A thick porous film was obtained by the film forming methods of Examples 1 and 2. Since the specific surface area was large and the amount of dye adsorption was large, a high photoelectric conversion efficiency η was exhibited. Moreover, since Example 1 in which the average particle diameter of primary particles used for film formation is smaller has a larger specific surface area than Example 2, by reducing the average particle diameter of primary particles, It was found that the specific surface area can be increased.
In the film forming method of Comparative Example 1, a thick porous film was obtained as in Examples 1 and 2, but the specific surface area was smaller than that in Example and the photoelectric conversion efficiency η was also inferior. In addition, as described above, since the porosity of the porous film is controlled only by the collision energy between the particles to be sprayed, much labor has been required for examining the spraying conditions.
In Comparative Example 2, since only particles with a small average particle diameter of 15 nm were sprayed, a green compact with only particles deposited was obtained. The structure of the green compact was so weak that it easily peeled off from the substrate, and there was no strength that could be used as a porous film of a dye-sensitized solar cell.
In Comparative Example 3, since a film obtained by further pulverizing a lump obtained by solidifying primary particles with a binder and sintering the film was formed, a thick porous film could not be obtained. The reason is that the average particle size of the particles to be sprayed is about 10 μm, and particles larger than 10 μm were also mixed in the particles to be sprayed, so that the film-forming effect and the blast effect antagonized during film formation, and the film growth stopped. It is thought that this is because it has been. In addition, depending on the film forming conditions, a phenomenon that the film breaks in the middle was also observed.

  The configurations and combinations thereof in the embodiments described above are examples, and the addition, omission, replacement, and other modifications of the configurations can be made without departing from the spirit of the present invention. Further, the present invention is not limited by each embodiment, and is limited only by the scope of the claims.

  The film forming method, the porous film, the photoelectrode provided with the porous film, and the dye-sensitized solar cell using the photoelectrode are widely applicable in the field of solar cells.

DESCRIPTION OF SYMBOLS 51 ... Film forming chamber, 52 ... Nozzle, 53 ... Base material, 54 ... Porous particle, 55 ... Cylinder, 56 ... Transfer pipe, 57 Mass flow controller, 58 ... Aerosol generator, 59 ... Crusher, 60 ... Product made Membrane device, 61 ... classifier, 62 ... vacuum pump, 63 ... base, 71 ... film-forming surface, 72 ... surface opposite to the film-forming surface, 73 ... mounting surface (upper surface) of the base

Claims (11)

  In the solvent containing the raw material compound, the fine particles of the inorganic substance using the raw material compound as a raw material are synthesized and the aggregated particles obtained by aggregating the fine particles are used to strengthen the bonding between the fine particles contained in the aggregated particles. The porous substrate is produced through the step of performing, the porous particle is sprayed on the base material, the base material and the porous particle are joined together, and the porous particles are joined together to form the base material. A film forming method comprising forming a porous film composed of the inorganic substance on the film.   2. The film forming method according to claim 1, wherein in the step of strengthening the bonding between the fine particles, the fine particles in the aggregated particles are joined by not densely filling the aggregated particles.   In the step of strengthening the bonding between the fine particles, the fine particles are baked at a temperature range from a temperature at which the fine particles are in contact with each other by a solid-phase reaction to a temperature above the melting point of the inorganic substance and below. The film forming method according to claim 1, wherein bonding is performed.   In the step of strengthening the bonding between the fine particles, a reactive compound containing a metal or a semiconductor constituting the fine particles and the aggregated particles are mixed, and the fine particles are chemically bonded via the reactive compound. The film forming method according to any one of claims 1 to 3, wherein:   5. The film forming method according to claim 1, wherein an average particle diameter of the aggregated particles and the porous particles is 200 nm to 2 μm.   The film forming method according to any one of claims 1 to 5, wherein an average particle size of the fine particles is 10 nm to 100 nm.   The film forming method according to any one of claims 1 to 6, wherein the porous particles sprayed onto the substrate do not include porous particles having a particle size of 5 µm or more. The said porous film is a porous film for the photoelectrodes of a dye-sensitized solar cell, The film forming method as described in any one of Claims 1-7 characterized by the above-mentioned. The porous film formed by the film forming method as described in any one of Claims 1-8. A photoelectrode comprising the porous film according to claim 9. A dye-sensitized solar cell comprising the photoelectrode according to claim 10.

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